基于ARM交通监测设计英语.docx

基于ARM交通监测设计英语.docx

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基于ARM交通监测设计英语

DesignofControlUnitofTrafficDetectionSystembasedonARM

DuRongyiYeQingLiXue

CollegeofElectricalandInformationEngineering,ChangshaUniversityofScience&

Technology,Changsha410076,ChinaE-mail:

Abstract

Accordingtothesystemrequirements,vehicle

detectionsystembasedondoubleinductionloopshas

beendesigned.Controlunitoftrafficdetectionsystem

designedwiththecoreofLPC2138hasbeendescribed

indetail.Andthefunctionofeachhardwaremodule

hasbeenanalyzed.Forbadexperimentenvironment

andvariousinterferencefactors,anti-interference

measureshavebeenconsideredandintroducedinto

softwareandhardwaredesign.Hardwareimplementationandsoftwareflowofcontrolunithave

beendescribedindetail.Theresultofthesystem

applicationshowsthat,comparedtotraditionalcontrolunitswiththecoreofsinglechip,thecontrolunithavecharacteristicsofbetterinformationhandlingability,fasterspeed,andbettercommunicationabilityetc.Themainfunctionofthetrafficdetectionsystemistoexaminethespeed,theflow,thevehicletypeandthelaneoccupancyofthemotorvehicles.ThemethodbasedonARMembedded

systeminthispaperprovidesanewmeansforthe

trafficdetectionsystemresearch.Finallytheprospectforfurtherresearchispresented.

1.Introduction

Alongwithglobaleconomicdevelopment,theresearchofthetrafficintelligentmonitoringbecomes

oneoftheresearchfocusesofcountries.Throughthe

real-timecollection,transmissionandprocessingoftherelatedtrafficinformation,thecurrenttrafficoperation

statusisgraspedandfuturetrafficconditionisforecast.

Andwiththeaidofvariousequipmentandmeans,differenttrafficconditionsaredealtwith.Alsothrough

powerfulinformationcommunicationmeans,the

trafficinformationwillbelearntbyusersrapidly.Thus,trafficefficiencyandsafetyareeffectively

improved,trafficfacilitiesarefullyutilized,andthe

trafficintensivedevelopmentisrealized.Roadtraffic

detectionsystem,speciallyitscontrolunitisthekey

linkoftheresearchoftheintelligencetransportationsystem（ITS.TheARMembeddedprocessor[2]asakindof32bitsRISCchipwithhighperformanceandlowpowerhasthecharacteristicsofsupportingmulti-operationsystem,highmainfrequency,andstrongoperationandprocessingabilityetc.ItalsohasmassandlowpriceSDRMdatamemory.ThisarticletakesARMratherthantraditionalsinglechipasthedetectionsignaltransmissionprocessingmoduletodesignroadtrafficdetectionsystem.Itprovidesabetterthinkingforthe

furtherresearchandawiderapplicationspace.2.DetectionAlgorithmTheconventionalsingle-coildetectorcandetectthevehicleflowandthelaneoccupancyinaperiodoftime.Toeachlaneburiedcoil,thedefinitionsofthetwobasicparametersareasfollows[3],TN

Q=（1∑

∑====Njj

i

NjjvlTtTO1111（2Where,Qisvehicleflow;OislaneoccupancyinsamplingperiodT;Nisthesumofvehiclespassingthroughinthesamplingperiod;jtistheusedtimeofthejthvehiclepassingthroughthecoil;jliseffectivevehiclelengthofthejthvehicleorthesumofthelooplengthandthevehiclelength;andjvisthejthvehicle’sspeed.Tothetrafficmanagementandthecontrol,thevehiclespeedisakeyparametertorespondroad

conditionsandquestionsappearsintraffic.Buttheconventionalsingle-coildetectorcannotmeasurevehiclespeed.Thereforedoubleloopsareusedtomeasurevehiclespeed.Italsocanmeasurevehicle2008InternationalConferenceonIntelligentComputationTechnologyandAutomation

lengthetc.tobeappliedinfuzzyrecognitionofvehicletypes.

Theprincipleofmeasuringthevehicle’sspeedand

lengthbasedondoubleloopsisasshowninFig.1.

Fig.1Principlegraphofmeasuringthevehicle’sspeedand

length

Measurethetimeinterval0tforvehiclefromtheloop1toloop2,andthetime1tfromenteringtoleavingtheloop2.Fortheloop’swidthis0landtheloopspaceis1l,sothevehiclespeedis[6]

010/（tllv+=（3

Andthevehiclelengthis

2（（1010llttvL+−+⋅=（4

3.HardwareDesign

Themainfunctionofthecoiltrafficdetectionsystemistoexaminethespeed,theflow,thevehicletypeandthelaneoccupancyofthemotorvehicles.Italsocancontrolthefunctionsofinformationdisplay,systemdetectionandschedulingofthevariableinformationboardinmonitoringsystemthroughdetectionsignal[1].Thus,itiswidelyappliedinthesituationsofexpresswaytoll-gate,expresswaysecuritybayonet,expresswayrampcontrol,urbanintersectionred-light-runningmonitoringandurbanintersectiontrafficsignalcontrol[5]etc.Thecoiltrafficdetectionsystemselectedforthisstudyiscomposedofloop-coilvehicledetectorsystemandhostcomputercontrol

system.ThesystemdiagramisasshowninFig.2.

Fig.2Trafficdetectionsystemdiagram

Theloop-coilisusuallyrealizedbyseveralcablelinesenwinding.Itssizeis2×1.5meters.Theloop-coilisconnectedtothevehicledetectormodulethroughwiringterminal.ItconstitutestheLCoscillationcircuittodetectvehiclespassingcondition.A5Vpowersourceanddouble-lanesloop-coilvehicledetectionmoduleisincludedinthevehicledetector.ThecommunicationbetweenthevehicledetectorandPCapplytheRS232orRS485accordingtoactualsystemsituation.Themainfunctionofthevehicledetectoristomonitoreachtrafficlane'strafficcondition,carryoutdataacquisitionandprocessing,aswellasfailuredetectionetc.Themajorfunctionofthehostcomputercontrolsystemistorealizethefieldsetofthevehiclesdetector’sworkingparameters.Simultaneously,itcaninquireandreceivethetrafficdatafromthelowercomputer.

Accordingtothedemandandapplicationenvironmentofthetrafficdetectionsystem,andcomprehensivelyconsideringthefactorsofperformancepriceratioandchipresources,thehigh-performance32bitsLPC2138ischosen.LPC2138isamicrocontrollerofPHILIPSCorporation.Itisbasedona16/32bitARM7TDMI-STMCPU[2]andhasa152KBhighspeedembeddedflashmemory.TheARM7TDMI-STMCPUcancarryoutreal-timesimulationandembeddedtrace.128bitsmemoryinterfaceandtheuniqueacceleratingstructureenable32bitscodestorununderthemaximumclockrate.Totheapplicationwithstrictdemandofcodesize,the16bitsThumbpatterncanbeusedtoreducethecodesizeabove30%,buttheperformancelossisalittle.

ThehardwareconstitutionofthecontrolunitofthetrafficdetectionsystemisshowninFig.3.Human-machineinterfacemoduleiscomposedofLEDdisplay,dialswitchinputandresetbuttoninput.8bitsLEDlampisusedtodisplaythedetectionparametersandvariouslanes’workingstates.Thedialswitchisusedtosetupdetectionparameters,andtheresetbuttonrealizesthemanualchipresetfunction.

DigitalI/Omoduleisconstitutedwith4-pathoptical-isolationinputs.Theoptical-isolationchipis

appliedwith4piecesofdipTPL521.ApieceofLM393isusedtotransferthesinecalibratesignalproducedbyoscillationcircuitintothe3.5Vsquare-wavesignal.ThenthesignalissenttoCPLD.The5VDCpowerisinputfromtheinterfacePlug1.ThediodeIN1isusedtolimitthetransientcurrentandfilter.Thenthepowerwillbeconstantto3.3VthroughtheLM1117/3.3.Thevoltageamplitudeofthewavereshapedisabout3.3V,whichmeetsourrequirement.LDOchipisoftheseriesM1117.Itsoutputcurrentmayreach800mAandtheprecisionofitsoutputvoltagemaylessthan1%.Italsohasthefunctionofcurrentlimitationandhotprotection.Inapplication,atantalumcapacitorabove10Fμisusuallynecessarytoconnectwiththeoutputend.Itcanimprovethetransientresponseandstability[6].

Totransplantembeddedreal-timeoperationsysteminARMcanmakethedetectorconvenientlyrealizeMulti-laneinformationcollectionandprocessingsimultaneously.Italsocanimprovethesystemreliabilityandgivefullplaytomulti-missionpotentialofthe32bitsCPU.

Fig.3Hardwarediagramofcontrolunit

4.SoftwaredesignforARM

ThemainfunctionsofARMaretoreadthecounter’svalueoftheCPLDandcalculatethetimeofvehicles’passingthroughtheloop.Thenitwillcarryontheprocessingtothevaluesofshiftandcharactertranslationetc.Andsendthevaluesprocessedtothehostcomputerbyserialport.

ThetimingprocessofARMisthat,（1whenvehiclearrivesatloop1,aactivatesignalpresentsanegativepulsetomaketheARMtimerstarttiming;（2anothersignalpresentsanegativepulsetomakeARMtimerstoptiming.ThenthetimevaluesobtainedwillbesenttoPCthroughtheserialport.

TheprocessreadingCPLDcounter’svaluesforARMisthat,whentheCPLDcountingfinished（DatebusOk=0,ARMreadstheCPLDcounter’s

valuesthroughits8-bitdatalines.Thedatawillbecarriedoutclassificationprocessingandstoredinthebufferarea.Whenthedatanumberinthebufferreachedthesettingmaximum,thedatawillbetransmittedtoPCthroughtheserialportbyARM.

TheentireworkingprocessofARMshowsinFig.4.

Fig.4Programflowchart.

Inthesoftwareanti-interferencedesign,theinternalwatch-dogoftheLPC2138isusedandinitializingprogramofthewatch-dogisasfollows,WDTC=0x10000;WDMOD=0x03;VoidWdFeed（void{

WDFEED=0xAA;WDFEED=0x55;}

Theanti-huntingprogramisintroducedinthejudgmentoftheinputpinsconditionforARM.Itistopreventthemisreadingcausedbythesignalshaking.Anti-huntingprogramisthat,voidWaitSignal（void{uint32i;While（1{

while（（IO0PIN&DateOK!

=0;

for（i=0;i<5000;i++;//softdelay,anti-huntingif（（IO0PIN&DateOK!

==0break;}

while（（IO0PIN&DateOK!

==0;}