CritterSitter:WeightSensingPetDoor

Author: ShelbyRichardson

Advisor:

Dr.MartinKaliski

SeniorProject

ELECTRICALENGINEERINGDEPARTMENT

CaliforniaPolytechnicStateUniversitySanLuisObispo

June2016

2

TableofContents

ListofFigures............................................................................................................................3

ListofTables.............................................................................................................................3Abstract.......................................................................................................................................4

Introduction..............................................................................................................................6Background...............................................................................................................................8

Requirements...........................................................................................................................9

Design.......................................................................................................................................11TestPlans................................................................................................................................13

DevelopmentandConstruction.......................................................................................14IntegrationandTestResults............................................................................................16

Conclusion...............................................................................................................................19

Bibliography...........................................................................................................................20Appendices.............................................................................................................................21SeniorProjectAnalysis................................................................................................................21SpecificationsandRequirements.............................................................................................27PartsListandCost..........................................................................................................................28Schedule–TimeEstimates..........................................................................................................30ICLocationDiagram......................................................................................................................31PCBoardLayout.............................................................................................................................32ProgramListing(forSoftware).................................................................................................33HardwareConfiguration/Layout..............................................................................................34

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ListofFiguresFigure1:SampleHighLevelLookatSystemFunctionality………………………...…………..7Figure2:SchematicfortheWheatstoneBridge……………………………………………………11Figure3:IntegrationoftheWheatstoneBridgetotheAmplifier.A0signifiesthe AnalogPortontheArduinoUno………………………………………………..…..12Figure4:PlotofVoltagevs.WeighttoShowtheLinearRelationshipofVoltageto Weightin5lb.Increments…………………………………………………………….18Figure5:HighLevelBreakdownofSystemComponentRequirements…………………27Figure6:FlowDownDiagramoftheStepsTakentoCompletetheProject…………...28Figure7a:Fall2015GanttChart………………………………………………………………………....30Figure7b:Winter2015GanttChart……………………………………………………………..……..30Figure7c:Spring2016GanttChart……………………………………………………………………..30Figure8:LinearTechnologyLT1679IntegratedCircuitPinOutDiagramfrom Datasheet………………………………………………………………………………..…...31Figure9:SolderlessBreadboardLayout……………………………………………………………..32Figure10:CompleteSchematicfortheCritterSitter:WeightSensingPetDoor……..34

ListofTablesTable1:WeightSensorandControlSystemRequirementsandSpecifications………10Table2:TestingPlanfortheFullProjectIntegration…………………………………………...12Table3:MeasuredResistanceValuesforEachWeightSensorandtheChangesis ResistancewhenForceisApplied………………………………………………….15Table4:MeasuredVoltageValuesusedtodeterminetheRelationshipBetween VoltageandWeight………………………………………………………………………17Table5:LongTermCostAnalysis……………………………………………………………………….23Table6:DecompositionoftheInputsandOutputsandDescriptionof Requirements………………………………………………………………………………27Table7:OverallBreakdownofthePartsUsedandEachPartsTotalCost…………….29

4

AbstractMartinKaliskiisatypicalpetowner.Hecurrentlyhousesbothcatsandadog.In

ordertokeepfromhavingtoconstantlylethispetsoutinthemiddleofthenighthe

hasinstalledapetdoorintohishome.Allwaswellandgooduntilearlyonemorning

MartinwokeuptothesoundofhisPomeranianbarkingviolently.Heran

downstairstoseewhattheproblemwas.Henotonlyfoundhisdogstandingthere

butalsoawildraccoon.Theraccoonhadslippedintothehouseintheearlymorning

andwasrummagingthroughthepets’food.Martinwassuccessfullyabletogetthe

wildanimaltoleavethroughthewayhecameonlytonoticeafewminuteslaterthat

theraccoon’sanimalaccomplicesoonsnuckoutbehindhim.Fromthatpointon

Martinrefusedtoleavethepetdoorunlockedandnolongerusesit.Wildanimals

enteringthroughahome’spetdoorisnotanuncommonthingandleavesasenseof

insecurityforapetowner.Withouthavingsomewayofmonitoringthis,apetowner

issubjecttootheranimalsenteringhis/herhomeandpotentiallydestroyinghis/her

propertyorcausingharmtolovedones.

Thegoalforthisprojectistoproduceanewandinnovativewayatmanagingpet

doors.Thereareafewproductsouttherethatalreadyhavesmartpetdoor

technologybutthisprojectwillprovideaneasytouseandlessinvasivewayof

monitoringwhichanimalscanandcannotenterthehome.Thiswillbe

accomplishedbyimplementingsometypeofweightsensorthatisabletoregister

thedistinctsizeoftheanimaltryingtoenterthehomewithinaprogrammedrange

between10–15lbs.andfromthatallowaccess.Inordertohelpwiththecost,a

preengineeredweightsensorwillbeusedaswellasalreadyautomatedpetdoors.

5

Theultimategoalistotakethisproductandbeabletoaddittoalreadyinstalledpet

doors.

6

IntroductionThegoalforthisproductistodesignalessinvasivepetdoorthatallowsonlya

homeowner’spetstoenterthehouseandlockoutanyotherunwantedcreatures.

Takingaweightsensorandusingittodetecttheweightofthehomeowner’spetand

sendingitsvaluetoacentralsystemthatwillcommunicatebetweentheautomated

doorandsensorwillallowthissystemtobesuccessful.Oncetheanimalhasbeen

detectedandregistered,theprogramwilldecidewhetherornottounlockthedoor

andlettheanimalin.CalPolyproffessorDr.MartinKaliskibroughtthisproblemto

meandhashelpedmefindawaytoimplementthedesignandgetittoworkwith

oneanimal.

Thesensorthatwillbeimplementedisanelectromechanicaltransducer.Inorderto

saveoncost,adigitalbathroomscalewillbeutilizedsinceitcontains4

electromechanicaltransducers[1].Themaingoalistobeabletotakethissensor

alongwithitsbuiltincapabilitiesandhaveitcommunicatewithanArduinoUno

(microcontroller)whichwillbehookeduptothepetdoor[2].AnArduinoUnois

implementedforthemaininterfacesduetoitssizeandaffordability.Manyfactors

willneedtobetakenintoconsiderationsuchasweather,efficiency,andaccuracy.

ThegoalfortheoverallfunctionalityandsystemcanbeseeninFigure1.

7

Figure1:SampleHighLevelLookatSystemFunctionality

8

Background

Beforebeginninganytypeoftesting,researchwasconductedinordertoprovide

thebestpossiblesolutionwiththeamountoftimegiven.Surveysweretakentosee

whatpeopleusetodistinguishbetweenacatandaraccoon.Theanswerswere

pulledandsomeofthecommonresultsweresize,gait,sounds,whiskerlength,and

nosesize.

Giventhescopeoftheproject,itwasdeterminedthatthebestdistinguishingfactor

tousewasweight.Accordingtoresearch,anadultcatweighsanywherebetween7.8

–14lbs.[3]andaraccooncanweighfrom15-40lbs.[4]Thereisenoughofa

differenceinweightthataweightsensorcanbeimplemented.

Ratherthancreatinganewtypeofpetdoor,thesolutionthatwasdeterminedwas

tocreatesometypeoflockingmechanismthatcouldbeattachedtoanalready

existingpetdoor.Thesensorisplacedontheoutsideofthehousewiththelocking

mechanismlocatedontheinside.Byplacingthelockingmechanismontheinside,

thehomeowner’scatcanleaveasitpleasesbutmustmeettheweightrequirements

inordertocomebackin.Thisweightrequirementhelpstofilterandpreventany

unwelcomedanimalsfromentering.

Sincecatsandraccoonscouldpotentiallyweighthesame,thelockingmechanismis

placedontheinsidetoinsurethatifaraccoonweretogetin,itwouldbeableto

freelyleavewithoutbeingtrappedinthehome.Thegoalistomaketheproduct

workasaccuratelyaspossiblewhilestillcompensatingforpotentialerrors.

9

RequirementsInordertoachievethebestresults,amarketingapproachwastaken.Thisapproach

helpedtoensurethatthebasicsystemrequirementswouldbemetalongwith

producingthemosteffectivesystempossible.Thefollowingrequirementswere

determined:

1. Thesystemshouldbeabletosensetheanimalthatistryingtoenterthe

homeatasafedistance.

2. Thesystemshouldhaveastrongtimertopreventotheranimalsfrom

followingthepetin.

3. Thesystemshouldbeasnoninvasiveaspossiblewithoutthepetowner

havingtoaddanyadditionalthingstothepet.

4. Thesystemshouldhaveastronglockingsystem.

5. Thesystemshouldalsobeabletopreventthingssuchasweatherdamage(to

thesystemitselfandthehome).

6. Thesystemshouldbeeasilyimplementedintoexistingpetdoorsorprovide

acosteffectivesolutionforinstallingtheautomatedtechnologyifthepet

doordoesnotalreadyhaveit.

7. Devicemustbeenergyefficientinordertobebeneficialforthecustomer.

8. Thedimensionsshouldnotexceedthatofthepetdooritselfandmustbe

aestheticallypleasingforthehome.

9. Thesystemshouldbeeasytouseforthepetwithouttheneedofmuch

trainingforthepet.

10. Thesystemshouldbeeasilyprogrammable.

10

Table1:WeightSensorandControlSystemRequirementsandSpecifications

MarketingRequirements

EngineeringSpecifications Justifications

3,8,9 Smallandportable • Floormatwithheight

ofapproximately0.5’’ • Dimensionsof

approximately3’’X4’’

Itmustbeabletofitinsideandoutsideahousewithouttakinguptoomuchspace

5 Weatherproofcasingandinsulation

Sincethisdoorwillcauseaccessbetweentheinsideandoutsideithastohavesometypeofweatherproofingtoprotectfromdamage.Alsosinceitisgoingtohaveelectricalcomponentsitwillhavetoprotectthephysicalsystemfromdamage

1,9 Sensormeasurementswithin+/-5lbs.

Thiswillhelpaccountforwaterweightoranyothersmallphysicalweightchangestheanimalmighthaveovershortperiodsoftime

2,9 Timebetweensensing:rangeof5-10seconds

Havingasetamountoftimeforthedoorwillhelpkeepfromotheranimalstrailinginbehindthepet.Italsoneedstohaveenoughtimesothatitdoesn’tletthedoorlockonthepet

6,8 Userinterfaceshouldattachtothepetdoorandnotbelargerthan3”by5”

Theuserinterfaceshouldbesmallenoughthatitdoesn’tcauseaneyesorebutitshouldbelargeenoughthattheweightandprogrammenucanbeseen

7 Powersuppliedfromthehomepoweroutlets

Reducesneedforabattery

4 SystemshouldbeabletohavealockingmechanismthatisdigitallycontrolledbyanArduinoboardimplementedwithamotor

The entire control system shouldbecontrolledbyasmallcontrollerand not be larger than the actualpetdoor.Thiswillalsohelpmakeitmorecosteffective

11

DesignAfterexposingthewiresonthesensorsfromthedigitalbathroomscale,the

WheatstonebridgewasconstructedtoresembleFigure2.

Figure2:SchematicfortheWheatstoneBridge

ThevoltagechangeproducedistoosmalltobereadbytheArduino.Tosolvethis

theoutputoftheWheatstonebridgeissenttoaLT1679-Dual/QuadLowNoise,

Rail-to-Rail,PrecisionOpAmp[5].Usingthedesiredvoltagecalculationfoundinthe

IntegrationandTestResults,thefollowingresistorvaluesweredetermined:

R15=330kΩ

R14=112Ω

R13=11Ω

R12=320Ω

R11=112Ω

R10=11Ω

R9=10kΩ

12

TheseresistorvalueswereplacedintoFigure3below.Theseresistorswerechosen

inordertoseevoltagechangeswithinthe0.1Vrange.Oncethesevoltagesare

verifiedtheoutputissenttoananalogportontheArduino.UtilizingtheArduino’s

AnalogtoDigitalconverter(ADC),adigitalsignalisproducedandusedtodrivea

servomotor.Thisservomotorisusedtocontrolthelockingmechanism.

Figure3:IntegrationoftheWheatstoneBridgetotheAmplifier.A0signifiesthe

AnalogPortontheArduinoUno

13

TestPlans

Severalstepsaretakentoensurethatthesystemfunctionsproperly.Thefollowing

planinTable2wasdesignedinordertocreateatestingstrategythatwouldprove

thesystemsfunctionality.Inorderforthisprojecttobesuccessful,theWheatstone

bridgecircuitmustbetestedfirst.Thisbridgeiscrucialwhenmeasuringthechange

involtageandcorrelatingittoweight.Thecircuitmustmakethesechangesandthat

thechangesreflectwhatistobeexpected.Next,theoperationalamplifieris

integratedandtheoutputvoltageshouldnowreflectalargervoltagesignaland

showtheappropriatechangesinvoltage.Thisamplifiedsignalissenttothe

Arduino.Wethencanprintthevaluesbeingreadbytheanaloginputtothe

computerscreenandverifythatthevoltagebeingdisplayedinconsistentwithwhat

isbeingsupplied.Converttheanaloginputtoadigitalsignaltodriveaservomotor.

Iftheservomotorrotatesproperlywhendesiredweightisapplied,theprojectis

completed.

Table2:TestingPlanfortheFullProjectIntegration

Component Test Pass/Fail

WheatstoneBridge

Testeachpressuresensorandverifytheresistivechanges.ConstructthecircuitandverifytheoutputchangesacrossE+andE-

Pass

Amplifier

Constructtheamplifierinordertoincreasethevoltagerange.IntegratetheamplifierwiththeWheatstonebridgeandmeasuretheoutputfromtheamplifier.Verifythatchangefollows0.1Vincrements.

Pass

ArduinoConnecttheoutputoftheamplifiertoananaloginputontheArduino.VerifythattheArduinoisreadingthevoltage.

Pass

ServoMotorConnectaservomotortoadigitalportonanArduino.Verifythattheservorotatesappropriatelytosimulatelockingandunlocking

Pass

14

DevelopmentandConstruction

Beforeassembly,eachelectromechanicaltransducermustbetested.Testingfor

ohms,placeamultimeteracrosstheblackandredwirewithredbeingground.

Applypressuretoseeiftheresistanceisstationaryorchanging.Recordwhetherthe

resistanceincreasesordecreases.Repeatandplacethemultimeteracrossthered

andwhitewires.Verifythatthewhiteandblackwiresareinseries.Determining

thesevaluesiscrucialwhenredesigningtheWheatstonebridge.Theresultscanbe

seenintheTestResultssectionunderTable3.

OncetheresistancesaredeterminedthecircuitinFigure2isconstructed.The

circuitneedstobesuchthataspressureisappliedthevoltageatports2&3

increaseand1&4decrease.Settingitupthiswaywillhelptoinitiallyamplifythe

signalbeforeanoperationalamplifierisadded.Whenconnecting5voltstotheS+

port,S-toground,andasensitivemultimeteracrossE+andE-,itcanbeverified

thatwhenpressureisappliedachangeinvoltageoccurs.Thischangeinvoltageisin

themicrovoltsrangeonamultimeterandisvalidatedsincetheresistorschange

withpressurecausingachangeinthevoltagecomingout.

ThissmallvoltagechangeisnotsufficientwhenbeingconnectedtotheArduino

Uno.Inorderforasufficientvoltagevaluetobesent,amplifythevoltagevia

implementationofanoperationalamplifierwithinthenewcircuit.Forthis

application,aLT1679-Dual/QuadLowNoise,Rail-to-Rail,PrecisionOpAmpchip

wasused.ThecircuitinFigure3isconstructedusingcalculatedresistorvalues.

Apply5voltstotheoperationalamplifierandtheWheatstonebridge.Measurethe

15

outputoftheoperationalamplifierandverifythattheoutputvoltagechangesin

0.1voltincrements.

Oncethevoltageisoutputtingsufficientvoltagechanges,developacorrelation

betweenweightandvoltage.Using5lb.weights,slowlyincrementwhilerecording

thechangeinvoltageforeachweight.Plotthevaluesanddeterminethelinear

relationshipbetweenthetwo.

Afterdeterminingthelinearrelationship,opentheArduinoprogrammingsoftware.

Writeaprogramthattakestheanaloginputfromtheoperationalamplifierand

convertsittoadigitalcommand.Forthisproject,puttheoutputoftheoperational

amplifiertoportA0ontheArduino.Scaledowntheinputsothatthevaluebeing

readcorrelatestotheexactvoltagebeingsentoutbytheamplifier.Theinputwill

thenbesenttotheAnalogtoDigitalconverterontheboardandthevaluewillbe

read.Setathresholdsothataservomotorwillonlyrotatefrom90–0degreesifthe

scalereadsbetween10-15lbs.Themotorshouldstayat0degreesfor5secondsand

thenreturnbacktothe90degrees.Connecttheservotoadigitalpinandapplythe

conditionsfortheoutput.Iftheweightiswithintherangeoflessthan10lbs.or

greaterthan15lbs.themotorshouldnotrotate.

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IntegrationandTestResultsAftercuttingthecircuitryoutofthedigitalbathroomscale,eachsensorwas

individuallymeasuredwithamultimeterandtheresistanceswererecorded.While

measuringresistances,pressurewasappliedtodeterminewhetherthecurrent

increasedordecreased.TheresultscanbeseeninTable3.

Table3:MeasuredResistanceValuesforEachWeightSensorandtheChangesis

ResistancewhenForceisApplied

Pressure

Resistor

Location

BlackIncrease/

DecreaseWhite

Increase/

Decrease

Blackand

Whitein

Series

TopLeft 1kΩ increase 1kΩ decrease 2kΩ

TopRight 1kΩ increase 1kΩ decrease 2kΩ

BottomLeft 1kΩ increase 1kΩ decrease 2kΩ

BottomRight 1kΩ increase 1kΩ decrease 2kΩ

DesiredVoltageCalculation:

Thefollowingequationwasusedtodeterminewhichresistorvalueswereselected.

Onceselected,theresistorswereplacedintotheamplifierdesign.

𝑽𝒐𝒖𝒕 = (𝑽𝟐 − 𝑽𝟏)(𝟏+𝟐𝑹𝟐𝑹𝟏

)(𝑹𝟒𝑹𝟑)

𝟓𝑽 = (𝑽𝟐 − 𝑽𝟏)(𝟏+𝟐𝑹𝟐𝑹𝟏

)(𝑹𝟒𝑹𝟑)

17

AfterincorporatingtheWheatstonebridgewiththeamplifier,constantweightwas

appliedtothebridgeinincrementsof5lbs.Foreachincrementthevoltagewas

measuredattheoutputoftheamplifier.TheresultscanbeseeninTable4.Initially,

thechangeinvoltagewasinthemicrovoltrangebutafterapplyingtheamplifierthe

changeswereseenwithinarangeof0.4V.

Table4:MeasuredVoltageValuesusedtodeterminetheRelationshipBetweenVoltage

andWeight

ThevaluesfoundinTable4wereplacedintoExcelandplottedinorderto

determinearelationshipbetweenweightandvoltage.FromFigure4alinear

relationshipwasdetermined.Thisrelationshipwaslaterusedinwritingthe

softwarefortheADContheArduinoUno.

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Figure4:PlotofVoltagevs.WeighttoShowtheLinearRelationshipofVoltageto

Weightin5lb.Increments

19

ConclusionInordertokeepthecosttoaminimumadigitalbathroomscalewasreverse

engineeredandtakenapartinordertoobtainfourelectromechanicaltransducers.

Eachtransducerhadthreewires,oneasasupplyandtheothertwocontained

resistors.Theresistorsweremeasuredtobeapproximately1kilohmandwere

sensitivetopressure.ItisconcludedthatthescaleimplementsaWheatstonebridge.

Thisbridgecircuittakesintwosignalvoltages(S+andS-)thatrepresentthevoltage

beingsuppliedandground.Itsoutputwhenmeasuredprovidesexcitesignals(E+

andE-)thatsendoutthechangeinvoltageduetotheincreaseordecreasein

resistance.Thischangeinvoltageprovedtohavealinearcorrelationtoweight.The

resistancechangeisminimalandinorderforthemicroprocessortoreadthesignal,

thevoltagechangeneededtobeamplified.Anoperationalamplifierwithahighgain

wasusedtoshowthechangeinvoltagewithina0.1Vdeviation.Thisvaluewasthen

senttoanAnalogtoDigitalConverter(ADC)andusedtodeterminewhenthedoor

wouldbecommandedtoopenorclose.

20

Bibliography[1] http://www.healthometer.com/ Websiteforthebrandofdigitalbathroomscalethatwasusedasthe pressuresensitiveWheatstonebridgecircuitforthesystem.[2] https://www.arduino.cc/en/Main/ArduinoBoardUno WebsitecontainingthecircuitschematicfortheArduinoUno.Thiswasused asthemicrocontrollerduetoitsbuiltinAnalogtoDigitalConverter.[3] www.wikipedia.com Websitethataidedintheresearchofthecharacteristicsofacat. Ultimately,thevarietyinweightwasusedasthedeterminingfactor forthecircuit.[4] http://wdfw.wa.gov/ Websitethataidedintheresearchofthecharacteristicsofaraccoon. Ultimately,thevarietyinweightwasusedasthedeterminingfactor forthecircuit.[5] http://cds.linear.com/docs/en/datasheet/16789fs.pdf WebsitecontainingtheschematicfortheLT1679QuadLowNoise,Railto Rail,PrecisionOPAmp.ThisOPAmpwasusedtoamplifythestrain gaugesthatwereusedincreatingtheWheatstonebridgecircuit.[6] R.FordandC.Coulston,DesignforElectricalandComputerEngineers, Mcgraw-Hill,2007,p37. Thisbookcontainsmanyusefultoolswhenbeginningthedesignfor electricalengineers.Itwasusedasareferenceincalculatingcost analysisforbothlaborandproduction.

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Appendices

SeniorProjectAnalysisProjectTitle:CritterSitter:WeightSensingPetDoor Student:ShelbyRichardson Advisor:Dr.MartinKaliski

1. SummaryofFunctionalRequirements

Thisprojectiscenteredontheconceptofincorporatingbothadigital

communicationsystemthatwillworkalongsideacontrolsystem.Therewill

beaweightsensorimplantedintoafloormatlocatedattheentranceofthe

petdoor.Thissensorwillmeasuretheweightofanobjectthatisplacedon

thematandwillunlockthedooriftheweightbeingmeasuredisequaltothat

ofthehomeownerspetwithadeviationofapproximately+/-5lbs.The

systemshouldworkfastenough(aroundapproximately5seconds)sothat

thepetdoesn’tgetfrustratedandmove.Theamountoftimethatthedoor

willremainunlockedwilllastfordurationofapproximately5secondsso

thattheanimalhasenoughtimetoenterthrough.

2. PrimaryConstraints

Themainconstraintthatthisprojectwillfaceistiming.SinceIamaone-

personteam,designingandimplementingthisproductwilltakeasignificant

amountoftime.Anotherhugeconstraintwillbemakingsurethatthesystem

canworkeffectivelywithinamatandbesecuredfromtheenvironmental

factorsthatwillcausesignificantdamage.Thesystemwillalsofacealotof

challengeswithtimingaswellasifanotheranimalisroughlythesamesize

22

asthehomeownerspetbeingabletoaccessthehomeaswell.Anotherhuge

constraintwillbekeepingitascosteffectiveaspossible.

3. Economic

Thegoalbytheendofthisprojectistohaveasystemthathasalreadybeen

testedandmodifiedbasedoffofconsumerreportsandsurveys.Someofthe

riskitemsthatmayaffectmyscheduleinclude:

-Failingtoreachdeadlines

-Componentsbreaking

-NottestingthesystemasIgowhichcanleadtoharderdebugging

-Programmingnotinterfacingwiththesystemproperly

-Faultydatabeingsentthroughthecommunicationnetwork

LaborEstimation

Thisproductasmentionedbeforewillbeverytimeconsuming.Sincethe

projectwillbedonebyonepersonthecostperhourwillrangeatabout$32

(matchingcompetitiveratesforwhatanelectricalengineerwouldbepaid).

Thetimespentondesigningandtestingwillrangeabout125-150man-hours.

ReferencingFordandCoulstonChapter10,theoptimalcostwouldbe(cost)=

125hrs.x$32=$4000[6].Theleastoptimal(cost)=150hrs.x$32=$4800.

4. IfManufacturedonaCommercialBasis

Ifthisprojectweretobemanufacturedonacommercialbasis,itwouldhave

thecharacteristicsasseenbelowinTable5Thecostwouldbedetermined

basedonthesizeofthepetdoorthatwasneededinordertoaccommodatea

specificpetorhowmanypetdoorsareusedinthehouse.Thecostshouldnot

23

changeverymuchconsideringahomeownerislikelytoonlyhaveonepet

doorinstalledinthehome.

Table5:LongTermCostAnalysis

Item Cost

Resistor 7@$0.05=$0.35

LT1679 $6.43

Wire $6.99

ArduinoUno $24.95

Servo $5.95

Wood $1.50

WeightSensor 4@$3.99=$15.96

Labor 12hours@$32.00anhour=$384

Total $446.13

5. Environmental

Thisproductshouldhaveveryfewenvironmentalimpacts.Thegoalisto

haveaproductthatusesminimalelectricityfromthehomeandnotcause

anyadditionalelectricalcoststotheconsumer.Themanufacturingofthe

printedcircuitboardswillincorporatemetalssuchassilicon.Thesystemwill

alsobesafeandeasyfortheanimalstouseandwillnotcauseanyadded

irritationtothemsuchasmicrochipsorbulkycollars.

6. Manufacturability

Someissuesthatmightoccurwithmanufacturabilityaretheinfringementon

24

otherpetdoorpatentrights.Thegoodpartaboutthisprojectisthatthe

majorityofthecomponentsbeingusedhavealreadybeendesignedand

manufacturedbyothercompanies.Thepriceofthesecomponentsand

dependingonwhoIpurchasefromwillenduphavingasignificantimpacton

thechangesthatmayoccurinthetotalcostofthefunctioningsystem.Ifat

anypointthesensorisdamagedthedoorwillnolongerbefunctionaland

mayeitherremainlockedorunlocked.Thiscomponentmostlikelywillbe

theonethatneedstobereplacedmostoften.

7. Sustainability

Somechallengesthatthissystemwillfacewillbemaintainingtheintegrityof

thesystemwhenconstantlysubjectedtoanimalsandthenatural

environment.Thegoalistomakesurethatthephysicalsystemisalways

protectedfromanysortofoutsidedamage.Thisiswherethephysicaldesign

ofthefloormatwillplayahugerole.Anotherkeythingismakingsurethat

thetimerandprogramdon’tglitchbecauseifittriestolockonthepetitmay

causethepettobecomefrightenedcausingthemtoinflictdamagetonotonly

themselvesbutthedoor.Damagetothepetscouldleadtoaneventual

lawsuit.

Ifthedesignneedstobeupgradedthenthemicrocontrolleritselfwillhaveto

bereplaced.Thiswilltakeawaythemaincontrollerofthesystem.This

shouldnotbeaproblemhoweverfortheweightsensorsandthoseshouldbe

easilyintegrated.Upgradingthedesignwouldcausetheconsumertohaveto

installandreprogramthenewsystem.Thiscouldbeahugeproblemfor

25

consumerswhostrugglewithnewtechnologyandhavingtointegrate

technicalthingssuchasthecontroller.

8. Ethical

InreferencetotheIEEECodeofEthics[6],thefollowinglistwascomprised

toshowthepotentialethicalissuesthatthisprojectmayexperience:

-Notenoughfunding

-Havingasystemthatfailsafterashortamountoftime

-Animalsphysicallybreakingthesystem

-Infringingonanotherpetcompanies’patents

-Weightsensorfailingtoweatheroranimalinvolvement

-Weightsensorfailingwithchangesinanimaldiets

-Physicaldamagetohome

-Promisingtokeepanimalsoutbuthavingthesystemfail

-Recognizingandreferencinguseofsimilarpetdoortechnologies

-Automatedsystemcausingharmtothepet/keepingthepetfrom

physicallyusingthesystem

9. HealthandSafety

Thebiggesthealthandsafetyriskwouldbethetimingsystemfailingandthe

doortryingtocloseandlockonthepetwhileitisintheprocessof

entering/leavingthedoor.Thiscancausetheanimaltohaveintenseanxiety

orcausephysicalharmtothepet.Anothersafetyriskwouldbethatawild

animalofasimilarsizetothepetisabletofakeoutthesystemandenterthe

homecausingthehomeowner’spersonalbelongingsandfamilytobeatrisk.

26

10. SocialandPolitical

TherearenopoliticalthingsthatIfeelthisproductwillaffect.Theonly

concernIcanseeispotentialanimalrightsactivistsworryingaboutthe

dangersthatitmayhaveontheanimalhoweverthissystemwillbeless

invasivethanmicrochippingthem.Icanseeanimalrightsactivistsbeing

morelikelytoapproveofaproductlikethisovermicrochipping.IfIfailto

provideaneffectivesolutiontopetdoorsthanthehomeownersarebackto

leavingtheirhomesatrisktowildanimalinvasions.

Development

Thedesignanddevelopmentofthisproductreferencesthespecificationsgivenby

theIEEEprotocol.Thisallowsmorecreativefreedomandtheabilitytomanipulate

boththecodinganddesignofthesystem.ThecreativesolutionthatIamofferingis

thattheweightsensorincorporatedintoaestheticallypleasingfloormats(allowing

theanimalstocleantheirpawsbeforeentering)willbeeasytouseandwill

effectivelykeepoutunwantedanimalswheremycompetitorshavealready

promisedtodoandfailed.

27

SpecificationsandRequirements

Forthisprojecttobesuccessful,therearethreecomponentsthatneedtobe

completed.Thesystemneedstobeabletobeinstalledeasily,theweightsensor

needstobeintegratedandcalibrate,andthemotorneedstofunctionproperly.

Figure5outlinesinmoredetailwhateachrequirementneedstosatisfy.

Figure5:HighLevelBreakdownofSystemComponentRequirements

Theinputandoutputsneedtobeestablishedtomakesurethateachcomponentis

incorporatedproperly.Table6givesamoredescriptivelayoutofwhateachinput

andoutputofthesystemdoes.

Table6:DecompositionoftheInputsandOutputsandDescriptionofRequirements

28

Figure6isaflowdiagramthatshowsthestepsthataretakeninordertocomplete

theprojectinasufficientamountoftime.Firsttheweightsensorneedstobe

designedintoaWheatstonebridge.Followingthisstepistheintegrationofan

amplifiertoamplifythevoltagesignalandthefoundationalprogrammingisstarted.

Oncethesestepsarecompletedtheentiresystemcanbeintegratedtogether.

Figure6:FlowDownDiagramoftheStepsTakentoCompletetheProject

PartsListandCost

Table7liststhepartsusedandthecostofeachindividualitem.Sinceadigital

bathroomscalewasused,theoverallcostwascheaper.Inordertogiveamore

realisticvalue,electromechanicaltransducerswereresearchedonlineandthatcost

isincludedinthetablebelow

29

Table7:OverallBreakdownofthePartsUsedandEachPartsTotalCost

Item Cost

Resistor 7@$0.05=$0.35

LT1679 $6.43

Wire $6.99

ArduinoUno $24.95

Servo $5.95

Wood $1.50

WeightSensor 4@$3.99=$15.96

TOTALCOST $62.13

30

Schedule–TimeEstimatesTheGanttchartsfoundbelowinFigures7(a-c)showthetimeframethatwas

constructedinFallof2015afordevelopingthisproject.Thechartsaresplitupby

quarterinordertocreateahigher-levelchecklisttofollow.Itisimportanttonote

thatthesechartsweremeantasaguide.Justaswithanytypeofengineeringproject

theschedulewasadjusted.Fallquarterwasusedasaninitialbrainstormingto

figureoutwhatwasnecessarytobedonetocompletetheproject.Winterquarter

involvedresearchanddevelopmentofthedesiredsystem.Springquarterwas

wheremostofthefinaldesignandtestingoccurred.

Figure7a:Fall2015GanttChart

Figure7b:Winter2015GanttChart

Figure7c:Spring2015GanttChart

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ICLocationDiagram

ThefollowingdiagramfortheLT1679wasobtainedfromtheLinearTechnology

websiteandincludedinFigure8below[5].

Figure8:LinearTechnologyLT1679IntegratedCircuitPinOutDiagramfrom

Datasheet

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PCBoardLayoutForthisprojectaPCboardwasnotcreated.Insteadasolder-lessbreadboardwas

used.Itisimportanttonotethatbecauseofthisdecision,thewiresneededtobe

shortenedasmuchaspossibleinordertoavoidunduesignaldistortion.Whenno

loadisappliedthereshouldbe0voltsbeingreadbytheArduino.IfaPCboardwas

used,thiswouldhavegivencloserresultsto0voltsthanthesolderlessbreadboard

did.ItisrecommendedforfutureproductionthataPCboardbeusedinorderto

increasetheaccuracyandsensitivityofthescale.Thesolderlessbreadboardlayout

canbeseeninFigure9below.

Figure9:SolderlessBreadboardLayout

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ProgramListing(forSoftware)#include<Servo.h>Servomyservo;voidsetup(){//putyoursetupcodehere,torunonce:Serial.begin(9600);//initializingserialcommunicationat9600bits//persecondmyservo.attach(9);//attachservotopin9myservo.write(90);//setservotolockingposition}voidloop(){//putyourmaincodehere,torunrepeatedly:intsensorValue=analogRead(A0);//readinputonanalogpinA0floatvoltage=sensorValue*(5.0/1023.0);//convertanalog//readingto0-5Vdelay(2000);//waittogetasolidreadingSerial.println(voltage);if(voltage>1.0&&voltage<1.4){//checkifvoltageisinrangemyservo.write(0);//unlockthedoordelay(5000);myservo.write(90);//lockthedooragaindelay(5000);}else{myservo.write(90);//doorremainslocked}}

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HardwareConfiguration/Layout

Figure10belowisthecompletelayoutoftheproject.Thisfigureshowsthe

connectionoftheWheatstonebridgetotheLT1679.TheLT1679connectstothe

analoginputoftheArduinoUno,whichthenconvertstheanaloginputtoadigital

value.Thisdigitalvaluedrivesthemotor.

Figure10:CompleteSchematicfortheCritterSitter:WeightSensingPetDoor