基于单片机数字电压表电路设计外文文献原稿和译文Word文件下载.docx

基于单片机数字电压表电路设计外文文献原稿和译文Word文件下载.docx

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Thisisaneasytobuild,butneverthelessveryaccurateandusefuldigitalvoltmeter.IthasbeendesignedasapanelmeterandcanbeusedinDCpowersuppliesoranywhereelseitisnecessarytohaveanaccurateindicationofthevoltagepresent.ThecircuitemploystheADC（AnaloguetoDigitalConverter）I.C.CL7107madebyINTERSIL.ThisICincorporatesina40pincaseallthecircuitrynecessarytoconvertananaloguesignaltodigitalandcandriveaseriesoffoursevensegmentLEDdisplaysdirectly.ThecircuitsbuiltintotheICareananaloguetodigitalconverter,acomparator,aclock,adecoderandasevensegmentLEDdisplaydriver.ThecircuitasitisdescribedherecandisplayanyDCvoltageintherangeof0-1999Volts.

TechnicalSpecifications-Characteristics

SupplyVoltage:

.............+/-5V（Symmetrical）

Powerrequirements:

.....200mA（maximum）

Measuringrange:

..........+/-0-1,999VDCinfourranges

Accuracy:

.......................0.1%

FEATURES

Smallsize

Easyconstruction

Lowcost.

Simpleadjustment.

Easytoreadfromadistance.

Fewexternalcomponents.

HowitWorks

InordertounderstandtheprincipleofoperationofthecircuititisnecessarytoexplainhowtheADCICworks.ThisIChasthefollowingveryimportantfeatures:

Greataccuracy.

Itisnotaffectedbynoise.

Noneedforasampleandholdcircuit.

Ithasabuilt-inclock.

Ithasnoneedforhighaccuracyexternalcomponents.

Schematic（fixed16-11-09）

7-segmentdisplaypinoutMAN6960

AnAnaloguetoDigitalConverter,（ADCfromnowon）isbetterknownasadualslopeconverterorintegratingconverter.Thistypeofconverterisgenerallypreferredoverothertypesasitoffersaccuracy,simplicityindesignandarelativeindifferencetonoisewhichmakesitveryreliable.Theoperationofthecircuitisbetterunderstoodifitisdescribedintwostages.Duringthefirststageandforagivenperiodtheinputvoltageisintegrated,andintheoutputoftheintegratorattheendofthisperiod,thereisavoltagewhichisdirectlyproportionaltotheinputvoltage.Attheendofthepresetperiodtheintegratorisfedwithaninternalreferencevoltageandtheoutputofthecircuitisgraduallyreduceduntilitreachesthelevelofthezeroreferencevoltage.Thissecondphaseisknownasthenegativeslopeperiodanditsdurationdependsontheoutputoftheintegratorinthefirstperiod.Asthedurationofthefirstoperationisfixedandthelengthofthesecondisvariableitispossibletocomparethetwoandthiswaytheinputvoltageisinfactcomparedtotheinternalreferencevoltageandtheresultiscodedandissendtothedisplay.

AllthissoundsquiteeasybutitisinfactaseriesofverycomplexoperationswhichareallmadebytheADCICwiththehelpofafewexternalcomponentswhichareusedtoconfigurethecircuitforthejob.Indetailthecircuitworksasfollows.Thevoltagetobemeasuredisappliedacrosspoints1and2ofthecircuitandthroughthecircuitR3,R4andC4isfinallyappliedtopins30and31oftheIC.ThesearetheinputoftheICasyoucanseefromitsdiagram.（INHIGH&

INLOWrespectively）.TheresistorR1togetherwithC1areusedtosetthefrequencyoftheinternaloscillator（clock）whichissetatabout48Hz.Atthisclockratethereareaboutthreedifferentreadingspersecond.ThecapacitorC2whichisconnectedbetweenpins33and34oftheIChasbeenselectedtocompensatefortheerrorcausedbytheinternalreferencevoltageandalsokeepsthedisplaysteady. 

ThecapacitorC3andtheresistorR5aretogetherthecircuitthatdoestheintegrationoftheinputvoltageandatthesametimepreventanydivisionoftheinputvoltagemakingthecircuitfasterandmorereliableasthepossibilityoferrorisgreatlyreduced.ThecapacitorC5forcestheinstrumenttodisplayzerowhenthereisnovoltageatitsinput.TheresistorR2togetherwithP1areusedtoadjusttheinstrumentduringset-upsothatitdisplayszerowhentheinputiszero.TheresistorR6controlsthecurrentthatisallowedtoflowthroughthedisplayssothatthereissufficientbrightnesswithoutdamagingthem.TheICaswehavealreadymentionedaboveiscapabletodrivefourcommonanodeLEDdisplays. 

Thethreerightmostdisplaysareconnectedsothattheycandisplayallthenumbersfrom0to9whilethefirstfromtheleftcanonlydisplaythenumber1andwhenthevoltageisnegativethe«

-«

sign.Thewholecircuitoperatesfromasymmetricalρ5VDCsupplywhichisappliedatpins1（+5V）,21（0V）and26（-5V）oftheIC.

Construction

Firstofallletusconsiderafewbasicsinbuildingelectroniccircuitsonaprintedcircuitboard.Theboardismadeofathininsulatingmaterialcladwithathinlayerofconductivecopperthatisshapedinsuchawayastoformthenecessaryconductorsbetweenthevariouscomponentsofthecircuit.Theuseofaproperlydesignedprintedcircuitboardisverydesirableasitspeedsconstructionupconsiderablyandreducesthepossibilityofmakingerrors. 

Toprotecttheboardduringstoragefromoxidationandassureitgetstoyouinperfectconditionthecopperistinnedduringmanufacturingandcoveredwithaspecialvarnishthatprotectsitfromgettingoxidisedandalsomakessolderingeasier.

Solderingthecomponentstotheboardistheonlywaytobuildyourcircuitandfromthewayyoudoitdependsgreatlyyoursuccessorfailure.Thisworkisnotverydifficultandifyousticktoafewrulesyoushouldhavenoproblems.Thesolderingironthatyouusemustbelightanditspowershouldnotexceedthe25Watts.Thetipshouldbefineandmustbekeptcleanatalltimes.Forthispurposecomeveryhandyspeciallymadespongesthatarekeptwetandfromtimetotimeyoucanwipethehottiponthemtoremovealltheresiduesthattendtoaccumulateonit.

DONOTfileorsandpaperadirtyorwornouttip.Ifthetipcannotbecleaned,replaceit.Therearemanydifferenttypesofsolderinthemarketandyoushouldchooseagoodqualityonethatcontainsthenecessaryfluxinitscore,toassureaperfectjointeverytime.

DONOTusesolderingfluxapartfromthatwhichisalreadyincludedinyoursolder.Toomuchfluxcancausemanyproblemsandisoneofthemaincausesofcircuitmalfunction.Ifneverthelessyouhavetouseextraflux,asitisthecasewhenyouhavetotincopperwires,cleanitverythoroughlyafteryoufinishyourwork.

Inordertosolderacomponentcorrectlyyoushoulddothefollowing:

Cleanthecomponentleadswithasmallpieceofemerypaper.

Bendthematthecorrectdistancefromthecomponent’sbodyandinsertthecomponentinitsplaceontheboard.

Youmayfindsometimesacomponentwithheaviergaugeleadsthanusual,thataretoothicktoenterintheholesofthep.c.board.Inthiscaseuseaminidrilltoenlargetheholesslightly.Donotmaketheholestoolargeasthisisgoingtomakesolderingdifficultafterwards.

Takethehotironandplaceitstiponthecomponentleadwhileholdingtheendofthesolderwireatthepointwheretheleademergesfromtheboard.Theirontipmusttouchtheleadslightlyabovethep.c.board.

Whenthesolderstartstomeltandflowwaittillitcoversevenlytheareaaroundtheholeandthefluxboilsandgetsoutfromunderneaththesolder.Thewholeoperationshouldnottakemorethan5seconds.Removetheironandallowthesoldertocoolnaturallywithoutblowingonitormovingthecomponent.Ifeverythingwasdoneproperlythesurfaceofthejointmusthaveabrightmetallicfinishanditsedgesshouldbesmoothlyendedonthecomponentleadandtheboardtrack.Ifthesolderlooksdull,cracked,orhastheshapeofablobthenyouhavemadeadryjointandyoushouldremovethesolder（withapump,orasolderwick）andredoit.

Takecarenottooverheatthetracksasitisveryeasytoliftthemfromtheboardandbreakthem.

Whenyouaresolderingasensitivecomponentitisgoodpracticetoholdtheleadfromthecomponentsideoftheboardwithapairoflong-noseplierstodivertanyheatthatcouldpossiblydamagethecomponent.

Makesurethatyoudonotusemoresolderthanitisnecessaryasyouarerunningtheriskofshort-circuitingadjacenttracksontheboard,especiallyiftheyareveryclosetogether.

Whenyoufinishyourwork,cutofftheexcessofthecomponentleadsandcleantheboardthoroughlywithasuitablesolventtoremoveallfluxresiduesthatmaystillremainonit.

0-2V............R3=0ohm1%

0-20V...........R3=1.2Kohm1%

0-200V..........R3=12Kohm1%

0-2000V.........R3=120Kohm1%

WhenyouhavefinishedallthesolderingontheboardandyouaresurethateverythingisOKyoucaninserttheICinitsplace.TheICisCMOSandisverysensitivetostaticelectricity.Itcomeswrappedinaluminiumfoiltoprotectitfromstaticdischargesanditshouldbehandledwithgreatcaretoavoiddamagingit.Trytoavoidtouchingitspinswithyourhandsandkeepthecircuitandyourbodyatgroundpotentialwhenyouinsertitinitsplace.

Connectthecircuittoasuitablepowersupplyρ5VDCandturnthesupplyon.Thedisplaysshouldlightimmediatelyandshouldformanumber.Shortcircuittheinput（0V）andadjustthetrimmerP1untilthedisplayindicatesexactly«

0»

.

Ifitdoesnotwork

Checkyourworkforpossibledryjoints,bridgesacrossadjacenttracksorsolderingfluxresiduesthatusuallycauseproblems.

Checkagainalltheexternalconnectionstoandfrom