HowtoMakeaHeadStickPointerforiPhone

ResearchersonProject:BenChater,Geoffrey

Edwards,ErikJakobsandJerryRussell

Background

InvoTekwascontactedthroughtheRERCbyBenChaterwhowantedtobeabletoaccesshisiPhoneusinghisheadstick.Bentriedusinga

commercialstylusdevelopedfortheiPhonebutitdidnotworkreliablyforhim.WestartedtestingusingoniPodTouch2Gwhichhasthesame

capacitivetouchscreenasaniPhone.Throughoutthedesignprocess,weworkedcloselywithBenviaemail.Benprovidedguidanceonhowour

intermediatedesignsworkedforhim.Healsoprovideddesignideastoimproveusability.

Afteracoupleoftestswhichincludedsandingtheendoftheheadstickandcoveringawoodenballwithconductivematerial,Geoffrecommendedthatwetryusingconductivefoamthatwehadinour

electronicsworkshop.Thefoamworkedwell.Wedeterminedthatthesurfaceareaofthefoamtouchingthescreenwasimportantforreliableoperation.Weexperimentallydeterminedthat3/8‐inchdiameterworks,butisnotcompletelyreliable,while½‐inchdiameterworksreliably.

Whatisneededforcreatingaconductivetipforaheadstick

1. Conductivefoam‐availablefromDigikey

2. ¼inchcoppertubing–availablefromanyautosupplystore3. PlastiDipbyPerfomix–availablefromLowe’s4. ¼starwasher–availablefromanyhardwarestore.

5. Solderironandsolder6. HeatGunandheatshrink

Measurementsmaybedifferentforyourspecificheadstickassembly.Ben’s,whichweusedforthemeasurements,isonethathehasbeenusingforalongtimeandhaspartsfromanumberof

differentplaces.TheassemblyispicturedbelowattheendofthearticlewhilebeingtestedbyErik.

Directionstoassemble

1. Cuta3inchlongsectionof¼inchcoppertubing.Thisisgoingtobebackboneofthetipwhichwillinsertintotheheadstickandcontaintheconductivefoamononeend.

2. Solder4linesabout13/8incheslongalongtheendthatwillnotbecoveredinfoam.Beforesoldering,makesuretocleanthecopperbyrubbingitwithfinesandpaperandwipingitdown

withrubbingalcohol.Thisholdsthetipsteadierwhenitisinsertedintotheheadstick.

3. Solder¼inchstarwasher(flattened)about3/4inchfromtheendthatwillcontainthefoam.Be

suretocleanthecopperwhereyousolderthesameasabove.Thiswillbeusedasanedgeto

helptheusermoveobjects.Aviceliketheoneinthepicturebelowisusefulsothatfingersarenotburnedwhilesolderingtothecopper.

4. Cuta1‐1/4inchsquareof1/8inchconductivefoam.Thethicknessofthefoamisimportantsinceitisthedecidingfactorinthesizeofthetipofthepointer.Thesizeofthesquareisalsoimportantbecausetheremustbeenoughtomakethearmslongenough(describedbelow)to

holdthefoaminplace.

Ifyouhave¼inchconductivefoam:a. Cutthe1‐1/4inchsquareasdescribedabove.b. Cutthethicknessofthefoaminhalfsothatitisthesamethicknessasitwouldbeifyou

had1/8inchfoam.

5. CutthefoamintotheformofanXwhereeacharmisaboutthewidthofthetubing(seepicturebelow).Bycuttingthefoamintothisshape,therearenotbulgesonthesidesofthepointer.

6. Applyadotofhotglueontheendofthetubingthatthefoamwillbeplacedandletdry.This

roundsthetipofthetubingsothatthecopperwillnotcutthroughthefoamandscratchthescreenortrackpaditisbeingusedon.

7. Oncetheglueisdry,applyanothersmallamountofglueandputthefoamonthetip.Thiswillhelpthefoamstayinplaceonthepointer.

8. Bendall4armsofthefoamdownandholdthemdownwithapieceof½inchdiameterheat

shrink.Theheatshrinkshouldbeabout1inchlongsothatonlyasmallamountofthefoamisexposedontheendanditextendspastthewasher.Theheatshrinkhastwopurposes:

a. Asitisheateditreducesthediameterofthefoamtip.

b. Itextendspastthewasherwhichhelpsholdthefoaminplace(inadditiontothegluedot).

9. Heattheheatshrinkstartingtowardtheexposedfoamandmovingtowardthewasherwhilerotatingthetubing.Thereasontoheattheexposedfoamsidefirstisthatwhileitshrinkswedon’twantittoexposemorefoam(whichhappensifitisheatedfromthewashersidefirst).By

heatingitthisway,thefoamissqueezedtightandthentheheatshrinkpullsthefoamtowardthewasher.

10. ThenextstepistocovertheheatshrinktubingwithPlastiDip.ThePlastiDipisasprayonrubberwhichallowstheusertohavemoregripwhenusingthewasheredge.Oncetheheatshrinkisthecorrectdiameter:

a. Covertheexposedfoamwithmaskingtape.IfthefoamiscoveredwithPlastiDip,it

willnolongerwork.b. Covertheendofthepointerwhichwillbeinsertedintotheheadstickwithmasking

tape.Wethinkthatthismakesthepointerlookbetterbutthisisoptional.

c. SpraythesectionofthepointerwhichisnotcoveredbytapewithPlastiDip.

11. LetthePlastiDipdryandthenremovethetape.Belowarepicturesofthefinishedproductin

theheadstick.AlsotherearepicturesofitbeingusedonaniPodTouch2Gandyoucanseethattheuserisswitchingpagesonthehomescreentoseemoreicons.