电动小车遥控器的设计外文翻译.docx

电动小车遥控器的设计外文翻译.docx

《电动小车遥控器的设计外文翻译.docx》由会员分享，可在线阅读，更多相关《电动小车遥控器的设计外文翻译.docx（13页珍藏版）》请在冰点文库上搜索。

电动小车遥控器的设计外文翻译

毕业设计（论文）外文翻译

毕业设计（论文）题目：

电动小车遥控器的设计

外文题目：

HowtoSimplifytheInterfacebetweenMicrocontrollerandTemperatureSensor

译文题目：

微控制器与温度传感器接口的简化

学生姓名：

金书宇

专业：

测控技术与仪器

指导教师：

周彬

HowtoSimplifytheInterfacebetweenMicrocontrollerandTemperatureSensor

Abstract:

 Temperatureisananalogquantity,butdigitalsystemsoftenusetemperaturetoimplementmeasurement,control,andprotectionfunctions.Ifyouapplytherighttechniquesandcomponents,thenecessaryconversionofanalogtemperaturetodigitalinformationwon'tbedifficult.Thisapplicationnotediscussesthermalcomparators,PWM-outputtemperaturesensors,andremotediode（orthermaldiode）temperaturesensors.

Readingtemperaturewithamicrocontroller（µC）issimpleinconcept.TheµCreadstheoutputcodeofananalog-to-digitalconverter（ADC）drivenbyathermistor-resistorvoltagedivider,analog-outputtemperaturesensor,orotheranalogtemperaturesensor（Figure1）.TheADCbuiltintosomecontrollerscansimplifythisdesign.ADCsrequireareferencevoltage,whichcanbegeneratedbyanexternaldevice.Forexample,thereferencevoltageforathermistorsensorisusuallythesameasthatappliedtothetopoftheresistor-thermistorvoltagedivider.However,thefollowingcomplicationscanariseinthesesystems:

1.Thesensor'soutput-voltagerangeissignificantlysmallerthantheADC'sinput-voltagerange.AtypicalADCforthispurposemighthave8-bitresolutionanda2.5Vreferencevoltage,whichisnormallyequivalenttotheinput-voltagerange.Ifthesensor'smaximumoutputforthetemperaturerangeofinterestisonly1.25V,theeffectiveresolutiondropsto7bits.Toachieve8-bitresolution,eitheraddgainviaanexternalopamporlowertheADC'sreferencevoltage（whichmayreducetheaccuracyofsomeADCs）.

2.Theerrorbudgetistight.Combiningtheerrorfromthethermistor-resistorcombinationoranalog-sensordevicewiththosecontributedbytheADC,theamplifieroffsetvoltage,thetoleranceofgain-settingresistors,andthevoltagereferenceerrormaybemoreerrorthanyoursystemcantolerate.

3.Youwantalineartemperature-to-codetransferfunctionandyou'reusingathermistor.Thetransferfunctionforthermistorsisverynonlinear,butitmaybesufficientlylinearoverthenarrowtemperaturerangerequiredinmanyapplications.Youcancompensateforthenonlinearitywithalook-uptable,butthisapproachrequiresresourcesthatmaynotbeavailable.

4.ADCinputsarelimited.IfthenumberoftemperaturesyouwanttomeasureexceedsthenumberofADCinputsavailable,youmayneedtoaddamultiplexer,whichwillincreasethecostanddevelopmenttime.

5.ThenumberofµCI/Opinsislimited.Thiswon'tbeanissueforaninternalADC,butanexternalserialADCwillrequiretwotofourI/OpinsasaninterfacetotheµC.

Figure1.Inthissimpleinterface,theADC'sreferencevoltageisderivedfromthepower-supplyvoltage.Ananalogtemperaturesensorcanreplacethethermistor-resistorvoltagedivider.Inthatcase,theADC（whichcanbeinternaltotheµC）requiresareasonablyaccuratevoltagereference.

Thedesignproblemsaresimplifiedifyouuseatemperaturesensorwithadigitalinterface.Similarly,temperaturesensorswithtime-orfrequency-basedoutputscanalleviatethemeasurementproblemwhenADCinputsandµCI/Opinsareinshortsupply（Figure2）.TheMAX6576temperaturesensor,forexample,producesanoutputsquarewavewhoseperiodisproportionaltoabsolutetemperature.Itcomesina6-pinSOT23packagethatrequiresverylittleboardspace.AsingleI/OpininterfacesthisdevicetoaµC;afteritsinternalcountermeasurestheperiod,theµCcalculatesthetemperature.

.

Figure2.TheMAX6576producesasquarewavewithperiodproportionaltoabsolutetemperature;theMAX6577producesanoutputfrequencyproportionaltotemperature.TheresultingproportionalityconstantissettooneoffourvaluesbytheTS0andTS1pins.Noexternalcomponentsarenecessary.

Applyingeithergroundorthepositivesupplyvoltagetoeachoftwologicinputsselectsoneoffourperiod/temperatureproportionalityconstantsbetween10µs/°Kand640µs/°K.

Arelatedtemperaturesensor（MAX6577）generatesanoutputsquarewavewhosefrequency/temperaturefactorisprogrammablebetween0.0675Hz/°Kand4Hz/°K.BothdevicessimplifytemperatureacquisitionbyreducingtherequiredPCboardrealestate,componentcount,andanalog/digitalI/Oresources.TheytransmittemperaturedatatotheµCthroughasingledigitalI/Opin,andtheadditionofasingleopticalisolatormakesthemidealforapplicationsthatrequireelectricalisolationbetweenthesensorandtheCPU.

Formeasuringmultipletemperaturesatvariouslocations,thechoicesbecomemorecomplicated.ThermistorsorconventionalanalogsensorscanbeplacedinappropriatelocationsandconnectedtotheADCinputs,providedtheADChassufficientinputsavailable.Asanalternative,theMAX6575transmitstemperaturedatadirectlytotheµC;asmanyaseightMAX6575scanbeconnectedtoasingleµCI/Oinput.AsingleI/OtraceconnectstheµCtotheseeightMAX6575s（Figure3）.Tomeasuretemperature,theµCbrieflypullstheI/Olinelow,andafterashortdelaythefirstMAX6575alsopullstheI/Olinelow.Thistimedelayisproportionaltoabsolutetemperature,withaproportionalityconstantprogrammedusingtwopinsontheMAX6575.

Figure3.Usingadelayschemetoencodetemperatureinformation,multipleMAX6575stransmituptoeighttemperaturestotheµCthroughasingledigitalI/Opin.

Thefirstsensorholdsthelinelowforaperiodproportionaltotemperature（5µs/°K）andthenreleasesit.Afterasecondtimedelay,selectedbysettingtheprogrammingpinsforalargerproportionalityconstant,thesecondMAX6575pullstheI/Olowandholdsitforanintervaldefinedby5µs/°K.FourMAX6575scanbeconnectedtotheI/Olinethisway.FourmoreMAX6575softheother,longer-delayversioncanbeaddedtothesameI/Oline.TheMAX6575Lhasdelaymultipliersrangingfrom5µs/°Kto80µs/°K,andtheMAX6575Hdelaymultipliersrangefrom160µs/°Kto640µs/°K.Thus,asmanyaseightMAX6575scanbelocatedindifferentplacesaroundthesystem,connectedtotheµCbyasingleI/Oline.

Forsomesystems,theinformationneededisnottheexacttemperature,butwhetherthetemperatureisaboveorbelowaspecificvalue.Thisinformationcantriggeracoolingfan,airconditioner,heater,orotherenvironmental-controlelement.Insystem-protectionapplications,an"overtemperaturebit"cantriggeranorderlysystemshutdowntoavoidlosingdatawhenthesystempoweriscutoff.Thissinglebitofinformationcanbeobtainedbymeasuringtemperatureasintheexamplesabove,butthatapproachrequiresmoresoftwareandhardwarethanthefunctiondemands.

ReplacingtheADCinFigure1withavoltagecomparatorproducesasimple1-bitoutputthatcandriveasingleI/OpinontheµC（Figure4）.Again,thethermistorshowncanbereplacedbyananalogvoltage-outputtemperaturesensor.Mostsuchdeviceshavearelationshipbetweentemperatureandoutputvoltagethatisunaffectedbysupplyvoltage.Topreserveimmunityfromsupply-voltagevariations,connectthetopofthecomparator'sresistor-dividertoavoltagereferenceinsteadofthesupplyvoltage.

Figure4.Combiningasensorwithacomparatoryieldsa1-bitdigitaloutputthatcanwarntheµCoftemperatureexcursionsbeyondapredeterminedthresholdortrippoint.

Thesystemcanbesimplifiedbyreplacingthesensor-comparatorcombinationwithathermalswitchliketheMAX6501.Thismonolithicdevicecombinesthefunctionsofasensor,comparator,voltagereference,andexternalresistors.Whentemperatureexceedsthepresettriplevel,theopen-drainoutputgoeslow.Somedevicesinthisfamilyhaveopen-drainoutputsthatgolowwhentemperaturefallsbelowthetrippoint（MAX6503）,andothershavepush/pulloutputsthatgohighwhentemperaturegoeseitheraboveorbelowthetrippoint（MAX6502,Figure5,orMAX6504）.Inaddition,thehysteresiscanbesetto2°Cor10°CbyconnectingapackagepintoV+orground.Theavailabletriptemperaturesrangefrom-45°Cto+115°Cin10°Cincrements.

Figure5.TheMAX6502producesalogic-highoutputwhenitstemperatureexceedsthepresetthresholdvalue.

AswiththeMAX6575,connectingseveralMAX6501sorMAX6503stoasingleI/OtraceenablestheµCtobenotifiedwhentemperaturecrossesthethresholdatoneormorelocations.Ifthesystemmustknowwhichlocationhascrossedthethreshold,eachswitchoutputmustbeconnectedtoaseparateI/Opin.

Thesesensorsmeasuretheirowndietemperatures,andbecausedietemperaturecloselytracksleadtemperature,eachsensorshouldbeplacedsoitsleadsassumethetemperatureofthecomponentbeingmonitored.Insomecases,however,youmustmeasureatemperaturenottightlycoupledtothesensor—suchasthatofapowerASIC,whosediecanbemuchhotterthanthesurroundingboard.AninternaltemperaturesensormayenabletheASICtoshutitselfdowninresponsetoatemperaturefault,butthatcapabilityalonelacksaccuracy,anditseldomwarnsthesystemofanimpendingthermaloverload.

Byaddinganexternallyaccessiblep-njunctiontotheASICdie,youcanmeasuredietemperaturedirectlybyforcingtwoormoredifferentforwardcurrentsthroughthesensingjunctionandmeasuringtheresultingvoltages.Thedifferencebetweenthetwovoltagesisproportionaltotheabsolutedietemperature:

WhereI1andI2arethetwocurrentlevelsforcedthroughthep-njunction,V1andV2aretheresultingforwardvoltagesacrossthejunction,kisBoltzmann'sconstant,Tistheabsolutetemperatureofthe