1 Welcome to this first course you will take on electronic engineering. This is my third time teaching this module. I had a great experience teaching this class last two years and hopefully I can repeat that or even improve upon it this year. This course presents a personal challenge: how to select and teach from a vast amount of materials we normally teach to first year EE students, and cover all that with you in a quarter of the available time? Even more challenging is: how to ensure that you retain what you learn in electronics for years to come, while you only encounter this topic rarely during the entire degree programme? All my teaching materials including lecture slides with notes, laboratory work and tutorial problem sheets, can be found on the course webpage shown here. Furthermore, all lectures will be recorded with Panopto.
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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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