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I.IntroductionThe74HC595isan8-bitserial-inorparallel-outshiftregisterwithastorageregisterand3-stateoutputs.74HC595withthecharacteristicsofhighspeed,lowpowerconsumptionandsimpleoperation,canbeeasilyusedinMCUinterfacetodriveLEDoperation.ThisarticleintroducesthecircuitdesignofLEDdisplaydrivedby74HC595.CatalogI.IntroductionII.BasicDescription2.1LEDDisplay2.274HC595III.CircuitDesign3.1HardwareCircuit3.2DisplayDriverIV.ConclusionFAQOrdering&QuantityII.BasicDescription2.1LEDDisplayA7SegmentLEDDisplay,alsoknownasLEDdisplay,hasbeenwidelyusedinvariousinstrumentsbecauseofitslowprice,lowpowerconsumptionandreliableperformance.TherearemanytypesofLEDdriversonthemarket,andmostofthemhavemultiplefunctions,butthepriceiscorrespondinglyhigher.Ifusedinasimplesystemwithlowcost,itisnotonlyawasteofresources,butalsoincreasesthecostofproducts.Using74HC595chiptodriveLEDhasvariousdisadvantages.Highspeed,lowpowerconsumption,unlimitednumberofLEDs.ItcancontrolboththecommoncathodeLEDdisplayandthecommonanodeLEDdisplay.Thecircuitdesignedwith74HC595isnotonlysimple,butalsolowinpowerconsumptionandstrongindrivingability.Itisalowcostandflexibledesignscheme.2.274HC595The74HC595isan8-bitserial-in/serialorparallel-outshiftregisterwithastorageregisterand3-stateoutputs.Boththeshiftandstorageregisterhaveseparateclocks.Thedevicefeaturesaserialinput(DS)andaserialoutput(Q7S)toenablecascadingandanasynchronousresetMRinput.ALOWonMRwillresettheshiftregister.DataisshiftedontheLOW-to-HIGHtransitionsoftheSHCPinput.ThedataintheshiftregisteristransferredtothestorageregisteronaLOW-to-HIGHtransitionoftheSTCPinput.Ifbothclocksareconnectedtogether,theshiftregisterwillalwaysbeoneclockpulseaheadofthestorageregister.Datainthestorageregisterappearsattheoutputwhenevertheoutputenableinput(OE)isLOW.AHIGHonOEcausestheoutputstoassumeahigh-impedanceOFF-state.OperationoftheOEinputdoesnotaffectthestateoftheregisters.Inputsincludeclampdiodes.ThisenablestheuseofcurrentlimitingresistorstointerfaceinputstovoltagesinexcessofVCC.Figure1.74HC595FunctionalDiagramFigure2.74HC595LogicSymbolIII.CircuitDesign3.1HardwareCircuitFigure3isadisplaypanelcircuitdesignedwithAT89C2051and74HC595interface.Figure3.CircuitofDisplayPanelTheP115,P116,andP117oftheP1portareusedtocontrolthedisplayoftheLED,andtheyareconnectedtotheSLCK,SCLKandSDApinsrespectively.Threedigitaltubesareusedtodisplaythevoltagevalue.Onthecircuitboard,LED3isonthefarleftandLED1isonthefarright.Whensendingdata,firstsendthedisplaycodeofLED3,andfinallysendthedisplaycodeofLED1.ThebrightnessoftheLEDiscontrolledbytheresistanceofPR1toPR3.2.2DisplayDriverUseDISP1,DISP2,andDISP3tostoredisplaydata.AftertheCPUinitializationiscomplete,calltheLRDISPsubroutinetocleartheregisterof74HC595.ThereisnoneedtocalltheclearsubroutinebeforecallingthedisplaysubroutineDISPLAY.Nowwritethetwosubroutinesasfollows.①CLRDISP:MOVR2,#24CLRBIT:CLRSCLKCLRCMOVSDA,CSETBSCLKDJNZR2,CLRBITRET②Display:CLRSLCKMOVR3,#3MOVR0,#DISP3DISP1:MOVA,@R0MOVR2,#8DISP2:CLRSCLKRLCAMOVSDA,CSETBSCLKDJNZR2,DISP2DECR0DJNZR3,DISP1SETBSLCKRETIV.ConclusionItcanbeseenfromtheaboveexamplesthattherearenocomplicatedtechnicalproblemsinthedesignofhardwareandsoftwarewhen74HC595isusedtodesignLEDdrivercircuit.Inaddition,74HC595canbeusednotonlytodriveLEDdisplays,butalsotodrivelight-emittingdiodes.Each74HC595candrive8LEDssimultaneously.Thissolutionisidealwhenthevolumerequirementsoftheproductarenothighandwanttoreducethecost.FAQWhatis74HC595?74HC595isashiftregisterwhichworksonSerialINParallelOUTprotocol.Itreceivesdataseriallyfromthemicrocontrollerandthensendsoutthisdatathroughparallelpins.Wecanincreaseouroutputpinsby8usingthesinglechip.Whatisa74hc595n?8-bitShiftRegister74HC595NAshiftregisterisachipyoucanusetocontrolmanyoutputs(8here)atthesametimewhileonlyusingafewpins(3here)ofyourArduino.Howdoesashiftregisterwork?Shiftregistersholdthedataintheirmemorywhichismovedorshiftedtotheirrequiredpositionsoneachclockpulse.Eachclockpulseshiftsthecontentsoftheregisteronebitpositiontoeithertheleftortheright.How74HC595ShiftRegiesterworks?The595hastworegisters(whichcanbethoughtofasmemorycontainers),eachwithjust8bitsofdata.ThefirstoneiscalledtheShiftRegister.TheShiftRegisterliesdeepwithintheICcircuits,quietlyacceptinginput.Howdoesan8bitshiftregisterwork?TheSN74HC595Nisasimple8-bitshiftregisterIC.Simplyput,thisshiftregisterisadevicethatallowsadditionalinputsoroutputstobeaddedtoamicrocontrollerbyconvertingdatabetweenparallelandserialformats.YourchosenmicroprocessorisabletocommunicatewiththeTheSN74HC595Nusingserialinformationthengathersoroutputsinformationinaparallel(multi-pin)format.Essentiallyittakes8bitsfromtheserialinputandthenoutputsthemto8pins.

IRF840ALPBF-VISHAY

Itwillalsoperformwellasanamplifierandcanbeusedasaseparateamplifierorinaudioamplificationstages.

P6KE51A-E3/54-VISHAY

LM358Description: LM358isanoperationalamplifier8pinICavailableindifferentpackages.

STM32F446RCT6-64-LQFP-STMicroelectronics

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STM32F051K8T6-32-LQFP-STMicroelectronics

highpowerandlowpowerLEDs.

S7100PH-C4-CEXOWNN100-MAXLINEAR

MJE340isnotonlylimitedtouseforabovementionedpurposeshoweveritcanalsobeusedforamplificationpurposes.

IRFD014PBF-VISHAY

darlingtontransistormeanstherearetwotransistorinonepackageconnectedtoincreasegainatoutput

STM32F469ZIT6-144-LQFP-STMicroelectronics

ButthepinconfigurationofthesetransistorsmaydifferentfromtheSS9015thereforecheckpinoutofthetransistor

SI2304BDS-T1-GE3-VISHAY

AlotofgoodfeaturesinitsTO-92packagemakesthistransistoranidealTO-92transistortohaveinyourlab.

STM32F427IGH6-176-UFBGA-STMicroelectronics

amplifyinganylowgainsignalstohighgain.

STM32F301C8T6-48-LQFP-STMicroelectronics

Donotoperateitincircuitsusingmorethan100V.

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