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I.IntroductiontoGalvanometerThegalvanometerisanimportanttestinginstrument.Itisahigh-sensitivitymechanicalindicatingmeterfordetectingweakelectricity.Itisusedasazero-pointinginstrumentinbridgesandpotentiometers.Itcanalsobeusedtomeasureweakcurrents,voltagesandcharges..Accordingtotheinputmode,itcanbedividedintovoltagetypeandcurrenttype.Generally,voltagetypeismorecommonlyused.Fromthepaneldisplaymodeofthegalvanometer,itcanbedividedintothreetypes:pointertype,digitaltype,andmixedtype.Figure1ThegalvanometerThepointergalvanometercanconvenientlyobservethecontinuouslychangingcurrent,andintuitivelyjudgethedirectionofthecurrentfromthedeflectiondirection,soithasitsuniqueadvantagesinthebridgeexperiment.Thepointergalvanometerscurrentlyusedinphysicalexperimentshavethefollowingshortcomings:(1)Use9Vlaminatedbatterywithsmallcapacity,shortbatterylifeandhighcost;(2)ItsinternalamplifyingcircuitadoptsOP07orICL7650design,withoutpowermanagementcapability,itiseasytocausethebatterytobeconsumedunnecessarily;(3)Duetotheuseofmanydiscretecomponents,theamplifierispronetodriftandunstable.Thispaperusesagalvanometerdesignedbasedonthethree-op-amphighcommon-moderejectionratioandhighstabilityinstrumentationamplifierAD620andMicrochips6-pinMCUPIC10F206tosolvetheaboveproblems.CatalogI.IntroductiontoGalvanometerII.HardwareSystemDesign2.1HardwareSystemBlockDiagram2.2InstrumentationAmplifierAD6202.3MicrocontrollerPIC10F2062.4AmplifyingCircuitofGalvanometer2.5PowerMonitoringandPowerManagementCircuitofGalvanometerIII.SoftwareSystemIV.ConclusionFAQOrdering&QuantityII.HardwareSystemDesign2.1HardwareSystemBlockDiagramTheblockdiagramofthehardwaresystemisshowninFigure2.TheDCvoltagesignalfirstpassesthroughananti-radiofrequencyinterferencelow-passfiltercircuit,weakenstheinterferencesignal,andthensendsittotheinstrumentationamplifierAD620fordifferentialamplification,andthendrivesthepointermetertodisplay.The6-pinmicrocontrollerPIC10F206isresponsibleforthepowermonitoringandpowermanagementofthegalvanometer.Thewholegalvanometeronlyuses3VDCpowersupplyconnectedinserieswithtwoAAbatteries.Figure2Thehardwaresystemblockdiagramofthegalvanomete2.2InstrumentationAmplifierAD620AD620isalow-costandhigh-precisioninstrumentationamplifierlaunchedbytheAmericanADIcompany.Ithasthecharacteristicsofhighaccuracy,lowoffsetvoltage(maximum50uV)andlowoffsetdrift(maximum0.6uV℃/),anditsmaximumoperatingcurrentisonly1.3mA,onlyanexternalresistorisneededtosetthegain,andthegainrangeis1to10000.Inaddition,AD620adopts8-pinSOICandDIPpackage,thesizeissmallerthanthediscretecircuitdesign,andthepowerconsumptionislower,soitissuitableforbattery-poweredinstrumentapplications.Figure3AD620BecauseitsinputstageusesSuperetaprocessing,itcanachievealowinputbiascurrentofupto1.0nA.AD620hasalowinputvoltagenoiseof9nV/Hzat1kHz,apeak-to-peaknoiseof0.28Vinthefrequencybandfrom0.1Hzto10Hz,andaninputcurrentnoiseof0.1pA/Hz,soitcanbeusedasapreamplifierwell.Atthesametime,the0.01%settlingtimeofAD620is15s,whichisverysuitableformultiplexingapplications;andthecostisverylow,enoughtorealizethedesignofaninstrumentationamplifierperchannel.2.3MicrocontrollerPIC10F206PIC10F206isalow-cost,6-pin8-bitflashmicrocontrollerintroducedbytheUSMicrochipcompanythatusesRISCarchitecture.PIC10F206has512wordsofFLASH,24bytesofSRAM,watchdogtimer(WDT),power-onresetcircuit(POR)anddeviceresettimer(DRT)and4MHzinternaloscillator,thuseliminatingtheneedforexternalresetcircuitandthecrystaloscillator,reducessystemcostandpowerconsumption,andenhancessystemreliability.Italsohasawideoperatingvoltagerange(20Vto5.5V).Theabovecharacteristicsmakeitsuitableforapplicationsinprice-sensitiveandbattery-poweredareas.Figure4PIC10F2062.4AmplifyingCircuitofGalvanometerTheamplifyingcircuitofgalvanometertakestheinstrumentamplifierAD620asthecoreelement,asshowninFigure5.ThedifferentialsignaloutputbytheDCbridgeisinputfromthesocketJ1,passesthroughtheanti-radiofrequencyinterferencelow-passfiltercircuit[2]formedbyR1,R2,C1,C2,C3,andreachestheinstrumentationamplifierAD620afterweakeningtheinterferencesignal.D1,D2andR1,R2togetherformtheinputprotectioncircuitofthegalvanometer,whichcanwithstandinputvoltagesoftensofvolts.R3,R4providealoopfortheinputbiascurrentofAD620[1]toensurethatitcanworkstablyandreliably.TheresistanceR0andpotentiometerRP1betweenpin1andpin8ofAD620aregainadjustmentresistors,denotedasRG.R0isconnectedinserieswithRP1tolimittheupperlimitofthemagnificationto495times.ThepotentiometerRP2andR5,R6formthezeroadjustmentcircuitofthegalvanometertogether,realizezeroadjustmentbychangingthevoltageoftheREFpinofAD620.R7andC7formtheoutputlow-passfilterofAD620.R7,D3,D4constitutetheprotectioncircuitofthepointermeterhead.Figure5TheamplifyingcircuitofgalvanometerThemaximumsensitivityofagalvanometerisusually10uV/degreeto15uV/degree,whichcanwellmeettherequirementsoftheexperiment.TheinternalresistanceRgofthegalvanometermeterheadis4.7k,thegainadjustmentresistanceRG=R0+RP1,takeR0=100,R7=1k,whenRP1is0,theamplificationfactorofAD620isTakingintoaccountthepartialpressureofR7andtheinternalresistanceRgofthemeter,themagnificationofthegalvanometerisThecurrentsensitivityofthemeterheadis1Aminute/degree,sothevoltagesensitivityofthemeterheadis4700Vminute/degree.ThesensitivityofthegalvanometerisS=4700/G=115V/divisionMeettherequirementsofphysicalexperiments.2.5PowerMonitoringandPowerManagementCircuitofGalvanometerFigure6isthepowermonitoringandpowermanagementcircuitofthegalvanometer.TheGP2pinofthemicrocontrollerPIC10F206isconnectedwiththeP-channelMOSFETtubeQ1,thepurposeistocontrolwhethertosupplypowertotheamplifyingcircuitofthegalvanometer.WhenGP2outputislowlevel,Q1isturnedon,andthesystemsuppliespowertotheamplifiercircuit.TheroleofICL7660inpowerconversionhereistoconvert+VSto-VS.R8,R9andtheanalogcomparatorinsidePIC10F206togetherformthepowersupplyvoltagemonitoringcircuit.ThenegativeinputterminalCINoftheanalogcomparatorisconnectedtotheinternalreferencevoltageofthesingle-chipmicrocomputer(thenominalvalueofthevoltageis06V),andthepositiveinputterminalCIN+isconnectedwiththepartialpressureofR8andR9.BecausethelowestoperatingvoltageofAD620is23V,fromaconservativepointofview,thelowerlimitoftheoperatingvoltageissetto2.5V.Whenthepositivepowersupplyvoltageislessthan2.5V,thevoltageofCIN+islessthan0.6V,andthecomparatoroutputisreversed.Afterthemirocontrollerdetectsthisevent,theGP2outputshighlevel,turnsoffthepowersupplyoftheamplifiercircuit,andthenexecutestheSLEEPinstructiontomakethemicrocontrollerentersleepstatus.Figure6PowermonitoringandpowermanagementcircuitofgalvanometerInordertosavepowerconsumption,whentheworkingvoltageisnormal,thegalvanometershouldenterthesleepstate(iesoftshutdown)afterworkingforaperiodoftime,anditcanbeawakenedatanytimewhenitneedstowork.ButtonS1issetforthisfunction.Theworkingtimeofthegalvanometerispresetto15minutes.Whentheworkingtimeisup,theGP2ofthesingle-chipmicrocomputeroutputsahighlevel,shutsoffthepowersupplyoftheamplifyingcircuit,andthenexecutestheSLEEPinstructiontomakethemicrocontrollerenterssleepstate.Inthesleepstate,ifS1ispressed,thepinlevelofGP3willchange.Thiseventwillresetthemicrocontroller(note:PIC10F206hasnoconventionalinterruptfunction)andwakeupthemicrocontroller.Inthesleepstate,thecurrentconsumptionofthegalvanometerislessthan0.1A,whichisverypower-saving,sothereisnoneedtoworryaboutforgettingtoturnoffthepowersupplyofthegalvanometerandconsumingthebattery.III.SoftwareSystemWhenthegalvanometerispoweredon,themicrocontrollerfirstperformssysteminitialization,thensuppliespowertoICL7660andAD620,andthenturnsontheanalogcomparatortocheckwhetherthesupplyvoltageisappropriate.Ifthevoltageisappropriate,continuetosupplypowertotheamplifiercircuit,andthenexecutea15-minutecountdown.IfS1ispressedduringthisperiod,thetimingtimeisresetto15minutes.Whenthe15-minutecountdownisup,thesingle-chipmicrocomputerturnsoffthepowersupplyoftheamplifiercircuit,andthenentersthesleepstate(ie,softshutdown).TheflowchartoftheprocedureisshownasinFig.7.Figure7FlowchartoftheprocedureIV.ConclusionThisarticlediscussesthegalvanometerbasedoninstrumentationamplifierAD620andmicrocontrollerPIC10F206,whichhasstableperformanceandlowpowerconsumption.Thecurrentisabout4mAduringnormaloperation,andthecurrentconsumedinsleepmodeislessthan0.1uA,whichisverysuitableforbatterypowersupply.TheuseoftwoAAbatteriesforpowersupplysavesbatterycost.Thesoftshutdownfunctioncaneffectivelypreventbatteryconsumptioncausedbyforgettingtoturnoffthepower.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstruments

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