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INTERNATIONAL

SATELLITE TV-how the IBA beat

the BBC intoorbit

VERSATILE ALARMMODULE

LASER DIODESUSERDEFINEDGRAPHICS ON

THE ZX81

Dave Bradshaw: EditorPeter Green: Deputy EditorPhil Walker. Project EditorJerry Fowler: Technical IllustratorGary Price: Divisional Ad. ManagerRon Harris B. Sc: Managing EditorAndrew Selwood: Copy ControlT. J. Connell: Managing Director

PUBLISHED BY:

Argus Specialist Publications Ltd.,145 Charing Cross Road, London WC2H OEE,DISTRIBUTED BY:

Argus Press Sales 8 Distribution Ltd.,12-18 Paul Street, London EC2A 4JS(British Isles)TYPESET AND ORIGINATION BY:

Design InternationalPRINTED BY

OB Limited, Colchester.COVERS PRINTED BY:

Alabaster Passmore

ABCMember of theAudit Bureau ofCirculation

Electronics Tod Is normally published on the first Friday inthe month pre eding cover date. The contents of thispublication including all articles. designs. plans, drawings andprograms and all copyright and other intellectual property rightstherein belong to Argus Spedalist Publications Limited. Allrights conferred by the Law of Copyright and other intellectualproperty rights and by virtue of international copyrightconventions are specifically reserved to Argus SpecialistPublications United and any reproduction requires the priorwritten consent of the Company. © 1986 Argus SpecialistPublications Ltd U All reasonable care is taken in the preparationof the magazine contents but the publishers cannot be heldlegally responsible for errors. Where mistakes do occur, acorrection will normally be published as soon as possibleafterwards. All prices and data contained in advertisements areaccepted by us in good faith as correct at time of going to press.Neither the advertisers nor the publishers can be heldresponsible, however, for any variations affecting price oravailability which may occur after the publication has dosed forpress.

Subscription Rates. UK 08.10. Overseas: E22.50..1USA: $29.50. E49.50.

MARCH 1983 VOL 12 NO 3EDITORIAL AND ADVERTISEMENT OFFICE

1 Golden Square, London W1 R 3AB, Telephone 01-437 0626,Telex 8811896.

DIGEST 11

The ETI alternative to breakfast television - assumingyou can find a way to prop up the magazine amidthe toast and marmalade.SATELLITE TV - THE SEQUEL 16Now that the Part Report on satellite broadcastingof television programmes has been published. VivianCapel takes a second look at the subject in the lightof the recommendation.LASER DIODES 30Not much use to the mad scientist designing deathrays; but with far reaching implications forcommunications technology, amongst other things.We look at a little-known property of the ubiquitoussemiconductor junction.BROADCAST STANDARDS 42

So the satellites will be beaming down TV signals in

MAC format, not E. PAL. Here we examine exactly

ZX81 USER -DEFINED GRAPHICS 23Bored with the characters that Uncle Clive Sinclairstuffed into your BASIC ROM? If you've got a 16KRAM pack, this hardware modification to your ZX81lets you display your own.ORGAN PART TWO 36This month we discuss the lower keyboard circuitry,the preset voice circuitry, and the Buylines wemissed bust last month!

NEXT MONTH'S ETI 7

COMPUTER EXHIBITIONS 22SUBSCRIPTIONS SPECIAL OFFER 28

how this came about, and the consequences for theTV manufacturers and the paying public.AUDIOPHILE 57It's Q and A time to start with, as Ron Harris answerssome typical reader enquiries. Then it's off to thearmchair/test bench for a report on Coral's newcartridge.TECH TIPS 68More circuit ideas supplied by our readers - designsfrom hobbyists for hobbyists.READ/WRITE 76A couple of massive missives as readers get theiropinions off their chests and into print.CONFIGURATIONS 79This month Ian Sinclair discusses audio poweroutput stages, with the more common configurationsand some advice on heat sinking.

6502 SOUND DAC/CARD 48It's possible to get computers to do other things thanfly spaceships across your TV. Here's a project thatgives you three sound channels and six DACs.ALARM MODULE 63Provided you don't have the misfortune to be visitedby a deaf burglar, this little box packs enoughdecibels to send him away screaming.LOGIC PROBE 73This elegant design features a host o diagnosticfacilities on a tiny PCB and uses only three ICpackages.FOIL PATTERNS 86

Due to lack of space in this issue and othercircumstances beyond our control the StageLighting Dimmer and Cortex BASIC articleshave been postponed until next month.

BOOK SERVICE 55PCB SERVICE 83

WATFORD ELECTRONICS33 34 CARDIFF ROAD, WATFORD, HERTS. ENGLAND

MAIL ORDER, CALLERS WELCOMETel. Watford 10923) 40588. Telex 8956095

ALL DEVICES BRAND NEW, FULL SPEC. AND FULLY GUARANTEED. ORDERSDESPATCHED BY RETURN OF POST. TERMS OF BUSINESS CASH/CHEQUE/P.OsOR BANKERS DRAFT WITH ORDER OR ACCESS. GOVERNMENT ANDEDUCATIONAL INSTITUTIONS' OFFICIAL ORDERS ACCEPTED. TRADE ANDEXPORT ENQUIRY WELCOME. PbP ADD S3p TO ALL CASH ORDERS. OVERSEASORDERS POSTAGE AT COST. AIR/SURFACE. ACCESS ORDERS WELCOME.

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ELECTROLYTIC CAPACITORS: (Values in uFI 50476 10uF 624; 47 Nip; 63V:0.47. 1.0, 1.5, 2.2.3.3 4.7 Sp;10 10p: 15, 22124; 3315p; 47 129:6821W 100190; 220 230: 1000 20116 2200 159;939: 88 201): 100174;22024p: 40V:6.8 16p; 22 94. 33 12p, 330, 470 324: 1000 41p; 2200 10p; 7 Sp; 100 11p;150 129: 220 150; 330 22p: 470 25., 680. 1000 34p: 1500 420; 230 100. 2200 50p;33001716; 4700 92p;NV:47. 68, 100 gp: 125 1744, 330 1111p: 470 10p, 680 34p: 1000 22p: 1400 314: 2200 31p; 4700 79p.

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POLYESTER CAPACITORS: Axial lend Typ.400V: InF. 1r6. 2n2, 3n3. 4n7. BM lip: 10n. 15n. I In, 22n 12p: 33n. 47n. 66n111p; 150n 20p; 220n 304.330n 4228.. 470n 524.680n loP Op; 2,.2 826NOV: lOnF, 12n, 39n. 100n Hp; 150n. 220n 17p; 330n. 470n 33: 680n 31p: loFNIA tub 46p: 2.2 411p; 4.7 919.10001/: 1 nE 170; lOnF 304: 15n 40p: 22n 36: 33n 42p; 47n, 100n 4210

POLYESTER RADIAL LEAD CAPACITORS: 30V16111. 15n, 22n, 27n Ip; 33n, 47n. 138n. 00n 7p; 150n, 220n10p: 330n, 470n 13p; 680n 111p: lu 33p; 1.6 404; 2n2 41p.

FEED -THROUGHCAPACITORS1000pF/450V 114

TANTALUM BEAD CAPACITORS0.1uF, 022, 0-33 16p; 0-47, 088,

I-0, 1.5104: 2.2. 3-3 110: 4.7, 6.8 220;10 2114; 151/. 2.2, 3.3 lip. 4.7. 6.8, 10lip; 15, 311p, 22 30p: 33. 47 40p: 100lip: 100: 15, 22, Up; 33, 47 36p; 100Sip; IV: 100 42p.

POTENTIOMETERS: RoTary Carbon.Track 0.25W Log 6 Ln values.5000. 1611 Et 2K0 iLlrear on6/ SingleGang 31).500-200 Snob Gang Log Er In 3065002740 S.W. Gang 13/P Switch 714560-2610 Doublet Gang 111.

MYLAR FILM CAPACITORS7007: inF, 2, 4, 4nF, 10 6: 16nF, 22n,30n, 40n. 47n 7p: 56n, 100n, 200n Op:.93V, 470n11126.

CERAMIC CAPACITORSRange: 0-5pF to 10nF 4p. 15nF, 22nF.33nF; 47nF Sp. 100nF .30V 7p.200nF/111/ Sp.

SUDER POTENTIOMETERS0.25W log and finest values 6Or1m560-50060 any* pang 7691000.50000 dual gang 1109SW Stick Graduated thuel 409

SIEMENS pcbType Moab". '

POIY 1400.11071150V

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POLYSTYRENE CAPACITORS:10PFlo 1.3 85, 1.5nr to 12nF 10p

PRESET POTENTIOMETERS0.1W600 6M0 MiniatureVerbal Et Horizontal 7p0.25W 1000 3.300 nom. large, 10p0-25W 2000 4-760 ren 111

SILVER MCA (Velum in p1)2. 3.3, 4.7. 8.8, 1.2, 10, 12 15, 1822. 27, 33,39. 47, 50. 56,68, 75, 8286, 100, 120. 150. 190pF I6p each200. 220. 250, 270, 300 330. 360390, 470. 800, 800, 820 21p inch1000, 1200, 1800, 2200 309 each3300,47009F 1113. each

RAMFOR

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MINIATURE TRIMMERS Capacitor. 1°°/1.24pF, 2 10pF 224 2 250F, 5 64/pF 30p10-4900 3b.22raRESISTORS Carbon Film Hi -Stab. 5%miniature

RANGE V. 1-99 100.2024147 E24 1p

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ZENERSRange. 2V7 to39V 400mW

I, eachRange 3V3 to33V 1.3W

I6p each

75 SERIE.,

75107/87511075114/57s121/2751507515475182/375188/9752227532475361/3753657545075451 /27545475491/1

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Minuture, endreed. PCB mount.SINGLE POLE1* -91 20511 CrrDC, 101/5 to19.6V). 10A at 30V DC or 260V AC

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Send SAE for details.

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SWITCHED MODE PSUSpecially for those interested in extending their knowledge ofelectronics (which must be about 100% of you), we arereturning to the Designer's Notebook feature with not onebut two articles. As you may gather from the .heading, one ofthese is not a million miles away from the subject of switchedmode power supplies, one of the design fields often regardedas a no-go area for the hobbyist -that is, until that hobbyistreads ETI. The other Designer's. Notebook will be on voltagemultipliers, so start queuing at the newsagents now.

REAL-TIME CLOCK CALENDARA project for all those readers with 6502 -based micros thatcan't tell the. time, or remember what day it is.lf you liked the6502 Sound/DAC card this month, you'll love this project:only in the April edition of ETI.

ZX81 MUSIC BOARDThis is a quite sophisticated though cost-effective music boardfor the ZX81. The board is capable of playing music withoutcontinuous CPU maintenance, and three notes may be playedat once, each with independently variable volume.lf you wantmore out of your micro, get next month's ETI.

NDFLNDF what? We're afraid you'll have to wait until the nextETI is published to find out what those letters stand for, but itwill culminate in an entirely new audio amplifier design.Sounds interesting.Meanwhile, here are a few clues ...

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lir THE LAZY WAY Phone your order through on Access. Barclaycard, Visa or American Expressfor immediete service: no extra charge, no minimum order.* THE TRADITIONAL WAY Send cheque, PO or credit card number Cash not encouraged butaccepted (no corns pleasel. All in stock items shipped same day* THE IDEAL WAY Call in and collect. We are on the main Edgware Rd IA5) lust I; miles fromStaples Corner and approx 3 miles born Marble Arch.VAT Please add VAT at the current rate to all orders except books. VAT not chargeable abroad.POST. PACKING 6 INSURANCE Standard mall order charge is 70p more for heavier goods).Export orders minimum 11 50.

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MULLARD SPEAKER KITSPt...pos.1011y designed 40 watt R.M.S. end 30wan R.M.S. 8 ohm speaker systems recentlydeveloped by MULLARD'S specialist teem inBelgium. Kits comprise Mallard woofer (8" or5") with foam surround and aluminium voice coil.Mulled 3' high power domed tweeter. B.K.E.bait and tested crossover based on Mullardcircuit. combining low loss components, glass fbre board and recessed loudspeaker terminals.SUPERB SOUNDS AT LOW COST. Kits suppliedin polystyrene packs complete with instructions.8' 40W system - recommended cabinet see 240x 216 x 445mmPrice E14.90 each + C2.00 P & P.5" 30W system - recommended cabinet size160 x 175 x 295mmPrice E13.90 each + £1.50 P 8 P.

Designer approved flat pack cabinet kits,including grill fabric. Can be finished with iron co.veneer or self adhesive vinyl etc.8' system cabinet kit E8.00 each + 92.50 P & P.;5' system cabinet kit MOO each + (2.00 P & P.

STEREO CASSETTE TAPE DECK MODULE.Comprising of a top panel and tape mechansm coupled toa record/play back printed board assembly. Supplied asone complete unit for horizontal installation into cabinet orconsole of own choice. These units are brand new. readybuilt and tested.Features: Three digit tape courtier. Autostop. Six pianotype keys, record, rewind, fast forward, play. stop andeject. Au Somatic record level control. Main inputs plussecondary inputs for stereo microphones. InputSensitivity: 100mV to 2V. Input Impedance: 68K.Output level: 400mV to both left and right handchannels. Output Impedance: 10K. Signal to noiseratio: 45dB. Wow and flutter: 0.1%. Power Supplyrequirements: 18V DC at 300rnA. Connections: Theleft and right hand stereo inputs and outputs are viaindividual screened leads. all terminated with phone plugs1phono sockets provided). Dimensions: Top pared 51inx 111in. Clearance required under top panel 21in.Supplied complete with circuit diagram and connectingdiagram. Attractive black and saver finish.Price E26.70 010 postage and packing.Supplementary parts for 18V D.C. power supply(transformer. bndge rectifier and smoothing capacitor)E3.50.

LOUDSPEAKERS15" 100 watt R.M.S. (HI-FI, P.A., DISCO,BASS GUITAR) Die cast chassis, 2"aluminim voice coil, white cone withaluminium centre dome. 8 ohm imp., Res.Freq. 20Hz., Freq. Resp. to 2.5KHz., Sens.97dB (As photograph). Price: £32.00 +£3 carriage.12" 100 watt R.M.S. (HI-FI) Die castchassis. 2" aluminium voice coil. Blackcone. 8 ohm imp., Res. Freq. 20Hz., Freq.Resp. to 4.5KHz. Sens. 95dB. (Asphotograph). Price: £23.50 + E3 carriage.13" 50 watt R.M.S. (HI-FI, PA.) 114"aluminium voice coil. White cone. 8 ohmimp. Res. Freq. 40Hz., Freq. Resp. to 6KHz.Sens. 92dB. Also available with block conefitted with black metal protective grille. (Asphotograph). Price: White Cone £8.90,Black cone/ grille E9.50 P&P f 1.25.12" 85 watt R.M.S. McKENZIE C1285GP (LEAD GUITAR, KEYBOARD, DISCO) 2"aluminium voice coil, aluminium centre dome, 8 ohm imp., Res. Freq. 45Hz.. Freq.Resp. to 6.5KHz., Sens. 98dB. Price: f22.00 + £3 carriage.12" 86 watt R.M.S. McKENZIE C1285TC (PA., DISCO) 2" aluminium voice coil. Twincone. 8 ohm imp., Res. Freq. 45HZ., Freq. Resp. to 14KHz. Price £22 + E3 carriage.15" 150 watt R.M.S. McKENZIE C15 (BASS GUITAR, PA.) 3" aluminium voice coil.Die cast chassis. 8 ohm imp., Res. Freq. 40Hz., Freq. Resp. to 4KHz. Price: £47 + E4carriage.

PIEZO ELECTRIC TWEETERS MOTOROLAJoin the Piezo revolution. The low dynamic mass (no voice coil) of aPiezo tweeter produces an improved transient response with a lowerdistortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of upto 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER.

TYPE 'E'

TYPE 'A' IKSN2036A )3" round with protectivewire mesh. ideal for bookshelf and mediumsized Hi-li speakers. Price E3.45 each.

TYPE 'B' (KSN1005A) 3 2," super horn. Forgeneral purpose speakers, disco and P.A.systems etc. Price E4.35 each.

TYPE 'C' (KSN6016Al2" v 5" wide dspersionhorn, For quality Hifi systems and qualitydiscos etc. Price E5.45 each.

TYPE 'D' (KSN1025Al2" 6" wide dispersionhorn. Upper frequency response retainedextending down to mid range (2KHz). Suitablefor high quality Hi-fi systems and qualitydiscos. Price £6.90 each.

TYPE 'E' IKSN1038A) 3%" horn tweeter withattractive silver finish trim. Suitable for Hi fimonitor systems etc. Price E4.35 each.

TYPE 'F' (KSN1057A) Cased version of type'E'. Free standing satellite tweeter. Perfgctadd on tweeter for conventional loudspeakersystems. Price E10.75 each.P&P 20p ea. for SAE for Piezo leaflets).

OMP80 LOUDSPEAKERThe very best in quality and value.Ported tuned cabinet in hard wearingblack vynide with protective corners andcarrying handle. Built and tested,

employing io in British driver and Piezotweeter. Spec: 8o watts RMS; 8 ohms;45Flz zoKHz; Size: win x 15in x 12in;Weight: 3olbs.

Price: £49.00 each. £90.00 per pairCarriage: £5.00 each. £7.00 per pair

1K.WATT SLIDE DIMMER Controls loads up to 1KW Compact size

414"x 13 " x 2 t4"16

Easy snap in fixing throughpanel/cabinet cut out

Insulated plastic case Full wave control using 8amp

mac Conforms to BSKO Suitable for both resistance

and inductive loadsInnumerable applications inindustry, the home, and discos/theatres etc.

Price: £11.70 each + 50p P&P(Any quantity)

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Belt driven Aluminium platter Precision calibrated counter balance Antiskate (bias device) Damped cueing lever 240 volt AC operation (Hzl Cut -ourtemplate supplied Completely manual arm.This deck has a completely manual arm and isdesigned primarily for disco and studio usewhere al the advantages of a manual arm are

required.Price: £28.50 + E2.50 PFtP

ditPOWER AMPLIFIER MODULES

BK ELECTRONICSPrompt Deliveries

VAT inclusiveprices

Audio EquipmentTest Equipment

Thabnydarand

Leader

KEYBOARDS

manufactured from a tough polycarbonate f dm mounted on introglass fibre printed circuit boardassembly incorporating silver platedCCCIIICt.16 way numeric keyboardStandard keyboard providing 0-9and A -F functidets.

t Sae: 100mm x teemm x 2min. Price. ES 99

Weise N..ed Keyboard Foil sue 55' key non encoded keyboard with the..arena* rmpired functions m a°softy array matrix output uses 16 pn1311. asdet.

.Siza:35Onsn x 101mm x 2mm. Price: £13.W + 50p p&p

I 11

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100 WAIT R.M.S. AND 300 WATTMODULESPower Arnold, Modules with integral toroidaltransformer power supply, and heat sink. Supplied,as one complete built and tested unit. Can be fittedin minutes. An LED Vu meter is available as enoptional extra.

SPECIFICATION:Mes Output Power: 110 watts R.M.S. 101101. 100)

310 watts R.M.S. ICIMP 300)loads: Open and short circuit proof. 4-16 ohm..Frequency Flespongs: 20Hz - 25KH. f 3dB.Sensitivity for Mae. Output:500mV et 1.0K COMP 100) 1V at 10K IOMP 300)

1T.H.D.: Lea than 0.1%'Supply, 240V 50HrSiege: OMP 100 360 x 115 x 72mm

OMP 300 460 x 153 x 66rnmr Prices. OMP 100 (31-50 each + C2.W PEW

OMP 300 £89.00 each + £3.00 PEWVu Meter f6 50 each + 50p PEW

Matching 3 -way loudspeakersand crossoverBuild a quality 60watt WS system 8ohms

Build a quality 60 watt R.M.S system.

* .10' Woofer 35Hz-4.5KHz* 3" Tweeter 2.5KHz-19KHz*5" Mid Range 600Hz-8KHz* 3 -way crossover 6dB/oct 1.3 and 6KHz

Recommended Cab-siziV26" x 13" x 13"Fitted with attractive cast aluminium fixing es-cutcheons arid mesh protective gi ills which areremovable enabling a uniquechoice of cabinetstyling. Can be mounted directly on to bafflewith or without conventional speaker fabrics.All three units have aluminium centre domesand rolled foam surround. Crossover com-bines spring loaded loudspeaker terminals andrecessed mountino panelPrice £22.00 per kit + E2.50 postage and pack-ing Available separately, prices on request

12" 80 watt R.M.S. loudspeaker.A superb general purpose twin cone loud-speaker. 50 oz. magnet 2 aluminiumvoice coil. Rolled surround. Resonant fre-quency 25Hz. Frequency response to13KHz. Sensitivity 95dB. Impedance Bohm.

Attractive blue cone with aluminiumcentre dome.Price £17.99 each + £3.00 P&P.

B.K. ELECTRONICS37 Whitehouse Meadows, Eastwood, Leigh -on -Sea, Essex SS9 5TY ._.

_VISA

* SAE for current lists.* Official orders welcome. * All -prices include VAT. * Mail order only. * All items packed (whereapplicable) in special energy.absorbing PU foam. Callers welcome by prior appointment, please phone 0702-527572.

TYPE 'c'

N EWS:N EWS:NEWS:NEWS:NEWS:NEWS:NEWS

DIGESTLow -PriceHighPerformanceOscilloscopes

STC Instrument Services haveintroduced the new Iwatsu

SS5710 and SS5711 4 -traceoscilloscopes which combine veryhigh performance with pricessignificantly lower than in-struments of comparable perfor-mance. Both models offer highaccuracy combined with easy touse controls and feature delayedtime base (50ns min. for the

SS5710 and 2Ons min. for theSS5711), four input channels, full10 x 8cm CRT screen, and anoperating temperature of - 10°C+ 50°C

The SS5710 has a rise time of5.8ns (approx.), a deflection fac-tor of 5mV/div - 10V/div. ±2%(1-2-5 sequence in 11 steps), anda frequency response ofDC-60MHz, - 3dB (x 1 GAIN).The instruments come completewith two probes, an instructionmanual and a storage bag foraccessories.

Prices are a mere £635 for theSS5710 and £950 for the SS5711.For further information contactSTC Instrument Services, Edin-.burgh Way, Harlow Essex. Tel.Harlow (0279) 29522.

31/2 inchMicro floppy

Adding to the proliferation of differentsized micro floppy disks, ShugartAssociates have launched a 3.5

inch floppy disc drive. Claimed

specifications for the new unit, the

SA300, include 500 kilobytes ofunformatted capacity, track -to -track

access time of six milliseconds,135 tracks per inch (80 tracks

per side), 300 rpm rotatingspeed, and transfer rate of 125 or

250 kilobits per second, in single ordouble density respectively. Price is

expected to be around $200 for highvolume orders. Evaluation units will

be available in the se-cond quarterof 1983, but when the production modelwill hit the streets is not yet known.

The multiplicity of standards

(see Will Industry Standardize on the 3"Floppy', Digest Dec '82) can onlybe harmful to end users. It's a greatpity that the manufac-turers couldn'thave got together at the start and

sorted out their own standards

first before laun-ching products. Of

course, it does mean that some userswill end up having to buy two rather thanjust one set of micro floppy drives,

which all goes to make money forsomeone.

Cheap PrintDatac Limited, of Tudor Road,Altrincham, Cheshire have

recently introduced a new rangeof printer mechanisms fromCitizen. The 555 and 575models are 24 and 40 column im-pact printers that featurered/black print, 2 and 1.2 linesper second printing speeds and 5lines per second paper feed.Operation is from 12V DC. Bothcost £49 for the mechanism only(1 -off price).

Interface boards should beavailable towards the middle ofthe year for around £80, andthese will have facilities for serialand parallel interfaces.

160 WattMonolithicSwitch modeSupplyReplacing costly hybrids the L296 PowerSwitching Regulator delivers 4A at a

voltage programmable from 5.1V to 40Vand incorporates features such as softstart, programmable current limiting,remote inhibit and a reset output formicroprocessors. The L296 is mountedin a MULTIWATT-15 plastic powerpackage and very few external

components are required.

For microprocessor systems, thereset output provides a delayed

reset signal when the supplyreaches a preset threshold.Both the delay time and threshold canbe programm-ed by external

components and either the inputvoltage or the output can be monitored.

Crowbar over voltage protec-tioncan be realized simply by ad -ding an

external SCR. The L296 incorporatesthe voltage sense and SCR drive

circuitry for this function.Internally, the L296 is pro-tectedagainst reverse polarity input voltagesand thermal overload. Output short circuitprotection is provided by the

programmable current limiter. Multi-pleL296s can be synchronised easily andremote on/off control is simplified by theTTL-level in-hibit input. The soft start risetime is programmed by an externalcapacitor. SGS-ATES (UK) Ltd.,1 WaltonStreet, Aylesbury, Bucks. Tel. (296) 5977.

HOME LIGHTING KITSTheca his contain all namasor component. andIni&ruChKon & are dmigned to Opiate . men Ow" oralseem and control up to 100. of beefing71311300K RemosConnol £14.30

Dimmer0.1K6 Transmitter toi above 4.20T0300. Touchdinirner £ 7.00

Firtension lire for 2 -waywinching for T0300K 2.00

L133001( Rotary Controlled 3.500,mmer

TOEilt

HOME CONTROLCONTROL CENTREThis New Remote Control Kit enables you tocontrol up to 16 different appliances any-where in the house from the comfort of yourarmchair. The transmitter injects codedpulses into the mains wiring which arereceived by receiver modules connected tothe same mains supply and used to switch onthe appliance addressed. Receivers areaddressed by means of a 16 -way keybOard,followed by an on or off command. Sincepushing buttons can become rather boring,the transmitter also includes a computerinterface so you can programme your favour-ite micro to switch lights, heating, electricblanket, make your coffee in the morning,etc. without rewiring your house. JUSTTHINK OF THE POSSIBIUT1E S. The KITincludes all PCBs and components for onetransmitter and two receivers, plus a drilledbox for the transmitter.Ortlet es XK112. £42.00

Additional Recta/tiers X1(/11 £10.00

ELECTRONIC LOCK KIT XK101This KIT contains a purpose designed lock IC,10 -way keyboard, PCBs and ell componentsto construct a Digital Lock, requiring a 4 -keysequence to open and providing over 5000different combinations. The open sequencemay be easily changed by means of a pre-y/voted plug. Size: 7 x 6 x 3 cm,. Supply: 5V to15 V d.c. at 40uA. Ouput: 750mA man.Hundreds of uses for doors and garages, caranti -theft device, electronic equipment, etc.Will drive most relays direct. Full instructionssupplied

ONLY £10.50Electric lock mechanism for use with latchlocks end above kit

E13.50

MINI KITSMoo TEISPERATLISIEalelaCILLEWTMEMAISTATUses LM3911 IC to sense temperstore (110"C met.) and tnec to switchheater. 1KW (400kW SAM Mate RaleyIdeal fcr switching motors. lights.heaters. etc. Prom logic. Outo-isolated with zero voltage switching.Supplied without frac C2.60

MAiDOT CAMAYDeploys an analogue vollego on alinear 10 element LED display as aber or single dot. Ideal for thermo-meters, bevel indicators. etc. May bestacked to obtain 2010 100 elementdeploys. Requires 5.20V supplyMKS P1IL.1311111311AL 1450TIOMPEPATLME CON111OLLERBased on the SL441 zero voltageswitch. this kit may be wired to form

"buret fire power controller.enabling the temperature of an en-closure to be maintained to within0.5T. Max. load 3KWPALS MANS 111IERB ased on the IN1034E Timer IC thiskit will switch a mein* load on for off )br preset time from 20 mine. to 35hrs. Longer or shorter periods maybe realised by minor componentchanges. Max. load 1KW. feta

J 3440TE DOOR CHIME eraBased on the SA80600 IC the kit is supplied with allcomponents. including loudspeaker, printed circuitboard. a pre -drilled boo (95 v 71 v 35mrn1 and fullinstructions. Requires only a PP3 9V battery and push -switch to complete. AN IDEAL PROJECT FORBEGINNERS. Order as %KIM ES.00

XK113 MW RADIO KITBaited on ZN414 IC. kit includes PCB, wound aerial andcrystal impose and all components to make a sensitiveminiature radio. Sin: 5.5 v 2.7 v 2crns. Requires PP39V battery. IDEAL FOR BEGINNERS. C5.00

COMPONENT ACKSPACK 1 1360 Resistors 47 ohm to 10 Mohan 10 per

value E4.00PACK 2 40 v 16V Electrolytic Capacitors tOpF ti

10000E - 5 per value 0.25PACK 360 Polyester Capectors 0.01 to 10F / 250V -

5 per value 05.65PACK 4 45 Sub -miniature Presets 100 ohm to 1 Mohm

- 5 per value C2.10PACK 5 30 Low Profile IC Sockets B. 14 and 16 - pis

- 10 of *soh f2.40PACK 6 25 Red LEDs 15mm dia,1[1.215

Have you got our FREE ORANGE CATALOGUE yet?NO?! Send S.A.E. 6' 9" TODAY I I

It's packed with details of all our KITS plus large rangeof SEMICONDUCTORS including CMOS, LS TTL,linear, microprocessors and memories, full range of

LEDs, capacitors, resistors, hardware, relays, switchesetc. We also stock VERO and Antex products as wellas books from Texas Instruments, Babani and Elektor.

ALL AT VERY COMPETITIVE PRICES.ORDERING IS EVEN EASIER - JUST RING

THE NUMBER YOU CAN'T FORGET FORPRICES YOU CAN'T RESIST.

5-6-7 8-9-10and give us your Access or Barclaycard No. Answeringor write enclosing cheque or postal order. service evngsOfficial orders accepted from schools, etc. & weekends

LCD 31/2 DIGIT MULTIMETER16 ranges including DC voltage (200 inv 1000v1 andC voltage. DC Current (200 mA-10A1 and resist nce 10-2 M1 a NPN Er PNP transistor gain andlode Check. Input impedance 101V1 Size 155

118 x 31mm. Requires PP3 9V battery 120.00

THE MULTI -PURPOSE TIMER HAS ARRIVEDNow you can run your central heating. lighting, hi-fi system and lotsmore with set one programmable timer. At your selection it isdesigned to control lour mains outputs independently, switching onand off at pre-set times over 7 day cycle, e.g.to control your centralheating (including different switching times for weekends/. justconnect it to your system programme and set it and forget it --theclock will do the rest.

FEATURES INCLUDE 0.5' LEO 12 hour display. Oey of week, smipm andoutput status indicetors. 4 zero voltage switched mains outputs. 50430elz mains operation. Battery backup saves stored programmes and continues

time keeping during power allures. (Battery not supplied). (Maley blanking during power 'ileum 10 conserve battery power.

IS programme limePowerful "Everyday' function enabling outputto switch everyday but um only one time set.Useful "Bleep' function -turns on output for one hour

Direct 'witch control enabling output to be furred onimmdietelV or she, s specified time interval.

20 function keypad for programme entry. Programme verification at the touch of a button

(Kit includes ell components, PCB, assemblyand programming Instructions). ORDER AS CT5000

For a detailed booklet on ALLremote control - send us 30p PRICESand S.A.E. (6" x 9") today. EXCLUDE VAT

DVM/ULTRA SENSITIVETHERMOMETER KIT

This new design is based onthe ICL7126 la lower powerversion of the ICL7106 chip)and 31/2 digit liquid crystaldisplay. This kit will form thebasis of digital multimeter(only few additional resistors and switchesare required -details supplied!. or sensitivedigital thermometer 1.-50C to +150r)reading to 0.1T. The basic kit hitssensitivity of 200mV for full scale reeding,automatic polarity indication and an ultralow power requirement -giving 2 yeartypical bonen/ life from standard 9V PP3when used 8 hours day, 7 days a week

Price £15.50

DISCO UGHTING KITSDI. 1000Kthus value 10r money kit teahen a to chieCtiOhal seouence speed of sequenceand Irequenc: of directionchange. being vaiiable by means of potentioneters and incorporates a master dim""ng contra £14.110012100.A Owen cost venial of the above. leaiuringundrectional channel sequence with speedvariable by reams of a pre set POI Outputsswitched only at mains zwo POSSing pointsto reduce radio int/Avenge to minimum.

Optional opto Owl OLA I Only MOOAllowing audio beet -I - tightresponse01.1000.This 3 Channel sound to light kit featureszero yo taw switching. automatic level con7rol and built inrnic No connectrons tospeaker or amp r equited No knobs to aqua- amply connect to mss supply endlamps. Kwchannell 01 196

"OPEN -SESAME"The XK 103 is general purpose infra -red Iran s.miner/receiver with one momentary (normallyopen) relay contact and two latched transistoroutput Designed primarily for controllingmotorised garage doors and two maxillary out-puts for drive/wigs lights ate range of up to40 IL The unit also has numerous soot icstionsin the home for switching lights, TV, dosingcurtains. etc. Ideal for aged or disabledparsons.The Kit cornprisess mains powered receiver,four button transmitter, complete with pre -drilled boo, requiring 9V Manny and oneoptoisolated solid state switch kit for inter-facing the receiver to mains appliances. Aswith all our kits, full instructions are supplied.

ONLY £23.75

REMOTE CONTROL KITSMU SIMPLE INFRA RED 11LAIMMITTERPulsed infra red source complete with hand held plastic box. Requires a 9V battery. 1420MK7 BORA RIM RECEIVERSingle channel, range approx. 2011. Mains powered with a Mac output to switch loads up to SCKNVat 240V ac 13.00 IRC5001( -Special Price for MK6and MK7 together E12.30WS COOED VORA RED TRANSMITTERBated on the SL490. the kit includes all components to make coded transmitter and onlyrequires 9V (PPP) Pottery and keyboard. 8 x 2 x 1 SunsM.10 1111-WAYKEYBOAROFor use with MKS end MK t8 to generate 16 different codes for decoding by the ML928 a ML9.26receiver (MK12) kit. 13.40MIK1110-Ocennel 4- 3 Anakpue alp Ft ReceiverBased on ML922 decoder IC. Functions include on,standby output. toggle. control of volume,tone and lamp luightness. Includes its own mains supply. f12.110MIK12 101J4AMMIL M RECEIVERFor use with MK8 kit with 16 onion outputs, which with further inert ace circuitry, such ea relaysor trees, WIN switch up to 113 items of equipment on or off remotely. Latched or momentary out-puts - please sPcsnen ordenng. Includes its Own mains supply. 111.16MK1311-WAT KEYBOARD For use with MK8. woe and MK11 kite (4.35M.16 Melee Powered M TransmittMains powered for continuous operation - single channel. for applications such as burglaralarms, automatic d000Gnerk etc. Range approx. 6h. 12.50MI.1713V q.t. MFor use with MKS or MK16. Relay output with OP 3 Amp change -over contacts, may be used aslatched. momentary or 'break beam' receiver. Operates from 13.13V d.c. 1150

Similar to to MKB but with rsnge 01 approx. 6Oit 11.20Amatory Kim M1L2 SAM Mate Relay

to isolated with zero voltage switching. No. tree supplied. 128015 DUAL LATCHED SOLID STATE RELAY

Comprise. 2a solid state relays and etch for use with momentaryversion of the MK 12. 2 output moos required (not supplied!. (4.50

24 HOUR CLOCK/APPLIANCE TIMER KITSwitches any appliance up to 1kWon and off at present times once perday. Kit contains: AY -6-1230 IC,

0.5' LED display. mains supply,display drivers, switches, LEDs.Macs, PCBs and lull instructions.

MT SERVICE TOP QUALITY- LOW LOW PRICES

Tit 11 Boston RoadLondon W7 3SJ

No circuit is complete without a call to -

ELECTRONICS 13/1*CUM

seeVGA)

waken.

CTI000K Basic Kit 614.111111

CTI000K with white boo (51/131e 71rom) E17.45

Add 55p postage & packing +15% VAT to total.Overseas Customers;

Add f2.50 (Eu rope I, £6.00 (elsewhere) for p&p.Send S.A.E. for further STOCK DETAILS.Goods by return subject to availability.

E9am to 5pm (Mon to Fri)10am m (Sat

aL 1431.100T.iii Vex )ukkokcal

Llama:1a MOMS

PARKCAP

w

0

8

TEL 01 567 8910 ORDERS01 579 9794 NCIUIRIES01 579 2842 TECHNICAL ,..

CloCJtala Rpm

hrelVVYELLC.RGE

NEWS:NEWS:NEWS:NEWS:NEWS:NEWS:NEWSNo, It Isn't AMock-upFerranti is now offering itswidely -used tuned radio frequency(TRF) circuit in a TO -92 style plasticpackage, designated ZN414Z:introducing the plastic packagedversion has led to pricereductions of up to 25 % , enablingthe device is to be used in a widerange of new products. One of thefirst of these new applications is inan electronics wrist watch/radio.

The circuit provides a com-plete RF amplifier, detector and AGCcircuit, requiring only six externalcomponents to give a high quality AMmedium wave tuner, operating from asingle cell supply with low powerconsumption.

Simple but effective AGC actionis available using one externalresistor. No setting -up oralignment is required and theZN414Z will give excellent audiooutput directly into an earphone or asuitable output stage. FerrantiElectronics Limited, Fields New Road,Chadderton, Oldham, Lancashire, OL9BNP. Telephone 061-624 0515 andTelex 666803.

Detect DampDesks!

Anew desktop indicator fromVaisala allows simultaneous

digital display of relative humidi-ty and temperature to 0.1 digitaccuracy. The HM 32 humidityand temperature indicator maybe us-ed with a range of Vaisalaprobes, or connected direct to arecorder for a continuouspermanent out -put reading.Relative humidity is displayed in% RH, and temperature in eitherdegrees

Celcius (°C) or Fahrenehit (°F),selected with an internal jumper.The indicator can be operatedfrom a standard power supply, orby a rechargeable NiCad batteryif required. Although designedfor desktop use, the HM 32 has itsown carrying handle for portabili-ty. Operation is simply a matterof switching on, with themeasured values being shownalmost immediately on the large34 digit liquid crystal displays.Full details of the HM 32 may beobtained from Vaisala (UK) Ltd,11 Billing Road, NorthamptonNN1 SAW (telephone 060422415).

Shorts The more observant amongstyou might have noticed a newcomponent supplier, EMOS,advertising in our hallowedpages. Whilst new to the hobbymarket, they are by no meansstrangers to electronics, as theparent company, the GrensonGroup, has been manufacturingstabilising power supplies formore than 20 years. Grenson'sdirector, Stuart Taylor, has said

. . the work that hobbyists aredoing these days is often anythingbut amateur . . .', which is som-thing we've been proving foryears. A portable, self-contained flop-py disk drive tester has been in-troduced onto the UK market byKontext, PO Box 11, East Horn-sey, Surrey (Tel 04865 3406). TheRedwood Supertest is intendedfor field service engineers, andprovides the means of quicklypositioning the heads of floppydisc drives over all the standardtracks of an alignment diskette.The UK price should be aroundf339 inclusive. The new Toolrange Catalogueincorporates a section on powersupplies and transformers. Cleverthese Toolrange people, they timethe release of their press releasesso that we can't keep them backand say what they have in the

catalogue all in one go. ToolrangeLimited, Upton Road, ReadingRG3 4$A, Berks. BICC-Vero have produced anew shortform catalogue special-ly for hobbyists. Productscovered include circuit boards,breadboards, boxes, tools and ac-cessories. Retail Department,BICC-Vero Electronics, Parr, St.Helens, Merseyside. Looking for a project but can'tfind the exact one you want? Newfrom EPI Sales, Central Library,Northumberlands Square, NorthShields, Tyne & Wear NE30 1QU,at a price of f2.50 inclusive, is theElectronics Projects Index No 3.The Index covers projects produc-ed by most mags with cover datesfrom January 1979 to December1980. The next edition, covering1981 and 1982 is almost ready,they tell us, though why anyonewould want to know about pro-jects in other magazines, we donot know . . .

Another new publication,slightly more expensive, is thenew IC Master. Weighing in at3,500 pages (no, we haven't ac-tually checked what the weight is)is a listing of over 50,000 ICs, in-cluding a section on gate arrays,addresses of IC manufacturersand distributors, reps and agents,and an applications note direc-tory. The directory will beavailable in March from Pater-son/Steadman & Partners, 34/36High Street, Saffron Walden,

Essex CB10 1 EP, at f65 a time,they're not cheap, but if youorder before March 1st, there's aspecial reduction to f55.25. Bothprices include post, packing andupdates. Flag waving time: ThandarElectronics have managed to sellf100,000 worth of electronics to a' "major" Japanese instrumentmanufacturer'. They're rathercoy about who it actually is thathas bought their gear. Tangerine Users' Group (TUG)has moved to a new HQ. They arenow at 1 Marlborough Drive,Work, Avon BS22 00Q, tel 093421315. A case for study? Semiconduc-tor Supplies International Ltd,Dawson House, 128/130 Car-shalton Road, Sutton, Surrey SM14RS are now supplying a range ofcases designed for desk -top andother uses, at prices starting fromf5.06 exclusive. Radio Rentals report that thefirst would-be TV thief has beencaught using their Burglar AlarmTV sets. The intruder was not onlydeafened by the alarm itself, butwas set upon by the owner's twodogs as well. The owner felt sosorry for the would-be thief thathe decided not to press charges!

Ambit International havebeen at it again - taking on newproducts, that is. Amongst themare the ALPS range of high -qualitylaser -trimmed potentiometers,the Ritel range of knobs and ac-

cessories, and some low-costpiezo-acoustic resonators. SeeAmbit's ad for their address andordering details. Got a gear? A geared motor,that is, from McLennan servosupplies, Doman Road,Camberley, Surrey. Motors areavailable with a new British -builtgearhead and AC synchronous,DC servo or stepped motors. Alsoavailable is a low-cost reversibleAC synchronous motor. An addition to the 'Way' range of

personal stereos fromPanasonic is the RQ-J20X;Panasonic say that it's the firstpersonal stereo to incorporatedbx noise reduction. At an RRP off110.95, it's not cheap, but if thedbx works anything like as well as itis capable of, and if dbx tapesbecome widely available, it maywell be worth it.

Ross Electronics have recentlyreleased four new mo dels ofheadphones, and also a pair of in-nerear fitting mini -phones, that bringtheir total range to over 20 models.Ross Electronics, 49/53 PancrasRoad, London NW1 2Q6.

Boss Industrial Mouldings Ltd,James Carter Road, Mildenhall,Suffolk IP28 7DE are now selling arange of snap -in lenses for 5mmLEDs. The one-piece lenses areavailable round or square in avariety of colours. The lens islocked in position when the LED isinserted - ingenious, eh?

POWER FET AMPLIFIERS

NEW DESIGNSWith the introduction of four new boards PANTECHNIC have pushed forward theperforman and reliability of their powerfet amplifiers. Four key improvementshave been qlcorporsted in these second generation modules -1.) The use of H-PAK powerfets, resulting in improved thermal efficiency and

consequently enhanced power output capabilities.2.1 Low COq drivers now in power transistor packages, maintaining the superb HF

performince and improving driver reliability.3.) Separate driver and input supply rails a Bowing a 10% increase in available output

power by Increasing output stage efficiency.4.) Weilfairgiada.41p4rgOdIkareriginstant bridging between any two amplifiers

PFA100 Specificationaendwidth 11:40400KHz 3 1d8Output Peeler into 80 100W IVs = t 55V1THD 12014z -2001z1 <OM%THD I1KHz at 100WI 0.004% typ.SNR 12048Slew rate >30 V/uSGan x23

Vs max ± 70V

Price£17.35 (Built & Tested)

£15.17 (KM

PFA200 180W into 811300W into 411IVs = ± 67V)

PFA200 Specification8extmdtx 10Hr100K1li ± 1±8Output ;owe .nto 80 180W IVs WeiTHD (213M -2001z) <COM%THD I1KHz at 1501A4 0.022% typSNR 120c18

Slew rate >30 V/uSGan x23Rir 30KVs mas ± 70V

Price03.87 (Built & Tested)

£21.70 (Kit)

And for those with a taste for power ...PFABOO Delivers 475W into 4 ohms and 600W into 2 ohms. These highly currentcapable units can deliver 25 amps continuous into a load whilst maintaining theexemplary performance figures of the smaller units £42.00 (built Er tested)PFNHV A very special module aimed at digital audio and wide dynamic rangeprogramme material. Delivers 300W into 4 ohms and 8 ohms on a continuousbasis, it will peak for musically significant periods of time at up to SdBs above this.The PFA/HV is the widest dynamic range power amplifier currently available

034.30 bui It Et tested ITHE HEAT EXCHANGER. Other people sell heatsinks. Pantechnic design,manufacture and sell hemexchangers. Reexamination of the heat transfer processhas resulted in a radically new design possessing greatly improved efficiency. Theunit 7" x 4" x r handles PF As up to 300W or 1.2KW when blown E7.50

POWER SUPPLY COMPONENTSToroidal Mains Transformers

Voltage / 160VA

40-0-40 9.71

45-0-45

50-0-50,

.225 VA k 1.300 VA .11.. l*INA_ 44.25 VA

11.36 12.32

11.36 12.32 16.05

16.05 18.80

Special low flux weidings. Carriage included

25A 400PIV Bridge rectifier10,000uF1313V Electrolytics30,000uF 75V Electrolytics

£2.17 For the PFA/HV 500VA£4.13

£10.00 10,000uF 100V Electrolytics

Phone or write} or advice on selecting the right components }or yourparticular application.

All prices excl. VAT. Carriage 75p. Trade supplied

Aak about our preamps, protection boardsand active crossovers

70-0-70£18.06

E5.70

THE POWERFET SPECIALISTS

pantechnic(incorporating J.W. Rimmer)

Willordermilvin

Dept ET1 3, 148 Quarry Street, Liverpool L25 6HQ051 4288485

I 111111.1111,11qiiir teS

Phil F11,,11111.11 01 8006657

NEW! T.V. SOUNDTUNER BUILTANDTESTEDIn the cutthroat world ofconsumer electronics, oneof the questions designersapparently ponder overis "Will anyone notice ifwe save money by chooping this out?" In thedomestic TV set, one of thefirst casualties seems to bethe sound quality. Small speakersend no tone controls ere commonend ell this is really quite sad, as the

V companies do their best to transmit the highest quality sound. Given this background ecompact and independent TV tuner that connects direct to your Hi-Fi isa must for qualityreproduction.This TV SOUND TUNER offers full UHF coverage with 5 preselected tuning controls. It canalso be used in conjunction with your video recorder. Dimensions: 1134"x 876"x 3V."E.T.I. kit version of above without chessis, case and hardware. £12.95 plus £1.50 p&p.

£22.95 £2.00 p&p.

PRACTICAL ELECTRONICSSTEREO CASSET TERECORDER KIT 1,,THP'eATSEEONLY £31.00 plus £2.75 p&p. NOISE REDUCTION SYSTEM. AUTOSTOP. TAPE COUNTER. SWITCHAB LEE.Q. INDEPENDENT LEVEL CONTROLS. TWIN V.U. METER. WOW & FLUTTER0.1%. RECORD/PLAYBACK I.C. WITHELECTRONIC SWITCHING. FULLYVARIABLE RECORDING BIAS FORACCURATE MATCHING OF ALL TYPES.Kit includes tape transport mechanism, ready punched and backprinted quality circuit board and all electronic parts. ia. semiconductors,resistors, capacitors, hardware, top cover, printed scale and mains transformer.You only supply solder & hook-up wire. Featured in April P. E. reprint 50p. Free with kit.

PERSONAL LS AMPLIFIER KITAmplifier for your personalstereo cassette player - asfeatured in January issue ofEveryday Electronics. Turnyour personal stereo into amains powered home unit.Parts:Stereo power amp PCB with allcomponents, £3.50 + 75p p&p.Power supply unit £1.95 + £1.50p&p. Pair of eliptical speakers,£1.50 the pair + E1 p&p. Input & output sockets and plugs, £1.50. Recommended case (for thepower supply and amp only), E2.95 + BOpp&p. P&P inclusive price of £1.75 for any two or more.

125W HIGH POWERAMP MODULESThe power amp kit isa module for highpower applications disco units, guitar amplitiers, public address systems and even highDower domestic systems. The unit is protectedagainst short circuiting of the load and is safein an open circuit condition. A large safetymargin exists by use of generously rated com-ponents, result, a high powered rugged unit.The PC board is back printed, etched and eedy to drill for ease of construction and thealuminium chassis is preformed and ready touse. Supplied with all parts,circuit diagramsand instructions.

ACCESSORIES: Suitable mains power supplykit with transformer: £8.50 + £2.00 D&D.Suitable LS coupling electrolytic. El + 25p p

SPECIFICATIONS:Max. output power IRMS): 125 W. Operatingvoltage (DCI: 50 - 80 max. Loads: 4 -15 ohm.Frequency response measured @ 100 watts:25Hz - 20KHz. Sensitivity for 100w: 400mV@ 47K. Typical T. H.D. @ 50 watts, 4 ohms:0.1%. Dimensions: 205x90 and 190x36mm.

KIT BUILT£10.50 £14.25

11.15p8iP 411.15p&P.

BSR RECORD DECKManual single play recorddeck with auto returnand cueing lever. Fittedwith stereo ceramic cart-ridge 2 speeds with 45rpmspindle adaptor ideallysuited for home or disco.£12.95 + £1.75 p&p. 13"x 11" app.

SPECIAL OFF ERI Replacement Stereo case -ens tape heeds -E1.80 mech. Mono E1.50e ach. Erase: E0.70 each. Add 50p p&p to order.

SPEAKER BARGAINS2 WAY 10 WATTSPEAKER KIT8" bass/mid range and 3)6"tweeter. Complete with screws,wire, crossover componentsand cabinet. All wood pre.cut - no cutting required.Finish - chipboard coveredwood simulate. size 1414-x8%"x 4". PAIR for ONLY

£12.50 plus £1.75 p&p.

All mail to:

21E HIGH STREET, ACTON, W3 13NG.Note Goods despatched to U.K. postal addresses only.All items subject to mailability. Prices ccerect at30/10/82 and subject to change without notice.Please allow 7 working days from receipt of orderfor dispatch. RtvC Limited rosary* the right to se-date their products without not ice. All enquiries sendS.A.E. Telephone cr mail orders by ACCESS welcome.

ALL CALLERS TO: 323 EDGWARE ROAD,LONDON W2. Telephone: 01-723 8432.IS minutes walk from Edgware Road Tube Station)Now open 6 days a week 9 -6 Prices include VAT.

R [qv]

NEWS:NEWS:NEWS:NEWS:NEWS:NEWS:NEWS

Give YourMicro An Eye

Digithurst Ltd are now sellingtwo vision systems suitable

for use with microcomputers.MicroSight 1 (pictured) is a CCTVbased system which uses a MicroEye camera interface to send im-ages back to the computer as 8 bitdigitised video. The system is aim-ed at the educational and R&Dmarket and will be of particularinterest to people who are look-ing for a low cost introduction tothe expanding field of microcom-puter vision and ArtificialIntelligence.

MicroSight 2 is a solid statecamera based system which usesa 128 x 128 CID sensor to capturean image and a high speed inter-face to pass images back to themicrocomputer either as 8 bitdigital video or as thresholdvideo.

Both systems use versions ofMicroSight software which con-sists of a command processor anddisk I/O routines, a camera con-trol routine and three displayroutines: one to allow interactiveadjustment of camera settings,one to display facsimile and oneto display binary images. Amachine code routine is used toprocess images and produce runlength encoded data which aswell as being a compact form ofimage data also allows applica-tions programs access to a struc-tured database. A boundary/edgedetection program is supplied togive the user an insight into theuse of run length encoded data.

The MicroSight 1 system in-duding camera, interface andsoftware costs f499 + VAT. Andfor the micro with a very richowner, the MicroSight 2 system,including camera, high speed in-terface and software costs a mere£1990 + VAT.

BritishCompany InOrbitC ignature of the L -Sat contract

between British AerospaceDynamics Group and the Euro-pean Space Agency on December30 1982 brought the value of BAecontracts for building newsatellites to more than f250millions in 1982. Worth f160millions alone, the L -Sat contractis the highlight of a very suc-cessful year for the company'sSpace and Communications Divi-sion which has also signed con-tracts as prime contractor for twoother new satellite programmes:Skynet 4, the defence com-munications satellite for theUnited Kingdom Ministry ofDefence worth f58 million, andGiotto (see below), worth £34million. Other space contractssigned last year amount to morethan £30 million.

L -Sat 1, a large communica-tions satellite scheduled forlaunch in 1986, is the most am-bitious communications satelliteprogramme yet undertaken bythe European Space Agency,making important advances insatellite platform capability andcommunications techniques. (L -Sat will be used for direct TVbroadcast services). L -Sat and itsderivatives will rank as one of theworld's most powerful satellitecommunications systems with arange of services that can includeTV broadcasts to the home, highdensity international telecom-munications, voice, data and

NO-ONE EXPECTS THESPANISH INQUISITION!

video links, for small earth terminals onbusiness premises, high quality voiceand data links to ships, aircraft androad vehicles and a very high capacityinter -city telecommunications service.

An agreement has been signed byBritish Aerospace (UK), Fokker(Netherlands), Aeritalia and Selenia(Italy), and Spar Aerospace (Canada) toco-operate in the worldwide marketingof L -Sat derivatives. (These signatoriesare the major contractors on the L -Satprogram, with British Aerospace as theprime contractor.) A demand is

foreseen for more than 100 largesatellites before the end of this century.L -Sat has the distinct advantage overmany smaller satellites filling similarneeds in that it reduces the multiplicityof spacecraft, orbital crowding and theneed for extensive ground controlfacilities.

A £34m contract was signed justbefore Christmas between theEuropean Space Agency and BritishAerospace Space and CommunicationsDivision for the Giotto spacecraft,Europe's first deep space probe. BritishAerospace are prime contractor,leading a consortium of. Europeancompanies and will deliver thespacecraft for launch in July 1985 tobegin an eight month journey tointercept Halley's Comet' in March1986.

The Russians and Japanese arealso launching satellites to observeHalley but Giotto is the most elaboratelyinstrumented and will pass closest tothe comet. Its instruments will providedata on the chemical composition of thecoma region surrounding the nucleusand of the tail of the comet. A camerawill take colour, photographs of thecomet's nucleus and measurements willalso be made of its magnetic field.

This is an exciting and technicallychallenging project and the total timefor observation as it passes the cometwill only be a few hours since theclosing speed will be about 70km persecond. A special shield is being built toprotect the satellite from impact of dustarticles that will be about 70km persecond. A special shield is being built toprotect the satellite from impact of dustparticles that will vaporise metal atthese speeds. The trajectory will beadjusted during flight using data fromthe NASA/ESA space telescope in whichBritish Aerospace is also in-volved.There will be no second chance andgreat emphasis will be placed on thereliability of the spacecraft systems.The satellite has been named Giottoafter the Renaissance painter whose1303 fresco 'The Adoration of theMagi', in Padua, depicts a comet torepresent the Star of Bethlehem. This isbelieved to have been based onpersonal observation of the Halleycomet during one of its periodic 76 yearappearances.

Major European companiessupporting British Aerospace in theproject include Dornier System in

Germany, Thom, CSF in France, LMEriccson in Sweden and Contraves inSwitzerland.

FEATURE

SATELLITE TVTHE SEQUELThe government recently chose a system proposed by the IBA for theway that TV signals will be transmitted from satellites, inpreference to one proposed by the BBC. Was it the right decision? VivianCa el explains the difference between the two systems.

Very shortly a milestone in TV broadcasting willcome to an end. The world's first 'high definition'1V transmissions on 405 lines which started

before the war from Alexandra Palace, will soon ceasehaving lasted, except for the break during the war, formore than forty years.

. .

While it was still going strong, the present 625 -linestandard was introduced, and later, the PAL coloursystem. These are serving very well and for most domesticapplications give results which are largely free from glaringinadequacies. The quality of the picture is probably nearlyas good as you can get with the present generation of TVdisplays.

The main drawback which sometimes intrudes is thatover areas of fine detail, such as a herringbone -patterncoat, a false colour is often displayed: this is called crossluminance.

The composite video signal consists of two main com-ponents: the black -and -white detail, termed theluminance signal, and the colour information (actually twocolour difference signals multiplexed), known as thechrominance signal. The picture is organised thus for tworeasons. One is that the transmission can be received byblack -and -white sets which simply ignore thechrominance signal. The other is that economies can bemade in transmitted bandwidth.

The latter reason needs a little explanation. Theamount of information that can be transmitted in a giventime is limited by the bandwidth of the channel. To givegood resolution over 625 lines a video signal of 5.5 MHz isrequired. When amplitude modulated on a carrier thisproduces frequencies of +5.5 MHz and -5.5 MHz or atotal bandwidth of 11 MHz. However, one sideband isredundant and is reduced to 1.25 MHz, giving a band-width of 6.75 MHz. Sound is FM modulated and spacemust be left to separate adjacent channels.

The total channel width is 8 MHz, so it can be seenthat there is little room for any colour information.However, the human eye is much less sensitive to colourdetail than light -and -shade. Hence, the colour signal canbe of a much lower resolution than the luminance withoutany subjective degradation of the picture.

A Red HerringboneThis is useful as it enables the colour to be accom-

modated without extending the bandwidth, by processingit separately as a lower -frequency signal. It is modulatedon a sub -carrier of 4.43 MHz. Why 4.43 MHz? Well, as

MAC has been tested and demonstrated over this experimentaltransportable 'up -link' dish aerial:

CHROMINANCE

linijiliAlltILTIT1171111T IIITI111111

16.646 HzLINE FREQUENCY

Fig 1 Spectrum of luminance signal showing how detailsoccur at multiples of the line frequency. The chrominancesignal is also at multiples of the line frequency, but beingcentred on 4.43 MHz, it interleaves with the luminancemultiples. If there is movement of luminance detail around 4MHz, the signals interact producing spurious colour.

FEATUREmost succeeding lines in the picture are largely repetitive,most of the video information is at multiples or harmonicsof the line frequency, which at 625 lines and 25 frames persecond is 15,625 Hz. In between these multiples there isnothing except on moving parts of the picture.

Now 4.43 MHz falls halfway between two multiples,and any modulation of information such as the coloursignal which is also based on the line frequency, willlikewise fall between other multiples. So, although thesubcarrier and its sidebands occupy the same frequencyspectrum as the luminance signal, they do not mutually in-terfere because the harmonics of each interleave with theother.

This is true of stationary pictures, but when there ismotion between successive frames the information nolonger is at line -frequency multiples, and so luminanceand chrominance signals interact. Hence the herringbonecoat looks tine as long as its wearer remains still, but theslightest movement sweeps the luminance signal detailacross the 4.43 MHz harmonics so producing a spuriouscolour.

Coarser detail does not have the same effect becauseits video frequencies fall below the limited colour regionwhich is just over 1 MHz either side of 4.43 MHz. So detailup to 3.5 MHz is innocuous. To minimise the effect, someset manufacturers limit the video response, rolling it offbetween 3.5 and 4 MHz. This reduces picture resolution,so one bad effect must be set against the other, and asusual, a compromise seems the best solution.

Extended PALSo here we have an evident area for improvement,

though little can be done with present channel bandwid-ths. When satallite TV comes on the scene matters will bequite different. The transmissions at UHF which carry thepresent TV service range from 470 to 854 MHz. However,the satellite transmission will be from 11.7 to 12.5 GHz (1GHz = 1,000 MHz). This will permit wider bandwidths foreach of the 40 channels which have been allocated to theEuropean broadcasting countries.

The actual bandwidth is 27 MHz, although the chan-nel separation is 19 MHz. Interference is unlikely in spiteof the overlap because adjacent channels are assigned todifferent countries with different satellite positions and op-posite polarisation (see ETI December 1982 for a fullerexplanation).

With a bandwidth of 27 MHz much can be done toimprove television standards (the technical ones that is).The BBC proposed a system called Extended PAL (E -PAL),which has as its object maintaining or even increasingluminance resolution without any interaction betweenluminance and chrominance signals.

So how is it done? Low video frequencies aremodulated on the carrier as with the existing system, butthey are cut off at the transmitter above 3.5 MHz. The

L.F. LUMINANCE CHROMINANCE H.F. LUMINANCE

DIGITALSOUND

2 8 10

Fig. 2 Frequency spectrum of Extended PAL. All luminancedetail above 3.5 MHz is frequency shifted upward wellbeyond the range of the chrominance signal. In additionthere is a 2 MHz gap which accommodates the digitalaudio channels.

FROMVISION 0

DETECTORMIX

13 PAH

COLOUR4-A. RED

DECODER -11. GREENCOLOUR

AND MATRIX BLUE

LUMINANCEOUTPUT

Fig. 3 Block diagram of decoder for Extended PAL. Theshifted HF video signals are filtered through a high-passfilter to a mixer which is also supplied with 4.43 MHz fromthe colour decoder. Resulting stepped -down HF signals arefiltered, then added to the LF video signals which are passedthrough a low-pass filter direct from the vision detector.

video frequencies above 3.5 MHz are not lost, but areshifted upwards in frequency by 4.43 MHz. So, detail at 4MHz in the original picture appears at 8.43 MHz and soon. Thus the highest video frequency of 5.5 MHz comesout at 9.93 MHz. Actually, the range extends to over 10MHz, so detail finer than 5.5 MHz is transmitted.

This leaves a gap between 3.5 MHz and 8 MHz. Thechrominance sub -carrier remains at 4.43 MHz and so fallswithin the gap. There is no interleaving except at the ex-treme lower chrominance sideband so there is no mutualinterference.

In the receiver all video frequencies above thechrominance and sound channels are changed back downto their original value and added to the low -frequencyvideo signal, thus reconstituting the full range of theoriginal. The reconstituted signal is applied to the displayto give a high resolution picture that is free from spuriouscolour effects.

A feature of this arrangement is the 4.43 MHz frequen-cy shift. In every PAL receiver there is a 4.43 MHzoscillator which is controlled by a synchronising signalknown as the colour -burst which is transmitted after everyline pulse. The purpose of thi,s is to decode the cplour in-formation, and it provides a phase reference whereby thealternate lines are reversed in phase to compensate torcolour discrepancies due to phase shifts in the transmis-sion and receiving links.

Part of the output of this oscillator can therefore beus-ed for the same purpose as the local oscillator in asuperhet receiver, to produce a change of frequency. Thenew frequency is the difference between that of the inputand the oscillator, so the down -conversion is ac-complished with the minimum of extra components andcircuitry.

A big advantage with E -PAL is that it is largelycompati-ble with existing receivers. These could justignore the band of up -converted high video frequenciesand give aresponse up to the roll off of 3.5 MHz. This is only a littlebelow what is commonly received at present, and noworse than many sets that are mis-tuned. However, thesesets will require some sort of sound adapter - see later.

Another potential advantage is that many countriesthat at present use the PAL system, which is most ofWestern Europe, may find the compatibility feature attrac-tive and adopt it themselves for their satellite broadcasts.

Enter the ChallengerWhat might have proved a simple and logical step to goahead with E -PAL was confused by the entry of IBA'scontender MAC. The letters stand for MultiplexedAnalogue Component which is not a particularly apt

FEATUREdescription, but one no doubt chosen to make a good -sounding acronym.

It is quite different from PAL or SECAM or in fact anyother known system and therefore is incompatible, andcannot be received with any existing receiver. It has onething in common with SECAM in that information istransmitted sequentially.

With both PAL and SECAM the colour information isresolved into two (red and blue) colour difference signals.The third primary colour, green, is obtained by a processof adding and subtracting these with the luminance signalwhich being white, contains all three. In the case of PAL,as we have seen, the two signals are phase and amplitudemodulated on to a sub -carrier which is interleaved withthe video signal. With SECAM, the red and blue differencesignals are transmitted sequentially on alternate lines. Eachis fed to a delay line which stores it for one line and thenmixes it with the incoming one. So each displayed line is a.mixture of the present and previous one which reducesthe vertical colour resolution by half although it avoids theluminance/colour interference of standard PAL.

With MAC, the composite colour signal and theluminance signal are transmitted sequentially, but not onalternate lines. Exactly how the signals are multiplexeddepends on the sound system chosen - see Fig. 4 fordetails. However, both signals have to be time -compressed, so that the luminance is transmitted over40µS and the chrominance over 20µS (compared to the53µS normally required for a line scan, and the 644 inter-val between starts of successive lines).

A -MAC

COLOUR

19.7uS

LUMINANCE

39AuS

ONE LINE

64uS

LUMINANCE/COLOUR

SOUND DATA

0 6 3 f 4 9 # 10

FREQUENCY (MHz) 7.5 9.5

CNACSOUNDDATA

riI

9uS

14

COLOUR

17uS

JLUMINANCE

\I-ONE LINE

64u5

35uS

LUMINANCE/COLOUR OR SOUND DATA

0 6 7 9 f 9 10

FREQUENCY (MHz) 8.4

Fig. 4 Structure of the MAC signal for A -type and C -typesound. Note that the luminance and chrominance signals aretime -compressed less for A -MAC than for C -MAC, thusobtaining the same eventual bandwidth for a lowertransmitted bandwidth.

Both signals are generated simultaneously in thecamera, but the chrominance signal is delayed until theend of the luminance signal for that line, then doubled infrequency and transmitted in compressed form. Theluminance signal undergoes a rather smaller speeding up.As we have already seen, the chrominance signal in anycolour system is of lower resolution, hence contains nohigh video frequencies, so the transmission of thechrominance signal at double frequency is still well withinthe video bandwidth of the system.

At the receiver, the reverse process takes place. Theluminance signal is delayed so that it starts at the sametime as the chrominance, and both are time expanded tooccupy the 53µS line scan period, and both are applied tothe display circuits together. Thus the same object isachieved as with Extended PAL, luminance andchrominance are prevented from mutual interaction but ina totally different manner.

The video bandwidth at present proposed for MAC is5.6 MHz for luminance and 1.3 MHz for chrominance.For a complete line to be transmitted in 4OµS, theluminance bandwidth must be 7.5 MHz; there is,however, room to spare if the same bandwidth is used forthe chrominance signal.

Incompatible - That's What You AreThe principal drawback of MAC is its incompatibility

with any other television system. Whereas existing PALreceivers could be used with front-end frequency con-verters to receive satellite transmissions in Extended PAL,this would not be so if the transmissions were in the MACformat. New sets would have to be purchased, which iswhy I think the TV manufacturers favour MAC! Thisdoesn't mean though that everyone's TV set would be ob-solete overnight when satellite transmissions commence.Terrestial UHF PAL broadcasts would continue for theforeseeable future, just as 405 line transmissions have. Butinevitably there would be pressure to move towards asingle system eventually.

Another factor that perhaps has not been considered,is that video recordings and games are usually playedthrough the family TV. A change of set to another systemwould mean all those tapes as well as the recorder wouldbecome unplayable unless the existing set was retained. Inmodern homes the space required for two full-sized TVreceivers may pose something of a problem. An answer tothis would be dual -standard sets such as were producedwhen 625 -line transmissions began. However, thedissimilarity between the two systems, in my opinion,makes dual -standard sets impractical.

No doubt the protagonists of MAC hope that it wouldbe accepted as a standard by other countries, but as thiswould mean running two separate systems, PAL or SECAMand MAC, then dropping their existing one eventually, thechances appear slim. They are not improved either bypolitical considerations. So, if MAC were adopted here,most likely it would leave the UK out on a limb with a non-standard system used nowhere else in the world.

Therefore, I find it surprising that the advisory panelappointed by the Government to recommend the stan-dard to be used for direct satellite TV broadcasting hascome down in favour of MAC rather than Extended PAL.The chairman, Sir Anthony Part said that 'it was bettertechnically, easier to manufacture, and has greaterdevelopment potential'. The PAL system, he said was 'bas-ed on technology that was becoming outdated'. Sir An-thony, it might be noted, is a chairman of an insurancecompany.

FEATURE

SoundIt is generally agreed that the sound accompanying

the satellite broadcasts should be digital, but there has yetto be any final decision as to its format. The EuropeanBroadcasting Union has looked at two systems, EBUSystem A and EBU System C (there was originally a SystemB, but this was withdrawn at a very early stage).

System A uses a single digitally -modulated sub -carrierwith six channels of sound multiplexed together. Eachchannel would, under the BBC's E -PAL proposals, havehad a 15 kHz bandwidth, sampled at 32 kHz, initially cod-ed into 14 -bit words but compressed to 10 -bits; theresulting 2.048 Mbits per second would have beenmodulated onto a sub -carrier using phase -shift keying.

System C takes a different approach and switches thewhole channel into digital mode during the 9.5 AS inter-vals between picture lines. Using the same techniques fordata compression and modulation as in the BBC's pro-posals, the IBA proposed putting eight sound channels in-to the signal. The IBA also had a proposal for using SystemA sound, though it did express a marked preference forSystem C.

There is no reason why the multiplexed informationshould always have to have equally sized components.The BBC have developed a system whereby a structuremap is transmitted periodically; this tells the receiver howto treat the informaiton it is receiving, ie which bits go towhich output.

Another system, called packet multiplexing splits theinformation up into packets, each one of which has itsown digital label to tell the receiver how it is to be treated.However, this system carries a higher overhead and one ofthe sound channels would have to be sacrificed to accom-modate it.

Further EnhancementWhatever system is finally chosen, further enhance-

ment of the picture is possible by various means. One wayis by the use of a frame store. These have already been us-ed to reduce picture noise.

The technique is based on the fact that each pictureframe is almost identical to its predecessor. Examination ofa short length of cine film will confirm this. Each frame cantherefore be mixed with several previous ones duringwhich time the picture will not have changed much.Noise, though, is different for each frame and the mixingaverages it out.

Mixing two frames by using a single frame -store pro-duces 3 dB noise reduction, but to achieve 10 dB a mix of10 frames would by required necessitating 9 stores. Asframe -stores are bulky and expensive, an alternative is touse a feedback loop across a single store. Feedback can beadjusted to control the mix, the greater the feedback, themore frames recycled and the greater the noise reduction.An optimum value has been found to give 8.5 dB.

While averaging has no detrimental effect on sta-tionary portions of the picture, it produces blurring onmoving parts as would be expected. To minimise this,feedback is regulated by a motion detector which com-pares successive frames. If there is appreciable difference,motion is assumed and feedback reduced.

Thus blurring is avoided to any great extent, but thenoise reduction is also decreased. This is not a majordrawback, as noise is less noticed in pictures with plentyof action than stationary ones in which reduction isgreatest. The system is used by the BBC to clean up noisyprogramme sources, but a frame -store could also be usedin a receiver to increase resolution. This is becoming morepractical now frame -stores are getting smaller andcheaper.

IN 0

MOTIONDETECTOR

AUTOCONTROL

0 OUT

FRAMESTORE

Fig. 5 Basic principle of frame -store noise reducer. Output isfed either direct from the input or from the frame -storeoutput depending on the auto control setting. This isgoverned by the motion detector which compares incomingand previous frames for differences.

Here again the idea relies on the fact that successiveframes are similar with large stationary areas. Instead ofunnecessarily repeating such areas in transmission, theycan be sent and stored, updating occurring when there isany deviation from the stored picture. The transmissiontime thus saved can then be filled with finer detail to addto the stored frame. The BBC claim that a resolutionequivalent to 900 lines can be obtained in this way.

Resolution varies over the picture just as noise doeswith the frame store noise reduction system. Stationary ob-jects appear with the greatest detail, while moving objectshave less. As we tend to examine visually stationary ob-jects, while having little time to do so with moving ones,the subjective effect is not greatly impaired by the dif-ference. It can though produce some rather strange effectswhen a stationary object starts moving slowly away,whereupon much of the detail disappears.

Lines and FramesNeither Extended PAL or MAC propose to change the

number of lines and frames. For all domestic and manyother purposes, 625 lines is perfectly adequate whendisplayed on normal -sized direct -view screens. Colouralso serves to render the line structure less noticeable thanmonochrome. Although having a better vertical resolu-tion, the 819 -line system in France is being phased out, sothe higher number of lines is evidently considered of lessbenefit than other factors. The 625 -line system has alsoestablished itself as a worldwide standard except in theAmerican continent and some Eastern countries.

When projected on to a large screen though, 625 linesdo give a liney appearance, which is a consideration ifthe large flat wall screens that have been said to be on theway for a long time, ever turn up. In such a case the linesmay have to be increased.

In Japan and America where the 525 -line standard is us-ed it is natural that there should be more urgent thoughtsof uprating their line standard. Most of us will not haveseen a 525 -line picture, but the effect can be judged beinghalfway between our 625 lines and the old 405 lines. Not apretty sight on large -screen direct -view sets to say nothingof projection screens!

It comes as no surprise then, that the Japanese Broad-casting Corporation NHK, has devised a new high -definition TV standard for use with satellites. It uses 1,125lines and has an aspect ratio of 5:3, which is closer to someof the wide-screen cinema films that so often appear ontelevision, and also to natural human vision. Bandwidthrequired is 20 MHz which although high by present stan-dards could be accommodated within the channel widthof 27 MHz allocated for the European satellites.

The Japanese hope that their high -definition systemwill become a world -standard. Most of the Japanesemanufacturers have lined up firmly behind it with JVC,Sony, Matsushita, Toshiba, Panasonic, Hitachi and

FEATUREIkegemi either developing equipment or actually having itin production.

America too is more than just interested. CBS are con-ducting trials and propose to launch it in 1987. It is to beexpected that many other countries in the American conti-nent of the 525 -line standard will leap -frog over 625 linesto the NHK system. Likely too, is it that some presently on625 will join them.

A demonstration was held at the EBU's annualmeeting in Killarney using the facilities of Radio Telefis.Material used was a CBS videotape of an American foot-ball match which was projected on to a 100 -inch screen. Itis reported that not only could the stitches be seen on thefootball, but during a scan of the stadium the seat numberscould be clearly read! As such details could hardly be visi-ble to a spectator actually present at the event it cannot beignored that the story came from the land of the BlarneyStone!

So what propsect does the NHK system hold out? On-ly a multiplicity of standards with the possibility of MACbeing used here and straight or enhanced versions of PALand SECAM being adopted elsewhere. It looks as thoughthe hope that the coming of satellite TV might havebrought a common international standard is rapidlyfading, if ever there was any grounds for its existence.

Line and Frame DoublingIn order to reduce the conspicuousness of the line

structure with large projection screens, it is possible todouble the line number artificially by scanning the sameline twice. This can be done with a minimum of modifica-tion to existing systems. As /he same amount of informa-tion is transmitted it does not increase the vertical defini-

tion, but it does give a better subjective effect.Some readers may remember the spot -wobble that

was introduced with some 405 -line receivers. It gave asmall vertical oscillation to the scanning spot and therebyfilled in the gaps between lines. It wasn't wholly successfulas the spot was lengthened as well as widened to form anellipse. This reduced the horizontal definition, and thewhole effect was that of being slightly out of focus. Mostviewers switched it off. Line doubling has the same objec-tive but would not impair horizontal resolution.

Another factor which may be considered for improve-ment is the flicker rate. Flicker is noticeable when the rateis low. This can be demonstrated with a cine projectorhaving variable speeds. As the speed is reduced, so theflicker become more pronounced.

Although the frame rate is 25 per second, the flickerrate is 50. This is because each frame is split into two fieldswhich are interlaced; that is the lines of one fall in betweenthose of the other. Thus lines 1, 3, 5, 7, and so on are scan-ned to be followed by lines 2, 4, 6, 8, to the bottom of thepicture.

Under normal conditions the flicker rate of 50 is notnoticeable, but on larger screens, large bright areas canproduce flicker, especially if seen out of the corner of theeye. The American frame rate of 30 giving a flicker rate of60 is better, though only marginally so.

To increase the number of frames would entail an in-crease of bandwidth, but as with the line, the flicker ratecould be doubled by scanning each field twice in thereceiver. A similar method of reducing flicker is employedin cine projectors where the light is interrupted not onlywhen each frame is pulled down but also once or twicewhen the frame is stationary in the gate.

MODULES FOR SECURITY Et MEASUREMENTINTRUDER ALARM CONTROL UNIT

CA 1250

Built-in electronic siren drives 2 bud speakers Provides exit and entrance delays together

with fixed'alarm time

Battery back-up with trickle charging facility Operates with magnetic switch°, u/Sone or

I R unite Ann -tamper and panic Lai ioty

This evening new module offers all the possiblefeatures likely to be required when building anintruder alarm system. Whether used with only 1 or2 magnetic switches or in conjunction with severalultrasonic alarm modules or infra -red units. a reallyeffective system can be constructed at a fraction ofthe cost of comparable ready-made units. Suppliedwith a I ulty explanatory Data Sheet that makesinstallation straight forward, the module is fullytested and guaranteed'available in kit form C16 95 VAT

Stabilised oupus voltage for external units 2 operating modes - full alarm/anti-tamper and

panic facility Screw connections for ease of installation Separate relay contacts for switching external

loads Test loop facility

DIGITAL VOLTMETER MODULE DVM 314Fully built ft tested

Positive b negative voltage with an FSD ol999 inV which is easily extended

Requires only single supply 7- I 2V High overall accuracy - 0 1% + 1 digit Large bright 0 43- LED displays Supplied with lull applications data

With this fully built and calibrated module a wide range of accurate equipment such as multimeters,thermometers. battery indicators etc can be constructed at a fraction of the cost of ready-made units. Fulldetails are supplied for extending the voltage range measuring current. resistance and temperatureFully guaranteed. the unit has been supplied to electricity authorities. Government departments. etc.

Temperature Measurement Kit DT.10 £2.25 + VATUsing the I.C. probe supplied, this kit provides a linear output ottOrnrC over the temperature rangefrom 10"C to 100'C The unit is deal for use in conjunction with the DVM module providing anaccurate digital thermometer

Power Supply PS.209 £4.95 4 VATThil fully built mains power supply provides two stabilised isolated outputs of 9V. 250mA each. The unitis ideally suited for operating the DVM at Temperature Measurement module.

ULTRASONICALARMMODULEUS 4012Fully built& tested

Adjustable rangefrom 5ft. to 25ft.

A reallyeffective fully built

module containing bothultrasonic transmitter and

receiver and circuitry for providingfalse alarm suppression. This module,

together with a suitable 12V power supplyand relay unit as shown, forms an effective

though inexpensive intruder alarm. Supplied withcomprehensive Data Sheet, it is easily mounted in

wide range of enclosures. A ready -drilled case and necessaryhardware is available below.

Power Supply Et RelayUnits PS 4012 £4.25 +VAT

Provides a stabilised 12V output and relay with 3Acontacts. The unit is designed to operate one or twoof the above ultrasonic units. Fully built and tested.

Siren ModuleSL 157 £2.95 + VAT

Produces a loud and penetrating sliding tone coveemg from 9.15V Capable of drivir39 2 off 8 ohmspeakers to SPL of 110db at 2M.Contains on inhibit facility for use with shopkhing bops etc or other break to activateCircuits

Add VAT & 50p post and packingto all orders.Shop hours 9.00 5.30 p.m.(Wed. 9.00 - 1.00 p m.)Units on demonstration callerswelcome. S.A.E. with allenquiries.

Hardware KitHW 4012 £4.25 + VATA suitable ready -drilled case with the various mount-ing pillars, mains switch socket and nuts and bolts.Designed to house the ultrasonic alarm moduletogether with its power supplySire 1 53mm x 120rnm x 45mm.

* ACCESSORIES *3 -position Key Switch to use withCA 1250 supplied with 2 keys

Magnetic switch (with magnet;5' Horn speaker for use with CA1250and SL157

E3.43

E1.17

CIAO

RiSCOMP LiMiTEDDept: ETI1521 Duke Street,Princes Risborough, Bucks.Pimp,- : ;

PROJ ECT

ZX81 US R -DEFINEDGRAPHICS

For our second example in the DIY guide to making yourZX81 a whole lot better, we present a project that gives 16K

RAM pack owners the facility for user -defined graphics.Design by G.N. Hill, MA Hons.

The restrictions imposed bythe Sinclair defined characterset can considerably reduce

impact of many programs and theattractions of having user -definablegraphics are apparent. While severalmanufacturers supply modules toexpand the character set, the cost of£20 plus must be a rather dauntingprospect to the impecunious '81owner.

It is possible, however, to obtainuser -definable graphics on the 16KZX81 for a total expenditure of lessthan f1 and some clever work with asoldering iron! It must be said,however, that this is not a project forthe fainthearted, involving as it doesa certain amount of modificationand soldering within the computer;it also renders the computerunusable without the RAM pack.

Principle of OperationIn normal operation the pattern ofeach character is defined by eightsuccessive bytes in the ROM. Eachbyte represents the display for oneof the eight lines of the character,and each binary bit one dot of thatline: Fig. 1 clarifies the way that thisworks. As there are 64 characters, atotal of 512 (64 x 8) bytes arerequired, and these are located atthe top of the ROM from addresses7680 to 8191 (1E00 to 1FFF inhexadecimal). An examination ofthese addresses reveals that thecharacter generator is beingaddressed exclusively when lines A9to Al2 are high.

The additional circuit operatesby detecting when these four linesare simultaneously high with theROM chip select fine, and instead of

allowing the ROM. IQ be switchedon, the Internal 1 K KAM is activated(this is not normally used when the16K RAM pack is attached). This canthen be filled with characters of

CHARACTER FORMATLETTER 14'

=MENNEN NENE NENE MEM MN NENE =MENNEN

MEMORY MAPADDRESS:

7680 7696 7712

BINARY No. DECIMALEQUIVALENT

0 0 0 0 0 0 0 0 0

0 1 1 1 1 1 0 0 124

0 1 0 0 0 0 1 0 66

o 1 0 0 0 o 1 0 66

0 1 1 1 1 1 0 0 124

0 1 0 0 0 1 0 0 68

0 1 0 0 0 0 1 0 66

0 0 0 0 0 0 0 0 0

8120

SPACE 19 Frl

8 BYTES/CHARACTER

//P 0 I R S T

0 124 66 66 124 68 66 0

Fig 1 Memory map of the character generator and the method charactergeneration, illustrated by the letter 'R'.

U

the programmer's choice. Thecircuit diagram is given in Fig. 2.

ConstructionThe circuit is constructed on a

PCB as shown. in Fig. 3. Use fairlythin (insulated) wire, preferably withcolour coding, for the leadsbetween the PCB and computer.The length of the leads will need tobe adjusted carefully duringconnection to the computer PCB inorder to keep the modification asneat as possible.

Installation And ComputerModifications

To open the computer removeall leads and accessories and thenpeel off the rubber pads on theunderside of the computer, takingcare to ensure that the adhesive filmis removed with the pads. Nowremove the five Phillips screwsvisible on the underside of thecomputer; note that these are of

different lengths and must not bemixed on re -assembly. The base ofthe computer can now be liftedaway to reveal the computer printedcircuit board held in place by afurther two Phillips screws, whichmust also be removed. The board isstill attached to the case through theribbon connector and should becarefully folded over the keyboardwhen you want to turn it over,since the ribbon connector is noteasy to disconnect or reconnect.

The positioning of the switchdoes need to be thought out fairlycarefully in order to ensure that itdoes not foul anything. Providingthe switch is not too big, it shouldfit through the top of the case. Justin front of the RAM pack, towardsthe centre of the computer offersthe most room, but do make surebefore drilling the hole that it willall go back together (including theRAM pack connection) withoutfouling. If you find the prospect ofdrilling holes in your beloved

PROJ ECT

computer a little daunting, the leadscan be brought out through one ofthe existing holes (eg round theaerial socket) to a floating switch.

The addressing of the RAM andROM chips is performed in a slightlydifferent way by the computer andit is therefore necessary todisconnect the 10 address lines tothe RAM chip(s), reconnecting nineof them to the (AO' to A8') ROMchip address lines and the tenth toeither an earth or a logic high. Thiscannot be done easily from theunderside of the board, as theaddress tracks servicing the 1K RAMalso service the 16K RAM pack. Themost straightforward (if somewhatinelegant) solution is to remove theRAMs from their sockets, to bendthe relevant legs through 90° andthen to replace the RAMs in theirsockets, but with 10 of the pinssticking out at right angles. It is nownecessary to solder the addressleads to these legs and into thecomputer PCB - Figs. 4a, b, c andd give details.

Spot Your RAMBefore doing this, it will be

necessary to decide whether yourparticular ZX81 is of the 2114 RAMor 4118 RAM type. The formerconsists of two separate chips asshown in Fig. 4a; the latter has onlyone and the position of this isshown as a dotted outline. Identifyeach of the address pin numbersfrom Fig. 4d and run a lead fromthis to the relevant computer PCBhole as shown in Fig. 4c. In the caseof the 2114 type it is also necessaryto run leads between the two ICs. Ifyou find difficulty in solderingdirectly to the IC pins, it may helpto have a very thin strip ofVeroboard pushed over the pinsand solder to this. The leads to theswitch can now be soldered intoplace.

Figure 5 shows the nineconnections to be made to theother side of the computer board;the letters for each connectioncorrespond with those of Fig. 3.Resistor 'R28' is removed from thecomputer PCB and the ROM chipselect input and outputconnections are made through theresulting holes as shown. Figure 5also identifies the RAMCS' track,which must be (carefully!) cutthrough. The PCB fits under thekeyboard by the side of theheat sink.

Testing And ReassemblyIt is worth quickly testing the

computer at this stage. First,

+5V

USER

NORMAL c:

A9A10AllAlt

ROMCS(FROM ULA)

NOTE:IC1 IS 7420N or 74LS201C2 IS 7400N or 74LS00

Fig. 2 Circuit diagram of the user -graphic modification.

HOW IT WORKS

R2680R

RAMCS'(TO INTERNALRAM ONLY)

ROMCS' (TO ROM)

The inputs of the quad NAND gate IC1aare connected to the four address linesA9 to Al2. The output of this gate is in-verted (using the NAND gate IC2b with itstwo inputs connected together) and us-ed as one of the four inputs for IC1b. Asecond input is produced by invertingthe ROMCS (ROM chip select) signalfrom the ULA using IC2a. The third in-put is provided by the switch, which in'user' mode supplies a high and in 'nor-mal' mode a low. The fourth input isheld permanently high.

Thus, when the switch is in 'user'mode and the ROM and the character

generator are being addressed, all the in-puts to IC1b will be high and the outputwill be low: in any other circumstancesthe output will be high. This, therefore,satisfies the condition required by theRAMCS' line to the internal 'user' RAM.

The output of IC2d vides the newROM chip select line by per-forming a_logical NAND between thepPIAI RA rq output and the inverse ofthe ROMCS input from the ULA. Thus,when the user RAM is being selected, theoutput will always be high, and whenthe RAM is not being selected the outputwill copy the ROMIS input.

*59 IX/SNITCH

A9 (R)A10119

ROMCS INPUT (Z)SWITCHAll (T)Al2 (U)

RAMCS' ma/UT tv)oV 1W)

110MCSOWTPOT (Y)

Fig. 3 Component overlay for the offboard components. The letterscorrespond to Fig. 5.

however, check, check and checkagain that all the joints andconnections are correct and thatthere are no solder bridges betweentracks.

Place the RAM pack in positionand connect the TV lead and powersupply lead. With the switch in'normal' mode the computer shouldoperate quite normally. In 'user'mode a regular pattern should coverthe screen (each space now callingup the same random character). Theprogram given below can beentered in 'normal' mode and runin 'user' mcide to ensure that themodification is functioning correctly:

10 SLOW20 FOR N -1 TO 6430 PRINT CHR$ N;40 NEXT N50 FOR N= 7680 TO 819160 POKE N, 25570 NEXT N

PARTS LISTResistors (all 1W, 5%)R1 lkOR2 680R

SemiconductorsICI 74L520IC2 74LS00

MiscellaneousSW1 SPST miniature toggle or

slide switchPCB (see Buylines).

When run in 'user' mode the screenshould suddenly black out apartfrom the top two lines, whichshould then progressively fill onecharacter position at a time from leftto right, each individual characterfilling from top to bottom.

Reassembly of the computer issimply a reversal of the disassemblyprocedure. Ensure that no leads aretrapped between the pillars and theboard and that the correct screwsare used; short ones at the front,long at the back.

Operation Of User GraphicsIt is unlikely that you will want

to redefine all 64 of the availablecharacters and the most likelyrequirement will be to have four orfive special characters amongst theexisting ones. As it is not possible todisplay both the Sinclair graphics

PROJ ECT

UHFMODULATOR

b.

c.

AO RA10 SAll I

Al2 U

RAMCS' V

0

9

7

6

4

2

9

6

7

6

4

2

d.

3

Fig. 4 General view of the componentside of the computer PCB,with 2114 RAM type (4118 type showndotted). Only six of the10 new connections are shown (a). TheRAM address pins arebent outwards (b). Connections into theZX81 PCB from theRAM chip(s) are shown in (c), while (d)gives the addresspin outs for the RAM.

RT)

O 0 00O 0 00O 0 00O 0 00O 0 00:0 00

0 00

O

0 0 AO0.-""

OV

11 CUT TRACKHERE

x

+5V

REMOVERESISTOR

111211)

ROMCS ROMCSITO ROM) (FROM ULA)

Fig. 5 Connections to the underside of thelX81 PCB.' RAMCS' connectionsare shown for both the 2114 type (dotted) and. the 4118 type (solid) RAM ICs.

and the user graphics at the sametime, the simplest solution is to copythe Sinclair graphic set into the userRAM, and then to select some little -

used primary characters (eg > ,f, ?) and redefine them.

The exact way that this is donecan vary, but my usual approach is tocopy the Sinclair graphics into theuser RAM at switch on. Listing 1 givesa short program (using machinecode) to achieve this. When enteringthe REM statement (line 1) it must beentered exactly as listed. Theoutlines of the graphic charactershave been added to clarify whichsymbols to use, and don't miss thethree spaces in line I which requirekeying in. The keyword in line 1 isentered by first . typing THEN(shifted 3), followed by GOSUB anddeleting THEN using the Editfunctions, but leaving the GOSUBintact. As a quick check that the linehas been entered correctly, PEEK16526 should return 118. The programborrows some of the unusedcomputer RAM to temporarily storethe 512 bytes read from the ROMand should not, therefore, be used aspart of a larger program, otherwisethis may be overwritten andcorrupted. If this is a problem, theprogram can be written entirely inBASIC and listing 2 gives such aprogram.

Having thus copied the Sinclairgraphics into the user RAM, eachprogram can then amend thecharacters as required andpreferably restore the original onesat termination.

1 REM Z 2) 2 COSUS WAN2 POKE 16522,803 LET u=LI5R 165144 PRINT -SWITCH TO5 STOP8 POKE 15522,307 POKE 16519,80R LET U=USR 16516POKE 16519,30

R

Listing -1 Program to copy Sinclaircharacter set into user RAM, using amachine code routine.

1@ FAST20 DIM C(512)30 FOR R=7880 TO 819140 LET C1R-7679)=PEEK50 NEXT A60 PRINT -SWITCH TO -"USER"- A

NO PRESS "-COAT-70 STOP0 FOR s TO 8191

AO POKEA A,C7680(A-78791100 NEXT A

Listing 2 BASIC program to copySinclair character set into user RAM.

BUYLIN ESAbsolutely nothing out of the ordinaryin this project, and any of the mail ordercomponent suppliers advertising in thisissue will be able to supply all the parts.The PCB Service order form is on page83.

PROJECT1 REM.00000000000000000000000

00000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

5 LET RD=1638010 DIM 11(8,8)20 FOR Ym1 TO 630 PRINT -XXXXXXXX",Y40 NEXT50 PRINT "ReCDEFGM-68 PRINT AT 150, 'INPUT PIXEL

COORD EO. R1 . MIT NEULINE TO 1.IRISH"70 INPUT A$80 IF 11$m"' THEN GOTO 16090 IF CODE A$(1)<CODE A$(2) TM

EN GOTO 70100 LET YmCODE A$(-28110 LET XmCODE 11$(1)2)-37120 IF )08 OR Xi1 OR Y,8 OR Yc1THEN GOTO 70130 LET R(X,Y)=R5S IRCX,Y1-11140 PRINT RT Y-1,X-1,CHR$ (61÷A(I)161 7010 CL5

TER1052 5TPAIN CHANNT AT G15,9 'WHICH CHRRRC

E,'170 INPUT A$180 LET CRm7580+8=CODE A$190 LET M6=INT (CR/256)200 LET LB=CR-256.HB210 POKE RD,Le220 POKE RD+1,He230 LET RD=RD+2240 FOR l=1 TO 8250 LET 0=0260 FOR X=1 TO 8270 LET D=D+AkX,Y)*2mt(8-X)280 NEXT X290 AD,0300 LETPOKE ROmAD+1310 NEXT320 IF RC(16671 ThEN GOTO 350330 PRINT RT 15,0, -YOU HAVE DEFINED THE MAXIMUM OF 10 CHARACTERS. IF YOU UISH TO DEFINE MORE CHRRRCTER5 PLER5E 5EE TEXT OF RRTICLE UTNERUISE TYPE PRINT U5R 16360'340 STOP*0 PRINT AT 15,41)"****iiiiTYPE Y OR N

60 INPUT RS370 IF R$11)= -Y- THEN PRINT U5R16560380 CL5390 GOTO 10

Listing 3 gives a programenabling up to 10 new characters tobe defined with the aid of a visualdisplay and the information storedin the REM statement of line 1.Only the primary characters (withtheir inverse) can be redefined andthese are the first 64 characters ofthe list on page 181 of the Sinclairmanual. When all the charactershave been defined and"FINISHED?" is answered with "Y",the program deletes itself, exceptingthe REM statement. This can thenbe used as the first line of the mainprogram and a call for USR 16514will exchange the Sinclair characterswith the new characters required; afurther call of USR 16514 willexchange them back.

When entering the REMstatement of listing 3, it is importantto use noughts and to have exactlythe right number (166). This can bechecked by PEEKING 16680, whichshould return 118.

This program (ie listing 3)requires the machine code valuesgiven alongside it to be POKED intothe REM statement. Listing 4 gives asuitable program for doing this andthis should be entered and runimmediately after entering the REMstatement. All of this program(except the REM statement) maythen be deleted and the rest oflisting 3 entered.

If more than 10 characters needto be defined, it will be necessary to

RODRE5516514 62 10 33 196 6416519 17 186 64 229 21316524 222 1 10 0 2371652915534

176222

4219

18612

541

289815539 e 237 176 aes 225

16544 38 35 1 8 016540 237 175 225 1 1016549 237 175 225 1 1016554 0 9 61 200 2416559 215 33 41 65 19516564 3 4

Listing 3 Program for defining newcharacters and storing the informationin the REM statement for later use(left): the values above are to bePOKEd into the REM statement of line1 using listing 4.

Listing 4 Program for POKEingmachine code values into the REMstatement of listing 3.

500 PRINT .UHAT IS THE START RCDRESS? [NORMALLY 16514)-510 INPUT A515 CL5520 PRINT RT 0,0, -INPUT NEXT NOTO SE POKED. TYPE 999 TO TERNS

ARTE-530 INPUT D540 IF 0=009 THEN STOP550 IF D(0 OR 0:255 THEN GOTO 5

38560 POKE R,D570 SCROLL580 PRINT RT 16,0,R,D590 LET AmF1+1608 GOTO 520

add 10 further noughts to the REMstatement for each extra characterrequired; the final address (currently16671) in line 320 will have to beincreased by 10 for each extracharacter, as will the value held bythe two bytes in addresses 16561and 16562 (currently 16681). Thislatter value is held in the usual Z80manner, ie. low byte first and highbyte second. Having added on therequired number of tens to 16681,divide by 256 to give the high byte

(being the whole number part of theresult) and multiply the remainderby 256 to give the low byte. Forexample, 16691/256 - 65.19922.Now 0.19922 x 256 - 51, so wehave to POKE 16561, 51 and POKE16562, 65.

Because the graphics arecompletely unaffected by RUN,NEW, LOAD, and so on, it is alsopossible to enhance many of yourexisting games and programs byredefining specific characters usedin the game before loading theprogram. Thus chess games using I,K, Q etc can have proper chesssymbols, missiles can magically turnfrom As into Cruise look-alikes, andso on.

Further HardwareModifications

While this project wasconceived as a very low-cost entryinto user -definable graphics, severalmodifications could be made tobring a greater degree ofsophistication to their operation.The manual switching could bereplaced by software switching, forexample: if you have aninput/output port, this can be doneby using one of the output portlines as the switch input for IC1b.

Only half of the 1K memory isused and the A10 address line fromthe RAM chip could be switchedbetween high and low instead ofbeing fixed to a high, thus allowingtwo pages of user graphics to beavailable. Again, this could be asoftware switch controlled by aninput/output port.

The PCB before modification; this is a 4118 type (compare with fig. 4a).

is an alternative to AUTOMATIC TEST EQUIPMENT which can be very expensive.MICRODOCTOR is perfectly adequate for diagnosing faults in microprocessorboards or computers in the REPAIR SHOP or on the PRODUCTION LINE. Reportsare PRINTED on the integral thermal printer. Tests supported are CHECKSUM,RAMTEST, WAIT, READ, WRITE, VO READ, I/0 WRITE, DUMP IN HEX, DUMP INASCII, TEST DATA LINES (for shortsbetween data, address and rails), SEARCH(for twospecifiedbytes), MAP (print a memory map of ROM, RAM, I/O and EMPTYSPACE).Supports both multiplexed and non -multiplexed address/data. Standardsoftware will also DISASSEMBLE in Z80 mnemonics - other disassemblers costextra. Programs for board -testing can be written in MINUTES - and retained forMONTHS even if the power is switched off (CMOS RAM is backed -up with

rechargeable battery). Capacity is 15 differentprograms of 12 tests each. Included are twoPROBE CONFIGURATION CARDS (One Z80, other

E29 uncommitted), PROBE with 24 inch cable and40 -pin DIL plug - and POWER SUPPLY. Extras

7 available are 6502 disassembler retrofit . f35,.1 Clip -over PROBE (only needed if uP is soldered-

in)...C35.

for ET121 and ET221 machines which permit the typewnter to be used as aDAISY WHEEL PRINTER for computers implementing the RS232, IEEE 488(PET) or CENTRONICSPARALLEL busses. almost all computers in fact. Greatfor wordprocessing and letter -writing, Same price, fitting I ree if requested (youpay carriage on typewriter if we fit). £195.00

Sandal ilnabsenZwkint,,,enzaThe THANDAR TA2080 LOGIC -ANALYSER was NOT designed by DATAMAN -but we like this instrument and use it for product development. When writingsoftware we use SOFTY for ROM.EMULATION, following the program -flow onthe TA2080 screen. We modified our TA2080 to make it more useful; adding anRS232 OUTPUT TO PRINTER - also ZBO and 6502 DISASSEMBLERS. Now wecan follow program operation in MNEMONICS on -screen and print TIMING orSTATE DIAGRAMS and DISASSEMBLED CODE. Cost of this RETROFIT kit (12Kof program ROM, socket for RS232, interface board, Instruction sheet) is, if

fitted by us and purchased with a TA2080 f195.00if purchased as a kit without TA2080 £295.00

Soity 1anaP5leYes, we still have a few old faithful 3 rail EPROM PROGRAMMERS around, asseen In Kensington Science Museum, if you are still using 2708's get yourselfthis fine old classic at a bargain price £95.00

ItertaftoketEftitowc giadeu ilont £33.00

74e NottAIZIR

uses the MOST POWERFUL LANGUAGE OF ALL - directASSEMBLER MNEMONICS. MENTA has VISUAL AIDS to programdevelopment which the big systems lack: a TV display of PROGRAM,REGISTERS and STACK single-step operation (watch the cursor move I rominstruction to Instruction, see the register -contents change, observe stackoperations, etc.) BUGS can be fixed immediately without reassembling. Fullspeed operation Is supported too- with or without BREAKPOINTS. Designedoriginally for the Schools' Council ioteach microprocessing, MENTA is acomplex CONTROLLER in its own right, like any other Z80 system, with practical,commercial applications in ROBOTICS. Features include CASSETTEINTERFACE, ASSEMBLER/EDITOR, serialDISASSEMBLER (now included asstandard), 24 bits of I/0 - also TV FLYLEAD,POWER SUPPLY and COMPREHENSIVEMANUAL with SOURCE -CODE LISTING.

SOFTY has functions equal, at least, to equipment which sells for over f500.SOFTY EMULATES AND PROGRAMS 2716, 2516, 2732, 2532 EPROMS. (The typeis selected by a personality switch. SOFTY will copy any of these EPROMS toany other). SOFTY has a HEX KEYPAD, a fast CASSETTE INTERFACE, aMEMORY MAP TV DISPLAY with powerful editing - such as INSERT, DELETE,SHIFT -BLOCK and many other facilities -too many to list here. RS232 SERIAL

and CENTRONICS PARALLEL routines for INPUTand OUTPUT are standard. The price includes TV

69FLYLEAD, POWER SUPPLY and ROM

EMULATOR CABLE WITH 24 PIN GIL PLUG.SOFTY is used as a DEVELOPMENT

SYSTEM for new products or 'Lint asSTAND-ALONE EPROM PROGRAMMER.

LOMBARD HOUSE.CORNWALL ROAD,DORCHESTER. DORSET DTI 1 RX.Telephone: Dorchester (0305) 68066TPlex 418442 DATAMAN

Prep.d orders normally shipped by returnPores include first-class recorded post .11 UKSec uric or Red Star etc at extra costVAT should be added at current rates

atatuartest yrs

Playthe AMBIT numbers game .......The long awaited implementation of on-line order processing is with us at last, and whilst this means that ordersfor in -stock items can now be processed more efficiently, it also means that orders should be submitted usingstock codes for best results. Our current catalogue (70p) includes all order codes (watch out for the newexpanded Spring edition), but here's an abstract from some. of the more popular lines to use as a quickreference.

Remember that you can also access our catalogue viaREWSHOP on REWTEL, which now includes on-line current priceand delivery information. You need a 300 baud MODEM andRS232 terminal, (various suitable configurations based onpopular micros have been published in recent past issues ofRadio and Electronics World).

Prices shown here exclude VAT, and the P&P charge is currently60p perorder(unless otherwise indicated).Remember that our telesales service operates with human beings (not 'dumb' machines)from 8am to 7pm {and frequently later) Monday to Friday, and9am to 5pm on Saturdays.REWSHOP operates 24 hours a day, 365days a year with full price and delivery information.

Ambit International200 North Service RoadBrentwood, EssexCM14 4SG

Telecom directory:Consumer 0277-230909Industrial 0.277-231616Telex 995194 AMBIT GDATEL 0277-232628

SPRING ISSUE(#5 - 75p)

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.4210 '54X21 IN IN IN115731 5107139 IN 1.1 1.010157 5100101 IN 151 11517331 53013% In .16 11117135 54 00361 111 8.187117 5100321 113 111 1011111/ 5064137 811 0.11 101

86111 51011 118 114 10712414 514414 111 199 IN50115 50005 111 040 417117414 500001 011 14 1.0.11516 513054 9.14 0.11 IN01150 5400550 III 111 1.140556 500551 111 11I IN50510 510000 112 8.11 IN51651 580009 811 57? 11106640 5100140 101 II/ III003113 31104073 0.11 115 1.255556463 54N003 100 1.25 12177001 540110 1111 500 111774717 540/20 170 5.18 117/74553 510/0 14 1.11 1.11714753 5101153 131 III 11144/101 540304 111 134 1283152505 54 0005 115 120 1213511105 500341 I if 114 1172514444 54 0106 111 1.17 1030511444 4/004 14 145 11100466/ 401061 Ile 137 1.33

50014111 510651 141 11.31 1515541724 510/77 ill 044 .1775110501 51 0'14 415 114 OA

240054 540105 els 824 13123311/4 5101775 111 III 1174522501 NI 000 24 IA OA

25135471 407517 124 013 1.01

AUDI() POWER51119 5415111 121 513 III113140 54 75710 017 12480165 5115145 111 1.42 131ODIN 5/157/1 141 144 14110171 Si 247 /, 111 811 114BO 10 5414100 1.4 111 111391/ 0173037 1.15 131 11119120. 5115022 5.31 112 OA

02156 510153 1.612151131 0 1St IN 1.50 14715010 50 15710 ON 154 III1507N 51110 IN I.0* $ 6171141 100104 315 1.N 17525.60 0007030 4.15 175 1112543 00101) 111 1.41 1.1126014 100004 11. 3.00 2.11

45015 20021 4.16 3 71 3 11

46717 4003211 )41 3.11NOM) 540753 434 1.1 1.15

SMAI L SIGNAL RI1754 SIDON I.11 Ill .1111241 011011741 111 114 1.17

4311 51104173 111 04 OA

11114 5/01154 101 111

55111 .910120 141 ON 1110440 510640 III 91. 11161441 SI 01.41 121 111 1.15117479 MONA ON Off 1.44111674 5/005177 .61 147 6.35

80 05 610091 113 I.II 0.1511195 38 70097 111 111 9.71

87492 510001: IN 151 143470 31 4001 IN 115 100542110 502'91 510 439 3.04

714313 SO 05231 500 .55 0.41173414 401169 131 034 554

11516.460173716.011.145MR74451

504745414/54111710

PINI I771370NNW270N001

RF POWER5108016 115 1.11 BA

SI 14737 111 4.11 14041411 16.N 1111 11.1441405 N 5611 OA

01449 15 51 1411 11.11

5114477 116 111 1/574471 400 4.75550

4741 404 175 3.35

SI INir IN 115 11.11

417Y0 1104 116 112900XN IN 1.7 4.111

SI 031111 I 46 .48 I.4151 13/4 1 5. 6.01 1.1

SMAL I SIGNAL EFT1/2511 540001 IIIMIN NNW IN II. 171VIM 4000 1. 1.2 .5187001 02000 1.91 4.15 175010 5901270 811 Is. 1642114 5400/ 116 111 14115065 51 0105 .40 1.01 1.1120151 51001 131 1.15 5015115 1004015 1.41 114 1.1131451 00337 114 1.64 811MOO NNW 111 141 1553501 100014 141 111 1.714473 1457 116114122 IN 1001

10133 100413 8.8 141 8711113 1170117 44 411 11

DIODES4013 71001 1.11 ell0424 700247 11/ 157 III843/9 751, 131 131 1515018854 1241111 III 104 131NM 11 005 117 III 1.145441 170171 11.11 14I 10*MO/ 116039 1.15 In I58504 11 24N. 141 441 911.10)5 711044 ..26 8 If 6115407 0 4101 Ill I Of 54104002 71 gem ill IN OA

MOH 721004 011 404 OA

MI41 1141411 Olt 1104 Ill1001 0 NON 015 I11 OA

1112152 11701'.8.67 IN III

V ARICAPS11107 0 0,015 110 111 14413111 1005 I38 821 110*10511 0 07055 131 .21 11111105 52045 117 924 8111516411 720045 135 131 11414717 72,2725 I16 100 1 /2177170 7101700 019 0.3 1197544111514 4133684111115 N 14171501150 717,0 III OA IA01211 re 55123101115 72 12355 178 4.10 10001735 777355 475 125 IN01718 711315 151 104 131stroll 74770 4.44 131 05101110 72720 041 131 041

ZENER DIODESIP360337 1227 2 1110 111 017141 111014 110 1/1 111111 22245 70 IN 017

720471 510 ON 017541 120057 111IN OA541 72030 III 1.44 800541 000011 110 III 551051 12414 110 in 06151 7249/ 1.10 1.4 19710 0201001 I70 . 1.0711 1101100 110 101 1141

00101 1.10 IN 0415 710501 ..75 III 84/11 130105 110 IN 51744 720200 LI. IN 1St

47

1201101 811 IN e4u

41

01351 I III

5411 1

541513000120111

12771144

11.14165/

111.53 12003 51.36 11.0

(SE,

SCRS TRIACS111 15 99 100

111755 111 52 55101 011 I.41 III770107 524706 171 151 55401257 5103122 115 Ill 12.01411 01003 012 5f I

15000 5/ 0011 IN 115 118

BALANCED MIXERS680 77003 400 411 OA

Nil/ 120212 5.00 151 OA

5410 710211 535 175 BA

041 7200013 5111 11.41 0411114

34544 rand 4001,202544.151000 III III 111417115.4 15074 all 111 9.103441020N041522307 all I tf 01441741,104 14017110 11 8.16 0.00454177.144. 751070 115 II/ 01571101 ram 75044 500 111 111(00474 0.41 IS 30410 119 1.11 017

51004 15750 DIA 1.1107010 10 15 70401 010 1111 eel607171 44, 15 10720 111 114 111COI /1 754 1510/4 8.11 III IIIC04311 001 131034 1.10 0 II 111145180 0 4146 11090 Ill 105 411

1.5110760 2.5 A lonni LEDs4070 444 7120740 III III III30411 09. 1510110 1.19 111 11760117 4471 7570760 004 I 1174040 00 153040 144 121 a 11

604 14501 1E0

.21551.070 /5104 158 OA OA

5045 00/44, 1.1000 111 OA OA

I FE Opt. utiple515737 1540117 I 41 1 11 119

IIA7 DIFFUSED4005 /MX 111 111 114550 1401210 011 II? 1.71

5377 1543110 1.28 111 1:7011 110311 111 .15 I0010 7503100 111 11I 1114131 7501110 4/6 111 1717131 75 03310 540 111 .175311 110314 IN $11 II/3434 150302 117 111 5001 70000 1111 34 all5322 758340 111 .11 .174344 150341 01 0.11 111010 /MIX 113 111 11S5511 1545513 Ill 100 1415511 13097/9 81 1.75 5170013 754571 121 111 III35/0 750514 117 871 I It071 75155710 1211 1.37 135432 75 MX 10 1.11 I/5523 75052X IN 135 117

4510 1503300 111 1.11 115047? 1505310 01 1.14 121750 1105310 144 1.11 111413 1505230 9.04 1.71 .173510 14071130 I/ 1.14 1.11

5511 75000 III 1.21 I.11542 400110 ON LI. 047IRO 5503430 Ill I.I. 1115550 750300 117 III .155551 150010 171 471 IN4557 454575 1/1 47 .111555 111 0 .17

TM COLOUR5518 1505131 041 157 153

LED, WITH CHROMEMOUNTING BEZEL

155050ent Typo 13.54 LED/AN 00150 III I 41 1410100 150460 111 117 1157710. 7603)0 114 111 14/05044 4 SONO 4.00 511 .4554s0540 Trw 434.07 1.0110.1 755150 l6, 5.4 1412441 15/7410 155 147 141roma 7541070 1.54 I41 141444 15040 IN .51 146

548108751 E45. 15.50 LE0115770 (80 151 IfI

4/14 7767000 If 851 554141. 7572070 IN 011 .5400 156100 14 162 151

5404540 Typo 10244 LEMRea 5763150 111 1.11 1317,.,. 15 63510 9 54 .11 1.51

7.60 11304 1.151 04 Ill0/ 044 /645450 111 .62 161

I !NEAR IC,11110211 el 00010 300 3.01 1118115 0100471 500 400 175

1145 1761742 I IN 155 11611434 113234/ 151 IN IA2113 000131 111 011 ill22111 VOL,' 111 011 11307871 41415'1 21 011 III47611 00,47 111 0.00 111112714 610300 417 514 1115804 0 ON, 127 531 .2414304 51010 171 016 III1030101 Valor I15 011 15019114 010 111 041 .410/305 110145 114 1.11 III

41234'700 141 OA

14341 fr MOO IN 111 17511151 47725110 141 141 11.41

11152 410351 .76 171 III111340 57170410 1.11 111 III14311 70141 III 712 OA

0312 01 000 104 111 OA

1941111 70017 IN I.13 I55144433 11071 14 In IN7047510 610400 158 1 N IA44401.1 170420 1N 211 011

04241 4104270 In 544 OA

154241 41 1242 4 71 4 14 411

0111111 7014 7 II 11 IA04327.210 00003 114 1412174154/10 410431 11 51 11 N OA

244147 510400 I.N 11 111

065564 17 NM 111 IN 11

16541 410410 100 115 915PEW 1100541 I.0* 1 M 117

45555 170650 108 171 111

41161 410301 441 1141

115806 /74504 1.0 III 0114507 1189562 4 01 51 84

11511 1190591 411 101 11151565 7000 198 651 11145164 07011 IA IR 175

647 17 011517 7.14 115 11

70670/1 11 04 1.11 1 15 1414614 1111114 3.11 200 1104/0104 0 010 1.81 161 IN6100 /10701 131 14 0.12

417104 40174 114 .11 10054100 8777 8.15 151 160.51/7151 17/7110 1.15 II. 111.473140 111731 III 6 If .110474136 61 01410 111 112 1554747131 1101477 III 119 11801410 110740 6.11 117 1.11

4674101 110000 5 30 1./I 15/0441 170074 115 OA OA

714101 /1 0%1 171 116 1457111121 ft 0101 5 11 111 I.51

7011021 57 0100 1 II Ill 150

380111 67 01031 1.11 1.11 1152147035 A/ 07034 5 70 111 I /570410501 67 07054 I 46 1 14 .151004/ 1101062 1.4 115 1.45

7011572 V 01072 1111 IA OA

154 16044114 74 7500 10.'041574 1111104 IN 414 1357041013 70711 In IN 1157041110 4140140 4% 211 IN

1561137 11 73177 111 1 11 14111.1111 4741138 34 171 116141197 41111711 1.41 III 1147097230 610110 344 1 12 514

147301 /7014.3 111 OA OA

051107 870517 715 OA IA4511106 410717 IN OA OA

46/24 870511 311 111 IA1541350 41073!0 1 01 111 OA

711370 1111119 191 045 145101311 0101318 010 I If 711414510/ Or 14501 040 14 147112141/ 41041 125 196 IA27910 0001 111 I 11 1

30111 077071 IN 114 04530612 170411 1.4 1.54 135

5/1413 011111 101 155 11/11131 /1 4741 24 001 1.50141 110101 051 025 5.15

61623 870143 144 135 731511121 II 01415 2.14 010 I

511625 mum11131 II 01130 110 100 1045116411 0101 335 1.00 11561141 0101147 1/1 154 115

7184 II 07140 3.15 IN 1751542003 110457 1.21 I54 1.15

1100240 410704 121 354 1111141217 11 0740 1.10 151 151251117 810101 1.N 0.14 III511440 0341 1.71 055 .

411010 1.64 1.1 11570115 4103123 IN I/1 III7131301 113745 LN 04 1720111431 8135301 IN ON III714741 3744 OM 042 13501/1111 11 41% 1.11 1 N 1001117101 /71004 1 47 7 71 I 14913357 874115) 2.85 100 115

81.3/51 uw 11110151114/1151 11 01151 2.n 701 In01001 1783701 (*N 1115 OA

583742 871345 1414 It It IA4300 11100 1111 lit 1.14

/83505 11 INN ON IIf 116.1514142 110414 1.00 754 111191053 410415 1.11 0.41 1 1444.05 al 044114 I .71 I 1111011 110412 IN 155 11404411 8104413 1 II I4 11455411/ 1704417 I.0* 1.51 1141/44101 0000 1.14 4.61 951101421 I, 744217 115 115 1 64104421 11144117 tlf 1.16 II10421 40421 114 In I If40121 40411 165 112 1/56610 01041 1.38 7 II 1454451 070441 IN 256 101011131 014133 1 15 155 1.1131433 6,041 111 145 11141411 11 NW 351 2 16645437 170017 1.11 131 11.41141/1 51 1417 0.11 181 1118441 11041 1.31 115 111.14445 51 144515 340 I N 111514141 4144424 7.11 235 11541441 001W 1.15 115 1151515044 4/0704 1.11 715 1.36

MC 514 1,05117 9.11 111 IA15551/ 17 55120 7.15 I 75 1511515024 VI 05614 4.15 01 OA

50440 11 MOO 1.75 41 N614170 114270 713 1 14 111515310 171170 111 205 7151:5444 6, OHM 331 111 171518800 /I INN 116 127 Ileuse. (10174 l4 I.5. 111SINN NM 271 714 46$15490 8744880 3 55 3 45 33005700 fl42770 175 135 5705156/10 /14110 141 IN 51115/275 I7 047J 315 3/1 150(1511551 473550 IN 175 57011114110E 701 400 117 185

1051.11152 6103)61 176 741 515M50761 I/ 09055 1.71 1.41 115415170 1110170 1.17 155 1.111410121 1770111 115 301 I 546111522 41 11213 1.15 7 04 1.51417120 0 11235 146 1 31 715

NA 1402 II 7103 111 111 1114.412017 87117 IN IN 11.54

0177447 171122 IA 1.354.7247 1201 711 5.4 In5617411 II 1412 151 1.04 111511770 0 13740 0.33 431 141544.104 8150115 1/6 155 156/15550335 415%3 1111 341 2.5610450100 53102 l.5. 154 412

PRFSCALER2744 170130 017 214 OA

J215 70004 3.16 2 0517751 OF 0.410 IN 10 48113600[ 510110 1316 1111 IA9515075 0 0372 3.00 / 71 2.411

9212118 11 0137 3.14 On 136405573 1705523 1131 IN III4595174 4105514 75 31 LN 1150115775 4105515 515 105 4.01110455/13 403516 711 116 4111311552/1 115570 915 115 5151511710600 41071% 011 OA IA57710767 1107107 956 54 84517757 61037, 14 s IS 41117871114 /511/7 11.61 .1 0412442181 611112 1191 09 54C1173151 1170721/ 50 OA OA

1141119 70439 315 74 41NMI 67167 IN 511 111

50711 1101293 174 111 SIS5540 74000 14 111 491401067 071055, 0.45 1 IS 171

MINA 17 1405 1.411 565 4.55

5441015 47W55 400 101 11544051 4752 1.01 575 3561111451511 01410 4.00 514 111471457535 114510 154 6 35 t14177115159 6115156 111 4 11 1.11

MIN ELECT ROLYTICS

RADIAL PCB MOUNTING114 2599 ,Oo

07 54 4131/8 .11 115 IN7. No 95100 111 114 105

7.2 WV 0523500 117 916 In0.1 10 051340 111 IN IN

401 505 05 47501 1.1 11111 106704 Mt Of 10606 1117 In .0115. NV 05 INN 117 1111 006114 705 02250 I.7 IN 80172. 756 0511527 117 IN 806735 435 051601 .66 1311 1.07

114 137 531101 II/ 111 LOS344 NI 05 5160, 111 117 14441 10 05 4411 611 I.0* 100

/ 11 44)0 411 111 111475 IN 04 445/ IN II/ INIII Ayr 44)0 111 IN IN44 IN 0518/05 101 116

745 31645 lel III IN70 0 01 19505 10 018 50714. 131 /3 10708 115 515 1 II22115 IN 02210 111 1111 IN2/01 35. 1417707 914 III .1117164 5111 OWN I II 115 I50 IN 0534701 III 110 I.II30 46 050107 III 115 5 714/61 11 040365 118 181 I IS474 10 04170 114 .12 111

410 257 01741 111 its 112Alb 50 054/701 111 113 1

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1100 474 0014 IN .is2750 0 4220 111 153 111711115 Xo 05711, I.0* 115 I4

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544I4 120, 010 511 103

10 117 0/ 1544724 277 05410 050 .51 5/1 5'040 110 111 911 114ULTRA MINIATURE 9655 046405 117 Ill 411

1.1 041505 1.01 11010 OS 70514 111 1.42.4 0522514 9.1 500

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2254 050772 114 111 III 4 I. 4100 515 022 1111510 010177 1.31 112 101

ULTRA LOW LEAKAGE 14 0470505 144 141 III742 0520, 1S 855 144

0 14 01410 1% 1.41 IN0 270 0 71104 113 111

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1094 111 1.11

151 057754 511 ellIIIIII 110 7801. .4 III 14

1101, 001 III 154047504 114 III05100 851 110

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POLYSTYRENE1161 07 3314 84 911 II. 14/ 841040 IN Ill In451 4100 1.14 1.1 III470 054404 116 III112 750 44140 ISO 191 111

110 01 1009 IN 117 111/OW 41013 011 III 113 110 04 2.'000 IN 117 111

HIGH RIPPLE CAPACITOR 710 0700 IN 1.17 IN

100000 00,015 111 041 44100 34000 1114 $47 IN500 44 HON 811 811 III

COMPUTER GRADE 000 04 Mel 100 .97 IN1000 047742 en en I07

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100,511.

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Ambit international200 North Service RoadBrentwood EssexCM l4 4SG

Telecom directory:Consumer 0277-230909Industrial 0277-231616Telex 995194 AMBIT CDATEL 0277-232628

FEATURE

LASER DIODESThe subatomic goings-on at a p -n semiconductor junctioncan, in some materials, generate pulses of laser light. PeterGatehouse explains how, and it'll disappoint anyone hopingto make a death -ray with a handful of 1 N4148s.

Since the first lasers were born on the laboratorybench in 1960, when ruby and helium -neon deviceswere first set up, a vast spectrum (pun intended) of

lasers has gradually been uncovered (or stumbled upon).There are now thousands of known laser lines; somematerials can emit many different lines according to theenergy levels between which laser action can occur.However, very few of these are convenient for use outsidethe laboratory as many require temperatures far below0°C or use very exotic and troublesome materials.

The ruby laser is not obsolete, and some manufac-turers are clearing their stock of these at reduced prices ofseveral thousand pounds. It is an example of the solid-statelaser, which, as its name suggests, has a solid lasermaterial. A modern type is the neodyium laser which is apowerful and robust device and probably the most com-mon solid-state laser, usually giving an infra -red output at1060 nm at up to a few hundred watts power.

It'sThere is no doubt that gas lasers are the most widely

used. This is perhaps surprisingas a gas is hardly as conve-nient to deal with as a solid, but gases have several endear-ing qualities: (usually) completely even distributionthroughout a container; the ability to flow so the lasermedium can be circulated to assist cooling; and they arefar easier to prepare as a laser medium than solids,because for the latter highly pure and perfect crystals oftenneed to be 'grown' and then cut and polished, which is ex-pensive. Gas lasers fall into one of three groups, depen-ding on what gives rise to the energy levels necessary tolaser action. Energy levels of neutral atoms are used in onetype, those of ions (atoms that have lost or gained one ormore electrons) in another and the third employs themodes of vibration of molecules.

The output from a gas laser is of high quality andsometimes the efficiency (power output in the laser beamdivided by the power fed in) is as high as 20% but usuallyonly a fraction of a per cent is obtained (which is typical oflasers in general). Helium -neon gas lasers are in the firstgroup: in the mixture of gases, helium is excited first, thentransfers its energy to the neon which releases it in laseremission. Helium -neon lasers are sold by some electronicscompanies and you will find them in many school physicslabs. They yield a high -quality continuous red beam whichis difficult to use without producing the interference ef-fects you can spend hours trying to discern with othersources of coherent light. At a cost of around f100=f200(with a power supply) this is the only type of laser withinreach of the (wealthy) amateur.

The Ion AgeThe second group, ion lasers, will be found in any

university physics lab, as they offer many different output

A typical infra -red emitting laser diode. The light is emittedthrough the clear window in the end.

frequencies. These are selected by placing a prism in thelaser cavity which sends different frequencies in differentdirections and putting the end mirror of the cavity in thepath of the desired frequency. Ion lasers also yield farmore power than the first group (which can provide onlymilliwatts), giving many watts continuous output. Typicalion lasers are the argon and krypton lasers which betweenthem can lase at various lines from 437 to 799 nm.

The third group, molecular vibration mode lasers, in-cludes the carbon dioxide (CO2) laser which is an extreme-ly powerful and efficient device that yields infra -red linesnear the 10600 nm 'atmospheric window' (ie the at-mosphere does not absorb it, unlike most infra -redwavelengths). In continuous operation it can yield severalkilowatts. Military scientists have shown much interest inthis device and the Americans have recently built one intoa large jet aircraft. The CO2 laser may one day fairly soonbear the dubious honour of being the first weapon fired inspace; on earth, it has less potential as a weapon, because,although the beam is not absorbed, it is spread andrendered ineffectual by the atmosphere.

Other devices include the dye laser which makes useof molecular energy levels. Electrons in many complexorganic chemicals can orbit not just a single atom but anentire molecule or part of a molecule, and can absorb -or emit - light by shifting between different orbits of dif-ferent energies; the bright colours of dyes occur as onlycertain wavelengths correspond to the energy differencesby Planck's relation.. The lasing material, the dye, is insolution in water or an alcohol and usually has to be ex-cited by another laser. Because of the useful property ofbeing tunable to any wavelength in broad bands of the

FEATUREspectrum, dye lasers are becoming very popular inlaboratories. Some chemical reactions release so muchenergy that laser action is possible with no external powersupply; the reaction of hydrogen and fluorine is an exam-ple, though special conditions are required to achievepopulation inversion (more atoms in the excited state thanthe stable one and thus great potential for emission ofphotons).

Diode LasersThese devices, which are basically p -n junctions(semiconductor diodes), have been around since 1962,when lasing took place in a GaAs p -n junction whoseends had been polished to form a cavity and which had anenormous current passed through it. The laser diode usesvery heavily doped extrinsic semiconductors .(Fig. 1). Theenergy diagram shows the valence band and conductionband separated by an energy gap called the band gap. Thegap is too large to allow electrons to gain kinetic energy (iemove) as there are no unfilled energy levels energeticallynear enough to those containing the electrons; yet it issmall enough for an electron which receives enoughenergy to ocupy an energy level in the conduction bandwhere it is free to move. Here we have an energy gapwhich an electron can cross if it receives a large enoughkick in the form of thermal vibrations in the crystal lattice- or by a photon with an energy sufficient to supply theband -gap energy to the electron.

In the p -region of the diode, an impurity which hasenergy levels (without any electrons in them) just abovethe valence band has been diffused into the semiconduc-tor. Electrons in the valence band are easily excited byeven weak thermal vibration and acquire more energy iemove up into the level marked 'a' for acceptor. This leavesholes in the valence band, so forming a p -type semicon-ductor in which the holes move under the influence of anelectric field (conduction). Similarly, in the n -region an im-purity whose occupied energy levels are marginally belowthe conduction band can donate electrons into the con-duction band where they are free to acquire kinetic energyas before.

Thus, in the n -region of this heavily -doped crystal of asemiconductor there are many electrons in the conductionband, and in the p -region many holes. Now apply a voltage asmarked; holes 'enter' the lattice at A (actually, electrons leavethe lattice at A which amounts to precisely the same thing),and electrons enter at K, as holes and

/ENERGY P.

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electrons move into the junction region. These electronsand holes are injected into the same physical space in thelattice, the junction between the p -region and the n -region(giving rise to the name injection laser) with the electronsall having virtually the same amount of energy more thanthe holes. The excitation of electrons by photons (men-tioned before) is reversed as free electrons 'fall' into theholes in mutual annihilation; the electron is no longer ac-tive in the conduction band and there is one less holeacive in the valence bends - they are replaced as describ-ed above. In moving from the conduction band to thevalence band, each electron releases the bandgap energyas a photon. Light is emitted from the junction region: allof it has exactly the same wavelength.

This diode is nothing more than an LED! To obtainlaser action, population inversion must be achieved. Thatis, there must be more electrons in the conduction bandready to drop down to the valence band than there are inthe valence band able to be promoted to the conductionband. In an LED, conduction band electrons decay spon-taneously to the valence band. The photon emitted can dotwo things that are of interest to us: it can stimulate theemission of another photon of exactly the same frequencyand, what's more, in phase with the first, provided it en-counters another electron in the valence band at the rightmoment; or it can be absorbed, and in doing so promoteanother electron to the conduction band. The first of theseprocesses iswhat gives rise to laser action; the second iswhat prevents it from occurring, and the way that this isavoided is by creating a population inversion, so that thefirst is more likely than the second.

In a laser, stimulated emission gives rise to thecoherent light output; to turn the LED into a laser diodeyou need an enormous rate of injection of electrons sothat there are plenty of them available for stimulated emis-sion; this takes a very large current. When the currentthrough a laser diode is increased, stimulated emissiontakes over and laser action takes place as a few photonsgive rise to an entire output of the same frequency andphase. The cavity is needed to reflect at least somephotons back into the junction region so that the ava-lance is CONTINUOUS. Unless the diode gets too hot,this emission can continue for as long as you apply acurrent.

The acronym laser stands for Light Amplification bythe Stimulated Emission of Radiation: the avalanche isprecipitated by perhaps a single photon and the frequencyand phase of that photon are (ideally) reproduced in theoutput of many millions of photons. This process is morefamiliar under the name amplification!

The Real Laser DiodeThese do exist; please don't try to turn any LEDs info

laser diodes (as I once did). RCA manufacture a range ofinfra -red laser diodes which are available in this country(the photograph shows one of this range). I have yet to findany ,manufacturer of visible -light laser diodes, thoughthese have been set up in laboratories. Most laser diodeshave to be operated in pulses of less than 1% duty factor;the 'large' current mentioned before to obtain laser action,called the threshold current, is responsible for this as itcauses immense heating. A typical device needs a current of36 A to lase, emitting at a rate of 20 W during a pulse. That isa respectable power for a laser, but this only occurs duringthe pulses. The duty cycle reduces the effective output,for this device, to a few milliwatts. So, at present, laserdiodes are somewhat disappointing - an invisible outputwhich may be useful for remote -control applications (assensors could hardly miss such enormous flashes), orfor fiber -optics.

The p -n junction is only a few millimeters square and thejunction is a few thousandths of an inch thick. At present, theoutput is not collimated, ie it isn't a beam of low divergence,and spreads out rapidly (divergence angles approach 20degrees). The efficiency of laser diodes is good (for lasers)at around 10% and is improved by adding layers whichchannel the photons into the junction area, as they tend tomove out into regions where population inversion has notoccurred; these are called heterostructure diodes.Continuous operation at high power has been obtained atlow temperatures (meaning in liquid nitrogen), and at lowpower {again in the infra -red) at room temperature indouble heterostructure diodes at around 5 mW - no better

FEATURE

than the helium -neon laser. As demand is still low, these. stillcost about .£100. Pulse -operated devices cost about . £20 - butyou need many hundreds of volts of power sup- ply to drive thatsort of current through! The low power and high divergence ofthe beam make the output harmless except at close range whenthe eye can be damaged as with all lasers.

The FutureIndustry is slowly picking up on the laser diode, and this

should speed the availability and flow of new devices. The laserdiode is a favourite for fibre optics; the pressure is on todevelop reliable continuous operation cheaply as it is really veryeasy to modulate laser diode output. Visible devices will occursoon with any luck, and in the distant future we may see theexotic devices such as frequency doubling crystals, electro-optic switches, beam deflection systems which are solid-state etc, all of which would doubtless find manyapplications outside the laboratories and military researchcentres - just as the laser itself did.

Data on laser diodes and many other electro-optic devices can be obtained from NorbainElectro Optics Ltd, Emitter and Sensors Division,Norbain House, Arkwright Road, Reading, BerksRG2 OLT. Anyone interested in lasers might find'Lasers and their applications' by M. J. Beesley(published by Taylor & Francis Ltd) interesting.We would like to thank RCA Ltd for their kindpermission to reproduce Fig. 2.

lee" ...

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1--1-I I\ 119 11 01-689 7702 -01-689 6800 Telex 27924

ORGAN PART2PROJECT

In this month's trip through the Victory organ circuitry, we look atthe lower keyboard and the filtering and envelope arrangements forthe preset voices. Design by Richard Watts.

Before we start to talk about thismonth's circuitry, there are a fewthings to mention about last

month's diagrams. For a start, some ofthe lettering dropped off Fig. 1 some-where between the drawing board andthe printers, so: the unmarked diodesby IC2a and IC2b are D4 and D5, whilethose by IC5c and IC5d are D11 andD12. The terminal marked PEDALTRIGGER should also be labelled C5and that marked MANUAL TRIGGERshould also be labelled C7. C heredenotes the switchbank controlling theautomatic functions of the organ. Thejunction just below D7 should have adot, ie it is a junction and not a crossingpoint.

In Fig. 2, pins 5 and 6 of IC9ashould be linked together. In Fig. 3,the op -amp marked IC10 is actuallyIC10a, the other half appearing thismonth. Also, the label 'TO RHYTHMCIRCUIT' on IC12a pin 5 should be'TO R127/128' (on Fig. 2 this month).

Finally, the number of letters andphone calls we've had in the last coupleof weeks prove how popular this projectis - what a shame we forgot to includea 'Buylines' last month! That's beenrectified this time round. So, get outlast month's ETI - you'll need to referto some of the circuits - and off we gowith some more of How It Works.

The Lower KeyboardThe lower keyboard or manual usesan M108 IC (IC14), which operates inexactly the same way as the M208 buthas one fundamental difference. BothICs have the facility to operate as eithera single 61 -note keyboard or as a splitkeyboard, with the lower section ableto perform the single finger chordfunction, amongst others. It is the sizeof this lower section that differsbetween the ICs. The M208 has a 17key lower section and the M108 a 24key lower section. The use of these ICsin their specific locations in the Victoryorgan is necessary to fulfil the totalspecification of the instrument.

Lower keyboard scanning is as forthe upper keyboard except that the datainput lines B1 to B5 are used. Thecircuitry comprising 1C13,.IC6e and Q5which sits between the M108 B lineinputs and the B line connections from

the keyboard is used to enable the key-board data information to be trans-ferred to alternative B inputs on theM108, and is necessary under certainswitch settings to maintain constantpitch outputs from the lower keyboard.

In normal operation the audio out-puts are taken from pin 17 through R98to amplifier IC16a, from where they aretaken to the passive filter networkR129, R130, C51 and C52. This filterproduces the lower keyboard melodiavoice. The audio is also taken via R137to the VCA IC19 which is used for therhythm guitar voice. Control current forthis IC is supplied from Q4 and C54 viaR142. Q5 base receives negative -goingpulses via C55 from the rhythm mem-ory IC pin 8 (see next month). Thedecay rate of C54 and thus the length ofdecay on the rhythm guitar voice can bereduced on application of a low signalto the cathode of D37. This effectivelydischarges C54 through R145 and D37.This low signal is also provided by therhythm memory IC. Without this lowon D37 cathode, the discharge pathfor C54 is through R142 and the3080E itself. The rhythm guitarvoice is therefore not availablewithout the rhythm unit on.

Switching of the lower keyboardvoices is as for the upper voices andmixing is accomplished in IC16b. Theoutput from the mixer is fed via R134,which is shorted out if Lower ManualAccent is selected, to R127 and themain mixer/amplifier.

Single finger chord is available onthe lower keyboard and, when selected,outputs a complete four -note chord plusbass note when only one key isdepressed. The four notes of the chordare output from pins 3-6 of IC14. TheSFC selection takes point Cl high whichturns on all the switch sections of IC15,thus connecting these outputs throughto the voicing circuits. Point Cl alsoconnects throult D33 to pin 12 of IC7dwhich enables F7 via D16 to B6. Thisperforms the keyboard split mentionedearlier and enables the lower section forits special functions.

The positive voltage at point Cl isalso connected to pin 5 of IC2d, thusconnecting F6 via D31 to B6. This givesthe SFC instruction to IC14 and causesthe chord contents to be output

to pins 3-6. The root note of the chordis available at pin 6, the third note at pin5, the fifth at pin 4 and an octave to theroot note at pin 3 (unless the 'seventh'feature is selected, in which case pin 3outputs the 7th note).

Lower Manual MemoryLower manual memory is also

available by removing 0 V from pointC3. This enables IC2c which connectsF4 and F5 to B6 via D21 and D22respectively. F4 latches the outputs ofthe upi.r section of the lower keyboardwhile F5 latches the outputs of thelower section of the lower keyboard.The bass note is latched at pin 7. If SFCand lower manual memory are bothselected, bass audio is automaticallyselected to come from the lower key-board since point C2 is disconnectedfrom +12 V by the SFC switch. Thebass trigger input point C6 must beconnected to point C7 by selecting bassfrom the lower keyboard on the change-over switch. Since lower keyboardmemory is being used and thereforekeys are being played and then released,utilisation of the KPA signal from IC14cannot be used to trigger the bass, other-wise it would be heard only when thekey is held, and leaving the chordoutput less a bass note when the key isreleased. To overcome this, anotheroutput signal from the M108 is used.

This signal is called NPA and goeslow whenever a memorised note ispresent in the accompaniment sectionie the lower section of the keyboardwhen it is split. This low voltage isinverted by IC5c which is enabled bythe state of point C10. The positiveoutput from IC5c is passed via Dll tothe bass trigger circuitry. This ensuresthat a memorised chord always has bassaccompaniment.

If the SFC is de -selected while achord is being memorised, the change atpoint Cl from +12 V to 0 V is coupledthrough C40 and D25 to pin 13 of IC2c.This momentarily disconnects F4 andF5 from B6, disabling the outputlatches and stopping the chord and bassoutputs. If a note is now played on thelower keyboard it will be latched at theoutput pin 17. Up to four notes played3simultaneously can be latched. Theoutput from the M108 is connected via

+12V PROJECT

810

1320

B3

B4 0B5 0

OF2 OF3 O

OO

goF7 OF8 O

goF100F11 0F120

TOS(PIN 13

IC14)

MINOR

+12V

7th

+12V 0

D19

R85100k

D2D

R86220k

R7310k

R7410k

R75101,

R766b8

C3622n

D16

IC7d

C1171

D18

121

22n

R8722k

EXP2(2)

R776k8

10

5

C37 C38220p 220p

R786k8

2IC6e

D21 D22

+12V

R80 R811M0 IMO

D23

11

10

4

3

TO D36ANODE

ICab

IC8c

D24

13

IC13a

14

12 71

10k9 028

C421 9 2011

12

6

R79 D2710k

05

4

R90 6k8

7

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IC5d PIN 1

8

4 B BASS10

CCODE

A

TDS R99R91 47k1k0

9

13

17

6V2

R921140

3

36 6V2IC14

220pZ

030

353433

32

31

3029

2827

26

2524

232221

D31 14

D25 CLK RESET

IC2c 2 IC2d

1 -r13 1RM820 +12V

3

5

40 2

04047n

D26 C41

C3LOWER

MANUALMEMORY

47n

C17

KPA

R93lk0

6V2 R982k2

R100IC15a o IkO 6V2

IC16a

-r13

IC15d

12

R1013 1k0

Fig. 1 Circuit diagram of the lower keyboard circuitry. The output from ICI 6a pin 7 passes to the circuit on the next page.

D17 to pin 13 of IC2c (the latch enable)to ensure that any previously latchednote or notes are cancelled when thenext is played.

A bass note corresponding to theleftmost or only note played will beoutput on pin 7. The enable for the splitkeyboard mode (connecting F7 to B6)to pin 12 of IC7d is supplied, when theSFC is off, by virtue of the fact thatpoint C4 is high (bass from lower key-board) and point Cl is low (SEC is off).This gives the AND gate IC9d highs onboth pins 1 and 2, giving a high at pin 3.This is connected via D32 to pin 12 ofIC7d.

Back now to the situation withboth SFC and lower keyboard memory

on. The chord can be modified to aminor (flattened third) or a seventh byuse of the pedals which are disabledfrom their normal function by the SFCswitch. Playing any black pedal (iesharps and flats) causes +12 V to beconnected through the second pole ofthe pedal switch via D19 to pin 13 ofIC9b. Since the other input (pin 12)of this gate is held high by R85, theoutput pin will go high, thusconnecting F3 via D23 and IC8b to B6.This tells IC14 to change the chordbeing output to a minor. Since theoutput of the AND gate is connectedback to its input by R83, the minorfunction remains latched on untilanother key is pressed to change the

TO IC7dC2 C4 PIN13

IC9d

2

6

IC6I

C4422n

Cl

5

D36

R104

+12V

R 10547k

FROMPIN 13IC2c

chord, or the same key is pressed again.This causes the M 1 0 8 to output a KPApulse which is coupled through C39 tothe AND gate input pin 12. This mom-entary low disables the AND gate andcauses the newly played chord to beplayed as normal. Operation of the 7thmodification to the chord is achieved byplaying any brown pedal (naturals). Theswitching arrangement is the same as forminor except that F2 gets connected toB6.

Preset Voices

These voices (the piano, harpsichord,Hawaiian guitar, banjo and accordion) all useIC18, another 3080E operationaltransconductance amplifier

C6TRIGGER

INPUT

FROM IC1PIN 7

C2

FROM IC14PIN 7

FROM IC15bPINS

FROM IC16aPIN 7

R106

C47+12V 22n

1

10k 8109 C46 R111 R1136k8 470" 100k 100k 5

R 107100k

R11868k

BASS ONACCENT

R119100k

330k 47kR120

C48 150k

R121R108 470R100k

6V2 0-0R129

OFFR130R131

10k 68k

C51 C52100n T 100n

+12V6V2

PR647k

8135100k

R1386V2 470R

R137 R13810k 22k

C53122n

6V2

2

3

10k

R132 1 310k

R140150k

R139470R

5

13

ON R133NsF4):10131A 68k

IC18b

BASS

ON6V2

6

R12210k

5

R124R123 22k470R

OFF

0-0 +12VON

OFFLOWER

MANUALo- ACCENT

ON

8V2 A3

R13410k

A-0 6V2OFF

RHYTHMGUITAR

R14147k

+12V0

R142220k

C54

R143 R1441k5 IMO

II

PROJECTTO IC 12a

R125 PIN 6100k

A/VR126100k

R127100k

TO IC12a

R12868k

PIN 5

C50

RHYTHM

(POTENTIOMETERVOLUME PLUG

CONNECTION)

FROMRHYTHMCIRCUIT

CHORD CHOPON M258

C55 (PIN 8)22n

R14568k D37

Fig. 2 The preset voicing circuitry. The rhythm volume plug allows the connection of a 25k logarithmicoff -board potentiometer.

HAWAIIANPIANO HARP6ICHORD GUITAR BANJO ACCORDION

Al A2 A3 A4 A5 A6 A7 A8 A9

Fig. 3 The wiring for the preset voice switch bank.

A10

PCB VIEWOF SWITCH

OFF

ON

1:0 0

SINGLE LOWERFINGER MANUAL BASS WALKING SWING RHYTHMCHORD MEMORY CHANGEOVER BASS BASS HANDCLAP ON/OFF

K il

(PINS/

AO

0 10

0 0

O 0

0 0

0 0 0 0C13 C 2 C1 C8 C2

10V) I+12V)

0-

/1C3 CA C7 C5 CS

0-

0

0

0

0

00

.0 0

0-, 0

0-

0 0 0 ), 0 0CB C 0 C11 C 5 C14 C16 C17

I+5V)

Fig. 4 The wiring for the automatic function switch bank.

PCB VIEWOF SWITCH

OFF

ON

lE0 0

CHORD LENGTHON M258(PIN 11)

configured as a VCA. The audio input isapplied to the point Al and the controlenvelope to the point A3. These pointsconnect, through an edge connector, tothe preset voice switch bank. As can beseen from Fig. 3, the selection of piano,harpsichord and Hawaiian guitar eachconnects an independent audio input toAl. The banjo and accordion select thesame voice but considerably differentenvelopes.

The piano voice which connects topoint A2 is actually a tap off thetrombone voice via RS1. The amplitudeenvelope on A4 is also utilised by theharpsichord preset and operates as

follows. When a key is depressed, theM208 (IC1), outputs a signal called(trigger decay solo) which, in commonwith KPS is active low, but unlike RPSdoes not remain low .for the durationthat the key is held. It is a pulse outputof approximately 9 ms which is

developed internally by the M208 and isoutput whenever a key is depressed,even if a previously depressed key isstill held down. TDS is inverted by Q10and applied to follower Q11 whoseemitter connects to C56. It is the chargeand discharge rate of C56 whichdetermines the piano and harpsichordamplitude envelope.

PROJECT

TDS

KPS

TO Q4COLLECTOR

(SUSTAIN) +12V

R1498209

C57100u

D38 11:::

C56100u

+12V

+12V0

R14722k 011

R14622k

010

R156220k

R15522k

R157012 10u 220k

rL

l/VV316110k

114 io-AAAt-

R16222k

C6247n

R1631k5

6V2

0 A4

A7

R150220k

D39

8 7 R1511440

4

KPS

6R152

IC20 D40 1k0

16'

C58 C591u0

+12V

R159100k

R158 01422k

D41

D42

C63 R165nn 22k

R16415k

6V2

R15433k

R15368k

R1602k2

A8

KPS

KEY DOWN KEY UP

*12V

OV

+12V

OV

-0.1 HE- APPROX 9mS

APPROXAPPROX 14mS

A9

WITH BANJOSELECTED

72m5PIN 3 IC20

POINT A3WITH BANJOSELECTED

A10 POINT A3 WITHACCORDIONSELECTED

1.4 APPROX 154c '1

Fig. 5 {Top) The circuitry to produce the piano/harpsichord envelope and the banjo repeat.(Middle left) The circuit for the Hawaiian guitar envelope. (Middle right) The accordion envelope circuit.(Bottom left) Filter for the harpsichord voice. (Bottom right) Filter for the banjo and accordion voice.

Two decay rates are possible: oneif a key is played and held and a second,shorter, delay if a key is played andreleased quickly, as is the case whenplaying a real piano or harpsichord.First, if a key is played and held, C56is charged very quickly through Q11,resulting in a fast (percussive) attack.After about 9 mS the TDS signalreturns to its normal state and no morecurrent is supplied to C56, which startsto discharg2 Since the key is still helddown, the -103 signal is still present andso the collector of Q4 is high. Thisreverse biases D38 so the only dischargepath for C56 is through R124 and IC18.This results in a long decay.

If a key is played and then released,)fie same attack is apparent but sinceKPS is no longer present, Q4 returns toits saturated state, thus providing adischarge path for C56 through D38,R148 and Q4. This gives a short decay.

The harpsichord voice is developedby mixing 8' and 4' square wave signalsvia R161 and R162, then filtering thismixture with C62 and R163. This audiosignal is then connected to the harpsi-chord switch through point A5.

The Hawaiian guitar voice at pointA6 is another 'tap off', this time via R50from the clarinet voice. The

amplitude envelope on point A7 is simi-lar in operation to the piano/harpsi-chord envelope excgpLthat there is onlyone decAyLate and US is used as thetrigger. KT'S is supplied to an inverter,Q12, and via Q13 to C60, resulting inthe same fast attack: however, sinceR57 is connected across C60 this will beits discharge path, giving a long decaybut only when all the keys are released.

The banjo and accordion voice isdeveloped from the 16' staircase (IC3bpin 1) through the filter network C63,R164 and R165, and is available atpoint A8. The banjo is a repeating voice,ie when a key is depressed and held, theaudio is alternately passed and blockedby the VCA (IC18) at about 11 Hz. Thistechnique is widely used on organs togive the effect of plucking or strummingthe instrument. The repeat oscillatorcomprises a 555 (IC20) and its associat-ed components. It is configured here asa gated astable multivibrator which willgive square wave pulses at pin 3 when-ever pin 4 is taken high. D39 is includedto give a very short pulse (about a 1:5mark/space ratio). Since pin 4 is con-nected to Q4 collector, output pulsesare produced whenever a KPS signal ispresent. The components between IC20pin 3 and point A9 act as attack and

POINT A3WITH PIANOSELECTEDNOTE PLAYEDAND HELD

I- 1Ik I

APPROX 1.2sc

POINT A3WITH PIANOSELECTED.NOTE PLAYEDAND RELEASED Hi

APPROX 300mS

Fig. 6 Waveforms associated with the presetvoicing circuitry, as described in the text below.

decay shapers for the output squarewaves and produce an exponential con-trol voltage.

In Accordion

The accordion amplitude enveloperequires a slow attack and, when thekey or keys are released, a fast decay.This envelope is available from pointA10 and is developed by KPS causingQ4 to shut off. This allows C61 tocharge through R159 and D41, resultingin the slow attack. Once charged, C61 isable to remain charged so long as thekey is held down (ie KPS is present)and therefore the voice remainsaudible. Once all the keys are releasedand KPS is removed, 014 returns to itssaturated state and provides a rapiddischarge path for C61 via R 160 andD42. The output from the preset VCA(IC18) is fed via R 126 to the outputmixer/amplifier IC12a.

BUYLINESThe response to this project has beenamazing! Unfortunately, the prices for allthe various options haven't been finalisedas we go to press, so interested partiesshould contact the designers: that'sLeighton Electronic Services, 17 BridgeStreet, Leighton Buzzard, Bedfordshire LU77 AH (telephone 0525 382504).

SinclairZXSpectrum1 6Kor48KRAM..full-size moving -

key keyboard..colourand sound..high -resolutiongraphics...

From only

025!First, there was the world-beating

Sinclair ZX80. The first personal computerfor under £100.

Then, the ZX81. With up to 16K RAMavailable, and the ZX Printer. Giving morepower and more flexibility. Together,they've sold over 500,000 so far, to makeSinclair world leaders in personalcomputing. And the ZX81 remains theideal low-cost introduction to computing.

Now there's the ZX Spectrum! Withup to 48K of RAM. A full-size moving -keykeyboard. Vivid colour and sound. High -resolution graphics. And a low price that'sunrivalled.

Professional power -personal computer price!

The ZX Spectrum incorporates allthe proven features of the ZX81. But itsnew 16K BASIC ROM dramaticallyincreases your computing power.

You have access to a range of 8colours for foreground, background andborder, together with a sound generatorand high -resolution graphics.

You have the facility to supportseparate data files.

You have a choice of storage capa-cities (governed by the amount of RAM).16K of RAM (which you can uprate laterto 48K of RAM) or a massive 48K of RAM.

Yet the price of the Spectrum 16Kis an amazing £125! Even the popular48K version costs only £175!

You may decide to begin with the16K version. If so, you can still return it laterfor an upgrade. The cost? Around £60.

BLUEEDIT

REDMAGENTA GREEN

CAPS LOCK TRUE VIDEO INV. VIDEO

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DEF FN FN

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Ready to use today,easy to expand tomorrow

Your ZX Spectrum comes with a mainsadaptor and all the necessary leads toconnect to most cassette recordersand TVs (colour or black and white).

Employing Sinclair BASIC (now usedin over 500,000 computers worldwide)the ZX Spectrum comes complete withtwo manuals which together represent adetailed course in BASIC programming.Whether you're a beginner or a competentprogrammer, you'll find them both of im-mense help. Depending on your computerexperience, you'll quickly be movinginto the colourful world of ZX Spectrumprofessional -level computing.

There's no need to stop there. TheZX Printer -available now- is fullycompatible with the ZX Spectrum. Andlater this year there will be Microdrives formassive amounts of extra on-line storage,plus an RS232 /network interface board.

OPEN #

INT

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FLASH BRIGHT

Key features of theSinclair ZX Spectrum Full colour -8 colours each for

foreground, background and border,plus flashing and brightness -intensitycontrol.

Sound -BEEP command with variablepitch and duration.

Massive RAM -16K or 48K.

Full-size moving -key keyboard- allkeys at normal typewriter pitch, withrepeat facility on each key.

High -resolution - 256 dotshorizontally x 192 vertically, eachindividually addressable for true high -resolution graphics.

ASCII character set -with upper- andlower-case characters.

Teletext -compatible- user softwarecan generate 40 characters per lineor other settings.

High speed LOAD & SAVE -16K in 100seconds via cassette, with VERIFY &MERGE for programs and separatedata files.

Sinclair 16K extended BASIC -incorporating unique 'one -touch'keyword entry, syntax check, andreport codes.

ZX Spectrum software oncassettes -available now

The Spectrum software library isgrowing every day. Subjects includegames, education, and business/household management. FlightSimulation ...Chess...Planetoids ..

History...Inventions. .VU-CALC ...VU -3D...Club Record Controller...there issomething for everyone.And they allmake full use of the Spectrum's colour,sound, and graphics capabilities.You'llreceive a detailed catalogue with yourSpectrum.

ZX Expansion ModuleThis module incorporates the three

functions of Microdrive controller, localarea network, and RS232 interface.Connect it to your Spectrum and you cancontrol up to eight Microdrives,communicate with other computers, anddrive a wide range of printers.

The potential is enormous, and themodule will be available in the early partof 1983 for around £30.

Sinclair Research Ltd, Stanhope Road,Camberley, Surrey GU15 3PS.Tel: Camberley (0276) 685311.

The ZX Printer -available now

Designed exclusively for use with theSinclair ZX range of computers, theprinter offers ZX Spectrum owners the fullASCII character set -including lower-casecharacters and high -resolution graphics.

A special feature is COPYwhichprints out exactly what is on the whole TVscreen without the need for furtherinstructions. Printing speed is 50 charac-ters per second, with 32 charactersper line and 9 lines per vertical inch.

The ZX Printer connects to the rear ofyour ZX Spectrum. A roll of paper (65ftlong and 4in wide) is supplied, along withfull instructions. Further supplies of paperare available in packs of five rolls.

The ZX Microdrive-coming soon

The new Microdrives, designedespecially for the ZX Spectrum, are set tochange the face of personal computingby providing mass on-line storage.

Each Microdrive can hold up to 100Kbytes using a single interchangeablestorage medium.

The transfer rate is 16K bytes persecond, with an average access time of3.5 seconds.And you'll be able to connectup to 8 Microdrives to your Spectrumlviathe ZX Expansion Module.

A remarkable breakthrough at aremarkable price. The Microdrives will beavailable in the early part of 1983 foraround £50.

How to order your ZX SpectrumBY PHONE -Access, Barclaycard or

Trustcard holders can call 01-200 0200 forpersonal attention 24 hours a day, everyday. BY FREEPOST -use the no -stampneeded coupon below. You can pay bycheque, postal order, Access,

Barclaycard or Trustcard.EITHER WAY -please allow up to 28

days for delivery. And there's a 14 -daymoney -back option, of course. We wantyou to be satisfied beyond doubt -and wehave no dou bt that you will be.

Fro: Sinclair Research, FREEPOST, Camberley, Surrey, GUI5 3BR.

Qty Item Code Item Price

Order1Total

Sinclair ZX Spectrum -16K RAM version 100 125.00Sinclair ZX Spectrum -48K RAM version 101 175.00Sinclair ZX Printer 27 59.95Printer paper (pack of 5 rolls) 16 11.95

Postage and packing: orders under £100 28 2.95orders over £100 29 4.95

Total

Please tick if you require a VAT receipt *1 enclose a cheque/postal order payable to Sinclair Research Ltd for £*Please charge to my Access/Barclaycard/Trustcard account no.*Please delete/complete 11

1 I 1 1 1 1 1 1 1 I I 1 1 1

as applicable

[SignaturePLEASE PRINT[Name: Mr/Mrs/Miss[

I I 1 1 I I 1 I I I I I I 1 1

[Address 111111111111111111111111111111111111111111111111111111111111111111 ET' 903

FREEPOST- no stamp needed. Prices apply to UK only. Export prices on application. I

BROADCASTFEATURE

STANDARDSWhat factors made the government choose .. the IBA'sMultiplexed Analogue Component system in preferenceto what seemed the logical choice, Extended PAL? DaveBradshaw investigates.

The two system proposals submitted by the BBC andIBA were examined by an 'Advisory Panel', chairedby Sir Anthony Part, and hence the report of the

panel is known as the Part Report. As already described byVivian Capel in his article (page 16), MAC uses System Csound, in which the sound is compressed into the intervalsbetween picture lines: this gives a capacity of up to eightsound channels. When the IBA originally submitted itsproposal, it wasn't known if System C would be a practicalproposition by the time that DBS was due to come into

service, and so their original proposal was for System A,using an 8.5 MHz sub -carrier. During the course of the Ad-visory Panel's deliberations, the British Radio and Elec-tronic Equipment Manufacturers' Association (BREMA, avery welcome acronym) stated that they thought thatSystem C would be practicable, and the IBA changed itsproposal to System C. Hence the panel actually con-sidered two MAC systems - known as A -MAC and C -MAC, though only C -MAC was put through the technicaltrials.

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FEATURETechnical Assessment

The competing systems were put on trial and the loca-tion was chosen, by drawing lots, to be the BBC researchdepartment at Kingswood in Surrey. Transmission andreception of two signals was simulated, as were the dif-ferent noise levels, and co -channel interference from thesame and different systems. However, the possible effectof an out -of -alignment receiver was not evaluated.

The panel reported that both systems showed a'noticeable improvement in definition compared withPAL', with MAC having the edge over E -PAL, though E -PALstill offered a considerable improvement over PAL.

Both systems began to show the effects of noise im-pairment on vision at around the same noise level, 14 dB,but were quite viewable at 11 dB. At lower carrier -to -noiseratios, E -PAL gave a less acceptable picture than MAC, thelatter having approximately a 2 dB advantage over theformer. Sound quality remained very good down to 7 dBcarrier -to -noise ratio.

MAC had a lower tolerance to co -channel in-terference than E -PAL. However, the interfering signallevels needed to produce any observable effect on eithersystem were quite unrealistic. So, round one to MAC.

War of the Words

As you may imagine, neither the BBC nor the IBAwere silent about the merits of their systems. Both madewritten and aural submissions to the Advisory Panel.Amongst the arguments advanced for E -PAL were:

Transmsuan Path

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I NICAM (ICON 1-

CIPSK - Phase Shift Keyer

NICAM - Near Instantaneous Cornpandmg

C/N - Carrier to Noise Ratio

C/I - Camer to Interference Ratio

Fig. 1 Set-up for comparative demonstrations:

rID HMSO

the PAL system has been in use since 1967 and thereare 14 million receivers operating on this standard. E -PALtransmissions are compatible with conventional PALdecoders (though a converter would be needed for thedigital audio). There would be a very marginal loss ofquality compared.to that obtained from PAL transmissions- so marginal that most users would not notice anydifference. the resolution of pictures at home is limited by thereceiver and display. High definition TV (HDTV) is about10 years away, so there is little point in radically alteringtransmission standards before its introduction. the extra circuity needed for an E -PAL receiver com-pared to a PAL receiver is very small, simple and wellunderstood.

Enter the IBAThe IBA's two -pennyworth included the following

points: MAC is more likely to be adopted as a common Euro-pean standard than E -PAL because of its technicalsuperiority (most of the rest of Europe is currently engagedin debating DBS systems, and the European BroadcastUnion, EBU, will be considering the possibility of a singlecommon standard later this year) because in the MAC system the components(luminance, Y, and colour differences U and V) are keptseparate, MAC is a closer complement to the emergingstudio practice of keeping and storing the componentsseparately rather than encoded into a composite singlevideo signal. MAC is designed from scratch to match the FM satellitechannel (rather than to be compatible with existing prac-tice) which leads to a better subjective noise performance. MAC has greater potential for enhancement or pro-viding the basis for HDTV systems. finally (and here's the rub), MAC is well suited to thescrambling systems that would be necessary for pay -TV.

A European Standard?

The situation in Europe is that countries are dividedbetween the PAL and SECAM systems, and for politicalreasons, SECAM countries are not very likely to adopt PAL,or vice -versa. Ironically, the only possible way of gettinguniformity is to make everyone change.

The European manufacturers' association, EACEM,has shown an interest in the MAC system. However, theEBU has expressed a strong preference for System -Asound, though this preference was expressed at a timewhen it appeared that System -C sound could not be im-plemented in time. France and Germany have alreadydecided to proceed at an early stage to DBS using their ex-isting SECAM and PAL systems for vision, though it is not

-clear whether either has ruled out the possibility of chang-ing to an enhanced system at some stage in the future (for-tunately the coding of the signals is done on the ground,the satellite being a 'transparent' device in this respect).

Incidentally, a note to all you cynics out there. Har-monisation of broadcast standards is not simply anothercase of rather pointless Euro-bureaucracy, because there isexpected to be a considerable international audience forTV programmes. In fact, the BBC thinks that its pay TV ser-vice could gain a lot of revenue from the continent.

What has Cable TV to do with it?Quite a lot actually, because cable companies stand to

make a penny or two out of satellite TV themselves. This is

FEATURE

HMSO

H h frequency Luminance

Insetted 6MHz Shifted Type A,FM sound carrier digital sound signsl

Freq..r.Y

Fig. 2 Modified E -PAL signal spectrum - an E -PAL signal withType A sound.

because the cost of putting up your own antenna will bemuch more than the cost of getting a cable company todeliver the signal to you via their network (provided you'reone of the lucky 60% or so of the population to whomcable TV will be offered . . .) So, because cable companieswill be carrying the DBS services, they too had their com-ments to deliver to the Advisory Panel.

As it happens, the cable companies wanted yetanother system, a modified E -PAL with both digital soundand conventional analogue sound, so that existing setswould be fully compatible with E -PAL without the digitalsound module. However, the panel felt that this would beimpractical, and, in its conclusions, said that it thoughtthat MAC would be more suitable for cable transmissionbecause of the absence of sub -carriers.

Judgment DayIn its recommendation, a recommendation that was

very rapidly accepted by the government, the AdvisoryPanel endorsed MAC, rejecting three of the BBC's centralpoints. Firstly, they considered that the results obtained us-ing an E -PAL signal with a standard PAL receiver wereunacceptable; secondly, that it would be worth develop-ing a new system before the introduction of HDTV; andthirdly, that the extra circuitry for MAC would be littletrouble to manufacture.

On the last point, there was felt to be some difficulty infabricating one of the filters for the E -PAL receiver,whereas, once integrated, the time multiplexing circuitsfor the MAC receiver would be relatively simple tofabricate. The panel accepted all the IBA's claims for theMAC system. The BBC is philosophic about the decisiongoing against it, and view the subject now as a dead issue.

Program And PaymentVery much a live issue is the way the BBC will use the

two DBS channels it has been allocated. One is presentlyplanned to be an open service, possibly called 'Windowon the World' and utilising the best of programmes fromabroad and the BBC's extensive archives. There will be asupplementary licence fee for DBS services, presentlyplanned to be comparatively small (around £10); after all,it won't be necessary to use special detector vans to spotDBS antennas.

The other channel is planned to be a pay service, us-ing some sort of signal scrambling; you will have to pay toget the unscrambling device (or, more likely, you will haveto pay to get the data that your receiver will need to do theunscrambling). There are all sorts of different proposals forhow the scrambling and unscrambling might be done, andthe scrambling method will be varied from time to time,

with a mode -shifting digital key being transmittedperiodically.

How viewers are going to be asked to pay for the ser-vice also has to be decided. The two possibilities are a sim-ple monthly subscription (this has the attraction ofsimplicity) and a pay-as-you-go system. The latter wouldgreatly ease negotiations for material such as feature films,because the BBC would be able to negotiate an apportion-ing of the income generated rather than a fixed fee; and itis very much a feature of plans for the pay channel that itshould have new films. However, the government has rul-ed out pay-as-you-go for cable TV, so DBS may also havethat option closed to it.

Despite the prediction that cable TV will reach, atmost, only 60% of the population, and despite the cablecompanies' plans to carry the DBS channels, the BBC isvery seriously worried by the prospect of direct competi-tion between DBS and cable pay services. The BBC hasundertaken that its DBS services will be self supporting,and that it should not place an additional burden on thestandard licence income. For a while there was seriousconsideration of withdrawing from DBS altogether, but ithas now been decided to go ahead - this may have beenhelped by some recent, rather pessimistic forecasts forcable TV.

As yet the IBA has not been granted a DBS channel,though three remain unallocated and it is thought certainthat the IBA will get at least one.

Hardware IssuesInitially, the average domestic installation will consist

of three parts: the antenna and out-of-doors unit that willbe mounted directly beneath the antenna and will do thedown -conversion of signal frequency; the indoor unit thatwill convert the MAC encoded video signals and thedigital sound signals into a form the TV can cope with; andthe TV set itself. It is possible to make indoor units thatwould produce a PAL output, but this would mean that alot of effort had been wasted!

Better would be an indoor unit that produced eitheran RGB or YUV output, and a TV set with inputs to match.Providing such component video inputs would add little tothe cost of the TV, and the indoor unit would actually becheaper to make. Eventually, dual standard TV sets wouldbecome available, incorporating both MAC and standardPAL circuits. Unfortunately there is not the bandwidthavailable to transmit MAC signals from terrestrial transmit-ters, so we are stuck with PAL for the foreseeable future.

One Final ThoughtThere is just one last horrible possibility: what if the

EBU does, against all the odds, decide on a European stan-dard, but one that isn't MAC? The BBC or the governmentmight be seriously tempted to change again, and we couldhave a re -run of all the arguments.

Direct Broadcasting by Satellite: Report of the Ad-visory Panel on Technical Transmission Standards, Chair-man Sir Anthony Part, is available from HMSO for f5.60.The BBC have withdrawn their leaflet detailing their plansbecause it dealt very largely with E -PAL; they do not intendto issue a replacement in the foreseeable future.

I would like to thank the BBC, IBA and BritishAerospace for their help in the preparation of this article;also Her Majesty's Stationery Office for permission toreprint the diagrams.

Finally, I think that Plymouth Poly deserve a mention;they too proposed a D85 system, though it obtained only acouple of rather dismissive mentions in the report. Fullmarks for trying, anyway, Plymouth.

SteP-by-stPfaV

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MEMOCALC The screen display behaves as a 'window' ona large sheet of paper on which a table of numbers is laid out.The maximum size of the table is determined by the memorycapacity, and with a MEMOPAK 64K a table of up to 7000numbers with up to 250 rows or 99 columns can be specified.Each location in the table can be either a number which is keyedin or a formula which generates a number. Every time thecommand to 'calculate' is given, all the formula in the table -arere-evaluated. Spreadsheet analysis started as an aid tocash -flow analysis, but this powerful tool has now beengeneralized and MEMOCALC with its special ability to performiterative calculations is invaluable in the performance ofnumerical tasks.

MEMOPAK16K For those just setting out on the road toreal computing, this pack transforms the ZX81 from a toy to apowerful computer. Data storage, extended programming andcomplex displays become feasible.For even greater capacity, memory packs can be addedtogether (16 + 16 + 16K or 16 + 32K). The MEMOPAK 32K andthe MEMOPAK 64K offer large memories at economical prices.

The Memotech approach to micro -computing is to take the well -proven andpopular ZX81 as the heart of a modular system. This small computer houses thepowerful ZBOA processing unit and acts as the central processor modulethrough which the MEMOPAKS operate.Memotech has a reputation for professional quality, producing units which aredesigned to fit perfectly, to look well-balanced, and to work efficiently andreliably.The modular approach gives ZX81 owners the freedom to design the systemthey really need. Furthermore, the inter -compatibility of the modules ensuresthat later additions will click straight in, to give you a system that grows with yourambitions and abilities.As one example, a system with 16K of memory and MEMOCALC is all that isrequired to perform sophisticated numerical calculations giving the same resultsas a computer at 10 times the price. The problem may be as complicated as acash flow or production schedule, or as simple as household accounts or pocketmoney budgeting. If the bank manager wants to see the cash flow, then a singleprint instruction to the Centronics 1/F will give a printout which is more thanacceptable to any bank.The example system which is shown, on the other hand, would satisfy the needsof someone who wanted to enter data via a light -touch keyboard, construct andlabel graphs, and then copy the screen to an BO -column printer. Only 16K ofmemory is used here but with additional memory, more than one video page canbe stored. Up to 7 successive pages can be displayed cyclically to give animateddisplays.

16K £26.00 + £3.90 VAT £29.9032K £43.43 + £6.52 VAT £49.9564K £68.70 + £10.30 VAT £79.00

HRG £34.70 + £5.20 VAT £39.90Cl/F £34.70 + £5.20 VAT £39.90

MEMOCALC £26.00 + £3.90 VAT £29.90Z80 ASSEMBLER £26.00 + £3.90 VAT £29.90

KEYBOARDWITH BUFFER £43.43 + £6.52 VAT £49.95

Memotech products are available at larger branches of WHSMITH

MEMOPAK HRG This pack breaks down the constraintsimposed by operating at the 2X81 character level and allowshigh definition displays to be generated. All 248 x 192individual pixels can be controlled using simple commands,and the built in software enables the user to work interactivelyat the dot, line, character, block and page levels. Scrolling,flashing and animation are all here.

MEMOPAK Z80 Assembler This click -in EPROMbased pack accepts standard Z80 assembly languagemnemonics to allow you to write faster and more compactprograms. It has its own ADD, EDIT, LIST, ASSM and QUITfunctions, the editor allowing insertion, deletion, automatic linerenumbering and error checking. Source code and object codelistings can be displayed and printed in decimal or hex format.

To ensure that your expectations are realised, care is taken at everystage to design features into the system to anticipate your frustrationsand to forestall them. For example:A) Memories are cumulative e.g. 16K and 32K can be added to theMEMOPAK 16K or even to the Sinclair 16K RAM pack.B) The HRG firmware allows commonly used constructions (such asscrolling, shading and labelling graphs), which might otherwise bebeyond the user's programming capabilities, to be evoked by a fewsimple commands.C) The Centronics liF converts ZX81 character codes into ASCII andextends the print line to the width of the printer, still using the LLIST,LPRINT and COPY commands.

Looking forward, Memotech will continue to back the ZX81 through1983 with fast storage devices, pressure sensitive electronic drawingboards and more software packs including a wordprocessor and anRS232 interface.

MEMOPAKS may be ordered by post (cheque, Access/Barclaycardquoting number) or by telephone. Please make cheques payable toMemotech Ltd. and please include £2.00 per unit for packaging andpostage inland (overseas £3.00).

MEMOPAK Centronics I/F The BASIC commandsLPRINT, LLIST and COPY are used to print on anyCENTRONICS type printer. All ASCII characters are generatedand translation takes place automatically within the pack.Reverse capitals give lower case. Additional facilities allow highresolution printing. The full capabilities of your printer are nowunder the control of the ZX81.

MEMOTECH Keyboard The light -touch positive stopkeys of this elegant typewriter -pitch keyboard allow you to workfaster, more accurately and more confidently. To speed youalong we have added an extra SHIFT key to the array at top right.The keyboard is attached by a cable to the Keyboard Bufferwhich fits in amongst your other Memopaks or straight onto theback of your ZX81.

We want to be sure you are satisfied with your Memopak - so we offera 14 -day money back guarantee on all our products.

VIEVIOTECHMEMOTECH LIMITED, WITNEY, OXON. 0X8 6BXTELEPHONE (0993) 2977 TELEX 83372 MEMTEC G

6502 -BASEDAUDIO BOARD

PROJECT

Here's a powerful and versatile peripheral for people requiring adigital -to -analogue or sound -generating capability for theircomputer. Although the PCB is designed for Tangerine users, thecircuit may be readily interfaced to any 6502 -based system.Design and development by M. D. Bedford.

When control applications ona microcomputer areproposed, it soon becomes

evident that DACs and ADCs arerequired to interface to the realworld. For more light-hearted usesand for games, the addition ofsound effects can do much toenhance a program. Althoughmultiplexed ADCs are available,giving eight or 16 channels andrequiring only one eight -bit portplus control lines to support them(see the ZX ADC in the January '83issue), DACs require eight bits perchannel and would quickly use upthe available I/O ports on mostsystems. For this reason, the circuitwhich is presented here wasdesigned so that it wouldn't usesystem I/O ports. The boardpresented here is specificallyintended for the Tangerine Microtansystem and as such will plug directlyinto any expansion slot on thesystem motherboard: DIL switchesor links are provided on the boardin order to configure it to start atany 16 -byte boundary within the 1KI/O area.

For users with other 6502 -basedsystems it should not prove difficultto interface the circuit. The onlynon-standard signal is the onedesignated 10 which is used in theMicrotan system to indicate that anaddress within the I/O area (iewithin the address range BC00 toBFFF) is being accessed. On anyother system, address lines A10 -A15should be decoded to generate sucha signal and Fig. 3 shows a simplecircuit which may be used:

The CircuitThe DAC0800 is a low-cost

high-speed multiplying DAC with anaccuracy of ± 1 LSB which, when

r -

The completed Sound/OAC board in a Tangerine Microtan rack -mounted system. The boardmay be used with other 6502 -based systems.

used in conjunction with an op -amp, is capable of giving a lowimpedance voltage output. Six ofthese devices have been used with747 dual op -amps to give outputs inthe range 0-10 V.

The General InstrumentsAY -3-8910 programmable soundgenerator IC forms the basis of thesound effect feature of this board,the LM380 being provided in orderthat a loudspeaker may be drivenwith no external circuitry. 6520PIOs are used as a simple andinexpensive means of interfacing theDAC0800 and AY -3-8910, but 6821smay also be used. Buffering ofsome signals limits the loadpresented to the bus signals.

The circuitry comprising IC16,IC17 and the bank of DIL switchesallows the positioning of the boardin any 16 -byte block within the I/Oarea. The start address is calculatedas the binary number given by thesix switches multiplied by 16, wherethe switches on the circuit diagramare shown in the '1' position andSW1 is the least significant. Forexample, if switches SW1-6 are in

positions 0,0,0,0,0,1 then the firstaddress on the board will be 16bytes from the start of the I/O area

ConstructionThe layout of a printed circuit

board is presented here and, due tothe fairly high packing density it issuggested that, for those intendingto incorporate the circuit into aMicrotan system, this layout beadhered to. It should be noted thatthe board is of the double -sided,pinned -through type with the resultthat every hole not intended for themounting of components should befitted with a pin and soldered bothon the top and the bottom of theboard. Scrutiny of the overlay willreveal that this must be carried outprior to the fitting of any DILsockets. If, however, it is notintended to fit the circuit board intoa card frame along with otherTangerine boards, then a largerboard may be used and some formof breadboarding techniqueemployed for construction. If thisoption is taken care should be

PROJECT

Fig. 1 Component overlay. The tinted tracks are the underside of the double -sided board:through -board pins soldered on both sides are required wherever a dot appears.

exercises in tHe positioning of certaincapacitors. C4 and C23-27 should, asfar as possible, be well distributedaround the board. C7, 10, 13, 16, 19and 22 decouple the -12 V rail, andthese components should bepositioned so that one capacitor fromeach of the two sets

is close to each of the DAC0800s.One final point applies

irrespective of the method ofconstruction: since DIL switches arerelatively expensive and in such anapplication will most probably beset up once and rarely changed, it issuggested that, as an alternative,

PARTS LISTResistbrs (all 1W, 5% except whenstated)R1-12 10k 2%R13 2R7R14 20kR15-26 12k 2%

PotentiometerRV1 22k logarithmic

CapacitorsCl, 5, 7, 8,10, 11, 13,14, 16, 17,18, 20, 21 100n ceramicC2 470u 16 V axial

electrolyticC3 2u2 10 V tantalumC4, 6, 9, 12,18, 19, 22-2710n ceramic

SemiconductorsICI -3 LM747IC4 LM380IC5, 6, 8, 9,11, 12IC7, 10, 13,15IC14IC16IC17IC18IC19IC20

DAC0800 or DAC0801

6520, 6820 or 6821AY -3-891074LS3074LS0874LSO474LS24574LS138

MiscellaneousSKI 3 -way, 5mm pitch, PCB

terminal blockSK2 14 -pin DIL socketSK3 2 x 32 way A + B DIN

Euro connector (male,angled pins)

SW1-6 hex DIL changeoverswitch (see text)

PCB (see Buvlines); DIL sockets to suit

BUYL'NES

No problems with the semiconductorsfor this project - it's all standard stuff andpeople like Technomatic, Watford andCricklewood should have no troublesupplying you. The only difficulty may liein finding a supplier for the DAC0800 whichseems to be a bit elusive: Maplin supplythe 0801 which is an acceptable substitute.The Euro socket required for Tangerine rackowners is available from Watford, while thePCB can be obtained from our PCB Serviceas usual. The order form is on page 83.

DIL headers with appropriatesoldered links are used and pluggedinto DIL sockets.

ProgrammingWhile it is beyond the scope of

this article to give a detailedfunctional description of the 6520and AY -3-8910 ICs, it is expectedthat the BASIC routines presentedhere will enable the board to beused without difficulty. In order tomake full use of the soundgenerator, however, it is suggestedthat an AY -3-8910 data sheet isconsulted (the company you buythe chip from should be able tohelp). In the routines given, the

PROJECTSK3

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Fig. 2 Circuit diagram of the sound/DAC card.

HOW IT WORKS

The circuitry consists of six DACs, ICs 5-12,

and one sound generator chip, IC14, which hasthree separate sound channels and a noise

generator. The circuitry for each of the DAC ICs Isidentical and we will only discuss IC6. The eight bitsof data are held on pins 5-12, while thecomplementary current outputs are on pins 2

and 4. The DAC is configured for positiveimpedance output operation with 100 on pin 2

connected to ground and the other output fed intothe buffer op -amp IC3a.

DILSOCKET

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7 AUDIO

The data Input to IC6 is latched by port A ofthe peripheral interface adapter IC7 (port B

of IC7 latches the data for ICS). Similarly ICs

10 and 13 latch the data for ICs 8,9 and 11,12 respectively.

The fourth PIA, IC15, utilizes both portsto control the sound generator chip, IC14.

The three audio outputs of this chip are fed viaC3, R14 and the volume control RV1 into IC

audio power amp IC4.Cl and R13 form the Zobel network and C2

C2 the DC blocking capacitor for the amp output. The audio signal andanalogue voltages are fed off board via SK2, a DIN socket with aheader -plug.

Address decoding for the board is performed by ICs 16, 18 and 20.SW1-6 select which 16 -byte block of memory the board occupies. Forpeople using systems other than the Microtan, which generates the 10signal required, the additional decoding circuit for lines A10-15 shownin Fig. 3 will be required. The data bus is buffered by IC19, with the R/W signal on pin 1 selecting the direc-tion and the output of IC16enabling the tri-state buffers via pin 19. Bus signals which are requiredby several chips in the circuit are buffered by IC17.

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PROJECT

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ALL LINKS IN 'a' POSITION10 - 0000 03FF

ALL LINKS IN b' POSITION10 = FCOO - FFFF

10

Fig. 3 Non-Microtan users who wish to build this project will require this circuitto produce the 10 signal.

IC1 1C2 IC3 IC4 ICS IC6 IC7 103 IC9 IC10 IC11 IC12 IC13 IC14 IC15 IC16 IC17 IC19 IC19 IC20

OV 3,4,57,1011,121

1 1 1 1 1 7 7 7 10 8

+5V 20 20 20 40 20 14 14 14 20 16

+12V 9,13 9,13 9,13 14 13 13 13 13 13 13

-12V 4 4 4 3 3 3 3 3 3

Table This is a I st of power supply connections to the various ICs for peopledoing their own board layout.

variable BA should be set to thebase address of the board.DAC Handling Routine. In thisroutine, which should be executedonce at the start of the program, Nshould be set to the number of DACchannels to be initialised. Afterexecution of the routine, thestatement:

POKE X, BA+2*(N-1)

will write the value X to the NthDAC channel.

10 REM ....DAC INITIALISATION20 FOR AD - BA TO BA + 2*(N-1) STEP230 POKE AD+ 1,0: REM....ALLOWACCESS TO DDR40 POKE AD,255: REM....SET DDRTO OUTPUTSPOKE AD+1,4: REM....ALLOWACCESS TO OUTPUT REGISTER60 NEXT AD

Sound Effect Routines. Theinitialisation routine should beexecuted once at the start of theprogram: after this subroutines 1000and 2000 may be called for writesand reads respectively to theAY -3-8910 registers. In these tworoutines, REG should be set to theregister number before entry: for awrite, DAT should be set to thevalue of the data to be written andwhen reading, DAT will contain thedata read after return from the

subroutine.

10 REM....AY-3-8910INITIALISATION20 POKE BA+ 15,0: REM....6520PORT B TO WRITE30 POKE BA+ 14,25540 POKE BA+ 15,4

1000 REM....AY-3-8910 WRITEROUTINE1010 GOSUB 3000: REM....LATCHADDRESS1020 POKE BA+ 12,DAT:REM....WRITE DATA1030 POKE BA+14,21040 POKE BA+ 14,01050 RETURN

2000 REM....AY-3-8910 READROUTINE2010 GOSUB 3000: REM....LATCHADDRESS2020 POKE BA +13,0: REM....6520PORT A TO READ2030 POKE BA+12,02040 POKE BA +13,42050 POKE BA+ 14,1: REM....READDATA2060 DAT- PEEK(BA+ 12)2070 POKE BA +14,02080 RETURN

3000 REM .. LATCH ADDRESSROUTINE3010 POKE BA+13,0: REM....6520PORT A TO WRITE3020 POKE BA +12,2553030 POKE BA +13,43040 POKE BA+12,REG:REM....LATCH ADDRESS3050 POKE BA +14,33060 POKE BA+ 14,03070 RETURN

Where it is only intended towrite to the AY -3-8910 registers, asaving in execution time andprogram size may be made byincorporating lines 3010-3030 of thelatch address routine into theinitialisation routine and using thefollowing routine for writing. In thiscase subroutines 2000 and 3000 arenot required.

1000 REM.:..AY-3-8910 WRITEROUTINE FOR WRITE -ONLYAPPLICATIONS1010 POKE BA+12,REG:REM....LATCH ADDRESS1020 POKE BA+14,31030 POKE BA+ 14,01040 POKE BA+ 12,DAT:REM....WRITE DATA1050 POKE BA+14,21060 POKE BA+ 14,01070 RETURN

A completed board, sporting the sound chip and three of the possible six DACchannels.

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COMPUTER BATTLESHIPSProbably one of the most popular electronicgames on the market. Unfortunately the designmakes it impractical to test the PCB as a working model, although it may well functionperfectly. Instead we have tested the soundchip, and sdl the board for its component valueonly (PCB may be chipped or cracked)SN76477 sound 1C: TMSI000 u -processor;bait clips, R's, C's etc. Site 160 x 140mm Only050. Instruction book and circuit 30p extra.

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GREENWELD443A Mill brook Road, Southampton SO1 OHX

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HIFI STEREO AMPLIFIER KITSFrom one of Britain's leading esoteric amplifier manufacturers comes an exciting new package of stereo amplifier kits, designed to offer at the advantages oftrue high fidelity but without theusual price penalty.These new kits offer the choice of moving magnet or moving coil inputs, 40 to 100 watts per channel, in fact, everything that made the previous models so popular is included but with addedstyle, easier construction and a full two year warranty.The new range consists of The CK 1010 Stereo Pre Amplifier, The CK 1040 WPC Power Amplifier, The CK 1100 WPC Power Amplifier.CK 1010Des kit contains all the necessary parts to build a complete pre -amp. The main PCB is ready assembled and tested therefore construction is simplya matter of point to point wiring andmechanical assembly of the connections and controls to the pre punched chassis.The CK 1010 takes its DC supply from the CK 1040, 1100 or, if using a different power amplifier a PSK power supply kit. Inputs for disc, tuner and tape are provided and an optional add-onmoving coil input can be frtted to extend its versatility. 1111C2K1

CK 1040This is a nominal 40 watt per channel power ampffier kit which features our dual power supply and the DC output for the CK 1010.AR components such as heatsinks, wire and connectors areincluded arid protection is provided from short circuit outputs.

CK 1100Similar to the CK 1040 this model provides a nominal 100 watts per channel with extra heatsinking and thermal cutouts are provided as standard.When correctly assembled these kits are guaranteed for two years.

'It would seem then that Crimson have maintained their position at the top of the commercial kit build field. There is no oriental amplifier I know of that can better the sound of this combinationsverall at any price and only a few - such as the KA- ICCIO awo + - are of comparable standard. . . . I can say no more than that for 1250 it (CK 1010/ MC2K/110.1) is a bargain and one thatsecomes the reference point for kit amplifiers from now on."

PRICES CK 1010 RRP (92.00; CK 1040 RRP E121.00; CK 1100 - RRP E151.00; MC2K - RRP E25.00; PSK RRP 820.00Barclaycard or Access accepted, otherwise send C.W.O. C.O.D. £1.00 extra. All prices include P&P to anywhere in the U .K Export: Write for pro -forma

SEND FOR FULL DETAILS ON OUR HIFI KIT PRODUCTS BY WRITING TO FREEPOST ADDRESS BELOW

Crimson ElectricLONDON DISTRIBUTOR BRADLEY MARSHALL LTD, 325 EDGWARE ROAD, LONDON W21 BN

PHOENIX WORKS500 KINGS STREETSTOKE-ON-TRENTTEL: 0782 330520

* *SATURDAY BARGAINS* *EMOS SATURDAY SALES

Starting February 12th we will be open from 10am to 4pm every Saturdayto sell our vast range of components at bargain prices. You will easily find

us in Daventry on the A45, opposite the John O'Gaunt Hotel.

LUIGI ILECTRILTEICS

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Dept 4C, High March, Daventry, Northants NN11 4HQTel: 03272 5523 Telex: 311245 GRENEL G

Please add 50p per order postage and packingincept where higher is indicated) plus 150'e VATon total. 'so 1 Al on overseas orders, postage atcost. Cheques and postal orders made pa) able toEmos Limited. Send Large S.A.E. forcomprehensive catalogue.

Are you interested in

CASSETTE TAPE HEADS,CASSETTE MECHANISMS,

FLOPPY DISK DRIVES,

TEST CASSETTES,

AMPLIFIER, KITS FROM 30 TO100 WATTS, FM

TUNER KITS, CASSETTERECORDER KITS,

COMPUTER PRINTERS? If youare, it would be a good idea

to write or telephone for yourcopy of our FREE list.

HART ELECTRONIC KITS LTDPenylan Mill. Oswestry. Shropshire SY10 9AF

Tel 0691 2894Personal callers are always welcome but please note that we are closed all

day Saturday.

electronics today international

BOOK SERVICEHow to order: indicate the books required by ticking the boxes and send this page, together with your payment, to ETI Book Service,Argus Specialists Publications Ltd, 145 Charing Cross Road, London WC2 OEE. Make cheques payable to ETI Book Service. Payment insterming only please. Prices include postage and packing. Prices may be subject to change without notice.

BEGINNERS GUIDES

Ej Beginner's Guide to Basic Programming StephensonEj Beginner's Guide to Digital ElectronicsD Beginner's Guide to ElectronicsD Beginner's Guide to Integrated CircuitsD Beginner's Guide to ComputersD Beginner's Guide to Microprocessors

£4.96£4.96£4.96£4.96£4.95£4.95

COOKBOOKS

LI Master IC Cookbook HallmarkLI Microprocessor Cookbook M. Hordeski IC Op Amp Cookbook Jung NA. Synthesise r Cookbook H. Kinley Active Filter Cookbook LancasterTV Typewriter Cookbook LancasterCMOS Cookbook Lancaster Tn. Cookbook LancasterEj Micro Cookbook Vol. 1 LancasterEj BASIC Cookbook K. Tracton MC6809 Cookbook C. Warren

£8.65E6.60

E13.15£6.60

£12.00E9.95

[10.85£10.00£14.00

£5.20£5.95

ELECTRONICS

Principles of Transistor Circuits Amos0 Design of Active Filters with experiments Berlin49 Easy to Build Electronic Projects Brown0 Electronic Devices Et Circuit Theory BoylestadID How to build Electronic Kits CapelD How to Design and build electronic instrumentation CarrL Introduction to Microcomputers DaglecsD Electronic Components and Systems DennisD Principles of Electronic Instrumentation De Sa10 Giant Handbook of Computer Software10 Giant Handbook of Electronic CircuitsD Giant Handbook of Electronic ProjectsD Electronic Logic Circuits Gibson Analysis and Design of Analogue Integrated Circuits Gray Basic Electronics GrobD Lasers - The Light Fantastic Hallmark'j Introduction to Digital Electronics Er Logic Joynson3 Electronic Testing and Fault Diagnosis LovedayD Electronic Fault Diagnosis LoVedayD Essential Electronics A -Z Guide LovedayI Microelectronics Digital Er Analogue circuits and systemsMillmanD 103 Projects for Electronics Experimenters MinisD VLSI System Design MurogaD Power FETs and their application Oxner Practical Solid State Circuit Design OleskyD Master Handbook of IC Circuits PowersD Electronic Drafting and Design Raskhodoff VOM - VTVM Handbook RisseD Video and Digital Electronic Displays Sherr Understanding Electronic Components SinclairID Electronic Fault Diagnosis Sinclairo Physics of Semiconductor Devices Sze Digital Circuits and Microprocessors TaubE Active Filter HandbookD Designing with TTL Integrated Circuits Texas Transistor Circuit Design TexasD Digital Systems: Principles and Applications TocciCI Master Handbook of Telephones TraisterCi How to build Metal/Treasure Locators TraisterO 99 Fun to Make Electronic Projects TymonyD 33 Electronic Music Projects you can build Winston

£8.50£10.40

£5.20£11.95£3.55(7.95£7.20

£15.00£11.40£11.00£14.75£9.95£5.55

£26.95£10.50

£6.60£5.25£6.60£5.75£7.20

£11.80£7.25

£30.00£23.00

£8.40£10.95£21.85

£7.25£25 40

£7.50£4.50

£14.50£32.00

£6.50£14.00£14.00£11.85

£8.65£5.20£7.25£5.95

COMPUTERS & MICROCOMPUTERS

0 BASIC Computer Games Ahl £6.350 From BASIC to PASCAL Anderson £7.950 Mastering Machine Code on your ZX81 T. Baker £6.960 UNIX - The Book Banaham £7.80D Z80 Microcomputer Handbook Barden £10.000 Microcomputer Maths Barden £10.75O Digital Computer Fundamentals Barter £9.20O Visicalc Book. APPLE Edition BeN £14.50O Visicalc Book. ATARI Edition Bell £14.500 Introduction to Microprocessors Brunner £22.000 Programming your APPLE II Computer Bryan £7.950 Microprocessor Interfacing Carr £6.60D Microcomputer Interfacing Handbook A/D Er D/A Carr £8.10D Musical Applications of Microprocessors Chamberlain £25.500 30 Computer Programs for the Home Owner in BASICD. Chance £7.95D Microcomputers Dirkson £7.95D APPLE Personal Computer for Beginners Dunn £8.500 Microcomputers/Microcomputers - An Intro Gioone £10.90D Troubleshooting Microprocessors and Digital Logic Goodman £7.95

0 Getting Acquainted with your VIC 20 Hartnell £8.500 Getting Acquainted with your ZX81 Hartnell £5.96CI Let your BBC Micro Teach you to program Hartnell £7.90C Programming your ZX Spectrum Hartnell £8.50ci The ZX Spectrum Explored HArtnell £6.96O How to Design. Build and Program your own working Computer

System Haviland £7.95O BASIC Principles and Practice of Microprocessors Hefter £7.15o Hints and Tips for the ZX81 Hewson £5.25D What to do when you get your hand on a MicrocomputerHoltzman £8.650 34 More Tested Ready to Run Game Programs in BASIC Horn £6.60cl Microcomputer Builders' Bible Johnson £10.750 Digital Circuits and Microcomputers Johnson £13.00- PASCAL for STudents Kemp £7.20

E The C - Programming Language KErnighan £17.200 COBOL Jackson 0.950 The ZX81 Companion Maunder £9.500 Guide to good Programming Practice Meek £5.700 Principles of Interactive Computer Graphics Newman £12.950 Theory and Practice of Microprocessors Nichols £11.350 Exploring the World of the Personal Computer Nilles £11.35O_Microprocessor Circuits Vol. 1. Fundamentals andMicrocontrollers Noll £8 .900 Beginner's Guide to Microprocessors Parr £5.10O Microcomputer Based Design Peatman £10.5013 Digital Hardware Design Peatman £9.10D BBC Micro Revealed Ruston £9.450 Handbook of Advanced Robotics Safford £12.15D 1001 Things to do with your own personal computer Sawusch £7.500 Easy Programming for the ZX Spectrum Stewart £7.150 Microprocessor Applications Handbook Stout £34.40III Handbook of Microprocessor Design and ApplicationsStout 07.60

Programming the PET/C BM West £17.80r0 An Introduction to Microcomputer Technology Williamson £6.20D Computer Peripherals that you can build Wolfe £10.500 Microprocessors and Microcomputers for Engineering Studentsand Technicians Wooland £6.60

REFERENCE BOOKS

Electronic Engineers' Handbook Fink Electronic Designers' Handbook Giacoletto Illustrated Dictionary of Microcomputer TechnologyHordeskiE Handbook for Electronic Engineering Technicians Kauffman0 Handbook of Electronic Calculators Kauffman0 Modern Electronic Circuit Reference Manual Marcus

0 International Transistor Selector Towers0 International Microprocessor Selector Towers0 International Digital IC Selector Towers0 International Op Amp Linear IC Selector Towers

VIDEO

Servicing Home Video CAssette REcorders Hobbs Complete Handbook of Videocassette Recorders KybettO Theory and Servicing of Videocassette Recorders McGinty111 Beginner's Guide to Video MatthewsonD Video Recording: Theory and Practice RobinsonO Video Handbook Van WezelD Video Techniques White

Please send me the books indicated. I enclose cheque/postal order for £Prices include postage and packing.wish to pay by Access/Barclaycard. Please debit my account.

£56.45£59.55

£7.25E27.50(34 .40£40.70£10.70£16.00£10.95£8.50

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mail orderproducts forelectronicprojects

SPECIAL INTRODUCTORYKIT OFFERS

To enable the price conscious enthusiast to be a

PROFESSIONALHObbyboard Systems are derivatives from well proven, high qualityPCB ma nu fa ctu ring techniques -they produce quality products fortechnical projects - why settle for less/

PRINTED CIRCUIT TRANSFER& ETCH (KIT HB/1)A complete kit which includes simple Foil Pattern transfer system, rubdowntransfers, copper clad PCB and all processing materials and requirementsincluding explicit instructions. (Up to 1 0 circults4el

Normal Price £15.00

PRINTED CIRCUIT PHOTO RESISTPRINT & ETCH (KIT HB/2)A complete kit which enables you to make top quality PCB's the professionalway. Includes lull set of artwork ads, photo resist PCB and all processmaterials and requirements. (Up to 10 circuits/kit)

Normal Price £24.00

DAYLIGHT PHOTOGRAPHICSYSTEM (KIT HB/3)Now you can make your own Pholoposilives and Negatives to professionalstandards - DARK ROOM - complete kit with Pos. & Neg film and allprocess aids

Normal Price £19.50

PHOTO LABEL & PANEL SYSTEM(KIT HB/4)Now make professional labels & panels for your propel cases - finish the jobproperly - complete kit includes artwork transfers and materials lo print fullyliminaied Plastic Panels in 5 colours (Up to 20 labels/kit)

Normal Price £22.50KITS HB/2, /3, /4 REQUIREUV EXPOSURE

BUILD YOUR OWN UV UNIT (HB/UV1)UV Lamp, Holder & Shade supplied with full assembly instructions to build aunit which will give superb results normally only obtained from very high costsystems -FAST EXPOSURES -FINE LINE RE PRODUCT

Normal Price £27.00

Hobbyboard UV ARTBOX (HB/UV2)A fully built, self-contained artwork table and UV exposure unit - TWO 1 or thepace of ONE - EXPOSURE AREA 9' x 6 - EXCELLENT VALUE

cpECIAL 0 !PER RICENormal Price £65.00

Even greater savings if you orderkits HB2, HB/3 and HB/4 with your new exposure unitKIT HB/5 FULL PHOTO KIT- E60.00 INCL VATKIT H/3/6 FULL PHOTO KIT- £90 00 INCL VAT

ORDER FORM (ocnr=gr°Ssigri'ea pliersPlease send me the following as quickly as possibleOTY DESCRIPTION Price Cat. TOTAL

KITHB/1- PCBT RANSF ER & ET CH KIT- £12.00-KIT HB/2- PCB PHOTO RESIST KIT - 16.00-

n K IT HB/3 -DAYLIGHT PHOTO KIT- £13.00- £

0 K IT HB/4 - PHOTO LABEL/PANEL KIT - £15.00- £

El KIT HB/5 -FULL UV/1 PHOTOKIT- £60.00- C

0 KIT HIE1/6 -FULL UV/2PHOTO KIT- 090.00-

0 HBAJV1 -DIY UV E XPOSU RE UNIT - 01 6.00- £

HB/UV2 -Hobbyboard UVARTBOX- £49.00- £

TOTALName P&P £ 0:60Address

Cheque,POE

Please Send further details

K ELAN (Hobbyboard)North Works, Hookatooe Perk,Harrogate, North Yorkshire.

0423-883672A dr vision of Kean Engirteenng Ltd ETr382

NEWS

AUDIOPHILEAfter dispensing, on tablets of newsprint, some wise words aboutvarious readers problems, Ron Harris turns his attention to the newcartridge from Coral.

I'm going to start this month with a selection of letters,chosen to illustrate a general point or two that crops upin a number of readers' enquiries. There are several

overall principles concerning setting up a hi-fi system,such as compatibility, component -matching, power re-quirements etc etc that have been repeated endlessly byall the hi-fi press - and will ever more be repeated - thatare so fundamental to the task they should be inscribedacross the walls of hi-fi emporia throughout the land.

I do not wish to go through ritual incantations herein,so please to accept a summary.

This can be as concise as: everything must be matchedto everything else (especially cartridge to speakers) andthe system is only as good as its weakest link.

With that in mind let us take up the discourse . . .

Getting Decked OutI have recently acquired a Sony PSX600 automaticrecord deck and wish to replace the cartridge (supplied)with something better. I am not sure what cartridge willmatch the deck and want your advice to choose a newone. How good is the Sony one anyway? My amplifier is aSony STRV55 and I use Mission 700 loudspeakers.J. BANKS, STRETFORD, MANCHESTER.

Answer The easy one first. If you'd read your December'82 copy of ETI properly (lose 10 points for inattention)you would have seen our review of the Goldring G910IGCwhich is designed to work in a range of the bet -terautomatic decks, such as yours. Taking into account thebright loudspeakers you favour, this would be a goodchoice. Have a listen to it yourself if you can manage itand see what you think. Others to try: Shure M97HE andDynavector DV20.

Unbalanced And BiasMy hi-fi system is made up of a Thorens TD1 50 and

Mayware arm and a Shure V15 III cartridge, a home-madeTexan amplifier and a pair of Mordaunt-Short Signifierspeakers that I got as a birthday present. I am happy with itexcept that it seems to have no bass since I changed thespeakers and it doesn't have the same power. The sound isa bit 'tinny' now and I get more surface noise. I had thespeakers checked by the shop and there was nothingwrong with them. Do they match the amplifier or should Ichange them again? If so what should I buy to match it?P. RAWLINGS, TUNBRIDGE WELLS, KENT.

Answer What car do you drive? A Lincoln -Continentalwith a Mini engine perhaps? There is nothing amiss withthe speakers by the sound of it, but that amp is just ever soslightly out of place. It is not powerful enough to drive theSignifiers. t is not good enough to be in the system at all.In fact it wants dropping out - from a great heightpreferably.

You are not getting increased surface noise: it is justthat the Signifiers are showing you what has always beenthere! (I shudder to think what sort of speakers you usedbefore . . . ) While I am at it, that record player could do

with sorting out, too. The Shure is a very bright cartridge,unless loaded properly - and the Texan won't do thateither. This is almost certainly aggravating the 'tinny'sound, as you so graphically describe it. The Mayware armwe have had problems with under test for similar reasons,but if it works in your system . . .

I would suggest you get yourself a decent amp ofaround 50-100W per channel, and the HE stylus upgradefor your V15 III. If the system still sounds bad to you then,you have two choices: (i) Sell the lot and buy a transistorradio. It'll still sound 'tinny' but at least you'll know why.(ii) Change your ears.

First Time NervesBeing of unsound mind and a little body I am about tobuy my first ever hi-fi. After a lot of research activities andreading up I have decided on the following. My room isabout 12' x 8' and I will be using it for all types of music.I am being foolishly brave I know, but could I have yourcomments and suggestions for improvement please.

Also which tape should I use with a Sony TCK-55deck? I know you reviewed it years and years ago and I

Ms D. COSTERN, OXFORD.System: - Oracle/SME III/Dynavector Karat Diamond,Carver C1/M-400 Cube, Celestion SL6 speakers.Answer First system???? A f600 record deck and £500 car-tridge and it's your first system . . . ?

The Cube and the SL6's are an inspired choice. Thatset-up will provide magnificent transients and a sound outof all proportion to the size of the units.

The record deck, however, is not so inspired. For astart, the arm and cartridge don't match. You will need toeither go down to the Karat Ruby, or change the arm up-wards to either the Ittok or 'The Arm' to get the best out ofthe cartridge.

Frankly, though, I wonder if you've auditionedsomething like a TD160S/SME III/V15 V against the Oraclecombination. Beyond reproach as your intended deckmay be (and it is the best turntable in the universe) it isprobably too expensive for your needs. Quite a way tostart, nonetheless.PS (It wasn't years and years either, and Maxell or Sony areyour best bet.)

All Things Being Equal I'm HelpingI have an unusually shaped living room and it's got a

wooden floor. No matter what sort of system we try in it,there is NO WAY to get a flat response. I think I need agraphic equaliser and wondered if you could help out witha circuit or something . . . (Preferably one-third octave.) Ithink your past projects are old-fashioned now andwondered if you are going to do a modern one.B. EVANS, BIRKENHEAD, MERSEYSIDE.

Answer How to win friends and influence people. Youwant me to give you a circuit for a one-third octaveequaliser after you dared to call our past attempts old-fashioned? Smooth talkers like you should be in politics.

NEWSYou'd go down well in the SDP.

Since you've been so charming about it, how could Irefuse? Below you will find the circuit for an ultra -highquality equaliser. ETI may well produce it in a projectlater, but for now it is simply a tried and tested design.Board layouts and all that are not forthcoming, so pleasedon't write in for them.

Coral MC -82This month's review is the new Coral moving -coil car-

tridge, the MC -82. A deal has obviously been done and itsports a (Goldring) van den Hul stylus! The unit is sold asan up-market version of the excellent MC -81, which bynow has probably reached 'Classic' status.

The MC -82 will cost around £130design, requiring step-up of some sort. As an ever-increasing number of betterdecent head -amp these days, this is a problemfast disappearing.

There are, in addition, a goodly number of specialisthead -amps to be had, and choosing is as much a matter oftaste as anything else.

The MC -82 is an interesting product, offering morethan just a new point to an old success story. As always it isimmaculately presented, in a thick clear perspex box.

The pickup itself is a pretty golden colour and thebody is identical to the MC -81 and MC -88E. Saves on theproduction, I suppose. The stylus is not user -changeableand must be returned to Coral for exchange.

Test RunAs can be seen from the results below, the MC -82

turned in the to -be -expected faultless technical perfor-mance. Optimum tracking was achieved at 2g1, abovewhich no improvement could be obtained. With a weightof round 5 g and a compliance at over 20 cu(x 10-6 cm/dyne), the unit will match a wide range ofarms and decks. (Tests were conducted using an SME III.)

The frequency response was flat 20-20 kHz ±1 dB, aremarkable result. Excellent control of tip resonancesshows in the smooth treble extension. Nothing to com-plain about and much to praise.

The van den Hul stylus is one recently covered in thisfeature, in connection with Goldring's own G910IGC.

2201.

1412;

2101.

INPUT

TEST RESULTS: CORAL MC -B2

Frequency ResponseChannel SeparationImpedance

Optimum Tracking WeightChannel BalanceComplianceOutput VoltageWeightPrice

: 20-20 kHz ± 1 dB: 27 dB at 1 kHz: 5 ohms (recommendedloading of 30R): 2g1: within 1.2 dB: approximately 22 cu0.25 mV into 30R:5: around f130

You are referred to ETI December 1982 for a detaileddescription. Basically it imparts better groove contact andthus better tracking. In addition it seems to reduce suscep-tibility to surface noise - a contention borne out in theMC -82, incidentally - and on the Goldrings has a veryopen and detailed presentation.

Sound Product?Having set up the MC -82 and settled back to listen,

amp glowing merrily (well it is Class A), I found it a rewar-

CI170n

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Pot8ntiometer Range5025B B

40F20

3(4_15

20L10

10 S

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50 dB Rectifier 3" Lower Lim Freq 20 Hz Wr. Speed:_!" mm/sec. Paper Speed: 3 mm/see.;I Si Rill I 1

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Multiply Freq. Scale by5Q 100 200 Hz 500 1000 2000 Hz 5000

Zero Level

Fig. 1 Frequency response of the Coral MC -82 moving coil cartridge.

ding experience. This Coral is very good. It is totally unlikethe MC -81, totally unlike the Goldrings and I can think of noother cartridge at all to which it is similar, except perhapsthe Ortofon MC -30 and that is high praise indeed.

The Coral has the open mid -range of all the bestmoving -coil units, with a good detailed bass, which isperhaps a trifle loose at the very bottom end of thespectrum. The treble is clean and sharp without everbeing hard or incisive. A cymbal sound demonstrates thisvery well.

The van den Hui once again seems to reduce itscarrier's susceptibility to surface noise and backgrounds,ac-cordingly, are quieter than with other cartridges.Voices are portrayed very well and the sound stage as awhole is well balanced and without undue emphasis in anypart of the spectrum.

At the price of £130 the MC -82 is not cheap. It is valuefor money, however, when you consider the competitionaround. Coral have produced a cartridge here whichperforms exceptionally well and at a level which forces meto compare if to far more expensive units. I can onlyrecommend that if you are looking for a cartridge in thisprice range - or higher - you give the MC -82 a try.

3 PIN OW SOCKETS (a)REAR VIEW

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10000 20000(1612/2112)

40000DABCLn.,A B C Lin. I

It must be the season for van den Huls, because here we go again!Goldring have just released their first ever moving coil cartridge,called the Electro II and retailing at around Z125.

The main design aim has been to improve upon the ability ofpresent cartridges to reproduce detail by eliminating non-linearenergy losses in the cartridge itself. To this end, no adhesive isemployed in the construction and a rigid die-cast assembly isused. Very high precision mouldings are required.

Audiophile is on the phone, trying to get hold of one and seehow it all manages to stay in one piece.

SW1

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Fig. 2 The circuit and PSU foran ultra -high quality one thirdoctave graphic equalizer. If youfancy building it - go ahead.Just don't ring us for PCBlayouts!

RIO10

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.11ms - 90 x 61 x 30mm.

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DOME TWEETERDoe Tweeter Ea systems up to SOW. Impotence 8ohms, Frectuancy Response 2000-20000Ha Owns98mm de e 31nn deer,

OUR PRICE £2.86 0/No. CIMT200

30.000 opv. Including test leads and case

/C worts 0 2 510-25-100-250-500.1.000

DC vans 0.025.1-2 5-10- 25- 100 250-1000

DC current- 0-50ua 0-5ma-50ma 0 -Ramon

Resistance - 0-6K dens -10K ohms-6meg ohms-

60meg ohms

Decibels- -20d5 to plus 5606

Short test- Internal hurter

Dms - 1E0 x 110 r 50mm

0/No. 1315. OUR PRICEONLY £24.75 tiv

BI -PA

SILICON BRIDGERECTIFIERS

cornprk.no 1j dm,rechhora onoonrod on PCB

TI-VRM - Myles ;

1FM - 1.5Amps

10 off £1.0050 off £4.50

100 off £7.50Order No. As: 4R1 BRect.

SPECIAL OFFER OF STEREO AUDIO MODULESFully built and tested in our factory

A COMPLETE SET TO GIVE YOU 70 WATTS TOTAL35 WATTS funs) PER CHANNEL 55v POWER SUPPLY

Kit compnses2 x AL80 Power Amplifiers 1 x SPM120 /55 Power Supply1 X PA 200 Stereo Pre.Amplifier 1 x Transformer 55v1 x Front Panel Black with White letterng 2 X Coupling Capacitors Er 1 ReServott Cahoot°,4 x Black Knobs with White Pointer FuN hook-up chartNORMAL RETAIL PRICE £52 COMPLETE SAVE £14OUR SPECIAL OFFER PRICE FOR 1 MONTH ONLYOrder by phone NOW rob; your Credo andRing: Sue on OM 3442/3182 foe Immediate despatch(Order es: SX7II won AUDIO KIT) COMPLETE

£38

KSend your orders to Deot ETI3. BI PAK PO BOX 6 WARE HERTSSHOP AT 3 BALDOCK ST. WARE. HERTS.

TERMS CASH WITH ORDER- SAME DAY DESPATCH. ACCESS.BARCLAYCARD ALSO ACCEPTED TEL 1092013182 GIRO 388 7084

Add 151, VAT AND 50p PER ORDER POSTAGE AND PACKING

Use pee oetht (404 Rmo us on Raw 3I12 SON and

Eel IMP Order men taste( Goods norm* seal 2nd

Class Mad

Remember fa, must add YE at 15'o blew ode,

Total Polite add SOp per Bohai ode.

el fro tie AUTO-EtECTRON1C PRODUCTSKITS OR READY BUILT

r ELECTRONIC IGNITIO

IS

YOUR CARAS GOOD AS IT* Is it EASY TO START in the cold and the damp? Total Energy

Discharge will give the most powerful spark and maintain fulloutput even with a near flat battery.

* Is it ECONOMICAL or does it "go off" between services asthe ignition performance deteriorates? Total Energy Dischargegives much more output and maintains it from service toservice.

* Has it PEAK PERFORMANCE or is it flat at high and low revs.where the ignition output is marginal? Total Energy Dischargegives a more powerful spark from idle to the engines max.(even with 8 cylinders/.

* Do the PLUGS and POINTS always need changing to bringthe engine back to its best. Total Energy Discharge eliminatescontact arcing and erosion by removing the heavy electricalload. The timing stays "spot on" and the contact conditiondoesn't affect the performance either. Larger plug gaps can beused, even wet or badly fouled plugs can be fired with thissystem.

PROTECTYOUR CARWITH ANELECTRON=ELECTRONIC ALARM* 2000 COMBINATIONS provided by an electronic key a

minatu re jack plug containing components which must matcheach individual alarm system. (Not limited to a few hundredkeys or a four bit code).

* 60 SECOND ALARM PERIOD flashes headlights and soundshorn, then resets ready to operate again if needed.

* 10 SECOND ENTRY DELAY allows owner to dis-arm thesystem, by inserting the key plug into a dashboard mountedsocket, before the alarm sounds. (No holes in externalbodywork, fiddly code systems or hidden switches). Re -closing the door will not cancel the alarm, before or after itsounds, the key plug must be used.

* INSTANT ALARM OPERATION triggered by accessories orbonnet/boot opening.

* 30 SECOND DELAY when system is armed allows owner tolock doors etc.

* Is the PERFORMANCE SMOOTH.The more powerful sparkof Total Energy Discharge eliminates the 'near misfires'whilstan electronic filter smooths out the effects of contact bounceetc.

Most NEW CARS already have ELECTRONIC IGNITION.Update YOUR CAR with the most powerful system on themarket - 311 times more spark power than inductive systems -3'Y2 times the spark energy of ordinary capacitive systems 3times the spark duration.

Total Energy Discharge also features:EASY FITTING, STANDARD/ELECTRONIC CHANGEOVERSWITCH, LED STATIC TIMING LIGHT, LOW RADIOINTERFERENCE, CORRECT SPARK POLARITY andDESIGNED IN RELIABILITY.

* IN KIT FORM it provides a top performance system at less thanhalf the price of competing ready built units. The kit includes:pre -drilled fibreglass PCB, pre -wound and varnished ferritetransformer, high quality 2pF discharge capacitor, case, easyto follow instructions, solder and everything needed to buildand fit to your car. All you need is a soldering iron and a fewbasic tools.

FITS ALL NEGATIVE EARTH VEHICLES6 or 12 volt, with or without ballast.

OPERATES ALL VOLTAGE IMPULSE TACHOMETERS:(Older current impulse types need an adaptor).

STANDARD CAR KIT £15.9Assembled and Tested £26.70

TWIN OUTPUT KIT £24.55For Motor Cycles and Cars with twin ignition systems

Assembled and Tested £36.45

PLUSP. 6. P:

El (U.K.)

PricesincludeVAT

Don't Wait UntilIts too LateFit one NOW!

* DISABLES IGNITION SYSTEM when alarm is armed.

* IN KIT FORM it provides a high level of protection at a reallylow cost. The kit includes everything needed, the case,fibreglass PCB, CMOS IC's, random selection resistors to setthe combination, in fact everything down to the last nut andwasher plus easy to follow instructions.

FITS ALL 12 VOLT NEGATIVE EARTH VEHICLES.SUPPLIED COMPLETE WITH ALL NECESSARY LEADSAND CONNECTORS PLUS TWO KEY PLUGS

\ PLUSCAR ALARM KIT 24.951 P. Er P.

£11U.K.1Prices

ASSEMBLED AND TESTED 37.95 includeVAT

NMIPro ' Access and Visa

Welcome. Write orPhone Quoting Number

9. wide Assa

ELECTRONIZE DESIGNDept. D Magnus Rd Wilnecote

Tamworth B77 5BYtel: 0827 281000

PROJECT

ALARM MODULEThis module is very small, very cheap, very simple and extremelyloud indeed. Use it to make an existing burglar alarm tamper -proofor as the basis of a new system. Design by Phil Walker.

This project is designed tomonitor the state of open andclosed loop alarm circuits,

together with the main powersupply. If disconnected from themain system or from its externalpower source, it will trigger theinternal noise source to drawattention. A rechargeable batteryinside should keep it going for somehours once triggered; the unitcannot be reset until the faultcondition has been removed.

A delay has been built into thetrigger circuit so that the initialalarm tone is at reduced volume:useful if you wish to dash into aprotected area and switch off thealarm circuit before all hell breaksloose, or if you've triggered it byaccident. This could be shortenedfrom the present 10 seconds or so ifmore immediate response isrequired. The sound output fromthe device is quite painful at closequarters even though the batterydrain is reasonably small: testing theproject in our workshop nearly ledto insurrection and multiplelynchings by the staff from our othermagazines! If used in a car thenormal current drain from the carbattery will be less than 5 mA. Thetime delay in this case may need tobe altered for best effect (C1 adjuststhis).

The Alarming TruthThe circuit for this project can

be considered as four basic blocks.The first is dedicated to detecting allthe alarm conditions, which arepower failure, closed loopdisconnection, and open loopcontact. All these conditions willstart the delay timer in the secondblock, and all except the powerfailure detector will make the alarmsound immediately.

The second block contains atime delay circuit, a thyristor latchand a power switch. When an alarmcondition is detected in the firstblock, the time delay circuit willstart. This may allow a small amountof current to flow through the outputpower switch, thus making a lowvolume sound as a

The Alarm module is completely self-contained. Here you can see the tweeter, thereset button and DIN socket for connecting the alarm sensor switches and optionalexternal alarm.

With the case apart you can see how the tweeter fixing screws hold the PCB stand-off pillars in place.

warning. If the alarm condition isnot a power failure, a larger currentwill be drawn to make a moredefinite sound.

If the alarm condition persistsuntil the delay circuit times out, theSCR switch can be turned on,switching the sound output tomaximum, activating the relaydriver and maintaining thiscondition until the reset button ispressed and released. However, thereset button is not effective unlessthe alarm condition has beenremoved from the input circuitry.The reset button also acts as a testbutton in that it causes the alarm tosound while it is pressed (but onlywhen everything else is in a normalcondition).

The third block is the alarmsound generator and outputtransducer. The basis of this is aself -oscillating transformer -coupledmultivibrator. This is tuned by the

capacitance of the piezo-electric tweeterto a frequency of a few kilohertz. Notethat a normal loudspeaker is not usablehere.

This circuit configuration takes the 8Vavailable from the battery and converts itto an approximate sine wave of around18V peak to

BUYLINES

here are a number of unusual com-onents for this project. The piezo-lectric tweeter is the Motorola type And can be obtained from BK Electronicstd, 37 Whitehouse Meadows,astwood, Leigh -on -Sea, Essex SS9 5TY.he pot core can be ordered as type9-835-41 from Neosid (Small Orders),O Box 86, Welwyn Garden City, HertsL7 1AS. The relay is RS type 349-658, orIse the Electrovalue type 42 should fit.lectrovalue are at 28E St Judes Road,nglefield Green, Egham, Surrey TW20H B. Watford Electronics, 33/34, Car-iff Road, Watford, Herts stock theN5062, and the PCB can be obtainedrom our PCB Service on page 83.

PROJECT

peak across the tweeter. As thesedevices are much more efficientthan moving coil loudspeakers, thesound output is pretty high. Inaddition the current drain from thebattery is only about 30 mA whilethe alarm is sounding. While notsounding, the battery is charged viathe LM334Z constant current device(this feature should be omitted if anormal PP3 battery is used).

The final block of the project isthe relay driver. This consists of aVMOS FET acting as a switch toturn on the current through a smallrelay. A diode is placed across thecoil to absorb the back EMF whenthe current is switched off. Thecontacts of the relay can be used toactivate an external alarm ifrequired.

A useful tip: when assemblingand testing this project connect theexternal +12 V supply first, thenensure that the 'closed loop'contact is connected to 0 V and the'open loop' is unconnected beforeconnecting the internal battery.Alternatively, a wool pullover orthick cushion may be used toprotect the ears!

ConstructionThe prototype unit fitted into a

small general purpose box. Thepiezo-electric tweeter was screwedto the outside and the circuit boardmounted with pillars to the samescrews. For better protection, themounting screws can be made looseat the case and PCB so that therecan be no possibility of undoing

TO 0EXTERNAL 0

ALARM 0

.10-18V o

OPEN LOOP

CLOSED LOOP

OV

them from the outside of the case.A trace of epoxy glue on thethreads should hold them in theright place. Then again, there'salways pop rivets.

The construction of the PCBposes no unusual problemsprovided that the componentpolarities are followed carefully(although some lead bending maybe necessary). The transformer, T1,is a standard RM10 ferritetransformer core. Starting at one ofthe inner pins of the single sectionformer, wind on 100 turns of 32swg wire and terminate it to one ofthe outer pins. Now wind on fromthe remaining outer pin,another 100 turns in the samedirection and terminate this to theinner pin adjacent to the start of thefirst winding. If desired, a layer oftape can be placed over each layerof wire to keep the windings neat.

When assembling thetransformer, place the ferrite coresaround the bobbin and withoutpressing the centre of the cores atall ease the clips provided into therecesses on the ferrite parts.

For connection to the outsideworld we used a seven -pin DINplug and socket. This was sufficientto carry all the necessaryconnections, including the relayoutput. However, you may prefer tosolder wires from the sensor directlyonto the PCB. For added protectionthe 'closed loop' connection couldbe used to ensure that the casecould not be opened without settingoff the alarm.

HOW IT WORKS

The sound output from the unit is pro-duced by TX1 (a piezo-electric tweeter)which is driven by the oscillator Q7,8,R18,19 and TI. The frequency ofoperation of the circuit is determined bythe inductance of TI and thecapacitance inherent in TX1.

If SCR1, Q2 or Q3 (via PB1) are onthen the current through R17 will makeQ6 conduct, thus applying the batteryvoltage to TI and the relay driver circuitaround Q9. This causes the alarm tosound and also activates any externaldevice connected to the relay contactsRLAI.

The presence of an external powersupply is sensed by Q4. This transistor iskept non -conducting while the inputvoltage is above about 10 V and thevoltage across RIl is greater than about8 V. If the supply voltage drops below 10V or Q2 conducts, then the voltageacross R11 will drop and allow Q4 toconduct. This causes CI to charge up viaR14 until Q5 conducts enough to turnSCR1 on via ZD2. This then sound thealarm.

Q2 can be turned on in two ways.Either the 'closed loop' input can bedisconnected from ground, allowingcurrent to flow down R2,3 and 02 intoits base, or the 'open loop' input can begrounded, thus turning on Q1 and sup-plying Q2 base via R6. Both these condi-tions are abnormal and will trigger thesound circuit after a short delay.

The reset switch PB1 is connected tothe anode of RI on one side and to Q3collector on the other. In order for theunit to be reset by this switch, Q3 mustbe on. This is only the case when Q2 isoff and the input supply voltage is con-nected. When Q3 is on and PB1 isoperated, the anode of SCR1 is pulledlow, thus removing its holding current.When PB1 is released, SCR1 will notconduct until it is triggered again. Notethat the alarm will sound when PB1 ispressed to test or reset the unit.

DI

R210k

R3242

021

R410k.

NOTE'IC1 IS LM334Z011,6 ARE BC212L023,7,8 ARE BC10806 IS BC182L09 IS VIWNIAF

R71k0

05

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COM

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07R810k

13V9 P81

SCR1 IS C103 OR SIMILARD1,11 ARE 1N400102.10 ARE 1N4148ZD1 IS 3V9 400 rnW ZENERZD2 IS 2V7 400 mW ZENER

R72IOk

R11101

R13'100k

R14100k

Cl100u

8V4

RLA

0

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Fig. 1 Complete circuit diagram of the Ell Alarm Module.

PROJECT

EXTERNAL OV

SUPPLY *12V)NOM)

TO TX1

FROM PP3 J OV

NICAD 1*8V4

CDkg

2N5062

C103

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Fig 2. Component overlay for the Alarm Module.

PARTS LISTResistors (all IW, 5%),R1, 2, 4-6, 8,9, 11, 12,15, 16 10kR3, 17 2k2R7 lkOR10 68RR13, 14,18-20 100kR21 220k

Capacitors

C1C2

100u 10 V tantalum100n ceramic

Semiconductors

IC1 LM334ZQ1, 4, 6 BC212LQ2, 3, 7, 8 BC108Q4 BC182L

VN66AFSCR1 C103 or 2N5062D1, 11 1N4001D2-10 1N4148ZD1 3V9 400 mW zenerZD2 2V7 400 mW zener

MiscellaneousPB1 single pole push-buttonRLA two -pole relay, 12 V 200 R

coil, PCB -mountingTi RM10 pot core (AL =

400), with 100 + 100turns of 32 swg copperwire on a single sectionbobbin (8 pin)

TX1 Motorola piezo-electrictweeter type A

PCB (see Buylines): PP3-sizedrechargeable Nicad battery; metal caseapproximately 100 x 100 x 50mm; bat-tery dips, nuts, bolts, pillars, etc; op-tional seven -pin DIN plug and socket.

TO EXTERNALALARM

5. 'OPEN' LOOP

CLOSED' LOOP

TO PB1HESE T;

This vertical view shows the internal layout of the project with the wiringconnections. With a case of the specified size, there is just enough room for aPP3 battery.

01-452 1500 TEctiNomsvric LT1) 01-450 6597Micro ComputerPlease phone for availability

WOR D PROCESSOR 'VIEW'16K ROM £52

TELETEXT ADAPTOR£195.00

ACORN SOFT/BBC SOFT/GAMES PADDLES IN STOCK

CASSETTE RECORDERFerguson 3T07 £26.50 8 £1.50 carr

Cassette Leads £3.50Computer Grade Cassettes

£0.50 each £4.50 for 10 8. £1 carr

NEC PC 8023 BE -C100CPS, BO colaLogic Seeking,Bid ifactio nal, Forward andReverse Line Feed,Proportional Spacing. AutoUnderline, Hi -Res and BlockGraphics, Greek Char. Set.

Only £320+ £8 carr.

BBC Model A £299BBC Model B £399(inch VAT) Carr £8/ unit

Model A to Model BFitting charge £15Individual upgrades

also available

PRESTEL ADAPTOR£90.00

2nd PROCESSOR 6502/280£170

FLOPPY DISC INTERFACEIncl. 1 .0 operating system

£95 + £20 installation

Phone or send for our BBC leaflet

BBC FLOPPY DISC DRIVESSingle drive 5Y4" 100K £235 + £6 carr.

Dual drive 5Y4" BOOK £799 + f8 carr.

BBC COMPATIBLE DRIVESThese are drives with TEAC FD50 mechanism

and are complete with power supply

SINGLE: 100K £190; 200K £260; 400K £340

DUAL 200K £360; 400K £490; 800K £610

OFFICIAL 000'DEALERMONITORS

3MC BM 1401 14in Colour MonitorRGB Input E166 + CB carr

KAGA RGBI 12in Colour MonitorRGB Input 4236 + CB carr

KAGA 12in Hi -Res Green MonitorE170 E6 carr

MICROVITEC 1431 M/S 14inColour Monitor 1269 + CB carr

Hi Res Green Monitor E99 + E6 carrRGB Lead for BMC/KAGA £10Composite Video Lead E3.50

RUGBY ATOMIC CLOCKThis Z80 micro controlled clock/calenderreceives coded time data from NPL Rugby.The clock never needs to be reset. Thefacilities include 8 independent alarms and foreach alarm there is a choice of melody oralternatively these can be used for electricalswitching. A separate timer allows recordingof up to 240 lap times without interruptingthe count. Expansion facilities provided.See July/August ETI for details. Complete Kit

120 + E2.00 p&p

MICROTIMER6502 Based Programme able clock timer with* 224 switching tunes/week CyCle* 24 hour 7 day timer* 4 independent switch outputs d rectly interlacing to

thyrisfutituacs* 6 digit 7 seg. displays to indicate real time, ON/OFF and Reset

tones* Output to drive day of week swach-and slims LEGS.Full details on request. Price for kit E57. 00

PRINTERSSEIKOSHA GP 100A

80 Cols 30 CPSFull ASCII e GRAPHICS10" Wide paper

Now only f175 + £6 carr.Ask for details on GP 250A

Parallel Printer lead for BBC/Atom to most printers £13.50Variety gf interfaces, ribbons in stock

2.000 fan fold sheets 9 " x 11" f13.50 - E3 p Et p

I.D. CONNECTORS(Speed block Typal

No of Header Ramo, Edgeway. Plug tech. Conn10 80p 90p 200p20 1465 125p 340p28 175p 160p 300p34 200p 140p 310p49 220p 190p EllOp

50 73bp 2009 SOOp

D -CONNECTORSaway 16 we,/ Zbway37w.y

MALESolder 90p 1300 140p 260pAngled 110p M:lp 296p 4269

FEMALEsower lisp mop 210p 350pAngled 17Ep 240p 310p 500pHood 96p 136p 13159 126p

MICRODOCTORThis is not a logic analyser oran oscilliscope. It tests amicrosystem and gives aprinted reprint on RAM,ROM and 1 /0 - it will printmemory map, search forcode, check dataline shortsand operates peripheralsMicrodoctorcomplete with PSU,Printer, probe cableand two configurationboards. E295.

PLEASE SEND SAE FOR PRICE LIST

II ACORN ATOMBasic Built £135 Expanded E175

(carr 0 per unit)Atom Disc Pack CM + f6 carr

3A 5V Regulated PSU + £2 carr.

Phone or send for our BBC Atomlist.

EPSON MX 80 and 1 00F/T3MX 80 80CPS 80 cols

MX 100 100CPS 136 colsLogic Seeking, Bi-

directional, Bit ImagePrinting, 9 x 9 Matrix

Auto UnderlineMX 80 F/T3 £325

MX 100 F/T3 E430(ES Carr/Printer)

CONNECTOR SYSTEMSJUMP LEADS AMPHENOL CONNECTORS

4in Ribbon Cble with headers14 pin 11 pin 34 ph 40 Pin

1 end 1450 105p 340o 35302 ends rap 23:IP 3460 540P241n Ribbon Cable with sockets

20 pin n pin 34 pbs 40 pin1 end 150p 210p 270p 300p2 ends 2110p 335p 410p 640p241n Ribbon C bee with D. Conn

25 way Male Map Female 1210p

36 way Solder Type PlugIcentronix type)

36 way Solder SocketIcentronix type)

36 way IOC Plugcentronix type)

24 way Solder Plug(IEEE type)

24 way Solder Socket24 way IOC Plug

560p

1150p

5009

600p504486p

RS232 CONNS 125 way 131 '

24" Single end Male £6.5024" Single end Female £6.0024' 'Female -Female E11.0024"Male-Male f10.0024" Male, Female £11.50

DIL HEADERSoid., !DCtype type

14 pin 413p 1000

18 on 5053 110p24 o 100p 180p40 pin 200p 2:Mp

EUROCONNECTORS

(Indirect Edge ConnlDIN STD Plug Skt41817 21 way 170p 173p41817 31 way 1965 190p

1812 2 a 32 way 290p 3200Anyto.12x.32 way 33p 3700

18123x32 way 215p 319353

Angled 33.32 way 40091.32 way noic + C - 625p

(for 2,32 way 1011/3113/ a+ b of a+ el

2.18 way2.22 way21(23 way2.25 way1.43 way2.43 way2.50 way107 way$100 Conn

SOFTY II INTELLIGENT PROGRAMMERThe complete wOCIO process., del/downers system tar Enamors end Hobtryerte. You candos bC wog ems, debtig, yeah/ end commis to MOMS or use in host computer by ueng

softy as a rawest. Powellul edlhn9 fanikbes permit Was, blocks of bytet eNsnged, deletedor aliened end memory contents can be observed on °Winery TV Accepts moat k 553 Eproms.

Softy II complete with PSU, 7V Lod and Rornuletor lead C1 09

UV ERASERS

UVIB up to 6Eproms E61.50

UVITwith Timer E50.1.0

UV140 up to 14 Eproms 01.50UV141 with Timer 17&00

(Carr 62/eraser)

All erasers are fitted withmains switches and safety

interlocks

TRAINER KITSi5 Junior Computer 015.03,

6802Nancomp I

6809 Nancomp II E86.00

1802 Micro Trainer E54

E80 Manta £116

280 Menta £116

(fully built and documented)Full details on request

RIBBONCABLE (Grey)

10 way14 way16 way20 way26 way34 way40 way50 way64 way

80p80psop

106p1100220p286p330p370p

EDGECONNECTORS

0.1In 0.1684n- 140p

2C0p 1709210p -2250 1295326053 -3865 -700p -- SCOp

PE IALOFFER

21141271625324116-24164-26116P-3

80p260p360p809

460p3192p

BOOKS (No VAT p&p £1)CMOS Cook Book 12.75CRT Controller H/BookProgramming the Z80 E11.50

ISO MIcrocomp. handbook C516Programming the 6602 E10.36502 Assy. Lang. 612.10

6502Applications 610.20

8602Sottware Design 13.05

6502 Games E10.52Large selection of data books, Inter-facing books, books on BBC, etc In

stock. As for our list.

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Microtan ClockSwitching ForSoftware TestsK. E. Knibbs, Huntingdon

designed this circuit because I

needed a system of switching theclocks on Microtan system from thenormal speed of 750 kHz to 1 MHz inorder to test software in real timewhich had been written for a stand-alone 6502 controller. The circuitfunctions as follows: the two

oscillators fire the monostables IC2and IC3 for their minimum period ofapproximately 20 nanoseconds. Onlywhen these fire at the same time doesan output appear at pin 3 of IC5d:This pulse is used to clock the D -typeflip-flop IC4, the input of which is thedebounced switch. The outputenables IC5a or IC5b which allowseither a 6 MHz or an 8 MHz clocksignal to enter IC5c. This ensures thatno clock pulse is either too short ortoo long and is glitch -free. The circuithas been in use for over three monthsand no system crashes have beencaused by it.

Low ResolutionPulse GeneratorG. Foote, Woodford Green

This circuit produces pulses whosewidth iscontrolled bya three bit wordand which can be used to controlmotors and similar devices wherehigh resolution isn't needed.

IC1 is a decade counter with out-puts '0' to '9' going high in turn. Hereit counts from '0' to '8' and is reset bythe '9' output which is connectedback to the reset pin. Outputs '0' to'7' are connected to IC2, an eight -line -to -one -line multiplexer. The out-put which is connected to pin 3 bythe internal switches of the ICdepends on the value of the three -bitword on pins 9, 10, 11.

IC3 is configured as a bistableand is set by the '8' output of IC1. It is

reset by one of the other outputs of10; the one selected by IC2. Thelength of the output pulse at pin 3 ofIC3a depends on which output of IC1is used to reset the bistable, the out-put being selected by the three -bitword input to IC2. Note that the 4051could be replaced by a 4512 dataselector.

CLOCK 014

FEATURE

Digital FrequencyMeterWilliam Leung, Harlow

The design shown is an alternative tothose projects for DF Ms that utilise oneof those new fangled all -in -one DFMchips. As you can see from the circuitdiagram, the only additional circuitryrequired is an input preamplifier and asuitable regulated 12V power supply.

IC5 is a real-time five -decade counterincorporating a multiplexed BCDoutput. With the aid of IC8 (a BCD -to -seven -segment decoder) andtransistors 01 to Q5, the counter anddisplay section of the DFM is formed.

The BLANK pin on IC8 is used toextinguish the displays while IC5 is

counting, otherwise pin 4 of IC8 shouldbe connected to the positive rail. Thefrequency reference oscillator is

somewhat unique in that a 500 kHzceramic resonator is used.

In practice it offers reasonableaccuracy: however, the circuit can beeasily modified to use a 1 MHz quartzcrystal. In this case, the connectionsbetween IC2 and IC7 of the frequencydivider section will require the inputsof IC7 to be connected to pins 3, 5, 12,14 and 15 of IC2. Pin 14 of IC3 shouldalso be connected to IC2 pin 2, and asuitable multiplexing frequency ofaround 1 kHz should be fed to pin 10of IC5.

Depending on the position ofSW1b, either 1 Hz, 10 Hz or 100 Hz willappear at IC9 pin 11 (see Fig. 2, pointP), where IC9a is a D -type flip-flopconfigured to divide by two.

Should IC9a be continuouslyenabled, the output of IC9a will, in fact,be a square wave of half the appliedfrequency with a mark/space ratio of1:1. This means that for a 1 Hz appliedfrequency, 0.5 Hz will appear at IC9apin 13 and the time for which the cyclewill be high is, in fact, one second. Thisis then fed to the gate IC6a. However,only one such gating

18

NOTE:IC1 IS 40178IC2 IS 40518IC3 154001B

3'

CLK IC1 ,

8

111

INK RES

13

14

15

2

5

2

6

9

113 8 115

3'

11- A10

9- CIC2

OUT

INH7 8 18

DATA IN

7

CONNECT PINS 8,9,12,13 OF tin TO GROUND

0 +VE

OUTPUT

0 OV

ICtaIC1b

11 14

12R1IMO

4.-A1W-XTAL1

8

5

CV122p

11

Ao

R2510R

MSF LSF

DISP1

c--1. AYBY

SW1a.--a+ CY

18

CLK

RS IC2

10 7 13 12 14IC1c

9

16

Fig. 1

4 10 11 9

IC14

2

5 11213 T2

13

01

24

DISP2

R310k

11

DISP3

R410k

DISP4

RS10k

16 114

CY

A

DISPS

0R8-14

ALL 510R

05

R6 /7)77 R710k 10k

4

IC3

12

8

3

5

14

IC4

12

C

SW1b

A

P1;

23

lomux[I OVERFLOW

13

P81RESET

IC5

+12V

INPUT a 6K:6

R151005

14 110

3

14

1C6b2

4ji

, R16IC9b

--177 LED1

13 0 12

12

pulse is produced, after a certain timeperiod set by C3 and R18. Themonostable formed round IC6c,d is

used to give the reading period of thedisplay, when triggered, by enablingIC8 and disabling IC9a. At the end of themonostable period, a short pulse is

produced at S which resets thecounter. IC1e is there to ensure thatIC9a is not enabled before the resetpulse to the counter is produced (see T),otherwise all hell will break out!

Finally, the D -type flip-flop thatremains is used as the basis of theoverflow indicator; on the transition ofthe counter from 99999 to 00000, apulse is produced at IC8 pin 15which latches IC9b pin 1 high, thuslighting up the LED. Pressing PB1resets the whole system.

IC&13

11

C32u2

518680k

9

CLK RES4

T

3

171819

FEATURE

0+12V

16 13

IC8

7

20

2 6

897

4 BL

0 +12V

F/jjk ID2

IF.- -NOTE:C51,p IC1 IS 40498

IC2 1540208IC3,4 ARE 40178IC5 IS 45348IC6 13402313

R IC7 IS 40688IC8 IS 45118IC9 IS 4013801-5 ARE BC109C

8 D1,2 ARE 154148LEDI IS ANY LEDDISP1-5 ARE ANY7 -SEGMENT

7 COMMON CATHODELED DISPLAYSXTAL1 IS CRM500ACERAMICRESONATOR

ICH

°17 1 L-

MONOSTABLE PERIOD

T

S

Fig. 2

1

I

II

DIVIDED REFERENCE SOURCE11.E. 10011z,10HOH4

GATING PULSE11.E. 10mS,100mS,ISI

ICON RESET

IC5 RESET

Tech -Tips is an ideas forum and is not aimed at the beginner. We regret we cannot answer queries on theseitems. ETI is prepared to consider circuits or ideas submitted by readers for this page. All items used will be paid

for at a competitive rate.Drawings should be as clear as possible and the text should be typed. Text and drawings must be on separatesheets. Circuits must not be subject to copyright. Items for considerations should be sent to ETI TECH -TIPS,

Electronics Today International, 145 Charing Cross Road, London WC2H OEE

G ETBIG POWER

w ModularAmplifiers

the third generationDue to continous improvements in components and design ILPnow launch the largest and most advanced generation ofmodules ever.

WE'RE INSTRUMENTALIN MAKING A LOT

OF POWERIn keeping with I LP's tradition of entirely self-contained modulesfeaturing, integral heatsinks, no external components and only 5connections required, the range has been optimized for efficiency,flexibility, reliability, easy usage, outstanding performance, valuefor money.With over 10 years experience in audio amplifier technology I LPare recognised as world leaders.

1111111

))

(E.1

41/10"-

AidDIP

BIPOLAR MODULES

ModuloNumber

OutputPowerWensma

LoadImpedancen

DISTORTIONT.H.O. I.M.D.TIM at NNW1KHR 7KHe 4.1

SopMyVoile's

Typ

Sa.met

WIems

PriceInc.VAT

HY.I0 lb 48 0.015% <0.0064 i 18 76 a 68 a 40 240 E8.40liY60 30 4-8 0.015% <0.006% i 25 76 a 68 a 40 240 E9.55I lY61160 30 30 48 0.016% <0.006% ± 25 133 a 78 a 40 420 E18.6910(124 60 4 0.01% <0.006% I 26 120 a 78 a 40 410 E20.75HY12/4 60 8 0.01% <0.006% ± 35 120 a 78 x 40 410 120.75HY244 120 4 001% <0.006% ± 35 120 a 78 a 50 520 £25.4710,248 120 8 0.01% <0.000% ± 50 120 x 78 a 50 520 E25.47HY364 180 4 0.01% <0.006% 145 120%78%100 1030 £38.41HY388 180 a 0.ani <0.008% i 60 120 a 78 a 100 1033 E3841

Protecnon. Full !owl line. Slew Rate: 15v/Ins. Meek.: Sps. S/Nr tio: 100db.requenc response -3dBl 15H - 50KHe. Input rens deity: 50OrnV rms.nitro Impedena. 100K fl . Demising I actor. 100H. >400.

PRE -AMP SYSTEMS

Module ModuleNumber

FwartIons

hi y6 Mono pre amo Mic/Mog. Cartricapi/Tuner/Tape/Aux a Vol/Bess/Treble

H Y66 Stereo ore amp 4.4/1,49. Cartridge/Tuner/Tone/Aux Vol/Eless/Treble/Balencs

Hv 73 Guater ore amp Two Guitar Mass Leedl and Mcseparate Volume Bess Treble Ms

Y 78 Stereo pre amp As H Y66 less tone controls

CuneneRegallnei

10mA

AIM Ines.VATE7.80

20mA E14.32

20mA E15.38

20mA C14.20

Most prelimp modules can bedrreen by the PSU driving the man Paean WVA separate PSU 30 is available purely for per amp modules if rerar.red forE5.47 Iwo. VAT). Prwarro and miring modules no 18 different veriatiors.Rase send for details.Mounting BoardsFor ease of constructon we recommend the BS for module. HY8-HY13 E1.05linc.VATIand the 885 for modules HY66-HY78 E1.20 (inc. VAT).

POWERSUPPLYUNI TS lincOrpOrating Our own toroidal transformers)

ModelNumbs,

For the With Prim Ira.VAT

PSU 21X tor 214V30 E11.93PSU 41K 1 or 2 HY00. 1 e HX6000. I e riX124 113113PSU42X I a 141/128 C15.90PSU 43X I . moms (16.70PSU 51 X 2 a HY12/11. I a HY244 017.07

MOSF ET MODULES

modiii. WIWI Load DISTORTION Supply Sue WT priesNumber Pew Impedance T.H.D. I.M.D. VoNeW own ems inc.

Watts il Typat 0014/ 7TP VATpm IKHe 7KHa 4:1

MOS 128 80 4-8 <0.005% <0.006% ± 45 120 x 78 . 40 420 C30.41MOS 248 120 4-8 <0.005% <0.006% i 55 120 x 78 x 80 850 C39.86MOS 364 180 4 <0,005% <0.006% ± 55 120 x 78 x 100 1025 £45.54

Protection: Able to cope with complex loads without he need for very 'PeedPnztec ion circuitry (fuses will suffice).

Slew rate. 20y/dais. Rae time 3p.. S/N ratio: 100dbFrequency response 1-3d13). 15H: - 100K Hz Input Sensitivity 500mV nnsInput impolsrce: 100K11. Dampog lector. 100Hz >400.

'NEW to 1LP' In Car EntertainmentsC15Mono Power Booster Ampirlier to increase the output of your tootling cat radioor cassette player to a nominal 15 watts rmt.

Very easy to ute.

R0OuncOnitrUctiOn. E9.14 (inc. VAT)Mounts anywhere in car.

OutOrriattc Switch on.

Output Dower maximum 22w peak into 411.Frequency remote. 1-3d13) 15He to 30KH:. T.H.O. 0.1%at lOw I K HzS/N ratio (DIN AUDIO) BOdB. Load lerwedence 311Input Sensalvity on] enpedence Iselectable) 700mV nns into 15KI1 3V ran into 811.Sae 95 x 48 x 60rnm. Weight 256 cans.

C1515Stereo version of C15.

Sae 95 x 40 x 80. Weight 410 pm.

£17.19 (inc. VAT)

NNWNesideer

Per Um With Ake Inc.VAT

PSU 52% 2a HY124 017.07PSU 53% 2 5 406128 E17.86PSU 54% 1 x HY248 C17.86PSU 55X 1 a MOS248 019.52PSU 71% 2 a HY244 021.75

MeadNumber

Poe Use With Mae Inc.VAT

PSU 72% 2 x HY248 (22.54PSU 73X 1 x HY364 E22.54PSU 74X 1 x HY388 [24.20PSU 75X 2 x MOS248. 1 x MO5368 C2420

Mire MIN X In met no: indicate, (sweaty voltage Amor moo t n Macs ofX for 11W. -1" in pram or X tot 230. and "r n mace of X for 240V.

WITH A LOT OF

HELP FROM D!!Elti,,,c, LTD

PROFS

CAN

SSIONAI

HAMUnicase

W W W

111 -fl THAT EVERY ENTHUSIAST

Over the years I LP has been aware of the need for a completepackaging system for it's products, it has now developed aunique system which meets all the requiremen% for ease ofassembly, adaptability, ruggedness, modern styling and aboveall price.

Each Unicase kit contains all the hardware required down tothe last nut and bolt to build a complete unit without theneed for any special tools.

Because of I LP's modular approach, "open plan" constructionis used and final assembly of the unit parts forms a compactaesthetic unit. By this method construction can be achieved inunder two hours with little experience of electronic wiringand mechanical assembly.

Hi Fi SeparatesUC1 PRE AMP UNIT: Incorporates the HY7B to provide a"no frills", low distortion, (<0.01%), stereo control unit,providing inputs for magnetic cartridge, tuner, and tape/monitor facilities. This unit provides the heart of the hi fisystem and can be used in conjunction with any of the UPUnicase series of power amps. For ultimate hum rejection theUC1 draws its power from the power amp unit.

POWER AMPS: The UP series feature a clean line front panelincorporating on/off switch and concealed indicator. They aredesigned to compliment the style of the UC1 pre -amp.Performance for each unit which includes the appropriatepower supply, is as specified on the facing page.

Power SlavesOur power slaves, which have numerous uses i.e.instrument, discotheque, sound reinforcement, feature inaddition to the hi fi series, front panel input jack, levelcontrol, and a carrying handle. Providing the smallest,lowest cost, slave on the market in this format.

UNICASES

HIFI SenentinsPrice inc.VAT

UC1 Preamp C29.95LPIx 30 + 30W/4-811 Bipolar Stereo HiFi £54.95UP2X sow/4n Bipolar Mono HiFi £54.95UP3X 60W/1311 Bipolar Mono H iF i £54.95UP4X 120W/4(1 Bipolar Mono HiFi £74.95UPSX 120W/811 Bipolar Mono HiFi E74.95UP8X 60W/4-811 MOS Mono HiFi £64.95UP7 X 120W/4 -13.Q MOS Mono HiFi £84.95

Pater SlavesUS1 X 60W/4 II Bipolar Power Slave E59.95US2X 120W/4 Q. Bipolar Power Slave E79.95US3X 60W/4-an MOS Power Slave E69.96US4X 120W/4 -8Q. MOS Power Slave £89.95

Please note X in part number denotes mains voltage. Please insert 'a in piece ofX for 110y. '1' in place of X for 220V (Europe), and '2' in place of X for 240V(U.K.) All units except UC1 incorporate our own toroidal transformers.

TO ORDER USING OUR FREEPOST FACILITYFill in the coupon as shown, or write details on a separate sheet of paper,quoting the name and date of this journal. By sending your order to ouraddress as shown at the bottom of the page opposite, with FREEPOSTclearly shown on the envelope, you need not stamp it. We pay postage foryou. Cheques and money orders must be crossed and made payable toElectronics Ltd. if sending cash, it must be by registered post. To pay C.O.D.please add El to TOTAL value of order.

PAYMENT MAY BE MADE BY ACCESS OR BARCLAYCARD IFREQUIRED

11LII70NICS LTD

Post to. ILP Elecoortot Ltd., hewing 4,Graham Bell House, Roper CJose.Centenary CT2 7EP, Kent, England.Telephone, 10227154778.Technical: 10227164723.Telex: 965780.

Please send me the following

Total purchase price

I enclose Cheque0 Postal Orders Int. Money Orders

Please debit my Access/Barclaycard No.Name

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ANN

LOGIC PROBEPROJECT

Are you probing logically? S. G. Applebaum describes a circuitthat will help if you are.

The logic probe circuitdescribed here has been foundto be invaluable in debugging

and fault-finding on logic systemsusing discrete CMOS ICS. Utilisingthree integrated circuits, the probewill allow the checks listed in Table1 to be carried out.

The probe is supplied from thelogic system under test - power ispicked up by a flying lead from theboard and terminated with crocclips or miniature connectors. Theprobe will work from a DC supply

SUPPLY

PROBEPROBE

-VESUPPL

DI

R110k

D2

R2220k

R5330k

OV

NOTE:IC1 IS LF353NIC2 IS MC14538IC3 IS 4011BD1-8 ARE 1N4148

STRAP UNUSED INPUTS OF 1C3(PINS 1 AND 2) TO OV

Fig. 1 Circuit diagram for the Logic Probe.

of 5 V to 15 V and consumes lessthan 10 mA. Input impedance isapproximately 100k and thresholdlevels are set at logic 0 .<1/3Vandlogic 1>- 2/3 V«.

The circuit diagram is shown inFig. 1 with a suitable componentlayout in Fig. 2 . Utilisingthe layout shown the probe may behoused in a length of i" diameterpolythene tubing as stocked by DIYshops for plumbing applications. Ifthis diameter tubing is used, thenthe two 47nF capacitors determining

Cl

R1047k

R1147k

14

IC3b

744

13

12

IC3t

10

*REDLED

R122k2

GREENLED

R132k2

FAULT1. Open circuit check2. Circuit at logic 03. Circuit at logic 1.4. Square wave input5. Negative -going pulse6. Positive -going pulse7. Presence of glitches

or pulses down to100nS duration

TABLE 1 INDICATIONBoth LEDs off Green LED onRed LED onRed and Green LEDs onRed LED on, Green LED flashingGreen LED on, Red LED flashingPulse stretching causing red orgreen LED to flash for approximately100mS.

TO PROBE

Fig. 2 Component overlay.

the timing of the MC,14538monostables should be mounted onthe track side of the PCB.

Alternative types of IC may be usedfor IC1 and IC2 e.g. TL062, CA3240E forIC1, and CD4098, MC14528 for IC2.Total component cost should be lessthan £5.00, plus PCB.

HOW IT WORKS121, D1 and D2 form the input protection;ICla detects high logic levels, and IC1bdetects lows. If neither of these arepresent, neither of the LEDs can light.

D8 and IC3a/D8 detect steady high andlow states respectively, whilemonostable IC2a and IC2b detectpositive and negative going pulsesrespectively. The cross -connectionsfrom the data outputs to the reset in-puts prevent both monostable firingconcurrently, so that, for example, apositive -going pulse will trigger IC2a.but IC2b will be held off until themonostable period has timed out, and sowill not be trigge red by the trailing edgeof the pulse.

NAND gates IC3b,c only allow the LEDsto light when there is a valid logic stateas detected by ICla,b.

PARTS LIST

Resistors (all 1/4 watt 5% carbon)R1 10kR2, 3 220kR4-6 330kR7, 10, 11 47kR8, 9 1MO

R12, 13 2k2

CapacitorsC1, 2 47n polycarbonate

SemiconductorsIC1 LF353NIC2 MC14538. 4098 etc.

D1 -D8LED 1

LED2

401161N4148Red high intensity 0.2in.Green high intensity 0.2in.

MiscellaneousPCB. connectors, case

OV

. 44.4.A.A.,111.411. mrj .LED2GREEN

111112Eqqg7.11d I miii) LED1

RED5-> R9 +VE

INSULATED LINK

The toroidal transformer is now accepted asthe standard in industry, overtaking theobsolete laminated type. Industry has beenquick to recognise the advantages toroidalsoffer in size, weight, lower radiated field and,thanks to I.L.P., PRICE.Our large standard range is complemented by our SPECIALDESIGN section which can offer a prototype service within71DAYS together with a short lead time on quantity orders whichcan be programmed to your requirements with no pnce penalty.

lye SfAISNo

SECO/WARY110114

PUSCo NM

PAO

as VA6439*..0 4514

213%

1.0101.0111.01214131.0141.0151.016

6.69.912,1215.15

IS22.2225.25

2501661 251 000 83068060

£5.124,44 .04

10,41 11 04

1.017 30.30 0 50

50 VA 2.010 6.6 4 1680.3544o 24011 9.9 2 77

0 911g 2.012 12.12 20811.90044.1

13%2.0132,014

15.1516 16

16636 £5.70

2.015 22.22 1 132.016 25.25 1 00 Val ti Ot210172.021

30.30110

0 830 45

?Wu [4 05

21029 220 0 222.030 243 0 20

is VA 3.010 6.6 6 6490 4304s, 3.011 9.9 444

'SiA.444Joo

12%

3.0123.0133.0143.015

12.1215.1516..1422.77

3 332662 221 81

£6.08Ivat,

3016 25.25 16o Al II IS3417 30 30 1 33 tOlk 1:511.

3402111 110 0113029 220 0 36

)4030 240 0 33

121VA 4.010 6.6 10 0090404441 4.011 9.9 666

2114 4.012 12.12 5 00646vtalt00

tl%4.0134.014

15+1518 IS

4 00313 £6.90

4.015 22.22 272 0,00 4/4.016 25.25 240 .14111 794.0174.016

3133035.35

2001 71

TOW Oaf

4.021 110 1094.029 220 0544.030 240 0 50

110 VA 5.011 9+9 ass10,42411.1

1649Aeouton

8%

5.0125.0135.0145.015

12+1215+1516.1622+22

666

5 n4 443 63

£7.915.016 25.25 3 20 .4,4416/5.017 30.30 2.66 .00,11 4.

5.018 35 35 226 r0. t, p,5.026 40.40 20054028 110 1 455.029 220 0 725.030 240 066

* 2t4 TTTES TO CHOOSE num

* ORDERS DUPATCIED WITNIN 7DIM OF liCUPT FOR MOLE 02IIIILL QUANTITY ORDERS

* S TIM NO PULE MINIM

TIPSSt PIS

NO

SECONOAAV40114

61.15

CurromPACE

225VA 6:012 12.12 9 38110 45orn 6.013 15.15 7.50

2 2 49

"At-6.014

66:2',

18 18

g'.22

625

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£9.206.0166° mss:3is 3213 ...",:":6.0266025

40.4045.45

2 SI250

+ --' '-m.'''.64033 50 50 2 256.026 110 2 04gem 220 1 0214030 240 0 93

300 VA 74013 15.15 10 00110.50x411 7.014 15.18 6 33

26 Kg 7.015 22.22 682ftgulailin 7.016 25.25 600 £1017

6% 7.0177.016

30.3035.35

S00421 .'"1"

7.026 40.40 3 75 ''''''' I.7.025 45+45 333 10141,1..7.033 50 50 3007.026 110 2 727.029 220 1 36ham 240 1 25

500 VA 6.016 25+25 10 00140.60..11

4 Kg8.0178.018

30.3035+35

633714

PI 3.53I., I

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8.0268.025

40.4045 45

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8.033 50.50 500 '..ml, P6.042 55+55 4 54 10141 05 n6.026 110 4548.029 220 2 271.330 240 2 00

625 VA 9.017 30.30 10 4114047546,1

51490189.026

35.3540 40 1 "1a £1613

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9.0259033

45.4550.50

694625

9.042 55+55 568.,.(''',,,''

'''" ' ''''9.029 ng 568 12.. (2. ..)9.029 220 2849.030 240 260

IMPORTANT Regulation -All voltages quoted art FULL LOAD. Meese add regulation figure tosecondary voltage to obtain all load voltage.

The benefits of ILP toroidal transformersILP toroidal transformers are only hall the weight and height of their laminated

equivalents. and are available with 110V, 220V or 240V primaries coded as follows.

For 110V primary insert "0" in place of "X" in type number.

For 220V primary (Europe) insert -1" in place of "X" in type number.

For 240V primary (UK) insert "2" in place of "X" in type number

How to order Freepost:Use this coupon, or a separate sheet of paper, to order these products, or any

Pioducts from other ILP Electronics advertisements. No stamp is needed if you address toFreepost Cheques and postal orders must be crossed and payable to ILP Electronics Ltd.Access and Barclaycard welcome. All UK orders sent within 7 days of receipt of order forsingle and small quantity orders.AISO available at Etectrovaiue Macho and Technomalic

Please send

Total purchase price

I enclose Cheque El Postal Orders EI

Debit my Access/Barclaycard No.

Address

Signature

Post to: ILP Electronics Ltd, Freepost 4 Graham Bell House. Roper CloseCanterbury CT2 7EP, Kent. England0Telephone Sales (0227) 54778 Technical 10227) 64723.Telex 965780

I IL IF (a division ofILP Electronics Ltd)

11/4440.,TRANSFORM

I

I

MONITORS

HIGH RESOLUTION -ANDLOW COST!Either cased or open frames to

OEM's. The specification is right, the priceis even better.

Phone or write to our Sales Manager,Richard Cox, for immediate action.

CROFTON ELECTRONICS LTD35, Grosvenor Road, Twickenham, Middx, TVVI 4AD. Telephone:

01-891 1923/1513 Telex: 295093 CROFTN G

Part type 1 off 25-29 100 up4116 200ns 0.77 0.69 0.664116 250ns 0.75 0.63 0.604816 100ns For BBC comp 2.01 2.25 1.954164 200ns 3.99 3.56 3.422114 200ns Low power 1.15 1.00 0.902114 450ns Low power 0.95 0.85 0.804118 250ns 3.25 2.85 2.656116 150ns CMOS 3,55 3.20 2.952708 450ns 2,60 2.25 2.102716 450ns 5 volt 2.35 2.10 2.022716 450ns three rail 5.75 5.00 4.652732 450ns Intel type 3.50 3.15 3.002532 450ns Texas type 370 3.30 3.00Z80A-CPU £3.95 280A-Pi0 2.99 280A-CTC £2.996522 PIA 3.70 7002 A -D £4.60 3691 2.7588LS120 £2.20 7805 reg 0.50 7812 reg 0.50

Low profile IC sockets:Pine 8 14 16 18 20 22 24 28 40'

Pence 9 10 11 14 15 18 19 25 33Soft -sectored floppy discs per 10 in plastic librarycase: 5 inch SSSD £17.00; 5 inch SSDD £19.25; 5inch DSDD £21.00; 8 inch SSSD £19.25; 8 inchSSDD £23.65; 8 inch DgDD £25.5074LS series TTL, large stocks at low prices withDIY discounts starting at a mix of just 25 pieces.

Write or phone for list.Please add 50p post Et packing to orders under £15 and VAT to total. Access EtBarclaycard welcome. 24 hour service on (054 422) 6113. Government Et Educa-tional orders welcome, £15 minimum. Trade accounts operated, phone or mite

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POWER DIMMER MODULESA range of electronic modular dimmers designed tosuit your custom channel and facility requirement

. Considerable saving over commercial equipment All the commercial facilities and more

1 Compatable special effects Preset/remote/master Easily installed and wired

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FEATURE

READ/WRITELetters for this page should be addressed to Read/Write atour Charing Cross Road address.

Dear SirI would like to ask Tim Orr why

he states that 'most complex filterdesigns require a large number ofprecision resistors and capacitors'.

What does he mean by 'mostfilters'? What is a 'complex filter' -is it in the forma + jb? What is alarge number' in this context? Doswitched capacitor filter systems usefewer components?

The accuracy of monolithiccapacitors of 1% tolerance is notlow but is typically within the range±1% . . . So what?

Switched capacitor techniquesdo not 'get over' many problems,but simply defer them, at theexpense of increased complexity,meaning more system components(eg, clock generators), and 'sweepthe real problems under the carpet.'

The fact is that there isabsolutely no way a normal,switched capacitor filter can be,component by component, anybetter, or less expensive, than itsanalogue counterpart, nor can itperform any better for a given set offixed requirements (in the sense ofclassical filter design or modernnetwork theory), nor can it handlehigh power, as wire -inductor typesdo. The only advantage I can seefor switched -capacitor filters is theirability to scale according to theclock frequency. Whereas this is anadvantage for certain, specificapplications, Tim Orr gives theimpression that it is universally true.It is not so.

I must point out that I have noconnection with commercialinterests regarding linear filtersuppliers, just an interest in yourmagazine and in the whole truth!

What, for example, are thephase characteristics and filtercharacteristics of switched -capacitorfilters? What are their time -delayequations? I find nothing, apart fromscaling, to recommend switchedcapacitor filters instead of analoguedesigns, for most applications. Bycomparison, one can easilydetermine the phase/time/responsecharacteristic of any analogue filter,construct it from published data (indesign tables) and accurately predicthow it will behave. It needs noclocks, etc, and transmits power.

Why use an untried technique

when there is a perfectly goodproven design methodologyavailable, which meets all therequirements?

Would it be possible, forexample, to construct the followingfilter (in which I do have an interest)using switched capacitortechniques:

Q=2.0, 0.1 dB, Cauer, 8thorder, band-pass, -40 dB stop,gain =1.0.

If it is possible, does it usefewer components than, or is itcheaper than, or any better than myLC version, and can we find itsphase delay?

Putting it another way, mostfilters in use today are simple RC 3dB per octave types - what couldbe simpler than one resistor andone capacitor?

Yours faithfullyTerence B LayzellEnfield

We take Mr Layzell's point, in thatswitched -capacitor filters will notreplace all discrete filters.However, they can be very usefulon occasion, and the two occasionsthat come to mind are theSpectrum Analyst andSpectracolumn published recently.In equipment manufacture, thecosts of any particular item ofequipment is largely determined bythe package count, and, withincertain fairly obvious limits, theprice of the packages has littleinfluence. So, in many cases, it maypay manufacturers to go to muchmore complex (Sorry!complicated) filter design usingfewer packages with many legs - ieusing a switched -capacitordesign with a very complicatedcircuit rather than a conventionalfilter with a relatively simplecircuit.

Dear SirHaving read several of the latestissues of ET/, I find it mostdistressing that a lot of the circuits Ihave made have come from theTech Tips section, not because yourdesigns do not interest me, butbecause the circuits I find in thissection have invariably been in ET/or one of the other leading magsbefore (OTHER leading mags? -

Ed.); but the readers have found acheaper way of doing the samething, in fact sometimes 50% ormore cheaper. For example thecircuit I am working on at presentwas featured in ETI Tech Tips inJanuary 1981: a simplecombination lock. With this circuitand asolenoid I made a combination boltfor my outside shed door, andmany of my friends have tried (atmyrequest) and failed to crack it. Acombination lock was featured inthe magazine some months beforebut not with a 4017 IC. Needless tosay, it cost me less than a quarter ofwhat it would have done if I hadmade i( from the magazine as it wasfirst featured. All can say is 'thankyou' tQ M. D. Chapman, as hesaved me a lot of money. Thewhole unit complete in a box butless the solenoid cost me 13 asopposed to f22.75 for the otherone.So, all you designers at ET/, get yourbrains working on somecheaper circuits for us, or, failingthat, make the Editor publish somemore of the readers' designs so thatwe can save enough money to buynext month's issue of ET/ Theremust be more than seven or eightdesigns sent in each month.How much longer must wewaste time and money putting in astack of components and /Cs when,with slightly different components,we can halve the time and cost ittakes to make these projects?

Yours sincerelyD SaundersSittingbourne

The original Combination Lockdesign you refer to was publishedin ETI in March 1981; since thenwe have published a rathercheaper design as a project in Juneand July 1982; and we've alsopublished yet another as a TechTip in November 1982, so youcan't say we don't give you a widechoice! The two designs wepublished as projects doincorporate rather more featuresthan the two Tech Tips, so, onbalance, all the circuits havesomething to offer.As to cost, we try to keep ETI at thefore -front in technology, andthis sometimes means that thecircuits we publish are rather moreexpensive to build than we'd like,because, for obvious reasons thecomponents used will not befoundin readers' spares boxes. We alsolike to publish designs that dosomething more cheaply and/ormore elegantly than existingdesigns when we get hold of them.

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Themagazinewithadifferentapproach

le -to microsliar *41tang

Electronics andComputing Monthly looks at acomputer as the beginning ofsomething interesting ratherthan an end in itself.

We thought that using amicro to drive something otherthan a TV screen could open upfascinating possibilities.

A few simple circuits,used as building blocks, canstretch your computer, yourimagination and your fun, along way.

If you understand thebasics of digital electronics,you'll appreciate the fun you can

have bylinking logiccircuits to your micro.

If you don't, thenread our new series whichstarts this month and explainsdigital electronic circuits frombasics.Also this month, weshow you how to build an infra-red remote controller for yourmicro.

That's what Electronicsand Computing is all about-giving you ideas for new

applications, and giving youthe software to expand your

micro. Project by project weshow you how to add anotherdimension to your computer.

For example in this month'sissue we explain dialogueprogramming using the PILOTsystem - whdt it is and how itworks.

And inside is enoughinformation to build you o wihi-res graphics computer.

All you need is ahot soldering iroand a cool 75

WHERE ELECTRONICS AND COMPUTING INTERFACE.

FEATURE

CONFIGURATIONSThe editor expressly forbids his neighbours from reading thismonth's Configurations, because it's all about audio power outputstages. Ian Sinclair shows the way to deafness for the quiet life.

Alot of people who feel quite happy with the designof voltage amplifier stages are never quite so confi-dent with power output stages. The reasons are not

difficult to find, because few textbooks go into much detailabout transistor power output stages, and one or two offerrather misleading advice.The essential problem of power output is to get powerdelivered into a load, and a theorem which is often quotedin this respect is the maximum power theorem - Fig. 1.This states that if the power source has fixed values of in-ternal resistance and supply voltage, then the maximumtransfer of power will occur when the load has the samevalue of resistance. The maximum power in the load willthen be 50% of the total power, with the other 50% beingdissipated across the internal resistance. The use of thistheorem governed the design of valve output stages fordecades.

Fig. 1 Maximum power theorem. This states that themaximum possible power, is transferred to the load when RL= Rs. This does not imply that the load gets the maximumshare of power.

Things have changed, however, and we can easily obtaintransistors with very low internal resistance values anduse them in circuits whose internal resistance can be asIttle as a fraction of an ohm. The maximum powertheorem isn't useful here, because we don't actuallywant maximum power, only as much as we can handle,and preferably most of it across the loudspeakerterminals. In any case, we don't want to have to useloudspeakers with im-pedances of only a fraction of anohm. When we use a loudspeaker whose impedance isseveral times that of the amplifier, we can be sure thatmost of the power dissipated is across the loudspeakerrather than across the output transistors, and that's justwhat we want, whether it's the maximum possiblepower or not.The very low output resistance of transistor poweramplifiers also explains why it is that the power output ofa transistor amplifier increases when you use aloudspeaker of lower impedance - your average pre-wartextbook can't explain that one! If we were to attempt touse a load that matched the resistance of the amplifieroutput stage, it's pretty certain we would burn out thetransistors.

Some Like It HotSpeaking of which brings us to the second point

about power output stages. With low internal resistance,there is no problem about delivering power, but theperformance

of a power amplifier in this respect is limited by the rate at whichthe transistors in the output stage can dissipate the heat whichis inevitably caused when current flows through them.As long as the rate of heat generation' (which isvolts x amps) equals the rate of heat dissipation, thetemperature will remain steady, but raising the dissipa-tion alsomeans raising the temperature, and this is the limitingfactor for transistors, because if the collector junction, whichis where the heat is generated, gets too hot, it will melt,and that's the end of the transistor. Many outputtransistors which could dissipate 150 W if the heat couldbe removed efficiently will dissipate only a miserable 20 Wunder realistic working conditions.

The design of a transistor power amplifier, therefore,starts with a consideration of heat -sinks. Thetraditional method is to use a quantity called thermalresistance, which is defined as the temperature rise perdegree (centigrade) of dissipated power. When a heat -sink has athermal resistance of 4° C/W, then it will be 4° C hotter thanthe air around it when it is dissipating 1 W, 40°C hotter thanthe air when it is dissipating 10 W, and so on - thetemperature rise equals thermal resistance times powerdissipated. For a transistor bolted on to a heat -sink, there areseveral thermal resistances in series (Fig.2) the thermal resistance of the collector junction to themounting surface of the transistor, the thermal resistance ofthe mounting surface to the heat -sink (which will beincreased if you use a mica washer for insulation), and thethermal resistance of the heat -sink itself to the air. Likeelectrical resistances, these can be added (that's why we usethem!), and when the result is multiplied by the intendedpower dissipation, the result will tell you how much hotterthan the air your transistor junction will be. Remember thatthe air actually around the area of the heat -sink may not beall that cool,- a conservative figure to use is 40°C - and then addon the rise in temperature that you have calculated. If theresult is well short of the maximum

JUNCTION TO MOUNTING FACE...0 .1

MOUNTING FACE OF TRANSISTOR TOMOUNTING FACE OF HEATSINK...02

HEATSINK TO AIR...03

TOTAL THERMAL RESISTANCE + B 1+ 6 2+ B 3

Fig. 2 Thermal resistances. For a single. transistor .on a

heat -sink, the thermal resistances are in series, and can beadded. For other configurations, these quantities can betreated exactly like electrical resistances.

FEATUREallowable figure for the transistor, well and good; if not,then you need to improve your heatsinking, or use a dif-ferent transistor, or both.

Making A TransformationWith that out of the way, we can now look at some

configurations. Most of us automatically think of the PNP-NPN direct coupled pair when we think of output stages,but there are still a lot of single -ended transformer -coupledstages around, similar to the design of Fig. 3. A Class Astage like this is designed by finding the maximum dissipa-

IN

E

LS1

R3 = VERY LOW VALUES 10.5R TO 10R)R1.R2 ARE LOW VALUE BIAS RESISTORS.THEY MUST BE CAPABLE OF MAINTAINING ENOUGHCURRENT TO BIAS THE BASE. THIS MAY BESEVERAL HUNDRED MILLIAMPS!

ov

Fig. 3 A single -ended Class A stage, using transformercoupling.

tion you can get away with, and then fixing the supplyvoltage and calculating the signal current. If we take it thatthe average DC level at the collector of the transistor isequal to the supply voltage (Fig. 4), then at peak poweroutput, the signal voltage (instantaneous voltage, that is)

TRANSISTOR DRAWINGLESS THAN BIAS

CURRENT

SUPPLY VOLTAGE Vs

TRANSISTOR DRAWINGMORE THAN BIAS

CURRENT

Fig. 4 The (ideal) output waveform at the collector of thecircuit of Fig 3. The inductance of the transformer isresponsible for the portion of the wave which is abovesupply voltage.

will drop to zero and rise to twice supply voltage. Thismakes the peak voltage of the output signal equal to thesupply voltage, and the RMS power is equal to

peak volts xxeak current

so that peak current, lo, equals8 x power

supply power- you will have to check for yourself that the transistorcan cope with this peak current. The next step is tocalculate the transformer ratio. The peak voltage V, acrossthe loudspeaker will be

powerti

and the transformer ratio will have to besupply voltage

VP

01

Q2

ON

OFF

OFF

ON

+VE

TO LOUDSPEAKER

Fig. 5 The basis of the single -end push-pull Class B stage,most succinctly known as the totem -pole output.

- this is usually a step-down ratio. The transformer shouldhave enough primary inductance to ensure that it will han-dle low frequencies reasonably well, but you don't wantto design the transformer in detail unless you are a card-carrying masochist.

The single -ended stage is not exactly brilliant from thepoint of view of distortion, and the voltage gain is usuallyvery low, so that negative feedback from the speaker ter-minals to the input of the power stage is rather ineffective.The negative feedback can be taken to an earlier stage, butthe drawback here is that the phase shifts may be ex-cessive, particularly since a transformer is present, andthese can make your negative feedback become positiveat one end of the frequency range, causing distinctly nastysounds to come from the speaker. The main merit of asingle -ended transformer -coupled stage of this type is thatit can deliver a fair amount of power from a low supplyvoltage, something that is not easy for the traditionaldirect -coupled design.

0INPUT

0

R1

R2

D1

D2

Cl+no

PR1

R3

R4

01

0 +VE

4.01--0 TO LOUDSPEAKERC2

oov

Fig. 6 Using two diodes in series to stabilize the bias of theoutput pair.

The Traditional TransistorsWith that brief introduction -meet the traditional

direct -coupled output stage as used in practically all of thehi-fi, medium-fi and no-fi amplifiers in the world. Thedesign consists of a pair of complementary emitter -followers in a Class B single -ended push-pull circuit (Fig. 5),with both transistors on one heat -sink, capacitor coupl-ingto the loudspeaker, and lots of negative feedback. It's adesign on which an incredible number of variations can beachieved, however, and also one whose performance canbe greatly enhanced by Careful choice of components,

FEATURE

andwell-planned construction. The driver stage for theoutput pair may use diodes to adjust the DC voltage dif-ference that is needed between the bases of the outputpair (Fig. 6) or an almost -saturated transistors (Fig. 7) orwith a common -emitter pair used in place of emitter -followers, and driven by an op -amp (Fig. 8).

TO BASES OFOUTPUT PAIR

470R

Fig. 7 An alternative method of stabilisation using a transistor.

Like all Class B stages, linearity, especially near thecrossover point (Fig. 9) where one transistor starts to con-duct as the other one stops, is always a problem. The gainin this region is very low, so that negative feedback is notthe cure-all that many designers seem to expect it to be.Since the basic output stage is a couple of emitter -followers, it has a voltage gain that is less than unity, andthe driver stage usually has a low gain also, so that thefeedback loop has to be taken over a number of stages(Fig. 10).

TO LOUDSPEAKER

C3 IS ABOUT 10n AND IS FOR STABILITY PURPOSESR3,R4 AROUND 100R -220R DEPENDING ON DRIVE NEEDS OFOUTPUT PAIR AND CAPABILITIES OF OP -AMP.RI ,R2 EQUAL AROUND 47k

Fig. 8 A circuit which uses an op -amp to drive an output pair.The transistors are NOT in the normal totem -pole configuration,because each is being used as a common emitter amplifierrather than as an emitter -follower. If Darlington power outputtransistors are used, this c:an be a very economical high -powerstage.

The problem of crossover distortion has driven severaldesigners to use Class A stages of very similar configura-tion. When both of the transistors of the output pair aredriven with a signal, the efficiency can be as high as 30%(as compared with 78% for Class B), and the availability ofhigh -power transistors with low thermal resistances hasencouraged the use of Class A - a typical circuit isshown. in Fig. 11. The distortion figure, measured beforeapplying feedback, is still fairly high (10% or more at fullpower), but feedback greatly improves this. Moreimportant, the distortion level tends to be least at lowpower outputs, unlike the Class B circuit in which thedistortion is greatest at low level - when it is also most Fig. 11 A Class A output stage - note that both outputnoticeable - due to the crossover problem. transistors are of the same type. For low distortion, they

should be carefully matched.

IC

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CROSSOVER

o I I

CROSSOVER

(b) ( d )

Fig. 9 Crossover distortion. (a) an ideal mutual characteristic for a

power transistor. (b) How the characteristics of two identicaltransistors would combine if each were just cut-off with no signalpresent. (c) The distortion of wave -shape caused at crossover withinsufficient bias. (d) Crossover distortion can be reduced byincreasing bias on each transistor, but unless the transistors haveunusually straight characteristics, a lot of bias will be needed.

INPUT

DRIVER AND OUTPUTBIASING STAGE STAGE

Fig. 10 Using feedback over several stages in a Class B outputcircuit.

+VE

PR1 SETS OUTPUT CURRENTR2,R3 SET BIASTO GET DC LEVEL AT OUTPUT CORRECT

TO LOUDSPEAKER

ov

ADAPTORS

10.

MARCO TRADING

PrPeery Secondary Cunene 1+ 10+ 100+240V 4.5-0-4.5V 400rn/a SOp 489 35p240V 6-0-6 100m/a 55p 52 p 43p240V 6-0-6 500m/a 65p SOp 43p

Manufacturers nuts: We can supply OFF THE SHELF1000+ quantities of the above transformers.

These high quality British made European Adaptors areideal for driving radio's, cassette recorders, TV games,calculators etc etc.

These adaptors fit the UK shaver socket.

1+ 10+ 100+E06 4.5V DC 200m/a 50p 45p 32p

EM3 6V DC 200m/a t1.00 80p 511pE09 6V DC 400m/a £1.60 t1.26 815p

UK POWER SUPPLY/CHARGER. Input 240V. Output 9V200m/A Fully Regulated and Stabilised. Complete withReversible 4 Way Plug.Price £2.95 + 75p p&p + VAT

MULTIMETER SPECIALRussian type U4324 20,000 O.P.V.DC Voltage: 06, 1.2, 3, 12, 30, 60, 120, 600,1200.AC Voltage: 3, 6, 15, 60, 150, 300, 600, 900.DC Intensity M/A: 0.06, 0.6, 6, 60, 600, 3000AC Intensity M/A: 0.3, 3, 30, 300, 3000.DC Resistance: 0.2, 5, 50, 500, 5000K.

Special Priceelinfileitiii/iCkria WTI 2.

Brand new 3 channel chart recorders from (16 including charts etc.

Send 35p Now for cu latest Catalogue. Fantastic Value it includes capacitors,diodes, resistors, transistors, LEDs, boxes, cable, prepaid envelopes and much,

much more.

Please add 35p postage and packing and 15% VAT to all orders.Send orders to:

MARCO TRADING ( Dept ETI)The Makings, High Street,Wem, Shropshire SY4 5EN

Telephone: WEM 109391 32763

Every order receives our latest special offer lists Or send SAEAN orders despatched by return of mail

SPECTRUM24 LINE INPUT/OUTPUT PORT(motherboard not required)

£18.95

MOTHERBOARD - SIX SLOTS..., £26.50MOTHERBOARD PCB ONLY £6.50SPECTRUM 28 WAY CONNECTOR £3.25MALE CONNECTOR £1.8034 WAY RIBBON GABLE per metre. £1.80

ZX8140 KEY KEYBOARD £20.00SPARE KEYS each £0.25MOTHERBOARD - 2 SLOTS £15.0024 LINE INPUT/OUTPUT PORT £18.9516K RAM PACK £25.00MUSIC BOARD £18.9523 WAY FEMALE CONNECTOR £2.50MALE CONNECTOR £1.6024 WAY RIBBON CABLE per metre £1.40GETTING ACQUAINTED WITH YOUR

ZX81 £4.95PROGRAMMING FOR REAL

APPLICATIONS £6.95REAL APPLICATIONS TAPE £11.44MASTERING MACHINE CODE £7.50Prices are for built items. Postage 40p under £4.00. Exportpostage (surface) £1.80. Access accepted. Send sae for fullcatalogue.

REDDITCHI ELECTRONICS

21 FERNEY HILL AVENUE, REDDITCHWORCS B97 4RU

ConstructorSeries Speakers

IT'SSO

EASYHave fun, savemoney, buildinga Kef designwith aWilmslow AudioCS Total kit.No electronic orwoodworkingknowledgenecessary andthe end result isa proven top-quality designthat you'll be proud of.Each kit contains all cabinet components, accurately machined for easyassembly, speaker drive units, crossovers, wadding, grille fabric,terminals, nuts, bolts, etc.The cabinets can be painted or stained or finished with iron -on veneerorself adhesive woodgrain vynil.Easy foolproof assembly instructions supplied. Set of constructor leafletssent free on receipt of large S.A.E.Prices: CS1 (As 101) £110 pr. inc. VAT, plus carr./ins. £ 5.50

CS1A (simplified LS3/5A) £103 pr. inc. VAT, plus carr./ins. f 5.50CS3 (as 103.2) £129 pr. inc. VAT, plus carr./ins. £10.00CS5 las Carlton f 192 pr. inc. VAT, plus carr./ins. £15.00CS7 (as Cantata) £250 pr. inc. VAT, plus carr./ins. £18.00

0625 529599

35/39 Church Street, Wilmslow, Cheshire SK9 1 AS

Catalogue £ 1.50 post freeLightning service on telephoned credit card orders!

Interak 1

HOME COMPUTERSDO NOT WORK!

You've already got a "home' computer -- am I right? Youmay be anyone - a Hospital Electronics Workshop, aUniversity Computer Dept., an Electronics ResearchEstablishment, or you may be just plain Joe Soap.

Either way round - you're fed up with the boss, or yourwife (may be the same thing), always asking you - "Verynice, but what does it do?" I know you can make it dothings, so you must be pretty clever, but what a mess.What's that heap of junk plugged n the back - talk aboutspaghetti!

They look lovely, home computers, don't they - until youbolt on all the things round the back that the designercouldn't (or wouldn't) include.

I think we both know what is needed; A "rack and card"build it yourself system (Interak ill. Something like Acorn'sand Tangerine's original plug in systems, before they wenton to more profitable things, but you don't want it 6502 -based - Interak 1 uses the Z80A, (doesn't everybody whohas any sense?).

If you use Interak 1, the ZBOA CPU is on one card, the VDUInterface is on another, Dynamic RAM on anotbet, and soon. Very tidy, and very modular because "any card fits inany slot". And that ugly expansion adaptor, and the specialbox of bits you've got sticking out of the back, can be neatlyre -packaged and slid into the spare slots in Interak 1.

I've got no space to say more (this advert's cost a fewhundred pounds already!), so send me a stamp (201P)and/or SAE, or neither, or 'phone if you prefer, and I'll sendyou the 38 -page low-down.David Parkins

P.S. Although this advert may sound a bit corny (we have toget your attention somehow) Interak 1 really is a serious,sensible system with thousands of cards sold, and in dailyuse. Cards, Manuals, all available separately inc. circuitdiagrams.

Greenbank

Greenbank Electronics (Dept. T3E), 92 New Chester Road,New Ferry, Wirral, Merseyside L62 5AG

Telephone: 051-645 3391

ETI PCB SERVICEUp till now PCBs were always the hardest component to obtain for a project. Of course you couldmake your own, but why bother anymore!Now you can buy your board straight from the designers - us! As of this issue all (non -copyright) PCBswill be available automatically from the ETI PCB Service. Each board is produced from the same masterused to build our prototypes, so you can be sure it's accurate, and will be finished to the high standardyou would expect from ETI.In addition to the PCBs for this month's projects, we are making available some of the more populardesigns from our recent past. See the list below for details. Please notes that NO OTHER BOARDS AREAVAILABLE. If it's not listed, we don't have it!

APRIL 79 0 LED Jewellery: Cross £1.47 MAY 82C Guitar Effects Unit £2.64 c Spiral (two boards) £2.64 0 DV Meg £2.720 Click Eliminator £6.64 Star(two boards) £2.65 0 Analogue PWM £3.06

0 Waa-phase £1.53 0 Slot Car Controller £4.51JUNE 79 0 Wattmiser £4.17

C Accentuated Beat Metronome £3.60 JULY 80 O_Sound Effects Boar' £2.25

FEBRUARY 80C Tuning Fork

0 System A A-MM/A-MC0 System A A -PR£2.64 0 Smart Battery Charger

£2.65 June 82£5.17 0 Ion Generator (two boards)£1.97 C Ion 'Blinker'

£5.53£2.47

MARCH 80 0 MOSFET Amp Module £6.78C Signal Tracer

AUGUST 80

£2.27AUGUST 81

0 System A Power Amp (A -PA)0 Logic Lock

£4.77 Digital PWM£3.06£334

0 CMOS Logic Tester £2.64 0 Flash Sequencer £3.44 0 Optical Senor £1.74C Capacitance Meter £2.93 0 Hand -clap Synthesiser £3.97 0 Stylus Timer £2.59O Ultrasonic Burglar Alarm £2.87 0 Heartbeat Monitor £1.83 0 Oscilloscope (four boards) £11.60

OCTOBER 800 Cassette Interface

0 Watchdog Home Security(two boards)

£2.93

JULY 82£5.31 Mike Switching Unit £1.87

0 Fuzz/Sustain BoxNOVEMBER 80

£3.27 SEPTEMBER 81O Mains Audio Link (three boards)

0 TV Bargraph main board)£7.35 0 TV Bargraph (channel card)

£4.56£2.28

0 Touch Buzzer £1.93 O Laboratory PSU £4.53 Hotwire £2.63O Light Switch £1.93 Bridging Adaptor £2.380 Metronome £1.93 OCTOBER 81 AUGUST 82C 2W Power AmpC RIAA PreamplifierC Audio TestOscillator

DECEMBER 800 Musical Doorbell

£1.93 0 Enlarger Timer£1.93 0 Sound Bender£3.13 ThermalAlarm

O Micropower Pendulum£2.80 NOVEMBER 81

£3.40 Playmate (three boards)£2.65 C Kitchen Scales£2.63 Sound Track£2.21

SEPTEMBER 82

£7.20£1.84£4.25

0 Bench Amplifier £2.53 0 Voice -Over Unit £3.97 C Auto Volume Control £1.84C Four InputMixer £2.64 0 Car Alarm £2.81 0 Dual Logic Probe £1.93

JANUARY 810 LED TachoC Multi -Option SirenC Universal Timer

O Phone Bell Shifter£4.13 DECEMBER 81£3.20 0 Alcohometer (two boards)£3.31 C Bodywork Checker

£2.96 OCTOBER 82 Message Panel (one card)

£5.21£1.75 NOVEMBER 82

£8.79

FEBRUARY 81 C Component Tester £1.40 Spectrum Analyst (3 boards) £14.33C Infra -red Alarm (four boards)C Pulse Generator

MARCH 81C Engineer's Stethoscope

APRIL 81

£6.64£3.57 JANUARY 82

0 Parking Meter Timer£2.65 0 Infant Guard

0 Guitar Tuner (two boards)

Pulse generator£2.20 El Message panel interface£1.56 DECEMBER 82£5.55 O ELCB

£5.29£1.91

£2.41C Musical Box £2.64 FEBRUARY 82 O Servo Interface (two boards) £5.870 Drum Machine (two boards)0 Guitar Note Expander

JUNE 81

£5.60 0 Ripple Monitor£3.20 0 Pest Monitor

0 I Ching Computer(two boards)

£1.92, 0 Spectracolumn£1.68 O Signal Line Tester£5.15,

£4.82£1.25

C Mini -drill Speed Controller £2.93 0 Moving -magnet stage £3.49; JANUARY 830 Antenna Extender £3.20 0 Moving -coil stage £3.49 0 ETI/831/1 Fuel Gauge £3.00

0 ETI/831/2 ZX ADC £2.25 ETI/831/3 Programmable PSU £3.00

MARCH 83 ETI/833/1 6502 Sound/DAC £11.16

How to order: indicate the boards required by ETI/833/2 Alarm Module £3.15ticking the boxes and send this page, together with ETI/833/3 ZX81 Graphics £0.93

your payment, to: ETI PCB Service, Argus ETI/833/4 Logic Probe £2.17Specialist Publications Ltd, 145 Charing Cross Signed

Road, London WC2H OEE. Make cheques payableto ETI PCB Service. Payment in sterling only please.

Name

Prices subject to change without notice. AddressTotal for boardsAdd 45p p & p 0.45Total enclosed

hi! perliormatoice hi! compel ive hi!

23 HIGH QUALITY ATLOW COSLiceol

.

acal

5,Name

OD

£34.00 EPhis VATINCLUDINGFREE

Teat Leads, 4Battery andInstruction 4Manualplus A full rzONE YEAR 7GUARANTEE

EASY TO USE

26 FULLY PROTECTED RANGES

111} LARGE 3% DIGIT LCD DISPLAY

rni -±0.5% basic DC ACCURACYAC and DC VOLTS and AMPS + OHMS

HC6010 has an additional 10 Amp RangeHC703 has a basic DC Accuracy of ± 0.1%HC7030 has an extra 10 Amp RangeHM101R - 102R and 102132 are Analog modelsAsk FOR FREE DATAEasy to Order: Fill in and post the coupon enclosingcheque/P.O./Credit Card details or Official Order.

VISAA.C.

.1 SS .0a meINTIM I SU.

In a hurry? Thenring (0799)24922

Address

A fiono

cio

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NIB

N M\

'MP

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111,

Please send:

HC601's at £40.25 (inc. VAT + P + DI

HC6010's at £43.70 (inc. VAT + P + DI

HC703's at £51.75 (inc. VAT + P + DI

HC7030's at £55.20 (inc. VAT + P+D)

HM101R's at £7.75 (inc. VAT + P + DI

HM102R's at £14.38 (inc. VAT + P+ D)

HM102BZ's at £16.10 (inc. VAT + P+DI

Total £Please tick and fill in number of card

iBarclaycard !Access American Express !Diners Club

Credit Card No.Please allow 14 days for delivery.

PI

4

f1111Ili! C(11111e ii I VP Ill House of Instruments Ltd

House of Instruments.Clifton Chambers. 62 High StreetSaffron Walden. Essex CBIO I EETelephone (0799)24922 Telex 818750

COMTECI1 ELECTRONICS

205 STURDEE ROAD, LEIC ESTER, LE2 9FYMAIL ORDER TEL. 10533) 779578

au DAYICES BRAND NEW, FULL SPEC. AND GUARANTEED.ri-tAbt ADD 302 P&P Tict,.4. LI ORDERS, THEN VAT TO

1 L/ 1AL

** ** COMPARE OUR PRICES ** ** EX STOCK BY RETURN * * * *

TRANSISTORSBCI 07E1 14pBC108C 149BC109C 14pBC114 17pBCI 15 19pBC140 28pBCI 41 29pBCI42 27pBCI43 27pBCI69C 10pBCI 71 10pBCI72C 109BCI73C 10pBCI77 18pBCI78 18pBCI79 199BC1826 9p6C1836 9P6C1846 9136C2126 9P8C2138 9P6C2146 SRBC237 lopBC238 10pBC239 10pBC307 12pBC3086 12pBC309 12pBC327 12pBC328 12pBC337 12pBC338 12.13

BC54613 12pBC5476 9pBC5486 9pBC549C 10pBC5576 9pBC5586 9PBC559C 10p

BCY70 18pBCY7I 18pBCY72 15p613131 op613132 46pB DI 35 37pBDI 36 37p

BDI 39 36p

El D140 36pBFY50 25pB FY5I /2 249mpsA05 npBPSA06 24pMPSA12 24MPSA13 29pMPSA55 24pMPSA56 26p2N2222 24p2N2222 A 2592N2904 24p2 N2904A 26p2 N2905A 242N2906 23p2N2906A 24p2N3053 24p2N3055E 58p2N3441 140p2N3442 140p2N3702 10p2N3704 10p2N3706

lop41°P2N37072N3708 PP2N3771 18592N3772 190p2N3903 10p2N3904 10p2N3906 1092N4058 10p

LINEAR ICs555 14556

.1,,...54:1

741 ._'v748C

rvirs747C "''''LF351 47pLF353

a2PLF355"P.n.sLF356

LF357 112pLM301A 25pLM324 4°PLM348 65pLM358 50pLM386 79pLM393 011p

LM3900 48pMC1458 34pMC3302 85pSN761 15 135pSN76660 115pTDA2002 96pTDA2030 220p

REGULATORS78L05 32978L12 32978L15 329LM309K ...LM317K 260p

LEDS.2"FI .125"RED 8PGREEN 12pYELLOW 14pClips 3p

SOCKETS8 pin Sp

14 pin 9p16 pin 10p

. BRIDGERECTIFIERS

I; Amp.W005 18pWOI 20pW02 22p

25pW06 29pwog 334)6 Amp.pw005

79ppm., 64pPW02 92pPW04

DIODESAAII9 1090A47 10p0A90/91 8 p

0A95 9P0A200 8p0A202 9P

1S44 9PIN16 5P1N4146 3p1N4001 41N4002 41N4004 5P1N4006 8P1N4007 7p1N5401 12p1N5402 13p1N5404 14p165406 15pIN5408 18p6A/100V 30p6A/200V 35p

ZENERS500mW2V7 to 36Veach

THE "INSTANT"PC BOARD

E -Z CIRCUIT..." quick, easy & reliable... the best way to make oneor two -of -a -kind PC boards"! That's what "Doc" Savage (hobbyeditor, Radio Electronics magazine) says about E -Z CIRCUIT.Why all the excitement?Simple, E -Z CIRCUIT's exclusive 1 oz., pressure -sensitive coppertapes & patterns apply directly to the PC board, creating an actualcurrent carrying circuit. Simply apply E -Z CIRCUIT's CopperMounting Configurations to the board, solder your componentsinto place, and you have a professional, production quality PCboard... instantly...without artwork, photography, screeningor etching.There's no need to worry about mistakes either. With E -ZCIRCUIT's special two-phase adhesive, you can make correc-tions, modifications or improvements quickly & easily...withoutdamaging the performance or appearance of your PC board.For building, prototyping or repairing PC boards instantly, E -ZCIRCUIT truly is the quick, easy, reliable way!Prove it to yourself, send for your FREE copy ofthe E -Z CIRCUIT Copper Products Printed CircuitTechnical Manual & Catalog EZ-3001. See why"Doc" Savage & thousands of other users recom-mend E -Z CIRCUIT for instant PC boards.

Send for your FREE E -Z CIRCUIT Printed Circuit CopperProducts Technical Manual & Catalog EZ-3001.

1 Engineering C ElectronicJ Design Services Ltd.

Unit 7, Enterprise Centre, Childers Road, Limerick.(061] 49366

Efil_ELIPITOPI SALES

CASIO TEXAS INSTRUMENTSFX 702P £71.95FX 602P £63.95 TI 35 £15.95

FX 2800P £16.95 TI 55-11 £29.95

FA 2 INTERFACE £19.95 TI Programmer LCD" Hex-

FX 78 £17.95 adecimal, Octal, Decimal

FX 550 £15.95 £44.95

FX 900 SOLAR £17.95 TC 58C £71.95

700P £71.95 PC 100C Printer 58/59

PB 100 £63.95 £169.95

FX 3600P £20.95 TI 44 Financial £23.95

FP 10 PRINTER £39.95 TI 57 LCD £24.95

FX 100 £14.95 TI 59 Magnetic Card

FX 350 £14.95 £121.95

FX 950 SOLAR £19.95 TI Library Modules....£35.95

SHARPEL 5103 80 steps E28.95EL 506H £15.95PC 1211 £86.95PC 1211 Printer interface

£71.95EL 5100 80 steps £54.95EL 507 £23.95PC 1500 £168.95PC 1500 colour printer

£145.95

HEWLETTPACKARD

HP11C £99.95HP 15C £109.95HP 41C £189.95HP 12C £119.95HP 16C £119.95HP 41CV £249.95

CASIOSend sae for catalogue

CALCULATOR SALESFREEPOST (no stomp required U K )P 0 Box 13 Redditch Worcestershire 898OBR Telephone Redditch (0527) 43169

IA\

LB ELECTRONICSDISC DRIVE BONANZAPERTEC FD650 DSDD 8" ....£199 + VATPERTEC FD200 514" SSDD ..£100 + VATThe above drives are suitable for the BBC Micro, we non supply full documentationif requested with purchase of the drives or ly Also available is a word processingpackage which Is a tape to disc program (i.e. will not run without destroyers).

Offered with Full documentation at £9.80 p&p 50p.BRAND NEW AND BOXED PLUS DATA P&P AT COST5} in Slimline for APPLE £2.25 + VATController Card for above f48.00 + VATASCU coded querty Keyboard manufactured by Alpamenc (Woking,UK). Model 60K brand new plus data £19.95 p&p £1.50SELLOUT used (Gar replacement by us) 2716 (5v) 1 50 each p&p 30p.12 for 05 pEtp 75p25 WAY Te' Types, plugs £1.85, sockets £1.85 (solder tail) p&p 30p.Telephone for bulk prices.CASE model 430 Data modem, no information £30 each p&p f3 .50

INTERSCAN ACCOUSTIC COUPLER10" x 4" x 5" WITH ELECTRONICS, SOUND

TIGHT UNIT, FOR STANDARD GPO HAND SET.NO DATA - £10.00 (INC VAT) P&P £1.75

LB ELECTRONICS11 HERCIES ROAD,

HILLINGDON,MIDDLESEX UB10 9LS,

ENGLANDTEL: UXBRIDGE 55399=Ruy e.rb Ans.

TELECtUtPMENT OSCILLOSCOPE type 083.Dual Dace 50MHZ. Delay Sweep /550TEKTRONIX OSCILLOSCOPE type T8355.Duel Trsce35MH2 Delay Sweep. AS NEW OMTELEQUIPMENT OSCILLOSCOPE type 067A.Dual Trace 25MHZ. Delay Sweep 006TELEQUIPMENT OSCILLOSCOPE type D65.Dual Trace 15M142 0125TELEQUIPMENT OSCILLOSCOPE type 1)61A.Dual Trace 10MHZ 1180TEKTRONIX OSCILLOSCOPE type 547 with1A1. Dual Trace 50MI-12. Dual TB DSOTEKTRONIX STORAGE OSCILLOSCOPE type564B . .... E225BRUEL ie ......... X;;;40 Reecho -meter type 2112 with BEtK 2305 Level Recorder

albB te K AUDIO Frequency Spectrometer type2112 £160B ft K LEVEL RECORDER type 2305 with 50dBPolentiometer E150B te K BAND PASS FILTER SET type 1612

E75B ft K RANDOM NOISE GENERATOR type1402 E75B te K EXTENSION FILTER SET type 1620

£40B a K ELECTRONIC VOLTMETER type 24092HZ-200KHZB a K AUTOMATIC VIBRATION EXCITERCONTROL type 1018 - ... --.140B S K AUTOMATIC VIBRATION EXCITERCONTROL type 1019MARCONI FM/AM SIGNAL GENERATORTF995A/2M 1.5-220MHZ. AM/FM Mod _ . 1180MARCONI CIRCUIT MAGNIFICATIONMETER TF1246 with TF12411 OSCILLATOR40HZ-50MZ C250MARCONI1/4% UNIVERSAL BRIDGE TF1313

MARCONI UNIVERSAL BRIDGE type TF868BE15

MARCONI UNIVERSAL BRIDGES typesTF868; TR368 /1; TF868AMARCONI VACUUM TUBE VOLTMETERtype TF1041B GSMARCONI VF UGNMENT OSCIL-LOSCOPE type TF1104...-- . - . .130DECCA PAL COLOUR BAR GENERATOREP6I35A GB MA)DECCA KORTING COLOUR TV SERVICEGENERATOR type 8251 5 ..........................._ /140FETRsR2OGRAPH RECORDER TEST SET type

1225LABGEAR PAL COLOUR BAR GENERATORtype CM3037 /DB . ..... .. . . -VSLABGEAR COLOURMATCH 426 kliERNGENERATOR type CM116004-PGVIDEO CIRCUITS TUBE TESTER type V33

.... . ....... ........... ......... ........... ......... ..... ....... .130RANK U.H.F. SIGNAL STRENGTH METER.....__....._..._.-_.-"....r

RANK E.H.T. METER 0.30KV DC .......METRIX WOBBULATOR type 210 . ...._E36PHILIPS WOBBULATOR type GM2877S ESO

ADVANCE RF SIGNAL GENERATOR type 62150KH 2.220 MHZ. CW/ Mod ... _ -...-- -. 130ADVANCE RF SIGNAL GENERATOR typeSG8213 150KH2.220MHZ CW/ Mod . . --EEOADVANCE WIDE RANGE LF OSCILLATORtype SG57A 1 H2.1MHZ 1E0ADVANCE AUDIO SIGNAL GENERATORtype Hl. 15HZ-50KHZ Sine/Square 476ADVANCE LF OSCILLATOR type ME 15HZ-501012 Sine/Squere E46ADVANCE RF SIGNAL GENERATOR type F2100KHZ-100MHZ CW/Mod . .. . 140PYE SCALAMP ELECTROSTATIC VOLT -METE RO-10KV £10ERNST TURNER r ELECTROSTATIC VOLT -M ET ER Model 32 0-2.5KV - E12ERNST TURNER r ELECTROSTATIC VOLT-METER Model 32 0-5KV E14ERNST TURNER r ELECTROSTATIC VOLT-METER Mode132 0 -10 KV.-- - ..ERNST TURNER ELECTROSTATIC VOLT-METER Model 32 0-20KV _ -ADVANCE DIGITAL MULTIMETER typeDMM2 126SOLARTRON DIGITAL VOLTMETER typeLM1240 . . - .. . 1215

TMK MULOME1ER ...... 700. 20Kohrn perVolt. Rang es to 10 Amps & 5KV EISAVO MULTIMETER Model 72. Compact 02LINSTEAD L.F. SIGNAL GENERATOR type G210H2-100KHZ. Sine/Square. Compact 130SOLARTRON DIGITAL VOLTMETER typeLM 1420.2ROBAND TRANSISTORISED SUPPLY Type7104. 0-30 /0-30V lA DC. Metered - 130RACAL DIGITAL FREQUENCY METER3 typeSA520 E10TEKTRONIX TIME MARK GENERATOR bye180A.. T... . . IseAVO EITE1 type TTI69 withleads. As New (P&P al 120ESP AUTOMATIC CAPACITANCE BRIDGEModel 300A. 1 pf 200fekl. Auto ranging. 0.5%accuracy (PEW E4)....-._ .... - E40WAYNE KERR UNIVERSAL BRIDGE. typeB221 ... ....... E70TAYLOR V-A1Xli.f E36ROBAND TRANSISTORISED SUPPLY typeT1060 -100V 1A DC. metered 130RANK FLUTTER METER type 1740 CIOPYE SCALAMP ELECTROSTATIC VOLT -

EQUIPMENT SOLD IN WORKING ORDERFor further details confect DWAYNESTEWART. Please check availability beforeordering. Carriage ell units £7. VAT to beadded to total of Goode et Carriage. S.A.E.for Lists.

STEWARToF READING110 WYKEHAM ROAD, READING, BERKS. RG6 1PL

Tel: 0734 011Callers welcome 9 em -5.30 pm Monday to Saturday Inclusive

CENTRONICS 301

Superb ousfessiortal queer),rant corepact line -printer 80cosonna 120 char/sec.Parallel i,t. Beautiful qualityat a saki price. Vertical totmat unX. To include copyof cperations manual. ON-LY £148.60 CarnagelEnglandl E17.50. Techmanual (223 pages)E10.00.

DISC DRIVEMemorex 550 8" Floppy drive, mounted in case withpower supply and fan. Room for second drive. OnlyEMS + £7.50

SHUGART 801 8" Floppy -2 only at 5250 + £7.50DRE 4000A (25B-99011 Hard disc -1 only E300.

BASF 6172 24 Megabyte Winchester with PSU £700

69 Key keyboard 5 volt CMOS - believed ASCIIbut no data hence 520

Multi Rail PSU 5 volt at 4 amp. 12 volt at 2.5A, 12 voltat 350mAonly517.150 + ELIO

5 V. 5 amp Regulator module 52.50 + 50p

Data dynamic R0390 printers 110 Baud ASCII RS23220mA 175

MAWSON ASSOCIATES136 Leonard Rd, Beckenham, Kent BR3 1QP

01-778 3600Callers welcome by appointment and ell 2nd hand goods

sold as seen waking but unpuerantrlecl

WE ALSO BUYSELECTEDCOMPUTERSAND COM-PUTERPERIPHERALS

C.M.O.S.4000 10p4001 10p4002 10p4006 40P4007 12p4008 10p4009 22p4010 22p4011 1004012 10p4013 18p4014 40p4015 35p4016 18p4017 3004018 4004019 22p4020 8004021 35p4022 35p4023 12p4024 30p4025 12p

Rocar ElectronicsX Edgeworth, Heron Garden, Yate, Ace rer

MALE ORDER ONLY

Please add 50p PttP and 15% VAT

40274028402940304035403740404041404240434044404540464047

18p35p40p14p50p

E1.0036p35935p40p40985p40936p

All devices fun specBrand new and guarankwd

40484049405040514052406040664068406940704071407240734075407640774078

35p20p20p40p46p40p20p12p12p12p12p12p12p12p40p12p12p

4081 12p4082 120

Voltage Regulators

SCRSC1060 40pC1160 6013

TriacsTIC 2060 609TIC 225D 60pTIC 2260 SOPTIC 2360 90oTIC 246D (1.90

7805 5V 1 amp 70220 30p7812 12V 1 amp 717220 .3097815 15V 1 amp £0220 309

l.C. SocketsII pin -ep 18 pin 10p 24 pin -

/Sp14 pin -7p 20 pin - 1.7p 28 pin20p16pki -7pLIED.*RedYellowGreen

0 Pin -213p3mm 5rryn

8p 8pBP3P 3P

PCB FOIL 0

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TECHNICAL TRAININGIN ELECTRONICS,TELEVISION AND AUDIOIN YOUR OWN HOME-AT YOUR PACEICS can provide the technical knowledge that is so essentialto your success,knowledge that will enable you to take advant-age of the many opportunities open to the trained man Youstudy in your own home. in your own time and at your ownpace and if you are studying for an examination ICS guaranteecoaching until you are successful.

City & Guilds CertificatesRadio AmateursBasic Electronic Engineering (Joint C&G/ICS)

Certificate CoursesTV and Audio ServicingRadio & Amplfier ConstructionElectronic Engineering* and MaintenanceComputer Engineering* and ProgrammingMicroprocessor Engineering*TV, Radio and Audio EngineeringElectrical Engineering,* Installationand Contracting *Quality for lET Airedale Membership

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ICS Po sto. Dept E262ICS School of Electronics160 Stewarts Road, 01-622 9911

500 000 000IN STOCK

WASHERS SPRING CLIPS CLAMPSSOLDER TAGS SOLID STATE INSULATORS

and many other pressed partsELECTROMECH SALES LTD.

MELDRETH RD., SHEPRETH, ROYSTON,HERTS. S68 6PSTEL: 0763 61372

I

Ambit Int . 28 29Audio Elec. . . . 53Bi-Pak . . . . 60 61BK Elec . . . 10 75Black Star . . . . 77BN RS. . . 72Bradley Marsha . 32

. . 85caitvw. fight Ele. . 85Clef Products . . 72t. onitech Elec . . 84( .icklewood E . .8 9Ciinisc.in Elec . 54(-lotion Ewe . 74Datanian Desig . . 27Display Elec . . 35Elect runiecti . . 86illeecct&roCniTe"°&iii .%:. on. . 78i. 62Electrovalue . . . 21Emos . 84Enfield Elec . . 77Europa Elec . . 56C.; S C . . 33Greenbank . . . 82Greenweld . . . 53Happy Mentor e . 74Hart Elec. . . . 84House of Inst . 54

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Input Design. . 77Ketan . . . 54

& B E tee . . /5i.B E tec. . . 85L EM Seiv . . 17Magunt aE set /5Mapiin ()BCMarti. i . 82Mawsnt, Assoc 85

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PCB FOIL PATTERNS

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CD GIPO_eS1 asoes ...

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IC50 ANALOGUE & AUDIO OUTPUT

IC8

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LOOKING FOR COMPONENTS!HARDWARE!

CASES! TRY YOUR LOCALLISTED STOCKIST

AVON

ANNLEY ELECTRO190 Bedminster Down RoadBedminster Down, Bristol I

Tel: 0272 832622Open Mon -Sat 9am - 6.30pm

Wed Ilam-2pm

BEDFORDSHIRE

BROADWAY ELECTRONICS1 The Broadway. Bedford,

Tel: 0234 2136311Open: 6.days 9-5.30 1/2 day Thur.

Lunch 1.30 - 2.30Specialists in components

and Acorn computers.

DORSET

D.J. ELECTRONICS64 Ensbury Park Road,

BournemouthTel: (0202) 515073

Open Mon - Sat 9am - 6pm

HERTFORDSHIRE

GODDARDS COMPONENTS110 Loridon Road, St. Albans.

Tel: St. Albans 64162Open, Mon -Sat 9.30am-5.30pm

(1/2 day Thur)

LANCASHIRE

ETESON ELECTRONICS158 Lower Green

Poulton-le-Fylde, BlackpoolTel: (0253) 885107

Open: 9.30am-12.30. 1.30-5.30. Closed Wed &Sun. Electronic Component Specialists

MERSEYSIDE

MYCA ELECTRONICS2 VICTORIA PL; SEACOMBE FERRY,

WALLASEY, L44 6NR,Tel: 051838 8847

Open Mon -Sat 10am-5.30pmMail Orderprice list 50p refundable

PROGRESSIVE RADIO93 Dale Street. Tel 051 236 0982 47

Whitechapel Tel 0512365489Liverpool 2

THEELECTRONICSSPECIALISTS

Open: Tues-Sat 9.30-5.30

W. MIDLANDS/WARCS

CoventrySt KidderminsterComponents, computers, car radios, C.B.s,

Amateur Radioand all electronic hobby equipment

Open: Mon -Sat 9-6, Sun 10-2Tel. 0562 2179

NORTHAMPTONSHIRE

* A new company selling electronic components* Mail order and walk round supermarket* Vast stocks and very competitive prices

High Mardi, Daventry NN11 4H0

Telephone 03272 5523 Telex 311245

Off A45 opposite John 0' Gaunt

FOR YOUR BUSINESS TOBE INCLUDED, CALLELECTROMART ON

01-437-1002

STAFFORDSHIRE

ELECTRONICS SUPPLIES105 HIGH STREET

WOOLSTANTONNEWCASTLE

Tel: 0782 636904Open Mon -Wed 9-6, Thurs 9-12 & 5-7,

Fri & Sat 9-9, Sun 11-2

S. WALES

STEVE'S ELECTRONICSUPPLY CO. LTD.

45 Castle Arcade, CardiffTEL: 0222 41905

Open: Mon -Sat 9-5.30For components to computers

WARWICKSHIRE

HorizonElectronics

Charlotte St, Rugby. Tel: Rugby 78138Open 5 Days 10-6 (closed Wed)

Wide range of components and R.S. stockists1983 Mail Order Catalogue 75p

YORKSHIRE

ACE MAILTRONIX LTD.3A COMMERCIAL STREETBatley. Tel: (0924) 441129

Open: Mon -Fri 9am-5.30pm. (Sat 1pm)Retail and Wholesale

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ADVERTISEMENTSemi -Display (min 2 ems)RATES

ss**0°..c. ,_,If\

1-3 insertions £10.00 per cm4-11 insertions £9.00 per cm12 + insertions £8.00 per cmLineage 35p per word (min 15 words)

co PkeN S P''---..c.N.x. - A3... ,.grb

Box Nos. £2.50Closing date 1st Friday in the month

1-199` A 0310. preceding publication date.

9)C0C;A:31 %All advertisements in this section must be prepaid.Advertisements are accepted subject to the terms and

.4#1 conditions printed on the advertisement rate card (available

4ton request)Send your requirements and cheque / P.O. to.

.E.T.I. CLASSIFIED ADVERTISING,145 CHARING CROSS RD, LONDONWC2H OEE

DIGITAL WATCH REPLACEMENT partsbatteries, displays, backlights etc. Alsoreports pubications, charts. S.a.e. for full listProfords Conersdrive, Holmergre,an, Bucks,HP15 6SGD

Al051-228 3483

INTRUDER ALARMS LTD

WHOLESALE SUPPLIES

MAIL ORDER DEPT

01.00 CONTROL PANELSDummy Boxes [4.50 Batten/ T/E/E £20.00Bell 6" F7.50 F S 20/40 036.00SIRENS CONTACTSMinimite £4.50 ALnunurn E1.35Electronic 0.50 Surface E0.75Cable (4 core) E7.00 Flush E11.85

PRESSURE MATS Ouickilts E0.75Stair E11.05 BEAMSStandard [1.50 Infra lied E31.50

Ultrasonic comp #313.00Hec Battery DJ.%

Discount on quantity - Pismo add 15%VAT

FOR ORDERS LESS THAN CIO P&P (ZOOOVER DO P&P FREE

Al ALARMS LTD86 Derby Lane, Old Swan, Liverpool 13

AERIAL AMPLIFIERS Improve weaktelevision reception. Price f6.70, S.A.E.for leaflets. Electronic Mailorder,Ramsbottom, Lancashire BLO 9AGH.

DESIGN - ARTWORKS - PRODUCTIONPROBLEMS? For electronic design / hard-ware / software. P.C.B. artworks/assemblytest. We offer a complete service at verycompetitive rates. For details contact: ColinHolloway, c/o Atom Computer Services Ltd,11 Sleighburn Avenue, Silverdale Not-tingham. Tel 0602 817471.

BIG BARGAIN BOXOur e.g Bergen Bo. contains over a thousand components -resistors, capacitors, pots. enctcnes, ctodes, versos:ors. panels.b4s erd penes odds and ends. Al useful 55;$11 cost manytitrtm the once we we asking if bought separately. Approx. weightAlbs.ONLY £5.00 Inc. poet - you're bound to come back for

enotber111ESP

147A FOUNDRY LANE, SOUTHAMPTON SO1 3LSLots of surplus bargains on our latest lest - send an SAE for your

copy now

BLEEPER Electronic Seat Belt Reminder,Flashers, full kit of parts, easy fitting, £6.95,c.w.o. Micro -Tech Industries, Brighouse,HD6 1PD.

BUMPER BOX OF BITSWOW111 We've got so many components in stock. we can'tpossibly hat them still - So buy a box, in it you'll lind resistors,capacnors, displays, swncties, panels with ti ansistors, diodes, IC'setc, cols, pots ... and so on. All modem parts - guaranteed atleast 1000 items, minimum weight 10Ibs. ONLY E8.50 inc.

ELECTRONICS WORLDle Dews Road, Salisbury. Wilts SP2 7SN

BURGLAR Alarm Equipment. Pleasevisit our 2,000 sq.ft showrooms or writeor phone for your free catalogue.C.W.A.S. Ltd, 100 Rooley Avenue, Brad-ford BD6 1DB. Telephone 0274 308920

ATTENTION ELECTRONICORGAN KIT BUILDERSShop soiled 60 note plastic keys E17.2530 note all timber pedal boards E86.25

Few only! Mini consoles oak or mahoganyE195 ex works including V.A.T.

George Sixsmith organ builders,Hillside Organ Works, Carrhill Rd.,

Mossley, Nr. Ashton-u-Lyne, Lancs.Tel: Mossley 3009

CLOSING DOWN SALEV. BANSAL

14 Deylgdor Road. Hove. E. Susses Tel. 10273) 732419PAS components we new. Minimum order 120.03. -

Free postage, No V.A.T.CMos4012......-_.........10p 4017 30p 4019 25p4022 .......... ......... 40p 4023 ... .... _. ..... .10p 4024 20p4025 10p 4049 .. ........... ...20p 4071 12p4076 46p 4081 10a 4518 . 35p4520 45p 4578 ... ......... _. 40p 455 / 222p

TTL7400 9p 7404 ..............13p 74161J ,4p7495 .... .... 46p

PRINTED CIRCUITS. Make your own sim-ply, cheaply and quickly! Golden Fotolaclight-sensitive lacquer - now greatly im-proved and very much faster. Aerosolcans with full instructions, £2.25. De-veloper 35p. Ferric Chloride 55o. Cleatacetate sheet for master 14p. Copper -cladfibreglass board, approx. 1mm thick£1.75 sq. ft. Post/packing 75p. WhiteHouse Electronics, Castle Drive, PraaSands, Penzance, Cornwall.

A really compact highperformance CCTV camerafor only IC 130.00 plus VATplus P/P, Total IC 152.95.Size 3-x 3-x 97 240v operation.1v p -p output. Lens extra.

CROFTON ELECTRONICS LIMITED35 GROSVENOR ROAD. TWICKENHAM,MIDDLESEX TVV1 4ADTelephone 01 891 1923/01 891 1513Telex 295093 CROF TN G

CIRCUIT DESIGN, Prototype construction,analogue or Digital, Siangle Circuits orComplete Instruments/Systems. Write A. J.ATTWOOD, C.Eng., MIERE, Heathercote,Heatherton Park, Taunton, Somerset, TA41ET, or Phone Bradford -on -Tone (082-346)536.

CENTURIONALARMS

We manufacture, you save £££'sSend s.a.e. or phone for our Free list ofprofessional D.I.Y. Burglar Alarm Equip-ment and accessories.Discount up to 20% off list prices.e.g. Control Equipment from £15.98,Decoy Bell Boxes from £5.95 Inc.

TRADE ENQUIRIES WELCOME

0484-21000or 0484 35527 124 hr. ans.)CENTURION ALARMSIETII65 Wakefield Road, -Huddersfield

9BE, W. YorkshireiAccess Et Visa

Orders Welcomed

CABINET RTTINGSFretcloths Coverings. Handles, Castors.Flight Case Locks a Parts, Jacks. XLRs.Bulgons Reverb Trays, P & N nuc Stands.ASS Glassfore Horns.CELESTION POWERSpeakers

Send30p cheque

PO for illustratedcatalogue Adam Hall (ET Supplies).

Unit B. Carlton Court. Grainger Road.Southend-on-Sea.

SHEETMETAL FOLDERS 18" x 18G.Steet, 16G. Aluminium, bench or vice held.Hobby or light industrial use. £38. 01-8907838 day/evenings.

CONVERT ANY TV into Large ScreenOscilloscope (by external unit). Costsapprox. £12 to build. Circuit and plans £3 orSAE details. J. Bobker, 29 ChaddertonDrive, Unsworth, Bury, Lancs.

BOUND SETS E.T.I. Complete years 1974,1980, also some 1973-1981. Offers.Wilmslow, 0625 533380.

U.V. LIGHT EXPOSER UNIT for use inprep. of photo -resist P.C.B.'s. Attractivewooden construction with exposer area of250 x 150mm. Case 350 x 250 x 95mm.240V operation. Only £37.00 inc. p&p. Sendcheque to V.E.P. Ltd., 116 Byron Way,Northolt, Middlesex or ring 01-845 5018.

COPPER CLAD Double Sided Fibreglass,12" x 8". 10 sheets £6. 5 sheets £4. Davron,Box No. E.T .1.202, Asp Ltd., 145 CharingCross Road, London WC2.

GOVERNMENT SURPLUS componentsand equipment, send s.a.e. for list: AFR Elec-tronics, School Lane, Moulton,Northampton.

WANTED: ELECTRONIC COMPONENTSand Test Equipment. Factories cleared. Goodprices given. Q Services, 29 Law -fordCrescent, Yateley, Camberley, Surrey. 0252871048.

SPECTRUM GAMES SALE. Venture (7games in 1), was £6. 3 compulsive games,was £5. The lot on one cassette for just £6.Bobker, 29 Chadderton Drive, Unsworth,Bury, Lancs.

SLIDE TAPE SYNCHRONISERSynchronise slides with music and/or commentary with our PLLslide tape synchroniser kit Any cassette/tape recorder or deck canbe used together with any projector with remote control Of

synchroniser socket.Units can be ganged together for multi -projector use and could beused in any project that requires tone goneration/detectionIreraote control devices, tape based programmable controller/sequencer etc. etc.) - full details supplied.Baltic kit [12.961 includes PCB, relay. electronic components anddetailed instructions.Compose kit (19.951as basic kit plus case and all switches, leads.plugs and connectors required/ All prices include p6p.

UNITECH (PalciandalDept ET3 FREEPOST. Sutton Goldfield. West Midlands B74 2BR

Ino stamp rapuited)

A LASER FOR £120. Complete in cabinetwith power supply. Send 50p for details, plusinformation regarding other Lasers,Holograms, available new and ex -exhibit.DHS Developments, Wellington Court, 11Alma Square, Scarborough.

Save money on drawer sets withthe BITSABOX

12 drawerwhilecardboardbench setfor yourbits andpiecesDrawer saze140 f f 50x 37mm

Cheques/PO to:DMW Boxes81 Somerset Rood London El?Prop R E DosidrionPERSONAI. CALLERS & TRADE ENQUIRIES WELCOME

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Get moving with these new developments in UK Robotics- advanced electrohydraulic designs foreducation, industry and now available tothe home constructor.Hebot II is a turtle -type robot which takes programmingout of the two dimensional world of the VDU into the realthree dimensional world Given a DC supply of 9-15V it canperform a bewildering number of moves under computercontrol - forwards, backwards, left and right - with eachwheel independently controlled It has blinking eyes. bleepswith a choice of two tones and has a solenoid operated pen tochart its progress Touch sensors coupled to its shell returndata, about its environment. to the computer for it to calculateevasive or exploratory action. Hebot II connects directly toan I/O port or alternatively with the universal interface boardto the expansion bus of a ZX81 or other computer.

HEBOTT II

Robotic experience is becoming as essential a subject as co outingMICROGRASP provides the lowest cost means of acquirmg thatexperience but despite its ultra low price the robot has considerableversatility There are 5 axes each using a servo motor and there isfeedback from each of the arm movements. Control is by anycomputer with an expansion bus - the ZX81 being particularly suitableServoing is achieved with hardware on the interface board to keepprogramming simple and the robot is operated under BASICcommands with no computer specific software required. The interfaceboard is memory mapped using only 64 bytes at any of 1024 switchselectable locationsMICROGRASP robot kit with power supplyUniversal computer interface board kit23 way edge connectorZX81 peripheral/RAM Pack splitter board

Up to the nano -second hard, firm and softwardevelopments embodied in a complete system.. ega Hertz 16 bit CPU; 64K upwardly compatiblDRAM; separate 16K video DRAM and 24K TI PoweBasic with overwrite. Supports up to four Disc drives omixed type with 16 serial I/O ports. Programmable Baud'ate and comprehensive E Bus interface designed tosupport real world applications.

Very high resolution graphics gives 3D simulation in 16colours on 36 prioritised planes of user definable characters.Software FORTH coming includes this trendy language along

h NOS C/PM.Hardware components available separately with details in Nov,Dec, and Jan issues of ETI. Software features include; Real timeclock, full renumber command, buffered I/O to free machine whilst

-op of the range is the Genesis P102 which has dual speedcontrol, continuous servo operation and double actingc, nders for increased torque on the wrist and arm rotationo n s. The microprocessor based control system has addi-

: nal memory, position interrogation via the RS232C inter--ace increasing the versatility of computer control and inputswe provided for machine tool interfacing.

a, s system READY BUILT £1950.00,enran CORTEX 16 bit 64K computer Kit £295.00; READY BUILT £395.00

(Electronics Today International December issue on CORTEX)

Example prices andspecifications

Genesis 5101Base 195" k 11" k 75"Lifting capacity 1500gmArm lift: 6 6"Weight 29Kg4 axis model in kit form5 axis model in kit form5 axis model Ready Built

£390£445£790

Genesis P101Base 19.5" . 11" . 75"Lifting capacity: 2000gmArm lengths between axles 14 0"Weight 34Kg4 axis model in kit form £4956 axis mode in kit form £5956 axis model Ready Built £950

Complete Systems as shown inPhotograph above

Genesis S1014 axis system in kit form £635.505 axis system in kit form £695.005 axis system Ready Built £1355Genesis P1014 axis system in kit form £742.006 axis system in kit form £852.006 axis system Ready Built £1525

All prices exclusive of VAT

GENESIS P102 PROCESSOR BOX, HAND HELDCONTROLLER AND CORTEX COMPUTER

11'1110 NI 0.111,1j;

'1111,

!

1,, ill

I ;!

I

ihiti

£125.00£48.50£2.50£3.00 MICROGRASP, INTERFACE BOARD AND ZX81

printing, call to machine code routines. hexadecimal support and user-friendly textual error trapping messages.

If computers interest you then the Cortex will expand your under-standing infinitely more than off the shelf machines. Use it inbusiness, education, research or just play with the incrediblegraphics capability. At Powertran we are using these machines inconventional roles, in product control and R & D. We shall co-ordinate the Cortex user group and distribute software for the

TMS 9995 CPU. Complete 16 bit 64K computer kit £295.00 +VAT Complete 16 bit 64K computer ready built £395.00 + VAT.

*it

With prices starting below £1.000 the Genesis range of general purpose robotsprovide a first rate introduction to robotics for both education and industryEach has a self -contained hydraulic power source. which enables loads ofseveral pounds to be smoothly handled The system operated from a singlephase 240 or 120V AC supply or a 12V DC supply. The machine can be suppliedwith up to 6 axes each of which is fully independent but capable of simultaneousoperation Position control is achieved by means of a closed -loop feedbacksystem based around a dedicated microprocessor. Movement sequences canbe entered, stored and replayed by use of a hand held controller. alternatively thesystems can also be interfaced to an external computer via a standard RS 232Clink

GENESIS S101 AND GENESIS P101 WITH PROCESSOR BOXESAND HAND-HELD CONTROLLERS

WORLDLEADERS

INELECTRONIC

KIT DESIGNAND SUPPLY

(CYBERNETIC DIVISION)PORTWAY INDUSTRIAL ESTATEANDOVER HANTS SP10 3NMPhone Enquiries (0264) 64455

SPEECH SYNTHESISERFOR ZX81 and VIC20

THE MAPLIN TALK -BACKNow your computer can talk!*Allophone (extended phoneme) system givesunlimited vocabulary.*Can be used with unexpanded VIC20 or ZX81- doesnot require large areas of memory.*In VIC20 version, speech output is direct to TV speakerwith no additional amplification needed.*Allows speech to be easily included in programs.Complete kit only £24.95.Order As LKOOA (VIC20 Talk -Back)

LKO1B (ZX81 Talk -Back)Full construction details in Maplin Projects Book 6Price 70p.Order AsXAO6G (Maplin Mag Vol. 2 No.6)

KEYBOARD WITH ELECTRONICSFORZX81

.ma

MUM

*Full size, full travel keyboard that'ssimple to add to yourZX81 (no soldering in ZX81)

*Complete with electronics to make "Shift Lock","Function" and "Graphics 2" single key selections.

*Powered (with adaptor supplied) from ZX81's ownstandard power supply

Full details in Project Book 3 (XAO3D) Price 60p.Complete kit (excl. case) £19 95. Order As LW72PCase £4.95. Order As XG17T.Ready built-in case £29 95 Order As XG22Y.

OTHER KITS FORZX81

3 -Channel Sounds Generator (Details in Book 5)Order As LW96E. Price £10 95.ZX81 Sound On Your TV Set (Details in Book 6).Order As LKO2C Price £19.95.ZX81 I/O Port gives two bi-directional 8 -bit ports(Details in Book 4).Order As LW76H. Price £9.25.

ZX81 Extendiboard will accept 16K RAM and 3 otherplumodules.

Order As GI3OBJ Price £2.32Edge Connectors (4 needed).

Order As RK35Q. Price £2.39.

HOME SECURITY SYSTEMSix independent channels- 2or 4 wire operation. Externalhorn High degree of protec-tion and long term reliabilityFull details in Projects Book 2

(XAO2C) Price 60p

Easy -to -build, superbspecification Compar-able with organs sellingfor up to £1000. Fullconstruction details in ourbook (XH55K) Price £2.50Complete kits available.Electronics (XY91Y) £299.95'Cabinet (XY93B) £99.504.Democassette(XX43W)£1.99

WHY DO YOUKEEP LOOKING ATME LIKE THAT 7.

- - *A.

.4.1'ss ....5.eige.%4ter,'

Carnage extra

25W STEREO MOSFETAMPLIFIER

*Over 26W/channel intoBoat1kHz bothchannelsdriven* Frequency response 20Hz to 40kHz ±1dB*Low distortion, low noise and high reliability power

MOSFET output stage.* Extremely easy to build Almost everything fits on main

pcb, cutting interwinng to just 7 wires (plus toroidaltransformer and mains lead terminations).

*Complete kit contains everything you need includingpre -drilled and printed chassis and wooden cabinet. Fulldetails in Projects Book 3. Price 60p IXAO3D). Complete kitonly /49.95 incl. VAT and carriage (LW71N).

end now for anapplication form - thenbuy it with MAPCARDMAPCARD gives youreal spending power -up to 24 times yourmonthly payments,instantly.

r- iI

Post this coupon now!Please send me a copy of your 1983 catalogue. I enclose £1 50 (inc p&p). I

IIf I am not completely satisfied I may return the catalogue to you and havemy money refunded If you live outside the U K. send £1.90 or 10 International

IReply Coupons.

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MAPLIN'S FANTASTIC PROJECTSFull details in our project books. Issues 1 to 5: 60p each

Issue 6: 70p.In Book 1 (XAO1B) 120W rms MOSFET Combo -Amplifier Universal Timer with 18 program times and4 outputs Temperature Gauge Six Vero Projects.In Book 2 (XAO2C) Home Security System TrainController for 14 trains on one circuit Stopwatch withmultiple modes Miles -per -Gallon Meter.In Book 3 (XAO3D) ZX81 Keyboard with electronics Stereo 25W MOSFET Amplifier DopplerRadar IntruderDetector Remote Control for Train Controller.In Book 4 (XAO4E) Telephone Exchange for 16 exten-sions Frequency Counter 10Hz to 600MHz UltrasonicIntruder Detector I/O Port for ZX81 Car BurglarAlarm Remote Control for 25W Stereo Amp.In Book 5 (XAO5F) Modem to European standard 100W 240V AC Inverter Sounds Generator for ZX81 Central Heating Controller Panic Button for HomeSecurity System Model Train Projects Timer forExternal SounderIn Book 6 (XAO6G)* Speech Synthesiser for ZX81 &VIC20 Module to Bridge two of our MOSFET Amps tomake a 350W Amp ZX81 Sound on your TV ZX81Interface for Modem Scratch Filter Doorbell for Deaf Simple FM Tuner' Damp Meter'. Projects for Book 6 were in an advanced state at the timed writing, but contents may change prior to publication(due 11th February 1983)

MAPLIN'S NEW 1983 CATALOGUEOver 390 pages packedwith data and picturesand all completelyrevised and includingover 1000 new items.On sale in all branchesof WHSMITH

mownIlweresqlt

MAPLIN ELECTRONIC SUPPLIES LTDPO. Box 3, Rayleigh, Essex SS6 RLRTelephone. Sales (0702) 552911 General (0702) 554155Shops at Note Shops 171,1Stl Mondays159 King St , Hammersmith. London W6 Telephone 01 748 0926284 London Rd , Westcliff on Sea. Essex Telephone (0702) 554000Lynton Square Perry Barr. Birmingham Telephone (021) 356 7297