Everyday Practical Electronics Online 02 05 May 2000

8/10/2019 Everyday Practical Electronics Online 02 05 May 2000

http://slidepdf.com/reader/full/everyday-practical-electronics-online-02-05-may-2000 1/90

Copyright © 1999 Wimborne Publishing Ltd and Maxfield & Montrose Interactive Inc

EPE Online, Febuary 1999 - www.epemag.com - XXX

Volume 2 Issue 5

May 2000

Click Here DownL

http://2a38106e.picturesetc.net/





EPE Online, May 2000 - www.epemag.com - 334

Copyright ©©©© 2000, Wimborne Publishing Ltd

and Maxfield & Montrose Interactive Inc.,

PO Box 857, Madison, Alabama 35758, USA

All rights reserved.

WARNING! The materials and works contained within EPE Online — which are made available

by Wimborne Publishing Ltd and Maxfield & Montrose Interactive Inc — arecopyrighted. You are permitted to download locally these materials and works and to

make one (1) hard copy of such materials and works for your personal use. Internationalcopyright laws, however, prohibit any further copying or reproduction of such materialsand works, or any republication of any kind.

Maxfield & Montrose Interactive Inc and Wimborne Publishing Ltd have used their best efforts in preparing these materials and works. However, Maxfield & MontroseInteractive Inc and Wimborne Publishing Ltd make no warranties of any kind, expressedor implied, with regard to the documentation or data contained herein, and specificallydisclaim, without limitation, any implied warranties of merchantability and fitness for aparticular purpose. Because of possible variances in the quality and condition of materials and workmanship used by readers, EPE Online, its publishers and agents

disclaim any responsibility for the safe and proper functioning of reader-constructedprojects based on or from information published in these materials and works.

In no event shall Maxfield & Montrose Interactive Inc or Wimborne Publishing Ltd beresponsible or liable for any loss of profit or any other commercial damages, includingbut not limited to special, incidental, consequential, or any other damages in connectionwith or arising out of furnishing, performance, or use of these materials and works.

Click Here DownL





Unit 14 Sunningdale, BISHOPS STORTFORD, Herts. CM23 2PA

ADD £2.00 P&P to all orders (or 1st Class Recorded £4, Next day(Insured £250) £7, Europe £4.00, Rest of World £6.00). We accept allmajor credit cards. Make cheques/PO's payable to Quasar Electronics.Prices include 17.5% VAT. MAIL ORDER ONLYFREE CATALOGUE with order or send 2 x 1st class stamps(refundable) for details of over 150 kits & publications.

FACTORPUBLICATIONS

SPEED CONTROLLER for any common DC motor upto 100V/5A. Pulse width modulation gives maximumtorque at all speeds.5-15VDC. Box provided. 3067KT£10.95 3 x 8 CHANNEL IR RELAY BOARD Control eight 12V/1Arelays by Infra Red (IR) remote control over a 20m range insunlight.6 relays turn on only, the other 2 toggle on/off. 3 oper-ation ranges determined by jumpers. Transmitter case & allcomponents provided. Receiver PCB 76x89mm. 3072KT£44.95 PC CONTROLLED RELAY BOARDConvert any 286 upward PC into a dedicatedautomatic controller to independently turn on/offup to eight lights, motors & other devices aroundthe home, office, laboratory or factory using 8240VAC/12A onboard relays. DOS utilities, sampletest program, full-featured Windows utility & allcomponents (except cable) provided. 12VDC.PCB70x200mm. 3074KT £29.95 2 CHANNEL UHF RELAY SWITCH Contains thesame transmitter/receiver pair as 30A15 below plusthe components and PCB to control two240VAC/10A relays (also supplied). Ultra brightLEDs used to indicate relay status.3082KT £26.95TRANSMITTER RECEIVER PAIR 2-button keyfobstyle 300-375MHz Tx with 30m range. Receiverencoder module with matched decoder IC.Components must be built into a circuit like kit 3082above. 30A15 £13.95 TELEPHONE LINE RELAY SWITCH Turn on/off 4relays over your phone line from anywhere in the world. 4-digit security code. Line protection circuitry built-in (non-approved). PCB 78x105mm. 3086KT £39.95 PC DATA ACQUISITION/CONTROL UNIT Use yourPC to monitor physical variables (e.g. pressure, tem-perature, light, weight, switch state, movement, relays,etc.), process the information & use results to controlphysical devices like motors, sirens, relays, servo &stepper motors. Inputs: 16 digital & 11 analogue.Outputs: 8 digital & 1 analogue.Plastic case with print-ed front/rear panels, software utilities, programmingexamples & all components (except sensors & cable)provided.12VDC. 3093KT £79.95 PIC 16C71 FOUR SERVO MOTOR DRIVERSimultaneously control up to 4 servo motors. Software &all components (except servos/control pots) supplied.5VDC.PCB 50x70mm. 3102KT £14.95

PC SERIAL PORT ISOLATED I/O BOARDProvides eight 240VAC/10A relay outputs & 4 opti-cally isolated inputs.Designed for use in various con-trol & sensing applications e.g.load switching, exter-nal switch input sensing, contact closure & externalvoltage sensing.Controlled via serial port & a termi-nal emulator program (built into Windows). Can beused with ANY computer/operating system. Plasticcase with printed front/rear panels & all components(except cable) provided. 3108KT £49.95 UNIPOLAR STEPPER MOTOR DRIVER for any5/6/8 lead motor. Fast/slow & single step rates.Direction control & on/off switch. Wave, 2-phase &half-wave step modes. 4 LED indicators. PCB50x65mm. 3109KT £14.95 PC CONTROLLED STEPPER MOTOR DRIVERControl two unipolar stepper motors (3A max.each)via PC printer port. Wave, 2-phase & half-wave stepmodes. Software accepts 4 digital inputs from exter-nal switches & will single step motors. PCB fits in D-shell case provided. 3113KT £16.95 12-BIT PC DATA ACQUISITION/CONTROL UNITSimilar to kit 3093 above but uses a 12 bit Analogue-

to-Digital Converter (ADC) with internal analogue mul-tiplexor. Reads 8 single ended channels or 4 differen-tial inputs or a mixture of both. Analogue inputs read 0-4V. Four TTL/CMOS compatible digital input/outputs.ADC conversion time <10uS. Software (C, QB & Win),extended D shell case & all components (except sen-sors & cable) provided.3118KT £47.95 LIQUID LEVEL SENSOR/RAIN ALARM Will indi-cate fluid levels or simply the presence of fluid. Relayoutput to control a pump to add/remove water when itreaches a certain level.1080KT £6.95 UNIVERSAL TIMER Seven crystal controlled tim-ing operations in steps of 0.1s from 0.1-6553.6s or 1second steps from 0.1-65536s. Allows 4 signal inputtypes from push button to electrically isolated volt-age switching sources. On-board relay will switch240V/5A. Box, software & all components provided.PCB 56 x 97mm.3054KT £24.95

STEREO VU METER shows peak music powerusing 2 rows of 10 LED’s (mixed green & red)moving bar display. 0-30db.3089KT £10.95AM RADIO KIT 1 Tuned Radio Frequency front-end, single chip AM radio IC & 2 stages of audioamplification. All components inc.speaker provid-ed. PCB 32x102mm. 3063KT £9.95 DRILL SPEED CONTROLLER Adjust the speedof your electric drill according to the job at hand.Suitable for 240V ACmains powered drills up to700W power. PCB: 48mm x 65mm. Box provided.6074KT £17.90 3 INPUT MONO MIXER Independent level con-trol for each input and separate bass/treble controls.Input sensitivity: 240mV. 18V DC. PCB: 60mm x185mm 1052KT £16.95 ELECTRONIC SIREN 5 Watt. Impressive 5Wpower output. Suitable for alarm systems, car,motorbikes, etc. Output frequency 1·2kHz. 6-12VDC. PCB: 37mm x 71mm. Siren not provided1003KT £5.95

NEGATIVE\POSITIVE ION GENERATORStandard Cockcroft-Walton multiplier circuit. Mainsvoltage experience required. 3057KT £9.95

LED DICE Classic intro to electronics & circuitanalysis. 7 LED’s simulate dice roll, slow down & landon a number at random.555 IC circuit.3003KT £7.95 STAIRWAY TO HEAVEN Tests hand-eye co-ordination.Press switch when green segment of LED lights to climbthe stairway - miss & start again! Good intro to severalbasic circuits. 3005KT £7.95 ROULETTE LED ‘Ball’ spins round the wheel,slows down & drops into a slot.10 LED’s. Good introto CMOS decade counters & Op-Amps. 3006KT£9.95DUAL LED DICE PIC 16C54 circuit performs sim-ilar function to 3003KT above but two dice. Goodintro to micro-controllers.3071KT £11.95 9V XENON TUBE FLASHER Transformer circuitsteps up 9V battery to flash a 25mm Xenon tube.Adjustable flash rate (0·25-2 Sec’s).3022KT £10.95 LED FLASHER 1 5 ultra bright red LED’s flash in7 selectable patterns. 3037MKT £4.50 LED FLASHER 2 Similar to above but flash insequence or randomly. Ideal for model railways.3052MKT £4.50 INTRODUCTION TO PIC PROGRAMMING.

Learn programming from scratch. Programminghardware, a P16F84 chip and a two-part, practical,hands-on tutorial series are provided. 3081KT£21.95 SERIAL PIC PROGRAMMER for all 8/18/28/40pin DIP serial programmed PICs. 3rd party softwaresupplied expires after 21 days (costs US$25 to reg-ister). 3096KT £14.95 ‘PICALL’ SERIAL & PARALLEL PIC PRO-GRAMMER for all 8/18/28/40 pin DIP parallel ANDserial PICs. Includes fully functional & registeredsoftware (DOS, W3.1, W95/8).3117KT £54.95ATMEL 89Cx051 PROGRAMMER Simple-to-useyet powerful programmer for the Atmel 89C1051,89C2051 & 89C4051 uC’s. Programmer does NOTrequire special software other than a terminal emu-lator program (built into Windows). Can be used withANY computer/operating system.3121KT £34.95

3V/1·5V TO 9V BATTERY CONVERTER Replaceexpensive 9V batteries with economic 1.5V batter-ies. IC based circuit steps up 1 or 2 ‘AA’batteries togive 9V/18mA. 3035KT £4.95 STABILISED POWER SUPPLY 3-30V/2.5A Idealfor hobbyist & professional laboratory.Very reliable& versatile design at an extremely reasonable price.Short circuit protection. Variable DC voltages (3-30V). Rated output 2.5 Amps. Large heatsink sup-plied.You just supply a 24VAC/3A transformer.PCB55x112mm. Mains operation. 1007KT £17.50.Custom Designed Box 2007 £34.95 STABILISED POWER SUPPLY 2-30V/5A As kit1007 above but rated at 5Amp. Requires a24VAC/5A transformer. 1096KT £29.95. CustomDesigned Box 2096 £34.95 RFI POWER SUPPLY Designed to power RFtransmitters/receivers. Blocks high frequencies &eliminates problems like noise, overheating, stand-ing waves, e tc . Output: 12-14VDC/3A.Thermal/short circuit protection & electronic stabili-sation. You just supply a 18VAC/3A transformer.PCB 72x82mm. 1171KT £24.95MOTORBIKE ALARM Uses a reliable vibration sen-sor (adjustable sensitivity) to detect movement of thebike to trigger the alarm & switch the output relay towhich a siren, bikes horn, indicators or other warningdevice can be attached. Auto-reset. 6-12VDC. PCB57x64mm. 1011KT £11.95 Box £5.95 CAR ALARM SYSTEM Protect your car fromtheft. Features vibration sensor, courtesy/boot lightvoltage drop sensor and bonnet/boot earth switchsensor. Entry/exit delays, auto-reset and adjustablealarm duration. 6-12VDC. PCB: 47mm x 55mm1019KT £11.95 Box £6.50

LIGHT ALARM Protect your valuables. Alarmsounds if circuit detects smallest amount of light.

Place in cash box etc. 3008KT £4.50 PIEZO SCREAMER 110dB of ear piercingnoise. Fits in box with 2 x 35mm piezo elementsbuilt into their own resonant cavity. Use as analarm siren or just for fun! 6-9VDC.3015KT £9.95 COMBINATION LOCK Versatile electronic lockcomprising main circuit & separate keypad forremote opening of lock. Relay supplied. 3029KT£9.95 ULTRASONIC MOVEMENT DETECTOR Crystallocked detector frequency for stability & reliability. PCB75x40mm houses all components. 4-7m range.Adjustable sensitivity. Output will drive externalrelay/circuits. 9VDC.3049KT £12.95PIR DETECTOR MODULE 3-lead assembled unit just 25x35mm as used in commercial burglar alarmsystems. 3076KT £7.95 INFRARED SECURITY BEAM When the invisi-ble IR beam is broken a relay is tripped that can beused to sound a bell or alarm. 25 metre range.Mains rated relays provided. 12VDC operation.3130KT £11.95 FUNCTION GENERATOR Quad Op-Amp oscilla-tor & wave shaper circuit generates audio rangesquare waves (6Hz-6KHz), triangle & pseudo sineoutputs. 9VDC.3023KT £3.95 LOGIC PROBE tests CMOS & TTL circuits &detects fast pulses. Visual & audio indication oflogic state. Full instructions supplied. 3024KT£6.95 SQUARE WAVE OSCILLATOR Generates

square waves at 6 preset frequencies in factors of10 from 1Hz-100KHz. Visual output indicator. 5-18VDC.Box provided. 3111KT £7.95 PC DRIVEN POCKET SAMPLER/DATA LOG-GER Analogue voltage sampler records voltagesup to 2V or 20V over periods from milli-seconds tomonths. Can also be used as a simple digitalscope to examine audio & other signals up toabout 5KHz. Software & D-shell case provided.3112KT £19.95 20 MHz FUNCTION GENERATOR Square, tri-angular and sine waveform up to 20MHz over 3ranges using ‘coarse’ and ‘fine’frequency adjust-ment controls.Adjustable output from 0-2V p-p. ATTL output is also provided for connection to afrequency meter. Uses MAX038 IC. Plastic casewith printed front/rear panels & all componentsprovided.7-12VAC.3101KT £49.95

X

338 Everyday Practical Electronics, May 2000

SURVEILLANCEHigh performance surveillance bugs.Room transmitters supplied with sensitive electret microphone & battery holder/clip.All transmitters can be received on an ordinary VHF/FM radio between 88-108MHz.Available in Kit Form (KT) or Assembled & Tested (AS).

ROOM SURV EILLANCEMTX - MINIATURE 3V TRANSMITTEREasy to build & guaranteed to tr ansmit 300m @ 3V.Long bat-tery life. 3-5V operation.Only 45x18mm. 3007KT £5.95AS3007 £10.95MRTX - MINIATURE 9V TRANSMITTEROur best selling bug.Super sensi tive, high power - 500m range@ 9V (over 1km with 18V supply and better aerial). 45x19mm.3018KT £6.95 AS3018 £11.95HPTX - HIGH POWER TRANSMITTERHigh performance, 2 stagetransmitter gives greaterstability & higher quality

reception. 1000m range 6-12V DC operation. Size70x15mm. 3032KT £8.95AS3032 £17.95MMTX - MICRO-MINIATURE 9V TRANSMITTERThe ultimate bug for its size, performance and price. Just15x25mm. 500m range @ 9V. Good stability.6- 18V operation.3051KT £7.95 AS3051 £13.95 VTX - VOICE ACTIVATED TRANSMITTEROperates only when sounds detected. Low standby current.Variable trigger sensitivity. 500m range. Peaking circuit sup-plied for maximum RF output.On/off switch. 6V operation.Only63x38mm. 3028KT £9.95 AS3028 £22.95HARD-WIRED BUG/TWO STATION INTERCOMEach station has its own amplifier, speaker and mic. Can beset up as either a hard-wired bug or two-station intercom.10mx 2-core cable supplied. 9V operation. 3021KT £13.95 (kitform only) TRVS - TAPE RECORDER VOX SWITCHUsed to automatically operate a tape recorder (not supplied)via its REMOTE socket when sounds are detected. All conver-sations recorded. Adjustable sensitivity & turn-off delay.115x19mm. 3013KT £7.95 AS3013 £19.95

TELEPHONE SURVEILLANCE MTTX - MINIATURE TELEPHONE TRANSMITTERAttaches anywhere to phone line. Transmits only when phoneis used! Tune-in your radio and hear both parties. 300m range.Uses line as aerial & power source. 20x45mm. 3016KT £7.95AS3016 £13.95 TRI - TELEPHONE RECORDING INTERFACEAutomatically record all conversations. Connects betweenphone line & tape recorder (not supplied). Operates recorderswith 1.5-12V battery systems. Powered from line. 50x33mm.3033KT £7.95 AS3033 £16.95 TPA - TELEPHONE PICK-UP AMPLIFIER/WIRELESSPHONE BUG

Place pick-up coil on the phone line or near phone earpieceand hear both sides of the conversation. 3055KT £10.95AS3055 £19.95 1 WATT FM TR ANSMITTER Easy to construct.Delivers acrisp, clear signal. Two-stage circuit. Kit includes microphoneand requires a simple open dipole aerial. 8-30VDC. PCB42x45mm. 1009KT £14.95 4 WATT FM TRANSMITTER Comprises three RFstages and an audio preamplifier stage. Piezoelectricmicrophone supplied or you can use a separate pream-plifier circuit.Antenna can be an open dipole or GroundPlane.Ideal project for those who wish to get started inthe fascinating world of FM broadcasting and want agood basic circuit to experiment with. 12-18VDC.PCB44x146mm.1028KT. £23.9515 WATT FM TRANSMITTER (PRE-ASSEMBLED &TESTED) Four transistor based stages with Philips BLY88 in final stage. 15 Watts RF power on the air. 88-108MHz.Accepts open dipole, Ground Plane, 5/8, J, orYAGI configuration antennas. 12-18VDC. PCB70x220mm.SWS meter needed for alignment. 1021KT£69.95 SIMILAR TO ABOVE BUT 25W Output. 1028KT £79.95

30-in-ONEElectronic Projects LabBAR

GAIN

BU Y!!

Great introduction to electronics.Ideal for the budding elec-tronics expert! Build a radio, burglar alarm, water detector,

morse code practice circuit, simple computer circuits, and

much more! NO soldering, tools or previous electronicsknowledge required.Circuits can be built and unassembled

repeatedly. Comprehensive 68-page manual with explana-tions, schematics and assembly diagrams. Suitable for age

10+. Excellent for schools. Requires 2 x AA batteries.ONLY £14.95 (phone for bulk discounts).

PROJECT KITSOUR PROJECT KITS COME COMPLETE WITH ALL COMPONENTS,

HIGH QUALITY PCBs, DETAILED ASSEMBLY/OPERATING INSTRUCTIONS

2 x 25W CAR BOOSTER AMPLIFIER Connects tothe output of an existing car stereo cassette player,CD player or radio. Heatsinks provided. PCB76x75mm. 1046KT. £24.95 1W+1W STEREO AMPLIFIER MODULE UsesSamsung KA2209 IC (equivalent to the TDA2822)designed for portable cassette players & radios. 1.8-9VDC.PCB 35x50mm. 3087KT £4.25 10W+10W STEREO AMPLIFIER MODULE UsesTDA2009 class audio power amp IC designed for highquality stereo applications.8-28VDC.PCB 45x80mm.3088KT £9.95 18W BTL AUDIO AMPLIFIER MODULE Low volt-age, high power mono 18W BTL amp using HA13118IC. Delivers 14W into 4 Ohm’s (1% THD) with 13.2Vsupply. Thermal/surge protection. 8-18VDC.Heatsinkprovided. PCB 57x55mm. 3105KT £8.95 3-CHANNEL WIRELESS LIGHT MODULATORNo electrical connection with amplifier. Light modula-tion achieved via a sensitive electret microphone.Separate sensitivity control per channel. Power hand-ing 400W/channel. PCB 54x112mm.Mains powered.Box provided. 6014KT £24.90 12 RUNNING LIGHT EFFECT Exciting 12 LEDlight effect ideal for parties, discos, shop-windows &eye-catching signs. PCB design allows replacementof LEDs with 220V bulbs by inserting 3 TRIACs.Adjustable rotation speed & direction. PCB54x112mm. 1026KT £16.95; BOX (for mains opera-tion) 2026KT £8.50 DISCO STROBE LIGHT Probably the most excit-ing of all light effects. Very bright strobe tube.Adjustable strobe frequency:1-60Hz.Mains powered.PCB: 60x68mm. Box provided. 6037KT £29.90 SOUND EFFECTS GENERATOR Easy to build.Create an almost infinite variety of interesting/unusu-al sound effects from birds chirping to sirens.9VDC.PCB 54x85mm. 1045KT £8.95 ROBOT VOICE EFFECT Make your voice soundsimilar to a robot or Darlek. Great fun for discos,school plays, theatre productions, radio stations &playing jokes on your friends when answering thephone! PCB 42x71mm. 1131KT £8.95 AUDIO TO LIGHT MODULATOR Controls intensi-ty of one or more lights in response to an audio input.Safe, modern opto-coupler design. Mains voltageexperience required. 3012KT £7.95 MUSIC BOX Activated by light.Plays 8 Christmassongs and 5 other tunes. 3104KT £6.95 20 SECOND VOICE RECORDER Uses non-volatile memory - no battery backup needed.Record/replay messages over & over. Playback asrequired to greet customers etc. Volume control &built-in mic.6VDC. PCB 50x73mm.3131KT £11.95 TRAIN SOUNDS 4 selectable sounds : whistleblowing, level crossing bell, ‘clickety-clack’ & 4 insequence. SG01M £4.95 ANIMAL SOUNDS Cat, dog, chicken & cow.Ideal

for kids farmyard toys & schools. SG10M £4.50 3 1/2 DIGIT LED PANEL METER Use for basicvoltage/current displays or customise to measuretemperature, light, weight, movement, sound lev-els, etc. with appropriate sensors (not supplied).Various input circuit designs provided. 3061KT£12.95 IR REMOTE TOGGLE SWITCH Use any TV/VCRremote control unit to switch onboard 12V/1A relayon/off. 3058KT £9.95

Full details of all X-FACTOR PUBLICATIONS can be found in our catalogue.N.B. Minimum order charge for reports and plans is £5.00 PLUS normal P.&P.

SUPER-EAR LISTENING DEVICE Complete plans tobuild your own parabolic dish microphone.Listen to distantvoices and sounds through open windows and even walls!Made from readily available parts. R002 £3.50TELEPHONE BUG PLANS Build you own micro-beetletelephone bug. Suitable for any phone.Transmits over 250metres - more with good receiver. Made from easy toobtain, cheap components.R006 £2.50

LOCKS - How they work and how to pick them. This factfilled report will teach you more about locks and the art oflock picking than many books we have seen at 4 times theprice.Packed with information and illustrations. R008 £3.50 RADIO & TV JOKER PLANSWe show you how to build three different circuits for dis-rupting TV picture and sound plus FM radio! May upsetyour neighbours & the authorities!! DISCRETIONREQUIRED. R017 £3.50 INFINITY TRANSMITTER PLANS Complete plans forbuilding the famous Infinity Transmitter. Once installed onthe target phone, device acts like a room bug.Just call thetarget phone & activate the unit to hear all room sounds.Great for home/office security! R019 £3.50THE ETHER BOX CALL INTERCEPTOR PLANSGrabstelephone calls out of thin air! No need to wire-in a phonebug. Simply place this device near the phone lines to hearthe conversations taking place! R025 £3.00 CASH CREATOR BUSINESS REPORTS Need ideasfor making some cash? Well this could be just what youneed! You get 40 reports (approx. 800 pages) on floppydisk that give you information on setting up different busi-nesses.You also get valuable reproduction and duplicationrights so that you can sell the manuals as you like. R030£7.50

Click Here DownL

http://www.quasarelectronics.com/



http://www.quasarelectronics.com/




EPE Online, February 1999 - www.epemag.com - XXX Copyright © 1999 Wimborne Publishing Ltd and Maxfield & Montrose Interactive Inc


PROJECTS AND CIRCUITS

TECHNOLOGY TIMELINES - Part 4 - by Clive Maxfield and Alvin Brown Who, what, where and when - the facinating story of how technology

developed in the last millennium373

CIRCUIT SURGERY - by Alan Winstanley and Ian Bell Opamps - outputs and short-circuit protection; Battery Flattery.

390

REGULARS AND SERVICES

NEWS - Barry Fox highlights technology’s leading edge. Plus everyday

news from the world of electronics.

408

READOUT - John Becker addresses general points arising. 412

SHOPTALK - with David Barrington The essential guide to component buying

for EPE Online projects.417

EDITORIAL 336

SERIES AND FEATURES

INGENUITY UNLIMITED - hosted by Alan Winstanley Sensitive Hall Effect Switch; Infra-red Remote Tester;Experimenter’s Power Supply

346

NET WORK - THE INTERNET PAGE surfed by Alan Winstanley Google Box; Free for All; Under the Surf; Looking Ahead

371

PIR LIGHT CHECKER - by Terry de Vaux-Balbirnie Be trigger happy with your outdoor security light system! 364

VERSATILE MIC/AUDIO PREAMPLIFIER - by Raymond HaighNew chip SSM2166 offers AGC compression, limiting and noise reduction 338

MULTI_CHANNEL TRANSMISSION SYSTEM

part 1 - by Andy Flind An 8 to 16-channel 2-wire signalling link with optional interface

355

LOW-COST CAPACITANCE METER - by Robert Penfold An easy-to-build Starter Project that adds a userful tool to your workshop

349

NEW TECHNOLOGY UPDATE - by Ian PooleLower operating voltages speed microprocessor rates, but heat dissipationbecomes more of a problem

387

PRACTICALLY SPEAKING - by Robert Penfold A novice’s guide to using stripboard

TEACH-IN 2000 - Part 7 - by John Becker Essential info for the electronics novice, with breadboard experimentsand interactive computer simulations

393

404

Click Here DownL






EPE Online, May 2000 - www.epemag.com - XXX

CHIPPER

Every so often a new chip comes along that looks like it will be very popular for a wide rangeof applications. Just such a chip forms the basis of our main cover subject this month – theVersatile Microphone/Audio Preamplifier. The problem with specialized chips of this nature isthat sometimes they don’t stay in production for a long period. This can obviously causeheadaches for hobbyists, who seem to like to build projects years after they have beenpublished. This is why we advise readers to check that all components are still available beforecommencing any project in a back dated issue. Whilst it is sometimes possible to find old chips(particularly via the internet) they are often highly priced and obviously supplies do eventually getexhausted.

We do, however, have high hopes that this chip will be around for some time as it appears tohave been designed to cover a very wide range of applications, including use for microphone

inputs to PCs. This fact alone will ensure high demand and therefore longevity, should it betaken up by the computer manufacturers. Let’s hope it is. However, that in itself does not entirelyget us out of the woods – the PC makers will no doubt use a surface mount device which doesnot necessarily guarantee continuing availability of the DIL version. Once development has takenplace, the industrial requirement for DIL versions often falls dramatically so they can sometimesbe discontinued.

NO WAY

We suppose the answer is to build it now and hope for the best. There seems to be no wayof knowing which chips will hang around and also no way of knowing of all the chips that havebeen discontinued. We usually only find this out when readers ring us with buying problems.Thankfully we can often help them out, but we have an ever-increasing list of past projects thatare no longer viable because of obsolete components. Unfortunately it is not a problem weexpect will improve as time goes by.


Click Here DownL






SOLO

Ω

Ω Ω Ω Ω Ω Ω Ω Ω

Click Here DownL







CANUTE TIDE PREDICTOR

For several years the author experimented with writing computer software intended to produce results thatmatched those given in published tide tables, and which could ultimately form the basis for a low-power micro-processor controlled tide predictor (long before PICs came along).

Eventually he became aware that official tide tables are compiled not just according to the geometries of the Earth-Moon-Sun system, but also in relation to local data compiled over generations. There was no hope,therefore, of developing a simple system that could match standard tide-table accuracy.

However, most people do not need the accuracy of official tide tables. All they might be interest in, for ex-ample, is whether it is better to go to the beach in the morning or afternoon in order to find the tide at the pre-ferred state of rise or fall.

That is what the Canute Tide Predictor is aimed at achieving – to show on a liquid crystal display(LDC) atide-state bar-graph and high-low tide times accurate to within about an hour. The use of a PIC16F876 micro-controller has allowed a very simple unit to be designed.

Anyone who loves the sea, sandy beaches, or rocky shore lines will find this design a useful guide whenconsidering a quick trip to the coast.

TECHNOLOGY TIMELINES – THE FUTURE

It’s been interesting and fun looking back over the last 100 years or so to see how we got where we are –quite a staggered path, with all sorts of odd developments coming together to produce major forward steps intechnology. Finally we get to peer into the future, it ’s not quite as exact an art as looking back, but Max and Alvin are taking a stab at it from their starting point at the forefront of technology in the USA. We may not needto wait long to see if what they predict actually happens with the rate of development of new technology.

ATMOSPHERIC ELECTRICITY

The ionized layers of the atmosphere extend from about 40km to 200km (25 to 125 miles) above the Earth.This ionization is caused by the “Solar Wind” passing the Earth and leaves the upper atmosphere positivelycharged.

There is thus an electric field between the upper atmosphere and the Earth and, given suitable instruments,this field can be detected as it results in a miniscule current through the atmosphere.

A potential of around 100 volts is often present just one meter off the ground. In other words, there may bea potential of 200 volts or more between your nose and toes! Of course, nobody gets electrocuted because theresistance of the air is so high that only a very tiny current is present. And this is why the actual values are gen-erally considered to be so difficult to measure. But in fact they can be measured quite easily and we will showyou how.

Click Here DownL





MAIL ORDER ONLY • CALLERS BY APPOINTMENT

135 Hunter Street, Burton-on-Trent, Staffs. DE14 2STTel 01283 565435 Fax 546932http://www.magenta2000.co.ukE-mail: [email protected]

All Prices include V.A.T. Add £3.00 per order p&p. £6.99 next day

MOSFET MkII VARIABLE BENCHPOWER SUPPLY 0-25V 2·5A.Based on our Mk1 designand prese rvi ng al l t he

features, but now withswitching pre-regulator formuch higher efficiency. Panelmeters indicate Volts andAmps. Fully variable down tozero. Toroidal mains trans-

former. Kit includes punchedand printed case and allparts. As featured in April1994 EPE. An essential pieceof equipment.

12V EPROM ERASERA safe low cost eraser for up to 4 EPROMS at a timein less than 20 minutes. Operates from a 12V supply(400mA). Used extensively for mobile work – up-dating equipment in the field etc. Also in educa-tional situations where mains supplies are not al-lowed. Safety interlock prevents contact with UV.

KIT 790............................£29.90

PORTABLE ULTRASONICPEsT SCARERA powerful 23kHz ultrasound generator ina compact hand-held case. MOSFET outputdrives a special sealed transducer with in-tense pulses via a special tuned transformer.Sweeping frequency output is designed togive maximum output without any specialsetting up.

KIT 842...................... ..£22.56

TENS UNIT DUAL OUTPUT TENS UNITAs featured in March ’97 issue.Magenta have prepared a FULL KIT for thisexcellent new project. All components, PCB,hardware and electrodes are included.Designed for simple assembly and testing andproviding high level dual output drive.

KIT 866.... Full kit including four electrodes £32.90

SEE ICEBREAK ADPAGE 367

ULTRASONIC PEsT SCARERKeep pets/pests away fromnewly sown areas, fruit ,vegetable and flower beds,children’s play areas, patiosetc. This project producesintense pulses of ultrasoundwhich deter visiting animals.

• KIT INCLUDES ALLCOMPONENTS, PCB & CASE

• EFFICIENT 100VTRANSDUCER OUTPUT

• COMPLETELY INAUDIBLE

TO HUMANSKIT 812...............................................£15.00

• UP TO 4 METRESRANGE

• LOW CURRENT DRAIN

1000V & 500V INSULATIONTESTER

Superb new design. Regulatedoutput, efficient circuit. Dual-scale meter, compact case.Reads up to 200 Megohms.Kit includes wound coil, cut-outcase, meter scale, PCB & ALLcomponents.

KIT 848.................. .£32.95

EPE MICROCONTROLLERP.I. TREASURE HUNTER

The latest MAGENTA DESIGN – highlystable & sensitive – with I.C. controlof all timing functions and advancedpulse separation techniques.

• High stabilitydrift cancelling

• Easy to build& use

• No groundeffect, worksin seawater

• Detects gold,silver, ferrous &non-ferrousmetals

• Efficient quartz controlledmicrocontroller pulse generation.

• Full kit with headphones & allhardware

KIT 847......................£63.95

SPACEWRITERAn innovative and excitingproject. Wave the wand throughthe air and your message appears.Programmable to hold any messageup to 16 digits long. Comes pre-loadedwith ‘‘MERRY XMAS’’. Kit includesPCB, all components & tube plusinstructions for message loading.

KIT 849.......................£16.99WINDICATORA novel wind speed indicator with LED readout. Kit comescomplete with sensor cups, and weatherproof sensinghead. Mains power unit £5.99 extra.

KIT 856...........................................£28.00

328 Everyday Practical Electronics May 2000

SUPER BATDETECTOR

1 WATT O/P, BUILT IN

SPEAKER, COMPACT CASE

20kHz-140kHz

NEW DESIGN WITH 40kHz MIC.A new circuit using a ‘full bridge’ audioamplifier i.c., internalspeaker, and head-phone/tape socket. Thelatest sensitive transducer,and ‘double balanced mixer’

give a stable, high peformancesuperheterodyne design.

KIT 861.......................£24.99ALSO AVAILABLE Built & Tested ... .£39.99

MICRO PEsTSCAREROur latest design – The ultimatescarer for the garden. Usesspecial microchip to give randomdelay and pulse time. Easy tobuild reliable circuit. Keeps pets/ pests away from newly sown areas,play areas, etc. Uses power sourcefrom 9 to 24 volts.

• RANDOM PULSES• HIGH POWER• DUAL OPTION

K I T 8 6 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . £ 1 9 . 9 9K I T + S L AV E U N I T . . . . . . . . . . . . . . . . . . . £ 3 2 . 5 0

Plug-in power supply £4.99

EPEPROJECT

PICsProgrammed PICs for

all* EPE Projects16C84/16F84/16C71

All £5.90 eachPIC16F877 now in stock

£10 inc. VAT & postage(*some projects are

copyright)

PIC PIPE DESCALER• SIMPLE TO BUILD

• HIGH POWER OUTPUT• AUDIO & VISUAL MONITORING

An affordable circuit which sweepsthe incoming water supply withvariable frequency electromagneticsignals. May reduce scale formation,dissolve existing scale and improvelathering ability by altering the waysalts in the water behave.Kit includes case, P.C.B, couplingcoil and all components.High coil current ensures maximumeffect. L.E.D. monitor

KIT 868 .........£22.95 POWER UNIT.........£3.99

• SWEPT

FREQUENCY

Kit No. 845.................£64.95

DC Motor/Gearboxes Our Popular and Versatile DC motor/Gearbox sets.Ideal for Models, Robots,Buggies etc. 1·5 to 4·5V Multi ratio gearbox gives wide range of speeds.

LARGE TYPE – MGL £6.95

SMALL – MGS – £4.77

Stepping Motors

MD38...Mini 48 step...£8.65MD35...Std 48 step...£9.99MD200...200 step...£12.99MD24...Large 200 step...£22.95

Set of4 spare

electrodes£6.50

EPE

TEACH-IN 2000 Full set of top quality NEW

components for this educationalseries. All parts as specified byEPE . Kit includes breadboard,wire, croc clips, pins and allcomponents for experiments, aslisted in Introduction to Part 1.*Batteries and tools not included.

TEACH-IN 2000 –

KIT 879£44.95

MULTIMETER£14.45

EE213

Click Here DownL

http://www.magenta2000.co.uk/








Everyday Practical Electronics May 2000 329

DEVELOPMENT AND

TRAINING KIT

Mini-Lab & Micro Lab

Electronics Teach-In 7As featured in EPE and nowpublished as Teach-In 7. Allpartsare supplied by Magenta.Teach-In 7 is £3.95 from us orEPE

Full Mini Lab Kit – £119.95 –Power supply extra – £22.55Full Micro Lab Kit – £155.95Built Micro Lab – £189.95

SIMPLE PIC PROGRAMMER

Based on February ’96 EPE.

Magenta designed PCB and kit.PCB with ‘Reset’ switch, Program switch, 5V regulator andtest L.E.D.s, and connection points for access to all A and Bport pins.

PIC16C84 LCD DISPLAY DRIVER

INCLUDES 1-PIC16F84WITH DEMO PROGRAMSOFTWARE DISK, PCB,INSTRUCTIONS AND16-CHARACTER 2-LINE

LCD DISPLAY

Another super PIC project from Magenta. Supplied with PCB,industry standard 2-LINE x 16-character display, data, allcomponents, and software to include in your own programs.Ideal develpment base for meters, terminals, calculators,

counters, timers – Just waiting for your application!

68000 NEW PCB DESIGN 8 MHz 68000 16-BIT BUS MANUAL AND SOFTWARE 2 SERIAL PORTS PIT AND I/O PORT OPTIONS I2C PORT OPTIONS

INCLUDES 1-PIC16F84 CHIPSOFTWARE DISK, LEADCONNECTOR, PROFESSIONALPC BOARD & INSTRUCTIONS

INCREDIBLE LOW PRICE! Kit 857 £12.99

Kit 863 £18.99

Kit 860 £19.99

Kit 862 £29.99Power Supply £3.99

DISASSEMBLERSOFTWARE £11.75

FULL SOURCE CODE SUPPLIED.ALSO USE FOR DRIVING OTHERPOWER DEVICES e.g. SOLENOIDS.

Power Supply £3.99FULL PROGRAM SOURCECODE SUPPLIED – DEVELOPYOUR OWN APPLICATION!

Power Supply £3.99

EXTRA CHIPS:PIC 16F84 £4.84

SUPER PIC PROGRAMMER READS, PROGRAMS, AND VERIFIES WINDOWS SOFTWARE PIC16C6X, 7X, AND 8X USES ANY PC PARALLEL PORT USES STANDARD MICROCHIP HEX FILES OPTIONAL DISASSEMBLER SOFTWARE (EXTRA) PCB, LEAD, ALL COMPONENTS, TURNED PIN

SOCKETS FOR 18, 28, AND 40 PIN ICs.

SEND FOR DETAILEDINFORMATION – ASUPERB PRODUCT AT ANUNBEATABLE LOW PRICE.

PIC STEPPING MOTOR DRIVER

Another NEW Magenta PIC project. Drives any 4-phase unipolar motor – upto 24V and 1A. Kit includes all components and 48 step motor. Chip ispre-programmed with demo software, then write your own, and re-program

the same chip! Circuit accepts inputs from switches etc and drives motor inresponse. Also runs standard demo sequence from memory.

INCLUDES: PCB,PIC16F84 WITHDEMO PROGRAM,SOFTWARE DISK,INSTRUCTIONSAND MOTOR.

PIC16F84 MAINS POWER 4-CHANNEL

CONTROLLER & LIGHT CHASER WITH PROGRAMMED 16F84 AND DISK WITH

SOURCE CODE IN MPASM ZERO VOLT SWITCHING

MULTIPLE CHASE PATTERNS OPTO ISOLATED

5 AMP OUTPUTS 12 KEYPAD CONTROL SPEED/DIMMING POT. HARD FIRED TRIACS

Kit 855 £39.95

All pricesinclude VAT. Add £3.00 p&p. Next Day £6.99

Now features full 4-channelchaser software on DISKand pre-programmedPIC16F84 chip. Easilyre-programmed for yourown applications. Softwaresource code is fully‘commented’ so that it canbe followed easily.

LOTS OF OTHER APPLICATIONS

KIT 621

£99.95

ON BOARD5V REGULATOR

PSU £6.99

SERIAL LEAD £3.99

EPE PIC TutorialAt Last! A Real, Practical, Hands-On Series

Learn Programming from scratch using PIC16F84

Start by lighting l.e.d.s and do 30 tutorials to SoundGeneration, Data Display, and a Security System

PIC TUTOR Board with Switches, l.e.d.s, and on boardprogrammer

PIC TUTOR BOARD KITIncludes: PIC16F84 Chip, TOP Quality PCB printed withComponent Layout and all components* (*not ZIFSocket or Displays). Included with the Magenta Kit is adisk with Test and Demonstration routines.

KIT 870 ...... £27.95, Built & Tested ...... £42.95Optional: Power Supply – £3.99, ZIF Socket – £9.99LCD Display ................£7.99 LED Display ..............£6.99Reprints Mar/Apr/May 98 – £3.00 set 3

Tel: 01283 565435 Fax: 01283 546932 E-mail: [email protected]

PIC TOOLKIT V1 PROGRAMS PIC16C84 and 16F84 ACCEPTS TASM AND MPASM CODE

Full kit includes PIC16F84 chip, top quality p.c.b. printed with componentlayout, turned pin PIC socket, all components and software**Needs QBASIC or QUICKBASIC

KIT 871 . . . £13.99. Built and tested £21.99

PhizzyB ALL PARTS FOR SERIES INCLUDING PCBs,PROGRAMMED CHIP, CD-ROM AND DISPLAYS

MAIN BOARD – FULL KIT £131.95 BUILT .......... £149.95I/O PORT KIT ................... £16.99 BUILT ............ £24.99L.C.D. ............................... £12.49 POWER SUPPLY ..£3.998-BIT SWITCH/LATCH ..... £7.95 INT. MODULE .£10.45

8-CHANNEL DATA LOGGERAs featured in Aug./Sept. ’99 EPE . Full kit with Magentaredesigned PCB – LCD fits directly on board. Use as DataLogger or as a test bed for many other 16F877 projects. Kitincludes programmed chip, 8 EEPROMs, PCB, case and all components.

KIT 877 £49.95 inc. 8 x 256K EEPROMS

PIC TOOLKIT V2 SUPER UPGRADE FROM V1 18, 28 AND 40-PIN CHIPS READ, WRITE, ASSEMBLE & DISASSEMBLE PICS

SIMPLE POWER SUPPLY OPTIONS 5-20V ALL SWITCHING UNDER SOFTWARE CONTROL MAGENTA DESIGNED PCB HAS TERMINAL PINS AND OSCILLATOR

CONNECTIONS FOR ALL CHIPS INCLUDES SOFTWARE AND PIC CHIP

KIT 878 . . . £22.99 with 16F84 . . . £29.99 with 16F877

Click Here DownL





Copyright © 2000 Wimborne Publishing Ltd and

Maxfield & Montrose Interactive Inc EPE Online, May 2000 - www.epemag.com - 338

Intended primarily as ameans of processing microphoneinputs to computers, theSSM2166P integrated circuit (IC)

– manufactured by AnalogDevices – has a wider range of

possible applications. Publicaddress and surveillance systemsimmediately spring to mind, andthe device will be of particular interest to radio enthusiasts,especially now that the popular Plessey 6270 IC mic/pre-amp,with voice gain, is no longer available.

This article describes how thenew IC can be used for a varietyof signal inputs, and additionalcircuitry is given for readers who

AMPLIFIERS The input impedance of

buffer amplifier, A, is 180kilohms (180k) and its gain can

be set, by external feedbackresistors, between 0dB and20dB. There is a standing DCvoltage on the input, and ablocking capacitor must beused.

The input and outputimpedances of the controlledamplifier, D, are 1k, and 75ohms, respectively. A standingDC voltage necessitates the useof a blocking capacitor at theoutput.

Use one of the latest chips on the block to produce an audio pre-amp with AGC

compression, limiting, and noise reduction.

VERSATILE MIC/AUDIO PREAMPLIFIER

by RAYMOND HAIGH

require a signal-strength meter.

THE CHIP The various amplifying and

control stages built into theSSM2166 chip are shown inFig.1.

Signal inputs are bufferedby opamp A, internallyconnected to a rectifier stage,B, which produces a DC voltagewhich varies in proportion tosignal strength.

After processing by thecontrol circuit, C, the DCvoltage is used to fix the largeand small signal gain of asecond opamp, D.

BUFFER AMPLIFIER

BUFFER AMPLIFIEROUTPUT

CONTROLLED AMPLIFIER

+ +

6

13

12

4

7

8

35

A D

B C

CONTROLLED AMP INPUTS

TRUE R.M.S.LEVELDETECTOR

CONTROLCIRCUITRY

BUFFER AMPINPUTS(AUDIO IN)

PROCESSEDOUTPUT

POWERDOWN(STAND-BY)

SET A.G.C.TIMECONSTANT

2 SETGAIN

111091

GROUND (0V) SET SQUELCHTHRESHOLD

SETCOMPRESSIONRATIO

SETLIMITINGTHRESHOLD

14

+5V LIMITING IS IMPOSED IN THIS REGION INORDER TO HOLD THE OUTPUT BELOW A PRE-DETERMINED LEVEL

THRESHOLD OFLIMITING SETBY VR4

DOWNWARDEXPANSIONOR SQUELCHTHRESHOLDSET BY VR2

SIGNAL OUTPUT

SIGNAL INPUT

IN THIS REGION GAIN REDUCES ASSIGNAL STRENGTH INCREASES INORDER TO COMPRESS THE DYNAMICRANGE. COMPRESSION IS SET BY VR3

IN THIS REGION GAIN REDUCES ASSIGNAL STRENGTH REDUCES INORDER TO PREVENT HIGH-LEVEL

AMPLIFICATION OF NOISE UNDERNO-SIGNAL CONDITIONS

Fig.1. Internal block schematic for the

SSM2166P microphone preamplifier, with

variable compression and noise gating.

Fig.2. Relationship between limiting, com-

pression, and downward expansion or

“squelch”.

Click Here DownL







Provision is made for setting the nominal gain of thecontrolled stage between 0dBand 20dB, but AGC action willincrease amplification, at thelowest signal levels, to as muchas 60dB. The output can bemuted.

Interestingly, the noisegenerated by the controlledstage is designed to be at aminimum when its gain is at amaximum, and this significantlyimproves the overall signal-to-noise ratio of the system.

RECTIFIER

The circuit of the rectifier, or level-detector stage (B), hasbeen specially developed for this application. It produces aDC control voltage, which isproportional to the log of thetrue RMS value of the inputsignal.

The speed at which thecontrol voltage responds tochanges in signal level, or the“attack time”, can be controlledby the user. Response to high-

level changes is automatically

speeded up by the IC in order tominimize the duration of any

overload.

CONTROL CIRCUIT The control circuit (C)

enables the user to program theperformance of the IC in a verycomprehensive way, and theamount of signal compressioncan be set between zero and60dB.

Signal limiting can also beapplied to prevent theoccasional transient exceeding

the desired maximum output. Itcan be set at outputs ranging

from 30mV to 1V. Above thisthreshold, the maximumcompression ratio of 15:1 isapplied.

The response of the systemto very low level inputs can bereduced in order to prevent theamplification of noise under no-signal conditions. The thresholdof this downward expansion (thelower the signal the less it isamplified), can be set at inputs of between 250uV and 20mV.

Constructional Project

b

c

e

VR522k

VR610k

VR710k

VR3100k

VR14k7

R61k

R310k

R11k

R210k

GAIN

OUTPUTSIGNALLEVEL

COMPRESSION

INPUTSIGNALLEVEL

C722µ

C41µ

C91µ

C64 7µ

C10470µ

C14 7µ

C54 7µ

IC1SSM2166P

VR21M

VR447k

R72M2

R915k

R41k

R51k

R8SEE TEXT(TABLE 2)

SQUELCH LIMIT

C8100n

C310n

C2100n

0V

0V

AUDIOINPUT 1

AUDIOOUTPUT

AUDIO

INPUT 2

WIRELINK

TR1BC547

+

VR810k

ME150 A TO 1mA SIGNALSTRENGTHMETER(SEE TEXT)

µ

R104k7

++8V TO

18V IC2LM78L05

INOUT

COM

AUDIO IN (1): ELECTRET MICROPHONES ANDINPUTS REQUIRING A D.C. BLOCKING CAPACITOR

AUDIO IN (2) DYNAMIC (MOVING COIL) MICROPHONES

5 3 9 11 14

4 8 10 1 2

6

7

12

13

LK1

SCREEN

SCREEN

+5V

Fig.3. Complete circuit diagram for the Versatile Mic/Audio Preamplifier.

Click Here DownL







Provision is made for thedevice to be placed in a “power-down” or stand-by mode, andthis feature will be of particular interest when it is used insophisticated surveillance

systems. In this state, currentconsumption is reduced toaround 10mA and the input andoutput ports assume a highimpedance.

User programmable controlcircuitry, coupled with thecomplex rectifier or level-detector, contributessignificantly to the chip’sperformance. The relationshipbetween the noise reduction,compression and limitingfunctions is displayed in Fig.2.

RATINGS No doubt with computer

circuit compatibility in mind, theSSM2166 is designed for a 5Vsupply. The absolute maximumsupply voltage is 10V. Currentconsumption is approximately10mA.

The maximum input to thebuffer is 1V, and the maximumoutput from the controlledamplifier is 14V RMS for 1 per

cent total harmonic distortion.Frequency response extendswell into the RF spectrum.

Static discharges candamage the IC, and the usualprecautions (discharging thebody) should be taken whenhandling and connecting it intocircuit.

The SSM2166P is embeddedin a 14-pin, dual-in-line package,and the suffix “P” refers to thestandard-size version. This is thetype most likely to be stocked bysuppliers. However, surface-mount types are alsomanufactured: these carry thesuffix “S”.

CIRCUIT DETAILS The full circuit diagram for

the Versatile Mic/AudioPreamplifier, incorporating asignal strength meter, is given inFig.3. Provision for controlling somany functions results in aplethora of preset potentiometer controls. However, they doenable the signal processing tobe tailored to individualrequirements, and their adjustment is not critical or difficult. A summary of their various functions is set out in

Table 1.

Preset VR1 permitsadjustment of the input signallevel to prevent overload and tooptimize the performance of the

circuit. Its value is appropriatefor moving coil and electretmicrophones, and for audiosignals derived from mosttransistor circuits. Keeping the


COMPONENTS Resistors

R1, R4, R5, R6 1k (4 off)

R2, R3 10k (2 off)

R7 2M2

R8 (see Table 2)

R9 15k

R10 4k7

See also the

SHOP TALK Page!

All 0.25W 5% carbon film

CapacitorsC1, C5, C6 4u7 radial electrolytic,

10V (3 off)

C2, C8 100n ceramic (2 off)

C3 10n ceramic

C4, C9 1u radial electrolytic

10V (2 off)

C7 22u radial electrolyticC10 470u radial electrolytic

SemiconductorsTR1 BC547 (or similar, e.g. BC239,

BC548) npn low-power transistor

IC1 SSM2166 microphone preamp

(Analog Devices)

IC2 LM78L05ACZ +5V 100mA

voltage regulator

MiscellaneousME1 50uA to 1mA FSD moving

coil meter (see text)

Printed circuit board available

from the EPE Online Store, code

7000260 (www.epemag.com);14-pin DIL socket; screened cable,

solder pins, solder, multistrand

connecting wire, etc.

$27 Approx. Cost

Guidance Only

(Excluding meter)

PotentiometersVR1 4k7 enclosed carbon preset,

horizontal

VR2 1M enclosed carbon preset,

horizontalVR3 100k enclosed carbon preset,

horizontal

VR4 47k enclosed carbon preset,

horizontal

VR5 22k enclosed carbon preset,

horizontal

VR6, VR7, VR8 10k enclosed

carbon preset, horizontal (3 off)

Preset Value

VR1

VR2

VR3VR4

VR5

VR6

VR7

VR8

4k7

1M

100k47k

22k

10k

10k

10k

Function

Set input signal level: clockwise to increase.

Set threshold of downward expansion (squelch):

clockwise to lower.

Set compression: clockwise to increase.Set threshold of signal limiting: clockwise to lower.

Set gain of controlled amplifier: clockwise to

increase.

Set output signal level: clockwise to increase.

Set signal strength meter pointer at full scale

(when strongest signal being processed):

clockwise gives clockwise pointer movement.

Set signal strength meter pointer at zero (under

no-signal conditions): clockwise gives clockwise

pointer movement.

Table 1: Preset Control Functions

Click Here DownL

http://www.epemag.com/














value below 5 kilohms increasesthe stability margin of IC1.

Power can be supplied to anelectret microphone’s integralFET (field-effect-transistor)

buffer via resistor R1, and C1acts as a DC blocking capacitor.The input arrangements for alternative microphones andother signal sources arediscussed at greater lengthlater.

The input signal to IC1 isapplied to the non-inverting (+)input of the buffer amplifier stage (Pin 7 – see Fig.1) viablocking capacitor C2. This IChas an extended frequency

response and C3 introduces ameasure of roll-off above 20kHzor so, again in the interests of stability.

BUFFER GAIN The gain of the buffer

amplifier is set at 6dB byresistors R2 and R3, and this islikely to be sufficient for mostpurposes. Gain can beincreased to a maximum of

20dB by decreasing R3 to about12 kilohms. Adding this to the

gain of the controlled amplifier results in an overall systemgain, when signals are too smallto initiate compression, of 80dB.

This is a great deal of amplification in a smallpackage, and particular caremust be taken with thescreening and routing of inputand output leads, and theconnections to a shared power

supply, if instability is to beavoided. Separate ground, or 0V leads, from signal sourcecircuitry, the preamplifier, andthe power amplifier, should berun to a common point at thepower supply. The screeningbraid of signal cables should beconnected to ground at thepreamplifier end only.


If desired, the gain of thebuffer can be set at unity bydeleting R3 and inserting a wirelink in place of resistor R2 (toconnect pin 5 and pin 6).Blocking capacitor C4 maintainsthe correct DC conditions.

CONTROLLED AMPLIFIER

The output from the buffer stage (pin 5) is connected, viaDC blocking capacitor C5 to thenon-inverting (+) input (pin 3) of the controlled amplifier stage. Acapacitor of identical value, C6,at pin 4 connects the inverting

(–) input to ground (0V). (Thisconnection makes any electricalnoise on the ground rail appear as a common mode signal tothe controlled amplifier and thedifferential input circuitry rejectsit).

The nominal gain of thecontrolled amplifier can be set,by preset VR5, between unityand 20dB. Resistor R6 ensuresthat the gain does not fall belowunity.

Switched muting can beachieved by grounding pin 2 viaa 330 ohm resistor (the switchshould be located at the groundor 0V rail end). Switch clickscan be suppressed byconnecting a 10nF capacitor between pin 2 and ground.

The IC can be put in stand-by mode by disconnecting pin12 from ground and connectingit, via a 100 kilohms resistor, tothe +5V rail. (Provision has not

been made for muting or powering-down on the PCB.)

The processed output istaken from pin 13 andconnected, via DC blockingcapacitor C9, to preset VR6.This enables the output signallevel to be adjusted to suit theinput sensitivity of the power

amplifier.

ATTACK TIME The response or “attack”

time of the AGC system can becontrolled by adjusting the valueof the rectifier reservoir capacitor C7. The ICmanufacturer suggests a valuewithin the range 22uF to 47uF,

with smaller capacitors beingsuitable for music and the larger for speech.

Too low a value will result in“pumping” effects, withbackground noise “rushing up”

between bursts of speech. Thiswill become increasinglyapparent as the compressionratio is raised.

Conversely, too high avalue will excessively slow theresponse of the system tochanges in signal level. The22uF component specified for C7 has been found to work wellwith both speech and musicinputs.

The attack time is controlled

mainly by the value of C7, butthe much longer “decay” time isdependant upon this capacitor and the internal control circuit.Fast attack and slow decay helpto reduce the pumping effect,which seems far lesspronounced with this IC thanwith simpler audio AGCsystems.

COMPRESSION

The amount of compressionis determined by preset VR3,which connects pin 10 toground. There is nocompression with thepotentiometer set to zero. Whenits resistance is at maximum, a60dB change in input level(above the downward expansionor squelch threshold) changes

Click Here DownL







the output by less than 6dB.

The onset of limiting iscontrolled by preset VR4.Setting this potentiometer tomaximum resistance fixes it at

30mV. With VR4 at minimumresistance, it is around 1V RMS. Above the threshold of limiting,a 15:1 compression ratio isimposed, irrespective of thesetting of compression controlVR3.

NOISE REDUCTION Preset potentiometer VR2

sets the threshold below whichdownward expansion (gain

reduces as the signals becomeweaker) is applied. Withmaximum resistance, downwardexpansion starts at signal levelsin the region of 250mV. Turnedto zero resistance, the thresholdis raised to around 20mV.

Gain rises to a maximumunder no-signal conditions withall conventional AGC systems,and the amplification of externaland internally generated noiseproduces a loud and tiresome

hiss in the speaker or ‘phones.The IC’s noise reduction facility,which operates as a “squelch”control, is very effective inovercoming this. It can reduceoutput noise below the level of audibility when signal levels fallto zero.

With any squelch system, aneed to resolve very weaksignals overlaid by noisecompromises the usefulness of the feature. Radio enthusiasts

with a particular interest in itcould mount VR2 as a panelcontrol so that the thresholdcould be adjusted to suitreception conditions.

POWER SUPPLY The maximum safe supply

voltage is 10V, and it should be

noted that, under a light load, afresh 9V alkaline battery willusually deliver a higher voltagethan this.

However, in order to ensure

the correct operation of thedevice, and provide a highdegree of isolation from other equipment sharing the samepower supply, a 5V 100mAvoltage regulator, IC2, isincluded in the circuit. Thisenables supplies with outputsranging from 8V to 18V (or more, depending on IC2 rating)to be used.

Bypass capacitors C8 andC10 shunt the noise in the

regulator output to ground. Notethat C8 is essential to thestability of IC1 and it must belocated as close as possible topin 14, even when the unit isbattery powered.

SIGNAL STRENGTH METER

Some readers, especiallythose wishing to incorporate theunit into a radio receiver, may

welcome the provision of asignal strength meter. This isincluded in the circuit diagramof Fig.1 and consists of transistor TR1, meter ME1 andassociated components.

The AGC control voltageappears on pin 8 of IC1. Itranges from 290mV under no-signal conditions toapproximately 720mV with highlevel inputs.

Transistor TR1, configuredas a DC amplifier, ensures thatIC1’s AGC line is only lightlyloaded, even when a 1mAmeter is used. It forms one armof a bridge circuit, the other

three being its collector load,R9, and the potential divider chain comprising preset VR8and resistor R10. The bridge isbalanced, and the meter set atzero under no-signal conditions,by preset potentiometer VR8.

When a signal is beingprocessed, the rising AGCvoltage on the base (b) of TR1increases its collector currentand, hence, the voltage dropacross resistor R9. Thisunbalances the bridge anddrives the meter pointer over.Preset VR7 adjusts thesensitivity of the meter so thatthe pointer can be set just shortof full-scale deflection (FSD)when registering a strong signal.

The circuit can be made toaccommodate meters with full-scale deflections ranging from50mA to 1mA by adjusting thevalue of resistor R8. Thisresistor controls the flow of current through the base-emitter

junction of transistor TR1, andvalues to suit a range of meter FSDs are given in Table 2. Biasresistor R7 provides a measureof negative feedback whichhelps to stabilize the operationof the circuit.

Almost any small-signal npntransistor should prove suitablefor TR1, and a 2N5827 or 2N5828 could be used inaddition to the types listed in theComponents list. These deviceshave different case styles andthe base connections must bechecked.

CONSTRUCTION All the components, with the

exception of the meter ME1, are


Meter FSD R8

50uA

100uA

500uA

1mA

1M

470k

100k

47k

Table 2: Signal StrengthMeter ( Values of R8 for differ-

ent meter sensitivities)

Click Here DownL







assembled on a small, single-sided, printed circuit board(PCB). The topside componentlayout, together with an(approximately) full-sizeunderside copper foil master pattern, is shown in Fig.4. Thisboard is available from the EPEOnline Store (code 7000260) at

www.epemag.com

Commence construction inthe usual way by mounting thesmallest components firstworking up to the largest, but fitIC1, IC2, and TR1 last (seeearlier comments about thestatic sensitive nature of IC1). Aholder for IC1 will facilitatesubstitution checking. Solder pins, inserted at the lead-outpoints, will ease the task of off-board wiring.

SPOT-CHECKS When all the components

have been soldered in positionon the PCB, double-check theorientation of electrolyticcapacitors, the ICs, and thetransistor. Also, check the PCBfor bridged tracks and poor

solder joints.

Next, with IC1 “out of circuit”, connect a supplyvoltage of between 7V and 9Vand check that the output fromregulator IC2 is producing 5V. Afault in this device, or its wrongconnection, could result in thedestruction of IC1 when higher voltages are applied.

Once all is well, place IC1in its socket (checking

orientation), connect, viascreened cable, a signal sourceand a power amplifier. Adjustthe various presetpotentiometers until theprocessing meets your requirements. All presetfunctions are summarized inTable 1 for ease of reference.


BC547BC239BC548

LM78L05ACZ

e b c

C2

C8 +

+

+

+

+

+

+

C4

C6

C7

C9

C5

C10

C1

R8

R1

R10

R7

R3

R2

R4C3

R5

R6

R9

VR6

VR1

VR5

VR4

VR3

VR2

VR8

VR7

AUDIOINPUT 1

AUDIOINPUT 2

INPUTSIGNALLEVEL

SIGNALSTRENGTHMETER

SQUELCH

DOWNWARDEXPANSION

THRESHOLDOF LIMITING

COMPRESSION

OUTPUTSIGNALLEVEL

GAIN

INPUTGROUND(0V)

POWER SUPPLY

NEGATIVE + +8V TO 18V

IN

COM

OUT

IC2

TR1

e b c

INCOM

OUT

+

–

SET METER AT FULLSCALE

SET METER AT ZERO

SIGNAL OUT

LK1

UNDERSIDE VIEW

UNDERSIDE VIEW

Fig.4. Printed circuit board component layout, inter-wiring de-

tails and (approximately) full-size underside copper foil master.

MICROPHONES The unit works well with

dynamic (moving coil), electret,crystal, and ceramicmicrophones. Screened cable

Click Here DownL













must, of course, be used toconnect any type of microphoneto the preamplifier.

Very high quality studiomicrophones can be insensitiveand require balanced feeders tominimize hum pick-up. The pre-amplifier described here isconfigured for unbalancedinputs, and is not likely to besuitable, as it stands, for microphones of this kind.

A few words about thevarious types of signal inputmay prove helpful.

Dynamic Microphones aremanufactured with impedancesranging from 50 ohms to 600ohms. Output tends to begreatest with the higher impedance units.

This type of microphoneshould be connected to Input 2(i.e., directly across presetVR1), and the wire link must beremoved to isolate resistor R1from the 5V rail.

Electret Microphones are amodern development of thecapacitor microphone (apermanently chargeddiaphragm, the electret,

eliminates the need for anexternal charging voltage). Theoutput from the actual unit islow and at a high impedance, sothese microphones have an

integral FET buffer. The drainload for the internal FET isprovided at the amplifier end of the cable (resistor R1 in Fig.3),to facilitate line powering.

Electret microphones mustbe connected to Input 1, and thewire link must be in place toconnect resistor R1 to thesupply rail. The 1 kilohm drainload (R1), fed from the 5Vsupply, should ensure theoptimum performance of most

microphones of this kind.

Crystal and Ceramic

Microphones rely upon thepiezo-electric effect to producea signal voltage. The vibratingdiaphragm induces stresses in awafer of crystal, often Rochellesalt, or in a barium titanate

element in the case of ceramicunits.

These microphones shouldbe connected to Input 2. Theyhave a high impedance, and

feeding them into preset VR1will reduce their response to lowaudio frequencies. Lowfrequency roll-off is, however,desirable for communicationswork, and more is said aboutthis later.

The use of long connectingcables will attenuate the signalbut have little effect onfrequency response (cablecapacitance is modestcompared to the self-

capacitance of thesemicrophones, which can be ashigh as 30nF).

If an extended frequencyresponse is required frommicrophones of this type, theuse of an external, line-powered, FET buffer, as builtinto electret microphones, is


g

d

s

VR12M2

C1

0V

+5V

R1

SCREENED CABLE

2N3819HIGH IMPEDANCEMICROPHONE

MICROPHONE CASE

R1, C1 AND VR1 ARE LOCATED ONTHE PREAMPLIFIER P.C.B.

1k 10µ

Fig.5. The line-powered buffer stage built into

electret microphones can also be used for ce-

ramic and crystal types. (Most FETs will func-

tion in this circuit with the source grounded,

eliminating the need for the source resistor

and bypass capacitor.)

Layout of components on the completed circuit board. The

“Signal Strength Meter” components, except the meter, have

been included on the board (bottom right).

Click Here DownL









ROLL-UP, ROLL-UP!

Ingenuity is our regular round-up of readers' owncircuits. We pay between $16 and $80 for all materialpublished, depending on length and technical merit.We're looking for novel applications and circuit tips, notsimply mechanical or electrical ideas. Ideas must be thereader's own work and must not have been submitted

for publication elsewhere. The circuits shown haveNOT been proven by us. Ingenuity Unlimited is open to

ALL abilities, but items for consideration in this columnshould preferably be typed or word-processed, with abrief circuit description (between 100 and 500 wordsmaximum) and full circuit diagram showing all relevantcomponent values. Please draw all circuit schematics

as clearly as possible.Send your circuit ideas to: Alan Winstanley,

Ingenuity Unlimited , Wimborne Publishing Ltd., AllenHouse, East Borough, Wimborne, Dorset BH21 1PF.They could earn you some real cash and a prize!

Win a Pico PC-Based Oscilloscope

•

50MSPS Dual Channel Storage Oscilloscope

• 25MHz Spectrum Analyzer

• Multimeter

• Frequency Meter

• Signal Generator

If you have a novel circuit idea whichwould be of use to other readers, then a PicoTechnology PC based oscilloscope could be

yours.

Using the UGN3503U linear Hall Effect sensor with a dualopamp allows the constructionof a simple but extremely sensi-

tive Hall Effect switch that couldprove useful in many applica-tions. A circuit diagram for justsuch a switch is shown in Fig. 1.The Hall Effect device is IC1,which has just three terminals,for positive and negative sup-plies and the output. A regu-lated 5V supply is suggested for most applications.

With a 5V supply and in theabsence of a magnetic field, theoutput from IC1 is about 25V.

On the approach of a magnet,the output will rise or fall, de-pending on the magnetic field’spolarity. With a 5V supply, the

AD8532 is an excellent choicefor the dual opamp IC2 as it isdesigned for this supply voltage,has rail-to-rail inputs and out-puts and, being a CMOS com-ponent, has very high input

Sensitive Hall Effect Switch – Feel the Field

Fig.1. Sensitive Hall Effect Switch circuit diagram.

In addition it can supply up to250mA of output current.

The first opamp, IC2a, isused as a non-inverting ampli-fier with a voltage gain of about20 to amplify the output of IC1to more useful levels. Because

AC coupling via capacitor C1 isused for the input, resistor R3sets the working point to half the

supply. This is necessary toavoid drift in the Hall Effect sen-sor IC1. The high value of R3allows the circuit to operate atvery low frequencies, down toless than 1Hz. The secondopamp IC2b is connected as acomparator with hysteresis setby resistors R7 and R8 to about500mV to ensure a rapid,

C1470n

OUT

0V

R210k

R610k

R4100k

R710k

V+

R110k R3

4M7

R510k R8

100k

1

2

3

4

8

+

+

5V

0V

IC1UGN

3503U

1

3

26

5

7

OUTPUT

IC2aIC2b

AD8532

AD8532

12

3 O/P

+VE0V

UGN3503U

Click Here DownL







bounce-free switching action.

With the values shown thiscircuit can detect the approachof a small bar magnet of thetype commonly used for operat-

ing reed switches, at a range of about 25mm. Sensitivity couldbe adjusted by altering the gainof the amplifier stage or thehysteresis. Note that thestrength of a magnetic field fallsin proportion to the square of the distance from its source.

The polarity of the outputchange from IC1 depends onthe polarity of the magneticfield. When the face bearing thedevice markings is approached

by a North pole the output volt-age falls, whilst the approach of a South pole will make it rise.The sensor is said to be capableof operating up to 23kHz, so for most practical applications theupper speed limit will not be anissue!

It is also possible to place amagnet behind the sensor sothat the flux passing through itwill change on the approach of a ferrous, but not necessarilymagnetic, object. Applicationsof this type might include sens-ing passing steel gearwheel

Ingenuity Unlimited

Infra-Red Remote Tester – Sounds Good

B1

9V

D1I.R.

PHOTO

DIODE

C122m

11

R110M

R21M

8

C2100n

IC1a4049BE

14

1

15

a

k

9 10

IC1f 4049BE

a k

IC1b4049BE D2

1N4148

R3

4k7

D3

12

7

a

k

X1PIEZO DISC

IC1c4049BE C3

22p

IC1e4049BE

R410M

R51M

6

3 2

5

IC1d4049BE

4

+

LOWCURRENT

L.E.D.

NOT USED

Fig.2. Circuit diagram for an Infrared Remote Tester.

An Infrared Remote Control Tester, which gives both an audioand visual indication that a remote control is functioning, is shown inFig.2. Its operation is as follows: D1 is a reverse biased photodiode,

which forms an infrared detector. Its output is buffered by IC1a andthen enters a pulse stretcher comprising capacitor C2, resistor R2and IC1b.

The pulse stretcher enables even the shortest of pulse trains totrigger the following oscillator. Diode D3 is a low current red LED,which sinks into the output of IC1b and provides the visual indication.

An oscillator is formed of IC1c and IC1d, which drives a piezodisc element X1. This is connected across IC1e (rather than moreconventionally to 0V) to provide a louder output. Oscillation isstopped by the normally high output from IC1b via diode D2. Whenan IR pulse train is detected, IC1b goes low and the input to IC1dsees only a high impedance from the diode and oscillation starts.The input of gate IC1f is grounded for stability.

The circuit runs from a 9V PP3, and the standby current of a little

Experimenter’s Power Supply – Variable States

A circuit for a handy Vari-able Power Supply which willmeet the needs of many elec-tronics hobbyists is shown in

Fig.4. It provides 0V to 25V atup to 250mA. The error ampli-fier within a 723-type voltageregulator chip (IC3) cannotfunction with rail-to-rail inputand therefore a precision, shuntreference, TL431C (IC2) biasespin 5 of the 723 regulator to+2·50V.

The regulator’s inverting

tential from potentiometer VR1,which can swing either above or below this level. Hence the out-put voltage, attenuated by the10k and 100k resistors R5 andR6 is forced to extend from 0V(CCW) to +25V (CW) to trackthe +250V reference.

An external TIP29C power transistor TR1 extends the cur-rent limit to 250mA and is offsetby a second programmableZener diode IC4 at pin 10 of the723 regulator. This voltage dif-

Click Here DownL









A typical multimeter canmeasure voltage, current andresistance over a wide range of values, and usually has a few“tricks up its sleeve” such ascontinuity tester and transistor

checker facilities. Somemultimeters have capacitancemeasuring ranges, but thisfeature remains something of ararity. This is a pity, becauseanyone undertaking electronicfaultfinding will soon need tocheck suspect capacitors and aready-made capacitance meter isan expensive item of equipment.

The unit featured here offersa low-cost solution to the problemof testing capacitors. It is an

analog capacitance meter thathas five switched ranges with full-scale values of 1nF; 10nF;

100nF; 1uF; and 10uF. It cannotmeasure very high or low valuecomponents, but it is suitable for

under test.

The duration of the outputpulse is proportional to thevalues of both components inthe CR network. If a 1nFcapacitor produces an output

pulse of one millisecond induration, components havingvalues of 22nF and 47nF would

respectively produce pulselengths of 22ms and 47ms.

Each output pulse must beconverted into a voltage that isproportional to the pulseduration. A moving coil panelmeter can then read thisvoltage, and with everything setup correctly it will provideaccurate capacitance readings.

If we extend the examplegiven previously, with apotential of one volt per millisecond being produced, ameter having a full-scale valueof 10V would actually read 0 to10nF. This time-to-voltageconversion is actually quitesimple to achieve, and isprovided by a constant currentgenerator and a charge storage

A simple starter project that will let you get the measure of most capacitors.

Five switched ranges: 1nF to 10uF.

LOW-COST CAPACITANCE METER

by ROBERT PENFOLD

testing the vast majority of capacitors used in everydayelectronics.

SYSTEM OPERATION The block diagram for the

Low-Cost Capacitance Meter isshown in Fig.1. Like mostsimple capacitance meter designs, this unit is based on amonostable circuit. Whentriggered by an input pulse amonostable produces an outputpulse having a duration that iscontrolled by a CR network. Inthis case the monostable istriggered manually using apushbutton switch each time areading is required.

The resistor in the timingnetwork is one of five resistorsselected via a switch, and theseresistors provide the unit with itsfive ranges. The capacitor in theCR network is the capacitor

MONOSTABLE CURRENT

GENERATOR

BUFFER

AMPLIFIER

METER

CHARGE

STORAGE

CAPACITORRESET

TEST

CAPACITOR

0V RAIL

MEASURE

Fig.1. Schematic block diagram for the

Low-Cost Capacitance Meter.





capacitor.

When charged via a resistor the potential across thecapacitor does not rise in alinear fashion. As the chargepotential increases, the voltageacross the resistor falls, giving asteadily reducing chargecurrent. The voltage thereforeincreases at an ever-decreasingrate (inverse exponentially).

A current regulator avoidsthis problem by ensuring that

the charge current does notvary with time, giving a linear rise in the charge voltage. Thecircuit therefore provides therequired conversion fromcapacitance to voltage, but it isimportant that loading on thestorage capacitor is kept to aminimum.

Tapping off a significantcurrent could adversely affectthe linearity of the circuit andwould also result in readings

rapidly decaying to zero. Themeter is, therefore, driven via abuffer amplifier that has a veryhigh input impedance. Once areading has been taken andnoted, operating the Resetswitch discharges the storagecapacitor and returns thereading to zero so that a newreading can be taken.

CIRCUIT OPERATION The complete circuit

diagram for the Low-Cost Capacitance Meter projectappears in Fig.2. Themonostable is based on a low-power 555 timer (IC1) used in

the standard monostableconfiguration.

Apart from the fact it givesmuch longer battery life, a low-power 555 is a better choice for this type of circuit due its lower self-capacitance. This producesmuch better accuracy on the 1nFrange, and a standard 555 is


b

c

e

b

c

e

B1

9V

TR1BC549

D21N4148

D11N4148

TESTCAP.C1

100n

R64k7

R110M1%

R21M1%

R3100k1%

1n

S1

100n

10n

6

R710M

S2

C2150p

2

MEASURE

THRES.

TRIG.

GND

R815k

1

R410k1%

R51k1%

7RANGE

1m

10m

IC1TS555CN

DISCH.OUT

RST +V

4 8

3

SENS

ON/OFF

RESET

R1210W

S3

C3220n

R1339k

VR147k

4

R94k7

R1110k

TR2BC559

R105k6

6

IC2CA3140E7

3

2

ME1100 Am

CAPACITANCE

S4

a

a

k

k

+

0V

SK1

SK2

POLE

Fig.2. Complete circuit diagram for the Low-Cost Capacitance Meter.


R1 10M 1% metal film

R2 1M 1% metal film

R3 100k 1% metal film

R4 10k 1% metal film

R5 1k 1% metal film

R6, R9 4k7 (2 off)

R7 10M

R8 15k

R10 5k6

R11 10k

R12 10 ohms

R13 39k

All 0.25W 5% carbon film, except

where otherwise specified

CapacitorsC1 100n ceramic

C2 150p ceramic plate

C3 220n polyester

MiscellaneousME1 100uA moving coil panel meter

SK1 2mm socket, red

SK2 2mm socket, black

S1 12-way single-pole rotary switch

(set for 5-way operation) (see text)

S2, S3 pushbutton switch,

push-to-make (2 off)

S4 s.p.s.t. miniature toggle switch

B1 battery (PP3 size), with

connector leads

Metal insrument case (or type to

choice), size 150mm x 100mm x 75mm;

stripboard 0.1-inch matrix, size 34 holes

by 21 copper strips; 8-pin DIL socket

(2 off); control knob; calibration capacitor

(see text); test leads (see text); solder

pins; multistrand connecting wire;

solder, etc.

See also theSHOP TALK Page!

$19 Approx. Cost

Guidance Only (Excluding batteries, case, & meter)

Potentiometer VR1 47k miniature enclosed or

skeleton preset, horizontal

SemiconductorsD1, D2 1N4148 signal diode (2 off)

TR1 BC549 npn transistor

TR2 BC559 pnp transistor

IC1 TS555CN low power timer

IC2 CA3140E PMOS opamp





therefore not recommended for use in this circuit.

Switch S1 sets the Rangeand R1 to R5 are the five timingresistors. Resistors R1 to R5respectively provide the 1nF,10nF, 100nF, 1uF, and 10uFranges.

One slight flaw in the 555for this application is that it willonly act as a pulse stretcher and

not as a pulse shortener. Inother words, the output pulsewill not end at the appropriatetime if the input pulse is stillpresent.

If it were used to directlytrigger IC1, the input pulse frompushbutton switch S2 wouldinvariably be far too long. Asimple CR circuit is therefore

used to ensure that IC1 willalways receive a very shorttrigger pulse, regardless of howlong Measure switch S2 ispressed.

Resistor R6 holds the trigger input of IC1 (pin 2) high under standby conditions, but it is brieflypulsed low when S2 is operatedand capacitor C2 charges via R6.When S2 is released, resistor R7discharges C2 so that the unit isready to trigger again the nexttime S2 is operated. Resistor R7has been given a very high valueso that the discharge time of C2is long enough to preventspurious triggering if S2 does notoperate “cleanly”. Mostmechanical switches suffer fromcontact bounce, and without thisdebouncing it is likely that re-

triggering would occur practically every time S2 wasreleased.

Under standby conditionsthe output at pin 3 of IC1 is low,and both transistor TR1 andTR2 are switched off.

Consequently, only insignificantleakage currents flow into thecharge storage capacitor C3. Anoutput pulse from IC1 switcheson TR1, which in turn activatesTR2.

Transistor TR2 is connectedas a conventional constantcurrent generator, and the valueof resistor R10 controls the

Constructional Project1

1

5

5

10

10

15

15

20

20

25

25

30

30

34

34

A

D

E

F

G

H

I

J

K

M

O

P

Q

R

T

U

B

N

L

C

S

A

D

E

G

H

I

J

K

M

O

P

Q

R

T

U

B

N

L

C

SME1

+

R5

R3

R

2

D1

D2

IC1

TR2

TR1

R

7

C

2

C

1

R

9

R

8

C3

R

12

R

6

R

11

IC2 R

13

VR1

SK1 SK2 S2

TEST CAP MEASURE

S3

RESET

CAPACITANCE

RED

BLACK

S4ON/OFF

TO B1

+

e

b

c

e

b

c

a

k

a

kP

S1

RANGE

R

10

R

1

R4

Fig.3. Stripboard component layout, interwiring, and details of

breaks required in underside copper tracks. Mount the Range resistors

directly on the switch tags

before the switch is fitted in

the case.





output current. This is around115uA with the specified value.Transistors TR1 and TR2 switchoff again at the end of the pulsefrom IC1, and the chargevoltage on C3 is then read bythe voltmeter circuit based onpanel meter ME1.

METER CIRCUIT Operational amplifier

(opamp) IC2 is used as thebuffer amplifier, and the PMOSinput stage of this deviceensures that there is nosignificant loading on the“charge” capacitor C3. The inputresistance of IC2 is actually

over one million megohms.

However, the voltage on C3will gradually leak away throughvarious paths, including C3’sown leakage resistance. Thereading should remain accuratefor at least a minute or two, andin most cases it will not changenoticeably for several minutes.There will certainly be plenty of time for a reading to be takenbefore any significant driftoccurs.

Briefly operating Resetswitch S3 discharges C3 andzeros the meter so that another reading can be taken. Resistor R12 limits the discharge currentto a level that ensures thecontacts of S3 have a longoperating life. The rate of discharge is still so high that itappears to be instant.

Preset VR1 enables thesensitivity of the voltmeter ME1

to be adjusted, and in practicethis is adjusted so that therequired full-scale values areobtained. In order to ensuregood accuracy on all fiveranges it is essential for rangeresistors R1 to R5 to be closetolerance (one or two percent)components.

There is no overload


protection circuit for the meter,but this protection is effectivelybuilt into the design. The circuitdriving the meter is onlycapable of producing minor overloads, and is incapable of inflicting any damage. Thecurrent consumption of thecircuit is only about 3mA, and aPP3 size battery is adequate topower the unit.

CONSTRUCTION The Low-Cost Capacitance

Meter is built up on a smallpiece of stripboard having 34holes by 21 copper strips. Thetopside component layout,

underside details and interwiringto off-board components isshown in Fig.3.

As this board is not of astandard size, a piece will haveto be cut from a large boardusing a small hacksaw. Cutalong rows of holes rather thanbetween them, and smooth anyrough edges produced using afile. Then drill the two 3mmdiameter mounting holes in theboard and make the 17 breaks

in the copper strips. There is aspecial tool for making thebreaks in the copper strips, buta handheld twist drill bit of around 5mm diameter does the

job very well.

The circuit board is nowready for the components, linkwires, and solder pins to beadded. The CA3140E used for IC2 has a PMOS input stagethat is vulnerable to damagefrom static charges, and theappropriate handlingprecautions must therefore betaken when dealing with this IC.

It should be fitted to theboard via a holder, but it shouldnot be plugged into place untilthe unit is otherwise finished,and the board and wiringdouble-checked for any errors.

It should be left in its anti-staticpacking until then. Try to handlethe device as little as possiblewhen fitting it in its IC socket,and keep well away from anylikely sources of static electricitysuch as televisions sets andcomputer monitors.

Although the TS555CNtimer used for IC1 is not static-sensitive it is still a good idea tofit it in an IC socket. Be carefulto fit IC1 the right way aroundbecause it has the oppositeorientation to normal, with pinone at the bottom. This chipcould easily be destroyed if it isfitted the wrong way around.

In all other respectsconstruction of the board isfairly straightforward. The linkwires can be made from thetrimmings from resistor leadoutsor 22 s.w.g. tinned copper wire.In order to fit into this layoutproperly capacitor C3 should bea printed circuit mountingcomponent having 75mm (03-

inch) lead spacing. Be careful tofit the diodes and transistorswith the correct orientation.

Note that transistors TR1 andTR2 have opposite orientations.

RANGE RESISTORS The five range resistors (R1

to R5) are mounted directly onthe Range rotary switch S1,which helps to minimize straycapacitance and pick up of electrical noise. This aids goodaccuracy, especially on the 1nFrange. It is best to mount theresistors on S1 before thisswitch is fitted in the case.

Fitting the resistors is mademuch easier if the switch isstuck to the workbench usingPlasticine, or Bostik Blu-Tack.Provided the tags and the endsof the leadouts are tinned withsolder it should then be quiteeasy to build this sub-assembly.





Try to complete thesoldered joints reasonablyswiftly so that the resistors donot overheat. It takes quite a lotof heat to destroy resistors, butrelatively small amounts canimpair their accuracy.

CASING UP A medium size metal

instrument case is probably thebest choice for a project of thistype, but a plastic box is alsosuitable. The exact layout is not

critical, but mount SK1 and SK2close together.

Many capacitors will thenconnect directly into the socketswithout too much difficulty, buta set of test leads will also beneeded to accommodate somecapacitors. All that is requiredare two insulated leads about

100mm long. Each lead is fittedwith a 2mm plug at one end anda small crocodile clip at theother.

Fitting the meter on thefront panel is potentiallyawkward because a large roundcutout is required. For mostmeters a cutout of 38mmdiameter is required, but it isadvisable to check this point byactually measuring the diameter of the meter’s rear section. DIYsuperstores sell adjustable holecutters that will do the jobquickly and easily, or the cutoutcan be made using a copingsaw, Abrafile, etc.

Four 3mm diameter holesare required for the meter’sthreaded mounting rods.Marking the positions of these isquite easy as they are usually atthe corners of a square having

32mm sides, and the samecenter as the main cutout. Onceagain though, it would beprudent to check this by makingmeasurements on the meter prior to drilling the holes.

The circuit board ismounted on the base panel of the case towards the left-handside of the unit, leavingsufficient space for the batteryto the right of the board. Thecomponent panel is mountedusing either 6BA or metric M25

bolts, and spacers or nuts areused to ensure that theunderside of the board is heldwell clear of the case bottom.To complete the unit the hardwiring is added. This offersnothing out of the ordinary, butbe careful to connect the batteryclip and meter ME1 with thecorrect polarity.


Layout of components inside the metal case of the completed Low-Cost Capacitance Meter.

The circuit board is mounted to one side to leave space for the battery





CALIBRATION Preset potentiometer (wired

as a “variable resistor”) VR1must be given the correct

setting in order to obtain goodaccuracy from the unit, and aclose tolerance capacitor isneeded for calibration. For optimum accuracy this capacitor should have a value equal tothe full-scale value of the rangeused during calibration.

In theory it does not matter which range is used whencalibrating the unit, but inpractice either the 1nF or 10nFrange has to be used. Suitable

capacitors for the other rangesare either unavailable or extremely expensive.

The 10nF range is thebetter choice as the small self-capacitance of IC1 is less

significant on this range,although this factor seems tohave very little affect onaccuracy. Probably the bestoption is to calibrate the unit onthe 10nF range using a 10nF

polystyrene capacitor having atolerance of one percent.

It is possible that a largereading will be produced on themeter when the unit is firstswitched on, but pressing Resetswitch S3 should reset themeter to zero. If it is notpossible to zero the meter properly, switch off at once andrecheck the entire wiring, etc.

If all is well, set preset VR1

at maximum resistance(adjusted full clockwise). Thenwith the unit set to the correctrange and the calibrationcapacitor connected to SK1 andSK2, operate pushswitch S2.This should produce a strong

deflection of the meter, andVR1 is then adjusted for precisely full-scale reading onmeter ME1. The unit shouldthen provide accurate readingson all five ranges.

IN USE The Meter is suitable for

use with polarized capacitorssuch as electrolytic andtantalum types. However, it isessential that they areconnected to SK1 and SK2 withthe correct polarity. The positive(+) lead connects to SK1 andthe negative lead connects toSK2.

Especially when using the1nF and 10nF ranges, avoidtouching the lead that connectsto SK1 when a reading is beingtaken. Otherwise electricalnoise might be introduced intothe system producinginaccurate results.

Avoid connecting a chargedcapacitor to this or any other capacitance meter, since doingso could result in damage to the

semiconductors in the meter circuit. If in doubt alwaysdischarge a capacitor beforetesting it.






This project provides up tosixteen channels of on-off signaling communication through just a single pair of wires, in one

direction or in both directionssimultaneously. In a one-waysystem the Transmitter may bepowered through the same pair of wires, which allows the monitoringof up to sixteen inputs fromlocations having no local power supplies. An interfacing option(next month) enables operationthrough audio circuits, such asprivate internal telephone andintercom systems.

Although ideal for remote

signaling and alarm systemmonitoring, other possibleapplications could include suchthings as environmentalmonitoring, model railway controlsand switching for advancedlighting or display systems. Theversatility of using circuit modules,and the ways in which they can beconnected together, means thatpossible applications are limitedonly by the constructor’s ownimagination.

HOSPITAL CALLLike many designs, this one

began with a request from afriend, who on this occasion is thevolunteer engineer for the local“Hospital Radio”. Althoughoperated by amateurs, thisservice manages to maintain

microphone is in use. Securitymonitoring channels are alsoneeded since the original studiois housed in a “Portacabin” andhas suffered from attemptedbreak-ins.

The request, then, was for the provision of sixteen “on-off”signaling channels to operatethrough a single circuit from thehospital’s internal telephonesystem. Plus, the icing on the

A PIC-based 8 to 16-Channel 2-wire on-off signaling communication link. An add-

on Interface (next month) will extend possible options to internal private telephoneand intercom systems.

MULTI-CHANNEL TRANSMISSION

SYSTEM by ANDY FLIND

impressively high operatingstandards.

At present a new studio isbeing constructed at some

distance from their existing oneand for a while they will beoperating these simultaneously,often with a disk jockey. workingin both. To make this possible, anumber of signaling channelsare required for functions suchas indicating when a

The three modules: Receiver board; Interface (next month)and, foreground, Transmitter board.







AC circuit. Furthermore, if the“low” and “high” states occupyaround 61 per cent of the totalperiod the energy content will besimilar to that of a cycle of sinewave. When passedthrough a suitable low-pass filter this produces a very goodapproximation of a sinewave asshown in Fig.2b, far more suitedto telephone circuits.

In passing, it’s worthmentioning that with a 5V supply

the current “wasted” by the tworesistors in the quiescent state isonly 25mA as they present a

series resistance of 2 kilohms,whilst the output impedance isonly 500 ohms as for this they are

effectively in parallel.

BI-DIRECTIONALOPERATION

Achieving bi-directionaloperation was more difficult. Intelephony there are “two-to-four-wire” converter circuits which splitthe conventional two wires intoseparate transmit and receivepairs. They work by coupling thecircuit to the receiver through an

impedance of some kind, often just a resistor, and injecting aninverted form of the locallytransmitted signal into thereceiver to cancel the bit of it thatcomes through this impedance.

Success with this type of circuit assumes that thetransmission path will have aknown and constant impedance,both resistive and reactive, andattempts to use it with theproposed telephone circuit failed

miserably. Eventually a softwaresolution was found in which eachtransmitter checks the line for silence before transmitting andmutes the local receiver beforedoing so. Two such transmitterscan be made to synchronize toeach other and take turns totransmit.

The PIC16F84 can haveinternal “weak pull-up” resistorsapplied to the eight bits of port Bwhen these are configured as

inputs, removing the necessity toprovide them externally. Eachinput can then be as simple as just a switch pulling it to ground if required.

A single PIC can only provideeight such inputs however, andthis project required sixteen.Since these ICs are now availableat a cost of less than 2 UK

pounds from some suppliers,the quickest and cheapest wayto obtain a further eight inputs isfrom a second PIC whichtransmits its inputs serially to thefirst upon request.

SOFTWARE OPERATION

An outline of the softwareoperation for the first PIC, IC1,in the Transmitter circuit isshown in the flow diagram Fig.3.The initial setting up includesconfiguring all of port B asinputs with active weak pull-ups.

This is followed by a brief delay. It is unlikely but quitepossible that both transmitters ina bi-directional system mightcheck the line, find it inactiveand transmit together in perfectsynchronization. The use of aslightly different delay in eachtransmitter will quickly breaksuch a pattern to ensure correctoperation. Five and tenmilliseconds are the values usedfor this.

Following the delay the PICmonitors the line for a period of

inactivity greater than 18ms,

after which it mutes the input tothe local receiver, collects theinput states from the secondPIC, IC2, and stores them in aregister named SW2, and thenstores its own input states inregister SW1. It then transmitsthe first clock “pulse” asdescribed earlier and checks thefirst bit of SW1. If this is clear,corresponding to an active input,a second pulse is transmitted. If

it is set, the input was inactiveso a delay lasting the period of apulse is called.

This action is repeated for the remaining seven bits of SW1followed by the eight bits of SW2, the whole process takingprecisely 32ms. After this theprogram returns to the start andthe entire sequence is repeated.


MAKE PORT A BIT 2 AN INPUT

MAKE PORT A BIT 2 OUTPUT

SET PORT A BIT 2 HIGH

IS PORT ABIT 2 HIGH?

GET PORT B STATESSTORE IN FILE SW1

IS PORT ABIT 2 LOW?

REPEAT FOR REMAININGSEVEN BITS OF SW1

SET PORT A BIT 2 LOW

DELAY FOR 100 sm

IS FIRST BITOF SW1 LOW?

INITIALISE:PORT A BIT 2 INPUT

ALL PORT B AS INPUTWITH WEAK PULL-UPS ON

START

YES

YES

YES

NO

NO

NO

Fig.4. Flow diagram for thesecond Transmitter PIC, IC2.












In contrast to theTransmitter there is nocommunication between the twoICs which both simply checkand store all sixteen bits andoutput the appropriate set. Thisallows them to use identicalsoftware and, as with theTransmitter, if just eightchannels are required thesecond IC can be simplyomitted.

An examination of thesoftware of this project willreveal that it is written instraightforward “top-down” stylewith most repetitive operations

simply repeated the appropriatenumber of times in preference tousing loop techniques. Thistends to improve reliability and iseasy to follow, even though it is

more tedious to write.

TRANSMITTER CIRCUIT

As with many PIC projects,the circuits are relatively simpleas so much of the work is doneby the software. The onlycomplexity is in the Transmitter

where the various methods of use make some of thecomponents optional.

These options will beexplained in more detail next

month. For now the simplestmethod will be described so thatconstruction and testing can becarried out.

The full circuit diagram of the Transmitter is shown inFig.7. The two 16F84 PICs, IC1and IC2, share a common clockusing the oscillator of IC1 with a

COMPONENTS

Resistors*R1, R5 22k (2 off)

R2 220k

*R3, *R4, R7 1k (3 off)

R6, R9 4k7 (2 off)

R8 10k


All 0.6W 1% metal film

CapacitorsC1, C2 22p resin-dipped

ceramic (2 off)

C3, C5, *C6 100n resin-dipped

ceramic (3 off)

C4 10u radial electrolytic, 63V

*C7 100u radial electrolytic, 25V

Semiconductors*D1 1N4148 signal diode

*TR1 BC184L npn transistor

IC1, IC2 PIC16F84 pre-prog-

rammed microcontroller (2 off)IC3 78L05 5V 100mA voltage

regulator

MiscellaneousX1 4MHz crystal

PL1 20-way IDC header plug

PCB available from the EPE

Online

Store, code 7000264 (Transmitter)

www.epemag.com; 18-pin DIL

socket (2 off); solder pins, solder,

multistrand connecting wire, etc.

Note, All components marked with

an asterisk are optional (see text).

$26 Approx. Cost

Guidance Only

TRANSMITTERR

3R4

R6

R5

D1

C3 IC1

R1

R2

R7

R8

X1

C1 C2

IC2

R9

C5

C4

C7

C

6

IC3

TR1PL1e

b

c

INCOM

OUT

+

+

COMMON

COMMON

OUTPUT 1

OUTPUT 2

OUTPUT 3

SENSE/MUTE

1 16INPUTS

+5 VOLTS

+12 VOLTS

GND (0V)

k

a

Fig.10. Printed circuit board topside component layout and (approximately) full-size under-side copper foil master pattern

for the Transmitter.












4MHz crystal X1 and capacitorsC1 and C2.

Both IC1 and IC2 have alleight inputs of port B pulled highinternally so these are simplybrought out to pins to whichexternal connections can bemade. The communicationbetween them is throughresistor R7 with pull-up resistor R8. A digital output is taken fromIC1 port A bit 2 (at pin 1), whichis normally high and goes lowfor clock and data pulses.

The sensing and mutingfunction, only required for synchronized bi-directional use,is performed with port A bit 1 (atpin 18) and operates as follows.When used in this way thesignal is coupled to the localreceiver through a 10k resistor,and the sense/mute pin is alsoconnected to the receiver side of this resistor.

Initially it is an input, andlistens for a continuous “high”signal to confirm that the other transmitter is not sending. Oncethis is detected it is converted toan output and set high for theduration of transmission, so thelocal receiver effectively sees acontinuous inactive line. Wherethis facility is not required,resistor R2 holds this pin high sothat transmission will take placeanyway.

Other optional bits areresistors R3 and R4 which are

only required if the unit is usedwith the Interface circuit to bedescribed next month, andresistors R1, R5, transistor TR1and diode D1, are needed if it isto be powered through a 2-wireconnection from the distantReceiver. The principle here isthat one of the two wires is acommon ground (0V), or negative, whilst the other isenergized from +5V through a220 ohm resistor (an option in

the Receiver) and chargescapacitor C4 via diode D1 whilstthe line is high. Then C4supplies the circuit whilst the lineis pulled low for pulses bytransistor TR1.

Finally, there is an optionalon-board 5V supply regulator,IC3. In most cases theTransmitter will be supplied with+5V from a Receiver, either local for a bi-directional systemor remote. However, if an

application requires that itshould be self-powered for anyreason, regulator IC3 can befitted together with inputdecoupling capacitors C6 andC7. In most cases these threecomponents will not be needed. Also, of course, where only eightchannels are needed IC2 maybe omitted.

RECEIVER CIRCUIT The Receiver circuit

diagram shown in Fig.8 is evensimpler. As with the Transmitter,the two PIC16F84s, IC1 and

IC2, share a common 4MHzcrystal clock. However, there isno communication betweenthem. Instead the input signal isconnected to RA2 (at pin 1) of both PICs. Each of the sixteenoutputs is provided with aresistor supplying a LED (light-emitting diode). These can beomitted if not required althoughthey are useful when testing. For clarity only one resistor and oneLED are shown for each IC in

Fig.8, since the others areidentical. The supply regulator IC3 is a robust 1A type mountedon a small heatsink as is has tosupply the LEDs and probablyalso some output circuits and aTransmitter. The only optionalcomponent is resistor R10 whichis needed if 2-wire operationwith the Transmitter poweredfrom the line is intended.

CONSTRUCTION Construction of this project

is straightforward. TheTransmitter and Receiver circuits, that make up the Multi-channel Transmission System,are both built up on single-sidedprinted circuit boards (PCBs).These boards are available fromthe EPE Online Store (codes7000264 (Transmitter) and7000265 (Receiver)). TheInterface PCB (next month) isalso available (code 7000266),

all from the EPE Online Store atwww.epemag.com

Starting with the Receiver,all the components exceptresistor R10, just above IC1,should be fitted as shown inFig.9. The use of DIL sockets isrecommended for the two PICs,IC1 and IC2.

OUTPUT 3

OUTPUT 1

OUTPUT 2

SENSE/MUTE

COMMON

COM

IN

+5V+5V

0V

0V

+12V

SUPPLY

TRANSMITTER

INPUTS

OUTPUTS

RECEIVER

Fig.11. Test set-up for checking out the two PCBs.
















Passive infrared (PIR) lamps,of the type that may be bought inany DIY store, are now verypopular with householders.Mounted on an outside wall, theymay be used to improve security

or simply to illuminate dark areaswhen a member of the familypasses by.

JUST PASSING THROUGH

These lamps are designed toswitch on for a certain time whensomeone walks in the detectionfield. This extends fan-shapedfrom a “window” in the front of thedetector. In simple units, the

operating time is fixed atmanufacture. However, it is moreusual to provide a control, whichmay be used to adjust it over a

on a filament bulb. In the larger security-type lamp, the bulb willbe a halogen unit of some 150Wto 500W rating. Smaller PIRlamps use an ordinary 60Whousehold bulb.

BLOWING IN THE

WINDWhen the PIR unit isproperly installed, the lamp doesits job well and rarely causesproblems. However, when it isnot properly set up it may beactivated by animals such asdogs and cats passing by.

Any warm object moving in(and especially across) thedetection field is likely to causethe unit to trigger – even warmair from a nearby central heating

flue. Tree branches and other objects moving in the windsometimes activate it –presumably because they reflectinfrared from somewhere else.

Any cause of false triggeringmay be difficult to track down. Itcan occur even when the user has taken every precautiondetailed in the installation guide. After supposedly “correct”setting-up, there is often atendency towards occasional

false triggering. This will requirefurther adjustment on a “trial anderror” basis to eliminate itcompletely.

Most PIR lamps have a“test” facility, which enablesthem to operate in daylight andthis helps with the initialadjustment process. However, itwill miss any false triggering

Be trigger happy with your outdoor security light system

PIR LIGHT CHECKER

by TERRY DE VAUX-BALBIRNIE

certain range.

Normally, the lamps operateonly when the ambient light fallsbelow a certain level so that theywill not switch on during daylighthours. Again, the point at which

this happens is often adjustableusing a control on the unit.

The working part of a PIRlamp is a sensor, which detectsthe infrared radiation that isnaturally emitted by a warmbody. The detector may becontained in a separate unitconnected remotely to the lamp.In most DIY units, however, it isattached to the lamp itself because this makes for simpler installation.

When a warm object movesin the sensitive zone, a signal isgiven which, after processing,operates a relay and switches





which happens only occasionally. There could be considerable difficultywhen the lamp is mounted in a position that cannot be seen from thehouse.

Normally, the only way to check for correct operation would be tostand outside and watch it for a long period of time! Unnecessary

operation of the lamp can be a nuisance to neighbors as well aswasting electricity and reducing the life of the bulb. With this PIR Light Checker , however, you can leave the monitoring to automaticelectronics!

CLOCKEDThis self-contained battery-operated unit will automatically monitor

a PIR lamp over aperiod of severalhours overnight. ALED (light-emittingdiode) displayregisters the number of times it has beentriggered, up to nine.If the count exceedsthis, the display willreturn to zero but thedecimal point will lightup. This shows the“overflow” – that is, anumber greater thannine. When the unit isswitched off then onagain, the count isreset to zero, ready

for a further test.By adjusting the

aim and sensitivitycontrol on the lamp (if one exists), re-sitingand cutting awayfoliage as necessary,any improvement canbe easily monitored.Multiple causes of false triggering maythen be eliminatedone by one over a

period of a few days.Note that if the unit isused to monitor thelamp overnight, it willrecord an extra countat dawn and this willneed to be subtractedfrom the total.

This circuit is onlysuitable for use at


a

f

b

g

e

c

d X 2

b

c e

B 1

6 V

R 6

1 M

R 5

3 M 3

+ I C 1

I C L 7 6 1 1

3 2

4

7

8

6

R 7

1 M

R 8

2 M 2

R 1 0

1 M

R 1 9

2 M 2

R 1 1

1 M

R 9

1 M

R 3

4 7 0 k

R 1

5 6 k

R 4

4 7 0 k

R 2

L . D . R .

( 2 M

D A R K )

V R 1

2 M 2

C 1

4 7 n C

2 1 0 0 n

C 4

1 0 0 n

C 3

1 0 0 n

C 7

1 0 0 n

C 5

1 µ

C 8

2 2 0 µ

I C 2 a

5 5 6

I C 2 b

5 5 6

I C 3

4 0 1 1 0

6

9

4

1 0

5 1

1 3

2

1 2

7

6

8

4

1 4

1 6

+ V E

+ V E

G N D

G N D

T R I G

T R I G

R E S E T

R E S E T

O

U T

O U T

D I S

D I S

T H R E S

T H R E S

9 5

C L O C K U P

R E S E T

T A G

E N

L A T C H

E N

1 2 3 1 2

1 3

1 4

1 5

1 0

C 6

1 0 0 n

R 1 2 T O R

1 8

2 7 0 Ω

R 2 0

2 7 0 Ω

X 1

7 1 0 9 1 2 4 6

a g f e d c b

5

D P

8

S 1

G N D

D I S P L A Y

O N / O F F

D 1

1 N 4 0 0 1

k

a

S 2

T R 1

2 N 3 9 0 3

3

Fig.1. Complete circuit diagram for the PIR Light


R1

R2

R3, R4

R5

R6, R7, R9 to R11

R8, R19

R12 to R18, R20


All 0.25W 5% carbon film

PCB available from the EP E Online Store, code 7000263(www.epemag.com); 8-pin DIL socket; 14-pin DIL

socket;

16-pin DIL socket; 1.5V AA-size alkaline cell (4 off) and

holder; plastic case, size 138mm x 76mm x 38mm

internal;

PCB suppor ts (2 off); connecting wire; solder, etc.

$32 Approx. Cost

Guidance Only (excl. battery pack)

56k

sub-miniature light-dependent resistor

(LDR), dark resistance 5M ohms

approximately (see text)

470k (2 off)

3M3

1M (5 off)

2M2 (2 off)

270 ohms (8 off)

Potentiometer VR1 2M2 miniature enclosed carbon preset,

horizontalCapacitors

C1

C2

C3, C4, C6, C7

C5

C8

47n metallised polyester, 2.5mm pitch

100n metalised polyester, 2.5mm pitch

100n metalised polyester, 5mm pitch

(4 off)1u radial electrolytic, 63V

220u radial electrolytic, 10V

SemiconductorsD1

TR1

IC1

IC2

IC3

1N4001 1A 50V rectifier diode

2N3903 npn transistor

ICL7611 micropower opamp

ICM75561PD dual CMOS timer

40110B decade up/down counter

MiscellaneousX1

S1

S2

7-segment, common cathode LED

display, 12.7mm

miniature s.p.s.t. push-to-make or

biased toggle switch

miniature s.p.s.t. toggle switch












night with the PIR lamp in“normal” mode. There must beno other bright sources of lightnearby which could result infalse counts.

BATTERY SAVING The circuit is housed in a

small plastic box. This has aseven-segment LED displayshowing through a hole in thelid. There are also two switches(see photograph). One of theseis simply an on-off switch whilethe other activates the display.This latter switch is operatedonly when a reading needs to betaken and so saves battery

power. A hole in the side of thebox allows light from the lampbeing monitored to reach asensor on the printed circuitboard (PCB) inside.

The unit draws power froma 6V battery pack consisting of four AA-size alkaline cells.Under standby conditions, thecurrent requirement of theprototype unit is some 400uA.

When the display isoperated, the current rises to a

value that depends on thenumber being displayed. This isbecause each digit is formed bylighting up the appropriatesegments in the display. Themost current-hungry case iswhen the number “8” is involved(since this uses all sevensegments) together with the“over-flow” decimal point.

Since each segment andthe decimal point require 12mAapproximately, the total current

will be about 100mA. However,this will only be needed for a fewseconds during each test and,as stated earlier, it is the “worst”case. In practice, the batterypack should last for at least ayear under normal conditions.

HOW IT WORKS The full circuit diagram for the

PIR Light Checker is shown inFig.1. Power is derived from a 6Vbattery pack (4 x 15V cell) B1 via

on-off switch S2 and diode D1.The diode prevents possibledamage if the supply were to beconnected in the opposite sense.If this were done, the diode wouldbe reverse-biased so no currentwould flow.

It will be found that the actualnominal supply voltage is 53V

taking into account the forwardvoltage drop of the diode (07V

approximately). Capacitor C8charges up almost instantly and

helps to provide a smooth andstable supply.

The light-sensing section of the circuit is centered on IC1 andassociated components. The lightdetector itself is a light-dependentresistor (LDR), R2. The resistanceof this device rises as theillumination of its sensitive surfacefalls.

The LDR works in conjunctionwith fixed resistor R1 and presetpotentiometer VR1 to form apotential divider connected acrossthe supply. Thus, as theresistance of the LDR increases,the voltage across it will rise. Thisvoltage will therefore be greater when the LDR is dark than when itis illuminated. The actual “dark”and “light” voltages can be variedwithin certain limits by adjustingVR1. The voltage appearingacross the LDR is applied to theinverting input (pin 2) of operational amplifier (opamp) IC1.

The non-inverting input (pin 3) isconnected to the mid-point of afurther potential divider consistingof fixed resistors R3 and R4.Since these have the same value,the voltage here will be equal toone-half that of the supply – thatis, 26V approximately.

A BIT DIM With preset VR1 suitably

adjusted, under dim conditionsthe voltage at the opampinverting input will exceed that at

the non-inverting one, so thedevice will be off with the output(pin 6) low. When the LDR issufficiently illuminated, theconditions will reverse with theinverting input voltage fallingbelow the non-inverting one.The opamp will then switch onand output pin 6 will go high.Resistor R5 applies somepositive feedback to the system,which sharpens the switchingaction at the critical light level.

Transistor TR1 inverts theoutput state of the opamp.When the output is high, currentflows into TR1 base (b) throughcurrent-limiting resistor R6. Thisswitches the transistor on andits collector (c) goes low. Whenthe opamp output is low, nocurrent will enter the base andthe transistor will remain off. Thecollector will then take on a highlogic state via load resistor R7.The state of the collector istherefore in the opposite senseto that of the opamp output.

MONOSTABLE Transistor TR1’s collector is

connected to the trigger input(pin 6) of a monostable basedon IC2a, which is one half of dual integrated circuit timer, IC2.

When TR1 collector goesfrom high to low (that is, theLDR is illuminated), the trigger

input receives a low pulsethrough capacitor C1. Themonostable output (pin 5) thengoes high for a time dependenton the values of resistor R10and capacitor C4. With thevalues specified, the timedperiod is 01s, approximately.

While the opamp output










way of anything else.

Add the diode and transistor to the PCB, taking care over their orientation. The flat face of transistor TR1 should face to theright as viewed in Fig.3.

Solder the display to thePCB (with the decimal point atbottom right, as shown in thephoto) using minimum heat fromthe soldering iron to preventpossible damage.

Solder 10cm pieces of light-duty stranded connecting wire tothe points labeled +6V and S1.Solder the negative (black)battery connector lead to the 0Vpoint. Adjust VR1 toapproximately mid-trackposition.

TESTING Immediately before handling

the pins of IC1, IC2 and IC3,

touch something which is“earthed” (such as a metal water tap). This will remove any staticcharge, which may be presenton the body. Insert the ICs intheir sockets with the correctorientation.

Before mounting the PCB inits case, perform a basic checkso that any minor problems may

be resolved more easily.

To do this, bare the end fewmillimeters of the wires for display switch S1 and connectthem together. Similarly, barethe end of the +6V wire. Insertthe cells for battery B1 into their holder and apply the connector.Twist the battery connector positive (red) wire to the +6Vwire from the PCB.

The display should light up

and read zero. The decimal

point should also be off. If itshows some other number, or the decimal point is on, theconnection was probably notdone “cleanly”, so disconnectthe battery, wait for 30 seconds

and try again!

Cover the LDR with thehand then remove it to allowlight to reach its window. Thedisplay should advance to acount of 1. If this does not work,it is likely that the LDR has notbeen properly covered. Tryworking in a dark cupboard andopen the door slightly to give theflash of light. If this still does notwork, re-adjust preset VR1 andtry again.

By allowing repeated flashesof light to reach the LDR, thecounter should increment to 9and the next flash should returnit to zero. However, the decimalpoint should now be seen to belit up. If you wish to reset thedisplay, you will need to wait for up to thirty seconds betweendisconnecting the battery andre-connecting it again.


Layout of components on the completed circuit board.Note, one corner of the board has been trimmed off so it will fit

in the case.

Completed PIR Light Checker front panel layout.The display cutout has been backed with a piece of translucent

filter material.





ENCLOSURE If all is well, the PCB may

now be mounted in the box.Note that when using thespecified unit, everything may

be attached to the lid section.This method places least strainon the battery connecting wires.

First, disconnect the positivesupply wire and detach thebattery connector. Decide onpositions for the PCB, batterypack and switches, checkingthat there is sufficient space for everything to fit. Arrange for theLDR to lie between 5mm and10mm from the side of the box.

In the prototype, a miniaturetoggle switch with “make”contacts was used for the on-off switch and a matching biasedtoggle switch was used for thedisplay. A biased switch is onethat springs back to the off position when pressure isremoved from the actuatinglever. It is best to use either abiased toggle switch or a push-to-make switch to activate thedisplay so that it cannot be lefton accidentally.

Mark through the PCB fixingholes. Measure the position of the display and mark around itsoutline. Mark also the positiondirectly in line with the LDR

window and VR1 on the top.Mark the position of theswitches. Remove the PCB anddrill all these holes.

The hole for the LDR should

have a diameter of approximately 4mm (about twiceas large if the ORP12 type LDRis used). The hole above thepreset VR1 position should belarge enough to allow it to beadjusted using a thinscrewdriver or trimming tool.

The easiest way to makethe hole for the display is to drillsmall holes within its outlinethen remove the plastic using asmall hacksaw blade, or sharp

chisel. Finally, smooth the edgesup to the line using a small file.

Attach the PCB temporarilyusing nylon fixings and withshort plastic stand-off insulatorson the bolt shanks. Adjust thelength of the stand-off insulatorsso that the display will end up1mm approximately below theinside face of the box. Whensatisfied, re-attach the PCB.

Check that the LDR windowlies directly in line with the hole

drilled for it. If not, adjust theposition of its end leads so that itis. Attach the switches. Securethe battery pack using a smallbracket or adhesive pads. Refer to Fig.3 and complete the

internal wiring.

In the prototype, a piece of red plastic filter was glued over the display hole on the inside of the box. This gives a

professional appearance andalso improves the contrast of thedisplay. If a piece of real filter isnot available, perhaps suitablematerial could be obtained froma sweet wrapper or somethingsimilar.

INTO SERVICE With switch S2 off, connect

the battery and attach the lid.Find a suitable place for the unitso that light from the PIR lamp

will reach the LDR directlythrough the hole in the side of the box. The fact that the LDR issome distance behind the holemakes the response directional.This is useful because it tendsto discriminate against other sources of light, which couldresult in false counting.

Make some tests at night.For initial trials, you may find ithelpful to use an elastic band or PVC tape to hold the display

switch (S1) on, so that the countmay be observed over a periodof time. Remember that thiswastes the batteries so don’t doit for too long.

Adjust preset VR1 for besteffect. Remember to protect theunit against rain entering if thisis a possibility.

No more disturbedneighbors with this “Trigger Happy” circuit!


http://www.veronica.co.uk/





GOOGLE BOX

Eagle-eyed readers willhave noticed that I recentlyplaced a Google search enginein the 100 percent revalidatedNet Work A-Z page on our website, which contains many of theexisting links I have highlightedin the past. Google is hugely fastand easy to use. Instead of try-ing to index every known website, Google actually indexes on

the basis of all the other linksmade to those same web sites.The search engine makes thereasonable assumption that thebetter a web site is, the greater the number of links pointing tothat site. More importantly,Google keeps a cache of storedweb pages, so that even if aweb site is taken down there isstill a possibility that you can re-trieve the content from Google’scache. Give it a try.

In March 2000 Net Work Ioutlined the evolution of AltaVista, Digital Equipment’s lead-ing search engine and portal sitewhich was acquired by computer manufacturer Compaq in early1998. There is no doubt that AltaVista is a first-rate search en-gine, offering further options tonon-English users courtesy of itsBabel Fish language translator. Alta Vista continues to roll outacross Europe, starting out inGermany almost a year ago, fol-lowed by Sweden and more re-cently the UK in December 1999. The Californian-basedcompany then launched intoFrance and the Netherlands lastmonth.

FREE FOR ALL

In early March Alta Vista UKtook the wind out of the sails of cable operator NTL(www.askntl.com) as well asBritish Telecom, by announcingits new free Internet access ser-vice for UK users. In fact it isn’tentirely free – there will be aone-off set-up charge of any-thing up to 50 UK pounds beingreported, and an annual cost of

say 20 UK pounds. The newservice, to be called Al-taVista0800, will be rolled out ata rate of 90,000 users per month starting in June 2000.

In the USA and Canada, aservice called AltaVista Free Ac-cess has been available since August 1999 (seewww.microav.com), offeringcompletely free Internet accessto its users. There are no set-upor subscription charges at all.

Instead, AltaVista Free Accessemploys a “Micro Portal” – awindow on the user’s computer screen which contains rotatingadverts and other customizablecontent. The technology behindthis is provided by 1stUp.com, aUS developer specializing inadvert-supported dial-up ac-counts. The advertising windowmust always remain open to en- joy free Internet access, which isa powerful incentive for manyconsumers already conditionedto banner adverts to remainloyal.

In the UK, by using an 0800access number, subscribers arerelieved of the worry of the cost

of the phone call, though obvi-ously they still have to pay linerental charges. Alta Vista UK’snew service will not allow a per-manent 24 x 7 connection to theInternet, because it will time outafter five minutes of inactivity.Furthermore, any attempt to“ping” an open connection with akeep-alive utility such asWakeUp will be treated as anabuse, presumably leading towithdrawal of the service.

UNDER THE SURF

The new service announcedby Alta Vista UK wrong-footedBritish Telecom into declaring itsown revised plan for un-meteredaccess. BT previously sug-gested its SurfTime package(see Net Work Feb ’00) couldcost anything up to 35 UKpounds a month for always-onaccess. I showed how this was

five times more than a user inDallas, Texas who pays just $12(7 UK pounds a month) after loyalty discounts, with local In-ternet and voice calls thrown infor free.

In light of Alta Vista UK’snew 0800 package, BT wasforced into firming up its ownposition. They make much of thefact that their SurfTime optionwill be available to businessesas well as home users, and they

are attempting to cater for users’differing habits, given that manyusers are obviously at work dur-ing the day and only access theInternet during evenings andweekends. The cheapest option

By Alan Winstanley

SURFING THE INTERNET

http://www.microav.com/










that BT now proposes is for oc-casional users, paying 1 penceper minute daytimes, 06 pence

evenings and 05 pence week-ends, on top of line rental at

9.26 UK pounds per month. As usual, BT’s press re-

lease is not entirely straightfor-ward, partly because they hint atan all-inclusive cost for Internetaccess by bundling in rental fig-ures plus an estimate of monthlyISP charges. For a service feeof 5.99 uk pounds a month ex-cluding rental, BT customerscan choose the evening andweekend package which allowsfor un-metered access plus up

to 80 minutes’ voice calls. BT’salways-on package is likely tocost 19.99 UK pounds per month plus rental for homeusers and 29.74 UK pounds ex-cluding VAT (including rental)for business users.

Realizing that the rates willbe scrutinized by an increasinglyimpatient audience, BT hasgone to extraordinary lengths toemphasize how competitive theysay their dial-up Internet pack-

ages are in comparison withsimilar ones in the USA.

The rates won’t be availableto end-users until June 2000,and there is a further complica-tion: BT SurfTime will requireusers to access their preferredISP by using an 0844 04 num-ber. If your preferred ISP doesn’toffer one, then you can’t use theSurfTime package. More prob-lems in store include the factthat no wholesale pricing had

been offered, therefore no other service provider (e.g. Freeserve)

would be able to compete by re-selling BT SurfTime.

As if BT’s convoluted phonetariffs aren’t enough, don’t forgetthe offerings over at BT Internet

(www.btinternet.com), thetelco’s Internet Service Provider arm. Un-metered 0800 eveningand weekend access is nowavailable at a new lower rate of 9.99 UK pounds a month or 109.98 UK pounds a year, andas a sign of their eagerness tohelp novices getting to grips withthe Internet, BT have actuallyincreased the cost of supportcalls to 50 pence a minute upfrom local rate.

LOOKING AHEAD

The UK Internet market re-mains as volatile as ever, andfurther sweeping changes areprobable over the next 12 to 18months before the market finallysettles down. For Freeserve, the18-month old pioneer of the freeISP model, interesting times areahead. As with all free ISPs,Freeserve makes its revenue

from that all-important slice of the cost of the BT 0845 phonecall, plus advertising and thecost of providing technical sup-port.

Consumers tend not to havemuch loyalty towards their ISPand if they suddenly decide to jump ship from the free ISPsand move to a service such as AltaVista0800, preferring to payan annual fee for free unlimitedcalls, this is bound to have aprofound impact on Freeservewhich charges nothing as an

ISP but makes you pay for thecalls instead. It is hard to knowwhat will happen to those freeISPs that also bundle your do-main name and technical sup-

port in with the deal.It is not as though any of

these free ISPs can levy even asmall monthly fee, as they don’thave any billing mechanism inplace. Freeserve’s latest moveinvolves offering free Internetaccess, provided customersmake 10 UK pounds of calls per month routed through Energis,its parent telco. However, BT isnow spending the interveningmonths rolling out the intercon-

nect components, and ISPswhich adopt the 0844 SurfTimetariff are expected to be able tocharge their subscription fees totheir customer using the user’sBT phone bill. When there arenew offers springing up all thetime, it makes sense not to com-mit to a long-term agreementuntil all the players have madetheir moves.

You can E-mail me [email protected].

My web site is at http://home-pages.tcp.co.uk/~alanwin

Net Work

http://www.btinternet.com/












The purpose of this series isto review how we came to bewhere we are today (technology-wise), and where we look like

ending up tomorrow. In Part 1 wecast our gaze into the depths of time to consider the state-of-the-art in electronics,communications, and computingleading up to 11:59pm on 31December 1899, as the world waspoised to enter the 20th Century.

Parts 2 and 3 coveredfundamental electronics andcommunications in the 20thCentury, respectively. Now, inPart 4 we consider some of the

key discoveries in computing thatoccurred during the 20th Century.These developments have set thescene for what is to come as weplunge forth into the thirdmillennium. But before we start,let’s first consider logic diagramsand logic machines, which usuallyreceive little mention …

LOGIC AND LOGIC DIAGRAMS

With the exception of CharlesBabbage’s proposal for amechanical computer called the Analytical Engine in 1832, verylittle thought was given tocomputing prior to 1900. Instead,effort was focused on simplemechanical calculators, and alsoon variations of another mechanism put forward in 1882

University called Allan Marquandinvented a graphical techniqueof representing logical problemsusing squares and rectangles.Marquand’s efforts set a number of people to pondering, includingthe Reverend Charles LutwidgeDodgson, who published hisown diagrammatic technique ina book called The Game of Logic in 1886. (The Reverend isbetter known to most of us asLewis Carroll, the author of Alice’s Adventures inWonderland .)

In the early 1890s, yetanother approach was putforward by the English logicianJohn Venn, who was extremelyimpressed by Boole’s work.Unlike earlier graphicaltechniques, Venn’s diagramswere based on the use of circlesand ellipses, which could beemployed to represent Booleanequations.

The rectangles and squaresof Marquand and Carrolleventually led to MauriceKarnaugh inventing a graphicaltechnique for both representingand minimizing Booleanexpressions in the 1950s. Thesetechniques were to become

tremendously useful todesigners of digital logic, andKarnaugh maps and VennDiagrams are both still taughtand used to this day.

LOGIC MACHINES In addition to speculating

about logic, it should come as

Part 4 – COMPUTERS 1900-1999

by Clive “Max” Maxfield and Alvin Brown

by Babbage called a DifferenceEngine, which could be used togenerate certain mathematicaltables.

However, this is not to saythat nothing of interest(computing-wise) was takingplace, because there were anumber of developments thatwould prove to be extremelyinteresting to computer scientists in the 20th Century.

First of all, the self-taughtBritish mathematician GeorgeBoole published two key papersin 1847 and 1854. These papersdescribed how logical

expressions could berepresented in a mathematicalform that is now known asBoolean Algebra. What Boolewas trying to do was to create amathematical technique thatcould be used to represent andrigorously test logical andphilosophical arguments.

We can only imagine whatBoole would have thought hadhe realized that his newmathematics would find

application in designing digitalcomputers 100 years in hisfuture. But we digress …

LOGIC WONDERLAND

In 1881, a lecturer in logicand ethics at John Hopkins

Boldly going behind the beyond, behind which no onehas boldly gone behind, beyond, before!





no surprise to learn that people

have been experimenting withso-called “logic machines” for quite some time. Perhaps theearliest example is a set of concentric, nested discsrevolving around a central axisas proposed by the Spanishtheologian Ramon Lull in 1274.Each disc contained a number of different words or symbols,which could be combined indifferent ways by rotating thedisks.

Lull’s disks were followed bya variety of other techniquesover the centuries, most of which we would now consider to

be “half-baked” on agood day.

The world’s firstreal logic machine(that is, one thatcould actually be

used to solve simplelogic problems, asopposed to Lull’swhich tended tocreate moreproblems than itsolved) was inventedin the late 1700s bythe British scientist

and statesmanCharles Stanhope(third Earl of Stanhope).

This device, the StanhopeDemonstrator , was a small boxwith a window in the top, alongwith two different colored slidesthat the user pushed into slots inthe sides. Although this doesn’tsound like much it was a start,but Stanhope wouldn’t publishany details and instructed hisfriends not to say anything aboutwhat he was doing.

In fact, it wasn’t until aroundsixty years after his death that

the Earl’s notes and one of hisdevices fell into the hands of theReverend Robert Harley, whosubsequently published an

Special Feature

Stanhope Square Demonstrator, late18th century. Courtesy Science Museum/

Science and Society Picture Library.

TIMELINES 1274: Spain. Theologian Ra-

mon Lull proposes a“logic machine” consist-ing of a set of concentric,

nested disks.1777: Charles Stanhope in-

vents a mechanical cal-culating machine.

Late 1700s: Charles Stanhopeinvents the StanhopeDemonstrator.

1822: England. Charles Bab-bage starts to build a me-chanical calculating ma-chine – the DifferenceEngine.

1832: England. Charles Bab-bage conceives the firstmechanical computer –the Analytical Engine.

1847: England. George Boolepublishes his first ideason symbolic logic.

1869: William Stanley Jevonsinvents the Logic Piano.

1881: Alan Marquand invents agraphical technique of representing logic prob-

lems.1886: Reverend Charles

Lutwidge Dodgson(Lewis Carroll) publishesa diagramatic techniquefor logic representation inThe Game of Logic.

1890s:John Venn proposeslogic representations us-ing circles and ellipses.

1925: America. Scientist, engi-neer, and politician Van-nevar Bush designs ananalog computer calledthe Product Intergraph.

1930: America. Vannevar Bushdesigns an analog com-puter called a Differential Analyzer.

1936: America. Efficiency ex-pert August Dvorakpatents his layout for

Stanhope’s calculating machine, 1777. Courtesy Science Mu-seum/Science and Society Picture Library.





article on the StanhopeDemonstrator in 1879.

Stanhope also invented acircular demonstrator and amechanical calculating machine.

LOGIC PIANOS Working on a somewhat

different approach was theBritish logician and economistWilliam Stanley Jevons, who, in1869, produced the earliestmodel of his famous Jevons’ Logic Machine. This device isnotable because it was the firstmachine that could solve alogical problem faster than thatproblem could be solved without

using the machine!Jevons was an aficionado of

Boolean logic, and his solutionwas something of a crossbetween a logical abacus and apiano (in fact it was sometimesreferred to as a “Logic Piano”).This device, which was about ameter (three feet) tall, consistedof keys, levers and pulleys,along with letters that could beeither visible or hidden. Whenthe operator pressed keys

representing logical operations,

the appropriate letters appearedto reveal the result.

The next real advance inlogic machines was made by Allan Marquand, whom wepreviously met in connection

with his work on logic diagrams.In 1881, by means of theingenious use of rods, levers,and springs, Marquandextended Jevons’ work toproduce the Marquand Logic Machine. Like Jevons’ device,Marquand’s machine could onlyhandle four variables, but it wassmaller and significantly moreintuitive to use.

ROCKET-POWEREDFRISBEES Things continued to develop

apace. In 1936, the Americanpsychologist Benjamin Burackfrom Chicago constructed whatwas probably the world’s firstelectrical logic machine.Burack’s device used light bulbsto display the logicalrelationships between acollection of switches, but for some reason he didn’t publish

anything about his work until1949.

In fact, theconnectionbetweenBoolean algebraand circuitsbased onswitches hadbeen recognizedas early as 1886by an educator called Charles

Pierce.However,nothingsubstantialhappened in thisarea until 1938,at which time the Americanengineer ClaudeE. Shannon

Special Feature

keys on a typewriter called the Dvorak Key-board.

1936: America. PsychologistBenjamin Burack con-structs the first electricallogic machine (but hedidn’t publish anythingabout it until 1949).

1937: America. George RobertStibitz, a scientist at BellLabs, builds a simple dig-ital calculator machinebased on relays calledthe Model K.

1937: England. Graduate stu-dent Alan Turing (of Colossus fame) writes

his ground-breaking pa-per: On ComputableNumbers with an Appli-cation to the Entschei-dungsproblem.

1937: England. Alan Turing in-vents a theoretical(thought experiment)computer called the Tur-ing Machine.

1938: America. Claude E.Shannon publishes anarticle (based on his

master’s thesis at MIT)that showed howBoolean algebra could beused to design digital cir-cuits.

1938: Germany. Konrad Zusefinishes the constructionof the first working me-chanical digital computer (the Z1).

1939: America. George RobertStibitz builds a digital cal-

culator called the Com-plex Number Calculator.

1939: America. John Vincent Atanasoff (and CliffordBerry) may or may nothave constructed the firsttruly electronic special-purpose digital computer called the ABC (but it didnot work until 1942).

Monroe’s “Full Automatic” calculating ma-chine, 1922, the first machine to offer fully au-tomatic multiplication and division. Courtesy Science Museum/Science and Society Picture Library.





published an article based onhis master’s thesis at MIT.

Shannon’s thesis has beendescribed as: “Possibly the most important Master’s thesis of thetwentieth century.” In his paper,which was widely circulated,Shannon showed how Boole’sconcepts of TRUE and FALSE

could be used to represent thefunctions of switches inelectronic circuits. (Shannon isalso credited with the inventionof the rocket-powered Frisbee,and is famous for riding downthe corridors at Bell Laboratorieson a unicycle whilesimultaneously juggling four balls.)

Following Shannon’s paper,a substantial amount of attentionwas focused on developing

electronic logic machines.Unfortunately, interest inspecial-purpose logic machineswaned in the 1940s with theadvent of general-purposecomputers, which proved to bemuch more powerful and for which programs could be writtento handle formal logic.

ELECTROMECHANIC AL COMPUTERS

In 1927, with the assistanceof two colleagues at MIT, the American scientist, engineer and politician Vannevar Bushdesigned an analog computer that could solve simple

equations. This device, whichBush dubbed a Product Intergraph, was subsequentlybuilt by one of his students.

Bush continued to develophis ideas and, in 1930, built abigger version, which he called aDifferential Analyzer . TheDifferential Analyzer was basedon the use of mechanicalintegrators that could beinterconnected in any desiredmanner. To provide

amplification, Bush employedtorque amplifiers, which werebased on the same principle asa ship’s capstan. The finaldevice used its integrators,torque amplifiers, drive belts,shafts, and gears to measuremovements and distances (notdissimilar in concept to anautomatic slide rule).

Special Feature

1940: America. George RobertStibitz performs first ex-ample of remote comput-ing between New Yorkand New Hampshire.

1941: Germany. Konrad Zusefinishes the first truerelay-based general-purpose digital computer (the Z3).

1942: Germany. Between 1942and 1943 Konrad Zusebuilds the Z1 and Z2computers for the Hen-schel aircraft company.

1942: Germany, Between 1942and 1945/6 Konrad Zusedevelops the ideas for a

high-level computer pro-gramming languagecalled Plankakul.

1943: England. Alan Turing andteam build a special-purpose electronic(vacuum tube) computer called Colossus.

1944: America. Howard Aikenand team finish buildingan electromechanicalcomputer called the Har-vard Mark I (also knownas the IBM ASCC).

1945: America. Hungarian/ American mathematicianJohann (John) Von Neu-mann publishes a paper entitled First Draft of areport on the EDVAC.

1946: America. John WilliamMauchly, J. Presper Eck-ert and team finish build-ing a general-purposeelectronic computer

called ENIAC.1948: America. Work starts on

the first commercial com-puter, UNIVAC 1.

1948: America. First commer-cial computer, UNIVAC1, is completed.

1949: England, Cambridge Uni-versity. Small experimen-

Hartree Differential Analyzer, 1935, based on that invented by Vannevar Bush. Courtesy Science Museum/Science and Soci-ety Picture Library.





Although Bush’s firstDifferential Analyzer was drivenby electric motors, its internaloperations were purelymechanical. In 1935 Bushdeveloped a second version, inwhich the gears were shiftedelectro-mechanically and whichemployed paper tapes to carryinstructions and to set up thegears.

In our age, when computerscan be constructed the size of

postage stamps, it is difficult tovisualize the scale of theproblems that these earlypioneers faced. To providesome sense of perspective,Bush’s second Differential Analyzer weighed in at awhopping 100 tons! In additionto all of the mechanicalelements, it contained 2000vacuum tubes, thousands of relays, 150 motors, andapproximately 200 miles of wire.

As well as being a major achievement in its own right, theDifferential Analyzer was alsosignificant because it focusedattention on analogue computingtechniques, and thereforedetracted from the investigationand development of digitalsolutions for quite some time.

FLASHLIGHT BULBS AND TIN CANS

However, not everyone wasenamoured by analogcomputing. In 1937, GeorgeRobert Stibitz, a scientist at BellLaboratories built a digitalmachine based on relays,flashlight bulbs and metal stripscut from tin-cans, which hecalled the Model K (becausemost of it was constructed on

his kitchen table).

Stibitz’s machine worked onthe principle that if two relayswere activated they caused athird relay to become active,where this third relayrepresented the sum of theoperation. For example, if thetwo relays representing thenumbers 3 and 6 wereactivated, this would activateanother relay representing thenumber 9. (A replica of the

Model K is on display at theSmithsonian.)

Stibitz went on to create amachine called the Complex Number Calculator , which,although not tremendouslysophisticated by today’sstandards, was an importantstep along the way. In 1940,Stibitz performed a spectacular

Special Feature

tal computer called ED-SAC performs its firstcalculation.

1949: England. EDSAC com-puter uses first assem-bler called Initial Orders.

1949: America. MIT’s first real-time computer, Whirl-wind.

1950: America. Jay Forrester atMIT invents magneticcore store.

1951: America. Computers aresold commercially.

1952: America. John WilliamMauchly, J. Presper Eck-ert and team finish build-ing a general-purpose(stored program) elec-tronic computer calledEDVAC.

1956: America. John Backusand team at IBM intro-duce the first widely usedhigh-level computer lan-guage, FORTRAN.

1956: America. John McCarthydevelops a computer lan-guage called LISP for artificial intelligence ap-

plications.1956: America. MANIAC 1 is

the first computer pro-gram to beat a human ina game (a simplified ver-sion of chess).

1957: America. IBM 610 Auto-Point computer is intro-duced.

1958: America. Computer datais transmitted over regu-lar telephone circuits.

1959: America. COBOL com-puter language is intro-duced for business appli-cations.

1961: Time-sharing computingis developed.

1963: In America, the LINCcomputer was designedat MIT.

Harvard Mark I, the first large-scale automatic digital computer.Courtesy of IBM.





demonstration at a meeting inNew Hampshire.

Leaving his computer inNew York City, he took ateleprinter to the meeting and

proceeded to connect it to hiscomputer via telephone. In thefirst example of remotecomputing, Stibitz astounded theattendees by allowing them topose problems, which wereentered on the teleprinter; withina short time the teleprinter presented the answersgenerated by the computer.

HARVARD MARK I Many consider that the

modern computer eracommenced with the first large-scale automatic digitalcomputer, which was developedbetween 1939 and 1944. Thisdevice, the brainchild of aHarvard graduate, Howard H. Aiken, was officially known asthe IBM automatic sequencecontrolled calculator (ASCC),but is more commonly referredto as the Harvard Mark I .

The Mark I was constructedout of switches, relays, rotatingshafts, and clutches, and wasdescribed as sounding like a“roomful of ladies knitting.” Themachine contained more than750,000 components, was 50feet long, 8 feet tall (15 2m x

24m), and weighed

approximately five tons(5080kg)!

Although the Mark I isconsidered to be the first digitalcomputer, its architecture wassignificantly different frommodern machines. The deviceconsisted of many calculators,which worked on parts of thesame problem under theguidance of a single control unit.

Instructions were read in onpaper tape, data was providedseparately on punched cards,

and the device could onlyperform operations in thesequence in which they werereceived. This machine wasbased on numbers that were 23digits wide – it could add or

subtract two of these numbers inthree-tenths of a second,multiply them in four seconds,and divide them in ten seconds.

KONRAD ZUSE In the aftermath of World

War II, it was discovered that aprogram controlled calculator called the Z3 had beencompleted in Germany in 1941,which means that the Z3 pre-

dated the Harvard Mark I. TheZ3’s architect was a Germanengineer called Konrad Zuse,who developed his firstmachine, the Z1, in his parents’living room in Berlin in 1938.

Although based on relays,the Z3 was very sophisticatedfor its time; for example, itutilized the binary number system and could handlefloating-point arithmetic. (Zusehad considered employingvacuum tubes, but he decided touse relays because they weremore readily available and alsobecause he feared that tubeswere unreliable).

In 1943, Zuse started workon a general-purpose relaycomputer called the Z4. Sadly,the original Z3 was destroyed bybombing in 1944 and thereforedidn’t survive the war (althougha new Z3 was reconstructed inthe 1960s). However, the Z4 didsurvive – in a cave in theBavarian Alps – and by 1950 itwas up and running in a Zurichbank.

It is interesting to note thatpaper was in short supply inGermany during the war, soinstead of using paper tape,Zuse was obliged to punchholes in old movie film to store

Special Feature

1965: John Kemeny andThomas Kurtz developthe BASIC computer pro-gramming language.

1968: First Static RAM ICreaches the market.

1970: First floppy disk (8.5inch) is used for storingcomputer data.

1970: America. Ethernet devel-oped at Palo Alto Re-search center by BobMetcalfe and DavidBoggs.

1971: America. Datapoint 2200computer introduced byCTC.

1971: CTC’s Kenbak-1 Com-puter is introduced.

1971: America. Ted Hoff de-signs (and Intel releases)the first computer-on-a-chip, the 4004 micropro-cessor.

1971: Niklaus Wirth developsPASCAL computer lan-guage (named after Blaise Pascal).

1972: November, America. Intelintroduce the 8008 mi-

croprocessor.

1973: America. Xerox AltoComputer is introduced.

1973: May, France. 8008-based Micral microcom-puter is introduced.

1973: June, the term micro-computer first appears inprint in reference to the8008-based Micral micro-computer.

1973: America. Scelbi Com-puter Consulting Com-pany introduce theScelbi-8Hmicrocomputer-baseddo-it-yourself computer kit.

1973: PDP-8 becomes the firstpopular microcomputer.

1974: America. Intel introduce





his programs and data. We mayonly speculate as to the filmsZuse used for his hole-punchingactivities; for example, were any

first-edition Marlene Dietrichclassics on the list? (MarleneDietrich fell out of favor with theHitler regime when sheemigrated to America in theearly 1930s, but copies of her films would still have beenaround during the war.)

Zuse was an amazing manwho was well ahead of his time.In fact there isn’t enough spaceto do him justice in this article,but you can find a “world-

exclusive” feature article onZuse at the EPE Online web siteat www.epemag.com. Thisarticle, which was written byKonrad’s eldest son, HorstZuse, contains over 100photographs from Horst’sprivate collection, many of whichhave never been publishedbefore!

FIRST ELECTRONIC

COMPUTERS We now turn our attention toan American mathematician andphysicist, John Vincent Atanasoff, who has the dubioushonor of being known as theman who either did or did notconstruct the first truly electronicspecial-purpose digitalcomputer.

A lecturer at Iowa StateCollege (now Iowa StateUniversity), Atanasoff wasdisgruntled with the

cumbersome and time-consuming process of solvingcomplex equations by hand.Working alongside one of hisgraduate students (the brilliantClifford Berry), Atanasoff commenced work on anelectronic computer in early1939, and had a prototypemachine by the autumn of thatyear.

In the process of creatingthe device, Atanasoff and Berry

evolved a number of ingeniousand unique features. For example, one of the biggestproblems for computer designers of the time was to beable to store numbers for use inthe machine’s calculations.

Atanasoff’s design utilizedcapacitors to store electricalcharge that could representnumbers in the form of logic 0sand logic 1s. The capacitorswere mounted in rotating

Bakelite cylinders, which hadmetal bands on their outer surface. These cylinders, eachapproximately 12 inches tall and8 inches in diameter (30cm x20cm), could store thirty binarynumbers, which could be readoff the metal bands as thecylinders rotated.

Input data was presented to

Special Feature

the 8080 microprocessor.

1974: August, America. Mo-torola introduce the 6800microprocessor.

1974: June, America. Radio

Electronics magazinepublishes an article byJonathan (Jon) Titus onbuilding an 8008-basedmicrocomputer called theMark-8.

1975: America. MOS Technol-ogy introduce the 6502microprocessor.

1975: January, America, EdRoberts and his MITscompany introduce the8080-based Altair 8800

microcomputer.1975: April, America. Bill Gates

and Paul Allen found Mi-crosoft.

1975: July, America. Microsoftrelease BASIC 2.0 for the Altair 8800 microcom-puter.

1975: America. MOS Technol-ogy introduce the 6502-based KIM-1 microcom-puter.

1975: America. Sphere Corpo-ration introduce the6800-based Sphere 1microcomputer.

1975: America. Microcomputer in kit form reaches UShome market.

1976: America. Zilog introducethe Z80 microprocessor.

1976: March, America. SteveWozniak and Steve Jobsintroduce the 6502-based

Apple 1: microcomputer.1976: April 1st, America. Steve

Wozniak and Steve Jobsform the Apple computer company.

1977: April, America. Apple in-troduces the Apple II mi-crocomputer.

1977: April, America. Com-

Rebuilt versionof Konrad

Zuse’s ZI computer. Theoriginal was

built in his par-ent’s living

room in Berlinin 1938. Cour-tesy of Horst

Zuse.














GENIUSES ANDECCENTRICS

Many of the people whodesigned the early computerswere both geniuses andeccentrics of the first order, andthe English mathematician AlanTuring was “first amongst

equals.” In 1937, while agraduate student, Turing wrotehis ground-breaking paper OnComputable Numbers with an Application to theEntscheidungsproblem.

Since Turing did not haveaccess to a real computer (notunreasonably, because theydidn’t exist at the time), heinvented his own as an abstract“paper exercise”. Thistheoretical model, which

became known as a Turing Machine, was both simple andelegant, and subsequentlyinspired many “thoughtexperiments”.

During World War II, Turingworked as a cryptographer,decoding codes and ciphers at

Special Feature

the machine in the form of punched cards, while intermediateresults could be stored on other cards. Once again, Atanasoff’ssolution to storing intermediateresults was quite interesting – heused sparks to burn small spotsonto the cards. The presence or absence of these spots could be

automatically determined by themachine later, because theelectrical resistance of acarbonized spot varied from thatof the blank card.

Some references report that Atanasoff and Berry had a fullyworking model of their machine by1942. However, while someobservers agreed that themachine was completed and didwork, others reported that it wasalmost completed and would have

worked, while still others statedthat it was just a collection of parts that never worked. Sounless more definitive evidencecomes to light, it’s a case of: “You pays your money and you takesyour choice”.

modore Business Ma-chines present their 6502-based CommodorePET microcomputer.

1977: August, America. Tandy/Radio Shack announce

their Z80-based TRS-80microcomputer.

1978: America. Apple introducethe first hard disk drivefor use with personalcomputers.

1979: America, the first truecommercial microcom-puter program, the Visi-Calc spreadsheet, isavailable for the Apple II.

1979: ADA programming lan-

guage is named after Au-gusta Ada Lovelace (nowcredited as being the firstcomputer programmer).

1981: America. First IBM PC islaunched.

1981: America. First mousepointing device is intro-duced.

1981: First laptop computer isintroduced.

1983: Apple’s Lisa is the first

personal computer to usea mouse and pull-downmenus.

1983: Time magazine namesthe computer as Man of the year.

1984: 1 MB memory chips in-troduced.

1985: CD-ROMs are used tostore computer data for the first time.

The Colossus computer, Bletchley Park, 1943. Used to de-cypher the German “ENIGMA” codes during WWII. Courtesy

Science Museum/Science and Society Picture library.





general-purpose electroniccomputer was the electronicnumerical integrator andcomputer (ENIAC ), which wasconstructed at the University of Pennsylvania between 1943 and1946.

ENIAC, which was the

brainchild of John WilliamMauchly and J. Presper EckertJr., was a monster – it was 10feet (3m) tall, occupied 1,000square feet (300m2) of floor-space, weighed in atapproximately 30 tons(30480kg), and used more than70,000 resistors, 10,000capacitors, 6,000 switches, and18,000 vacuum tubes. The finalmachine required 150 kilowattsof power, which was enough to

light a small town.One of the greatest

problems with computers builtfrom vacuum tubes wasreliability; 90 percent of ENIAC’sdown-time was attributed tolocating and replacing burnt-outtubes. Records from 1952 show

that approximately 19,000vacuum tubes had to be replacedin that year alone, which averagesout to about 50 tubes a day!

In August 1944, Mauchly andEckert proposed the building of another machine called theelectronic discrete variable

automatic computer (EDVAC ).This new machine was intendedto feature many improvementsover ENIAC, including a new formof memory based on pulses of sound racing through mercurydelay lines.

FIRST DRAFT In June 1944, the Hungarian-

American mathematician Johann(John) von Neumann first became

aware of ENIAC. Von Neumann,who was a consultant on theManhattan Project, immediatelyrecognized the role that could beplayed by a computer like ENIACin solving the vast arrays of complex equations involved indesigning atomic weapons.

Special Feature

one of the British government’stop-secret establishmentslocated at Bletchley Park. Duringthis time Turing was a keyplayer in the breaking of theGerman’s now-famous code

generated by their ENIGMAmachine. However, in addition toENIGMA, the Germans hadanother cipher that wasemployed for their ultra-top-secret communications. Thiscipher, which was vastly morecomplicated that ENIGMA, wasgenerated by a machine called aGeheimfernschreiber (secrettelegraph), which the alliesreferred to as the “Fish”.

In January 1943, along with

a number of colleagues, Turingbegan to construct an electronicmachine to decode theGeheimfernschreiber cipher.This machine, which theydubbed Colossus, comprised1,800 vacuum tubes and wascompleted and working byDecember of the same year!

By any standards Colossuswas one of the world’s earliestworking programmableelectronic digital computers. But

it was a special-purposemachine that was really onlysuited to a narrow range of tasks (for example, it was notcapable of performing decimalmultiplications). Having said this,although Colossus was built asa special-purpose computer, itdid prove flexible enough to beprogrammed to execute avariety of different routines.

ENIAC AND EDVAC By the mid-1940s, the

majority of computers werebeing built using vacuum tubesrather than switches and relays. Although vacuum tubes werefragile, expensive and used a lotof power, they were much faster than relays (and much quieter).If we ignore Atanasoff’s machineand Colossus, then the first true

One small sec-tion of the re-ceiver unit for

ENIAC. Another photo of ENIAC

was shown inPart 2. Courtesy

Science Museum/Science and Society Picture Library.

Electronic vacuum tubes, 1946, which replaced electric re-lays and made operational programs that could multiply two10-digit numbers 40 times per second. Courtesy of IBM.





Von Neumann wastremendously excited by ENIACand quickly became aconsultant to both the ENIACand EDVAC projects. In June1945, he published a paper entitled First Draft of a report on

the EDVAC , in which hepresented all of the basicelements of a stored-programcomputer:

o) A memory containing bothdata and instructions. Alsoto allow both data andinstruction memorylocations to be read from,and written to, in anydesired order.

o) A calculating unit capableof performing botharithmetic and logicaloperations on the data.

o) A control unit, which couldinterpret an instructionretrieved from the memoryand select alternativecourses of action based onthe results of previousoperations.

Special Feature

The key point made by the paper was that the computer couldmodify its own programs, inmuch the same way as wasoriginally suggested by CharlesBabbage in the 1830s. Thecomputer structure resultingfrom the criteria presented inthis paper is popularly known asa von Neumann Machine, andvirtually all digital computersfrom that time forward havebeen based on this architecture.

Unfortunately, although theconceptual design for EDVACwas completed by 1946, severalkey members left the project topursue their own careers, andthe machine did not becomefully operational until 1952.When it was finally completed,EDVAC containedapproximately 4,000 vacuumtubes and 10,000 crystal diodes. A 1956 report shows thatEDVAC’s average error-free up-time was approximately eighthours.

EDSAC TO UNIVAC In light of its late completion,

some would dispute EDVAC’sclaim-to-fame as the first stored-program computer. A small

experimental machine based onthe EDVAC concept consistingof 32 words of memory and a 5-instruction command set wasoperating at Manchester University, England, by June1948.

Another machine calledEDSAC (Electronic DelayStorage Automatic Calculator)performed its first calculation atCambridge University, England,in May 1949. EDSAC contained

3,000 vacuum tubes and usedmercury delay lines for memory.Programs were input usingpaper tape and output resultswere passed to a teleprinter.

Additionally, EDSAC iscredited as using one of the firstassemblers called Initial Orders,which allowed it to beprogrammed symbolicallyinstead of using machine code.Last but not least, the firstcommercially availablecomputer, UNIVAC I (Universal Automatic Computer), was alsobased on the EDVAC design.Work started on UNIVAC I in1948, and the first unit wasdelivered in 1951, whichtherefore predates EDVAC’sbecoming fully operational.

MAGNETIC CORE STORES

One of the biggest problems

faced by early computer designers was the lack of small,efficient memories. In GermanyKonrad Zuse experimented withpurely mechanical memories(which were surprisinglyreliable), whilst other engineersworked with a variety of esoterictechniques, including thephosphorescent effect in

Magnetic core memory store. Logic 0 and 1 depended on the polarity of the magnetized field for each bead.

Courtesy of IBM.







equipped with 1Kbyte of RAM.

In June 1974, Radio

Electronics magazine publishedan article by Jonathan Titus onbuilding a microcomputer calledthe Mark-8, which, like theMicral and the Scelbi-8H, wasbased on the 8008microprocessor. The Mark-8received a lot of attention fromhobbyists, and a number of user groups sprang up around theUS to share hints and tips anddisseminate information.

LAUNDROMATS IN ALBUQUERQUE

Around the same time that

Special Feature

Jonathan Titus was penning hisarticle on the Mark-8, a mancalled Ed Roberts waspondering the future of hisfailing calculator companyknown as MITS (which was nextdoor to a laundromat in Albuquerque, New Mexico).Roberts decided to take agamble with what little fundsremained available to him, andhe started to design a computer called the Altair 8800 (the name“Altair” originated in one of theearly episodes of Star Trek ).

Roberts based his system

on the newly-released 8080microprocessor, and theresulting do-it-yourself kit was

advertised in Popular Electronics magazine in January1975 for the then unheard-of price of $439 US. In fact, whenthe first unit shipped in April of that year, the price had fallen to

an amazingly low $375 US.Even though it only

contained a miserly 256 bytes of RAM and the only way toprogram it was by means of aswitch panel, the Altair 8800proved to be a tremendoussuccess. (These kits weresupplied with a steel cabinetsufficient to withstand mostnatural disasters, which is why aremarkable number of themcontinue to lurk in their owner’s

garages to this day.)

BASIC GATES Also in April 1975, Bill Gates

and Paul Allen foundedMicrosoft (which was to achievea certain notoriety over thecoming years), and in July of that year, MITS announced theavailability of BASIC 2.0 on the Altair 8800. This BASICinterpreter, which was written byGates and Allen, was the firstreasonably high-level computer language program to be madeavailable on a home computer –

Altair 8800b microcomputer, 1975. Courtesy ScienceMuseum/Science and Society Picture Library.

A Commodore PET 32K computer, 1979. Cas-sette recorders provided external data stor-

age. Courtesy John Becker

An early IBM PC. Its architecture became thefoundation that all PC-compatibles must emu-

late. Courtesy of IBM.





MITS sold 2,000 systems thatyear, which certainly made EdRoberts a happy camper, whileMicrosoft had taken its firsttentative step on the path towardworld domination.

In June 1975, MOSTechnology introduced their 6502 microprocessor for only$25 US (an Intel 8080 woulddeplete your bank account byabout $150 US at that time). Ashort time later, MOSTechnology announced their 6502-based KIM-1microcomputer, which boasted2K bytes of ROM (for themonitor program), 1K byte of RAM, an octal keypad, a

flashing LED display, and acassette recorder for storingprograms. This unit, which wasonly available in fully-assembledform, was initially priced at $245US, but this soon fell to anastoundingly low $170 US.

The introduction of newmicrocomputers proceededapace. Sometime after the KIM-1 became available, the SphereCorporation introduced itsSphere 1 kit, which comprised a

6800 microprocessor, 4K bytesof RAM, a QWERTY keyboard,and a video interface (but nomonitor) for $650 US.

JOBS AND WOZNIAK In March 1976, two guys

called Steve Wozniak and SteveJobs (who had been fired withenthusiasm by the Altair 8800)finished work on a home-grown6502-based computer whichthey called the Apple 1 (a fewweeks later they formed the Apple Computer Company on April Fools day).

Although it was nottremendously sophisticated, the Apple 1 attracted sufficientinterest for them to create the Apple II, which many believe tobe the first personal computer

Special Feature

that was both affordable andusable. The Apple II, whichbecame available in April 1977

for $1,300 US, comprised 16Kbytes of ROM, 4K bytes of RAM,a keyboard and a color display.

Apple was one of the greatearly success stories – in 1977they had an income of $700,000US (which was quite a lot of money in those days), and justone year later this had soaredtenfold to $7 million US! (whichwas a great deal of money inthose days).

Also in April 1977,

Commodore Business Machinespresented their 6502-basedCommodore PET, whichcontained 14K bytes of ROM,4K bytes of RAM, a keyboard, adisplay and a cassette tapedrive for only $600. Similarly, in August of that year, Tandy/Radio Shack announced their Z80-based TRS-80, comprising4K bytes of ROM, 4K bytes of RAM, a keyboard and a cassettetape drive for $600.

WOT! NO SOFTWARE?

One aspect of computingthat may seem strange today isthat there were practically noprograms available for theseearly machines (apart from theprograms written by the users

themselves). In fact, it wasn’tuntil late in 1978 thatcommercial software began to

appear.Possibly the most significant

tool of that time was the VisiCalcspreadsheet program, whichwas written for the Apple II by astudent at the Harvard BusinessSchool and which appeared in1979. It is difficult to overstatethe impact of this program, but itis estimated that over a quarter of the Apple machines sold in1979 were purchased bybusinesses solely for the

purpose of running VisiCalc. Inaddition to making Apple veryhappy, the success of VisiCalcspurred the development of other applications such as wordprocessors.

When home computers firstbegan to appear, existingmanufacturers of largecomputers tended to regardthem with disdain (“It’s just a fad . .. it will never catch on” ).However, it wasn’t too long

before the sound of moneychanging hands began toawaken their interest. In 1981,IBM launched their first PC for $1,365 US, which, if nothingelse, sent a very powerful signalto the world that personalcomputers were here to stay.

The advent of the general-purpose microprocessor

Two of the bal-listic track mon-itors of SAGE,

the massive USmilitary com-

puter that helped defend the WesternWorld during the Cold War.Courtesy of

IBM.




EP E Online, May 2000 - www.epemag.com - 386

heralded a new era in computing – microcomputer systems smallenough to fit on a desk could beendowed with more processingpower than monsters weighingtens of tons only a decade

before. The effects of thesedevelopments are still unfolding,but it is not excessive to say that

Special Feature

digital computing and thepersonal computer havechanged the world moresignificantly than almost anyother human invention, andmany observers believe that

we’ve only just begun our journey into the unknown!

EVER SO HUMBLE We crave your indulgence

and ask you to accept our humblest apologies for all of thethings we had to leave out.Surely computer languages likeFORTRAN, COBOL, BASIC, C,LISP, FORTH and … (the listgoes on) deserve a mention?

How could we neglectmicrocomputers such as thePDP and VAX from DigitalEquipment Corporation (DEC)that had such an impact on theindustry? Are operating systemslike VMS, UNIX, and Windowsto be ignored? What aboutbehemoths like SAGE (whichconsumed a million watts of power) and CRAYSupercomputers?

The problem is that onecould go on forever, so wechose to restrict ourselves onlyto those topics that we felt wereparticularly germane to thisseries. As usual you may of course disagree (or you maysimply crave more once thisseries is finished), in which caseplease feel free to vent your feelings by inundating the Editor with your letters and emails.

ACKNOWLEDGEMENT

Portions of this article wereabstracted from our book,Bebop BYTES Back (AnUnconventional Guide toComputers), with the kindpermission of its publisher,Doone Publications. (BebopBYTES Back is available fromthe EPE Online Store atwww.epemag.com)

NEXT MONTH In the fifth and final

installment of this series weshall gird up our loins andpontificate on the future. Where

do you think the technologyroller-coaster will take us in thenext 10, 100 or 1000 years?Start pondering now and see if you agree with us in nextmonth’s exciting issue – sametime ... same place ... samechannel!

QUOTABLE QUOTES

“Computers in the futuremay weigh no more than 1·5 tons.” Popular Mechanics, fore-casting the relentless march of science, 1949.

“I think there is a world mar-ket for about five computers.”

Thomas Watson, Chairman of IBM, 1943.

“I have traveled the lengthand breadth of this country and talked with the best people, and I can assure you that data pro-cessing is a fad that won’t last out the year.” The editor incharge of business books for Prentice Hall, 1957.

“There is no reason for any individual to have a computer intheir home.” Ken Olson, Presi-

dent of Digital Equipment Cor-poration (DEC), 1977

“So we went to Atari and said, ‘Hey, we’ve got this amaz-ing thing, even built with some of your parts, and what do youthink about funding us? Or we’ll give it to you. We just want to doit. Pay our salary, we’ll comework for you.’ And they said,‘No.’ So then we went toHewlett-Packard, and they said,‘Hey, we don’t need you. You

haven’t got through college yet.’’ Apple Computer Inc. founder Steve Jobs on attempts to get Atari and HP interested in hisand Steve Wozniak’s personalcomputer.

“640K of memory ought tobe enough for anybody.” BillGates, CEO of Microsoft, 1981.















It is a commonly known factthat microprocessor clockspeeds are increasing all thetime. Only a few years ago,clock speeds of 1GHz werethought to be many years away.Now a number of manufacturershave offerings with speedsaround 1GHz that will shortly hitthe marketplace. IBM have a 64-

bit Power PC chip. Compaq,have their 1GHz Alpha, and Intela version of a Pentium III. Thesedevices have been able toachieve their speed as a resultof a number of developmentsthat have been undertaken inmany research institutes anddevelopment areas.

All of the devices havegeometries that are less than 0 2

microns, and this means that theoperating voltages are low. For

example the Alpha operates ona voltage of 165 volts. Not only

is this low voltage requiredbecause of the low breakdownvoltages associated with theminute geometries, but it alsoreduces the power consumption.

HEAT PROBLEMS

Power consumption is anincreasing problem asdemonstrated by the fact that

even modest Pentium chipsrequire cooling. However when itis realized that IBM’s 64-bitPowerPC uses 19 milliontransistors, it is hardly surprisingthat very significant amounts of heat are dissipated. Some of thenew chips now under development dissipate levels of heat well in excess of 50 watts,

and the trend of increasinglevels of power dissipation islikely to continue. With theincreasing levels of power dissipation, thermal control of chips is an integral part of thedesign and it is every bit asimportant and challenging as theelectrical performance.

It is interesting to note that

when the first bipolar integratedcircuits were introduced, limits of around 20 transistors werethought to be the limit of integration as a result of thermalconsiderations. The introductionof CMOS techniques enabled aquantum leap to be made in thelevels of integration and thetrend towards ever-larger ICshas increased since then.

More recently, the reductionof supply voltage has been of

assistance as the thermalboundaries have beenapproached, because power levels are proportional to thesquare of the voltage. Even soother effects prevent the picturefrom being quite so rosy. Thedesign of the transistors in thechip has to be altered to enablethem to operate at low voltages.One of the results of this is thatthey become far more leaky andthis effect means that theyconsume power even when theyare switched off.

TEMPERATURE

RISES

To ensure the highestspeed of operation, devicesshould be operated at a lowtemperature. The unwanted

additional power consumptionfrom the leaky transistors raisesthe temperature and thisreduces the electron mobilitybecause of the increasednumber of collisions that occur as the electrons move aroundthe crystal lattice.

Accordingly, it makes themethods and techniques used

for heat extraction from the IC apoint of major importance if speeds are to increase at thecurrent rate. A company namedKryotech is already marketing achip that is cooled, increasing itsperformance by a half again. Tothe same end, IBM areoptimizing the performance of their basic silicon designs for low temperature operation with aview to this being one of theways forward for the future.

However, even thoughspeed generally increases withcooling, it also increases thethreshold voltage for theindividual devices, and this inturn increases the level of leakage and partially offsets anygains that are made. This is oneof the factors that makesoptimizing the design for low-temperature operation soimportant. By choosing theoptimum level of thresholdvoltage, the maximum use canbe made of any cooling that isused.

EXTRACTING HEAT

There are a number of waysin which heat can be extractedfrom the chips. One method isto use a system that iseffectively a small-scale version

WHILST LOWER OPERATING VOLTAGES ENABLE MICROPROCESSORS TO RUN

FASTER, THE PROBLEM OF HEAT DISSIPATION BECOMES MORE SIGNIFICANT.IAN POOLE REPORTS.





of a domestic refrigerator.These systems are verysuccessful, being alreadyemployed in a number of highend products and they are ableto cool chips down to atemperature of around –50°C.

Whilst this can givesignificant advantages inperformance, lower temperatures can provide evengreater improvements. Toachieve this there are a number of methods that can be adopted.The most popular idea is that of thermo-electric heat pumps.These do not involve the samelevel of mechanical hardwareand are accordingly less

expensive. They can also beinterfaced to the basic chip moreeasily, and can actually be madeas part of the same assembly.

However, the basic Peltier devices, although attractive atfirst sight, leak too much heatback into the chip, and as aresult they are not as efficient asthey are required to be for thisfunction. Fortunately, new workundertaken at theMassachusetts Institute of

Technology has resulted in theproduction of new materials andstructures that give far moreeffective and efficient solutions.

The requirement is to beable to remove a considerableamount of heat from a smallarea. One of the new solutionsusing a thin film semiconductor heat pump can extract as muchas 100 watts per squarecentimeter. With further work itis expected that these devices

could be built into the basic chippackage, providing a veryconvenient, efficient and reliablemethod of extracting heat fromthe devices.

PACKAGES

Whilst heat is a major problem that is being overcome,new package technology is alsopart of the solution. Long goneare the days when dual-in-linepackages were able to meetmost requirements. Even thequad flat packs are not suitable,and in addition to this,equipment manufacturers dislikethem because they are easily

damaged. Flip chip packageswhere the silicon is directlybonded to the package are ableto give performanceimprovements. This gives aspeed increase as a result of itslower resistance and RC delaysas well as giving a physicallyshorter connection.

Further improvements havebeen made by adopting asystem that enables the criticalleads to be kept as short as

possible. Although thistechnique requires the additionof an extra layer of metalisationand a complete re-layout of thechip, it provides an increase thatalthough small still helps toincrease the overall speed of operation.

A further increase inperformance is achieved byusing a dielectric with a lowvalue. In turn this reduces thelevels of capacitance and cross

talk, which were large enough toslow down the speed of operation. The material chosenfor this is silicon oxyfluoride(SiOF).

SUMMARY

Although differentmanufacturers use differenttechniques to give the newhigher clock speeds, the overallpattern is clear, and it is likelythat in a few years time they willall be used as standard. Many of them give minor improvementson their own, but when usedwith the other techniques theyenable a significant

improvement in performance tobe achieved in the chip as awhole. This demonstrates thefact that is commonly true intechnology that a variety of improvements are required togive the overall improvement inperformance.

New technology Updates





This month we round off our exploration of the opamp bylooking at the level shifter circuits which are used to getthe DC bias levels correct indifferent stages of an opamp.We outline typical short-circuit

protection techniques and alsooutput stages, which are power amplifiers that share some of the features of basic audiopower amplifier output stages.Some of the principles we’lloutline also apply to designs,which use discrete transistorsinstead of integrated circuits.

SHIFTY CIRCUITS No coupling capacitors can

be used between stages withinopamps – they have to workwith DC and very low frequencyinputs. Biasing is easy inmultistage capacitively-coupledamplifiers, because the biasingof each stage is isolated by thecoupling capacitor.

In an opamp, life is not sosimple. We might, for example,have one stage with an outputwhose signal varies around abias point of half the positivesupply, which has to beconnected to a stage that needsa signal which varies around 0V(ground) instead. Thereforewhat we would need to do is“shift” the DC bias level of asignal.

Ideally, a circuit for thispurpose should provide a stableshift in DC level without

introducing noise, it should notattenuate the signal, andshould allow the designer toselect any level shift required(within reason). We couldachieve a shift using a two-resistor potential divider, butthis attenuates the signal. Wecould use a Zener diode toprovide a voltage drop, butthese are noisy. We could usediode voltage drops, but theseonly come in steps of about06V per diode used.

The circuit in Fig.1a actsas a level shifter, changing theDC level from Vin to Vout

without significant attenuationof the signal. The currentsource (see Circuit Surgery ,May and June ’99) provides acurrent I that flows through R to give a fixed voltage drop of IR . The voltage drop is fixed (itdoes not depend on the signal)because the current sourceproduces the same currenteven if the voltage across itvaries due to the signal.

The total fixed voltagedrop from Vin to Vout alsoincludes the VBE voltage of thetransistor, which will also notvary a great deal as the signalvaries. Thus the circuit shiftsthe DC level of the signal downby (IR + VBE) volts.

OUT OF THE OPAMP

An opamp output stagemust be capable of supplying

sufficient current to the externalload (i.e. out of the chip onwhich the opamp is fabricated).In order to do this it must havelow output resistance and

Our circuit surgeons provide more advice to help with reader’s problems and conclude their mini-series investigating the inner workings of operational

amplifiers, looking at output stages and short-circuit

by ALAN WINSTANLEY

Fig.1a. A level shifter circuit.

Fig.1b. Emitter follower circuit.

Fig.1c. Basic push-pull amplifier.







constant 2 x VBE difference between the twobase voltages. The actual base voltages willvary with the signal, but the differencebetween them is fixed by this biasingarrangement.

The diodes are ideally at the sametemperature as the output transistors so thatchanges in their voltage drop withtemperature tracks those of the outputtransistor. This applies on opamp ICs andfor discrete component power amplifiersusing this type of circuit.

SHORT CIRCUITS The push-pull amplifier is likely to be

damaged if its output is short-circuited toground, due to excessive collector current in

the conducting transistor. A short-circuitprotection arrangement may be added toovercome this problem. The protectioncircuit monitors the current flowing in theoutput and turns off the output transistor if the current exceeds some pre-defined limit.The current detection is usually achieved byusing a small resistor in the output signalpath, and a transistor to switch off the output(see Fig.4); the output current causes avoltage drop across the resistor.

A protection transistor switches on whenthe resistor voltage reaches about 06V to

07V. The protection transistor is connected

so that when it is on, it effectively short-circuits the input to the power transistors, sothey have no signal to amplify. Theprotection resistor values, Rp1 and Rp2 maybe chosen using Rp1 = Rp2 = VbeTRP1 / Imax

where VbeTRP1 is the turn-on voltage of theprotection transistor (typically 06V to 07V)

and Imax is the maximum output current, i.e.the current at which the protection kicks in.This kind of protection circuit is whatenables opamps to have the “infinite outputshort circuit duration” quoted on many data

sheets.

AUDIO POWER AMP The circuit shown in Fig.5 is a discrete

component version of the circuit in Fig.4,which could form the basis of an audiopower amplifier output stage. Resistors areused instead of the current sourcesubiquitous in IC circuits.

Circuit Surgery

Fig.4. Output stage with protection circuit (protectioncomponents are shown using bold lines).

Fig.5. Audio power amplifier using similar configura-tion to opamp output stage.

transistors’ bases (see Fig.3). The diodes are biased withthe current required to give the correct VBE value by meansof a current source.

As the input signal varies the diodes maintain a





Circuit Surgery

Biasing is achieved usingwhat is known as a VBE multiplier and is manually adjustable usingpreset VR1 to give the requiredquiescent current for the circuit(the degree to which the output

transistors are “just on” with nosignal). The VBE multiplier circuitconsists of TRa, preset VR1 andresistor R2. The voltage Vbias iseffectively fixed by virtue of thefact that TRa’s VBE voltage doesnot vary much, resulting in afixed voltage across R2 andhence a fixed current through it.

If the preset VR1 andresistor R2 are chosen so thattheir current is much larger thanTRa’s base current then we can

assume all of the current in R2also flows in VR1. Thus the totaldropped across VR1 and R2(i.e. Vbias) is equal to VBE

multiplied by the ratio of the totalresistance of VR1 and R2 to thevalue of R2, i.e.

Vbias = VBE (VR1 + R2) / R2

We hope that our discussionon the opamp over the past fewmonths has given you someinsight into what is inside these

chips that get used in so manyconstructor’s projects. Of course, there is a lot more to thecircuitry of modern opamps thanwe have space to discuss in thisseries – as a browse throughthe schematics inmanufacturers’ data sheets willreveal.

Hopefully, however, youwould also be able to recognizeat least some of the basic sub-circuits (e.g. differential

amplifier) in these schematics,even if there are one or twoextra transistors present. Wealso hope that some of youmight find other uses for thecircuits we have shown in your own designs – let us know if youdo. Ian Bell.

BATTERY FLATTERY Briefly on the subject of

troubleshooting lead acidchargers, Mr. Alister Bottomleywrote: “Am I correct in assuming

that in order to charge a 12V lead acid battery it must receive avoltage greater than 12V across it – the greater the voltage thegreater the charging current?

My battery charger hassuddenly reduced its output to11 7V as measured on its ‘high’

tapping. I can’t find any losses or problems in the circuit.”

A lead acid battery requires

something like 22V per cell or

higher constant voltage to charge. A higher voltage could be usedbut the battery life will beshortened, and it is true that thegreater the applied voltage, thegreater the charge current will be.Current gradually reduces to atrickle as the battery charges up.

The reason you aremeasuring a strange DC voltageis because it isn’t a smooth levelDC voltage you are actually

testing. Ordinary car batterychargers have a rectified DCoutput, which is unsmoothed.However, your multimeter willwant to read a pure DC voltage,or it will read an RMS voltage onits AC range instead. Anoscilloscope would highlight theproblem.

An electronics mains power supply uses a smoothing or “reservoir” capacitor to iron outthe ripple, to produce a higher

peak value and much smoother DC voltage. The capacitor thencharges to the peak value of therectified DC sinewave. In fact, it’sthe car battery itself that acts as agiant smoothing capacitor acrossthe supply. Hooking this acrossthe battery charger means thatthe voltage seen across thebattery will then increase.

Also, your test equipmentmay actually cause you tomisinterpret the result, andsometimes the very use of testequipment can affect theoperation of the circuit as well.

Constructors gradually learn tocompensate for this withexperience.





Probably the most importantelectronic component in theanalog designer’s armory is theoperational amplifier. Better known, perhaps, by itsabbreviated name of opamp (or op-amp, or even op.amp) thisfamily of devices seemingly hasmore applications than there aredesigners who use it!

In this month’s Tutorial weillustrate some of the opamp’smajor features as an amplifier. Innext month’s Tutorial we follow onby going into a bit more simpleexperimental detail, discussingwhat else opamps can do, andgetting you to try it.

FIRST

DEMONSTRATION

From your stock of

components (as described in Part1), select one of the 8-pin dual-in-line (DIL) devices labeled LM358,call it IC4. Now assemble your breadboard according to Fig.7.1. Any previous components in thearea illustrated should beremoved (all your counting andlogic gate experiments from lastmonth have already served their

PART PART 7 – Op.ampsby John Becker

purpose, we hope!). Leave theoscillator components intact for now.

The equivalent circuitdiagram and the componentvalues are shown in Fig.7.2.

Connect the oscillator waveform from the junction of

Over the previous six parts of Teach-In

2000, which we know you have been greatly

enjoying, we have covered passive

components and several digital logic circuits.

Via the interactive computer programs and the

simple interface you assembled, you have also

been able to observe the various waveforms

generated by the experimental breadboard

circuits, showing how a few electronic

components can be connected to achieveinteresting results.

We now move on from the “interesting” to

the “practical”, in terms of describing active

components which can be used to amplify and

otherwise modify the waveforms generated. it

is opamps we now examine, those simple

robust components that feature so frequently

in audio and other analog circuits. This month

we demonstrate their basic nature, next month

we get you experimenting with some useful

applications.

capacitor C1 and IC1a pin 1(see Fig.4.3 of Part 4) to thepoint marked “DC INPUT”. Usea crocodile-clipped link.

Ignore the points labeled“Buffer Input” and “Buffer Output”, their purpose will bediscussed later on in theTutorial.

The oscillator should havediodes D2 and D3 included; its

Breadboard showing thecomponents for the first

opamp experiments, part of IC1 is just visible at the left.

1 6

1 6

1 5

1 5

1 7

1 7

1 8

1 8

1 9

1 9

2 0

2 0

2 1

2 1

2 2

2 2

2 3

2 3

2 4

2 4

2 5

2 5

2 6

2 6

2 7

2 7

2 8

2 8

2 9

2 9

3 0

3 0

3 1

3 1

A.C.INPUT

D.C.INPUT

(SEE TEXT)

(SEE TEXT)INPUTOUTPUT

OUTPUT

IC4VR2 VR3

VR4

C2

+

TO R.H.SIDE OF

BOARD

TO R.H.SIDE OFBOARD

Fig.7.1 Breadboard layout for the first opamp experiments.




EPE Online, M ay 2000 - www.epemag.com - 394

capacitor C1 value should be100uF. Set the frequency controlVR1’s wiper to midway, so thatthe generated waveform will beroughly triangular.

Set each of the Fig.7.1presets (VR2 to VR4) so thattheir wipers (moving contacts)are also in a midway position,

providing approximately equalresistance to either side of thewiper.

Referring to Fig.5.6 of Part5, connect IC4 pin 1 to the inputto the analog-to-digital converter (IC2 pin 2), and then connectIC2’s output to IN1 of thecomputer interface section. Runthe Analog Input WaveformDisplay program.

Connect up your battery tothe breadboard (as you’ve done

a good few times before – is thebattery power still OK?) andobserve the computer screendisplaying the triangular waveform being generated byIC1a and associatedcomponents.

VARIABLE

AMPLITUDE

We are now going to askyou to make various

adjustments on the opamp’sthree presets and observe thescreen responses. We shalldiscuss what you observe in duecourse. First, carefully adjust thewiper position of VR4 until thewaveform is roughly central onthe screen.

Next, slowly adjust the wiper

of VR3 in a clockwise direction(to the “right”) while observingthe screen. This actionincreases the resistancebetween the wiper and the endconnected to IC4 pin 1, theopamp’s output.

It will no doubt interest youto see that the vertical size of

the waveform increases, in other words, its amplitude increasesthe further you adjust VR3. Thelimit will be reached when youcannot turn the wiper anyfurther. The amplitude will nowbe about twice that you startedwith.

Note, though, how thewaveform’s relative position onthe screen probably changes as

you rotate VR3. Carefully adjustthe wiper of VR4 to set thewaveform back to a mid-screenposition if it does.

Now rotate VR3’s wiper anticlockwise. The waveform

amplitude will be seen todecrease, and once the wiper goes beyond the midway position,the waveform amplitude will beginto fall below that at which itstarted. The waveform is now saidto have been attenuated.

Towards the far end of theanticlockwise rotation thewaveform should be seen just asa straight-ish horizontal line.

Set VR3’s wiper to its fullyclockwise position and leave itthere.

PEAK FLATTENING

Turn your attention now topreset VR2. First rotate itclockwise, to increase theeffective resistance between itswiper and IC4 pin 2, one of theopamp’s two inputs. Note how an

TEACH-IN 2000

+

C222m

A.C. INPUT

0V

+6V

D.C. INPUT

VR2100k VR4

100k

3

2

VR3100k

IC4aLM358

4

8

1OUTPUT

+

Fig.7.2.Circuit dia-gram asso-ciated with

Fig 7.1

PANEL 7.1 – OPAMP MANUFACTURING CON-

STRUCTIONThe opamp type (LM358) used in this Teach-In is manufactured

using a structure called bipolar. In essence, this uses many transis-tors internally interconnected on the opamp chip and which requirecurrent to flow through them. In most cases the current is not great,but can still place a load on the circuit, which is being fed into theopamp inputs.

Another type of opamp manufacturing process uses the field ef-fect transistor (FET) technique. FET devices operate on a differentprinciple to those used in bipolar devices and respond to the voltage(field) on their inputs rather than through their inputs. These devices,therefore, do not draw current from the circuit feeding into them and

so place no load on them. All the circuits discussed in this Teach-In part could probably have

used FET opamps instead of the bipolar LM358. Such devices in-clude TL062, TL072 and TL082.

Component suppliers’ catalogs and manufacturers’ data sheetsshould be consulted for information about the different opamp typesavailable. Internet access to various manufacturers’ web sites anddata sheets can be gained via the EPE web site at

www.epemag.wimborne.co.uk

http://www.epemag.wimborne.co.uk/










increase in resistance herecauses a decrease in thewaveform amplitude.

Next adjust VR2’s wiper anticlockwise. Once it goesbeyond the original midway

position, note how rapidly thewaveform amplitude increases.You may also notice a change inthe waveform’s frequency (fewer cycles per screen-full!). Notealso that its top and bottompeaks become flattened themore that VR2’s resistance isdecreased. The peaks areunlikely to be evenly flattened,however. Carefully adjust VR4until they become more equal.

As you further rotate VR2’s

wiper, you will eventually see awaveform somewhat resemblinga square wave instead of atriangle. Adjusting VR4 willchange the waveform’s mark-space ratio (discussed in Part4). Before VR2 reaches itsminimum resistance, and withVR4 set too much to either sideof midway, the oscillator mightstop functioning.

WAVEFORM

INVERSION

That’s the first set of observations – on to the next.Return all three opamp wipers(VR2 to VR4) to a midwayposition. If the oscillator hadindeed ceased functioning, thisaction should restart it. If itdoesn’t, briefly disconnect thepower and then reconnect it.

Adjust IC1’s preset VR1 sothat a rising-ramp waveform is

seen (ramps were discussed inPart 5). Leave all presets asthey are and connect the ADC

input to the input of IC1a (pin 1).Look back at the screen.Whereas you had a rising rampa few moments ago, you shouldnow see a falling ramp –curiouser and curiouser!

Time, then, to discuss your findings in relation to anopamp’s basic nature.

BASIC OPAMP

NATURE

In essence, an opamp is atwo-input single-output device,which has the capability of greatly amplifying a voltagedifference between its twoinputs. For this reason, it can becalled a differential amplifier.Within limits, the amplification isaccording to a linear relationship. (You will recall thatwe discussed linear relationships when wediscussed potentiometers inPart 3.) For each unit of changeat the input, an equivalent butlinearly amplified increase willresult at the output.

For some purposes (but notall) the amount of amplification

(gain) available is far too greatto be of use – it can be severalhundred thousand times for some opamps. However, thereis a simple technique that canbe used to restrict theamplification to a moremanageable level.

In Fig.7.3 is shown the basicsymbol for an opamp (no longer cluttered as it is Fig.7.2). Thesymbol shows that one input ismarked as inverting (–), and the

other as non-inverting (+). Thedifferent input modes have greatsignificance to the way in whichthe opamp can be used andcontrolled.

Note that the “–“ and “+”symbols have nothing to do withpower supply connections, theymerely symbolize the inverting

and non-inverting nature of therespective input.

INPUT TO OUTPUT

First, suppose that both

inputs have the same voltagelevel applied to them. Becausethere is no difference betweenthe voltages, the output will beheld at the same voltage. If thevoltage on the non-invertinginput rises fractionally abovethat on the inverting input, theoutput voltage will try to rise bythe same amount amplified(multiplied) by the gain factor (of, say, 100,000).

Conversely, should the

voltage on the non-invertedinput fall below that on theinverted input, so the output willtry to fall by an equivalentlyamplified amount.

Obviously, a similar effectwill occur, but in the oppositedirection, if it is the invertinginput voltage that changes whilethe non-inverting input voltageremains constant.

NEGATIVE

FEEDBACK

Consider, though, whathappens if part of the outputvoltage is fed back to theinverting input, see Fig.7.4.Feedback into this input (viaresistor R2 in this case) isknown as negative feedback.The output will try to swing in thedirection prompted by therelative voltage difference

TEACH-IN 2000

+

INVERTING INPUT ( )

NON-INVERTING INPUT ( )

OUTPUT

+

Fig.7.3. Opamp symbol and connection names.

R2

INPUT

BIAS

0V

R1

+

OUTPUT

+

Fig.7.4. Feeding back part of the output voltage to the in-

verting input.





TEACH-IN 2000

connected so that it feeds backpart of the output voltage to theinverting input. Jointly, the effectof both resistances, VR2 andVR3, determines the amount of negative feedback that occurs.Respectively, they are theequivalent of R1 and R2 inFig.7.4.

If both resistances areequal, then the negativefeedback amount is the same asthe basic input amount, butinverted. The result is that thevoltage actually “seen” at theinverting input is the inputvoltage minus the feedbackvoltage, i.e. nil! At least, that

across the two inputs, but theeffect will be diminishedaccording to the amount of thatchange which is fed back tocounteract it.

The output might be tryingto change by 100,000 times, butthe feedback might be set for 99,990 times. The net differenceis thus only 10. Therefore, theeffective amplification is only 10times that of the differenceoriginally fed into the two inputs.The gain is thus said to have avalue of 10.

More strictly, when thesignal is being applied to theinverting input, the gain should

be said to be –10 (minus 10)because of the inversion. For the most part here, though, weshall just refer to the gain as apositive value.

Low gain values are of much better use if you want to justslightly raise the amplitude of awaveform, as you have justdone with the triangle waveform.In fact, when you first adjustedpreset VR3 to its maximumresistance, the gain you gave to

the waveform was about 2, i.e.you doubled the waveformamplitude. So let’s explain themechanism that is used in thecircuit of Fig.7.2 to control thesignal gain.

CONTROLLING GAIN

First, assume that thewaveform being sent to theinverting input of IC4 via presetVR2 is alternating about amidway voltage level. Let’s say

the midway level is at 3V (half the voltage applied to the fullcircuit, as supplied by your 6Vbattery).

Your initial adjustment of preset VR4 applied just aboutthe same midway voltage (whichwe refer to as the bias) to thenon-inverting input (you will

recall that you were asked tooriginally set its wiper to amidway position). This actionroughly balanced the two inputsat the midway voltage. Thechanges in voltage caused bythe triangle waveform’s swingthus became evenly balancedas seen across the two opamp

inputs.

The voltage being fed intothe inverting input, however,passes through the resistanceoffered by preset VR2. On itsown that resistance has noappreciable affect on the voltageactually reaching the input.Preset VR3, though, is

PANEL 7.2 – OPAMP PACKAGESOpamps are manufactured with encapsulations (packages) con-

taining one, two or four individual opamps – these packages beingknown respectively as single, dual and quad.

The vast majority of opamps have the same pinout configurationper packaging type, as shown here. Afew of the opamp types available arelisted below their packages. There arehundreds of other type numbers manu-factured. Note that some specialistopamps do not conform to thesepinouts.

With single opamp types, there arevarious functions that can be per-formed via pins 1, 5 and 8. These aretoo numerous to discuss here and for most simple amplification-type circuits

they can be ignored. They can

control such matters as, for

instance, the fine adjustment of theDC output level (offset) to match the basic zero-differential input volt-age. Manufacturers’ data sheets should be consulted for more infor-mation.

2 7

8

4 5

63

1

++INPUT ( )

INPUT ( )

OUTPUT

+ VE

VE

SINGLE

EXAMPLES

741 (VARIOUS PREFIXES) BIPOLAR

TL061 F.E.T.

TL071 F.E.T.

TL081 F.E.T.

NE531 BIPOLAR

2 7

8

4 5

63

1

INPUT A

+( )INPUT A

+( )INPUT B

( )

INPUT B ( )

OUTPUT B

OUTPUT A + VE

VE

+

+

DUAL

EXAMPLES

LM358 BIPOLAR

TL062 F.E.T.

TL072 F.E.T.

TL082 F.E.T.

NE5532 BIPOLAR


VE

2

7 8

4

5

6

3

10

9

13

11

12

141

+

+

+

+

INPUT A INPUT D

+( )INPUT A +( )INPUT D

+( )INPUT B +( )INPUT C

( ) ( )

INPUT B ( ) INPUT C ( )

OUTPUT B OUTPUT C

OUTPUT A OUTPUT D

+ VE

QUAD

EXAMPLES


TL064 F.E.T.

TL074 F.E.T.

TL084 F.E.T.







them whilst allowing alternatingcurrent (AC) to pass through. Weshall discuss this ability more fullyin a future Teach-In part, but for the moment let’s accept this as afact. But bear in mind that futurediscussions will point out that thisability is governed by thecapacitance value and the loadresistance into which the “output”side of the capacitor is fed. Twoother terms come into use in thatdiscussion, differentiation andintegration.

AC COUPLING

So let’s prove the point eventhough we don’t explain it.Remove the oscillator connectionfrom the “DC Input” point on your breadboard and connect it to the“AC Input” point. This nowprovides the input path with whatis known as AC coupling (as

opposed to DC coupling, whichhas been the situation so far).

Run the same group of adjustments using opamp presetsVR2 to VR4 as you did earlier andobserve the screen results.

You should find that onceVR4 has been set midway, thereshould be no vertical shift of the

waveform as you adjust gain, just the amplitude change.

There is, though, a muchmore pronounced effect that youmay observe, that of a reduction

in oscillator frequency with theadditional capacitor in circuit.Furthermore, the frequency andshape of the waveform are likelyto vary when adjusting opamppreset VR2.

The effect is due to theoscillator now seeing twocapacitors in parallel, its ownC1, and C2 of the opamp circuit.The effective value of the latter is also changed by the amountof resistance it sees from VR2.

We have a cure for this aswell!

SIGNAL BUFFERING

There is a scenario that wehave not yet explored, that of feeding a voltage into the non-inverting input, and merelyfeeding the output straight backinto the inverting input, butwithout any additional voltage or current being fed into that input.

Such a circuit is shown inFig.7.5.

The interesting thing aboutthis circuit is that the totalnegative feedback ensures thatthe voltage applied to the non-inverting input receives neither amplification nor attenuation atthe output. Whatever changethere is on this input is exactlyfollowed by the output, and inthe same direction. In thisconfiguration, the circuit isknown as a unity gain amplifier,i.e. the gain is 1. The circuit isalso said to function as a buffer.

What is now worth noting isthat inputs to opamps draw verylittle current (some types drawnone at all, see Panel 7.1). Theyare said to have high impedanceinputs, where impedance canloosely be described as

TEACH-IN 2000

INPUT CAPACITOR

Earlier, we drew your attention to the likelihood that,when the gain was beingadjusted, the waveform positionseen on screen would changeas well as amplitude. This is inpart due to the fact that thetriangular waveform tapped fromIC1a pin 1 may not be swingingabout an exact midway voltage

level.

Consequently, any DCvoltage difference between thewaveform’s midway level andthat set by VR4 is amplified bythe opamp, causing the verticalshift observed.

There is a very easy cure for this – to stop the DC level fromthe oscillator reaching theopamp, just allowing the ACvoltage change through.

In Teach-In 2000 Part 2 wediscussed capacitors in terms of their ability to be charged anddischarged through aresistance. We displayed it viaone of the computer demos andgave formulae for it.

Capacitors have another attribute, the ability to stop directcurrent (DC) passing through

PANEL 7.3 – OPAMP POWER LINESMost opamps are designed to be run from a dual-rail power sup-

ply, i.e. one having positive, negative and zero (ground) output voltagerails, typically 15V but may not be as high as this with some devices.

As we deliberately demonstrate in this Teach-In, opamps can alsobe powered from a power supply having only positive and 0V (ground)connections. In this case the middle rail voltage is provided by usingthe voltage at the center of an equally-divided potential divider (asused in the demos).

Note that whilst in theory all opamp circuits shown in this Teach-Inpart can be powered from dual-rail supplies, on no account shoulddual-rail supplies be used if the circuit is to be connected to the ADCdevice or to a computer. Additional circuitry would be required in order to permit computer connection. Failure to observe this could seriouslyharm the ADC and/or computer.

For optimum stability of an opamp circuit, the power supplyshould be regulated at fixed voltage levels. Power supplies will be dis-

cussed in Part 9.







control must also be taken intoaccount.

TEACH-IN 2000

breadboard layout to that shownin Fig.7.8.

The signal is still being fedin via capacitor C2 in order toisolate the amplification from the

affects of the DC bias that mightexist from the oscillator.However, we must provide theopamp side of C2 with adischarge path, as supplied viapreset VR4.

Note that in the “real world”,the discharge resistance valuein relation to the value of capacitor C2 affects thefrequency range that can becorrectly handled (to bediscussed when we examine

integration in a later part of theseries), and should be chosenaccordingly. For the sake of thisdemo, however, we’ll ignoresuch niceties – the relationshipis OK for what are trying toshow.

We retain presets VR2 andVR3, but have to provide asecond midway bias voltage intothe now “loose” wiper of VR2.This is provided by the voltagedivider formed by resistors R3

and R4. At their junction isadded a capacitor (C3) to“smooth” the voltage here,which could otherwise varysignificantly with the changingsignal levels in the feedbackpath. As we discussed whenconsidering voltage dividersfeeding into another resistance(Part 1), the resistance of R3and R4 should be equal in order to provide the midway voltage,but also of a value about tentimes less than the load

resistance (effectively VR2 inthis case). A value of 4k7 has

been chosen on the assumptionthat VR2 is set about midway(about 47k ). Fine adjustment

of the midway level can bemade using preset VR4.

Note that the wrong figurewas published for Fig.1.12 of

OUTPUT

C322m

22mC2

0V

6

5INPUT

7

VR2100k

VR4100k

R44k7

3

2

4

1

+6V

R34k7

VR3100k

+

+

+

+

IC4bLM358

8

IC4aLM358

Fig.7.7. Non-inverting

opamp ampli-fier circuit.

1 6

1 6

1 5

1 5

1 7

1 7

1 8

1 8

1 9

1 9

2 0

2 0

2 1

2 1

2 2

2 2

2 3

2 3

2 4

2 4

2 5

2 5

2 6

2 6

2 7

2 8

2 9

2 9

3 0

3 0

3 1

3 1

TO R.H.SIDE OF

BOARD

TO R.H.

SIDE OFBOARD

INPUT

OUTPUT

IC4VR2 VR3

VR4

C2 C3

+ +

R4

R3

Fig.7.8 and photo. Breadboard layout for Fig.7.7. Note that thesecond half of IC4 is now required to be connected into

the circuit.

There are severalapproaches to this problem. We

shall just take an option that iseasy to implement with thebreadboard layout we arealready using. The circuit isshown in Fig.7.7. Change the

Interactive computer display illustrating an inverting opamp circuit.









TEACH-IN 2000

be changed.

Signal input amplitude andfrequency rate (Cycle Count)can also be changed. Thepower supply voltage is fixed at+5V/0V. Note that the demo

opamp has been given outputmin/max limits of 1V and 4V.

The controls are stated onscreen, press the appropriatekeys to activate the function tobe changed. Note the varyingconditions under which the

output signal can becomeclipped. You can press the<PAUSE> key to stop thewaveform scrolling, then pressany other key to restart scrolling.

NEXT MONTH

This seems a convenientpoint at which to end thismonth’s Tutorial. We do nothave room for an Experimentalsection as such, this has been

moved forward to next monthand becomes Tutorial Part 8.

In reality, Part 7 and Part 8are both a mixture of Tutorialand Experimental. What wediscuss in Part 8, though, is all

based on the characteristics wehave been describing here inPart 7, and illustrates someinteresting ways in whichopamps can be used.





Robert Penfold looks at the Techniques of Actually Doing It!

It is said that the simplestinventions are the best ones,and, for the electronics hobbyist,stripboard possibly ranks along-side sliced bread and the wheelin the “best inventions” stakes.

Stripboard is a proprietaryprinted circuit board that is notedfor its versatility. For most projects it represents the only prac-tical alternative to using a cus-tom printed circuit board (PCB).

A project based on a cus-tom board is actually the bestchoice for a complete beginner due to the relatively foolproof nature of these boards. How-ever, many small and mediumsized projects are based onstripboards, and newcomers tothe hobby soon find themselvesusing this method of construc-tion.

Although stripboard is notquite as straightforward to useas custom PCBs, it is not reallythat difficult to use either. Thereare a few traps waiting for theunwary, but once you are awareof the pitfalls it is not too difficultto obtain perfect results almostevery time.

RIGHT PITCH

So what exactly is strip-board? It is based on a boardabout 16mm thick that is made

from an insulating material. Pre-

sumably the color of the boardvaries from one manufacturer toanother, but it seems to be sup-plied in a variety of yellow-browncolors from almost white to virtu-ally black.

The board is drilled withone-millimeter diameter holeson a regular matrix. In the past it

was possible to obtain strip-boards with the holes spaced at01-inch, 015-inch, or 02-inch

intervals, but these days only01-inch boards are readily avail-

able. It is only 0 1-inch pitch

boards that are of any real usewith modern projects, becausemany components will not fit

onto 0

15-inch or 0

2-inchboards.

One side of stripboard isplain, while the other side hascopper strips running alongthe rows of holes. It is, of course, from these copper strips that the stripboardname is derived. Many peo-ple still refer to this materialby the old proprietary nameof “Veroboard”.

Like an ordinary single-

sided printed circuit board,the components aremounted on the plain side.The leadout wires aretrimmed short on the other side and soldered to thecopper strips, which thencarry the connections fromone component to another.Fig.1 shows the plain and

copper sides of two scraps of stripboard.

BRITTLE EXPERIENCE

With a custom PCB there isusually no preparation required.When you are ready to startconstruction you simply beginfitting the component to theboard. With stripboard a smallamount of work is needed be-fore the board is ready to accept

Fig.1. Stripboard only has the copper strips on one side.

Fig.2. The underside view of theboard will clearly show the positions

of any breaks required in thecopper strips.





the components, and the normalfirst step is to cut out a board of the required size.

As pointed out previously,stripboard comes in a range

yellow-brown colors, reflecting arange of materials used in theboard. Some of these materialsare tougher than others, butmost stripboards seem to beslightly brittle. It is best to err onthe side of caution and assumethat all these boards are brittle,

duces some very rough edges,but these are easily filed to aneat finish using a flat file.

The finished board mightslot into place in the case, but it

is more likely that it will bebolted in place. Any mountingholes should be drilled at thisstage using an ordinary HSStwist drill. Use a piece of scraptimber, chipboard, etc. under-neath the board, and use onlymoderate pressure. This shouldgive good “clean” holes andavoid any cracking around them.

When drilling any form of copper laminate board it is bestto drill the board with the copper

side uppermost, as there is oth-erwise a risk of the copper beingtorn away from the board.

BIG BREAKS

With anything but the mostsimple of projects it is necessaryto make some breaks in thecopper strips. Without any cutseach strip can only carry one setof interconnections, but bybreaking a strip into (say) three

pieces, it can carry three sets of connections.

The article describing theproject should include a diagramthat clearly shows the positionsof the breaks, as in the exampleof Fig.2. Double-check the posi-tion of each break before actu-ally making it. If a mistakeshould be made it is possible tosolder a small piece of wire over

the break, but more than the oc-casional repair will give scrappylooking results and poor reliabil-ity.

A special strip-cutting tool is

available, and it is often referredto as a “spot face cutter” in com-ponent catalogs. This is basi-cally just a drill style cutting toolfitted in a handle. In order to cuta strip the point of the tool isplaced in position and the han-dle is given a couple of rotationswhile applying moderate pres-sure (Fig.3).

If you will be producing any-thing more than the occasionalstripboard project, it is certainly

worthwhile buying this tool. Ini-tially you may prefer to use ahandheld twist drill bit of about5mm in diameter, which will dothe job quite well.

Either way, make quite surethat the strips are cut rightacross their full width. Very fineresidual tracks of copper can bedifficult to see with the nakedeye, so it is worth checking theboard with the aid of a magni-fier.

Although you need to makesure that the strips are cut prop-erly, do not go to the other ex-treme and practically drillthrough the board. With a largenumber of breaks this would se-riously weaken it. Brush awayany copper shavings as thesecould otherwise cause short cir-cuits.

Practically Speaking

Fig.3. Using the special tool provides the easiest way of

making breaks in thecopper tracks.

and exercise due care when

working on them. Use the“hammer and tongs” approachand you may well end up withthree or four small boards in-stead of one large one!

Over the years various sug-gestions have been made for quick and easy ways of cuttingstripboard to size using imple-ments such as glass and tilecutters. The problem with thesemethods is that they work wellwith some makes of stripboard,

but can produce disastrous re-sults with others.

The only truly reliablemethod found so far is to care-fully cut along rows of holes us-ing a hacksaw. Due to the closespacing of the holes and widthof the blade it is not practical tocut between rows. Cutting alongrows of holes inevitably pro-

Fig.4. An example stripboard layout diagram.

Fig.5. Removing some ex-cess flux rendered this solder

bridge fairly obvious.





MOVING IN

At this stage the board isready for the components to beadded. This is one respect in

which stripboard is rather moreawkward than a custom printedcircuit board. With a PCB thereis one hole per leadout wire or pin, but with stripboard less than10 percent of the holes are nor-mally used.

Mistakes with componentplacement are more easilymade, and when they do occur they can be difficult to spot. Tocompensate for this it is neces-sary to proceed more carefully

and to double-check the posi-tioning before fitting and solder-ing each component in place.

Having to remove and refit asmall component occasionally isnot a major disaster, but gettinga multi-pin component, such asan integrated circuit (IC), in thewrong place can be more diffi-cult to deal with. Removing thistype of component requiresproper desoldering equipmentand risks damaging the board.

Getting a large number of components shifted out of posi-tion is time consuming to cor-rect, and all the soldering anddesoldering could take its toll onthe board. It is much better toproceed carefully and get thingsright first time.

ON YOUR MARKS

Stripboard layout diagramsoften have letters to identify the

copper strips and numbers toidentify the columns of holes, asin the dummy layout diagram of Fig.4. Many constructors find ituseful to mark the board itself with these letters and numbers,so that they can quickly andeasily match any point on theboard with its equivalent pointon the diagram.

A fine point fiber-tip pen isrequired, as there is not a greatdeal of space available for thelabels. Also, it needs to be atype that is capable of writing on

glass and other non-porous sur-faces. Otherwise it will not markthe board properly, or the labelswill rub off the first time you han-dle the board.

It is difficult to mark num-bers for all the columns of holes,but navigating your way aroundthe board should still be easy if only every fifth or tenth columnis labeled. Similarly, it is onlynecessary to label every other copper strip, or even every

fourth or fifth strip.Do not make the classic

mistake of getting the orientationof the board wrong so that allthe components are fitted in thewrong places. There are usuallymounting holes that make thecorrect orientation obvious, butthe diagrams for the two sides of the board normally have amarker that indicates the samecorner of the board in bothviews. This is included in Fig.2

and Fig.4, and leaves no excusefor getting it wrong.

MISSING LINK

With the preliminaries out of the way, assembling a compo-nent panel is much the samewhether it is based on stripboardor a PCB. There are a couple of differences though, one of whichis the higher number of link-wires encountered when build-ing projects based on strip-board.

The copper tracks of a cus-tom PCB can weave all roundthe board if necessary, but thisis clearly not possible with strip-board. Link-wires provide ameans of compensating for thelack of versatility in the trackpattern, and enable connections

to run from any given point onthe board to any other point. Vir-tually every stripboard layouthas at least a few link-wires, andthe larger boards can have

dozens of them.The usual way of fitting link-

wires is to pre-form a piece of wire to fit into the layout in muchthe same way as resistors andaxial capacitors are fitted. Theends of the wires are thentrimmed to length and solderedto the board in the usual way.

An alternative method is tocut a piece of wire that is slightlyover-length and then solder oneend of it to one of the holes in

the board. Next thread the other end of the wire through the sec-ond hole and pull it tight using asmall pair of pliers. Finally trimthe wire and solder it to theboard.

The trimmings from resistor leadout wires are ideal for shortlink-wires, but for longer wires22s.w.g. or 24s.w.g. (or about06mm diameter) tinned copper

wire is needed. Where a layouthas a lot of link-wires be sure to

meticulously check that everylink has been fitted to the board.

There is no need to insulateshort links, but with wires of around 25mm or more in lengththere is a slight risk of short cir-cuits occurring, particularlywhere there are several wiresrunning side by side. In thiscase, it is advisable to fit thelonger link-wires with pieces of PVC sleeving.

BUILDING BRIDGES

The second potential prob-lem with stripboard is accidentalshort circuits due to solder splashes and excess solder on joints. This can be a problemwith any form of printed circuitboard, but it tends to be moreproblematic with stripboard due

Practically Speaking







A team of researchers fromIBM’s laboratory in Zurich re-cently revealed their road mapfor the future of data storage.One surprise is that punchedcards are due for a comeback,but around a million timessmaller than they were the firsttime round.

The real density of hard diskrecorders is now increasing at120 percent per year, thanks toIBM’s 1988 discovery of GMR,the giant magneto-resistive ma-terial which was ready for com-mercial exploitation two yearsago and is now used in 70 per-cent of all hard drive read heads – either made by IBM or under license.

GMR is a multi-layer sand-wich of magnetic and non-

magnetic materials, which showdramatic changes of resistancein a changing magnetic field.This makes the read head tentimes more sensitive, and solets it detect smaller magneticdomains.

Hard Drive Density

Currently hard drives canrecord around 20 Gigabits of data for every square inch(6.45cm

2) of surface area and

35 Gigabit per square inchdrives are already working in thelab. The likely practical limitlooks like being 100 Gigabits. Atthis density, the individual mag-netic domains are so small andclose that they affect each other,making storage unreliable. Be-fore this limit is reached, the cur-

rent method of recording a sig-nal, with a miniature inductivehead, will have become unwork-able.

IBM’s Magneto-electronicsteam leader, Dr Stuart Parkin,believes that in two years timehard drives will have to use ver-tical recirding (VR) instead of

horizontal recording (HR). For VR the domains are switched bya field that aligns the magneticparticles through the disk coat-ing.

IBM’s Microdrive, the harddrive no bigger than a largepostage stamp, currently stores340 Megabytes, or nearly 900

BACK TO THE FUTURE WITH MILLIPEDESMillipedes may help bring back punched card technology

for PC data storage. Barry Fox reports

A ROUNDUP OF THE LATEST EVERYDAY NEWS FROM THE WORLD OF ELECTRONICS

Microchip Handbook

Many of you will already have found how useful Microchip’sEmbedded Control Handbook can be when writing PIC microcon-troller software. The latest update to this book has been releasedand provides a comprehensive reference tool for anyone usingPICs and related products.

The 848-page updated handbook provides current applicationnotes, technical briefs and reference designs which have beenwritten and published since the previous edition. The book can beobtained through any authorized Microchip representative. Thematerial is also available individually on Microchip’s website atwww.microchip.com

It is interesting to note from another Microchip press release

that the organization is offering a comprehensive University Pro-gram within the UK, designed to help university professors givetheir engineering students a hands-on understanding of PICs and

related products. Details can be found via www.microchip.com/

university

Microchip’s UK HQ is at Microchip House, 505 Eskdale Road,Winnersh Triangle, Wokingham, Berks RG41 5TU, UK.

Tel: +44 (0) 118-921-5858

Fax: +44 (0) 118-921-5835

http://www.microchip.com/


http://www.microchip.com/university











The fundamental science on Atomic Force Microscopy wasdone in 1980, and won a NobelPrize for IBM’s Dr Gerd Binnig in1986. The first laboratorydemonstrations are now nearly

ready. “It’s back for the future” ,says Gerd Binnig, alluding to theoriginal punch card, developedin the last century for censusdata processing and then usedby early computers.

But whereas original punchcards had permanent perfora-tions, the new Millipede record-ing material can be erased, byheating the plastic to re-flow de-pressed areas. The chip movesacross the surface, in a scan-

ning raster, writing 1GB of datain a 3mm x 3mm area.

The write/read system mustbe kept surgically clean, but thetechniques used to keep harddrives clean are applicable. Air is continually blown over the sur-face, through very fine filters.

Tunneling Ram

There are also new develop-ments coming in Random Ac-

cess Memory. Current RAMneeds power to retain data. TMJ(tunneling magnetic junction)-RAM retains data even when the

power is switched off. So itworks like flash memory, butwith much higher capacity, andmuch lower power needed for writing. With Magnetic RAM aPC could boot up within sec-

onds.

The system relies on theability to detect and control thespin parameters of electrons inferromagnetic materials. Switch-ing at low power is possible be-cause of the quantum physicsphenomenon known as tunnel-ing, whereby if enough electronsconfront a barrier, some willpass through, even though their energy state is theoretically toolow to allow it.

NEWS......

still pictures from a video cam-era. The next Microdrives willhold 1GB. By comparison an8MB Compact Flash card holdsaround 20 pictures.

So what happens when diskdrives run out of space? Dr Bernard Meyerson, IBM’s Direc-tor of TelecommunicationsTechnology, dismisses the ideathat optical disk can take over from magnetic hard disks.

“IBM has worked for yearson optical storage, includingdisks with several layers to in-crease density. But there is abasic limiting factor – the wave-length of light”.

Millipede Tips

Big Blue’s Blue Sky re-search efforts are now concen-trated on an extraordinary newtechnology called Millipede. Asilicon chip, the size of a finger-nail, is made with a matrix of 1024 tiny cantilever arms, eachwith a sharp tip, around 1nm insize. When the tips are moved,by feeding current to activatedrive coils, they press down on a

spinning plastic film disk to cre-ate tiny indentations. These canthen be read by sensor tips.

Greenweld

CatalogYou will be glad to hear that

Greenweld have reopened.Chris Knight tells us that after

many months of work they havefinally got the business goingagain. You will probably recallthat the original Greenweld Elec-tronics ceased trading last year,but the remaining stock was as-tutely bought by Chris and TimKnight and Geoffrey Carter.

The trio have a scientificbackground and wide business

experience, along with interestsranging from computers to carsand robots to recycling.

We are pleased to have re-ceived the new Greenweld cata-log, the first under the new own-ership and management team.

The catalog lists many ranges of the types of component thatanyone involved in electronics islikely to need, not only resistors,capacitors, potentiometers, logicICs, LCSs and so on, but alsoitems such as meters and tools,hardware and surplus stocks,and there is a selection of booksas well.

Good wishes to Greenweldfrom us all at EPE and EPE On-line.

For more information, con-tact Greenweld Ltd., Dept EPE,PO Box 144, Hoddesdon, Herts,EN11 0ZG, UK.

Tel: +44 (0) 1277-811042

Fax: +44 (0) 1277-812419

E-mail: ad-

[email protected]: www.greenweld.co.uk

WIND

POWER A book called Windpower

Workshop: Building Your OwnWind Turbine, has been writtenby Hugh Piggott, the technical

consultant to the BBC 1 docu-soap Castaway 2000, in whichthe castaways rely on renewableenergy for their power needs.

Hugh has lived for 25 yearson a similar island and runs hisown wind turbine company. Hisbook is based on his knowledgeof wind power harnessing and isaimed at helping budding sur-

http://www.greenweld.co.uk/








sent to the project throughoutthe year 2000. The site will besealed in 2001 and shall remainburied for 200 years. A trust isbeing established to ensure thesite is excavated in 2200. Any-

one can take part by filling atime capsule pack and sendingit back to the project. Each packcontains a time capsule measur-ing 340mm x 250mm x 80mm,along with specialized foldersand envelopes which help topreserve the items within it.

Records of the project, in-cluding the participants and lo-cation of the site shall be keptwith The International TimeCapsule Society in Atlanta, key

regional record repositories inBritain and within the records of the project itself.

The location of the site willbe announced later this year.

Everyone who takes partreceives a certificate givingthem legal title to their time cap-sule and its contents, allowingthem to leave their legacy to fu-ture generations.

Packs can be ordered by

sending a check for 41 UKPounds made payable to: TheMillennium Time Capsule Pro- ject and sent with the partici-pants name and address to: TheMillennium Time Capsule Pro- ject, PO Box 736, Newcastleupon Tyne NE99 1LQ, UK. Al-ternatively, packs can be or-dered through the websiteshown below.

Tel: +44 (0) 191-261-6784

Fax: +44 (0) 191-232-1274

E-mail: editorial@millennium-

timecapsule.com

Web: www.millennium-

timecapsule.com

Why not tell us, for possibleinclusion in Readout, what youare sending or would like to

have sent if the capsules hadbeen large enough? Repliesmay be serious or humorous(but at least loosely connectedwith electronics)!

NEWS......

vivalists, hobby engineers, self-sufficiency hopefuls and stu-dents of renewable energy tolearn more about wind power.

The book is priced 10 UKpounds (plus 1.75 pounds ship-

ping and handling), and is avail-able by mail order from the Cen-ter for Alternative Technology,Machynlleth, Powys SY20 9AZ,UK.

Tel: +44 (0) 1654-702400

Fax: +44 (0) 1654-702782

Email: me-

[email protected]

Web: www.cat.org.uk

Three Counties Ra-dio

& Computer RallySunday 21 May 2000. By pop-

ular demand following the 1999rally, the Three Counties annualradio and computer rally is to bestaged a week before the SpringBank holiday. It will be held at thePerdiswell Leisure Centre, BilfordRoad, Worcester, UK.

For those not familiar with thevenue, the following facilities areavailable: full restaurant servicesfrom 7 AM, licensed bar from 11 AM, all traders in two adjacenthalls, easy access to the hallswhich are at ground level, freeparking for 900 cars and coaches.

The organizers point out that,being close to the City Center,wives and children can spend apleasant day in Historic Worces-

ter, sight seeing, shopping or aboat trip on the river Severn (we’dlike to ask why wives and childrenshould be shuttled off – we aresure they are just as interested inwhat the rally has to offer as therest of us are!).

For more details contactWilliam E. Cotton G4PQZ, Tel/Fax: +44 (0) 1905-773181 (for faxplease ring first).

Farnell’s CatalogNo longer need you complain

that “the Farnell catalog is great but it’s just too big”! Thisrenowned supplier is separatingits catalog into six books, split byproduct. It will be available from April.

Farnell say that this allowsemphasis to be placed on their

MILLENNIUMTIME CAPSULE

The Millennium Time Cap-sule is a major national UK project in celebration of the newmillennium. Businesses,schools, clubs and the generalpublic are invited to take part inthis prestigious event and tosend a personal message to fu-ture generations. The Millen-nium time capsule will be buriedfor 200 years. Inside, contribu-tors will have their own box con-taining whatever they wish toinclude. Photographs, videos,books, tapes, letters – the list isas long as your imagination.

The time capsule will be thelargest ever constructed, provid-ing a snapshot of the UK at theend of the millennium. But it willalso be a very personal record.Every contributor will be sentcertification, identifying their boxwithin the capsule. In this wayindividual boxes can be passeddown from generation to gener-ation and inherited by our de-scendants in the year 2200.

The massive site will housethousands of time capsules frompeople from all over Britain andabroad. Time capsules can be

http://www.millenniumtimecapsule.com/




http://www.cat.org.uk/









NEWS......

core product strengths, marketthe full range, provide the“ultimate one stop shop” and tofocus on new products threetimes a year instead of twice, asat present.

From the summer editiononwards, color pages will alsobe made available for suppliersto advertise their products inthese books.

Tel: +44 (0) 113-263-6311

Fax: +44 (0) 113-263-3411

Web: www.farnell.com

Farnell’s catalog always hasbeen a “must” to have in your electronics workshop. Thischange of binding will surely bewelcomed. Don’t forget, also,that Farnell have product data

on CD-ROM as well.For more information con-

tact Farnell, Canal Road, LeedsLS12 2TU, UK.

http://www.farnell.com/













I’ve not come up against your Port C problem. Are you sure that your PIC is fully healthy? I haveseen erratic waveforms on other devices when part of them hasdied for some reason. You might want to buy another PIC and try the program on it.

Both your TK suggestionsseem useful. Thank you Roger.Perhaps one day …!

PATENTLY DIFFICULT

Dear EPE,

I have designed amicroprocessor-based PC Cardfor the ISA bus, but no one wantsto know. I have tried over 40 UKmanufacturers that were specifi-cally selected to do the job of buy-ing the manufacturing rights of mycard, and have contacted a tele-coms company here as my carduses Distinctive Ring Patternsfrom them, but not one of themhas had the decency to reply.

Are all UK-based inventors of electronic devices treated this pa-thetic way all the time? Or is theresomeone you know out there whowould be interested in manufac-turing my card? I am made to feelthat I am insignificant, a has-been, a nobody.

You would not believe theamount of E-mail and snail-mail Ihave sent out, but nothing what-soever has come back. I am sodepressed with it all. I think thequestion is, after the Patent, whatnow ?

I would be ever so grateful toyou and your colleagues if you

could publish this and your reply,as I feel it would benefit other UKElectronics Inventors in the samesituation.

Jim Delaney

Sheffield, UK

Jim’s plea was E-mailed toour Online Editor, Alan, who of-fered the following extremely

practical reply:

I’ve worked on both sides of the desk, both designing a widevariety of products as a develop-ment manager and also receiv-ing proposals from outside de-signers hoping that my company would take on their idea. It hap-

pens all the time, and it’s sur- prising how badly presented theapplicant’s case can be. Not ev-ery manufacturer would be assympathetic to the aspiring de-signer as I was, so first impres-

sions count, and a crispbusiness-like approach can only help as well as setting youabove all the other (amateur)applications vying for the samespot.

However, I was one of thefew who would always spare alittle time to look at an external idea, but my next problem would be selling the merits of the ideato the senior management. If adesigner couldn’t sell the con-

cept to me, I had no hope selling it up the ladder.

Often designers had no ideaof the investments needed intooling, production and distribu-tion either. No basic market re-search, no sales projections, nobudgeting – a design without such initial marketing researchreally would need to set theworld alight. James Dyson found out the hard way and perse-vered, now everyone buys his

vacuum cleaners (even me!).The Black & Decker Lawnraker and their WorkMate bench aretwo more examples of productsdesigned by amateur designers.The Bayliss wind-up radio is an-other.

In my career in product de-

velopment, I have only comeacross one really switched-on

professional-looking designer (areal “ideas man”) who presented a very powerful case, with good quality prototypes and lots of

ideas that forced us to sit up and listen. He was immensely enthu-siastic and positive, and had re-ally thought of everything and had come up with some very cute answers.

A personal meeting sold uson the concepts. He had all theideas and we were prepared todevelop the product and tool upfor mass production, which iswhat we did (for a special typeof tool kit). It would also be truethat, sometimes, manufacturers

just don’t know what they’relooking at and are being very shortsighted, so you have nohope with such firms.

Manufacturers usually havetheir own agenda with their own

products currently on the draw-ing board (CAD screen anyway),so to take on an external designcould mean dumping one of their own in-house designs.There would need to be a very good reason to do that.

In the case of electronics,there is also the development cost involved with making the

product EMC compatible and gaining CE-approval. Maybe thefact it’s an ISA card rather than,say, PCI might also detract fromit, I couldn’t say. I believe that ISA is being phased out in thePC2000 specification, althoughof course ISA slots will bearound on legacy systems for some time to come.

It’s only worth patenting if you can afford the legal costs of fighting an infringement. A pend-ing patent enables designers togo with an NDA instead and then try to sell All Rights. I think

Readout





it’s not just the treatment of inven-tors that is the problem, morelikely it’s the pressure the manu-facturers are already under withtheir own product lines. They get too wrapped up in their own prob-lems to want to go looking for more! But a forward-thinking and

progressive company (e.g. Black & Decker) will listen to outsideideas, if only to get the feel for anidea that may subsequently be

proposed to their competitors.

You should ask yourself whether it’s worth sub-contracting the production yourself, and maybe get a small batch madeand sell direct if you have to (e.g.on a web site). CE approval isyour next hurdle, then give a few samples away and get the market talking about it. If you can make abig enough nuisance of yourself inthe marketplace, it could then bethat someone will buy the rights.Just make sure you are fully pro-tected with design rights. Thereare plenty of good electronic engi-neers who can CAD up a board and polish off its development.

Try looking at James Dyson’s

web site (www.dyson.com/co.uk), there used to be an inven-tor’s resource there. There is alsoan alt. newsgroup for inventorswhere I’m sure you’ll get morehelp. Also you could try a local University – an example in my case would be the new Product Design & Development Centrebased at the University of Hull,with whom I’m working.

I’m sorry I can’t be of moreassistance, but hope the above

helps – good luck! Alan Winstanley

REGEN RECEIVER AND FETs

Dear EPE,

I am writing to you as a sub-scriber to EPE and an electronicsconstruction enthusiast for some35 years. First, thank you for the

superb series of articles on RFDesign by Raymond Haigh, cul-minating in the High Perfor-mance Receiver (March ’00),which I have decided to con-struct.

I am not “new” to construc-tion, having built over 23 re-ceivers for short waves over theyears, designing and producingmy own PCBs for these re-ceivers.

It is the power gain of the2N3819 FETs used in RaymondHaigh’s design that I wish toquery. The problem is that manycomponent suppliers use thesame manufacturer for 2N3819s

and the spread in characteristicsof these devices may affect thereceiver’s performance. In myown designs I use BF244 andBF245. Your comments are re-quested.

John B. Dickinson

Tamworth, Staffs, UK

John Dickinson gave a lot more information in his letter and sent an example 2N3819.

We forwarded everything toRaymond Haigh, who replied:

Thank you for letting meread Mr. Dickinson’s interesting and helpful letter. I should begrateful if you would thank himfor having taken so much trou-ble and for his very kind remarksabout my recent series of arti-cles. I would offer the following observations:

He is, of course, quite cor-rect in pointing out the widespread in FET characteristics.He is also correct when he saysthat the specifications for theBF244 and BF245 are tighter than the specification for the2N3819. Referring to the tables

published in Farnell’s catalog,the transconductance spread for

the BF244 and BF245 is 3 to6 5mA/V, whilst the spread for

the 2N3819 is slightly greater at 2 to 6 5mA/V.

Unfortunately, the BF244

and BF245 may not be readily available outside Europe, and regard must be had to the world-wide circulation of EPE. Be-cause of this, I will have to con-tinue specifying the ubiquitous2N3819.

I have built about six ver-sions of the circuit using thistransistor as a drain bend detec-tor. They all worked well with thecomponent values quoted and without any selection of the

2N3819s.I have, however, explored

this question. The outcome of the trial was as follows:

(a) Thirty-three 2N3819transistors were connected intocircuit and provision made for monitoring the audio output volt-age. Of these, 23 performed in acompletely satisfactory way,three were marginally better than the rest, and seven per-formed badly, or would not work

at all, unless the detector sourceresistor was increased in value.The transistor kindly supplied by Mr. Dickinson was one of thosethat would not work at all.

(b) When the source biasresistor (R5) was increased to15k, all 33 specimens of the2N3819 performed in a com-

pletely satisfactory way. Withthe source bias resistor in-creased, several specimens of 2SK168, MPF102, TIS14 and J310 (about twenty transistors intotal) all worked well in the cir-cuit also.

(c) The few transistors that were marginally better than therest gave a very slightly higher output with the specified 4k7 source resistor. It would seemmy earlier endeavors to milk the

Readout

http://www.dyson.com/co.uk















PIR Light Checker

Nearly all the componentsneeded to build the PIRLight Checker project should beobtainable from your usual local

supplier. The miniature light-dependent resistor (LDR) andthe 7-segment, commoncathode, display both came fromMaplin (codes AZ83E andFR41U) respectively. (You can,of course, use the good oldORP12 LDR.)

Details and prices for all of this month’s printed circuitboards can be found at the EPE

Online Store at

www.epemag.com

Teach-In 2000

No additional componentsare called for in this month'sinstallment of the Teach-In 2000 series. For details of specialpacks readers should contact:

ESR ElectronicComponents – Hardware/Toolsand Components Pack.

Magenta Electronics –Multimeter and components, Kit879.

FML Electronics (Tel: +44(0) 1677-425840) – Basiccomponent sets.

N. R. Bardwell (Tel: +44 (0)114 255-2886) – Digital

Multimeter special offer.

PLEASE TAKE NOTE: Micro- PICscope April '00

Unfortunately a digit was missedfrom the order code for theorange box, which should be281-6841. We apologize for thiserror

Shop Talk





Date post:	02-Jun-2018
Category:	Documents
Upload:	hossimo33
View:	221 times
Download:	4 times

Everyday Practical Electronics Online 02 05 May 2000

Documents