CHAPTER 3

LED ProjectsINTHISCHAPTERWEAREGOINGTOstartbuildingsomeLEDbasedprojects.WewillkeepthehardwarefairlysimplesothatwecanconcentrateontheprogrammingoftheArduino.

Programmingmicrocontrollerscanbeatrickybusinessrequiringanintimateknowledgeoftheinnerworkingsofthedevice:fuses,registers,etc.Thisisdue,inpart,tothefactthatmodernmicrocontrollersarealmostinfinitelyconfigurable.Arduinostandardizesitshardwareconfiguration,which,inreturnforasmalllossofflexibility,makesthedevicesagreatdealeasiertoprogram.

Project 2Morse Code S.O.S. FlasherMorsecodeusedtobeavitalmethodofcommunicationinthe19thand20thcenturies.Itscodingoflettersasaseriesoflongandshortdotsmeantthatitcouldbesentovertelegraphwires,overaradiolink,andusingsignalinglights.ThelettersS.O.S.(SaveOurSouls)arestillrecognizedasaninternationalsignalofdistress.

Inthisproject,wewillmakeourLEDflashthesequenceS.O.S.overandoveragain.

ForthisprojectyouwillneedjustthesamecomponentsasforProject1.

COMPONENTSANDEQUIPMENT

Hardware

ThehardwareisexactlythesameasforProject1.SoyoucaneitherjustplugtheresistorandLEDdirectlyintotheArduinoconnectorsoruseabreadboard(seeChapter1).

Software

Ratherthanstarttypingthisprojectinfromscratch,wewilluseProject1asastartingpoint.SopleasecompleteProject1beforeyoubeginthisproject.

Ifyouhavenotalreadydoneso,downloadtheprojectcodefromwww.arduinoevilgenius.com(http://www.arduinoevilgenius.com)thenyoucanalsojustloadthecompletedsketchforProject1fromyourArduinoSketchbookanddownloadittotheboard(seeChapter1).However,itwillhelpyoutounderstandArduinobetterifyoumodifythesketchfrom

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Project1assuggestednext.

ModifytheloopfunctionofProject1sothatitnowappearsasshownhere.Notethatcopyandpastearehighlyrecommendedinthiskindofsituation.

Thiswouldallwork,andfeelfreetotryithowever,wearenotgoingtoleaveitthere.Wearegoingtoalteroursketchtoimproveitandatthesametimemakeitalotshorter.

WecanreducethesizeofthesketchbycreatingourownfunctiontoreplacethefourlinesofcodeinvolvedinanyflashoftheLEDwithoneline.

Aftertheloopfunctionsfinalcurlybrace,addthefollowingcode:

Nowmodifytheloopfunctionsothatitlookslikethis:

ThewholefinallistingisshowninListingProject2.

LISTINGPROJECT2

Thismakesthesketchalotsmallerandaloteasiertoread.

Putting It All Together

ThatconcludesProject2.WewillnowcoversomemorebackgroundonprogrammingtheArduinobeforewegoontolookatProject3,wherewewilluseoursamehardwaretowriteaMorsecodetranslator,withwhichwecantypesentencesonourcomputerandhavethemflashedasMorsecode.InProject4wewillimprovethebrightnessofourflashingbyreplacingourredLEDwithahighpowerLuxeontypeLED.

ButfirstweneedalittlemoretheoryinordertounderstandProjects3and4.

LoopsLoopsallowustorepeatagroupofcommandsacertainnumberoftimesoruntilsomeconditionismet.InProject2,weonlywanttoflashthreedotsforanS,soitisnogreathardshiptorepeattheflashcommandthreetimes.However,itwouldbefarlessconvenientifweneededtoflashtheLED100or1000times.InthatcasewecanusetheforlanguagecommandinC:

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Theforloopisabitlikeafunctionthattakesthreearguments,althoughherethoseargumentsareseparatedbysemicolonsratherthanbytheusualcommas.ThisisjustaquirkoftheClanguage.Thecompilerwillsoontellyouwhenyougetitwrong.

Thefirstthingintheparenthesesafterforisavariabledeclaration.Thisspecifiesavariabletobeusedasacountervariableandgivesitaninitialvalueinthiscase0.

Thesecondpartisaconditionthatmustbetrueforustostayintheloop.Inthiscasewewillstayintheloopaslongasiislessthan100,butassoonasiis100ormore,wewillstopdoingthethingsinsidetheloop.

Thefinalpartiswhattodoeverytimeyouhavedoneallthethingsintheloop.Inthiscase,thatisincrementiby1sothatitcan,after100tripsaroundtheloop,ceasetobelessthan100andcausethelooptoexit.

AnotherwayofloopinginCistousethewhilecommand.Thesameexampleshownpreviouslycouldbeaccomplishedusingawhilecommand,asshownhere:

Theexpressioninparenthesesafterthewhilemustbetruetostayintheloop.Whenitisnolongertrue,thesketchwillcontinuerunningthecommandsafterthefinalcurlybrace.

Thecurlybracesareusedtobrackettogetheragroupofcommands.Inprogrammingparlance,theyareknownasablock.

ArraysArraysareawayofcontainingalistofvalues.Thevariableswehavemetsofarhaveonlycontainedasinglevalue,usuallyanint.Bycontrast,anarraycontainsalistofvalues,andyoucanaccessanyoneofthosevaluesbyitspositioninthelist.

C,likethemajorityofprogramminglanguages,beginsitsindexpositionsat0ratherthan1.Thismeansthatthefirstelementisactuallyelementzero.

Toillustratetheuseofarrays,wecouldchangeourMorsecodeexampletouseanarrayofflashdurations.Wecanthenuseaforlooptostepthrougheachoftheitemsinthearray.

Firstletscreateanarrayoftypeintcontainingthedurations:

Youindicatethatavariablecontainsanarraybyplacing[]afterthevariablename.Ifyouaresettingthecontentsofthearrayatthesametimeyouaredefiningit,asintheprecedingexample,youdonotneedtospecifythesizeofthearray.Ifyouarenotsettingitsinitialcontents,thenyouneedtospecifythesizeofthearrayinsidethesquarebrackets.Forexample:

Nowwecanmodifyourloopmethodtousethearray:

Anobviousadvantageofthisapproachisthatitiseasytochangethemessagebysimplyalteringthedurationsarray.InProject3wewilltaketheuseofarraysastagefurthertomakeamoregeneralpurposeMorsecodeflasher.

Project 3Morse Code TranslatorInthisprojectwearegoingtousethesamehardwareasforProjects1and2,butwearegoingtowriteanewsketchthatwillletustypeinasentenceonourcomputerandhaveourArduinoboardconvertthatintotheappropriateMorsecodedotsanddashes.

Figure31showstheMorsecodetranslatorinaction.ThecontentsofthemessageboxarebeingflashedasdotsanddashesontheLED.

Figure31 Morsecodetranslator.

Todothis,wewillmakeuseofwhatwehavelearnedaboutarraysandstringsandalsolearnsomethingaboutsendingmessagesfromourcomputertotheArduinoboardthroughtheUSBcable.

Forthisproject,youwillneedjustthesamecomponentsasforProjects1and2.Infact,thehardwareisexactlythesamewearejustgoingtomodifythesketchofProject1.

COMPONENTSANDEQUIPMENT

Hardware

PleasereferbacktoProject1forthehardwareconstructionforthisproject.

YoucaneitherjustplugtheresistorandLEDdirectlyintotheArduinoconnectorsorusethebreadboard(seeChapter1).YoucanevenjustchangetheledPinvariableinthesketchtobepin13sothatyouusethebuiltinLEDanddonotneedanyexternalcomponentsatall.

Software

ThelettersinMorsecodeareshowninTable31.

TABLE31MorseCodeLetters

SomeoftherulesofMorsecodearethatadashisthreetimesaslongasadot,thetimebetweeneachdashordotisequaltothedurationofadot,thespacebetweentwolettersisthesamelengthasadash,andthespacebetweentwowordsisthesamedurationassevendots.

Forthesakeofthisproject,wewillnotworryaboutpunctuation,althoughitwouldbeaninterestingexerciseforyoutotryaddingthistothesketch.ForafulllistofalltheMorsecharacters,seehttp://en.wikipedia.org/wiki/Morse_code.

ThesketchforthisisshowninListingProject3.Anexplanationofhowitallworksfollows.

LISTINGPROJECT3

Wekeeptrackofourdotsanddashesusingarraysofstrings.Wehavetwoofthese,oneforlettersandonefornumerals.So,tofindoutwhatweneedtoflashforthefirstletterofthealphabet(A),wewillgetthestringletters[0]remember,thefirstelementofanarrayiselement0,notelement1.

ThevariabledotDelayisdefined,soifwewanttomakeourMorsecodeflashfasterorslower,wecanchangethisvaluebecauseallthedurationsaredefinedasmultiplesofthetimeforadot.

Thesetupfunctionismuchthesameasforourearlierprojectshowever,thistimewearegettingcommunicationsfromtheUSBport,sowemustaddthecommand

ThistellstheArduinoboardtosetthecommunicationsspeedthroughtheUSBtobe9600baud.Thisisnotveryfast,butfastenoughforourMorsecodemessages.ItisalsoagoodspeedtosetittobecausethatisthedefaultspeedusedbytheArduinosoftwareonyourcomputer.

IntheloopfunctionwearegoingtorepeatedlyseeifwehavebeensentanylettersovertheUSBconnectionandifwehavetoprocesstheletter.TheArduinofunctionSerial.available()willbetrueifthereisacharactertobeturnedintoMorsecode,andtheSerial.read()functionwillgiveusthatcharacter,whichweassigntoavariablecalledchthatwedefinedjustinsidetheloop.

Wethenhaveaseriesofifstatementsthatdeterminewhetherthecharacterisanuppercaseletter,alowercaseletter,oraspacecharacterseparatingtwowords.Lookingatthefirstifstatement,wearetestingtoseeifthecharactersvalueisgreaterthanorequaltoaandlessthanorequaltoz.Ifthatisthecase,wecanfindthesequenceofdashesanddotstoflashusingthelettersarraythatwedefinedatthetopofthesketch.Wedeterminewhichsequencefromthearraytousebysubtractingafromthe

characterinch.

Atfirstsight,itmightlookstrangetobesubtractingoneletterfromanother,butitisperfectlyacceptabletodothisinC.So,forexample,aais0,whereasdawillgiveustheanswer3.So,iftheletterthatwereadfromtheUSBconnectionsweref,wewouldcalculatefa,whichgivesus5asthepositionofthelettersarray.Lookingupletters[5]willgiveusthestring....andwepassthisstringtoafunctioncalledflashSequence.

TheflashSequencefunctionisgoingtoloopovereachofthepartsofthesequenceandflashitaseitheradashoradot.StringsinCallhaveaspecialcodeontheendofthemthatmarkstheendofthestring,andthisiscalledNULL.SothefirstthingflashSequencedoesistodefineavariablecalledi.Thisisgoingtoindicatethecurrentpositioninthestringofdotsanddashes,startingatposition0.ThewhileloopwillkeepgoinguntilwereachtheNULLontheendofthestring.

Insidethewhileloop,wefirstflashthecurrentdotordashusingafunctionthatwearegoingtodiscussinamomentandthenadd1toiandgobackroundtheloopflashingeachdotordashinturnuntilwereachtheendofthestring.

ThefinalfunctionthatwehavedefinedisflashDotOrDashthisjustturnstheLEDonandthenusesanifstatementtoeitherdelayforthedurationofasingledotifthecharacterisadotorforthreetimesthatdurationifthecharacterisadashbeforeitturnstheLEDoffagain.

Putting It All Together

LoadthecompletedsketchforProject3fromyourArduinoSketchbookanddownloaditontoyourboard(seeChapter1).

TousetheMorsecodetranslator,weneedtouseapartoftheArduinosoftwarecalledtheSerialMonitor.ThiswindowallowsyoutotypemessagesthataresenttotheArduinoboardaswellasseeanymessagesthattheArduinoboardchoosestoreplywith.

TheSerialMonitorislaunchedbyclickingtherightmosticonshownhighlightedinFigure32.

Figure32 LaunchingtheSerialMonitor.

TheSerialMonitor(seeFigure33)hastwoparts.Atthetop,thereisafieldintowhichalineoftextcanbetypedthatwillbesenttotheboardwhenyoueitherclickSendorpressRETURN.

Figure33 TheSerialMonitorwindow.

BelowthatisalargerareainwhichanymessagescomingfromtheArduinoboardwillbedisplayed.Rightatthebottomofthewindowisadropdownlistwhereyoucanselectthespeedatwhichthedataissent.Whateveryouselectheremustmatchthebaudratethatyouspecifyinyourscriptsstartupmessage.Weuse9600,whichisthedefault,sothereisnoneedtochangeanythinghere.

SoallweneedtodoislaunchtheSerialMonitor,typesometextintotheSendfield,andclicktheSendbuttonorpressRETURN.WeshouldthenhaveourmessageflashedtousinMorsecode.

Project 4

High-Brightness Morse Code TranslatorThelittleLEDonProject3isunlikelytobevisiblefromtheshiponthehorizonbeingluredbyourbogusEvilGeniusdistressmessage.So,inthisproject,wearegoingtoupthepowerandusea1WLuxeonLED.TheseLEDsareextremelybright,andallthelightcomesfromatinylittleareainthecenter,sotoavoidanypossibilityofretinadamage,donotstaredirectlyintoit.

Wealsolookathow,withabitofsoldering,wecanmakethisprojectintoashieldthatcanbepluggedintoourArduinoboard.

COMPONENTSANDEQUIPMENT

HardwareTheLEDweusedinProject3usedabout10mAat2V.Wecanusethistocalculatepowerusingtheformula

P=IV

Powerequalsthevoltageacrosssomethingtimesthecurrentflowingthroughit,andtheunitofpoweristhewatt.SothatLEDwouldbeapproximately20mW,orafiftiethofthepowerofour1WLuxeonLED.WhileanArduinowillcopejustfinedrivinga20mWLED,itwillnotbeabletodirectlydrivethe1WLED.

Thisisacommonprobleminelectronicsandcanbesummedupasgettingasmallcurrenttocontrolabiggercurrent,somethingthatisknownasamplification.Themostcommonlyusedelectroniccomponentforamplificationisthetransistor,sothatiswhatwewillusetoswitchourLuxeonLEDonandoff.

ThebasicoperationofatransistorisshowninFigure34.Therearemanydifferenttypesoftransistors,andprobablythemostcommonandthetypethatwearegoingtouseiscalledanNPNbipolartransistor.

Figure34 TheoperationofanNPNbipolartransistor.

Thistransistorhasthreeleads:theemitter,thecollector,andthebase.Andthebasicprincipleisthatasmallcurrentflowingthroughthebasewillallowamuchbiggercurrenttoflowbetweenthecollectorandtheemitter.

Justhowmuchbiggerthecurrentisdependsonthetransistor,butitistypicallyafactorof100.Soacurrentof10mAflowingthroughthebasecouldcauseupto1Atoflowthroughthecollector.So,ifwekeptthe270resistorthatweusedtodrivetheLEDat10mA,wecouldexpectittobemorethanenoughtoallowthetransistortoswitchthehundredsofmilliampsneededbytheLuxeonLED.

TheschematicdiagramforourcontrolcircuitisshowninFigure35.

Figure35 SchematicdiagramforhighpowerLEDdriving.

The270resistor(R1)limitsthecurrentthatflowsthroughthebase.WecancalculatethecurrentusingtheformulaI=V/R.Vwillbe4.4Vratherthan5Vbecausetransistorsnormallyhaveavoltageof0.6Vbetweenthebaseandemitter,andthehighestvoltagetheArduinocansupplyfromanoutputpinis5V.Sothecurrentwillbe4.4/270=16mA.

ThedatasheetforthisLEDstatesthattheabsolutemaximumforwardcurrentis350mA,andtheforwardvoltageis3.4V.Sowewillaimforaround200mA,whichwillmaketheLEDgoodandbrightwithoutshorteningitslife.

R2limitsthecurrentflowingthroughtheLEDtoaround200mA.Wecameupwiththefigureof4.7byusingtheformulaR=V/I.Vwillberoughly53.40.6=1.0V.5Visthesupplyvoltage,theLEDdropsroughly3.4Vandthetransistor0.6V,sotheresistanceshouldbe1.0V/200mA=5.Resistorscomeinstandardvalues,sowewillselecta4.7resistor.Wemustalsousearesistorthatcancopewiththisrelativelyhighcurrent.Thepowerthattheresistorwillburnoffasheatisequaltothevoltageacrossitmultipliedbythecurrentflowingthroughit.Inthiscase,thatis200mA1.0V,whichis200mW.Thismeansthataregular0.5Woreven0.25Wresistorwillbejustfine.

Inthesameway,whenchoosingatransistor,weneedtomakesurethatitcanhandlethepower.Whenitisturnedon,thetransistorwillconsumepowerequaltocurrenttimesvoltage.Inthiscase,thebasecurrentissmallenoughtoignore,sothepowerwilljustbe0.6V200mA,or120mW.Itisalwaysagoodideatopickatransistorthatcaneasilycopewiththepower.Inthiscase,wearegoingtouseaBD139,whichhasapowerratingofover12W.InChapter10youcanfindatableofcommonlyusedtransistors.

NowweneedtoputourcomponentsintothebreadboardaccordingtothelayoutshowninFigure36,withthecorrespondingphotographofFigure38.ItiscrucialtocorrectlyidentifytheleadsofthetransistorandtheLED.Themetallicsideofthetransistorshouldbefacingtheboard.TheLEDwillhavealittle+symbolnexttothepositiveconnection.

Figure36 Project4breadboardlayout.

LaterinthisprojectwearegoingtoshowyouhowyoucanmovetheprojectfromthebreadboardtoamorepermanentdesignusingtheArduinoProtoshield.Thisrequiressomesoldering,soifyouthinkyoumightgoontomakeashieldandhavethefacilitiestosolder,IwouldsoldersomeleadsontotheLuxeonLED.Soldershortlengthsofsolidcorewiretotwoofthesixtagsaroundtheedge.Theyshouldbemarked+and.Itisagoodideatocolorcodeyourleadswithredforpositiveandblueorblackfornegative.

Ifyoudonotwanttosolder,thatsfineyoujustneedtocarefullytwistthesolidcorewirearoundtheconnectorsasshowninFigure37.

Figure37 AttachingleadstotheLuxeonLEDwithoutsoldering.

Figure38showsthefullyassembledbreadboard.

Figure38 PhotographofcompletebreadboardforProject4.

Software

Project4usesexactlythesamesketchasProject3.

Putting It All Together

IfyoudonotstillhavethesketchfromProject3loaded,thenloadthesketchforProject3fromyourArduinoSketchbookanddownloaditontoyourboard(seeChapter1).

Again,testingtheprojectisthesameasforProject3.YouwillneedtoopentheSerialMonitorwindowandjuststarttyping.

TheLEDactuallyhasaverywideangleofview,soonevariationonthisprojectwouldbetoadaptanLEDtorchinwhichtheLEDhasareflectortofocusthebeam.

Making a Shield

ThisisthefirstprojectthatwehavemadethathasenoughcomponentstojustifymakinganArduinoShieldcircuitboardtositontopoftheArduinoboarditself.WearealsogoingtousethishardwarewithminormodificationsinProject6,soperhapsitistimetomakeourselvesaLuxeonLEDShield.

Makingyourowncircuitboardsathomeisperfectlypossiblebutrequirestheuseofnoxiouschemicalsandafairamountofequipment.Butfortunately,thereisanothergreatpieceofArduinorelatedopensourcehardwarecalledtheArduinoProtoshield.Ifyoushoparound,thesecanbeobtainedfor$10orlessandwillprovideyouwithakitofallyouneedtomakeabasicshield.Thatincludestheboarditself,theheaderconnectorpinsthatfitintotheArduino,andsomeLEDs,switches,andresistors.PleasebeawarethatthereareseveralvariationsoftheProtoshieldboard,soyoumayhavetoadaptthefollowingdesignifyourboardisslightlydifferent.

ThecomponentsforaProtoshieldareshowninFigure39,themostimportantpartbeingtheProtoshieldcircuitboard(PCB).Itispossibleto

justbuythePCBonitsown,whichformanyprojectswillbeallyouneed.

Figure39 Protoshieldinkitform.

Wearenotgoingtosolderallthecomponentsthatcamewithourkitontotheboard.WearejustgoingtoaddthepowerLED,itsresistor,andjustthebottompinsthatconnecttotheArduinoboardbecausethisisgoingtobeatopshieldandwillnothaveanyothershieldsontopofit.

Agoodguideforassemblingcircuitboardsistosolderinplacethelowestcomponentsfirst.Sointhiscasewewillsoldertheresistors,theLED,theresetswitch,andthenthebottompinconnectors.

The1Kresistor,LED,andswitchareallpushedthroughfromthetopoftheboardandsolderedunderneath(Figure310).Theshortpartoftheconnectorpinswillbepushedupfromunderneaththeboardandsolderedontop.

Figure310 TheundersideoftheProtoshield.

Whensolderingtheconnectorpins,makesurethattheyarelinedupcorrectlybecausetherearetwoparallelrowsfortheconnectors:onefortheconnectiontothepinsbelowandoneforthesockets,whichwearenotusing,thatareintendedtoconnecttofurthershields.

AgoodwaytoensurethattheheadersareintherightplaceistofitthesectionsofheaderintoanArduinoboardandthenplacetheshieldontopandsolderthepinswhileitsstillpluggedintotheArduinoboard.Thiswillalsoensurethatthepinsarestraight.

Whenallthecomponentshavebeensolderedinplace,youshouldhaveaboardthatlookslikeFigure311.

Figure311 AssembledbasicProtoshield.

Wecannowaddourcomponentsforthisproject,whichwecantakefromthebreadboard.First,lineupallthecomponentsintheirintendedplacesaccordingtothelayoutofFigure312tomakesurethateverythingfitsintheavailablespace.

Figure312 Project4Protoshieldlayout.

Thiskindofboardisdoublesidedthatis,youcansoldertothetoporbottomoftheboard.AsyoucanseefromthelayoutinFigure312,someoftheconnectionsareinstripslikeabreadboard.

Wearegoingtomountallthecomponentsonthetopside,withtheleadspushedthroughandsolderedontheundersidewheretheyemergefromtheboard.Theleadsofthecomponentsunderneathcanthenbeconnectedupandexcessleadssnippedoff.Ifnecessary,lengthsofsolidcorewirecanbeusedwheretheleadswillnotreach.

Figure313showsthecompletedshield.Powerupyourboardandtestitout.Ifitdoesnotworkassoonasyoupoweritup,disconnectitfromthepowerrightawayandcarefullychecktheshieldforanyshortcircuitsorbrokenconnectionsusingamultimeter.

Figure313 CompleteLuxeonshieldattachedtoanArduinoboard.

Congratulations!YouhavecreatedyourfirstArduinoShield,anditisonethatwecanreuseinlaterprojects.

SummarySowehavemadeastartonsomesimpleLEDprojectsanddiscoveredhowtousehighpowerLuxeonLEDs.WehavealsolearnedabitmoreaboutprogrammingourArduinoboardinC.

InChapter4wearegoingtoextendthisbylookingatsomemoreLEDbasedprojects,includingamodeltrafficsignalandahighpowerstrobelight.

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