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ReportTechnologyMasterclassMartijnJansen

AnOpticalMouseSensoras

anextensionforLEGONXT

MartijnJansen

[email protected]

S030887


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Index:

1.Introduction

2.SensorChoice

3.Hackingtheopticalmouse

4.HackingLEGONXT

5.Implementation

6.PossibleApplications

7.References

8.Appendix


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1.Introduction

AssignmentDescription

ThisprojectispartoftheTechnologyMasterclassofIndustrialDesignattheTechnicalUniversity

Eindhoven.Duringthisclass,Masterstudentsgettheopportunitytodiveintosomeverydiverseelementsoftechnologylikeelectronics,mechanics,programmingintelligentrobotsandcreatinga

newinnovativesensorforLEGONXT.Thisreportdescribestheelaborationofthelatterassignment.

Deliverables

workingmodeloftheextensionpack reportinMSWorddescribingtheextensionpack technicaldocumentationoftheextensionpack,suchastechnicaldrawingsandUMLmodels photosoftheextensionpack movieoftheextensionpackinactionuploadedinhighqualitytoSurfMediaandavailablefor

downloadfromthere.


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2.SensorChoice

Forarobotthatisabletomoveitself,itisessentialtoknowinwhatenvironmentitisandwherein

thatenvironmentitislocated.Location,distanceandspeedarevariablesthatcanhelparobotdetermineitscurrentstate.AGPSsensorisabletogivethesevariables,butarequiteexpensiveand

notasaccurateasyoumightneed.Acomputermouseismoreaccurateandcandetectmovement

smallerthanamillimeter.ForthisreasonIdecidedtolookatcomputermiceasanewsensorfor

LEGONXT.

Anoldcomputermouse(fig.1)detectsmovementmechanicallythroughaballinsidethatcanrotate

inanydirection.Therearethreewheelsinsidethatarepositionedagainsttheball,sothatthewheels

areturningwhentheballrolls.Thesewheelschoplightbeamsinfrontoflightsensorssoa

movement,speedofmovementanddirectioncanbedetected.Thiskindofmouseisalsocalledaball

mouse.

Fig.1:Aballmouse

1

Adifferentkindofcomputermouseistheopticalmouse(fig.2).Theopticalmousehasa

sensorinsidethatisactuallyaverysmallcamera.Itdetectschangesinpicturesofthesurface

underneathit.ThisisthenconvertedtoanamountofmovementintotheXorYdirection.AredLED

illuminatesthesurfacetoincreasethecontrastofthepictures.

fig.2:Myopticalmouse(beforethisproject)

Ichosetogofurtherwiththeopticalmousesensorforthefollowingreasons:

ithasnomechanicalpartsthatcanbreakorwearoff; itcanbeusedonmoresurfacesthantheballmouse; aballmousecollectsdebrisinsidethecasing itsquitesmall(smallerthantheballmouse); itscheap; Iseealotoflearningopportunitieshere.

ThefollowingchapterswilldescribehowtocreateanopticalmousesensorfortheNXTfromacheapopticalmouse.


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3.Hackingtheopticalmouse

IhaveusedsometutorialsIfoundoninternet2,3.Myapproachwasquitesimilar,buteventuallyIneed

toreadthedatawiththeLEGONXT.Myfirststepistohackthemousereadthedatafromthesensor

withArduino4.

TutorialforhackingtheopticalmouseThistutorialwillexplainwhatstepsyouneedtotaketohacktheopticalmouseandreadthedata

withArduino.Firsttakeanoldopticalmouseorbuyacheapone.Fig.2showshowmymouselooked

like.

1.Openupthemouse

Underneaththemousetheresascrewyouneedtounbolt.Thiswillopenupthemouse.Hereyou

findthecircuitboardwiththesensor(thechipinthemiddle),aLED,buttonsandthescrollwheel(fig.

3).Underneaththecircuitboardisthelensclip(fig.4),thatisusedtoamplifythelightandfunctions

asalensforthesensor.

fig.3:Mouseopenedup

fig.4:lensclip

2.Lookupthedatasheet

Thesensorislocatedinthemiddleofthecircuitboard.Searchforthedatasheetofthesensoronthe

internetandlookupthepinconnections.Youneedthefollowingpins:

+5V(inputvoltage) GND(ground) SCK(serialportclock) SDIO(serialportdata)

InthecaseofmysensorIneedpin3,4,6and7(fig.5)


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fig.5mechanicaldrawing+pinouttableofthedatasheet

5

MakesurethatyoursensordoesnthavetheUSBcontrollerembeddedinsidethechip.Thefirst

mouseItriedtoopenhadthiskindofchip(seefig.6),whichmeansthatyoucantcapturethedata

withoutaUSBprotocol.Usinga2wireserialportcommunicationismuchmorepreferable.

fig.6:amousewiththeUSBcontrollerembeddedinthechipofthesensor

3.SolderwiresSolderwirestothe4neededpins.Itsusefultochoosedifferentcolors,soyoureabletodistinguish

theclockanddatalineseasily(fig.7).

fig.7Wiressolderedtopins3,4,6and7

4.RemovetheUSBcontroller

Thisstepisnotnecessary,butifyourenotgoingtousethemouseanymoreitmightbebetterto

removetheUSBcontrollertopreventthecontrolleroftakingoverthedataconnection.Removing

thecontrollercanbedonebyremovingthesolderedtinandscrapethecontrollerofthecircuitboard.

5.ConnectittoArduino

ChoosetwodigitalpinsontheArduinofortheclocklineandthedatalineandconnectthe+5Vand

GNDofthemousetothe5VandGndofArduino.Uploadthesketches(programsforArduino)

providedbyMartijnThbasedonsketchesofBenotRousseau.MakesurethattherightregistersIf

youopentheSerialmonitorintheArduinosoftwareyoullseethexandyvalues.Inthenext

paragraphIllexplainhowthisworks.


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GetthedatafromtheopticalmousetoArduino

Inthedatasheetofthesensorthereisawholesectionaboutthesynchronousserialport.Thisportis

usedtosetandreadparametersfromthesensor.Theportusestwowiresandisahalfduplexport,

whichmeansthatitcantalkbothways,butnotatthesametime.Themicrocontroller,inmycasethe

Arduino,alwaysinitiatescommunicationandiscalledthemaster(thesensoristheslave).Thetwo

wiresaretheserialportclock(SCK)andthedataline(SDIO).Theserialportclockisgeneratedbythe

microcontroller.

ThemicrocontrollercantrytoreadparametersliketheXandYmovement,butcanalsowritetothe

sensortochangeparameterslikeforexampletheconfigurationofthesensor.Forthisweneedaread

andawriteoperation.Theclocklineisgeneratedbythemicrocontrollerandispreferablypulsingata

lengthof250nsperpulse.Thefunctionoftheclockistosynchronizedatatransfers.

Writeoperation

Awriteoperationisinitiatedbythemicrocontrollerandconsistsoftwobytes.Thefirstbytecontains

a7bitaddressandhasa1asitsmostsignificantbit(MSB).This1meansthatthemicrocontroller

wantstowritedataandtheaddressisaregisterwhereyouwanttowriteto.Thesecondbytecontainsthedatayouwanttowrite.Theclocksynchronizesthedatatransfer,becausethe

microcontrollerchangesSDIOonfallingedgesoftheclockandthesensorreadsSDIOonrisingedges

oftheclock.

fig.8:Writeoperation

ReadOperation

Awriteoperationworkskindofthesame;italsoconsistsoftwobytes.Thefirstbytehasa0asMSB

(toindicateareadoperation)andasevenbitaddresstorequestthedatafromacertainregister.The

secondbyteisthedatasendfromthesensortothemicrocontroller.Afterthelastbitoftheaddress

thereisadelayof100usforthesensortopreparethedata.

fig.9:ReadOperation

Registers

Inthedatasheetthereisalistofaddresses(fig.10).Fromaddress0x42and0x43youcangetthe

Delta_YandDelta_X(XandYmovement).Letmegiveanexample:IfIwanttoreadtheYmovement

Ihavetoperformareadoperation.Thefirstbytethemicrocontrollersendsis0x42,butwitha0as

MSBbit.Inbitformthislookslikethis:01000010.Thenthereisadelayof100microsecondsand

afterthatthesensorwillgiveabytecontainingthemovementofthesensorintheYdirection.


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fig.10:AddressesoftheregistersoftheADNS2083

InthenextchapterIllexplainhowtogetthisdatatotheLEGONXT.


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4.HackingLEGONXT

TheNXTisactuallyamicrocontrollerlikeArduino.ForthisassignmentweneedtoprogramtheNXT

withleJOS,aJAVAbasedlanguagefortheNXT.Icouldntfigureouthowtoreadthesensordirectly

withtheNXTusingleJOS.ThereforeIchosetotoreaddatafromthesensorwithArduinoandletthe

NXTcommunicatewiththeArduino.

LEGONXTcables:ThecablesoftheNXTareactuallyslightlymodifiedJR12cables(telephonecables).Themodification

liesintheconnector.Insidethecableare6wiresthatconnecttoaninputportoftheNXT(fig.12).

fig.12:InputportoftheNXT

6

CommunicationbetweenLegoNXTandArduinothroughI2C:

I2CisaprotocoldevelopedbyPhilips.Theprotocolofreadingtheopticalmousesensorisquitesimilar

tothis,butnotentirely.Inthecaseoftheopticalmousesensor,thereisnodeviceaddress.Youneed

thistostartupthewholecommunication.ForthisreasonIcouldntreadthesensordirectlyfromthe

NXT.

Inmyproject,theArduinoistheslaveandtheNXTisthemaster.InArduinotheresalibrarycalled

Wire.hthatcanbeusedforI2C.Withthislibraryyoucansetthedeviceaddress,Iusedthenumber

127.WhenevertheNXTrequestsdata,Iusethislibrarytosendanarrayoftwobytes;thexandy

value.

InleJOSIrequestdatabyusingtheI2CSensorclass.Icreatedaclassfortheopticalmousesensorthat

extendstheI2CSensorclass.NowIcanmakeseveralobjectsofthisclass,whichcanbeusefulwhenI

wanttousemorethanoneofthesesensorsatthesametime.AftertheNXThasinitializedcommunicationwithdeviceaddress127,itcanrequestdata.Afterthis

requestIgetaresponseoftwobytes,whichIstoreinanarraywithtwoindexes.Thefirstindexof

thearrayisthexvalueandthesecondistheyvalue.


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5.Implementation

Thischapterdescribestheimplementationintoaworkingprototype.

CircuitblockdiagramThecircuitblockdiagram(fig.13)islargelybasedonthecircuitblockdiagramoftheADNS2083.By

removingtheunnecessarypartsliketheUSBcontrollerandthebuttonsyoullhaveablockdiagramof

thesensorwiththeLED.Connectthefourpins(+5V,GND,SCKandSDIO)ofthesensortotheright

pinsontheArduinoboard.ConnecttheI2CpinsoftheArduinoboard(SCK=ANALOG5,SDIO=

ANALOG4)totheNXTcable.Theotherendofthecablecanbeinsertedintoanysensorportofthe

NXT,exceptsensorport4(isnotcapableofI2C).Iusedsensorport1.

Fig.13:CircuitblockdiagramforreadingthesensorinNXT(rotateyourpage)


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MechanicalDrawingIwantedtomakeasensorhasalmostthesameformastheexistingNXTsensors.Thefirstdrawings

(fig.14)giveagoodimpressionofthedimensionsoftheouterbody.

fig.14:Firstimpressionofthedimensions

AfterImadethisIstartedtocreatea3Dmodelfor3Dprinting.Thethicknessofthematerialis2mm.

Insidethecasingadifferentconstructionwasneeded.Thecircuitboardhadtobeexactly7.45mm

abovethesurface(fig.15).ThemouseIhackedusedadifferentlensclipthanthedatasheet

recommended.InmydesignIneededtofixthelensclipbymakingaraisedrectangleandcutouta

passageforthelighttogothroughandapassageforthelenstomakepictures(justlikeinsidethe

casingofthemouse,fig.16).Theimplementationisshowninfig.17andtheeventualmodelinfig.18.

fig.15:Assemblydrawingofcircuitboardinsideview


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fig.16:Lensclipholderinthemousecasing

fig.17:Twoscreenshotsofthe3DCADmodelmadeinSolidWorks

fig.18:Theprototype3Dprintedwiththetechnologyinside


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NextstepsIvetriedoutthesensorondifferentsurfacesanditworksverywellonwhiteorbrightsurfaces.On

darkorblacksurfacesithasmoretroubletoswitchon.Thereisasettingofthemousesensorthat

switchestheLEDtolessbrightwhenitisntmovedformorethanasecond.Whenthesensordetects

movement,theLEDwillgetbrighteragain.Thisisasettingtosaveenergy.Theproblemondark

surfacesisthatthesensordoesntdetectthefirstmovementverywell,sotheLEDwillnotemitatfull

power.Incaseofemittingwithfullpowerthesensorworksfineagain.Iwouldrecommendwhenthe

sensorisusedondarksurfacestochangetheconfigurationofthesensorandlettheLEDalwayson

withfullpower.

Therearealsosomeminorimprovementsthatcanbemadetothedesignofthecasing.Thelensclip

onlyfitswhenitisputinwithalotofforce.Tryingalitbiggermarginwouldbebetter.

Asmallercircuitboardcanbedesignedwiththetechnicaldrawingprovidedinthisreport.Thismeans

thatthesensorwoulddecreaseinsizeandmightevendecreaseitsbroadthtwice.


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6.PossibleApplications

SomeexamplesofapplicationsusingtheNXTopticalmousesensorare:

Measuremovement

Arobotcanmeasurehowfarithasdrivenyet.

Measurevelocity

Forrobotsthathavetogowithacertainspeedyoucandividethemovementwiththetimeandyou

getvelocity

Feedbackloopfordrivingstraight

BecausethesensormeasuresXandYvaluesitcanalsogivefeedbackaboutmovementsideways.This

isunwantedforexamplebecauseonmotorisstrongerthantheother.Becauseyoudetectthe

movementsidewaysyoucanfeedthisinformationbacktothemotors(justlikethepotentiometerin

aservomotor).

DrivingtocoordinatesArobotcandrivetoanexactpointintheenvironment,whenitkeepstrackofthemovementsofar

andthebendsithasmade.


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7.References

1. Picturefrom:http://upload.wikimedia.org/wikipedia/commons/2/2c/Ball_Mouse_semiinside_view.jpg

2. http://www.gurulib.com/_project/optical_mouse_hack_files/optical_mouse_hack.htm3. http://www.martijnthe.nl/optimouse/4. http://www.arduino.cc/5. DatasheetADNS2083(SDNS2083)fromAvagotechnologies6. LegoMindstormsNXTHardwareDelopmentKit


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8.Appendix

A.DatasheetADNS2083

B.LegoMindstormsNXTHardwareDelopmentKit

C.ArduinoSketch

D.leJOSclasses

E.Videooftheworkingprototype

BecauseAppendixC&Dcontaintoomanypagestoprintandaremoreusefulto

havedigital,Ihavemadethemavailableonline.AppendixEisavideoandcanbe

downloaded.

C.http://www.kansloosdesign.nl/portfolio/wp

content/uploads/2008/12/coordinates_in_mm_i2c.zip

D.http://www.kansloosdesign.nl/portfolio/wp

content/uploads/2008/12/lejosopticalmousesensor.zip

E.http://www.kansloosdesign.nl/portfolio/wp

content/uploads/2008/12/filmpje.m4v

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