Tkool Electronics

I.DescriptionNowadays,LCD,VFD,LEDandotherdisplaydeviceshavebroughtinfinitecharmtointelligenthouseholdappliances.Atpresent,majorchipmanufacturershaveintroducedvariousdedicateddisplaydriverchips,theyhavebecomethemainstreamofdisplaydrivetechnology.However,thedisplayrequirementsofwhitegoodsarerelativelylow.Basedoncostconsiderations,thisarticleintroducesa74HC164-baseddisplaydrivecircuitdesignscheme,whichnotonlyachievesthesamedisplayeffect,reducescosts,butalsoimprovessystemreliability.74HC164CatalogI.DescriptionII.74HC164AdvantageAnalysisIII.74HC164ChipIntroductionIV.74HC164DisplayDriveCircuitV.74HC164DisplayCircuitDriverVI.ProcedureDescriptionFAQOrdering&QuantityII.74HC164AdvantageAnalysisUndernormalcircumstances,thedisplaycircuitofsmarthomeappliancesiscontrolledbyasingle-chipmicrocomputer,suchasthedisplayedcontentandthedisplaymode.Thesingle-chipmicrocomputerplaysanimportantroleinthecontrolcircuitofsmarthomeappliances.Itsselectionnotonlydeterminestherealizationofthecontrolcircuit,butalsohasagreatinfluenceonthecostofthecontroller.Weusetheserialinputandparalleloutputfunctionsofthe74HC164chiptocarryoutserialcommunicationwiththemicrocontroller,andtheparalleloutputportdirectlydrivesthedisplaydevice.ThissolutioncanexpandtheI/Oportofthesingle-chipmicrocomputerandreducetheresourcerequirementsofthesingle-chipmicrocomputer.Moreover,thechipinstallationmethodisveryflexible,whichcanreducethenumberofconnectingwiresofthedisplaypanel,improvethereliabilityofthesystem,andhasagreatercostadvantage.,Itiswidelyusedinbuttonsanddisplaydrivecircuits.III.74HC164ChipIntroduction74HC164isahigh-speedsilicongateCMOSdevice,whichispincompatiblewithlow-powerSchottkyTTL(LSTTL)devices.74HC164isan8-bitedge-triggeredshiftregister,serialinputdata,andthenparalleloutput.Dataisseriallyinputthroughoneofthetwoinputterminals(DSAorDSB);eitherinputterminalcanbeusedasahigh-levelenableterminaltocontrolthedatainputoftheotherinputterminal.Eitherconnectthetwoinputterminalstogether,orconnecttheunusedinputterminalstoahighlevel,sotheymustnotbeleftfloating.Thepindistributionof74HC164isshownasinFig.1.CompatiblewithTTLlevel,thehighestoperatingclockfrequencyis20MHz,thefan-outfactoris10,thepowerdissipationis500mW,andtheoutputcurrentIo(eachend)is25mA,whichcandirectlydriveLEDdisplaydevices.Figure174hc164pinoutAccordingtothelogicfunctionofthechip,thewaveformdiagramoftheinputandoutputsignalscanbeobtained,asshowninFigure2.TheoutputsignalsQ0~Q7aredelayedbyoneclockcyclerespectively,andcanform8scansignals.Figure274HC164signalwaveformIV.74HC164DisplayDriveCircuitThecircuitshowninFigure3isahybriddisplaycircuitcomposedoftouchswitches,nixietubesandLEDs.Amongthem,16buttons,2nixietubes,and8LEDsareatypical538scanningcircuit.The8pinsofthe74HC164chipQ0~Q7outputcolumnscansignals,andthemicrocontrollerdirectlyprovides5rowsofscansignals.Thesingle-chipmicrocomputerprovidesclockinputanddatainputsignalsfor74HC164tocontrolthedisplaycontent.Thecircuitrequires8pinsofthesingle-chipmicrocomputerintotal,whichsaves6pinresourcescomparedwiththeconventionalscanningcircuitandhascertaincostadvantages.DiodeD2-D23playsanisolationroletopreventthemutualinterferenceof74HC164chippinpotential.Forexample:whenachannelisselected,the74HC164outputpinsQ0~Q6arehighlevel,andQ7islowlevel.Atthistime,ifSW1andSW2arepressedatthesametime,pinQ7andpinQ6areinashort-circuitstate,whichwilldamagethechip.Clockinputpinsanddatainputpinsneedtobeconnectedtoceramiccapacitorstoresisthigh-frequencyinterference,butthecapacitanceshouldnotbetoolargetoavoidexcessivedistortionoftheinputwaveformandmakethecircuitunabletoworknormally.Itisrecommendedtouse100-1000pF.Figure3showsapracticalexampleofthecircuitV.74HC164DisplayCircuitDriverTakethe78K0Sseries8-bitMCUUPD78F9116fromNECCorporationofJapanasanexample,thedriverneedstodetect16,thenumberofkeystobedetected,thedisplaydrive28-segmentdigitaltubes,andthenumberofLEDs16(8expandedonthebasisofthereferencecircuit).Thesingle-chipmicrocomputerdirectlyprovides6linescansignals,andatthesametimeprovidesclockinputanddatainputsignalsfor74HC164tocontrolthedisplaycontent.TheIOportisdefinedasfollows:Eachsubroutinescans2groupsof31keys,andscansallkeyswithin8times.Displayscanchannelnumber0~3,displaytimeofeachchannel(1digitaltubeor1groupofLED)occupies1/4,andtherefreshcycledependsonthefrequencyofsubroutineexecution.Theprogrammustbeexecutedcyclically.Itcanbecalledasaregularsubroutineordirectlyembeddedinthemainprogramfile.Itismoreappropriatetoexecuteitevery1~3mS.Theconfirmationtimeforabuttontobeliftedorpressed(24mS~32mS)--(72ms~96mS),theresponsespeedcanmeetpeoplesoperatinghabits,thedisplayrefreshfrequencyissetto250Hz--83Hz,ifitislowerthan40~50HzFlashing.TheprogramflowchartisshowninFigure4.Figure4ProgramflowchartVI.ProcedureDescription(1)ExternalnameandglobalvariabledeclarationFAQHowdoesthe74HC164transmitdatainthemicrocontrollercircuit?Onepinofthesingle-chipmicrocomputerislikeafaucet,andthedataissentonebyone,thatis,likethewaterfromthefaucet,drippingdropbydrop.The74H164islikeasmallbowlreceivingwater.Itisjustfullafterreceiving8dropsofwater.Atthistime,itissenttothedigitaltube.Thesingle-chipmicrocomputermustsendan8-bit(ormore)data,ifitissentatthesametime,itisaparalleltransmission,ifitisabitbybit,itisaserialtransmission.Thedataofthesingle-chipmicrocomputerissenttothe74HC164bitbybit,whichisserial,andthe74HC164sendsthedatatothedigitaltubeatonce,whichisparallel.So74HC164playsarolefromserialtransmissiontoparalleltransmission.Whatisthedifferencebetween74HC164Dand74HC164NMCU?TheDin74HC164Drepresentsachippackage.TheNin74HC164Nmeansdualin-lineplasticpackaging.Whatisthedifferencebetween74HC164and74LS164,cantheybeusedtogether?74ls164isaTTLcircuit,thepowersupplyvoltageis5V,thehigh-leveloutputcurrentIohis-0.4MA,andthelow-leveloutputcurrentis8MA.74HC164isaCMOScircuit,thepowersupplyvoltageis2V~6V,theoutputdrivecurrentcanreachplusorminus20MA.Ifthepowersupplyvoltageyouuseis5Vandtheoutputdrivecurrentissuitablefor74ls164,theycanbeusedtogether.Whatdevicescan74hc164bereplacedwith?74HC164isaCMOSdevicewithapowersupplyvoltageof2V-6V.Itcanbedirectlyreplacedby74HCT164,40H164.Ifthepowersupplyvoltageis5Vandtheoutputdrivecurrentissmall,itcanalsobereplacedby74164,74LS164,74F164,74ALS164.Whichof74LS164and74HC164hashigherdrivingcapability?74LS164isaTTLdevicewithahigh-leveldrivingcapabilityofabout0.4mAandalow-leveldrivingcapabilityofabout8mA.74HC164isaCMOSdevice,withhigh-levelandlow-leveldrivecapabilityupto20mA.TheabovedatacomesfromDATASHEET.Butgenerallyspeaking,thehigh-leveloutputcapabilityofmanyCMOSdevicesisweak,smallerthanTTL,andthelow-leveldrivecapabilityisstronger.Can74hc164nbeusedtodrivethedigitaltube?Ofcourse,youcanusethe164chiptodrivethenixietube,whichismostlyusedinsituationswheretheIOportresourcesaretightandthedisplaydatarefreshofthenixietubeisslow.Whendesigningthecircuit,multiple164chipsareusedincascade,nomatterhowmanydigitaltubesaredriven,only2IOportsofthesingle-chipmicrocomputerareoccupied.ItcanbesaidthatitisthemostIOport-savingdrivingmethod,anditisstilldrivenstatically,withoutstrobeandbrightnessLowphenomenon.Thedisadvantageisthatmultiple164sareusedincascadeconnection,whichwillcausethesingle-chipmicrocomputertosendalargeamountofdisplaydata(1bytepernixietube)atonetimewhenrefreshingthedisplaydata.Duringthisprocess,thenixietubewillbeallon,althoughthedataissentTheprocessdurationisveryshort,butitstillaffectsthedisplayeffect.Itisrecommendedtoturnoffthedigitaltubewhenrefreshingthedata.

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thresholdapproachandPrincipalComponentAnalysis(PCA)methods.

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