DesigningthePCBased4Chann精.docx
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DesigningthePCBased4Chann精.docx
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DesigningthePCBased4Chann精
The5StudentConferenceonResearchandDevelopment–SCOReD200711-12December2007,Malaysia
th
DesigningthePC-Based4-ChannelDigitalStorageOscilloscopebyusingDSPTechniques
N.SulaimanandN.A.Mahmud
HISdocumentexplainsanddemonstrateshowtheDSOcanbeoperatedvirtually,namely,runningatPC.Inaddition,thedocumentalsoexplainshowtheGUIisdeveloped,testedandhowtheintegrationbetweenhardwareandsoftwareisdone.DSOhasbeenpreferableequipmentbyscientistsorengineersoracademiciansorstudentsaswelltoverifytheelectricalorelectroniccircuitoperationandtosavetheanalyzedsignalforfuturereference.DSOwilldisplaythesignalamplitude,frequency,periodandwaveshapeandchangesinvoltageovertime.DSOusesADCtosamplethesignalandconvertthevoltagebeingmeasuredintodigitalform.ThevitalcriterionindesigningthePC-BasedOscilloscopeisthecapabilitytomeasureanddisplaythesignalcorrectlyandaccurately.Inordertoachieveit,severalfactorsneedtobeconsidered.Amongthemarethesamplingrate,goodamplifierbandwidth,gooddataacquisitiondevices,
IndexTerms—DSO,ADC,GUI,PIC,PC-Based4-ChannelnumberofADCchip,sizeofRAM,agoodPIC,external
FlashADCwithdirectmemoryaccessandDSPtechniquesOscilloscope
usedtoprocessthesignalandfilterthesignalfromnoise.
Besides,thefunctionalbuttonoftheDSOneedtobestudied
I.NOMENCLATUREsothatthebuttoncreatedinGUIwillcarrythesame
functionalityasthenormalDSO.Moreover,DSOisselectedDSO-DigitalStorageOscilloscope
inthisresearchnottheanalogtypeOscilloscopebecauseofPC-PersonalComputer
thecapabilityoftheequipmenttoobserveslowmovingGUI-GraphicalUserInterface
signalsasasolidpresentationonthemonitorscreen[6].TheADC-Analog-to-DigitalConverter
DSOalsohasanabilitytoholdorretainasignalinmemoryRAM-RandomAccessMemory
forlongperiodsoftime.InordertosamplethecorrectsignalPIC-PeripheralInterfaceComputer
andtoavoidaliasing,Low-passanti-aliasingfilterisused.For
thedisplayformattorepresentthecapturedwaveformontheTheresearchwasdonebyastudentunderherfinalyearengineering
projectsubjectandguidedbyalecturer.Theresearchwascarriedoutatscreen,sineinterpolationtechniqueisusedbecauseitcanUniversitiMalaysiaPahang(UMP).provideagoodrepresentationwithasfewas2.5samplesperAllauthorsareattachedtoFacultyofElectrical&ElectronicEngineeringcycle[6].(FKEE),UniversitiMalaysiaPahang(UMP),LockedBag12,25000Kuantan,
ThebrainofthehardwareisPICwhichwillprocessthePahangDarulMakmur,Malaysia.
receivedsignalandthensendthedatatoPCthroughRS232E-mail:
norizam@ump.edu.my
Abstract—Nowadays,theDigitalStoragestartstoreplace
analogtypeOscilloscopeduetothebetterfunctionalityandfeatures.DigitalStorageOscilloscope(DSO)isadeviceusedbyengineers,scientistorengineeringstudentstoverifyorchecktheelectroniccircuitoperationwherethedisplayedsignalintheDSOmonitorcanbeanalyzedandsavedforfuturereference.DSOusesanAnalog-to-DigitalConverter(ADC)toconverttheelectricalvoltageorcurrentbeingmeasuredintodigitalformatcertainsamplingtime.Thesampleofthesignalwillbesavedandaccumulateduntilitabletodescribeawaveformandreassemblesthewaveformforviewinginonthemonitorscreen.ThepurposeoftheresearchistodesignthePC-Based4-ChannelOscilloscopewheretheelectricalsignalbeingmeasuredwillbedisplayedonthePC(PersonalComputer)monitorequippedwithfunctionalitybuttonshownintermofWindowbasedGUI(GraphicalUserInterface).TheGUIisdevelopedbyusingMicrosoftVisualC++6.0.ThePIC(PeripheralInterfaceController)isusedfordataacquisitionwhichtransfersthedatabeingmeasuredtoPCthroughRS232.Here4built-inADCsareusedinordertoproduce4channelsOscilloscope.ThePICisprogrammedbyusingClanguagetoreadthedatafromADCandthentransferthedatatoPC.Frequencyof5kHzisusedasasamplingrate.Meanwhile,theclockspeedof20MHzisselectedinordertoreducethepowerconsumptionandnoise.Inaddition,8KbytesRAMchipisusedforstoringpurpose.Theresearchoutcomeshows3typesofwaveformssuchasSinusoidal,SquareandTriangulararedisplayedwiththecorrectfrequencyandamplitude.ItistestedbyusingSignalGeneratorasaninputtoproducethewaveformtothehardware.Theintegrationbetweenhardware(PIC)andsoftware(GUI)isfullyworking.Besidethat,theGUIisveryuserfriendlyandeasytobeconfigured.Thedatafromthesignalbeingmeasuredalsocanbesavedandrestored.
USART-UniversalSynchronousAsynchronousReceiverTransmitterSPI-SerialPeripheralInterfaceI2C-InterIC
UART-UniversalAsynchronousReceiverTransmitter
TACQ-TimeAcknowledgementforPICBOR-Brown-Out-Reset
TC-HoldCapacitorChargingTime
II.INTRODUCTION
T
1-4244-1470-9/07/$25.00©2007IEEE.
Authorizedlicenseduselimitedto:
ZhengzhouUniversity.DownloadedonMay12,2010at02:
40:
10UTCfromIEEEXplore.Restrictionsapply.
accordingtotheinstructionembeddedtothechip.ThePICcontains4built-inADCstorepresentthe4channelscope.ThePICusesHarvardarchitectureduetofast,efficientandeffectiveprocessors.
InordertomakethecommunicationbetweenPICandPCworkcorrectlyandeffectively,theUSARTisused[8].ThedatafromPICthensenttotheMAX232bufferandthentransferredtoPC’sportthroughRS2329-pin.TheGUIatPCneedstobeconfiguredinordertointerpretthedataandshowthewaveformonthemonitorscreen.Theillustrationhowthe
dataistransmittedtoPCthroughRS232isshowninFigure1.
Fig.2.Simplifiedblockdiagramofresearchcomponents
FromFigure2,itcanbeclearlyseenthat8KbytesRAMisusedforstoragepurpose,8datalineconnectedtoportB(D7–
Fig.1.DatatransmissiontoPCthroughRS232D0)and13addresslinesconnectedtoportCandpotD.Since
2bytesarerequiredperreading.Hence,4000readingscanbe
III.METHODOLGYstored,that’s1000foreachchannel.Noticealsoonecontrol
lineconnectedfromPICtoRAMchip.ThislineisusedtoputTheresearchbeganbyselectingthecorrectandsuitabletheRAMchipinreadorwritemode.TheMAX232linecomponents.ThemaincomponentareFlashtypebufferisconnectedtopinRC7andRC6ofthePIC.PortDisMicrocontroller(PIC16F877)with4built-inADCs,SPI,I2C,usedforthefirst8-bitsofthe13-bitsaddressbus(213=8192UART,8-channel10bitADC,two8-bittimers,one16-bitaddress).PortEisusedtoselectRS232baudrateasshownintimer,watchdogtimer,BORandIn-Circuit-SerialTable1.TheRC4toRC0isusedfortheupper5-bitsoftheProgramming,RS-485typeUART.OthercomponentsaddressbusandPortBisusedfor8-bitdatabus.Theonlyinclude8KbytesRAMchip,MAX232(forlinebuffer)andcomponentmakinguseofthedataandaddressbusesistheRS2329-pinconnectedatPCanda5VvoltageregulatorexternalRAMchip.Inaddition,onelineisneededtoput(7805)topowerthecircuit.TheMAX232bufferisusedtoRAMchipinReadorWritemode[5].converttheTTLseriallogicofthePIC’sUARTtothecorrectRS232format[5].ThefourPIC’sADCpinsareusedfordataTABLE1
DIP-SWITCHCONFIGURATION
acquisition.TheUARThasbaudratesof300bpsto115kbps
with8or9bits,parity,startandstopbits.Aclockspeedtothe
PICissetto20MHznotonlytoreducepowerconsumptionandnoise,buttoobtainamaximumbaudrateof115kbpsoftheUARTforthefastercommunicationbetweenPICandPC[5].ThesimplifiedblockdiagramoftheresearchcomponentisshowninFigure2.
A5VVoltageRegulatorisneededinthedesigninordertogeneratea5VoltDCoutputtopowerthecircuit[9].The0.1µFcapacitorsareusedtoabsorblinenoise.Meanwhile,100µFcapacitorsareusedforstorageinthecaseofminordropinpowerinmillisecondsoftime;theoperationofthecircuitwillbenotaffected.
Forcommunicationprotocoldevelopment,therearetwomaincommunicationprotocols;real-timeandstorage[10].Theblockdiagramofreal-timecommunicationprotocolisshowninFigure3.
Authorizedlicenseduselimitedto:
ZhengzhouUniversity.DownloadedonMay12,2010at02:
40:
10UTCfromIEEEXplore.Restrictionsapply.
below.
TC=CHOLD(RIC+RSS+RS)In(1/2047)(3)=(-120pF)(1kΩ+7kΩ+10kΩ)In(0.0004885)=16.47µs
Thus,theTACQissetasbelow:
TACQ=2µs+16.47µs+[(50oC–25oC)](0.05µs/oC)
=19.72µs
Fig.3.Real-timemodewithfourchannels
TheGUIfortheresearchisdevelopedbyusingMicrosoft
TheRS232communicationisthebottleneckasthe
VisualC++6.0.TheprogramiscalledScope.exe.The
maximumsamplingfrequencyofPIC16F877Microcontroller
programisshowninFigure4.
ADCishigherthancanbetransmittedoverRS232[8].
Therefore,itmakessensetocalculatethemaximumsampleratebasebasedoncapacityofdatatransmittedthroughRS232atdifferentbaudrates.Twobytesaresentperframewhicheachbytecontains8-bitsplusastartbitandstopbit.Hence,20-bitsaresentperreading.Theformulaforcalculatingthesamplerateisshownbelow.
Samplerate=Baudrate/20
(1)No.ofChannels
Table2showsthetheoreticalreal-timesampleratesfor10-bit
ADC.
Fig.4.DisplayofScope.exeprogram
TABLE2
THEORETICALREAL-TIMESAMPLERATESThelefthalfofthewindowdisplaysthewaveformandthe
(10-bitADC)
righthalfofthewindowdisplaythecontrolpanels.The
controldialogishiddenanditcanbeactivatedbyclickingonthewaveformdisplayasshowninFigure5.ChannelsRaterateSample
at230Kbpsat1
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