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.

0

Do‐it‐YourselfElectronicsLaboratory

BrianRasnowDept.ofPhysics

CaliforniaStateUniversityChannelIslands

1

For further information:

http://phys106fall08.wetpaint.com/page/Basic+Electronics Prof. Brian Rasnow brian.rasnow@csuci.edu

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

2

Classphilosophy

•  Electronicsishardtolearn–  Noinnatesenseofweakelectricity

•  Relyonmachinestodetectit

–  Abstractandunintui?ve•  Differentphysicsthanourinnatesenses

–  Daun?ngcomplexity•  Technologyprovidesuswithasmorgasbordofdeviceswithvariousbehaviors

•  Butlearninghowtolearnaboutelectronicswillhelpyoulearnaboutothercomplex,unintui?vesystemsinlife

3

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

4

Firstac?vity:Baberies&bulbs

•  Whatgeneralrulespredictcircuitbehavior?

•  Howdovoltageandcurrenthelppredictcircuitbehavior?–  Howcanweframegeneralrulesintermsoftheseabstractconcepts?

–  Whatevidencedowehavethatelectronsexist?

•  Whatexcep?onstotheserulesarethere?–  Wheredotherulesbreakdown?E.g.,

Jacob’sladder

5

MysteryBoxes

•  Canyoufigureoutwhat’sinsideeachoftheseboxes?•  Drawtheschema?csforthesimplestcircuitwithineachand

explainhowyouconcludedthat.

•  Tosolvethis,webuiltcrudevoltmetersandohmmeterswithlightbulbsandbaberies.

•  Abstrac?onisobvious.

A =?

6

Mul?meters

•  Exploreamul?meter–  Humaninterfaceandelectricinterfacetomeasure…

•  Howcanyoudamageone?•  Howcanonedamageyou?

7

VariableDCpowersupply

•  ExploreavariableDCpowersupply–  Humaninterfaceandelectricinterface

•  Howcanyoudamageone?

•  Howcanonedamageyou?

8

Func?onGenerator

•  Exploreafunc?ongenerator–  Humaninterfaceandelectricinterface

•  Howcanyoudamageone?

•  Howcanonedamageyou?

Oscilloscope•  Exploreascope

–  Humaninterfaceandelectricinterface–  Botharequitecomplex

•  Howcanyoudamageone?•  Howcanonedamageyou?

9

Circuitslabs

•  WeusedtheseapparatustoexploreOhm’slaw,voltagedividers,andsimpleresistor,capacitor,inductor,diode,transistor,andFETcircuits

10

Componenttransferfunc?ons

•  Amajorgoalofthelabsistoexplore/discoverthecharacteris?csofcomponents&theirinnumerablecombina?onsincircuits

…

11

Logis?cs&Abstrac?on

•  Moving>100poundsofmul?meters,powersupplies,func?ongenerators,andoscilloscopesbackandforthfromcabinetstoclassroomandlabbenchwasbecomingaburden–  Doingthesimplestexperimentwasonerous

•  Somestudentsperceivedthelabsasexercisesinhowtoconnectthesemagicalboxestogethertoachieveadesiredstate–  Theirunderstandingofwhattheirapparatusdidwaslacking–  Theapparatuswasobviouslycomplexandexpensive,andin?mida?ng

12

MatlabSimula?on•  Simula?onsolvesthelogis?csproblem,butitsabstract

Produces:>>|Vr|=3.0V,phase=82.8degat1kHz

>>|Vr|=18.8V,phase=38.5degat10kHz

13

BodePlot

•  Approximatelypiecewiselinearbehavioronloglogamplitudeandlog‐linearphaseplotsallowsforgraphicales/matesofcomplexcircuits

“cornerfrequency”

14

Timedomain

•  Simula?ngwaveformsthatmatchoscilloscopedatamakesthesimula?onsmorecredible

•  ThisMatlabfunc?onf2t()convertsfromfrequencydomainto?medomain,withtheinverseFouriertransform(ifft)

15

Simulatedwaveforms

•  Sinewavesareeigenfunc?onsoflinearcircuits•  Butwewanttogetmorehands‐on

16

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

17

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

19

Powersupplyschema?c

Notepolarityofcaps.

Thepinoutsofeachvoltageregulatorisdifferent!

Whyaretheretwo1kresistorsinserieswiththeLED?

Whyisitonthenega?vesupply?

20

Layout

•  Powersupplyoccupies~1/4ofthecircuitboard

•  Itispoweringprototypedfunc?ongeneratoronasmallsolderlessbreadboard

21

Construc?on

+12 ‐12

‐V

+V

gndgnd

PowerLED

22

Powersupplysolderside

•  Note:Bycarefullayout,onlytwotracescrossothers

•  Onetraceismorecommonthanothers,henceit’scalled“common”or“ground”.

23

Powersupplysolderside

•  Note:Bycarefullayout,onlytwotracescrossothers

•  Onetraceismorecommonthanothers,henceit’scalled“common”or“ground”.

•  Ifthiswereaprintedcircuit,thisconductorcouldcovermuchoftheboard.

24

X‐rayview

25

3

200

Func?ongeneratorschema?c

•  FirstprototypeisthesimplestcircuitfromFigs.2&11ofthedatasheet.

•  f=1/RCfmin=100Hz

fmax=100kHzw/.01uf

•  SineoutputisoffsetbyVcc/2

•  Squareoutputisopen‐collector

26

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

28

PCBdesign

•  Printedcircuitboard,designedinAdobeIllustrator,implementsallinterconnec?onsbut2(blue)ononesideofa2”x2”coppercladcircuitboard.

•  Componentsideviewwithcopperpaberngrayed.Gridis100mil(.1”).

•  Notethattracesgenerallyrunver?callyand“vias”(blue)arehorizontal.Geometrydoesmaberinthisphysicalabstrac?onofthecircuit.

29

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?

30

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

Func?ongeneratorpcb

33

Mountedonmotherboard

Wiresholdingit

down

34

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

35

Morelessons

•  Solderingisaskillpickedupbysomestudentsfasterthanothers,andittakes?me–  SolderingthePCBwasmuchquickerandeasierthantheperfboard

•  Layoutisalsoaslowlylearnedskill–visualizingtopandbobomsimultaneously–  CouldithelptobuildthePCBbeforethePS?

•  Awalk‐in,openlabbench,equippedwithsolderingsta?on,oscilloscope,voltmeter,toolsandparts,helpedstudentscompletetheirprojectsoutsideofclass

•  Triedtoengagetheclassindebuggingindividualboards

36

Othertopicsexplored

•  Transistors&FETsinsatura?onandop‐ampcomparatorsseguedtothedigitalabstrac?on–  ExploredtheArduinomicrocontroller

•  Appreciatethecomputa?onalpoweroffeedback–  ReadBraitenberg’s“Vehicles”

•  Timedomainreflectometry(withoutaTDR)–  Measuedspeedoflight&lengthofa

wire–  RelatedtoSWRandradio

•  Transducers:sensorsandactuators

37

Finalcomments

•  Lowenrollmentandhaven’tcollectedfinallabreportstomoreformallyassessstudentoutcomes

•  Didn’tgetanyipodsorhomeelectronicstoexplore

•  CanbeberCADtoolsbeincorporatedintheclass?

•  BuildingthePS/func?ongeneratorcircuitswasthehighpointoftheclass

•  Somestudentsboughtusedoscilloscopesfor<$100

•  Hopefullythey’llcon?nueexploringelectronics!

38

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?

39