Createyourown8x8x8LEDCube3dimensionaldisplay!

WebelievethisInstructableisthemostcomprehensivestepbystepguidetobuildan8x8x8LEDCubeeverpublishedontheintertubes.Itwillteachyoueverythingfromtheoryofoperation,howtobuildthecube,totheinnerworkingsofthesoftware.Wewilltakeyouthroughthesoftwarestepbystep,boththelowleveldrivers/routinesandhowtocreateawesomeanimations.ThesoftwareaspectofLEDcubesisoftenoverlooked,butaLEDcubeisonlyasawesome

(http://cdn.instructables.com/FUX/O1RW/GICYBAOS/FUXO1RWGICYBAOS.LARGE.jpg)

AboutThisInstructable

Posted:Jan1,20113,855,842views

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asthesoftwareitruns.

AbouthalfwaythroughtheInstructable,youwillactuallyhaveafullyfunctionalLEDcube.Theremainingstepswillshowyouhowtocreatethesoftware.

Avideoisworthathousandwords.I'lljustleaveituptothisvideotoconvinceyouthatthisisthenextprojectyouwillbebuilding:

ImadethisLEDcubetogetherwithmyfriendchiller.Thebuildtookabout4daysfromsmallscaleprototypingtocompletedcube.Thenanothercoupleofhourstodebugsomefaultytransistors.

Thesoftwareisprobablyanother45daysofworkcombined.

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Step1:SkillsrequiredRelated

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Group

Addinstructableto:

LEDCube4x4x4(/id/LEDCube4x4x4/)bychr(/member/chr/)

CHR's8X8X8LEDCubeRevisitedwithimprovements!(/id/CHRs8X8X8LEDCubeRevisitedwith444LedCube(/id/LedCube8/)bypbajusz(/member/pbajusz/)

SimpleLEDCube4xwithArduino/328p(/id/SimpleLEDCube4xwithArduino328p/)byakki5230MakingaflexibleringofLED's(/id/MakingaflexibleringofLEDs/)bycontrechoc(/member/contrechoc/)

http://www.instructables.com/tag/type-id/?q=http://www.instructables.com/member/SuperTech-IT/http://www.instructables.com/id/Led-Cube-8/http://www.instructables.com/member/akki5230/http://www.instructables.com/member/pbajusz/http://www.instructables.com/id/CHRs-8X8X8-LED-Cube-Revisited-with-improvements/http://www.instructables.com/id/LED-Cube-4x4x4/http://www.instructables.com/member/contrechoc/http://www.instructables.com/id/Making-a-flexible-ring-of-LEDs/http://www.instructables.com/id/Simple-LED-Cube-4x-with-Arduino328p/http://www.instructables.com/member/chr/http://www.instructables.com/id/Making-a-flexible-ring-of-LEDs/http://www.instructables.com/id/LED-Cube-4x4x4/http://www.instructables.com/id/Led-Cube-8/http://www.instructables.com/id/CHRs-8X8X8-LED-Cube-Revisited-with-improvements/http://cdn.instructables.com/FOL/S1PK/GI0TMHA2/FOLS1PKGI0TMHA2.LARGE.jpghttp://www.instructables.com/id/Simple-LED-Cube-4x-with-Arduino328p/

Atfirstglancethisprojectmightseemlikeanoverlycomplexanddauntingtask.However,wearedealingwithdigitalelectronicshere,soeverythingiseitheronoroff!

I'vebeendoingelectronicsforalongtime,andforyearsistruggledwithanalogcircuits.Theanalogcircuitsfailedoverhalfthetimeevenififollowedinstructions.Oneresistororcapacitorwithaslightlywrongvalue,andthecircuitdoesn'twork.

About4yearsago,Idecidedtogivemicrocontrollersatry.Thiscompletelychangedmyrelationshipwithelectronics.Iwentfromonlybeingabletobuildsimpleanalogcircuits,tobeingabletobuildalmostanything!

Adigitalcircuitdoesn'tcareifaresistoris1kohmor2kohm,aslongasitcandistinguishhighfromlow.Andbelieveme,thismakesitALOTeasiertodoelectronics!

Withthatsaid,therearestillsomethingsyoushouldknowbeforeventuringoutandbuildingthisratherlargeproject.

Youshouldhaveanunderstandingof:Basicelectronics.(Wewouldrecommendagainstbuildingthisasyourveryfirstelectronicsproject.ButpleasereadtheInstructable.You'llstilllearnalot!)Howtosolder.Howtouseamultimeteretc.WritingcodeinC(optional.Weprovideafullyfunctionalprogram,readytogo)

Youshouldalsohavepatienceandagenerousamountoffreetime.

Step2:Componentlist

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HereiswhatyouneedtomakeaLEDcube:512xLEDs(plussomeextraformakingmistakes!)64xresistors.(seeseparatestepforohmvalue)1xor2xlargeprototypePCBs.Thetypewithcopper"eyes",seeimage.1xATmega32microcontroller(youcanalsousethepincompatibleATmega16)3xstatusLEDs.Youchoosecolorandsize.3xresistorsforthestatusLEDs.8x74HC574ICs16xPN2222transistors16x1kresistors1x74HC138IC1xMaximMAX232IC1x14.7456MHzcrustal2x22pFceramiccapacitors16x0.1uFceramiccapacitors3x1000uFelectrolyticcapacitor3x10uFelectrolyticcapacitor

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ShowAll12Items

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1x100uFelectrolyticcapacitors8x20pinICsockets1x40pinICsocket2x16pinICsocket1x2pinscrewterminal1x2wirecablewithplugs9x8pinterminalpins1x4pinterminalpins,rightangle2x16pinribboncableconnector1x10pinribboncableconnectorRibboncable2xpushbuttons2xribboncableplugs9x8pinfemaleheaderplugsSerialcableand4pinfemalepinheaderPieceofwoodfortemplateandbase8xoptionalpullupresistorsforlayers5vpowersupply(seeseparatestepforpowersupply)

Totalestimatedbuildcost:67USD.Seeattachedpricelist.

pricelist.xls (/files/orig/FI7/UP2U/GIJG3QAC/FI7UP2UGIJG3QAC.xls)12KB

Step3:Orderingcomponents

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WeseealotofpeopleaskingforpartnumbersforDigiKey,Mouserorotherbigelectronicsstores.

Whenyou'reworkingwithhobbyelectronics,youdon'tnecessarilyneedthemostexpensivecomponentswiththebestquality.

Mostofthetime,itismoreimportanttoactuallyhavethecomponentvalueathandwhenyouneedit.

WearebigfansofbuyingreallycheapcomponentlotsoneBay.Youcangetassortmentsofresistor,capacitors,transistorsandeverythinginbetween.Ifyoubuythesetypesofassortments,youwillalmostalwayshavethepartsyouneedinyourpartcollection.

For17USDyoucanget2000resistorsof50differentvalues.Greatvalue,andveryconvenient.

TrydoingsomeBaysearchesandbuysomecomponentsforfutureprojects!

AnotheroneofourfavoritestoresisFuturlec(http://www.futurlec.com/(http://www.futurlec.com/)).Theyhaveeverythingyouneed.Thethingtheydon'thaveis1000differentversionsofthatthingthatyouneed,sobrowsingtheirinventoryisalotlessconfusingthanbuyingfromthosebiggercompanies.

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Step4:WhatisaLEDcube

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ALEDcubeislikeaLEDscreen,butitisspecialinthatithasathirddimension,makingit3D.Thinkofitasmanytransparentlowresolutiondisplays.Innormal

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displaysitisnormaltotrytostackthepixelsascloseaspossibleinordertomakeitlookbetter,butinacubeonemustbeabletoseetroughit,andmorespacingbetweenthepixels(actuallyit'svoxelssinceitisin3d)isneeded.Thespacingisatradeoffbetweenhoweasythelayersbehinditisseen,andvoxelfidelity.

SinceitisalotmoreworkmakingaLEDcubethanaLEDdisplay,theyareusuallylowresolution.ALEDdisplayof8x8pixelsisonly64LEDs,butaLEDcubein8x8x8is512LEDs,anorderofmagnitudehardertomake!ThisisthereasonLEDcubesareonlymadeinlowresolution.

ALEDcubedoesnothavetobesymetrical,itispossibletomakea7x8x9,orevenoddlyshapedones.

Step5:HowdoesaLEDcubework

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ThisLEDcubehas512LEDs.Obviously,havingadedicatedIOportforeachLEDwouldbeveryimpractical.Youwouldneedamicrocontrollerwith512IOports,andrun512wiresthroughthecube.

Instead,LEDcubesrelyonanopticalphenomenoncalledpersistenceofvision(POV).

Ifyouflashaledreallyfast,theimagewillstayonyourretinaforalittlewhileaftertheledturnsoff.

Byflashingeachlayerofthecubeoneafteranotherreallyreallyfast,itgivestheillusionofa3dimage,whenintfactyouarelookingataseriesof2dimagesstackedontoponeanother.Thisisalsocalledmultiplexing.

Withthissetup,weonlyneed64(fortheanodes)+8(foreachlayer)IOportstocontroltheLEDcube.

Inthevideo,theprocessissloweddownenoughforyoutoseeit,thenitrunsfasterandfasteruntiltherefreshrateisfastenoughforthecameratocatchthePOVeffect.

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Step6:TheanatomyofaLEDcube

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Wearegoingtobetalkingaboutanodes,cathodes,columnsandlayers,soletstakeamomenttogetfamiliarwiththeanatomyofaLEDcube.

AnLEDhastwolegs.Onepositive(theanode)andonenegative(cathode).InordertolightupanLED,youhavetoruncurrentfromthepositivetothenegativeleg.(Ifiremembercorrectlytheactualflowofelectronsistheotherwayaround.Butlet'ssticktotheflowofcurrentwhichisfrompositivetonegativefornow).

TheLEDcubeismadeupofcolumnsandlayers.ThecathodelegsofeveryLEDinalayeraresolderedtogether.Alltheanodelegsinonecolumnaresolderedtogether.

Eachofthe64columnsareconnectedtothecontrollerboardwithaseparatewire.Eachcolumncanbecontrolledindividually.Eachofthe8layersalsohaveaseparatewiregoingtothecontrollerboard.

Eachofthelayersareconnectedtoatransistorthatenablesthecubetoturnonandofftheflowofcurrentthrougheachlayer.

Byonlyturningonthetransistorforonelayer,currentfromtheanodecolumnscanonlyflowthroughthatlayer.Thetransistorsfortheotherlayersareoff,andtheimageoutputtedonthe64anodewiresareonlyshownontheselectedlayer.

Todisplaythenextlayer,simplyturnoffthetransistorforthecurrentlayer,changetheimageonthe64anodewirestotheimageforthenextlayer.Thenturnonthetransistorforthenextlayer.Rinseandrepeatveryveryfast.

Thelayerswillbereferredtoaslayers,cathodelayersorgroundlayers.Thecolumnswillbereferredtoascolumns,anodecolumnsoranodes.

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Step7:CubesizeandIOportrequirements

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TodriveaLEDcube,youneedtwosetsofIOports.OnetosourcealltheLEDanodecolumns,andonetosinkallthecathodelayers.

Fortheanodesideofthecube,you'llneedx^2IOports,wherex^3isthesizeofyourLEDcube.Foran8x8x8(x=8),youneed64IOportstodrivetheLEDanodes.(8x8).Youalsoneed8IOportstodrivethecathodes.

KeepinmindthatthenumberofIOportswillincreaseexponentially.SowillthenumberofLEDs.YoucanseealistofIOpinrequirementfordifferentcubesizesintable1.

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ForasmallLEDcube,3x3x3or4x4x4,youmightgetawaywithconnectingthecathodelayersdirectlytoamicrocontrollerIOpin.Foralargercubehowever,thecurrentgoingthroughthispinwillbetoohigh.Foran8x8x8LEDcubewithonly10mAperLED,youneedtoswitch0.64Ampere.Seetable2foranoverviewofpowerrequirementsforaLEDlayerofdifferentsizes.ThistableshowsthecurrentdrawwithallLEDson.

Ifyouareplanningtobuildalargercubethan8x8x8orrunningeachLEDatmorethan10ishmA,remembertotakeintoconsiderationthatyourlayertransistorsmustbeabletohandlethatload.

Step8:IOportexpansion,moremultiplexing

Wegatheredfromthelaststepthatan8x8x8LEDcuberequires64+8IOlinestooperate.NoAVRmicrocontrollerwithaDIPpackage(thekindofthroughholechipyoucaneasilysolderoruseinabreadboard,DualInlinePackage)havethatmanyIOlinesavailable.

Togetgettherequired64outputlinesneededfortheLEDanodes,wewill

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createasimplemultiplexercircuit.Thiscircuitwillmultiplex11IOlinesinto64outputlines.

Themultiplexerisbuiltbyusingacomponentcalledalatchoraflipflop.Wewillcallthemlatchesfromhereon.

Thismultiplexerusesan8bitlatchICcalled74HC574.Thischiphasthefollowingpins:

8inputs(D07)8outputs(Q07)1"latch"pin(CP)1outputenablepin(OE)

Thejobofthelatchistoserveasakindofsimplememory.Thelatchcanhold8bitsofinformation,andthese8bitsarerepresentedontheoutputpins.ConsideralatchwithanLEDconnectedtooutputQ0.ToturnthisLEDon,applyV+(1)toinputD0,thenpulltheCPpinlow(GND),thenhigh(V+).

WhentheCPpinchangesfromlowtohigh,thestateoftheinputD0is"latched"ontotheoutputQ0,andthisoutputstaysinthatstateregardlessoffuturechangesinthestatusofinputD0,untilnewdataisloadedbypullingtheCPpinlowandhighagain.Tomakealatcharraythatcanremembertheon/offstateof64LEDsweneed8oftheselatches.TheinputsD07ofallthelatchesareconnectedtogetherinan8bitbus.

Toloadtheon/offstatesofallthe64LEDswesimplydothis:Loadthedataofthefirstlatchontothebus.pulltheCPpinofthefirstlatchlowthenhigh.Loadthedataofthesecondlatchontothebus.pulltheCPpinofthesecondlatchlowthenhigh.Loadthedataofthethirdlatchontothebus.pulltheCPpinofthethirdlatchlowthenhigh.Rinseandrepeat.

Theonlyproblemwiththissetupisthatweneed8IOlinestocontroltheCPline

foreachlatch.Thesolutionistousea74HC138.ThisIChas3inputlinesand8outputs.Theinputlinesareusedtocontrolwhichofthe8outputlinesthatwillbepulledlowatanytime.Therestwillbehigh.Eachouttheoutputsonthe74HC138isconnectedtotheCPpinononeofthelatches.

Thefollowingpseudocodewillloadthecontentsofabufferarrayontothelatcharray:

//PORTA=databus//PORTB=addressbus(74HC138)//charbuffer[8]holds64bitsofdataforthelatcharray

PORTB=0x00//ThispullsCPonlatch1low.for(i=0i

multiplex_theoretical.sch (/files/orig/FHJ/ASA2/GICYB6DA/FHJASA2GICYB6DA.tmp)21KB

Step9:IOportexpansion,alternativesolution

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Thereisanothersolutionforprovidingmoreoutputlines.Wewentwiththelatchbasedmultiplexerbecausewehad8latchesavailablewhenbuildingtheLEDcube.

Youcanalsouseaserialinparalleloutshiftregistertoget64outputlines.74HC164isan8bitshiftregister.Thischiphastwoinputs(mayalsohaveanoutputenablepin,butwewillignorethisinthisexample).

dataclock

Everytimetheclockinputchangesfromlowtohigh,thedatainQ6ismovedintoQ7,Q5intoQ6,Q4intoQ5andsoon.Everythingisshiftedonepositiontotheright(assumingthatQ0istotheleft).ThestateofthedatainputlineisshiftedintoQ0.

Thewayyouwouldnormallyloaddataintoachiplikethis,istotakeabyteandbitshiftitintothechiponebitatatime.ThisusesalotofCPUcycles.However,wehavetouse8ofthesechipstogetourdesired64outputlines.Wesimplyconnectthedatainputofeachshiftregistertoeachofthe8bitsonaportonthemicrocontroller.AlltheclockinputsareconnectedtogetherandconnectedtoapinonanotherIOport.

Thissetupwilluse9IOlinesonthemicrocontroller.

Intheprevioussolution,eachbyteinourbufferarraywasplacedinit'sownlatchIC.Inthissetupeachbytewillbedistributedoverall8shiftregisters,withonebitineach.

Thefollowingpseudocodewilltransferthecontentsofa64bitbufferarraytotheshiftregisters.

//PORTA:bit0connectedtoshiftregister0'sdatainput,bit1toshiftregister1andsoon.

//PORTB:bit0connectedtoalltheclockinputs//charbuffer[8]holds64bitsofdata

for(i=0i

Thisstepiseasytooverlook,asLEDsthemselvesdon'tdrawthatmuchcurrent.Butrememberthatthiscircuitwilldraw64timesthemAofyourLEDsiftheyareallon.Inadditiontothat,theAVRandthelatchICsalsodrawscurrent.

TocalculatethecurrentdrawofyourLEDs,connectaledtoa5Vpowersupplywiththeresistoryouintendtouse,andmeasurethecurrentinmA.Multiplythisnumberby64,andyouhavethepowerrequirementsforthecubeitself.Addtothat1520mAfortheAVRandacoupleofmAforeachlatchIC.

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Ourfirstattemptatapowersupplywastouseastepdownvoltageregulator,LM7805,witha12Vwallwart.Atover500mAand12Vinput,thischipbecameextremelyhot,andwasn'tabletosupplythedesiredcurrent.

Welaterremovedthischip,andsolderedawirefromtheinputtotheoutputpinwherethechipusedtobe.

Wenowusearegulatedcomputerpowersupplytogetastablehighcurrent5Vsupply.

Step11:Buyapowersupply

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Ifyoudon'thavethepartsnecessarytobuilda5VPSU,youcanbuyone.

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eBayisagreatplacetobuythesethings.

Searchfor"5vpowersupply"andlimitthesearchto"Business&Industrial",andyou'llgetalotofsuitablepowersupplies.About15buckswillgetyouanicePSU.

Step12:Buildapowersupply

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AcoupleofyearsbeforewebuilttheLEDcube,wemadeourselfanicelittlelabpowersupplyfromanoldexternalSCSIdrive.ThisiswhatwehavebeenusingtopowertheLEDcube.

PCpowersuppliesarenice,becausetheyhaveregulated12Vand5VrailswithhighAmpereratings.

YoucanuseeitheraregularATorATXpowersupplyorandoldexternalharddriveenclosure.

IfyouwanttouseanATXpowersupply,youhavetoconnectthegreenwireonthemotherboardconnectortoground(black).Thiswillpoweritup.

Externalharddriveenclosuresareespeciallynicetouseaspowersupplies.Theyalreadyhaveaconvenientenclosure.Theonlythingyouhavetodoistoaddexternalpowerterminals.

Powersupplieshavealotofwires,buttheeasiestplacetogetthepoweryouneedisthroughamolexconnector.Thatisthekindofplugyoufindonharddrives(beforetheageofSATA).

BlackisGNDYellowis+12VRedis+5V

HereisanimageofourlabPSU.Wehave12Voutput,5Voutputwithanamperemeterand5Voutputwithoutanamperemeter.Weusethesecond5Voutputtopoweran80mmPCfantosuckorblowfumesawaywhenwesolder.

Wewon'tgetintoanymoredetailsofhowtomakeapowersupplyhere.I'msureyoucanfindanotherinstructableonhowtodothat.

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Step13:ChooseyourLEDs

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TherearemanythingstoconsiderwhenchoosingLEDs.

1)YouwanttheLEDcubetobeequallyvisiblefromallsides.ThereforewestronglyrecommendusingdiffusedLEDs.AclearLEDwillshootthemajorityofit'slightoutthetopoftheLED.AdiffusedLEDwillbemoreorlessequallybrightfromallsides.ClearLEDsalsocreateanotherproblem.IfyourcubeismadeupofclearLEDs.TheLEDswillalsopartiallyilluminatetheLEDsabovethem,sincemostofthelightisdirectedupwards.Thiscreatessomeunwantedghostingeffects.

WeactuallyordereddiffusedLEDsfromeBay,butgot1000clearLEDsinstead.ShippingthembacktoChinatoreceiveareplacementwouldhavetakentoomuchtime,sowedecidedtousedtheclearLEDsinstead.Itworksfine,butthecubeisalotbrighterwhenviewedfromthetopasopposedtothesides.

TheLEDsweorderedfromeBaywereactuallydescribedas"DefusedLEDs".Maybeweshouldhavetakenthehint)Defusingissomethingyoudotoabombwhenyouwanttopreventitfromblowingup,hehe.

2)LargerLEDsgivesyouabiggerandbrighterpixel,butsincesincethecubeis8layersdeep,youwantenoughroomtoseeallthewaythroughtothefurthestlevel.Wewentwith3mmLEDsbecausewewantedthecubetobeas"transparent"aspossible.Ourrecommendationistouse3mmdiffusedLEDs.

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3)Youcanbuyverycheaplotsof1000LEDsoneBay.Butkeepinmindthatthequalityoftheproductmaybereflectedinit'sprice.WethinkthatthereislesschanceofLEDmalfunctionifyoubuybetterquality/moreexpensiveLEDs.

4)SquareLEDswouldprobablylookcoolto,butthenyouneedtomakeasolderingtemplatethatcanaccommodatesquareLEDs.With3mmroundLEDs,allyouneedisa3mmdrillbit.

5)Sincethecubereliesonmultiplexingandpersistenceofvisiontocreateimages,eachlayerisonlyturnedonfor1/8ofthetime.Thisiscalleda1/8dutycycle.Tocompensateforthis,theLEDshavetobebrightenoughtoproducethewantedbrightnesslevelat1/8dutycycle.

6)Leglength.ThecubedesigninthisinstructableusesthelegsoftheLEDsthemselvesastheskeletonforthecube.TheleglengthoftheLEDsmustbeequaltoorgreaterthanthedistanceyouwantbetweeneachLED.

Step14:Chooseyourresistors

Therearethreethingstoconsiderwhenchoosingthevalueofyourresistors,theLEDs,the74HC574thatdrivetheLEDs,andthetransistorsusedtoswitchthe

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layersonandoff.

1)IfyourLEDscamewithadatasheet,thereshouldbesomeampereratingsinthere.Usually,therearetworatings,onemAforcontinuousload,andmAforburstloads.TheLEDswillberunningat1/8dutycycle,soyoucanrefertotheburstrating.

2)The74HC574alsohassomemaximumratings.IfalltheLEDsononeanodecolumnareon,thischipwillsupplycurrent8/8ofthetime.YouhavetokeepwithinthespecifiedmaximummAratingfortheoutputpins.Ifyoulookinthedatasheet,Youwillfindthisline:DCOutputSourceorSinkCurrentperOutputPin,IO:25mA.AlsothereisaVCCorGNDcurrentmaximumratingof50mA.Inordernottoexceedthis,yourLEDscanonlyrunat50/8mAsincethe74HC574has8outputs.Thisgivesyou6.25mAtoworkwith.

3)Thetransistorshavetoswitchonandoff64xthemAofyourLEDs.IfyourLEDsdraw20mAeach,thatwouldmeanthatyouhavetoswitchonandoff1.28Ampere.Theonlytransistorswehadavailablehadamaximumratingof400mA.

Weendedupusingresistorsof100ohms.

WhileyouarewaitingforyourLEDcubepartstoarriveinthemail,youcanbuildtheguyinthepicturebelow:http://www.instructables.com/id/Resistorman/(http://www.instructables.com/id/Resistorman/)

http://www.instructables.com/id/Resistor-man/

Step15:Choosethesizeofyourcube

WewantedtomaketheLEDcubeusingasfewcomponentsaspossible.Wehadseensomepeopleusingmetalrodsfortheirdesigns,butwedidn'thaveanymetalrods.Manyofthemetalroddesignsalsolookedalittlecrooked.

WefiguredthattheeasiestwaytobuildaledcubewouldbetobendthelegsoftheLEDssothatthelegsbecomethescaffoldingthatholdstheLEDsinplace.

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WebentthecathodelegononeoftheLEDsandmeasuredittobe26mmfromthecenteroftheLED.BychoosingaLEDspacingof25mm,therewouldbea1mmoverlapforsoldering.(1inch=25.4mm)

Withasmall3mmLED25mmbetweeneachledgaveusplentyofopenspaceinsidethecube.Seeingallthewaythroughtothefurthestlayerwouldn'tbeaproblem.Wecouldhavemadethecubesmaller,butthenwewouldhavetocuteverysingleleg,andvisibilityintothecubewouldbecompromised.

OurrecommendationistousethemaximumspacingthatyourLEDcanallow.Add1mmmarginforsoldering.

Step16:Howtomakestraightwire

InordertomakeanicelookingLEDCube,youneedsomestraightsteelwire.Theonlywirewehadwasonspools,soithadtobestraightened.

Ourfirstattemptatthisfailedhorribly.Wetriedtobenditintoastraightwire,butnomatterhowmuchwebent,itjustwasn'tstraightenough.

Thenwerememberedanepisodeof"Howit'smade"fromtheDiscoveryChannel.Theepisodewasabouthowtheymakesteelwire.Theystartoutwith

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aspoolofreallythickwire,thentheypullitthroughsmallerandsmallerholes.Werememberedthatthewirewastotallystraightandsymmetricalafterbeingpulledlikethat.

Sowefiguredweshouldgivepullingatry,anditworked!100%straightmetalwirefromaspool!

Hereishowyoudoit.cutofthelengthofwireyouneedfromthespool,plusaninchortwo.Removetheinsulation,ifany.GetafirmgripofeachendofthewirewithtwopairsofpliersPullhard!Youwillfeelthewirestretchalittlebit.

Youonlyneedtostretchitacoupleofmillimeterstomakeitniceandstraight.

Ifyouhaveavice,youcansecureoneendintheviceanduseonepairofpliers.Thiswouldprobablybealoteasier,butwedon'townavice.

Step17:Practiceinsmallscale

WheneverMythBustersaretestingacomplexmyth,theystartbysomesmallscaleexperiments.

Werecommendthatyoudothesamething.

Beforewebuiltthe8x8x8LEDcube,westartedbymakingasmallerversionofit,4x4x4.Bymakingthe4x4x4versionfirst,youcanperfectyourcubesolderingtechniquebeforestartingonthebigone.

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Checkoutour4x4x4LEDcubeinstructableforinstructionsonbuildingasmaller"prototype".

http://www.instructables.com/id/LEDCube4x4x4/(http://www.instructables.com/id/LEDCube4x4x4/)

Step18:Buildthecube:createajig

http://www.instructables.com/id/LED-Cube-4x4x4/

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InordertomakeanicelookingLEDcube,itisimportantthatitiscompletelysymmetrical,thatthespacebetweeneachLEDisidentical,andthateachLEDpointsthesameway.Theeasiestwaytoaccomplishthisistocreateatemporarysolderingjig/template.

1)Findapieceofwoodorplasticthatislargerthanthesizeofyourcube.

2)FindadrillbitthatmakesaholethatfitsaLEDsnuglyinplace.Youdon'twantittobetotight,asthatwouldmakeitdifficulttoremovethesolderedlayerfromthejigwithoutbendingit.Iftheholesaretoobig,someoftheLEDsmightcomeoutcrooked.

3)Usearulerandanangleirontodrawupagridof8by8linesintersectingat64points,usingtheLEDspacingdeterminedinapreviousstep.

4)Useasharppointyobjecttomakeindentionsateachintersection.Theseindentionswillpreventthedrillfromslidingsidewayswhenyoustartdrilling.

5)Drilloutalltheholes.

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6)TakeanLEDandtryeveryholeforsize.Iftheholeistoosnug,carefullydrillitagainuntiltheLEDfitssnuglyandcanbepulledoutwithoutmuchresistance.

7)Somewherenearthemiddleofoneofthesides,drawasmallmarkorarrow.Asteelwirewillbesolderedinhereineverylayertogivethecubesomeextrastiffening.

Step19:Buildthecube:solderingadvice

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YouaregoingtobesolderingVERYclosetotheLEDbody,andyouareprobablygoingtobeusingreallycheapLEDsfromeBay.LEDsdon'tlikeheat,

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cheapLEDsprobablymoresothanothers.ThismeansthatyouhavetotakesomeprecautionsinordertoavoidbrokenLEDs.

SolderingironhygieneFirstofall,youneedtokeepyoursolderingironniceandclean.Thatmeanswipingitonthespongeeverytimeyouuseit.Thetipofyoursolderingironshouldbecleanandshiny.Whenevertheyouseethetipbecomingdirtywithfluxoroxidizing,thatmeansloosingit'sshinyness,youshouldcleanit.Evenifyouareinthemiddleofsoldering.HavingacleansolderingtipmakesitALOTeasiertotransferheattothesolderingtarget.

SolderingspeedWhensolderingsoclosetotheLEDbody,youneedtogetinandoutquickly.Wipeyourironclean.Applyatinyamountofsoldertothetip.Touchthepartyouwanttosolderwiththesideofyourironwhereyoujustputalittlesolder.Letthetargetheatupfor0.51seconds,thentouchtheothersideofthetargetyouaresolderingwiththesolder.Youonlyneedtoapplyalittlebit.Onlythesolderthatistouchingthemetalofbothwireswillmakeadifference.Abigblobofsolderwillnotmakethesolderjointanystronger.Removethesolderingironimmediatelyafterapplyingthesolder.

MistakesandcooldownIfyoumakeamistake,forexampleifthewiresmovebeforethesolderhardensoryoudon'tapplyenoughsolder.Donottryagainrightaway.AtthispointtheLEDisalreadyveryhot,andapplyingmoreheatwiththesolderingironwillonlymakeithotter.ContinuewiththenextLEDandletitcooldownforaminute,orblowonittoremovesomeheat.

SolderWerecommendusingathinsolderforsolderingtheLEDs.Thisgivesyoualotmorecontrol,andenableyoutomakenicelookingsolderjointswithoutlargeblobsofsolder.Weuseda0.5mmgaugesolder.Don'tusesolderwithoutflux.

Ifyoursolderisveryoldandthefluxisn'tcleaningthetargetproperly,getnewersolder.Wehaven'texperiencedthis,butwehaveheardthatitcanhappen.

Areweparanoid?Whenbuildingthe8x8x8LEDCube,wetestedeachandeveryLEDbeforeusingitinthecube.WealsotestedeveryLEDafterwefinishedsolderingalayer.SomeoftheLEDsdidn'tworkafterbeingsolderedinplace.Weconsideredthesethingsbeforemakingasinglesolderjoint.Evenwithcarefulsoldering,someLEDsweredamaged.ThelastthingyouwantisabrokenLEDnearthecenterofthecubewhenitisfinished.Thefirstandsecondlayerfromtheoutsidecanbefixedafterwards,butanyfurtherinthanthat,andyou'llneedendoscopicsurgicaltools)

Step20:Buildthecube:testtheLEDs

WegotourLEDsfromeBay,reallycheap!

WetestedsomeoftheLEDbeforewestartedsoldering,andrandomlystumbledonaLEDthatwasalotdimmerthantherest.SowedecidedtotesteveryLEDbeforeusingit.WefoundacoupleofdeadLEDsandsomethatweredimmerthantherest.

ItwouldbeverybadtohaveadimLEDinsideyourfinishedLEDcube,sospend

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thetimetotesttheLEDsbeforesoldering!ThismightbelessofaproblemifyouareusingLEDsthataremoreexpensive,butwefounditworthwhiletotestourLEDs.

Getoutyourbreadboard,connectapowersupplyandaresistor,thenpoptheLEDsinoneatatime.YoumightalsowanttohaveanotherLEDwithitsownresistorpermanentlyonthebreadboardwhiletesting.Thismakesiteasiertospotdifferencesinbrightness.

Step21:Buildthecube:solderalayer

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Eachlayerismadeupof8columnsofLEDsheldtogetherbythelegsofeachLED.AtthetopofeachlayereachLEDisrotated90degreesclockwise,sothatthelegconnectswiththetopLEDofthenextcolumn.Onthecolumntotherightthislegwillstickoutofthesideofthelayer.WeleavethisinplaceanduseittoconnectgroundwhentestingalltheLEDsinalaterstep.

1)Prepare64LEDsBendthecathodelegofeachLED90degrees.MakesurethelegsarebentinthesamedirectiononalltheLEDs.LookingattheLEDsittinginaholeinthetemplatewiththenotchtotheright,webentthelegupwards.

2)StartwiththerowatthetopStartbyplacingthetoprightLEDinthetemplate.Thenplacetheonetotheleft,positioningitsothatit'scathodelegistouchingthecathodelegofthepreviousLED.RinseandrepeatuntilyoureachtheleftLED.Solderallthejoints.

3)Solderall8columnsIfyouarerighthanded,werecommendyoustartwiththecolumntotheleft.Thatwayyourhandcanrestonthewoodentemplatewhenyousolder.Youwillneedasteadyhandwhensolderingfreehandlikethis.StartbyplacingtheLEDsecondfromthetop,aligningitsoit'slegtouchesthesolderjointfromthe

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previousstep.ThenplacetheLEDbelowthatsothatthecathodelegtouchestheLEDabove.Repeatuntilyoureachthebottom.Solderallthejoints.

4)AddbracesYounowhavealayerthatlookslikeacomb.Atthispointthewholethingisveryflimsy,andyouwillneedtoaddsomesupport.Weusedonebracingnearthebottomandonenearthemiddle.Takeastraightpeaceofwire,roughlyalignitwhereyouwantitandsolderoneendtothelayer.Finetunethealignmentandsoldertheotherendinplace.Now,makesolderjointstotheremaining6columns.Dothisforbothbraces.

5)TestalltheLEDsThisiscoveredinthenextstep.Justmentioningheresoyoudon'tremovethelayerjustyet.

6)RemovethelayerThefirstlayerofyourLEDcubeisalldone,nowallyouhavetodoisremoveitfromthetemplate.Dependingonthesizeofyourholes,someLEDsmighthavemoreresistancewhenyoutrytopullitout.SimplygrabbingbothendsofthelayerandpullingwouldprobablybreakthewholethingifacoupleoftheLEDsarestuck.

StartbyliftingeverysingleLEDacoupleofmillimeters.Justenoughtofeelthatthereisn'tanyresistance.WhenalltheLEDsarefreedfromtheirholes,tryliftingitcarefully.Ifitisstillstuck,stopandpullthestuckLEDsout.

Repeat8times!

Noteonimages:Ifyouarehavingtroubleseeingthedetailinanyofourpictures,youcanviewsthefullresolutionbyclickingonthelittleLiconinthetopleftcornerofeveryimage.Allourcloseuppicturesaretakenwithaminitripodandshouldhave

excellentmacrofocus.Ontheimagepage,choosetheoriginalsizefromthe"Availablesizes"menuonthelefthandside.

Step22:Buildthecube:testthelayer

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SolderingthatclosetothebodyoftheLEDcandamagetheelectronicsinside.WestronglyrecommendthatyoutestallLEDsbeforeproceeding.

Connectgroundtothetabyouleftstickingoutattheupperrightcorner.Connectawireto5Vthrougharesistor.UseanyresistorthatlightstheLEDupanddoesn'texceeditsmaxmAratingat5V.470Ohmwouldprobablyworkjustfine.

Takethewireandtapitagainstall64anodelegsthatarestickingupfromyourtemplate.IfaLEDdoesn'tflashwhenyoutapit,thatmeansthatsomethingiswrong.

1)Yoursolderingisn'tconductingcurrent.2)TheLEDwasoverheatedandisbroken.3)Youdidn'tmakeaproperconnectionbetweenthetestwireandtheled.(tryagain).

Ifeverythingchecksout,pullthelayerfromthecubeandstartsolderingthenextone.

Step23:Buildthecube:straigthenthepins

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Inouropinion,aLEDcubeisapieceofartandshouldbeperfectlysymmetricalandstraight.IfyoulookattheLEDsinyourtemplatefromtheside,theyareprobablybentinsomedirection.

Youwantallthelegstopointstraightup,ata90degreeanglefromthetemplate.

Whilelookingatthetemplatefromtheside,straightenallthelegs.Thenrotatethetemplate90degrees,toviewitfromtheotherside,thendothesameprocess.

Younowhaveaperfectlayerthatisreadytoberemovedfromthetemplate.

Step24:Buildthecube:bendthepins

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IntheLEDcubecolumns,wewanteachLEDtositcenteredpreciselyabovetheLEDsbelow.ThelegsontheLEDscomeoutfromtheLEDbodyhalfamillimeterorsofromtheedge.Tomakeasolderjoint,wehavetobendtheanodelegsothatittouchestheanodelegontheLEDbelow.

Makeabendintheanodelegtowardsthecathodelegapproximately3mmfromtheendoftheleg.ThisisenoughforthelegtobendaroundtheLEDbelowandmakecontactwithit'sanodeleg.

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Nowcomesthetrickypart,solderingitalltogether!

Thefirsttwolayerscanbequiteflimsybeforetheyaresolderedtogether.Youmaywanttoputthefirstlayerbackinthetemplatetogiveitsomestability.

Inordertoavoidtotaldisaster,youwillneedsomethingtoholdthelayerinplacebeforeitissolderedinplace.Luckily,thewidthofa9Vbatteryisprettycloseto25mm.Probablycloserto25.526mm,butthat'sOK.

Warning:The9voltsfroma9VbatterycaneasilyoverloadtheLEDsifthecontactsonthebatterycomesincontactwiththelegsoftheLEDs.WetapedoverthebatterypolestoavoidaccidentallyruiningtheLEDsweweresoldering.

Wehadplentyof9Vbatterieslyingaround,soweusedthemastemporarysupports.Startbyplacinga9Vbatteryineachcorner.Makesureeverythingisalignedperfectly,thensolderthecornerLEDs.

NowsolderalltheLEDsaroundtheedgeofthecube,movingthe9Vbatteriesalongasyougoaround.Thiswillensurethatthelayersaresolderedperfectlyparalleltoeachother.

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Nowmovea9Vbatterytothemiddleofthecube.Justslideitinfromoneofthesides.SolderacoupleoftheLEDsinthemiddle.

Thewholethingshouldbeprettystableatthispoint,andyoucancontinuesolderingtherestoftheLEDswithoutusingthe9Vbatteriesforsupport.

However,ifitlookslikesomeoftheLEDsaresaggingalittlebit,slideina9Vbatterytoliftthemup!

Whenyouhavesolderedallthecolumns,itistimetotesttheLEDsagain.Rememberthattabstickingoutfromtheupperrightcornerofthelayer,thatwetoldyounottoremoveyet?Nowit'stimetouseit.Takeapieceofwireandsolderthetabofthebottomlayertothetabofthelayeryoujustsolderedinplace.

Connectgroundtothethegroundtab.

Testeachledusingthesamesetupasyouusedwhentestingtheindividuallayers.Sincethegroundlayershavebeenconnectedbythetesttabs,andalltheanodesineachcolumnsareconnectedtogether,allLEDsinacolumnshouldlightupwhenyouapplyvoltagetothetopone.IftheLEDsbelowitdoesnotlightup,itprobablymeansthatyouforgotasolderjoint!ItisALOTbettertofigurethisoutatthispoint,ratherthanwhenallthelayersaresolderedtogether.Thecenterofthecubeisvirtuallyimpossibletogettowithasolderingiron.

Younowhave2/8ofyourLEDcubesolderedtogether!Yay!

Forthenext6layers,usetheexactsameprocess,butspendevenmoretimealigningthecornerLEDsbeforesolderingthem.Lookatthecubefromabove,andmakesurethatallthecornerLEDsareonastraightlinewhenlookingatthemfromabove.

Rinseandrepeat!

Step26:Buildthecube:createthebase

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Wedidn'thaveanyfancytoolsatourdisposaltocreateafancystandorboxforourLEDcube.Instead,wemodifiedthetemplatetoworkasabaseforthecube.

WeencourageyoutomakesomethingcoolerthanwedidforyourLEDcube!

Forthetemplate,weonlydrilledacoupleofmmintothewood.Totransformthetemplateintoabase,wejustdrilledalltheholesthroughtheboard.Thenwedrilled8smallerholesforthe8cathodewiresrunninguptothe8cathodelayers.

Ofcourse,youdon'twanttohaveyourLEDcubeonawoodcoloredbase.Wedidn'thaveanyblackpaintlyingaround,butwedidfindagiantblackmagicmarker!Stainingthewoodblackwithamagicmarkerworkedsurprisinglywell!Ithinktheoneweusedhada10mmpoint.

Step27:Buildthecube:mountthecube

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Mountthecube.Thatsoundsveryeasy,butit'snot.Youhavetoalign64LEDlegstoslidethrough64holesatthesametime.It'slikethreadinganeedle,times64.

Wefounditeasiesttostartwithoneend,thengraduallypoppingthelegsintoplace.UseapenorsomethingtopokeattheLEDlegsthatmisstheirholes.

Onceall64LEDlegsarepokingthroughthebase,carefullyturnitonit'sside.

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Thenbendall64legs90degrees.Thisisenoughtoholdthecubefirmlymountedtothebase.Noneedforglueoranythingelse.

Step28:Buildthecube:cathoderisers

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YounowhaveaLEDcubewith64anodeconnectionsontheundersideofthebase.Butyouneedtoconnectthegroundlayerstoo.

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Rememberthose8smallholesyoudrilledinapreviousstep?Wearegoingtousethemnow.

Makesomestraightwireusingthemethodexplainedinapreviousstep.

Westartwithgroundforlayer0.Takeashortpieceofstraightwire,Makeabendapproximately10mmfromtheend.Pokeitthroughtheholeforgroundlayer0.Leave10mmpokingthroughtheundersideofthebase.Positionitsothatthebendyoumaderestsonthebackwireofgroundlayer0.Nowsolderitinplace.Layer1through7arealittletrickier.Weusedahelpinghandtoholdthewireinplacewhilesoldering.

Takeastraightpieceofwireandbendit90degrees10mmfromtheend.Thencutittolengthsothat10mmofwirewillpokeoutthroughtheundersideofthebase.Pokethewirethroughtheholeandletthewirerestonthebackwireofthelayeryouareconnecting.Clampthehelpinghandontothewire,thensolderitinplace.

Rinseandrepeat7moretimes.

Carefullyturnthecubeonit'ssideandbendthe8groundwires90degrees.

Step29:Buildthecube:attachcables

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64+8wireshavetogofromthecontrollertotheLEDcube.Weusedribboncabletomakethingsalittleeasier.

Thegroundlayersusean8wireribboncable.

Thecathodesareconnectedwith416wireribboncables.Eachoftheseribboncablesaresplitintwoateitherend,togettwo8wirecables.

Atthecontrollerside,weattached0.1"femaleheaderconnectors.Theseplugintostandard0.1"singlerowPCBheaderpins.

Theheaderconnectorisamodularconnectorthatcomesintwoparts,metalinsertsandaplasticbody.

Themetalinsertsaresupposedtobecrimpedonwithatool.Wedidn'thavetheappropriatetoolonhand,soweusedpliers.Wealsoaddedalittlesoldertomakesurethewiresdidn'tfallofwithuse.

1)Prepareone8wireribboncableand416wireribboncablesofthedesiredlength2)Crimporsolderonthemetalinserts.

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3)Insertthemetalinsertintotheplasticconnectorhousing.4)Solderthe8wireribboncabletothecathoderisers.Pretinthecablesbeforesoldering!5)Solderintherestofthecables.Theredstripeonthefirstwireindicatesthatthisisbit0.6)Tightenthescrewsonthestrainrelieftomakesureeverythingstaysinplace.7)ConnectalltheribboncablestothePCBsinthecorrectorder.Seepicturesbelow.Our8wireribboncabledidn'thavearedwire.Justfliptheconnector180degreesifyourcubeisupsidedown.

Step30:Buildthecontroller:layout

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WetookoutthebiggesttypeofPCBwehadavailable(9x15cm)andstartedexperimentingwithdifferentboardlayouts.Itsoonbecameclearthatcrammingallthecomponentsontooneboardwasn'tagoodsolution.Insteadwedecidedtoseparatethelatcharrayandpowersupplypartofthecircuitandplaceitonaseparateboard.Aribboncabletransfersdatalinesbetweenthetwoboards.

Choosingtwoseparateboardswasagooddecision.Thelatcharraytookupalmostallthespaceofthecircuitboard.Therewouldn'thavebeenmuchspaceforthemicrocontrollerandotherparts.

Youmaynothavetheexactsamecircuitboardsaswedo,ormaywanttoarrangeyourcomponentsinadifferentway.Trytoplaceallthecomponentsonyourcircuitboardtoseewhichlayoutbestfitsyourcircuitboard.

multiplexer_board.sch (/files/orig/FAU/I50K/GICYB6CJ/FAUI50KGICYB6CJ.tmp)238KB

avr_board.sch (/files/orig/FA9/26YI/GICYB6CH/FA926YIGICYB6CH.tmp)249KB

Step31:Buildthecontroller:clockfrequency

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Weuseanexternalcrystalof14.7456MHztodrivetheATmegasystemclock.

Youmaybethinkingthatthisisanoddnumbertouse,andwhywedidn'truntheATmegaatthe16MHzitisratedfor.

WewanttobeabletocontroltheLEDcubefromacomputer,usingRS232.Serialcommunicationrequiresprecisetiming.Ifthetimingisoff,onlybyalittlebit,somebitsaregoingtobemissedorcounteddoublefromtimetotime.Wewon'tberunninganyerrorcorrectingalgorithmsontheserialcommunications,soanyerroroverthelinewouldberepresentedintheLEDcubeasavoxelbeingonoroffinthewrongplace.

Togetflawlessserialcommunication,youhavetouseaclockfrequencythatcanbedividedbytheserialfrequencyyouwanttouse.

14.7456MHzisdividablebyallthepopularRS232baudrates.(14.7456MHz*1000*1000)/9600baud=1536.0(14.7456MHz*1000*1000)/19200baud=768.0(14.7456MHz*1000*1000)/38400baud=384.0(14.7456MHz*1000*1000)/115200baud=128.0

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TheformulainsidetheparenthesesconvertsfromMHztoHz.First*1000givesyouKHz,thenextHz.

AsyoucanseealloftheseRS232baudratescanbecleanlydividedbyourclockrate.Serialcommunicationwillbeerrorfree!

Step32:Buildthecontroller:protoboardsolderingadvice

WeseepeopledoalotofweirdstuffwhentheysolderonprototypePCBs.

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Beforeyoucontinue,wejustwanttosharewithyoutheprocessweusetocreatetracksonprototypePCBswithsoldereyes.Onceyoumasterthistechnique,youwillprobablystartusingitalot.

1)Filleachpointofthetrackyouwanttomakewithsolder.2)Connecteveryotherpointsbyheatingthemandaddingalittlesolder.3)Connectthe2holelongpiecesyounowhavespanningthedesiredtrack.4)Lookhowbeautifultheresultis.

Youcanseeinthevideohowwedoit.Wehadtotouchsomeofthepointstwicetojointhem.Itwasabithardtohavethecamerainthewaywhenweweresoldering)

Step33:Buildthecontroller:Powerterminalandfilteringcapacitors

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Thecubeiscomplete,nowallthatremainsisamonstercircuittocontrolthething.

Let'sstartwiththeeasiestpart,the"powersupply".

ThepowersupplyconsistsofascrewterminalwhereyouconnecttheGNDandVCCwires,somefilteringcapacitors,aswitchandaanLEDtoindicatepoweron.

Initially,wehaddesignedanonboardpowersupplyusinganLM7805stepdownvoltageregulator.However,thisturnedouttobeabigfail.

Weusedthiswitha12Vwallwart.Butasyoumayalreadyknow,mostwallwartsoutputhighervoltagesthantheonesspecifiedonthelabel.Oursoutputtedsomethinglike14volts.TheLM7805isn'taverysophisticatedvoltageregulator,itjustusesresistancetostepdownthevoltage.Toget5voltsoutputfrom14voltsinputmeansthattheLM7805hastodrop9volts.Theexcessenergyisdispersedasheat.Evenwiththeheatsinkthatyouseeinthepicture,itbecameveryveryhot.Waytohottotouch!Inadditiontothat,theperformancewasn'tgreateither.Itwasn'tabletosupplythenecessarycurrenttorunthecubeatfullbrightness.

TheLM7805waslaterremoved,andawirewassolderedbetweentheinputandoutputpins.Insteadweusedanexternal5Vpowersource,ascoveredina

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previousstep.

Whysomanycapacitors?

TheLEDcubeisgoingtobeswitchingabout500mAonandoffseveralhundredtimespersecond.Themomentthe500mAloadisswitchedon,thevoltageisgoingtodropacrosstheentirecircuit.Manythingscontributetothis.Resistanceinthewiresleadingtothepowersupply,slownessinthepowersupplytocompensatefortheincreaseinload,andprobablysomeotherthingsthatwedidn'tknowabout)

Byaddingcapacitors,youcreateabufferbetweenthecircuitandthepowersupply.Whenthe500mAloadisswitchedon,therequiredcurrentcanbedrawnfromthecapacitorsduringthetimeittakesthepowersupplytocompensatefortheincreaseinload.

Largecapacitorscansupplylargercurrentsforlongerperiodsoftime,whereassmallercapacitorscansupplysmallbutquickburstsofenergy.

Weplaceda1000uFcapacitorjustafterthemainpowerswitch.Thisworksasourmainpowerbuffer.Afterthat,thereisa100uFcapacitor.ItiscommonpracticetohavealargecapacitorattheinputpinofanLM7805andasmallercapacitoratit'soutputpin.The100uFcapacitorprobablyisn'tnecessary,butwethinkcapacitorsmakeyourcircuitlookcooler!

TheLEDisconnectedtoVCCjustafterthemainpowerswitch,viaaresistor.

Step34:Buildthecontroller:ICsockets,resistorsandconnectors

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Inthisstepyouwillbesolderinginthemaincomponentsofthemultiplexerarray.

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Ourmaindesignconsiderationherewastominimizesolderingandwiring.WeoptedtoplacetheconnectorsasclosetotheICsaspossible.Ontheoutputside,thereisonlytwosolderjointsperLEDcubecolumn.ICresistor,resistorconnector.Theoutputsofthelatchesarearrangedinorder07,sothisworksoutgreat.Ifweremembercorrectly,thelatchweareusingisavailableintwoversions,onewiththeinputsandoutputsinsequentialorder,andonewiththeinandoutputsinseeminglyrandomorder.Donotgetthatone!)Don'tworry,ithasadifferent74HCxxxname,soyou'llbegoodifyousticktoourcomponentlist.

Inthefirstpicture,youcanseethatwehaveplacedalltheICsockets,resistorsandconnectors.Wesqueezeditastightaspossible,toleaveroomforunforeseenstuffinthefuture,likebuttonsorstatusLEDs.

Inthesecondpicture,youcanseethesolderjointsbetweentheresistorsandtheICsocketsandconnectors.NotethattheinputsideofthelatchICsocketshaven'tbeensolderedyetinthispicture.

Step35:Buildthecontroller:PowerrailsandICpower

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Rememberthatprotoboardsolderingtrickweshowedyouinapreviousstep?Wetoldyouitwouldcomeinhandy,andhereiswhereyouuseit.

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Largecircuitboardslikethisone,withlotsofwires,canbecomequiteconfusing.WealwaystrytoavoidliftingtheGNDandVCClinesofftheboard.Wesolderthemascontinuoussolderlines.ThismakesitveryeasytoidentifywhatisGND/VCCandwhatissignallines.

IftheVCCandGNDlinesneedstocrosspaths,simplyrouteoneofthemovertheotherusingapieceofwireonthetopsideofthePCB.

Inthefirstpictureyoucanseesomesoldertracesinplace.

Thetwohorizontaltracesisthe"mainpowerbus".ThelowestoneisVCCandthetoponeisGND.ForeveryrowofICsaGNDandVCClineisforkedoffthemainpowerbus.TheGNDlinerunsundertheICs,andtheVCClinerunsundertheresistors.

Wewentalittleoverboardwhenmakingstraightwireforthecube,andhadsomepiecesleftover.WeusedthatfortheVCClinethatrunsundertheresistors.

Inthebottomrightcorner,youcanseethatwehavestartedsolderingthe8+1bitbusconnectingallthelatchICs.Lookhoweasyitistoseewhatissignalwiresandwhatispowerdistribution!

Inthesecondpicture,youcanseetheboardrightsideup,withsomeadditionalcomponentssolderedin,justignorethemforthemoment.

ForeverylatchIC(74HC574),thereisa100nF(0.1uF)ceramiccapacitor.Thesearenoisereductioncapacitors.Whenthecurrentontheoutputpinsareswitchedonandoff,thiscancausethevoltagetodropenoughtomesswiththeinternalworkingsoftheICs,forasplitsecond.Thisisunlikely,butit'sbettertobesafethansorry.Debuggingacircuitwithnoiseissuescanbeveryfrustrating.

Besides,capacitorsmakethecircuitlookthatmuchcoolerandprofessional!The100nFcapacitorsmakesurethatthereissomecurrentavailablerightnexttotheICincasethereisasuddendropinvoltage.Wereadsomewherethatitiscommonengineeringpracticetoplacea100nFcapacitornexttoeveryIC,"Usethemlikecandy".Wetendtofollowthatprinciple.

Beloweachrowofresistors,youcanseeatinypieceofwire.ThisistheVCClinemakingalittlejumptothetopsideoftheboardtocrossthemainGNDline.

Wealsoaddedacapacitoronthefarendofthemainpowerbus,forgoodmeasure.

Step36:Buildthecontroller:ConnecttheICs,8bitbus+OE

Inthepicture,you'llnoticealotofwireshavecomeintoplace.

Allthetinybluewiresmakeupthe8+1bitbusthatconnectsallthelatchICs.8bitsarefordata,andthe+1bitistheoutputenableline.

Atthetopoftheboard,wehaveaddeda16pinconnector.Thisconnectsthelatchboardtothemicrocontrollerboard.Nexttothat,youseethe74HC138.

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ThetinybluewiresareKynarwire.Thisisa30or32AWG(americanwiregauge)wire.Verytiny.Weloveworkingwiththistypeofwire.Becauseitissothin,itdoesn'ttakeupthatmuchspaceonthecircuitboard.Ifwehadusedthickerwire,youwouldn'tbeabletoseetheboardthroughallthewires.Kynarwireiscoatedwithtin,soyoucansolderdirectlyafterstrippingit.Noneedforpretinning.ThetinybluewiresareconnectedtothesamepinoneverylatchIC.

Fromtheconnectoratthetop,youcansee8greenwiresconnectedtothebus.Thisisthe8bitdatabus.Weuseddifferentcolorsfordifferentfunctionstobettervisualizehowthecircuitisbuilt.

Theorangewireconnectedtothebusistheoutputenable(OE)line.

Ontherighthandsideoftheconnector,thefirstpinisconnectedtoground.

Step37:Buildthecontroller:Addressselector

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The74HC138isresponsiblefortogglingtheclockpinonthe74HC574latchICs.Wecallthisanaddressselectorbecauseitselectswhichoneofthe8bytes

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inthelatcharraywewanttowritedatato.Thethreebluewiresrunningfromtheconnectortothe74HC138isthe3bitbinaryinputusedtoselectwhichofthe8outputsispulledlow.Fromeachoftheoutputsonthe74HC138,thereisawire(white)runningtotheclockpinonthecorresponding74HC574latchIC.

StartbysolderingtheGNDandVCCconnections.IfyouusethesoldertracemethodtorunGND/VCClinesyouwanttodothisbeforeyousolderanyotherwiresinplace.A100nFceramicfilteringcapacitorisplacedclosetotheVCCandGNDpinsofthe74HC138.

Thenconnecttheaddresslinesandthe8clocklines.

Ifyoulookcarefullyattheconnector,youcanseetwopinsthatarenotused.ThesewillbeusedforabuttonanddebugLEDlater.

Step38:Buildthecontroller:AVRboard

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Braaaaainzz!!!

ThisboardisthebrainoftheLEDcube.ThemaincomponentisanAtmelAVRATmega32.

Thisisan8bitmicrocontrollerwith32KBofprogrammemoryand2KBRAM.TheATmega32has32GPIO(GeneralPurposeIO)pins.Twoofthesewillbeusedforserialcommunication(TX+RX).ThreeIOpinsareusedforISP(IncircuitSerialProgramming).Thisleavesuswith27GPIOtodrivetheLEDcube,buttonsandstatusLEDs.

Agroupof8GPIO(8bits,onebyte)iscalledaport.TheATmega32has4ports.PORTA,PORTB,PORTCandPORTD.OnPORTCandPORTDsomeofthepinsareusedforTX/RXandISP.OnPORTAandPORTB,allthepinsareavailable.Weusetheseportstodrivethedatabusofthelatcharrayandlayerselecttransistorarray.

PORTAisconnectedtothedatabusonthelatcharray.

EachpinonPORTCisconnectedtoapairoftransistorsthatdriveagroundlayer.

Theaddressselectoronthelatcharray(74HC138)isconnectedtobit02onPORTB.Outputenable(OE)isconnectedtoPORTBbit3.

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Inthefirstimage,youseetheAVRboardrightsideup.

Thelarge40pinPDIP(PlasticDualInlinePackage)chipinthecenteroftheboardistheATmega32,thebrainz!JusttotheleftoftheATmega,youseethecrystaloscillatorandit'stwocapacitors.OneithersideoftheATmegathereisa100nFfilteringcapacitor.OneforGND/VCCandoneforAVCC/GND.

Inthetopleftcorner,thereisatwopinconnectorsandtwofilteringcapacitors.One10uFandone100nF.TheLEDisjustconnectedtoVCCviaaresistor,andindicatespoweron.

Thelarge16pinconnectordirectlyabovetheATmegaconnectstothelatcharrayboardviaaribboncable.Thepinoutonthiscorrespondstothepinoutontheotherboard.

Thesmaller10pinconnectortotheleft,isastandardAVRISPprogrammingheader.IthasGND,VCC,RESET,SCK,MISOandMOSI,whichareusedforprogramming.Nexttoit,thereisajumper.Whenthisisinplace,theboardcanbepoweredfromtheprogrammer.

Caution:DONOTpowertheboardfromtheprogrammerwhentheactualLEDcubeisconnectedtothecontroller.ThiscouldpossiblyblowtheprogrammerandeventheUSBporttheprogrammerisconnectedto!

Thesecondimageshowstheunderside.AgainallGNDandVCClinesaresolderedastracesontheprotoboardorbarewire.Wehadsomemoreleftoverstraightmetalwire,soweusedthis.

TheorangewiresconnecttheATmega'sRESET,SCK,MOSIandMISOpinstotheISPprogrammingheader.

TheGreenwiresconnectPORTAtothedatabus.

Thebluewiresaretheaddressselectlinesforthe74HC138andoutputenable(OE)forthelatcharray.

1)Startbyplacingthe40pinICsocket,the10pinISPconnectorwithajumpernexttoitandthe16pindatabusconnector.2)Solderinplacethepowerconnector,capacitorsandpowerindicatorLED.3)ConnectalltheGNDandVCClinesusingsoldertracesorwire.Placea100nFcapacitorbetweeneachpairofGND/VCCpinsontheATmega.4)Solderinthecrystalandthetwo22pFcapacitors.EachcapacitorisconnectedtoapinonthecrystalandGND.5)Runallthedatabus,addressselectandOEwires,andtheISPwires.Transistors,buttonsandRS232willbeaddedinlatersteps.Atthistime,theAVRboardcanbeconnectedtoanISPprogrammerandtheATmegashouldberecognized.

Step39:Buildthecontroller:Transistorarray

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ThetransistorarrayisresponsibleforswitchingonandoffGNDforeachlayerintheLEDcube.

Ourfirstattemptatthiswasanepicfail.Weboughtsometransistorsratedforover500mA,thinkingthatwouldbeplentyofjuice.Wedon'trememberthemodelnumber.

TheLEDcubeworked,butitwasn'tverybright,andthebrightnesswasinverselyproportionaltothenumberofLEDsswitchedoninanygivenlayer.Inadditiontothat,therewassomeghosting.Layersdidn'tswitchcompletelyoffwhentheyweresupposedtobeoff.

Needlesstosay,wewerekindofdisappointed,andstarteddebugging.Thefirstthingwedidwastoaddpullupresistorstotrytocombattheghosting.Thisremovedalmostalltheghosting,yay!Butthecubewasstillverydim,bah!

Wedidn'thaveanypowerfultransistorsorMOSFETslyingaround,sowehadtocomeupwithanothersolution.

WepostedathreadintheelectronicssectionoftheAVRFreaks.netforum,askingifitwaspossibletousetwosmallertransistorsinparallel.Thisistheonlyoptionavailabletoususingthepartswehadonhand.Thegeneralresponsewas,thiswillneverworksodon'tevenbothertrying.Theyevenhadvalidtheoriesandstuff,butthatdidn'tdeterusfromtrying.Itwasouronlysolutionthatdidn'tinvolvewaitingfornewpartstoarriveinthemail.

WeendeduptryingPN2222A,NPNgeneralpurposeamplifier.Ideally,you'dwantaswitchingtransistorforthiskindofapplication,butweneeded16transistorsofthesametype.Thistransistorwasratedat1000mAcurrent,sowedecidedtogiveitatry.

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Foreachlayer,weusedtwoPN2222Asinparallel.ThecollectorsconnectedtogethertoGND.Theemittersconnectedtogether,thenconnectedtoagroundlayer.Thebaseofeachtransistorswasconnectedtoit'sownresistor,andthetworesistorsconnectedtoanoutputpinontheATmega.

Wesolderedinallthetransistorsandturnedthethingonagain,anditworked,perfectly!

Ifyouknowwhatyouaredoing,youshouldprobablydosomeresearchandfindamoresuitabletransistororMOSFET.Butoursolutionistriedandtestedandalsodoesthetrick!

1)Startbyplacingall8alltransistorsonthePBCandsolderingeachoftheirpins.

2)Runasoldertracebetweenthetheemittersofall16transistors.ConnectthissoldertracetoGND.

3)Solderinaresistorforeachtransistor,thesoldertheresistorstogetherinpairsoftwo.

4)RunkynarwirefromtheoutputpinsontheATmegatoeachofthe8resistorpairs.

5)Soldertogetherthecollectorsofthetransistorsinpairsoftwoandrunsoldertraceorwirefromthecollectorpairstoan8pinheader.

Step40:Buildthecontroller:ButtonsandstatusLEDs

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YoucanmakeaLEDcubewithoutanybuttonsatall,butit'snicetohaveatleastonebuttonandsomestatusLEDsfordebugging.

WeaddedoneawesomelookingbuttonwithtwobuiltinLEDs,andoneregularbuttonwithanLED.

ThefirstbuttonismountedonthelatcharrayPCB,sincethiswillsitontopoftheAVRboard,andwewantthebuttoneasilyaccessible.Thewiresareroutedthroughtheribboncable.ThesecondbuttonandLEDsitsontheAVRboardandwasmostlyusedfordebuggingduringconstruction.

ThebuttonsareconnectedbetweenGNDandtheIOpinontheATmega.AninternalpullupresistorinsidetheATmegaisusedtopullthepinhighwhenthebuttonisnotpressed.Whenthebuttonispressed,theIOpinispulledlow.Alogic0indicatesthatabuttonhasbeenpressed.

TheLEDsarealsoconnectedbetweenGNDandtheIOpinviaaresistorofappropriatesize.Don'tconnectanLEDtoamicrocontrollerIOpinwithouthavingaresistorconnectedinseries.Theresistoristheretolimitthecurrent,andskippingitcanblowtheIOportonyourmicrocontroller.

Tofindtheappropriateresistor,justplugtheledintoabreadboardandtestdifferentresistorswitha5vpowersupply.ChoosetheresistorsthatmaketheLEDlightupwiththebrightnessyouwant.IfyouuseLEDswithdifferentcolors,youshouldtestthemsidebyside.DifferentcolorLEDsusuallyrequiredifferentresistorstoreachthesamelevelofbrightness.

WewillleaveituptoyoutodecidetheplacementofyourstatusLEDs,butyoucanseeinthepicturesbelowhowwedidit:

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Step41:Buildthecontroller:RS232

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Togetthetrulyamazinganimations,weneedtoconnecttheLEDcubetoaPC.ThePCcandofloatingpointcalculationsthatwouldhavetheAVRworkingin

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slowmotion.

TheATmegahasabuiltinserialinterfacecalledUSART(UniversalSynchronousandAsynchronousserialReceiverandTransmitter).

TheUSARTcommunicatesusingTTLlevels(0/5volts).ThecomputertalksserialusingRS232.ThesignallevelsforRS232areanywherefrom+/5voltsto+/15volts.

ToconverttheserialsignalsfromthemicrocontrollertosomethingtheRS232portonaPCcanunderstand,andviceversa,weusetheMaximMAX232IC.Actually,thechipweareusingisn'tfromMaxim,butitisapincompatibleclone.

Therearesome100nFceramiccapacitorssurroundingtheMAX232.TheMAX232usesinternalchargepumpsandtheexternalcapacitorstostepupthevoltagetoappropriateRS232levels.Oneofthe100nFcapacitorsisafiltercapacitor.

TheRS232connectorisata90degreeangleforeasyaccesswhenthelatcharrayboardismountedontopoftheAVRboard.Weuseda4pinconnectorandcutoneofthepinsouttomakeapolarizedconnector.ThisremovesanyconfusionastowhichwaytoplugintheRS232cable.

InthesecondpictureyoucanseetwoyellowwiresrunningfromtheATmegatotheMAX232.ThesearetheTTLlevelTXandRXlines.

1)ConnecttheGNDandVCCpinsusingsoldertraceorwire.Placea100nFcapacitorclosetotheGNDandVCCpins.

2)Solderinplacetherestofthe100nFcapacitors.Youcansolderthesewithsoldertraces,soitsbesttodothisbeforeyouconnectthetx/rxwires.

3)Solderinplacea4pin0.1"headerwithonepinremoved.ConnectthepinnexttotheonethatwasremovedtoGND.

4)Connectthetx/rxinputlinestothemicrocontroller,andthetx/rxoutputlinestothe4pinheader.

Thewiresgoingtothe4pinheaderarecrossedbecausethefirstserialcableweusedhadthispinout.

Step42:Buildthecontroller:MakeanRS232cable

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ToconnecttheLEDcubetoaserialportonyourcomputer,youneedtomakeaserialcablewithafemaleDSub9pinconnector.

Ouremployerdeployed70Ethernetswitcheswithmanagementlastyear.WitheachswitchcomesanRS232cablethatisneverused.WeliterallyhadabigpileofRS232cable,sowedecidedtomodifyoneofthose.

OntheLEDcube,a0.1"pinheaderisused,sotheRS232cableneedsanewconnectoronthecubeside.

Wedidn'thavea4pinfemale0.1"connector,soweuseda4pinfemalePCBheaderinstead.

TheconnectorontheLEDcubePCBhasonepinremoved,tovisualizethedirectionalityoftheconnector.Thepinnumbersgoesfromrighttoleft.

PinoutoftheRS232connector:

1)GND(DSub9pin5)2)Notconnected3)RX(DSub9pin3)

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4)TX(DSub9pin2)

FollowthesestepstomakeyourownRS232cable:

1)Cutoftheconnectoratoneendofthecable.Ifyourcablehasafemaleandamaleconnector,makesuretoremovethemaleconnector!

2)Stripawaytheoutersheathontheendwhereyouremovedtheconnector.

3)Stripallthewiresinside.

4)Setyourmultimetertocontinuitytestmode.Thismakesthemultimeterbeepwhentheprobesareconnected.Ifyourmultimeterdoesn'thavethisoption,usetheresistancemode.Itshouldgetcloseto0ohmwhenyouconnecttheprobes.

5)ConnectonemultimeterprobetotheDSub9'spin5,thenprobeallthewiresuntilyouthemultimeterbeeps.YouhavenowidentifiedthecolorofGNDinyourcable.Repeatforpin2and3(TXandRX).

6)Writedownthecolorsyouidentified,thencutofftheotherwires.

7)Cutthethreewiresdowntosize,30mmshoulddo.

8)Pretinthewirestomakesolderingeasier.Justapplyheatandsoldertothestrippedwires.

9)Slideashrinktubeoverthecable.Slidethreesmallershrinktubesovertheindividualwires.

10)Solderthewirestotheconnector.

11)Shrinkthesmallertubesfirst,thenthelargeone.Ifyouusealighter,don't

holdtheshrinktubeabovetheflame,justholditclosetothesideoftheflame.

Don'tmakeyourcablebasedonthecolorsweused.Testthecabletofindthecorrectcolors.

Step43:Buildthecontroller:Connecttheboards

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Thetwoboardsareconnectedbytwocables:AribboncablefortheDATAandAddressBUS.

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A2wirecableforGNDandVCC.

Afterconnectingthesetwocables,yourboardiscomplete.

Step44:Buildthecontroller:Connectthecube

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Connecttheribboncablesaccordingtothepinoutsshowninpicture2and3.Thegroundlayerribboncableconnectstothepinheadernearthetransistorarray.Ifthecubeisupsidedown,justplugitintheotherway.

Step45:ProgramtheAVR:Setthefusebits

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TheATmega32hastwofusebytes.ThesecontainsettingsthathavetobeloadedbeforetheCPUcanstart,likeclocksourceandotherstuff.YouhavetoprogramyourATmegatouseanexternalhighspeedcrystaloscillatoranddisableJTAG.

Wesetthelowerfusebyte(lfuse)to0b11101111,andthehighfusebyteto0b11001001.(0bmeansthateverythingafterthebisinbinary).

WeusedavrdudeandUSBtinyISP(http://www.ladyada.net/make/usbtinyisp/)toprogramourATmega.

Inallthefollowingexamples,wewillbeusinganUbuntuLinuxcomputer.ThecommandsshouldbeidenticalifyourunavrdudeonWindows.

avrdudecusbtinypm32Ulfuse:w:0b11101111:mavrdudecusbtinypm32Uhfuse:w:0b11001001:m

Warning:Ifyougetthiswrong,youcouldeasilybrickyourATmega!Ifyouforexampledisabletheresetbutton,youwon'tbeabletoreprogramit.Ifyouselectthewrongclocksource,itmightnotbootatall.

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Step46:ProgramtheAVRwithtestcode

TimetotestifyourbrandnewLEDcubeactuallyworks!

WehavepreparedasimpletestprogramtocheckifalltheLEDsworkandif

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theyarewiredcorrectly.

Youcandownloadthefirmwaretest.hexinthisstep,ordownloadthesourcecodeandcompileityourself.

Asinthepreviousstep,weuseavrdudeforprogramming:avrdudecusbtinypm32B1Uflash:w:test.hex

cusbtinyspecifiesthatweareusingtheUSBtinyISPfromLadyadapm32specifiesthatthedeviceisanATmega32B1tellsavrdudetoworkatahigherthandefaultspeed.Uflash:w:test.hexspecifiesthatweareworkingonflashmemory,inwritemode,withthefiletest.hex.

test.hex (/files/orig/FQX/H9M5/GICYB93T/FQXH9M5GICYB93T.tmp)14KB

Step47:Testthecube

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Thetestcodeyouprogrammedinthepreviousstepwillletyouconfirmthateverythingiswiredupcorrectly.

Itwillstartbydrawingaplanealongoneaxis,thenmovingitalongall8positionsofthataxis.(byplanewemeanaflatsurface,notanairplane:p)Thetestcodewilltraverseaplanethroughallthreeaxis.

Afterthat,itwilllighttheLEDsinalayeronebyone,startingatthebottomlayer.

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Ifanyofthelayersorcolumnsseemtolightupinthewrongorder,youhaveprobablysolderedthewrongwiretothewronglayerorcolumn.Wehadonemistakeinourcube)

Ifyoufindanythingthatisoutoforder,justdesolderthewiresandsolderthembackintherightorder.Youcouldofcoursemakeaworkaroundinsoftware,butthatwouldeatCPUcycleseverytimetheinterruptroutineruns.

Youcancompareyourcubetothetestvideobelow:

Step48:ProgramtheAVRwithrealcode

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Soeverythingcheckedoutinthetest.It'stimetoprogramtheATmegawiththerealfirmware!

Forthemostpart,theprocessisthesameasinthepreviousprogrammingstep.ButinadditionyouhavetoprogramtheEEPROMmemory.TheLEDcubehasabasicbitmapfontstoredinEEPROM,alongwithsomeotherdata.

Firmwareisprogrammedusingthesameprocedureaswiththetestcode.

Firmware:avrdudecusbtinypm32B1Uflash:w:main.hex

EEPROM:avrdudecusbtinypm32B1Ueeprom:w:main.eep

Ueeprom:w:main.eepspecifiesthatweareaccessingEEPROMmemory,inwritemode.AvrgccputsalltheEEPROMdatainmain.eep.

Ifyoudon'twanttoplayaroundwiththecode,yourLEDcubeisfinishedatthispoint.Butwerecommendthatyouspendsometimeonthesoftwaresideofthingsaswell.That'satleastasmuchfunasthehardware!

Ifyoudownloadthebinaryfiles,youhavetochangethefilenamesinthecommandstothenameofthefilesyoudownloaded.Ifyoucompilefromsource

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thenameismain.hexandmain.eep.

ledcube_8x8x8_eeprom.eep (/files/orig/F53/QFDQ/GICYB944/F53QFDQGICYB944.tmp)1KB

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Step49:Software:Introduction

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ThesoftwareiswritteninCandcompiledwiththeopensourcecompileravrgcc.ThisisthemainreasonweuseAtmelAVRmicrocontrollers.ThePICseriesfromMicrochipisalsoanicechoice,butmostoftheCcompilerscostmoney,andthefreeversionshavelimitationsoncodesize.

TheAVRrouteismuchmorehasslefree.Justaptgetinstalltheavrgcccompiler,andyou'reinbusiness.

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ThesoftwareontheAVRconsistsoftwomaincomponents,thecubeinterruptroutineandeffectcodeformakingfancyanimations.

Whenwefinallyfinishedsoldering,wethoughtthiswouldbetheeasypart.Butitturnsoutthatmakinganimationsinmonochromeatlowresolutionsisharderthanitsounds.

Ifthedisplayhadahigherresolutionandmorecolors,wecouldhaveusedsin()andcos()functionsandallthattomakefancyeyecandy.Withtwocolors(onandoff)andlowresolution,wehavetousealotofif()andfor()tomakeanythingmeaningful.

Inthenextfewsteps,wewilltakeyouonatourofsomeoftheanimationswemadeandhowtheywork.Ourgoalistogiveyouanunderstandingofhowyoucanmakeanimations,andinspireyoutocreateyourown!Ifyoudo,pleasepostavideointhecomments!

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Step50:Software:Howitworks

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Asmentionedinthepreviousstep,thesoftwareconsistsoftwopars.Theinterruptroutineandtheeffectcode.

Communicationbetweenthesetwohappensviaavoxelarray.ThisarrayhasabitforeveryLEDintheLEDcube.Wewillrefertothisasthecubearrayorcubebufferfromnowon.

Thecubearrayismadeof8x8bytes.Sinceeachbyteis8bits,thisgivesusabufferthatis8voxelswide,8woxelshighand8voxelsdeep(1bytedeep).

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volatileunsignedcharcube[8][8]

TheinterruptroutinereadsfromthecubearrayatgivenintervalsanddisplaystheinformationontheLEDcube.

TheeffectfunctionswritesthedesiredLEDstatusestothisarray.

Wedidnotuseanysynchronizationordoublebuffering,sincethereisonlyoneproducer(eithertheeffectscurrentlyrunning,orinputfromRS232)andoneconsumer(theinterruptcodethatupdatesthecube).Thismeansthatsomevoxelscouldbefromthenextorprevious"frame",butthisisnotaproblem,sincetheframerateissohigh.

Whenworkingwithmicrocontrollers,codesizeiscritical.Tosavecodesizeandprogrammingwork,andtomakethecodeeasiertoread,wehavetriedtowritereusablecodeasoftenaspossible.

TheLEDcubecodehasabaseoflowleveldrawingfunctionsthatareusedbythehigherleveleffectfunctions.Thedrawfunctionscanbefoundindraw.c.Drawfunctionsincludeeverythingfromsettingorclearingasinglevoxeltodrawinglinesandwireframeboxes.

Step51:Software:IOinitialization

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ThefirstthingtheATmegadoesafterboot,istocalltheioinit()function.

ThisfunctionsetsupIOports,timers,interruptsandserialcommunications.AllIOportsontheATmegaarebidirectional.Theycanbeusedeitherasaninputoranoutput.Weconfigureeverythingasoutputs,excepttheIOpinswherethetwobuttonsareconnected.TheRXpinfortheseriallineautomatically

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becomesaninputwhenUSARTRXisenabled.

1)DDRxsetsthedatadirectionoftheIOpins.(DataDirectionRegister).1meansoutput,0meansinput.

2)Afterdirectionalityhasbeenconfigured,wesetalloutputsto0toavidanyblinkingLEDsetcbeforetheinterrupthasstarted.

3)Forpinsconfiguredasinputs,thePORTxbitchangesitsfunction.Settinga1inthePORTxregisterbitenablesaninternalpullupresistor.TheportispulleduptoVCC.ThebuttonsareconnectedbetweentheportandGND.WhenabuttonispressedthecorrespondingPINxbitreadsalogic0.

4)Timer2isconfiguredandatimerinterruptenabled.Thisiscoveredinaseparatestep.

5)Serialcommunicationsisconfiguredandenabled.Thisisalsocoveredinaseparatestep.

Step52:Software:Modeselectionandrandomseed

Whenwefirststartedwritingeffectsanddebuggingthem,wenoticedthatthefunctionsusingrandomnumbersdisplayedtheexactsameanimationseverytime.Itwasrandomalright,butthesamerandomsequenceeverytime.TurnsouttherandomnumbergeneratorintheATmeganeedstobeseededwitharandomnumbertocreatetruerandomnumbers.

Wewroteasmallfunctioncalledbootwait().Thisfunctionservestwopurposes.

1)Createarandomseed.2)Listenforbuttonpressestoselectmodeofoperation.

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Itdoesthefollowing:

1)Setcounterxto0.

2)Startaninfiniteloop,while(1).

3)Incrementcounterxbyone.

4)Usexasarandomseed.

5)Delayforawhileandsetredstatusledon.

6)Checkforbuttonpresses.Ifthemainbuttonispressed,thefunctionreturns1.IfthePGMbuttonispresseditreturnes2.Thereturnstatementsexitsthefunctionthusendingtheinfiniteloop.

7)Delayagainandsetgreenledon.

8)Checkforbuttonpressesagain.

9)Loopforeveruntilabuttonispressed.

Thelooploopsveryfast,sotheprobabilitythatyouwillstopitatthesamevalueofxtwotimesinarowisveryremote.Thisisaverysimplebuteffectivewaytogetagoodrandomseed.

Bootwait()iscalledfromthemain()functionanditsreturnvalueassignedtothevariablei.

Ifi==1,themainloopstartsaloopthatdisplayseffectsgeneratedbytheATmega.Ifi==2,itentersintoRS232modeandwaitsfordatafromacomputer.

Step53:Software:Interruptroutine

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TheheartoftheLEDcubecodeistheinterruptroutine.

Everytimethisinterruptruns,thecubeisclear