文献翻译——设计一个基于单片机的温度数据记录器

第1页外文文献资料“DesigningaMicrocontrollerBasedTemperatureDataLogger”Abstract-Withtheadvancementoftechnology,theprocessesarebecomingmoreandmorecomplex.Duetothisincreaseincomplexity,forefficientanalysisofprocessthenumberofparametersrequiredfordataacquisitionalsoincreases.DataAcquisitionissimplythegatheringofinformationaboutasystemorprocess.Itistheprocessofcollectingdatainanautomatedfashionfromanaloganddigitalmeasurementsourcessuchassensorsanddevicesundertest.Beforethecomputerage,mostdatawasrecordedmanuallyoronstrip-chartrecorders.Manynewgenerationdataacquisitionproductshavebeendevelopedduetoemergenceofmicrocontrollerthatenablesreal-timegathering,analysis,loggingandviewingofdata.Tomeettheserequirementsthedemandofanimproved,efficientandup-to-datedataloggerisincreasing.Adataloggerisanelectronicinstrumentthatcanrecorddigitaloranalogmeasurementsoveraperiodoftime.Itconsistsofasensor,microcontroller,andadatastoragedevice.Dataloggershaveanon-boardmemorythatislargeenoughtoholddatathatisrecordedoveralongerperiodoftime.Thememoryinthesedataloggersmaybeflashmemory,EEPROMorStaticRandomAccessMemorythatisbatterybacked.Dataloggersareprovidedwithrealtimeclockstorecordthedateandtimeofacquisition.Inthisthesis,adataloggerforspecificapplicationhasbeendesigned.Thesystemworksaroundthefamous8051family.ThesystemisdesignedanddevelopedtomeasurethetemperaturewiththehelpoftemperaturesensorsandtheresultisstoredinmemorysuchasEEPROMforpostprocessanalysis.Duringthetesting,itisverifiedthatthereiscontinuousandcorrectacquisitionofdata.Itisalsoverifiedthatthedataissequentiallystoredinmemory.ThisverificationisdonebyusinganLCDdisplay.Thefocusofdesignisonportabilityandlowpowerconsumptionforbatteryoperated第2页applications.Thedesignedsystemistestedunderdifferentconditions:atroomtemperatures,atlowtemperatures,atdifferenttemperatures,readingstakenoverlongtime.Foralltheseconditions,thesystemperformedaccurately.Theprocessestocollect,analyzeandstorethedataforlateruseiscalledlogging.Itisaprocesstorecordeventsduringatestormeasurementwiththeuseofasystemoraproduct.Thehumanbrainanditsmemory,thenaturescreation,nodoubtisthebestdataloggingmechanism.Wherethereistheneedtocollectinformationfasterthanahuman,dataloggerscanpossiblycollecttheinformationandincaseswhereaccuracyisessential.Adataloggerisadevicethatcanbeusedtostoreandretrievethedata.Dataloggingalsoimpliesthecontrolofhowsensorcollectsandanalyzesthedata.Itiscommonlyusedinscientificexperimentsandinmonitoringsystems.Dataloggersautomaticallymakearecordofthereadingsoftheinstrumentslocatedatdifferentpartsofplant.Thetypeofinformationrecordedisdeterminedbytheuser.Theiradvantageisthattheycanoperateindependentlyofacomputerandtheyareavailableinvariousshapesandsizes.Therangeincludessimpleeconomicalsinglechannelfixedfunctionloggerstomorepowerfulprogrammabledevicescapableofhandlinghundredsofinputs.Temperatureistheever-changingparameterbecauseofexpositiontohugearrayofstimulifromtheirenvironment.Itcanbemeasuredviaadiversearrayofsensors.Alloftheminfertemperaturebysensingsomechangeinaphysicalcharacteristic.Onemustbecarefulwhenmeasuringtemperaturetoensurethatthemeasuringinstrument(thermometer,thermocouple,etc)isreallythesametemperatureasthematerialthatisbeingmeasured.Undersomeconditionsheatfromthemeasuringinstrumentcancauseatemperaturegradient,sothemeasuredtemperatureisdifferentfromtheactualtemperatureofthesystem.Insuchacasethemeasuredtemperaturewillvarynotonlywiththetemperatureofthesystem,butalsowiththeheattransferpropertiesofthesystem.Theobjectiveofthisworkistousedataloggingfortemperaturemeasurement.Inordertomeettheaboverequirements,alowcost,versatile,第3页portabledataloggerisdesigned.AmicrocontrollerbasedtemperaturedataloggerhasbeendevelopedformeasuringtemperatureatdifferentinputchannelsofADC.Thedeviceisdesignedtoreceivedatafromtemperaturesensorsandtostoretheresultsonexternalnon-volatileelectricallyerasableprogrammablereadonlymemory(EEPROM)forpostprocessanalysis.AnintegratedLiquidcrystaldisplay(LCD)isalsousedforrealtimedisplayofdataacquiredfromvarioussensors.Inthepresentwork,temperaturesindicatedbythreechannelsarecomparedwithstandardtemperatureobtainedfromclinicalthermometeraftertheintervalsoftime.Basedontheseresults,theaccuracyofthechannelsisnotedandbycomparingthem,themostaccurateoneamongtheseisfound.1.IntroductiontodataloggersThedataloggerisaninvaluabletooltocollectandanalyzeexperimentaldata,havingtheabilitytoclearlypresentrealtimeanalysiswithsensorsandprobesabletorespondtoparametersthatarebeyondthenormalrangeavailablefromthemosttraditionalequipment.Thedifferencesbetweenvariousdataloggersarebasedonthewaythatdataisrecordedandstored.1.1.DefinitionofDataLoggersDataloggerisanelectronicdevicethatautomaticallyrecords,scansandretrievesthedatawithhighspeedandgreaterefficiencyduringatestormeasurement,atanypartoftheplantwithtime.Thetypeofinformationrecordedisdeterminedbytheuseri.e.whethertemperature,relativehumidity,lightintensity,voltage,pressureorshockistoberecorded,thereforeitcanautomaticallymeasureselectricaloutputfromanytypeoftransducerandlogthevalue.Adataloggerworkswithsensorstoconvertphysicalphenomenaandstimuliintoelectronicsignalssuchasvoltageorcurrent.Theseelectronicsignalsarethenconvertedintobinarydata.Thebinarydataistheneasilyanalyzedbysoftwareandstoredonmemoryforpostprocessanalysis.1.2.CharacteristicsofDataLoggersDataloggerspossessthefollowingcharacteristics:1.)Modularity:Dataloggerscanbeexpandedsimplyandefficientlywheneverrequired,withoutanyinterruptiontotheworkingsystem.第4页2.)ReliabilityandRuggedness:Theyaredesignedtooperatecontinuouslywithoutinterruptionevenintheworstindustrialenvironments.3.)Accuracy:Thespecifiedaccuracyismaintainedthroughouttheperiodofuse.4.)ManagementTool:Theyprovidesimpledataacquisition,andpresenttheresultsinhandyform.5.)Easytouse:Thesecommunicatewithoperatorsinalogicalmanner,aresimpleinconcept,andthereforeeasytounderstand,operateandexpand.1.3.OperationofdataloggerTheabilitytotakesensormeasurementsandstorethedataforfutureuseis,bydefinition,acharacteristicofadatalogger.However,adata-loggingapplicationrarelyrequiresonlydataacquisitionandstorage.Inevitably,theabilitytoanalyzeandpresentthedatatodetermineresultsandmakedecisionsbasedontheloggeddataisneeded.Acompletedata-loggingapplicationtypicallyrequiresmostoftheelementsillustratedbelow.1.4.AdvantagesofDataLoggers1.)DataLoggersdontinterferewiththeusersinperformingtheirtasks.2.)Theycanoperateindependentlyofacomputerandtheyareavailableinvariousshapesandsizes.3.)Therangeofdataloggersvariesfromsimplechannelinputstomultichanneldevices.2.SystemDesignandImplementationForthedesignanddevelopmentofthesystem,themethodologyusedinvolvesthesoftwareandhardwareimplementation.Theactualimplementationofthesysteminvolvesthefollowingsteps:1.)SystemDefinition:Broaddefinitionofsystemhardwareincludingmicrocontrolleranditsinterfacewithdisplay,ADC,memory,keypadetc.2.)CircuitDesign:Selectionof8051microcontrollerandotherinterfacingdevices,aspersystemdefinition.Designofhardwarecircuitanditstestingonlaboratorykitswithsomesimplemicrocontrollersoftwareroutines.3.)PCBDesignandFabrication:Generationofschematicdiagramsandthe第5页productionofcircuitboardlayoutdatafortheprocurementofthecircuitboard.4.)HardwareModifications:Makinganyhardwarechangesfoundnecessaryaftertheinitialhardwaretests,toproducearevisedcircuitboardschematicdiagramandlayout.5.)SoftwareDesign:Developingalgorithmforthesystem,allocatingmemoryblocksasperfunctionality,codingandtesting.6.)IntegrationandFinalTesting:Integratingtheentirehardwareandsoftwaremodulesanditsfinaltestingfordataloggingoperation.Thusthecompletedesignisdividedintotwoparts:1.)HardwareImplementation.2.)SoftwareImplementation.3.HardwareImplementationItinvolvesthedetailsofthesetofdesignspecifications.Thehardwaredesignconsistsof,theselectionofsystemcomponentsaspertherequirement,thedetailsofsub-systemsthatarerequiredforthecompleteimplementationofthesystemandfullhardwareschematicsforthePCBlayout.Designofthecircuitanditstestinghasbeencarriedout.Itinvolvesthecomponentselection,componentdescriptionandhardwaredetailsofthesystemdesigned.3.1.ComponentselectionanddescriptionTemperaturemeasurementusingmicrocontrollerbaseddataloggerincludesthefollowingcomponents:1.)TemperatureSensor(LM35)2.)AnalogtoDigitalConverter(ADC0808)3.)Microcontroller(AT89C51)4.)KeypadMatrix(44matrix)5.)LiquidCrystalDisplay(HD44780)6.)ExternalMemory(AT28C64)3.2.SelectionofSuitableTransducerFormeasuringthetemperature,thechoiceofsensorisofutmostimportance.ThesensorsareusedinmanyfieldsincludesThermocouples,Resistivetemperaturedevices(RTDsandthermistors)andbimetallicdevices.Thefactorsfortheselectionofsensorthatwetakeinto第6页accountincludestheinherentaccuracyfordurability,rangeofoperation,susceptibilityoutsidenoiseinfluences,easeofmainmaintenanceandinstallation,handlingduringinstallation(delicacy),easeofcalibration,andtypeofenvironmentitwillbeusedin.ThetemperaturesensorusedforthispurposeisLM35becauseofthefollowingfeatures:TheLM35seriesareprecisionintegrated-circuittemperaturesensors,whoseoutputvoltageislinearlyproportionaltotheCelsius(Centigrade)temperature.TheLM35thushasanadvantageoverlineartemperaturesensorscalibratedinKelvin,astheuserisnotrequiredtosubtractalargeconstantvoltagefromitsoutputtoobtainconvenientCentigradescaling.TheLM35doesnotrequireanyexternalcalibrationortrimmingtoprovidetypicalaccuraciesof14Catroomtemperatureand34Coverafull55to+150Ctemperaturerange.TheLM35slowoutputimpedance,linearoutput,andpreciseinherentcalibrationmakeinterfacingtoreadoutorcontrolcircuitryespeciallyeasy.Itcanbeusedwithsinglepowersupplies,orwithplusandminussupplies.3.3AnalogtoDigitalConverter(ADC)Inphysicalworldparameterssuchastemperature,pressure,humidity,andvelocityareanalogsignals.Aphysicalquantityisconvertedintoelectricalsignals.Weneedananalogtodigitalconvertertotranslatetheanalogsignalstodigitalnumberssothatthemicrocontrollercanreadthem.Thus,ananalog-to-digitalconverter(ADC)isanelectroniccircuitthatconvertscontinuoussignalstodiscretedigitalnumbers.Analogtodigitalconvertersarethemostwidelyuseddevicesfordataacquisition.TheADC0804ismostwidelyusedchip.Forthiswork,theanalogtodigitalconverterchosenisADC0809.BecauseADC0804hasonlyoneanaloginput,thischiphas8oftheanaloginputs.Thischipallowsustomonitorupto8differenttransducersusingonlyasinglechip.The8analoginputchannelsaremultiplexedandselectedaccordingtotherequirement.InADC0808/0809,Vref(+)andVref(-)setthereferencevoltage.IfVref(-)=GndandVref(+)=5V,thestepsizeis5V/256=19.53.Thereforetogeta10mVstepsizeweneedtosetVref(+)=2.56VandVref(-)=Gnd.第7页WeuseA,B,CaddressestoselectIN0-IN7andactivateAddresslatchenable(ALE)tolatchintheaddress.SCisforStartConversion.EOCisforEndofConversionandOEisforOutputEnable.TheoutputpinsD0-D7providesthedigitaloutputfromthechip.Vref(-)andVref(+)arethereferencevoltages.SincethereisnoselfclockinginthischipsotheclockmustbeprovidedfromanexternalsourcetotheClock(CLK)pin.3.4.Microcontrollerchip3.4.1.AT89C51MicrocontrollerThe8051familyofmicrocontrollersisbasedonanarchitecturewhichishighlyoptimizedforembeddedcontrolsystems.Itisusedinawidevarietyofapplicationsfrommilitaryequipmenttoautomobilestothekeyboard.SecondonlytotheMotorola68HC11ineightbitprocessorssales,the8051familyofmicrocontrollersisavailableinawidearrayofvariationsfrommanufacturerssuchasIntel,Philips,andSiemens.Thesemanufacturershaveaddednumerousfeaturesandperipheralstothe8051suchasI2Cinterfaces,analogtodigitalconverters,watchdogtimers,andpulsewidthmodulatedoutputs.Variationsofthe8051withclockspeedsupto40MHzandvoltagerequirementsdownto1.5voltsareavailable.Thiswiderangeofpartsbasedononecoremakesthe8051familyanexcellentchoiceasthebasearchitectureforacompanysentirelineofproductssinceitcanperformmanyfunctionsanddeveloperswillonlyhavetolearnthisoneplatform.TheAT89C51isalow-power,high-performanceCMOS,8-bitmicrocomputerwith4KbytesofFlashprogrammableanderasablereadonlymemory(PEROM).ThedeviceismanufacturedusingAtmelshigh-densitynonvolatilememorytechnologyandiscompatiblewiththeindustry-standardMCS-51instructionsetandpinout.Theon-chipFlashallowstheprogrammemorytobereprogrammedin-systemorbyaconventionalnonvolatilememoryprogrammer.Bycombiningaversatile8-bitCPUwithFlashonamonolithicchip,theAtmelAT89C51isapowerfulmicrocomputer,whichprovidesahighly-flexibleandcost-effectivesolutiontomanyembeddedcontrolapplications.3.5.KeypadMatrixAtthelowestlevels,keyboardsareorganizedinamatrixofrowsand第8页columns.TheCPUaccessesboththerowsandcolumnsthroughports,therefore,withtwo8-bitports;an88matrixofkeyscanbeconnectedtothemicrocontroller.Whenakeyispressed,arowandacolumnmakeacontact,otherwise,thereisnoconnectionbetweenrowsandcolumns.Thedetectionofthekeyvariesfromscanningofthekeytogroundingtherowsandcolumns.3.6.LiquidCrystalDisplayAliquidcrystaldisplay(LCD)isathin,flatdisplaydevicemadeupofanynumberofcolorormonochromepixelsarrayedinfrontofalightsourceorreflector.Itusesverysmallamountsofelectricpower,andisthereforesuitableforuseinbattery-poweredelectronicdevices.Eachpixelconsistsofacolumnofliquidcrystalmoleculessuspendedbetweentwotransparentelectrodes,andtwopolarizingfilters,theaxesofpolarityofwhichareperpendiculartoeachother.Withouttheliquidcrystalsbetweenthem,lightpassingthroughonewouldbeblockedbytheother.Theliquidcrystaltwiststhepolarizationoflightenteringonefiltertoallowittopassthroughtheother.MoremicrocontrollerdevicesareusingsmartLCDdisplaystooutputvisualinformation.LCDdisplaysdesignedaroundHitachisLCDHD44780module,areinexpensive,easytouse,anditisevenpossibletoproduceareadoutusingthe8x80pixelsofthedisplay.HitachiLCDdisplayshaveastandardASCIIsetofcharactersplusJapanese,Greekandmathematicalsymbols.Foran8-bitdatabus,thedisplayrequiresa+5Vsupplyplus11I/Olines.Fora4-bitdatabusitonlyrequiresthesupplylinesplussevenextralines.WhentheLCDdisplayisnotenabled,datalinesaretri-statewhichmeanstheyareinastateofhighimpendence(asthoughtheyaredisconnected)andthismeanstheydonotinterferewiththeoperationofthemicrocontrollerwhenthedisplayisnotbeingaddressed.3.7.ExternalMemoryThemicrocontrollerAT89C51thathasbeenusedindesigningadataloggerhasinternalmemoryof8k.Inthedesignofdatalogger,theneedistowriteinthememorythatiswhyusingtheexternalmemoryissignificantasitisnotpossibletowritedataininternalmemoryofmicrocontroller.Forthisapplication,thecontentsofmemoryareneededtobewrittenanderased第9页anumberoftimesandforthisreasonelectricallyerasableandprogrammablememory(EEPROM)istobeused.InternallyEEPROMissimilartoerasableprogrammablereadonlymemory(EPROM).AT28C64hasbeenusedsinceithaslargememoryi.e.64k.TheAT28C64isaccessedlikeaStaticRAMforthereadorwritecycleswithouttheneedforexternalcomponents.Duringabytewrite,theaddressanddataarelatchedinternally,freeingthemicroprocessoraddressanddatabusforotheroperations.Followingtheinitiationofawritecycle,thedevicewillgotobusystateandautomaticallyclearandwritethelatcheddatausinganinternalcontroltimer.4.HardwaredetailsofsystemdesignedFigure3.1showstheschematicfortheimplementationofthehardwareforthispurpose.Figure3.1SchematicdiagramFigure3.2showstheblockdiagramofthesystemhardware第10页Figure3.2Blockdiagramofsystemhardware5.SoftwaredesignanddevelopmentSoftwaredesignincludesdevelopingalgorithmforthesystem,allocatingmemoryblocksasperfunctionality,writingtheseparateroutinesfordifferentinterfacingdevicesandtestingthemonthedesignedhardware.InterfacingofmicrocontrollerwithADC,LCD,MEMORY,etchasbeencarriedoutusingvarioussoftwaremodules.Thecontrolprogramiswritteninassemblylanguage.Thesoftwareisabletoshowtherealtimevaluesfromtheanalogchannelsforimmediateanalysis.Fordesigningthesoftwareforthiswork;theflowofsoftwarebetweenthehardwarecomponentsistobeunderstoodfirst.6.ResultsInthissystem,Temperaturemeasurementsfromthethreechannelsaretaken.Theperformanceofthethreechannelsisdistinguishedonthebasisoftheiraccuracy.Allthesensorsarespecifiedwithaccuracy.Theaccuracyindicateshowcloselythesensorcanmeasuretheactualorrealworldparametervalue.Themoreaccurateasensoris,betteritwillperform.Thereadingsaretakenunderdifferentconditionsforsometimeinterval.Alsothereadingsaretakenatdifferenttemperaturesinatimeinterval.Comparingthereadingsobtainedfromthethreechannelsunderthedifferentconditionsthemostaccuratechannelamongthemisfound.7.ConclusionThedataloggerisaninvaluabletooltocollectandanalyseexperimentaldata,havingtheabilitytoclearlypresentrealtimeresults,withsensorsandprobesabletorespondtoparametersthatarebeyondthenormalrangeavailablefrommosttraditionalequipment.Dataloggersusedformeasuring第11页thetemperaturemighthavecertainlimitationsintermsofspeed,memoryandcost.Alsodataloggerswithincreasednumberofchannelsarecomplex.Inthiswork,anattempthasbeendonetodesignadatalogger,whichisoflesscost,portable,verylowpowerconsumption,selfcontained.Itisanefficientdatalogger,whichworksinrealtimemode.Thereducednumberofchannelsalsomakesthesystemsimple.Theloggercanuseupto8channelsofanalogtodigitalconverterinperformingitstaskbutthatwillresultinincreasednumberofchannels.Astep-by-stepapproachindesigningaMicrocontrollerbasedsystemfortemperaturemeasurementhasbeenfollowed.Accordingtothestudyandanalysisofvariouspartsofthesystem,adesignhasbeencarriedout.Theresultsobtainedfromthemeasurementhaveshownthatthesystemperformwellunderalltheconditions.Fromthiswork,itisconcludedthatinthissystemamongthethreechannels,Channel2moreaccuratelymeasuresthetemperatureinthegivenspanoftime.8.FutureScope1.)Theperformanceofmicrocontrollerbasedtemperaturedataloggerhasbeenfoundontheexpectedlines.However,thereexistsascopeforfurtherimprovementinitsspeed,numberofchannels,powerconsumption,andPCinterfacesoftwareforpostdataanalysis.2.)ThesystemcanbemodifiedwiththeuseofgraphicalLCDpanelsothattheanalysisisdonebythesystemitself.Thenumberofanalogchannelscanbeincreasedtomonitormoresensoroutputs.3.)Thelowpowerrequirementofthisdataloggermakesiteasytouse.Thedevicecanbemadetoperformbetterbyprovidingthepowersupplywiththehelpofbatterysourcewhichcanberechargeableornon-rechargeable,toreducetherequirementofmainACpower.4.)Thissystemcanbeconnectedtocommunicationdevicessuchasmodems,cellularphones,orsatelliteterminaltoenabletheremotecollecti