I

1

QUICKROUTE

Quickroute Makes it Easy

SPECIFICATION

Modern user interfacewith dockable tool bars &active buttonsMulti -sheet schematic

capture at the press of abutton.Power rail & data bus

support32 Bit mixed mode

analogue & digitalsimulationSupport for a range of

SPICE .MODEL statements.

Copper flood fillNetlist import & exportCAD/CAM file

import/export. GerberViewer.

PCB Design with 1-8layer autorouterWMF, DXF, & SPICE file

export1000+ Library SymbolsEngineering Change &

Design Checking

FREE DEMO

Download a freedemonstration version from

our web site athttp://www.quickroute.co.uk

It's not hard to see why Quickroute is so easy to use! We've integrated mixed mode

simulation, schematic capture, PCB design with autorouting and CAD -CAM support intoone integrated environment. Best of all, prices start at just £99.88 inclusive* for thecomplete system with support for 300 pins - less than the price of some simulators alone!

Quickroute 4.0 features a modem user interface with active buttons and dockable toolbars. Frequently used tools can appear on floating tool pallettes for quick access, andwith tool -tips and on-line help you can be sure of getting information on Quickroute'sfeatures fast.

To create a schematic in Quickroute 4.0, simply click on the symbol browser and selectand place symbols onto the design area. Use the 'intelligent' wires, power rails and databus elements toquickly wire up yourschematic andsimulate the designas required. Whencompleted, simplypress a button tocapture theschematic, a PCB

rats nest will thenappear (no messynetlists required!).

Use the multi layerautorouter, and/or

manual routing to complete your PCB together with copperfill, etc as required. Finally print your design, or create CADCAM files suitable formanufacture (we even include a Gerber viewer for checking).

But it doesn't end there! Quickroute 4.0 includes engineering change for automatic

updating of your PCB from the schematic, netlist import & export so that you can link toother EDA packages (including many simulators), DXF, SPICE, and WMF file exporttogether with over 1000 library symbols.

Call us now and find out why Quickroute 4.0 Makes it Easy!

Prince UK Inclusive Puce'

QR4 300 Pin £79.00 £99.88 11P1

30 DAY MONEY QR4 800 Pin £149.00 £182.13BACK GUARANTEE QR4 Full £249.00 £299.63

*includes TX P&P and VAT. Phone for EC4V.ted Feces- -Design cycle fig,re shows screen thats from csiterent proitts.Prices & specification sect to change without notice.

FREEphone Ref 410

0800 731 28 24FAX 0161 476 0505 TEL 0161 476 0202Quickroute Systems Ltd Regent HouseHeaton Lane Stockport SK4 1BS UKCopyright IC) 1998 Quickraute Systems lid. NIrights reserved. All trademarks are the propertyof their respective owners.

isLLEL-7-7,61:WCDA17Deg

1J..11:J

JJJj .:DeJIJfL..11 .!)

L CONTENTSMarch 1998 Volume 24Number 264 ISSN 0268/4519

FREE 16 -page SUPPLEMENT

PC TopicsCentrefold

AUDIO & HI-FI

22 PROJECT: Balanced/unbalancedconverters for audio signalsDesign by J.E Brange

COMPUTERS & MICROPROCESSORS

40 PROJECT:8002 BASIC control computer 'Design by H.J. Bahlinp

,FOCUS ON

34 Digital AudioBy our Editori?

IIMEESEMM28 Introductioi

Digital Sig'A six -part cby Dr. lng.

46 PROJECT: Io.Design by H.

64 PROJECT: FlashDesign by K.A.

POWER SUPPLIES &

16 PROJECT: Variable IDesign by K.A. Walra%

TEST & MEASUREMENTalf YKUJr.cr: IL tester

Design by L. Lamesch

MISCELLANEOUS INFORMATION71 Data sheets: Line driver/receiver

SSN42141/214211 Electronics now62 Electronics on line: Semiconductor

overviews74 Index of advertisers66 New books74 Next month in Elektor Electronics68 Readers' services63 Switchboard Sr Corrections

A B CAMR MAO Of ClICILITIOIS

The Low Cost ControllerThat's Easy to Use 57 -Features

The K-307 Module provides the featuresrequired for most embedded applications

4 Channels in 1 Channel out36 Digital in or out & Timers

RS -232 or RS -485 plus 12C LCD both text and graphics

Upto 8 x 8 matrix keyboard> 2Mbytes available on boardMany modes co choose from

AnalogueDigitalSerial

Display

KeyboardMemoryLow Power

DevelopmentThe PC Starter Pack provides the quickest methodto get your application up Si runningOperating System Real Time Multi TaskingLanguages C ' , Modula-2 and AssemblerExpansion Easy to expand to a wide range

of peripheral cards

Other FeaturesReal Time Calendar Clock, Battery Back Up,Watch Dog, Power Fail Detect, STE 1/0 Bus,8051 interface, 68000 and PC Interface

Cambridge MicroprocessorSvc*-- -is Limited

E.J

Units 17 - 18 Zone 'D.Chelmsford Road Ind EstGreat Dunmow Essex CM6 1XGE-mail sales@cms.uk_com

Phone 01 371 875 644

EKTORI)

ag

e Offices:

995 (National)International)National),huemational)

..avornpuserve.com,urworld.compuserve.

uk

E: In case of technical queries,suit P 0 Box 1414 elsewhere in thisue before writing or phoning in.

U.K. Advertising Office:3 Crescent TerraceCHELTENHAM GL5O 3PETelephone: (01242) 510 760Fax: (01242) 226 626e-mail: ttemardhubbard@msn.com

International Advertising Office:Segment BVP.O. Box 756190 AB BEEKThe NetherlandsTelephone: +31 46 438 9444Fax: +31 46437 0161e-mail : elektuurCieuronetni

Subscriptions:

World Wide Subscription Service Ltd.Unit 4. Gibbs Reed FarmPashley RoadTICEHURST TN5 7HE

Telephone: (01580) 200 657 (National)or +44 1580 200 657 (International)

Fax: (01580) 200 616 (National)or +44 1580 200 616 (International)e-mail: wws-subscriptionEivirein.net

Head Office:Segment BVP.O. Box 756190 AB BEEKThe NetherlandsTelephone: +31 46 438 9444Fax: +31 46 437 0161

Managing Director.Merino MJ. Landman

Editur-in-ChieffPublisher:Pierre EL. Kersemakers

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NDB.Zoeterwoude

Overseas editions:

FRANCEPublitronic sari21-23 Rue des Ardennes75019 PARISEditor: G.C.P. Racdersdorf

GERMANYElektor Verlae GmbHStisterfeldstr. 2552072 AACHENEditor. E.J.A. Krempelsauer

GREECEElektor EPEKaraiskaki 1416673 Voula-AIHtNAEditor. E. Xanthoulis

See our websitehttp://www.cms.uk.com

ITALYProgetto ElektorGruppo Editoriale J.C.E.Via Ferri 620092 Cinisello BalsamoGeneral Manager: J. Castclfranchi

INDIAElektor Electronics PVT LtdChhotani Building52C, Proctor Road. Grant Road (E)BOMBAY 400 007Editor. C.R. Chandarana

NETHERLANDSSegment BVPeter Treckpoelstraat 2-46191 VK BEEKEditor P.H.M. Baggen

POLANDAVT Korporacja Spolka coo01-939 VVarzawaUI. Burleska 9Editor. W. Marciniak

PORTUGALFerreira & Bento Lda.Campo Grande, 56-8W1700 USBOAEditor: F. Ferreira de Almeida

SPAINLarpress S.A. -Plaza Republica Ecuador 2, r28010 MadridEditorial Director.

J. Rodriguez Fernandez

SWEDENElectronic Press ABBox 550514105 HUDDINGEEditor. Bill Cedrum

Elektor Electronics is published monthly. except in August. by Elektor Electronics (Publishing), P.O. Box 1414. Dorchester, Dorset DT2 8YH, England. The mae-azine is available from newsagents, bookshops, and electronics retail outlets, or on subscription at an annual (1998) post paid price of 1:31.50 in the United King-dom; AIRMAIL f4000 in Europe, £50.00 in Africa. the Middle East and South America; £57.410 inAustralia, New Zealand and the Far East; and SUS 67.00 in theUSA and Canada.Periodicals Postage Paid at Rahway NJ.Postmaster: please send address corrections to Elektor Electronics, cio Mercury Airfreigbt International Inc, 2323 Randolph Avenue. Avenel, New Jersey. NJ. 07001.

Elektor Electronics 3/98

=.. PROTkilygSchematic Capture

*Produces attractive schematics like you see in the magazines(Monist, Parts List & ERC reports. *Hierarchical Design. *Fullsupport for buses including bus pins. *Extensivecomponentimodel libraries. *Advanced Property Management.*Seamless integration with simulation and PCB design.

SimulationSe. IAN16.1 1.414 Pin

MIKEMEEETTri

New FeaturesComponent Auto -Placer

Pinswap/Gateswap OptimizerBackground Regeneration of Power Planes

Enhanced Auto routing with Tidy PassFull Control of Schematic Appearance

Extensive New Component libraries

Available in 5 levels - prices from £295 to £1875 + VAT.Call now for further information & upgrade prices.

T=-Ccitm 3el WIte .10s, AS US as"

*Automatic Component Placement. Rip -Up & RetryAutorouter with tidy pass. PinswapiGateswap Optimizer &Backannotation. 532 bit high resolution database. *FullDRC and Connectivity Checking. *Shape based gridlesspower planes. *Gerber and DXF Import capability.

'Non-linear & Linear Analogue Simulation. *Event drivenDigital Simulation with modelling language. Parlitionedsimulation of large designs with multiple analogue & digitalsections. *Graphs displayed directly on the schematic.

Ti JiTiEVVW January 1997

u.- -Amei

Write, phone or fax for your free demo disk, or ask about our full evaluation kit.

0bcen en. Tel: 01756 753440. Fax: 01756 752857. EMAIL: inlaelabcenter,comk53-55 Main St, Grassington. BD23 5AA. 4./WW: Imv.labcentercauk

Electronics Fully interactive demo versions available for download from our WWW site.Call for educational, multi-user and dealer pricing - new dealers always wanted.Prices exclude VAT and delivery. All manufacturers trademarks acknowledged.

ELEKTOR ELECTRONICS isTHE magazine for

electronics and computer enthusiasts

In your work or hobby in electronics and/or comput-ers, you need to have the right information to hand.This is where Elektor Electronics can help you. Thismonthly magazine is aimed at practising profession-al electronics engineers and techracians, as well asactive hobbyists. Every month it contains a varietyof construction projects and informative/descriptivearticles on subjects ranging from audio and hi-fi,through computers and microprocessors to testand measurement. It also contains a 'FREE supple-ment, this month dealing with hi-fi loudspeakers.

Do not take our word for it, but seefor yourself that the magazine isreolly the most complete for yourpurposes. Therefore, take out anannual subscription by completingthe Subscription Order form in theReaders Services section towardsthe end of this issue and sending it toWorldwide Subscription Service atthe address shown on the form.Subscribing to Elektor Electronicsbrings other advantages as well,which are advertised in the magazinefrom time to time.

Elektor Electronics, morn than pllls: magnzlincil

milittuttaraga!

Do ice Prodrimuning Solutions

(6,0

47 ,, '218,

_

9,0 cot??

~-11az11tabe 48

Islogrammers from 4,135 MQP Elec rohie, Park Road Cen re, Malmesbury, Wilts SNI6 OBX, England

Phone: 01 666 825 666 Fax: 01 666 825 141 email: mqp@compuserve.com

0 0

TEACH YOURSELF A

each Yourself

Elektor Elektronics ( PO

D Box 1414

orchester England Tel:+ -44(0 )/ 1 305

ax:+44(0)/1 305

In straightforward language, Teach Yourself Word 97 describes all basic functions of word

processing program Word 97. Not only entering, editing and formatting text, but

also more advanced aspects such as Tables and Graphics Layout are explained. Auto

correction, auto text and WordArt, and many more, are discussed briefly but

effectively. A clear list of contents and an index make this a very accessible and easy -

to -use booklet, in which any information on how to use the extensive word

processing package can always be found readily and speedily.

80 Pages, Size 17 x 23,5 cm ISBN 0905705 59 9

Price:f6.00

b .khing u) 8YH 50 995 50 996

ORELECTRONICS %oil THE ELECTRONICS & COMPUTER MAGAZINE

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(111G), subject to change without prior notice, exclusive of 11.5% VAT

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P&P: Airmail, recorded delivery. Europe: 111G 15.00 for weight to 1kg.Outside Europe: BIG 15.00 for weight up to 250g. Extensive orderinginfo supplied with catalogue. Please ask for a C -I orderform.

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ELECTRONICSgoo,

WOMAN ENGINEERS CONTINUE TO SUCCEED20th 'Young Woman Engineer of the Year' Award

At the 1997 'Young Woman Engineer of the Year' ceremony, Bernard Hubbard,advertising manager of Elektor Electronics (Publishing), presented the finalistsfor the award with a complimentary subscription to Elektor Electronics. In thepicture with Bernard are (I to r): Claire Drew (winner of the 1997 Young WomanEngineer of the Year Award). Clare Johnson (finalist for the Mary GeorgeMemorial Prize), Patricia Dooley (third -prize winner), Vicki Houston (runner-upfor the Award and winner of the WISE prize), Abigail Small (winner of the MaryGeorge Memorial Prize), Anita Hales (finalist) and Donna Meakin (finalist).

Claire Drew, a systems engi-neering manager with GECMarconi Avionics, waselected '1997 Young WomanEngineer of the Year' at aspecial ceremony held inLondon in January, makingher the twentieth recipient ofthe coveted engineeringaward, which was inaugu-rated in 1978.

Claire, 30, who decided togo into electronics after at-tending a Careers Conven-tion, was presented with acheque for £1000 and a silverrose bowl by Claire Curtis -Thomas, Member of Parlia-ment for Crosby, which is, co-incidentally, the town whereClaire was born and edu-cated.

Runner-up and winner ofthe WISE Prize was VickyHouston, a Technical Authorwith Yarrow Shipbuilders,GEC Marine, Scotstown,Glasgow, who received acheque for £600. The WISEPrize is donated by the theWISE (Women Into Science

and Engineering) e.The third prize, a cheque

for £300, was won by PatriciaDooley, 29, Software Devel-opment Manager with GPTin Coventry.

The other two finalists forthe award were Anita Hales,29, and Donna Meakin, 27.Anita is a software engineerwith GPT Payphone Systemsin Liverpool. Donna is aStage 4 Systems Engineerwith the British AerospaceMilitary Aircraft Division atWarton Aerodrome.

The Mary George Memor-ial Prize was won by AbigailSmall from Preston, Lan-cashire. Abigail, aged 23, is aDesign/Support Engineerwith British Aerospace Mili-tary Aircraft Division atWarton Aerodrome. Thisaward, a cheque for £300 anda silver salver, is made to ayoung entrant showing par-ticular promise as an Incor-porated Engineer.

Runner-up for the MaryGeorge Memorial Prize was

Clare Johnson, 22, fromBournemouth, who is an As-sistant Engineer with Sie-mens Plessey at Christ-church.

At the presentation cere-mony, Claire Curtis -Thomas,an engineer and mother aswell as an MP, told the audi-ence: "If you are a woman,the odds are still stackedagainst you being an engi-neer."

The President of theIELIE, the Institution of theElectronics and Electrical In-corporated Engineers, whojointly with the CarolineHaslett Memorial Trust spon-sored the awards, Mr C WDonnay, said that when thefirst 'Young Woman Engineerof the Year' award wasstaged in 1978, only sevenper cent of incorporated en-gineers were women; thisfigure has now risen to 14per cent.

Claire Curtis -Thomas re-ported that UK engineerscreated 40 per cent of the

c-ountry's Gross DomesticProduct (GDP). "If we cre-ated a few more engineers,what an impact that wouldhave on the country's econ-omy."

In bringing the ceremonyto an end, the President pon-dered whether in a fewyears's time, if girls contin-ued to out -perform boys insecondary and tertiary edu-cation, the 1EEIE would haveto stage a male equivalent ofthe competition.

Present at the ceremonywas The Rt Hon BaronessWilliams of Crosby (ShirleyWilliams), who presented thefirst YWEY award in 1978 toErzsebet Kibble, who wasalso present. in fact, fifteen ofthe previous nineteen hold-ers of the title were present atthe ceremony.

DIGITAL TELEVISIONTO BE SWITCHED ON

THIS YEAREuropean authorities havegiven the go-ahead for digi-tal terrestrial television ser-vices to start in the UK thisyear; British Digital Broad-casting (BDB) has beengranted the licenses to oper-ate 15 television channels inthe UK.

BDB, a joint venture be-tween the Carlton andGranada companies, had toget clearance from the Euro-pean commission for theventure, originally an-nounced last June, owing tofears of monopoly.

Granada owns shares inboth BDB and BSkyB. As wellas providing paid -for chan-nel content to BDB's services,BSkyB will begin offering itsown digital satellite services.The European Commissionexamined the situation forpossible conflicts of interest.

Digital television is ex-pected to bring about a revo-lution in television whenbroadcasts begin. New tech-nology means that peoplewill be able to pick up manymore channels with their ex-isting sets and aerials; all thatis needed is a set -top box thatis expected to sell for about£200 (SUS320).

All existing terrestrialchannels wilt be availabledigitally and free, and theywill be joined by several newfree channels. In addition,

Elektor Electronics 3/98 liL

ELECTRONICSgoat

SOME EVENTS INMARCH

ICAT'98 - Integrating CAD/CAM and associatedtechnology at the NEC,Birmingham 3-5 March.

4 March-Writing GoodTechnical Reports(IE.E1E*)

10 March-Earthing andbonding (IEEIE*)

17 March-EMC for ProjectEngineers (IEEIE*)

17-19 March-NepconElectronics at the NECBirmingham

27 March-Effective Tech-nical Presentation(IEEIE')

30 March-Fibre Optics forEngineers (IEEIE')

30 March-Mobile Internet98 (IBC, phone0171 453 2161)

* Phone 0171 836 3357Fax 0171 497 9006

extra channels will be avail-able for a subscription fee:these include dedicated filmand sports services, amongthem names already knownto satellite and cable televi-sion viewers.

This is made possible be-cause digital broadcast sig-nals take up less frequencyspace and can therefore besqueezed together in a nar-row channel without affect-ing picture quality. In fact,digital television should offercrisper pictures and higherquality sound. It also allowsextra services such as Teletextand Ceefax to offer greatlyenhanced pages, includingpictures, that will appearmuch more like Internetpages.

Digital television alsoopens up the possibility of in-teractive services, such ashome shopping and banking.These are expected to emergesome years after basic pack-ages have been taken up, asit would be too difficult tostart them up at the sametime as many new channels.British Digital Broadcasting25 KnightsbridgeLondon SW1X 7RX.

NEW HIGH -BANDWIDTHPHONE CONNECTIONS

BT (British Telecommunica-tions) has announced a trial

of a digital service offeringhigh -bandwidth Internet andmultimedia access via exist-ing telephone lines. The tech-nology, called BT HomeHighway, gives householdersthe choice of analogue or dig-ital connections, so that theycan make phone calls anduse a computer connected tothe Internet simultaneously.

Another benefit would bethat customers could retaintheir existing phone number,equipment and additionalphone services. The system isto be tried in 300 homes start-ing early next year. It will beseveral times faster than mostexisting modem connections.

During the trial, BT willtest a number of price op-tions to see how much peo-ple are prepared to pay forsuch a service.

The service is designed tobe as easy to use as possible,with users simply having toadd additional connectionports (analogue or digital, asrequired) in their home, inaddition to their existing tele-phone outlets.BT, 81 Newgate StreetLondon EC1A 7AT

BRITAIN GOES DIGITALBritain is fast becoming a dig-ital nation. Five per cent ofhomes in the UK are con-nected to the Internet, and 22per cent have access to a mo-bile phone, according to fig-ures released by the Officefor National Statistics. The re-sult of a survey carried outlast year showed that thenumber of households withaccess to digital technologysuch as the Internet, mobiletelephones, fax machines,and satellite and cable televi-sion is growing steadily.

Other findings were: 29 per cent of households

have a home computer;in 1997, 94 per cent ofhouseholds had a tele-phone, compared with 42per cent in 1972;of those with telephones,eight per cent also had afax and 35 per cent had ananswering machine orservice;Only one per cent ofhousehold have no televi-sion, but 27 per cent ofthose with a televisionhave a satellite or cable re-ceiver;

ten per cent of house-holds have a second tele-phone line supplied by acable company.

Office for National Statistics1 Drummon GateLondon SWIV 2QQ

NEWLY FORMED ENGI-NEERING INSTITUTION

WELCOMES THIRD BODYAt the Extraordinary GeneralMeeting of the Institute ofEngineers and Technicians(IET), members voted over-whelmingly to amalgamatewith the Institution of Incor-porated Engineers in Elec-tronic, Electrical and Me-chanical Engineering.

Formation of the Institu-tion of Incorporated Engi-neers in Electronic, Electricaland Mechanical Engineeringwas agreed early last year bymembers of the Institution ofElectronics and Electrical In-corporated Engineers (IEEIE)and the Institution of Me-chanical Incorporated Engi-neers (IMechIE) to combine.

The merger of IET, IEEIEand IMechIE will create acombined membership ofsome 38,000. It will be thefourth largest of all the engi-neering institutions, creatinga powerful voice and a posi-tive and exciting way for-ward for Incorporated Engi-neers and Engineering Tech-nicians across the disciplinesof electronic, electrical andmechanical engineering.IEEIE (Jenny Poulton)Savoy Hill House, Savoy HillLondon WOR OBS

LAPTOP MISERYPeople using laptop comput-ers can, and frequently do,suffer from a catalogue ofhealth problems, includingheadaches and eye, back andarm pain, according to theUK's largest union, Unison,Which surveyed 500 careersadvisers. It called for achange in working practicesand to have laptops replacedby office -based PCs.

Careers advisers have tocarry laptops between schooland college sites, often overlong distances and some-times work on them whilethey travel on buses or trains.Unison says some laptopsweigh up to nine kilogramswhen they include printers

and paper.Unison, 1 lvlabledon Place,London, WOE 9AJ.

DATABASE REGULA-TIONS NOW IN FORCE

On 1st January this year theCopyright and Rights in Data-bases Regulations 1997 cameinto force. These new regula-tions are designed to imple-ment a European Union di-rective aimed at protectingthe investment of money,time and effort that goes intocompiling databases.

The regulations makechanges to the system ofcopyright for databases: theycreate an important new,free-standing right to beknown as 'database right'.This is a right to prevent theunauthorized extraction ofthe whole or a substantialpart of the contents of a data-base, except for use in re-search, or by educational orlibrary facilities; in otherwords, to bring the protec-tion of the Copyright, Designsand Patents Act 1988 to bearon databases.DTI Press Office1 Victoria StreetLondon SW1H OET

NEW EURO COMPANYFOR TOSHIBA

Japanese computer manufac-turer Toshiba has created anew London -based sub-sidiary company to maintainand develop its interests inEurope. The new company,Toshiba of Europe, will over-see the operations of the cor-poration's 27 affiliates andsubsidiaries in Europe andRussia.

The new company willsurvey market trends andgather information on thebusiness environment of Eu-rope, and support ToshibaCorporation in developingregional business strategies.Toshiba Europe LtdAudrey House, Ely PlaceLondon EC1N 6SN.

'SILENCE MACHINE'CAN BLOCK OUT NOISE

POLLUTIONRarely does a day pass with-out some form of 'off-stageoffensive noise polluting theenvironment where wework, live or sleep. Whether

412Elektor Electronics 3/98

ELECTRONICSNew

it is from traffic, constructionequipment, over -amplifiedmusic, animals or the howlsof a child having a tantrum,noise remains an ever-grow-ing problem.

Now, Professor Selwyn.Wright in the School of Engi-neering at the University ofHuddersfield in northernEngland has developed theworld's first device for block-ing out sound electronicallyboth indoors and out. It iscalled the Electronic Con-trolled Acoustic Shadow Sys-tem (ECASS) and creates a'silent shadow' that can maskmost sound over a wide area.ECASS has already proved asuccess at masking single -fre-quency noise, such as thatcreated by generators orother machinery, and Profes-sor Wright is now workingon a commercial version.

The basic principle behindthe device is simple: a com-puter generates the samenoise as the 'problem sound',but reverses the sound waves(phase reversal). This is callednegative replica. A bank ofmicrophones picks up the of-fending noise and feeds itinto the computer, whichthen analyses the sound andbroadcasts its exact electronicopposite via a further bank ofloudspeakers, thus cancellingout the original sound to pro-duce ... silence.

Although sound -blockingdevices using this type oftechnology have beenaround for some years, theyhave been capable of work-ing indoors only and over asmall are, for example, in air-craft cockpits. Research onthe problem started in theUnited States and concen-trated on reducing noisefrom air-conditioning sys-tems in hotel rooms.

There are large physicaldifferences between this typeof device and the freefieldapproach used for ECASS.For example, the quiet zonein enclosures is confined to afraction of a wavelength ofthe detector, whereas forECASS the zone extends toinfinity,_no matter what thefrequency.

Conventional methods ofreducing low -frequencysound over large areas in-volve building heavy and ex-pensive structure to providea solid barrier. These struc-

tures are not only expensiveto install, but also difficult toremove once built. Electronic'walls', on the other hand,can be tailored to a particularapplication and are light andeasily removed to a new site.

Computer modelling hasdemonstrated that 'shadows'such as those created byECASS can be superior tothose generated by solid bar-riers. Detailed analysis pre-dicts that deep shadows(more than 100 dB) are possi-ble, indicating that practicalshadows (>20 dB) are poten-tially achievable.

The initial work on ECASSwas funded by YorkshireElectricity, a power distribu-tion company that wanted tosilence low -frequency hum-ming from its electricity sub-stations in residential areas.Since then, many industrialconcerns have expressed aninterest in continuing devel-opment work.

The construction industryin particular has approachedProfessor Wright look intothe problem of noise onbuilding sites. Other organi-zations to have approachedhim range from the RoyalOpera House, Covent Gar-den, London, to the Euro-pean Space Agency. Al-though proven to work,ECASS is still in the develop-ment stages and it is ex-pected to be three years be-fore a commercial system isavailable.

The costs is likely to be afew thousand pounds ster-ling, which would make itpractical only for commercialuse. This would tackle prob-lems of constant machinerysounds from rotating ma-chinery, such as generators/motors and mills, many ofwhich have to operate 24hours a day to remain com-petitive.

Nevertheless, ProfessorWright does not rule out thepossibility of a domestic ver-sion in the near future."Computers are now sophis-ticated enough to handle un-predictable noise such ashuman speech and music",he said. "It does sound likescience fiction, but it is nowscience fact. This could havea real impact on people'slives."

Eventually, ProfessorWright would like to see the

machine used to restorepeace in the natural environ-ment by creating 'quietzones' where all excessivenoise from cars, trucks andfactories would be blotted.

The system developed byhim and his team over thepast three years comprisesthe computer, eight loud-speaker and eight micro-phones and has been set upin a purpose-built room atthe university.

The anechoic facility mea-sures 6 x 6 x 5 metres. Theeight -channel system isbased on a Texas InstrumentTMS320C32 processor usinga two -tap filter and a circularbuffer technique to imple-ment the delayed version ofthe update algorithm.

This allows easy algo-rithm implementation insoftware and significantly re-duces computation time for alarge number of channels. A16 -input, 8 -output PC16108provides a 12 -bit interfacewith the external equipment.This board contains three se-lectable levels of gain: 1, 10 or100.

The cancelling stereoloudspeakers (secondarysources) are each 20 W con-taining their ow -n power am-plifier and power supplies (inpairs); their frequency re-sponse is 32 Hz to 20 kHz.The battery -powered stereopreamplifiers have a fixedgain of about x100 and a fre-quency response of 30 Hz to15 MHz_

The simulated primarysource is constructed from 1620 cm (8 in) high loudspeak-ers rated at 20 W. These aremounted on a square baffleand powered by a 120 W am-plifier. There is provision todrive individual banks ofspeakers with relative phasevariation.Professor Selwyn WrightSchool of EngineeringUniversity of HuddersfieldQueensgate, HuddersfieldWest Yorkshire BM 3D11

MICROCHIP CREDITCARD GOES ON TRIAL

A new type of credit cardwith a concealed microchiphas gone on trial for the pay-ment of goods and servicesin two towns in the UK.

The microcard, which isexpected to make enormous

CORRECTIONSWe apologize for some er-rors in the final instalmentof the 'You can win thismagnificent prize' conteston page 9 of our February1998 issue.

At the right-hand bot-tom of this page it isstated:'...the correct an-swer to question 3 andstick ...'; this should haveread:'...the correct answerto question 4 and stick...'.

The months on thefour stickers were statedincorrectly as January1998'; they should haveread 'February 1998' (Ion-ization Circuit: March1998). Obviously, thesestickers will be accepted asif they had carried the cor-rect month.

changes in the way Britishshoppers pay for their goods,is on trial until the middle ofthe year. The project is beingadministered by the Associa-tion for Payment ClearingServices.

Fifteen of the biggestnames in banking havejoined forces in the trial ofthe microcard that providesnot only a far more secureservice for both cardholdersand suppliers than the tradi-tional plastic payment cards,but has a great potential topresent a variety of informa-tion about the cardholder.

The prototype microcardon trial retains the traditionalmagnetic stripe on the back,but has a microchip hiddenunder a gold square on itsfront. It operates as a credit,debit and loyalty card, andelectronic purse, all rolledinto one.

Assuming that no particu-lar problems emerge, it isthought likely that an indus-try decision will be made tostart a rolling programme ofproducing microchip cardsover the next two or threeyears. This will involve re -is-suing credit, debit and cashmachine cards together withthe national installation ofchip -enabled terminals.The Association for PaymentClearing Services, MercuryHouse, Triton Court, 14 FinsburySquare, London EC2A 18R.

Elektor Electronics 3198 13

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14 Elektor Electronics 3198

POWER AMPLIFIER MODULES -TURNTABLES -DIMMERS -LOUDSPEAKERS -19 INCH STEREO RACK AMPLIFIERS

1 I SERVICE v LARGE (Ael) S.A. SO STAMPED FOR CATALOGUE *

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THOUSANDS PURCHASEDBY PROFESSIONAL USERS

THE RENOWNED MXF SERIES OF POWER AMPLIFIERSFOUR MODELS:- MXF200 (100W - 100W) MXF400 (200W -,- 200W)

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FEATURES: *Independent pone: supplies with two tercklal transformers Twin LED. Vureters taw: canoe:1 a Litserinatri en./o6 switch a XLR connectors * Standard 77UnV inputs Open and short wantprod a Salmi Mos-Feta for stress tree pow delivery into vinualty any toad * High slew rate e Wry !owdistortion * Altroiniurn cases MUM A 140900 fan cooled with D.C. loudspeaker and Surreal protection.

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MXT-400W19'11145` (3U),1312"MXF600W19-s145' (3 U). 01 3.UMW W10-0415 (3U)&1144.^

PRICES:-MXF200 £175.00 MXF400 £233.85MXF800 £329.00 MXF900 C449.15SPECIALISTCARRER DEL 612.56 EACH

Advanced 3 -Way Stereo Active Cross:Ores housed in a 14" z 1U case. Each channel has Ewee level controlstan. mid A too The removable front fascia allows access to the programmable OIL switches to adjust the:roes -user Ire '4. e -Of. Bass -Mid 2501500400Hz. MidiTop 1.6119CHz all at 24d8 per octave. Hass invert twiddlesen each bay, c- - mommif 775nW input,outzst FLOE cons:At:We with OMP rain arneiliT yr and cocottes

Price 0117.44 - £5.00 P&P

STEREO DISCO MIXER wit.. 2 a 7 band& R graph,: equallars rem bar ;rapt

LED Vu maim. MANY OUTSTANDINGFEATURES:. Madders Echo with repeal Aspeed control, OJ Me with talk -overswitch, 6 Channels with individual fadersplus =CIA fade, Cue Headphone Monitor.Sound Effects. Useful combination of thefollowing Lipids: 3 turntables (meg). 3mies 5 Line for CO, Tape, Video etc.

Price £144.99 C5.00 P&P SIZE 4a 2 1240 :120mim

I ,(81 4A iq:1--rvIaltehtelli

,r1111.'111--41a411:141713:1-11:ialaitia.1.111110 SUPPLIED READY BUILT AND TESTED.115ne ratefitda ace eatiate a Ivarklt Ands repetadon Sr dusky. no Lee. oe Afte .patlarituna n a reuse prim_ rowmodels are avadeate to sari eta needs of the EveleastonaI and bobby ,artel I A-ea:retry, irowoneertat ad 14-F1etc. Yawn oRspArlaq Pratt. NOTE that MI rausels iriclada toroidal pa., .494. talastal haat stet ghee Mr. P CR. motin.. cams te power cerivAtiala W. envier. AN stnEels are open ant s. --et tinted prod

THOUSANDS OF MODULES PURCHASED BY PROFESSIONAL USERSOMP/MF 100 Mos-let Output power 110 wattsR.M.S. into 4 ohms, frequency response 1Hz 100KHz-3dB. Damping Faclor 300, Slew Rate 45ViuS.T.H.D. typical 0.002%, Input Sensitivity 500mV, S.N.R-110 dB. Size 300 x 123 z 60mm.PRICE C40.85 - C3.50 P&P

OMP/MF 200 Mos-Fot Output power 200 wattsR.M.S. into 4 ohms, frequency response 1Hz - 100KHz-3dB. Damping Factor -300, Slew Rate 50V/uS,T.H.D. typical 0.001%, Input Sensitivity 500mV. S.N.R.-110 dB. Size 300 x 155 x 100mm.PRICE £64.35 - C4.00 P&P

OMP/MF 300 Mos-let Output power 300 wattsR.M.S. into 4 ohms, frequency response 1Hz 100KHz-3dB. Damping Factor 300. Slew Rate 60V/uS,T.H.D. typical 0.001%. Input Sensitivity 500mV, S.N.R.-110 dB. Size 330x 175 x 100mm.PRICE C81.75 - C5.00 PAP

OMP/MF 450 Mos-Fet Output power 450 wattsR.M.S. Into 4 ohms. frequency response 1Hz - 100KHz-3dB. Damping Factor >300. Slew Rate 75V/uS.T.H.D. typical 0.001%, Input Sensitivity 500mV, S.N.R.-110 dB, Fan Cooled. D.C. Loudspeaker Protection, 2Second Anti -Thump Delay. Size 385 x 210 x 105mm.PRICE C132.85 - £5.00 P&P

OMP/MF 1000 Mos-let Output power 1000 wattsR.M.S. into 2 ohms, 725 watts R.M.S. into 4 ohms,frequency response 1Hz - 100KHz -3dB, DampingFactor - 300, Slew Rate 75V/uS, T.H.D. typical0.002'.. Input Sensitivity 500mV. S.N.R. -110 dB, FanCooled, D.C. Loudspeaker Protection. 2 SecondAnti -Thump Delay. Size 422 z 300 a 125mm.PRICE C259.00 - C12.00 PAP

NOTE MOS-FEY MODULES ARE AVAJ LA SEE IN TWO VERSIONS.STAN ONTO INPUT SENS SOOrnV, RAND WIDTH I 001012.PEC (PROFESSIONAL EQUIPMENT COMPATIBLE) INPUT SENS77Srnli, KANO WIDTH SOKH. ORDER STANDARD OR PEC.

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I. .16-

Join the Piero rerobrbiont The kw dynamic MESS (no voice coil) Cl a Piezo tweeter produtes an imorored,rnsient response wit a lower distortion level titan ordinary dynansk tweeters. As a crossover is not requiredWiest amts can be added to emitting speaker systems of up to 100 watts (more 11 two are pal m series_ FREEEXPLANATORY LEAFLETS ARE SUPPUED WITH EACH TWEETER.

TYPE 'A' (KSN1036A) 3' round with protective wire mesh. Ideal for74,4 bookshelf and medium sized Hi-Fi speakers. Price £4.90 - 50p P&P.1, TYPE '13' (KSN1005A) super horn for general purpose speakers.

disco and P.A. systems etc. Price C5.99 - 50p P&P.TYPE 'C' (KSH1016A) z5" wide dispersion horn for quality Hi -Fl sys-tems and quality discos etc. Price C6.99 - 50p P&P.TYPE '13' (K5H1025A) 2'x6" wide dispersion horn. Upper frequencyresponse retained eslendlng down to mid -range (2KHz). Suitable for high

C Ton e quality Hi -F1 systems and quality discos. Price 09.99 - 50p P&P.TYPE'E' (KSN1038A)31." horn tweeter with attractive silver finish trim.Suitable for Hi -Fl monitor systems etc. Price 05.99 - 50p PAP.

- LEVEL CONTROL Combines. on a recessed mounting plate, level controland cabinet input jack sockeL 85185mM. Price 04.10 - 50p P&P.

ALL EMINENCE UNITS e OHMS IMPEDANCE8" 100 WATT R.M.S.RIE8-1 00 GEN. PURPOSE, LEAD GUITAR, EXCELLENT MID, DISCO.RES. FREQ. 72Hz. FREQ. RESP. TO 4KHz, SENS 97d8. PRICE C32.71 - C2.00 PAP10' 100 WATT RMS. MET 0-100 GUITAR. VOCAL KEYBOARD. DISCO. EXCELLENT MID.RES. FREO. 71Hz., FREO. RESP. TO 7Kfir., SENS97d8. PRICE 033.74 - C2.50 P&P10' 200 WATT R.M.S. ME1 0-200 GUITAR. KEY ETD. DISCO. VOCAL, EXCELLENT HIGH POWER MID.RES. FREO. 694z. FREQ. RESP. TO ISKHz... SENS 99dB. PRICE 043.47 - C2.50 PAP12. 100 WATT R.M.S. ME1 2-100LE GEN-PURPOSE, LEAD GUITAR, DISCO. STAGE MONITOR.RES.FREQ. 49Kr_ FREQ. RESP. TO EKHz. SENS 100dB. PRICE 035.64 - C3.50 PAP12' 100 WATT R.M.S. MET 2-1 OOLY (TWIN CONE) WIDE RESPONSE, P.A.- VOCAL STAGEMONITOR. RES. FR E0 4220.. FREO. RESP. TO 10KHz, SENS 913d8. PRICE 036.67 - C3.50 P&P12" 200 WATT R.M.S. MEI 2-200 GEN. PURPOSE. GUITAR. DISCO. VOCAL EXCELLENT MID.RES. FREO. 55Fiz. FREQ. RESP. TO MHz, SENS sees. PRICE 046.71 - C3.50 PAP12 300 WATT R.M.S ME12-300GP HIGH POWER BASS. LEAD GUITAR. KEYBOARD. DISCO ETC.RES. FREQ. 47Hz. FREQ. RESP. TO Skits SENS 10348. PRICE 070.19 - C3.50 P&P15" 200 WATT R.M.S. MEI 5-200 GEN. PURPOSE BASS. INCLUDING BASS GUITAR.RES. FREQ. 46Hz. FREO. RESP.TO 5KHz, SENS 99d8. PRICE 050.72 - C4.00 PAP15' 300 WATT R.M.S. M Et 5-300 HIGH POWER BASS. INCLUDING BASS GUITAR.RES. FREQ. 3914z. FREO RESP. TO 3KItz. SENS 10348. PRICE 073.34 - C4.00 PAP

z.,a Fly lec....test,Ks. leSsqr.&: raze advantage al die ta-1- arsderclosuredesigra_ Baal mOdets sh.ctio wzbty_ .".03speakers wan ,...are fined gnites axle dispersmn

_ _ , extruced aRminnovi crui.w.i...wv and steel: nent*i with h...41.1 &n Stack c0.-EnnO The enelesures

- , =-wilt Pod taK far 0170.7 -al im.rlsrwaker sm-lCs

POWER RATINGS QUOTED IN WATTS RMS FOR EACH CABINETFREQUENCY RESPONSE FULL RANGE 45Hz - 20KHz

ibl FC 1 2-1 00WATTS (100d8) PRICE C159.00 PER PAIRtbt FC 1 2 -2 00WATTS (100d8) PRICE £1 75.00 PER PAIR

SPEC/ALISTCARR ER DEL £12 SO PER PAIR

OPTIONAL STANDS PRICE PER PAIR 049.00Delivery £6.00 per pair

'Pt.?

0O

PRICES: 150W 049.99 250W £99.99

isiii

400W C109.95 PAP C2.00 EACH

THREE SUPERB HIGH POWERCAR STEREO BOOSTER AMPLIFIERS150 WATTS (75 - 75) Stereo, 100WBridged Mono250 WATTS (125 - 125) Stereo, 250WBridged Mono400 WATTS (200 - 200) Stereo, 400WBridged MonoALL POWERS INTO 4 OHMSFeatures:* Stereo. bridgable mono * Choice ofhigh A low level Inputs * L A R levelcontrols * Remote on.olf * Speaker &

on . - 2 R. 4IALL EARBENO ER UNITS 8 OHMS sitcor ESE-WIEEII0-50Mmon an 1,m1 erpsesnrAtare,.... 416 ohm)B ASS, SINGLE CONE, HIGH COMPLIANCE, ROLLED SURROUND8' SOwatt E88.50 DUAL IMPEOENCE. TAPPED 418 OHM BASS. HI -Fl. IN:CAR11 ES. FREQ. 4014z. FREQ. RESP. TO 7K Hz SENS 97d8. PRICE £8.90 - C2.00 P&P10' 50WATT 6310..50 DUAL IMPEDE/4CE. TAPPED 41 OHM BASS. HIFl. IN -CAR.RES. FREQ. 40Hz. FRED. RESP. TO Mts, SENS. 99dB. PRICE 013.65 - C2.50 P&P10' 1 00WATT 6310.100 BASS. HI-FI, STUDIO.RES. FREQ. 35Hz. FREQ. RESP. TO MHz. SENS 9648. PRICE C30.39 - £3.50 PAP12' 1 OOWATT EDT 2-100 BASS. STUDIO. HI -Fl. EXCELLENT DISCO.RES. FREO. 26Hz. FREQ. RESP. T03 ICHz. SENS 93dB. PRICE 042.12 - £3.50 PAPFULL RANGE TWIN COME, HIGH COMPLIANCE, ROLLED SURROUND

60WATT ES 5.6 OTC awn CONE) HIFl, MULTIARRAY DISCO ETC.RES. FREO. 63Hz. FREQ. RESP. TO 20KHz, SENS 92dB. PRICE £9.99 - C1.50 P&P

60WATT E86-60TC (TWIN CONE) HI -Fl, MULTI -ARRAY DISCO ETC.RES. FREQ. 33Hz. FREQ. RESP. TO 20KHz., SENS 94d8. PRICE 010.99 - 1.50 P&P8' 60WATT EBB-60TC (TWIN CONE) HI -Fl. MILTI-ARRAY DISCO ETC.RES. FREQ. 40Hz. FREQ. RESP. TO IEKHz. SENS 89d8. PRICE C12.99 - C1.50 P&P10' 60WATT EB1 0-60TC (TWIN CONE) HI-FI. MULTI ARRAY DISCO ETC.RES. FREQ. 35141. FREO RESP. TO 1 2KHz. SENS 9548. PRICE 0111.49 - C2.00 PAP

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Elektor Electronics 3 98

variable power supply0-241Aor2A

ideal for the small workshop

The variable power supply described inthis article is the latest in a long line ofpower units published in this magazine

over the past fifteen years or so.Because of its wide voltage range andpresettable current limiting, it is ideally

suited to general-purpose applications ina small electronics workshop.

Design by K.A. Wa[raven

A variable power supply, a soldering ironand a multimeter form the minimumbasic equipment required in a small elec-tronics workshop. Unfortunately formany, a commerdal variable power unitis not exactly cheap, which is an excellentreason for building one from scratch. Thepower source described in this article isideal for that purpose. It has a number ofpreset facilities, its design is straightfor-ward, and it has the facility to be con-nected to a digital voltmeter - DVM -module to display the output voltage andcurrent. Moreover, apart from somepower field-effect transistors -FEB - it isconstructed from readily available stan-dard components. Finally, it may be con-structed to provide an output current ofI Aorof2A.

416 Elektor Electronics 3/98

Visit our Web site at http: ourworld.compuserve.com hoinepages eiektor_uk

DESIGNThe basic setup of a power source isfairly simple see Figure 1. The alter-nating voltage available at the sec-ondary of the mains transformer isconverted into a direct voltage by full -wave rectifier bridge B1. The level ofthe direct voltaft is raised by two par-allel -connected field-effect transistors,Ti and 17, located between the nega-tive output terminal and ground.

The transistors are driven by twocontrol circuits based on operationalamplifiers - op amps - IC1 andThese circuits continuously comparethe output voltage and the output cur-rent with preset wanted values.

In contrast to usual power supplydesigns, the FErs are not arranged assource followers. This is a deliberatechoice intended to save energy. Thisbecomes clear when it is realized thatthe potential at the gate of the transis-tors needs to be about 6 V higher thanthat at the source. In the presentdesign, this is effected by driving thegate with reference to the internalearth of the power unit and not withreference to the positive output rail asis usual.

An auxiliary voltage of +9 V for thecontrol circuits is provided by regula-tor IC3. This voltage also functions asreference potential: the wanted valuesfor the voltage control and currentcontrol circuits are set with P1 and P.,respectively.

VOLTAGE REGULATIONThe output voltage across capacitor C2floats, that is, the positive capacitorterminal is linked to the non -regulatedsupply voltage (++). The negative out-put rail is linked to the drains of tran-sistors T1 and T,.

The reference voltage is measuredwith reference to the negative outputrail, which is why the input of IC1 isconnected via R3 -R4 and R6 -R2. Theseresistor combinations ensure that theoutput voltage is compared with thewanted value set by P1

This arrangement works fine aslong as the ratios R3:124 and R6:R2 areprecise, which means that the resistorsmust have a tolerance 5 1%.

The differential voltage at the out-put of ICI is used to control the poten-tial at the gates of the FErs via diodeD1. Normally, the transistors are dri-ven into saturation via R3 and cut offby the voltage circuit or the currentcontrol circuit. Diode D7 is added tolimit the maximum gate potential ofthe two transistors; this shortens thereaction time when the devices are inthe saturation mode.

Resistors R10 and RH prevent anyhigh -frequency oscillations.

CURRENT REGULATIONThe output current is monitored in the

Figure 1. Circuit diagram of the variable power supply.The output voltage is set with P1 and the output currentlimit with P2. Digital voltmeter and ammeter modules maybe connected to +V and -V, and +1 and -1, respectively.

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traditional manner by measurement ofthe voltage drop across a shunt resis-tor. In the present circuit, this shuntresistor is formed by the source resis-tors, R12 and R13, of the 1-t s.

Since the differences ,betweenrrs may be significant, the

transistors have been given a fairlylarge source resistor of 1 I. So, whenthe output current is, say, 2 A, that is,a current of 1 A flows through eachtransistor, the potential drop across

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each resistor is 1 V.The two voltages are averaged by

resistors R0 and R14, so that, even if thesplit between the two transistors is farfrom ideal, the total current is mea-sured at all times. The average voltagelevel is compared with the wantedvalue, set with P. in IC,. If the currentis unduly large, the output voltage ofthe op amp drops and the transistorsare cut off via diode 133. To ensure thatthey are firmly cut off, diodes D1 and

V

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Elektor Electronics 3198 17

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Figure 2. The design of the printed -circuit board allows it to be mountedbehind and in parallel with the front panel of the enclosure.

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D3 are Schottky types.Light -emitting diodes 13, and D4

serve to indicate that the voltage reg-ulation and current regulation respec-tively operate correctly. Note that thesediodes cannot be connected in serieswith Di and D3, since then the tran-sistors cannot be cut off completely.

It would be possible to give theop amps a negative supply line, but itis, of course, much simpler (and lessexpensive) to place the ups as shown.It is true that this raises the current byabout 2 mA, but in a power unit thishardly matters.

ALSO...Diodes D5 and D6 protect the circuitagainst too high a voltage and againstan incorrectly polarized voltage.

Resistor R15 drains away the tiny

Figure 3. Photographof the completed pro-totype of the variablepower supply. Themains transformerdictates the height ofthe enclosure.

18 Elektor Electronics 3 98

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Parts list

Resistors:= 1 kfl

R2. R4 = 46.4 kit 1%R3. R6 = 274 1%R5= 3.9 kialR7 = 15 kit (1 A version): 8.2 MI

(2 A version)R8, R. Al4 = 4.7 kitR/0. R,1 = 220 itRt2,R,3=1 it, 5WR15 = 3.3 kJ/ 1 WR16, R17 = 3.3 kftRla, R20 = 22 kitR19 = 2.7 kitR21. Res = 1.02 kft, 1%R22. R24 = 100 ICU, 1%Pi, P2 = 1 kit linear potentiometer

Capacitors:C,. C3 -C6. CI, = 0.1 pFC2 = 100 pF, 40 V, radialC7. Ca = 1000 pF, 63 V (1 A version):

2200 pF. 63 V (2 A version)C, = 100 pF. 16 V. radialC" = 10 pF. 63 V

Semiconductors:o = E380C3300:2200 rectifierDI. D3 = BAT85D,. D4 = LED, red. high efficiencyD5. D5 = 1N4001D7 = zener diode 5.6 V. 400 mW

12 = BUK455-100A orBUK106-50S (Philips Semiconduc-tors) - see text

Integrated circuits:IC,. IC, = TLC271CP

IC:= 7809

Miscellaneous:K1 = mains entry with integral on off

switch and 0.16 A slow -blow fuseTi, = mains transformer. 24 V. 1.25 A

(1 A version) or 24 V, 2.5 A (2 A ver-sion)

heat sink (for T, -T2): 1.2 K W'2 off chassis socket. 3.5 mmenclosure 80-100 x200 x 180 mm

(1 Aversion) or 100-120 x200x180mm (2 A version)

PCB order no. 980024 (see ReadersServices towards the end of thisissue)

optional: instruments for measuringthe output voltage and output cur-rent - see text

current through R6 and any leakage ofthe FEN and so, in fact, determines theminimum output voltage.

Capacitors C1 and C, improve thestability of the circuit and its perfor-mance at sudden variations in load.

VOLTMETERS ANDAMMETERSSeveral potential dividers (R1s-R24) areprovided on the printed -circuit boardto enable digital measuring instru-ments to be connected.

Divider 12.18-R20 is intended for cur-rent measurement It is in parallel withsource resistors RI, and Ri3 (II and 12).The digital ammeter or DVM module isconnected to +I and -L Most digitalmodules have a sensitivity of 0.2 V.Since the potential drop across R12 andR13 is 1 V when the output current is2 A, the attenuation of R1rRI9 is x 5.

The attenuator for voltage mea-surement consists of resistors R23 -R24(remember that the output voltagefloats). Assuming the same sensitivityof the module (0.2 V), the attenuationshould be x100 (20/02). The module isconnected between +V and -V.

Since most standard 3'h -digit mod-ules can measure up to 1.999 only, themaximum voltage that can be dis-played is 19.99 V. This difficulty may beovercome by the use of a module thatcan measure up to 3.999, or by increas-ing the attenuation to x 1000 (that is,giving R,1 and R23 a value of 100 14.In the latter case, the 'hundredths'digit is no longer available.

MODULE SUPPLYLINESPower for the modules maybe drawnfrom the regulated +9 V rail (via 0 Vand +9 V), but this is not always pos-sible. Many standard inexpensivemodules need a separate supply Infact, the available +9 V line may beused only when the supply rails andthe test voltage can be equal, that is,the common -mode range must liewithin the power supply range. Mod -

ides with an IC from the 7106 familydo not meet this requirement andthese must, therefore, be given a sep-arate supply.

There are, however, digital modulesthat can be used with the aid of a smallintegral voltage converter The specifi-cation of these invariably statesemphatically that they do not need anat Yilia y voltage. In all other cases, itmust be assumed that the moduleneeds an auxiliary voltage.

CONSTRUCTIONThe power supply is best built on theprinted -circuit board shown in Fig-ure 2.

Depending on the enclosure,potentiometers P1 and P, may bemounted directly on the board, sincethis is to be mounted behind, and inparallel with, the front panel on anumber of spacers. The heat sink forthe power transistors is mounted atthe back of the board. With luck, thefixing holes of the board coincide withthe space between two adjacent fins ofthe heat sink This would give a com-pact unit and ensure that the heat sinkcannot be touched accidentally - itgets pretty hot!

The transistors are soldered to theunderside of the board and screwedfirmly to the heat sink It is best to dothis in reverse order: bend the terminalsof the transistors to the required shape,mount the board on the heat sink,screw the transistors in place and thensolder them carefully with the solder-ing iron between board and heat sink.

It is not necessary to isolate thetransistors; in fact, from a thermalpoint of view, it is better not to. It is,however, essential to make sure thatthe heat sink does not touch otherparts and is well isolated from its sur-roundings. The use of insulating wash-ers, provided they are of good quality,is safer (use aluminium oxide types,not mica). Also, the use of heat con-ducting paste is a must.

Drill some additional ventilation

holes in the enclosure, both above andunderneath the heat sink. Considera-tion should be given to the use of asmall fan, because the inside of thesmall enclosure gets very hot. Stan-dard 12 V PC fans run well on 9 V (andare then also quieter). It is, of course,possible to provide a 12 V line with theaid of an additional 7812 voltage reg-ulator.

It is advisable to use a mains entrywith integral fuse mounted at the backof the enclosure. This _keeps the pres-ence of mains voltage inside the unitto a minimum

Note that DVM modules with inte-gral lighting draw a current of20-30 mA, and it is, therefore, advis-able to mount the voltage regulator ona separate heat sink of about 201CW-1.

A photograph of the completedprototype is shown in Figure 3. Notethat the operating controls on the frontpanel are limited to the two poten-tiometers, the indicator tins, and twochassis sockets for the output.

CHOICE OF OUTPUTCURRENTIf the power unit is intended to pro-vide a current of up to 1 A only, a2x12 V, 1.25 A mains transformer canbe used. It may then be possible to fitthe unit in an enclosure of 8-10 cmhigh. If an output current of up to 2 Ais envisaged, the current rating of thetransformer must be doubled, inwhich case the enclosure needs to be10-12 cm high.

The values of the components inFigure 1 are for the 1 A version. Somealterations in addition to the trans-former are necessary for the 2 A ver-sion: the value of smoothing capacitorsC-) and C7 must be increased to 2200µF,and the value of R7 must be halved to82 ka to ensure that when lc', is fullyopen, the output current is 2 A.

TEST AND INSPECTIONWhen the construction has been com-pleted, switch on the mains and check

Elektor Electronics 3/98 19

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the voltage at the test points indicatedin Figure 1 with a digital voltmeter.14Iote that the values in the voltage reg-ulation section based on ICI refer to aninput voltage of 28 V. an output volt-age of 24 V and no load. Those in thecurrent regulation section based on IC,and around the transistors refer to aninput voltage of 28 V, an output volt-age of 20 V, and a load of 1 A. ,

The circuit does not require settingup or calibration, but after verificationof the test voltages, it should be ascer-

tained that the output voltage is 24 Vand that an output current of 1 A or2 A, depending on the version, can beattained.

Also, check that the output voltagecan be reduced to nearly 0 V with Pi. Avalue of 0.2-0.3 V is acceptable, but ifthe output voltage cannot be reducedto below 1 V, the ratios R.:R3 and R6:R-,

are not equal This may be remedied byshunting It, or R4 with a resistor ofabout 1 Mil (the precise value needs tobe ascertained by trial and error) until

BUK series field-effect transistors

Many readers will be familiar with the Buz and inF types of field-effect transistor, but the BUK series used in the present power sup-ply is not (yet) so well-known.

The aux series comprises a number of versions permitting everlarger voltages and currents. The BUK455-100A used in the powerunit, for instance, can handle voltages up to 100 V. A noteworthyproperty of this FEr is its low thermal resistance of 1.2 K W. Thisenables it to dissipate more power (125 W) in a TO220 case thanthe popular 2N3055 in an S03 case (115 W). These are, of

the output voltage is a minimum.In case of the voltage module con-

nected to +V and -V, the meter mayshow a voltage that is not there. Theonly possible reason for this is anapparent inequality in the ratios

and 1:,4:R-5, which may hap-pen even if resistors with a 1% toler-ance are used. The error may be erad-icated by shunting R,1 or R-13 with aresistor of about 100 (the precisevalue needs to be ascertained by trialand error). (9a1.11241

course, theoretical values (cooling would have to be perfect), butin practice, with a heat sink of 1.2 K W--1, the transistor wouldbe able to dissipate 62.5 W at a :ST of 150 which is a lot. Nev-ertheless, to play safe, the dissipation in the power supply isdivided over two transistors.

The BUK106-50S, a so-called TOPFET from the same series,may also be used. This device is more expensive but has somespecial properties. It has two additional pins: one for a protec-tion supply input and the other for a flag output. When a supplyvoltage is applied to the protection supply input, the device willauto -protect itself against voltages higher than 50 V. When thathappens, the transistor conducts slightly, which is not necessar-ily a good thing in a power unit. It will switch itself off when itstemperature rises above 150 'C. which is a worthwhile facility ina power supply.

The flag output indicates when a protection circuit is enabled.This circuit is disabled by briefly switching off the supply volt-age at the protection supply input.

Both types of FEr may be used on the printed -circuit board.The protection supply input pin of the BUK106-50S is then auto-matically linked to the +9 V rail provided by IC3. The flag outputis not used.

Component sets to ELEKTOR ElectronicsWe are a mail order company and martu-factoring parts sets dedicated to ELEKTORsince 1985. The following sets included ellrequired components :

ELEKTOR-PCBIsoftvrare,according to the components list.to on ELEKTOR PCB.in high quality from maior manufacturerIC -sockets.

The sets included not description. mainstransformer and erictosure.

For prices and more informarons Wriase-x.s:t cur hOrnertacehttpillounvorld.compuserve.corn/

homepages/stelektron

970075 JFET tester 0 7 9115 digit DVM module 6 40

980002-1 80032 BASIC computerinc. BASIC -EPROM 986503 £ 32.39

980002-2 Extensionboard £ 43.45980004 Frequency dplayNFO stabilizer

rid PIC 986502 and dIsotay £ 38.18980023 .10.0 ': 2-t 47980025 E 11

970085 0. 21.585.36

980007 ,ophicirie f. FC £ 27.67970053 L. : Dower supply 12.51980021 E hatte^, 9 39

970068 5,aitnio reaz. competeint1. 976512 and 976014 47.75

970086 Running bah% si.ristmas 34.05970090-1 Electronic handyman

AT90S1200 7.18970090.2 Docktrigst_ 1. handyman £ 36.33

AT91351200 -16 £ 3.44974001 PIC controlled light barrier £ 25.41974010 D.C. protector £ 5.83974020 Octopush £ 11.09

STE

974037974038974053974070974072974076

Auto volume control £ 29.88Bass extension incl. trans! £ 19.25Carbooster incl. housing £ 20.67Object protect £ 8.05Rev(Mution) counter E. 25.61PIR-doorbell £ 14.24

970065 Hygrometer £ 26 22970066 Video copy processor

mains transformer £ 46.74970083 Stereo iiiii..uphone amplifier

incl. mains transformer £ 66.55970087 69 -metres receiver 7.58

970027 Distortion fun) unit £ 24.75970057 4 -way serial port switch £ 35.33970060 Analogue measurement £ 26.92970063 DC nullifier for oscilloscope

excl. PZ 41r42 43.25976513 PZ 5032 programmed £ 19.00976016 Disk source code PZ 5032 E 4.67970064 IR-volume control (10 k) E 30.30970077 Frequency meterievent cur 50.44970079 D;rsvi.or.ai n-i,orcr.thOnS. £ 16.76

970020 D.acc!:: :ester £ 10.24970023 Electron -c code lock E. 27.36970050 Chipcard reader/programmer

incl. ITT -connector £ 20.64Chipc.-ard connector ITT -Canon 6.45970053 Centronics relay card E 38.65970055 Charging buster 51 25.22970059 Data aquisition system £ 58.70

962008 Hexaciec keyboard for PC £ 37.03974012 Digttal tester E 2024974019 Active windscreen wiper £ 12.74974024 Switch mode power supply E 15.70974041 Stepper motor controller £ 8.91974042 ROB video amplifier £ 30.44974077 Supply board £ 34.05974078 Mains on delay circuit £ 10.11974100 Stand -alone -MIDI -synthesizer

'o Yamaha- ^_=_.i E 27_42

970025 Battery cc,.-:tion monitor 37.76970028 LRC-meter incl. transform. 0163.67

Stippler-ElektronikInh. Georg Stippler

P.B. 1109 D-86656 Bissingen / GERMANYTel. and Fax -49 9084 463

eMai I 0908-1463-0001 @i-online.de

970028 Enclosure -set £ 47.40970039 Temp.volt. contr. for DIAM £ 737970045 RC biswitch £ 14.08970046 Earth teackage crater

incl. case 435 E 36.97970048 800537 single board computerwo IC 2. incl.. software and battery £ 91.63972015 Mini progr. EEPROM £ 5.20972016 Mini proor PIC £ 4.70976005 E 7.50976007 :roars --s, £ 4.80

970021 1. r.---_er-',...-F.,tfE. 0440 w DVME 46.96

3.5 digit LC DVI.1 module £ 6.40970041 Long distance IrDa £ 38.89970042 4 -channel logic analyser £ 6.18970043 Compact 50 -watt audio amplifier

ind heatsink w/0 power supply 66.71970043-N Power snooty £ 65.15i7hr-

960112 Digital thermostat £ 57.33970022 2 -wire domestic alarm system

wio eur.kaure £ 35.43970031 Opticattcoax converter £ 17.22970036 Universal newer supply £ 12_58

r' 2793960096 Electronic fuse970003 Battery -operated AF -

signal generator £970006 Battery simulator970010 Eprom programmer976003 Software970037 tie -controlled mixer -board £

22.0317.8234.8314.8574.96

960094 Battery -operated AF -amp. £153.55UC 202 enclosure 2628

960095 'Actor contr. f. RIC models £ 33.42970007 Mutt LED running light £ 5.72970008 681-1011 emulator £ 78.67970009 Self-inductance meter £ 21.05970015 'Sneaking cloorheli £ 24.55

960089 Diongle switch incl. case £ 13.12960100 Magnetic -field meter incLease 22.63960113 Speed regulator Mot enclosure

arid knobs £ 29.55

970001 Monitor to guard fridge temperatr eincl. enclosre £ 26.01

966022 Small workshop disc 10.00

960068 Remote control by visible lightwin case. battery, brass E 23.18

960082 Guitar -effects switch £ 35.79960098 RS 232 data aquisition card

software 956508. 956018 £ 39.42960106 Primary -battery refresher £ 24.51960110 20 -bit A -D converter

Ma mains transformers £ 169.03964031 AC -mV -adaptor loci. case E. 10.96964062 Electrically isol. 12C bus 12.43964070 Mains voltage cleaner £ 25.49964082 EMI tracer £ 17.57964088 Stroboskop f. motorcycles £ 24.38964089 Capacitance comparator £ 11.62

".t

960079 50 Watt AF -amplifierpower supply Incl. heatsink £ 22_48

960107 10A -interface w/o optionind enckisure, software 966020 £ 32.63

960107-0 Parts 'optionally' £ 3.76960109 Headphones amplifier £ 12.03

Not mentioned sets for past issues arestill available !

All components and PCBs as singleparts available.

You also get these setsb our native dealer :

Indonesia :PATTRA ELECTRONICS41.Pagarish no.184:87 Bandung 40262JI.Dulatip no. 67 BandungTeliFax 022 433179Israel :Elektorcal Ltd.P.O.B. 41096 Tel Aviv 61410Tel. 03 6591991 Fax 03 6596244Sweden :PB Elektronik ABBox 5516 S-14105 HuddirmeTel. 08 7100370 Fax 08 7401806

r 000, 0 - ; c arges:All prices in without 15 % VAT (81W). Customers inside EU add price + P&P + VAT 15 -sReese send orders only by mail or fax After we received your order you wig get a proformainvoice intln details row to pay. Please do not send cheques or giro transfer In advance ICredit card Please don't forget card number. expiry date and signature !We accept American Express, Diners Card. Eurocard, Mastercard, VISACharges for P&P (air mail):Inside of EU : £ 4.00 up to £ 25. outside of EU £ 8 up to C. 50.00. (Depends on weight)

Elektor Electronics 3/98 21

Ir

Balanced/unbalancedconverters for audio signals

In the Quest ForQuality, a quasi -meta-physical activity zest-

fully practised bycountless audio-

philes, the use of`balanced' (or sym-metrical) signals is

believed to contributeconsiderably to the

end result. In this arti-cle we take pleasure

in presenting bal-anced/unbalanced

converters for audiosignals. The designs,

we are convinced,offer a solution to

many problems youmay stumble on

when it comes toconveying small

audio signals overlarge distances.

Design by J. F Brange

for high -end applications

First things first. Let's recall that anunbalanced (asymmetrical) signal isdefined as existing with respect to theground line in a circuit. Consequently,conveying an unbalanced audio signalfrom one preamplifier stage to anotherby way of a cable may pose variousproblems including parasitics and radi-ation which degrade the quality of theaudio signal. The use of shielded cableis an insufficient remedy, particularlywhen the signal source supplies lowsignal levels (say, a couple of milli-volts).

The panacea in these cases is tomake the signal balanced, that is, float-ing with respect to ground. Doing soallows a weak source signal to be con-veyed over long distances (if neces-sary) without it being 'modified'underway. Sure, the problem of para-sitics remains. However, the balancedsignal being converted to unbalancedagain at the input of the 'receiver',

noise is effectively cancelled out by thedifferential effect. The floating signalon the two wires arrives at the inputsof the differential circuit. Whereas thewanted audio signal arrives withopposite phases on the two wires, anynoise picked up by the symmetricalcable will have the same phase on thetwo wires. Consequently, this noise iseffectively eliminated by the subtract-ing operation of the differential circuit.

There are, without doubt, many cir-cuits which enable an audio signal tobe converted from balanced to unbal-anced and the other way around. Theoperational amplifier (opamp) lendsitself quite well to this kind of opera-tion. Provided you use quality audioopamps, ample results will beobtained. However, a couple of pre-cautions should be taken to preventdegrading the performance that maybe achieved in theory. One of theseconditions is the use of 'hand picked'

422 Elektor Electronics 3/98

Visit our Web site at http:,:ounvorld.compuserve.com'homepages elektor_uk

resistors with a tolerance of 0.1 percent or better.

UNBALANCED -TO -BALANCEDCONVERSIONThere is a modern solution to thisproblem. Analog Devices has devel-oped integrated circuits which arctotally geared to this application. TheseICs boast internal resistors which arelaser -trimmed to a precision of0.0001%! Not surprisingly, these ICsachieve 'professional -grade' perfor-mance as far as noise rejection, para--

sitics suppression and distortion areconcerned. These ICs now being rela-tively well distributed in Europe, wehave few hesitations about presentingyou practical circuits for a stereo appli-cation. Obviously, the two stereo chan-nels being identic31, it will be sufficientto describe only one of these.

The circuit diagram of the unbal-anced -to -balanced converter is shownin Figure 1. The SSM2142 opamp fromAnalog Devices is a buffer/amplifierwith an internal differential output dri-ver. Its main function is to convert anunbalanced input signal into a high-level balanced signal. Based on an elec-tronically balanced cross -coupled chiptopohigy, the SSM2142 comes dose toachieving the performance of balanc-ing circuits that make use of a trans-former for line driving. As a matter ofcourse, the IC has the advantage of amuch smaller footprint than that of atransformer, while offering compara-

mliC12

non 100_

PI

1k.60

2511

MIN

Rs

IC1

O

'lit

S

-s

,-F 8

-F

C4 IC3

MI=100n700

25V R4

2

SSI,12142

+ 15V

(D

*see text

1

15V

ble common -mode rejection. Those ofyou who are interested in the chieftechnical specs of the SSM2142 will nodoubt find this month's Datasheetpages of particular interest

The input signal is applied to thechip via a 10-kil preset, P1, whosefunction is to adjust the output signallevel while also matching the IC inputimpedance recommended by the man-ufacturer The preset may, of course, bereplaced by either a potentiometerwith the same value, or a 3 -way pin -header on to which a jumper is

4 -

IC2 TC3

MEI MIM100n 100..

25V

980026 - 12

Figure 1. Circuit dia-gram of the unbal-anced -to -balancedconverter based onthe SSM2142 fromAnalogue Devices.

Figure 2. The hal-anced-to-onbalancedconverter is designedaround the SSM2142and an NE5534 bufferopamp.

RE

IC1

RI

Ill

SEUSEREF

SSM2141

P2

imLE

100n1-1 47,125V

2

3

10k

CI

22p

1

R3NE5534

R4

I 5V

C4

700n700-

25V RE

[71

CE

100n 147

25V

9E0026 - 11

15V

Elektor Electronics 3/98 23

of 9.1 Ic o DI R2 10 01 HI 10 0 DI R2 10

"1+00E0.10"_ 7101141117 "+n,0 1-20E010 11110

0 0 4"

1----rk 0 0 0.4.+1,26-1,F0 0 0+NMI 00WM 0 01.31110011611110 0

6_L n:Ai 0+ 1 P1DO+

0 = 0 o ei000 -o 0.2..2. -o

Oq-Tot R. OTT° 8410

Figure 3. Copper tracklayout and componentmounting plan of theprinted circuit boarddesigned for two bal-anced -to -unbalancedconverters and twounbalanced -to -bal-anced converters(board available ready-made through theReaders Services).

installed whichtakes the signalfrom the 'input'pin to the centrepin. This is thesolution weadopted. Theoutput is alsosimple: pin 8 ofthe SSM2142supplies in -phase (±) out-put signal, whilepin 1 supplies

the inverted (-) signal. Since both out-puts are loaded with a 30142 resistorto ground, an output impedance ofabout 600 12 is created.

The SSM2142 is protected againstparasitic signals arriving by way of thesupply lines. This is achieved by con-necting elementary RC filter networkscomprising of R3 -C1 -C2 and R4 -C3 -C4to the respective supply pins of theSSM2142. The output of the circuitsupplies an audio signal which shouldbe worthy of the very best home-brewaudio projects.

A final word or two about thepower supply: although a ±12 V sym-metrical supply will be fine in manycases, we recommend using ±15 V asshown in the circuit diagram becausethat value results in an improveddynamic range. The absolute maxi-mum supply voltage is ±18 V.

BALANCED -TO -UNBALANCEDCONVERTERFor this purpose you need theSSM2141. This IC, a direct relative ofthe SSM2142, is an integrated differ-ential -amplifier designed to receivebalanced 'line' signal levels in audio

Figure 4. Finished prototype ofeach of the converters.

Elektor Electronics 3/98

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COMPONENTS LIST

Printed circuit board: order code980026-1.

Balanced-tounbalanced converter

Resistors:R1 R2 = 23k5122 1%R3 = 1 NMR4 = 680.QR5516 = 10052P1 = Ik52 preset verticalP2 = 10k0 logarithmic potentiome-

ter (may be replaced by jumper)

Capacitors:Cl = 22pFC2.C4.C6,C7 = 100nF03,C5 = 100.1iF 25V radialC8,C9 = 47riF 25V radial

Semiconductors:ICI = SSM2141 (Analog Devices)IC2 = NE5534 (Philips Semiconduc-

tors)

Unbalanced -to -balanced converter

Resistors:R1.R2 = 301Q 1%R3,R4 = 1000PI = 10kf2 logarithmic pot (or

jumper)

Capacitors:C1 = 100pF 25V radialC2.C4 = 100nF

Semiconductor:ICI = SSM2142 (Analog Devices)

circuit:, requiring high noise immunityand common -mode noise rejection.This IC achieves a typical CMR (com-mon -mode rejection) spec of 100 d13.By comparison, an opamp with fourregular resistors around it will be hardpressed to achieve a CMR rating ofanything over 40 dB or so, which is byno means enough for high -end audiodesigns. Let's cast a look at Figure 2which shows the schematic of this sub -circuit. The resistor networks betweenthe SIG+ (pin 3) and SIG- (pin 2) inputsof the SSM2I41 fix the input imped-ance at about 47 k_Q. Preset P1 (1 kil)allows the CMR value to be fine-tuned(see also further on). This componentis optional, however, and may be omit-ted. As indicated by the componentoverlay of the balanced -to -unbalanced

converter, it may be replaced by wirelinks. This was also done on our pro-totype. Note, however, that the sourceimpedance has to be perfectly con-trolled, as the slightest imbalance ofthe source resistance will reduce theachievable CMR value. For example, adifference of just 5 fl is punished witha CMR increase of no less than 20 dB.

The output signal of the SSM2141is applied to an NE5534 voltage fol-lower by way of a 10-1d2 preset. The(low -impedance) output of the NE5534should be able to drive almost any pre-amplifier input. The remarks on thesupply filtering of the SSM2142 alsoripply to the SSM2141.

if used, the CMR fine-tuning presethas to be adjusted with the aid of a dif-fer er tfial input signal. What better wayto generate such a signal than use theSSM2142? Apply a 50 -Hz, 100 -mV sig-nal to the input of the 2142. Connectits output signal to the 2141. Next,tweak P1 for the smallest possible sig-nal at the output. This setting corre-sponds to the best possible CMR.Those of you who do not have anoscilloscope (or access to one) mayreplace the 1-k52 preset by two wirelinks, as mentioned earlier. If you canget hold of two 232-k0 resistors witha tolerance of 0.1%, no adjustmentshould be necessary

As already mentioned, the circuitsare powered by a ±15-V symmetricalsupply. Current consumption beingvery modest indeed, you can make dowith a mains adaptor with stabilized±15 V outputs.

CONSTRUCTIONAs you can see from the artwork inFigure 3, a printed circuit board wasdesigned for the two converters. Theartwork comprises the copper tracklayout and the component mountingplan (overlay). The PCB design foreach converter is duplicated so youneed just this one board for a stereoapplication.

As a matter of course, it is best tostart by separating the four smallboards. The two smaller boards areused to build the unbalanced -to -bal-anced converters, while the boardswith two IC sockets on them areintended for the balanced -to -unbal-anced converters. Neither of these dr-CLAUS should present undue difficultywhen populating the boards. The only

points to be made here are to observethe polarity of the electrolytic capaci-tors and the orientation of the inte-grated circuits when they are insertedinto their sockets. Also be sure not tomix up the two 8 -pin integrated cir-cuits on the balanced -to -unbalancedconverter board.

The large unetched copper areas onthe boards acts as ground planeswhich help to make the circuitsimmune to noLce and other stray sig-nals.

Having finished the construction ofthe converter boards you may mountthem in small boxes, and wire them upto the external parts. The input andoutput connectors may be mini -DINtypes of which only three pins areused. The unbalanced -to -balancedconverter is best located dose to thesignal source. Its complement, the bal-anced -to -unbalanced converter, willtypically be installed near the'receiver'. Note the connections- theoutputs of the unbalanced -to -balancedconverter are the mirror -image of theinputs of the balanced -to -unbalancedconverter.

The circuits should function spot-on. The photograph in Figure 4 shouldallow you to compare your own effortsat building the circuits with those ofour engineering laboratory. In particu-lai, you should be able to detect miss-ing components immediately in the(unlikely) case of a problem.

A final note aimed at those with akeen interest in figures: Below are thevery encouraging results of exhaustivemeasurements on a pair of these con-verters built up in our design lab:

unbalanced -to -balanced converter:THD (total harmonic distortion)between 0.0008% and 0.0015% from20 Hz to 20 kHz.

balanced -to -unbalanced converter.THD between 0.0008% and 0.0011%from 20 Hz to 20 kHz; CMR between-140 dB and -70 dB from 20 Hz to20 kHz.

All measurements were made with anAudio Precision test system.

GREAT NEWS FOR YOU!Over the past 11 years ULTimate Technology supplied more than 20.000commercial versions, but also thousands of educational versions, which, havingno Gerber Interface (high resolution photoplotter) are not suitable for commercialuse, but are otherwise, identical to the, naturally far more expensive, commercialversions. After a worldwide test on Internet the ULTlboard Studio evolved, withthe same well -considered limitation, at a price at which everybody can afforda professional design system.

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SEE ALSO THE REPLYCARD ELSEWHERE IN THIS ISSUEElektor Electronics 3198 25

Data AcquisitionVirtual Instrumentation

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TC-08 £199.00Supplied with serial cable and adaptor.Calibration certificate £25.00.Thermocouple probes available.

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Video Surveillance

Pinhole Board Camera (B& V)12v DC. 0.1 LUX. 380 TV ResolutionSize: 35mm x 35mm

£35.00

Pinhole Board Camera (Color) £190.0012v DC. 0.5 LUX. 420 TV Resolution2 board foldableSize: 40mm x 40mm ,

Audio!'Video Transmitter Module- 12v DC, 4 Channel Selection £190.00

900MHz - 1200MHz. FM Modulation

4 Channel Receh'er +SwiteherI 2v DC. CompositeAudio,Video Output £150.00

We also stock:Time & Date Generator. T.F.T LCD Color Monitor.Miniature PIR etc.

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London W9 3EFTel: (44)(0) 181 968 0227 Fax: (44)(0) 181 968 0194

Email: 106075.2760±Compuserve.com

Loudspeaker Projects19 top-quality designs

from Speaker BuilderIn this special issue from Audio Amateur Corporation. USpublishers of the well-Imownmagazine Speaker Builder, each project gives you

all instructions needed to complete theproject:parts lists. including box materials, drivers, and crossovercomponents;performance measurements-assuring the builder of asuccessful and satisfying undertaking.

As a bonus, two technical articles include a treatment ofcoupling between loudspeaker and power amplifier and asurvey of loudspeaker types.The drivers specified in this special issue include some of theworld's best-known manufacturers: Audax Axton Dynaudio Focal Peerless Scan Speak Seas Vifa Visaton and more.Offering superb and reliable guidance to both the beginnerand the experienced constructor, this 100+ page booklet willhelp you get the very best in reproduced sound.Price £6.5/0 plus p&p. Order yours today from

Elektor Electronics (Publishing)P 0 Box 1414 Dorchester, Dorset DT2 8YH

Telephone +44 (0)1305 250 995Fax +44 (0)1305 250 996.

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Elektor Cl.ntrnsi.. 2 MO rt-7I

introduction todigital signal processingPart 3 Digital bandpass filters

After last month's dis-course on the com-

putation of frequencyspectra, that knowl-

edge is used in this,the third, instalment

to acquaint the readerwith the ins and outs

of digitalbandpass filters.

By Dr.Ing. M.Ohsmann

13

4096 4096samples samples

window winaow

I

Figure 13. Schematicshowing how longersignals are computed.

4096samples

window

SPECTRAOF LONG SIGNALSIn the foregoing, the DFT (DiscreteFourier Transform) of a signal of fixedlength (that is, n = 4096) was used tocompute the spectrum. The computa-tion of a much longer signal may becarried in a number of ways describedin a number of books (see References).Our analyser makes it much simpler(see Figure 13). The input signal isdivided into segments all 4096 bitslong which are multiplied with thewindow function described in Part 2.The DFT of each segment is then com-

window

980015 - 3 - 11

puted, the nm.s. amplitudes are addedtogether, so that the entire signal maybe analysed, whereupon the resultantspectrum is displayed.

APPLICATIONWe now wish to view the spectrum ofa real signal and take for this purposefile morse2.way. This contains twomorse (telegraph) signals of differentfrequency.Experimen t XMORSEISPP

then computes the spectrum, which isshown in Figure 14. The spectrumclearly shows two peaks, whose fre-quency may be determined by mea-surement, even when the signals areweak and superimposed on manyother signals. The reader is invited totry to analyse the 19 kHz stereo pilotcarrier which is frequently still present

A28 Elektor Electronics 3/98

Visit our Web site at http: ourworld.compuserve.com homepages elektor_uk

in the output signal of an Fm receiver(available on the co -Rom as a file).

NOISE ANALYSIS OF ALOW-PASS FILTERNow for experiment xu.6.st,P, whichsimulates the setup shown in Fig-ure 15. Signal generator NOISELEXE pro-vides white noise, which is applied toa simple low-pass filter. Theinput sig-nal and output signal are analysedwith spectrum analyser srEcl. Theresult is shown in Figure 16.

DFT AND FFTThe algorithm that computes the spec-trum from the sampled values is calleda Discrete Fourier Transform (DFT).The Fast Fourier Transform (FFT) is amethod for carrying out the DFT com-putations rapidly and effectively. Thenumber of multiplications carried outwith both transforms is given belowfor three values of n, that is, the num-ber of sampling points. In the table, cis the factor indicating how muchfaster a computation with an FFT isthan one with a DFT.

n DFT FFT16 256 64 4128 16384 896 184096 16777216 49152 341

FROM SINE WAVEGENERATOR TOBANDPASS FILTERReaders who may have forgotten mostof the trigonometry they learned atschool are reminded that

cos(att3) = cosacos,8-sinasin5

sin(a+A = sinasinfii-cosarosfr

These simple equations enable a digi-

Figure 16. Spectrum of whitenoise before (left) and afterbeing passed through a low-pass filter.

16

14

°

at,

tal sine wave generator to be realizedfrom which, with some modifications,a bandpass filter may be derived.

Enter these values into the upperline:

p = cosy,q = singeck = cosky;St = sin*

if fo= 2afffs, ck and sk are the sampledvalues of, respectively, a cosinusoidaland a sinusoidal signal of frequency fthat is sampled at a rate fr

To digitally generate these signals,the values of ck and sk must be com-puted rapidly, starting, for instance,with k= 0. By substitution in the sine

15NOISE1.EXE

white noise

t mpl. way (u) ya =f a = 0.0 fb

LP1 EXE

41,P.Ntliritvi

Figure 14. Two morse (tele-graph) signals almost sub-merged in noise.

and cosine equations, we obtain

ck+1 = Pck-gsksk+i = qco-psk

This means that once parameters pand q have been derided, the values ofck+1 and sk+i can be computed by fourmultiplications, one addition and one-ubtraction from the values of ck and

Figure 15. The removal ofwhite noise with the aid of alow-pass filter.

low-pass

SPEC1 EXE

spectrum analyser98015 -3-13

0. 0 yb 100.0 19-0.-oav Co) = 0.0 yt. = 100.05000.0 cur = -1.0 -Fa = 0. 0 f b= 57000.0 cur= -1.0

Elektor Electronics 3 98 29

880015 -3 - 14

start('sin-wave-generator') ;

nsamples:=10000 ; set_parfs:=22050 ; set_parf0:=100 ; set_par_realy\f0=',f0)scale:=500 ; set_parout_fn:='sinl.way. ; set_par_

open_out(out_fn) ;

p:=cos(2*pi*f0/fs) ;

cp=sin(2*pi*f0/fs) ;

ck:=1 ;

sk:=0 ;

for k:=1 to nsamples dobeginoutput(scale*ck) ;

ck_new:=p*ck-g*sk ;sk_new:=q*ck+p*sk ;ck:=ck_new ;sk:=sk_new ;end ;

stop ;

end.

17program sin() ;

uses dos,graph,crt ;

SIGLIB.PAS}

var k:int ;

f0,scale:float ;p,g,ck,sk,ck_new,sk_new:float ;

begin

_longC\n=',nsamples) ;

_long('\fs=',fs) ;

real('\scale=',scale) ;

string('\out=',out_fn) ;

Figure 17. Program fordigitally generating asinusoidal signal.

wirawr

tap. uav L.200 AUTO

sk. This can be done very rapidly andis readily programmed on a signalprocessor. For example, programmingof a simple oscillator as in programSINO.PAS (or .tom) is child's play. The list-ing is given in Figure 17.

The program generates a sinusoidalsignal (x5N1.sPr), which is displayed inFigure 18. To start the oscillator, startvalues co and s0 must be entered as rel-evant, since these determine the phaseand amplitude of the signal.

Although so far matters have notbeen very complicated, we havealready simulated an undamped reso-nant circuit. In this, the value ck repre-sents, say, the value of the currentthrough the inductor, and sk the valueof the potential across the capadtot

We have come very close to adamped resonant circuit as shown inFigure 19. In the case of a dampedoscillation, the values within succes-sive sampling intervals reduce by afactor r, that is, the damping factor <1.Consequently, the computationinstruction must include a multiplica-tion by r.1. Moreover, to excite the res-onant circuit, the instruction must also

Figure 18. A constant sinu-soidal signal (tipper curve)and a decaying one.

trnp2. uav 1.. 200

430

AUTO

Elektor Electronics

980015-3-15

3(98

Visit our Web site at http: ourworld.compuserve.com homepages'elektor_uk

indude an input signal uk. The result-ing equations are:

ck+i = Ock-fisk)+Ilk5k+1 = r(qcki-psk)

This represents a simple bandpass fil-ter and also forms the basis of the asso-dated program sNFti.l.eAs (or _EcE). Totest that this is really a bandpass func-tion, a single pulse is used as input sig-nal and the output of the filterobserved. If all is well, this should bea damped oscillation, constitutingMINII.SPP as shown by the lower curvein Figure 18. This is an exponential)damped waveform generated by flirbandpass filter, that is, the resonant cir-cuit

Experiment XBANDP1.SPP enables asweep signal to be passed through thefilter. Again, various values of fo and rmay be used; particularly interestingare the values r = 0.5; r = 0.9; r = 0.99;r= 0.999; and r = 0.9999.

An unusual aspect of the filter isthat it computes not only the cosinu-soidal, but also the sinusoidal, oscilla-tion. This may be inverted to obtain

Ck+2 = 61Ck+1+61Ciflek

which yields with the aid of the so-called filter coefficient:

bl = -r2b2 = 2rcos(2irjes)

The filter is realized in programBANDP1.PA5 (or .EXE).

INFINITE IMPULSERESPONSE FILTERA comparison between the filter justderived and the earlier low-pass filtershows a general aspect. The output atone dock period affects the outputduring the next period. This will havesome sort of exponential effect, so thateach output has a smaller effect on thenext output. These filters are calledInfinite Impulse Response (DR) filters,sometimes recursive filters.

The output value of the low-passfilter depends on only the precedingoutput value and the filter is, there-fore, a first -order AR filter.

The output of the bandpass filterrefers back two output values and isthus a second -order RR filter

There are, of course, higher orderfilters, but these normally consist of anumber of cascaded second -order sec-tions.

APPLICATIONS OFBANDPASS FILTERSBandpass filters are normally used toselect a specific frequency or band offrequencies. File MOR5E2AVAV containsthe signal of an amateur radio setreceiving two closely spaced morse

19

signals. A bandpass filter enables oneof these signals to be enhanced sig-nigicantly. Detection of the signal maybe effected automatically with experi-ment xmoRsE3see, which passes signalMOR_5E3.WAV through two bandpass fil-ters with centre frequencies of 700 Hzand 1400Hz respectively. The two sep-arated signals are dearly recognizablein Figure 20.

Working with these associated filesand experimenting with the filter para-meters quickly clarifies the operationof a bandpass filter. Pass a music signal(musl.wAv) through a bandpass filterand listen to the result.

Next nwnth's instalment will discuss anecho generator and show how thiscan bemodified to make it suitable for digitalteriug.

1..

.. accrit

195A115aj

980015 - 3 17

Figure 19. A damped and anundamped oscillator circuitand associated oscillations.

References

Electronic Filter Design Handbook, ISBN0 07 070434 1, by Arthur B. Williams andFred J. Taylor; McGraw-Hill, 1988

Digital Audio Signal Processing, ISBN 0471 97226 6, by Udo Zalzer, John Wiley& Sons, 1997.

Digital Signal Processing, by Schafer &Oppenheim, Prentice -Hall, 1975

Digital Processing of Signals, C.M. Raderand B. Gold, McGraw-Hill.

Figure 20. Two morse signalsat 700 Hz and 1400 Hzrespectively before and afterfiltering. After filtering, thetwo separated signals areclearly recognizable,

IS:1715 11

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Elektor Electronics 398 33'

Digital AudioBroadcasting (DAB)Radio programmes with CD quality

The European Union'sEureka* 147 DAB Pro-ject is the only digital

audio broadcastingsystem to be fully

specified and to meetthe ITU's (International

TelecommunicationsUnion) requirements

for a world standard. Itprovides radio broad-

cast data transmissionat a bit rate of 1.2-1.5Mbit/sec and is highlyimmune to noise and

interference, even in mobile use. Its mainapplication is a radio system with CD quality

for mobile and domestic use. It is intended toreplace VHF/FM broadcasts within the next 10

years. Apart from providing additional dataservices for graphics and text, the new multi-

media system can also transmit television pro-grammes

0*M- Fjp):71

IIIMMI=11111E

Eureka is an enabling organization set up by the Criniznksion of the European Union in 1963 topromote and fund research, development and cooperation for the implementation of advancedtechnologies..

By our Editorial Staff

The VHF broadcasting system intro-duced in 1949 has reached the end ofthe road. Owing to the overcrowdingof the 88-108 MHz band and signalechoes, serious interference, especiallyin mobile use, is inevitable. Also, thetransmission of additional digital data(RDS - radio data services) is possiblein only a limited way. And finally, theVHF/FM service could never achievethe quality associated with compactdisks (CD).

Against this background, the DigitalAudio Broadcasting system (DAB) wasintroduced to provide CD -qualityaudio services, as well as a host of addi-tional data services, to domestic andin -car receivers. It was originally devel-oped under the Eureka* 147 (E147)programme within the European

434 Elektor Electronics 3198

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Union, but is now being accepted bymany countries outside Europe. UnlikeFM transmissions, DAB does not sufferfrom multi -path effects.

The manufacturers and researchorganizations that took part in theEureka 147 development project asso-ciated themselves in 1995 into theEuroDAB Forum to promote DABtechnology in Europe and to developthe formal standard? for E147. Butinterest was shown also from outsideEurope and so the EuroDAB Forumbecame the WorldDAB Forum earlylast year.

The two most important stepstoward the realization of DAB werethe development of MUSICAM (Mask-ing Universal Subband IntegratedCoding And Multiplexing) for signalencoding and an innovative modula-tion technique called COFDM (CodedOrthogonal Frequency Division Multi-plexing).

In the past, the large bandwidthrequired to digitize audio signals pre-vented the use of digital broadcastingtechniques, but the MUSICAM encod-ing method allows a significant reduc-tion in bit rates without affecting theaudio quality. It uses irrelevance andredundancy reduction by using certainpsychoacoustic properties of humanhearing. Consequently, high audioquality can be achieved with bit ratesas low as 192 kbit/sec per stereo chan-nel, compared with the 1411 kbit/secrequired in the recording of CDs, inwhich a non -compressed technique isused.

The COFDM technique enables ahigh -quality, reliable and efficienttransmission to be obtained. It is amulti -carrier, digital modulation sys-tem based on the principle of dividingthe information over a large numberof dose -spaced, orthogonal (mutuallyperpendicular) carriers. There are 1536orthogonal carriers in a 1.5 MHz DABBand 117 block, and 384 or 768 orthog-onal carriers in a 1.5 MHz DAB L -bandblock.

The technique uses advanced errordetection and correction methods toprovide unimpaired reception evenunder difficult conditions. DAB canoperate with a signal-to-noise level aslow as 10 dB without any degradationas compared with 50 dB for a VHF/FMtransmission. Furthermore, it avoidsinterference, and the resulting distor-tion, caused by multipath propagation.The resistance to multipath propaga-tion prevents reflection from buildingsor mountains to affect reception qual-ity. In -fact, these signals increase thereliability of the DAB service. The resis-tance makes it possible to provide aDAB service via a terrestrial single -fre-quency network.

In contrast to VHF/FM stations,DAB allows blocks of stations on one

Sound level(dB) 80

60

40

20

Figure 1. The MUSICAM technique usespsychoacoustic effects to reduce the datarate of DAB transmissions.

absolute hearing/ threshold

additional soundsnot audible

minimal audiblefield threshold

0

0,02 0.05 0.1 0.2 0.5 1 2

Pitch (kHz)

single DAB channel (1.5 MHz band-width) without resulting in interfer-ence. In conjunction with a single -fre-quency network, a block of at least sixstations per country can be broadcastnationwide via the same DAB channelBy using one or more additional DABchannels, it is possible to provide fur-ther blocks of stations for regional andlocal programmes. In theory, DABenables three times as many stations asbefore to be broadcastin the same fre-quency range.

Since a block of stations can betransmitted via DAB and the outputpower required to broadcast COFDM-modulated signals is reduced, theenergy required for a DAB network issignificantly smaller (up to 90 per cent)than that needed for a current FM net-work This also means a much smallerE -field around the transmitter.

A DAB provides the associated dig-ital receiver with indication ofthe transmitter name and thetype of music programme. Italso gives accompanying text

ofr

5 10 20

555017

information about the radio pro-gramme.

In addition to, or instead of, radioprogrammes, the transparent and flex-ible transmission path opens the wayfor many new and innovative services:from text and picture information tothe transmission of moving pictures oreven television programmes, whichmay be received in a car or train.

Many electronics companies arebuilding and developing a range ofDAB -compatible units, ranging fromcar radios and multimedia mobilehandsets to PC cards that will capturethe data transmitted alongside theaudio signal and display it on a PC.

AUDIO ENCODINGRecording a stereo audio signal on toa compact disk (CD) requires a datarate of 1411 kbit/sec. At a comparable

Figure 2. The continuous redistribution ofthe programmes over 1536 carriers, in con-junction with extensive error protection,prevents a partial loss of data throughinterference and reflections from affectingthe received signal.

SAY. 6 PROGRAMMES

interference

Bandwidth of the DAB signal: .5 MHz divided into 1536 carrier frequencies217-52-

Elektor Electronics 3/98 35

Table 1 Specification of DAB coding with MUSICAMAudio modes

Sampling frequencyLower sampling frequency' (LSF)Transmitted AF range

Resolution of PCM signalAudio bit rate

Duration of audio frame

monostereotwo -channelmulti -channel (MUSICA41 surround)48 kHz24 kHz0 Hz to 20.25 kHzWith LSF" 0 Hz to 11.25 kHzup to 22 bit/sample32 kbit/sec (mono) to 384 kbitrsecWith LSF* 8 kbit/sec (mono) to160 kbitsec24 ms. equivalent to 1152 PCM samplesWith LSF' 48 ms

(stereo) in 14 steps(stereo) in 14 steps

Halving the sampling frequency during transmission enhances the audio quality at low bit rates of about 32-64 kbitisec.This is of particular interest in spoken -word programmes. such as newscasts. Owing to the doubled duration of the audioframe, only half the bit rate is available for Programme Associated Data (PAD) services.

Other applications of MUSICAM comprise:Astra Digital Radio (ADR)Cable and satellite television (DVB. Directly in the USA)Dubbing between radio stations over telephone/ISDN linesMultimedia applications in PCsElectronic interfaces for sound processing in computers

TableRadio -frequency characteristicsBandwidthNumber of carriersSymbol durationGuard periodModulationError protection

(convolution code rate,average for sound.greater for control data)

Service characteristicsFrequency range

Transmitter spacing(terrestrial networks)

Multiplex characteristicsGross transmission bit rateNet transmission bit rateConfiguration

ReconfigurationNon -uniform configuration

Data services

Technical parameters of DAB transmissionsMode I, tvlode fl, Mode II.1.536 MHz (all modes)1536 (I); 384 (II); 192 (III);1.246 ms (I); 312 ps 156 ps246 ps (I); 62 ps (11): 31 ps (Ill);differential quadrature phase -shift keying (QPSK)grade 1: 0.39grade 2: 0.47grade 3: 0.55 (for mobile services)grade 4: 0.64grade 5: 0.80 (for instance, for cable services)

Mode IV

768 (IV)623 ps (IV)123 ps (IV)

mountainous terrain: <375 MHz (individual transmitters) (Mode I)flat terrain: <1.5 GHz (Mode II)flat terrain: <3.0 GHz (Mode 111)flat terrain: <1.5 GHz (Mode IV)supra -national: satelliteup to about 80 km (<375 MHz - Mode I)up to about 20 km (<1.5 GHz - Mode 11))up to about 10 km (<3 GHz - Mode Ill)up to about 40 km (<1.5 GHz - Mode IV)

2.304 Mbit/secabout 1.2 Mbitisec (grade 3)up to 64 audio programmes and data services:typically 5-8 audio programmes and several data servicesdynamic during ongoing transmissiontypically six stereo programmes at a rate of 192 kbitlsec, incl. ProgrammeAssociate Data (PAD). and several data services at a rate of 24 kbit/sec

Programme Associated Data (PAD) at 0.6-16 (later 64) kbit/sec,embedded in the audio signalstream mode: capacity selectable in steps of 8 kbit.secpacket mode: capacity selectable as necessary

36 Elektor Electronics 3 98

Visit our Web site at http://ourworld.compuserve.conlihomepages/elektor_uk

Table 3 Frequency ranges available for DABBand I

Band Ill

Band III

L -band

47-68 MHz; previously used for television broadcasts (2-4 channels) and mobile communications;can accommodate 12 DAB blocks (2A -4D)

174-230 MHz; previously used for television broadcasts (5-12 channels) and mobile communications;can accommodate 32 DAB blocks (M -12D)

230-240 MHz; previously used for mobile and military communications-; can accommodate six blocks(13A-130

1452-1467.5 MHz; previously used for mobile and fixed communication services; can accommodatenine blocks (LA-LI)

The DAB blocks are identified by the number of the previous A/ channel and a letter. For instance, since four DAB blockscan be accommodated in each former TV channel, the four blocks replacing TV Channel 12 are identified by 12A, 12B,12C and 12D.

* These frequencies are apparently still used by the military in France, since it is feared there that the introduction ofDAB could interfere with French defence communications.

rate, DAB, thanks to MUSICAM, cantransmit up to 20 audio signals (with-out additional services) without loss ofaudio quality. MUSICAM was devel-oped under the European Eureka Ini-tiative by the Institute of Radio Tech-nology (IRT) in Munich, Germany,Philips in the Netherlands, andCCETT, a French research centre.

MUSICAM is based on special algo-rithms, which are founded on twopsychoacoustic effects in humans. Thefirst one of these is that human hear-ing is not capable of discerning soundsthat lie below the absolute hearingthreshold. The second is that softsounds which lie below the minimalaudible field threshold cannot be per-ceived when they are masked by loudones of about the same frequency.

MUSICAM makes use of theseeffects and conveys only those parts ofthe sound information that can reallybe perceived (see Figure 1).

Depending on the signal contentand the quality requirements, differentdata rates may be used - the band-width of each mono(phonic) channelstretches from 8 kbit/sec to 192 kbit/sec.Stereo signals are conveyed in the nor-mal stereo mode as 2 -channel signals(that is, double the mono rate).

Low bit rates result in the commonstereo mode, in which the informationcommon to both channels is conveyedonly once.

During the audio encoding, bits arealready reserved for (additional) Pro-gramme Associated Data (PAD).

The mast important parameters foraudio encoding are listed in Table 1.

TRANSMISSIONCHARACTERISTICSIn a VHF/AM or FM transmissionthere is only one carrier frequency

modulated (amplitude, frequency orphase) with the audio information.

The DAB system uses codedorthogonal frequency division modu-lation (COFDM), whereby a group ofprogrammes are multiplexed into asingle broadcast channel. Althoughthis requires a relatively wide band-width, the concept allows the use of asingle frequency network (SFN) witha number of interleaved parallel pro-grammes, thus making better use ofthe limited spectrum.

The system operates in various fre-quency bands (see Table 3). There arefour modes of operating conditionsthat depend largely on the transmis-sion frequency and the degree ofacceptable Doppler shift

The audio signals are first MUSI-CAM encoded to achieve bit ratereduction and then applied to theCOFDM modulator using binaryQPSK coding.

The time slot structure is also modedependent; for instance, Mode III hasa frame of 24 rns, a symbol* durationof L%p.s (of which only the last 125 psis quality critical) and a guard periodbetween time slots of 31µs. The sys-tem defeats multi -path effects becausethe first part of each symbol is dis-carded.

Continuous redistribution of theprogrammes over the carriers preventssequential data of a given source to beaffected simultaneously by reflections(see Figure 2). However, use of thereflections intercepted during theguard periods enhances the quality ofthe transmission.

After long and extensive researchinto the best ratio between bandwidthand received signal quality, it wasdecided to use frequency blocks1.5 MHz wide. Each of these blocks

can contain between 192 and 1536orthogonal carriers, depending on Themode of transmission and the fre-quency band.

A single television channel, 7MHzwide, can contain four DAB blocks,which means that in practice a singletelevision programme can be replacedby 24 stereo audio programmes and anumber of digital services. The com-bined information (programmes anddata) is transmitted in one of theseblocks, termed an ensemble, at a grossbit rate of 2.304 kbit/sec, equivalent toan overall net bit rate of1.2-1.5 Mbitlsec, depending on thedegree of error -protection. The mostimportant technical parameters of aDAB transmission are listed in Table 2.

The frequency bands allocated tothe introductory DAB transmissionsare listed in Table 3. For national cov-erage, Band III was deemed most pro-pitious, and the L -band for regionaland local stations. A simple rod sufficesas the receive antenna.

Table 2 also shows that, dependingon the frequency range, a differentmode of transmission may be selected.Mode I provides the highest number ofcarriers and the longest guard periods,and is therefore particularly suitable forVHF co -channel networks in whichthe transmitters are well spaced. ModeII is for use in local co -channel net-works. Model is best suited to use incable and satellite systems, and alsomobile systems operating at frequen-cies up to 3 GHz. It is particularlyimmune to phase noise. Mode W isintended for use in L -band systemswith well -spaced transmitters, It is sus-ceptible to interference, particularly inthe case of fast-moving mobile stations.

continued next month

In modem data cummmticztions, the symbol replaces the baud as the unit of transmitted data. Like the baud, a symbol may (and frequently does) repre-.,ent more than one data bit.

Elektor Electronics 3/98 37

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remote measurement andcontrol by telephone line

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In a situation where we have two or more computerswhich exchange large amounts of data, share a printerand are separated by 10 metres or more, setting up a net-work is the best solution. If you have never worked with anetwork, this may appear to be a complicated task.Nonetheless it is a lot easier than you might expect; inaddition the cost of a pair of network adapter cards is notall that high and a standard Ethernet network can achievedata transfer rates of 10 Mbit/s.

By P Srriit

How do I set upa network?

-- termination resistor

network card

T piece termination resistor -

network card network cardmoat -

Figure L A simple network for three computers, based on three BNC network cords. The network cable must be terminated at eachend by a suitable impedance.

In addition to simple data exchange, anetwork can be used to 'pep up' aless -powerful PC. For example, a 200 -MHz Pentium computer with a 3 -GBhard disk could 'loan' 1 GB of diskcapacity to a 486DX4-100 machinewith a 500 -MB drive. The CD-ROM drivein the Pentium computer can also beread by the 486DX4-100 computer, sothat in many cases a second CD-ROMdrive for the 486 PC is no longer need-ed. Even a floppy -diskette drive andan internal 100 -MB [omega Zip drivecan be shared via the network.

An Ethernet network

There is actually only one networktopology which is suitable for smallernetworks, namely the bus topologybased on Ethernet. In this case thereare two completely different physical

implementations. The so-called10Base-2 network uses coaxial cableswith BNC connectors. The more mod-ern version is called 10Base-T andworks with Unshielded Twisted Pair(UTP) cables.A bus structure consists in principle of along cable with a terminating resistorat either end. Network cards (some-times called transceivers, from a con-traction of transmitter and receiver)are connected to the bus cable viashort branch cables. The protocolwhich governs how data is exchangedvia the cable can for example be Eth-ernet.The Ethernet protocol was originallydeveloped by Xerox in 1976. (The 'thinktank' of the Palo Alto Research Center,or PARC, where Ethernet was devel-oped was also responsible for thedevelopment of the mouse and the first

operating system which worked withwindows, called Smalltalk. This was thebasis from which Apple latter distilled itsGEM and Microsoft its Windows.)Ethernet Is based on a mechanismcalled Carrier Sense MultipleAccess/Collision Detection (CSMA'CD).A network station which wants to trans-mit data first checks whether the carri-er tone is present on the cable (Carri-er Sense). If it is not, then the stationitself can send data. However. multiplestations can be attached to the net-work bus (Multiple Access). The net-work checks whether two or more net-work stations attempt to send data viathe network at the same time. If thishappens then there is a 'collision'between the data transmissions of thevarious senders, which results in cor-ruption of the data. The senders arethus forced to resend their data. The

2 - 3/98 Elektor Electronics EXTRA Poo= rc,F,/,=.s

ripcord

jacket

conductor

wistedpairs

Ta

Figure 2. A UTP cable (Unshielded TwistedPair) contains eight conductors arranaedas four twisted pairs.

t

Ethernet protocol manages the net-work traffic. It determines which net-work card may communicate at agiven time and performs collisiondetection for Ethernet data packets.

UTP or BNC?

If we want to set up an Ethernet net-work for two computers, we are faced',with the fundamental choice betweenUTP and BNC. For somewhat larger net-works UTP is preferred. In the case ofonly a few computers which are con-nected to each other, BNC is just asgood a choice.

A BNC networkTne simplest BNC network consists oftwo computers each equipped with aBNC network card. A BNC T -connectoris attached to the BNC connector ofeach network card. A terminator is

attached to one arm of each of the T -connectors, and a standard coaxialcable (patch cable) is connectedbetween the other two arms. The pur-pose of the termination resistors is toavoid signal reflections in the cable.A single network cable may be up to185 metres long. A maximum of 30 sta-tions (PCs) can be connected to thecable. The minimum separationbetween two connection points (T -

connectors) is 0.5 metre. Several BNCcable sections may be connectedtogether via hubs, routers andrepeaters, so that it is possible to cre-ate a Local Area Network (LAN) whichis much larger in extent than the lengthof a single cable section.For two computers we need two net-work cards with T -connectors and twoterminators. A third computer is addedto the network bus by simply removingthe terminator from the T -connector ofone of the network cards, connectinga coaxial patch cable from that T -con-nector to a third T -connector, and

A router serves to contain local traffic within a particular section of a network, sothat it does not load the entire network. When routers are used, the network isconfigured as several interconnected local 'regions', and the only traffic whichis passed out of a given region to the remainder of the network is that which isdestined for a different region.A repeater amplifies the network signals, so that a greater distance can bereached.A hub in its simplest form is equivalent to an electrical 'multiple outlet' box.More expensive hubs are suitable for higher data rates, support more connec-tions and provide additional functions. An 'intelligent' hub can be remotely con-trolled.A patch cable is a ready-made extension cable, available in various standardlengths (up to 20 m).

reconnecting the terminator to theother arm of the third T -connector. Anetwork card for the third computercan then be attached to the third T -connector. As one can see, the termi-nators are always located at theextreme ends of the bus cable (seeFigure 1).

The same bus structure is used for alarger network. However, with a largernetwork a special kind of connectorbox is used. to which a special sort ofBNC extension cable is attached. Sev-eral T -connectors can then be incor-porated into this extension cable.A disadvantage of a BNC network isthat a single open cable or bad con-nection can bring down the entire net-

work. Every station which is included inthe affected loop can no longer workwhen this happens. The use of BNCconnector boxes helps to remedy thisshortcoming, since such a box is con-structed such that the network cable isautomatically connected 'through'inside the box when the extensioncable is disconnected from the box. Itis thus possible to remove an extensioncable without disturbing the operationof the network.

A UTP networkUTP is a more recent development. It ispreferred in place of BNC for newinstallations. For a continuouslyexpanding network. UTP offers clear

cross--.ner patch caste

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=figure 3. For a UTP network with two computers, a cross -over parch cable is sufficient;a). With three or more computers a hub is required (b).

Fo TC:01:01CS Elektor Electronics EXTRA 3 - 3198

advantages. The cable is less expen-sive, and the network is more reliableand easier to maintain. In addition. anISDN-based telephone network andan Ethernet network can use the samecable. which makes for a simpler infra-structure in a large building. A stan-dard BNC or UTP Ethernet runs at 10MHz. but a UTP Cat 5 cable can beused at up to 100 MHz. This allows forthe possibility of a migration to a faster100Base-T or 100Base-T4 network at alater date. A UTP Cat 5 cable, as illus-trated in Figure 2. contains eight leadsarranged as four twisted pairs. Whenthe same signal flows back and forthin the two wires of a twisted pair, theresulting magnetic fields cancel eachother out. This allows for interference -free data transfers. For 10Base-T and100Base-T two of the four pairs areused. All four pairs are used for100Base-T4. In principle, all four pairscan be connected. since the system isupwards -compatible.10Base-T and 100Base-T systems usethe Dl and D2 pairs, while ISDN usesthe D3 and D2 pairs. Thus, if we con-nect a UTP connector box as thoughwe were using 100Base-T4 (all fourpairs). it is then possible to use it forISDN. 10Base-T, 100Base-T or 100 -Base -T4. To be sure. it is extremely importantto take care that an ISDN primary leaddoes not become (accidentally) con-nected to the UTP network. A supplypotential of up to 90 V can be presentwilh an ISDN NT1 connection, and thiscan find its way into the UTP networkvia the D2 pair. If this ever happens,you had better hope that you havegood insurance coverage...In a 100Base-T4 network. all four pairsare used. For this reason such a net-work is sometimes called a 200 -MHznetwork. In fact it is a 'doubled' 100 -MHz network. which is adequately sup-ported by a 100 -MHz UTP Cat 5 cable.There are cables which allow evenfaster data transfers, such as Cat 5-(up to 300 MHz) and Cat 6 (up to600 MHz), but these are not of interestfor everyday applications. They arenaturally also more expensive.

To hub or not to hub...

When only two computers are to beconnected together, then UTP andBNC cabling are equally suitable.However, as soon as a third computeris added there is a financial disadvan-tage associated with UTP. With UTP acentral hub must be acquired to allowmore than two computers to be con-nected to the network (see Figure 3).and this can easily cost £70. With BNC

cabling a hub is not required.A hub works as a central connectorbox for UTP cables. The actual busstructure is based on the hub, and thehub manages the bus. For each com-puter connected to the network, thereis one UTP port necessary in the hub.Multiple hubs can be connected toeach other via patch cables anduplink ports. The smaller sorts of hubshave 4, 8 or 16 UTP ports.Ethernet cards are available for pricesranging from £20 apiece to over £70.If we assume a price of £25 per cardand a separation of 10 metresbetween the two computers, then wecan set up a two -computer network forroughly £70. The cost differencebetween BNC and UTP for a two -com-puter network is negligible. With threecomputers the cost of the networkusing BNC rises to roughly £100, whilewith UTP the cost jumps to roughly £170due to the addition of the hub.

The Ethernet card

Network cards are available for thestandard ISA bus which is present inevery PC, and also for the more recentPCI bus. A PCI network card is faster.but also more expensive. For homeuse an ISA card is adequate.With older -model cards, one mustconfigure the address and the inter-rupt channel on the card usingjumpers. Modern cards are set up withthe help of configuration software.With some operating systems the com-puter must be first started up using aMS-DOS boot diskette in order to con-figure the card, since the operatingsystem will otherwise not be able doanything with the card.The most obvious choices for the inter-rupt channel for a network card areIRQ5. 10 and 11. A sound card usuallyuses IRQ7 or IRQ5. THe standardSoundblaster value is IRQ7, which isalso shared with the printer port (LPT1).With the current generation of printerports (ECP)EPP) this is no longer possi-ble. In such cases, the sound cardinterrupt usually moves to IRQ5, and allinterrupt channels below IRQ9 are thusalready allocated. IRQ9 is not recom-mended. IRQ11 is sometimes used fora third IDE port (CD-ROM), and IRQ12is used by a PS,'2 mouse (if present).The most -commonly used interrupt forthe network card is IRQ10, with a stan-dard address of 300h.In a Plug -and -Play system (PnP) thenetwork card itself searches for a freeaddress and interrupt channel. Theselected values are passed to theoperating system via the driver. With

Windows 95 this technique does notalways work properly with some older -model PnP cards. The network cardchooses an address and an interruptvector while Windows 95 is still startingup, and then when Windows 95 is upand running it sees that this combina-tion is not free and thus assigns a dif-ferent address!interrupt set to the Win-dows 95 driver. Subsequently, the net-work card and the operating systemcheerfully chatter away withoutachieving any communication, andWindows 95 insists that there is no net-work card installed. The only remedy insuch a situation is to disable the PnPfunction of the network card via a MS-DOS utility program. With more modernsystems, 'Plug and Play' means thatWindows 95 automatically recognizesthe card during the startup and asksfor software. This does not alwaysmean that the user does not have toassist with the system configuration.A PnP motherboard reports duringstartup which interrupts have beenassigned in hardware by the PnP logicto the PCI VGA -card and a PCI networkcard. If the network card is an ISA cardwhich has been software -configuredfor IRQ10 and there is a PCI cardinstalled (for example. a VGA card)which is automatically assigned IRQ10by the PnP logic, then you naturallyhave a problem. In such a case IR010must be explicitly assigned to the ISAcard. This can be done by invokingthe Setup screen during the startupand configuring the computer to allowIRQ10 to be used for ISA cards only.The PnP BIOS will then skip this interruptchannel when assigning interrupts dur-ing subsequent startups.If you decide to start with BNC, but youanticipate that your network will even-tually grow significantly, then youshould go for a combination card.Such a card supports both BNC andUTP. At a later date you can add a huband replace the BNC cable with UTP.For a small firm which is just starting upit is in any case advisable to beginwith combination cards or go directlyto UTP.

There are several characteristics ofnetwork cords which together deter-mine the overall speed of the network.The most important of these is the net-work type (10 MHz or 100 MHz), butfeatures such as duplex mode. paral-lel tasking and bus mastering are alsosignificant.The duplex -mode capability of a net-work card can only be used if the cen-tral hub also supports this feature. Induplex mode the network card cansimultaneously send and receive data

4 - 3.98 Eleklor Electronics EXTRA

pair 1

pair 2

pair 2

Ethernet 10/100Base-T

1 TX+ D1 Transceive Data+2 TX- D1 Transceive Data -3 RX+ 02 Receive Oats+4 NC5 NC6 RX- D2 Receive Data -7 NC8 NC

Ethernet 100 Base -T4

962001 -113

1 TX+ D1 Transceive Data+ whitelorange 10/100Base-T2 TX- D1 Transceive Data- orange 10/100Base-T3 RX+ D2 Receive Data+ white/green 10/100Base-T. ISDN B14 81 D3 Bi-direct Data+ blue ISDN B25 BI D3 BI -direct. Data- white/blue ISDN 826 RX- 02 Receive Data- green 10/100 Base -T, ISDN B17 131 04 Bi-direct. Data+ white/brown

8 BI D4 8i -direct. Data- brown re01 - 1re

Figure 4. UTP cable connections.

via the hub. This results in an effectivedoubling of the network speed.With parallel tasking. several differentactivities can be processed by thenetwork card concurrently (and thusfaster overall). This also reduces theload on the computers processorchip. This feature is certainly advisablefor a central server.Bus mastering means that the networkcard can take over control of the PCIbus and thereby reduce the load onthe processor chip. Not all mother-boards support bus mastering. In somecases this can be remedied by a BIOSupdate.If you are interested in picking up sec-ond-hand network cards at a jumblesale, you should make sure that youget 16 -bit cards which allow the inter-rupt to be set higher than IRQ9, andthat a suitable driver is available(NE2000 or 3Com -compatible). Everyimitation -brand manufacturer takescare that his card is compatible withNE2000, for which generic drivers arealways available. The disadvantage ofgeneric drivers is that they do notalways realize the full performancewhich a particular card can provide.The performance of a driver which ismatched to the card is usually better.Support for 3Com Ethernet cards isgenerally adequate but not more thanthat. Even Linux (freeware Unix) firstsupported NE2000-compatible net-work cards and only later 3Com Ether -link cards.

Installingthe network softwareAfter the cables have all been pulledand the PnP adventure has been

brought to a successful conclusion,one is faced with a choice between anumber of different network operatingsystems. Ethernet is only the low-levelnetwork protocol. What is communi-cated via Ethernet is a different sub-ject entirely. One can compare Ether-net to the alphabet, and the networkoperating system to a particular lan-guage which uses the alphabet.

There are three important types of net-work operating systems for use withEthernet:1. NetBEUI Windows 4.11, Win-dows 95 and Windows NT2. IPX/SPX Novell Netware3. TCP/IP Internet

If we work with Windows 95 as ouroperating system, then the choice iseasy: NetBEUI. Windows 95 has a nastytendency to also routinely installIPX/SPX. This is a leftover from severalyears ago, when Novell Netware hada large market share. In the meantimethat is ancient history, but Microsofthas not quite caught up to the currentsituation.Under Windows, you can see what isinstalled via the selections Start/Set-tings/Control Panel/Network. A cleardistinction is made between adapters(network cards) and protocols (networkoperating systems). If more than onenetwork card is present, then the cou-pling between each adapter and itsassociated protocol is also shown. Thesecond adapter is as a rule the dial -upadapter which is used for an Internetconnection. This dial -up adaptermakes the computer appear to theInternet as though it has a networkcard installed which works with the

TCP/IP protocol. In actual fact the net-work card is generated by the Internetservice provider and the combinationof the modem and telephone con-nection acts as a sort of extension ofthis network card. The TCP/IP protocol isrequired for the Internet connection.In the worst case you will have a net-work card plus a modem (for Internet),with the following standard installation:

Client for Microsoft NetworksAdaptennehvork cardAdapter:dial-up adapterProtocol:NetBEUI network cardProtocol:NetBEUI -. dial -up adapterProtocol:IPX/SPX network cardProtocol:IPX/SPX --F dial -up adapterProtocol:TCP/IP -+ network cardProtocol:TCP/IP dial -up adapterFile and printer sharing for MicrosoftNetworks

It's truly a technological wonder thatsuch a babelesque situation actuallyworks: here we have two adapters'speaking' three different languages(protocols), all mixed together.In principle it is possible to have multi-ple network operating systems allworking over the same cable, but thisis not to be recommended. Perfor-mance will certainly suffer in such asituation.There are only two reasons to useIPX/SPX. The first reason is that one willbe working together with a Novell net-work. For home applications this willpractically never be the case. Thesecond reason is somewhat moreimportant for the home situation: thereare many multiplayer games whichuse IPX/SPX or TCP/IP to establish a con-nection between the various comput-ers. Some of these games run fasterwith IPX/SPX than with TCP/IP In suchcases it makes sense to leave IPX/SPXcoupled to the network card in thosecomputers.For the Internet only TCP/IP is neces-sary, so that all couplings of NetBEUI orIPX/SPX with the dialup card can beremoved. Throw away everythingwhich Is not required! After a rigorouscleanup exercise our minimal net-work/Internet system configurationappears as follows:

Client for Microsoft NetworksAdapternehvork card (eg NE2000)Adapter:dial-up adapterProtocol:NetBEUI network cardProtocol:TCP/IP dial -up adapterFile and printer sharing for MicrosoftNetworks

P Topics Elektor Electronics EXTRA 5 - 3/98

For many applications, the use of an on -site computer toperform measurements or control processes is a goodsolution. A limitation of all of the data -acquisition systemswhich we have published up to now is that a direct elec-trical connection is required be-ween the computer andthe acquisition system. The system described here worksvia a modem, which allows data to be exchanged withthe PC via the telephone line. This makes possible a con-siderable physical separation between the computerand the acquisition system. For example, one no longerneeds to guess at the temperature in the weekend cot-tage: with a suitable sensor you can just ring up, log inand read it out.

Data acquisition bymodemremote measurement and control by telephone line

to modem

RS232

MAX232

S2

1-1AUTO

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Si

13iRESET!

03

AT89C52

JP2

6

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T24001 Menu9600 on/off

AT93C46

DCF8591

4

962037 -11

L 3 ports

co.,nter input

frequency muterinput

analoguecut

analogueoutput

Figure 1. Block diagram of the complete circuit. A lot of capability Is bundled into afew components.

Our demand for information seems toincrease in step with the progress oftechnology. Now that a PC can befound in almost every household, usersdesire to expand their horizons. Addinga data acquisition system is an obviouspossibility. Most such systems are con-nected to the PC via a parallel or serialport: a few of them are connecteddirectly to the internal bus. Such sys-

tems are the natural choice when thecomputer is located at the site wherethe measurements are to be made.The data acquisition card which isdescribed here allows measurementsto be made, or functions to beswitched on or off. at almost anydesired location. The only condition isthat there must be access to a tele-phone connection. The hardware and

software of the card are configured sothat they can control a standardHayes -compatible modem via a serialinterface. This system supports a datarate of 2400 or 9600 baud. This meansthat even rather ancient modems canbe given a new lease on life.The design is based on an AtmelAT89C52 processor. In addition to anumber of analogue and digital inputs,it has a serial port which can be con-nected to a standard modem. There isalso a separate AD -D A converter andan EEPROM. In the present design thereare 16 digital I 0 lines available. Theseare supplemented by four 8 -bit ana-logue inputs, one 8 -bit analogue out-put. a 16 -bit counter and an input formeasuring the frequency of signals upto 65 kHz.The available software includes a ter-minal emulator. which allows if to com-municate with an ANSI or VT102 termi-nal program on the PC. Password pro-tection is incorporated in the software.and the password can be stored in theEEPROM.

For the user, logging in to the dataacquisition system is similar to connect-ing to a bulletin -board system. Afterstarting the terminal program. oneselects the proper telephone number,waits for the connection to be estab-lished and then logs in with the correct

6 - 3/98 Elektor Electronics EXTRA PP4= Tc=o1:0/4=.s

Technical specifications16 digital I/O lines4 analogue inputs (8 -bit resolution) with a range of 0-2.55 V1 analogue output (8 -bit resolution) with a range of 0-2.55 V

.-_-, 1 16 -bit counter with reset and overflow indication1 frequency measurement input (range 0 to 65 kHz)

r.:".; supports Hayes -compatible modemscompatible with ANSI and VT102 terminal programstwo data transmission rates: 2400 and 9600 baud

Ci built-in password protectionuser -configurable communications protocol r r

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password. For those who have theambition to do so, it is possible to writeone's own communication programand disable the built-in terminal pro-gram.

A flexible approach

Figure 1 shows the system block dia-gram. The heart of the system is theAtmel AT89C52. This processor is com-patible with the well-known MCS51processor family, and has the advan-tage that it includes an 8-kB flash mem-ory for storing program code.The processor has three 8 -bit parallelports and a single serial port. The P1and P2 ports are made available forexternal connections; together they

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form a 16 -bit digital I/O port. The thirdport (P0)15 used to control the operationof the PCF8591. This integrated circuitincorporates a four -channel ND con-verter and a single D/A converter. AnAT93C46 EEPROM with a capacity of128 x 8 bits is also present. This chiphas a guaranteed lifetime of 1 millionwrite cycles - and will retain data forat least 100 years. It is used in this caseto store configuration data. The con-version of signal levels between TTL andRS232 is handled by an old friend, theMaxim MAX232.A Reset switch is provided to allow theboard to be re -initialized. The Auto -answer switch allows the board to betemporarily placed in a mode in whichit does not respond to the ring signal.

JC

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P.-71

Two jumpers enable the selection of thecommunication data rate (2400 or9600 baud) and select whether or notthe built-in menu functions are used.Finally, there are two LED indicatorswhich display the operating status ofthe board.Note that the modem is not shown inthe block diagram. In practice, themodem will be an external devicewhich is connected to the serial port ofthe data acquisition card.

A compact circuit

Given its specifications, one might thinkthat the data -acquisition card wouldbe a large and complex construction.Nothing could be less true, and in factwe have here a project using very fewcomponents. Figure 2 shows the fullschematic of the card. It incorporatesonly seven integrated circuits. includ-ing the voltage regulator and the ref-erence source.The central element is IC4, the AT89C52processor, which runs at a clock rate of12 MHz. The required clock oscillator isconstructed using Cl , C2, X1 and logicinternal to the processor chip. 110 portsP1 and P2 are connected via 2.7-1d2series resistors to the 'C' -row of the 64 -way connector Kl. A set of eight pullupresistors is provided for the third port

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PC Yolks Elektor Electronics EXTRA 7 - 3/98

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Figure 3. The copper track layout and the component overlay of the circuit board for this project (not available ready -mode).

(P0), which is connected to the EEPROMIC3 (an AT93C46). jumpers JP1 and JP2,the auto -answer switch S2, the SDA andSCL lines for IC2 (AD-D(A converterPCF8591) and finally to the AA input ofKl. The fourth and final port (P3) is alsoused for a variety of tasks. P3.0 -P3.3are assigned to the serial communica-tion port. P3.4 and P3.5 are used for thecounter and frequency -measurementfunctions respectively. and P3.6 and

P3.7 drive the two LED indicators.The design of the serial port is straight-forward, although it is wired as a DCE(data communication equipment)instead of DTE (data terminal equip-ment). The serial port has five leads:RxD and TxD. DCD (input) and DCR(output) and of course the earth(Ground) connection. In addition. theRTS and CTS lines are directly con-nected to each other at the connector.

The MAX232 chip (101) used here workswith a supply potential of 5 V and con-verts signal voltages between the TTLlevels used by the processor and thelevels employed for the external RS232connection. The DCD signal is invertedby a logic element consisting of R28,R29 and Tl. A change in signal level onthe P3.3 input indicates to the proces-sor that a connection is being madeand that a response is desired.

8 - 3198 Elektor Electronics EXTRA

COMPONENTS LIST

Resistors:

R1 -R16 = 2k.Q7

R17 -R20 = 10kc2

R21 = 470QR22 = 8k522

R23 = 1002R24 = 330QR25 = 82053

R26 = 33k2R27 = 47102 preset. multiturn

R28 = 100kgR29 = 4k27R30 = 10k2 SIL array

Capacitors:C1.C2= 22pF

C3 -C7 = 10uF 16V. radial

C8.C9 = 4uF7 10V. tantalumC10 = 22011F 25VC11,C13 = 100nF

Semiconductors:T1 = BC557T2 = BC547D2 = LED 5 mm. green03 = LED 5 mm. redD4.D5 = 1N4148D6 = 1N4002IC1 = MAX232IC2 = PCF8591IC3 = AT93C46IC4 = AT89C52-PC16 (order code986504-1)IC5 = LF356IC6 = 7805IC7 = LM336-5.0

Miscellaneous:X1 = 12-MHz-kristalK1 = 64 -pin DIN connector, AC IOWK2 = 2 -way PCB terminal blockK3 = 9 -way sub -D connectorS1 ,S2 = single -pole push-buttonJP1.JP2 = jumperDisk (program source codes). ordercode 986504-1.

The NO-D/A converter design is simple.It is based on the Philips PCF8591 chip.This device communicates via the l2Cbus. The required control signals aregenerated by the processor via its P0.6and P0.7 y0 port connections. In addi-tion to an 8 -bit analogue output, thePCF8591 has four 8 -bit analogueinputs. The required 2.55-V referencepotential is generated by a referencesource built around a current source

(T1) and a voltage reference chip (IC7).The reference potential of IC7 is 5.0 V;this is reduced to the desired value of2.55 V by a resistive divider consistingof R26 and R27. For expansion pur-poses, the reference potential is alsobought out to Kl. Resistors R17 - R20protect the inputs of the AD converteragainst excessive input voltages.Not much needs to be said about theinterface to the EEPROM. This IC has acapacity of 128 x 8 bits and is used bythe software for storing configurationsettings.The last item is the power supply. Thispart of the circuit is based on a provendesign and provides a stabilized poten-tial of 5 V. The unregulated input volt-age is connected directly to the refer-ence -potential generator.

Construction:relatively simpleAlthough this is a reasonably advancedproject, its construction should certainlynot be difficult for an experienced hob-byist. Even making one's own circuitboard should not be all that challeng-ing, seeing that it is single -sided andthe layout is relatively open. Figure 3shows the copper track layout and thecomponent overlay. If you solder care-fully and use IC sockets to avoid possi-ble damage to the ICs, success is prac-tically guaranteed. Mount the wire linksand connectors Kl, K2 and K3 beforemounting other components.Check the supply voltage after IC6 andIC7 have been installed, and theninsert the remaining chips in their indi-cated positions. The system is now justabout ready for use; if is only necessaryto first adjust the reference potential.Use a digital multimeter to measure thevoltage between pins 14 and 8 of IC2.Adjust R27 until this measures exactly2.55 V.It is not necessary to connect amodem at this point. Connect thepower and wait for a little while. If

everything is in order, the red LEDshould start to flash after about 1 sec-ond, which is a sign that the EEPROMchecksum is incorrect. This is a normaloccurrence with a new (and thusempty) EEPROfv1. The processor will nowinstall the default configuration settingsin the EEPROM. Press briefly on the Resetswitch (S1) and then wait about 25 sec-onds. The red and green LEDs will lightalternately for 5 seconds. Afterwardsthe green LED will start flashing. as asign that the system could not initializethe modem. This cycle repeats itselfevery 25 seconds. which is evidencethat the system is operating.

The software

The software can be installed withouthoving a modem connected to the sys-tem. However. a special cable is nec-essary for this. Make up the cable usingtwo female 9 -pin sub -D connectors.Cross -connect pins 2 and 3 betweenthe two connectors, and directly inter-connect the remaining pins. The boardcan be directly connected to the PC asa peripheral device by means of thiscable. Select the desired serial port set-tings (2400. N. 8, 1 or 9600, N, 8, 1) andstart the terminal emulation program(ANSI or VT102). The Xon'Xoff communi-cations protocol is used. Now pressboth Reset (S1) and Auto -answer (S2) atthe same lime and hold the latterswitch pressed until the setup menuappears on the screen. The menuselections provide access to a set of sixfunctions which are self-explanatory.The password may contain numeralsand letters. Note that the software dis-tinguishes between uppercase andlowercase letters.The modem initialization function is suit-able for all commonly -available mod-ern modems. In case a modem is notused, such as with a direct serial con-nection to the PC, the initialization stringcan be deleted. If desired, a user -specified initialization string can beinstalled. Note the following restrictionswith regard to modem configuration:

7. a connection must be indicatedvia the DCD signal (&C1)

C` a falling edge on DTR invokes thecommand mode (&D1)

n use Xon,Xoff (&K4)'s the modem must be in auto -

answer mode and respond afterthree ring tones (S0=3)

The following menu options are used toenter the basic configuration settingsfor the I/O port and the OA converter.These settings are used after a hardreset (cold start). If the Reset switch ispressed, the last -used configuration set-tings are retained. Note that port lineswhich are used as inputs will first bebriefly set to a high level ('1') as a con-sequence of the internal design of theprocessor. If one selects the option'Load default settings in ROM' then thecontroller selects the settings whichhave been stored in ROM by thedesigner. These are as follows:

n system ID: nonen password: a single space charac-

ter' modem initialization string:

AT&FEOLOVO&D1&K4&R1S0=3S7=90

Tc)FPi4cs Elektor Electronics EXTRA 9 - 3198

oden data -acquisition systen v. 1.2 --al-tine I/O status ...

I/O PORTS (pin levels)

Systen ID: Deno

PORT1 Pin O Status : 1 PORT2 Pin 0 Status : 1

PORT1 Pin 1 Status :1 PORT2 Pin 1 Status : 1PORT1 Pin 2 Status : 1 PORT2 Pin 2 Status : 1

PORT1 Pin 3 Status : 1 PORT2 Pin 3 Status : 1

PORT1 Pin 4 Status : PORT2 Pin 4 Status : 1PORT1 Pin 5 Status : 1 PORT2 Pin 5 Status : 1

PORT! Pin 6 Status : 1 PORT2 Pin 6 Status : 1PORT1 Pin 7 Status : 1 PORT2 Pin 7 Status : 1

A/D D/A Converter status

A/D Input channel 0A/D Input channel 1A/D Input channel 2AID Input channel 3D/A Output register

: 0.00 U: 0.00 U: 0.00 U: 0.00 U: 0.00 U

Press ESC to return to nain nenu

Counter register : 000000Frequency Input : mem Hz

1

Figure 4. The assembled board can communicate with any ANSI or VT102-comparibleTerminal via a modem.

^ after a cold start. all 16 I 0 lines arehigh and the output potential of theD A converter is 0 V.

The system also stores these default set-tings in the EEPROM if an incorrect EEP-ROM checksum is detected.The (new) configuration settings orestored in the EEPROM upon exiting thesetup menu. In the case of certainolder -style modems for which a delayof several seconds is desired betweencarrier detection and the start of dataexchange. the Auto -answer switch mustbe activated and held (depressed)

while leaving the setup menu. By thismeans a supplementary 10 -seconddelay is programmed. Whenever thesetup menu is subsequently exited with-out holding the Auto -answer switchdepressed. this extra delay is deleted.

Operation

Now it's time to put the card to use.Attach a modem to connector K3 via anormal serial cable. Select the desiredbaud rate with JP1 and leave JP2 openfor the time being. (Note that thejumper positions are only read during

'1.71v11.21.122.1C

oden data -acquisition systen v. 1.2 -- Systen ID: Deno

SETUP MEHU

General z;ettifyishildcil initialisation -String1/0 ports - default valuesDA converter default settingsLoad default -settings in ROMSave settings & exit

Use arrow keys + return to select

1

41 1

figure 5. The status of at inputs and outputs appears on the screen at the press of a

the startup sequence. so that anychanges made between startups willnot affect the current selection.) Thesystem is now ready for use. First switchon the modem. and then apply powerto the data acquisition card. The redand green LED indicators will flash alter-nately. As soon as the modem initial-ization has been successfully com-pleted, the green LED will light continu-ously. By the way. the configuration ofthe modern initialization string can beeasily checked out by sending it fromthe PC in terminal mode to the modem,The response from the modem shouldbe 'OK' or '0'.Disable the auto -answer mode bybriefly pressing the Auto -answer switch.The green LED will flash at a slow rate,and the modem will now not respondto a ring tone on the telephone line.Press the Auto -answer switch again tore -enable the normal auto -answermode.

Logging in and more...

Logging in to the system is similar tologging in to a BBS. Immediately afterthe connection is established. the useris requested to enter the password. Ifan incorrect password is entered. therequest is repeated. Pressing 'ESC' or'Ctrl -C' terminates the login process. Ifthe correct password is entered. thenthe initial menu appears. The followingfunctions are available in turn:

real-time l'O statuswrite to output register PORT1write to output register PORT2

r..% write to the D/A output' reset the counter registerti " disconnect

The functions of the various options areself-explanatory. You will find that a fewminutes' experimenting is enough tofamiliarize yourself with card's opera-tion. As previously noted. the menufunction can be disabled by means ofa jumper setting. In this case a user -written procedure must be used to pro-vide the communications functions. Allcommands are formed by a combi-nation of the upper-case letters A- Fand the numerals 0-9. followed asappropriate by a carriage return('Return' character). After the connec-tion has been established the systemsends the text "ID:- followed by a sys-tem identification string and a carriagereturn. Following this the password mustbe entered. The correct password isconfirmed via the 'ACK' character; thesystem responds to an incorrect pass-word with the 'NACK' character. The

10 - 3198 Elektor Electronics EXTRA TopicsPC

LED indicatorsRed LED offonflashingoffoffalternately flashing

Green LEDonoffoffslow flashingfast flashing

Statusstandby/operation without modemconnection with another modemEEPROM checksum errorauto -answer disabledmodem initialization errorwaiting for ti teu.'1*:alization

procedure can be terminated bysending the 'ESC' character.

Summary of the commandsCO - Control commandThis command is answered with 'OK'.This only works if no modem is beingused: otherwise a 'NACK' character issent in response.

C1 - Request I/O dataThis command causes a string of char-acters to be sent after a delay of onesecond. This string has the followingconstruction:

AABBCCDDEEFFGGHHI-IJJJJKKKKLLMfv1< CR >in which the data is presented as fol-lows:

AA = Port 1 register dataBB = Port 1 input levelsCC = Port 2 register dataDD = Port 2 input levelsEE-HH = A D channels 1 x4 values

uu i sued from pac_a,

With this configuration there is no longerany extra ballast, but vie have a func-tioning local network connection (viaNetBEUI) and an Internet connection(via TCP:IP).The options 'Client for Microsoft Net-works' and 'File and printer sharing'must be present to allow our computerto share devices or files via the network.V/e can use 'File and printer sharing' toindividually configure our computer forprinter sharing alone or file sharing as.'ell.

Let's share...

It we wish to shore files, we must clearlyindicate this via the MS Explorer. If wewish to make the contents of a subdi-rectory available on the network, thenwe identify the subdirectory and clickonce on the subdirectory with the right-most mouse button. The option 'sharing'is displayed in the menu which thenappears. After this option is clicked aconfiguration menu appears. In the

TOP/CS

II = D/A output register dataJJJJ = value of 16 -bit counterKKKK = frequency measurement resultLL = flag register data:- bit 0 indicates an I2S communication

error- bit 1 indicates a counter overflow- bit 3 indicates a frequency measure-

ment overflow- bits 4-7 are not usedMM = checksum value

C2 - Write to I/OThis command should be followedwithin one second by a character stringcontaining the following data:AA = new value for Port 1 registerBB = new value for Port 2 registerCC = new value for DA output registerDD = checksum

If the received checksum is correctthen the system responds by sendingan 'ACK' character; if the checksum isincorrect then the system responds witha 'NACK' character.

configuration menu we can make thesubdirectory shareable. assign a nameto it and determine whether it is sharedread-only or read/write. We can alsoprotect shared access with a password.Further down in Windows Explorer wefind 'Network'. If we open this, we see apresentation of the various workgroupsand computers. The sharable subdi-rectories are listed under the individualcomputers. If both file and printer shar-ing are disabled in a particular com-puter, then it is not visible to the NetBEUInetwork.In a small network we work with a singleviorkgroup, which has the defaultname of 'workgroup'. V/e can assign aname of our choice via 'Network:iden-tification'. If a lot of data is exchangedwith a particular computer via the net-work, then it is as a rule more conve-nient to assign the hard -disk drive of theother computer to our own computer inthe form of a drive letter. To do so wefirst use the Explorer to display the net-work directories. A click on the desiredsubdirectory with the rightmost mousebutton causes a menu to appear with

C3 - Reset counterThis command resets the counter tozero and clears the counter overflowflag.

C4 - Break the connectionThis command only works in combina-tion with a modem. If it is used in theabsence of a modem, a 'NACK' char-acter is sent in response.

In general. the interval between acommand and its associated datastring may not exceed one second.

Perhaps this has been a bit much inone go, but we've now gotten throughthe complete design description. Fromnow own, you should remember therule that 'experience is the bestteacher', and thus put the system touse in some practical applications. Thismeans soldering and programming.and looking for suitable applications.Here we limit ourselves to the interfaceprovided by the data acquisition sys-tem and leave the question of its appli-cation to you. However. numerouspotential applications may be found inpast issues of Elektor Electronics. sohappy hunting! (tip: use the ElektorElectronics Item Tracer).

the option 'Map Network Drive'. Herewe can enter a drive letter. The mostimportant option appears at the bot-tom: 'Reconnect at logon'. If we wish tocreate a permanent coupling, then weenable this option.A network printer may be assigned toone's own system by selecting Start.Set-tings:Printers'Add Printer. In the secondwindow we can specify whether wewant a local printer or a network printer.Select 'network printer'. A particular net-work printer can then be selected viathe 'Browse' option. If vie wish to printfrom a system running MS-DOS. then wemust reply 'yes' in response to the ques-tion 'Do you print from MS-DOS basedprograms?'. This option can also beenabled at a later stage via 'CapturePrinter Port'.With this information presented in thisarticle it should not prove difficult to setup a small Windows 95/3.11 network.Such a network need not be all thatexpensive, and it offers a lot more pos-sibilities than a collection of isolatedcomputers.

- Elektor Electronics EXTRA

082C01 -2j

11 - 3/98

Many older PCs have accumulated lots of dust inside the case and canbenefit from cleaning a number of areas and essential components.Although the build-up of dirt, dust, grime and debris inside the PC case willrarely be the cause of immediate hardware malfunctions, it does obstructto some extent the absolutely vital airflow inside the computer case. This,in turn, lessens the cooling capacity of ventilators, in particular, the noisyone at the most dreaded and ugliest side of computer: the back! Spring-cleaning PC hardware is often forgotten as most PC users seem to associ-ate the term maintenance with orphan -DLL clearing, hard -disk defrag-menting and the like.

dust in the PCspring-cleaning old dust eaters

Figure 1. Illustrating the airflow in a typical medium -size tower case. Assuming that thecover is fitted on to the case, the ventilator at the rear of the power supply unit (PSU)causes air to be sucked Into the case along various paths. Unfortunately, the main air-flow causes dust particles from the floor to be carried into the case. For obvious rea-sons, the air intake of the PSU may not be obstructed by cables. Note that this PC wasbeing overhauled when we made the photograph. Normally, it contains a number ofextension cards, and all slot cover plates at the rear ore fitted so there is no air intake inthis area.

Browsing through the latest computermagazines and reading about newand ever faster machines (and someof the incredible problems they pre-sent), it's easy to forget that there arethousands of PCs around lhai havebeen in use for many years in homesand offices. In most cases, there'snothing amiss with these trusty 386 and486 based machines. except, per-haps, that they are slow and theirstreet value may be a disappointingfew tenners or so. So. many of you willargue that such old beasts are bestleft to do whatever they are still able todo. And yet, cleaning the inside ofthese oldies is rewarding because itensures that they continue to function:sometimes even better than before!

Airflow in a PC

If you put your hand near the ventila-tor at the rear of a running PC. you willnotice that the fan produces an out-ward bound air stream. The tempera-ture of the air stream will depend onthe size of the PC and the amount ofelectronics inside. In our experience,desktop and tower PCs for home andoffice use never produce hot air. It

your PC does, it's high time to reviewthe situation inside the case!

The function of the PSU (power sup-ply unit) ventilator is to establish asteady flow of (relatively) fresh airacross and around electronic compo-nents that may be damaged if theybecome too hot. The PSU fan has beenan essential component in PC designever since the first PC -XTs and clonesappeared on the market about

12 - 3/98 Elektor Electronics EXTRA

15_years ago. Okay, modern PCshave temperature -controlled ventila-tors which are much quieter than theearly types, but that does not detractfrom the necessity of a cooling airstream in the case. The reason formentioning the PSU fan in this article isthat it has two unwelcome side -effects.The first is that it produces noise. Noise,although not the main subject of thisarticle, may be redirced to a certainextent, as will be discussed further on.The second problem with the fan isthat it collects dust which may ulti-mately cause it to run slower, and soendanger the life of the componentslhat should be cooled. because theairflow is vastly reduced.

The build-up of dust in certain areasinside the PC may be explained on thebasis of the air flow created by the PSUfan. Basically, (relatively) cool air is

sucked into the case along variouspaths. passed through the PSU case,and blown out of the case. The air flowin a typical (medium -size) tower case isillustrated in Figure 1. It is, of course,assumed that the PC case is closed.Usually, 'fresh' air is sucked into thetower case via openings (slots, a perfo-rated area or a grille -like structure) inthe PC front side. near the base of thecase. Air flows over the motherboard.along extension cards, and is eventual-ly sucked into the PSU through ventila-tion holes in the PSU case. PC PSUs aretypically switched -mode types whichcontain a number of components thatrun pretty hot, so cooling is really inorder here. As you can see in Figure 2,the typical air flow in a desktop PCcase is basically the same as in a towercase. You may not have realized that asmall amount of air is also sucked in viathe small openings in and around afloppy disk drive, hard disk drive, CD-ROM drive or tape drive mounted in thedrive boy. Some cooling of these drivesis essential, however, as some hard diskdrives and tape drives run much hotterthat one would imagine.

The PSU and CPU fans

There is a fairly simple way to make aneducated guess about the amount ofdust waiting to greet you when youopen up an antediluvian PC. Withoutopening the PC case. look at theamount of dust which has settled inand around the PSU fan. In somecases. you may have to remove theprotective grille. Typically, desktop PCscollect less dust than big -towers. This islogical in view of the air stream dis-cussed above: tower cases 'inhale'more dust because the main air intake

Figure 2. Illustrating the airflow in a typical desktop PC (this vintage one happened to beportly salvaged).

Figure 3. A dusty PSU fan like this one indicates that the inside of the PC is long overduefor cleaning.

PC TOPICS Elektor Electronics EXTRA 13 - 3/98

Figure 4. Dismantled PSU case with the fan removed separately. It is easily cleaned witha small brush and a vacuum cleaner filled with a small nozzle. Check the fan forsmooth operation, and if necessary replace it by a new quieter, one.

Figure 5. A dusty CPU fon like this ultra -low cost one we found in an ageing 486 PC canbe the cause of a costly repair job if it is not cleaned and inspected for wear and tear.Like the PSU fan, the CPU fon is often best replaced by a more up to date type.

point is nearer the floor. Figure 3 showsa likely candidate for cleaning. Dust isrife and clearly visible on this PSU fanboasting ten years of faithful opera-tion.

Before we continue our story, animportant point must be mentioned.Removing dust from the inside of aPC involves opening the case anddisassembling some of the internalcomponents. This should not beattempted by beginners, or if the PCis still covered by a warranty. Also, allactions should be carried out withthe mains cord and all peripheralsdisconnected. Observe all precau-tions relevant to electrical safety.

Fortunately. cleaning the PSU fan isnot required on a weekly or evenmonthly basis, the amount of dust hav-ing settled in and around the fanblades depending mainly on the num-ber of hours the PC has been in use.and its location the office. study, cel-lar. broom cupboard. kitchen, attic orliving room!

In some cases, it will be sufficient ifthe dust on and around the fan is

removed using a small brush and avacuum cleaner. However. for a thor-ough spring-cleaning job, you have toremove the PSU from the case. Usually.two or three Phillips screw drivers areall you need for this purpose. Be care-ful not to damage the screw heads asdoing so may make it impossible tosecure the screws properly again later.All power supply cables inside thecase have to be disconnected fromthe motherboard, the drives (floppydisk, hard disk, tape drive, CD-ROMdrive. etc.) and the CPU fan, if fitted.Sometimes the entire PSU has to beremoved before you can get yourhands on the motherboard supplyconnectors. insertion cards being inthe way. and the connectors stashedaway under the PSU block. Most PSUshave an attached cable for the mainsswitch connections. and this cablemay only be disconnected at thepower switch. It's just as well to disas-semble the switch unit and give the lota thorough cleaning. too. as it is anunexpected but serious dust collector.

The PSU is typically secured with fouror six screws on the rear panel of thePC's internal frame. In many desktopcases. it is additionally secured to abracket close to the bottom of thecase. Fortunately, none of these con-structions are complex or tricky to dis-assemble (we're not talking of the lat-est notebooks and other 'crammed'PC technology here).

The next step is to open the PSUproper. As there are countless varia-

14 3/98 Eleklor Electronics EXTRA

Lions on this theme, it is difficult to givehard and fast advice here. Take sometime to study the structure of the PSUcasing. The screws that need to beloosened at this point should be nearthe edges of the casing. Others furtherremoved from the edges are bestgiven a miss because they typicallysecure intend components live powersemiconductors that require the metalside panels for cooling.

Take the PSU casing apart, and givethe inside a thorough cleaning usingthe brush -and -vacuum -cleanermethod already mentioned. Now'salso a good opportunity to remove thefan, and clean it separately (Figure 4).Make sure you know how the thing is tobe mounted again, however, as yourun the risk of accidentally reversingthe air flow on re -assembly. Sometimesthese fans have an arrow printed onthem to indicate the direction of theairflow at the correct polarity. You maynot want to mount the same old fanagain, however, because an attrac-tive opportunity is available to replaceit with a new and better one, i.e., tem-perature -controlled. quieter and/orwith real (metal) ball bearings. Such an(inexpensive) upgrade is sure to elimi-nate much of the appalling noise pro-duced by many ageing PC.

to an air com-pressor (the local garage may be ableto help you) which you can use out ofdoors, then the PSU casing and the fanmay be cleaned in one go. In gener-al, however, it is not recommended toremove dust by any kind of blowingaction as it presents a potential healthhazard. and may cause the stuff youwanted of get rid off to end up a cou-ple of inches further on, in placeswhere it wreaks havoc.

The other, much smaller, fan whichmay need cleaning is the one fitted ontop of those hot-headed 486 and Pen-tium CPUs (Figure 5). Dusting off andinspecting it will be relatively simple asthere are no screws involved. and thesame general guidelines apply asthose for the PSU fan. This fan, too, is agood candidate for replacement asmuch quieter and longer lasting typesare now readily available from manycomputer shops. Note, however, that486 -type coolers are becomingscarce, and that they are not inter-changeable with Pentium coolers(which is not to say that the fan can'tbe removed and replaced separate-ly). Here, too, go for a fan with ballbearings rather than friction bearingas found in most inferior, all -plastic,incredibly -cheap products. Remem-ber, any dust permanently lodged on

Figure 6. Mice eating dust? The ones in our offices do.

the CPU fan will result in reduced cool-ing capacity, and, eventually, totalbreakdown with possibly catastrophicconsequences for the CPU. And then,to odd to the misery, a replacementfor, say, a once stalwartly 486DX66 willbe surprisingly hard to get. making thewhole PC useless.

Heaps of dust may also be found atother spots in the PC, for example, inthe rear corners of the metal frame,near the slot cover brackets. and atthe outside of the air intake grillewhere the loudspeaker is secured.

Once the PSU is in place again, youmay want to inspect its air intake area.In not a few cases, this is partlyblocked by power supply cables anddisk drive flatcables squeezed togeth-er in a chaotic manner. Organizethese cables to clear the PSU air intakearea. and remove any dust you mayfind lodged on the flatcables. Thesemay be zigzag -folded where neces-sary, and held in place by a paper-clip (watch out for short-circuits howev-er). In some cases, it's even worthwhileto reshuffle the disk/CD-ROIVVtape dri-ves in the drive bay and. of course,extension cards in older PCs. Reshuf-fling also allows you to properly secureall cables.

Of mice and dust

Instructions on cleaning the mouseshould be given in the manual thatcame with it. Figure 6 shows a smalldust ball collected by a mouse usedin office surroundings over a period ofabout six months. In general, cleaningthe mouse will only involve removingthe internal ball and gently removingany dust build-up inside. In rarecases, the internal rollers or wheelsthat keep the ball in place may needcleaning also.

Keyboard shake -out

You'll be amazed at the amount ofdebris collected by an ordinary PCkeyboard which is not protected by aplastic cover. Most PC users do notseem to bother about this, however,until one or more keys remains stuck,or does not produce a particularcharacter any more. Such problemsmay be prevented by holding the key-board upside down and shaking it vig-orously. say, once a month. You mayalso rap one of the keyboard cornerson the desktop (Figure 7). Don't beafraid to do this: all reasonably builtkeyboards will survive this gentle mal-

1:3.(C 7-0::ppcs Elektor Electronics EXTRA 15 - 3/98

Figure 7. Illustrating the keyboard shake -out. You'll be amazed at the amount of debrislodging in a PC keyboard.

Figure 8. Internal cleaning of a PC monitor should not be attempted by beginners. Thearrows in this photograph point of spots which are likely to be covered in dust.

treatment. For extra fun, put a largesheet of white paper on your desk. Wefound (among other bits best leftunmentioned) hairs, bits of paper,bread crumbs, chocolate sprinkles,cigarette ash and tobacco.

Only if you are really serious aboutcleaning the keyboard, you may wantto take it apart and remove each andevery foreign particle encounteredtherein. This may be tricky however assome low-cost keyboards contain asingle, very fragile circuit board.

The monitorWhen it comes to cleaning, the PCmonitor is a separate story. There are anumber of risks to be taken intoaccount before opening any PC dis-play. The main dangers are the highCRT (picture tube voltage, implosion ofthe CRT, and upsetting the (delicate)picture geometry adjustments. Theundaunted among you may have alook at Figure 8 which shows typicaldust build-up spots: around the CRThigh -voltage connector, the high -volt-age cage, and the picture controls atthe edge of the PCB (on modern mon-itors, these controls are usually digitaland fitted at the front side). Cleaningthe HV parts in particular will result infewer crackling and other unnervingsounds from the monitor when it is

switched on and off. It also allows youto get rid of the stuffy smell producedby some older monitors.

Sales ploys

Although the shelves of computerstores are loaded with special prod-ucts for computer cleaning, most ofthe products on sale are overkill, andnone are essential in our view. Com-puter sales people will first try to dis-suade you from cleaning the comput-er internals yourself, and then try to talkyou into buying 'professional' prod-ucts. This is just sales talk, however.Plain pressurized air in a can (like DustBlaster from HCS Global), for instance,is pretty expensive, yet only marginallyuseful for cleaning the debris found inkeyboards. Other 'aerosol dusters' arenot all they are cracked up to be, andshould be used with extreme carebecause they make existing dust landin other places. By contrast, a cleanbrush and the vacuum cleaner bor-rowed from The Mrs do a much betterjob. What's more, these tools are saferand available in nearly every house-hold.

16 - 3/98 Elektor Electronics EXTRA 1=` TOP/GS

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Elektor Electronics 3/98 39

80C32 BASICcontrol computer

Part 2: constructipn and testing

Main FeaturesProgrammable in BASIC16 digital inputs8 digital outputs. max. 24 V 0.5 A4 analogue inputs2 analogue outputs, max. 22 V 400 mAAll interrupt and counter inputs availableWatchdog timerAll inputs and outputs accessible on screw terminal blocks

Design by H. -J.

'40

Because of their double -sided layouts,the printed circuit boards are probablydifficult to reproduce with hobbyist

tools. That's why we advise to buythem ready-made through our

Readers Services, or as part of a kitfrom a kit supplier. Populating

the boards is not likely to causeproblems as all integrated dr-

cuits are inserted in sockets.The most difficult part is

probably the fitting ofthe pinheaders which

enable the twoboards to be assem-

bled in 'sandwich' fash-ion. On the main com-

puter board (Figure 1),these pinheaders arebest fitted from the

underside of theboard. They are

inserted thewrong wayaround, i.e.,

with the long sidesto the board. Next, the

isolating plastic part is carefullypried off by pushing it downwards.

On the multifunction extensionboard (Figure 2), you have to fit threesolder pins: one for 0 V (ground), onefor the PWM output of the CPU, andone the EOC output of the A -D con-verter. Although solder pins may alsobe used for the I/O pins, it is morepractical to employ the PCB terminalblocks stated in the parts list. Unfortu-nately, these may prove hard to obtainlocally as they have a rather unusualpin distance of 3.5 mm.

To enable them to lose at least asmall amount of their dissipated heat,the two voltage regulators have to bebolted to the board. The piezo-buzzershould be an all -passive type, i.e., withno internal electronics. It should alsohave a plastic enclosure because it sim-ply goes into the space between thecircuit boards. The buzzer is solderedstraight to the 0 V and PWM pins.

Before you take the circuit into use,you should connect the extensionboard to the I2 -V supply, with no ICs

Elektor Electronics 3/98

COMPONENTS LIST

Main computer board

Resistor:Ri = 8kt.12

Capacitors:C1,C2 = 22pFC3-C6,C13,C14.C15 = 100ntC7 -C11 = INF 16V radial

Semiconductors:IC1 = 80C32IC2 = 74HC573IC3 = 62256 RAMIC4 = 27256 (BASIC EPROM,986503-1)

IC5 = 27128IC6 = 74HC00IC7 = MAX232

Miscellaneous:K1 = 20 -way SIL pinheader with

long pins (Fischer SL5 156 20 G)X1 = 11.0592MHz quartz crystalJP1 = 3 -way pinheader w. jumperK2.K3 = 14 -way SIL pinheader with

long pins (Fischer SL5 156 14 G)K4 = 9 -way sub -D socket (female)

PCB mount, angled pins.

Order codes for available products:

Main computer board: 980002-1Multifunction extension board:

980002-2Diskette (example programs and Ter-

minal program): 986007-1EPROM loaded with MCS51-BASIC:

986503-1

For prices and ordering information.please refer to the Readers Servicespages elsewhere in this issue.

installed, and not connected to themain computer board. Carefully checkthe presence of the 5 V supply voltageon all IC sockets. Switch off, and insertIC4 on the extension board. Fit jumperJP1 and apply power. LED D5 shouldlight at this stage, and go out for about3 s when the reset switch, Si, ispressed. If JP1 is removed, then D5flashes at an interval of 10 s. If thi,works so far, you may insert all otherICs (watch their orientation).

The main computer board is alsotested step by step. Having checkedthe supply voltage, and switched offagain, you may insert the CPU into itzsocket. Switch on again, and use anoscilloscope to verify that the CPUoscillator comes alive (CPU pins 18and 19). Pin 11 of the socket for 1C2should supply a periodic signal.Switch off and insert IC2, IC3, IC7 andIC4 (the EPROM programmed withthe MCS-51 BASIC interpreter). Next,hook up a PC to K4, using a null-

C\im,

0C13! A B T B. 27256

0-0-11114 « 10 (00 JP1

Oil 0

,..C_I0 0

0O 0 0O 0 0O 0 0O 0 0

0 00O 0 0O 0 0

O 0 0O 0 0

1

0

0 0 0 ca oil

1 (111j1)0

0K3

0 /

a000

0 0 6)00 0

modem cable. Run a terminal emula-tion program like HyperTerminal,Telix or Procomm on the PC. Press thereset switch, Sl, and then the space-bar on the PC keyboard. The welcomemessage

ID 0310 CM

CO C33

03 CD

03 CD

CO

CO CD

CO CO

CO 0:1

CO CD

CD

00 0

133

011-0

03CD

4040

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101

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03

4000

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03

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CO

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0

Figure 1. The main com-puter is accommodatedon this board, wick isfitted on top of the multi-function extension board.

Elektor Electronics 3/98 41

Iv 0000000ec cr

T,Q

L.,cr CC

0 0 0 0 00o00 0 0 00000

(..) 0000 00 0

98000

00000000

Art

oo 41118

0000000

C

---\0 0O 0 '2

- durr j 0 0O 0 °O 0

/ O 0C24 / / 0 0

00 0Of 00, 0O 00 0 0

10

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is l;; ,Y39CI 40

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*-K4 -K5-K6- K7 KO K9 K10 K11 -K12--K13-K1-4-K45-K16-K1-7-K-18-K19 K24 K21 K220-0 0-0 0-0 0-0 0-0 0-0 0-0 0-0 0-0 (>0 0-0 0-0 0-0 0-0 0-0 0-0 0-0 0-0

D5

ICI 0

C I 00111-0-0 C2 p u

0

K23 Kr -k-- K250-0-0 0;0CI 0 to r- c,00 00 00 0

ci in to 8 cs i0 0 ac) ca

41111,1.

4 - 12 s 6' -I r es 0. > >t -E E 7

Figure 2. Multifunction extension board featuring digital and analogue I/O as wellas some auxiliary functions.

COMPONENTS LIST

Multifunction extension board

Resistors:R1,1714,R10-R17 = 220k0R2,R36,R37,R54,R55.R59-R74

100kc.1

R3 = 11(1.15R5 =

R6 = 8 -way 4k07 SIL arrayR7,R8 = 8 -way 8200 SIL arrayR9 = 8 -way 11(05 SIL arrayR18,R19 = 10k..2 1%R20-R28,R38-R46 = 2001(Q 1%R29-R35,R47-R53 = 100162 1%R56,R57,R58 = 47k0P1,P2 = 100k.O. preset (optionally

multiturn)

Capacitors:C1,C2,C1C7-C10,C16,C21-C24 =

100nFC4 = 100trF 16V radialC5 = 47riF 16V radialC6,C12 = 100oF 40V radialC11 = 33reF 10V radialC13,C14 = 22pFC15,C17-C20 = 15nF

42 Elektor Electronics 3 98

o0 0 0 0 0 0 0 0 0 0000

0000000 00 0 000000

00000000O 000090000 0

8 8 8 888 88-/

0000000000098898888900000000

00000000Viaatiatiaa

0000 0000000000000000

0,0 0 0 0 0 0 0 0O 9000000000

e 8 8

0 0 0 000 00

0 0 0 0 0 0 0? 0 0 0 0 0 0 0 0

ca a a aaaa..... 13 CI CB CICB 0 0 CB 0

O 0 0 0 0 0 0 0 0

O 0 0 00 00 0ogggcj113

o co 0ca. (13

es fa 0CM 63

1:1 000co eo 0

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O 8888888888888 000000 00 0 000 0 000000000000 0000

88888888oagogoo

996999899

008900930 0 0 0 0 0 0 10 10 0 00 CI CI 0 0 CI 0 0 0 0 0

0

000 0000C9 63

00ww

CD

GO 0 0

000 0

000

0000 a511o

0 0

000

8 8 800 0

00

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00

*MCS-51(tm) BASIC V1.1READY >should appear on the display. Onbeing powered up, the CPU checksthe size of the available RAM (memorytop), and indicates it if you type>PRINT MTOP. The BASIC inter-preter is now ready to run your appli-cation programs. Its complete instruc-tion set may be found on the datasheetpages in last month's issue.

TERMINAL SOFTWAREThe project diskette, order code986007-1, contains a number of test,auxiliary and example programs,which are briefly described in theinset. The disk also contains extensivedescriptions of the programs. The pro-grams may be burned into EPROMIC5, or downloaded to the 80C32 com-puter using one of the terminal pro-grams mentioned above.

The author has supplied a terminalemulation program called Terminal-MCS-51, which aims to meet the spe-cific requirements of the 80C32 BASICcomputer and other MCS51-BASICsystems. This program enables simpledownloading, storing and renumber-

ing (only in the full version) of MCS51-BASIC programs. It also comprises anMCS51-BASIC line editor and allowsany ASCII word processor to beembedded. A shareware version of thisprogram may be found on the projectdiskette supplied through the ReadersServices or a kit dealer.

Alternatively, use the terminal pro-gram that comes with Windows toestablish communication with the80C32 BASIC computer. In general, allyou have to do is select the communi-cations port and the protocol. Thenyou press the reset button, followed byany key on the PC keyboard. The80C32 computer will report back withthe message MCS51 ... (depending onthe BASIC version) and READY>.Next, you may type in a line of (syn-tactically correct and hopefully mean-ingful) BASIC, and send it to the 80C32computer by pressing the Enter key.The BASIC interpreter on the 80C32computer turns the received ASCII textinto 'tokenized' BASIC, and returnsthe > prompt to the PC to signal thatit is ready to accept a new line.

If you use TerminaLexe under Win-dows 3.1, go to Settings/Communica-tion and set up this protocol: up to

0

0

0

19,200 bits/5 (the highest speeddepends on the serial cable), 8 databits, no parity, 1 stop bit. Select: Flowcontrol: none. Under Settings, TextTransfer, enable the options Line at atime and Wait for prompt string. Enter

M> for this prompt, where ^ Mstands for 'carriage return' and > forthe prompt returned by the MCS51BASIC interpreter. This setting isextremely important because the MCS-51 BASIC interpreter needs some timeto tokenize (evaluate) the received text.

HyperTerminal which comes withWindows 95 is set up in a slightly dif-ferent way. Run the program(Start/Programs/Accessories) and firstthink of a name and select an icon forthe communication sessions with theBASIC computer (Figure 3). If nomodem is installed on the PC, theModem Wizard is automaticallylaunched. Do not select a modem!Quit the Wizard by pressing 'cancel'.You are then allowed to create a newconnection. Use 'direct to COMx' (x =1-4) and select the right COM port. Tomake sure you use a free COM port,check the relevant information in theSystem Control Panel (Start/Control Elm-els/Systenz/Device Manager/Ports). Unfor-

Semiconductors:D1.D2,D3 = 1N4001D4,D6-D11,D36-D43 = 1N4148D5,D12-D35 = LEDD44 = 5V6 zener diodeIC1 = 7808IC2 = 7805IC3 = 74HCT1391C4 = 74HCT14

IC5.1C6 = 74HCT541IC7.1C10.1C11 = 74HCT574IC8 = ULN2803IC9 = UPD7002C (NEC) (Farnell)IC12 = LM324

Miscellaneous:S1 = switch, single -pole make con-

tact. CTL3JP1 = jumper

K1 = 20 -way SIL socket (FischerBL5 20 S)

BZ1 = buzzer 5VX1 = 2A576MHz quartz crystalPC1 = PCB solder pin1(2,K3 = 14 -way SIL socket (Fischer

BL5 14 S)K4 -K25 = 45 PCB solder pins or 5 off

9 -way PCB terminal blocks (pitch3.5mm, Lumberg type KRMC9)

Elektor Electronics 3 98 43:

B2 SpiceB2 Logic New Features

Outstanding Performance150..111

g .Z4V! 'IF l anzint.401(41.1x1fral

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tOltml A 0 ocewsenott171-.11.2

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JCS

ti! D.= 1.4.1m 32.a.L.:11R _Lill J1J125..;0-

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tunateh; this screen will not tell you towhich COM port the mouse is con-nected, so some experimenting may bein order if you can't tell from the labelsat the rear of the computer. If amodem is installed on your computer,the Wizard is not started. In that case,select direct to COM instead of'[modem type]'. The Modems ControlPanel will then also reveal The mouseconnection (use Diagnostics).

Once the COlvt port has beenselected, a window appears showingthe port settings. The required com-munication parameters are identicalwith those for Windows 3.1 (seeabove). The Advanced button in thiswindow is not relevant to our appli-cation. Once the connection with theBASIC computer has been defined, allrelevant setting are recalled simply viathe File Open menu.

Now, select Properties from the Filemenu, then the Settings tab. CheckANSI Terminal Emulation. Press theASCII Setup button, and enter '500' forLine Delay. Although a value of 400 msalso worked during our lab tests,smaller values are bound to causeproblems with the tokenizing of rela-tively long BASIC lines. UnfortunatelyHyperTerminal does not allow thedata exchange to be synchronized bya specific character sequence (like theMCS-51 prompt). Consequently, com-munication with the 80C32 BASICcomputer will be slower than with Ter-minal running under Windows 3.1.

IKSEICIT1-2;

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What's on the disk?The program CLOCK.LIS (background clock) with watchdogtimer shows how an Ontime interrupt may be used to generatea pulse for the watchdog timer. The clock may run in the back-ground of your main program. To be able to use it. the clockprogram has to be stored in a boot EPROM (105) on the com-puter board, and jumper JP1 on the multifunction board has tobe removed. An INPUT instruction is not allowed in your pro-gram, because the Ontime interrupt is then no longer serviced.causing the system to be reset. Input into the running programis then only possible by means of the GET instruction, whichis also used to adjust the clock. The keys on the terminal(console) then have the following functions:

HhMS

T

w00J

increase hoursdecrease hours

increase minutesincrease seconds

decrease secondsincrease daydecrease day

increase day of the weekdecrease day of the weekincrease month

decrease monthincrease yeardecrease year

The program DO-DI.LIS (digital -out, digital -in test) performs acyclic count from 0 to 255 on the digital output port. The out-put value may be read back via one of the two input ports. As

bCONt Pfcmptglics El

:.1

k- cort7.- IMEMEIMEIMI I

Aersrced

I

dASCII Setup 1112

ASCII Sencing

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a matter of course, that requires fitting eight wire links betweenthe relevant inputs and outputs.The program DA-AD.LIS (digital -analogue / analogue -digitaltest) produces output voltages on the two D -A channels.These voltages may be read back via the A -D channels. Thisis achieved by first adjusting the two D -A outputs to +5 Vusing presets P1 and P2. The program writes the highestvalue. 255, to the relevant D -A outputs and then prompts youto do the adjustment. To perform this test, you obviously haveto link the respective D -A (output) and A -D (input). Next, theoutput value of channel 1 is indicated, along with the currentvalues of all four A -D channels.The other programs on the disk are not specifically designedfor the 80C32 BASIC computer described in this article.Rather, they are intended for MCS-51 BASIC boards in gen-eral. The program ROMCOPY.LIS (see also Elektor ElectronicsSeptember 1990) extracts the 8-kByte large BASIC interpreterfrom the ROM of an 8052AH-BASIC chip, and copies it into anEPROM. Alternatively, you may find the interpreter on the Inter-net, Intel having released it in the freeware domain! Thesource code (BASIC52.ZIP or BASIC-52.ZIP) may be down-loaded from the Intel ftp server atftp:/lintel.com/pub/mcs511toolsorftp://funetli/publmicropnacs/MCS-5l/signetics-bbsThe latter server also supplies the file BASIC31.ZIP, whichdoes basically the same as ROMCOPY.LIS.Finally, the disk contains a file called EPROM.US, which turns thecontrol computer into an EPROM programmer. For that function.however, certain hardware conditions have to be satisfied.

Elektor Electronics 3/98 45

ionization circuitdo negatively charged ionsimprove the quality of life?

Do you suffer from recurring headaches,chronic tiredness or a general feeling of being

(slightly) unwell? It may well be that in yourhome or place of work there is an imbalance

between positively charged ions and nega-tively charged ions. Although not medically

proven, it appears that some people areadversely affected by a surplus of positively

charged ions. The balance may be restored bythe present circuit, which form a simple means

of producing negatively charged ions. Thisaddition to the range of alternative medicine

may help sufferers, but readers with the symp-toms described are well advised to seek the

help of a qualified medical practitioner.

Design by H.Bonekamp

In this article, the definition of an ion(there are several) is 'an electricallycharged atom or group of atoms. Posi-tively charged ions have a deficiency ofelectrons, and negatively charged ionshave a surplus of electrons. Some peo-ple say that in gases the negativelycharged ions are, in fact, free electrons,while the positively charged ions are theremaining parts of the atom where mostof the mass resides.

In air, there is normally a balancebetween negatively charged ions andpositively charged ions, but in somecircumstances this balance is disturbed.Some people seem to be affected bythis, as shown, for instance, by the factthat they feel (more) pleasant or morealive in the vicinity of waterfalls and in'air spas. Is this psychosomatic, coin-cidence, or what?

This phenomenon can also beobserved after a thunderstorm, whensome people have an overwhelmingdesire to go for a brisk walk in the'fresh air' (this may also be due to the

46 Elektor Electronics 3/98

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Figure 1. The oscilla-tory voltage is raisedby -:60 by transformerTri. After the sec-ondary voltage hasbeen rectified anddoubled, a direct volt-age of about 3 kV isavailable.

fact that a thunderstorm drives all dustparticles from the air, so the air is'cleaner").

The reverse can also be seen inMediterranean countries where somepeople feel nervous or depressedwhen the mistral (cold northerly ornorthwesterly wind) or the Fahn(warm dry wind on the ice side ofmountains) blows. These weather con-ditions frequently (but not always) gohand in hand with high concentra-tions of positively charged ions. Thepeople who appear to be sensitive tothe imbalance of ions say that they feelthe effect not only out of doors butalso indoors. There are people whomaintain that certain buildings exudea 'bad air'. Again, there is no impartialevidence for these sensations.

POSSIBLE REMEDIESIf you suffer at home or at work fromfeelings of discomfort or difficult -to -define ailments, it may not always benecessary to rush to the doctor. Maybethe culprit is the atmosphere (whichmay be dusty or humid) in the build-ing. Often, this may be improved byadded or improved ventilation. Freshair not only provides more oxygen, butalso tends to contain more negativelycharged ions.

Unfortunately, it is not always pos-sible to add or even improve the ven-tilation. In air-conditioned buildings,windows often cannot be opened (ifthe air-conditioning is sound, thisshould, of course, not be necessary)and cold or wet weather outside mayalso prevent the opening of windows.(It may be argued, of course, that goodventilation should not depend onopen windows). In these circum-stances, some people may like a sourceof negatively charged ions and this isprovided by the present circuit

VERY HIGH VOLTAGEWith the aid of a strong electric field,

ETD29

I11.100n01 D2

BC5468

it is possible to ionize the air and soproduce negatively charged ions. Inthe present circuit, the field is pro-duced with the aid of four electrodesthat carry a direct voltage of about3 kV. Owing to the small diameter ofthe electrodes, there is such a strongelectric field around their pointed endsthat the spray effect, typical of ioniza-tion, occurs. Because of the effect, dis-lodged electronics fly away in all direc-tions. After they have travelled only ashort distance, they collide with airmolecules and ionize them. Since oxy-gen molecules also become ionized,ozone (triatomic oxygen, 03) isformed. However, because the poten-tial is not very high, the amount ofozone is not great. Nevertheless, use ofthe ionizer is not recommended in thevicinity of asthma sufferers. Also, donot place the ionizer too dose towhere humans sit, since even a smallamount of reactive ozone may causeirritation of the respiratory system.

The ionizer has a secondary func-tion: the dislodged electrons not onlyionize air, but also give dust particlesan electric charge. Such charged parti-cles are deposited on the ionizer andits immediate vicinity. This removal of

3kV

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particles in the air is applied in someindustries to remove soot from smokegases.

CIRCUIT DESCRIPTIONThe high direct voltage is generated bya Meissner oscillator-see Figure 1. Inthis, feedback is arranged via a trans-former which has an additional high -voltage winding that provides a poten-tial of about 3 kV.

The circuit is based on transistors T1and 12, and transformer Tri which isconnected between their collectors.The requisite positive feedback for theoscillator so created is provided bycapacitive potential dividers CT -CZ andC3 -C4. The d.c. operating point of thetransistors is set with resistors R1 -R4.

The tuned circuit of the oscillator isformed by the primary winding of Triand capacitor C5. The resonance fre-quency is about 50 kHz. With a supplyline of 12 V, the oscillatory voltageacross the primary is about 25 V perbranch. Zener diodes Dt and D, pre-vent this voltage from exceeding toohigh a level. Networks 11,-C, andRi-C4 provide the requisite time con-stants and determine the operation ofthe transistors, that is, the level of the

FOR PRIVATE USE AT E 69U LII BOARD STUDIO LITE INCL. VAT

SEE ALSO THE RE

PROFESSIONAL HOBBYISTSthe Studio Lite consists of ULTIcap schematic capture. ULTIbirard PCB design andULTIroute GXR autoroutes. Both Windows 95 and DOS versions are included in theCD-ROM. Actually you only pay for the 5 manuals !In which. besides tutorials andmanuals. even shapes are described! Ideal forliobby and study and with sufficientcapacity (500 pins). If higher capacity is needed you can opt (now or later) for anupgrade to the Studio Unlimited, without capacity limits. for E 68 (incl VAT). Thereare no further options or hidden extras, the ULTIboard Studio program is complete!

L6TLC ition.ourliNt 1 1...91ges firm Cada) ureSt Bray 61.15 681vxre 01504 -MIDI

01S -114102,M

Eleklor Electronics 3 98

PLYCARD ELSEWHERE IN THIS ISSUE47

Parts list

Resistors:

R1, R3 = 3.91(0R2, R4 = 390 12135-Ro = 1 MO. 1.6 kV d.c.R9 = 39 IIRio = 2.7 10.-2

Capacitors:Cl, C3 = 0.01 pF, metallized poly-

ester (MKT)C2, C3 = 0.047 NF, metallized poly-ester (MKT)

C5 = 0.1 pF, metallized polyester(MKT)

C6, C7 = 0.001 pF. 2 kV d.c.Cs = 10 NF, 25 V, radialC, = 0.1 pF, high -stability

Semiconductors:D. D, = zener diode, 30 V. 500 mWD3, 04 = high -voltage silicon diodes.e.g.. Type BY709 (Philips Compo-nents)

D5 = LED, red, high efficiencyD6 = 1N4001Ti, T2 = BC546B

Miscellaneous:M1 = miniature fan. 12 V. 900

40x40x 10.5 mmETD29 former with N27 coresEnamelled copper wire as described

in the text.Plastic enclosure. e.g.. Bopla E430

current pulses driving them.The turns ratio of the transformer

ensures that the potential across thesecondary winding is about x60 thatacross the primary. This potential isrectified and doubled by high -voltagediodes D3 -D4 and capacitors C6 -C7.

Ionization takes place around the'electi-odes formed by four lengths of

2+ 12V 0 0 +

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iFil111111C4 R3 I°

wire placed at a distance of about2 mm from the 'mother electrode.Resistors R5R8 reduce the risk to life ifthe electrodes are accidentally touched.

Network R10 -D5 forms an on/offindicator.

Capacitors C8 and C9 are decou-pling elements.

Diode D6 provides protection

980016-1

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Figure 2. The printed -circuit board for theionizer, which is how-ever, not availableready-made.

Figure 3. The requisiteparts for making thetransformer. Plasticfoil or insulating tapemust be used toensure that the twoE -shaped cores justdo not touch eachother in the centre.

448 Elektor Electronics 3/98

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4

against wrong polarity.Fan MI provides better dispersion

of the exigent electrons. Series resistorR9 ensures that the fan does not maketoo much noise while still displacingsufficient

The circuit may be powered via a12 V or 15 V standard mains adaptor,which need not be a heavy-duty type,since it draws a current of only about150 mA.

CONSTRUCTIONThe ionizer is best built on the printed-circuit board shown in Figure 2. Pop-ulating the board should provestraightforward. Plenty of space hasbeen reserved for high -voltage capac-itors C6 and C7, so that a variety oftypes may be used for these compo-nents. These capacitors should have aworking voltage rating of not less than2 kV d.c.

The reverse bias rating of diodes D3and D4 as specified is 14 kV, but lowerrated types, down to 4 kV, may beused as long as their recovery timedoes not exceed 0.2µs.

The 'electrodes are mounted on sol-der pins and may be made from1-13 mm dia. circuit wire (mother elec-trode: 54 mm long) or 0.6 nun dia.(slave electrodes: 7 mm long). The slaveelectrodes may be filed to a sharp point,but this is not essential The distance

between the electrodes must be 2 mm.

TRANSFORMERUnfortunately, transformer Tri cannotbe purchased ready-made. It is woundon a Type ETD29 former which con-tains two E -shaped Type N27 cores-see Figure 3. Laying the windings isnot difficult but time-consuming.

The secondary winding consists of900 turns enamelled 0.2 mm dia.cop-per wire in 12 layers of 75 turns each.Place a short length of insulatingsleeve over the start of the windingand solder this to the outer pin (1) ofthe former.

Each layer must be well insulatedfrom the adjacent one(s) by two layersof appropriate tape. Note that morethan two layers make the winding toofat and one provides insufficient insu-lation. Seal the edges of each layer aswell as the sides of the completedwinding with nail varnish or similar.

When the winding has been com-pleted, place a short length of insulat-ing sleeve over the the end of the wireand solder this to pin 6 of the former.

Cover the secondary winding withan additional layer of insulating tapeand lay the primary winding on top ofthis. The primary consists of 14 centre-tapped turns of OA mm dia. enamelledcopper wire Solder the start of thewire to pin 9 on the former, lay seven

Figure 4. Photograph of the com-pleted prototype. The capacitorsused in the C6 and C7 positionsare fairly small and occupy onlyhalf of the available space forthem on the board.

turns and solder the wire, without cut-ting it, to the centre pin (10). Next, laythe remaining seven turns in the samedirection as the first seven and solderthe end to pin 11. 'Wind a double layerof insulating tape over the primarywinding.

Finally, push the two E -shapedcores into the former after taping adouble layer of insulating tape on thetwo outer edges of one of the cores.This ensures an air -gap between themof about 0.25 mm. Subsequently, clampthe assembly together with two springclips and solder the transformer on tothe board.

A photograph of the completedboard is shown in Figure 4.

FINALLYIn view of the necessary safety mea-sures, the ionizer must be housed in astrong, plastic enclosure. This must, ofcourse, be provided with fixing holesfor the on/off indicator and a numberof holes for air inlet and ion outlet.

Fit the fan just above the electrodeswith either plastic screws and nuts orstrong double -sided sticky tape. Lookat the introductory photograph.

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The Studio Lite consists of ULTIcap schematic capture, ULT lboard PCB design andULTlroute GXR autorouter. Both Windows 95 and DOS versions are included in theCD-ROM. Actually you only pay for the 5 manuals !In which, besides tutorials andmanuals, even shapes are described! Ideal forhobby and study and with sufficientcapacity (500 pins). If higher capacity is needed you can opt (now or haler) for anupgrade to the Studio Unlimited, without capacity limits, for E 68 (incl. VAT). thereare no further options or hidden extras, the ULTiboard Studio program is coniplete!

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SEE ALSO THE REPLYCARD ELSEWHERE IN THIS ISSUEElektor Electronics 3 98 49

IC testerPart 1: circuit description

and construction

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This article describes a stand-alone IC tester forlogic ICs (with up to 24 pins) from the well-known74xx (TTL) and 40xx (CMOS) series. The elemen-tary building blocks that make up the design are

an 800535 microcontroller, a large EPROM, anLCD display, a small keyboard and an RS232

interface. In this first instalment, our main subjectswill be hardware -related.

This design was awarded the International First prize in the Elektor Electron :s1997 Design Competition. A condensed description of the project appeared in

the January 1998 Supplement on prize-winning contest entries.

Design by L. Lamesch

In the January 1998 issue we promiseda full-blown and tested version of theIC Tester, complete with PCB layoutsand a ready -programmed GAL andEPROM. Many of you will haveeagerly looked fonvard to the presentarticle, which, we hope, lives up toexpectation.

The IC tester is a fairly complexproject, and an interesting combina-tion of mixed -mode (analogue/digital)electronics on the one hand, and soft-ware (microprocessor as well as PC -hosted), on the other. The IC tester iscapable of working in stand-alonemode, i.e., any connection to a PC isentirely optional. The standard versionof the tester is capable of testing all ICslisted in Table 1. A number of softwareutilities are available which allowadvanced users to add ICs to thelibrary as listed in Table 1, and thissubject will be covered in detail inpart 2 of this article. We do, however,reckon that the 'default' library will besufficient in the majority of cases -extending it with 'new' devices is spe-cialist work!

This tester is a great tool for anyonewho's ever had to do go/non-go testingon a vast amount of integrated circuitsfrom the '74' TTL and '4000' CMOSseries. These ICs are still extensivelyused by hobbyists because (1) they canoften be salvaged from surplus equip-ment or bought 'ten a penny' or at leastat knock -down prices, and (2) theirdatasheets are widely available, so youknow how to use them in a design ofyour own. As a matter of course, thetester is also perfectly suitable for usein an electronics repair shop, where itwill be necessary from time to time tocheck suspect devices. Lastly, the ICtester may also be used to identifyunknown ICs, i.e., those with obscureprint or a label someone painstakinglyground off...

HOW IT WORKSThe circuit diagram of the IC tester isshown in Figure 1. It may be dividedinto a digital control (microcontroller)section, a precision power supply, anRS232 interface, a zero -insertion -force(ZIF) socket (which receives the deviceunder test, DUT), a keyboard section,an LCD and a power supply.

A50 Elektor Electronics 3/98

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Around the OUTLet's start with a look at the electron-ics around the ZIF socket, positionIC12. All input pins of the DUTinserted in the zero -insertion forcesocket may be pulled to the logic high(H) or logic low (L) level using currentlimiting resistors and appropriate con-trol levels at the outputs of twoZ8OPIO I/O blocks, 1c2 and IC4. Theoutput states of the DUT may be inter-rogated via the same PIOs for subse-quent evaluation by the CPU (IC3).The power supply pins of DUTs with14, 16, 18, 20, 22 and 24 pins may beconnected to ground or a current -lim-ited supply voltage via BC639/BC640switching transistors. These are con-trolled by outputs on counter cascadeIC1-1C9. While the PIOs enable theexact logic states of the DUT outputsto be checked (i.e., 0 or 1), ports P1, P4and P5 of the 800535 are used todetect which DUT pins represent ahigh impedance (high -Z).

DUT power supplyThe voltage source used to power theDUT is built around quad opamp 106.It supplies an accurately regulatedvoltage of 5.2 V, and its output currentis limited to about 0.2 A. The outputcurrent is converted into a propor-tional voltage for measurement by the

800535 CPU via its ANO (analogue)input. The current -sense resistors areR94 and R95. The output voltage is5.2 V rather than 5.0 V (the typical sup-ply voltage of all TTL ICs) in order tocompensate the collector -emitter dropof the BC640 transistors when they areswitched on.Logic circuitry= and firmware EPROMThe control program of the IC testerand the test vectors for the [Cs thatmay be tested are contained in a sin-gle 27C512 EPROM, which may beobtained ready -programmed from thePublishers under order code 986507-1.Larger (32 -pin) EPROMs like the27CO20 or 27CO21 may also be used inthis design. For the 27CO21 EPROM,jumper JP1 has to be set to the A17position. More about this in nextmonth's concluding instalment. Theselection between the 64-kByte banksin the EPROM is accomplished by out-puts B6 and B7 of 1C2. These lines areapplied to GAL 105, which containslogic to control the A16 and A17address lines of EPROM 1C7. Basically,when a 28 -pin EPROM is used, JP1 isset to the bevelled edge position (N).When a 32 -pin EPROM is used, theA17 signal is required, so JP1 is set tothe other position.

The 800535 CPU runs at a dockspeed of 12 MHz. The CPU does notcontain firmware code, and fetches all

of its instructions and data from thesystem EPROM. None the less, itdirectly controls the LC display and akeyboard with 6 keys. The GAL, IC5,looks after the address decoding, andalso generates the PHI signal for theZ8OPIOs, as well as other essential con-trol signals in the circuit. The GAL, likethe EPROM, is supplied ready -pro-grammed by the Publishers, the ordercode is 986506-1.

The reason for using the Z8OPIO tocontrol and monitor the DUT inputsand outputs is that this chip is the onlywidely available 16 -bit parallel port ICof which all port line directions areindividually controllable, while theoutput drivers for all port lines consistof push-pull circuits.

User I/OThe system interacts with the user viaa small keyboard (circuit diagram inFigure 2), an LED, 06, and an LCD(liquid crystal display). The LCD is ageneral-purpose type with 24416 char-acters, optionally with back -lighting.Its contrast is adjustable with presetPl. The LED lights to inform the userthat the DUT is being powered andshould not be removed from the aPsocket.

An RS232 serial interface, tradition-ally designed around the MAX232,enables the IC tester to (optionally)

Table 1. Index of ICs that may be tested [default EPROM contents)Librati: 74zu 74:38 74:139 74:23974.05 74:39' 74:140' 7424074:01' 74:40 74:147 74:24174:02 74:42 74:145* 74242'74:03 74:45 74:148 7424374:04 74:46' 74:150 74:24474:05 74:47 74:151 74:24574:06 74:48' 74:153' 74:247'Parent 74:05 74:49- 74:154 74:248'74:07 74:51 St.S" 74:155 74249'74:08 74:51 LS,L 74:156' 74250'74:09 74:54' 74:157 74:25174:10 74:55' 74:158' 7425374:11 74:73 74:159' 7425774:12' 74:74 74:160 74258'74:13 74:75 74:161 74.25974:14 74:76 74:162 74260'74:15' 74:83 74:163 74:26674:16 74:86 -CA 74:164 74:27374:17 74:86 C,L' 74:165 7428074:18' 7410 74:166 7428374:19' 74:92 74:168' 74290*7420 74:93 74:169 74:29374:21 74:95A.B 74:170 7429974:22' 74:100 74:173 74:3237424' 74:107 74:174 74:347'7425 74:109 74:175 74:348'7426 74:119 74:180' 74:352'7427 74:125 74:184' 74153'7428' 74:126' 74:185' 74:36574:30 74:128' 74:190 74166'74:31'74:32 74:131'

74:13274:19174:192

74:36774:368'

74:33 74:133' 74:193 74:37374:34' 74:136' 74:194 74:37474:35* 74:137 74237' 74:37574.37 74:138 74:238' 74:377'

74:385' 74:596' 74:758 74:7541' 405°- 4016174:390 74:620' 74:759' 4051 4016274:393 74:621- 74:760* Library: 40ux 4052 4016374:412 74:622' 74:762' 4001 4053 4017474:425' 74:623' 74:763' 4002 4056 4017574:426'74:445'

74:638-74:639'

74:810'74111* 4009'

4010'

40604066

4019240193

74:447' 74:640 74:1000' 4011 4067 4019474:465' 74:641' 74:1002' 4012 4068 -RCA 450-274:466' 74:642' 74:1003' 4013 4068 RC4 450874:467' 74:643' 74:1004' 4014' 4069 451074:468' 74:644' 74:1008' 4015 4070 451174:518* 74:645 74:1010' 4016 4071 451274:519' 74:646 74:1020' 4017 4072 451474:520'74:521

74:647'74:648' 741032'74:1034'

4019

4020

40734075

4515'4516'

74:522' 74:649' 74:1035' 4021 4076 451874:533' 74:688' 74:1036' 4022' 4077 452074:534' 74:669* 74:1240' 4023 4078 -RCA' 452274.540' 74:670 74:1244' 4024 4078 RCA' 452674:541 74:682 74:1245' 4025 4081 452974:563' 74:683' 74:1640' 4027 4082* 453974:564' 74:684 74:1645' 4028 4093 4543'74:573 74:685' 74:2240' 4029 4094 455574:574 74:688 742241' 4030 4099' 4556'74:576' 74.689- 74:2244' 4040 40014' 458474.580' 74:699 74:2540' 4041' 40102 472474:590 74:746- 74:2541' 4042 401037,P591* 74:747" 74:7245' 4043 4010574:592 74:756' 74:7266' 4044' 4010674:595 74:757' 74:7540' 4049" 40160

Test vector for this IC not yet verified with a correctly operating IC.This IC has not been My tested using the IC test vectors.Amy MAR* identifier. except if the type number has a suffix_Test vectors not yard for X family device of this IC (e.g. 74:86 -C means not for 74085)Test vectors apply only to X family device of this 10 (e.g. 74:86 C means for 74C86 only,

Elektor Electronics 3/98 51

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communicate with a PC running spe-cially written programs. Details onthese programs will be given in nextmonth's final instalment. Briefly, thePC may be used to write your own IC

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test vectors and debug them withoutremoving the system EPROM. Thelink between the 9 -way sub -D socketand the MAX232 on the board isaccomplished via pinheader ICI as

52 Elektor Electronics 3/98

visit our web site at http: ourworld.compuserve.com homepages elektor_uk

4

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illustrated in Figure 2. Mote that noactive handshaking is used; the ICtester only uses RxD (received data),GNI) (ground) and Tx! (transmitteddata).

Power supplyThe on -board 5 -volt power supply forthe IC tester is based on a single 78053 -pin voltage regulator (1C11). A smallnegative voltage is created mainly forolder LCDs by a stealer diode (D5)between the negative line of theunregulated input voltage and the cir-cuit ground. This negative voltage pro-vides a proper range for the LCD con-trast setting, Pl.

The circuit may be powered by aninexpensive mains adaptor with anoutput voltage between 9 VDC and15 VDC. Battery powering is also pos-sible. The unregulated voltage is alsoapplied to the DUT supply discussedabove_ The current consumption of thecircuit will be of the order of 150 mA.

CONSTRUCTIONAs you can see from the photographson this article and the artwork in Fig-ure 3, the printed circuit boarddesigned for the IC tester is denselypopulated. The board being double -sided and through -plated, productionwith hobbyists tools %%rill be almostimpossible, hence our recommenda-tion to buy it ready-made through ourReaders Services or one of the kit sup-pliers advertising in this magazine.Remember, successful constructionalmost entirely depends on accuracyand soldering skills.

Start by separating the keyboardfrom the main board. Put the key-board section aside for later

Populating the main board maytake quite some time as there are rela-tively many components to sort andsolder in place.Resistors, diodes, capacitors, crystalStart by fitting the SMD (surface -

mount device) resistors, R25 -R48.This should be done with a low-power (8 -watt) soldering iron andlots of care and precision. Use anohm -meter to check your work oneach and every SMD resistor. Allother resistors are mounted uprightto save space on the board. Makesure you know the value of each andevery resistor and capacitor beforemounting it. If necessary, use yourDMM and the component overlayprinted on the board (and shown inFigure 3) to be absolutely sure. Also,the SIL resistor arrays on the boardmust be fitted the right way around,so make sure you know where the'common' terminal goes. Likewise,observe the orientation of the elec-trolytic capacitors and diodes. Capac-itors Cl (100 nF miniature ceramic)and C2 (10pF, 16V, also miniature) aremounted at the solder side of theboard. The two presets are fitted andset to mid -travel.SemiconductorsFitting the transistors and the voltageregulator should not present problems,

Figure 2. RS232 con-nection diagram andcircuit diagram of thekeyboard.

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although you have to be careful not tomix up the BC639s and the BC640s. AllICs are mounted in sockets. With thepossibility of future extensions inmind, it is recommended to fit a 32 -pinIC socket in position 1C7. However, as32 -pin wide-DIL are few and farbetween, you may have to make oneyourself by truncating a 40 -pin socket.If you use the ready -programmed (28-pin) 27C512 EPROM supplied throughthe Readers Services, its pin 14 shouldgo in socket pin 16. In other words, theEPROM is then inserted with its cor-ner pins 14/15 close to the edge of theboard.

The CPU socket has a bevellededge which is also indicated on theoverlay to assist in positioning.

The socket in position [C12 is notintended for an integrated circuit andit is fitted at the solder side of theboard_ You can (carefully) solder thesocket pins at the component side ofthe board.

Do not insert the ICs in their sock-ets yet.

Connectors and ZIF socketSimple 3 -way pinheaders are used inpositions K1 and WI. The formerreceives a mating socket, the second, ajumper There are two longer pin -headers, K4 and K3. The latter is

Elektor Electronics 3/98 53

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COMPONENTS LIST

Resistors:R1 -R24.R56-R62,R75-

R79.R90.R92,R96 = 10k.QR25 -R48 = 1800 SMDR49-R55,R63-R74,R83 = iknR80 =R81.R82 = SIL resistor array 4 x

4/cf.?.7

R84 = 6k08R85,R88 = 1Mn 1%R86,R87 = 100k22 1%R89 = 39k51R91 = 100kfl

R93 = 1kn 1%R94,R95 = 14 1%R97 = 2k.0.2R98 = 47kS"2R99 = 270.R100,R101 = SIL resistor array 8 x

4k0.7R102 = SIL resistor array 8 x 10k0R103 = SIL resistor array 8 x 10kilP1 = 10k52 presetP2 = 1k9. preset

Capacitors:C1,C4-C8,C11.C13,C20,C22.C23 =

100nF

C2,C16.C17,C18,C21 = 10fiF 16Vradial

C3,C19 = 1nFC9,C12 = 27pFC10 = 470.1iF 35V radialC14 = 10riF 25V radialC15 = 4itF7 16V radial

Semiconductors:D1.D3 = 1N4148D2,D4.D5 = 1N4001D6 = LEDT1,T2 = BC547T3 = BD139T4 -T13 = BC640

54 Elektor Electronics 3 98

Visit our Web site at http: ourworld.compuserve.com homepages'elektor_uk

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Items available from the Publishers:PCB. disk. GAL and EPROM: set. order code 980029-C.PCB only, order code 980029-1.GAL 16V8 only, order code 986506-1.EPROM 27C512 only, order code 986507-1.Disk only, order code 986014-1.

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T14 -T22 = BC639IC1,1C9 = 74HC4094IC2,1C4 = Z8OPIOIC3 = SAB80C535-NIC5 = GAL 16V8 (order code986506-1)

IC6 = LM324IC7 = EPROM 27C512 (order code

9865_07-1) (but use 32 -pin socket!)1C8 = 74HC5731010 = MAX232IC11 = 7805IC12 = 24 -pin ZIF-socket (wide slots;

Aries, Farnell)

Miscellaneous:X1 = 12MHz quartz crystalK1 = 3 -pin SIL headerK2 = 2 -way PCB terminal block

(pitch 5mm)K3 = 14 -pin SIL headerK4,K5 = 8 -pin SIL headerSt -S6 = Digitast push button (ITTSchadow), 4 black caps, 1 white(Ent), 1 red (Esc)

JP1 = 3 -pin SIL header + jumperLCD module, 2x16 characters9 -way sub -D socket (female)

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mounted at the solder side of theboard (and soldered at the componentside). Its long pins receive a matingsocket whose pins are soldered to the14 copper spots on the LCD module.Doing so allows the LCD to be given aslant angle for optimum viewing.

Insert a second 24 -pin socket intothe one you soldered at the solder sidein position IC12, and then insert theZIF socket to make a nice stack.

K2 is a two-way PCB mount termi-nal block which receives the mainsadaptor output voltage.

Elektor Electronics 3 98 55

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lou 7 for Kits'Whether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area ofelectronics SUMA DESIGNS has a kit to fit the bill. We have been designing electronic surveillance equipment for over 12 yearsand you can be sure that all our kits are very well tried, tested and proven and come complete with full instructions, circuitdiagrams, assembly details and all high quality components including fibreglass PCB. Unless otherwise stated all transmittersare tuneable and can be received on an ordinary VHF FM radio.

Genuine SUMA kits available only direct fromUTX Ultra -miniature Room TransmitterSmallest room transmitter kit in the word! Incredible 10mm x 20mm including mic.3-12V operation. 500m range £16.45

MTX Ililicre-edniature Room TransmitterBest-selling micro -miniature Room TransmitterJust 17mm x 17mm including mic. 3-12V operation. 1000m range__ ._ £13.45

STX High-performance Room TransmitterHi performance transmitter with a buffered output stage for greater stability and rangeMeasures 22mm x 22mm including mic. 6-12V operation, 1500m range.______£15.45

VT500 High -power Roam TransmitterPowerful 250mW output providing excellent range and performance. Size 20mm x40mm. 9-12V operation. 3000m

VXT Voice Activated TransmitterTriggers only when sounds are detected. Very low standby current_ Variable sensitivityand delay with LED indicator. Size 20mm x 67mm. 9V operation. 1000m range £19.45

HVX400 Males Powered Room TransmitterConnects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm.500m range £19.45

SCRX Svhcarrier Scrambled Room Transmitter

Scrambled output from this transmitter cannot be monitored without the SCDM decoderconnected to the receiver Size 20rrim a 67mm. 9V operation. 1000m range £22.95

Snit Subcenter Telephone TransmitterConnects to telephone line anywhere, requires no batteries. Output scrambled sorequires SCDM connected to recerver. Size 32mm x 37mm_ 1000m range £23.95

SCOM Subcarrier Decoder Unit for SCRXConnects to receiver earphone socket and provides decoded audio output toheadphones. Size 32mm x 70mm. 9-12V operation 12295

ATR2 Micro Size Telephone Recording InterfaceConnects between telephone line (anywhere) and cassette recorder. Switches tapeautomatically as phone is used. All conversations recorded. Size 16mm x 32mm.Powered from line £13.45

*** Specials ***DLTX/131.AX Radio Control SnitchRemote control anything around your home or garden, outside lights, alarms, pagingsystem etc. System consists of a small VHF transmitter with digital encoder and receiverunit with decoder and relay output. momentary or alternate, 8 -way dit switches on bothboards set your ov,n unique security code. TX size 45mm x 45mm. RX se 35mm x90mm. Both 9V operation. Range up to 200mComplete System (2 kits) £50.95individual Transmitter DLTX. £19.95Indiiiclual Receiver DLRX £37.95

ht8X-1 HI -Fl Micro BroadcasterNet technically a suneillance device but a great idea! Connects to the headphone outputof your Hi -F. tape or CD and transmits Hi -F1 quality to a nearby radio. Listen to yourfavourite music anywhere around the house, garden, in the bath or in the garage andyou dont have to put up with the DJ's choice and boring waffle. S4e 27mm x 60mm.9V operation. 250m range __120.95

Suma Designs. Beware inferior imitations!UTLX Ultra -miniature Telephone TransmitterSmallest telephone transmitter kit available. Incredible size of tOmm x 20mm!Connects to line (anywhere) and switches on and off with phone use.All conversation transmitted. Powered from line. 500m range .£15.95

TLX700 Micro -miniature Telephone TransmitterBest-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble thanUTLX. Connects to line (anywhere) and switches on and off with phone use. Allconversations transmitted. Powered from line. 1000m range .£13.45

STLX High-performance Telephone TransmitterHigh performance transmitter with buffered output stage providing excellent stabilityand performance. Connects to line (anywhere) and switches on and off with phone use.All conversations transmitted. Powered from fine. Size 22mm x 22mm.1500m range £16.45

TKX900Signallleg/TrackIng TransmitterTransmits a continous stream of audio pulses with variable tone and rate. Ideal forsignalling or tracking purposes. High power output giving range up to 3000m. Size25mm x 63mm. 9V operation.... £22.95

C0400 Pocket Bog DetectosiLocatorLED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as youapproach signaL Gain control allows pinpointing of source. Size 45mm x 54mm. 9Voperation £30.95

CD600 Professional Bug Detector/LocatorMulticolour readout of signal strength with variable rate bleeper and variable sensitivityused to detect arid locate hidden transmitters. Switch to AUDIO CONFORM mode todistinguish between localised bug transmission and normal legitimate signals such aspagers, cellular, taxis etc. Size 70mm x 100mm. 9V operation £50.95

CITX1130 Crystal Controlled Room TransmitterNarrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz andrequires the use of a scanner receiver or our ORX180 kit (see callogue). Size 20mm x67mm. 9V operation. 1000m range £40.95

CILX180 Crystal Cotntrolled Telephone TransmitterAs per OT)(180 but connects to telephone line to monitor both sides of conversations..

4.9 520mm x 67mm. 9V operation. 1003m rang' iQSX1817 Line Powered Crystal Controlled Phone TraesreitterAs per OLX180 but draws power requirements trom line. No batteries required. Size32mm a 37mm Range 500m £35.95

QUIN Crystal Controlled FM ReceiverFor monitoring any of the '0' range transmitters. High sensitivity unit. All RF sectionsupplied as a pre -built and aligned module ready to connect on board so no difficultysetting up. Outpt to headphones. 60mm x 75mm. 9V operation

A build-up service is available on all our kits if required.UK customers please send cheques, POs or registered cash. Please addE 2.00 per order for P&P. Goods despatched ASAP allowing for chequeclearance. Overseas customers send sterling bank draft and add £5.00 perorder for shipment. Credit card orders welcomed on 0827 714476.

OUR LATEST CATALOGUE CONTAINING MANY MORE NEWSURVEILLANCE KITS NOW AVAILABLE. SEND TWO FIRSTCLASS STAMPS OR OVERSEAS SEND TWO IRCS.

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BAXTERLEY. NEAR ATHERSTONE,WARWICKSHIRE CV9 2LE

VISITORS STRICTLY BY APPOINTMENT ONLY

Tel: 01827 714476Fax: 01827 714476

456 Elektor Electronics 3/98

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KeyboardThis is a simpler and smaller boardwhich should not present any diffi-culty. Although a connector (K5) isindicated on the overlay, the 8 -wayflatcable between the keyboard PCBand the main board may be soldereddirectly to the spots at the solder side.One separate wire is used to controlthe LED, D6. It goes to a ,older pinmarked 'LED' on the main board.

That concludes the construction of thePCBs. Now's a good time to reviewyour work so fan Any blatant errors?

TESTINGWith the ICs still waiting to be insertedin the respective sockets, connect -upthe input voltage and run a quickcheck on the presence of the 5 -voltsupply voltage at the relevant pins ofall IC sockets. Switch off and insert theLM324 (IC6). Connect the DM.M. toground and the top wire of R61,switch on again and adjust P2 for areading of 52 V.

Switch off and carefully insert allICs. Note their orientations on theboard! Switch on again. The LCDshould read

IC Tester1:Test

Okay so far? Congratulations!

ADJUST NIENTSThe DUT supply output voltage, U+,has to be set to 5.2 V ±0.05 V usingpreset P2. Next, P1 is adjusted for opti-mum contrast of the texts that appearon the LCD.

OPERATIONThe tester is operated using six keyslabelled Ent (enter), Esc (escape), dn(scroll down), up, dn2 (fast scrolldown), and up2 (fast scroll up). The upand dn keys have an auto -repeat func-tion which causes the repeat rate to beautomatically increased as the key isheld depressed i FT) D6 lights to indi-cate that the IC under test is beingpowered, and should not be removedfrom the ZIF socket. All ICs to betested should be aligned towardspins 12/13 of the ZIF socket. Their'top' notch is at the side of the ZIFsocket lever.

Pressing the Esc (escape) key takesyou to the main menu. There, the fol-lowing functions may be selected:L Test IC: the user picks an IC from an[C library, and the DUT is checked forcorrect' operation. The test may berepeated. If indicated by the test vec-tors, the current consumption of the ICunder test is measured and displayed.2. Identify: this allows you to identifythe type number of an unknown IC. Ifthe GND and Vcc pins are unknown,

only those test vectors are used thathave the GND and Vcc pins at thesame positions. The GNDNcc pinentry is optional. Next, you can selectthe libraries that have to be scanned.3. Retest IC: once an IC has beentested or identified, it may be testedagain without haying to pick it fromthe libraries.4. Trace: all test vectors and theresponse of the DUT to these vectorsappear in succession on the LC dis-PlaY-5. Options: here, you can define globaloptions.6. Info: information on version andcopyright7. Self Check: the IC tester hardwaremay be checked using this functionand a voltmeter.

Figure 4. The LCD ismounted at a slantangle of about 15degrees at the solderside of the board.

1111111111I1111111 roue llilliiitilk1111%

8. Remote Mode: connect a PC to theR5232 interface and debug test vectorsusing the DOS program TVCHKEXE

The up dn keys are used to scroll oneitem up or down. The up2/dn2 keysdo the same, but then five items at atime. The Ent key is used to confirm aselection. Esc, finally, jumps to themain menu.

NEXT MONTHNext month's second and final instal-ment will discuss the structure of thevarious menus which appear on theLCD, as well as the ins and outs of testvector creation, downloading, debug-ging and EPROM programming.

igalnx).0

Figure 5. General viewof the completed mainboard and keyboard.

Elektor Electronics 3/98 57

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K.P. HOUSE , UNIT 15 , POP IN COMMERCIAL CENTRE,SOUTHWAY , WEMBLEY , MIDDLESEX. HA9 OHB ENGLAND

Telephone : 0181 900 2329 Fax : 0181 903 6126E Mail : GRANDATA.LTD@BTINTERNET.COM

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PLEASE PHONE US FOR TYPE'S NOT LISTED AS WE HAVEOVER 50,000 ITEMS IN STOCK.

QUOTATIONS GIVEN FOR LARGE QUANTITIES

GRANDATA LTD TEL : 0181 900 2329 FAX : 0181 903 6126

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electr Tics r-iinesemiconductor overviews

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have their own website which presents

new products andallows datasheets to

be downloaded. Aproblem arises, how-ever, if you are stuckwith an IC or a tran-

sistor of unknownmake. Fortunately,

there are a numberof manufacturer -inde-

pendent overviewsand search engines

on the Web.

The Chip Direc-tory is probablythe largest inde-pendent ICoverview on theInternet. It can befound atzirardirslall.n1/-ganswijk/chipdhlchipdir.htm.

This site, con-structed andmaintained byJaap van Ganswijkfrom the Nether-lands, containsinformation onmany semicon-ductors, with spe-cial emphasis onIC used in com-puter technology.

The collection grows every day, asanyone is invited to contribute rele-vant data and/or links to interestingsites. The Chip Directory hasmany mirror sites, includingsites in Africa. North America,Australia and Europe.

The Chip Directory allowsusers to search for semiconduc-tor families, names, numbersand prefixes. Information onICs from the former SovietUnion is also available. In addi-tion to all this IC data the ChipDirectory also offers a substan-tial list of other electronics -related web sites. Furthermore,there's information on impor-tant electronics venues, manu-facturers, CD-ROMs with com-ponent data, and addresses ofall important electronics maga-zines (yes, including Elektor).

Questlink at wurw.questlink.tom is another search engine forintegrated circuits. The site alsooffers quite some informationon motherboards. It is, however,mainly a source for semicon-ductor company profiles andthe latest industry news.Questlink is a free service forengineers by engineers, as theycall it.

Yet another address you maywant to use for finding compo-nent data is Semidex(uranv.semidex.com). The makersof this site claim that it offersdata on about 75,000 integrated

circuits, mainly memory chips. Semi-dex also supplies data on PC mother-boards, as well as information on man-ufacturers and the latest news onmemory technology. The searchengine on this site provides you witha search system based on number,function, manufacturer and keyword.For the time being, the search serviceis offered free of charge. This will bechanged to a paid -up service shortly.The IC overview may also be boughton CD-ROM.

If your chief interest is in processors,then the Chiplist (chtstein.et.tudelftml/-of ermanichiplist.html) is certainlyworth a visit. This site contains a heftyoverview of CPUs and coprocessors.

Finally, if you are looking for dataon distributors, representatives, ser-vices and semiconductor manufactur-ers in the electronics industry, theaddress to go to is wrirmelectrobase.cotriwhich takes you to the site run byElectrobase.. exc--4e1-1)

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462Elektor Electronics 3/98

orrections irc UpdatesSimple ElectronicMetronomeFebruary 1998 - 980006-1

The PCB artwork for this projectwas not properly reproduce& byour image setter. The correctdrawings are given here.

Prize ContestFebruary 1998, page 9.

We apologize for a few errors inthe final instalment of the 'youcan Win this magnificent prize'contest on page 9 of our Febru-ary 1998 issue. At the right-handbottom of this page it is stated:

the correct answer to ques-tion 3 and stick ...; this shouldhave read: the correct answerto question 4 Also, themonths on the four stickers wereincorrect: they should have read'February 1998' (Ionization cir-cuit: March 1998) and not Jan-uary 1998. Obviously, thesestickers will be accepted as ifthey had carried the correctmonth.

Switchboard allows PRIVATE READERS of Elektor Electronics oneFREE advertisement of up to 106 characters, including spaces, com-mas. numerals, etc., per month. The advertisement MUST relate toelectronics, and it MUST INCLUDE a private telephone number orname and address: post office boxes are NOT acceptable.Elektor Electronics (Publishing) can not accept responsibility for anycorrespondence or transaction as a result of a free advertisement orof any inaccuracy in the text of such an advertisement.Advertisements will be placed in the order in which they arereceived. Elektor Electronics (Publishing) reserve the right to refuseadvertisements without giving reasons or without returning them.

WANTED Understand Electrical &Electronic Maths by Owen Bishop.P Hall, phone (01623) 26969.

FOR SALE Due to workshop clear-ance: 3 multimeters, transistortester, frequency counter, valve volt-

meter. Phone for detailed list. Ken

Phillips, phone (01376) 323164(Essex).

FOR SALE Sony SMC-70GP video

tiller with books, software, etc. Twin

3.5" drives, integral keyboard, gen-locker, PAL superimposer and sep-arate colour monitor. Job lot:

SWITCHBOARDuntested and sold 'as seen'. First£50 secures. Trevor Wiltshire,Reading (0118) 9701163.

FOR SALE kits for 80C32/51 com-puter, Elektor Oct. 92, completewith doc. and PCB, £25 incl. P&P(Europe). Anita, fax (+31) 436014470, email techtext@worl-donline.nl.

FOR SALE PSU PCB's, 45W, UP240VAC, 0/P DC +5V (x2). +12V.-12V, £5 each. Tel. Paul on

(01942) 706769 after 6pm.

FOR SALE CCD camera module,B&W, 6 IR LEDs, 0.2 Lux. 1 Vppcomposite video output, £49.Phone Alan on (0181) 755 3509

SWAP Tektronixifelequipment D65dual -beam scope in g.w.o. for Bbclarinet, must also be in g.w.o.Phone Graham on (01142)483587.

FOR SALE 30 textbooks Tec 2,3,4HNC C & Guilds on computers,processors, colour TV, video. Price£1 each, or £25 for all 30. Suitablefor club or school. W. Allen, 47Westhorpe Gdns, Hendon, LondonNW4 1TU. Tel. (0181) 203 6023.

WANTED Printer Buffer; standalone version (Elektor 6/92); anycondition considered. Please phoneMichael John Rutland on +44(0)1256 881338.

Elektor Electronics 3/98 63k

* flashing broochoptoelectronics in pocket format

This is the third andlast in a series of

three miniaturedesigns for beginners

in electronics. Eachof the designs is

powered by a 3 Vlithium manganese

dioxide non -

rechargeable batteryand is provided with

some sort of visualindication. The

brooch presented inthis article is an ele-

mentary flashingcircuit which has no

pretensions otherthan that of an

optoelectronic toy.

Design by K.A. Wa!raven

1/4

With its, dare we say, intricate lighteffect, the flashing circuit may be seen,in all its simplicity; as a cute little trin-ket that will, no doubt, catch a fewglances at a party or some cimilar get-together. And, indeed, like the die andtrinket published in the past fewmonths, the brooch is intended pri-marily as an eye-catching, optical orna-ment.

CIRCUIT DESCRIPTIONDesigned to create an optically inter-esting miniature effect, the brooch hasabsolutely no practical use. Howeverthe designer wanted the light effect tobe quite different from the usual arrayof flashing and running lights, most ofwhose patterns quickly become drab,dreary, and predictable.

The aim was therefore to drive anumber of LEDs in a way to producea truly random light pattern and withan absolute minimum of electroniccomponents. This resulted in a tinycircuit containing only two I4 -bitcounters and six LEDs-see Figure 1.

The use of two counters preventsthe circuit exhibiting the same pre-dictability of so many others. If onlyone were used, the effect would of

oenecessity be repetitive. So, the secondcounter serves to avoid monotony.

Should ICI work on its own, diodesD2-137 would light in perfect order andregularity, since they are linked to thesuccessive outputs (Q7 -Q13) of thecounter. However, with IC, also in cir-cuit, when Q7 of ICI is high, D, canlight only if Q13 of IC, is low at thesame time. In the same way, when Q8of ICI is high, D3 can light only if Q12of IC, is low at the same time. And soon ...

So, whether the diodes will actuallylight, although they are driven in per-fect succession by ICI, depends onother factors as well. Not only are theylinked to outputs Q7 -Q13 of IC, inopposite order flout their connectionsto ICI, but the integrated circuits countin different tempi. This is effected bymaking the value of C3 almost fivetimes greater than that of Cl.Consequently, the clock oscillator inICI runs at a frequency about fivetimes higher than that in IC,. Thesefactors combined result in the LEDslighting in a truly random way.

Power for the circuit is derived froma 3 V lithium battery. Switch S, is theon/off switch.

464Elektor Electronics 3/98

Visit our Web site at http: ourworld.compuserve.com homepages elektor_uk

Figure 1. The use oftwo counters enablesa completely randomlight pattern to beobtained.

Push-button switch S1 serves tobriefly enable the counters if the circuitis used as a die, but if this.function isnot envisaged, this switch, as well asDI and D8, may be omitted.

CONSTRUCTIONThe brooch circuit is best built on theprinted -circuit board shown in Fig-ure 2, which is, however, not availableready made.

Completing the board cannot besimpler: Start with the passive compo-nents (resistors, capacitors), followedby the ICs and LEDs. The use of IC

Figure 2. The tinyprinted -circuit boardfor the flashingbrooch is not availableready made.

sockets is left to personal choice: theiruse prevents any risk of damage to the1Cs during soldering, while withoutthem, the brooch is rather flatter. Mindthe polarity of C1 and D1-D8.

The circuit is powered by a 3 Vlithium manganese dioxide non -rechargeable battery, TypeCR2032 or the rather flatterCR2025. The diameter ofboth types is 20 mm. Thebattery is fitted on tothe board with theaid of a speciallyavailable holder.Note that its+ve terminalmust pointupward. (Recently,types have become avail-able for direct mounting onthe PC board - see Parts list).

On/off switch S2 may be

3V

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replaced by a three -pin PCB jumpersystem, where-upon on/offswitching iseffectedby the

short-ing link.

The clipfor fastening

the brooch toclothing should

be soldered or glued(superglue!) at the

underside of the boardnear the battery.

Figure 3. Completedprototype of the flash-ing brooch.

Parts list

Resistors:R. R, = 1 MOR.,, R4 = 220 kt

Capacitors:C. = 10 pF. 63 VC, = 0.001 pFC3 = 0.047 pF

Semiconductors:D.. D5 = 1 N4148 (may be omitted -

see text)D2 -D7 = LED, high efficiency

Integrated circuits:ICI, IC2 = CD4060

Miscellaneous:S1 = push-button switch with single

break contact (may be omitted -see text)

S2 = SPST or three -pin PCB jumpsystem (wire -wrap pin -strip headerwith shorting link - available fromRS Components) - see text

BT, = 3 V lithium manganese diox-ide non -rechargeable battery TypeCR2025 or CR2032 '.with holder forboard mounting (there are typesavailable for direct mounting on aPC board from RS Components)

Figure 3 shows the completed proto-type brooch.

With components as specified inthe Figure 1, the circuit draws a cur-rent of about 10 mA. At that rate, aCR2025 battery will have a life of10-12 hours, and a CR2032 one of14-17 hours.

EXPERIMENTATIONA simple circuit as described lendsitself readily to experimentation. Forinstance, the light effect may be alteredby changing the dock frequencies ofthe two counters. This only requiresaltering the value of C, and C3.

19&1328]

980028 - 11

Elektor Electronics 3/98 65 1116._

Digital Audio SignalProcessingBy Udo ZolzerISBN 0 471 97226 6280 pages - illustratedPrice E45.00(Hardback)John Wiley & SonsWell established in the consumer elec-tronics industry, Digital Audio Signal Pro-cessing (DSP) is used for recording andstoring music and speech signals, forsound mixing and production of digitalprograms, in digital broadcasts, and inconsumer products like CD players andpersonal computers.

Digital Audio Signal Processing pro-vides the basis of an advanced course inDSP and is directed at students studyingelectronics engineering, computer sci-ence and physics, but is also aimed atprofessionals who look for solutions toproblems in audio signal processing inthe fields of studio engineering, con-sumer electronics and multimedia. Themathematical and theoretical funda-mentals of DSP systems as well as typicalapplications with an emphasis on designaspects are discussed. Prior knowledgeof systems theory, basic DSP and multi -rate processing are assumed.

The book is divided into two parts,the first of which deals with the hard-ware systems used in DSP (studio tech-nology; digital audio broadcasting,quantization, AD and DA conversion,and audio processing systems. The sec-ond part discusses algorithms for pro-cessing digital audio signals (equalizers,room simulation, dynamic range con-trol, sampling;ing rote conversion, anddata compression).

This is as up-to-date a book on thesubject of DSP as you can get and onethat many will wish it had been pub-lished earlier.

Practical RadioFrequency HandbookSecond EditionBy Ian HickmanISBN 0 7506 3447 2302 pages - illustratedPrice £19-99 (Soft cover)NewnesThis book provides a practical introduc-tion to modern RF circuit design. Its con-tent is aimed at those learning to designRF circuitry and users of modem RFequipment, such as signal generators,swept -frequency generators, and spec-trum and network analysers. Pressure onthe RF spectrum has never been greaterand it is people with knowledge andskills of RF design who are now in de-mand in the electronics industry to de-sign, produce, maintain and use equip-ment capable of working in this crowedenvironment.

The new edition of this handbook,which is a valuable source for all RF en-

gineers, covers antennas and propaga-tion in more detail, hos new appendicesgiving useful addresses and contacts, oswell as details of frequency allocations.

Newnes books may be ordered fromCustomer Services DepartmentHeinemann Publishers OxfordP 0 Box 382, Halley CourtJordan Hill, Oxford OX2 8RUTelephone +44 (0)1865 314 301Fax: +44 (0)1865 314 029

Stereophonic SoundRecordingBy Christian Hugonnet & Pierre WolderISBN 0 471 97487 0292 pages - illustratedPrice £29.95(Hardback)John Wiley & SonsRecent advances in digital radio haveheralded substantial innovations insound recording techniques and in-creases the importance of applying thelatest microphone techniques. The au-thors of this book focus on these innova-tions, giving numerous examples of theiruse within the framework of an analysis -based recording engineering theory.

The book provides a completeoverview of well-known sound recordingprocedures practised world-wide, whilstalso presenting a methodology that willprovide the reader with an efficient op-

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Building on their considerable experi-ence of creating innovative recordingtechniques, the authors provide an au-thoritative analysis of the subject that of-fers valuable, practical guidance thatwill aid the development of new record-ing methods. Their inside knowledge ofthe requirements of the phonographic,broadcasting, film and other media in-dustries ensures expert coverage of newproducts and approaches, including:

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in-depth analysis of the principlesand use of stereophonics;

influence and role of the venueacoustics on the sound recording;

guidelines for mastering and mixingdifferent levels of sound from differentsources.

For professional audio engineers, thismanual provides systematic advice forgetting optimal performance from studioequipment. For students of audio engi-neering, it will form o comprehensive in-troduction to the area of stereophonicrecording, backed up by real -world casestudies and a wealth of practical experi-ence.

Books from Elektor ElectronicsBuild your own Electronic Test Instruments (0 905705 37 8)Build your own AF valve amplifiers (0 905705 39 4)Build your own high -end audio equipment (0 905705 40 8)Short Course 8051/8032 Microcontrollers

& Assembler (0 905705 38 6)SATT Projects (0 905705 35 I)306 Circuits (0 905705 43 2)305 Circuits (0 905705 36 X)304 Circuits (0 905705 34 3)303 Circuits (0 905705 26 2)302 Circuits (0 905705 25 4)301 Circuits (0 905705 12 2)Microprocessor Data Book (0 905705 28 9)Data Sheet Book 2 (0 905705 27 0)Data Book 3: Peripheral Chips (0 905705 30 0)Data Book 4: Peripheral Chips (0 905705 32 7)ST62 Microcontrollers (0 905705 42 4)SCSI: The Ins and Outs (0 905705 44 0)P1Cs in Practice (0 905705 51 3)12C Bus (0 905705 47 5)PC Service & Repair (0 905705 41 6)Lasers: Theory and Practice (0 905705 52 1)The CD-ROM Sstenz (0 905705 46 7)NEW: Teach Yourself Word 97 (0 905705 59 9) (Page 7)NEW Loudspeaker Projects (See page 27)

f 15.95 SUS38.25£ 14.95 SUS36.00f 14-95 SUS36.00

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Planned for publication:Matchbox Single Board Computer (0 905705 53 X) - February/March 1998Designing Audio Circuits (0 905705 50 5) - March/April 1998Handbook for Sound Technicians (0 905705 483) - ApriliMay 1998

66 Elektor Electronics 3/98

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EIJECTRONICSCYLI3 MOCZ Fril4POTEtt

P.O. Box 1414 Dorchester DT2 8YH EnglandTelephone +441011305 250 995 Fax +44 (011305 250 996

Get into PIC Programming withForest Electronic Develoments!PIC Basic Controller Modules - from £27.00

PIC BASIC controllers offer a N.:ell featured BASIC language runnino in realtime directly on a PIC Microcontroller. The 16C74 version has 8k EEPROMwith up to 2000 lines of BASIC, 27 lines of programmable liO, a serialinterface and a 4MHz clock, 8 x AID inputs and a PWM output, 3 timers andinterrupt support in BASIC, and an interrupt driven serial RS232 interface.

16C57 module kit Bk EEPROM £27.00 Prebuilt £33.0016C74 module kit 4MHz £35.00 Prebuilt £42.0016C74 module kit 20MHz £40.00 Prebuilt £46.00Instructions. development software and documentation on 3.5- disk are included.

PIC BASIC Compiler - available for the 16C74 £50.00

PIC Programmers - kit £40.00, pre -built £50.00Original: Programs 16C5x. 16C55x, 16C6x, 16C7x, 16C84.Serial: Programs 12C5xx, 16C55x, 16C6x, 16C7x, 16C/F84, PIC14000Both operate over a serial link to a PC. Includes all components, PCB andprogrammed PIC, Windows sofmare plus our Windows based developmentenniironment. Serial programmer has a ZIF socket

PIC Development Environment and SimulatorA Windows based PIC Simulator and Development Environment, up to 50times faster than MPSIM. £25 inc. P&P if bought with Programmer.otherwise £30.00 inc. P&P.

Add f3.00be

Visit

Blank PICs 161'84-04 £6, 16C741JW f24. 16C57-04 OTP E5.0012C508 -04P E2.20, 120509-04P f2.70. PIC14000 04P £10.00

for Postage. Packing and Handling. all orders which are held in stock witsent by return, first class post. Payment by Visa/Access 'Mastercard or

cheque430 payable to :

RDForest Electronic Developments(C. J.Abbott C M Warner)

10 Holmhurst Avenue, Christchurch. Dorset, BH23 5PQ.Phone/fax: 01425-270191

our web site at http://www.ibmpcirg.co,uk/-gmwarner/fed.htm

Elektor Electronics item tracer 1985-97Our new Item Tracer is now available!It contains the digital contents list of all articles (except news columns) published inthe magazine during the period 1985-1997 incl. It is a user-friendly program on a3.5" diskette. run under Windows 95, which offers an attractive graphics interface.

The program allows a search to be made on various bases orcombinations. such as name of article; name of component;classification (audio, computers, etc); special components; ordernumber of PCB or software item.

Since the printer is driven by the Windows program, any suitableprinter may be used.

Minimum computer requirements: PC3861486/pentium; at least 4 MB RAM;Windows 3.1/3.11/95; at least 2 MB free space on hard disk.

Order now on the Order Form in the ReadersServices section towards the end of this issue.The recommended retail price is £ 11.75 (S23.50),but subscribers pay only £ 10.00 (S20.00).

Elektor Electronics(Publishing)P 0 Box 1414Dorchester. DorsetEngland DT2 8YH

NEw

L71.--.11(7--"IieWCAkifig

READERS

SERVICES

ISLISOVikcDave.t.:MARCH

1998

GENERALPriiet-civs: baits (P08s) se5a4TheSied 1,0-1 pi.- si

ROMs. EPROSIs. Pki, GU. rikrzcd=31V1Cnk0Ses roe prOects riekn Nye -0,1prired in ReatorDearoti= Ray Ye cetenl ust; On 000e ForM

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.04.ts. GMs. PALS. MACK. Res and atieciactm'Ners ra la -,..**4 0101-proyerrn

Prices and item dm oriel/Nis 0.:Diect to change TN.pi:I:she; *sera 00 raft 40614¢0 vets wr::.-A Vet0.0.ff-0.&05. Prices sad him description stows heresmarm& atm U pr team issues. E L 0 E.

PAST ISSUESPas -1 14a -i1^75 be orderad fromVic nth. ide obscrigice -SErvi:t Ltd. Unit 4. Gabs ReedFarm. Patkley Road. TICEHURST 1N5 711E. Eisend.telepeme 1,44) 1550 200657, In (+44) 1550 200615,email annaitscripbortgrirgiarelPrr ci cast tr.0,000 0eurr0001,irg:uNci; comps tm sts714. swim, 80 £320 /04Ever. E1.50 (surface reel outside UK). £3.75 (alt itaiEurope): £4.50 (a4maa ovrsidit Europa). Prices of00y-/Aogtis1 and DeNeker Imes. indudne Naga forsale miss. as 04 25 RN, 54 50 ikdase 004 oastsal: £4.75 rermel (11090): 001 E500 rairmse misINrays)

PAST ARTICLESFO, r=racer Cr: pail ere3. '4,515.1 edzaland Addiregrid.re Otke on 00mieste. 19e079 (01305)250995: ha 250M. ens51a 00Z-..arip.0.000 cap

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SPECIAL PRODUCTI

HIATORZLECIROWCS VOLUME 1997 ON CD-ROMBletrd7t31494tedOn

ardtd9 dem* /....% ElED redraw Etee itir Ribr-F.ter5 price Y3550 or

115571.0]al5t71RES:".=' ITEM TRACER 1985-1997.(cr 3_500- o0.- .?5011-1 10.00.2090

eleittC 7:: 77',..tiattri. Wend once: £11.75 is015523 53

ELEATORELEcuilyam 'RP -pc HARDWARESOFTWARE 97-98.0!1 ED -ROMCp.010:001 or 103, pire-atreig 000.0 EN 1097110....1,0.ess0 Mar COrrc,..X01sodvre 5056901 as d.;IX Lt1 by Belie 03701-1 16.50 33.00Ell4aNtiLECIREKICS DATASHEET COLLECTION

ON CD-ROM 16:0 33 COVIKTOR ELK -ROWS VOLUME 1996 ON CD-ROMrcL aa-x.c.5 WerttemAwan cf*-7-* 31.56.63 CO' red-ef dice Is sus /00m-.0 dice: £135 50 or

UW1 .170NEATEN NECIRCROCS VOLUME 1995 ON CO -ROM

3.7C0* 74 CD riktrad pr>x for pisscroes. ?War cece: £41 CO or

1.155$240RECUR fiLTIPC9K5 SOFTWARE COMPETITION1996;97 ON 010/10.11.CoCa9od n a1prize-istr0sle,"

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liandyrneVAT0051203ProguaTer- Dock:r4 ea00-1' KB. sh..VePea, 96e.0s 970090-C 2025 40 50

- Dockirg 0.-3.0-1P15 ply 97E090-2 7.50 15_00

Nr0oNi0csse KB crty 970090-1 425 8.5.3

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NOVEMBER 1997Hysil.000 97X45-1vac, Copy- PCB & EPT.17032 970056-0- mummy 976514-1510001000010.0-0 Amager 97-01S3-1PC as 4-ctarrel Lazt 4014 -se.-PEE

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3100 66101225 24508.75 17-W

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074342-1074012-1

974024-1974025-1

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MAY 1997110.;12istrgte 5Dh Lot- KB & 0902051 971041-C 8012M1 976505-1

Atrinced IDA 0020- PCB. GAL + EPROM 970325-C-GA122V10 976505-1- PROM 270512 976507-1Fro0 p d t 070003-F

5000a-0 1A050 1 _Art. r 970021-1Carped: Rm. Arralfer 97E043-1

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MARCH 1997EPROM Prp;ram0er.- K8 97E010-1 15 75 3100- Co-ta 00-R01.1 nos 975E04Eta-, -OcerstAr Wa!Em0010r 9700334 10.00 2000

FEBRUARY 1997Rgi-wy-PoemM Preampl0ar 960004-1Motor Wander for ECMors-PC8 &id P11E654 950095-C PC 16084 my 966510-136.iC11 Ern..M0.0.

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DECEMBER 1996205 oxrerre 050110-1Rra-is C.0-00 by11701 900e3-1

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APRIL 1996

- PCB r 51519x0055 -1I 060352-0- Disk 09001:041 5038-1PC -Caere AT Mews 00- Sam= 955031-1

MARCH 1996RC-Gs-irzi0913-D 075- PCB + RC 4466505-11 S0030 -C-PC 16104 96C--06-1

FEBRUARY 1996850 1700 50041011-0-.

-P03 + PROM 1965503-11050039-C603 1600 -EPROM 965503-1

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030 PCB + 5510 (0462024) 9950563-0.

- cortd 57:732 en eEsk 946202-1

7930 159 W3909 750324.50 49017.00 1403

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Elektor Electronics slipcase

Elektor Electronics 3/98

8.50 1703 7.75 1550 Prce +F&P retese of Ofd! Fotml.

xPlease send this order form to -(see reverse for conottions)

Elektor Electronics (Publishing)P.O. Box 1414Dorchester DT2 8YHENGLANDTel.. (01305) 250995Fax (01305) 250996E-mail: elektor_uk@compuserye.com

C-4-.1 ritikkaitt may I.V.4 are ha atitged to) use S promsm-4 be caw !am t9 Cry Colony Sottal Lab, P.O. Bet 243,

Nterbstough. Mt 034,S. Tel 0303)924-6371. 924-6526. Faxiti33? E24 -94F

ORDER FORM 03-98

VAT No.GB 454 135 463

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Tel. FaxPost codeDate

Please supply the following. For PCBs. front panel foils, EPROM5. PALs. GALs, microcontrollers and diskettes,state the part number and description; for books, state the full title; for photocopies of articles, state fullname of article and month and year of publication. Please use block capitals.Qty. Order Code Description Price each

£16.50

Total986001.1 CD-ROM 'pP-pC Hardware & Software 97-98' (comp/Ratko of 100+ prize-wihn:IO entnieS)

CD-ROM Dalasheels 1 CD-ROM Dalasheal Collection 1'£16.50

976003-1 CO -ROM 'Software for Electronics Competition 1998/97' (corriodation ata6 prize-winning entries) £15.75

E11.75110.00'986011-1 Beinor Bectronics Item Tracer 1985.1997 on 3.5 -inch disk (Windom 3.11A5)

CO -ROM Bettor 1997 Bator Bectronics Volume 1997 on CD-ROM (Windows 111195) E35.50131.50'

£2.95deface Elektor Bectrorks slipcase

Method of payment (see reverse before ticking as appropriate)nOle cheques not msde ou: in stoning must be increased by Me equivalent of £15.00

1.,1 Bank draft :_j Cheque (payable to Elektor Electronics Publishing)

tr4 dest,r7.,:rs s_ --,*-1 w z.-4,The publishers reserve tne rignt to change/ices )%i7.ftfIP-a rCL4CZat. tees Erd eretescritaions shcam nem suiotrsece truor 11weer..,-.iss C 8 Oil

Sub -total,.. mP&P

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on the reverse of this form.Worldwide SubscriptionService Ltd.Unit 4, Gibbs Reed FarmPashley RoadTicehurst, nr. WadhurstEast SussexENGLAND TN5 7HETel. (01580) 200657Fax (01580) 200616Email wws.subscription@virgin.nel

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rORDERING INSTRUCTIONS, P&P CHARGES COMPONENTS

Except in the USA and Canada, all orders. except for subscriptions andpast issues (for which see below), must be sent BY POST to ourDorchester office using the Order Form overleaf. Please note that we cannot deal with PERSMI. CALLERS, as no stock is carried at the editorial andadministrative office.Readers in the USA and Canada may (but are not obliged to) send orders,except for subscriptions (for which see below), to the USA address givenon the order form. Please apply to Old Colony Sound for applicable P&Pcharges. Please allow 4.6 weeks for delivery.Orders placed on our Dorchester office must include P&P charges(airmail - now called 'Priority' = or 1st class unless stated otherwise) asfollows. Up to 500 grammes (most small parcels) UK and Eire £2.50;Europe £4-00; outside Europe £10.00; surface mail £5-00. Up to 1 kg

(average per book): UK/Eire £3.00; Europe £5.00; outside Europe £14-00;surface mail £6-00. Up to 2kg (average per two books): UK/Eire £5.00;Europe MOO; outside Europe £18.00; surface mail £8-00.

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Unless you have an approved credit account with us, all orders must beaccompanied by the full payment, including postage and packing chargesas stated above.Payment may be made by cheque drawn on a London clearingbank (but see para. 4 below), postal order. VISA. Access. MasterCard orEuroCard (when paying by credit card, the order must go the cardholder'saddress). Do not send cash through the mail. Cheques and postal ordersshould be crossed and made payable to 'Elektor Electronics (Publishing)'.Payment may also be made by direct transfer from a private or businessGiro account to our Giro account No. 34 152 3801 by completingand sending to the National Giro Centre, in a National Giro postage paidenvelope, a National Giro transfer/deposit form. Do not send Giro transfersdirect to us. as this will delay your order.If you live outside the UK. payment may also be made by Bankers' sterlingdraft drawn on a London clearing bank, Eurocheque made out inpounds sterling (with holder's guarantee card number written on the back).or US or Canadian dollar cheque drawn on a US or Canadian bank.If you pay by Bankers' sterling draft, make clear to the issuing bank thatyour full name and address MUST be communicated to the Londonclearing bank.Our bankers are National Westminster Bank, 49 South Street,DORCHESTER, Dorset DT1 1 DW, England. Our account number is6966 3440.

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Components for projects appearing in Elektor Electronics are usuallyavailable from certain advertisers in this magazine. If difficulties in thesupply of components are envisaged, a source will normally be advised inthe article. Note, however, that the source(s) given is (are) not exclusive.

TERMS OF BUSINESS

Delivery Although every effort will be made to dispatch your orderwithin 2-3 weeks from receipt of your instructions, we can not guaranteethis time scale for all orders.Returns Faulty goods or goods sent in error may be returned forreplacement or refund, but not before obtaining our consent. All goodsreturned should be packed securely in a padded bag or box, enclosing acovering letter stating the dispatch note number. If the goods are returnedbecause of a mistake on our part. we will refund the return postage.Damaged goods Claims for damaged goods must be received at ourDorchester office within 10 days (UK): 14 days (Europe) or 21 days (allother countries) from the date on our 'Recorded delivery' slip.Cancelled orders All cancelled orders will be subject to a 10%handling charge with a minimum charge of £5.00.Patents Patent protection may exist in respect of circuits, devices,components, and so on. described in our books and magazines. ElektorElectronics (Publishing) does not accept responsibility or liability for failingto identify such patent or other protection.Copyright All drawings, photographs, articles, printed circuit boards,programmed integrated circuits, diskettes and software carriers publishedin our books and magazines (other than in third -party advertisements) arecopyright and may not be reproduced or transmitted in any farm or by anymeans, including photocopying and recording, in whole or in part, withoutthe prior permission of Elektor Electronics (Publishing) in writing. Suchwritten permission must also be obtained before any part of thesepublications is stored in a retrieval system of any nature.Notwithstanding the above, printed -circuit boards may be produced forprivate and personal use without prior permission.Limitation of liability Elektor Electronics (Publishing) shall not beliable in contract. ton. or otherwise. for any loss or damage suffered by thepurchaser whatsoever or howsoever arising out of. or in connexion with, thesupply of goods or services by Elektor Electronics (Publishing) other than tosupply goods as described or. at the option of Elektor Electronics(Publishing), to refund the purchaser any money paid in respect of the goods.Law Any question relating to the supply of goods and services by ElektorElectronics (Publishing) shall be determined in all respects by the laws ofEngland. January 1998

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September 1997

470Elektor Electronics

m

o S

SM

2142

0 m cgIn

tegr

ated

circ

uits

rz;

Aud

io

5-4

cip co

glE

ffff

ulov

ream

vag

DA

TA

SH

EE

T3/

98S

SM

2142

Bal

ance

d Li

ne D

river

Man

ufac

ture

r

Ana

log

Dev

ices

, One

Tec

hnol

ogy

Way

,

P.O

. Box

910

6, N

orw

ood,

MA

020

62-9

106,

U.S

.A.

Tel

: 617

/329

-470

0 F

ax: 6

17/3

26-8

703.

Inte

rnet

: ww

w.a

nala

g.co

m.

Gen

eral

des

crip

tion

The

SS

M21

42 is

an

inte

grat

ed d

iffer

entia

l -ou

tput

buffe

r am

plifi

er th

at c

onve

rts

a si

ngle

-en

ded

inpu

t

sign

al to

a b

alan

ced

outp

ut s

igna

l pai

r w

ith h

igh

out-

put d

rive.

By

utili

zing

low

noi

se th

erm

ally

mat

ched

thin

film

res

isto

rs a

nd h

igh

slow

rat

e am

plifi

ers,

the

SS

M21

42 h

elps

mai

ntai

n th

e so

nic

qual

ity o

f aud

io

syst

ems

by e

limin

atin

g po

wer

line

hum

, RF

inte

rfer

-

ence

, vol

tage

dro

ps, a

nd o

ther

ext

erna

lly g

ener

ated

nois

e co

mm

only

enc

ount

ered

will

s lo

ng a

udio

cab

le

runs

. Exc

elle

nt r

ejec

tion

of c

omm

on -

mod

e no

ise

and

onse

t err

ors

is a

chie

ved

by la

ser

trim

min

g of

the

onbo

ard

resi

stor

s, a

ssur

ing

high

gai

n ac

cura

cy,

The

car

eful

ly d

esig

ned

outp

ut s

tage

of t

he S

SM

2142

is c

apab

le o

f driv

ing

diffi

cult

load

s, y

ield

ing

low

dis

-

tort

ion

perf

orm

ance

des

pite

ext

rem

ely

long

cab

les

or

load

s as

low

as

600

O.,

and

is s

tabl

e ov

er a

wid

e

rang

e of

ope

ratin

g co

nditi

ons.

Bas

ed o

n a

cros

s -c

oupl

ed, e

lect

roni

cally

bal

ance

d

topo

logy

, the

SS

M21

42 m

imic

s th

e pe

rfor

man

ce o

f

fully

bal

ance

d tr

ansf

orm

er -

base

d so

lutio

ns fo

r lin

e

driv

ing.

How

ever

, the

SS

M21

42 m

aint

ains

low

er d

is-

tort

ion

and

occu

pies

muc

h le

ss b

oard

spa

ce th

an

tran

sfor

mer

s w

hile

ach

ievi

ng c

ompa

rabl

e co

mm

on -

mod

e re

ject

ion

perf

orm

ance

with

red

uced

par

tsco

unt.

- F

OR

CE

-{C

/111

11

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UN

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VIII

pin

conn

ectio

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8 -P

inD

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P S

uffix

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16 -

pin

Wid

e B

ody

SO

L (S

suf

fix)

The

SS

M21

42 In

tand

em w

ith th

e S

SM

2141

diff

er-

entia

l rec

eive

r es

tabl

ishe

s a

com

plet

e, r

elia

ble

solu

-

tion

for

driv

ing

and

rece

ivin

g au

dio

sign

als

over

long

cabl

es. T

he S

SM

2141

feat

ures

an

Inpu

t Com

mon

-

Mod

e R

ejec

tion

Rat

io o

f 100

d6

at 6

0 H

z. S

peci

fica-

tions

dem

onst

ratin

g th

e pe

rfor

man

ce o

f thi

s ty

pica

l

syst

em a

re in

clud

ed in

the

full

data

she

et.

Fea

ture

s

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rans

form

er -

like

bala

nced

out

put

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rives

10

V r

ms

Into

a 6

00 5

2 lo

ad

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tabl

e w

hen

driv

ing

larg

e ca

paci

tive

load

s

and

long

cab

les

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w d

isto

rtio

n: 0

.006

% ty

p. 2

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z -2

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into

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p

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plifi

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aram

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aliz

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ynam

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cess

ors

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ors

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Sys

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ance

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ch 1

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e R

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Rec

eive

r

Man

ufac

ture

r

Ana

log

Dev

ices

, One

Tec

hnol

ogy

Way

,

P0,

Box

910

6, N

orw

ood,

MA

020

62-9

106,

U.S

.A.

Tel

: 617

/329

-470

0 F

ax: 6

17/3

26-8

703.

Inte

rnet

: ww

w.a

nalo

g,co

m.

Gen

eral

des

crip

tion

The

SS

M21

4 I

Is a

n In

tegr

ated

diff

eren

tial a

mpl

ifier

inte

nded

to r

ecei

ve b

alan

ced

line

Inpu

ts in

aud

io

appl

icat

ions

req

uirin

g a

high

leve

l of n

oise

imm

unity

and

optim

um c

omm

on -

mod

e re

ject

ion.

The

SS

M21

41 ty

pica

lly a

chie

ves

100

dB o

f com

mon

-

mod

e re

ject

ion

(CM

R),

whe

reas

impl

emen

ting

anop

amp

with

four

off

-the

-sh

ell p

reci

sion

res

isto

rs w

ill

typi

cally

ach

ieve

onl

y 40

dB

of C

MR

- In

adeq

uate

for

high

-per

form

ance

aud

io.

The

SS

M21

41 a

chie

ves

low

dis

tort

ion

perf

orm

ance

by m

aint

aini

ng a

larg

e sl

ow r

ate

of 9

.5 V

/ps

and

high

open

-lo

op g

ain,

Dis

tort

ion

Is lo

ss th

an 0

.002

% o

ver

the

full

audi

o ba

ndw

idth

. The

SS

M21

41 c

ompl

e-

men

ts th

e S

SM

2142

bal

ance

d lin

e dr

iver

. Tog

ethe

r,

thes

e de

vice

s co

mpr

ise

a fu

lly in

tegr

ated

sol

utio

n fo

r

equi

vale

nt tr

ansf

orm

er b

alan

cing

of a

udio

sig

nals

Fun

ctio

nal d

iagr

am

RE

FE

RE

NC

E

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N.C

.

V. OU

TP

UT

SE

NS

E

Pin

con

necl

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8 -P

in P

last

ic M

ini -

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(P

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out t

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robl

ems

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isto

rtio

n, E

MI f

ield

s, a

nd

high

cos

t.

Add

ition

al a

pplic

atio

ns fo

r th

e S

SM

2141

incl

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sum

min

g si

gnal

s, d

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entia

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ampl

ifier

s, a

nd 6

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plifi

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CC;All articles published In 1995, Incl. circuit diagrams and PCB layouts,with an extensive search program

Price (subscribers) £37.00 (USS74.00): RRP £41.00 (USS82.00)

Elektor Electronics Digital Circuit Library (1)Contains over 300 circuits complete with diagram and text. Zoom andprint module. Fast search facility. Error -tolerant Index search system.

Clear instructions In English. Many printed -circuit board layouts.RRP £12.75 (USS25.50)

All articles published In 1996, Incl. circuit diagrams and PCBlayouts, with an extensive search program and simulationsoftwarePrice (subscribers) £31.50 (USS63.00); RRP £35.50 (USS71.00)

_-eronics Digital Circuit Library (2)A second selection of over 300 circuits complete with diagrams and text.

RRP £12.75 (USS25.50)

Software 96-97From the 1996-97 software competition: more than 80 programs(DOS or Windows), including PLC course, AF spectrum analyser,teletext decoder, fuzzy logic simulation program, PCoscilloscope. Source code for most programs included.RRP £15.75 (USS31.50)

Learn electronics In four languages!Electronics terms in Dutch, English, French and German. Includes trainingaids, exercises and self -tests In understanding and translating electronics

text In any of these four languages. includes parsing function.RRP £35.00 (USS70.00)

°P-pC hardware & software 9798All the winning entries of the July/August 1997 microprocessorcompetition: more than 100 designs in Dutch, English French, andGerman, frequently supported by programs for the PC (DOS orWindows).RRP £16.50 (USS33.00

Elektot/Elektuur IC databankIncludes all important types of IC, such as HCMOS, TTL, CMOS, linear ICs,

and many more. Detailed manufacturers' data and application circuits.Multiple search routines.

RRP £25.00 (USS50.00). Price for subscribers £20.00 (USS40.00)

' " ' tor/Elektuur CollectionUsable on PCs and Macintosh computers, this CD-ROM contains morethan 300 original complete datasheets In English in electronic PDF format.Included are logic circuits (74)0(00 and 4000 series), voltage regulators,linear circuits, data converters, and miscellaneous devices.RRP £16.50 (USS33.00)

Lidiwnik-41Pr/nit/Ent/tit:

Elektronical114

ALL PRICESEXCLUSIVE OF P&P

The CD-ROMs may be ordered on the order form in the Readers Services sectiontowards the end of this issue.

Lill-,LitZtLedLOL10Elektor Electronics (Publishing)

P 0 Box 1414Dorchester

Dorset England DT2 8YH

Next month in Elektor Electronics

Focus on: Internet accessIn view of the growing popularity of the Internet,subscribers need more and better links to the net.Where not so long ago the only means of privatecommunication was via the telephone. there arenow other ways and means. For instance. cableoperators offer two-way Internet traffic via their net-works and there are already facilities for private useof satellite links. Another promising high-speedcandidate is ADSL (asymmetrical digital subscriberline). The options offered by the various systems inuse today and in the near future will be discussedin some detail.

Electric FieldStrength MeterThis instrument measuresthe strength of alternatingelectric fields. Its range(10 Vim to 100 V, m). fre-quency span (10 Hz to2 kHz) make it ideal formany in-house measure-ments. including radiationlevel testing to the SwedishMPR2 and MPR3 standardsas applied to computermonitors. The sensordevice for the meter is ametal assembly designed tocatch as much radiation asa typical human body.

And more for you fo enjoy!Reserve your April copy of Elektor Electronics now.Article titles and magazine contents subject to change.

20 -Metre SSB/CW ReceiverThe 20 -metre amateurradio band (14 MHz) isbuzzing with RTTY, fax,CW and SSB activity. Inthis article Eric EdwardsGW8LJJ describes apretty sensitive andselective direct -conver-sion receiver for CWand SSB. A areat intro-duction to amateurradio, this low-cost andsimple to build single -board receiver is idealfor budding SWLs.

Parking Distance MeterA compact com-bination of anultrasonicreceiver andtransmitter isdescribed thatenables you topark your carwith great accu-racy and hope-fully withoutcausing dentsor scratches (we

don't accept damage claims!). The parking aid has anadjustable detection range of 30 cm to 3 m, and usesan LED or a buzzer to tell you when to start braking.

Index of AdvertisersAdvertising Standards AuthorityB K ElectronicsBull ElectricalCambridge Microprocessor Systems - CMSC -I Electronics

Confidential CommunicationsCrossware ProductsDisplay ElectronicsElektor ElectronicsEquinox TechnologiesForest Electronic DevelopmentsGrandataLabcenterLeading EdgeMOP

Pineapple PresentationsPico Technology

_Ouickroute Systems

R D Research

Smart CommunicationsSpeaker BuilderStewart of ReadingSlippier ElektronikSuma Designs

33

15

14. 32

10

27

33

20

6. 7. 27, 67. 73Inside back cover

67

58-61

5

39

7

33

26. 27

Inside front cover44

Outside back cover33

39

21

56

Those Engineers 10

Tsien (UK) Ltd 38

Ultimate Technology 25.47,49Viewcam Electronics 3,9VIP Matchmaking 26

ADVERTISING SPACE

for the April 1998 issue may be reserved

not later roan 17 February 1998 with

Elektor Electronics (Publishing)

Advertisement Office3 Crescent Terrace

Cheltenham GL50 3PE

England

Telephone 01242 510 760; Fax 01242 226 626

e-mail: bernardhubbard@msn.com

to whom all correspondence, copy instructions andartwork should be addressed.

74Elektor Electronics 3/9

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Suppo Imel 90S (AVR)RISC mi controller familySuppo Parallel Programmingmode in ZIF socket

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tA mel AVRTM Assembler

AVRTM Basic Lite Compiler (NEW)1. Atmel Databook on CD ROM

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Write in BASIC, Run in ,a FLASH Compiled BASIC generates tight AVR"' machine code

Not a Run -Time Interpreter; NO code overhead!

Target speeds comparable with assembler

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From Only £24.95! Ideal for educational, hobbyist and professional use

V Order Code: AVIIST £59.95

AVR*" BASIC LITE only supportsthe AT90S1200 (512 words code)

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....the experts'''"111