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Welcometothisfirstcourseyouwilltakeonelectronicengineering.Thisismythirdtimeteachingthismodule.IhadagreatexperienceteachingthisclasslasttwoyearsandhopefullyIcanrepeatthatorevenimproveuponitthisyear.Thiscoursepresentsapersonalchallenge:howtoselectandteachfromavastamountofmaterialswenormallyteachtofirstyearEEstudents,andcoverallthatwithyouinaquarteroftheavailabletime?Evenmorechallengingis:howtoensurethatyouretainwhatyoulearninelectronicsforyearstocome,whileyouonlyencounterthistopicrarelyduringtheentiredegreeprogramme?Allmyteachingmaterialsincludinglectureslideswithnotes,laboratoryworkandtutorialproblemsheets,canbefoundonthecoursewebpageshownhere.Furthermore,alllectureswillberecordedwithPanopto.

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Beinganelectronicengineeringprofessor,myopinionisbiased.However,Iwouldarguethatelectronicsisnowubiquitousinthemodernworld.Therearenowmoreelectronicpartsinacarthanmechanicalones.Shownhereisapartiallistofwhatyoucanexpecttolearnfromthiscourse.Evenmoreimportantly,beforeIstartedprepareforthecontentsofthiscourse,IwroteadocumentstatingtheprincipleonwhichIwilldesignthiscourse.Init,Istatedfivebasicprinciples:1. Lessismore– takingmaterialoutwillresultinstudentslearningmore.2. Conceptwithrigour – focusonconceptualunderstandinginsteadof

details,butatthesametimenotloosingrigour.Focusonfundamentals.3. Top-down,notbottom-up– wherepossiblegofromsystemlevelviewto

componentviewwherepossible.4. Confidencenotignorance– bringaboutstudent’sconfidenceon

electronics.Knowwhatyouknow,butevenmoreimportant,knowwhatyoudon’tknow!

5. Formalteachingvs problembasedlearning– blendingtogetherpracticallaboratoryandprojectworkwiththecoursematerialstaughtformallyinlectures.

Acopyofthisdocumentisputonthecoursewebpage.

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Hereisthecurrentplanformymodule.Iwillinformeveryoneiftheschedulechangesovertheterm.

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Irecommendonlyonetextbook– Practicalelectronicsforinventors.ThisbookisparticularlysuitableforDesignEngineersbecauseithasagoodbalancebetweentheoryandpractice,itisrelativelylowcostinspiteofsize(>1000pages)anditcoverseverythingyouneedinelectronicsatsufficientdepth.Inthisintroductorylecture,Iwillbelayingthefoundationfortherestofthemodule.Iwillfocusonthebasicideasbehindelectricalsignalsandcircuits.

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Thiscourseisaboutelectronicscircuitsandhowtousethem. Inthiscourse,youwillbebuildingsomesimpleelectroniccircuitsusingprototypingboardknownasabreadboard (shownontheleft).Thisishowwenormallytryoutsomesimplecircuitstoseeiftheywork.Eventually,weputallcomponentsonaprintedcircuitboard(PCB).Mostelectronicssystemscomeinthisform.YouarenotgoingtobuildanyPCBonthiscourse,butyouwillbeusinganARMmicrocontrolleronsuchaboardlater.Finally,mostelectronicscircuitsarealsointegratedinsideachip.Infactisamazinghowmuchyouwillfindincludedinasinglechippackagenowadays.NotethatIalsoputtherelevantpagenumbersinthetextbookonthebottomrightcornerwhereappropriate.Thisismeanttohelpyoutoreaduponthetopicifyoufoundthatmynotesarenotsufficient.

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Weoftenrepresentelectroniccircuitsintheformofcircuitschematicinadiagramform.Hereisacircuitwithcomponentsconnectedtogether.Thelinesconnectingthecomponentstogetherarecalled“Nodes”.Inthiscircuit,wehavefournotes.Theoneshowninredisquitelarge,butweassumethatnomatterwhereyouareonthisrednode,youwillhavethesameelectricalvoltage.Inotherwords,thewiresassociatedwiththisnodeisassumedtohavezeroresistance.Youshouldbecarefulwithnodesthatarecomplexandcouldbeconnectedtogetherindifferentways.

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Thefoundationofelectronicsisofcoursetheelectronsyoufoundinsideatoms.Eachelectronhaselectricalcharge,whichismeasuredinCoulombs(C).Anelectron’schargeisnegative,andismeasuredas-1.6x1019 C,whichisprettysmall.Thisisbalancedoutbytheprotonintheatom,whichhasapositivechargeof+16x1019 C.Chargeparticleswithsamesignrepeleachother;thosewithdifferentsignsattracteachother.Theforceexertedbychargeisamazinglylarge.Twopeople,oneonthemonthandoneonearth,eachsomehowacquires1%extraelectronswouldexertaforceof360,000timestheirweight!Thiscanbecalculated.Thekeytakeawaymessagehereisthatduetothisforcebetweenelectrons,chargeparticularsneveraccumulatesinaconductor.

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Electricalcircuitswouldnotbedoinganythingusefulunlesscurrentflowsinthem.Electricalcurrentistheflowofcharge(electrons)asmeasureatacertaincrosssection.Thisisreallysimilartowatermoleculesflowingthroughapipe.CurrentismeasuredinAmperes,orA.Wealwaysuseanarrowtodenotethedirectionoftheflowofpositivecharge.OneAmpere(1A)istheflowof1Coulombofpositivechargeflowingpassingthroughthecrosssectioneverysecond.Thedirectionofthearrowisnotimportant.Ifyougetitwrong,thenthecurrent(positivecharge)flowis-1A,whichindicatesthatitisintheopposedirection.Oneinterestingfact:whileelectricalSIGNALtravelsat,say,50%ofspeedoflight(dependingonmanyfactorssuchaswhetherisitthroughairorconductorcableoropticalfibre),electronstravelveryslowly(around1mm/s).Why?Haveadiscussionamongyourselves.Inreality,whatactuallyflowsinmetalarenegativecharge,i.e.electrons.Thereforecurrentisflowisalwaysnegative.Butwewillignorethisthroughoutourcourse– weonlyconsiderpositivechargeflowing.

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Youareallfamiliarwithgravitywhichrelatestopotentialenergyofobjects.Thelostofpotentialenergyofanobjectofmassm,droppingadistanceofh,ismgh.Thekeytakeawaypointshereare:1. ThedifferenceinpotentialenergyduetogravitydoesNOT dependonthe

routetakenbetweentwopoints.

2. Thepotentialenergydifferenceisindependentofthereference point(i.e.youcantakethesealevelasthereferenceorthebottomofthehillasareference).

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Voltage istheelectricalpotentialdifferencebetweenanytwonodesinacircuit.Itistheenergyrequiredtomove1Coulombofpositivechangechargebetweenthetwonodes.Inthecircuitshownhere,wepicknodeGasthereference.Wenormallycallthisthe“ground”node,anditisassociatedwiththespecialsymbolshown.NodeGisthenodethatis“common”(i.e.shared)bymostcomponents.Itisusuallythebestnodetobeusedasthereferencenode.However,justlikegravitationalpotentialenergy,YOUCANUSEANYNODEASAREFERENCENODE.Itwouldmakenodifferencetoanycalculations,exceptthatthecalculationsmaybemorecomplexasaresult.Theanswerstoanyanalysiswouldremainthesame.ThevoltageatnodeAisVA,anditisassumedtoberelativetothegroundnodeG. Wecallthis“thevoltageatA”.ThepotentialdifferencebetweenAandB(withBbeingthereference)isVAB.Thearrowalwayspointsawayfromthereferencenode.

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Themostbasiccomponentinelectronicsistheresistor.Itsvalue,theresistanceRprovidesthesimplerelationshipbetweenvoltageandcurrentthroughOhm’slaw.Therearemanytypesofresistors,mostlydependentonthespecificationrequired.Thecheapestandmostcommontypeofresistorismadeofathinstripofmetalic filmonaceramicsubstrate.Someresistorsaremadefromaresistivewirewoundroundthesubstrate. Thesearemoreexpensiveandusuallyofahigheraccuracy.AllofyoushouldhavecomeacrossOhm’sLawinphysicsathighschool.R=V/I.ElectricalengineerssometimesusethereciprocalofresistanceG=1/R,whichiscalledtheconductance(measuredinSiemensS).Notethatthevoltageacrossaresistorandthecurrentflowingthroughtheresistorisinthepositivedirection.Inourconvention,weassumethatcurrentflowsfromthemorepositivenodetothemorenegativenode.

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Resistorissaidtobea“linear”component,becausethecurrentvs voltagecharacteristicisalinearfunction(i.e.straightline).Thegradientofthelineistheconductance.

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Whenevercurrentflowsthrougharesistor,energyisdissipatedasheat.Thisisanalogoustofallingbyadistanceandconvertingthelostpotentialenergyintokineticenergy.ThepowerdissipatedinaresistorisVxIandthisismeasureinwatt.WhichisoneJouleofenergypersecond.(Power=Energy/time)Powerisalwayspositive.(Otherwise,wewillbegeneratingandnotdissipatingenergy.)

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Aresistorischaracterised byanumberofparameters:1. Itsnominalvalue;2. Itstoleranceoraccuracy(e.g.±5%);3. Itspowerrating(i.e.maximumpowerthatitcandissipate);4. Itstemperaturecoefficient(howmuchtheresistancevarywith

temperature);5. Itsstability(i.e.howmuchitchangesovertime);6. Itsselfinductance(somethingwedon’tworryaboutunlessyouareusing

resistorsatveryveryhighfrequencies).Thesecharacteristicsareoftenshownontheresistoritselfasacolour code.Thecolour codeisasshownabove.(Theprintednotesarenotincolour.YoucandownloadthePDFfilefromthecoursewebpage,whichwillbeshowninfullgloriouscolours.)Considerthetopresistor.Ithasfourbands,andthebandcolours are:RED,GREEN,ORANGE,agap,BROWNThefirsttwocolour bandsarethefirsttwodigitsoftheresistance,i.e.RED=2,GREEN=5.Thethirdbandinthiscaseisthemultiplier.ORANGE=103 or1k.Thegapisalwaystheretoseparatevaluebandsfromtoleranceband.BROWN=±5%.

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Sinceresistorshavetolerances,itisnotnecessarynormalevensensibletoprovideresistorsofALLvalues.Letussupposeyouhavea1kΩ resistorwithatoleranceof10%.Thisresistorcouldvaryfrom900Ω to1.1kΩinvalue.Youwanttoguaranteethatanotherresistorwithlowernominalvalueisalwayslowerinresistance.Thereforeitdoesnotmakesensetoprovideanyresistancewithavalueabove820Ω,say850Ω. Thisisbecause850Ω at10%wouldgiveyouarangeof765Ω to935Ω, whichwouldbehigherthanthelowestvalueofthe1kresistor!Thereforeinindustry,onlyselectedvalues(knownasPreferredValues)ofresistorsaremade,dependentonthetolerance.Shownherearethe±20%,±10%and±5%resistorsvaluesinadecaderange.TheyarecalledE6,E12andE24respectivelybecausethereare6,12and24valuesineachdecade(similartomusicalnodes).GOODENGINNERINGPRACTICE:youcanseethatsinceinengineeringdesign,wealwayshavetoconsidertolerance,andeventhehumbleresistoronlyexistsindefinedvalues,itdoesnotmakesensetouseprecisioninyoursolutionshavingmanydigits.Inourlaboratory,wewillbemostlyusingtheE24seriesofresistorsat±5%tolerance.

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Therearetwoothercommoncomponents:1)anidealvoltagesourcethathasaconstantvoltagevaluenomatterhowmuchcurrentareflowingfromit;2)anidealcurrentsourcethatcanprovidethefixedamountofcurrentnomatterwhatthevoltageisacrossthesource.

Abatteryapproximatesthecharacteristicsofanidealvoltagesource,althoughinrealityitisfarfromideal.Wewillbeusingbatteriesalotonourcourse.Wewon’tbeusingcurrentsourceinourpracticalwork,butyouwillbeusingtheminanalysisofelectroniccircuits.Notethedirectionofcurrentflow.Inabatteryactingasasource,currentisflowingOUTfromthebattery.ThereforeIisnegative.ThereforeabatterysupplyingcurrentIatavoltageVisprovidingpowerVxI,andthepowerisnegative.Whenyouchargeabattery,currentisflowingintothevoltagesourceandpowerispositive.

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Thelawofconservationofenergy(hencepower)appliesinelectroniccircuits.Considerthesimplecircuitabove.Powerabsorbedbythe1kresistorconnectedtoa10vbatteryis0.1W.Ifyoureversethevoltage(V2)thecurrent(I2)mustflowfromhighvoltagetolowvoltage,andthereforeisreversed(i.e.pointingup).Usingthissecondconvention,thepowerisstill0.1W.Powerabsorbedbythe10vbattery(source)is-0.1WbecausethecurrentIS isflowingintheoppositedirectionandisthereforenegative.Totalpowerinthecircuitis0.

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Herearethecommonquantitiesusedinelectricalengineering,theirunitsandsymbolicrepresentationsfortheunits.Furthermore,wedonotgenerallyusealldecadesformultipliers(sayofresistors),butthemultipliersareinstepsofTHREEdecade.

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