67981186 teach in 2011 electronics course

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50 Everyday Practical Electronics, November 2010

Teach-In 2011

By Mike and Richard Tooley

0ARTªª)NTRODUCTIONªTOªSIGNALSªINªELECTRONICªCIRCUITSªANDªSYSTEMS

/URª4EACH)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROADBASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEªª

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Everyday Practical Electronics, November 2010 51

Teach-In 2011

3IGNALS CAN ALSO BE QUITE EASILYCONVERTEDFROMONEFORMTOANOTHER&OR EXAMPLE THE SIGNAL FROM THESTAGE MICROPHONE AT A LIVE RADIO

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Teach-In 2011

0LEASENOTEØ4O AVOID CONFUSION BETWEEN THE

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u1,000,000 u Mega M 2.2M: (2.2 million Ohms)

u1,000 u Kilo k 4kbs (4,000 bits per second)

u1 u None none 220: (220 Ohms)

u u Milli m 45mV (0.045 Volts)

u u Micro P 33PA (0.000033 Amps)

u u Nano n 450nW (0.00000045 Watts)

4ABLE3OMEªCOMMONªMULTIPLESªANDªSUBMULTIPLES




Teach-In 2011

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Teach-In 2011

REPLACE THE ENTIRE UNIT IN MUCH THESAMEWAYASWEWOULDREPLACEASETOFEXHAUSTEDBATTERIES

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Teach-In 2011

0LEASENOTEØ

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Teach-In 2011

2.% OF THE PROBLEMS WITH ELECTRONICSISSIMPLYTHEAMOUNTOF

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!NSWERSªTOª1UESTIONS!NALOGUESIGNALSVARYCON

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SHALL BE LOOKING AT RESISTORS AND CAPACITORS%XAMPLESOFTHESETWOPASSIVECOMPONENTSAREFOUNDINALMOSTEVERYELECTRONICCIRCUIT&URTHERMOREWHENUSEDTOGETHERTHESETWOCOMPONENTSFORMTHEBASISOFAWIDERANGEOFELECTRONICTIMINGANDDELAYCIRCUITS

7E SHALL BE INVESTIGATING THE BEHAVIOUROFTHESECIRCUITSUSING#IRCUIT7IZARD

For more information, links andother resources please check out our Teach-In website at:

www.tooley.co.uk/ teach-in

www.technobotsonline.com

TechnobotsElectronic & Mechanical Components

With over 5,100 products available to order online, Technobotsprovides one of the widest range of components for the

Shop callers welcome: Technobots Ltd, 60 Rumbridge Street,Totton, Hampshire SO40 9DS Tel: 023 8086 4891

Get our 120 page A4 catalogue free with your next order by quoting 'discount coupon code'

EPE05 at the checkout

Battery ProductsChargers & PSU's

Opto Electronics

Gears, Pulleys& Cams

Controller BoardsIncluding Arduino

Chain & sprockets

Breakout Boardsfrom Sparkfun

Bearings from 1mm bore

Switches &Relays

Projects & kits

Robotics & Wheels

LCD displays

Pneumatics Shafts & Adaptors

Tools

Cable, Fuses &etc..

160+ dc modelmotors + speed

controllers

Passsives,Semiconductors

Sensorsconnectors

etc..

E d u c a t i o n

A c c o u n t s

W e l c o m

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50 Everyday Practical Electronics, December 2010

Teach-In 2011


0ARTªª2ESISTORSªCAPACITORSªTIMINGªANDªDELAYªCIRCUITS








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Everyday Practical Electronics, December 2010 51

Teach-In 2011

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Teach-In 2011

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Teach-In 2011

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Teach-In 2011

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5 $ ¯3

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'JH(SBQIPG DBQBDJUPSWPMUBHFBHBJOTUUJNFGPSUIFDIBSHJOHDJSDVJU

'JH(SBQIPG DBQBDJUPSWPMUBHFBHBJOTUUJNFGPSUIFEJTDIBSHJOHDJSDVJU

Circuit WizardA Standard orProfessional version

of Circuit Wizard can be purchased

from the editorial office of EPE – see

CD-ROMs for Electronics page and

the UK shop on our website (www.

epemag.com) for a ‘special offer’.

Further information can be found

on the New Wave Concepts website;

www.new-wave-concepts.com. The

developer also offers an evaluation

copy of the software that will operate

for 30 days, although it does have

some limitations applied, such as only

being able to simulate the included

sample circuits and no ability to save

your creations, this is the software that

is free with EPE this month.

However, if you’re serious about

electronics and want to follow ourseries, then a full copy of Circuit

Wizard is a really sound investment.

Virtually fullydischarged

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Teach-In 2011

,.4()3MONTHmSl,EARNmSECTIONWEmVE INTRODUCED YOU TO THE

BASICSOF RESISTORSANDCAPACITORS!LMOSTALLELECTRONICCIRCUITSWILLCONTAINONEORBOTHOFTHESETYPESOFCOMPONENTSSOITmSREALLYIMPORTANTTHATWEUNDERSTANDWHATTHEYDOANDHOWTHEYWORK%LECTRONICSTEXTBOOKSOFTENHAVE

LENGTHYANDCONFUSINGEXPLANATIONSWITHLOTSOFMATHEMATICALFORMULAE(OWEVERTHEBESTWAYTOREALLYGETTOGRIPSWITHWHATmSGOINGONISTOEXPERIMENTWITHSOMESIMPLECIRCUITS7EAREGOINGTOLOOKATAFEWOFTHESAMPLECIRCUITSINCLUDEDWITH

#IRCUIT7IZARDASWELLASGIVINGYOUSOMENEWCIRCUITSTOENTERANDTRYOUTFORYOURSELF

/HMSª,AWªINªPRACTICE4OSTARTWITHWEmLLHAVEALOOK

AT/HMmS,AWINPRACTICE/PENTHEl/HMmS ,AWm SAMPLE CIRCUIT FROMTHE !SSISTANT PANEL ON THE RIGHTHANDSIDEOFTHESCREENBYSELECTINGl3AMPLE#IRCUITSmTHENl%LEMENTARY#IRCUITSmANDSCROLLINGDOWNTOTHEl%LECTRICAL4HEORYmSECTION4HECIRCUITSEE&IGISABOUT

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DUCEDCHECKTHEVALUESFORVOLTAGE

ANDCURRENTWHENTHEVARIABLERESISTORISATANDKANDCHECKTHATTHEYOBEY/HMmSLAW

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%XPLAINBRIEÛYWHATISMEANTBYRESISTANCE7HATUNITSAREUSEDFORRESISTANCEANDWHATSYMBOLISUSEDTODENOTETHESEUNITS

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!CURRENTOF!ÛOWSINA:RESISTOR 7HAT POTENTIAL DIFFERENCEAPPEARSACROSSTHERESISTOR

7HATCURRENTWILL ÛOWWHENA:RESISTORISCONNECTEDTOA6 BATTERY

!CURRENTOFM!ÛOWSINARESISTORWHENITISCONNECTEDTOA6POWERSUPPLY7HATISTHEVALUEOFTHERESISTANCE

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! RESISTOR IS RATED AT :77HATISTHEMAXIMUMVOLTAGETHATCANBESAFELYAPPLIEDTOTHISRESISTOR ! & CAPACITOR IS

CHARGEDTOAPOTENTIALOF67HATCHARGEISPRESENT

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!RESISTANCEOFK:ISCONNECTEDTOACAPACITOROF&7HATIS THE TIME CONSTANT OF THIS CIRCUITAND HOW LONG WILL IT TAKE FOR THE

CAPACITOR TO BECOME APPROXIMATELYFULLYCHARGED

7HATCOMPONENTSAREREPRESENTEDBYTHECIRCUITSYMBOLSSHOWNIN&IG

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! RESISTOR OF : AT ISREQUIRED7HATSHOULDBETHECOLOURCODEFORTHISCOMPONENT

For more information,links and other resources

please check out our

Teach-In website at:www.tooley.co.uk/

teach-in

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Teach-In 2011

#APACITORSªINªACTION.OWWEmLLTAKEALOOKATCAPACITORS

INACTION/PENl#APACITOR#HARGINGm BY SELECTING 3AMPLE #IRCUITS THEN

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DISCHARGING PRINT OUT YOURGRAPHSEE&IG

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Teach-In 2011

3TART THE SIMULATION ANDTEST THECIRCUITmSOPERATION!STHECAPACITORCHARGESTHEVOLTAGEACROSSITINCREASES/NCE THE VOLTAGE REACHES A CERTAINVALUETHETRANSISTORSlTURNONmALLOWINGCURRENTTOÛOWFROMTHEPOSITIVEOFTHEBATTERYTHROUGHTHEBULBTOGROUND6ANDTHEREFORELIGHTINGIT4HELONGERITTAKESFORTHECAPACITOR

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HandsOn Technologyhttp://www.handsontec.com

SP to ICP Programming Bridge: HT-ICP200

In-Circuit-Programming (ICP) for P89LPC900

Series of 8051 Flash ȝControllers. ICP uses a

serial shift protocol that requires 5 pins to

program: PCL, PDA, Reset, VDD and VSS.

ICP is different from ISP (In System

Programming) because it is done completely

by the microcontroller’s hardware and does

not require a boot loader.

Program whole series of P89LPC900 µController from NXP Semiconductors…

USB-RS232 Interface Card: HT-MP213A compact solution for missing ports…

Thanks to a special integrated circuit from Silicon

Laboratories, computer peripherals with an RS232

interface are easily connected to a USB port. This

simple solution is ideal if a peripheral does not have a

USB port, your notebook PC has no free RS232 portavailable, or none at all !

Classic P89C51 Development/Programmer Board: HT-MC-02

HT-MC-02 is an ideal platform for small to

medium scale embedded systems

development and quick 8051 embedded

design prototyping.

HT-MC-02 can be used as stand-alone

8051ȝC

Flash programmer or as a development,

prototyping, industry and educational

platform.

For professional, hobbyists…



48 Everyday Practical Electronics, January 2011

Teach-In 2011


0ARTªª$IODESªANDª0OWERª3UPPLIES









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worldmags



Everyday Practical Electronics, January 2011 49

Teach-In 2011

AMOUNTOFCURRENTANDBEHAVESLIKE

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Teach-In 2011

2ECTIlERS4HE MOST COMMON APPLICATION FOR

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worldmags




Teach-In 2011

,IGHTEMITTINGªDIODES,IGHTEMITTINGDIODES,%$CANBE

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(a) Transformer symbol,voltages and turns

(b) A typical transformer

3 3

6 6

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9 9 5

,

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worldmags




Teach-In 2011

3KETCHTHECIRCUITSYMBOLFORADIODEANDLABELTHEANODEANDCATHODECONNECTIONS

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Teach-In 2011

ªª"UILDªnª4HEª#IRCUITª7IZARDªWAY

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.OWREPEATTHISFORSOMEMORE:ENERVOLTAGEVALUES(EREmSOURRESULTS FORTHREE:ENERDIODES 6 6 66AND66)FYOUCARRIEDOUTYOUREXPERIMENTS

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46 Everyday Practical Electronics, February 2011

Teach-In 2011


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Everyday Practical Electronics, February 2011 47

Teach-In 2011

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Teach-In 2011

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Teach-In 2011

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worldmags




Teach-In 2011

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dmags s

worldmags




Teach-In 2011

SHOWSASIMPLETRANSISTORSWITCHING

CIRCUITINWHICHTHECURRENTISBEING

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For more information, links and

other resources please check out

our Teach-In website at:



of Circuit Wizard can be purchased from

the editorial office of EPE – see CD-

ROMs for Electronics page and the UKshop on our website (www.epemag.

com) for a ‘special offer’.




developer also offers an evaluation copy

of the software that will operate for 30

days, although it does have some limita-

tions applied, such as only being able

to simulate the included sample circuits

and no ability to save your creations.

However, if you’re serious aboutelectronics and want to follow our

series, then a full copy of Circuit

Wizard is a really sound investment.

#HECKªnª(OWªDOªYOUªTHINKªYOUªAREªDOING3KETCHTHECIRCUITSYMBOLFORAAN/1/ "*4ANDBA1/1 "*4

ANDLABELTHECONNECTIONS

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IS THAT YOU CAN POP VOLTMETERS

AND AMMETERS INTO YOUR CIRCUIT

DESIGNSSOTHATYOUCANTAKEREAD

INGSANDSEEWHATmSGOINGONIN

YOURCIRCUITWITHEASE

dmags

worldmags




Teach-In 2011

.OWRUNTHECIRCUITANDÛICKTHE

SWITCH.OT THEMOST INTERESTINGOF

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dmags s

worldmags




Teach-In 2011

4RANSISTORªAMPLIlERªCIRCUIT

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s

worldmags




Teach-In 2011

SEEITRISINGABOVEDIPPINGBELOW

THEAXIS4HEREDLINEHOWEVERISAMUCHLARGERVERSIONOFTHEBLUELINE

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dmags s

worldmags




Teach-In 2011

4HECIRCUITOFASIMPLEAUDIOAM

PLIÚERISSHOWNIN&IG3TUDY

THE CIRCUIT CAREFULLY LOOK BACK AT

WHATWEDID IN4EACH)N0ART TO0ARTANDTHENSEEIFYOUCANANSWER

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42ANDB42

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dmags s

worldmags




Teach-In 2011

DESIGNTHATYOUCANTHENTESTlVIRTU

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YOUCANNOWDOWITHYOURDESIGN)F

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3EEPAGE

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By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce an electronics project from

start to finish – even including on-screen testing of the PCB prior to construction!

&,5&8,7:,=$5' 6 S H F

L D O ( 3 (

2 I I H U

Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in onecomplete package. Two versions are available, Standard – which is on special offer from EPE – and Professional.

Special EPE Offer ends 31 Jan, 2011

Special EPE Offer - Standard version only.

EPE is offering readers a 10% discount on Cicuit Wizard Standard software if purchased before 31 Jan, 2011.This is the software used in our Teach-In 2011 series.

Standard ( EPE Special Offer) £59.99 £53.99 inc. VAT

Professional £89.99 inc. VAT

* Circuit diagram design with component library (500 components Standard, 1500 components Professional)

* Virtual instruments (4 Standard, 7 Professional)

* On-screen animation

* PCB Layout

* Interactive PCB layout simulation

* Automatic PCB routing

* Gerber export

dmags s

worldmags



48 Everyday Practical Electronics, March 2011

Teach-In 2011


0ARTªª/PERATIONALªAMPLIlERS

/URª4EACH)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROADBASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEª


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TEACH-IN 2011 A BROAD-BASED INTRODUCTION

TO ELECTRONICS

,EARN

ircuit izard to siuate a variety

OF OPERATIONAL AMPLIÚER CIRCUITS

whie Investigate chaenges you

to expain the operation of a sipe

OSCILLATORCIRCUIT&INALLYIN Amaze

we sha ook back at the techno-

ogy that we used before integrated

circuits becae avaiabe.

I circuits (s) co-

prise arge nubers of transis-

tors and other coponents buit

on a singe sa sice of siicon.

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buit in a package that’s saer

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as inductors and capacitors (dif-

ÚCULTTOMANUFACTUREININTEGRATED

circuit for) and other coponents

that need to be externay accessi-

be are then connected as externa

‘discrete’ coponents.

n this instaent of each-n

2011WEWILLBEINVESTIGATINGONEOFthe ost coon types of integrated

CIRCUITTHEOPERATIONALAMPLIÚERop

amp). n Build YOU WILLBEUSING

)NTEGRATEDªCIRCUITS

sed in a huge variety of different

APPLICATIONSOPERATIONALAMPLIÚERS

are probaby the ost coon and

versatie for of anaogue integrated

circuit. ig. 5.1 shows the ubiuitousOPERATIONALAMPLIÚERWHILE&IG

5.2 shows what’s inside the 8-pin

dua-in-ine package.

ig.5.1. he famous 71 operational BNQMJÜFS XIJDI JT TVQQMJFE JO BOQJOEVBMJOMJOFQBDLBHF



Everyday Practical Electronics, March 2011 49

Teach-In 2011

ou can think of an operationa

AMPLIÚERASAUNIVERSALlGAINBLOCKmTO

WHICHAFEWEXTERNALCOMPONENTSARE

ADDEDINORDERTODEÚNETHEPARTICULARFUNCTIONOFACIRCUIT&OREXAMPLEBY

ADDINGJUSTTWOEXTERNALRESISTORSYOU

CAN PRODUCE AN AMPLIÚER HAVING A

PRECISELYDEÚNEDGAIN&ROMTHISYOU

MIGHTBEGINTOSUSPECTTHATOPERATIONAL

AMPLIÚERSAREREALLYEASYTOUSE4HE

GOODNEWSISTHATTHEYAREØ

p amp

4HESYMBOLFORANOPERATIONALAM-

PLIÚERISSHOWNIN&IG4HEREAREA

FEWTHINGSYOUNEEDTONOTEABOUTTHIS4HEDEVICEHASTWOINPUTSANDONE

output and no coon connection.

OTICE ALSO THAT ONEOF THEINPUTS IS

MARKEDlqmANDTHEOTHERISMARKEDlm

4HESEPOLARITYMARKINGSHAVENOTHINGTO

DOWITHTHESUPPLYCONNECTIONSqTHEY

INDICATETHEOVERALLPHASESHIFTBETWEEN

EACHINPUTANDTHEOUTPUT4HElmSIGN

INDICATESZEROPHASESHIFTWHILETHElqm

SIGNINDICATESPHASESHIFT

3INCE PHASE SHIFT PRODUCES

ANINVERTEDIETURNEDUPSIDEDOWN

WAVEFORMTHElqmINPUTISOFTENREFERRED

TOASTHElinverting input m3IMILARLYTHE

lmINPUTISKNOWNASTHElnon-

inverting mINPUT&URTHERMORE

WEOFTENDONmTSHOWTHESUP-

PLYCONNECTIONSASITISOFTENCLEARERTOLEAVETHEMOUTOFTHE

CIRCUITALTOGETHERANDJUSTAS-

SUMETHATTHEYARECONNECTED

TOEVERYCHIPØ

OST BUT NOT ALL OPERA-

TIONAL AMPLIÚERS REQUIRE A

SYMMETRICALSUPPLYOF TYPI-

CALLYBETWEEN6AND6

4HISALLOWSTHEOUTPUTVOLTAGE

TOSWINGBOTHPOSITIVEABOVE

6 AND NEGATIVE BE-

LOW 6 &IGURE SHOWSHOWTHESUPPLY

CONNECTIONS WOULD

appear if we decided

to incude the. ote

THAT WE USUALLY HAVE

TWOSEPARATESUPPLIES

APOSITIVE SUPPLYAND

ANEQUALBUTOPPOSITE

NEGATIVE SUPPLY 4HE

coon connection

TO THESE TWO SUPPLIESIETHE6RAILACTSAS

the coon rai in our

CIRCUIT4HEINPUTAND

ig.5.2. nternal circuit of the 71 operational BNQMJÜFSPQBNQ

'JH4ZNCPMGPSBOPQFSBUJPOBMBNQMJÜFS

'JH4VQQMZSBJMTGPSBOPQFSBUJPOBMBNQMJÜFS




Teach-In 2011

is the short-circuit output current(in aps).

Example 1!N AMPLIÚER PRODUCES AN OUTPUT

VOLTAGEOF6WHENSUPPLIEDWITHANinput of . eterine the vaue of VOLTAGEGAINOFTHEAMPLIÚER

Solutionow:

OUTPUTVOLTAGESAREUSUALLYMEASURED

reative to this rai.

ain

efore we take a ook at soe of

the characteristics of operationa

AMPLIÚERSITISIMPORTANTTODEÚNE

SOME OF THE TERMS AND PARAMETERS

THATWEAPPLYTOAMPLIÚERSGENERALLY

ne of the ost iportant of these is

THEAMOUNTOFAMPLIÚCATIONORlgain’

THATADEVICEPROVIDES4OKEEPTHINGS

as sipe as possibe we wi use an

lEQUIVALENTCIRCUITm TO REPRESENTAN

AMPLIÚERASSHOWNIN&IG4HIS

is uch easier to work with than theCIRCUITTHATWEMETEARLIERIN&IG

N &IG THE AMPLIÚER IS REPRE-

SENTEDBYAlBLACKBOXmWITHTWOINPUT

ANDTWOOUTPUTTERMINALSOTETHAT

INPRACTICEONEOFTHEINPUTTERMINALS

ISOFTENDIRECTLYLINKEDTOONEOFTHE

OUTPUT TERMINALS AND THEN REFERRED

TOASlCOMMONm4HEINPUTRESISTANCE

(inIN&IGISTHERESISTANCETHATWE

WOULDlSEEmLOOKINGINTOTHETWOINPUT

TERMINALSWHILETHEOUTPUTRESISTANCE

(outIN&IGISTHERESISTANCETHAT

WEWOULDlSEEmLOOKINGBACKINTOTHE

TWO OUTPUT TERMINALS 4HE VOLTAGE

PRODUCEDBYTHEAMPLIÚERISSHOWN

ASAlCONSTANTVOLTAGEGENERATORmTHE

CIRCLEWITHTHESINEWAVEINSIDE

ain is sipy the ratio of what

WEGETOUTTOWHATWEPUTIN3OFOR

EXAMPLEVOLTAGEGAINISDEÚNEDAS

the ratio of output votage to input

VOLTAGE!SAFORMULATHISIS

&INALLY THE POWER GAIN OF THE

AMPLIÚER ISDEÚNED AS THE RATIOOF

output power to input power. s a

FORMULATHISIS

where AvREPRESENTSVOLTAGEGAINAND

outAND inARETHEOUTPUTANDINPUT

votages respectivey.

3IMILARLYCURRENTGAINISDEÚNED

as the ratio of output current to input

CURRENT!SAFORMULATHISIS

outv

in

V AV

=

outi

in

I A

I =

where AiREPRESENTSCURRENTGAINAND


current respectivey.

out p

in

P A

P =

whereApREPRESENTSVOLTAGEGAINAND


votages respectivey.

OWPOWERISTHEPRODUCTOFVOLT-

AGEANDCURRENTTHUS

out out out P I V = × and

in in in P I V = ×

obining these reationships gives:

out out p i v

in in

I V A A A

I V = = ×

4HIS TELLSUS THAT THE power gain OFANAMPLIÚERISTHE product of thecurrent gainANDvoltage gain.

nput resistance4HE input resistanceOFANAMPLIÚER

ISDEÚNEDASTHERATIOOFINPUTVOLTAGEto input current:

in

inin

V

R I =

where in is the input resistance (inOHMS in is the input votage (in vots)AND in is the input current (in aps).

utput resistance4HEoutput resistance of an api-

ÚER ISDEÚNED AS THE RATIOOFOPENcircuit output votage to short-circuitOUTPUTCURRENT4HUS

out(oc)

out

out(sc)

V R

I

=

where out is the output resistanceINOHMS out(oc) is the open-circuitOUTPUTVOLTAGEINVOLTSAND out(sc)

outv

in

V A

V =

4HUS

3

v 3

2 2 10500

4 10 4 A

−

×= = =

×

Example 2!NAMPLIÚERHASANINPUTRESISTANCE

of 2:7HATCURRENTWILLÛOWINTOTHEINPUTOFTHEAMPLIÚERWHENAVOLT-AGEOFM6ISAPPLIED

Solutionow:

inin

in

V R

I =

4HUS 3

inin 6

in

50 10

2 10

V I

R

−

×= = = ×

×

Please note!%QUIVALENTCIRCUITSPROVIDEUSWITH

AWAYOFUNDERSTANDINGTHEBEHAVIOUROF ELECTRONIC DEVICES AND CIRCUITSoperate.

/PERATIONALªAMPLIlERª

characteristicsAVINGNOWDEÚNEDTHEPARAMETERS

THATWEUSETODESCRIBEAMPLIÚERSITISWORTHCONSIDERINGTHECHARACTERISTICS

'JH&RVJWBMFOUDJSDVJUPGBOBNQMJÜFS

925 10 A = 25 nA−

= × nA

and




Teach-In 2011

that we would associate with an ‘ideal’

(a) The voltage gain should be aslarge as possible, so that a large outputvoltage will be produced by a smallinput voltage

(b) The input resistance should be aslarge as possible, so that only a smallinput current will be taken rom thesignal source

(c) The output resistance should beas low as possible, so as not to limit theoutput current and power delivered by

(d) Bandwidth should be as wideas possible so as not to limit the re -

Fortunately, the characteristics o most

close to those o an ‘ideal’ operational

bandwidth o making the closed-loopgains equal to 10,000, 1,000, 100,and 10. Table 5.2 summarises theseresults. You should also note that the

(gain × bandwidth) product or this6Hz (ie, 1MHz).

We can determine the bandwidth

voltage gain is set to a particular valueby constructing a line and noting the

.evrucesnopserehtnotnioptpecretni

Please note! The product o gain and bandwidth

-stant. Thus an increase in gain canonly be achieved at the expense o

bandwidth, and vice versa .

Please note!When negative eedback is applied

produce a negative output voltage, andvice versa ). To preserve symmetry andminimise ofset voltage, a third resis -tor is oten included in series with thenon-inverting input. The value o thisresistor should be equivalent to the par -allel combination o R IN and R F. Hence:

Parameter Ideal Typical

Voltage gain Very high 100,000

Input resistance Very high 100MΩ

Output resistance Very low 20Ω

Bandwidth Very wide 2MHz

Table 5.1. Ideal and typical characteristics

Gain and bandwidthIt is important to note that the

product o gain and bandwidth isa constant or any particular opera -

increase in gain can only be achievedat the expense o bandwidth, and viceversa . In practice, we control the gain(and bandwidth) o an operational

o negative feedback .

Figure 5.6 shows the relationshipbetween voltage gain and bandwidth

(note that the axes use logarithmic,rather than linear scales). The open-loop voltage gain (ie, that obtainedwith no external eedback applied) is100,000 and the bandwidth obtainedin this condition is a mere 10Hz. Theefect o applying increasing amountso negative eedback (and consequent -ly reducing the gain to a more manage -able amount) is that the bandwidthincreases in direct proportion.

Frequency response The requency response curves

in Fig.5.6 show the efect on the

Voltage gain (A V ) Bandwidth

1 DC to 1MHz

10 DC to 100kHz

100 DC to 10kHz

1000 DC to 1kHz

10000 DC to 100 Hz

100000 DC to 10 Hz

Table 5.2. Relationship between voltage gain and

with a gain-bandwidth product of 1MHz

reduced and the bandwidth is in -creased. When positive eedback is

gain increases and the bandwidth isreduced. In most cases this will resultin instability and oscillation.

The three bas ic congurations

are shown in Fig.5.7. As mentionedearlier, supply rails have been omit -ted rom these diagrams or claritybut are assumed to be symmetricalabout 0V.

The voltage gain or the inverting

by the expression:

Fig.5.6. Frequency response curves for

The voltage gain or the non-invert -

given by the expression:

out FV

in IN

1V R

AV R

= = +

Finally, the voltage gain or the di -

is given by the expression:V A =

out F

in IN

V R

V R= −

R F IN

F IN

R R

R R

×=

+

The minus sign in the voltage gainexpression is included to indicate in -version (ie, a positive input voltage will

out out FV

in 2 1 IN

V V R A

V V V R= = =

−




Teach-In 2011

Where V 1 and V 2 are the voltages atthe input resistance ( R IN ) connectedto inverting and non-inverting inputsrespectively.

Limit capacitor-

scribed previously have used directcoupling and thus have requencyresponse characteristics that extendto DC. This, o course, is undesirableor many applications, particularlywhere a wanted AC signal may besuperimposed on an unwanted DCvoltage level.

In such cases a capacitor o ap -propriate value may be inserted

in series with the input, as shownbelow. The value o this capacitorshould be chosen so that its reac -tance is very much smaller than theinput resistance at the lower appliedinput requency.

We can also use a capacitor to re -strict the upper requency response o

is connected as part o the eedback path. Indeed, by selecting appropri -ate values o capacitor, the requencyresponse o an inverting operational

tailored to suit individual require -ments (see Fig.5.8 and Fig.5.9).

The lower cut-of requency isdetermined by the value o the inputcapacitance, C1, and input resistance,R 1. The lower cut-of requency isgiven by:

Provided the upper requency re -sponse it not limited by the gain ×bandwidth product, the upper cut-of requency will be determined by theeedback capacitance, C2, and eed -back resistance, R 2, such that:

Where C2 is in Farads and R 2 is inohms.

Example 3

is to be designed to the ollowing

Voltage gain = 20

Input resistance (at mid-band) =10k ?

Lower cut-of requency = 100Hz

Upper cut-of requency = 10kHz

Devise a circuit to satisy the above

Solution To make things a little easier, we can

break the problem down intomanage -able parts. We shall base our circuit

-

lower cut-of requencies, as shownin the Fig.5.8.

The nominal input resistance is thesame as the value or R 1.

both the low and the high frequency response

11 0.159

2 1 1 1 1 f

C R C Rπ

= =

11 0.159

2 2 2 2 2 f

C R C Rπ

= =

Thus:

R1 = 10 kΩ

To determine the value o R 2 we canmake use o the ormula or mid-bandvoltage gain:

AV = R2/ R1

Thus:

kΩ

R2 = Av × R1 = 20 × 10 kΩ

= 200 kΩkΩ

kΩ

kΩWhere C1 is in arads and R 1 is in

ohms.




Teach-In 2011

To determine the value o C1 we willuse the ormula or the low requencycut-of:

1 0.1591 1

f C R

=

From which:

31

0.159 0.1591 0.159 10 F 159 nF

1 100 10 10 1 10C

f R= = = = × =

× × ×

6

6

0.1590.159 10 F 159

1 10

−

= = × =

×

nF

Finally, to determine the value o C2 we will use the ormula or highrequency cut-of:

20.159

2 2 f

C R=

in Fig. 5.10.

Other applicationsAs well as their application as a

general purpose ampliying device,

o other uses. We shall conclude thismonth’s Learn by taking a brie look at two o these, voltage followers andcomparators .

A voltage ollower using an operation -

circuit is essentially a non-inverting

is ed back to the input. The result is an

‘unity’), a very high input resistance anda very high output resistance. This stageis oten reerred to as a bufer and is usedor matching a high-impedance circuitto a low-impedance circuit.

Typical input and output waveormsor a voltage ollower are shown inFig.5.12. Notice how the input andoutput waveorms are both in-phase(they rise and all together) and thatthey are identical in amplitude.

A comparator using an operational

no negative eedback has been ap -plied, this circuit uses the maximum

Fig.5.11. A voltage follower

Fig.5.12. Typical input and outputwaveforms for a voltage follower

Fig.5.13. A comparator

Fig.5.14. Typical input and outputwaveforms for a comparator

The output voltage produced by the

the maximum possible value (equalto the positive supply rail voltage)whenever the voltage present at thenon-inverting input exceeds thatpresent at the inverting input. Con -versely, the output voltage produced

to the minimum possible value (equalto the negative supply rail voltage)whenever the voltage present at theinverting input exceeds that present

at the non-inverting input.

From which:

3 3 92

0.159 0.159 0.1592 0.159 10 F 159 pF

2 10 10 100 10 1 10C

f R= = = = × =

× × × ×2

9

0.159

1 10=

×20.50.159= × ×

910 F 1−

=80 pF

80




Teach-In 2011

Typical input and output wave -orms or a comparator are shownin Fig.5.14. Notice how the outputis either +15V or –15V depending

on the relative polarity o the twoinputs.

NOW we’ve heard the theory,let’s use Circuit W izard to try

out some practical operational am -

really neat way to explore this kindo theory because students oten

prototyping boards. This might be due to needing dual

rail power supplies, or the act that

the schematic diagram into a ‘reallie’ circuit where incorrect layoutcan cause conusing results! Fortu -nately, we can do away with theseproblems when investigating thesedevices using Circuit Wizard. Solet’s look at a simple operational am -

Please note!W hen capturing

a schematic basedon operational am -pliers it is im -portant to double

check the orien -tation o the twosignal input pins.By deault, CircuitWizard will drawan operational am -plier with thenon-inverting in -put (labelled ‘+’)at the top and thenon-inverting in -put (labelled ‘−‘)at the bottom. Thismay or may not be

the same as the

circuit you are entering – so makesure that you double check!

Fortunately, it’s really easy tochange this; just right-click the opamp and click ‘arrange’ then ‘mir -ror’ (see Fig.5.15). It is importantto note that by ‘mirroring’ the opamp, the supply connections re -main unchanged, ie the positivesupply at the top and negative atthe bottom.

With the oregoing in mind, enterthe circuit shown in Fig.5.16. In thiscircuit we have a 2V variable inputvoltage connected to our invert -ing input, with our non-invertinginput connected to ground (0V).Recalling what we learned earlier,

Check –

5.1. Sketch the circuit symbol or

o the connections.

5.2. Sketch an equivalent circuit

and output resistances. Label your

drawing .

5.3. List our desirable characteris -

.

5.4. -put o 1.5V when an input o 7.5mVis present. Determine the value o

the voltage gain.

5.5.o 50 and a current gain o 2,000.W hat power gain does the ampli -

5.6. Sketch the circuit o an invert --

and identiy the components thatdetermine the voltage gain o the

.

5.7. An inverting operational ampli -

gain o –15, an input resistance o 5k ? , and a requency response ex -tending rom 20Hz to 10kHz. Devisea circuit and speciy all component

values required.

you are doing?

How do you think

The Circuit Wizard way

the correct orientation of inverting and non-inverting

inputs

For more information, links and

other resources please check out

our Teach-In website at:

www.tooley.co.uk/teach-in




Teach-In 2011

we know that the basic principle o

the diference in voltage between thetwo inputs.

-vided by the circuit shown in Fig. 5.16is determined by the gain, which willdepend on the arrangement and valueso the resistors in the circuit. We learntthat we can calculate the gain o an

the ormula:

In our circuit, R F (R2) is 2.5k ? andR IN (R1) is 500 ? . Use the ormulaabove to prove that the gain o thiscircuit is –5. In simple terms, thismeans that we should expect ouroutput voltage to be –5 times largerthan the input voltage. Note the minussign; the output will be inverted, as itsname suggests.

Now set the input voltage to 1V andrun the simulation. We would expectthe output voltage to be −5 × 1V = −5V.Now experiment with changing the in -put voltage and monitoring the outputvoltage. You should see that the gainholds true whatever the input voltageup until the output reaches the supplyvoltage. At this point, the output volt -age will remain constant, even withincreased input voltage. Whereas this

used in audio circuits this can causeclipping o the waveorm, which can

distort the sound.Modiy your circuit by replacing thevariable input voltage with a unction

generator and adding some probes, asshown in Fig.5.17. The waveorm dis -

play in Fig.5.18 shows how the signal

ComparatorIn our second circuit we’ll inves -

-

‘compares’ two input voltages and

The inverting input is a simple poten -tial divider that sets the voltage to hal o the supply voltage, in this case 5V. The non-inverting input is connected

to a potentiometer; efectively a vari -able potential divider. This allows us to

control the voltage to this input.In practical circuits this might be

replaced with a potential divider in -volving a resistive input device, suchas a light dependent resistor (LDR) orthermistor (we’ll be lookingat a circuitusing an LDR next). Some circuits evenuse two variable inputs to be com -pared – or example a line ollowingrobot might compare the inputs romtwo LDRs to determine its orientationon a line.

Enter the comparator circuit shown

in Fig.5.19 and experiment with thecircuit by changing the potentiometerand observing the input/output volt -

or ‘voltage level’ views to analyse theoperation o the circuit. By changingthe potentiometer you are changing thevoltage at the non-inverting input. Theinverting input is held at a constantvoltage o about 5V.

When the non-inverting input volt -age is higher than the inverting input,

-

back resistors the gain is very large,and thereore the output swings to themaximum voltage possible; the supply

F

IN

Voltage gainR

R= −

Fig.5.18. Waveform graphproduced by the modi -

is shown in blue and theoutput in red

Fig.5.19. A simple circuit to demonstrate

comparator




Teach-In 2011

VOLTAGE#URRENTÛOWSFROMTHEOPERA-TIONALAMPLIÚERTHROUGHTHEBICOLOUR,%$$TOGROUND6LIGHTINGITREDTODEMONSTRATEAPOSITIVEOUTPUT#ON-VERSELYWHENTHENONINVERTINGINPUTISLESSTHANTHATOFTHEINVERTINGINPUTTHEAMPLIÚERAMPLIÚESTHENEGATIVEINPUTBYALARGEAMOUNTRESULTINGINANOUTPUTATTHENEGATIVESUPPLYANDHENCELIGHTINGTHEGREEN,%$

.OTICETHATDESPITEWHATYOUMAYHAVETHOUGHTITISPRACTICALLYIMPOS-SIBLETOGETANEXACT6OUTPUT4HISWOULD THEORETICALLY BE POSSIBLE IFWECANENSURETHATBOTHINPUTSWERE

EXACTLYTHESAME(OWEVERINPRACTICEITISNOTPOSSIBLETOBETHISACCURATEANDTHELARGEGAINANDTINYVARIATIONRESULTSINAFULLSWINGEITHERTOFULLYPOSITIVEORNEGATIVE

Auto Light Switch)NOURÚNALCIRCUITWEmLLSEEAPRAC-

TICAL APPLICATION OF THE COMPARATORCIRCUITWEPLAYEDWITHABOVE)NTHISCIRCUITWEmLLUSEAN,$2TOMONITORTHELIGHTLEVELANDAUTOMATICALLYTURNONALAMP,!FOREXAMPLEFORAN

AUTOMATIC LIGHT CIRCUIT %NTER ANDSIMULATETHECIRCUITSHOWNIN&IGANDOBSERVEITSOPERATION"YADJUSTINGTHEPOTENTIOMETERWECANSETTHEPOINTATWHICHTHELAMPTURNSON)NPRACTICETHISWOULDBEHOWDARKITISWHENYOUWOULDLIKETHELIGHTTOTURNON

9OUMAYBEWONDERINGWHYUSINGANOPAMPFORTHISPURPOSEISBETTERTHANUSINGASIMPLETRANSISTORSWITCH

The Circuit Wizard way

ig.5.20. An automatic light switch using a comparator circuit

CIRCUIT"YUSINGANOPERATIONALAMPLI-ÚERASSOONASWEHITTHEPRESETVOLTAGETHENONINVERTINGINPUTVOLTAGETHEOPERATIONALAMPLIÚERWILLGREATLYAM-PLIFYTHEINPUTANDIMMEDIATELYGIVEUSTHEFULLSUPPLYVOLTAGE(OWEVERUSINGONLYATRANSISTORSWITCHYOUTENDNOT TO GET A PRECISE ONOFF BECAUSEOFTEN THERE IS A PERIOD WHERE THETRANSISTORISNOTCOMPLETELYSATURATED

!N OSCILLATOR CIRCUIT IS SIMPLY ACIRCUITTHATPROVIDESANOUTPUTSIGNALWITHOUTNEEDINGANYINPUTAPARTFROMAPOWERSUPPLYqOFCOURSEØ&IGSHOWSTHECIRCUITOFASIMPLEOSCILLATORCIRCUITBASEDONASINGLEOPERATIONALAMPLIÚER%NTERTHECIRCUITIN#IRCUIT7IZARD INVESTIGATE THE OUTPUT THATITPRODUCESANDTHENSEEIFYOUCAN

EXPLAINHOWTHECIRCUITWORKSint: 9OUMIGHTNEEDTORECALLEAR-

LIERWORKTHATYOUDIDON-RCHARGINGANDDISCHARGINGCIRCUITSANDCOMBINETHISWITHWHATYOUNOWKNOWABOUTOPERATIONALAMPLIÚERCOMPARATORS

9OUWILL ÚNDTHAT#IRCUIT7IZARDWILLDOAGREATJOBOFSIMULATINGTHEOSCILLATOR CIRCUIT (OWEVER BECAUSETHEREmSALOTGOINGONINASHORTAMOUNTOFTIMEITCANmTDOITINREALTIME)FYOUTRYATFULLSPEEDYOUmLLMOSTLIKELYGETVERYCONFUSINGRESULTS4OlSLOWTHINGSDOWNmYOUCAN REDUCE THE SPEEDOF

SIMULATIONBYCLICKINGONl4IMEmONTHEGREYBARATTHEBOTTOMOFTHE#IRCUIT7IZARDWINDOWMS SHOULDWORKNICELYWITHMOSTCOMPUTERS

Investigate

'JH"OPQFSBUJPOBMBNQMJÜFSCFJOHVTFEJOBO

an oscillator circuit

ig.5.22(right). hanging simulationTQFFEJO$JSDVJU8J[BSE




Teach-In 2011

f your coputer is a bit on the sow

side opt for ess unti you get a niceooking trace see ig5 ou wiaso need to adjust the scae on yourgraph; ig53 shows soe suggestedvaues that wi give you a graph ikethat shown in ig5 he rest is foryou to investigate… so how does it doit? he bue trace/probe in ig 5shoud give you soe cues

ig.5.23(above). uggested graph parameters

ig.5.24(right). ypical waveforms produced by the oscillator circuit

Amaze

Answers to Questions

51 ee ig53

5 ee ig55

53 ee page 51

5 00

55 100000 5 ee ig5a 5 ee ig58 with 1 = 5k:

= 5k: 1 = 15μ = 1p

efore we coud use transistorsin eectronic circuits we had to usevaves hese ooked a bit ike ight bubs hey needed ots of space otsof power and often produced a ot of heat they had to be heated up inter-nay before they coud work hisade designing sipe circuits uitecopicated – not ony did we need aow-votage high-current heater sup-

py but we aso needed a high votagesuppy of around 00 or orehen transistors cae aong they

revoutionised eectronics akingit possibe to have sa copexcircuits that operated fro ow vot-age oday we can ake transistors soTINYTHATWECANÚTLITERALLYMILLIONSof the on an area the size of yourSMALLÚNGER

he current generation of icroproc-essors are anufactured using a processthat’s capabe of producing individuatransistors 1000 ties saer than the

diaeter of a huan hair hat eansthat the in-d i v i d u a seicon-ductor ay-

ers ight onyhave a few tensor hundredsof atos nfact the at-est techno-ogy is capabeof producingtransistors thatare ess than5n across –that’s a ere000005

Next month!

n next onth’s each-n we wi beinvestigating ogic circuits



from the editorial office of EPE – see



epemag.com).




developer also offers an evaluation copyof the software that will operate for 30





ig.5.25. alves from the 1940s and 1950s compared with transistors from the 1960s and 1970s

ig.5.26. his 1970s semiconductor memory device contains the equivalent of more than 65,000 individual transis-tors. he latest chips have more than100 million devices in the same space!



44 Everyday Practical Electronics, April 2011

Teach-In 2011


Part 6: Logic circuits

Our Teach-In series is designed to provide you with a broad-based introduction to electronics. We have

attempted to provide coverage of three of the most important electronics units that are currently studied in

many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronics

units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experiencedREADERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª



you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge


TEACH-IN 2011

A BROAD-BASED INTRODUCTION

TO ELECTRONICS

Digital logic

Logic circuits are the basic build-

ing blocks of digital circuits and

systems. Logic circuits have inputs

and outputs that can only exist inone of two discrete states, variously

known as ‘on’ and ‘off’, ‘high’ and

‘low’, or ‘1’ and ‘0’.

Logic circuits usually have several

inputs and one or more outputs. At

any instant of time, the state of the

inputs will determine the state of

the output, according to the logic

function provided by the circuit.

If this is beginning to sound a little

complicated, let’s look at a couple

of simple logic functions that can be

SATISÚEDUSINGNOTHINGMORETHANA

IN THIS instalment of Teach-In

we introduce the basic build-

ing blocks of digital circuits.

We explain the operation of each

of the most common types of logic

gate and show how they can be

combined together in order to solvemore complex logic problems. We

also introduce bistable circuits and

show how they can be used to re-

member a momentary event.

We shall be using Circuit Wizard

to investigate each of the basic

logic gates before moving on to

explore some applications. Finally,

in Amaze we look at how recent

advances in technology have pro-

vided us with digital circuits that

are capable of operation at speeds

that are increasingly fast.

couple of switches and a lamp and

battery.

Consider the circuit shown in

Fig.6.1. In this circuit, a battery

is connected to a lamp via two

switches, A and B. It should be

obvious that the lamp will onlyoperate when both of the switches

are closed (ie, both A AND B are

closed).

Let’s look at the operation of the

circuit in a little more detail. Since

there are two switches (A and B)

and there are two possible states for

each switch (open or closed), there

is a total of four possible conditions

for the circuit. We have summarised

these states in Fig.6.2.

Note that the two states (ie, open

or closed) are mutually exclusive

Learn



Everyday Practical Electronics, April 2011 45

Teach-In 2011

and that the switches cannot exist

in any other state than completely

open or completely closed. Because

of this, we can represent the state of

the switches using the binary digits,

0 and 1, where an open switch is

represented by 0 and a closed switch

by a 1. Furthermore, if we assume

that ‘no light’ is represented by a 0

and ‘light on’ is represented by a 1,

we can rewrite Fig.6.2 in the form

of a truth table, as shown in Fig.6.3.

Another circuit with two switches

is shown in Fig.6.4. This circuit

differs from that shown in Fig.6.1

by virtue of the fact that the two

switches are connected in parallelrather than in series. In this case,

the lamp will operate when either of

the two switches is closed (in other

words, when A OR B is closed).

As before, there is a total of four

possible conditions for the circuit.

We can summarise these conditions

in Fig.6.5. Once again, adopting the

convention that an open switch can

be represented by 0 and a closed

switch by 1, we can rewrite the truth

table in terms of the binary states,

as shown in Fig.6.6.

The basic logic functions can

be combined to produce circuits

that satisfy a more complex logi-

cal operation. For example, Fig.6.7

shows a simple switching circuit

in which the lamp will operate

when switch A AND either switch

B OR switch C is closed. The truth

table for this arrangement is shown

in Fig.6.8.

Logic gates

Logic gates are building blocks

that are designed to produce the

basic logic functions, AND, OR,

NOT, etc. These circuits are de-

signed to be interconnected into

larger, more complex, logic circuit

arrangements.

Each gate type has its own symbol

and we have shown both the Brit-

ish Standard (BS) symbol together

with the more universally accepted

American Standard (MIL/ANSI)

symbol. Note that, while inverters

and buffers each have only one in-

put, exclusive-OR gates have two

inputs and the other basic gates

Fig.6.1. AND switch and lamp logic

Fig.6.4. OR switch and lamp logic

Fig.6.2. Possible states for the circuit of Fig.6.1

Fig.6.5. Possible states for the circuit of Fig. 6.4

Fig.6.3 (right). Truth table for the AND switch and lamp logic

Fig.6.6 (right). Truth table for the OR switch and lamp logic

Fig.6.7. Simple switching circuit using AND and OR logic

Fig.6.8 (right). Truth table for the simple switching circuit shown in Fig.6.7




Teach-In 2011

Buffers

Buffers do not affect the logical

state of a digital signal (ie, a logic

1 input results in a logic 1 output,

and a logic 0 input results in a logic

0 output). Buffers are normally used

to provide extra current drive at the

output, but can also be used to regu-

larise the logic levels present at an

interface. The Boolean expression

for the output, Y, of a buffer with

an input, X, is Y = X.

(eg, AND, OR, NAND and NOR)

are commonly available with up to

eight inputs.

Some of the logic gates shown

in Fig.6.9 have inverted outputs.

These gates are the NOT, NAND,

NOR, and Exclusive-NOR and the

small circle at the output of the

gate (see Fig.6.10a) indicates this

inversion. It is important to note

that the output of an inverted gate

(eg, NOR) is identical to that of the

same (ie, non-inverted) function

with its output connected to an

inverter (or NOT gate) as shown

in Fig.6.10b).

The logical function of a logic gate

can also be described using Boolean

notation. In this type of notation, the

OR function is represented by a ‘+’

SYMBOLTHE!.$FUNCTIONBYAlpm

sign, and the NOT function by an

overscore or ‘/’. Thus the output, Y,

of an OR gate with inputs A and B

can be represented by the Boolean

algebraic expression:

Y = A + B

Similarly, the output of an AND

gate can be shown as:

9!p"

7ESHALLNOWBRIEÛYSUMMARISE

the logic functions of each of the

basic logic gates that we met earlier

in Fig.6.9:

Fig.6.9. Logic gate symbols and truth tables

Fig.6.10. Logic gates with inverted outputs

Fig.6.11 (above). Majority vote logic circuit

Fig.6.12 (right). Truth table for the majority vote logic circuit




Teach-In 2011

Inverters

Inverters are used to complement

the logical state (ie, a logic 1 input

results in a logic 0 output and vice

versa). Inverters also provide extra

current drive and, like buffers, are

used in interfacing applications

where they provide a means of

regularising logic levels present

at the input or output of a digital

system. The Boolean expression for

the output, Y, of an inverter with an

input, X, is Y = /X.

AND gates

AND gates will only produce alogic 1 output when all inputs are

simultaneously at logic 1. Any other

input combination results in a logic

0 output. The Boolean expression

for the output, Y, of an AND gate

WITHINPUTS!AND"IS9!p"

OR gates

OR gates will produce a logic 1

output whenever any one, or more

inputs are at logic 1. Putting this

another way, an OR gate will only

produce a logic 0 output wheneverall of its inputs are simultaneously

at logic 0. The Boolean expression

for the output, Y, of an OR gate with

inputs, A and B, is Y = A + B.

NAND gates

NAND (ie, NOT-AND) gates will

only produce a logic 0 output when

all inputs are simultaneously at

logic 1. Any other input combina-

tion will produce a logic 1 output.

A NAND gate, therefore, is nothing

more than an AND gate with its

output inverted! The circle shown

at the output denotes this inversion.

The Boolean expression for the out-put, Y, of a NAND gate with inputs,

!AND"IS9!p"

NOR gates

NOR (ie, NOT-OR) gates will only

produce a logic 1 output when all

inputs are simultaneously at logic

0. Any other input combination

will produce a logic 0 output. A

NOR gate, therefore, is simply an

OR gate with its output inverted.

A circle is again used to indicate

inversion. The Boolean expressionfor the output, Y, of a NOR gate with

inputs, A and B, is Y = A + B.

Exclusive-OR gates

Exclusive-OR gates will produce a

logic 1 output whenever either one

of the two inputs is at logic 1 and

the other is at logic 0. Exclusive-

OR gates produce a logic 0 output

whenever both inputs have the

same logical state (ie, when both

are at logic 0 or both are at logic

1). The Boolean expression for the

output, Y, of an exclusive-OR gate

WITHINPUTS!AND"IS9!p

""p!

Exclusive-NOR gates

Exclusive-NOR gates will produce

a logic 0 output whenever either one

of the two inputs is at logic 1 and

the other is at logic 0. Exclusive-

NOR gates produce a logic 1 output

whenever both inputs have the same

logical state (ie, when both are at

logic 0 or both are at logic 1). The

Boolean expression for the output,

Y, of an exclusive-NOR gate with

inputs, A and B, is

9!p""p!

Combinational logic

The basic logic gates can be com-

bined together to solve more complex

logic functions. This is made possible

by adopting a standard range of logic

levels (ie, voltage levels used to repre-

sent the logic 1 and logic 0 states) so

that the output of one logic circuit is

compatible with the input of another.

As an example, let’s assume thatwe require a logic circuit that will

produce a logic 1 output whenever

two, or more, of its three inputs

are at logic 1. This circuit (shown

in Fig.6.11) is often referred to as a

majority vote circuit, and its truth

table is shown in Fig.6.12.

Note that the outputs of the three

two-input AND gates are fed to the

three inputs of the OR gate, and

that the output of the OR gate will

become logic 1 whenever any one

or more of the two-input AND gatesdetects a condition in which two

of the inputs are simultaneously

at logic 1.

As a further example, consider

how we might combine several

of the basic logic gates (AND, OR

and NOT) in order to realise the

exclusive-OR function. In order

to solve this problem, consider

the Boolean expression for the

exclusive-OR function that we

met earlier:

9!p""p!

/A and /B can be obtained by

simply inverting A and B respec-

TIVELY4HEN!p"AND"p!CAN

be obtained using two two-input

AND gates. Finally, these two can

be applied to a two-input OR gate

in order to obtain the required

LOGICFUNCTION!p""p!

The complete solution is shown in

Fig.6.13.

Fig.6.13. An exclusive-OR gate produced from AND, OR and NOT gates




Teach-In 2011

Bistables

Bistable circuits provide us with

a means of remembering a transient

logic condition. For example, the

logic that controls a lift must re-

member that the lift has been called

in response to a push-button that

only requires momentary operation.

As its name suggests, the output

of a bistable (or ÝJQÝPQ) circuit has

two stables states (logic 0 or logic

1). Once set , the output of a bist-

able will remain at logic 1 or logic

FORANINDEÚNITEPERIODORUNTILthe bistable is reset . A bistable thus

forms a simple form of memory, re-

maining in its latched state (either

set or reset) until a signal is applied

to it to change its state (or until the

supply is disconnected).

The simplest form of bistable is

the R-S bistable. This device has two

inputs, SET and RESET, and comple-

mentary outputs, Q and Q. A logic 1

applied to the SET input will cause

the Q output to become (or remain at)

logic 1, while a logic 1 applied to theRESET input will cause the Q output

Two simple forms of R-S bistable

based on cross-coupled logic gates are

shown in Fig.6.14. Fig.6.14(a) is based

on two cross-coupled two-input NAND

gates, while Fig.6.14(b) is based on two

cross-coupled two-input NOR gates.

D-type bistable

Unfortunately, the simple cross-cou-

pled logic gate bistable has a number

of serious shortcomings (consider what

would happen if a logic 1 was simulta-

neously present on both the SET and

RESET inputs!) and practical forms of

bistable make use of much improved

purpose-designed logic circuits, such

as D-type and J-K bistables.

The D-type bistable has two inputs:

D (standing variously for data or de

lay ) and CLOCK (CLK). The data input

(logic 0 or logic 1) is clocked into the

bistable such that the output state only

changes when the clock changes state.

Operation is thus said to be synchro-

nous. Additional subsidiary inputs

(which are invariably active low) are

provided, which can be used to di-rectly set or reset the bistable. These

are usually called PRESET (PR) and

CLEAR (CLR). D-type bistables are

used both as latches (a simple form

of memory) and as binary dividers.

The simple circuit arrangement in

Fig.6.15, together with the timing

diagram shown in Fig. 6.16 illustrate

the operation of D-type bistables.

to become (or remain at) logic 0. In

either case, the bistable will remain

in its SET or RESET state until an

input is applied in such a sense as

to change the state. Note also that

the Q and Q outputs

always have oppo-

site logical states.

Thus, when the Q

output is at logic 1

the Q output will be

at logic 0, and WJDF

versa.

'JH%UZQFCJTUBCMF

'JH5JNJOHEJBHSBNGPSUIF%UZQFCJTUBCMF

'JH 4JNQMF 34 CJTUBCMFT BCBTFEPO/"/%HBUFTBOECCBTFEPO/03HBUFT

'JH+,CJTUBCMF




Teach-In 2011

J-K bistables

J-K bistables (see Fig.6.17) have

two clocked inputs (J and K), two

direct inputs (PRESET and CLEAR),

a CLOCK (CK) input, and outputs (Q

and Q). As with R-S bistables, the

two outputs are complementary (ie,

when one is 0 the other is 1, and vice

versa). Similarly, the PRESET and

CLEAR inputs are invariably both

active low (ie, a 0 on the PRESET

input will set the Q output to 1,

whereas a 0 on the CLEAR input

will set the Q output to 0). Fig.6.18 summarises theinput and corresponding output states of a J-K bistable

for various input states. J-K bistables are the most so-

PHISTICATEDANDÛEXIBLEOFTHEBISTABLETYPESANDTHEY

CANBECONÚGUREDINVARIOUSWAYSINCLUDINGBINARY

dividers, shift registers, and latches.

The circuit arrangement of a four-stage binary coun-

ter, based on J-K bistables, is shown in Fig.6.19. The

timing diagram for this circuit is shown in Fig.6.20.

Each stage successively divides the clock input signal by a factor of two. Note that a logic 1 input is transferred

to the respective Q-output on the falling edge of the

clock pulse, and all J and K inputs must be taken to

logic 1 to enable binary counting.

Practical logic circuits

You should now have a basic grasp of the theory of logic

circuits, but what we haven’t done yet is give you an idea

of what these devices look like and how they appear in

practical logic circuits. So, let’s end this month’s Learn

BYSHOWINGYOUTWOEXAMPLESOFMODERNLOGICCIRCUITS

4HEÚRSTOFTHESEISADUAL$TYPEBISTABLEWHILETHE

SECONDISA&QUADTWOINPUT.!.$GATE

Fig.6.19. Circuit for a four-stage binary counter using J-K bistables

Fig.6.20. Timing diagram for the four-stage binary counter of Fig.6.19

Fig.6.18. J-K bistable operation

(ie, Q is reset

(ie, Q is reset

(ie, Q is reset

(ie, Q is reset

whatever state it was before, while




Teach-In 2011

The 4013 dual D-type bistable

is supplied in various packages,

including the dual-in-line (DIL)

package shown in Fig.6.21. This de-

vice uses standard complementary

metal oxide semiconductor (CMOS)

technology, and its pin connections

are shown in Fig.6.22. Note that pin

14 and pin 7 supply power to both

of the D-type bistables.

The 74F08 quad two-input

NAND gate is also available in

several different packages. We

have shown the small integrated

circuit (SOIC) package in Fig.6.23.

This package is ideal for surface

mounting rather than through-hole

mounting used with the DIL pack-

age that we met before. The 74F08

contains four independent NAND

gates and uses ‘fast’ transistor-

transistor logic (TTL). The pin

connection diagram for the chip

is shown in Fig.6.24. As with the

4013, the supply connections (pin

14 and pin 7) are common to all

four of the internal logic gates.

Please note!

Some logic devices, particularly

CMOS types, are static-sensitive

and special precautions are needed

when handling and transporting

them.

Circuit WizardA Standard or Professional version


from the editorial office of EPE – seeCD-ROMs for Electronics page and


epemag.com).










Fig.6.21. A 4013 dual D-type bistablein a plastic dual-in-line (DIL) package.This chip was manufactured in 1992

Fig.6.23. A 74F08 quad two-input NAND gate in a small surface-mount

package (SOIC). This chip was manufactured in 2001

Fig.6.22. Pin connections for the 4013dual D-type bistable IC

Fig.6.24. Pin connections for the74F08 quad two-input NAND gate IC

Check – How do you think you are doing?

6.1. Identify each of the logic

symbols shown in Fig.6.25

6.2. Draw the truth table for the

logic gate arrangement shown in

Fig. 6.26.

6.3. Show how three two-input

AND gates can be connected togeth-

er to form a four-input AND gate.

Fig.6.25. See Question 1


6.4. State the Boolean logic ex-

pression for the output of each

of the gate arrangements shownin Fig.6.27 – opposite.

6.5. Devise

a logic gate

arrangement

that provides

an output

d e s c r i b e d

by the truth

table shown

in Fig.6.28.





Teach-In 2011


Build – The Circuit Wizard way

Y OU’VE learnt the theory about

logic gates, so now let’s try it

out using Circuit Wizard. Anyone

who’s experimented or prototyped

with discrete logic circuits before

will be all too familiar with hope-

lessly prodding a logic probe into

an incomprehensible ‘rat’s nest’ of

breadboard and link wires.

Fortunately, nowadays we can

do all this and more using soft-

ware packages before we commit

any copper to PCB. Circuit Wizard

really does have a few aces up its

sleeve when it comes to working

with logic.

First, you can work directly

with the logic gates themselves

and let it worry about the chip

packages (see later on), as well

as a number of dedicated in-

puts/outputs and simulation

schemes that bring the circuits to

life and visually convey what’s

really going on in the circuit. In

this instalment of Build we’ll be

trying out some logic gates to

see how they operate, as well as

experimenting with some real

life applications.

Opening the gates

Circuit Wizard includes a

large range of logic devices in

both CMOS and TTL versions

(note that the extent of the

logic devices may depend on the

Gate numbers

When you add a gate to the draw-

ing area you should notice that it

will automatically number your

gate in accordance with the cor-

responding IC required. As each

IC contains a number of gates, an

ALPHABETICALSUFÚXWILLBEADDEDTO

the chip reference (eg, IC1a) to show

which has been allocated. Once the

total number of gates has exceeded

that of the IC, Circuit Wizard willautomatically include a new chip,

and so on.

You are able to change

which gate has been al-

located within the chip.

This can be useful when

it comes to generating the

MOSTEFÚCIENT0#"LAYOUT

However, the automatic

allocation works great for

most users. Circuit Wiz-

ard will also add powerFig.6.29. Changing logic families for a logic gate

connections ‘in the background’,so that these are accounted for in

net lists when moving on to PCB

generation.

The best way to understand the

operation of the basic gates is to

drop one on to the drawing area,

add inputs and outputs and see

how the output changes in re-

sponse to changes in the inputs.

Circuit Wizard has some really

useful input toggles and output

indicators which can be found at

the top of the ‘Logic Gates’ folder(see Fig.6.30).

Switching to the ‘Logic View’

(click on the vertical tab on the left

of the drawing area) is a particularly

useful way to analyse any logic

version of Circuit Wizard thatyou are running).

The first thing that you may

notice is that in the Gallery

(right-hand panel) you can ac-

cess standard and Schmitt varie-

ties of gates in the ‘Logic Gates’

folder, as well as each family of

chip separately in the ‘Integrated

Circuits’ folder. We can only as-

sume that this is for the purpose

of providing quick access to the

more common gates.

By default, 4000 series ICswill be used. However, you are

able to select the family of gate

by se le ct in g the appropri ate

model in the properties context

box; see Fig. 6.29 (double-click

the component to

access this). This

default behaviour

can also be altered

in the software’s

setting if required.Fig.6.30. A simple arrangement to test an AND gate




Teach-In 2011


Logic circuits usually contain a number of

different gates and can get very complicated. De-

SIGNERSCANSPENDALONGTIMETRYINGTOÚGUREOUT

the simplest arrangement of gates to perform thelogical function that’s required.

However, with the widespread use and avail-

ability of microprocessors, complex combinational

logic circuits are becoming a thing of the past. Have

a go at entering and testing the logic circuit shown

in Fig.6.32, and produce a truth table. Could the

function of this circuit have been reproduced with

fewer gates?

If you think about actually producing the cir-

cuit above you would need three logic ICs and

two of the ICs would only have one gate used in

THEM/BVIOUSLYTHISISAPRETTYINEFÚCIENTWAY

to do things. Fortunately, logic designers cameup with a great idea; what if we could use just

a single gate and wire them in such a way to act

like the other gates? In this way, you would only

need to buy one type of IC.

It turns out that the NAND gate is the ideal

candidate for this as you can produce all of the

other gates using them – we call them ‘NAND

equivalents’. Fig.6.33 shows the NAND equiva-

lent for an AND gate. Enter the circuit in to

Circuit Wizard and verify that the combination

acts just like an AND gate. In this case, the first

gate is a straight forward NAND and the second

circuit. This view uses both colour coding as well

as 1s and 0s at the inputs/outputs of each pin to

show the logic state. This can really help you see

what’s going on around the circuit.

One important thing to note about the logic

indicators and the ‘Logic Level’ view is that the

logic high state is indicated by red, and the logic

low by green. This might seem a little counter-

intuitive to some people – the author included!

Give it a try

Experiment with some of the basic gates; AND,

OR, NAND, XOR and NOT. Draw up a truth tablefor each gate and check that this matches what

you’ve seen in Learn.

Alternatively, we’ve developed an interactive

logic gate worksheet (see Fig.6.31). This can be

downloaded from the Teach-In 2011 website;

www.tooley.co.uk/teach-in – follow the link to

Circuit Wizard downloads. Print out the worksheet

and complete the truth tables by simulating them

on screen.

gate acts as a NOT gate. Hence, the result is ‘NOT

NAND’ or AND.

7HYNOTSEEIFYOUCANÚGUREOUTTHE.!.$EQUIVALENTS

for the other gates. You can also download our NAND

Gate Equivalent simulator (Fig.6.34) from the Teach-In

website, which includes a number of other equivalents

for you to explore.

Fig.6.31. A view of our logic gate worksheet, which can bedownloaded from: www.tooley.co.uk/teach-in

Fig.6.32. A combinational logic circuit

Fig.6.33. An AND gate made using NAND gates (in other words, a ‘NAND equivalent’ of an AND gate




Teach-In 2011

Fig.6.33. Download our NAND gate

equivalent simulator from: www.

tooley.co.uk/teach-in

Intruder alarm

Now we’ll look at a real-life ap-

plication of a simple logic circuit.

Fig.6.35 shows an intruder alarm

circuit. When any one of the links

(simulated by push-to-break but-tons) is broken, the alarm is acti-

vated. Enter the circuit and try it

out for yourself! Advanced readers

might like to see if they can adapt

the circuit to latch the alarm on

once a link has been broken.

Ripple counter

Another area of logic design is

sometimes described as sequen-

tial logic. Often this involves

counting and/or timing. Fig.6.36

shows what is commonly knownas a ripple counter or cascade

counter. It produces a binary

count using a series of J-K bista-

bles or ‘ flip-f lops’ .

Enter the circuit and look

closely at its operation. The ‘Logic

View’ is excellent for this kind of

circuit, and you should be able to

see how the logic high ‘ripples’

along the flip-flops in order to

generate a four-bit binary count-

ing sequence.

Fig.6.35. Intruder alarm circuit. When one of the ‘links’ is broken, the alarm sounds

Fig.6.36. Four-bit ripple counter using J-K bistables

The world’s fastest microprocessor resulted from an investment of $1.5 billion,and operates at a speed of 5.2GHz (courtesy of International Business Machines Corp.)




Teach-In 2011

Decade counter

A binary count could be really

useful for lots of applications.

Apart from possibly a few com-

puter nerds, not all that many

people can easily read a binary

number!

Therefore, if we need to dis-

play a number to a consumer we

need to convert this to a display-

able number. This can be easily

achieved with a 74LS47 seven-

segment display decoder, a driver

chip and a seven-segment LED

display (common anode).

The chip decodes the four-

bit lines of the binary count

and outputs a number on the

seven-segment LED display by

turning on/off the appropriate


Fig.6.37. A decade (ie, 0-9) counter circuit using J-K bistables and a seven-segment display

lines. Amend your ripple counter

circuit as shown in Fig.6.37. The

NAND gate is used to reset the

flip-flops when the count reaches

9, the highest single-digit number

that can be displayed.

A block schematic diagram of a

logic system used in a large aircraft

is shown in Fig.6.38.

InvestigateThe system is designed to alert

THEÛIGHTCREWBYGENERATINGVIS-

ible and audible warnings that one

or more of the aircraft’s undercar-

riage doors remain open when the

AIRCRAFTISINNORMALÛIGHT

4HEÚVEDOOR SWITCHES PROVIDE

logic 1 signals when the respec-

tive door is open and logic 0 when

closed. All of the warning indicators

are ‘active low’ and require a logic

0 to produce a visible or audible

output.

Study the circuit carefully and

then see if you can answer each of the following questions:

1. What logic level appears at

points X, Y and Z with all of the

doors closed?


points X, Y and Z with the left

wing door open and all other doors

closed?


points X, Y and Z with the nose door

open and all other doors closed?

4. When any one or more of the

doors opens, the audible warningFig.6.38. A block schematic of a logic system used in an aircraft



44 Everyday Practical Electronics, May 2011

Teach-In 2011


Part 7: ier circuits

ur each-n series is designed to provide you with a broad-based introduction to electronics. We have

attepted to provide coverage of three of the ost iportant electronics units that are currently studied in

any schools and colleges in the K. hese include dexcel B Level 2 awards as well as electronics

units of the new iploa in ngineering (also at Level 2). he series will also provide the ore experiencedREADERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª



you an opportunity to build and test siple electronic circuits. nvestigate will provide you with a challenge


TEACH-IN 2011


TO ELECTRONICS

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extend this further with a detaied

ook at soe practica tier and

puse generator circuits. inay, in

Amaze we ook at ways in which

o begin to understand how tier

circuits operate, it is worth spend-

ing a few oents studying the

interna circuitry of the tier,

see ig..2. ssentiay, the chip

coprises two operationa api-

ÚERSUSEDASCOMPARATORSTOGETHER

with an - bistabe. n addition,

ANINVERTINGTRANSISTORAMPLIÚERIS

incorporated so that an appreciabe

current can be deivered to a oad.

Learnhe 555 tier

he tier is, without doubt,

one of the ost versatie integratedcircuit chips ever produced. ot

ony is it a neat ixture of anaogue

and digita circuitry, but its appica-

tions are virtuay iitess in the

word of digita puse generation.

he chip aso akes an exceent

case study for beginners because it

brings together a nuber of ipor-

tant concepts and techniques. he

standard tier is suppied in

a standard 8-pin dua-in-ine ()

package with the pinout shown in

ig..1.

ig..1. iout coectios for astadard tier



Everyday Practical Electronics, May 2011 45

Teach-In 2011

inking and sourcing

nike the standard ogic devices

that we et ast onth, the tier

can both sik and source current. t’s

worth taking a itte tie to expain

what we ean by these two ters:

s hen sourcing current, the ’s

output (pin 3) is in the high state,

ANDCURRENTWILLTHENÛOWout of the

output pin into the oad and down

to , as shown in ig..3(a).

s hen sinking current, the ’s

output (pin 3) is in the low state, in

WHICH CASE CURRENTWILL ÛOW FROM

the positive suppy (+cc) through

the oad and ito the output (pin 3),

as shown in ig..3(b).

eturning to ig..2,

the singe transistor

switch, 1, is provided

as a eans of rapidy dis-

charging an externa ti-

ing capacitor. ecause the

series chain of resistors,

coprising 1, 2 and 3,

a have identica vaues,the suppy votage ()

is divided equay across

the three resistors.

he votage at the non-

inverting input of 1 is

one-third of the suppy

votage (), whie that

at the inverting input of

2 is two-thirds of the

suppy votage ( ).

hus, if is 9, 3

wi appear across each

resistor and the uppercoparator wi have 6

appied to its inverting

input, whie the ower

coparator wi have 3

at its non-inverting input.

he 555 faily

he standard tier

is housed in an 8-pin

package and operates fro

suppy rai votages of be-

tween . and 1. his,

of course, encopasses

Feature FunctionA A potential divider comprising R1, R2 and R3 connected in series. Since all threeresistors have the same values the input voltage (VCC) will be divided into thirds, i.e.

one third of VCC will appear at the junction of R2 and R3 while two thirds of VCC will

appear at the junction of R1 and R2.

B Two operational amplifiers connected as comparators. The operational amplifiers are

used to examine the voltages at the threshold and trigger inputs and compare these withthe fixed voltages from the potential divider (two thirds and one third of VCC

respectively).

C An R-S bistable stage. This stage can be either set or reset depending upon the output

from the comparator stage. An external reset input is also provided.

D An open-collector transistor switch. This stage is used to discharge an external capacitor

by effectively shorting it out whenever the base of the transistor is driven positive.

E An inverting power amplifier. This stage is capable of sourcing and sinking enough

current (well over 100mA in the case of a standard 555 device) to drive a small relay or

another low-resistance load connected to the output.

Table 7.1: Main features of the 555 timer IC

ig..2. teral scheatic arrageet of the stadard tier

ig..3. Loads coected to the output of a tier: (a) curret sourced by thetier whe the output is high, (b) curret suk by the tier whe the output is low




Teach-In 2011

goes ow. he device then reains

in the inactive state unti another

faing trigger puse is received.

utput wavefor

he output wavefor produced by

the circuit of ig.. is shown in

ig... he wavefor has the fo-

owing properties:

ie for which output is high:

the nora range for devices (±%) and thus the device is ideay

suited for use with circuitry.

he foowing versions of the stand-

ard tier are coony avaiabe:

Low power 555

he ow power tier is a

version that is both pin and func-

tion copatibe with its standard

counterpart. y virtue of its

technoogy, the device operates over

a soewhat wider range of suppy

votages (2 to 18) and consues

inia operating current (12 Ptypica for an 18 suppy).

ote that, by virtue of the ow-power

technoogy epoyed, the

device does not have the sae output

current drive as that possessed by its

standard counterparts. owever, it can

suppy up to two standard oads.

556 dual timer

he 6 is a dua version of the

standard tier housed in a 1-

pin package. he two devices

ay be used entirey independ-enty and share the sae eectrica

characteristics as the standard .

Low power 556

he ow power 6 is a dua version

of the ow power tier

contained in a 1-pin package.

he two devices ay again be used

entirey independenty and share the

sae eectrica characteristics as the

ow power .

Please note!ow power tiers use tech-

noogy and shoud be handed using

anti-static precautions.

Monostable pulse generator

ig. . shows a standard tier

operating as a monostable puse

generator. he ter ‘onostabe’

refers to the fact that the output has

ony one stabe state, and it wi

aways return to this state after a

period of tie spent in the opposite

state. he onostabe tiing period(ie, the tie for which the output is

high) is initiated by a faing edge

trigger puse appied to the trigger

input (pin 2).

hen this faing edge trigger

puse is received and fas beow

one third of the suppy votage,

the output of 2 goes high and the

bistabe wi be paced in the set

state. he inverted Q output (ie, Q)

of the bistabe then goes ow, the

interna transistor 1 is paced in

the off (non-conducting) state andthe output votage (pin 3) goes high.

he capacitor, , then charges

through the series resistor, , unti

the votage at the threshod input

reaches two thirds of the suppy

votage (cc). t this point, the

output of the upper coparator

changes state and the bistabe is

reset . he inverted Q output (ie, Q)

then goes high, 1 is driven into

CONDUCTION AND THE ÚNAL OUTPUT

'JH"UJNFSJONPOPTUBCMFDPOÜHVSBUJPO ig... Wavefors for oostable operatio

ton = 1.1 C R

ecoended trigger puse width:

ontr

tt <

4

here ton and ttr are in seconds,

is in farads and is in ohs.

he period of the onostabe

output can be changed very easiy

by sipy atering the vaues of the

tiing resistor, , and/or tiing

capacitor, . oubing the vaue of

wi doube the tiing period.

iiary, doubing the vaue of

wi doube the tiing period.

Please note!

he usua range of vaues for ca-

pacitance and resistance in a on-

ostabe tier are p to P

and 1k: to 3.3: respectivey.

utside this range operation is ess

predictabe.

Example 1

ow et’s work through a sipe

design exape. or this we sha




Teach-In 2011

assue that we need a circuit that

wi produce a 1s puse when a

negative-going trigger puse is ap-

pied to it. sing the circuit shown

in ig. ., the vaue of onostabe

tiing period can be cacuated

fro the forua:

ro which: in order to avoid aking the vaue

of too high.

vaue of 1 P shoud be ap-

propriate and shoud aso be easy

to obtain. aking the subject of

the forua, and substituting for

= 1 P gives:

ton = 1.1 C R

e need to choose an appropriate

vaue for that is in the range stated

earier. ince we require a fairy

odest tie period, we wi choose

a id-range vaue for .his shoud hep to ensure that

the vaue of is neither too sa

nor too arge. vaue of 1n

shoud be appropriate and shoud

aso be easy to obtain. aking the

subject of the forua and substitut-

ing for = 1n gives:

6 610R = ×10 = 0.091×10

110:

or 9.1 k :

ternativey, the graph shown in

ig..6 can be used.

Example 2

ext, we sha design a tier circuit

that wi produce a + output for a

period of 6s when a ‘start’ button

is operated. he tie period is to

be aborted when a ‘stop’ button is

operated. or the purposes of this

exape we sha assue that the

‘start’ and ‘stop’ buttons both have

noray-open () actions. he

vaue of onostabe tiing period

can be cacuated fro the forua:

ton = 1.1 C R

e need to choose an appropri-

ate vaue for that is in the range

stated earier. ince we require

a fairy ong tie period we wi

choose a reativey arge vaue of

ont 60s 60R = = =

1.1C 1.1×100ȝF

-6

60=

110×10

ro which:

n practice 6k: (the nearest

preferred vaue) woud be adequate.

he ‘start’ button needs to be con-

nected between pin 2 and ground,

whie the ‘stop’ button needs to

be connected between pin and

ground. ach of the inputs requires

ig.. (above). ircuit diagra for a 60 secod tier (seeExaple 2)

ig..6. (left) raph for deteriig values of , t o ad for a operatig i oostable ode. he red lie shows how a 10s pulse will be produced whe = 100 ad = 91k :(see Exaple 1)

ont 10 msR = = =

1.1C 1.1×100 nF-3

-9

10×10=

110×10

ms

nF

k :

6 660R = ×10 = 0.545×10

110:

or 545 k :k :

1




Teach-In 2011

a ‘pu-up’ resistor to ensure that the

input is taken high when the switchis not being operated.

he precise vaue of the ‘pu-up’

resistor is uniportant, and a vaue

of 1k: wi be perfecty adequate

in this appication. he copete

circuit of the 6s tier is shown

in ig...

stable pulse generator

ow the standard can be con-

ÚGUREDASANastable puse genera-

tor, is shown in ig..8. n order to

understand how this circuit oper-ates, assue that the output (pin

3) is initiay high and that 1 is

in the non-conducting state. he

capacitor, , wi begin to charge

with current suppied by series

resistors, 1 and 2.

ie for which output is ow:hen the votage at the threshold

input (pin 6) exceeds two thirds of the suppy votage, the output of the

upper coparator, 1, wi change

state and the bistabe wi becoe

reset , due to the votage transition

that appears at . his, in turn, wi

ake the Q output go high, turning

1 on and saturating it at the sae

tie. ue to the inverting action of

THEBUFFER)#SEE&IGTHEÚNAL

output (pin 3) wi go ow.

he capacitor, , wi now dis-

CHARGEWITHCURRENTÛOWINGTHROUGH

2 into the coector of 1. t a

certain point, the votage appearing

at the trigger input (pin 2) wi have

faen back to one third of the sup-

py votage, at which point the ower

coparator wi change state and

the votage transition at (ig..2)

wi return the bistabe to

its origina set condition.

he inverted Q output then

goes ow, 1 switches off

(no onger conducting),

and the output (pin 3) goeshigh. hereafter, the entire

charge/discharge cyce is

REPEATEDINDEÚNITELY

he output wavefor

produced by the circuit of

ig..8 is shown in ig..9.

he wavefor has the fo-

owing properties:

ie for which output is

high:

1 2

1.44 p.r.f. =

C R +2R

ton = 0.693 C (R 1 + R 2)

eriod of output wavefor:

toff = 0.693 C R 2

use repetition frequency:

t = ton + toff = 0.693 C (R 1 + 2R 2)

'JHBTUBCMFDPOÜHVSBUJPO

ig..9. Wavefors for astable operatio

'JH (SBQI GPS EFUFSNJOJOH WBMVFT PG $ QSGBOE32 for a operatig i astable odeXIFSF3231JFGPSTRVBSFXBWFPQFSBUJPO5IFSFEMJOFTIPXTIPXB)[TRVBSFXBWFXJMMCFQSPEVDFEXIFO$O'BOE3L :TFF&YBNQMF

ark-to-space ratio:

on 1 2

off 2

t R +R =t R

uty cyce:

on 1 2

on off 1 2

t R +R = ×100%

t +t R +2R




Teach-In 2011

here t is in seconds, is in

farads, 1 and 2 are in ohs.

hen 1 = 2, the duty cyce of the

astabe output fro the tier can

be found by etting = 1 = 2. n

this condition:

be a probe if we need to produce

a precise square wave in which ton

= toff .

owever, by aking 2 very

uch arger than 1, the tier can

be ade to produce a reasonaby

syetrica square wave output.

(ote, that the iniu reco-

ended vaue for 2 is 1k: – see

Please note!).

f 2 >> 1, the expressions for p.r.f.

and duty cyce sipify to:

the forua, and substituting for

= 1 P gives:

on 1 2

off 2

t R + R R+ R 2= = = = 2

t R R 1

n this case, the duty cyce wi be

given by:

on 1 2

on off 1 2

t R + R = ×100% = ×100%t + t R + 2R R + 2R

R + R = ×100%

R + 2R

hus:

on

on off

t 2R 2= ×100%

t +t 3R 3

2= ×100% = 67%

3

he p.r.f. of the astabe out-put can be changed very easiy by

sipy atering the vaues of 1,

2, and . he required vaues of

, 1 and 2 for any required p.r.f.

and duty cyce can be deterined

fro the foruae shown earier.


ig..1 can be used when 1 and

2 are equa in vaue (corresponding

to a 6% duty cyce).

Please note!

he usua range of vaues for

capacitance and resistance in anastabe tier are 1n to P

for , and 1k: to 1: for 1 and

2. s for the onostabe circuit,

operation is ess predictabe out-

side this range.

quare wave generators

ecause the high tie (ton) is aways

greater than the ow tie (toff ), the

ark-to-space ratio produced by a

tier can never be ade equa

to (or ess than) unity. his coud

2

0.72 p.r.f. =

CR

on 2

on off 2

t R 100%

t + t 2R 2 u u

1100% 50%

2 u

Example 3

et’s design a puse generator that

wi produce a p.r.f. of 1z with a

6% duty cyce (ie, the output wi

be high for one third of the tieand ow for two thirds of the tie).

sing the circuit that we et in

ig..8, the vaue of p.r.f. can be

cacuated fro:

1 2

1.44 p.r.f. =

C R +2R

3INCE THE SPECIÚEDDUTY CYCLE IS

6%, we can ake 1 equa to 2.

ence, if = 1 = 2 we obtain the

foowing reationship:

1.44 1.44 0.48

p.r.f. = = =C R+2R 3CR CR

e need to choose an appropriate

vaue for that is in the range stated

earier. ince we require a fairy

ow vaue of p.r.f., we wi choose

a vaue for of 1 P. his shoud

hep to ensure that the vaue of

is neither too sa nor too arge.

vaue of 1 P shoud aso be easy

to obtain. aking the subject of

0.48R = = =

p.r.f.×C

-6

0.48=

p.r.f.×1×10

ence:

33480×10

R = = 4.8×10 = 4.8 k 100

k ȍ

Example 4

ow et’s design a z square

wave generator using a tier.

sing the circuit shown in

ig..11, when 2 >> 1, the vaue

of p.r.f. can be cacuated fro:

2

0.72 p.r.f. =

CR

e sha use the iniu reco-

ended vaue for 1 (ie, 1k:) and

ensure that the vaue of 2 that wecacuate fro the forua is at east

ten ties arger, in order to satisfy

the criteria that 2 shoud be very

uch arger than 1.

hen seecting the vaue for ,

we need to choose a vaue that

wi keep the vaue of 2 reativey

ig..11. ircuit for a 0z squarewave gerator (see Exaple 4)

104 = 48k :




Teach-In 2011

arge. vaue of 1n shoud be

about right, and shoud aso be easy

to ocate. aking 2 the subject of

the forua and substituting for

= 1n gives:

2 -9

0.72 0.72R = = =

p.r.f.×C 50×100×10

-6

0.72=

5×10

ence:

6

20.72 × 10R =

5


ig..1 can be used.

he vaue of 2 is ore than 1

ties arger than the vaue that we

are using for 1. s a consequence,

the tier shoud produce a good

square wave output. he copete

circuit of our z square wave

generator is shown in ig..11.

heck – ow do you think you are doing?

7.1. xpain the difference be-

tween onostabe and astabe

tier operation.

7.2. ketch the circuit of a on-

ostabe tier and identify the

coponents that deterine the

tie for which the output is high.

7.3. ketch the circuit of an asta-

be puse generator and identify

the coponents that deterine

the tie for which (a) the output

is high, and (b) the output is ow.

7.4. esign a tier circuit that

wi produce a 6 2s puse

when a 6 negative-going trigger

puse is appied to it.

7.5. esign a tier circuit that

wi produce a 6% duty cyce

output at 2z.

7.6. tier is rated for a

axiu output current of

12. hat is the iniu

vaue of oad resistance that can

be used if the device is to beoperated fro a 6 suppy?

For more information, links andother resources please check out our Teach-In website at:


Kitchen tier

OÚRSTPRACTICALCIRCUITUSESTHETIMER

CONÚGURED AS AMONOSTABLETO OPERATE ASA

kitchen tier, as shown in ig..12. hen 1 is

cosed the buzzer wi sound unti 2 is pressed

to start the tier. he two probes hep us to see

the charge buiding in 1 and the status of the

output. sape trace is shown in ig..13. his

is particuary usefu for testing ong deays where

the circuit ay see to being inactive.

Build – he ircuit Wizard way

ig..13. aple trace for the kitche tier circuit

'JH,JUDIFOUJNFSVTJOHBJOBNPOPTUBCMFDPOÜHVSBUJPO

ig..14. harge buildig o1 i ‘oltage Levels’ view

iiary, in ‘otage eves’

or ‘urrent ow’ we are abe to

visuaise the charge buiding on

the capacitor as a series of ‘+’

and ‘-’ appear on the pates (see

ig..1).

6= 0.144×10 = 144k ȍ




Teach-In 2011

he aount of eapsed tie before

the buzzer activates can be atered by changing the vaue of pot 1.

xperient with running the tier

for various settings of 1 to ascer-

tain the iniu/axiu ties,

THENCONÚRMTHISUSINGTHEAPPRO-

priate foruae that was introduced

in ‘earn’ (you ay have to be very

patient for the axiu deay).

soft boied egg is cooked for four

inutes (2 seconds) – cacuate

the vaue required for 1, then set

this on your circuit and check outyour theory in practice.

,%$ªmASHER

n our second circuit (see ig..1),

we utiise the in an astabe

CONÚGURATIONTOGENERATEALTERNATE

ÛASHINGLIGHTS4YPICALEXAMPLEAP-

pications ight incude chidren’s

toys, signs, aar systes, and eve

crossings. arying the vaue of 1

'JH"BTUBCMFBMUFSOBUF-&%ÝBTIFSDJSDVJUTIPXOJO$VSSFOU7JFX

'JH5SBDFGPSBMUFSOBUF-&%ÝBTIFSDJSDVJU

'JH"TJNQMFCJTUBCMFmPOPGGnDJSDVJU

wi ater the frequencyOFTHEÛASHING

ircuit izard’s ‘ur-

rent iew’ coes in to

its own here for visua-

ising the continuousy

changing state of the

circuit, as shown in

ig..16. part fro

ooking ike a s disco,

the coours ceary show

how current is sinking

and sourcing though the

output (pin 3) as each of

the s is it. ou can

aso onitor how the

capacitor charges unti

the threshod votage

is reached, and is then dischargedthrough pin .

!SWITHTHEÚRSTCIRCUITTHEPROBES

and trace (ig..16) aso hep us to

understand the inputs and outputs.

he bue probe/ine showing the

votage to pin 2 and pin 6, and the

red ine showing the output (pin 3).

/N/FFªCIRCUIT

s we as using the as a tier

in onostabe ode, it can aso

be used as a bistabe. neat ap-pication of this is a sipe ‘on-off’

circuit, where 1 is pressed to

turn on or ‘set’ the output and 2

is pressed to ‘reset’ or turn off the

output (see ig..1).

further appication of this ight

be a signaing circuit, where 1

is pressed to ‘set green’ and 2

is pressed to ‘set red’, as shown in

ig..18.

$ECADEªCOUNTERn art 6 (-PHJD $JSDVJUT), we

constructed a decade (ie, to 9)




Teach-In 2011

o use both tiers contained

within the 6 in ircuit izard,

you need to drag two separate in-

stances of the 6 on to the circuit

PAGE4HEÚRSTTIMERWILLBESUFÚXED

‘a’ and the second ‘b’ (eg, 1a and

1b). s both are contained within

ONEPHYSICALPACKAGETHISWOULDBE

REÛECTEDWHENCONVERTINGTOA0#"

FOREXAMPLE

5NLIKE THE SYMBOL THAT HAS

NUMBEREDPINS#IRCUIT7IZARDLA-

BELSTHEPINSOFTHEVERBOSELY

FOREXAMPLETHETHRESHOLDINPUTISLABELLEDl4m!SWITHANYINTEGRAT-

EDCIRCUITBYHOVERINGOVERTHEPIN

YOUAREABLETOSEETHEPHYSICALPIN

LOCATIONINTHETOOLTIPSEE&IG

onstruct the circuit shown in

&IGANDOBSERVEITSOPERATION

"OTHTIMERSARECONÚGUREDINASTA-

BLEMODE4HEÚRSTTIMER#AHAS

A FREUENCY OF ABOUT Z 4HE

output fro this tier is then used

TOSUPPLYTHESECONDTIMER#B

WHICHHASAFREUENCYOFABOUTZuring the period when the

output of tier one is high, the

SECONDTIMERWILLBEACTIVATEDAND

OSCILLATEFOURTIMESHENCEGIVING

FOURÛASHES#ONVERSELYWHENTHE

OUTPUTOFTHEÚRSTTIMERISLOWTHE

second tier is not powered and

SOTHEOUTPUT$REMAINSUNLIT

4RYEXPERIMENTINGWITHTHECIRCUIT

perhaps changing the sequence to

GIVEONLYTWOÛASHESBYCHANGINGTHE RELATIVE FREUENCIES OF EACH

tier.

OTETHATDURINGTHEÚRSTlHIGHmOF

EACHCYCLEBOTHFOR#AAND#B

THEDURATIONOFENERGISEDOUTPUTWILL

BESLIGHTLYLONGER4HISISBECAUSE#

AND#STARTTOCHARGEFROMONTHEINITIALCHARGERATHERTHANRDOFTHE

SUPPLYVOLTAGEONSUBSEUENTCHARGES

4HISCANBESEENCLEARLYONTHETRACE

BELOWWHERETHEREDLINEINDICATES

the output of tier one (1a) and the

BLUELINETIMERTWO#B4HISHAS

the effect that on the iitial sequence

oly THE$WILLÛASHSEVENTIMES

rather than four an you design a

CIRCUITUSINGYOURKNOWLEDGEFROM

PREVIOUSPARTSOFeach to producethe sae sequence, but without the

sae issues?

'JH"ÝBTIFSTFRVFODFDJSDVJU

'JH"ÝBTIFSTFRVFODFDJSDVJUUSBDF


of Circuit Wizard can be purchasedfrom the editorial office of EPE – see



epemag.com).













Teach-In 2011

he copete circuit diagra of

a variabe puse generator is shownin ig..23. ook at this circuit care-

fuy and then answer the foowing

questions:

1. dentify the coponent or co-

ponents that:

(a) deterine the puse repeti-

tion frequency

(b) provide variabe adjustent

of the puse width

(c) provide variabe adjustent

of the output apitude

(d) iit the range of variabe

adjustent of puse width

(e) protect 2 against a short-

circuit connected at the

output

(f) reove any unwanted signas

appearing on the suppy rai

(g) for the trigger puse re-

quired by the onostabe

stage.

2. ketch wavefors to a coon

tie scae showing the signas at (a)

and (b) ‘test points’.

3. eterine the puse repetition

frequency of the output.

day. owever, with the advent of

teegraph, teephone and radio

in the 2th century, tie signas

coud be broadcast internationay

and ade accessibe to anyone that

needed the.

nvestigate

ig..23. ractical circuit diagra for a variable pulse geerator

. eterine the axiu and

iniu puse width of the output.

. eterine the axiu

and iniu apitude of the

output.

aze

n ast onth’s Aaze we de-

SCRIBEDSIGNIÚCANTADVANCESINTHE

speed at which digita ogic can

operate. his onth, we wi be

ooking at the way in which we ac-

curatey easure tie:

ipe audibe and visibe signas

were once used to infor peope

about the passing of tie and as a

eans of setting their own cocks.

or exape, a canon coud be

ÚREDATPRECISELYONEOmCLOCKEVERY

ig..24. 1, a cotiuous cold caesiu foutaiatoic clock i witzerlad. he clock started operatig i 2004 ad keeps tie to a accuracy of oe secod i30 illio years

ig..2. Atoic clocks are usually large ad cubersoedevices, but uch effort has bee directed i akig the sall eough to be carried aroud. his is ’srecetly developed chipscale atoic clock




Teach-In 2011

odern atoic cocks are based

on caesiu and rubidiu, and they

offer uncertainties of better than one

second in 2 iion years. ut, if that’s not good enough for you to set

your watch by, the atest generation

of quantu ogic cocks, deveoped

in 28 at the ationa nstitute of

tandards and echnoogy ()

in the , offer an uncertainty

of better than one second in over a

biion years

Next month!

n next onth’s each-n, we wi

be ooking at soe appications of

ANALOGUECIRCUITSINCLUDINGÚLTERS

and attenuators.

ince tie is the reciproca of

frequency, a tie standard can be

easiy derived fro an accurate fre-

quency standard or ‘cock’. youneed to do is count the nuber of

cyces generated by the cock and, as

ong as the frequency is accuratey

known, the nuber of cyces wi

be an accurate easure of tie. o-

day’s off-air broadcast tie signas

use osciators that are ocked to

atoic cocks.

toic clocks

4HEÚRSTATOMICCLOCKUSEDTHEVI-

brations of aonia oecues andwas invented over sixty years ago.

toic cocks use the vibrations

of atos or oecues, but because

the frequency of these osciations

is so high, it is not possibe to use

the as a direct eans of contro-

ing a cock. nstead, the cock

is controed by a highy stabe

crysta osciator whose output

is autoaticay utipied and

copared with the frequency of the atoic syste.

f two atoic cocks are copared

there is aways the possibiity of a

difference in their readings. his

‘uncertainty’ is the difference in

indicated tie if both were started

at the sae instant and ater co-

pared. or the eary atoic cocks,

this ack of certainty was estiated

to be around one second in three

thousand years.

7.1. ee pages 6 and 8

7.2. ee ig.. and associated

text

7.3. ee ig..8 and associated

text

7.4. ee ig.. with = 182k:

and =1n and operating

fro a 6 suppy

7.5. ee ig..8 with 1 = 19.2k:,2 = 19.2k: and = 1n

7.6. :.

nswers to heck

questions

By integrating the entire design process, Circuit Wizard provides you with all the tools necessary to produce

an electronics project from start to finish – even including on-screen testing of the PCB prior to construction!

CIRCUIT WIZARD – featured in

this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation

and CAD/CAM manufacture in one complete package.Two versions are available, Standard and Professional.

This is the software used in our Teach-In 2011 series.

Standard £61.25 inc. VAT Professional £91.90 inc. VAT

See Direct Book Service – pages 75-77 in this issue




* PCB Layout



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46 Everyday Practical Electronics, June 2011

Teach-In 2011


Part 8: Analogue CircuitApplications




units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experiencedREADERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª





TEACH-IN 2011


TO ELECTRONICS

frequency response can be altered

in order to modify and enhance the

SOUNDPRODUCEDBYANAMPLIÚER

We also introduce decibels (dB)

ASAMEANSOFDEÚNINGGAINANDLOSS

INANANALOGUEELECTRONICSYSTEM

Build and Investigate extend thisfurther with a detailed look at some

PRACTICALÚLTERCIRCUITS&INALLYIN

AmazeWELOOKATTHERANGEOFSIG-

NALSFOUNDINRADIOANDTELEVISION

IN LAST month’s instalment of

Teach-In 2011WEINTRODUCED

YOUTOTHEHIGHLYVERSATILE

INTEGRATEDCIRCUITTIMER7ESHOWED

you how you can quickly and easily

DESIGN CIRCUITS THATWILL PRODUCE

time delays from a few hundrednanoseconds to several hundred

SECONDSANDSQUAREWAVEPULSES

OF GIVEN FREQUENCY PERIOD AND

DUTYCYCLE

)NTHISINSTALMENTWEINTRODUCE

some practical applications of

ANALOGUECIRCUITSINCLUDINGACTIVE

ANDPASSIVEÚLTERSANDTONECONTROL

CIRCUITS )N Learn we will show

YOUHOWCIRCUITSCANBEDESIGNED

SOTHATTHEYACCEPTORREJECTSIGNALS

WITHINASPECIÚEDBANDOFFREQUEN-

CIES AND HOW THE SHAPE OF THE

produce loss or attenuation we only

need a network of passive compo-

NENTSANDIFSIGNALSATALLFREQUEN -

cies are to be attenuated by the same

AMOUNTWEONLYNEEDTOUSERESISTORS

IN OUR NETWORK 3EVERAL DIFFERENT

TYPES OF NETWORK ARE POSSIBLE IN-CLUDINGTHEBASIC4AND S-networks

SHOWNIN&IG

)N ORDER TO WORK CORRECTLY IE

provide the required amount of at-

tenuation) an attenuator needs to be

matched to the system in which it is

USED4HIS SIMPLYMEANSENSURING

THATTHEIMPEDANCEOFTHESOURCEAS

WELLASTHATOFTHELOADMATCHESTHE

characteristic impedance of the atten-

UATOR)NTHISCONDITIONWESAYTHAT

an attenuator is correctly terminated

&IGILLUSTRATESTHISCONCEPT

LearnAttenuatorsAttenuators provide us with a means

OF REDUCING THE LEVEL OF A SIGNAL

PRESENTINANANALOGUECIRCUIT4HEY

PROVIDETHEOPPOSITEOFGAINANDWE

refer to it as attenuation)NORDERTO



Everyday Practical Electronics, June 2011 47

Teach-In 2011

Before we take a look at the opera-

tion of two simple forms of atten-

uator, it is worth pointing out thatthe impedances used in attenuators

are always pure resistances. The

reason for this is that an attenuator

must provide the same attenuation

at all frequencies and the inclusion

of reactive components (inductors

and/or capacitors) would produce

a non-linear attenuation/frequency

characteristic.

Balanced/unbalancedThe simple T and S-networks that

we’ve just met can exist in two basicforms, balanced and unbalanced .

In the former case, none of the net-

work’s input and output terminals

are connected directly to common

or ground. The unbalanced and

balanced forms of the basic T and

S-networks are shown for compari-

son in Fig.8.3.

The networks shown in Fig.8.3 all

have two ports. One port (ie, pair of

terminals) is connected to the input,

while the other is connected to the

output. For convenience, many two-port networks are made symmetri-

cal and they perform exactly the

same function and have the same

characteristics, regardless of which

way round they are connected.

Please note!It is conventional to express the val-

ues of the resistances present in an

attenuator in terms of the effective

series or parallel resistance. Thus,

for example, the two series resis-

tors in an unbalanced T-network

on whether they are based on net-

works of passive components (ie,

resistors, capacitors and inductors)

or active components (ie, transistors

ANDOPERATIONALAMPLIÚERSWORKING

together with resistors, capacitors

and/or inductors.

The symbols used to represent

THESEFOURTYPESOFÚLTERINBLOCKSCHE -matic diagrams are shown in Fig.8.4.

,OWPASSÚLTERS,OWPASS ÚLTERS EXHIBIT VERY LOW

attenuation of signals below their

SPECIÚEDcut-off frequency . Beyond

the cut-off frequency, they exhibit

increasing amounts of attenuation,


A simple C-R LOWPASSÚLTER IS

shown in Fig.8.6. The cut-off fre-

QUENCYFOR THEÚLTEROCCURSWHEN

the output voltage has fallen to

attenuator are both

labelled R1/2 where

R1 is the effectiveseries resistance.

Similarly, the

two parallel re-

sistors present in

an unbalanced

S-network are la-

belled 2R2 where

R2 is the effective

resistance of the

two components

when connected in

parallel. We will be

adopting a similarconvention when

we label the cir-

CUITSUSEDFORÚLTERS

FiltersFilters provide us with a means of

passing or rejecting signals within

ASPECIÚEDFREQUENCYRANGE&ILTERS

are used in a variety of applications,

INCLUDING AMPLIÚERS RADIO TRANS-

mitters and receivers. They also

provide us with a means of reducing

noise and unwanted signals thatmight otherwise be passed along

power lines.

Filters are usually described ac-

cording to the range of frequencies

that they will accept or reject. The

following types are possible:

p Low-pass

p High-pass

p Band-pass

p Band-stop.

Filters can also be categorised as

either passive or active, depending

Fig.8.1. Basic T and S-network attenuators Fig.8.2. A matched network

Fig.8.3. Balanced and unbalanced forms of the T and S-networks




Teach-In 2011

0.707 of the input value. This occurswhen the reactance of the capacitor,

X C, is equal to the value of resist-

ance, R. Using this information we

can determine the value of cut-off

frequency, f , for given values of C

and R:

Since

Please note!The term ‘cut-off’ can be a bit mis-

leading because it might imply that

AÚLTERWILLPRODUCENOOUTPUTATALL

beyond a certain point. This is not

the case. The response of a practical

ÚLTERWILLSIMPLYlROLLOFFmBEYOND

the cut-off frequency and one of

the most important characteristics

OFAÚLTERISTHERATEATWHICHTHIS

roll-off occurs.

R = X Cor

1

2 R

C S

from which:

1

2 f

CRS

where f is the cut-off frequency (in

Hz), C is the capacitance (in F), and

R is the resistance (in :).

(IGHPASSÚLTERS(IGHPASS ÚLTERS EXHIBIT VERY LOW

attenuation of signals above their

SPECIÚEDCUTOFF FREQUENCY "ELOW

THECUTOFF FREQUENCY THEYEXHIBIT

increasing amounts of attenuation,


A simple C-R HIGHPASS ÚLTER IS

shown in Fig.8.8. Once again, the

CUTOFFFREQUENCYFORTHEÚLTEROCCURS

when the output voltage has fallen

to 0.707 of the input value. This

occurs when the reactance of the

capacitor, X C, is equal to the value

of resistance, R. Using this informa-

tion we can determine the value of

cut-off frequency, f , for given values

of C and R:

Since

R = X C

or1

2 R

C S

and once again:

1

2 f

CRS

where f is the cut-off frequency (in

Hz), C is the capacitance (in F), and

R is the resistance (in :).

'JH4ZNCPMTVTFEUPSFQSFTFOUÜMUFSTBMPXQBTTCIJHIQBTTDCBOE QBTTBOEECBOETUPQ

'JH'SFRVFODZSFTQPOTFGPSB

MPXQBTTÜMUFS

'JH"TJNQMF$3MPXQBTTÜMUFS

'JH'SFRVFODZSFTQPOTFGPSBIJHIQBTTÜMUFS 'JH"TJNQMF$3IJHIQBTTÜMUFS




Teach-In 2011

Example 1A simple C-RLOWPASSÚLTERHASC =

100nF and R = 10k:$ETERMINETHE

CUTOFFFREQUENCYOFTHEÚLTER

7ECANÚNDTHECUTOFFFREQUENCY

using:

OFTHEINDUCTORRECALLTHATAPRACTICAL

COILHASSOMERESISTANCEASWELLASIN-

DUCTANCE4HEBANDWIDTHISGIVENBY

EQUALTOTHEVALUEOFTHEREACTANCE

OFTHEINDUCTOR X L4HISINFORMATION

ALLOWSUSTODETERMINETHEVALUEOF

FREQUENCYATTHECENTREOFTHEPASS

BAND f 0:

1

2 f

CRS

9 4

1

6.28 100 10 10 10

u u u u

10015.9 Hz

6.28

Example 2A simple C-R LOWPASSÚLTER ISTO

HAVE A CUTOFF FREQUENCY OF K(Z

)FTHEVALUEOFCAPACITANCEUSEDIN

THEÚLTERISTOBEN&DETERMINETHE

VALUEOFRESISTANCE

2EARRANGINGTHEEQUATIONFORCUT

OFFFREQUENCYGIVES

1

2 R

fC S

:

3 96.28 1 10 47 10

u u u u6

103.39 k

295.16 :

"ANDPASSÚLTERS"ANDPASS ÚLTERS EXHIBIT VERY LOW

ATTENUATIONOFSIGNALSWITHINASPECI -

ÚEDRANGEOFFREQUENCIESKNOWNAS

THE pass-band ANDINCREASINGATTEN-

UATIONOUTSIDETHISRANGE4HISTYPE

OFÚLTERHASTWOCUTOFFFREQUENCIES

a lower cut-off frequency f 1 AND

an upper cut-off frequency f 24HE

DIFFERENCEBETWEENTHESEFREQUENCIES

f 2 – f 1ISKNOWNASTHEbandwidth

OFTHEÚLTER4HERESPONSEOFABAND

PASSÚLTERISSHOWNIN&IG

A simple L-C BANDPASS ÚLTERIS

SHOWNIN&IG4HISCIRCUITUSES

an L-C RESONANTCIRCUITANDISOFTEN

REFERREDTOASANacceptor circuit .

4HE FREQUENCY AT WHICH THE

BANDPASSÚLTERIN&IGEXHIBITS

MINIMUMATTENUATIONOCCURSWHEN

THECIRCUITISresonant IEWHENTHE

REACTANCE OF THE CAPACITOR X C IS

X C = X LTHUS

0

0

12

2 f L

f C S

S

FROMWHICH

2

0 2

1

4 f

LC S

ANDTHUS

0

1

2 f

LC S

WHERE f 0ISTHERESONANTFREQUENCY

IN(ZL ISTHEINDUCTANCEIN(

and C ISTHECAPACITANCEIN&

4HE BANDWIDTH OF THE BANDPASS

ÚLTERISDETERMINEDBYITSquality factor

ORQ-factor 4HISINTURNISLARGELY

DETERMINEDBYTHELOSSRESISTANCER

WHERE f 0ISTHERESONANTFREQUENCY

IN(ZL ISTHEINDUCTANCEIN(

and RISTHELOSSRESISTANCEOFTHE

INDUCTORIN:

"ANDSTOPÚLTERS"ANDSTOPÚLTERSEXHIBITVERYHIGHAT-

TENUATIONOFSIGNALSWITHINASPECIÚED

RANGEOFFREQUENCIESKNOWNASTHE

stop-band ANDNEGLIGIBLEATTENUATION

OUTSIDETHISRANGE/NCEAGAINTHIS

TYPEOFÚLTERHASTWOCUTOFFFREQUEN-

CIESa lower cut-off frequency f 1AND

an upper cut-off frequency f 24HE

DIFFERENCEBETWEENTHESEFREQUENCIES

f 2 – f 1ISKNOWNASTHEbandwidthOF

THEÚLTER4HERESPONSEOFABANDSTOP

ÚLTERISSHOWNIN&IG

0 0

2 1Bandwidth f f

Q

02 f L

R

S

Fig.8.9. Frequency response for a

CBOEQBTTÜMUFS

Fig.8.10. A simple L-C band-pass

ÜMUFSPSBDDFQUPS

Fig.8.11. Frequency response for aCBOETUPQÜMUFS

Fig.8.12. A simple L-C band-stop ÜMUFSPSSFKFDUPS

Hz

k :




Teach-In 2011

A simple L-C band-stop filter

is shown in Fig.8.12. This circuit

uses an L-C resonant circuit and is

referred to as a rejector circuit .

The frequency at which the band-

STOPÚLTERIN&IGEXHIBITSMAXI -

mum attenuation occurs when the

circuit is resonant, ie, when the re-

actance of the capacitor, X C, is equal

to the reactance of the inductor, X L.

This information allows us to deter-

mine the value of frequency at the

centre of the pass-band, f 0:

frequency at which minimum attenu-

ation will occur.

The frequency of minimum attenu-

ation will be given by:

X C = X L

0

0

12

2 f L

f C S

S

thus

from which

2

0 2

1

4 f

LC S

and thus

0

1

2 f

LC S

where f 0 is the resonant frequency

(in Hz), L is the inductance (in H)

and C is the capacitance (in F).

!SWITHTHEBANDPASSÚLTERTHE

BANDWIDTHOFTHEBANDPASSÚLTERIS

determined by its quality factor (or

Q-factor). This, in turn, is largely

determined by the loss resistance, R,

of the inductor (recall that a practical

coil has some resistance as well as

inductance). Once again, the band-

width is given by:

0 02 1Bandwidth f f f

Q

02 f L

R

S

where f 0 is the resonant frequency

(in Hz), L is the inductance (in H),

and R is the loss resistance of the

inductor (in :).

Example 3A simple acceptor circuit uses L =

2mH and C = 1nF. Determine the

Fig.8.13. The characteristic impedance (Z 0) of a network is determined by thevalues of resistance (or impedance) within the network – see text

0

1

2 f

LC S

3 9

1

2 2 10 1 10S

u u u

610

112.6 kHz8.88

Example 4A 15kHz rejector circuit has a Q-fac-

tor of 40. Determine the bandwidth

of the circuit.

The bandwidth can be found from:

3

015 10

Bandwidth 375 Hz40

f

Q

u

375 Hz

kHz

Hz

Termination, matching andcharacteristic impedance

&OR THE PERFORMANCE OF A ÚLTER OR

an attenuator to be predictable we

need to take into account the input

(source) and output (load ) imped-

ances. These impedances are said to

terminateTHEÚLTERqWITHOUTTAKING

them into account the performance

can be somewhat unpredictable!When a filter or attenuator is

correctly terminated it is said to

be matched. Analogue systems are

often designed so that they have a

particular input/source and output/

load impedance. In many audio

systems the impedance chosen is

600: but in radio frequency (RF)

applications impedances of 50:,

75: or 300: are common.

It is often convenient to analyse

the behaviour of a signal transmis-

sion path in terms of a number




Teach-In 2011

of identical series connected net-

works. One important feature of any

NETWORKIS THATWHEN ANINÚNITE

number of identical symmetrical

networks are connected in series,

the resistance (or impedance) seen

looking into the network will have a

DEÚNITEVALUE4HISVALUEISKNOWN

as the characteristic impedance of

the network

4AKE A LOOK A T &IG )N

&IGA AN INÚNITE NUMBER OF

identical networks are connected in

SERIES"YDEÚNITIONTHEIMPEDANCE

seen looking into this arrangement

will be equal to the characteristic

impedance, Z 0.

Now suppose that we remove the

ÚRSTNETWORKINTHECHAINASSHOWN

IN&IGB4OALLINTENTSANDPUR-

poses, we will still be looking into an

INÚNITENUMBEROFSERIESCONNECTED

NETWORKS4HUSONCEAGAINWEWILL

see an impedance equal to Z 0 when

we look into the network.

&INALLYSUPPOSETHATWEPLACEAN

impedance of Z 0

across the output

terminals of the single network that

WEREMOVEDEARLIER4HISTERMINATED

NETWORKSEE&IGCWILLBEHAVE

exactly the same way as the arrange-

MENTIN&IGA)NOTHERWORDS

by correctly terminating the network

in its characteristic impedance,

we have made one single network

section appear the same as a series

of identical networks stretching to

INÚNITY

4HECHARACTERISTICIMPEDANCEZ 0)

of a network is determined by the

values of resistance (or impedance)

within the network, as we shall see

next.

-OREªCOMPLEXªlLTERS4HESIMPLEC-R and L-C ÚLTERSTHAT

we have described in earlier sections

have far from ideal characteristics.

)NPRACTICEMORECOMPLEXCIRCUITS

are used and a selection of these

(based on matched T-section and

S-section networks) are shown in

&IG4HEDESIGNEQUATIONSFOR

these circuits are as follows:

where Z 0 is the characteristic im-

pedance (in :), f C is the cut-off fre-

quency (in Hz), L is the inductance

(in H), and C ISTHECAPACITANCEIN&

Example 5Determine the cut-off frequency and

CHARACTERISTICIMPEDANCEFORTHEÚL -

TERNETWORKSHOWNIN&IG

Fig.8.14. Improved T-section and STFDUJPOÜMUFST

0

L Z

C

'JH4FF&YBNQMFJOUFYU

Comparing the circuit shown in

&IGWITHTHATSHOWNIN&IG

SHOWSTHATTHEÚLTERISAHIGHPASS

type with L M(ANDC N&

(note that the value of C is the ef-

fective series capacitance and is

EQUIVALENTTOTHETWON&CAPACI -

tors connected in series).

Now

and

C

1

2 f

LC S

0

C2

Z L

f S

C 0

1

2C

Z S

C

1

2 f LC S

3 9

1

6.28 5 10 20 10

u u u

5101.59 kHz

6.28

33

0 9

5 10 510

20 10 20

L Z

C

u u u

u

3

0.5 10 500 u :

)NDUCTANCE:

Capacitance:

Characteristic impedance:

Cut-off frequency:

kHz




Teach-In 2011

!CTIVEªlLTERSThe simple R-C filters that we

described earlier in Fig.8.6 and

Fig.8.8 require a very low source

impedance and a very high load

impedance in order to behave in a

predictable manner (ie, to satisfy

the equation for cut-off frequency

that we met earlier). One way of

improving the performance of these

ÚLTERS IS TO TERMINATE THEM USING

AUNITYGAINOPERATIONALAMPLIÚER

buffer, as shown in Fig.8.16 and

Fig.8.17. These circuits maintain

the predicted frequency response,

but the rate at which the output

voltage falls above cut-off may be

INSUFÚCIENTFORMANYAPPLICATIONS

Fortunately, we can easily solve

this problem by exploiting the gain

available from the operational am-

PLIÚER&IGAND&IGSHOWS

popular second-order Sallen and

+EYLOWPASSANDHIGHPASSÚLTERS

4HESEÚLTERSROLLOFFATTWICETHERATE

that can be obtained with the simple

ÜSTUPSEFS ÚLTERSSHOWNIN&IG

The cut-off frequency of the second-

ORDERÚLTERSSHOWNIN&IGAND&IGISGIVENBY

and Fig.8.17. Later, in Build you

will have the opportunity to build

and test these circuits.

'JH'JSTUPSEFSBDUJWFMPXQBTTÜMUFS 'JH'JSTUPSEFSBDUJWFIJHIQBTTÜMUFS

'JH4FDPOEPSEFS4BMMFOBOE,FZBDUJWFMPXQBTT ÜMUFS

'JH4FDPOEPSEFS4BMMFOBOE,FZBDUJWFIJHIQBTT ÜMUFS

One of the most important pa-

rameters of an analogue circuit

is the amount of gain or loss

that it provides. Gain can be

expressed in various ways, but

basically it is just the ratio of

output to input expressed in

terms of either voltage, current

or power. Since gain and loss

can sometimes be quite large we

often use a logarithmic scale to

express our ratios.

This measurement is based on

decibels (dB), where one decibel

is equivalent to one tenth of a

Bel (the logarithm of the volt-

age, current or power ratio). In

case this is beginning to sound a

little complicated we have sum-

marised all of this in Table 8.1.

Table 8.1. Gain or loss expressed in decibels of voltage, current and power

Basis of measurement Gain or loss as a ratio Gain or loss expressed indecibels (dB)

Voltageout

in

V

V

out

10in

20log§ ·¨ ¸© ¹

V

V

Currentout

in

I

I

out

10in

20log§ ·¨ ¸© ¹

I

I

Power out

in

P

P

out

10in

10log§ ·¨ ¸© ¹

P

P

$ECIBELS




Teach-In 2011

Please note!4HEÚRSTORDERÚLTERSTHATWEMETIN

&IGAND&IGROLLOFF THEIR

RESPONSEATTHERATEOFD"PEROC

TAVEWHILETHESECONDORDERÚLTERS

SHOWNIN&IGAND&IGHAVEARESPONSETHATROLLSOFFATD"PER

OCTAVE.OTETHATlPEROCTAVEmSIM

PLYMEANSADOUBLINGORHALVINGOF

FREQUENCY

Example 6!N AMPLIÚER USED IN A MATCHED

SYSTEMPRODUCESANOUTPUTVOLTAGE

OF6FORANINPUTOFM67HAT

ISTHEVOLTAGEGAINOFTHEAMPLIÚER

WHENEXPRESSEDINDECIBELS

4HEVOLTAGEGAINA6CANBECAL

CULATEDFROM

4AKINGINVERSELOGARITHMSIEANTI

LOGSOFBOTHSIDESWEARRIVEAT

01

2 1 1 2 2S

u

f C R C R

7HENC1 = C2 = C ANDR1 = R2 = R

THISEQUATIONSIMPLIÚESTO

0

1

2S

f CR

out

V 10 10 10in

20log§ ·

u ¨ ¸ ¨ ¸© ¹ © ¹

V A

V

10

220log

0.02

§ · ¨ ¸

© ¹

Example 7 !D"MATCHEDATTENUATORISUSEDTO

REDUCETHEPOWERLEVELPRODUCEDBY

ANAMPLIÚERTHATPRODUCESANOUTPUT

OF77HATPOWERWILLAPPEARATTHEOUTPUTOFTHEATTENUATOR

2EARRANGING THE EQUATION FOR

POWERGAININ4ABLEPRODUCES

NowP

out

10in

10log§ ·

¨ ¸© ¹

P A

P

2EARRANGINGTHISEXPRESSIONGIVES

2EARRANGINGTHISEXPRESSIONGIVES

.OTETHATWEHAVEINSERTEDAMINUS

SIGNINORDERTOINDICATEAlossOFD"

Check – How do you think you are doing?OFTHEATTENUATORISM6FORAN

INPUTOF M6WHAT LOSSDOES

ITPRODUCE%XPRESSYOURANSWER

IND"

8.8. !N AMPLIFIER USED IN A

MATCHEDSYSTEMPROVIDESAPOWERGAINOFD"7HATINPUTPOWER

ISREQUIREDTOPRODUCEANOUTPUT

POWEROF7


P A

10

out

10in

log§ ·¨ ¸© ¹

P

P

1020log 100 20 2 40 dB u dB

8.1.)DENTIFYEACHOFTHECIRCUITS

SHOWNIN&IG

8.2. 3KETCH THE CIRCUIT OF A A

SIMPLEL-C ACCEPTORCIRCUITAND

BASIMPLEL-C REJECTORCIRCUIT

8.3.!SIMPLE2#HIGHPASSÚLTER

HASRK:ANDC N&$E

TERMINETHECUTOFFFREQUENCYOF

THEÚLTER

8.4.4HEOUTPUTOFALOWPASSÚLTER

IS6AT(Z)FTHEÚLTERHASA

CUTOFF FREQUENCY OF K(ZWHAT

WILLTHEAPPROXIMATEOUTPUTVOLT

AGEBEATTHISFREQUENCY

8.5.!NL-C TUNEDCIRCUITISTOBE

USEDTOREJECTSIGNALSATK(Z)FTHEVALUEOFCAPACITANCEISN&

DETERMINE THEREQUIREDVALUEOF

INDUCTANCE

8.6. 3KETCH THE FREQUENCY RE

SPONSEFORAASIMPLEL-C ACCEP

TORCIRCUITANDBASIMPLEL-C

REJECTORCIRCUIT

8.7. !N ATTENUATOR IS USED IN A

MATCHED SYSTEM )F THE OUTPUT

&ROMWHICH

10 10

6antilog

10

§ ·¨ ¸

© ¹

out

10in

antilog 0.6 P

P

P out out

10 10 10antilog10 A§ · § ·¨ ¸ ¨ ¸© ¹

out out

10 10in in

antilog log P P

P P

ª º§ ·¨ ¸« »

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out in 10antilog 0.6 P P u u

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Please note!

7HEN PLOTTING THE FREQUENCY RE

SPONSE OF A ÚLTER WE OFTEN USE A

LOGARITHMIC SCALE FOR FREQUENCY

BECAUSETHIS ALLOWSAMUCHWIDER

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THE CUTOFF FREQUENCY AND ONE OFTHEMOSTIMPORTANTCHARACTERISTICS

OFAÚLTERISTHERATEATWHICHTHIS

ROLLOFFOCCURS




Teach-In 2011

WE ARE now going to try out

SOMEPRACTICALÚLTER CIRCUITS

and see how they behave when we

apply different signals to them.

One of the features that Circuit

7IZARDLACKSTHATWEOFTENÚNDIN

higher-end electronics packages is

the ability to directly carry out AC

ANALYSISTOAGIVENCIRCUIT5SUALLY

this would involve modelling the

CIRCUIT ENTERING THE SIGNAL CHAR-

ACTERISTICS AND LIMITS THENLETTING

the software ‘sweep’ through the

frequency range and plot the output

amplitude and phase.

There are a number of useful appli-

CATIONSTHATCANDOTHISFOREXAMPLE

5Spice Analysis (www.5spice.com).

"EWARNED THOUGH THESE SOFTWARE

PACKAGES ARE OFTEN RATHER DIFÚCULT

to use unless you are familiar with

similar SPICE analysis programmes.

SIGNALS THAT CHANGE VERY RAPIDLY

it just can’t keep up in real-time.

4HEREFOREWENEED TO SLOWDOWN

the simulation speed in order to give

the software a chance to accurately

simulate.

)N THE AUTHORmS EXPERIENCE THE

PROCESSOFÚNDINGASUITABLESPEED

FORACIRCUITTOSIMULATEISTOBEHON -

ESTABITOFAÚDDLE4HEREFOREYOU

WILLNEEDTOEXPERIMENTTOSOMEDE-

gree to get your traces looking right.

Speed trapUnder certain circumstances Circuit

Wizard will warn you about accurate

high speed simulation (see Fig.8.21).

(OWEVERINPRACTICEITWILLHAPPILY

present you with bizarre results

with no warning. Fig.8.22 shows an

EXAMPLETRACEOFAK(ZSINEWAVE

simulated in real time!

Changing the simulation speed

is achieved by clicking on ‘Time:’

FOUNDALONGTHEBOTTOMGREYBARAND

selecting an appropriate timing (see

Fig.8.23). Note that this only appears

when the simulation is running.

,OWPASSªlLTERªTESTªCIRCUIT,ETmSBEGINBYLOOKINGATAÚRSTORDER

LOWPASSÚLTERCIRCUIT%NTERTHECIRCUIT

shown in Fig. 8.24 below. This is an ac-

TIVEÚLTERCIRCUITUSINGANOPERATIONAL

AMPLIÚER"ESURETOUSETERMINALSFOR

the output terminals and voltage rails

for the supply to the operational am-

PLIÚERGETTINGTHISWRONGISACOMMON

mistake that students make.

Please note that in order for our

Circuit Wizard circuits to match the

circuit diagrams you have seen in

Learn you will need to ‘mirror’ the

OPERATIONALAMPLIÚERSYMBOLSOTHAT


Although Circuit Wizard can’t do

THEANALYSISFORUSAUTOMATICALLYIT

still does a great job of modelling

ÚLTERCIRCUITS ASWEWILL SEE LATER

We can then bring our results to-

gether and plot our own frequencyCURVES)NFACTTHISISAGREATWAYTO

understand what’s really going on

and what happens to the signals as

we vary the frequency of the input.

3IMULATIONSCircuit Wizard carries out literally

thousands of mathematical calcula-

tions in the background in order to

show you how the circuit operates

OVERTIME(OWEVERWHENWEARE

working with higher frequency

Fig.8.21. Simulation speed warning

Fig.8.22. The bizarre result of simulating a high frequency circuit in real-time

Fig.8.23 (below). Changing

simulation speed




Teach-In 2011

the inverting (‘-’) input is at the top

(see Fig.8.25).

Using your new knowledge from

Learn you should be able to calculate

the cut-off frequency to be around

159Hz. This means that we should

expect it to happily pass low fre-

quency signals below this frequency

and reject high frequency signals.In order to test this out we’ll

simulate the circuit with various fre-

quencies and record the amplitude

of the output. We can then plot this

in Excel and see the characteristics

OFTHEÚLTER

Start by simulating the circuit with

a 1Hz input frequency (ie, set the

frequency of the function generator

to 1Hz – Circuit Wizard will do this

happily in real time.

You should alter the properties

of the graph as follows; maximum:

6V, minimum: 6V, time: 200ms.

Your trace should look similar toFig.8.26. You should also notice that

the output (blue) and input (red) are

basically identical, meaning that the

signal has passed directly through

THEÚLTERUNCHANGED

Now change the frequency of the

signal generator to 100Hz. You will

also need to decrease the simulation

speed and graph properties. These

were 5ms and 2ms in the author’s

case, but you should experiment to

get the best results. The resulting

waveform is show in Fig.8.27. Notice

that the amplitude has been reduced

or attenuated to around 4.2V, and theoutput waveform has been delayed

and is out of phase.

Experiment with various fre-

quencies between 1Hz and 200Hz,

recording your results. When you

have a number of results plot them

on a graph with frequency along

the x-axis and amplitude along the

y-axis. If you are using Excel to plot

the graph, make sure that you select

the ‘scatter’ graph type, as this will

'JH'JSTUPSEFSMPXQBTTÜMUFSUFTUDJSDVJU

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'JH")[JOQVUUSBDFrMPXQBTTÜMUFS 'JH")[JOQVUUSBDFrMPXQBTTÜMUFS




Teach-In 2011

correctly plot the two values against

each other. Fig.8.28 shows our re-

sults taking readings every 10Hz.

(IGHPASSªlLTERªTESTªCIRCUIT%DIT THE LOWPASS ÚLTER CIRCUIT BY

essentially swapping the capacitor

and resistor. You should now have

THEÚRSTORDERHIGHPASSÚLTERSHOWN

in Fig.8.29.Experiment to see how the output

changes with different frequen-

cies from 1Hz to 600Hz recoding

your results and plotting them on

A GRAPH 9OUSHOULD ÚNDTHATIN

CONTRASTTOTHELOWPASSÚLTERLOW

frequencies are attenuated while

higher frequencies are passed un-

altered. You should also notice that

the lower the frequency the higher

the phase difference. Our results

are shown in Fig.8.30.

3ECONDORDERªlLTERSNow we’re going to ramp things up

a little and look at

second-order fil-

ters. Fig.8.31 and

Fig.8.32 show a

low-pass and high-pass second-order

ÚLTER RESPECTIVELY

Use your theory

knowledge from

Learn to calcu-

late the cut-off fre-

quency for each

circuit and use this

to help you select

an appropriate

frequency range to test the circuit.

Simulate the circuit and collect a

series of results in order to help you

produce graphs for each circuit show-

ing how they respond.


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Teach-In 2011

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For more information, links and otherresources please check out our Teach-In

website at:

www.tooley.co.uk/teach-in

8.1. A3IMPLEC-R UNBALANCED

LOWPASSÚLTERBBALANCED4NET-WORKATTENUATORCUNBALANCED

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!NSWERSªTOª#HECKª

QUESTIONS



CIRCUIT WIZARD – featured in

this Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation


This is the software used in our Teach-In 2011 series.

Standard £61.25 inc. VAT Professional £91.90 inc. VAT

See Direct Book Service – pages 75-77 in this issue




* PCB Layout



* Gerber export




Teach-In 2011

The data shown in Table 8.2 was

obtained during an experiment

on an active tone control. Plot the

frequency response curve using the

logarithmic grid shown in Fig.8.35

and use it to determine:

(a) the maximum value of voltagegain (in dB)

(b) the maximum value of voltage

gain (expressed as a ratio)

(c) the approximate voltage gain at

50Hz and 30kHz

(d) the two frequencies at which the

voltage gain falls to zero

(e) the range of frequencies over

WHICHTHEGRAPHISlÛATmTOWITHIN

-1dB of the maximum

InvestigateFrequency

(Hz)

20 40 70 100 200 700 1k 2k 4k 7k 10k

Voltage gain

(dB)

-3 +5 +12.5 +15 +16 +16 +16 +16 +16 +15 +12.5

20k 40k 60k

+5.5 -2 -7.5

(f) the two frequencies at which

the gain has fallen by 6dB from its

maximum value.

Fig.8.35. See Investigate

AmazeIn most electronic circuits, the sig-nal voltages that we have to deal

with range from a few millivolts to

a few volts. Similarly, the power

levels present in these circuits tend

also to be rather modest and usually

range from a few milliwatts to a few

WATTS)TmSWORTHCONSIDERINGAFEW

examples where signal voltages andpower are either very much smaller

or very much larger than this.

When you receive a signal on your

radio or TV at home, the signal volt-

age present at the input of the radio

or TV receiver is often only a few tens

or hundreds of microvolts. Since the

impedance of the aerial, coaxial cable

and input of the receiver is invariably

75:, this suggests that, for a signal of

1 mV, the actual power present at the

input of your radio or TV will be in

the region of:

(digital) to reach an estimated view-ing population of 11 million people.

!FTERlDIGITALSWITCHOVERm$3/THE

digital power output will increase

tenfold to 200kW.

If it were possible to absorb all of the

currently radiated 1MW of analogue

power in a single 50 ohm resistor the

voltage generated across the ends of

the resistor would be given by:This 50-foot dish antenna at the NorthKennedy Space Center is supplied with a power of 3kW from a C-band radar to produce an effective radiated

power (ERP) of around 3MW!

2

32 6

R

1 10 10

75 75

u

V P

Z

0.0133 ȝW

At the other extreme, consider

the power that is delivered to the

aerial of a high power transmitting

station. This is very much larger.

For example, the Crystal Palace

TV transmitter currently radiates a

power of 1MW (analogue) and 20kW

61 10 50 u u u V P R

7.07 kV

If the 1MW of radiated power from

#RYSTAL0ALACEISNmTQUITEENOUGHFOR

you, the Boshakova transmitter (used

until recently by the Voice of Russia)

produced a staggering 2.5MW of out-

put, and its output was radiated by

no less than eight guyed masts, each

around 250 metres tall.

Next month!)N NEXTMONTHmS 4EACH)N WEWILL

look at digital-to-analogue and

analogue-to-digital conversion.

Table 8.2.

ȝW



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HandsOn Technology



46 Everyday Practical Electronics, July 2011

Teach-In 2011


Part 9: Digital-to-Analogue andAnalogue-to-Digital Conversion



many schools and colleges in the UK. These include Edexcel BTEC Level 2 awards, as well as electronicsunits of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced

READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª





TEACH-IN 2011


TO ELECTRONICS

IN THIS instalment of Teach-In

2011, we introduce some com-

bined applications of analogue

and digital circuits in the form of

digital-to-analogue and analogue-

to-digital converters (DAC, ADC). In

Learn we explore the circuits and

techniques used in DAC and ADC.

Investigateextends this further with

a look at a popular DAC, which is

available from several semiconduc-

tor manufacturers.

Build looks at some further ap-

plications of digital circuits using

both combinational and sequential

logic techniques. Finally, in Amaze

we look at the way that very large

numbers are handled in digitalsystems.

QuantisationBecause signals in the real world exist

in both digital (on/off ) and analogue

(continuously variable) forms, digital

and computer systems need to be able

to accept and generate both types of

signal as inputs and outputs respec-

tively. Because of this, there is a need

for devices that can convert signals

in analogue form to their equivalent

in digital form, and vice versa.

This chapter introduces digital-

to-analogue and analogue-to-digital

conversion. We shall begin by look-

ing at the essential characteristics of

analogue and digital signals and theprinciple of quantisation.

In order to represent an analogue

signal using digital codes, it is neces-

sary to approximate (or quantise) the

signal into a set of discrete voltage

levels, as shown in Fig.9.1 The six-

teen quantisation levels for a simple

analogue-to-digital converter using

a four-bit binary code are shown in

Fig.9.2. Note that, in order to accom-

modate analogue signals that have

both positive and negative polarity

we have used the two’s complement

representation to indicate negative

voltage levels.

Thus, any voltage represented by a

digital code in which the MSB (most

SIGNIÚCANTBITISLOGICWILLBENEGA-

tive. Fig.9.3 shows how a typicalanalogue signal would be quantised

Learn



Everyday Practical Electronics, July 2011 47

Teach-In 2011

into voltage levels by sampling at

regular intervals (t 1, t 2, t 3, etc).

Digital-to-analogue conversionThe basic digital-to-analogue

converter (DAC) has a number of

digital inputs (often 8, 10, 12, or

16) and a single analogue output,

as shown in Fig.9.4. The simplest

form of DAC shown in Fig.9.5(a)

uses a set of binary-weighted resis-

TORS TODEÚNETHEVOLTAGEGAINOF

ANOPERATIONALSUMMINGAMPLIÚER

and a four-bit binary latch to storethe binary input while it is being

converted.

.OTE THATSINCE THE AMPLIÚER IS

connected in inverting mode, the

analogue output voltage will be

negative rather than positive. How-

EVER A FURTHER INVERTING AMPLIÚER

stage can be added at the output to

change the polarity if required.

The voltage gain of the inputs to

the operational amplifier (deter-

mined by the ratio of feedback to

input resistance and taking into ac-COUNT THE INVERTING CONÚGURATION

is shown in Table 9.1. If we assume

that the logic levels produced by the

four-bit data latch are ‘ideal’ (such

that logic 1 corresponds to +5V and

logic 0 corresponds to 0V), we can

determine the output voltage corre-

sponding to the eight possible input

states by summing the voltages that

will result from each of the four

inputs taken independently.

For example, when the output of the

latch takes the binary value 1010 theoutput voltage can be calculated from:

Fig.9.1. The process of quantising an analogue signal into its digital equivalent

Fig.9.2. Quantisation levels for a simple ADC that uses a four-bit binary code

Fig.9.3. An analogue signal quantised into voltage levelsby sampling at regular intervals (t 1, t 2, t 3, etc.)

Fig.9.4. Basic DAC representation

Similarly, when the output of the

latch takes the binary value 1111

(the maximum possible) the output

voltage can be determined from:

Table 9.1. Table of voltage gains forthe simple DAC shown in Fig.9.5(a)

Vout = (–1 × 5) + (–0.5 × 0) +

(–0.25 × 5) + (–0.125 × 0) = –6.25V

Vout = (–1 × 5) + (–0.5 × 5) +

(–0.25 × 5) + (–0.125 × 5) = –9.375V

Bit Voltage gain

3 (MSB) – R/ R = –1

2 – R/2 R = –0.5

1 – R/4 R = –0.25

0 (LSB) – R/8 R = –0.125




Teach-In 2011

The complete set of voltages corre-

sponding to all eight possible binarycodes is given in Table 9.2.

Binary-weighted DACAn improved binary-weighted DAC

is shown in Fig.9.5(b). This circuit

operates on a similar principle to

that shown in Fig.9.5(a), but uses

four analogue switches instead of

a four-bit data latch. The analogue

switches are controlled by logic

inputs so that a switch’s output isconnected to the reference voltage

(V ref ) when its respective logic input

is at logic 1, and to 0V when the cor-

responding logic input is at logic 0.

When compared with the previous

arrangement, this circuit offers the

advantage that the reference voltage

is considerably more accurate and

stable than using the logic level to

DEÚNETHEANALOGUEOUTPUTVOLTAGE

A further advantage arises from thefact that the reference voltage can

be made negative, in which case the

analogue output voltage will become

positive. Typical reference voltages

are –5V, –10V, +5V and +10V.

Unfortunately, by virtue of the

range of resistance values required,

the binary-weighted DAC becomes

increasingly impractical for higher

resolution applications. Taking a

10-bit circuit as an example, and

assuming that the basic value of Ris 1k:, the binary weighted values

would become:

Bit 0 1k:

Bit 2 2k:

Bit 3 4k:

Bit 4 8k:

Bit 5 16k:

Bit 6 32k:

Bit 7 64k:

Bit 8 128k:

Bit 9 256k:

Fig.9.5. Simple DAC arrangements

Bit 3 Bit 2 Bit 1 Bit 0 Output voltage

0 0 0 0 0V

0 0 0 1 –0.625V

0 0 1 0 –1.250V

0 0 1 1 –1.875V

0 1 0 0 –2.500V

0 1 0 1 –3.125V

0 1 1 0 –3.750V

0 1 1 1 –4.375V

1 0 0 0 –5.000V

1 0 0 1 –5.625V

1 0 1 0 –6.250V

1 0 1 1 –6.875V

1 1 0 0 –7.500V

1 1 0 1 –8.125V

1 1 1 0 –8.750V

1 1 1 1 –9.375V

Table 9.2. Output voltages produced by thesimple DAC shown in Fig.9.5(a)




Teach-In 2011

)NORDER TOENSURE ASUFÚCIENTLY

HIGHDEGREEOFACCURACYALLOFTHESE

RESISTORSWOULDNEEDTOBECLOSETOLER

ANCETYPESTYPICALLYORBETTER

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.OTETHATONLYTWORESISTANCEVALUES

AREREQUIREDANDTHATTHEYCANBEANY

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VALUEISDOUBLETHEOTHERITISRELATIVELYEASYTOMANUFACTUREMATCHED

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ERANCEONANINTEGRATEDCIRCUITCHIP

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ONLYONTHEVALUESOFTHERESISTANCE

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ANDSUPPLYVOLTAGES4YPICALACCURA

CIESOFBETWEENANDCANBE

ACHIEVEDUSINGMOSTMODERN LOW

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PONENTS IE THOSE THAT CAUSE THE

lSTEPSm IN THE ANALOGUESIGNAL ARE

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OF THEÚLTER AND ARE SUBJECT TO AN

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INPUTVOLTAGEEXCEEDSTHEREFERENCE

Fig.9.6. Filtering the output of a DAC

Fig.9.7. Basic ADC representation




Teach-In 2011

types and typical conversion times (ie, the time between

the SC and EOC signals) are in the range 10 Ps to 100 Ps.Despite this, conversion times are fast enough for most

non-critical applications, and this type of ADC is rela-

tively simple and available at low-cost.

Ramping it upA ramp-type ADC is shown in Fig.9.10. This type of ADC

USESARAMPGENERATORANDASINGLEOPERATIONALAMPLIÚER

comparator, IC1.

The output of the comparator is either a 1 or a 0 depend-

ing on whether the input voltage is greater or less than the

instantaneous value of the ramp voltage. The output of

the comparator is used to control a logic gate (IC2) whichpasses a clock signal (a square wave of accurate frequency)

to the input of a pulse counter whenever the input voltage

is greater than the output from the ramp generator.Fig.9.11. Waveforms for a single-ramp ADC

The pulses are counted until the

voltage from the ramp generator

exceeds that of the input signal, at

which point the output of the compa-

rator goes low and no further pulses

are passed into the counter. The

number of clock pulses counted will

depend on the input voltage and the

ÚNALBINARYCOUNTTHUSGIVESADIGITAL

representation of the analogue input.Typical waveforms for the ramp-type

waveform are shown in Fig.9.11.

Dual-slope ADC&INALLYTHEDUALSLOPE!$#ISAREÚNE-

ment of the ramp-type ADC, which

Check – How do you think you are doing?9.6. The binary codes produced

by a four-bit bipolar analogue-to-

digital converter (see Fig.9.2 andFig.9.3) sampled at intervals of

1ms, have the following values:

9.1.Explain with the aid of a sketch

what is meant by quantisation.

9.2. A DAC can produce 256 dif-ferent output voltages. What is the

resolution of the DAC?

9.3. How many discrete voltage

levels can be produced by a 10-

bit DAC?

9.4. Explain the advantage of an

R-2R ladder DAC compared a

binary-weighted DAC.

9.5.3TATETHEADVANTAGEOFAÛASH

ADC and suggest an application

in which it can be used.

Fig.9.12. Waveforms for a dual-ramp ADC

If the ADC uses two’s comple-

ment to represent negative val-

ues (ie, 1111 represents -1, 1110represents -2, and so on) sketch

and identify the waveform of the

analogue voltage.

Time (ms) Binary code

0 0101

1 0100

2 0011

3 0010

4 0001

5 0000

6 1111

7 1110

For more information,

links and other resources


Teach-In website at:





Teach-In 2011

IN this edition of Build we will try

out some of the DAC circuits that

we introduced in Learn (Fig.9.5).

As we have seen, these can be con-

STRUCTEDUSINGOPERATIONALAMPLIÚERS

with cleverly arranged arrays of

input resistors.

Binary-weighted DACFirst enter the simple binary-weighted

DAC circuit shown in Fig.9.13. This

is a practical circuit based on the one

shown in Learn Fig.9.5(a). We have

used a series of logic input toggles to

simulate standard logic level inputs,

with the output voltage shown on avirtual voltmeter instrument.

Set various input bit patterns and

monitor the resulting output voltage.

Using your theory from Learn to

calculate the expected output voltage

for two different input bit patterns

and then test your answers using

the simulation. Take readings of the

output voltage for the binary coded

decimal inputs from 0 (0000) to 15

(1111) and produce a graph of your

results. Fig.9.14 shows our example

results plotted using Microsoft Excel.

Fig.9.13. A simple four-bit binary-weighted DAC

ϰ

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ϳ

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ϵ

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^ŝŵƉůĞŝƚͲtĞŝŐŚƚĞĚtŝƚŚhŶŝƚǇ/ŶǀĞƌƚĞƌ

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ϭ

Ϯ

ϯ

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K Ƶ

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'JH5IFNPEJÜFEGPVSCJUCJOBSZXFJHIUFE%"$

Fig.9.14. Graphof results for thesimple four-bit binary-weighted DAC

Fig.9.16. Graphof results for UIFNPEJÜFE four-bit binary-weighted DAC shown inFig. 9.15

involves a similar comparator arrange-

ment, but uses an internal voltageREFERENCEANDANACCURATEÚXEDSLOPE

negative ramp which starts when the

positive going ramp reaches the ana-

logue input voltage. The important

thing to note about this type of ADC

is that, while the slope of the positive

ramp depends on the input voltage,

THENEGATIVERAMPFALLSATAÚXEDRATE

Hence, this type of ADC can provide

a very high degree of accuracy and can

also be made so that it rejects noise

and random variations present on the

input signal. The main disadvantage,

HOWEVER ISTHAT THEPROCESSOFÚRST

ramping up and then ramping down

requires some considerable time, and

hence this type of ADC is only suitable

for ‘slow’ signals (ie, those that are not

rapidly changing). Typical conversion

times lie in the range 500 Ps to 20ms.




Teach-In 2011

One of the drawbacks to the sim-

ple DAC circuit is the fact that by

USING AN OPERATIONAL AMPLIÚER IN

ANINVERTINGCONÚGURATIONTHEOUT-

put is negative. A common way of

dealing with this issue is to add an

ADDITIONALINVERTINGAMPLIÚERWITH

a gain of -1. This is often referred to

as a unity gain inverter.

Modify your binary-weighted DAC

circuit (Fig.9.13) to that shown in

Fig.9.15 below, and experiment withchanging the input bits. Notice that

THE OUTPUT OF THE ÚRST OPERATIONAL

AMPLIÚER 6 IS EQUAL IN MAGNI-

tude to the output voltage (V out)

but opposite in polarity. Plotting

V out against BCD input for this new

arrangement should now look as

shown in Fig.9.16.

! FURTHER MODIÚCATION TO THE

binary-weighted DAC is shown

in Fig.9.17. Here the output volt-

age is taken across the outputs of

THE TWO OPERATIONAL AMPLIÚERS

In this way the output voltage is

effectively doubled. In fact, this

method is commonly employed in

many commercial DAC integrated

circuit devices.

Fig.9.18. Binary-weighted DAC using analogue switchesand a negative voltage reference

Fig.9.19. Four-bit DAC using an R-2R ladder arrangement

Fig.9.17. Improved binary weighted DAC with differential output

A switch in timeIn Fig.9.5(b) we described an im-

proved DAC circuit using analogue

SWITCHES7ECANMODELTHISQUITE

simply for simulation purposes us-

ing single-pole double-throw (SPDT)

switches, as shown in Fig.9.18. Note

that in a real circuit these would be

controlled by logic inputs.

Simulate the circuit by changingthe binary input patterns by tog-

gling switches SW1 to SW4. Notice

that by having a negative reference

voltage we achieve a positive output

voltage. Experiment by changing the

reference voltage (V ref ) and note how

this affects the output voltage range.

On the ladderFinally, we will try out a third type of

DAC circuit that utilises a so called

R-2R resistor ladder arrangement,

like that shown earlier in Fig.9.5(c).

As we discussed in Learn, there are

practical advantages to this type of CIRCUITFOREXAMPLEONLYREQUIRING

one matched pair of resistor val-

ues. Construct the circuit shown in

Fig.9.19 and experiment with the

simulation.





Teach-In 2011

ADCs and DACs invariably take the

form of integrated circuit devices.

Obtain data sheets for a DAC0800

digital-to-analogue converter (these

can be freely downloaded from the

websites of semiconductor manu-

facturers like National Semicon-

ductor and Motorola) and use them

to answer each of the following

questions:

1. How many data bits are used?

2. What range of supply voltages can

be used with this device?

3. What package styles are used for

Investigatethe device and how many connect-

ing pins do the packages have?

4. What is the typical power con-

sumption of the device when used

with a ±10V supply?

5. What is the absolute maximum

power dissipation for the device?

6. Which pins are used for (a) the

LSB input and (b) the MSB input?

7. On what principle does the DAC

operate?8. What is the typical time taken

for the output voltage to settle in

response to a change at the input?

9.1. See page 46 and Fig.9.1

9.2. 8-bit

9.3. 1024

9.4. Only two values are needed

in the resistor chain of an R-2R

ladder (the ratio of the two resist-

ances is more important than

their absolute values). The resist-

ance values in a binary-weightedDAC can become very large when

a large number of bits are used

9.5. High speed of operation. A

typical application would be for

use with high-quality audio and

video signals (ie, analogue signals

at relatively high frequencies)

9.6. Falling ramp (the analogue

value falls linearly)

Answers to Checkquestions

AmazeAs you have seen, the resolution of

a DAC or ADC is determined by the

number of data bits that it uses. The

simple four-bit DAC that you met in

Build was only capable of generat-

ing sixteen different voltage states.

By increasing the number of bits wecan gain a corresponding increase in

THERESOLUTION3OAÚVEBIT$!#CAN

produce 32 different output voltages,

a six-bit DAC is able to produce 64

different output levels, and so on.

In many applications, the digital

output of an ADC is processed using

a computer or some form of embed-

ded processor (such as those used in

the engine control and management

systems of motor vehicles). The

unit of data in a computer (ie, the

number of bits that can be handled

by its processing unit as one single

entity) is referred to as a word . So,

ultimately, the digital output of an

ADC must be converted into words

that the computer or embedded

system’s processor can operate on.

The number of bits in a word is animportant characteristic of a par-

ticular processor family or computer

architecture. This, in turn, has an

impact on the size and range of the

quantities that it can manipulate.

Early computers, such as the IBM

PC and Commodore Amiga, as well

as early console systems, such as

the Sega Genesis, Super Nintendo,

Mattel Intellivision, used a word

length of 16-bits. This allowed them

to manipulate integer numbers hav-

ing a total of 65,536 different values.

More powerful 32-bit computers(such as the Apple Macintosh,

Pentium-based PC and popular

console systems, including the Sony

PlayStation, Nintendo GameCube,

Xbox, and Wii) have word lengths

of 32-bits and this allows them to

manipulate integer numbers that

can represent 4,294,967,296 differ-

ent values.

However, if that’s not quite

enough in terms of resolution, the

most recent 64-bit systems includ-

ing some games consoles, such asNintendo 64, PlayStation 2, Play-

Station 3, Xbox 360, can cope with

integer numbers having a staggering

18,446,744,073,709,551,616 differ-

ent values!

Next month!In next month’s Teach-In we will

look at practical aspects of test

instruments, measurements and

testing circuits (including an intro-

duction to PCB layout using Circuit Wizard ).



CIRCUIT WIZARD – featured in this

Teach-In series Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation


This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90inc. VAT. See Direct Book Service – pages 75-77 in this issue




* PCB Layout



* Gerber export



42 Everyday Practical Electronics, August 2011

Teach-In 2011


Part 10: Electronic circuitconstruction and testing

Our Teach-In series aims to provide you with a broad-based introduction to electronics. We have attempt-

ed to provide coverage of three of the most important electronics units that are currently studied in many

schools and colleges in the UK. These include Edexcel BTEC Level 2 awards as well as electronics units of the

new Diploma in Engineering (also at Level 2). The series will also provide the more experienced reader with

ANªOPPORTUNITYªTOªhBRUSHªUPvªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª





TEACH-IN 2011


TO ELECTRONICS

THIS month, we look at the practical aspects

of electronic circuit construction and testing.

In Learn we introduce you to two of the most

common and versatile items of test equipment, the

multimeter and oscilloscope. Build looks at techniques

that can be used to design, construct and test printed

circuit boards (PCB) within Circuit Wizard.

Investigate involves taking measurements and

FAULTÚNDINGONA SIMPLE VOLTAGE REGULATOR CIRCUIT

Finally, Amaze looks at the reliability of electronic

components.

LearnAt BTEC Level 1 and Level 2 you need to be able to

make measurements on simple DC and AC circuits

including:

pMeasuring voltage, current and resistance using a

multi-range meter (or multimeter )

pDisplaying waveforms and making measurements

of voltage (peak and peak-to-peak) and time using

an oscilloscope.

Fig.10.1. Multimeters can be either analogue (left) or digital (right)



Everyday Practical Electronics, August 2011 43

Teach-In 2011

estimation of the pointer’s position,

and then the application of some

mental arithmetic based on the range

switch setting (see Fig.10.2)

Unlike their analogue counter-

parts, digital multimeters are usu-

ally extremely easy to read and

have displays that are clear, unam-

biguous, and capable of providing

a very high resolution. It is also

possible to distinguish between

readings that are very close. This is

just not possible with an analogue

instrument.

Digital multimeters offer a number

OFSIGNIÚCANTADVANTAGESWHENCOM -

pared with their analogue counter-

PARTS4HEDISPLAYÚTTEDTOADIGITAL

multimeter usually consists of a

3½-digit seven-segment display—

THESIMPLYINDICATESTHATTHEÚRST

digit is either blank (zero) or 1.

In all cases, you will need to ensurethat you work safely and observe

correct procedures (for example,

switching off and disconnecting the

power supply before connecting test

leads). We begin this month’s Learn

by introducing the test instruments

that you will be using.

MultimetersOne of the most common, versatile

and easy-to-use instruments is the

multi-range meter, or multimeter.

This instrument combines the func-tions of a voltmeter, ammeter and

ohmmeter into a single instrument.

Many multimeters also have addi-

tional ranges, for example to check

continuity, measure capacitance or

to check diodes and transistors.

Most multimeters operate from

internal batteries, and are thus

independent of the mains supply.

This allows you to easily carry them

around and make measurements

on electronic equipment when you

are away from the laboratory or

workshop.

There are two main types of mul-

timeter: analogue and digital (see

Fig.10.1). Analogue multimeters

employ conventional moving coil

MOVEMENTS THE DISPLAY TAKES THE

form of a pointer moving across a

calibrated scale.

This arrangement is not so con-

venient to use as that employed

in digital instruments because the

position of the pointer is rarely ex-

act and may require interpolation.

Analogue instruments do, however,

offer some advantages, not least, is

that it’s very easy to make adjust-

ments to a circuit, while observing

THERELATIVEDIRECTIONOFTHEPOINTER

a movement in one direction repre-

senting an increase and in the other

a decrease.

Despite this, the main disadvan-

tage of analogue meters is the rather

cramped and sometimes confusing

scale calibration. To determine

THE EXACT READING REQUIRESÚRST AN

Fig.10.2. A comparison of the displays provided on analogue and digital mul-timeters. Both meters indicate the same value.

Fig.10.3. The procedure for making current and voltage measurements using a digital multimeter




Teach-In 2011

Consequently, the maximumindication on the 2V range will

be 1.999V. This suggests that the

instrument is capable of offering a

resolution of 1mV on the 2V range

(in other words, the smallest incre-

ment in voltage that can be measured

is 1mV).

Depending on the size and calibra-

tion markings on the instrument’s

scale, the resolution obtained from

a comparable analogue meter would

typically be about 50mV, and so the

digital instrument provides us with aresolution that is many times greater

than its analogue counterpart.

Multimeter measurementsThe procedure for making current

and voltage measurements using

a digital multimeter, is shown in

Fig.10.3. We’ve chosen this type of

instrument for our example because

you will probably be using a modern

digital instrument rather than an

older analogue type.

Note how it is necessary to break

the circuit and insert the meter when

making a current measurement. No-

tice also how the voltmeter is con-

nected in parallel with the circuit at

the point at which you are making a

measurement.

It is essential that you get these two

connections right and that you select

the correct ranges on the multimeter.

Failure to observe these two simple

precautions can result in damage to

the meter and/or the circuit under

test!

In Fig. 10.3, one of the meters is

used to measure the supply current

(note that the circuit must be broken

and the meter inserted into it), while

the second instrument is being used

to measure the potential difference

(voltage drop) across diode D1.

The initial range settings (200mA

for the current measurement, and

20V for the voltage measurement) are

chosen so that they are both greater

than those that we would expect to

ÚNDINTHECIRCUIT&OREXAMPLEWE

WOULDCALCULATETHECURRENTÛOWINGin the circuit to be (9 – 5.6)/100 amps

or 34mA.

Similarly, we could assume that

the voltage that we would measure

should be 5.6V (the same as the Zener

voltage), but in no event would we

expect it to be greater than the supply

voltage (9V). We have, therefore, left

quite a margin for safety with the two

ranges that we’ve selected!

Please note!

It is essential to switch off and dis-connect the power supply before at-

tempting to connect test leads. When

the meter ranges have been set and

the connections made, the supply can

be reinstated and switched back on,

so that measurements can be made.

Please note!In your school/college course you

will only be working with equip-

ment that uses safe low voltage sup-

plies. Even so, it is essential to ob-

serve Health and Safety precautions

whenever you are working on live

electrical and electronic circuits.

When in doubt, you should always

refer to your tutor!

Please note!When the circuit on test uses large

value capacitors it may be necessary

to wait a few minutes in order to al-

low them to discharge safely before

making connec-

tions to the circuit.

Please note!Make sure that you

only use properly

insulated test leads

to make connec-

tions to a circuit

on test. The leads

SHOULDBEÚTTEDWITH

clips and probes to

make connections

to a circuit.

Never use bare

wires and test prods

as these can cause short-circuits toadjacent connections!

OscilloscopesOscilloscopes can be used in a variety

of measuring applications, the most

important of which is the display of

time related voltage waveforms.

Older oscilloscopes (Fig.10.4) used

cathode ray tubes (CRT) for their

displays. In order to make accurate

measurements, the face of the CRT

WASÚTTEDWITHAgraticule that was

either integral with the tube or tookthe form of a separate translucent

sheet. Modern oscilloscopes use

ÛAT,#$DISPLAYSEITHERCOLOUROR

monochrome, which incorporate

an electronically generated meas-

uring scale. Accurate voltage and

time measurements are made with

reference to the scale or graticule,

applying a scale factor derived from

the appropriate range switch.

The use of the graticule is illus-

trated by the following example. An

oscilloscope screen is depicted in

Fig.10.5. This diagram is reproduced

at a reduced size. If shown full-size,

the gratical markings would be spaced

ATCMANDTHEÚNEGRATICULEMARKINGS

would be every 2mm along the central

vertical and horizontal axes.

The oscilloscope is operated with

ALL RELEVANT CONTROLS IN THE l#!,m

position. The timebase (horizontal

DEÛECTIONISSWITCHEDTOTHEMSCM

Fig.10.4. A typical two-channel general purpose oscil-loscope that uses a CRT display




Teach-In 2011

RANGEANDTHEVERTICALATTENUATORVERTICALDEÛECTIONISSWITCHEDTOTHE6CMRANGE

4HEOVERALLHEIGHTOFTHETRACEISCMANDTHUSTHE

PEAKTOPEAKVOLTAGEIS¯663IMILARLYTHETIME

FORONECOMPLETECYCLEPERIODIS¯MSMS

/NEFURTHERIMPORTANTPIECEOFINFORMATIONISTHE

SHAPEOFTHEWAVEFORMTHATINTHISCASEISSINUSOIDAL

4HEFUNCTIONOFSOMEOFTHEMORECOMMONCONTROLS

ANDADJUSTMENTSFORAGENERALPURPOSEOSCILLOSCOPE

ARELISTEDIN4ABLE

BECOME AVAILABLE 2ATHER THAN USING CONVENTIONAL

ANALOGUEDIGITALOR#24DISPLAYSTHESEvirtual instru-

mentsUSEPLUGINADAPTERSOR53"CONNECTEDINTER-

FACESTOGETHERWITHA0#EITHERDESKTOPORLAPTOP

4HEINTERFACECIRCUITCAPTURESADIGITALSAMPLEOFTHE

ANALOGUEINPUTWHICHCANTHENBESTOREDINMEMORY

ANDRECALLEDFORLATERDISPLAY

6IRTUAL INSTRUMENTSOFFERA NUMBEROFADVANTAGES

WHENCOMPAREDWITHCONVENTIONALTESTINSTRUMENTS

INCLUDINGTHEABILITYTODISPLAYWAVEFORMPARAMETERS

SUCHASTIMEVOLTAGEFREQUENCYANDPHASEASWELL

ASBEINGABLETOSTORERECALLANDPRINTWAVEFORMDATA!TYPICALVIRTUALSOUNDCARDOSCILLOSCOPEDISPLAYIS

SHOWNIN&IG

Please note!"EFORE TAKING MEANINGFUL MEAS-

UREMENTS FROM A#24 SCREEN IT IS

ABSOLUTELY ESSENTIAL TOENSURE THAT

THEFRONTPANELVARIABLECONTROLSARE

SETINTHEcalibrate#!,POSITION

2ESULTSWILLALMOSTCERTAINLYBEINAC -

CURATEIFTHISISNOTTHECASEØ

Oscilloscope measurements!TYPICALOSCILLOSCOPEMEASUREMENT

ISSHOWNIN&IG)NTHISAPPLICA-

TIONTHEOSCILLOSCOPEISBEINGUSEDTO

DISPLAYTHEWAVEFORMSINASIMPLEHALFWAVERECTIÚERPOWERSUPPLY

!SWITHTHEMULTIMETERMEASURE-

MENTSTHATWEMETEARLIERITISESSENTIAL

TOMAKE INITIAL ADJUSTMENTS TO THE

OSCILLOSCOPE"%&/2%CONNECTINGTHE

OSCILLOSCOPETOTHECIRCUITANDSWITCH-

INGONTHESUPPLY/NCEAGAINWHENIN

DOUBTYOUSHOULDREFERTOYOURTUTORØ

Virtual instruments)NRECENTYEARSANEWTYPEOFELEC-

TRONIC MEASURING INSTRUMENT HAS

Fig.10.5. Using an oscilloscope scale

'JH0TDJMMPTDPQFNFBTVSFNFOUT POB TJNQMF IBMGXBWFSFDUJÜFSQPXFSsupply

Fig.10.7. A typical display produced by a PC-based virtual oscilloscope




Teach-In 2011

Control Adjustment

Focus Provides a correctly focused display on the screen

Intensity Adjusts the brightness of the display

Astigmatism Provides a uniformly defined display over the entire screen area and in both x and y directions. The control is normally used in conjunction with thefocus and intensity controls

Trace rotation Permits accurate alignment of the display with respect to the graticule(CRT displays only)

Scale illumination Controls the brightness of the graticule or scale

Horizontal deflection system

Timebase (time/cm) Adjusts the timebase range and sets the horizontal time scale. Usually thiscontrol takes the form of a multi-position rotary switch and an additionalcontinuously variable control is often provided. The ‘CAL’ position isusually at one, or other, extreme setting of this control

Stability Adjusts the timebase so that a stable waveform display is obtained

Trigger level Selects the particular level on the triggering signal at which the timebasesweep commences

Trigger slope This usually takes the form of a switch that determines whether triggeringoccurs on the positive or negative going edge of the triggering signal

Trigger source This switch allows selection of one of several waveforms for use as thetimebase trigger. The options usually include an internal signal derivedfrom the vertical amplifier, a 50Hz signal derived from the supply mains,

and a signal which may be applied to an External Trigger input

Horizontal position Positions the display along the horizontal axis (CRT displays only)

Vertical deflection system

Vertical attenuator (V/cm) Adjusts the magnitude of the signal attenuator (V/cm) and sets the verticalvoltage scale. This control is invariably a multi-position rotary switch;however, an additional variable gain control is sometimes also provided.

Often this control is concentric with the main control and the ‘CAL’ position is usually at one, or other, extreme setting of the control

Vertical position Positions the display along the vertical axis of the display

AC-DC-ground Normally an oscilloscope employs DC coupling throughout the vertical

amplifier; hence a shift along the vertical axis will occur whenever a directvoltage is present at the input. When investigating waveforms in a circuit,one often encounters AC superimposed on DC levels; the latter may be

removed by inserting a capacitor in series with the signal. With the AC-DC-ground switch in the DC position, a capacitor is inserted in the inputlead, whereas in the DC position the capacitor is shorted. If ground is

selected, the vertical input is taken to common (0V) and the oscilloscopeinput is left floating. This last facility is useful in allowing the accurate positioning of the vertical position control along the central axis. Theswitch may then be set to DC and the magnitude of any DC level present atthe input may be easily measured by examining the shift along the verticalaxis.

Chopped-alternate This control, which is only used in dual-beam CRT oscilloscopes, providesselection of the beam splitting mode. In the chopped position, the trace

displays a small portion of one vertical channel waveform followed by anequally small portion of the other. The traces are, in effect, sampled at arelatively fast rate, the result being two apparently continuous displays. Inthe alternate position, a complete horizontal sweep is devoted to eachchannel alternately.

Table 10.1. Oscilloscope controls and adjustments

AC




Teach-In 2011


(b) Focus

(c) Stability

(d) Trigger source

(e) Vertical attenuator.

10.5. Explain why it is impor-

tant to ensure that the variable

controls of an oscilloscope are

placed in the ‘CAL’ position beforeattempting to make an accurate

measurement.

10.6. What adjustment should be

made to an oscilloscope when it

is to be used to display a small

AC voltage superimposed on a

much large DC voltage? Explain

why this adjustment is necessary.

10.1. Briefly explain the dif-

ference between analogue and

digital multimeters. Which type

of instrument offers the greatest

resolution? Why is this?

10.2. What indications are dis-

played on the analogue and digital

multimeters shown in Fig.10.8?

10.3. What information (eg, ampli-

tude, period) can be obtained from

the oscilloscope displays shown

in Fig.10.9?

10.4. Explain the function of each

of the following oscilloscope

controls:

(a) Brightness

Fig.10.8. See Question 10.2

Fig.10.9. See Question 10.3

For more information,

links and other resources


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By integrating the entire design process, Circuit Wizard provides you with a ll the tools necessary to produce an electronics project from

start to finish – even including on-screen testing of the PCB prior to construction!

CIRCUIT WIZARD Circuit Wizard is a revolutionary new software system that combines circuit design, PCB design, simulation and CAD/CAM manufacture in one complete package.

Two versions are available, Standard and Professional.




* PCB Layout



* Gerber export

This is the software used in our Teach-In 2011 series. Standard £61.25 inc. VAT Professional £91.90

inc. VAT. See Direct Book Service – pages 75-77 in this issue

1 ms/cm




Teach-In 2011

Therefore, select ‘Single-Sided;

Normal Tracks’ and then click on

‘Next’. The next screen allows us

to change the size and shape of the

board. In this case, we’ll leave these

as the default and click on ‘Next’.

,AST ON THE ÚNAL PAGE SELECT

l#ONVERTm AND KEEP YOUR ÚNGERS

crossed! As Circuit Wizard carries

out the conversion of your circuit

to a PCB, it will animate the plac-

ing of the components, followed

by the calculation of the optimumtrack layout. If all goes well, after

from yours. It should be noted that

the automatic routing functionality

of Circuit Wizard is a little limited,

and it does struggle to route much

more than the simplest circuits

without a little help. However,

we’ll be looking at tactics for cre-

ating more complex PCBs later in

this article.

Now that we have created our PCB

layout, there are a number of excit-

ing things that we can do with it. A

superb feature of Circuit Wizard isthat as well as simulating the circuit

Make sure that you select the Off-

board Component variant,not a PCB

Component. Wire the PP3 battery’s

positive and negative connections to

the two-pin screw terminal block by

dragging from the ends of the battery

connector wires (Fig.10.14).

Virtual testYou are now ready to virtually test

your PCB; start the simulation us-

ing the ‘Run’ button on the toolbar,

as you would for a standard circuit,

and try out the function of the circuit

by changing the light level on the

LDR. On the left-hand side of the

screen you may select various dif-

ferent views of the PCB. The default

is ‘Real World’, which shows a full

colour representation of what the

board will actually look like whenconstructed. ‘Normal’ is a more tra-

ditional PCB design view. As with

schematic simulation, the PCB may

also be simulated in a ‘Current Flow’

and ‘Logic Level’ view.

In ‘Current Flow’ view, the tracks

are colour coded depending on the

instantaneous voltage and ‘marching

ANTSmDEMONSTRATETHE RATE OFÛOW

of current (Fig. 10.16). This is par-

ticularly useful for understanding

the operation of the circuit, as well

a short period of time you should

receive a completion message de-

tailing the success of your conver-sion (Fig.10.13). Closing this should

reveal your new PCB layout!

Fig.10.14 shows our example

PCB layout; this may vary slightly

Fig.10.12 (above left). The ‘Convert to PCB layout’ toolbar button

'JH"VUPNBUJDSPVUJOHDPOÜSNBUJPO

Fig.10.14. Example PCB layout for the simple light-operated switch circuit inFig.10.11, and wiring the PP3 9V battery to the PCB

schematic, you can also simulate a

virtual copy of your PCB design.

!SWITHAREALCIRCUITWEMUSTÚRSTattach a suitable power supply. Drag

and drop across a PP3 9V battery

from the Off-board Components in

the Component Gallery (Fig.10.15).

Fig.10.15. Off-board Components inthe Component Gallery




Teach-In 2011

Build – The Circuit Wizard wayas providing a comparison for fault

ÚNDINGTESTING OF THE COMPLETED

CIRCUIT 4RY SIMULATING THE CIRCUIT

INTHISMODE

4HEl,OGIC,EVELmVIEWISEXCELLENT

WHENDEALINGWITHDIGITALCIRCUITS

ASITHIGHLIGHTSTHELOGICSTATEOFPINS

AND TRACKS l!RTWORKm SHOWS THE

OUTPUT0#"MASKANDl5NPOPULATEDm

SHOWSTHEPHYSICALBOARDALONGWITH

THESILKSCREENLAYERWHICHCANBE

VERYUSEFULASACONSTRUCTIONALAID

Design output(OWYOUNOWOUTPUTYOURDESIGN

READYFORPRODUCTIONWILLDEPEND

ONYOURCHOSENCIRCUITBOARDPRO-

DUCTIONMETHOD4HEPRINT MENU

&IG ALLOWS YOU TO PRINT

VARIOUSARTWORKINCLUDINGTOPAND

BOTTOM COPPER LAYERS SILK SCREEN

ASWELL ASMIRRORED AND INVERTED

DESIGNS

&OR THOSE USING STANDARD 56

PHOTORESISTBOARDANDATRADITIONAL

ETCHING TECHNIQUE l3OLDER 3IDE"OTTOM!RTWORKmWOULDBEPRINTED

USINGALASERPRINTERONTOACETATE

READYFOR56EXPOSURE)FYOUUSE

ISOLATION GAP ROUTING OR SENDING

YOURDATAAWAYTOATHIRDPARTYFOR

PRODUCTION THEN THE #!$#!-

MENU &IG PERMITS YOU TO

OUTPUTTHE0#"DATAIN$8&.#AND

'ERBERFORMATS3CHOOLSWITH4ECH-

SOFT#!-EQUIPMENTMAYCOPYTHE

0#"DATAANDPASTEITINTO4ECHSOFT

$0#"READYFOR#.#ROUTINGAND

drilling.

More complex circuits!SYOUmVESEEN#IRCUIT7IZARDDOESA

NICEJOBOFAUTOMATICALLYCONVERTINGA

SIMPLECIRCUITINTO0#"WITHNOHELP

FROMTHEUSER(OWEVERWITHAMORE

COMPLEX CIRCUIT YOU MAY NEED TO

MAKEAFEWTWEAKSANDGETABITMORE

INVOLVEDINTHEGENERATIONPROCESS

4ODEMONSTRATETHISWEWILLCONVERT

ASLIGHTLYMORECOMPLEXCIRCUITTHIS

TIMEAASTABLEMODE,%$ÛASHER

CIRCUIT %NTER THECIRCUIT SHOWN IN&IG AND VERIFY ITS OPERATION

THROUGHSIMULATION

&OLLOWTHROUGH THE0#"CONVER-

SIONPROCESSASYOUDIDFORTHEÚRST

Fig.10.16. Current Flow view of the PCB

Fig.10.17. The Circuit Wizard PCB print menu

Fig.10.18. Circuit Wizard’s CAD/CAM menu 'JHBTUBCMFNPEF-&%ÝBTIFS




Teach-In 2011

CIRCUIT/NCECOMPLETEYOUMAYÚND

that you receive a routing message

similar to that shown in Fig.10.20,

explaining that the software was

unable to completely convert your

circuit automatically.

In our example, you can see that

ONLYOFTHECONNECTIONSCOULD

BEMADE)TISIMPORTANTTONOTETHAT

you may be more or less successful

THANOUREXAMPLECIRCUITDEPENDING

ONHOWYOUHAVEDRAWNYOURCIRCUIT

ANDYOURSOFTWARESETUP4HEDESCRIPTIONHEREISINDICATIVE

OFHOWTODEALWITHA0#"THATFAILS

to completely route using the auto-

matic routing feature. Inspecting the

GENERATED DESIGN &IG YOU

CANSEETHATTHESOFTWAREINSERTEDA

JUMPER ANDONECONNECTIONCOULD

NOTBEMADEATALLSHOWNBYATHIN

GREENLINE

.OTETHISDOESNOTMEANTOSAYTHAT

it is impossible to wire the circuit,

just that the software was unable to

DOSOAUTOMATICALLYANDORUSINGTHECURRENT CONÚGURATION &ORTUNATELY

we can step in here to make the job

of the software a little easier.

Rats nest2ETURN TO YOUR CIRCUIT DIAGRAM

ANDREPEATTHECONVERSIONPROCESS

However, this time select ‘Rats Nest;

.O 0LACEMENT OR 2OUTINGm ON THE

SECOND SCREEN OF THE WIZARD 9OU

SHOULD THEN BE PRESENTED WITH A BLANK 0#" BOARD AND A SET OF THE

REQUIREDCOMPONENTSASSHOWNIN

Fig.10.22.

The pins of the components are

LINKEDBYGREENLINESSHOWINGWHERE

THECONNECTIONSAREREQUIRED4HIS

mass of criss-crossing wires is often

REFERREDTOASAlRATSNESTm

We now have to place the com-

PONENTSONTOTHE0#"2ATHERTHAN

simply placing components at ran-

DOMWHATWEARELOOKINGTODOHERE

is to place the components so that

THEYCANBEROUTEDWITHTRACKSINTHE

EASIEST ANDMOSTEFÚCIENTMANNER

We might also require componentsINSPECIÚCLOCATIONSFOREXAMPLEAN

OFFBOARDCONNECTORATTHESIDEOFTHE

0#"ORTHEÚXEDLOCATIONOFAN,%$

so that it locates in the right place

ONAÚNISHEDPRODUCT

To achieve the former, it is es-

sentially a case of placing the

components so that there are as few

cross-overs of green lines as possible.

Hence, this will make the job of rout-

INGTHETRACKSASEASYASPOSSIBLEAND

AVOID THEREQUIREMENT OF JUMPERS

Fig.10.20. Automatic routing message for the circuit of Fig.10.19

Fig.10.21. The generated PCB layout showing incomplete routing Fig.10.22. Starting point for the ‘rats nest’ PCB layout




Teach-In 2011


links. As well as component position,

their orientation may be altered by

rotation (keyboard shortcut CTRL+R).

Notice that as you move compo-

nents to a new location, the green

lines will update to the nearest com-

mon point for that net. This allows

YOU TO SIGNIÚCANTLY SIMPLIFY THE

rats nest prior to routing the tracks.

Fig.10.23 shows an example layout

which places the battery connector

at the edge of the board and attempts

to leave the rats nest as clean as

possible.

On trackAt this point we can either start to

draw our tracks manually in-line

with the green nets, or instruct

Circuit Wizard to attempt to auto-

matically route the board now that

we have prepared the component

LAYOUTMOREEFÚCIENTLY4HEAUTHORmSpersonal preference is to have the

software route the tracks automati-

cally, then go in and modify the

results as required to achieve a

NICENEATJOB(OWEVERITmSUPTO

the individual user to experiment

and decide upon their favoured

approach.

To initiate automatic routing, click

ONTHEl0#",AYOUT4OOLSmICONFROM

THETOOLBARANDSELECTl!UTO2OUTEcm

(Fig.10.24). Our completed auto

Fig.10.23. Improved layout using ‘rats nest’ technique

Fig.10.25. The completed auto-routed layout

Fig.10.24. Selecting auto-

matic routing from the PCBLayout Tools menu

Fig.10.26. The track button

Fig.10.27. A manually add-ed PCB track

routed layout looks as shown in Fig.10.25. The layout is now complete

and ready for virtual simulation and

output for production.

If you prefer to draw the tracks

manually (or indeed if Circuit Wiz-

ard fails to route your circuit auto-

matically) select the track button

from the toolbar (Fig.10.26). Tracks

are started by left-clicking with ad-

ditional segments added by further

LEFTCLICKING AND ARE ÚNISHED BY

right-clicking.

Previous users of PCB drafting

SOFTWAREWILLÚNDTHETRACKDRAWING

PROCESSFAMILIARWHEREASÚRSTTIME

USERSMAYÚNDITTAKESALITTLEPRAC-

tice for it to become intuitive. You

MAYÚNDIT EASIER TOUSE l.ORMALm

view for manual track drawing.

Fig.10.27 shows a track manually

added to the 555 circuit.

#ONlGURATIONªOPTIONSA number of additional PCB con-

VERSION CONÚGURATION OPTIONS ARE

available through the PCB wizard.

On the second screen, tick ‘Allow

me to customise the PCB layout con-

VERSIONm9OUWILLTHENBEPROVIDED

with many additional options as

you proceed through the conversion

process.

One of these additional con-

ÚGURATIONS IS THE ABILITY TO ALTER

the physical component mappings.When converting to a PCB, Circuit

Wizard selects the most appropriate

PCB component footprint based on

the component variant and values

selected.

However, there may be times when

you wish to specify a different model

from that chosen by default. The

screen shown in Fig.10.28 will be

included in the wizard when the tick

box is checked as described earlier,

allowing you to alter the package




Teach-In 2011

used for each component (in this

case showing the package selection

window for the battery, B1).

On the subsequent wizard screen

you are given a number of compo-

nent placement options. An inter-

esting option is ‘Take into account

component positions’. When Circuit

Wizard converts to a PCB it tries to

order the components as you have

set them out on your schematic.

This may be convenient for keep-ing component numbering sequen-

tial. However, in practice this is not

always the best way to place com-

PONENTSFOREFÚCIENTROUTING

)FYOUÚND YOURCIRCUITSARE NOT

automatically routing and/or the

components are being placed in a

Fig.10.28. Specifying different component models

Fig.10.29. An example of a Quality Check Report

poor manner, try unticking this op-

tion. This can have a dramatic effect

on the results.

Finally, one really

useful tool is Qual-

ity Check. This may

be accessed from the

PCB Layout Tools

icon on the toolbar, or

by selecting ‘Project’,

‘PCB Components’

then ‘Quality Check’

from the menu.

This will analyse

the PCB layout in

comparison to your

circuit diagram, to

ensure that all of the

connections have

been made correctly,

as well as various

other checks. This is

particularly usefulwhen routing manu-

ally to check the con-

nectivity of your de-

sign. Fig.10.29 shows

an example Quality

Check Report.

We’ve really only

scratched the surface

of the PCB conver-

sion and drafting

tools within Circuit

Wizard. As with any

software tool, the best way to learn

more is to get ‘hands on’ and use

the software.

In the next edition of Build we’ll be

giving you the opportunity to do just

that with a range of project circuits

for you to enter, test, convert and

build using all of the skills you’ve

learnt throughout the series.

Answers to Check

questions

10.1 See page 43 and page 44

10.2 (a) 83.0mA AC

(b) 180:

10.3 (a) Sine wave; 5ms period(frequency = 200Hz); am-

plitude 6V pk-pk

(b) Pulse wave; 8ms period(p.r.f. = 125Hz; high time= 2ms, low time 6ms; 25%duty cycle (mark-to-spaceratio = 1:3; (amplitude2.5V pk-to-pk

10.4 See page 46 and Table 10.1






Teach-In 2011

Fig. 10.30 shows a simple regulated power

supply and three common items of test

equipment.

1. Photocopy the diagram and add connect-

ing wires to the diagram in order to show:

(a) How the collector current of transistor

TR1 is measured

(b) How the base-emitter voltage of TR1 is

measured.

2. For (a) and (b) above, list the initial ad-

justments that should be made to the test

equipment.

3. If the output voltage of the circuit is meas-

ured at 0V and the input voltage as 15.1V, what

measurements would you make, and in what

order, to locate the fault? Explain your answer.

Amaze

Investigate

In our everyday lives we are increas-

ingly reliant on highly complex

electronic systems that involve large

numbers of individual component

parts. However, because each indi-

vidual part can be prone to failure,

we need to ensure that each com-

ponent has a very high reliability in

order to ensure that the equipment

as a whole remains free from failure.

Reliability (ie, the ability to operate

without failure) is thus a paramount

consideration for those involved with

the design of electronic equipment.

To put this into context: suppose

that we know that one out of every

100000 of a particular component

type is likely to break down every

hour. This implies that an item of

equipment that makes use of 100

of these components would break

down at an average interval of 1000

hours or less than 42 days operation.

In many cases this would be woe-

fully inadequate!

The requirement for a very high

degree of reliability is crucial in

many applications. In satellite com-

munications, the electronics is often

expected to operate for at least 20

years without failure, simply because

it would be impossible to recover and

repair the satellite without spending

far more than the satellite was actual-

ly worth. Added to this, there would

be considerable loss of revenue while

the satellite was out of service: in

many cases this might amount to

millions of pounds or dollars.

The failure rate of individual com-

ponents depends on the situation and

environment in which they are used.

A satellite experiences extreme forces

and temperatures during launch and

MANOEUVREINTOÚNALORBIT

In consequence, the environment

in which a satellite operates is con-

sidered severe when compared with

that in which most consumer elec-

TRONICEQUIPMENTÚNDSITSELF&ORTHIS

reason, we need to ensure that only

the most reliable types of electronic

component are used in satellites.

But just how reliable are the elec-

tronic components used in the circuits

that you construct? A single low-cost

metal oxide resistor operated within

its rating and in a benign environment

can be expected to a have working life

of more than 1000 years. The same

ITEMÚTTEDINTOASATELLITEWOULDNEED

to have a reliability that is at least ten

times and preferably more than 100

times greater than this!

Next month!In next month’s Teach-In 2011 we

round up the series with a brief

look back at previous parts. We shall

also be including some fun revision

activities as well as essential refer-

ence information. Our series con-

cludes with a selection of electronic

projects that you can build and test

using Circuit Wizard.

Fig.10.30. See Investigate



HandsOn Technology http://www.handsontec.com

1

ISP to ICP Programming Bridge: HT-ICP200

In-Circuit-Programming (ICP) for P89LPC900 Series of 8051 Flash μController…

…ICP uses a serial shift protocol that requires 5 pins to program: PCL, PDA, Reset, VDD and

VSS. ICP is different from ISP (In System Programming) because it is done completely by

the microcontroller’s hardware and does not require a bootloader…

That the 80C51-based controllers are extremely popular is nothingnew, certainly when considering the large number of designs thatcan be found on the web. The reason may well be the fact that thetools (both hardware and software)that are available for this controller are very affordable and there isan enormous amount of information readily available. In addition, avery active forum provides answers to many questions.One of the most significant features of the P89LPC900 Family isthat the core now requires only 2-clock Cycles Per Instruction

(CPI). 8051 experts will already know that this used to be 12 or 6cycles until now. In practice, this means that the crystal frequencycan be drastically lowered to achieve the same processing speed astheir classic counter parts.

ISP Programming is only available for 20, 28 and 44pin parts. IAP is only available once your IAP program has beenloaded in to the LPC900 part. ICP -can be used to program all the LPC900 parts.

The LPC90x devices can only be programmed using a ICP programming method. In contrast to some of the largerLPC900 family members, the LPC90x devices do not offer other programming methods like Parallel Programming, In-System Programming (ISP) or complete In-Application Programming (IAP). HOWEVER - ICP requires hardware control/signaling of the LPC900 to be programmed.In some high-end applications, there may be a need to replace the code in the microcontroller without replacing the ICitself. This article described in detail the operation of the In-Circuit-Programming (ICP) capability which allows these

microcontrollers to be programmed while mounted in the end product.

P89LPC9xx parts (affectionately know as the LPC900 series of micro-controllers) can be programmed 4 ways...

1. ISP (In-System-Programmed) using the UART of the LPC900.2. IAP (In-Application-Programmed) .. or "self programmed" by reprogramming the flash under code execution.3. ICP (In-Circuit-Programming)... using "Synchronous Serial".... Similar to SPI signaling - each data bit is clocked

in/out under clock signal control.4. Parallel Programmer, available in expensive industry grade tools.

1. INTRODUCTION

HT-ICP200P89LPC900 Target

Application Board

To communicate between a PC (running Flash Magic) and the LPC900 Micro-Controller to be programmed an "ICPBridge" circuit is required as shown in Figure 1.

Figure 1: Hooking up ICP to the P89LPC900 Application Board



46 Everyday Practical Electronics, September 2011

Teach-In 2011


Part 11: Summing it all up




units of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced

READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª





TEACH-IN 2011


TO ELECTRONICS

I

N THIS instalment of Teach-In

2011, we bring our series to aconclusion with a quick review

of the previous ten parts, and include

a comprehensive index that will

help you to locate the key topics

that we’ve introduced as the series

has progressed. There’s also a selec-

tion of questions and fun activities,

including a crossword, that will help

you to check your understanding.

For good measure, we’ve also in-

cluded eight additional circuits for

you to investigate using the Circuit

Wizard software.

,OOKINGªBACKWe began our Teach-In series by

looking at the signals that are used

to convey information in electronic

circuits. We discussed the units and

quantities that we use when making

measurements in electronic circuits,

and how waveforms are used to

show how the voltage and current

in an electronic circuit vary with

time. We also introduced batteries

and power supplies that we use to

provide power to electronic circuits.

Part 2 dealt with resistors, capaci-

tors, timing circuits and Ohm’s Law.We also found out what happens

when a capacitor is charged or dis-

charged.

Part 3 provided you with an intro-

duction to diodes and power sup-

plies. We investigated the voltage/

current characteristics for two dif-

ferent types of diode, and showed

how they could be used together

with a transformer to produce a

power supply. We also looked at

light emitting diodes (LEDs) and

Zener diodes.

Learn



Everyday Practical Electronics, September 2011 47

Teach-In 2011

Crossword Check – How do you think you are doing?

11.1. Solve the crossword shown in Fig.11.1.

Clues across

5 Amplitude (4)

7 Instrument for measuring current (7)

8 Polarised capacitor (12)

10 Commonly used for logarithmic ratios (7)

15 Most positive connection of an

NPN transistor (9)

18 Very common type of waveform (4)

19 Stores electric charge (9)

20 Unit of potential difference (4)

21 Instrument used to display waveforms (12)

22 P in PRF (5)

26 Most positive connection on a conducting diode (5)

27 ×0.000001 (5)

29 Peak or maximum value (9)

30 Unit of frequency (5)

Clues down

1 Used to produce delays (5)

2 Diode voltage reference (5)

3 Present on the plates of a capacitor (6)

4 Time for one cycle (6)

6 Circuit that has no stable state (form

of oscillator) (7)

9 !LLOWSCURRENTTOÛOWINONE

direction only (5)

11 C in CRT (7)

12 )NPUTOFACOMMONEMITTERAMPLIÚER

13 Fast analogue-to-digital converter (5)

Transistors were the subject of

Part 4. We described the opera-

tion of NPN and PNP transistors,

and explained how they are used

to amplify current and operate as

saturated switches.

An introduction to operational

AMPLIÚERSOPAMPSWASTHESUBJECT

of Part 5. We showed how opera-

TIONALAMPLIÚERSCANBECONNECTED

in inverting , non-inverting and dif-

ferential arrangements, as well as

showing how they could be used as

comparators, where one voltage is

compared with another.

Logic circuits were explained in

Part 6. Here we met the symbols,

truth tables and Boolean logic for

each of the most common types of

logic gate. We also introduced bist-

able devices, and showed how they

could be used in binary counters.

The highly versatile electronic timer

(555/6) was introduced in Part 7.

These versatile circuits can be used

to produce accurate time delays and

repetitive pulse waveforms.

Analogue circuit applications, in

THEFORMOFATTENUATORSANDÚLTERS

were described in Part 8. We ex-

plained the characteristics of low-

PASSHIGHPASSANDBANDPASSÚLTERS

and showed how these could be built

using simple arrangements of resis-

tors, capacitors and inductors. We

also introduced some simple active

The month’s Check panels provides you with an opportunity to test your understanding of the previous

ten parts of our Teach-In 2011 series.

5IFÜSTURVFTUJPOUFTUTZPVSLOPXMFEHFPGTPNFPGUIFUFSNTUIBUBSFDPNNPOMZVTFEJOFMFDUSPOJDT

14 ×1,000,000 (4)

16 Steps alternating voltage up or down (11)

17 Most positive connection of a PNP transistor (7)

19 Smallest indivisible part of a battery (4)

23 L in LED (5)

24 Unit of capacitance (5)

25 ×0.001 (5)

28 Unit of resistance (3)

Crossword solution – page 53

'JH$PNNPOUFSNTVTFEJOFMFDUSPOJDT




Teach-In 2011


The next question tests your ability to recognise

the symbols used in circuit diagrams:

11.2. Identify each of the symbols shown in

Fig.11.2.

Question11.3 and Question 11.4 test your ability

to extract information from a waveform:

11.3. For the waveform shown in Fig.11.3(a):

(a) What type of waveform is shown?

(b) What is the frequency of the waveform?

(c) What is the periodic time of the waveform?

(d) What is the amplitude (peak value) of the

waveform?

11.4. For the waveform shown in Fig.11.3(b):

(a) What type of waveform is shown?

(b) What is the pulse repetition frequency of

the waveform?

(c) What is the periodic time of the waveform?

(d) What is the duty cycle of the waveform

(e) What is the peak-peak value of the waveform?

Fig.11.2 See Question 11.2

Fig.11.3 (right). See Question 11.3 and Question 11.4

ÚLTERSBASEDONOPAMPS&ORGOOD

measure, we explained how decibels

are used to express gain or loss in

electronic circuits.

In Part 9, we showed how an

analogue signal can be converted

to digital data, and vice versa. We

described the process of quantisa-

tion and explained how the number

of data bits affects the accuracy and

resolution of a DAC and ADC.

Part 10 dealt with the practical

aspects of constructing and testing

electronic circuits. We introduced

some basic items of test equipment in

the form of multimeters and oscillo-

scopes, and showed how these could

be used to measure voltage, current,

frequency, time and waveform in an

electronic circuit.




Teach-In 2011

Quantity Unit Abbreviation

Electric potential Volt

Ampere A

Electric power W

Capacitance F

Resistance Ohm

Frequency Hz

Bit rate Bps

Definition Unit

The potential that appears between two points when acurrent of 1 Ampere flows in a circuit having aresistance of 1 Ohm

The current that flows in an electrical conductor whenelectric charge is being transported at the rate of 1Coulomb per second

1 Watt

The resistance of a circuit when a current of 1 Ampereflowing in it produces a potential difference of 1 Volt

1 Hertz

Question 11.7 tests your ability to convert multiples and sub-multiples to fundamental units:

The next two questions test your knowledge of some of the units and quantities used in electronics:

11.5. Complete the table of electrical quantities and units of measurement

11.6.#OMPLETETHETABLEOFDEÚNITIONSSHOWNABOVE

11.7. Express:(a) 250mV in V(b) 0.15mA in PA

(c) 68000: in k:(d) 0.235W in mW(e) 0.22M: in k:

(f) 885Hz in kHz(g) 1500pF in nF(h) 1.2kbps in bps

The next question tests your ability to recognise some common electronic components:

11.8. &IG SHOWS A KIT OF PARTSneeded to build a simple astable LEDÛASHER)DENTIFYTHEPARTSMARKED!TO)

Question 11.9 checks a basic under-standing of basic digital logic:

11.9. 3KETCH LOGIC CIRCUITS SHOWINGHOW

(a) a four-input AND gate can be builtUSINGTHREETWOINPUT!.$GATES

(b) a four-input OR gate can be builtUSINGTHREETWOINPUT/2GATES

CATWOINPUT!.$GATECANBEBUILTFROMTWOTWOINPUT.!.$GATES

DATWOINPUT/2GATECANBEBUILTFROMTWOTWOINPUT./2GATES

Finally, Question 11.10 tests your abil-ity to read and understand a simpleelectronic circuit diagram:

11.10&IGSHOWSTHECIRCUITOFASIMPLEHEADPHONEAMPLIÚERINWHICHALLOFTHEÚXEDRESISTORSHAVEATOLER -ance of ±5%.

A7HATTYPEOFCOMPONENTIS#

B7HATTYPEOFCOMPONENTIS42C7HICHTWOCOMPONENTSARE CON-NECTEDTOTHEBASEOF42

D7HATCOLOURCODEWOULDBEMARKEDON2

E7HICHCOMPONENTISADJUSTABLE

F7HATVOLTAGEWILLAPPEARACROSS#WHEN3ISCLOSED

G)FACURRENTOFM!ÛOWSIN2WHATVOLTAGEWILLAPPEARATTHEBASEOF42

H7HICHCOMPONENTPROVIDESNEGA-TIVEFEEDBACK

Fig.11.5. Seequestion 11.10

Fig.11.4. See question 11.8 The answers to these questions are shown on page 54

volt

ampere

ohm

The potential that appears between two points when acurrent of one ampere flows in a circuit having aresistance of one ohm

The current that flows in an electrical conductor whenelectric charge is being transported at the rate of onecoulomb per second

The resistance of a circuit when a current of one ampereflowing in it produces a potential difference of one volt

1 watt

1 hertz




Teach-In 2011

OVER the Teach-In series, our

Build section has put theory

into practice using Circuit Wizard

to simulate a whole range of elec-

tronic circuits. We’ve shown how

using simulation software is great

for allowing you to really get to the

bottom of how a circuit actually

operates, as well as being a crucial

tool for electronic designers.

In this, the last edition we are giv-

ing you the opportunity to try out

your ‘wizard’ skills with a selection

of practical circuits that you can en-

ter and investigate. For each circuit,

we’ve included a brief description,

along with some suggestions for

experimentation and a few ques-

tions to help test and extend your

understanding of the underpinning

theory. These circuits are a great

starting point for your own projects

and circuit designs.

COIN TOSS

DescriptionThe circuit shown in Fig.11.6 uses a J-K

ÛIPÛOPTHATISCLOCKEDATAVERYHIGH

speed. When switch SW1 is pressed,

THEÛIPÛOPISCLOCKEDANDALTERNATES

at 1kHz (that’s one thousand times a

second).

During this time, the LEDs will ap-

PEAR TO ÛICKER RAPIDLY ORMAY SEEM

dimly lit. When the button is released,

THEÛIPÛOPWILLREMAININONESTATE

and hence one LED will remain lit to

signify either ‘heads’ or ‘tails’. The

circuit is not truly random, but becausethe output is changing so quickly it

would be hard to get a consistent output

by timing the button press.

Investigate:

1. We’ve used the in-built clock de-

vice – try to create your own clockgenerator (perhaps using a 555 asta-

ble or a Schmitt oscillator circuit).

2. The coin toss circuit is not truly


random – how could we generate a

real random selection?3. How could we extend the circuit

to give six outputs – ie, to create an

electronic dice?

Fig.11.6. Coin tosscircuit diagram

EGG TIMER

Description

The egg timer circuit shown in Fig.11.7 is a classic 555

bistable circuit. Switch SW1 selects between a soft-boiled

(~3 min) and hard-boiled (~5 min) egg by changing the

resistor through which capacitor C1 is charged. When

the circuit is powered, the buzzer (BZ1) will sound until

switch SW2 is pressed to start the timer. For this reason a

practical version of this circuit should include a further

toggle switch to connect/disconnect the power supply.

Investigate:

1. Monitor the charge on capacitor C1 by placing a probe

on pin-6/7.

2. Use the theory that you learnt in Part 2 to calculate

the time period for the circuit when timing both soft- and

hard-boiled eggs (note that resistor R3 is in series with

either R1 or R2 when you calculate the total resistance

through which C1 is charged).

3. How would you alter the circuit to give a four-minute egg? Fig.11.7. Egg timer circuit diagram




Teach-In 2011

KNIGHT RIDERLIGHTS

Description

In Fig.11.8, a 4017 dec-

ade counter is used

to produce a ‘running

lights’ sequence illumi-

nating each LED in turn.

Each LED is connected

to two outputs, so that

as the 4017 counts up

further, the LEDs are litagain in reverse order.

This gives the effect of the LEDs run-

ning alternately forward/backwards.

Investigate:

1. The speed of the lights can be

varied by ‘adjusting’ potentiometer

VR1. Check that this works.

Fig.11.8. Knight Rider ‘chaser’ lights

2. The 4017 is clocked by a simple

Schmitt oscillator circuit (IC1a). Use

the Internet and/or other resources to

HELPYOUÚNDOUTMOREABOUT3CHMITT

devices and how they may be used to

make a simple clock signal.

3. What is the purpose of diodes D1

to D8?

INTRUDER ALARM

Description

The circuit shown in Fig.11.9 uses

a thyristor (or silicon controlled

RECTIÚER $7EmVENOTMET THIS

particular device before, but it acts

as a latch to hold the circuit in the

‘on’ state once pushswitch (push-to-

break) SW1 is pressed.

The alarm will remain on until

the circuit is disconnected from the

battery (for example with keyswitch

SW2), even if SW1 is released.

Switch SW1 could be replaced with

a normally closed (NC) pressure

pad, a trip wire or a door contact in

a real circuit.

Investigate:

1. Extend the circuit to include more

than one trigger.

2. Use the Internet and/or other re-

SOURCESTOÚNDOUTHOWATHYRISTOR

works.

3. What would happen if (a) resis-

tor R1 became open-circuit or (b) if

transistor Q1 became short-circuit

between collector and emitter?

Fig.11.9. Circuit diagram for a simple intruder alarm

For more information, linksand other resources please

check out our Teach-Inwebsite at:


4. Why is only one series resistor

(R10) required?




Teach-In 2011


PUSH-ON/PUSH-OFFCONTROL SWITCH

Description

In Fig.11.10, a J-K flip-flop is

clocked on/off when pushswitch

(push-to-make) SW1 is pressed.

The Schmitt trigger inverter (IC2a)

and capacitor C1 are used to de-

BOUNCETHECLOCKINPUTOFTHEÛIP

ÛOP4HEOUTPUTTRIGGERSTRANSISTOR

Q1, which in turn allows current

TOÛOWTHOUGHTHECOILOFTHERELAY

(RL1), and hence completes the

mains voltage circuit and powers

THE LAMP )N THIS WAY THE SAME

PUSHBUTTONMAY BEUSED TO TURN

the light on and off.

Investigate:

7HATISSWITCHlBOUNCEmANDWHY

do we need to reduce it?

2. What would happen if SW1 was

NOTDEBOUNCEDPROPERLY

3. What is the purpose of diode D1?

9V BATTERY TESTER

Description

4HEBATTERYTESTERCIRCUIT&IG

USES THREE CONSECUTIVELY HIGHER

breakdown voltage Zener diodes to

control red, amber and green LEDs

TOINDICATETHEBATTERYVOLTAGE7E

HAVEUSEDAVARIABLEPOWERSUPPLY

TOSIMULATETHEVOLTAGEOFTHEBATTERY

on test.

Investigate:

7HYDORESISTORS2TO2NEEDTO

be different values?

2. What would the effect be of chang-

ing the breakdown voltage of the

Zener diodes?

(OWWOULDYOUALTERTHISCIRCUIT

TO TESTOTHERBATTERYVOLTAGESq EG

5V, 12V etc.?

Fig.11.10. Circuit for a push-on/push-off control switch

Fig.11.11. An LED 9V battery tester circuit



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Teach-In 2011

METRONOME

Description

A 555 timer is used in Fig.11.12 in an

ASTABLECONÚGURATION4HEFREQUENCY

OFTHEOUTPUTISCONTROLLEDBYADJUST-

ING VARIABLE lRESISTORm 62WHICH

VARIESTHESPEEDATWHICHCAPACITOR

# IS CHARGEDDISCHARGED !S THE

OUTPUTPINCHANGESFROM6TO6

,%$S$AND$ARELITALTERNATELY

.OTE THAT #IRCUIT7IZARDWILL NOT

SIMULATETHElTICKmTHATYOUWOULD

HEARFROMTHESPEAKERASTHEOUTPUT

CHANGESINTHEREALCIRCUIT

Investigate:

7HATISTHEPURPOSEOFCAPACITOR#

(OWCOULDYOUADDANADDITIONAL

RANGE OF TEMPO THAT WOULDBE A

TEN TIMES SLOWER OR B TEN TIMES

FASTERTHANTHEORIGINALRATE7HAT

SINGLE COMPONENT WOULD NEED TO

BECHANGED

TEMPERATURE-CONTROLLED FAN

Description

! SIMPLE POTENTIAL DIVIDERDRIVEN

SENSORCIRCUITISSHOWNIN&IG

!S THE TEMPERATURE CHANGES THE

RESISTANCE OF THE THERMISTOR 2

CHANGESACCORDINGLY4HISAFFECTSTHE

VOLTAGEATTHEBASEOFTHETRANSISTOR

/NCETHISVOLTAGEISSUFÚCIENTTHE

TRANSISTORWILLALLOWCURRENTTOÛOW

TROUGHTHECOILOFTHERELAYDOWNTOGROUND6THUSCOMPLETINGTHEFAN

CIRCUIT6ARYING62WILLADJUSTTHE

POINTATWHICHTHEFANISACTIVATED

Investigate:

(OWCOULDYOUIMPROVETHISCIRCUIT

BYUSINGANOPERATIONALAMPLIÚER

7HATWOULDHAPPENIFTHETHER-

MISTORWENTOPENCIRCUIT

7HATDOESDIODE$DO5SETHE

)NTERNET ANDOR OTHER RESOURCES TO

ÚNDOUT

Fig.11.12. Metronome circuit using a 555 timer IC

Fig.11.13 (above).Temperature-con-trolled fan circuit

Fig.11.14 (right).Answer to

Question 11.1




Teach-In 2011

Answers to Check questions

11.1. See Fig.11.14

11.2. (a) switch (SPST)

BRESISTORÚXED

CTRANSFORMERIRONCORED

DLIGHTEMITTINGDIODE,%$

ECAPACITORÚXEDNONELECTROLYTIC

FVARIABLEPOTENTIOMETER

GELECTROLYTICCAPACITORH!.$GATE

IOPERATIONALAMPLIÚER

JCELLORBATTERY

(k) preset potentiometer

LVARIABLECAPACITOR

M.0.BIPOLARJUNCTIONTRANsistor (BJT)

N23BISTABLEORÛIPÛOP

OBRIDGERECTIÚER

11.3. (a) sinewave

(b) 40Hz

(c) 25ms

D6

11.4.APULSEREPETITIVE

(b) 5ms

(c) 200Hz

D

E6

11.5.6ELECTRICCURRENTWATTFARAD:HERTZBITSPERSECOND

11.6.ONEVOLTONEAMPAPOWEROFONEWATTISEQUIVALENTTOONEJOULEOFENERGYBEINGUSEDEVERYSECONDONEOHMASIGNALHASAFREQUENCYOFONEHERTZIF ONECOMPLETECYCLEOCCURSEVERYSECOND

11.7.A6

(b) 150 PA

(c) 68k:

DM7

(e) 220k:

(f) 0.885kHz

(g) 1.5nF

(h) 1200bps.

11.8. (a) resistors (4)

(b) preset potentiometers (2)

CSLIDESWITCH$0$4

DLIGHTEMITTINGDIODES

(e) transistors (2) FELECTROLYTICCAPACITORS

GPRINTEDCIRCUITBOARD

HBATTERY600TYPE

IBATTERYCONNECTOR

11.9. See Fig. 11.15

11.10.AELECTROLYTICCAPACITOR

(b) PNP transistor

C2AND2

DBROWNREDYELLOWGOLD

E26

F6

G6

(h) R2.

Fig.11.15. Answer toQuestion 11.9

Round-up/VERTHELASTTENPARTSOFOURTeach-

In 2011SERIESWEmVEATTEMPTEDTO

COVERTHECOREELECTRONICSSYLLABUS

TAUGHTINMANYSCHOOLSANDCOLLEGES

INTHE5+7EmVEINTRODUCEDEACH

OFTHEMAINTOPICSSTUDIEDAT,EVEL

EQUIVALENTTO'#3%ASWELLASA

FEWTHATBRIDGETHEGAPINTOFURTHER

STUDIES AT ,EVEL EQUIVALENT TO

!LEVEL

l"UILDm PROVIDES YOUWITHEIGHT

ADDITIONALCIRCUITSTOBUILDANDIN

VESTIGATEUSING THE#IRCUIT7IZARD

SOFTWARE!LLOFTHESECIRCUITSCANBE

MODIÚEDANDEXTENDED ANDWEmVE

SUGGESTED HOW THIS CAN BE DONE

ANDTHINGSTHATYOUMIGHTWANTTO

TRY!SMENTIONEDPREVIOUSLYINOUR

SERIESYOUCANLEARNAGREATDEALBY

EXPERIMENTATION

&INALLY WE TRIED TO KEEP THE

MATHEMATICSTOALEVELTHATISSUF

ÚCIENTTOUNDERSTANDANDAPPLYTHE

UNDERPINNINGTHEORYFOREXAMPLE

TOCALCULATETHEVALUESREQUIREDTO

ACHIEVEAPARTICULARTIMECONSTANT

in a C-RCIRCUIT)FYOUAREINTENDING

tOPROGRESSTOHIGHERLEVELCOURSES

IN ELECTRONICS YOU WILL REQUIRE

FURTHER STUDY OF MATHEMATICS AT

,EVEL BUTPLEASEDONmT LETTHIS

PUTYOUOFFqTHEMOSTIMPORTANT

THINGISTODEVELOPAlFEELmFORHOW

ELECTRONICCIRCUITSBEHAVEANDTHE

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lPRACTICALWAYm

'OOD LUCKWITH YOUR STUDIES OF

ELECTRONICS AND DONmT FORGET THAT

lSUMSCIRCUITSUNDERSTANDINGmØ

Mike and Richard Tooley




Teach-In 2011

555 timer 4-53, 7-44, 7-45556 timer 7-46, 7-53

741 operational amplifier 5-48ADC 1-51, 9-49, 9-51AND logic 6-45, 6-47Acceptor circuit 8-49Accuracy 9-49Active filter 8-50Ampere 1-51, 2-51Amplitude 1-53Analogue meter 10-43Analogue signal 1-51, 9-47Analogue-to-digital conversion 1-51, 9-46, 9-49Anode 3-48Astable oscillator 4-55Astable pulse generator 7-48Attenuators 8-46Automatic light switch 5-56Automatic routing 10-49

BJT 4-46, 4-47, 4-48,4-49

Balanced attenuator 8-47Band-gap reference 9-49Band-pass filter 8-47, 8-48, 8-57Band-stop filter 8-47, 8-48Bandwidth 5-51, 8-50Base 4-46Batteries 1-54Bias 3-48, 4-50Binary 6-49, 9-46Binary-weighted DAC 9-48, 9-52Bipolar junction transistor 4-46, 4-47Bistable 6-48

Bits per second 1-51Block schematic 1-55Boolean logic 6-46Bridge rectifier 3-50Buffer 6-46

C-R circuits 2-54C-R high-pass filter 8-48C-R low-pass filter 8-48CLEAR input 6-48, 6-49CMOS 6-50CRT 10-44Capacitors 2-53, 2-57, 2-58Cathode 3-48Cathode ray tube 10-44Cells 1-54

Characteristic impedance 8-50Charge 2-54Circuit Wizard 1-56, 10-48Collector 4-46Collector load 4-50Colour code 2-52Combinational logic 6-47Common base 4-48Common collector 4-48Common emitter 4-48Common-emitter amplifier 4-49, 4-51Comparator 5-53, 5-55Complex waveform 1-52Counter 7-52Current 1-51Current gain 4-49, 4-53, 5-50,

8-50Current measurement 10-43, 10-44

Cut-off frequency 5-52, 8-51, 8-49

D-type bistable 6-48, 6-50

DAC 1-51, 9-47, 9-49DIL package 6-50Darlington transistor 4-48Decade counter 6-54Decay 2-55Decibels 8-50Depletion mode MOSFET 4-48Dielectric 2-53Differential amplifier 5-52Digital logic 6-44Digital meter 10-43Digital signal 9-47Digital-to-analogue conversion 9-47Digital-to-analogue converter 1-51Diode characteristics 3-49, 3-51Diodes 3-48, 3-52Discharge 2-54Dual timer 7-52Dual-in-line 6-50Dual-slope ADC 9-51Duty cycle 1-54

Electric charge 2-54Electrolytic capacitor 2-53Emitter 4-46Energy storage 2-54Enhancement-mode MOSFET 4-48Equivalent circuit 5-50Exclusive-NOR logic 6-46, 6-47Exclusive-OR logic 6-46, 6-47Exponential decay 2-55Exponential growth 2-55

FET 4-46, 4-47Feedback 4-51Field effect transistor 4-46, 4-47Filters 8-47, 8-51Fixed resistor 2-51Flash ADC 9-50Follower 5-52, 5-53Forward bias 3-48Frequency 1-53Frequency response 5-51, 5-52Full-wave rectifier 3-50

Gain 4-53, 5-50, 5-51Gain-bandwidth product 5-51Gates 6-45Germanium 3-49

Giga 1-52Graticule 10-44Growth 2-55Half-wave rectifier 3-50Hertz 1-51High-frequency cut-off 5-52High-frequency roll-off 5-52High-pass filter 8-47, 8-48, 8-51,

8-50, 8-56Input resistance 5-50Integrated circuits 5-48Intruder alarm 6-53Inversion 6-46Inverter 6-46, 6-47Inverting amplifier 5-52, 5-54Inverting input 5-49

J-K bistable 6-48, 6-49JFET 4-48

TEACH-IN 2011 – Topic Index




Teach-In 2011Kilo 1-52Kitchen timer 7-50

L-C band-pass filter 8-49L-C band-stop filter 8-49LDR 2-51LED 3-50, 3-51, 3-55LED flasher 7-51Light-dependent resistor 2-51Light-emitting diode 3-50Light-emitting diodes 3-51Load 4-48, 4-50Logic 6-44, 6-47Logic 0 6-44Logic 1 6-44Logic gates 6-45, 6-46, 6-52Low-frequency cut-off 5-52Low-frequency roll-off 5-52Low-pass filter 8-47, 8-48, 8-51, 8-50, 8-55

MOSFET 4-48MSB 9-46

Matching 8-50Mega 1-52Micro 1-52Mid-band 5-52Milli 1-52Monostable pulse generator 7-46Most significant bit 9-46Motor control circuit 4-53Multimeters 10-42, 10-43Multiples 1-52Music 1-52

N-type material 3-48, 4-46NAND logic 6-46, 6-47NOT logic 6-46NPN transistor 4-46, 4-47

Nano 1-52Negative feedback 4-51, 5-51Non-inverting amplifier 5-52Non-inverting input 5-49

OR logic 6-45, 6-46, 6-47Off state 6-44Off time 1-53Ohm 1-51, 2-51Ohm’s Law 2-50, 2-56On state 6-44On time 1-53, 7-46Operating point 4-50Operational amplifier 5-48, 5-49Oscillator 4-55, 5-56Oscilloscope 10-44, 10-45Output resistance 5-50

P-type material 3-48, 4-46PCB 10-48PNP transistor 4-46, 4-47PRESET input 6-48, 6-49Parallel plate capacitor 2-53Periodic time 1-53Phase shift 5-49Photodiode 3-50Pi-network 8-47Polarising voltage 2-53Potentiometer 2-51Power gain 5-50, 8-50Power supplies 1-54Pre-set resistor 2-51Printed circuit board 10-48

Pulse generator 7-46, 7-48Pulse period 1-53

Pulse repetition frequency 1-53, 7-48Pulse waveform 1-52, 1-53

Q-factor 8-50Quantisation 9-46, 9-47

R-2R ladder DAC 9-48RESET input 6-48Ramp waveform 1-52Ramp-type ADC 9-50, 9-51Rats nest 10-51Rectifier 3-50Rectifier diode 3-49, 3-50Rejector circuit 8-49Resistor colour code 2-52Resistors 2-51Resolution 9-49Resonance 8-49Reverse bias 3-48Ripple counter 6-53Roll-off 5-52

SET input 6-48

Sallen and Key filter 8-50Saturated switch 4-52Sawtooth waveform 1-52Schematic diagram 1-55Second-order filter 8-56Semiconductor 3-48Signal diode 3-50Signal diodes 3-49Signals 1-51, 1-50Silicon 3-49Simulation 1-56Sinking 7-45Sourcing 7-45Speech 1-52Square wave generator 7-49

Sub-multiples 1-52Successive approx. ADC 9-50

T-network 8-47TTL 6-50Temp.-sensitive resistor 2-51Termination 8-50Thermistor 2-51Time constant 2-55Timer circuit 7-47Timing diagram 6-48, 6-49Tolerance 2-51Transfer characteristic 4-49Transformers 3-50Transistor amplifier 4-54Transistor switch 4-51Transistors 4-46

Triangle waveform 1-52Trigger input 7-48

Unbalanced attenuator 8-47

Valves 5-57Variable capacitor 2-53Variable resistor 2-51Virtual instrument 10-45Virtual test 10-49Volt 1-51, 2-51Voltage follower 5-52, 5-53Voltage gain 5-50, 5-51, 8-50Voltage measurement 10-43, 10-44

Watt 1-51Waveform measurement 10-45Waveforms 1-52, 1-58

Zener diode 3-50, 3-51, 3-54



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