iireavirrm THE INTERNATIONAL ELECTRONICS MAGAZINE ...

iireavirrm THE INTERNATIONAL ELECTRONICS MAGAZINE'June 1996

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LgaffLzat-Izn.cor,i7Lesf CONTENTS

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June 1996Number 245

Volume 22ISSN 0268/4519

COMPUTERS & MICROPROCESSORS

32 PROJECTIt Flash EPROM programmer

Design by: C.E Urban

40 PROJECT:IV Keyboard swap for PCs

Design by K. Viernickel

FOCUS ON

46 Digital video recorders17 By our Editorial Staff

GENERAL INTEREST

12 PROJECT: Stop that barking!rDesign by K. Walraven

54 PROJECT:77 Burglar deterrent lighting

Design by K. Walraven

POWER SUPPLIES & BATTERY CHARGERS

68 PROJECT: Active power buffer3TE Design by W. Steimle

RADIO & COMMUNICATIONS

18 PROJECT:Tf 23 cm ATV preamplifier

Design by J. KOring, DL4EBJ

TEST & MEASUREMENT

26 PROJECT: Pulsimeterler Design by Fritz Grueber

MISCELLANEOUS INFORMATION

59 Corrections and updates65 Data sheets74 Index of advertisers15 In passing ...50 New Books9 News from the World of Electronics74 Next month in Elektor Electronics58 Readers letters60 Readers' services62 Software for electronics: SpiceAge

for Windows59 Switchboard

copyright*1996 Segment BV

A B CAUNT BUREAU OF CUICULATIOhS

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The publishers of Speaker Builder invite you to use your electronics knov. -how to explore the world of better sound. To subscribe, simply return thisform with your payment or FAX your credit card order and receive 8 issuesof Speaker Builder for a low introductory rate of S45. That's a S5 savings offthe regular subscription rate. Or, double your savings and subscribe for 16issues (2 years) at S80 (that's S10 off).

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Producrand published by ELEKTORELECTRONICS (Publishing)(Copyright Segment RV 1996)

Editor. Len SeymourTechnical Editor. Jan Bulling

Editorial & AdministrativeOffices:PO. Box 1414DORCHESTER DT2 811-1EnglandTelephone:011305)250 995 (National)or +44 1305 250 995 (international)Fax: (01305) 250 996 (National)or +44 1305 250 996 (International)

U.K. Advertising Office:3 Crescent TerraceCHELTENHAM GISt) 3PETelephone: (01242) 510 760Fax: (01242) 226 626

International Advertising Office:Segment BVP.O. Box 756190 AB BEEKThe NetherlandsTelephone: (+31) 46 438 9444Fax: (+31) 46437 0161e-mail: [email protected]

Subscriptions:World Wide Subscription Service Ltd.Unit 4, Gibbs Reed FarmPasltley RoadTICEHURST TN5 7HETelephone: (0158(1)200657 (National )or. +44 1580 200 657 (International)Fax: (01580) 200 616 (National)or +44 1580 200 616 (International)

Head Office:P.O. Box 756190 AB BEEKThe NetherlandsTelephone: +31 46 438 9444Fax: +31 46.437 0161Managing Director:

Johan H. BoermannDeputy Managing Director:

Menno MJ. LandmanEditor-in-Chief/Publisher:

Pierre E.L. KersemakersCommercial Manager.

Paul E. de Graaf

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NDB.Zoetemoude

Overseas editions:FRANCEElektor sariLes Trois TulleulsB.P. 59: 59850 NIEPPEEditor: G.C.P. Raedersdorf

GERMANYElektor Verlag GmbHSusterfeldNtr. 25521)72 AACHENEditor. EJ.A. Krempelsaucr

GREECEElcktor EPEKaraiskaki 1416673 Voula-ATHENAEditor. E. Xanthoulis

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

ISRAELElektorcalP 0 Box 41096TEL AVIV 61410Publisher. M. Avraham

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

POLANDElektor Elcktronik02-777 Wirszawa 130Skrytka Pocztowa 271Editor. W. Marciniak

PORTUGALFerreira & Bento Lda.Campo Grande. 56 -8 t91700 LISBOAEditor: E Ferreira do Almeida

SPAINResistor Electronica Aplicada SAP.. de la Castellana. 212-4 lzda28046 MADRIDEditor: Agustin Gonzales Buelta

SWEDENElectronic Press ABBox 550514105 liUDDINGEEditor. Bill Cedrum

4Elektor Electronics is published monthly. except in August. by Elektor Electronics (Publishing). P.O. Box 1414. Dorchester. Dorset DT2 8Y11. England. The mag-azine is available from newsagents, bookshops, and electronics retail outlets, or on subscription at an annual (1996) post paid price of L30-00 in the United Kingdom:air speeded: 08-00 in Europe. L47-00 in Africa, the Middle East and South America; L49-00 in Australia, New Zealand and the Far East; and SUS 64.00 in the USAand Canada. Second Class Postage paid at Rahway NJ.Postmaster please send address corrections to Elektor Electronics.cio Mercury Airfreight International Inc. 2323 Randolph Avenue, Avenel. New Jersey. NJ. 07001.

A4 Elektor Electronics 6196

YOUNG ELECTRONIC DESIGNERSSHOW THEIR PACES

As in previous years, the finals ofthe Young Electronic DesignerAwards, held at the Science Mu-seum in London recently,showed the creativity and theimagination of young British de-signers in electronics.

As before, the competition,sponsored by Mercury Commu-nications Ltd and Texas Instru-ments, in association with the In-stitution of Electrical Engineers(IEE), was open to students be-tween the ages of 12 and 25 yearsfrom secondary school, collegesand universities. The competitionchallenges young designers to in-vent and produce novel elec-tronic devices that meet aneveryday need.

Winning the Duke of York'sAward for Creative Technologywas Gemma Wicks, a 15 -year oldfrom Bancroft's School, WoodGreen, Essex, who devised a sys-tem for displaying the stoppingdistances for vehicles. Gemrna,whose project had already wonthe Young Engineer Award's Sil-ver Crest at the British Youthence Fair, held at G-Mex, Man-chester; recently; is a member ofan electronics club at her schooland discovered the need for theproject when her friend waslearning to drive.

Receiving the Mercury PlanetAward of ±2,500 for school andstudent for the most socially orenvironmentally aware projectwas Marc lien, an I8 -year oldstudent formerly from the Mer-

chant Taylors School, North-wood, Middlesex, whose projectwas a quadriplegic computer aid.Marc, while taking a level Maths,Physics and Design Technology,designed a remarkable piece ofhardware and software, whichenables the disabled to control acomputer by head movementsand also to replace the use of amouse by blowing through atube_

Marc came upon the idea forthe project while working withthe section of society now knownas et-taes-Physically Handi-capped Able-Bodied-as part ofhis schooling. Marc told ElektorElectronics: "I cam to realize justhow difficult it was for many ofthem to use an ordinary com-puter'.

For the project, a major partof his Design and Technology Alevel work, Marc created a head-set with a series of electronic sen-sors that follow head move-ments; the software, which hewrote in assembler language;and a computer keyboard on thesaeen_ His software will evenallow the computer to do thetalking for FHABS.

The project has been field-tested and already several com-mercial companies have ex-pressed an inteiest.

Taking the Texas Instrumentprize of £2,500 for school and stu-dent for the most commerciallyviable project was 15 -year oldChristopher Caulldn, a fourth -year student from Radley Col-lege, Abingdon, Oxfordshire,who is taking electronics at GCSElevel

Christopher's device, a mi-crocontroller-based instrumentfor controlling sunbathing wasthe result of a painful experiencein the sun.

Christopher told Elellor Elec-tronics: was looking for a pro-ject which would be a solution toa problem and not a solutionlooking for a problem. Peoplenowadays spend more and moretime in the sun and as a resultwe need a system that tells themwhen to cover up. The safety de-vice provides a simple and at-tractive solution against sunburnand the potentially resultant skincancer" (In western Europe, eachyou more HMI lell thousand peopledie from skin centre& in many castscaused by sunluthing. Editor]

"It is very simple to use,merely requiring the user to se-lect his/her skin tone and thestrength of the suncream ap-plied_ This is selected by pressing

the relevant button until the re-quired value is shown on thescreen. The safe tan device isthen set and will beep when it'stime for the sunbather to get outof the sun If he/she decides to goindoors for any reason, the de-vice can be stopped by a pausebutton. The device even turns it-self off automatically after it haswarned the user to go indoors. Itcan also be switched off manu-ally by pressing and holding aswitch for three seconds. There isa power saving sequence if thedevice is left untouched for morethan thirty seconds: this endswhen any button is pressed. Thedisplay constantly updates therecommended time the user hasremaining. It is small, light andconvenient, and operates fromstandard batteries."

In electronic terms, the deviceuses one linear TI light sensor,three pcb mounted push-buttonswitches; a buzzer; a dual highbrightness 7-segrnerittio display,and a Type PIC16C73XS micro -controller. Power is derived fromthree series -connected AAA bat-teries. The device cost about £15to build, but Christopher believesthat this would be halved forproduction quantities of 100 andover He estimates the marketpo-tential in the Uk alone at 10 mil-lion. Needless to say, Christopherhas already applied for a patentfor his device, while a number ofcommercial organizations haveexpressed an interest in it.

Peter Tonge, a 16 -year oldfrom Bolton School, took the IEEAward of £1,000 for school andstudent for the best new entrantto yeda with his audio preampli-fier Peter, who is taking his G-sr.s., indudingTechnology, this sum-mer, decided to solve the prob-lem of how to control the volumeof a video recorder and a hi-fiunit at the same time. He toldElektur Electronics: 'The most dif-ficult part was the decoding ofthe iv remote controller."

Wmning the YEDA trophy and£1,000 for the Senior Category(18-25 years) was Alan Capper; a22 -year old student from theUniversity of Wales, Bangor,whose project was dubbed

Alan Capper

'rEo'-The Electronic DoctorThis is a system that allows theduty GP to remotely monitor apatient's vital signs by telephone,that is, We -medicine, before de-ciding whether to visit, call anambulance or give other advice.

TED uses only four electronicsensors housed in an easy -to -usehand-held unit, to measureseven or more parameter directly,including temperature, respira-tory rate, breathing sounds, ECG,blood oxygen level, blood pres-sure and pulse rate. Other para-meters are derived mathemati-cally by the GP's computer.

Alan said: "The aim of theproject is to provide the GP witha range of relevant informationthat can be readily viewed, ma-nipulated and recorded, on a lap-top computer in the form of suf-ficient quality to enable a rea-sonable, preliminary diagnosis tobe made. Its purpose is to filterunnecessary night-time calls,thereby reducing the load on GPswho are becoming increasinglydisillusioned with their increasedwork load. By providing TEDwith a dedicated computer inter-face and software, data can bevalidated by inspection and aim-plete records created without ef-fort."

Coming second in the SeniorCategory was Marc Lien with hisquadriplegic computer; and thirdwas Louise Jens, 22, from BrunelUniversity Egham, Surrey, withher universal remote controller

Highly commended in thiscategory were Ben Curren, 18,from Bolton School, with his re-mote control light filter changerfor stage lighting: Matthew Wil-son, 22, also from Brunel Univer-sity for his unit to adapt a videorecorder to record teletext subti-tles with programmes; and An-drew Lyness, 18, from BallyclareHigh School, Ballyclare, North -.ern Ireland, for his fully inte-grated electrical guitar and am-plifier effects project.

In the Intermediate Category(15 -17 -year olds), first prize wentto Christopher Caulkin for hismicrocontroller sunbathingwarning device. Second prizewas for Andrew Gough, 17, from

Elektor Electronics

EventsMay21-23: The Internet WorldExhibition in London.

30-2 June: The Home PCShow. For details, phone'181 849 6200

June2: Northern Mobile AmateurRadio Rally at Ripon Race-courseOpen: 11:00 amTalk -in on S22 from 09:30 amFollow signs to Ripon Race-course from A61 Ripon By -Pass.Details: phone 01765 640229

4-5: The ICET 96 conferenceon electronics technologiesin Brighton, UK.

18-20: Multimedia 96 at theBusiness Design Centre, Lon-don. For details. phone0171 359 3535

30: The 39th Longleat Ama-teur Radio RallyOpen 10.00 am to 1700 pm.Free car parking150 trade stands20 local and national clubstandsAdults E2.50Senior Citizens £2.00Children 50pFollow the brown touristsigns for 'Longleat House'(Not Safari Park) from the A36near Warminster, Wiltshire.Details: phone 0117 940 2950

July16-18: The Semicon/West96 exhibition and conferencein San Francisco.

September2-8: The Farnborough Air -show at Farnborough, UK.

October8-10: The Euro-EMC exhibi-tion at Sandown, UK.18-27: The Connect 96 con-sumer electronics show atthe NEC, Birmingham.

November12-15: The Electronics 96exhibition in Munich, Ger-many.26-28: The ManufacturingWeek Exhibition at the NEC,Birmingham.

December8-11: The InternationalElectronic Devices Meetingin San Francisco.

Portadown, Northern Ireland, forhis audio multit-ter; and thirdprize went to Paul Canner, 17,from Ballydare High School, Bal-lycLire, Northern Ireland, for hisAutomatic Temperature Embed-ded Sensing Equipment-ansE.

Highly commended in thiscategory were Rebecca Largo, 15,Shama Chaudrev, 15, JoannaStagg, 16, and Bevan Davies, 15,for their electronic device to aidyoung children with mathematicsystem. Also highly commendedwere Peter Tonge with his audiopreamplifier, and Gemma Wicksfor her head -up stopping displayfor vehicles.

Topping the Junior (under -15)Category for a YEDA trophy andENO for school and student wasDavid Kelnar, a 14 -year old fromMerchiston Castle School, Edin-burgh, who devised an accessi-ble, mufti -Media' educational sys-tem, creating both the hardwareand the software.

Second in this category wasTimothy Short, 14, fromSevenoaks School, Sevenoaks,Kent, for his programmablewindscreen wiper controllerThird place was for James An-derson, 14, from Radley College,Abingdon, for his finder unit toaid the blind.

Highly commended in thissection were Eileen Parks, GayleDoulton and Natelia Smith, al114and from Ballyclare High School,Ballyclare, Northern Ireland, fortheir electronic Fast UnfreezingNozzle (FLw for short). Alsohighly commended were ClairePalmer, 14, from Bancroft'sSchool, Wood Green, Essex, foran electronic device to alert a dri-ver that the vehicle in front isbraking heavily; and Karen Sc-holes, 14, from Ridley HighSchool, Blyth, Northumberland,for her blood -sugar level testerfor diabetics.

Despite ADA being in itstenth year, there is no evidencethat the innovation and creativ-ity of young electronic designersin the United Kingdom is show-ing any waning. During thecourse of its ten-year history,',WA innovations have included

a hand-held elec-tronic meter probe tomeasure brake fluidcontamination foruse in service sta-tions; the- beammusic, a series ofinfra -red light beamsthat are broken byhand movementsand sensed by acomputer -controlledkeyboard which gen-erates music notes; asafety iron for hand-

icapped or visually impairedpeople; an electronic hand-heldanemometer windspeed measur-ing device with no moving parts.

Details of the YEDA Schememay be obtained fromThe YEDA Trust24 London RoadHorshamWest Sussex RH12 lAHTelephone 01403 211048Fax: 01403 210770.

ELECTRONIC CETHEIR

Novel machining techniques andrecent developments in moreprecisely controlled conventionalmachining, achieving accuraciesin component parts of within50 run, has led to significantprogress in the use of ceramics ina bid to reduce the size and in-crease the rewonse speed of elec-tronic circuits.For

some time, ceramics havebeen widely employed in manyelectrical and electronic compo-nents such as insulators, conduc-tors, resistors, capacitors, andsensors.

Reducing stressesHowever, the more complex andhighly developed electronic de-vices, involving high densitypackaging for example, will de-mand ceramics that exhibit ther-mal expansion in line with siliconso that thermal stress are re-duced, a uniform low dielectriccapability for signal processingenhancement, and superior ther-mal conductivity to disperse theheat from integrated circuits.

Such materials as alumina,beryllium oxide, aluminium ni-tride, silicon nitride, mullite, zir-cona, and ferrite, meet many ofthese criteria, with alumina prob-ably being the most widely used.Several oxide compositions,mainly silicon oxide, some glass -ceramics as well as silicon nitride,have been developed as thin-filminsulators for integrated circuits.Modified lead magnesium mo-bate, which exhibits high dielec-tric content among its properties,is being used for disc, multilayerand thick -film capacitors, whilelead zimonate-titariate formula-tions are the primary materialsfor ferroelectric thin films em-ployed in memory applications.

Significant developmentOne of the most significant de-velopments in machining tech-

RAMICS NOW ANDFUTURE

niques has been developed atWarwick University where theobject of reducing spacing be-tween conductor trade has beenfurthered by laser drilling. Thelasers have been employed indrilling green -state dielectrics toproduce high -density intercon-nections for microelectronics sys-tems. They are used to drill ver-tical holes in layers of multi -layerdielectric where layers of con-ductors, voltage reference planes,decoupling mpacitors, ra-istors,and so on, are separated by lay-ers of dielectric. The holes arethen filled with conductor mate-rials to form 'vias for connectionto the printed circuit on eachlayer

The drilling is carded out inthe green state of the dielectricwhich is produced by standardthick -film techniques. To satisfythe particular requirements ofthe dielectric, various combina-tions of glass and glass -ceramicmaterials were subjected to thelaser -drilling process and to sub-sequent sintering. Tests show thatthe optimum combination in-duded a medium softening pointglass -ceramic and high softeningpoint glass which underwentcrystallization during the sinter-ing process.

This technique provides forsmall vias of 50-60 pm to beachieved with a carbon dioxidelaser using only a small numberof steps and conventional seven -printing technology. The laserdrilling process is selective asonly the dielectric is drilled be-cause absorption characteristicsare matched to the laser %%rave -length. It is also self-limiting be-cause the underlying metal con-ductor reflects the laser light.

Super abrasivesLaser optics have also been de-veloped to drill thin film organicdielectrics with exchner lasers.

A10 Elektor Electronics 6196

With the more conventional ap-proach to high -precision grind-ing of advanced ceramics, the so-called 'super abrasives' are usu-ally prefetted for the appropriatecutting and grinding processes.Cubic boron nitron (cbn), for in-stance. is harder and more wear -resistant than conventional abrasives such as aluminium oxideand silicon carbide.

Although cbn resists chemicalattack by iron, cobalt and nickel,diamond is the super abrasivegenerally best suited for grindingceramics formulations. Amongthe latest of the more conven-tional type machines using dia-mond abrasive is an ultra -stiff,computer numeric controlled(cnc) aspheric generating grind-ing machine developed by Cran-field Precision Engineering.Known as the nanocentre, themachine is a new ultra -precisioncnc aspheric generator.

Detail of the Nanocentre atCranfield Precision Engi-neering.

Excellent stabilityIt features high loop stiffness,thus ensuring efficient ductileregime grinding of a range ofbrittle materials on componentsup to 600 mm diameter and250 mm axial length and to ac-curacies of within 50 nm. TheNanocentre -a six -axis diamondturning and ductile regimegrinding machine - is bedded ingranitan 5100, a synthetic gran-ite, to give excellent dimensionalstability, high specific stiffness,and high internal damping.

Further stability needed forprecision machining of ceramiccomponents is provided by sup-porting the base on a three-point,self -levelling pneumatic isolationsystem that stands on a large,damped -mass, concrete founda-tion. The nano -grinding facilityfor this machine was designed toexploit the latest technologicaladvances in grinding of glass, ce-ramics, and other hard materials.

To achieve this, the highestpossible loop stiffness, a criticalfactor in ductile -mode machining

of brittle materials, was incorpo-rated. These capabilities meanthat the machine can take thereal sub -p.m cuts that are essen-tial for accuracy while minimiz-ing sub -surface damage.

A major manufacturer andsupplier of advanced technicalmamba for the microelectronicindustry is Coors Ceramic Elec-tronic. Among the company'sproducts are ceramic substratesfor microelectronic circuitry,laser -machined substrates, dry -pressed ceramics, and metallizedceramics.

To meet the needs of elec-tronic pacloging the companyoffers 92 per cent alumina, alu-mina nitride, and low -tempera-ture cofire glass ceramic. Coorsmanufacturing processes includecontinuous tape casting, drypresing, roll compaction, and ex-trusion, involving alumina, zir-ctanias, and other advances ce-

ramics. Laser machiningand numerically con-trolled punching of sub-strates, refractory metal-lizing, tapping polishingand grinding of ceramics,and applying epoxy toceramics are among theprocesses undertaken bythe company.

The futureBut what of the future? Itis considered that 5 nmline widths of gold on sil-icon substrates is theoret-

ically possible. This next genera-tion of electronic devices is calledstatic induction transistors (sit).However, that is not all. A majorpotential competitor to the elec-tronic sit is the optical (photonic)transphasoc This optical systempromises switching speeds of,perhaps, a few ps. Unlike theelectronic transistor, it could alsobe capable of more than two sta-ble states, a potential that wouldrevolutionize present-day com-puting logic.

Photon transmission technol-ogy could eventually achieve bet-ter performance than the indiumantimonide, gallium arsenide,and zinc selenide, used in manyresearch progamm&r. These andother exciting developments in-volving new specialized ceramicswill`put even greater demandson a new generation of precisionengineering machines.[kis - 3565]

ESR CATALOGUEThe new 1996 PCB Production Cat-alogue from ESR Electronic Com-ponents is sure to be of interestto most readers. It is fully illus-trated and covers all aspects of

printed -circuit board (PCB) pro-duction for hobby, education andprofessional use. It is ideal forsmall volume and prototypework.

The catalogue tames all thatis required to take an idea onpaper, from a simple prototypeon breadboard, matrix board orstripboard through to a PCB lay-out, and finally to a professionallooking pcb. All materials, chem-icals, equipment, tools, and safetyequipment, are included.

Contents include Develop-ment, Drafting materials, PCB

laminates,PCB equipment, Chem-icals, Tools, and Health andSafety. Many new products areincluded, all competitivelypriced, making this catalogue acomprehensive one -stop sourcefor PCB production.

For a free copy, send an A4SAE (with 4.T p of stamps). Alsosent free when requested withany order over C: 7-50.ESR Electronic Components, Sta-tion Road; Cullercoats, Tyne &We -at NE30 4PQ. Telephone 0191252 4363; Fax 0191 252 2.196.

TROUBLE WITHAUDIO PARTS?In the UK: many high -precisionresistors (1%, 0.1% and 0.01%)are available ex standard stockfrom Rhopoint Components. Theresistors include wirewound,metal foil, power film, and man-ganin foil types.Full design -in information isavailable from Rhopoint Compo-nents, Holland Road, HurstGreen, Oxted, Surrey RH8 9AX,England. Phone 01883 717 988;fax 01883 712 938.

In the USA: a wide variety ofparts for the serious and not -so -serious audio constructor is avail-able from Sescom, Inc_ Send for acatalogue on hardware, trans-formers, sips, and many otherparts to Sescom, Inc., 2100 WardDrive, Henderson, NV 89015-4249 USA. Phone (702) 365-3400;fax (702) 565-4828.

SUPER DISKETTE3M, in cooperation with Compaqand Matshushita Kotobuki (*,m),have developed a new genera-tion of floppy disks to replace thecurrent 2 MB diskettes. The newdiskettes will have a storage ca-pacity of LW MB. The new drivesrequired will be fully compatiblewith the current generation ofdiskettes. It is expected that thenew diskettes will be on the mar-ket during the course of this year.

In briefTelevison and all that

On the 1 June this year, it willbe 50 years ago that the firsttelevision receiver licenceswere issued in the UK.

On 6 June, 1954, the Eurovi-sion television link -up wasinaugurated.

On 21 June 1937 a male -dominated phenomenonbegan: the first televisionbroadcast of a sporting event- the Wimbledon tennischampionships.Now it seemsthat television is ruled bysport to the chagrin of themajority of women who feelthat there are far too many TVsports broadcasts. Perhapsthis is the reason that ...

... more than £ 1,200 millionwas spent in Britain last yearon the sale and rental ofvideo cassettes. Most popu-lar were Pocahontas, StarTrek - the New Generationand The X Files.

It all started with ...

... the first patent for 'com-munications by electromag-netic waves'.which wasgranted to Marconi on 2June 100 years ago.

Three developments maymake it possible to listen tocos via the Internet in thenear future: (1) the us gov-emment's relaxation on theuse of encryption on theInternet; (2) a cable modemby which a 60 -minute co canbe copied in ten minutes;and (3) a chip from Philipsthat will reduce the cost ofrecording music from theInternet on to a blank Co.

Dolby Laboratories is work-ing on refining the Dolby ProLogic encode -decode sys-tem for computer applica-tions. The new system.called Dolby Surround Multi-media, will produce surroundeffects with the use of onlytwo channels. In this way,Dolby reckons that with thissystem centre front and rearspeakers can be dispensedwith.

Elektor Electronics 6/96 11L

stop that barking!

It is often said thatthere is no better pro-

tection against bur-glars than a good

watchdog. Well, thatmay be, although we

have our doubts. Afact is, however, that

many of these 'bio-logical alarm sys-

tems' often bark andkeep on barking forno apparent reason.Normally, no blameattaches to the dog

for this: it just has notbeen trained properly.The unit described inthis article may prove

useful in providingcorrect training.

Oesign by: K. Walraven

A loudly barking dog may be a deter-rent to tresspassers and other wrong -

I doers. Unfortunately, some dogs havenever been taught when and whythey should bark. A few barks for agood reason are fine, but continualbarking soon becomes a nuisance toeveryone around, not least the neigh-bours. And, of course, a dog that al-ways barks is not a good watchdog (bythe same reasoning that a burglaralarm which frequently goes off falselyhas become useless as an alarm).

The problem often occurs when thedog is left alone in the house. Beforea dog is ever left alone, it should betaught a few 'soda! gaces% This takestime and effort. The dog must be spo-ken to sternly when it goes on bark-ing: the correct moment is very im-portant. It makes no sense to rebukea dog in the evening for what it hasdone wrong during the day: a dog'sbrain just cannot understand this.

It is appreciated that not every-body can stay at home days on endto speak sternly to a barking dog. Itis for these owners that the presentcircuit may prove a godsend. It is at-tached to the collar of the dog andcontains a small microphone and abeeper. The microphone registers thebarking of the dog. If this lasts only ashort while, nothing happens. If thebarking continues, the threshold of

an acoustic switch is exceeded,whereupon the beeper is actuatedand produces an irritating (to thedog) sound. If the dog stops barking,the beeps cease also.

The idea of this is that the dog soonwill learn that its barking and the irri-tating beeps have something to dowith one another. The hope is that itwill soon learn not to bark unless thereis a very good reason for it.

TINY CIRCUITSince the 'anti -bark' unit has to be at-tached to the dog's collar, it is, ofcourse, essential that it is kept smalland light. Moreover, since the unit hasto be powered by a battery, its currentdrain must be small. These require-ments mean an absolute minimum ofcomponents. Figure 1 shows that thedesign meets these requirement.

It will already be clear that the dr-cult consists of three distinct parts: themicrophone and associated compo-nents, including an amplifier stage(ICI.), an acoustic switch formed by apeak detector and a Schmitt trigger (R3up to ICk), and the buzzer and associ-ated components (1Cid-ICii).

The circuit needs a supply voltageof 3-43 V, at which it draws a currentof 0.5 mA when the buzzer is operat-ing. In quiescent operation, the cur -

12 Elektor Electronics 6/96

47pR2

100[

IC1a

1

rent drain is negligible (which makesan on/off switch superfluous).

OPERATIONWhen the dog barks, the sound ispicked up by the microphone, Mice,and converted into an electrical po-tential. The sensitivity of the micro-phone is set with P1.

The signal is applied via R1 -C3 toinverter ICia, which functions as anamplifier. Actually, it is a 'selectiveamplifier, since C1, RI and C4 have alow-pass response, whereas C3 has ahigh-pass response. In practice, thismeans that only frequencies in theband 200-1000 Hz (roughly the barkfrequency band of an average dog)are amplified.

To create an acoustic switch, thesignal amplified in ICia is applied topeak detector R3 -D1 -05 -R4 -P2. The de-tector is designed such, particularlythrough the value of R3, that short -duration barking has no effect on thecircuit. If, however, the barking con-tinues, C5 is charged until Schmitttrigger ICib-ICic changes state. Pin 13

IT) ri;9/ 9 g)\O--(1S/1 QVa°

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of ICl/ is then nolonger at earth po-tential, whereuponoscillator IC le-IC f

is actuated and thebuzzer emits abeep.

The oscillator isa conventionalastable multivibra-tor, ICk.-ICif, whichdrives the buzzer via buffer ICid. Ca-pacitor C7 prevents ICid being fedwith half the supply voltage, whichwould increase the current drain.

When the dog stops barking, ca-pacitor C5 is discharged rapidly via R4and P2, whereupon the Schmitt trig-ger changes state and the oscillator isdis`abled. The period during whichthe buzzer goes on emitting beeps isthus set with P2.

Since high tones are more irritat-ing to dogs than low ones, the oscil-lator frequency is set to 7-8 kHz. Inthe design this created a few prob-lems. As loudspeakers tiny enough tobe attached to a dog's collar are noteasily found, and in any case their

low impedance wouldrequire relatively appre-ciable drive power, asmall a.c. buzzer has tobe used. Unfortunately,these normally have aresonance frequency of3-4 kHz and are very in-efficient at higher fre-quencies. The solutionproved to be a smallchoke, LI, in parallelwith the buzzer: this in-creases the resonancefrequency to 7-8 kHz.

ICI

3V6

06

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ICid

MINS IM

100n LI.

4069U8

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Fig. 1. The circuit maybe divided into three:microphonetamplifier(Mice-lCia); acousticswitch (R3--ICic); andoscillator/buzzer(D2-Bzi). The sensitiv-ity is set with P1 andthe reverberation timewith P2.

Fig. 2. The small di-mensions of the PCBensure a tiny unit.

21m

TOKO

960035 - 11

EASY TO BUILD

The circuit is best built onthe printed -circuit boardshown in Fig. 2. Populat-ing the board should nottake more than an hour.Less experienced construc-tors: see, however, undertesting.

The finished boardjust does not fit in a standard sizematchbox, but it should not be too dif-ficult to find or make a suitable case.This should also take into considera-tion what batteries will be used.

Because of the tiny current drain,two or three silver -oxide batteriesshould suffice. If the dog in question is

Parts list

Resistors:R1, R3 = 10 kitR, = 10 MQR4. R5. R8 = 100 kg.R6. R7 = 1P1 = 10 ki2 preset (but see text)

= 1 MQ preset

Capacitors:C1 = 22 nFC2, C5 = 10 pF, 63 V, radial

= 100 pFC, = 47 pFC6 = 330 pFC- = 100 nF

Semiconductors:D1. D2 = 1N4148

Integrated circuits:= 4069UB (non -buffered version)

Miscellaneous:L1 = choke. 27 mHBzi = a.c. buzzer (Toko)Mic1 = electret microphone insertPCB order no. 960035 (see p. 60)

Elektor Electronics 6 96 1 3 IL

medium-sized to large,the case does not haveto be that small, so thatstandard Fug (R6) bat-teries can be used.Small rechargeableNiCd batteries are alsosuitable.

The supply voltage should be I3-4.5 V The buzzer works, of course,best at the higher voltage, but the cur-rent drain is then slightly higher In theprototype, the supply voltage is 3.6 Vand the current drain 0.5 mA.

Fig. 3. The supply forthe prototype is pro-vided by two HP? (R6;AA) batteries. If buttonbatteries are used, theunit becomes evensmaller.

When fitting themicrophone, take goodcare to observe correctpolarity (see Fig. 1). Inalmost all currenttypes, the earth con-nection (-ve supplyrail) is connected to the

casing.Although the filtering in the input

circuits prevents acoustic feedback toa large extent, it is nevertheless advis-able to keep the buzzer and micro-phone as far apart as feasible.

TESTING

Since the design of the circuit is nei-ther complex nor critical, it is morethan likely that it functions correctlythe first time it is connected to the bat-tery, provided, of course, that it hasbeen built properly.

Less experienced constructors mayfind it more convenient to build andtest the circuit in stages. Start with theoscillator: ICI, R7, R8, C6, C7, L1 andthe buzzer. Decoupling capacitor C,may also be fitted.

When the battery is connected tothe circuit, a well audible tone shouldemit from the buzzer. If not, tem-porarily earth pin 13 of ICI and, witha multimeter, check the voltages indi-cated in Fig. I around Ifvery different voltage levels are mea-sured, the likelihood is that the valueof one of the components is wrong.

If all is well, remove the battery andthe short from pin 13 of ICI and addthe Schmitt trigger and peak detector:D2, RI, R5, R6, P2, and C5. If then thebattery is connected, the buzzershould not sound. If it does, check therelevant voltages indicated in Fig. 1.For an additional check, temporarilylink junction R4 -R5 to the -Eve supplyline, which should make the buzzeremit a beep. The reverberation timecan be set with P2.

Remove the battery and temporarylink from R4 -R5 to the +ve supply line.

Finally, fit all the remaining com-

MicrophonesMicrophones are transducers that convert sound energyinto electrical energy The most common types are car-bon. crystal. capacitor, moving -coil, ribbon. and electret.

In the moving -coil microphone, a small coil is at-tached to the centre of the diaphragm. When the di-aphragm is made to move. by sound waves, in a steadymagnetic flux. an e.m.f. is produced in the coil by elec-tromagnetic induction.

Fig. A

Sound

+ -microphone element

I-0

impedance transformersiszsa-z-1

In a capacitor microphone, also called electrostaticmicrophone. the diaphragm forms one plate of a capac-itor. Variations of sound pressure cause movements ofthe diaphragm and these alter the capacitance. Corre-sponding changes in potential difference across the ca-pacitor are thus produced. Since the potential changesare very small, an electrostatic microphone is always fol-lowed by an impedance transformer:amplifier-seeFig. A.

An electret microphone is also an electrostatic typein which the capacitor is provided with a fixed charge

by chemical means. This means that the sup-ply to it can be limited to a small battery forthe (integral) amplifier.

Where hi-fi is not important. but sensitivityis, a crystal microphone is often used. Thiscontains a piezoelectric crystal in the form oftwo plates separated by a small air gap.Sound pressure variations cause displace-ment of the plates and corresponding e.m.f.sare produced across them. The relationshipbetween sound pressure and produced e.m.f.is fairly linear.

Greater sensitivity is obtained by the useof a separate diaphragm that is mechanicallycoupled to the centre of the crystal. This con-struction is more directive. but has a poorerfrequency response than the former.

14 Elektor Electronics 6 96

In passing ...4

Cl

Mid

ponents, including themicrophone. Test theunit by setting P1 tomaximum sensitivityand blowing into themicrophone: thebuzzer should emit asound.

The best setting ofP1 has to be found em-pirically: it depends to some extent onthe tolerances of the microphone. Ifthe sensitivity of the electret type is notsufficient for individual requirements,a crystal type should be tried. Thisshould give enough voltage to make

C5

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960035 - 12

Fig. 4. On the PCB is in-dicated not only whereto connect the variouscomponents, but alsowhere the test pointsare. (1, 2, 3, 4 = U6; 5,6, 7 = U,12 -±0.3 V; 0=ground = -ye supplyline)

the circuit react to eventhe most subdued bark.If this is done, it is ad-visable, however, to in-crease the value of Pi to100 kit and reduce thatof C1 to 2.2 nF. I1

The Internet and otherInformation HighwaysWe have to get used to the idea that theInternet is an irreversible phenomenon ofpresent day society. The past few yearshave seen the consecration of what, withall its treasures to be discovered, is notunlike the cave of Ali Baba or the storeroom of a medieval alchemist, giving ac-cess to all sorts of document, some confi-dential, some almost secret, and somewhose publication is illegal in some coun-tries: the text of the Charter of theChurch of Scientologists, the disclosureof the private design of a Eurocrypt card,and others.

Once the cobwebs have been removed,as it were, there are countless treasures tobe found, pearls of wisdom, forming afount of information and knowledgewhose data base is a hundred times morepowerful than that of the Library atAlexandria at its height. In other words,a source of information that is second tonone on earth.

Even so, do not be mistaken in think-ing that this is all: there are already anumber of formidable competitors, suchas Compuserve, Microsoft Network Sys-tem (Avis), and America on Line (Am).

It will be essential to actually employthe, sometimes unsuspected, potential ofthe Internet, enabling it to be turned intothe primary source of services of manykinds, from automatic adjustment of thepc's real-time clock (yes, it is possible al-ready), to on-line employment exchanges,and promote it so that the net does notcollapse like a house of cards when thereare not tens of millions of people seekingaccess like today, but several hundreds ofmillions. There remains plenty to do forthose who have the difficult task to steerthe Internet to a full blossoming tree ofknowledge, whose fruits we can all gatherand eat.

It is, however, essential for the survivalof the Internet, and others, to guaranteethat its freedom of access extends to allinformation. It must not become a ques-tion of accepting that whatever country,however powerful it may be, whether it bethe Federal Republic of Germany, theUnited States of America, or France, canpropose and obtain a blocking, even apartial one, of access to any source of in-formation.

On close examination, it is industrialconglomerates that provide line telephoneservices who have the ways and means ofmaking the Internet, and others, a com-monplace. This applies particularly toAT&T in the USA, which proposes a free,permanent access to the services of the In-ternet via its international telephone net-work, and the many European telephoneadministrations, private or public.

The greatest priority today is the as-surance of free access to the availablemass of information, potential and ac-tual, not to the maximum number of peo-ple, but to those who can, in one way oranother, take advantage, if possible intel-lectual and cultural, rather than com-mercial or financial, from the networks.

Elektor Electronics 6 96 15

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Elektor Electronics sass 17

23cm ATV preamplifierAmateur television (ATV)

is among the mostpopular, technically ad-

vanced and excitingsub -activities available to

the licenced radio ama-teur with an interest incentimetre -wave tech-

nology. These days, themain ATV activities are in

the 23cm band (1252-1285 MHz) where pri-

vately operated transmit-ters and relay stations

may be received, oftenin full colour and com-plete with sound. The

fun is not restricted to li-censed amateurs,

though! These transmis-sions can be picked up

by anyone having a suit-able antenna, an old

satellite TV receiver anda preamplifier like the

one Johannes, DL4EBJ,describes in this article.

Based on GaAs-FET,MSA and microstrip

technology, the designcouples low noise with

high gain. Althoughaimed at the advancedradio amateur, the pre-

amplifier is relativelyeasy to build and adjust.

Design by J. Kering, DL4EBJ

MAIN SPECIFICATIONSGain:Noise figure:Filter:Frequency range:Peak frequency:Current consumption:Simple adjustmentHigh repeatability (SMD)Remote powered by Sat -TV receiver

>35 dB (3 -stage)<1 dB (MGF1302)

microstrip, 3 -element interdigital1,250-1,300 MHz

1,285 MHz<60 mA

This article presents a challenge to gi-gahertz newcomers by describing alow -noise preamplifiPr, which is one ofthe key elements in a receive -only sta-tion for 23cm amateur television. Theother elements are a suitable antenna(loop-yagi), a satellite TV tuner and aTV set or video monitor Most of thesewill be available to the beginning radioamateur. If not, then local dub mem-bers may be able to help out! Actually,the preamplifier and the loop yagi an-tenna are often the only elementswhich are home-made. Let's look ateach of the elements in some detail tosee which requirements they shouldmeet.

THE SATELLITE TVRECEIVERMost satellite TV receivers have a fre-quency range of 950 MHz to1,750 MHz, which means that they canbe tuned across the entire 23cm band(1,240 to 1298 MHz). The good news isthat almost any satellite receiver, irres-

pective of its age can be used to receive23cm ATV. A good example is the rowobsolete Amstrad SR,X200 receiver,which can be picked up for a tenner orless at rallies and car boot sales. Anumber of features of the satellite re-ceiver are, however, advantageous ifyou want to 'go ATV':

* continuously tuneable sound (5MHzto 8 MHz). Most ATV-ers use asound subcarrier at 6.0 MHz or5.5. MHz. The former frequency ap-pears to be preferred for new design.

* sound bandwidth reduction ('nar-row') mode, this may help to drag aweak sound subcarrier out of thenoise.

* selectable IF bandwidth. Only high -end (expensive) receivers allow thevideo detection bandwidth to be re-duced from 27 MHz to 18 MHz. Aswith sound, being able to switch to'narrow' bandwidth may mean thedifference between a picture lost innoise and one which shows at least


a legible callsign.*a frequency readout is helpful, be-

cause a weak ATV station may be aneedle in a haystack

*adjustable video gain: most ATV sta-tions use a quite low FM video de-viation as compared to satellite TVstations. Obviously, some extra gainis then useful to boost the contrastand brightness. '

*an S meter is useful and practicalwhile you aim the antenna, or peakthe preamplifier, for best reception.

Again, almost any old satellite TV re-ceiver may be used without modifica-tions, as long as the sound demodula-tor can be tuned between 5.5 MHz and6.0 MHz.

THE ANTENNAThe antenna is the best prannplifier is anage-old maxim among VHFISHF radioamateurs. On 23cm, a gain of 16 to18 dBd is readily achieved without un-wieldy antenna sizes or complex con-structions. Small, home-made anten-nas, too, give acceptable results inmany cases. When selecting an an-tenna for 23 -cm AN, however, there isan important restriction: the antennabandwidth.

An antenna designed for the SSBsub -band (1296-1,298 MHz) achievesits high gain and directivity by virtueof the small bandwidth only. A con-siderably lower gain has to be takeninto account if you use such an an-tenna in the ATV range of the band,1,250 to 1,285 MHz. if you are aftergood results across the entire 23cmband, be sure to purchase any of thewide -band antennas already on themarket.

Those of you who already have a23cm antenna system for SSB may,however, use it for ATV receptionwithout problems. Once you have a23 -cm ATV transmitter however, moreprudence is required.

THE ANTENNAPREAMPLIFIERWhen the receiver is used as part of aregular satellite TV receive system, it issupplied with an RF signal by theI.NC fitted on the disk An LNC has atypical conversion gain of 50 dB. Thisis not only necessary to overcomecable losses, but also to raise the RFsignal to a level which is sufficient todrive the tuner in the receiver.

These tuners are relatively insensi-tive. In particular, the FM PLL de-modulators they contain require muchhigher input levels than an antennacould ever supply without a pream-plifier. Even preamplifiers as used forSSB (narrow band) do not quite makeit in this respect.

The preamplifier described in thisarticle is specially designed for 23an

band ATV, and meets all of the abovementioned requirements for use incombination with almost any satelliteTV tuner Not convinced? Then look atthe specs box.

CIRCUITDESCRIPTIONThe circuit diagram of the preamplifieris shown in Figure 1. The antenna sig-nal is d.c decoupled by C9. The sourceof the MGF1302 GaAS FET is matchedto the antenna impedance (50 L1) bytwo small inductors, Ll and L2. Thematching used here does not have thetraditional trimmer capacitor at theinput The advantages of omitting thetrimmer are a higher Q factor of theinput circuit, lower input losses, alower noise figure and, last but notleast, a much simpler adjustment.

The MGF1302 is a low -noise GaAsFET designed for use up to 10 GHz

.=6

(see datasheet extractselsewhere in thisissue). The frequencybeing 'only' 1.2 GHzhere, the device can berelied on to supplysubstantial gain at anultra -low noise figure(<1 dB). To keep theMGF1302 electricallystable, each of its source connections isdecoupled by a disc capacitor (C13,C14) which guarantees the lowest pos-sible stray inductance. Also, the gain issubtly reduced by inserting a 10-11 re-sistor in the drain supply line. In gen-eral, the first stage of an RF preampli-fier determines the overall noise figure.The theory underlying this phenome-non is given in the inset with the head-ing 'please keep the noise down.

The GaAs FET provides a gain ofabout 14 dB here. Its output signal is

fed to a tuned three -element induc-tively coupled interdigital microstripfilter which defines the pass -band ofthe preamplifier, and serves to rejectstrong out -of -band signals (UHF TVtransmitters and cellular radio re-peaters). The inductors in the filter aresmall copper tracks (strips) on theprinted circuit board. The input signalfor the second active element, 1C1, istaken from a tap on the last printed in-ductor, L9. This is done to ensure cor-rect matching (approx. 50 SI) to theinput of the MSA0685 (HewlettPackard, formerly Avantek). The circuitaround the two 50-11 'drop -in RF am-plifiers, 10 and IC2, should be famil-iar to most amateurs, as these deviceshave been used in many recently pub-lished designs. The noise figure of theMSA0685 is about 3.2 dB, but that isreally insignificant in this application.

The total gain of the preamplifier is

GUI

Figure 1. Circuit dia-gram of the 23cm ATVpreamplifier. A mi-crostrip interdigital fil-ter is used to selectthe ATV section of the23cm amateur radioband. The input has anultra low noise GaAsFET from Mitsubishi.

®:-

greater than 35 dB,which is ample to over-come output cablelosses as mentionedabove.

To keep stray ca-pacitance and induc-tance as low as possible,most passive compo-nents in the RF path are

surface -mount devices (SMDs).The input supply voltage is ob-

tained from the satellite TV receivervia the downlead coax cable. Most re-ceivers supply either 14V or 18 V, de-pending on the LNC polarity selection(which is of no consequence here). Avoltage regulator type 781.06 is used tostep down the LNC voltage to a reg-ulated 6-V rail for the GaAs FET andthe MSNs. The overall current con-sumption will be smaller than 60 mA.Diode Dl provides a polarity reversal

Elektor Electronics 6/96

Please keep thenoise down

CIO CI I CI?

The three -stage preamplifier described here is no ex-ception to the rule that the first stage determines the over-all noise figure, provided the following stages supplyenough gain.

Assuming that each stage has a gain, G, and an as-sociated noise figure, NF the system (or overall) noisefigure, NFs, may be written as

NF.s= NFI+NF,-1+NF3-1.

G, G2

This proves that the noise figures of the second and thirdstage of the amplifier, NF2 and NF3, hardly contribute tothe system noise figure because these stages providehigh gain. In practice, a system noise figure of about 1 dBmay be achieved, which comes very close to the valuespecified by the manufacturer of the GaAs FET used inthe preamplifier described here. Such a low valukwasunheard of less than ten years ago. However, any mis-match between the antenna and the input stage seriouslydegrades the noise figure, as do losses ahead of the

protection. Choke L5 prevents the RFoutput being short-circuited by thesupply. Each of the MSA stages drawsabout 15 mA, while the MGF1302 op-erates at a current of about 12 mA.These settings may be verified withthe aid of the test voltages indicated inthe circuit diagram.

CONSTRUCTION HINTSThe printed circuit board designed forthis project is a bit of a small master-

HF in

top view

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piece, and a great help to prevent allof the notorious problems said to existin relation with gigahertz construction.The artwork is shown in Figure 2. Youare looking at a double -sided copper -dad epoxy board, which is availableready-made through our Readers Ser-vices. As shown by the componentoverlay, nearly all parts are fitted at thetop side of the board. Only the threeSky trimmer capacitors are mounted atthe other side of the board. That is

done to prevent unwanted in-ductive coupling which couldcause feedback and oscillation.It also helps to prevent the'cover-on/cover-off' effectwhich some of you may knowfrom adjusting centimetre -wave amplifiers. The printedcircuit board fits in a tin-platecase with a standard size of37x 74 x 30 mm.

Now take a look at the con-struction drawing in Figure 3.Carefully drill the two 5.2 -mmholes for the disc capacitors atthe source terminals of the

Figure 3. Construc-tion drawing showinghow to mount thecomponents thatmake up the low -noiseinput stage.

Figure 2. Printed circuitboard artwork. Only the threeminiature trimmers are fittedat the reverse side of theboard.

GaAs FET. At the reverse side of theboard, these capacitors are connectedto ground with the aid of small piecesof copper foiL The MGF1302 and theMSNs require 2 -mm dia. holes to bedrilled. Next, drill and fraise the slot forthe coffin -style leadless ceramic capac-itor, C15. The length of the slot shouldmatch the width of the microstrip in-ductor, I.7. C15 should not fall throughthe slot, instead, its wider part shouldrest on the top surface of the board.

Prepare the tin-plate case so that itcan receive the circuit board. Drillholes in the short sides for the RFinput and output sockets (use BNC orN, whichever is available), using thePCB as an orientation aid. The centrepins of the sockets are later soldereddirectly on to the copper tracks on theboard. If necessary remove the PTFEcover around the centre pin, and re-duce the pin to a length of about 3 mmfrom the inside of the flange. Securethe sockets at the outside of the case,then align the board so that the centrepins rest on the respective copperstrips. Next, secure the board in thecase by soldering all around the edges,at both sides.


COMPONENTS UST

Resistors:RI ,R2 = 150i1 SMDR3 = 470 SMDR4,R5 = 56f1R6 = 1012 SMD

Capacitors:01.C2,C3,C9 = 10pF SMDC4.C5 = 11iF 16V tantalumC6 = 1)1F 35V tantalumC7,C8 = 1nF SMDC10.C11,C12.= 5pF miniature PTFEtrimmer (Sky)

C13,C14 = 1nF disc ceramic (seeFig. 3)

C15 = 1nF coffin style tearless ce-ramic

Inductors:L1 = 5 turns 0 2mm (32SWG) e.c.w..

inside dia. 1mmL2 = 4 turns 0.2mm (32SWG) e.c.w..inside dia. 1mm + 1 turn through3mm ferrite bead

L314 = 5 turns 0.3mm (30SWG)e.c.w.. inside dia. 2mm

L5 = 4 turns 0.3mm e.c.w. (30SWG)through 3mm ferrite bead

LS = 10pH chokeL71819 = microstrip (see text

Semiconductors:D1 = 1N4148T1 = MGF1302 (Mitsubishi)IC1,1C2 = MSA0685 (Hewlett

Packard). or MARS (Mini CircuitLaboratories)

IC3 = 78L06

Miscellaneous:K1,K2 = BNC or N socket, fiance

typeTin plate case 37x74x30 mmPrinted circuit board, order code

960072-1 (see Readers SerVces r.E.7.e)

Populate the board, starting withthe passive parts. The ICs and the ex-tremely delicate GaAs FET are fittedlast, observing precautions against sta-tic electricity. The pinning of these de-vices is shown in the circuit diagram.

The partly three-dimensional con-struction around the GaAs FET shouldbe copied from the drawing in Fig-ure 3. Start by fitting the small pieces ofcopper foil at the reverse side of theboard. Nod, pre -tin the inside surface.Insert the disc capacitors into their re-spective holes, and make sure they fitsnugly. Then apply heat to the copperfoil until the disc capacitor starts to floatin the solder tin, and sinks into place.The same for the other disc capacitorAt the component side, solder thetinned area of the coffin capacitor, C15,to the 'cold' end of L7. This is quite del-icate work, so be sure to avoid a short-circuit to ground. The other side of thecapacitor is soldered to ground, at thereverse side of the board.

The capacitors, resistors and so onshould be mounted with the shortest

Elektor Electronics 6/96

Figure 4. View of thecomponent side of theboard (above) and re-verse side of theboard (below).

possible wires. Wires that go to groundare soldered at both sides of the boardto provide through -contacts. When allparts (except the MGF1302) are fittedon the board, use your multimeter totrack down short-circuits, dry jointsand unwanted ground connections.

The most delicate component to fitis the GaAs FET Mark the gate termi-nal on the body, then carefully shortenall terminals. Solder the two source ter-minals flush on the disc capacitors.The drain is soldered to the copperpad, and the gate terminal is lifted upa little so that it can be soldered di-rectly to inductor Ll as indicated bythe side view in Figure 3.

ADJUSTNI ENTConnect the antenna cable to the RFinput, then the downlead coax cable tothe RF output In some cases, the pre-amplifier is then 'on' already, becausesome satellite TV receivers supply theLNC voltage even if they are switchedto standby

Now take your time to verify thetest voltages indicated in the circuit di-agram. You should have no problemsfinding these points on the circuitboard.

The fun begins once you havefound a kind soul who can put astrong local 23 -cm ATV signal on theair. If you do not live near an ATV re-peater, use the ATV calling/talkbackcalling channel, 144.750 MHz, to find afellow amateur with the requiredequipment

Tune the satellite

TV receiver to the transmit frequencyof the station you wish to receive, forexample, 1285 Wiz_ The adjustment islimited to the three Sky trimmers. As aguide, the stator plates should beturned 'in' at about 10% only of theavailable travel. This corresponds to asetting of about 1 pE A plastic trimmertool is recommended for the adjust-ment The cover should be fitted onthe case during the adjustment.

Those of you who want the pre-amplifier to cover the entire ATV sec -don of the 23cm band may have to in-crease the bandwidth of the interdigi-tal filter. This is achieved by fitting al-pF capacitor between the 'hot' end

'o) L7 and L8 (i.e, directly on the Skytrimmers), and another between L8and L9, also at the 'hot' ends:

Provided you power the preampli-fier with an edernalvoltage, it is pos-sible to connect a 23 -cm 'phone'(SSB/FM) transceiver, and peak it forthe highest S meter reading on a weakrepeater or beacon signal (better leavethe transmitter in the transceiver offfor the moment, 1-11).

Assuming that the preamplifier isproperly adjusted, it is ready formounting as close as possible to theantenna. You will then be amazed atthe not inconsiderable distances thatcan be covered with excellent picturequality.

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LARGE SELECTION OF SPECIALIST LOUDSPEAKERSAVAILABLE, INCLUDING CABINET FITTINGS, SPEAKERGRILLES, CROSS-OVERS AND NIGH POWER, NIGHFREQUENCY BULLETS AND HORNS, LARGE (A4) S.A.E.(80p STAMPED) FOR COMPLETE LIST.

McKenzie and Fane Loudspeakers are also available.

aiiiialadaaUlllaidALIMILINALISSEalgALL EMINENCE UNITS 8 OHMS IMPEDANCE8 100 WATT R.M.S. M E8-100 GEN. PURPOSE. LEAD GUITAR, EXCELLENT MID, DISCO.RES. FREQ. 72Hz. FREO. RESP. TO 4104z, SENS 97d8. PRICE C32.71 02.00 PAP10' 100 WATT R.Y.S. 14E10-100 GUITAR. VOCAL KEYBOARD. DISCO. EXCELLENT MID.RES. FREO. 7111z, FREO. RESP. TO 7KHZ.SENS97d8. PRICE 033.74 - C2.50 PIP10' 200 WATT R.M.S. ME10-200 GUITAR, KEYEI'D, DISCO. VOCAL EXCELLENT HIGH POWER MID.R ES. FREQ. 6SHA. FREO. RESP. TO 3-5Kliz, SENS 99dB. PRICE C43.47 - C2.50 PAP12' 100 WATT R.M.S. ME12-100LE GEN. PURPOSE. LEAD GUITAR. DISCO. STAGE MONITOR.RES FREO. 49Hz. FREO. RESP. TO 6KHz. SENS 10048. PRICE 035.64 - C3.50 PAP12' 100 WATT R.M.S. ME12100LT (TWIN CONE) WIDE RESPONSE. P.A., VOCAL STAGEMONITOR. RES. FREO 42Hz. FREQ. RESP. TO 10100- SENS MEL PRICE £313.67 - C3.50 PAP12 200 WATT R.M.S. ME12-200 GEN. PURPOSE. GUITAR, DISCO, VOCAL EXCELLENT MID.RES. FREO. SEHz. FREO. RESP. TO 6KHz. SENS 98dB. PRICE 046.71 - C3.50 PIP12' 300 WATT R.M.S MEI 2.3000P HIGH POWER BASS, LEAD GUITAR, KEYBOARD. DISCO ETC.RES. FASO. Z7Hz. FREO. RESP. TO 5KHz. SENS 10348. PRICE 070.19 - £3.50 PIP15' 200 WATT R.M.S. M El 5-200 GEN. PURPOSE BASS, INCLUDING BASS GUITAR.RES. FASO. 48Hr_ FREQ. RESP. TO 5KHz, SENS 55dB. PRICE C50.72 - C4.00 PAP15' 300 WATT R.M.S. ME1 5-300 HIGH POWER BASS. INCLUDING BASS GUITAR.RES. FREO. 35Hz. FREO- RESP. TO 3KHz. SENS 10345. PRICE 073.34 - C4.00 PIP

411:1:1 A .] A ;1421.11:11153 Al DI EMI: Kg11.1[40ALL EARBENDER UNITS 8 OHMS iErcrus EU-SO ..- ate 4.41 www,..,rax-x* Uppet = 4 a Bohm)BASS, SINGLE CONE, HIGH COMPLIANCE, ROLLED SURROUND8' 50watt EB8-50 DUAL IMPEDENCE, TAPPED 418 OHM BASS. HI -Fl. IN -CAR.RES. FREO 40Hz. FREO. RESP. TO "MHz SENS 9748. PRICE 06.90 C2.00 PAP10' SOWATT EB10-50 DUAL IIMPEDENCE. TAPPED 41 OHM BASS. HI -F1, IN -CAR.RES. FREO. 4014z. FREQ. RESP. TO 5KHz, SENS. 95413. PRICE £13.65 - C2.50 Pa P10' IOOWATT E810-100 BASS. STUDIO.RES. FREQ. 35Hz. FREQ. RESP. TO 3KHz, SENS 96.38. PRICE 030.39 - C3.50 PAP12' 1 OOWATT E1312-1 00 BASS, STUDIO. HI -Fl, EXCELLENT DISCO.RES. FREO. 2EHz. PREO. REP. TO 3 KHz, SENS 9340. PRICE £42.12 - C3.50 PIPFULL RANGE TWIN CONE, HIGH COMPLIANCE, ROLLED SURROUND5` 60WATT EB 5-60TC (TWIN CONE) HI -Fl. MULTI -ARRAY DISCO ETC.RES FREQ. 63112. FREQ. RESP. TO 20KHz. SENS 9208. PRICE 09.99 C1.50 PAP6' s' 60WATT E.B6-60TC (TWIN CONE) HI-FI, MULTI -ARRAY DISCO ETC.RES. FREQ. 38Hz. FREO. REAP. TO 20KHz. SENS 9448. PRICE 610.99- 1.50 PAP8- 6 OWATT EB8-BOTC (TWIN CONE) HI -Fl. MILTI.AR RAY DISCO ETC.RES. FREQ. 40Hz. FREQ. RESP. TO lliKHz, SENS 6905. PRICE 012.99 - C1.50 PAP10' 60WATT E81 0-60TC (TWIN CONE) HI -Fl. MULTI ARRAY DISCO ETCRES. FREO 35Hz. FREO. RESP. TO 12KHz. SENS 95413. PRICE C16.4 C2.33 PAP

THREE SUPERB HIGH POWERCAR STEREO BOOST ER AMPLIFIERS150 WATTS t75 75) Stereo. 150WBridged Mono250 WATTS (125 125) Stereo. 250WBridged Mono400 WATTS (200 203) Stereo. 400WBridged MonoALL POWERS INTO 4 OHMSFeatures:17WreT. bridgable mono Choice ofhigh A low leel inputs L & R levelcontrols a Remote on -c9 a Speakerthermal oratc-ctier

POSTAL CHARGES PER ORDER £1.00 MINIMUM. OFFICIALORDERS FROM SCHOOLS, COLLEGES, GOVT. BODIES, PLC. ETC.PRICES INCLUSIVE OF V.A.T. SALES COUNTER. VISA AND

ACCESS ACCEPTED BY POST, PHONE OR FAX.

I ;711:Ez1 !Anil :1: [5] :RV/PROVEN TRANSMITTER DESIGNS INCLUDING GLASS FIBREPRINTED CIRCUIT BOARD AND HIGH QUALITY COMPONENTS

COMPLETE WITH CIRCUIT AND INSTRUCTIONSTRANSMITTER 8.1tethit. tAILCAP CONTROLLED PROFE-550412.3a .MAKE. RANGE LIP TO 3 VIES. WI 31 sinews_ 5L7PLT lri = 10.5.9A

PRICE C1445 - C1.00 PAPFM MICRO TRANUMTER 1334£416{2. YAP -CAP 10440 COMPLETE 11TH1 CRT SENS FEET ire. RUISE1:0100et 511E 55 a LAMS SWIM SI LATTER!.

PHOTO, 31V rM TrEA iiirr CA

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22 Elektor Electronics 6196

ING OFF...If you are the fortunate owner of a1satellite TV receiver which remains inthe shack and can be used exclusivelyfor ATV, it is definitely worth while toincrease the video gain in the receivesUse your oscilloscope to measure thevideo signal level (approx. 1 Vpp), andadjust the AGC in the tuner for thebest signal-to-noise ratio of the re-ceived picture.

If you omit the entire pre -stage be-tween C9 and L9, interrupt the con-nection to L6, and omit everything tothe left of it, you have a multi -purpose25 -dB wideband amplifier which maybe used to compensate cable losses lie-tween the receiver and the output ofan LNC.

Finally, the contributions and co -

Figure 5. The bestknown antenna for 23 -cm ATV use is the loopyagi. Pictured here is ahome-made loop-yagiscaled for 13 cm (cour-tesy Rob. PE1CHY).

operation of Reiner,DB9JC and Hans,PE117R, are grate-fully acknowledged_Lots of success with

the construction,and happy ATVviewing! (96007Y)

Editorial notes:1. This article ap-peared in shortenedform in Electron,issue September1995. We thank theeditors of Electron fortheir permission to

run this article in Elektor Electronics.

2. Readers in the UK with an interestin ATV should contact the British Am-ateur Television Society (BATC), do IanPawson G81QU, 14 Lilac Avenue,Leicester LE1 IFN.

For information on ATV repeaterstations in the UK, write to GrahamHankins G8EMX, 11 CottesbrookRoad, Acocks Green, Birmingham B276LE.The BATC may be found on the Inter-net athttp://ourworld.compuserve.comihomepageslipawson

3. A 23cm ATV transmitter was de-scribed in the February 1994 issue ofElektor Electronics.

I6ANHJ021XW

ARNHEM

PI6ANHIN 1252MHzIN 1I)1400GHzOUT 2387MHzAUDIO 6MHz

PI6ANH875°

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230° s FREE

IFigure 6. What do you meanhome construction is on thedecline? Pictured here are theelectronics of a 23cm-in/13cm-out cross -band ATVrepeater station, PI6ANH,which was recently taken intouse. The QTH of this station isJ021XW, ERP is about 50 W,and the antenna height is40 m a.s.l. A wonderful exam-ple of high -end equipmentbuilt and operated by radioamateurs, this repeater is oneof dozens located at elevatedsites all over Europe. PI6ANHeven has its dedicated Inter-net site athttp://www.regio.rhein-ruhrdelhamradia'atv.

Eisktor Electronics 6 96 23

Pico Releases PCPotentialPico's Virtual Instrumentation enable you to use yourcomputer as a variety of useful test and measurementinstruments or as an advanced data logger.

NOW

Hardware and software are supplied together as a package- no more worries about incompatibility or complex set-upprocedures. Unlike traditional 'plug in' data acquisition cards,they simply plug into the PC's parallel or serial port, makingthem ideal for use with portable PC's.

Call for your Guide on 'Virtual Instrumentation'.

NEW from Pico TC-08 Thermocouple to PC8 channel Thermocouple Interface Connects to your serial port - no power supply required. Supplied with PicoLog datalogging software

for advanced temperature processing. min max detection and alarm. 8 Thermocouple inputs (B,E,J.K,N,R.S and T types) Resolution and accuracy dependant on thermocouple type.

For type K the resolution is better than 0.1 C

TC-08 £ 199TC-08 + Calibration Certificate £ 224complete with PicoLog. software drivers and connecting cable.

LA range of thermocouple probes is available.

,f 6 cg 5.64-32 Logic AnalysersPocket sized 16/32 channel Logic Analysers

Connects to PC serial port. Up to 50MHz sampling.

Internal and externalclock modes.

8K Trace Buffer.

rlae-101 Channel 8 bit Lowest cost in the Pico range Up to 22kHz sampling 0 -5V input range

544- 1 6 219.5.64-32 349with software, powersupply and cables

PicoLogAdvanced data

logging software.

41)e- /00 Virtual InstrumentDual Channel 12 bit resolution

O Digital Storage Scopefi) Spectrum Analyser

Frequency MeterO Chart RecorderO Data Logger

Voltmeter

PicoScope'Virtualinstrument'software.

Po -d temperature

L

The ADC -100 offers both a highsampling rate (100kHz) and a highresolution. It is ideal as a general

purpose test instrument either in thelab or in the field. Flexible input ranges

(-±200mV to 20V) allows the unit toconnect directly to a wide variety of signals.

/42)e-100 with PicoScope £199with PicoScope & PicoLog £219

The ADC -10 gives your computer a single channel ofanalog input. Simply plug into the parallel port.

rilpe-10 with PicoScope £49LOarriage UK free. 0'.'erseas £9 Oscilloscope Probes ( x1. x10) £10 PicoScope & PicoLog 259

Z;ZPico Technology Ltd. Broadway House. 149-151 St Neots Rd, Hardwick. Cambridge. CB3 7QJ

Tel: (0)1954 - 211716 Fax: (0)1954 - 211880 E-mail: 100073.2365 @compuserve.com

Phone or FAX for sales, ordering information, data sheets, technical support. All prices exclusive of VAT

424Elektor Electronics

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No MinimumOrder valueElectraliticnItadisvl Capacitors Electroly Btic Aatiol Capacitors

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New 1996 PCBProduction Catalogue

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A Fully illustrated catalogue covering evert hing yourequire to Prototype & Design circuits and Manufac-ture Printed Circuit Boards. From simple Stripboardor Breadboard Development to Artwork Design, PCBMaterials, Chemicals, E. ui 'meat and Tools.

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Elektor Electronics 6/96 25L

If, for whatever reasons-health, corn

petition-you jogcycle, row, you willknow that after acertain amount

of time yourpulse beats

faster. This is, ofcourse, the inten-

tion, because in thatway you exercise

your heart and cir-culatory system.

This is fine, but theheart beat must not

become too high,because that is dan-gerous. How far you

can let it rise de-pends on various fac-tors, such as age and

physical condition.The present meter

enables you to checkthat you do not ex-

ceed your maximumpulse rate.

In sporting circles, there is a rale of fistto determine your maximum pulserate: depending on your physical con-dition, it should not go over 180-200less your age in years. Thus, if you arein good condition and 40 years old,your maximum pulse rate should notexceed 140-160 bpm (beats perminute).

Design by: F Hueber

pulsimeter

This is not a problem as long as youknow what your pulse rate is_ It is, ofcourse, simple to take your pulse orcount your heart beats, but to do soyou have to interrupt your sportingactivities for a minute or so. There arevarious pulsirneters (also called pul-someter) on the market, most of whichhave additional functions, such as aVHF radio alarm clock, telephone costcounter, data bank with 100 words in19 European languages, and so. Be-cause of these extras, such meters areunnecessarily expensive. Moreover,some of these instruments appear tobe fragile and not at all suitable for useduring sporting activities. The presentmeter is straightforward: it measuresonly one thing: your heart beat andshows this by means of a bar of LEDS.

A particular problem with this kindof meter is the kind of sensor-andthere are several. One could consist ofstick -on or suction electrodes as usedfor taking an ECG-ElectroCardio-Gram. However, although they areideal for measuring the heart beats, foreveryday use they are a little too cum-bersome (they have to be secured tothe skin of the chest).

A second method is the acoustic de-termination of the heart beat, whichcan be carried out with a sphygmo-manometer (blood pressure meter)and a stethoscope or microphone in

0.

the inflatable bag around the arm. Theheart beat is then heard. Of course, thismethod is not very practical duringsporting activities either.

Less well known, but very usable, isthe optical measurement. The translu-cence of human tissue changes witheach heart beat: when the heart pumpsblood through the arteries, the tissuebecomes less translucent. (Shine atorch at one of your fingertips and lookat the tip from the opposite side fromthe torch). This phenomenon is not, orhardly, noticeable with the naked eye,but can easily be made so by electronicmeans. The light source in the presentmeter is an infra -red (lit) um, while thedetector consists of an infra -red -sensi-tive phototransistor. These two devicesmay form a hybrid light barrier or a re-flection light barrier (when they are inparallel with one another). Whatever,they are connected to a more or lesstranslucent part of the body, such as afingertip or an ear lobe.

ANALOGUEAND DIGITALAs shown in Figure 1, the circuit of thepulsimeter is fairly straightforward. Itconsists of an analogue section, inwhich an LM324 amplifies andprocesses he signal from the sensor,and a digital section, which deals with


the counting and the Ndisplay.

The sensor output isapplied to input socketK2 (top left). Low-passfilter R14 -C8 preventshigh frequencies beingprocessed: it only passesrelatively slow signals.The value of bipolar coupling capacitorsC6 -C7 accords with thelow frequencies: 50 bpm

4 is equivalent to 0.78 Hzand 200 bpm to 3.33 Hz.This composite capad-to4 formed by two po-larized types, preventsany direct ioltages,which vary appreciablyaccording to whether ornot the sensor is con-nected or whether it de-tects spurious light,from reaching ICia.

The op amp, ICta,functions as a linear am-plifier (x200). NetworkR11-05 forms a furtherlow-pass filter (cut-offfrequency is 15 Hz) tosuppress any residualinterference.

The output of ICI, isa reasonably usable sig-nal that looks a little likea pulsating sine wavewith superimposednoise. This signal is con-verted into a clean rec-tangular waveform bycomparator IC Id. Thethreshold of this stage isset with P2 to a levelwithin the amplitude ofthe sine wave. The setting of the pre-set is not critical, since all that is left atthe inverting input of analogue mono -stable multivibrator ICic are positiveand negative needle pulses.

In quiescent operation, the outputof the monostable is low and C3 is notcharged. With incoming signal, theoutput of the monostable goes high ateach trailing edge of the comparatorinput. It remains so until C3 has beencharged via R6. Then, in about 20 ms,the potential at the non -invertinginput of the op amp falls below thelevel at the inverting input (the needlepulse has long passed), whereuponthe monostable changes state again(output low). The 20 ms long pulse isclearly visible by the lighting of D14(green Jim).

Potential divider R3 -R4 halves the9 V supply voltage: the consequent4.5 V supply is buffered by ICib andused as reference for the monostable.Because of this arrangement, the bat-tery voltage can drop as low as 6 V.

In contrast to that to the analogue

1

si.

section, thethe supply lineto the digital section isheld stable at 4.5 V Al-though the cmos-icscan work from 3-15 Vsupplies, the frequencyof the oscillator, deter-mined by RI -CI -Pp de-pends on the level ofthe supply line. There-fore, the supply is sta-bilized at 42-1.5 V by presettable reg-ulator IC5. This type of regulator ismuch more economical than, for in-stance, a 7805, and can work with bat-tery voltages below 6 V.

The pulsimeter draws a current ofsome 15 mA, which allows the use ofa 9 V (PP3) battery. It is, however, ad-visable to use a rechargeable battery,which can be charged via a 12 V mainsadaptor via when Si is in the posi-tion shown in Figure 1. If the batteryis charged by a standard batterycharger (with the pulsimeter off), R23must be replaced by a wire bridge, sothat the battery is connected directly

Figure 1. The circuitof the pulsimeter con-sists of an analoguesection (measurementand processing) and adigital section (evalu-ation and display).The scale of the LEDSis non-linear.

-II-Q

-D.

to the terminals of K1.The voltage level

between the output ofthe monostable andIC, must be loweredfrom 6-9 V to 3-5 Vand this is effected byvoltage divider R16 -R17.

Each pulse emanat-ing from the analoguesection triggers mono -

stable IC,,, whose output is used as astrobe pulse that is applied to 4 -to -16decoder IC4. The trailing edge of thestrobe pulse triggers a second mono -stable, IC2a. The output of this stage,1 As pulses, is used to reset counter IC3to zero.

The oscillator in IC3 clocks thecounter at a rate of about 850 Hz. Thelonger the time interval between twoheart beats, the higher the counterstate will be. The oscillator frequencyis arranged so that at the lowest heartbeat the range used by the counter(CT6-9) just does not overflow, butcounts exponentially up to 1111, dur-

Elektor Electronics 6/96 27

2

mg which D13 is switchedon by IC4. Decoder IC4has four input latches thatbecome transparent whenthe strobe pulse arrives atpin 1. The following de-coder converts the 4 -bitbinary number at the re-spective output terminals.

Scale correlationsbpm

ofseconds

the LED chainHz LED

50 1.28 0.78 D13

53 1.125 0.89 012

57 1.050 0.95 Dll61 0.975 1.03 D10

66 0.9 1.11 09

73 0.825 1.21 08

80 0.750 1.33 D7

89 0.675 1.48 I D6

700 0.6 1.67 D5

124 0.525 1.91 I D4

133 0.450 2.22 D3

160 0.375 2.67 D2

200 0.3 3.33 D1

dipped on to a finger or an ear lobe.Some more elegant and less 'press-

ing' designs are shown in Figure 2.Those in a and b use a 40-50 mm longtube (electrical conduit will do nicely)with a diameter that just, but comfort-ably, fits over a fingeE One end of thetube must be sealed off light -tight.Drill two 5 mm holes as shown moreor less where the fingernail will be(where best results will be obtained).Insert the m diode into one hole andthe lit phototransistor into the other, so

that they fit snuglyover the fingernail.Fix them in that po-sition with super -glue. Connect themto K, with 2 -corescreened cable asshown in Figure 1.If instead of the hy-

brid light barrier areflection type is

used, make the construction as shownin Figure 2b. In this case, a rectangularhole must be cut and filed in the tubeinto which the device just fits. Theelectrical connection is as with the ear -

Figure 2. Three waysof making a sensor;(a) hybrid light bar-rier; (b) reflectionlight barrier, and (c)flexible hybrid con-structed from springwire.

THE SENSORThe sensor for the pulsimeter is notcommercially available and must,therefore, be made by you. Since itdoes not have to be a work ofart, the simplest and cheapestsensor is made from a clothes -peg. Drill a 5 mm dia. hole ineach of the short legs, about5 mm from the top. Insert them diode into one hole and them photo transistor into theother. Connect the two devicesto K2 with two -core screenedcable. This sensor can be

Figure 3. Although theprinted -circuit boardis not densely popu-lated, the construc-tion remains compact.

78

lier construction.If the sensor is to be fitted on to the

ear lobe, the best design is really theclothes peg or something like it asshown in Figure 2c. With this design,it is important to make sure that thepressure on the ear lobe is as light asfeasible, without the risk that it will falloff during the sporting activity.

Whatever the design, it is essentialthat the sensor is absolutely light -tight

CONSTRUCTIONThe pulsimeter is best built on theprinted -circuit board shown in Fig-ure 3 and then fitted in a small enclo-sure measuring 125x65x40 mm(5x2'hx13A in).

Drill the holes for the LErts in ac-cordance with their positions on thePCB: this will ensure that afterwardsthe lid can be easily removed from theenclosure if need be.

Fit the socket for the sensor cableon one side of the enclosure, and thecharging socket and switch on theother side.

In many cases, it is advisable to fita securing clip, such as a belt strap, at

T. ilggAggililAfolAil,-.-_--

SD14 D1 13.? D3 D4 05 D5 D7 03

21ch r '100.-6-1)1cco()(ioimO2. .y. tO27 Ii

tq (600000000000IC4

C3 clo 60

Elektor Electronics

4

the outside of the bottom of the en-closure.

When all soldering work has beencompleted, the board may be fittedinto the enclosure, whereupon IC3 andIC4 (but not IC1 and IC2) can be in-serted into their respeCtive sockets.

As a first check, connect a 1 kfl re-sistor across C42, and supply the circuitwith 9 V from a workshop power unit.Check that the voltage at the output ofregulator IC3 is 4.2-4.3 V. This voltageshould be retained when the output ofthe power unit is reduced to below 6 V.Remove the 1 kS2 resistor.

The LED chain is tested by short-cir-cuiting pins 4 and 6, and pins 10 and11, of the socket for IC2. The LEDSshould then light in sequence as inrunning lights. Remove the short-cir-cuits.

Remove the sensor, insert ICI andIC, into their respective sockets, andconnect a frequency meter to pin 11 ofIC4. Adjust P1 until the meter reads

FLT, Ad 6.6R66A n n

ddel

Figure 4. The batterymay be fixed with aclip (well insulated!)inside the cover of theenclosure withouttouching the board.

847-849 Hz. Remove the meterWith a DVM (digital voltmeter) mea-

sure the voltage at pin 1 of IC1, whichshould be about half the supply volt-age, and adjust P, until the -meterreading has risen by about 200 mV

Reconnect the sensor, connect it toa finger or ear lobe, and switch on thepulsimeter. After a few seconds (toallow C6 -C7 to get charged), the metershould work satisfactorily. It may bethat the sensitivity of it should be cor-rected with P2. If the wiper of this pre-set is at or near to half the supply volt-age, the circuit is at its most sensitive.It is, however, better to adjust P2 sothat the heart beat is detected clearly,shown by D14 pulsating in an identi-cal rhythm, without small sensormovements upsetting the circuit. TheLED chain should show between60 bpm and 80 bpm when the pulse isnormal. So don't get too excited aboutthe success of your work! 1l

PARTS LISTResistors:

= 470 Ica11!)--R4, R18 = 47 kO.

R5 = 680 S2R6. R7, R/1 = 1 MOR8 = 220 kit

= 22 kOR10 R19, R20 = 10 16.1

R1, = 4.7 K2R13, R14 = 56 kitR15 = 270 f2R17 = 39 Id)

R18 = 1R21 = 1.5 kitR22 = 3.3 1(12

1:1;,3 = 330 52

P1. P, = 10 kI) preset

Capacitors:C,. C5 = 10 nFC2 = 1 pF, 16 V. verticalC3 = 47 nFC4. C10 = 1 nFC. C7 = 4.7 pF. 16 V, verticalC5 = 220 nFC9 = 100 pFC11 = 100 mF, 16 V. verticalC12 = 100 nF

Semiconductors:D1-013 = LED, high -efficiency. 3 mm,

red= LED, high -efficiency. 3 mm.

greenDI, = 1N4148

Integrated circuits:IC1 = LM324IC2 = 4528IC3 = 4060IC4 = 74HC4514IC5 = CNY70 (Telefunken) or dis-

crete iR diode and In phototransis-tor (see text)

IC6 = LM317

Miscellaneous:K1 = 2 off soldering pin

= 3 -pin terminal strip for boardmounting

51 = single -pole change -over switchBT1 = 9 V dry or rechargeable bat-

tery (see text)Enclosure, 120x65x40 mm. Bopla

E430 or OKW N120


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.1500m range....£16 45TI(X900 Signalling/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 £22.95C11400 Pocket Bug Detector/LocatorLED 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 £30.95C11600 Professional Bug Detector/LocatorMulticolour readout of signal strength with variable rate bleeper and variable sensitivityused to detect and 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 150.95IITX1110 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 catlogue). Size 20mm x67mm. V operation. 1000m range £40.95

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Elektor Electronics 6.96 31

77Flash EPROM

programmer/emulatora multi-purpose programinerlemulator,

not just for inicrontroller circuit developmentThe most comfortable aswell as expensive way of

developing microcon-troller circuits is to emu-

late the relevant controllerwith the aid of an in -cir-

cuit emulator. Among theless costly options are a

monitor programand an EPROM

emulator. Un-fortunately, amonitor pro-gram uses upsome of the con-

troller's resources. Thisserious disadvantage is

avoided by using anEPROM emulator whichbehaves basically like a

dual -ported RAM: oneside has an interface likethat of an EPROM, while

the other provides thelogic that pumps a data -

stream into the RAM.

EPROM emulators are by no meansnovelties to regular readers of ElektorElectronics. Although a number ofthese projects were presented in the

Design by C. F Urban

past, and built successfully by thou-sands of users around the globe, wehave to admit that the most recent de-sign dates back to 1992, and is nolonger up to date in view of its maxi-mum data capacity of 'only' 64 Kbyte.

When companies like AMD first in-troduced 'Flash' EPROMs featuring asingle 5-V programming voltage and alifetime of about 100,000 programmingcycles, a totally new perspective be-came available for the design of a newtype of EPROM emulator The presentdesign not only acts as an EPROM em-ulator with a huge storage capacity, italso doubles as a Flash EPROM pro-grammer, saving you the expense thatwould have gone into purchasing adedicated programmer.

Having finished with the EPROMemulator during the design phase, theFlash EPROM containing the latest,tested code may be removed from theemulator and plugged into the appli-cation circuit Because prices of FlashEPROMs are not much higher thanthose of regular EPROMs, the addi-tional luxury described above comesfree of charge, in other words, it doesnot even add to the cost of buildingthe present design.

WHAT IS AFLASH EPROM?Apart from the fact that Flash EPROMshave a write input, their actual behav-iour in normal use does not differmuch from regular EPROMs. The dif-ference is only apparent from the waythe data are loaded into the EPROM,and erased again. While ordinaryEPROMs require a well-defined pro-gramming voltage to be present for acertain period of time, and the compo-nent may be erased again by exposingthe chip to a certain dose of UV light,these two processes are internally con-trolled and carried out in a FlashEPROM. To that effect, the FlashEPROM receives an accurately definedcommand sequence (erase, program)which indudes special precautions (setup by the manufacturer) to ensure thatan erase action can not happen justlike that.

The relevant command is trans-ferred to the Flash EPROM via a seriesof write operations, as illustrated byTable 1. The two first commands,Rimilltiset, reset the Flash EPROM, andprepare it for normal read operations.The Autoselect command allows themanufacturer code and the device type


a

Table 1. Flash -EPROM

Cycles

commands

First BusWrite Cycle

Second BusWrite Cycle

Third BusWrite Cycle

Fourth Bus Fifth Bus Sixth BusWrite Cycle Write Cycle Write Cycle

Command

Addr. Data Addr. Data Addr. Data Addr. Data Addr. Data Addr. Data

Read/Reset 1 VOC FO

Read/Reset 4 5555 AA 2AAA 55 5555 FO RA RD

Autoselect 4 5555 AA 2AAA 55 5555 90

Byte Program 4 5555 AA 2AAA 55 5555 AO PA PD

Chip Erase 6 5555 AA 2AAA 55 5555 80 5555 A4 2AAA 55 5555 10

Sector Erase 6 5555 AA 2AAA 55 5555 80 5555 AA 2AAA 55 SA 30

Address bits A15 -A18 are X (don't care) for all address commands except Program Address (PA) and Sector Address (SA)

All data and addresses are in hexadecimal notation

RA = Address of memory location to be read.

PA = Address of memory location to be programmed (on negative WE edge).

SA = Address of sector to be erased.

RD = Contents of memory location RA

PD = Contents of memory location PA (on negative WE edge)

to be read. The command Byte loadsthe program into the EPROM, whileChip Erase actuates the erasing processwhich should normally take less thana minute to complete. From a point ofview of logic, the Flash EPROM is di-vided into sectors which may be readindividually with the aid of the SectorErase command.

A Hash EPROM offers yet anotherprotection mechanism to protect itagainst unintentional write or read ac-tions on a sector -by -sector basis. A sec-tor protected in this way can not beread or (over)written with just a 5-Vvoltage. This is an important fact tokeep in mind with used devices. Theprotection may only be undone withthe aid of a special programmer.

During the program or eraseprocess, the status of the FlashEPROM may be read from the samelocation as the programmed or erasedbyte, after a command with normal'read' access. With sector erasing, thestatus information may be read fromany address within the sector

During the programming se-quence, the highest -order bit, DQ7, inthe byte being read holds the negatedvalue of the one being programmed,while bit DQ5 holds a 0. After success-

ful programming, this inversion is un-done, bits 5 and 7 then holding theplanned values.

Because all memory locations ap-pear to be programmed with the valueFFH during an erase sequence, bit 7 isthen invariably 0 during the process.When an internally fixed time limit isexceeded during either of these twoprocesses ('timing error'), bit 5 togglesto 1, and bit? retains its inverted state.The function of bit 6 is implementedbecause of compatibility requirements.Bit 3 is used when several sectors areto be erased simultaneously. Neither ofthese features are, however, used inthe EPROM emulator described here.Detailed information which you mayrequire for your own software designsmay be found in the databooks pub-lished by the manufacturer AMD (ad-dress at the end of this article).

ADDRESSES AND DATAThe block diagram of the emulator/pro-grammer is shown in Figure 1. Behindthe parallel interface with the PC area couple of address registers, a dataregister and a multiplexer which re-duces the number of data lines to thePC to just two. The Flash EPROM is at

erasure operationsDQ6 DQ5 DQ3Status DQ7

WorkingAuto -Programming DQ7 toggles 0 0

Program Erase in Auto Erase 0 toggles 0 1

Time limit exceededAuto -Programming DQ7 toggles 1 1

Program. Erase in Auto Erase 0 toggles 1 1

the centre of the circuitWhen the Flash EPROM has to be

programmed only, all other circuitblocks are inactive. In emulator mode,the Flash EPROM is read by the ap-plication circuit, via a buffer. The ap-plication circuit is connected to theblock marked 'emulator probe'.

The EPROM Emulator we pub-lished in 1992 uses the Centronics stan-dard to communicate with the PC.That was easy, really, because a staticRAM was used that required only one

write operation per byte. With the pre-sent circuit, a pure Centronics -basedcommunication would not be possiblewithout highly complex hardware andsoftware. Thus, although the program-mer/emulator makes use of the PC'sparallel printer port, the protocol usedfor the actual communication is defi-nitely not to the Centronics standard.

In addition to eight datalines, theparallel port offers four control lines inthe direction of the EPROM emulator,and five status lines which may beused individually for simple read orwrite commands.

Three of the latter lines are used tosupply clock signals to an equal num-ber of registers IC2, IC3 and IC4, whichlatch a total of 19 address lines (A0through A18), one line for OE, and fourlines for the selection of a CE signal(CEI through CE4). The fourth controlline generates the WE signal. Becausethe Flash EPROM only copies the byteon the databus on the edge of the WEsignal, the registers and the FlashEPROM share the eight datalines avail-able on the parallel interface. Duringread operations (OE = low), bus driver10 disconnects the datalines from theHash EPROM. This is achieved by in-verting the OE signal fm IC1c) and ap-plying it to the enable signal for IC5.

Only five lines are available to read

Elektor Electronics 6 96

a byte, so that it is necessary for two 4 -to -1 multiplexers to reduce the eightdatalines to just two. Consequently,the PC has to access these lines fourtimes for every complete byte. Becausethe registers only copy the data on thedatalines on the low -to -high edge ofthe drive signals CLK1, CLK2 andCLK3, they may be used for control-ling the multiplexers. As regards thecontrol software, however; one shouldtake into account that on each statechange of the control lines only thatspecific byte is available which belongswith a register whose CLK linechanges from low to high. Thearrangement of the data lines on themultiplexer is such that bit 7 and bit 5are automatically selected after the lastwrite operation of a command se-quence. The remaining sig-nal distribution across themultiplexers just enables asimple software solution tobe applied for reading acomplete byte.

The switching betweenemulator and programmermode is realized likewise.When one of the three con-trol lines CLK1, CLK2 orCLK3 is logic high, then the wired -ORconfiguration of three open -collectorinverters (1C1d, ICle, IC1f) ensuresthat the Load signal is actuated (i.e.,goes low). This causes the outputs ofregisters IC2, IC3 and IC4, as well asbus driver IC5, to be enabled, so thatthe address and datalines of the hostcircuit are separated from those of theFlash EPROM.

At the same time, a Reset signal isbeing prepared which allows the pinmarked RST (on FET T1) to go activelow, and the pin marked RST+ to goactive high. When Active-HighResetisapplied, it is possible to apply either a+5-V level (jumper fitted), or 'steal' acorresponding level from the applica-tion circuit (via the RST+ pin). The lat-ter option is particularly interestingwhen a member of the 80051 micro -controller family is used because it al-lows the usual reset capacitor to beshunted. Resistor R22 then limits thecurrent to an acceptable level. It doesnot, however, act as a continuous cur-rent limiter, because T1 may be dam-aged if too much current flows.

This mode selection operating viathe three CLK lines on the parallel in-terface enables the PC software toreset the host (application) circuit with-out having to reload the emulator. Thesame function is carried out by the RE-SETAPP utility program, which maybe found on the distribution diskettewhich is available for this projectthrough our Readers Services (ordercode 956017-1).

R -C networks R4 -C13, R5 -C14, R6 -C15 and R13 -C16 suppress internal

1

Figure 1. Block di-agram of the FlashEPROM program-mer/emulator, andthe setting onswitch block S4for differentEPROM capacities.

PA

A

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L

P

R

c

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ADDRESSREGISTERS

DATAREGISTERS

DATAP.tuLTIPLEXER

E

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AllAllA17

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OFFOFFOFF

OFFOFFOFF

OFFOFFOFF

ONOFFOFF

ONOFFON

ONOttOtt

AltA13A15

OFFOFFOFF

OFFONOFF

ONONOFF

ONONON

ONONON

ONONON

ONOilON

and external spurious pulses on thecontrol lines. The delays caused bythese networks should be compen-sated by the software. The delay is,therefore, measured by the program:if the multiplexer is disabled (CE inac-tive), a logic one is programmed onthe 04 and 06 lines. Next, the multi-plexers are enabled (CE active), anddata lines DO and D2 are selected.When these two lines supply l's, thetime may be measured that haselapsed between outputting the pulseedge on the CLK3 line and the instantthe level changes of DO and D2.

The measured (and slightly length-ened) period strictly applies to thedelay which is valid for the CLK3 line.To make sure that this delay is suffi-cient for the other control lines too, theR -C time of R6 -C15 is about twice thatof the other R -C networks. The delayalso helps to avoid problems whichmay arise from the use of computerswith different speeds.

PROGRAMMINGFLASH EPROMsWhen the emulator is used as a pro-grammer, S3 allows the Flash EPROMto be removed without any risk, andwithout having to disconnect the pro-grammer from the PC or the powersupply. The switch simply disables the5 V supply for the Flash EPROM. It alsocauses the W signal to be pulled to 0 V(via T2 and inverter IC1f) and effec-tively disconnects the Load signal sothat the register and bus driver outputsare disabled. Diode D3 and the inverter

-e-hr

IA

LU

T

P

R

950077 - 12

then block the signals of the addressline drivers in the application circuit. Alllines are pulled to 0 V by means of re-sistor arrays (R7, R8, R9 and R10). TheFlash EPROM may be removed fromthe socket when LED D1 goes out

Switch SI allows the emulator to beused autonomously. When the emula-tor is disconnected from the PC, pull-up resistors R1 and R2 pull all lineslogic high. That would normally causethe circuit to switch to programmermode, but the Load signal is effectivelyblocked by switch S1 and a pull-up re-sistor in array R2. So, the circuit re-mains in emulator mode.

POWER SUPPLYThe emulator may be powered via theEPROM socket of the host circuit viaD8 and D9. It is, however, better topower it from its own regulator, IC8,which is protected by D6 and D7, orfrom an external 5-V voltage sourceconnected to K8. Jumpers 28 and 32determine whether the supply voltagearrives via pin 28 or 32 of the socket orEPROM. They must, however, be fit-ted only when the supply voltage ar-riving via D8 or D9 is not reliable.

The address and data lines of theEPROMs are compatible. Be sure,however; to avoid a situation in whichthe host circuit receives no supplyvoltage, because 102 then drives thedatalines in the host circuit. The un-stabilized input voltage for the regula-tor may be obtained from an inexpen-sive 12-V mains adaptor which is con-nected to socket K3 on the board.


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Figure 2. Circuit dia-' gram of the FlashEPROMprogrammeriemulator.Two 4 -to -1 multiplex-ers reduce the eight -bit wide data bus toonly two lines.

Elekior Electronics 6 96 35'

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CONSTRUCTIONExperienced constructors should notrun into problems when building thiscircuit, most of which will be plain sail-ing. Special attention should be given,though, to the combination socket forIC14/connector K9. The press -on DIL

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connectors come in two different ver-sions: pin 1 = wire 1, or pin 1 = wire 2,so do take care. To prevent difficulties,use the same type of DIL connector atboth cable ends. This cable should bekept as short as possible. A (probably)less expensive alternative is to use a


COMPONENTS LIST

Resistors:R1 R2,R18 = 9 -way 3k113 SIL arrayR4.R5.R6.R13,R24-R31 = 470 11R7 R10 = 8 -way 10kil SIL arrayR14 = 22011R15 = 21(112R16 = 10k11R17.R20 = 33011R21,R22 = 1811R23 = 3kin

Capacitors:C1-C12.C18 = 100nFC13.C14.C16 = 47pFC15 = 100pFC17 = 270pFC19 = 1001iF 25VC20 = 100uF 25V

Semiconductors:DI = LED. redD3,04,D8,D9 = BAT85D5 = LED. yellowD6.07 = 1N4002D2 = LED, greenT1 = BS250T5 = BS170T2 = BC547BICI = 74LS06IC2.1C3,1C4 = 74HCT574IC5,1C9-IC12 = 74HCT541IC7 = 29F040 or 29F010 (see text)IC8 = 7806IC6 = 74HCT1531C13 = 74HCT14

Miscellaneous:K1 = 40 -pin pinheaderK2 i= 25 -pin sub -D plug, angled pinsK3,K8 = 2 -pin PCB terminal blockK9 = 34 -pin pinheaderSI.S3 = (slide) switch 2 x cioS2 = 4 -way DIP switch54 = 6 -way DIP switch or 2x6 -pin

pinheader w. jumpers32 -pin ZIF socket for IC7 (optional)2x32 -pin DIL hateable connector with

approx. 30cm 34 -way flatcable (seetext)

Printed circuit board (960077-1) andsoftware on disk (956017-1). com-bination order code 960077-C.

pinheader or boxheader at the emula-tor side. This is fitted either in the solidor the dashed box outline indicated bythe component overlay on the board.If you mount it in the solid box outline,the other end of the cable should befitted with a DIL connector that has apin 1 -to -wire 2 contact arrangement.The second option is for a DTL. con-nector with a pin 1 -to -wire 1 structure.

There are also two options for theconnection to the PC. The first isformed by pinheader Kl, which is con-nected to an IDC-style Centronicssocket via a short piece of flatcable(pin 1 to pin 1). From there, an ordi-nary printer cable is used to establishthe connection with the PC. The alter-native is to connect the circuit to thePC via 25 -pin sub -D plug K2, forwhich a 25 -way male/fernale cable is

sufficient (again with pin 1 to pin 1correspondence).

Depending on the enclosure usedand other construction methods ap-plied, it may be worth while to solderDIP switches S2 and S4 at the solderside of the board. That allows theEPROM size and the CE lines to be setwith a small screwdriver or similar,without having to open the enclosure.Please note that the cables to switchesS1 and S3 should be shorter than40 mm.

PRACTICAL USEThe programmer/emulator is compat-ible with the 29F040 and 29F010 FlashEPROM from AMD. Because bothhave the same command sequences, itis not necessary to make a distinction.Problems may only occur if you try toload a file which is larger than the stor-age capacity of the Flash EPROM. Thisis not checked by the software.

Up to four emulators may con-nected to a single parallel port. Sincemost PCs support three parallel ports(LPTI, LPT2, LPT3), up to twelve em-ulators may be controlled. Resistors RIand R2 are only fitted in the last emu-lator! The selection of an emulator ona particular port is carried out via DIPswitch S2 (CE1 = first emulator). Ad-dress lines may be switched off viajumpers or DIP switch S4 if theEPROM to be emulated has a smalleraddress range than the Flash EPROMon the emulator. When a switch isopened and the associated juniperalso, then the relevant address line isheld at a logic low level by a pull -down resistor

It should be noted that there areEPROMs which expect a logic highlevel at a non -used pin. If the relevantaddress line is not properly discon-nected with these EPROMs, the emula-tor will not work as it shoukL It is, there-fore, recommended to always checkthat all switches and jumpers are prop-erly set, and that all used address lineswhich are not used by the EPROM tobe emulated, are switched off.

Another mistake which may easilyoccur is an attempt to load hex files.The software supports binary filesonly.

THE SOFTWAREControl software for the program-mer/emulator is available on a diskettewhich may be obtained through theReaders services. The disk also con-tains a number of small utilities. Al-ways read the README file on thedisk, because it may contain importantinformation which was not available atthe time this article was being pre-pared.

All utility programs on the disk

share a common parameter set,/L<port> <ce>. This selects the em-ulator which is to be addressed by theprogram. The parameter <port> is ei-ther 1, 2 or 3 depending on the LPTport you wish to use. The other para-meter, <ce>, is either 1 for CE1, 2 forCE2, 3 for CE3 or 4 for CE4.

An example: the emulator is con-nected to port LPT2, and switch CE1is closed. The parameter string thenbecomes /L21.

The order of the parameters is im-portant to observe with the individualprograms. A space should be typed be-fore all file names and parameters!

Flash EPROM programmer utilities:

ERAFLASH /L<port> <ce>erases the Flash EPROM installed inthe emulator

PRGFLASH /L <port> <ce> <bin -file>programs the file <binfile> into theFlash EPROM installed in the emula-tor. No check is performed whetherthe file actually fits in the EPROM. Ifthe file size exceeds the memory ca-pacity, the verify routine reports anerror.

RDFLASH /L<pOrt> <ce> <file>Ai <nmbr>reads <nmbr> of bytes from the con-tents of the Flash EPROM installed inthe emulator, and copies them into<file>. Because the program does notknow the size of the currently installedFlash EPROM, no check is performedwhether <nmbr> actually fits, or istoo large.

Emulator utilities:

LOADEMLJ /L<port> <ce> <bin -file>The program switches the emulator se-lected with the /L parameter to 'load'mode, erases the Flash EPROM, loads<binfile>, and returns to emulatormode.

RESETAPP /L <port> <ce>This utility allows you to reset the host(application) circuit via the emulatorselected via the /L parameter set. Areset pulse with a length of about 1 sis generated and transferred to thehost circuit.

Note: technical data on Flash EPROMsmay be obtained from:Advanced Micro Devices (AMD) Ap-plications Hotline and Literature, UKand Europe, tel. (01256) 811101.


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Elektor Electronics 6.96 39 L.,

)4*KEYBOARD SWAP FOR PCs

In some situations,for instance, in edu-cation or in process

control systems, it ispractical to have at

least two keyboardsconnected to a single

IBM PC (or compati-ble, of course). Thecircuit presented

here en-ables

any PC \

to be fit-ted withan extra

key-board, at a small out-lay only, and without

any kind of internalmodification to the

computer or the key-boards.

Having two keyboards hooked up onone PC can be very useful in a numberof situations. Such a setup does, how-ever, require that the switching be-tween the two keyboards is fully auto-matic, and, therefore, 'transparent' tothe user. In addition, it would also benice if the interface for the keyboardscould be used in a simple way, that is,without extra cables, difficult settingsor software extensions. Last but notleast, it would be extremely useful ifthe interface would accept keyboardswith the familiar 5 -pin DIN plug aswell as types with the compact PS/2type plug.

For maximum ease of use, and min-imum risk of operating errors, it is es-sential that the circuit always has oneof the keyboards selected for a certain

Design by K. Viernickel

11111111,-11111111

I__ I I 1 1 I I La.L.,1

r cird1414.,i

Zaa..

two keyboardson one PC

period. In practice, the keyboard swapinterface would throw the system indisarray when keyboard 2 is enabledimmediately after a key is released onkeyboard 1, or the other way around.So, the system discussed here is pro-vided with a certain wait period (ap-prox. 10 seconds) before the secondkeyboard is connected to the PC again.Despite all the requirements men-tioned above, we have been successfulin cramming all of the above men-tioned features in a circuit containingjust two integrated circuits, a handfulof passive components, and a fewPCB -mount connectors. The conver-sion from a PS/2 style plug to the morefamiliar DIN socket is achieved withthe aid of a special adaptor plug(which is available commercially) or ahome-made cable. Details on this typeof adaptor are given in a short insetelsewhere in this article.

SPEAKING OF KEYS...Keyboards for today's PCs are rela-tively simple devices. The keyboard in-terface has four signals on it, irrespec-tive of the connector type. Two pins areused to feed the supply voltage to thekeyboard (+5 V and ground). Theother two are for the clpck signalwhich indicates whether or not a keyis pressed, and for the actual serialcode which goes with the key which isbeing pressed. The clock signal (foundat pin 1 of the 5 -way DIN socket) ispresent as long as a key is pressed.Next, the serial data code which be-longs to the pressed key appears atpin 2 of the plug.

Basically, there are two types of key-board in the world of IBM PCs andcompatibles: `XT keyboards and 'AT'ones. XT keyboards go back to theearly years of the PC industry, and arehardly sold any more. All new key-

440Elektor Electronics 6196

boards supplied these days are of theAT type - search as you may, youwon't find XT keyboards any more inthe computer shops!

Electrically, the main difference be-tween XT and AT type keyboards isthe bidirectional communicationwhich is made possible by an AT -stylekeyboard. This option is used, amongothers, to activate theLED indicators (NumLock, Caps Lock andScroll Lock) on thekeyboard. In an XTkeyboard, the LEDsare controlled (i.e.,switched on and off)by bistables (flip-flops)which form part of theinternal keyboard hardware. In an ATkeyboard, this control is taken over bythe PC. The communication betweenthe PC and the keyboard, and the as-sociated interrupt processing worksproperly (in most cases!) when theLEDs on an AT -style keyboard can beswitched on and off by the PC.

FROM THEORY TOPRACTICE

The complete circuit diagram of thekeyboard swap circuit is shown in Fig-ure 1. You will probably, agree with usthat the circuit has remained prettysimple. Connector K1 is linked to thePC, while connectors K2 and K3 maybe used to hook up the keyboards. Thecircuit contains two mono -stable multivibrators(MMVs) built around 1Claand ICIb (CD4098). Each ofthese is set to an RC time ofabout 10 seconds (by meansof R2 -C3 and R4 -C4 respec-tively). ICla is actuatedwhen a key is pressed onthe keyboard connected toK2_ Similarly, the keyboardconnected to K3 actuatesmonostable IC1b. When akey is pressed, the level atpin 2 of K2 (or K3) changes,and the negative triggerinput (-T) of the relevant(retriggerable) monostable isactuated. The logic highlevel which exists at theQ output of the monostableduring the monotime thencauses two analogueswitches to close (IClaswitches IC2b and IC2c,while ICIb controls IC2aand IC2a). Both switches(for example, IC2b/c) dosewhen the associated Q out-put is logic high, and thenconnect the active keyboardto the computer. At thesame time, an indicationLED lights, so that the user

Figure 1. Full circuitdiagram of the key-board swap interface.This circuit enablestwo keyboards to behooked up to a singlePC.

IC1b

1 I i®?I- ?Ti

can actually see which keyboard is cur-rently connected to the PC.

Because the Q output of each of thebistables is crossed over to the RESET

From thin toToday's PC market offers keyboards withIwo types of plug. Traditionally, the 5 -wayDIN plug is used. A couple of years ago,IBM ('Big Blue) introduced a much morecompact connection with their PS/2 lineof PCs. Not surprisingly, PSI2-style key-board connectors are found on manyoriginal IBM computers and portables. Al-though they look entirely different, the 5 -pin DIN plug and the PS/2 plug do con-vey the same signals. An adaptor tobridge the physical differences is there-fore easily made.Figure 1 shows the pinout and pin/signalfunctions of the 5 -way DIN connector.Only four pins are used on this connec-tor: two for the data exchange, and twofor the 5-V supply voltage, which origi-nates from the PC.Figure 2 shows the layout of the PS/2keyboard connector. Use is made of acompact 6 -way mini-D1N plug and socket.An adaptor to link the two standards iseasily made from a length of 4 -way cable,a PSI2 cable socket and a 5 -way DINplug. Incidentally, these adaptors shouldbe available from any reasonably stockedcomputer shop.

input of the other bistable, the twomonostables can never be actuated si-multaneously The non -active mono -stable can not be actuated until the

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Aylesby HouseWenny Road, ChatterisCambridge. PE16 6UT

Tel 01354 695959Fax 01354 695957

E-mail [email protected] tsien42 Elektor Electronics 6 96

OMPONENTS LIST

Resistors:R1 -R4 = 4 x 10MLIR5.R6 = 2 x 2205I

Capacitors:C1,C2 = 2 x 1()OnF03,C4 = 2 x 1 ttF05 = 1 x 100tF 16V

Semiconductors:D1.D2 = 2 x LED101 = 1 x 4098102 = 1 x 4066

Miscellaneous:Kl.K2,K3 = 3 x 5 -pin DIN socket

180-. PCB mountPrinted circuit board, order code950126-1

monotime of about 10 s has elapsed onthe active monostable. Thanks to thisapproach, only one keyboard is actu-ally connected to the PC at any time,and cross -interference between thetwo keyboards is avoided.

THE SOLDER WORKFigure 2 shows the copper track layoutand the component mounting plan ofthe printed circuit board we designedfor this project. The board is availableready-made through our Readers Ser-vices (see page 60). Stait by installingthe two wire links on the board. Next,you may fit the sockets, resistors andcapacitors in their re -

3

2 Is 0 C

4 :I 4K2t_i ,a_14Nr; riTTL/7

01 Fi6 10 D2 klDI 01 R5 /0

spective positions.Observe the polarityof the LEDs whenyou mount them. Itis recommended touse IC sockets on theboard. The ICs arefitted last.

All that remains

Figure 3. Finished proto-type of the circuit, which isconnected to the PC via ahome-made 4 -way cable.

len 9 9 9 9 MPlalo

Figure 2. Copper track lay-out and component mount-ing overlay of the printedcircuit board designed forthe interface (hoard avail-able ready-made, seepage 60). The three DINsockets are neatlyarranged side by side atone edge of the board.

to be done is makethe connectingcable to the PC. Viathis connection, thecircuit is poweredby the computer. Inpractice, the currentconsumption isvery low or evennegligible when thetwo LEDs are out.

It should not be too difficult to finda suitable case for the keyboard swapcircuit. The choice is left to you!

The connecting cable is easily madefrom a piece of four-way cable andtwo ordinary 5 -pin 180' DIN plugs.The connections are not crossed, thatis, pin 1 of one plug goes to pin 1 ofthe other, pin 2 to pin 2, and so on.Fortunately, the pin numbers are usu-ally printed next to the pins, at the sol-der side.

CONNECTING UPUse the home-made cable to connectthe circuit board to the PC's keyboardinput. Next, connect the two key-boards to the sockets on the keyboardswap circuit. Switch on the PC. In casethe pre -defined selection time of themonostables (approx. 10 s) is shorterthan the boot time of the PC, the com-puter will probably produce an errorreport 'Keyboard error, press <F1> toRESUME' or similar. Fortunately,pressing the Fl key on one of the key-boards is always sufficient to completethe 'boot -up' procedure successfully.Both keyboards should now be able toalternately communicate with the PC.From then on, keyboard swapping isonly possible when both LEDs are out.

(950126)


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Call 01705 591037 or Fax 01705 599036 + VAT &Elektor Electronics 6/96 45

All Trademarks Acknowledged

Since the immenselysuccessful introduction

of the music compactdisc, all things digitizedare much sought after.In spite of the only

moderate successso far of digital

audio recorderslike DAT, DCCand the Mini -

Disc (which \,,failed to set box "

office records,and will not do so

for some time tocome), manufactur-

ers of audio/video con-sumer electronics seemconvinced that the digi-tal video recorder does

have the potential ofbecoming a market 'hit'.All large manufacturers

of consumer electronicsare highly likely to intro-

duce digital videorecording equipment

before the end of thisyear. Let's have a look

at what these giantshave up their sleeve.

By our editorial staff

FOCUS ON: DIGITALVIDEO RECORDERS

new arrivals every day

As most of you will know, the digitalapproach to signal processing has itsdistinct advantages because it looksupon any event as true or false. Sincethere is nothing in between true andfalse, external things like noise signalscan not affect the signal quality. Inprinciple, picture signals which havebeen stored digitally retain their qual-ity for many years. The reproductionof digital signals is still perfect aftermany years of storage and generationsof copies. Also, manipulations of thesignals will not degrade the quality,provided these manipulations are car-ried out in the digital domain.

Leaving the massive impact of dig-itized audio behind as an accom-plished fact, the industry has movedon, and is now at a stage where videosignals may be processed digitally,without major problems, in consumerequipment for high -volume produc-tion. Digital video standards likeMPEG I and MPEG 11 (which are usedwith Video CD and digital television),are already applied in practice. It allseems to indicate that the days of ana-logue video recorder will soon be past,that is, if the manufacturers have theirway - as we all know, the market maydictate otherwise.

A46 Elektor Electronics 6/96

D VI D E 0 ,A WORLD STANDARDOnce bitten, twice shy: having learnedtheir lesson from the problems thatarose with the introduction of a stan-dard for the analogue video recorder(once upon a time three different sys-tems, Video 2000, Betamax and VHScontested fiercely for the title 'worldstandard'), manufacturers of consumerelectronics have agreed upon a com-mon standard for digital video. CalledDVideo, this standard was the result ofthe Digital VCR Conference held inJuly 1993. It is currently supported byat least 52 manufacturers, including allgiants like Philips, Sony and Mat-sushita.

Meanwhile, a number of manufac-turers of consumer electronics (includ-ing Sony) have started to introducevideo systems (camcorders as well ashomedecks) which are based on Digi-tal Video.

The new digital video system al-lows any user to produce recordingsand edited work with professionalquality using an extremely compactvideo cassette. The differences be-tween recordings made with the newdigital system and the current ana-logue VHS system are remarkable. Theresolution of the digitally stored videoimage is much higher, and fully re-tained despite endless copying andediting. The digital recording systemalso offers many new picture effectsand editing options, induding soundinsertion only, picture insertion only,audio dubbing and video -on -sound.Many picture effect may be employedwithout modifying the digital record-ing. A simple computer program and

careers:

0=N 1i -a101GGEI©01121114

t=tvideo camera

a serial link be-tween the PC andthe recorder areall it takes to actu-ally use these in-teresting effects.

JVC recentlydemonstrated thatall these featuresmay be integratedinto an extremelycompact system.Their camcordertype GR-DV1 eas-ily fits in a singlehand, yet con-tain.: a digitalvideo deck with aplethora of effectand picture edit-ing features, notforgetting a com-plete camerafunction, ofcourse. The digi-tal video outputenables the digi-tized video signalto be transferred to another medium(carrier). Most edit functions may beactivated directly via the infra -red re-mote control that comes with the GR-DV1. The price tag is moderate at lessthan £2,000 right from the introduc-tion.

A NEW CASSETTE, TOONo new video system to go without anew video cassette, of course. Unfor-tunately, that means loss of compati-bility: in other words, a DVideorecorder cannot be used to play backanalogue VHS and 8 -mm cassettes.

DVideomakes useof two cas-sette for-mats, onefor station-ary applications (size 125 x 78 x14.6 mm), and one for use in cam-corders (size 66 x 48 x 12.2 mm). Thestandard cassette has a maximum playtime of 4.5 hours. The mini cassette isavailable in versions that allow 30 or60 minutes of digital video to berecorded. The mini cassette is threeand a half times smaller than a VHS -C

cassette, and less thanhalf the size of an 8 -mmcassette. The big advan-tage of the new cassetteconcept is that mini cas-settes, too, may be useddirectly in the homedeck. A special adapteras used with the currentVHS system is not re-quired.

There is yet anothernovelty in the video sys-tem. In addition to theregular video cassette,there is also a versionfeaturing a separate cas-sette memory. The use-ful 'index' function cou-pled to this memory al-lows certain fragmentsto be found faster andsimpler As soon as a cas-sette with memory is in-serted into the cam-corder, the relevantindex appears in theviewer With a home -deck, the same informa-

Figure 1. JVC recentlyintroduced an ex-tremely advanced dig-ital camcorder with abuilt-in DVideo driveunit.

Figure 2. A Ct-VHSrecorder only recordsdigital datastreams.The recorder is easilyintegrated into exist- 01

ing digital video sys-tems.


belt guideroller (2)

supply hub

read/writehead

belt -drivepulley

flat belt drive take-up hub

rubber -covered ---drive roller

drive motor direction of forward tape motion

fixed tapeguides (2)

Figure 3. Magnetic recording usingthe helical -scan principle requires arelatively complex drive unit. Philipsare currently researching the possi-bilities of applying QIC tapes as usedin computer tape backup systems.

tion appears on the TV screen.The tape inside the digital cassette

has a width of 635 mm, and consistsof two magnetic layers deposited onthe tape by evaporation. This con-struction ensures the best possible pic-ture registration. A special diamond-like carbon protection then ensureshigh durability of the magnetic tape.

DIFFERENT FORMATSA part of the DVideo standard is a de-finition of the SD (Standard Definition)as well as the HL) (High Definition)format. The SD format has been de-signed for recording NTSC as well asPAL transmissions. The improvementwith respect to analogue recordings isremarkable with camcorders andlarge -screen displays. The video im-ages are much more lifelike and a lotdearer with large -screen projection.This improvement is due to the factthat Digital Video stores images at aresolution of 500 picture lines. Forcomparison: up to 250 lines are dis-played with VHS and 8 -mm record-ings, 405 lines with S -VHS, or 420 lineswith Hi8.

The HD format offered by DVideois intended for the recording of HighDefinition broadcasts. This format ismarked by a horizontal resolution of600 lines, and offers a doubling of thecurrently used number of picture lines(1,250). Disregarding these resolution

//11\ light

sensing

tape path(oxide out)

fileprotect

SC C-317 - 13

differences, the HD format is identicalto the SD format.

D -VHS, A LOGICALSTEP FORWARDJVC, the inventors of the VHS system,have come up with a digital version,D -VHS, which is to co -exist with S -VHS, the enhanced version of ana-logue VHS. Meanwhile, other manu-fiicturers including Hitachi, Thomson,Matsushita and Philips are also busy

developing the D -VHS system andmaking contributions to the technol-ogy. Because practically all videorecorder manufacturers have shownan interest in this extension of the VHSstandard, there is a reasonable chancethat D -VHS will be with us in the nottoo distant future.

The main advantage of D -VHS isthat you may continue to use existingVHS tapes, giving the digital videorecorder plenty of time to supersedethe analogue tapes in a gradual take-over process QVC reckon this will takeat least 15 to 20 years). A D -VHSrecorder has no problems playing ex-isting VHS and S -VHS recordings. Theprice of the digital extension will bearound f250. JVC describe D -VHS asbit stream data recording'. No com-pression or expanding of the recordedsignal is used. The main aim of D -VHSis the ability to record digital video sig-nals on a magnetic tape. In playbackmode, the very same data stream issupplied as the one originallyrecorded. It is, therefore, not possibleto record and play back existing, ana-logue, TV broadcasts without the helpof an external ND and D/A converter.

As regards its internal construction,the D -VHS recorder is largely similarto present-day analogue VCRs. Thesame tape path is used in the drive,and the heads that used to record ana-

Figure 4. Experimentalset-up in the PhilipsPhysics Lab in Eind-hoven, the Nether-lands. A regular QIC isused for linear record-ing of digital videosignals.


logue information only are now usedto transfer analogue as well as digitalinformation to and from a magnetictape. The drum rotates at the normalPAUSEC_AM speed of 1,500 rpm (1,800for NTSC), obviating the need tochange the speed for analogue record-ing. Metal tape has also been avoided,S -VHS tape is used in a conventionalcassette, but with an additional identi-fication hole to switch the recorder todigital mode.

Three recording modes are pro-posed: Standard, High Definition andLong play. The first has a maximuminput data rate of 14.1 Mbit/s and arecording rate of 19.1 Mbit/s. The dif-ference is necessary to able to incor-porate error correction, which takesthe form of the much -used Reed -Solomon code. The modulation systememploys the Serial Interface Non Re-turn To Zero Information used in anumber of digital systems, such as CD.This system cuts interference by notsupplying a signal when it reads azero. The recording time is 5 hourswith a capacity of 31.7-GBytes, or7 hours and 44.7 GBytes with thintape. Although the detailed specifica-tions for the HD and LP modes hayet to be decided, the input data ratefor the former has been set at a maxi-mum of 28.2 Mbit/s. Tracking isachieved with the aid of a separatetrack. The first D -VHS recorders areexpected to appear on the market laterthis year. Because the recorder has noin-built provision to convert analoguevideo signals to digital datastreamsand the other way around, the first D -VHS recorders willprobably appear inmarkets where digitaltelevision is alreadywidely available. TheU.S.A. represent such amarket. D -VHS alsolooks promising forstoring huge computerfiles.

is essential to create sufficient band-width for the recording of analoguevideo information_ Furthermore, thevideo signal is recorded in such a waythat each track contains exactly one,complete, TV field scan. In a linearvideo registration system (Le., a systemwithout a rotating head), all informa-tion is transferred to tracks which runin parallel with the tape_ Examples ofsuch linear -track systems are the goodold audio tape deck and the cassetterecorder. The DCC (digital compactcassette) is an advanced version of thelinear recorder which reads and writesa Large number of parallel tracks withthe aid of a head produced in thick -film technology. Because only the tapemoves, a linear drive unit has a muchsimpler construction than a drive unitbased on helical scanning.

So far, Q1Cs are only used asbackup devices, i.e, for the storage of

Figure 5. The firstDVideo systems arebeginning to appearon the European ANconsumer market. Thephotograph shows aSony product.

A DIFFERENTAPPROACHWhereas both DVideo and D -VHS arebased on firmly established technicalsolutions like a drive unit with rotat-ing heads, a quite different approachis used by researchers at the PhilipsPhysics Laboratory Based on thewidely used Quarter Inch Cartridge(QIC), a new type of data recorder isbeing developed which has a station-ary head, offering a data throughputof up to 16 MBit/s. QIC tapes are fa-miliar to computer users because theyare used in tape streamers.

With analogue video recorders, thehelical scan principle is used to recorddata on to a magnetic tape. This tech-nique allows a high head -to -tapespeed to be achieved. This high speed

computer data. Thedrive and the associ-ated cartridge are inex-pensive, compact and

stable. QIC tapes usually offer suffi-cient capacity to enable the contents ofa PC hard disk to be archived. Com-pared with advanced archiving sys-tems such as DAT and 8 -mm Exabyte,QIC has a limited storage capacity ofabout 4001\4byte. Recently, enhancedversions of this cartridge have ap-peared on the market, offering a ca-pacity of 850 MByte. The track distanceon these tapes being 150 gm, a 0.25 -inch tape allows 42 tracks to berecorded. The data recording densityis 1.6 bit/gm, and the tape speed is 13to 2 rn s.

The combination of these featuresfinally results in a maximum datatransfer speed of 2 Mbit/s. Because thisrate corresponds to the capacity of adata channel for MPEG I video oraudio, it is possible to use QIC tapes to

record video with a limited picturequality (comparable to VHS). Techno-logically, it is realistic to expect furtherminiaturization - eventually, fourtracks will fit in the 150µm which isnow used by one data track. This willquadruple the storage capacity from850 MByte to 3 Gbyte.

With digital video, the throughputrate in the data channel is just as im-portant as the storage capacity. Cur-rent research is aimed at a recordingdensity of 0.3 gm per one bit. At a tapespeed of 2 nils that yields a maximumdata speed of 6 Mbit/s. Unfortunately,that just happens to be the absoluteminimum for high -quality video sys-tems. However, if a multiple readAvritehead is used with eight parallel tracts,a capacity of 16 Mbit/s is achieved,which is more than enough for highvideo quality. Real HDTV becomespossible only at 20 Mbit/s and up. In

theory, HDTV recording would bepossible using multiple heads withmore than 8 tracks, or an enhancedtape which requires less than 0.3 gmfor one bit.

Towards the end of the tape, thetape speed has to be switched quickly,and the head position changed, so thata new group of tracks may be trans-ferred to the tape, alongside the tracksalready recorded. To guarantee an un-interrupted supply of TV images, abuffer is used to compensate the timeneeded for the switching operation.

Linear registration has yet anotherimportant advantage: by adapting thetape speed, the digital bandwidth maybe reduced or increased for 'simple'and 'complex' images respectively. Fur-thermore, the search time is very shortindeed. Rewinding a tape completelytakes only 45 seconds. Because thehead remains in contact with the tape,the recorded material may be viewedall the time. exeam

Etektor Electronics 6196 49

Wireless for theWarrior - Vol. 1By Louis MeulsteeISBN 189 8805 08 3Price £ 27.50 (UK)Softback. 360 pages A4

For those who, like this re-viewer, have spent part of theirlives in the development of mili-tary communications equip-ment, this book is like opening aphotograph album. Nostalgia?Yes, but above all pride inremembering the fine communi-cation equipment the BritishArmy has always had.

This volume is the first in aprojected series of books, subti-tled A Technical History of RadioCommunication Equipment in theBritish .41 -ray, which it is plannedwilt eventually cover transmit-ters and receivers from the FirstWorld War up to the 'Larlzpur'system.

This first volume is devotedto Wireless Sets No. 1 to No. 88,and contains over 150 pho-tographs, 320 drawings, and 130tables. It is based on more thanfifteen years research in a num-ber of official and privatearchives in the United Kingdomand elsewhere.

An explanation of the vari-ous Type Nomenclature systemsused for army radio equipmentfrom WWI to the present day isfollowed by descriptions of thesets themselves. The aim in eachcase has been to describe thehistory, technical details, and theaerials and accessories used witheach set, together with sparesschedules.

Several versions and adapta-tions of the sets produced inAustralia and Canada are alsodescribed.

The descriptions of the setsare followed by a series ofAppendices: Glossary of Terms;Condensed Data of Equipment;Accessories List; Army ValvesDesignations and Equivalents;Table of Frequency Coverage.

In his foreword to the bookDr P.J. Thwaites, Deputy Direc-tor of the Royal Signals Museumat Blandford, Dorset, has wel-comed it as forming a valuablereference source for all thoseinterested in historical militaryradios. Response from readers,many of whom placed orders inadvance of publication, has beenvery favourable.

Wireless for the Warrior,Vol. L is published by G CArnold Partners, who also pub-lish Radio Bygones and MorsurnMagnificat magazines, as well asa number of other books for vin-tage radio and telegraphy

enthusiasts.G C Arnold Partners9 Wetherby CloseBroadstone, DorsetEngland BH18 8JBPhone/fax 01202 658474

Introduction toElectronic DevicesBy Michael ShurISBN 0 471 10348 9Price £ 18.95 (hardback)John Wiley & Sons Ltd

This is a textbook for electricalengineering students takingtheir first course. For many stu-dents, such a course may be theonly one they will take on elec-tronic devices; for others, it maybecome a gateway to an excitingcareer in this important engi-neering field.

In either case, the coursemust form a solid foundation forunderstanding the basics of elec-tronic device technology. A tech-nician may treat an electronicdevice simply as a black box withcharacteristics described in man-ufacturers' data sheets, but anelectrical engineer cannot. She orhe must understand how thesedevices work because the pre-sent dominance of solid-statedevices svif surely pale com-pared with what is expected tocome in the near future.

This book does more thanjust underpin such a course andis, therefore, an invaluable aid tounderstanding electronicdevices.

The LoudspeakerDesign CookbookBy Vance DickasonISBN 1 882580 10 9Price SUS 34.95Audio Amateur Press

The fifth edition of this success-ful book comes almost twentyyears after the first. Between thetwo, many changes and modifi-cations, reflecting the then cur-rent engineering trends in loud-speaker design, were intro-duced. The fifth edition is noexception and is marked by thecurrent trend towards hometheatre and more advanced,serious car audio. These twofields have become so importantto loudspeaker design, and haveso many specific applicationdetails, that each deserves achapter.The book is available from OldColony Sound Lab, P 0 Box 243,Peterborough, New Hampshire03458-0243 USA.

Battery ReferenceBook - 2nd EditionBy T R CromptonISBN 0 7506 2567 8Price 50.00Softback, 782 pagesButterworth Heinemann*

When the first edition of thisbook appeared, the review inthis magazine (June 1990) saidthat it should prove to be a god-send to countless designers. Inthe intervening years, the bat-tery world has become evenmore complex and manufactureof batteries worldwide hasincreased six -fold, so that thissecond edition should proveeven more valuable than thefirst. This reviewer and his col-leagues have had many occa-sions when they were verythankful to have a copy of theBattery Reference Book.

The book will no doubt bewelcomed by designers of alltypes of equipment using batter-ies, and should also prove usefulfor research organizations in theprivate and public sector..

Books from BernardBabaniThe Internet and World WideWeb explainedBy 1. Shelley £ 5.95

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Toshiba Medium PLCPrimerBy Ed DropkaISBN 0 7506 9694 XPrice £ 27.50Softback, 146 pages,with demonstration diskButterworth Heinemann*

This book provides an introduc-tion to programming with theEX-PDD250 software commonto Toshiba Medium rtes and isdesigned for electricians, engi-neers, students, and technicians,who are not very familiar withprogrammable logic controllers(rtes) and relay ladder logic(Ru.). If you are just starting touse Toshiba Medium rtes, or areplanning to use them, this bookwill help you to get acquaintedwith the specifics of the softwarein a quick, straightforward, step-by-step way. The book may alsobe used as a general introduc-tion to RLL and PLC program-ming for any brand of rte.

The demonstration diskincluded with the book allowsyou to become familiar withbasic techniques before youhave to work on the real thing.The circuits in the book can becopied directly to your program,and modified to suit.

Books in he MaplinSeriesButterworth Heinemann*

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Moreover, all components anddevices described in this book arereadily available from Maplinhigh street stores, or throughtheir mail-order service.

*Butterworth Heinemann bookscan be ordered from:Customer Services DepartmentHeinemann Publishers OxfordPO Box 382Halley Court, Jordan HillOxford OX2 8RUPhone ;-41(0)1865 314301Fax: +44 (0)1865 314029

Elektor Electronics 6196

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IiV

burukira

A simple switching clockwhich keeps one light on

in the eveninghours when you

are not at home isno longer taken

seriously as a bur-glar deterrent. The

circuit describedhere tackles the jobof fooling the burglarin a much more soph-isticated way by adding

a human touch. Whiletraditional clocks switch

lamps on and off at fixed,preprogrammed times,

the circuit presented heredoes so at random inter-vals, providing a realistic

suggestion of peoplebeing at home.

It is an unfortunate and well-knownfact that burglars prefer to break intopremises when they have reason to as-sume that nobody is home. To bur-glars, the absence of lighting or anyother sign of life during the eveninghours provides reasonable assurancethat they can go about with their ne-farious activities for a while. So, usinga time -controlled dock which switcheson at least one light in the home is notbad for a start to scare off the occa-sional burglar and petty thief, who willfind the risk too great, and look foreasier targets.

The matter becomes less simple ifthe interest of the burglar in question

Design by K. Walraven

rit

is more specific. The more experiencedmembers of the burglars fraternity areby no means idiots, and will soon dis-cover the regularity of the on/offswitching instants. After some obser-vation, their conclusion will be that aswitching dock is being used, particu-larly, when there is no sign of life in oraround the home. To keep this ad-vanced class of thieves out of yourhome, you need to go one step furtheras regards effective deteniag measures.

The clock described here offerssuch ingenious operation that evencareful observers will be fooled intobelieving that someone is home. Theoperation of the control we have inmind is partly the same as that of aregular switching dock: the circuit isactivated when it gets dark, andswitches on a lamp. After a predefinednumber of hours, a timer arranges forthe control to be switched off again. Sofar, nothing special. But here comesthe clever bit: the lamp is not left on allthe time during the predefined period,but is switched on and off at quasi -ran-dom intervals.

When used with the light(s) in thereception hall, corridor or staircase, thecircuit gives a very convincing im-

pression of people walking about inthe home. In practice, this will have aconsiderable deterring effect againstburglars. Moreover, because the circuitis relatively simple and inexpensive tobuild yourself, this ingenious piece ofelectronics is highly recommended toall of you who are 'out' a lot duringevening hours.

THE SECRET?Two OSCILLATORSThe above description of the basic fea-tures of the burglar deterrent lightingcould give the impression that a mas-sive amount of electronic componentsis required to build the circuit. Not so,fortunately. The block diagram of thedeterrent is shown in Figure 1. The ac-tual circuit diagram being hardly morecomplex, there should be no cause forconcern about the size and complexityof the circuit.

Let's have a closer look at figure 1.Where is the ingenious bit? It will beclear that a block marked 'timer', aswell as the Iliac control for the lamp,would also feature in an 'ordinary'switched dock. The novel aspect of thepresent circuit is the use of two oscil-lators which work together in perfect


harmony, and so form the previouslymentioned 'quasi -random timer'.

Actually, the operation of the circuitis quite simple. As indicated in theblock diagram, there is a marked dif-ference between the output signalssupplied by the two oscillators. Theupper oscillator has a period of about1.7 s, while the lower one toggles onceevery five minutes. The upper oscilla-tor is started by a comparator whichmeasures the ambient light intensitywith the aid of an LDR (light -depen-

dent resistor). As soon as it getsdark, the oscillator starts to

supply its output pulses.The timer is then also

started - it ensures that theoscillator is stopped again

after a certain number of hours.In other words, the timer deter-

mines the daily period duringwhich the burglar deterrent lighting isactive. The length of the period (dur-ing the hours of darkness) is adjustablebetween one and seven hours.

The period of 5 minutes suppliedby the lower oscillator determines therate at which the lampis switched on and offduring the eveninghours. That does notmean, however, thatthe lamp is being,switched on and off atfixed intervals of fiveminutes! The random-ness is provided by,among others, a D -typebistable (flip-flop)marked 'FF' in the dia-gram. The signal sup -

2

as

plied by the lower oscillator acts as adock for this bistable, while the outputof the 'fast' oscillator supplies the datasignal. As you may know, a D-bistableis a special kind of change -over switchwhich is operated by its dock signaLEach time the clock signal changesfrom 'low' to 'high', the level at thedata input is copied to the output.However, because that level changespretty rapidly in this application, it isnever certain whether the data inputis 'high' or 'low' whenthe five-minute period ofthe lower oscillator haselapsed. The result isthat there are two possi-bilities after each periodof five minutes: eitherthe lamp is switched on,or it is switched off. Or,rather, four possibilities,because it is also possiblefor the lamp to remainon or remain off duringthe next five minutes.

The resulting operation is best de-scribed as fairly random: for example,

the lamp may first beon for five minutes,then remain off for10 minutes, remain onfor ten minutes, remainoff for fifteen minutes,remain on for five min-utes, etc On average,the lamp will be onabout half the evening.That may seem ratherlong for lighting in acorridor or a receptionhall, but it is better to

V

Figure 1. Block dia-gram of the burglardeterrent lighting. Aquasi -random stategenerator is used toswitch a lamp on andoff during the eveninghours. The random-ness is achieved bycombining two oscilla-tors.

Figure 2. This com-plete circuit diagramof the burglar deter-rent allows the blocksin figure 1 to be rec-ognized with ease.The total active timeof the circuit is setwith three jumpers.The light sensitivity isadjusted once with Pl.The mains voltage andthe lamp are con-nected to terminalblock Kl.

IC2a

IC2h

3 Q4

exaggerate a little inthis application. Re-member, choosing amore realistic rate ofabout five minutesper hour would in-crease the likelihoodof the deterrent light-

ing not being noticed at all by a po-tential burglar, who would have noscruples about breaking into yourhome.

PRACTICAL REALISATIONThe schematic in Figure 2 shows youhow the block diagram is expandedinto an actual electronic circuit dia-gram. Even at first glance there is astriking similarity with the block dia-gram. The only marked difference isthat the fast oscillator and the hourstimer are combined in IC3, an inte-grated 14 -stage binary counter/oscilla-tor type 4060. The other blocks from

C=1 --O

--0

Elektor Electronics 6/96 55 N

Comparing / N M ILike many other circuits. the burglar deterrentlighting requires the use of a comparator. Inmost cases, a comparator is actually anopamp with no feedback. In the circuit dis-cussed in this article, opamp ICla acts as acomparator. When the voltage at the positiveinput of the opamp exceeds that at the nega-tive input, the output swings high to a leveljust below the supply voltage. When the othersituation exists, the output voltage is effec-tively at the negative supply voltage, or atground level. This happens because any volt-age difference between the inputs is ampli-fied by an extremely high factor (approx.30,000 times).

A major advantage of a comparator is thatit allows very accurate voltage monitoring tobe realized. Simply by applying a (fixed) refer-ence voltage to one input, and the voltage tobe monitored, to the other, the comparatorwill respond briskly when the voltage to be

watched showsup any devia-tion from thereference. Inour circuit. thereference volt-age is suppliedby potential di-vider R3 -P1The voltage tobe monitoredalso originatesfrom a potentialdivider: R17 -R1. The lattervoltage is light -dependent, be-

cause the effective resistance of the LDR is afunction of the measured light intensity. Con-sequently, the output of 1Cla will toggle whenthe resistance of Al (i.e., the ambient light in-tensity), exceeds or drops below thethreshold set with preset Pl.

figure 1 are easy to recogniie in theirpractical version. Circuit ICla acts as acomparator, while the slow oscillator isbuilt around IC1b. The bistable isformed by IC2a.

Although the operation of the cir-cuit should not have secrets by now,the circuit diagram will be explored inthe usual way. Light -dependent resis-tor (LDR) R1 acts as the light sensor.Together with components R3, P1 andR17, it forms an adjustable bridgewhose balance determines the outputlevel of comparator ICla. During day-light hours, the resistance of R1 will berelatively low. Consequently, the out-put of ICla is logic high, so that IC3and IC2a remain reset. When it getsdark, the resistance formed by theLDR rises, causing the comparator totoggle when the threshold set withpreset PI is exceeded. The reset con-dition is then ended, and the oscillatorcontained in IC3 is allowed to startworking. The length of the period dur-ing which the oscillator operates de-pends on the wire link(s) fitted on theboard. The wire links allow the Q11,

Q12 and/or Q13 out-puts of IC3 to pullpin 11 of the same IClogic high, thereby dis-abling the oscillator.The periods set by thewire links are as fol-lows:link 1: one hourlink 2: two hourslink 3: four hours

Figure 3. The printedcircuit board for thisproject is compact,and easily built up.Mind the polarity ofthe diodes and theelectrolytic capaci-tors! (board availableready-made, see Read-ers Services page)

Combinations of theseare also possible: forexample, fitting bothlink 1 and link 2 yieldsa period of three hours.As you can see, anynumber of hours be-tween one and sevenmay be set.

The oscillator signal of IC3 istapped from pin 10 and fed to the datainput (pin 5) of bistable IC2a. Note thatIC2, a 4013, actually contains two ofthese bistables. However, because thesecond one, IC2b, is not required here,its inputs, Set, Data and Clock, are per-manently tied to ground. The dockinput of IC2a, pin 3, is driven by theoutput signal of the 5 -minutes oscilla-tor. This is built in the simplest possi-ble way from an opamp, IC1b, and acouple of passive parts. Of these, Cland R6 determine the frequency. Re-sistor R4 and R7 ensure that the posi-tive input of the opamp is neatly bi-ased at half the supply voltage.

When, after about five minutes, thelow -to -high level transition at the out-put of IC1b coincides with a high levelat pin 10 of IC3, the Q output ofbistable 1C2a copies this high level.Transistor T1 then starts to conduct,causing triac Tril to be triggered. Thetriac in turn switches on the lamp(max. 220 watts). Should the low -to -high level transition at the output ofIC1b coincide with a low level atpin 10 of IC3, the Q output of IC2agoes low or remains low, so that thelamp goes out, or remains out. So, akind of lottery is held every five min-utes, with fifty-fifty chances for thelamp.

That really completes our discus-sion of the operation of the circuit. Afew details must be added, though.With a circuit such as the one dis-

950022-1o R15 1001 914 10 0000

COMPONENT LIST

Resistors:Al = LDR (small model)R2 = 47k(.2RIR10.R17 = 22kf/R4,R5.R7.R11 = 4k117R6 = 10M(.1R8 = 820ki2R9 = 4M1.17R12.R16 = 11(0R13 = 10kf21:114.R15 = 470k0PI = 22K1 (251(Q) preset

Capacitors:CI = 220F 16V radialC2 = 111F MKTC3 = 220nF 250 VAC (X2 -class)C4 = 2204F 10V radial

Semiconductors:Dl = 1N4002D2 -D5 = 1N4148D6 = zener diode 5.6 V1400 mV/T1 = BC547BTri1 = TIC216MICI = TLC272IC2 = 4013IC3 = 4060

Miscellaneous:KI = 3 -way PCB terminal block.

pitch 7.5 mmJ1 = 3 -way pin header with 1. 2 or 3

jumpers (wire links)Plug-in PSU casePrinted circuit board, order code

960022-1


cussed here it is practically impossibleto avoid the presence of the extremelydangerous mains voltage. It's an un-fortunate fact which you can do verylittle about. The mains voltage is usedhere for two purposes: firstly, and obviously, to power the lamp, and sec-ondly, to power the control circuit. Thelatter function is realized in the sim-plest possible way, by deriving the cir-cuit supply voltage directly from themains. That is achieved with the aid ofa zener diode (D6) and an alternatingcurrent resistance, capacitor C3. Resis-tors R14 and R15 ensure that C3 is dis-charged reasonably quickly when thecircuit is disconnected from the mains.That is necessary to eliminate the riskof an electrical shock when you touchthe plug pins.

CONSTRUCTION ANDTESTINGThat brings us to the practical aspectsof the burglar deterrent lighting, inother words, to the construction. Theprinted circuit board is shown in Fig-ure 3. This board is available ready-made through our Readers Services.Before you start fitting components, itis essential to realize that the entire cir-cuit is connected to the mains voltage,and that the construction deservesmore than average care to ensure thenecessary degree of safety. So, be sureto solder as neatly as you can, and doyour utmost to prevent short-circuits.

The board is populated in the fa-miliar order: first, the (isolated) wirelinks, then the resistors, followed bythe IC sockets, the capacitors and, fi-nally, the tallest parts, i.e., terminalblock K1, triac Tril and capacitor C3.The latter must be a high -voltage ratedtype (250 VAC), and, preferably, anextra -safe X2 version.

It is recommended not to cut thewires of the LDR, RI, until the best po-sition for this device has been estab-lished.

Do not insert the ICs in their sock-ets yet, and first give the populatedboard a thorough visual inspection. Al-though the circuit may be expected towork spot-on, some prudence and anextra check are in order here. Do notconnect the circuit to the mains yet.

Solder two wires to the terminals ofcapacitor C4, and clip on the probewires of a multimeter set to the 'DCVolts' range. Temporarily connect aproperly isolated mains cable to theouter contacts of terminal block Kl.Keep your finger away from the cir-cuit, and briefly insert the mains pluginto the mains socket. The metershould indicate approximately 5 V. Pullthe plug out of the socket. Wait a fewseconds, then insert thelCs into the re-spective sockets.

For the sake of security, the re-maining checks and test are best car-

ried out with the aid ofan auxiliary supply.This may be a bench -top power supply set to5 V, or three series con-nected AA batteries. Ifthe batteries are fresh, you will get suf-ficiently close to 5 V. The auxiliary sup-ply is connected across C4 (mind thepolarity: + to +, and -to - ). Switchon, and you may check the voltagesindicated in the circuit diagram with-out the presence of the dangerousmains voltage.

The drawing in Figure 4 tells youwhere to find the various test points inthe circuit. The negative terminal ofelectrolytic capacitor C4 may be usedas the ground reference for these mea-surements. Make sure at least onejumper is fitted in position J1. If not,IC3 will remain reset forever.

Initially, the adjustment of preset P1is fairly uncritical. Generally, it is suffi-cient to adjust it until pin I of ICla islogic high when the DR 'sees' light.

The oscillator in IC3 has a period ofabout L7 second. These level changesmay be measured at pins 9 or 10. Theoscillator will only operate if the LDRhas detected a sufficiently high lightintensity (even briefly) for IC3 to bereset, after which the light may disap-PeaL

The ocrillator bat around IC1b hasa period of approximately 5 minutes,which may be verified by measuringat pin 7.

FINISHING: THE CASEThe auxiliary supply may be discon-nected and put away if the voltagetests give satisfactory results. The cir-cuit then works properly, and my befitted into a suitable case. When se-lecting an enclosure, avoid false econ-omy because ruggedness and electri-cal safety are paramount in this case.

00

Figure 4. Showing thelocations of the vari-ous test points in thecircuit, and how theboard should bewired.

It is recommended touse a so-called plug-inPSU box, e.g. Maplintype BN57M, andmount a mains socketin the cover. If that is

not possible, use a short extensioncable and a separate mains socket Thewiring should follow the indicationsgiven in Figure 4, which shows how toconnect the plug, the socket and theterminal block on the board. Do notforget to connect the earth wire be-tween the plug and the socket!

The LDR is mounted such that itcan 'peep' outside through a smallhole in the case cover. For security'ssake, that hole should be covered witha piece of opaque self-adhesive tape.Also, be sure to mount the LDR in aposition where it can not detect thelight from the lamp.

Assuming that the right jumper(s)is (have) been fitted in position ii, andthe sensitivity has been adjusted in therelevant location with the aid of P1,the circuit should really do exactlywhat is expected to do.

Finally, attach the suggested elec-trical security label to the case. Thepower of the lamp connected to thecircuit should not exceed 220 watts.

Although it was mentioned earlieron in the article, we once more stressthat the circuit may need to be startedafter it is plugged in for the first time.Some light has to be detected by theLDR to enable IC3 to be reset. The nextdark -to -light transition then forms theactual start signal! cu


MAINS VOLTAGE MONITOR

(May 19%)Dear Editor-The above articlehas a preliminary comment:most of the United Kingdom, weare assured of a stable 240 Vmains supply voltage.- This state-ment is correct in fact but wrongin law.

In response to the Cenelec har-

monization document HD 4772S1:1988, the mains supply volt-age in the United Kingdom hasofficially been lowered to 230 V.Similar other EU countries willhave to raise their official mainssupply voltage from 220 to 230 V.(Most have done so -Editor) In theUnited Kingdom, the change wasmade in The Electricity Supply(Amendment) (No. 2) Reguations1994 [SI 1994 No. 30211 whichcam into effect on 1st January1995.

In fact, the lowering of theelectricity supply voltage has beenperformed by manipulation of theallowable variation of the supplyvoltage. Previously (1988 Regula-tions), the mains supply wasrequired to be within six per centof the nominal voltage. Under thepresent regulations the permittedvariation is plus ten per cent orminus six per cent A few minuteswith the calculator you are givingto new subscribers will show that230 volts plus ten per cent is(nearly) the same as 240 voltsplus six per cent.

The net result is that the elec-tricity supply organizations canlegally lower the supply voltage toa greater extent than before. Inpractice, as the customer pays forpower consumed, lowering thevoltage would reduce income andis unlikely. For this reason, thenominal 230 V mains supply willbe about 240 V for years to come!Guy Selby-LowndesBiiiingshurst, West Sussex

Thank you for clarifying the posi-tion, which will, no doubt, putmany readers' mind at ease.

(Editor)

FROM OPTICAL TO COAX

AND VICE VERSA

Dear Editor-The 'Copybit Elimi-nator Revisited' in your Septem-ber 1995 issue is based on theconversion of electrical signalsonly. Some equipment has only anoptical input or output. I therefore

wonder whether it is possible toconvert digital signals on a coaxline to signals on an optical line toenable, for instance, the copyingof a digital signal at the coax out-put of one unit to the optical inputof another unit. I have enquired invarious shops, but nobody couldenlighten me. Can you?N. Maaswinkel, Belgium.

Your question is answered by'Splitter for SI PDIF coax/opticaloutput' in our July/August 1995issue. (Editor)

MAKING GOOD PCBS CHEAPLY

Dear Editor-After experimentingwith a number of methods formaking PCBS, I have succeeded in

developing a procedure that, as faras I know, has not been usedbefore. The underlying idea was toproduce a board in fewer stepsthan is usually the case.

Using a board layout program,I design a layout, or use a layoutfrom your magazine. This is print-ed on a laser printer with a reso-lution of not less than 300 dpi ona sheet of satinpaper. (It shouldalso be possible to do this on astandard copying machine, but Ihave not tried this).

The master board is thorough-ly cleaned and sand -papered witha 400 grain (medium fine) paper.Next, the copper side of it is uni-formly heated with a blowlamp toabout 200 °C. When this temper-ature has been reached. the tonerside of the printed sheet is laid onthe heated board and presseddown firmly with a roller. This fixesthe toner on to the copper.

Then, keep the board under run-

ning tepid water, so that the paperis wetted uniformly. After about 2minutes, the paper can be removed

(carefully!) from the board.If tiny bits of toner remain on

the paper, the corresponding partson the board can be patched withan etching pen (such as an Edding

3000). When you have tried thismethod a couple of times, you willfind that there is less and lesspatching to be done.

The board is then ready foretching.

Using this method, I have beenable to create tracks of 0.35 mmbetween the pads for two lc pins.C. Ates, The Netherlands

We have never heard of thismethod either, so we are

rOONSTRUCTION GUIDELINES1

Elektor Electronics (Publishing) does not provide parts and components otherthan Petty. form panel foils and sofnvare on diskette or ii (not necessarily forall projects). Components are usually available form a number of retailers -see the adverts in the magazine.

Large and small values of components are indicated by means of one of thefollowing prefixes :

E (Ina) = 101sP (petal = 1015T (tent) = 1012G = 109

M (mega) = 104Ikilo)

h (hecto) = 102da (decal = 101

a Iambi = 10-11'f ifeintoi = 10-15p (pied) = 10-12

n (nano) = 10-9K (micro) = 10-6m = 104c (caul) = 10-2d (dcci) = 10-1

In some circuit diagrams. to avoid confusion. but contrary to 1EC and as recom-mandations. the value of components is given by substituting the relevant pre-fix for the decimal point. For example.

3k9 = 3.9 kit 4µ7 = 4.7 ft.LF

Unless otherwise indicated. the tolerance of resistors is ±5% and their ratingis 'A -J/1 watt. The working voltage of capacitors is 50 V

The value of a resistor is indicated by a colour code as follows.

Bcolor 1st digit 2nd digit mull. factor tolerance

blackrbainmn

oranneeel leonw

blue

I %rhlie

goldsilvernone

0

1 x1012 x10=

3 3 x1034 4 x1045 5 x 105 Al.5%6 6 x1067

S 89 9

x 10-1 +ccx 10-2 ilOft

Examples:brown -red -brown -gold = 120yellow -violet -orange -gold = 47 kfl. 5%

In populating a PCB. always stan with the smallest passive components. thatis. wire bridges. resistors and small capacitors: and then IC sockets, relays. elec-trolytic and other large capacitors. and connectors. Vulnerable semiconductorsand ics should be done last.

Soldering. Use a 15-_011' soldering iron with a fine tip and tin with a resincore 160/40) Insert the terminals of components in the board. bend them slight-ly, cut them short. and solder. wait 1-2 seconds for the tin to flow smoothlyand remove the iron. Do not overheat. particularly when soldering ics and semi-conductors. Unsoldering is best done with a suction iron or special unsolder-ing braid.

Faultfinding. If the circuit does not work. carefully compare the populatedboard with the published component layout and parts list. Are all the compo-nents in the correct position! Has correct polarity been observed? Have thepowerlines been reversed? Are all solder joints sound? Have any %vire bridgesbeen forgotten?

If voltage levels have been given on the circuit diagram. do thosemeasured on the board match them - note that deviations up to -2:10% fromthe specified values are acceptable.

Possible corrections to published projects are published from time to time inthis magazine. Also. the readers letters column often contains useful com-mentsia-dditions to the published projects.

L J


I r

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Write the advertisement, which MUSTrelate to electronics, in the coupon on thispage; it MUST INCLUDE a private telephonenumber or name and address; post officeboxes are NOT acceptable.

Elektor Electronics (Publishing) can not ac-cept responsibility for any correspondence ortransaction as a result of a free advertisementor of any inaccuracy In the text of such an ad-vertisement.

Advertisements will be placed in the orderin which they are received.

Elektor Electronics (Publishing) reservethe right to refuse advertisements withoutgiving reasons Cr without returning them.

WANTED: Fairchild UA726 dual transistors; Sadi024A tc_s: AD533, AD534, AD532, SS/v12050. Writeto K Singh, 89 Fountain Road, Birmingham B178M; England.

FOR SALE: A08 pen plotter, HP compatible; excel-lent condition, little used, still boxed, £1750 o.n.o.Phone 01654 781335.

FOR SALE: Microchip PICstart 16B1 dvelopmentsystem, complete. £80 (half price). Phone01202 518665.

WANTED: Silicon Systems SSI263A speech chip.Please phone 002711 881 0802 (SA - office hoursor write to Lood Strydom, P 0 Box 1632, Paulshof2056, South Africa.

FOR SALE 465 Tektronix oscilloscope, dual trace,

sweep delay, with manual, E50. PhoneAllan on 01705 599 200.FOR SALE: Valor Eltchunics 1980-1994. Two8051 boards with Micro software. £100.Ring Fred on 0191 372 0923.

ctFArtour of computer items, peripherals,etc. Send SAE for list to M. Brown, 2Glentworth Avenue, Coventry CV6 21-11V.

FOR SALE: Magbase databace Demo = 100articles. Free via e-mail. Working progr =4000+ articles_ £10 plus p&p. DOS3.3+.Demo £2 plus p&p via postsandeman C plessey.co.sa.

WANTED: Sage Audio Supermos 2 ampmodule. Phone 0047 3701 6367 or write toTor Sundsdal, Nordre Kirkefiell, 29 4800Arendal, Norway.

FOR SALE: Cable for connecting Casio SFseries digital diaries with PC, with Windowssoftware. 1-.) plus p&p_ Write or phone toMilan Urosevic, Am Kaltenborn 2, 61462,Koenigstein, Germany. Phone 0049 617422764.

FOR SALE: 200+ valves, £ 50. Phone 01473(Ipswich) 230 362..

WANTED: Circuit drawings for BT DMAphone/fax. Will pay for postage and anyother costs. Write to Paul Orman. 117McAlroy Road, Ferny Grove 4055,Queensland, Australia.

watkrrEcc 100 W+ power amplifier circuits.Also want to exchange ideas and informa-tion with other hobbyists. Write to KrishnaMununareddi, 2549 Stow Ct, Crofton,MD -21114, USA.

Send this coupon toElektor Electronics (Publishing)

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Bock capitals please - one character to each box

ELEKTOR ELECTRONICS 06/95

Name and address MUST be elven

FOR SALE: Shaclunan 7000 oscilloscope cam-era. Used once. Cost £ 328. Offers of around£ 200. Phone 01493 655149 (evenings)

FOR SALE: 200 5}i in double density disks,

£10 post paid. Phone Matthew on 0181 5238058 or 0973 301882.

FOR SALE: Circuit diagram of capacitancemeter for DMSt. £ 1.00 Payable by postal ormoney order or cheque to Raj K Gorkhali,5112 Basamtapur, Kathmandu, Nepal.

pleased to pass it on to otherreaders. To these readers awarning: be very careful whenheating the board-mind yourtinge's: use kitchen tongs-andconsider the fire risk. Withouthaving tried this method our-selves, it nevertheless appearsto be an excellent and simpleway of producing boards.

Readers should also notethat print layouts of projects inthe 1995 issues of this maga-zine - even those not availableready made -may be taken fromthe CD-ROM that will soonbecome available. [Editor]

950098-1overlay

missing from May

Ccfrrections and UpdatesDigital VU Meter - Part 2

(May 1995)

The illustration of the PCB inFigure 3 of this article (page 57)contains an error: the lowestpart of the figure is not the

overlay of the component lay-out; this is now given belowWe apologize for any inconve-nience this error may havecaused.

o0 00 0

CIo 0(=i10 00 0o

CI

0o 000 00 00 00 080

Satellite Finder(March 1996. p. 52-55)

In the circuit diagram,Figure 2, the + and - con-nections of the moving -coilmeter, Ml, should be trans-posed. (ralou-t)

Elektor Electronics 6/96 5966k

READERS

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112_,GirrikaR1ije MAY 1996

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DECEMBER 1994rc-viter Op swarm 343 25 6050

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Those Engineers Ltdare regular advertisers

in this magazine andwell established as

developers and sup-pliers of simulation pro-grams for various elec-

tronics applications,ranging from simple fil-ters to complex Smith

diagrams. The wonder-ful software products

supplied by ThoseEngineers certainly

deserve to be put in thelimelight by means of

this column. This monthwe look at a Spice -like

network simulation pro-gram called SpiceAge

for Windows.

Simulation of electronic circuits is notpossible without the help of a power-ful computer and some appropriatesoftware. Many programs available inthis area are based on the Spice stan-dard are, in fact, further developmentsof it. Those Engineers apparently leftthe Spice standard for what it is, andstarted to develop a simulation pro-gram from scratch. Although they ob-viously did take into account that theirproduct had to be compatible with theSpice standard, SpiceAge has a struc-ture which is markedly different fromother Spice programs.

SpiceAge for Windows meanwhilematured into version 5.015 and runsunder Windows 31 or Windows 95, asindicated by its name. A number oflevels are available, ranging from ahobby version with up to 16 nodes toa top -of -the -range version offering1,800 nodes digital simulation options,Spice primitives and multi -dimension-al polynomials. A remarkable featureof the program is its ability to importWAy (wave) files, which may beanalysed and used as a signal source.The program also allows you to sendthe output signals produced by simu-lated circuits to the soundcard in yourPC. In this way you can actually hearthe results of your design work!

As with most Windows programs,installing the product is very simple in-

deed. The real work begins once youhave the program up and running.You then have to load an existing net-work file, or enter a new network withthe aid of the built-in editor_

The editor assists you during thecircuit entry phase by offering buttonsthat bring up most commonly usedcomponents. Double-clicking on sucha button pops up a basic line with allnecessary details in the netlist, allow-ing you to enter the relevant valuesand junctions. Next, an analysis maybe run which, depending on the pro-gram level you have, enables circuitparameters like quiescent current set-ting, frequency characteristic, transientresponse and impedance response tobe computed, or a Fourier analysis tobe performed on a certain signaL

Countless options are available forthe various types of analysis. Of courseit is possible to see how the circuit re-acts to temperature variations or com-ponent tolerances. Likewise, it is easyto have the program do an X -Y plot foryou, or create a Lissajous figure_

SpiceAge has a library which com-prises most standard components. Ontop of that, it is possible to build com-plex blocks that represent a certaincomponent. A number of such blocksare available in the standard library(for example, a 555 -based timer).

The higher levels of the programfeature a Zetex-Spice libary as a stan-dard. This libary contains a wide rangeof transistor and diode models. As amatter of course, it is possible to extendthe library yourself - Spice modelsfrom semiconductor manufacturersmay be used without problems.

BELLS AND WHISTLESA number of add-on utilities are avail-able for SpiceAge for Windows. One ofthese is Modelmaker, which allowsyou to create electrical models ofopamps, transformers, attenuators andtransistors. Another utility, SuperFilte4calculates and analyzes active, passive,switched -capacitor and digital filtersbased on a number of user -specifiedparameters. We found the informationreceived from Those Engineers on thisextension interesting enough to putthe program on our list of review soft-ware for future articles. We will keepyou posted.

Finally, there is Geseca for Win-dows, a graphics entry program forSpiceAge which allows the user todraw a circuit diagram in a simplemanner, and then have the programconvert it into a netlist. Geseca wassupplied with our test version ofSpiceAge for Windows. After someexperimenting, it soon appeared that


Geseca is really invaluable becausethe alternative, compiling the netlistmanually, is pretty tedious. Potentialbuyers of SpiceAge are, therefore,well advised to consider purchasingthe Geseca extension as well - it iscertainly worth the investment.

CONCLUSIONSpiceAge for Windows offers a pletho-ra of options, and during the our brieftest period we failed to discover any-thing that could not be simulated bythe program. The wide range of avail-able signal sources, simple and com-plex models, analysis and sweep func-tions, plot features and additional util-ities all help to make this a reallycomplete package from a reputablesupplier.

In practice, we also discovered thatthe program makes good use of allfeatures offered by the modern Wm-dows environment As such, SpiceAgefor Windows sets an example formany competing products.

SpiceAge for Windows and Gesecafor Windows form a perfect combina-tion for advanced electronic simula-tion. Those Engineers have obviouslysucceeded in producing a remarkablyextensive and versatile (but still user-

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For further information, contactThose Engineers Ltd., 31 BirkbeckRoad, London NW7 4BP. Tel. (0181)906 0155, fax (0181) 906 0969. [email protected].

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meeCigeRapid digital filter modelling with links toSuperFILTER digital and analogue filtersynthesizer (optional extra)Non-linear magnetic modelling includingferromagnetic hysteresisExtended scope of Modelmaker(optional extra), the utility that synthesizesopamps, transformers, attenuators,bipolar, JFET and MOSFET transistorlibrary models*Other benefits from this mature productwhich enjoys dilligent maintenance andprofessional support include: a newmanual; new (rationalised) pin convention;faster calculating; larger circuits; tougherconvergence; helpful customer base (formutual problem solving and modelsharing); widening third party support withlinks to schematic capture and synthesisprograms (native schematic capture also available as an optionalEngineers Ltd at 31 Birkbeck Road, LONDON NW7 4BP.

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Frequently,a direct

voltage isrequired in

a circuitthat must

be free ofhum and noise,

but not regu-lated. For in-

stance, the sup-ply to an audiooutput stage mustbe able to vary with the

mains voltage and theload. Another example

is when in the work-shop a variable -ratio

transformer (variac) isto produce a well -fil-

tered direct voltage withgood loading capacityfor general purposes.

Design by W. Steimle

activepower buffer

with temperaturetemperaturemonitor

The hum emanating from an unregu-lated power supply is normally causedby too high a current drain or toosmall a reservoir capacitor. Enlargingthe capacitor is often the simplest, butnot always the most effective, way ofdealing with the problem. Hum is themanifestation of a ripple on the outputvoltage and it is best to suppress thisin an active manner,

The circuit diagram in Figure 1looks like that of a conventional seriesregulator, but has no regulating am-plifier with control comparator There-fore, the output voltage automaticallyadapts itself in accordance with the

input alternating voltage and the cur-rent through the load. Consequently,the entire hum voltage is applied to thecollector -emitter junction of darlingtontransistor T3. The advantage of such anarrangement lies in a drastic reductionof the maximum dissipated power (atthe highest mains voltage).

The lower part of the figure is atemperature monitor in which T4 is thesensor If this transistor detects an over -temperature, the monitor drcuit pullsthe base of driver T2, and thus that ofT3, to ground. This effectively cuts offthe output current, so that no morepower is dissipated.

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CIRCUITDESCRIPTION

ICI

IA1317

0110 23V5 C> 1V6 C> 2V5 C> 15V

O. 23V O. 115V Cp OV57 C)i. Os

The circuit is arranged so that thepower section (upper part of the fig-ure) and the temperature monitorhave their own rectifier. That for themonitor is the bridge rectifier, shuntedby reservoir capacitor CL, while Di and13, serve the power section.

Whereas the potential across CL hasa ripple whose level depends on theload current, the voltages across C1and C, are virtually free of ripple,since the load is small. The potentialacross C1 is about equal to the peakvalue of the alternating voltage ap-plied to the bridge rectifier. The volt-age across C, depends on the mini-mum level across CL, //ow,* becauseit is pulled down by D3 twice in eachmains period to 1.10(d) + Uo3. The po-tential across C2, 1.1,2, determines theoutput voltage, which is about

Diode D4 is necessary to ensurethat 1.6 of emitter follower T, retainsa nominal value when the potentialacross C1 is a minimum. Resistors R4and R5 ensure that the direct currentthrough T4 is not too dependent onthe current amplification of the tran-sistor and the load current.

Resistor R1 provides the chargingcurrent for C2, which must, of course,always be greater than the current

through 1D4 and the base current of T2.Since the drop across R1 increases thedissipation of T3, the resistor should bekept as small as possible. It should benot too small, however, because atlarge load currents it determines theripple on U. Its specified value is acompromise between these conflictingrequirements.

Since the base of T3 is fed from theinductive output of T2, resistor R6 isnecessary to obviate any tendency ofthe darlington to oscillate. Note that R7and C3 already tend to make the reac-tance more resistive.

Resistor R8 provides a minimumload for the circuit.

-10 ms

56C.373 - 12

Figure 1. Circuit dia-gram of the activepower buffer, includ-ing temperature moni-tor.

Resistor R5 prevents driver T, fromswitching off during the quiescentstate when T3 draws only a tiny basecurrent.

Transistor T1 draws a currentthrough 135, which is more or less di-rectly proportional to the peak humvoltage and inversely proportional tothe value of R3. This means that the

0 s2 ms/div

Figure 2. A 100 Hzhum voltage and thedirect voltage at theoutput that dependson the load current;input alternating volt-age is 20.7 V.

0500 mV/div

offset: 0,000 V10 : 1 AC

010,0 mV/div

offset: - 10,00 mV1 : 1 AC

10 ms460073 - 13


30

U0 [V] 1

UH [mV]

20

10

00 2

Figure 3. Hum voltage vs timeat the input and at the outputof the circuit.

brightness of the w increases with ris-ing load current

Diode D6 comes into action onlywhen, for instance, the circuit is beingused to charge a battery and the mainsfails. The diode then prevents too higha reverse -bias voltage at the base -emit-ter junctions of T, and T3.

The output resistance, R., of the cir-cuit depends in the first instance onthe value of C, and the peak -to -peakvalue of the hum voltage, U,00,across this capacitor:

R, 111.1(pp) flo 1/21CL,

where f is the mains frequency. Thus,if CL = 10 mF, R. = 1 Q.

The residual hum voltage at theoutput depends on load currentThis is shown diagrammatically. in Fig-ure 2, which assumes an output volt-age of 24 V. When the load current is10 A, hum suppression is about 30 dB.Note that the frequency of //11 is100 Hz. Figure 2 also shows the rela-tionship between 1.10 and to. From thisit will be seen that Ro = 0.3'11

These measurements were carriedout with the input alternating voltageheld constant at 20.7 V. In practice, thisvoltage drops somewhat owing to theinternal resistance of the transformer

Figure 3 shows the hum voltage atthe input and output. Note that thehum suppression at peak -to -peak val-ues is about 50, that is, 34 dB, or a lit-tle better than previously.

If the average direct voltage at T3 ismade equal to half the hum voltage,the dissipated power, P, is

P = Ua io = /02/ 4fC,_.

Thus, when 10 = 10 A and CL =10 InF,the power dissipation is 50 W. Notethat this value is independent of theoutput voltage.

4 6 8 10--16. I [A] wawa - 14

T PERATUREONITOR

For input voltages greater than about6 V, the circuit is not proof against sus-tained short-circuits.

It has, however, a temperaturemonitor which arranges for the load tobe disconnected when the tempera-ture rises above a preset level. Thisarrangement is particularly sensible foroccasions when, for instance, the pre-sent circuit is used in conjunction witha variac for various purposes when anunwanted overload can happen all tooeasily.

The sensor is a Type BD139 transis-tor, which should be mounted on asuitable heat sink. The sensor action iseffected by the temperature depen-dence of the base -emitter voltage,which is easily computed. The sensorand T5 form a Schmitt trigger withtemperature -dependent threshold andhysteresis.

The base -emitter voltage of T4 isheld constant by IC, at a value set withP1, at which the monitor comes intoaction when the temperature of theheat sink reaches 85-90 °C. When thathappens, T6 pulls the base of T, toground via RI, whereupon T3 is cut offand the output is open -circuited.

Bower for the monitor circuit is de-rived from a mains adaptor that mustprovide at least 18 V. It may also betaken from the + terminal of C, if thepotential across this capacitor lies be-tween 18 V and 40 V If it is higherthan 40 V, it is pulled to this value byD7. The rating of this zener diode mustbe such that the voltage at the input ofICI remains below 40 V when UQ is amaximum and above 18 V when Uo_ isa minimum.

CONSTRUCTIONThe circuit complete with temperaturemonitor is best built on the printed -cir-cuit board shown in Figure 4 (whichunfortunately is not available readymade). The two sections of the circuit

are linked on the board by the com-mon earth track at the centre and theconnection from T6 to the base of 1,via R,. If this resistor is omitted, thetwo sections are completely isolatedfrom one another (apart from the com-mon earth track).

If D7 is not used, it should be re-placed by a wire bridge.

Note that T3 and T4 are fitted at thetrack side of the board. When theboard is fitted on to the heat sink as inFigure 5, these transistors must be fit-ted on to the heat sink with the aid ofinsulating washers, screws and nuts.Two holes are provided in the boardnear 17 and T3 to allow access to therelevant screws.

Connect the - terminals from thebridge rectifier to the relevant termi-nals on the board via light -duty insu-lated circuit wire, and the + and 0 ter-minals to the relevant terminals on theboard by medium -duty insulated cir-cuit wire.

The buffered output is available atthe emitter terminal of T3.

INITINI, TESTThe circuit may be tested by checkingwhether the voltages measured at var-ious points indicated in Figure 1 coin-cide with the values shown in that fig-ure. The values were measured in theprototype with an input voltage of25 V and an open -circuit output.

SETTING UPThe temperature at which the monitorswitches off the output is set with P1.This temperature is determined by theheat resistance of the heat sink onwhich T3 is fitted. If this is 1.8 Kfor instance, and the output power is40 W the temperature of the heat sinkis 1.8 x 40 = 72 K with respect to theambient temperature. The tempera-ture of the power transistor itelf is an-other 40 K above this, so that, whenthe ambient temperature is 25 `C, itreaches 137 °C. The maximum per-missible temperature of the T1P142 is150 °C

Set P1 fully anticlockwise and loadthe circuit with a power resistor of0.5 Q, rated at 32 W and set the inputvoltage derived from a variac to such avalue that the output current is 8 A(maximum current through the T1P142is 10 A). If only a fixed alternating volt-age is available as input, the load resis-tance should be chosen to cause a cur-rent of about 8 A to flow through it.The voltage at the power transistor de-pends on the value of C1, and it is wellknown that the tolerances of elec-trolytic capacitors vary widely. There-fore, it is better to measure the collec-tor -emitter voltage and multiply this bythe current to arrive at the dissipatedpower, which should be about 40 W Atthis power, the LED should light


11=

Parts list

Resistors:R1. = 1 KO. 5 ViR2 = 39R4 = 1.2 kS2R5 = 3.9R6, R7, R18 = 47 0R8= 680 SI, 5WR9 -R11 = 4.7R12 = 820 01113 = 15 kitR14 = 220 1(0R15 = 27 kilR16 = 2.2 k.C2R17 = 22 ki.1P1 = 2.5 k0 preset

Capacitors:C1 = 100 pF. 63 V. uprightC, = 470 pF. 63 V. uprightC3 = 33 pFC4 = 47 pF. 63 V. uprightC5 = 100 nF

Semiconductors:D1 -D3 = 1N4007D4, D6 = 1N4004D5 = ic. high -efficiency. redD7 = see text

= BC327T, = BC141-16

= TIP142T4 = BD139Ts = BC337T6 = BSS101 (Siemens)

Integrated circuits:IC, = LM317LZ (National Semicon-

ductor)IC2 = LT1004-2.5 (Linear Technol-

ogy) or LM336-2.5 (National Semi-conductor)

Miscellaneous:Heat sink 1.8 K W -IInsulating washers, s,:sews ani

nuts for T3 and T4

Wait about 30 minutes, after whichthe heat sink temperature should beabout 72 K higher than the ambienttemperature (as computed earlier). Itis, of course, better to measure thetemperature, but this presupposes thata suitable thermometer is available.

When the stated temperature hasbeen reached, turn the wiper of P1carefully clockwise until the LED lightsbrightest. The monitor then comes intoaction: the current is cut off and thetemperature drops.

Wait a while for the temperature toreach a lower value, when the moni-tor should be deactivated, and an out-put current flows again.

Increase the power dissipationslightly and repeat the foregoing. Inthis way, average cut-off and switch -on temperatures will be set.

1960E173)


Figure 4. Theprinted -circuitboard for the ac-tive power buffer,including tempera-ture monitor.

Figure 5. Photo-graph of the com-pleted prototype.

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