abstract - u4ea ranch enterprises€¦ · · 2017-12-17– doing the simplest experiment was...
TRANSCRIPT
Abstract
Teachinglaboratoryelectronicsinageneralphysicslaboratoryclassroomrequireshaulinghundredsofpoundsofapparatusfromstockroomtolabbenchandbackeachday.Somestudentsseetheequipmentas"magicalmysteryboxes"thatmustbeconnectedinjusttherightwaytofunc?onproperly.Suchabstrac?oncanbeanimpedimenttolearningelectronicprinciples.CSUCIisexploringanalterna?ve,wherethestudentsdesignandbuildaverycompactandsimple"open"electronicsworkbenchwithadjustableDCpowersupplies,aversa?lefunc?ongenerator,anaudioamplifier,andasolderlessbreadboard.Theyconstructallofthisonasmallperforatedcircuitboardfor~$25.Alongwithadigitalmul?meter(~$10),theyareabletobuild,troubleshoot,andstudyawidevarietyofcircuitswithoutanoscilloscopeorotherapparatus.Dr.Rasnowwillpresenttheresultsandlessonslearnedfromthisexperimentalcurriculum.
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Do‐it‐YourselfElectronicsLaboratory
BrianRasnowDept.ofPhysics
CaliforniaStateUniversityChannelIslands
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For further information:
http://phys106fall08.wetpaint.com/page/Basic+Electronics Prof. Brian Rasnow [email protected]
New Course * Spring 2009
Phys 310 Electronics
Do you wonder how gadgets work? How to fix broken stereos, Ipods, computers? How to design sensors, actuators, control systems, or computers?
4 Units, M 10-11:50 am & W 9 – 11:50 am
Prerequisites Phys 101 or 201. All majors welcome.
C.S.U. Channel Islands
This new course explores electronics
• from simple devices to complex instruments
• from wavefunctions to software
• mixing theory with practical methods
We will
• build amplifiers, transducers, rail guns, microcontrollers
• measure the speed of light
• fix broken Ipods, computers, stereos
Anewclassinnewmajorinanew(small)schoolrequiredrecrui?ngstudentsfromothersciencemajors
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Classphilosophy
• Electronicsishardtolearn– Noinnatesenseofweakelectricity
• Relyonmachinestodetectit
– Abstractandunintui?ve• Differentphysicsthanourinnatesenses
– Daun?ngcomplexity• Technologyprovidesuswithasmorgasbordofdeviceswithvariousbehaviors
• Butlearninghowtolearnaboutelectronicswillhelpyoulearnaboutothercomplex,unintui?vesystemsinlife
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OurApproach
• Emphasizelabac?vi?es– Buildprac?calunderstanding– Buildhands‐onskills
• Keytounderstandingadvancedelectronicstopicsare– Understandbasicconcepts– Learntheartofmeasurement
• Usingavoltmeter&oscilloscope• Whattodowhenthingsdon’twork
– Iden?fysimplecircuitsandlearntoparseschema?cs– Familiaritywithsimplecomponents– Artofbuilding,tes?ng,designing– Keepingitsimplewithhierarchicalabstrac/on
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Firstac?vity:Baberies&bulbs
• Whatgeneralrulespredictcircuitbehavior?
• Howdovoltageandcurrenthelppredictcircuitbehavior?– Howcanweframegeneralrulesintermsoftheseabstractconcepts?
– Whatevidencedowehavethatelectronsexist?
• Whatexcep?onstotheserulesarethere?– Wheredotherulesbreakdown?E.g.,
Jacob’sladder
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MysteryBoxes
• Canyoufigureoutwhat’sinsideeachoftheseboxes?• Drawtheschema?csforthesimplestcircuitwithineachand
explainhowyouconcludedthat.
• Tosolvethis,webuiltcrudevoltmetersandohmmeterswithlightbulbsandbaberies.
• Abstrac?onisobvious.
A =?
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Mul?meters
• Exploreamul?meter– Humaninterfaceandelectricinterfacetomeasure…
• Howcanyoudamageone?• Howcanonedamageyou?
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VariableDCpowersupply
• ExploreavariableDCpowersupply– Humaninterfaceandelectricinterface
• Howcanyoudamageone?
• Howcanonedamageyou?
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Func?onGenerator
• Exploreafunc?ongenerator– Humaninterfaceandelectricinterface
• Howcanyoudamageone?
• Howcanonedamageyou?
Oscilloscope• Exploreascope
– Humaninterfaceandelectricinterface– Botharequitecomplex
• Howcanyoudamageone?• Howcanonedamageyou?
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Circuitslabs
• WeusedtheseapparatustoexploreOhm’slaw,voltagedividers,andsimpleresistor,capacitor,inductor,diode,transistor,andFETcircuits
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Componenttransferfunc?ons
• Amajorgoalofthelabsistoexplore/discoverthecharacteris?csofcomponents&theirinnumerablecombina?onsincircuits
…
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Logis?cs&Abstrac?on
• Moving>100poundsofmul?meters,powersupplies,func?ongenerators,andoscilloscopesbackandforthfromcabinetstoclassroomandlabbenchwasbecomingaburden– Doingthesimplestexperimentwasonerous
• Somestudentsperceivedthelabsasexercisesinhowtoconnectthesemagicalboxestogethertoachieveadesiredstate– Theirunderstandingofwhattheirapparatusdidwaslacking– Theapparatuswasobviouslycomplexandexpensive,andin?mida?ng
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MatlabSimula?on• Simula?onsolvesthelogis?csproblem,butitsabstract
Produces:>>|Vr|=3.0V,phase=82.8degat1kHz
>>|Vr|=18.8V,phase=38.5degat10kHz
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BodePlot
• Approximatelypiecewiselinearbehavioronloglogamplitudeandlog‐linearphaseplotsallowsforgraphicales/matesofcomplexcircuits
“cornerfrequency”
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Timedomain
• Simula?ngwaveformsthatmatchoscilloscopedatamakesthesimula?onsmorecredible
• ThisMatlabfunc?onf2t()convertsfromfrequencydomainto?medomain,withtheinverseFouriertransform(ifft)
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Individual/classproject
• Objec?ve:Wewilleachbuildourownmul?‐outputDCpowersupply,func?ongenerator,andaudioamplifier,asaconvenient,compact,affordabletestbedforexploringsimpleelectroniccircuits.Wewilllearnmanyprac?callessonsintheprocessofdesign,prototyping,construc?on,anddebugging,andul?matelyusingthesystemforfuturelabs.
• DesignSpecifica?ons:– size<6"x8"x3”;weight<2lbs;costofmaterials<$30
– DCpowersupplies:• +&–12VDCconstantvoltageat0‐100mA,<10mVrippleandnoise
• +&‐1.2‐15VDCvariableat0‐100mA– Func?ongenerator:10‐100kHz;0‐10Vamplitude;sine,triangle,squarewave
– Audioamplifier:protectedinput;0.05‐50,000gain;50Hz‐15kHzbandwidth
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Methods
• Designsmodifiedfromdatasheetsfoundonline– 3pinvoltageregulators:7812,7912,LM317,LM337– TransformerspecsandRMS– ExarXR2206func?ongenerator– LM386audioamplifier– Prototypeddesignsonsolderlessbreadboard
• Learnedwheretoacquireparts:– Ebay,www.allelectronics.com,www.futureelectronics.com,etc.– Recycledfromconsumerelectronics– Weneededtobeextremelyfrugaltomeetbudgetconstraints
• Construc?on:– perforatedcircuitbreadboard– Posi?vephotoresistsinglesidedPCB– Smallsolderlessbreadboard
• “Bootstrapped”approach18
Interfaces
• Controls– +/‐V=5kpots– Frequency=500kpot– Amplitude=50kpot
– DCoffset=50kpot– Volume50kpot
• Inputs– Powerplug– Audioinput– Solderlessbreadboard
• Outputs– +/‐12V,+/‐1.2‐15V– Fgenout– Syncout– Speaker– LEDindicator– Solderlessbreadboard
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Powersupplyschema?c
Notepolarityofcaps.
Thepinoutsofeachvoltageregulatorisdifferent!
Whyaretheretwo1kresistorsinserieswiththeLED?
Whyisitonthenega?vesupply?
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Layout
• Powersupplyoccupies~1/4ofthecircuitboard
• Itispoweringprototypedfunc?ongeneratoronasmallsolderlessbreadboard
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Powersupplysolderside
• Note:Bycarefullayout,onlytwotracescrossothers
• Onetraceismorecommonthanothers,henceit’scalled“common”or“ground”.
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Powersupplysolderside
• Note:Bycarefullayout,onlytwotracescrossothers
• Onetraceismorecommonthanothers,henceit’scalled“common”or“ground”.
• Ifthiswereaprintedcircuit,thisconductorcouldcovermuchoftheboard.
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3
200
Func?ongeneratorschema?c
• FirstprototypeisthesimplestcircuitfromFigs.2&11ofthedatasheet.
• f=1/RCfmin=100Hz
fmax=100kHzw/.01uf
• SineoutputisoffsetbyVcc/2
• Squareoutputisopen‐collector
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Func?onGeneratorprototype
• Verifysineandsquarewaveoutputsonascope,&bothpotsworkasexpected(volumeandfrequencyincreaseclockwise).
• Whatchangesorfeaturesshouldweconsider?
• Howwillwelaythiscircuitouttosolder(withminimalcrossingofwires)?
Gnd
+12Sineout
sqrout
freqamplitude27
• Thiscircuitproduces~100Hz‐100kHzsine,triangle,andsquarewaveswithadjustablefrequency,amplitude,andDCoffset.
• Breadboardtheupperle{partfirst,thenwe’llbuilditonaprintedcircuitboard
Freq
Finaldesign
10k
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PCBdesign
• Printedcircuitboard,designedinAdobeIllustrator,implementsallinterconnec?onsbut2(blue)ononesideofa2”x2”coppercladcircuitboard.
• Componentsideviewwithcopperpaberngrayed.Gridis100mil(.1”).
• Notethattracesgenerallyrunver?callyand“vias”(blue)arehorizontal.Geometrydoesmaberinthisphysicalabstrac?onofthecircuit.
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Designques?ons
• Doyouunderstand…– Whatisthetheore?calmaximumandminimumfrequency?
– WhyR1+R2(i.e.,isn’tR2<<R1,sowhyisitthere?)– WhyR3||R4(vs.oneresistor?)
– What’stheroleofR5andtheZener?Whyisn’tR510kor1k?Hint:you’llneedtounderstandthe“opencollector”configura?oninsidepin11.
– WhyisR6fixedinsteadofvariableasinmostcircuitsinthedatasheet?
– WhatistheroleofC4?WhatconstrainsthevaluesofC4andR9?
– Whatistheopampgain?Phase?Vs.frequency?– MighttherebeaproblemwiththepolarityofC4?
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PCBlayout• 6func?ongeneratorsfitona4”x6”circuitboard.– Largegroundplane(andV+)minimizesetching
– Etchedcomponentholesaredrillguides
• Tomakeaprintedcircuitboard:1. Printthispabernontransparencyfilm
2. Placefilmonphotoresist3. Exposetosunlight(exposuredeterminedempirically,~1min)
4. Developtoremoveexposedphotoresist
5. Examine,touchuperrors(withSharpie)Writeyourini?alsornamewithSharpie
6. Etchunprotectedcopper7. Drill8. Scrapeordissolvephotoresist(acetone)9. Placecomponentsandsolder
10. Cleanandtest31
PCBconstruc?on
1.Developedphotoresist 2.Etchedbarecopper 3.Drilled
4.Removedphotoresist 5.Solderedcomponents 6.Componentside 32
Somelessonslearned
• Hands‐onexperiencesandbuildingusefulthingswasrewardingandengaging– Thiswasthefirst?memoststudentsusedasolderingiron&drillpress– Conver?ngrecycledACorDCadaptersintoLEDnightlightswas“cool”– Buildingfromscratchandowningsophis?catedtestequipmentwascool
• Theartofcompromiseinengineeringwasrepeatedlyexperienced– Cost,simplicity,robustness,user‐friendliness,capabili?esaretradedoff
• Buildingpowersuppliesdemys?fiedwhatapowersupplydoes– Undersizingfiltercapacitorsletthestudentsseepoorregula?on– Theadjustablesupplieswerenotnecessary
• Buildingthefunc?ongeneratorandaudioampletstudentsexploremanydevicesandcircuitswithoutusinganyschoolequipment– Thisappearedtoempowerandmo?vatesometoexploremore
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Morelessons
• Solderingisaskillpickedupbysomestudentsfasterthanothers,andittakes?me– SolderingthePCBwasmuchquickerandeasierthantheperfboard
• Layoutisalsoaslowlylearnedskill–visualizingtopandbobomsimultaneously– CouldithelptobuildthePCBbeforethePS?
• Awalk‐in,openlabbench,equippedwithsolderingsta?on,oscilloscope,voltmeter,toolsandparts,helpedstudentscompletetheirprojectsoutsideofclass
• Triedtoengagetheclassindebuggingindividualboards
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Othertopicsexplored
• Transistors&FETsinsatura?onandop‐ampcomparatorsseguedtothedigitalabstrac?on– ExploredtheArduinomicrocontroller
• Appreciatethecomputa?onalpoweroffeedback– ReadBraitenberg’s“Vehicles”
• Timedomainreflectometry(withoutaTDR)– Measuedspeedoflight&lengthofa
wire– RelatedtoSWRandradio
• Transducers:sensorsandactuators
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Finalcomments
• Lowenrollmentandhaven’tcollectedfinallabreportstomoreformallyassessstudentoutcomes
• Didn’tgetanyipodsorhomeelectronicstoexplore
• CanbeberCADtoolsbeincorporatedintheclass?
• BuildingthePS/func?ongeneratorcircuitswasthehighpointoftheclass
• Somestudentsboughtusedoscilloscopesfor<$100
• Hopefullythey’llcon?nueexploringelectronics!
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References&Acknowledgements
• Horowitz&Hill,“TheArtofElectronics”• A.Agarwal,MITOpenCourseware,6.002CircuitsandElectronics• R.Middlebrook,Design‐orientedAnalysisParadigm• V.Braitenberg“Vehicles:ExperimentsinSynthe?cPsychology”• Circuitcellarmagazine&website• TheArduinoonlinecommunity• CSUCIPhysicsDept.• StudentsofPhys310
Thankyou!Ques?ons?
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