EEL4924Design2
FinalProjectReport
TeamLimbitless(ProstheticArm)
AlexBlacher
JoseSuarez
Introduction
Ourdesignprojectwasthedesign,fabrication,andimplementationofafully3Dprinted
prostheticarmwiththetargetaudiencebeingchildren.Thisprostheticarmincludestheuseof
aninhousebuiltanddesignedmusclesensor.Thisisbecauseourprostheticarmworksonthe
principles of electromyography. Electromyography, EMG in short, is an electro-diagnostic
medicine technique for evaluating and recording the electrical activity produced bymuscles.
EMGisperformedusinganinstrumentcalledanelectromyograph,toproducearecordcalledan
electromyogram.InourDesign2projecthowever,wehavesuccessfullydesignedandcreated
ourownprintedcircuitboardsforthismusclesensor.
Ourprostheticarmhasaremovable,rechargeablelithium-ionbatterysimilartothosein
moderncellphones.Thisbatteryisreplaceableandcanbeeasilytakenoutandreplacedwitha
fullychargedoneforcontinueduse.Inordertodothis,webuiltanddesignedarechargecircuit
tofabricateaseparatechargerforthebatteries.Thehandhasthesameflexibilityasthereal
thing.Thiswasdonewithcleverlydesignedand3Dprintedjointsusingspecialflexiblefilament
calledNinjaFlex®.Thisfilamentallowsthefingerstobeflexibleenoughtograspordinaryobjects
likewaterbottles,bikehandle,cellphones,etc.
Thesoftwareintelligenceissuchthattheproductseemsnaturalandunobtrusivetouse.
Thegoalwithourdesignprojectwastomaketheproductasseamlesslyintegratedintotheuser’s
lifeaspossible,sortoflikeaplug-and-playinputdeviceonacomputer.Oursoftwarewillallow
foraccurateandinstantaneousmusclereadingforlowlatencyandfastresponsetime.Thiswas
achieved by actively filtering the signals coming from themuscle and filtering out the noise
accompanyingthatsignal.This,mixedwithahighspeed,hightorqueservo,makesourprosthetic
armtheclosestthingtoarealarm.
ConceptandTechnologyUtilized
WechosetoimplementtheprostheticarmwithElectromyography,orEMG,technology
becauseitisthemoreintuitivemethodofmovingabodypartlikeanarm.Wearealsotargeting
ayoungaudiencemeaningthatforthem,triggeringamusclewouldbeeasierthansaythinking
aboutmovinganarm.ThisleadstoanothertechnologycalledElectroencephalography,orEEG
forshort.EEGwasequallyapossiblemethodofcontrolforourarmbutwefoundittobeless
effectiveintermsofourchosenaudience.
Anotherwayweapproachedthisdesignisbymakingthebatteryexternallyrechargeable.
Sinceouraudienceisayoungone,wewantedourproducttobringcountlesshoursofuseand
didn’twanttolimitthisusebybatterylife.Inmakingthebatteriesexternallyrechargeable,we
can swap batteries with ease and continue using the product easily.We initially speculated
makingthebatteryinternal,andthenhaveitchargethroughamicro-USBcablebutwefigured
thiswouldbeanintrusiveactionthatwouldinterrupttheeaseofuseofthearm.
All-in-allwefirmlybelievethatchoosingEMGoverEEGtechnology,andmanufacturing
ourownsensorforthis,gaveusgreatercontrolovertheexperienceoftheprosthetic.Goingwith
an externally rechargeable battery also further enhanced the experience by having a more
continuoususeoftheproductwithoutsacrificingtheexperience.
ProductDesign
Anyprostheticdevice is generallydoneby sensinga signal thenperforminganaction
basedon this.Theprostheticarm isnodifferent.Thearmwas3-Dprintedand ismadeof4
fundamentalcircuitblocks.Theyarethebatterycircuit,musclesensors,processor,andservos.
Themusclesignalcomesfromthebicepsandtriceps,andwillbeamplifiedandfilteredthrough
themusclesensorPCBcircuit.Thesignalwillthenbereadbythemicroprocessorandcontrola
servo throughPulseWidthModulation (PWM).Asimpleblockdiagramof the4 fundamental
circuitblocksisshownbelow.
PowerSupply/Charging SensingProcessing ActuatingPowerSupply Ourprojectfeaturesauniquepowersupplyboardthatsuppliespowertoourentire
system.Usinga3.8V,3000mAhLithium-ionbatterycellwecanstepupthevoltageto5Vforuse
withthemusclesensorandtheservomotors.Toup-convertthisvoltageweusedtheboosting
capabilityoftheLT1073MicropowerDC/DCConverter.Inorderforourmusclesensorstowork
properly,wealsoneedtosupplya-5Vrailfortheoperationalamplifiers.Toinvertthisvoltage,
weutilize the ICL7660Awhich isaCMOSVoltageConverter.Figure1below is the schematic
diagramofthedesignthatwasimplemented.Ourpowersupplyboardhastogoseparatefrom
ourmusclesensorboardsbecauseofcertainsafetyhazardsthatcanoccurifbothareonthethe
PCB.Assuchwehavestrictlydesignedthispowerboardseparatelyfromtherestofthecircuits.
TheDC/DCconverteroperatesbystoringenergyasmagneticflux,inaninductorcoreand
thenswitchingthisenergyintotheload.Sinceit isflux,notcharge,that isstored,theoutput
voltage can be higher, lower, or opposite in polarity to the input voltage by choosing an
appropriate switching technology. To operate as an efficient energy transfer element, the
inductor must fulfill three requirements. First, the inductance must be low enough for the
inductortostoreadequateenergyundertheworst-caseconditionofminimuminputvoltageand
switchONtime.Theinductancemustalsobehighenoughsothatmaximumcurrentratingsof
3.8VLi-ionBattery(BoostConverterto5Vandinvertedfor-5V)
MuscleSensor(Amplifies/Filters) Microprocessor Servo
theLT1073andinductorarenotexceededattheotherworst-caseconditionofmaximuminput
voltageandONtime.Additionally,theinductorcoremustbeabletostoretherequiredflux,i.e.,
it must not saturate. Lastly, the inductor must have sufficiently low DC resistance so that
excessivepowerisnotlostasheatinthewindings.
Figure1:PowerSupplyBoardSchematic
Figure 2: PowerSupplyPCB
Figure3:DC/DCUp-converter
Immediately after switch turn-off, the SW1 voltage pin starts to rise because current
cannotinstantaneouslystopflowinginL1.WhenthevoltagereachesVOUT+VD,theinductor
current flows throughD1 intoC1, increasingVOUT.Thisaction is repeatedasneededby the
LT1073tokeepVFBattheinternalreferencevoltageof212mV.
Figure 4: Voltage Converter
TheICL7660Acircuitperformsthecompletesupplyvoltageconversionfrompositiveto
negativeforanyinputvoltagebetween+1.5Vand+10V,andprovidesthecomplementaryoutput
voltageof-1.5Vto-10V.Thedeviceoperatesbychargingapumpcapacitortotheinputsupply
voltage and then applying the capacitor across theoutput supply, transferring thenecessary
chargetoanopen-circuitstoragecapacitor.TheICL7660deliversanopen-circuitoutputequalto
thenegativeoftheinputvoltagetowithin0.1%.Capableofproducing20mA.
BatteryCharger
Figure5:BatteryChargerSchematic
Figure6:BatteryChargerPCB
Ourprojectfeaturesanexternalbatteryrechargecircuitthatwillbeusedtochargethe
rechargeablebatteries that theprostheticarmwilluse.Wedecideduponabattery recharge
circuitthatwillchargeastandardflat-packbatteryliketheonesyouwillfindinacellphone.This
allowsforourdesigntobemorespaceefficientaswellasbecomemoreefficient intermsof
usabilityanddesign.Wedidmuchresearchinbatterychargingcircuitsanddeterminedthatfor
thecurrentmodelandspecificationsofthebatterythatwehadinmindwewouldwanttogo
witha500mAhchargingrate.
While amaximumcharging currentof 1c is allowed for Li-Ionbatteries, charging at a
slightlyhigherratewaspossible(withacorrespondinglyshorterchargetime).Theimplemented
designinFigure5aboveusesanLM317withtwo2N2222NPNGeneral-PurposeAmplifiers.Q2
isusedtocontroltheflowofcurrentintotheadjustpinoftheLM317.U1andresistorsR2,R3,
andR4areusedtocreateavoltageregulator(whichsetstheterminationvoltage).Whatoccurs
isthat,U1willtrytomaintainaconstantvoltageacrossR3andthevoltagedividercreatedbyR3-
R4areusedtosetthecurrenttotheadjustpintogetthedesiredoutputvoltagevalue.
As the voltage on R6 approaches ~ 0.7V, Q2 will turn on and IQ2 will increase, thus
decreasingthecurrentintheadjustpin.Thistrickstheregulatorintothinkingthattheoutput
voltage is toohigh, so theoutput current is reduced inorder to compensate.As for the LED
portionofthecircuittotheleft.R5isinparallelandisforcedtohavethesame0.7Vdropacross
itasthediode.IfRsdoesnotreceivethecurrentnecessaryfora0.7Vdrop,then0.7Vcannotbe
achievedandthediodenolongerconducts,soQ1isnotproperlybiasedandtheLEDwillturnoff
whendonecharging.
Microprocessor
Figure7:MicroprocessorBoardSchematic
Figure8:MicroprocessorBoardPCB
The ATtiny85 was decided on for our purpose as it had 4 working ADC channels on
differentpinsthanthe2outputcomparepinsthatwereneededtorunthePWMfortheservos.
This would allow us to sense the differentmuscles andmakes themovements of the hand
withoutwastingtoomuchspacewithalargerprocessor.
MuscleSensor
Figure9:MuscleSensorSchematic
Figure10:MuscleSensorPCB
One of the focal points of our project was the muscle sensor, which used
electromyographytodetectthemovementofthetricepandbicepmusclesandthenmovethe
accordingpartofthehand.Whenusingelectromyographytodetectsurfacemuscles,thereare
a few usual blocks to include. These are the pre-amplification, filtering, and then the post-
amplification.Thiswasthesameideaforthedesignofourmusclesensor.Theideaofthedesign
isthatthepre-ampworkstoamplifythesignalfromthearm,whichisintherangeofmicrovolts,
withouthavingtoamplifytoomuchnoise.Thefilteringworkstofilterthehighfrequencyand
lowfrequencynoisefromthesignalwhiletherectificationmakesitsothatapulseonlyregisters
a positive peak and gets rid of the negative one. The amplifier at the end is purely for gain
purposes andworks to take the clean signal and amplify it large enough to be used by the
microprocessor.
Figure11:Closeupofinstrumentationampcircuit
The pre-amplifier was done through the use of an instrumentation amplifier, the
INA114P.This instrumentationampwasaprettysimpleonetoimplement.Theinputswerea
differentialsignalthatwouldcomefromeitherthebiceportricep.Thesignalcominginwasan
ACsignalcenteredon0Vwithamicrovoltamplitude.Thereisaresistor,Rg,whichisusedforthe
gain,which isdefinedinthedatasheet.Thegainforourapplicationaschosentobe200asa
largergainthanthatwouldamplifynoisetoomuchandagainsmallerthanthatwouldcausethe
signal to get buried in the filtering stages. For these purposes, the signal-to-noise ratio was
importantbecauseitneededtobehighenoughtobeabletoaccuratelyfilterthenoise.
Figure12:CloseupofFiltering/Rectifyingstagesofthemusclesensor
Thefirstpartofthefilteringstageisthehighpassamplifierwhichworkstofilterthelow
frequencynoisefromthecircuit.Thefrequencyofthemusclesisaround50-60Hzsothecutoff
frequenciesweredesignedaroundthis.Becauseof this, thecutoff for thehighpass filterwas
designedtobearound102Hz.Therectifierwasthenextstageinthefilteringpart.Thiswasdone
withasimplehalfwaverectifierwhichwouldget ridof thenegativehalvesof thesinewave
comingfromthearm.Theideaofthisisthattheprocessoronlyseesthepositivepeaksanyways
so getting rid of the negative halves creates a larger average peak, which would help with
processordetection.Thelastpartofthefilteringprocesswasthelowpassfilter.Thefunctionof
thisstageistogetridofhighfrequencynoise.Thecutoffforthisstageshouldusuallybechosen
low,around0-10Hzandforourpracticewaschosentobearound2Hz.Theresultofthesestages
isthatwhenthebiceportricepisflexed,asmallpulsewilloccur(around+20mV),whichwillbe
cleanandhavenonegativehalf.
Figure13:Closeupoffinalamplificationstage
Thisiswherethelastamplificationstagecomesintothedesign.Forourpractice,itmade
sense to use a regular non-inverting amplifier thatwould have a 50kΩpotentiometer in the
feedbackloopwhichwouldallowustoadjustthegainfrom0-50tofitdifferentneedsgiventhe
sizeoftheperson’smuscle.Thisishowthemusclesensorworksinourpractice.Whenflexed,
themusclesensorcreatesapositivepeakwhichcanthenbedetectedbythemicroprocessoras
amovementbythearm.
Whenactuallycreatingthedesign,afewproblemscameupwhichcreatedamuchlarger
delay thanwhatwas firstexpected.Themainproblemthatwehadto figureoutwas theDC
offsets thatpermeated throughourentiredesign.The first revisionofourPCBhadboth the
power,ground,andsignal traceson thebottomof theboard,whichwereonly separatedby
around7milfromeachotherwhichwethoughtmighthavebeencreatingtheproblemsthatwe
had.Wedecidedtohaveasecondrevisionoftheboardbutthistimerouteallofthepowertraces
ontopoftheboardandthesignaltracesonthebottomoftheboard.Howeverthisdidnotfix
the DC issues thatwewere seeing. These DC issueswere even present on the input to the
instrumentationampfromtheelectrodeswhichwouldcausetheinstrumentationampnotto
workwhenourmusclewasflexed.Wefinallyrealizedthatthisissuewaspresentduetotheway
PCBsaremadewiththelaserprinteroncampus.Theboardswouldberunthroughthemachine
twice, or “double-burned”, which would inject carbon between the traces and create small
resistanceswherethereshouldn’tbeany.Throughheavilyscrapingthetraces,wenoticedthe
DCoffsetsstartedtogoawayfromtheinputtotheinstrumentationamp.
OurnextlargestproblemcameintheformofaDCoffsetthatwouldbepresentonthe
outputofthefinalamplifier.Thiscausedamajorproblemforourapplication,astheprocessor
wouldn’tbeabletodistinguishbetweentheACsignalcausedbythemuscleflexandtheDCoffset
thatwasinherentlypresentontheoutputnode.ThefirstthoughtforthiswastoACcouplethe
outputofthemusclesensortotheprocessor,intheformofputtinga1uFcapacitorfromthe
outputnode to the inputof theprocessor. The resultof thiswas thatwhen the systemwas
powered,theDCvoltageontheoutputofthemusclesensorwouldstarttodecreaseuntilitgot
toaround60-70mVbutwhentheADCwouldtrytoreadthevoltagefromthesensor,theDC
voltagewouldgoalothigher(around500mV–2V)andmaketheprocessorincapableofdoing
accurate readings. For a while, we couldn’t figure out why the DC was getting through the
capacitor,asitshouldbeblocked.Whatweendedupfiguringoutwasthattheinputimpedance
onthemicroprocessorwasaffectingit.Theinputimpedance,totheADCchannelswouldalter
between1MΩand10MΩastheADCwouldbereadingandswitchingbetweenchannels.This
wouldcausethecapacitortoseedifferentimpedancesasthesensingwentonwhichcausedthe
charginganddischargingthatwewereseeing.Tofixthis,weendedupputtinga1MΩresistor
betweentheoutputnodetogroundsothatthecapacitorcontinuouslysawthatresistanceand
wouldkeepalowDCvalue.ThiscausedtheDCvoltageontheoutputnodetobebetween3-
10mVwhichmadetheprocessoraccuratelyseeeverytimethemusclewasflexedwhiletheAC
voltagewasamplifiedtoaround200-400mV.
EmbeddedCode
#define F_CPU 1000000 #define Resolution .0098039 #include <avr/io.h> #include <util/delay.h> int VoltageInput; void ADC_Init() ADMUX = 0x86; //1.1V internal voltage w/o cap. ADC3/4 differential. ADCSRA = 0xE7; //Enable ADC, start conversion, auto trigger, prescalar 128 ADCSRB = 0x80; //bipolar differential mode, free running mode (constantly updating ADC) DDRB = 0x03; //pin 2 (ADC3 input); pin 3 (ADC2 input); pin 6 (PB1) output; pin 5 (PB0) output DIDR0 = 0x3C; //disable digital input buffer // initialize PWM void pwm_init() // initialize timer0 in (non-inverting) PWM mode TCCR0A |= (1<<WGM01)|(1<<WGM00)|(1<<COM0A1)|(1<<COM0B1); //Clock Select, select the clock source to be used by Timer/Counter TCCR0B |= (1<<CS01)|(1<<CS00); // pre-scaler (clk/64) to Divide high timer clk freq. to feed to timer. // make sure to make PB0 as output pin //DDRB |= (1<<DDB0)|(1<<DDB1); void read_ADC() VoltageInput = ADC; // read ADC value if( (VoltageInput & 0x200) == 0x200) //if MSB is 1 --> means number is negative VoltageInput = signExtension(VoltageInput); //sign extend the integer to convert to negative number asm("nop"); int signExtension(int value) value += 0xFFFFFC00; //take integer and add 1s to bits 31 through 10. return value; int main(void) ADC_Init(); //initialize pwm_init(); VoltageInput = 0;
asm("nop"); read_ADC(); if((VoltageInput > -249) && (VoltageInput < 249)) //our first ADC value is 0 OCR0A = 7; //so initially set both servos to min OCR0B = 7; asm("nop"); _delay_ms(1000); while(1) //infinite loop read_ADC(); //read ADC if((VoltageInput > -349) && (VoltageInput < 249)) //if no bicep or tricep is triggered OCR0A = 7; //set servo 1 to min OCR0B = 7; //set servo 2 to min asm("nop"); if ( VoltageInput > 250) //if bicep is triggered asm("nop"); _delay_ms(1000); //delay just in case bicep peak is long enough to trigger twice while(1) //loop to wait until another bicep read_ADC(); //keep reading ADC, checking for another movement if(VoltageInput < -300) // when tricep is triggered asm("nop"); OCR0A = 36; //move servo 1 to max OCR0B = 36; //move servo 2 to max _delay_ms(1000); while(1) read_ADC(); if(VoltageInput < -300) //if tricep is triggered again asm("nop"); OCR0A = 7; //move servo 1 to min OCR0B = 7; //move servo 2 to min _delay_ms(1000); break; //break out of waiting loop asm("nop");
break; //break out of waiting loop if(VoltageInput > 250) // when bicep is triggered asm("nop"); OCR0A = 35; //move servo 1 to min _delay_ms(1000); while(1) read_ADC(); if(VoltageInput > 250) asm("nop"); OCR0A = 7; _delay_ms(1000); break; //break out of waiting loop asm("nop"); break; read_ADC(); if (VoltageInput < -300) //if a tricep is triggered asm("nop"); _delay_ms(1000); //again delay to prevent tricep movement from triggering twice while(1) //loop until tricep or bicep is triggered again read_ADC(); //keep reading ADC to check for another movement if(VoltageInput < -300) // when tricep is triggered asm("nop"); OCR0B = 36; //move servo 2 to max _delay_ms(1000); while(1) read_ADC(); if(VoltageInput < -300) asm("nop"); OCR0B = 7; //move servo 2 to min _delay_ms(1000); break; //break out of waiting loop asm("nop");
break; //break out of waiting loop if(VoltageInput > 250) // when bicep is triggered asm("nop"); OCR0A = 36; //move servo 1 to max OCR0B = 36; //move servo 2 to max _delay_ms(1000); while(1) read_ADC(); if(VoltageInput > 250) asm("nop"); OCR0A = 7; //move servo 1 to min OCR0B = 7; //move servo 2 to min _delay_ms(1000); break; //break out of waiting loop asm("nop"); break; asm("nop");
ThecodestartswithinitializingthePWMoutputsandtheADCinputsfortheprocessor.
TheADCneededtobe inbipolardifferentialmodesincethisallowsfortheADCtoreadboth
positiveandnegativevalues.Thedifferentialmodeworksbytakingthedifferencebetweentwo
ADCregistersthatareattachedtoourmusclesensorsandcomingupwithavaluebasedonthat.
Theregisteris10bitsbutthe9thbitofthisisthesignbit.Therestofthe9bitsareusedtoread
the actual value. Our value is then stored in an integer that was call VoltageInput. Because
integersinCarestoredas32bitnumbersandweareonlyreadinga10bitvalue,thesignbit
needstobecheckedfirstandtheintegerneedstobesignextendedifthisnumberisanegative.
ThisisalldoneintheRead_ADCfunctionofourcode.Thisfunctionchecksthesignbitandmakes
theintegerclosetotheactualoneweareusingfordetection.
Thefirststepofourcodeistosaythatwhenneitherthebiceportricepisbeingdetected,
theservosshouldbeattheirminimumvalues.Thisprotectstheservosfromstallingwhichcreates
ahighcurrentdrawandcanmesswiththepowerboard.Ourarmworksbyfirstdetectingatricep
orbicepmotion.Forexample,whenabicepisdetected,thisputsusinanendlessloopwaiting
foreitheranotherbiceporatriceptobedetected.Whenanotherbicepisdetected,oneservo
movesbysettingtheoutputcompareregisterthismoveshalfofthehand.Togetthatpartofthe
handtomoveback,anotherbicepmotionmustbedone.Whenatricepisdetectedinthisendless
loop,thefullhandcloses.Onlyanothertricepmotionwillmovethehandbacktoitsinitialstate.
Whenwestartoutwithatricepmotion,itworksverymuchthesamewayasthefirstalgorithm.
Thecodewaitsforeitheranothertricep(whichwillmovetheotherhalfofthehand)orabicep
(whichwillmovethefullhand).Thehandwillonlygobacktoitsinitialstateonceasecondbicep
ortricepmotionistriggered.
Thetriggeringofthebiceportricepisdonethroughpeakdetectionofthemusclesensor
signals.TheendlessloopsonlycomeaboutwhentheVoltageInputintegerregistersthesepeaks.
Thiscausesalittlebitofaproblembecausethepeaksofthemusclesfordifferentpeoplearen’t
always thesame.This iswhy thepotentiometer is important in the final stageof themuscle
sensor.Thepotentiometerallows foranadjustablegainso that thecodedoesn’tneed tobe
augmented,onlythefinalstagegainwhichisveryeasilydoable.
Therealsoneededtobeabitofadelaybetweendetectingamusclemovementanddoing
anything incode.TheATtiny85runsat1MHzwhichmeanseveryaction isdone in justa few
microseconds. The peak of themuscle sensor is around 100-200ms though which creates a
problem.Ifthereisnodelay,therecouldbeacircumstancewhereonemusclemovementtriggers
afewdifferentmotionsonthemusclewhichcouldcauseproblemswiththeservo.Wetested
multipledelaysbutendedupdecidingononesecondbetweenmovementsbecauseitaccurately
separateddetectingamusclefromthenextmotionwhilenotcausingadecreaseinfunctionality.
3D-PrintedMaterials
Figure14:Closeupof3-Dprintedhand
The3-Dprintedhandisexplainedinthebeginningpartofthisreport.Thearmandhand
itselfareregularABSplasticwhilethejointsbetweenthehandareamaterialcalledNinjaFlex™.
Therubberizedinsertsoneachfingerallowforthehandtohavegripsothatitcanpickupcertain
kindsofmaterials.Thestringsineachfingerarefishingwirewhichruntoboththeservoswhich
areattachedontothearm.Whenacertainmotion istriggered,theservomoves,movingthe
correspondingpartofthehand.TheziptiesthatyouseeinFigure14aretoholdtheservosin
place so the arm canmove without anything jiggling around. A fewmore pictures showing
differentanglesofthearmandtheinside(placementoftheelectronics)canbeseenbelow.
Figure15:Anotherangleofthe3-Dprintedarm
Figure16:Photooftheinsideofthearmtoshowtheplacementofelectronics
Figure17:Solidworksphotoofthehanddesignandassembly
BillofMaterialsPart Value Qty. PartNumber PriceProcessor N/A 1 ATTiny85 1.67ProcessorBoardPCB N/A 1 N/A N/A Inductor 82uH 1 AIRD-01-820k 0.65Resistor 100Ω 1 EVU-F2AF30B00 0.28Capacitor 10uF 3 272-1025 1.5Capacitor 100uF 1 272-1026 0.5Diode N/A 1 1N5818 0.1DC/DCConverter N/A 1 LT1073 3.67VoltageConverter N/A 1 ICL7660A 0.66PowerBoardPCB N/A 1 N/A N/A Resistor 1Ω 1 EVU-F2AF30B19 1.5Resistor 47Ω 1 EVU-F2AF30B16 0.25Resistor 470Ω 3 EVU-F2AF30B10 0.42Resistor 1kΩ 2 EVU-F2AF30B14 0.21Resistor 2.2kΩ 1 S22CACT-ND 0.25Capacitor 0.1uF 6 272-1024 1.3NPNTransistor N/A 2 2N2222 0.1Diode N/A 3 1N4001 0.13LED N/A 1 XPEBRD-L1-0000-00601 0.853-TAdj.Regulator N/A 1 LM317 0.15Battery 3.8V 1 3000mAhBattery 8BatteryChrg.PCB N/A 1 N/A N/A 3D-PrintedHand N/A 1 N/A 203D-PrintedCasing N/A 1 N/A 10JewelryString 1Roll H20-1695BS 5Crimps 10 000-SS-CRM7-100BP 2WoodScrews 1.5" 2 N/A 0.5 Capacitor 1uF 1 478-8949-3-ND 0.19Resistor 150kΩ 5 150KQBK-ND 0.1Resistor 100Ω 1 100H-ND 0.1Resistor 150Ω 1 CF18JT150RCT-ND 0.1Resistor 82kΩ 2 82KQBK-ND 0.1Potentiometer 50kΩ 1 3362P-503LF-ND 1.02INA114P N/A 1 INA114AP-ND 10.41TL084CN N/A 1 296-1784-5-ND 0.633.5mminputJack N/A 1 CP-1409-ND 1.16
Total $84.91
Conclusion
Thearmworksthewayitwasintendedinthepreliminarydesignreport.Therewerea
fewissuesthatweren’texpectedbutneededtobeworkedoutalongtheway.Givenmoretime,
oneofthethingswewould’velikedtoaddontothearmisadigitalpotentiometerintheoutput.
Thiswouldhavemadethefinalstagegaindigitallyadjustablesothatanyusercanusethearm.
Wewould’vehadastartupfunctionwheretheuserwouldflextheirmusclesacertainamountof
timesandthepotentiometerwouldadjustthefinalstagegainsothattheirindividualpeakscould
bedetectedbythemicroprocessor.Thiswould’vemadethearmeasilyadjustabletoanyuser.
Overall,otherthanthe3-Dprinting,theelectronicsinthearmwereallratherinexpensive.
Thereareonlyafewintegratedchipsusedintheentiredesign,nonecostingthatmuch.Thearm
wouldbeabletobeusedinmanydifferentpracticesandapplications,andwithabitmorework
andfinetuning,couldbeacosteffectivesolutionforamputees.
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