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| SRF02Ultrasonicrangefinder http://www.robotelectronics.co.uk/htm/SRF02techI2C.htm SRF02Ultr asonicr angefinder TechnicalSpecification I2CMode ForSerialmodeclickhere I2CCommunication TousetheSRF02inI2Cmode,makesurenothingisconnectedtothemodepin,itmustbeleft unconnected. TheI2CbusisavailableonpopularcontrollerssuchastheOOPic,StampBS2p,PicAxeetc.aswellasa widevarietyofmicrocontrollers.TotheprogrammertheSRF02behavesinthesamewayasthe ubiquitous24xxseriesEEPROM's,exceptthattheI2Caddressisdifferent.Thedefaultshippedaddressof theSRF02is0xE0.Itcanbechangedbytheusertoanyof16addressesE0,E2,E4,E6,E8,EA,EC,EE, F0,F2,F4,F6,F8,FA,FCorFE,thereforeupto16sonar'scanbeused. Connections TheconnectionstotheSRF02areidenticaltotheSRF08andSRF10rangers.The"Mode"pinshouldbe leftunconnected,ithasaninternalpullupresistor.TheSCLandSDAlinesshouldeachhaveapullup resistorto+5vsomewhereontheI2Cbus.Youonlyneedonepairofresistors,notapairforevery module.Theyarenormallylocatedwiththebusmasterratherthantheslaves.TheSRF02isalwaysaslave neverabusmaster.Ifyouneedthem,Irecommend1.8kresistors.SomemodulessuchastheOOPic alreadyhavepullupresistorsandyoudonotneedtoaddanymore. Registers TheSRF02appearsasasetof6registers. Location 0 1 2 3 www..com 4 5 Read Software Revision Unused(reads 0x80) RangeHighByte RangeLowByte Autotune MinimumHigh Byte Autotune MinimumLow Byte Write CommandRegister N/A N/A N/A N/A N/A Onlylocation0canbewrittento.Location0isthecommandregisterandisusedtostartaranging 1of4 06/11/200622.24 SRF02Ultrasonicrangefinder http://www.robotelectronics.co.uk/htm/SRF02techI2C.htm session.Itcannotberead.Readingfromlocation0returnstheSRF02softwarerevision.Theranginglasts upto65mS,andtheSRF02willnotrespondtocommandsontheI2Cbuswhilstitisranging. Locations,2and3,arethe16bitunsignedresultfromthelatestranginghighbytefirst.Themeaningof thisvaluedependsonthecommandused,andiseithertherangeininches,ortherangeincmortheflight timeinuS.Avalueof0indicatesthatnoobjectsweredetected.Donotinitiatearangingfasterthanevery 65mStogivethepreviousbursttimetofadeaway. Locations,4and5,arethe16bitunsignedminimumrange.Thisistheapproximateclosestrangethesonar canmeasureto.SeetheAutotunesectionbelowforfulldetails. Commands Thearethreecommandstoinitiatearanging(80to82),toreturntheresultininches,centimetersor microseconds.Anothersetofthreecommands(86to88)dothesame,butwithouttransmittingtheburst. Theseareusedwherethebursthasbeentransmittedbyanothersonar.Itisuptoyoutosynchronizethe commandstothetwosonar's.Thereisacommand(92)totransmitaburstwithoutdoingtherangingand alsoasetofcommandstochangetheI2Caddress. Command Decimal Hex 80 0x50 81 0x51 82 0x52 86 87 88 92 0x56 0x57 0x58 0x5C Action RealRangingModeResultininches RealRangingModeResultincentimeters RealRangingModeResultinmicroseconds FakeRangingModeResultininches FakeRangingModeResultincentimeters FakeRangingModeResultinmicroseconds Transmitan8cycle40khzburstnorangingtakes place ForceAutotuneRestartsameaspowerup.Youcan ignorethiscommand. 1stinsequencetochangeI2Caddress 3rdinsequencetochangeI2Caddress 2ndinsequencetochangeI2Caddress 96 160 165 170 0x60 0xA0 0xA5 0xAA Ranging Toinitiatearanging,writeoneoftheabovecommandstothecommandregisterandwaittherequired amountoftimeforcompletionandreadtheresult.Theechobufferisclearedatthestartofeachranging. Theranginglastsupto66mS,afterthistherangecanbereadfromlocations2and3. CheckingforCompletionofRanging Youdonothavetouseatimeronyourowncontrollertowaitforrangingtofinish.Youcantake advantageofthefactthattheSRF02willnotrespondtoanyI2Cactivitywhilstranging.Therefore,ifyou trytoreadfromtheSRF02(weusethesoftwarerevisionnumberalocation0)thenyouwillget255 (0xFF)whilstranging.ThisisbecausetheI2Cdataline(SDA)ispulledhighifnothingisdrivingit.As soonastherangingiscompletetheSRF02willagainrespondtotheI2Cbus,sojustkeepreadingthe registeruntilitsnot255(0xFF)anymore.Youcanthenreadthesonardata.Yourcontrollercantake advantageofthistoperformothertaskswhiletheSRF02isranging.TheSRF02willalwaysbeready 70mSafterinitiatingtheranging. www..com 2of4 06/11/200622.24 SRF02Ultrasonicrangefinder http://www.robotelectronics.co.uk/htm/SRF02techI2C.htm LED TheredLEDisusedtoflashoutacodefortheI2Caddressonpowerup(seebelow).Italsogivesabrief flashduringthe"ping"whilstranging. ChangingtheI2CBusAddress TochangetheI2CaddressoftheSRF02youmusthaveonlyonesonaronthebus.Writethe3sequence commandsinthecorrectorderfollowedbytheaddress.Exampletochangetheaddressofasonar currentlyat0xE0(thedefaultshippedaddress)to0xF2,writethefollowingtoaddress0xE0(0xA0, 0xAA,0xA5,0xF2).ThesecommandsmustbesentinthecorrectsequencetochangetheI2Caddress, additionally,Noothercommandmaybeissuedinthemiddleofthesequence.Thesequencemustbesent tothecommandregisteratlocation0,whichmeans4separatewritetransactionsontheI2Cbus.When done,youshouldlabelthesonarwithitsaddress,howeverifyoudoforget,justpoweritupwithout sendinganycommands.TheSRF02willflashitsaddressoutontheLED.Onelongflashfollowedbya numberofshorterflashesindicatingitsaddress.Theflashingisterminatedimmediatelyonsendinga commandtheSRF02. Address Decimal Hex 224 E0 226 E2 228 E4 230 E6 232 E8 234 EA 236 EC 238 EE 240 F0 242 F2 244 F4 246 F6 248 F8 250 FA 252 FC 254 FE LongFlash Shortflashes 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Takecarenottosetmorethanonesonartothesameaddress,therewillbeabuscollisionandvery unpredictableresults. NotethereisonlyonemoduleaddressstoredintheSRF02.Ifyouchangeit,theequivalentSerialMode addresswillalsochange: 0xE0,0xE2,0xE4,0xE6,0xE8,0xEA,0xEC,0xEE,0xF0,0xF2,0xF4,0xF6,0xF8,0xFA,0xFC, 0xFEI2Caddresses 0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, 0x0FEquivalentSerialaddresses www..com AutoTune TheSRF02doesnotrequireanyusercalibration.YoupowerupandgorightaheadandusetheSRF02. Internally,therearetuningcycleshappeningautomaticallyinthebackground.Aftertheultrasonicbursthas beentransmitted,thetransducerkeepsonringingforaperiodoftime.Itisthisringingwhichlimitsthe closestrangetheSRF02canmeasure.Thistimeperiodvarieswithtemperatureandfromtransducerto transducer,butisnormallytheequivalentof11to16cm(4"to6"),abitmoreifthetransduceriswarm. 3of4 06/11/200622.24 SRF02Ultrasonicrangefinder http://www.robotelectronics.co.uk/htm/SRF02techI2C.htm TheSRF02isabletodetectthetransducerringtimeandmoveitsdetectionthresholdrightuptoit,giving theSRF02theverybestperformancepossible.Onpowerup,thedetectionthresholdissetto28cm(11"). Thetuningalgorithmsquicklybackthisrightuptothetransducerring.Thishappenswithin56ranging cycleslessthanhalfasecondatfullscanspeed.Afterthisthetuningalgorithmscontinuetomonitorthe transducer,backingthethresholdupevenfurtherwhenpossibleoreasingitoutabitwhennecessary.The tuningalgorithmsworkautomatically,inthebackgroundandwithnoimpactonscantime. Theminimumrangecanbechecked,ifrequiredbyreadingregisters4and5.ThisvalueisreturnedinuS, cmorinches,thesameastherange.ItisalsopossibletomaketheSRF02retunebywritingcommand96 butyoucanignorethiscommand.Itisusedduringourtesting. www..com 4of4 06/11/200622.24 |
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