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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TORECOGNISESIGNALSFROMTHESHAPEOFTHEIRWAVEFORMS
"EINGABLETOlREADmANDINTERPRETACIRCUITDIAGRAMOR lSCHEMATICm IS ANESSENTIALSKILLREQUIREDOFEVERYELEC
TRONICTECHNICIANANDENGINEER-ANYDIFFERENTPARTSANDDEVICESAREUSEDINELECTRONICCIRCUITSANDITISIMPORTANTTHATYOUSHOULDBEABLETORECOGNISETHEMBOTHFROMTHESYMBOLSTHATWEUSETO REPRESENTTHEMIN THEORETICALCIRCUITDIAGRAMSANDALSOFROMTHEIRPHYSICALAPPEARANCE
ERSFORMSOFlBODYLANGUAGEm)NFACTLIFEWOULD BEVERY DIFÚCULTWITHOUTSIGNALS q THINK ABOUT DRIVING A CARORMOTORBIKEINHEAVYTRAFÚCØ)NTHISSECTIONWEWILLLOOKATHOWSIGNALSARE
USEDINELECTRONICSHOWTHEYCANBECONVERTEDFROMONEFORMTOANOTHERANDHOWTHEYAREMEASURED
)N ELECTRONICS SIGNALS CAN TAKEMANY FORMS INCLUDING CHANGES INVOLTAGELEVELSPULSESOFCURRENTANDSEQUENCESOFBINARYCODED DIGITS ORCJUT3IGNALSTHATVARYCONTINUOUSLYINLEVELAREREFERREDTOASANALOGUESIGNALSWHILETHOSETHATUSEDISCRETEIEÚXEDLEVELSAREREFERREDTOASDIGITAL SIGNALS 3OME TYPICAL ANALOGUE ANDDIGITALSIGNALSARESHOWNIN&IG.OTICE HOWTHEDIGITAL SIGNAL EXISTS
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3IGNALSªINªELECTRONICªCIRCUITSªANDªSYSTEMS
4HISÚRSTPARTOFOUR4EACH)NSERIESWILLPROVIDEYOUWITHANINTRODUCTION TO THE SIGNALS THAT CONVEY JO GPSNBUJPOINELECTRONICCIRCUITS7EWILLALSOINTRODUCEYOUTOSOMEOFTHEUNITSTHATAREUSEDWHENMEASURINGELECTRICAL QUANTITIES SUCH AS CURRENTVOLTAGEANDFREQUENCY9OUWILLLEARNABOUTTHEDIFFERENCEBETWEENANALOGUEANDDIGITALSIGNALSANDHOW
,EARN3IGNALSªANDªSIGNALªCONVERSION
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4HESIGNALSTHATWEUSEINEVERYDAYLIFE CANTAKEMANY FORMS INCLUDINGÛASHINGLIGHTSSHOUTINGWAVINGOURHANDS SHAKING OUR HEADS AND OTH
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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
BROADCASTWILLBEANANALOGUESIGNALAT THE POINT AT WHICH THE ORIGINALSOUND IS PRODUCED IE ON STAGE!FTERAPPROPRIATEPROCESSINGWHICHMIGHTINVOLVEAMPLIÚCATIONANDORREMOVALOFNOISEANDOTHERUNWANTEDSOUNDSITMIGHTTHENBECONVERTEDTOADIGITALSIGNALFORRADIOTRANSMISSIONANDTHENCONVERTEDBACKTOANANALOGUESIGNALBEFOREBEINGAMPLIÚEDANDSENTTOTHELOUDSPEAKERATTHEPOINTOFRECEPTION
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%LECTRONICªUNITS!NUMBER OFUNITSARE COMMONLY
USEDINELECTRONICSSOWESHALLSTART BYINTRODUCINGSOMEOFTHEM,ATERWEWILLBEPUTTHESEUNITSTOUSEWHENWE
SOLVESOMESIMPLECIRCUITPROBLEMSBUTSINCEITmSIMPORTANTTOGETTOKNOWTHESEUNITSANDALSOTOBEABLETORECOGNISETHEIR ABBREVIATIONS AND SYMBOLS WEHAVESUMMARISEDTHEMIN4ABLE
0LEASENOTEØ&REQUENCY AND BIT RATE ARE VERY
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52 Everyday Practical Electronics, November 2010
Teach-In 2011
0LEASENOTEØ4O AVOID CONFUSION BETWEEN THE
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USEFORUNITSTHEFORMERARENORMALLYDISPLAYEDINITALICFONT&OREXAMPLEACAPITALLETTER6ISUSEDASBOTHTHEABBREVIATIONFORVOLTAGEANDFORITSUNITSYMBOLTHE6OLT7HENUSEDASASYM BOLIN AFORMULA ITISCONVENTIONALLYSHOWNINITALICAS7 ANDWHENUSEDASSHORTHANDFORVOLTSITISSHOWNINNORMALNONITALICFONTASl6m
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OFTHEELECTRONICUNITSCANBECUMBERSOMEFOREVERYDAYUSE&OREXAMPLETHEVOLTAGEPRESENTATTHEANTENNAOFAMOBILEPHONECOULDBEASLITTLEASONETENMILLIONTHOFAVOLTOR6#ONVERSELYTHERESISTANCESEENATTHEINPUTOFANAUDIOAMPLIÚERSTAGECOULD BEMORETHANONEHUNDREDTHOUSANDOHMSOR:
4OMAKELIFEALOTEASIERWEUSEASTANDARDRANGEOFMULTIPLESANDSUBMULTIPLES4HESEUSEAPREÚXLETTERINORDERTOADDAMULTIPLIERTOTHEQUOTEDVALUEASSHOWNIN4ABLE
0LEASENOTEØ%XPONENTNOTATIONISOFTENUSEFUL
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0LEASENOTEØ-ULTIPLYINGBYISEQUIVALENT
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Multiple Exponent notation Prefix Abbreviation Example
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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
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Everyday Practical Electronics, November 2010 53
Teach-In 2011
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54 Everyday Practical Electronics, November 2010
Teach-In 2011
REPLACE THE ENTIRE UNIT IN MUCH THESAMEWAYASWEWOULDREPLACEASETOFEXHAUSTEDBATTERIES
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0RIMARY CELLS PRODUCE ELECTRICALENERGYATTHEEXPENSEOFTHECHEMICALSFROMWHICHTHEYAREMADEANDONCETHESECHEMICALSAREUSEDUPNOMOREELECTRICITYCANBEOBTAINEDFROMTHE CELL!NEXAMPLE OFA PRIMARY
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Everyday Practical Electronics, November 2010 55
Teach-In 2011
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56 Everyday Practical Electronics, November 2010
Teach-In 2011
2.% OF THE PROBLEMS WITH ELECTRONICSISSIMPLYTHEAMOUNTOF
KITTHATYOUNEEDTOGETSTARTED%VENABASICSTARTERSETUPCOULDRUNINTOHUNDREDSOFPOUNDSSOLDERINGIRONHANDTOOLSCIRCUITBOARDWIRESLEADSCOMPONENTSTESTEQUIPMENTq ITALLADDSUPØ4HEREFORETHEl"UILDmSECTIONOFOUR4EACH)NSERIESISGOINGTOFOCUSAROUNDUSING#IRCUIT7IZARDAREALLYGREATPIECEOFCIRCUITSIMULATIONSOFTWARETHATRUNSONYOUR7INDOWS0#
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58 Everyday Practical Electronics, November 2010
Teach-In 2011
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!NSWERSªTOª1UESTIONS!NALOGUESIGNALSVARYCON
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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
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Bearings from 1mm bore
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Tools
Cable, Fuses &etc..
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50 Everyday Practical Electronics, December 2010
Teach-In 2011
By Mike and Richard Tooley
0ARTªª2ESISTORSªCAPACITORSªTIMINGªANDªDELAYªCIRCUITS
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Everyday Practical Electronics, December 2010 51
Teach-In 2011
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52 Everyday Practical Electronics, December 2010
Teach-In 2011
VALUEANDTHEPOWERRATINGWHICHMUST BE EQUAL TO OR GREATER THANTHEMAXIMUMEXPECTEDPOWERDISSIPATION
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Everyday Practical Electronics, December 2010 53
Teach-In 2011
CHARGE4HEYAREWIDELYUSEDINPOWERSUPPLIESWHERETHEYACTASlRESERVOIRSmFORCHARGEANDALSOINMANYTIMINGANDWAVESHAPINGCIRCUITS#APACITORSWILLPASSALTERNATINGCURRENTSBUTTHEYWILLlBLOCKmDIRECTCURRENTONCECHARGED4HEY ARE THUS USED FOR COUPLINGSIGNALSWHICHARE!#INANDOUTOF
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54 Everyday Practical Electronics, December 2010
Teach-In 2011
PROPERLY4HISVOLTAGEMUSTBEAPPLIEDWITH THECORRECTPOLARITY INVARIABLYTHISISCLEARLYMARKEDONTHECASEOFTHECAPACITORWITHAPOSITIVESIGN
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Everyday Practical Electronics, December 2010 55
Teach-In 2011
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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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56 Everyday Practical Electronics, December 2010
Teach-In 2011
,.4()3MONTHmSl,EARNmSECTIONWEmVE INTRODUCED YOU TO THE
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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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Everyday Practical Electronics, December 2010 57
Teach-In 2011
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58 Everyday Practical Electronics, December 2010
Teach-In 2011
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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…
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48 Everyday Practical Electronics, January 2011
Teach-In 2011
By Mike and Richard Tooley
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Everyday Practical Electronics, January 2011 49
Teach-In 2011
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50 Everyday Practical Electronics, January 2011
Teach-In 2011
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and other resources please
check out our Teach-In
website at:
www.tooley.co.uk/ teach-in
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46 Everyday Practical Electronics, February 2011
Teach-In 2011
By Mike and Richard Tooley
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Everyday Practical Electronics, February 2011 47
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48 Everyday Practical Electronics, February 2011
Teach-In 2011
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Everyday Practical Electronics, February 2011 49
Teach-In 2011
5SINGTHERELATIONSHIP
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50 Everyday Practical Electronics, February 2011
Teach-In 2011
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Everyday Practical Electronics, February 2011 51
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52 Everyday Practical Electronics, February 2011
Teach-In 2011
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For more information, links and
other resources please check out
our Teach-In website at:
www.tooley.co.uk/ teach-in
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 UKshop 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 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
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AGEWOULDYOUEXPECTTOMEASURE
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IS THAT YOU CAN POP VOLTMETERS
AND AMMETERS INTO YOUR CIRCUIT
DESIGNSSOTHATYOUCANTAKEREAD
INGSANDSEEWHATmSGOINGONIN
YOURCIRCUITWITHEASE
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Everyday Practical Electronics, February 2011 53
Teach-In 2011
.OWRUNTHECIRCUITANDÛICKTHE
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54 Everyday Practical Electronics, February 2011
Teach-In 2011
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IDENTIFY THEM LATER ON!S YOUPLACE YOUR
ÚRST PROBE YOUSHOULDNOTICE THAT A GRAPH
WILLAPPEARALONGTHEBOTTOMOFTHESCREEN
4HIS IS GREAT FOR ALLOWING YOU TO MONITOR
HOW VOLTAGES AROUND YOUR CIRCUIT CHANGE
OVERTIME
"EFOREYOUHITlSIMULATEmDOUBLECLICKONTHE
GRAPHANDCHANGETHEGRAPHPROPERTIESTOTHOSE
SHOWNIN&IG4HISWILLSETTHEMINIMUM
ANDMAXIMUMVOLTAGESSHOWNONTHEGRAPH
SEE&IGANDTHETIMESCALETOGIVEYOUANICELOOKINGTRACEFROMTHECIRCUIT
.OW SIMULATE THE CIRCUIT AND
KEEP AN EYE ON THE GRAPH 9OU
SHOULD SEE TWO SINUSOIDAL WAVES
TRACEDOUTSEE&IG4HEÚRST
BLUELINEISTHEINPUTqITHASA RE
ALLYSMALLAMPLITUDEYOUCANBARELY
'JH"EEQSPCFCVUUPO 'JH(SBQIQSPQFSUJFTEJBMPHVFGPSUIFUSBOTJTUPSBNQMJÜFSDJSDVJU
'JH4JNQMF5SBOTJTUPSBNQMJÜFSDJSDVJU
s
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Everyday Practical Electronics, February 2011 55
Teach-In 2011
SEEITRISINGABOVEDIPPINGBELOW
THEAXIS4HEREDLINEHOWEVERISAMUCHLARGERVERSIONOFTHEBLUELINE
4HISISTHEAMPLIÚEDOUTPUTSIGNAL
)THASAMUCHHIGHERAMPLITUDETHAN
THEINPUTSIGNAL
)NTHISCIRCUITTHETRANSISTORACTSAS
ANAMPLIÚER4HETRANSISTORISBEING
PROGRESSIVELYSATURATEDBYTHESMALL
SIGNALINPUTANDSOTHEOUTPUTVARIES
COINCIDENTLYTOTHEINPUT)TmSACTING
ABIT LIKE A TAP BEINGOPENED AND
CLOSEDTOCONTROLTHEÛOWOFCURRENTINTHEOUTPUT
!STABLEªOSCILLATORªCIRCUIT
.OWWEmREGOINGTOSTEPTHINGSUP
ALITTLEANDENTERANOTHERUSEFULREAL
WORLD CIRCUIT INTO#IRCUIT7IZARD
4HECIRCUITSHOWNIN&IGISA
SIMPLECIRCUITTHATÛASHESTWO,%$S
ALTERNATELY
4OGIVEITITSCORRECTNAMEITmSAN
ASTABLEª OSCILLATOR CIRCUIT BECAUSE
ITTURNSONANDOFFCONTINUOUSLY)TUSESAPAIROFTRANSISTORSTHATCONTROL
THECHARGINGANDDISCHARGINGOFTWO
CAPACITORSALTERNATELYqALITTLELIKE
ASEESAW
%NTER THE C IRCUIT SHOWN IN
&IGMAKINGSURETHATYOUGET
ALLOFTHECOMPONENTVALUESCORRECT
ANDTHENHITTHEPLAYBUTTONONTHE
TOPBARTOSTARTTHESIMULATION$ID
ITWORK
4RY OUT THE DIFFERENT DISPLAY
STYLESBYCLICKINGTHETABSALONGTHELEFTOFTHESCREENTHElCURRENTÛOWm
DISPLAYSEE&IGWORKSREALLY
WELL SHOWING HOW THE CURRENT IS
ÛOWING AROUND THE CIRCUIT WITH
THECOLOURSHOWINGTHEVOLTAGESEE
SAWINGONEITHERSIDEOFTHECIRCUIT
ANDTHECHARGESBUILDINGDIMINISH
INGONTHECAPACITORS
&INALLY SAVE YOUR CIRCUIT AS
WEmLLBEUSINGTHEMTOCONSTRUCT
A PRINTED CIRCUIT BOARD LAYOUTLATERON
ªª4HEª#IRCUITª7IZARDªWAY
'JH&YBNQMFUSBDFGSPNUSBOTJTUPSBNQMJÜFSDJSDVJU5IFPVUQVUXBWFGPSNJTTIPXOBUUIFUPQBOEUIFJOQVUXBWFGPSNBUUIFCPUUPN
'JH5XPUSBOTJTUPSBTUBCMFPTDJMMBUPSDJSDVJU
'JH5SBOTJTUPSBTUBCMFPTDJMMBUPSJODVSSFOUÝPXEJTQMBZTUZMF
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56 Everyday Practical Electronics, February 2011
Teach-In 2011
4HECIRCUITOFASIMPLEAUDIOAM
PLIÚERISSHOWNIN&IG3TUDY
THE CIRCUIT CAREFULLY LOOK BACK AT
WHATWEDID IN4EACH)N0ART TO0ARTANDTHENSEEIFYOUCANANSWER
EACHOFTHEFOLLOWINGQUESTIONS
7HAT TYPEOF TRANSISTOR IS A
42ANDB42
7HATOPERATINGMODEISUSED
FORA42ANDB42
7HATTYPEOFDIODEIS$AND
WHATVOLTAGEWOULDYOUEXPECTTO
MEASUREACROSSIT
4HEMAINSOPERATEDPOWERSUP
PLYFORTHEAMPLIÚERISRATEDAT7
7ILLTHISBESUFÚCIENT%XPLAINYOUR
ANSWER
7HATTYPEOFCAPACITORIS#
ANDWHATSHOULDITSRATEDWORKING
VOLTAGEBE
7HATCOLOURCODESHOULDAPPEAR
ONA2B2ANDC2
)FAPOTENTIALDROPOF6AP
PEARSACROSS2WHATCURRENTWILL
BEÛOWINGINIT7HATISTHETIMECONSTANTOFTHE
SERIESCIRCUITFORMEDBY#AND2
3O FAR IN 4EACH)N WEmVE BEEN
USING#IRCUIT7IZARDTOSIMULATEA
VARIETYOFSIMPLEELECTRONICCIRCUITS
SO THAT WE CAN BETTER UNDERSTAND
HOWTHEYWORK(OWEVERYOUMAY
BEWONDERINGHOWWEGETFROMSOME
THINGTHATLOOKSNICEONACOMPUTER
SCREEN TO SOMETHING THAT WE CAN
ACTUALLYBUILDANDUSE
7ELL#IRCUIT7IZARDHASASUPERB
SETOFTOOLSTOHELPSUSDOJUSTTHAT
,OADUPTHETRANSISTORASTABLECIRCUIT
THATYOUMADEINOURl"UILDmTUTORIAL4HENCLICKONTHEl#ONVERTTO0#"
,AYOUTmBUTTONONTHETOOLBAR SEE
&IG
4HISWILLINITIATEASIMPLEWIZARD
THATLETSYOUCONVERTACIRCUITDESIGN
INTO A PRINTED CIRCUIT BOARD 0#"
!MAZE)NVESTIGATE
'JH4FFRVFTUJPOTCFMPX
'JH$POWFSUUP1$#CVUUPO
'JH4FMFDUJOH1$#UZQF
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Everyday Practical Electronics, February 2011 57
Teach-In 2011
DESIGNTHATYOUCANTHENTESTlVIRTU
ALLYmANDORCREATEARTWORKTOPRODUCE
THE0#"FORREAL
3TEPTHROUGHTHEWIZARDBYCLICKING
l.EXTmWEmLLLEAVETHEDEFAULTSETTING
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ASKEDTOCHOOSEA0#"LAYOUTqSELECTl3INGLE3IDED .ORMAL 4RACKSm SEE
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&INALLYCLICKONTHEl#ONVERTmBUTTON
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PONENTSBEINGPLACEDONTOTHECIRCUIT
BOARDANDTHENTHETRACKSAUTOMATICALLY
ROUTEDRIGHTBEFOREYOUREYES
7HEN ITmS COMPLETED CONVERTING
YOURCIRCUITITWILLPOPUPAWINDOWTELLINGYOUHOWSUCCESSFULITmSBEEN
HOPEFULLY ITWILL REPORT THAT
OFTHECONNECTIONSHAVEBEENMADE
#LICKON/+ANDADMIREYOUR0#"
DESIGN#IRCUIT7IZARDGIVESYOU A
REALLYNICEl2EAL7ORLDmVIEWOFWHAT
YOUR PRODUCED CIRCUITWOULD LOOK
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ALONGTHELEFT
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YOUWANTTOGOAHEADANDPRODUCE
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TOOPERATETHECIRCUIT'RABONEFROM
THEl/FF"OARD#OMPONENTSml0OWER3UPPLIESmFOLDERINTHEGALLERY)NTHIS
CASEYOUmLLNEEDA600ALTERNA
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6AS THIS IS THE USUAL
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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!
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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.
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48 Everyday Practical Electronics, March 2011
Teach-In 2011
By Mike and Richard Tooley
0ARTªª/PERATIONALªAMPLIlERS
/URª4EACH)NªSERIESªISªDESIGNEDªTOªPROVIDEªYOUªWITHªAªBROADBASEDªINTRODUCTIONªTOªELECTRONICSª7EªHAVEª
ATTEMPTEDªTOªPROVIDEªCOVERAGEªOFªTHREEªOFªTHEªMOSTªIMPORTANTªELECTRONICSªUNITSªTHATªAREªCURRENTLYªSTUDIEDªINª
MANYªSCHOOLSªANDªCOLLEGESªINªTHEª5+ª4HESEªINCLUDEª%DEXCELª"4%#ª,EVELªªAWARDSªASªWELLªASªELECTRONICSª
UNITSªOFªTHEªNEWª$IPLOMAªINª%NGINEERINGªALSOªATª,EVELªª4HEªSERIESªWILLªALSOªPROVIDEªTHEªMOREªEXPERIENCEDªREADERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
YOUªANªOPPORTUNITYªTOªBUILDªANDªTESTªSIMPLEªELECTRONICªCIRCUITSª)NVESTIGATEªWILLªPROVIDEªYOUªWITHªAªCHALLENGEª
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
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.
4HISALLOWSCOMPLEXCIRCUITSSUCH
ASACOMPLETERADIORECEIVERTOBE
buit in a package that’s saer
THANTHENAILONYOURLITTLEÚNGER
!NYADDITIONALCOMPONENTSSUCH
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
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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
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50 Everyday Practical Electronics, March 2011
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
outAND inARETHEOUTPUTANDINPUT
current respectivey.
out p
in
P A
P =
whereApREPRESENTSVOLTAGEGAINAND
outAND inARETHEOUTPUTANDINPUT
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
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Everyday Practical Electronics, March 2011 51
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= = =
−
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52 Everyday Practical Electronics, March 2011
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.
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Everyday Practical Electronics, March 2011 53
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
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54 Everyday Practical Electronics, March 2011
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
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Everyday Practical Electronics, March 2011 55
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
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56 Everyday Practical Electronics, March 2011
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
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Everyday Practical Electronics, March 2011 57
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
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).
Further information can be found
on the New Wave Concepts website;
www.new-wave-concepts.com. The
developer also offers an evaluation copyof 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.
ig.5.25. alves from the 1940s and 1950s com- pared 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!
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44 Everyday Practical Electronics, April 2011
Teach-In 2011
By Mike and Richard Tooley
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
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
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
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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
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46 Everyday Practical Electronics, April 2011
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
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Everyday Practical Electronics, April 2011 47
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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
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48 Everyday Practical Electronics, April 2011
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
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Everyday Practical Electronics, April 2011 49
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
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50 Everyday Practical Electronics, April 2011
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
of Circuit Wizard can be purchased
from the editorial office of EPE – seeCD-ROMs for Electronics page and
the UK shop on our website (www.
epemag.com).
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 limita-
tions applied, such as only being able
to simulate the included sample circuits
and no ability to save your creations.
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 manu- factured 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
Fig.6.26. See Question 2
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.
Fig.6.28. See Question 5
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Everyday Practical Electronics, April 2011 51
Teach-In 2011
Fig.6.27. See Question 4
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
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52 Everyday Practical Electronics, April 2011
Teach-In 2011
Build – The Circuit Wizard way
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
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Everyday Practical Electronics, April 2011 53
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.)
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54 Everyday Practical Electronics, April 2011
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
Build – The Circuit Wizard way
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?
2. What logic level appears at
points X, Y and Z with the left
wing door open and all other doors
closed?
3. What logic level appears at
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
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44 Everyday Practical Electronics, May 2011
Teach-In 2011
By Mike and Richard Tooley
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
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test siple electronic circuits. nvestigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
TEACH-IN 2011
A BROAD-BASED INTRODUCTION
TO ELECTRONICS
we easure tie with a very high
degree of accuracy.I instaent of each,
we wi bring together severa
iportant ideas and concepts
that we’ve aready et in the
earier parts. t the sae tie,
we wi introduce you to a highy
versatie integrated circuit (), the tier .
sing this , we wi show you
how you can quicky and easiy
design circuits that wi produce
tie deays fro a few hundred
nanoseconds to severa hundred
seconds, and square wave puses of
known frequency, period and duty
cyce. Build and Investigate wi
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
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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
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46 Everyday Practical Electronics, May 2011
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
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Everyday Practical Electronics, May 2011 47
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
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48 Everyday Practical Electronics, May 2011
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
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Everyday Practical Electronics, May 2011 49
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.
ternativey, the graph shown in
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 :
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50 Everyday Practical Electronics, May 2011
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
ternativey, the graph shown in
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:
www.tooley.co.uk/ teach-in
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
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Everyday Practical Electronics, May 2011 51
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 $JSDVJUT), we
constructed a decade (ie, to 9)
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Everyday Practical Electronics, May 2011 53
Teach-In 2011
o use both tiers contained
within the 6 in ircuit izard,
you need to drag two separate in-
stances of the 6 on to the circuit
PAGE4HEÚRSTTIMERWILLBESUFÚXED
‘a’ and the second ‘b’ (eg, 1a and
1b). s both are contained within
ONEPHYSICALPACKAGETHISWOULDBE
REÛECTEDWHENCONVERTINGTOA0#"
FOREXAMPLE
5NLIKE THE SYMBOL THAT HAS
NUMBEREDPINS#IRCUIT7IZARDLA-
BELSTHEPINSOFTHEVERBOSELY
FOREXAMPLETHETHRESHOLDINPUTISLABELLEDl4m!SWITHANYINTEGRAT-
EDCIRCUITBYHOVERINGOVERTHEPIN
YOUAREABLETOSEETHEPHYSICALPIN
LOCATIONINTHETOOLTIPSEE&IG
onstruct the circuit shown in
&IGANDOBSERVEITSOPERATION
"OTHTIMERSARECONÚGUREDINASTA-
BLEMODE4HEÚRSTTIMER#AHAS
A FREUENCY OF ABOUT Z 4HE
output fro this tier is then used
TOSUPPLYTHESECONDTIMER#B
WHICHHASAFREUENCYOFABOUTZuring the period when the
output of tier one is high, the
SECONDTIMERWILLBEACTIVATEDAND
OSCILLATEFOURTIMESHENCEGIVING
FOURÛASHES#ONVERSELYWHENTHE
OUTPUTOFTHEÚRSTTIMERISLOWTHE
second tier is not powered and
SOTHEOUTPUT$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
Circuit WizardA Standard orProfessional version
of Circuit Wizard can be purchasedfrom the editorial office of EPE – see
CD-ROMs for Electronics page and
the UK shop on our website (www.
epemag.com).
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 limita-
tions applied, such as only being able
to simulate the included sample circuits
and no ability to save your creations.
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54 Everyday Practical Electronics, May 2011
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
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Everyday Practical Electronics, May 2011 55
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
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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.
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46 Everyday Practical Electronics, June 2011
Teach-In 2011
By Mike and Richard Tooley
Part 8: Analogue CircuitApplications
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
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
TEACH-IN 2011
A BROAD-BASED INTRODUCTION
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
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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,
as shown in Fig.8.5.
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
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48 Everyday Practical Electronics, June 2011
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,
as shown in Fig.8.7.
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$3IJHIQBTTÜMUFS
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Everyday Practical Electronics, June 2011 49
Teach-In 2011
Example 1A simple C-RLOWPASSÚLTERHASC =
100nF and R = 10k:$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 :
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50 Everyday Practical Electronics, June 2011
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
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Everyday Practical Electronics, June 2011 51
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
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52 Everyday Practical Electronics, June 2011
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
$ECIBELS
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Everyday Practical Electronics, June 2011 53
Teach-In 2011
Please note!4HEÚRSTORDERÚLTERSTHATWEMETIN
&IGAND&IGROLLOFF THEIR
RESPONSEATTHERATEOFD"PEROC
TAVEWHILETHESECONDORDERÚLTERS
SHOWNIN&IGAND&IGHAVEARESPONSETHATROLLSOFFATD"PER
OCTAVE.OTETHATlPEROCTAVEmSIM
PLYMEANSADOUBLINGORHALVINGOF
FREQUENCY
Example 6!N AMPLIÚER USED IN A MATCHED
SYSTEMPRODUCESANOUTPUTVOLTAGE
OF6FORANINPUTOFM67HAT
ISTHEVOLTAGEGAINOFTHEAMPLIÚER
WHENEXPRESSEDINDECIBELS
4HEVOLTAGEGAINA6CANBECAL
CULATEDFROM
4AKINGINVERSELOGARITHMSIEANTI
LOGSOFBOTHSIDESWEARRIVEAT
01
2 1 1 2 2S
u
f C R C R
7HENC1 = C2 = C ANDR1 = R2 = R
THISEQUATIONSIMPLIÚESTO
0
1
2S
f CR
out
V 10 10 10in
20log§ ·
u ¨ ¸ ¨ ¸© ¹ © ¹
V A
V
10
220log
0.02
§ · ¨ ¸
© ¹
Example 7 !D"MATCHEDATTENUATORISUSEDTO
REDUCETHEPOWERLEVELPRODUCEDBY
ANAMPLIÚERTHATPRODUCESANOUTPUT
OF77HATPOWERWILLAPPEARATTHEOUTPUTOFTHEATTENUATOR
2EARRANGING THE EQUATION FOR
POWERGAININ4ABLEPRODUCES
NowP
out
10in
10log§ ·
¨ ¸© ¹
P A
P
2EARRANGINGTHISEXPRESSIONGIVES
2EARRANGINGTHISEXPRESSIONGIVES
.OTETHATWEHAVEINSERTEDAMINUS
SIGNINORDERTOINDICATEAlossOFD"
Check – How do you think you are doing?OFTHEATTENUATORISM6FORAN
INPUTOF M6WHAT LOSSDOES
ITPRODUCE%XPRESSYOURANSWER
IND"
8.8. !N AMPLIFIER USED IN A
MATCHEDSYSTEMPROVIDESAPOWERGAINOFD"7HATINPUTPOWER
ISREQUIREDTOPRODUCEANOUTPUT
POWEROF7
Fig.8.20. See Question 1
P A
10
out
10in
log§ ·¨ ¸© ¹
P
P
1020log 100 20 2 40 dB u dB
8.1.)DENTIFYEACHOFTHECIRCUITS
SHOWNIN&IG
8.2. 3KETCH THE CIRCUIT OF A A
SIMPLEL-C ACCEPTORCIRCUITAND
BASIMPLEL-C REJECTORCIRCUIT
8.3.!SIMPLE2#HIGHPASSÚLTER
HASRK:ANDC N&$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§ ·¨ ¸« »
© ¹¬ ¼
out in 10antilog 0.6 P P u u
1.6 0.25 0.4 Wu W
Please note!
7HEN PLOTTING THE FREQUENCY RE
SPONSE OF A ÚLTER WE OFTEN USE A
LOGARITHMIC SCALE FOR FREQUENCY
BECAUSETHIS ALLOWSAMUCHWIDER
RANGEOFVALUESTOBEACCOMMODATED
ANDAVOIDSCRAMPING
4HETERMlCUTOFFmCANBEABITMIS
LEADINGBECAUSEITMIGHTIMPLYTHAT
AÚLTERWILLPRODUCENOOUTPUTATALL
BEYONDACERTAINPOINT4HISISNOT
THECASE4HERESPONSEOFAPRACTICAL
ÚLTERWILLSIMPLYlROLLOFFmBEYOND
THE CUTOFF FREQUENCY AND ONE OFTHEMOSTIMPORTANTCHARACTERISTICS
OFAÚLTERISTHERATEATWHICHTHIS
ROLLOFFOCCURS
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54 Everyday Practical Electronics, June 2011
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
ªª"UILDªnª4HEª#IRCUITª7IZARDªWAY
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
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Everyday Practical Electronics, June 2011 55
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
'JH.JSSPSJOHUIFPQFSBUJPOBMBNQMJÜFS
'JH")[JOQVUUSBDFrMPXQBTTÜMUFS 'JH")[JOQVUUSBDFrMPXQBTTÜMUFS
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56 Everyday Practical Electronics, June 2011
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.
ªª"UILDªnª4HEª#IRCUITª7IZARDªWAY
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Everyday Practical Electronics, June 2011 57
Teach-In 2011
"ANDPASSªlLTERLast, we are going to produce a
BANDPASSÚLTERUSINGTHETWO
SECONDORDERÚLTERS%NTERTHE
CIRCUITSHOWNIN&IG9OU
MAYÚND ITQUICKER TOCOPY
and paste your two second
ORDERCIRCUITSONTOONESHEET
RATHER THAN DRAWING IT FROM
SCRATCH &INALLY BY ALTERING
THE INPUT FREQUENCY MONI-
TOR HOW THE ÚLTER RESPONDS2ECORDYOURRESULTSANDPRO-
DUCEAFREQUENCYRESPONSEGRAPHOUREXAMPLEIS
SHOWNIN&IG
5SINGEVERYTHINGTHATYOUmVELEARNTPRODUCEAND
TESTAÚLTERCIRCUITWITHALOWERCUTOFFFREQUENCY
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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
LOWPASS SNETWORKATTENUATOR
8.2.3EEPAGE
8.3.K(Z
8.4.6
8.5.M(
8.6.3EEPAGE
8.7D"
8.8M7
!NSWERSªTOª#HECKª
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
* 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
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58 Everyday Practical Electronics, June 2011
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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Products Catalog011
…from engineers to engineers
50W Audio Power Amplifier HT-AV50W
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This integrated power output amplifier consists of
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High power output through Class-H operation
80Wx2 Class-D Audio Power Amplifier HT-AU280With efficiencies as high as
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This is primarily made possible bythe very high efficiency of the
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HandsOn Technology
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46 Everyday Practical Electronics, July 2011
Teach-In 2011
By Mike and Richard Tooley
Part 9: Digital-to-Analogue andAnalogue-to-Digital Conversion
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 electronicsunits of the new Diploma in Engineering (also at Level 2). The series will also provide the more experienced
READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
TEACH-IN 2011
A BROAD-BASED INTRODUCTION
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
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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
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48 Everyday Practical Electronics, July 2011
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)
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Everyday Practical Electronics, July 2011 49
Teach-In 2011
)NORDER TOENSURE ASUFÚCIENTLY
HIGHDEGREEOFACCURACYALLOFTHESE
RESISTORSWOULDNEEDTOBECLOSETOLER
ANCETYPESTYPICALLYORBETTER
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AREREQUIREDANDTHATTHEYCANBEANY
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VALUEISDOUBLETHEOTHERITISRELATIVELYEASYTOMANUFACTUREMATCHED
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ERANCEONANINTEGRATEDCIRCUITCHIP
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AGEUSEDTODEÚNETHEVOLTAGELEVELS
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4HE RESOLUTION OF A $!# IS AN
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VOLTAGELEVELS4HEPRESENCEOFTHESE
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UNDESIRABLEFORSOMEAPPLICATIONS
ANDHENCETHEYAREREMOVEDINORDER
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4HISCANBEEASILYACCOMPLISHED
BYPASSINGTHEOUTPUTSIGNALTHROUGH
ALOWPASSÚLTERASSHOWNIN&IG
4HE ÚLTER IS DESIGNED SO THAT THERESIDUALSAMPLINGFREQUENCYCOM
PONENTS IE THOSE THAT CAUSE THE
lSTEPSm IN THE ANALOGUESIGNAL ARE
WELL BEYOND THECUTOFF FREQUENCY
OF THEÚLTER AND ARE SUBJECT TO AN
APPRECIABLEAMOUNTOFATTENUATION
Analogue-to-digital conversion4HEBASIC ANALOGUETODIGITAL CON
VERTER!$#HASASINGLEANALOGUE
INPUTANDANUMBEROFDIGITALOUT
PUTSOFTENORLINESAS
SHOWNIN&IG6ARIOUS FORMS OF ANALOGUETO
DIGITAL CONVERTER ARE AVAILABLE FOR
USEINDIFFERENTAPPLICATIONSINCLUD
INGMULTICHANNEL!$#SWITHUPTO
ANALOGUE INPUTS 4HE SIMPLEST
FORMOF!$#ISTHEÛASHCONVERTER
SHOWNIN&IGA)NTHISTYPEOF
!$#THEINCOMINGANALOGUEVOLTAGE
ISCOMPAREDWITHASERIESOFÚXED
REFERENCEVOLTAGESUSINGANUMBER
OF OPERATIONAL AMPLIÚERS )# TO
)#IN&IG7HENTHEANALOGUE
INPUTVOLTAGEEXCEEDSTHEREFERENCE
Fig.9.6. Filtering the output of a DAC
Fig.9.7. Basic ADC representation
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Everyday Practical Electronics, July 2011 51
Teach-In 2011
types and typical conversion times (ie, the time between
the SC and EOC signals) are in the range 10 Ps to 100 Ps.Despite this, conversion times are fast enough for most
non-critical applications, and this type of ADC is rela-
tively simple and available at low-cost.
Ramping it upA ramp-type ADC is shown in Fig.9.10. This type of ADC
USESARAMPGENERATORANDASINGLEOPERATIONALAMPLIÚER
comparator, IC1.
The output of the comparator is either a 1 or a 0 depend-
ing on whether the input voltage is greater or less than the
instantaneous value of the ramp voltage. The output of
the comparator is used to control a logic gate (IC2) whichpasses a clock signal (a square wave of accurate frequency)
to the input of a pulse counter whenever the input voltage
is greater than the output from the ramp generator.Fig.9.11. Waveforms for a single-ramp ADC
The pulses are counted until the
voltage from the ramp generator
exceeds that of the input signal, at
which point the output of the compa-
rator goes low and no further pulses
are passed into the counter. The
number of clock pulses counted will
depend on the input voltage and the
ÚNALBINARYCOUNTTHUSGIVESADIGITAL
representation of the analogue input.Typical waveforms for the ramp-type
waveform are shown in Fig.9.11.
Dual-slope ADC&INALLYTHEDUALSLOPE!$#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
please check out our
Teach-In website at:
www.tooley.co.uk/ teach-in
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52 Everyday Practical Electronics, July 2011
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
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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.
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Everyday Practical Electronics, July 2011 53
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.
Build – The Circuit Wizard way
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54 Everyday Practical Electronics, July 2011
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 ).
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 £91.90inc. VAT. See Direct Book Service – pages 75-77 in this issue
* 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
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42 Everyday Practical Electronics, August 2011
Teach-In 2011
By Mike and Richard Tooley
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
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
TEACH-IN 2011
A BROAD-BASED INTRODUCTION
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)
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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
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44 Everyday Practical Electronics, August 2011
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
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Everyday Practical Electronics, August 2011 45
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
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46 Everyday Practical Electronics, August 2011
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
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Everyday Practical Electronics, August 2011 47
Teach-In 2011
Check – How do you think you are doing?
(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
please check out our
Teach-In website at:
www.tooley.co.uk/ teach-in
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.
* 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
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
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Everyday Practical Electronics, August 2011 49
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
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50 Everyday Practical Electronics, August 2011
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
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Everyday Practical Electronics, August 2011 51
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
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52 Everyday Practical Electronics, August 2011
Teach-In 2011
Build – The Circuit Wizard way
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
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Everyday Practical Electronics, August 2011 53
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
10.5 See page 45 and Table 10.1
10.6 See page 46 and Table 10.1
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54 Everyday Practical Electronics, August 2011
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
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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
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46 Everyday Practical Electronics, September 2011
Teach-In 2011
By Mike and Richard Tooley
Part 11: Summing it all up
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 experienced
READERªWITHªANªOPPORTUNITYªTOª@BRUSHªUPªONªSPECIlCªTOPICSªWITHªWHICHªHEªORªSHEªMAYªBEªLESSªFAMILIARª
%ACHªPARTªOFªOURª4EACH)NªSERIESªISªORGANISEDªUNDERªlVEªMAINªHEADINGSª,EARNª#HECKª"UILDª)NVESTIGATEªANDª
!MAZEª,EARNªWILLªTEACHªYOUªTHEªTHEORYª#HECKªWILLªHELPªYOUªTOªCHECKªYOURªUNDERSTANDINGªANDª"UILDªWILLªGIVEª
you an opportunity to build and test simple electronic circuits. Investigate will provide you with a challenge
WHICHªWILLªALLOWªYOUªTOªFURTHERªEXTENDªYOURªLEARNINGªANDªlNALLYª!MAZEªWILLªSHOWªYOUªTHEª@WOWªFACTORªª
TEACH-IN 2011
A BROAD-BASED INTRODUCTION
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
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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
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48 Everyday Practical Electronics, September 2011
Teach-In 2011
Check – How do you think you are doing?
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.
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Everyday Practical Electronics, September 2011 49
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
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50 Everyday Practical Electronics, September 2011
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
Build – The Circuit Wizard way
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
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Everyday Practical Electronics, September 2011 51
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 sim- ple intruder alarm
For more information, linksand other resources please
check out our Teach-Inwebsite at:
www.tooley.co.uk/ teach-in
4. Why is only one series resistor
(R10) required?
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52 Everyday Practical Electronics, September 2011
Teach-In 2011
Build – The Circuit Wizard way
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
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
* 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
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Everyday Practical Electronics, September 2011 53
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$DO5SETHE
)NTERNET ANDOR OTHER RESOURCES TO
ÚNDOUT
Fig.11.12. Metronome circuit using a 555 timer IC
Fig.11.13 (above).Temperature-con-trolled fan circuit
Fig.11.14 (right).Answer to
Question 11.1
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54 Everyday Practical Electronics, September 2011
Teach-In 2011
Answers to Check questions
11.1. See Fig.11.14
11.2. (a) switch (SPST)
BRESISTORÚXED
CTRANSFORMERIRONCORED
DLIGHTEMITTINGDIODE,%$
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
BESTWAYTODOTHISISTODO IT THE
lPRACTICALWAYm
'OOD LUCKWITH YOUR STUDIES OF
ELECTRONICS AND DONmT FORGET THAT
lSUMSCIRCUITSUNDERSTANDINGmØ
Mike and Richard Tooley
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Everyday Practical Electronics, September 2011 55
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
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56 Everyday Practical Electronics, September 2011
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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HandsOn Technology
Low Cost 8051PC Starter Kit/ Development 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 8051P C
Flash programmer or as a development, prototyping and educational platform
Main Features:
x 8051 Central Processing Unitx On-chip Flash Program Memory with In-System Programming (ISP) and In Application
Programming (IAP) capability
x Boot ROM contains low level Flash programming routines for downloading via the RS232
x Flash memory reliably stores program code even after 10,000 erase and program cycles
x 10-year minimum data retention
P bl it f th d i th Fl h Th it f t t t i t ft