HARDWARE METAPAPER

Vibration Alert Bracelet for Notification of the Visually and Hearing ImpairedKelsey Conley, Alex Foyer, Patrick Hara, Tom Janik, Jason Reichard, Jon D’Souza, Chandana Tamma and Cristinel Ababei

This paper presents the prototype of an electronic vibration bracelet designed to help the visually and hearing impaired to receive and send emergency alerts. The bracelet has two basic functions. The first function is to receive a wireless signal and respond with a vibration to alert the user. The second function is implemented by pushing one button of the bracelet to send an emergency signal. We report testing on a prototype system formed by a mobile application and two bracelets. The bracelets and the application form a complete system intended to be used in retirement apartment communities. However, the system is flexible and could be expanded to add new features or to serve as a research platform for gait analysis and location services. The medical and professional potential of the proposed system is that it offers a simple, modular, and cost-effective alternative to all the existing medical devices with similar functional-ity currently on the market. The proposed system has an educational potential as well: it can be used as a starting point for capstone projects and demonstration purposes in schools to attract students to STEM disciplines.

Keywords: Vibration bracelet; Hearing impaired; Alert signals; WiFi communication; 3D printing

Metadata Overview• Maindesignfiles:https://zenodo.org/record/3406788• Target group: undergraduate students, trained engi-neers,scientistsinembeddedsystemsandbiomedicalengineering

• Skills required: Hardware assembly – easy; surfacemountPCB–easy;embeddedCfirmware–easy;An-droidprogramming–easy

• Replication:Nobuildsknowntotheauthorssofar.

1. IntroductionAccordingtotheWorldHealthOrganization(WHO),onethirdofpeopleolderthan65sufferfromadisablinghear-ingloss[1].Accordingtothereportedstatistics,thereare466millionpeoplesufferingfromdisablinghearinglossandthisnumberisexpectedtoincreasetoover900mil-lionbytheyear2050.Inthiscontext,caregivingforpeo-ple suffering from visual and/or hearing impairment isveryimportantandagrowingchallenge.There are several commercial products and solu-

tionstotheproblemofeffectivelyalertingpeoplewithvisual/hearing impairment of potentially dangeroussituations.One such example isGoSafe2 fromPhilips[1]. This is a pendant device that the user needs to

weararoundtheneck.It issimple,userfriendly,anditfeatures fall detection capabilities, advanced locatingtechnologies, and two-way voice communication. Thependanthasonebuttonthatcanbeusedtosendadis-tresssignal.Themaindrawbackofthissolutionisthatitcannoteffectivelynotifythewearer(whomayhaveavisual/hearingimpairment)ofpotentiallife-threateningdangers.Forexample,inthecaseofabuilding-widefirealarm, it is not clear how people with visual/hearingimpairmentcouldbenotifiedeffectivelyviatheGoSafe2 device. In addition, this product uses a subscriptionmodelwithinitialactivationandmonthlyfeesthatcanbecomecostlywhendesiredtodeployonalargescale.Manyexistinghearing-impairedalertdevices includeadesktop base station with peripheral devices that willalert theuser of certain events such as a fire alarmora doorbell [2]. Devices like the Central Alert SystemReceiver and Clock and the Clarity Alertmaster AL10Alert Device resemble an alarm clock with connecteddevices that are used to alert the user. The downsideofthesesystemsisthatmostofthemareeffectiveandlimitedtothelocationoftheactualdevices.Othersolu-tions,suchastheBellmanVisitAlertSystem,mayuseapager-likedevice that theuserneeds to carry thatwillvibrate when one of the alerts is activated. These sys-temsaremostlydesigned for consumerhomeuseandthey require additional purchases to add functional-ity to the system, such as smoke or carbonmonoxidedetectors, which add to the initial cost of the system.

Ababei, C, et al. 2019. Vibration Alert Bracelet for Notification of the Visually and Hearing Impaired. Journal of Open Hardware, 3(1): 4, pp. 1–11. DOI: https://doi.org/10.5334/joh.17

Department of Electrical and Computer Engr., Marquette University, USCorresponding author: Cristinel Ababei (cristinel.ababei@marquette.edu)

Ababei et al: Vibration Alert Bracelet for Notification of the Visually and Hearing ImpairedArt. 4, page 2 of 11

Moregenerally,theSituationalAwarenessandResponseAssistant(SARA)isariskmanagementsolutionandmassnotificationsystem.Whileintendedprimarilyforsmart-phone as end points, this system can integrate withexisting alarm systems installed already in homes [3].Suchsystemsaregenericinnature,anddonotnecessar-ilyhelppeoplewithvisual/hearingimpairment.In addition to the commercial solutions described

in the previous paragraph, one can also find severaldesignsdevelopedbyhobbyists anddescribed inonlinearticles. For example, theprojects listed or described in[4,5]presentideastoimplementemergencybuttonsforelderly care.Manyof thesedesign ideasuseboards liketheArduinoorRaspberryPI,whichwhileconvenientandeasytouse,maybetoolargetobeusedaswearables,theyimplementjustonefeature(emergencybutton,whichinthisworkwe refer toas thedistress signal feature), andoftenonlypartialorincompletedesignfilesareprovided.In this paper, we present a complete free and open-

source design of a visual/hearing-impaired alert device.Itconsistsofanelectronicbracelet,whichvibrateswhenit receives a notification signal from a centralmanager.In addition, the bracelet has a button that upon beingpressed sends an alert or distress signal. For reliabilityandextendedrange,Wi-Fiisusedasthecommunicationtechnology. The central manager is implemented as a

smartphoneapplication.Thevibrationalertbraceletseekstosolvesomeoftheshortcomingsofthecurrentlyavail-able solutions.Designed tobe cost-effective yet extend-able,wehopethisdesignwillbeadoptedandimprovedinotherpractical,educational,andresearchsettings.

2. Overall Implementation and Design2.1. Hardware description2.1.1. System-level DiagramThe system-level diagram of the overall Vibration AlertBracelet(VAB)systemisshowninFigure 1,foraspecificcaseoftwousers.Themajorcomponentsincludeanum-ber(e.g.,2)ofbraceletswornbytheusersandthemobileapplication (VabApp) installedon the centralmanager’ssmartphoneortablet.

2.1.2. Vibration Alert Bracelet UnitThe VAB unit is the primary hardware component oftheproposedsystem.TheblockdiagramoftheVABunitis shown inFigure 2. Theunit is constructedprimarilyaroundtheESP-12Fmodulethatusesasimplelow-powermicrocontrollerunit(MCU)withWiFibuilt incapability,the ESP8266 System-on-Chip (SoC). The MCU controlsthe vibrationmotorwhen the control signal is receivedvia WiFi as well as the LED. In addition, the MCU hasconnected apush-button that isused for triggering the

Figure 1:System-leveldiagramoftheproposedvibrationalertbracelet(VAB)systemasanIoTapplication.

Figure 2:Simplifiedblockdiagramofthevibrationalertbracelet(VAB)unit.

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generation and transmission of a distress signal. Uponpressingthebutton,theVABunitsendsviaWiFiasignalwhichwillbe receivedat thecontrolmanager’sapplica-tion.TheapplicationwillindicatetheunitnumberorIDthat generated the distress signal. Situations when theuser isoutside thedesignatedapartment (e.g., commonroomsorsimilar)arenotconsideredinthecurrentversionofthedesign.The design’smain supply voltage is VCC = 3.3V and

isproducedbyaBuck converter. TheBuckconverter isa step-down high-efficiency and low-ripple monolithicintegrated circuit optimized for portable applications.Thevoltagelevelisselectedtobe3.3VbecauseitisthesupplyvoltagerequiredbytheESP-12Fmodule.Thecir-cuitisdesignedsuchthattheinputtotheBuckconvertercanbesuppliedbythebatteryorbythe5VUSBconnec-tion. The rechargeable battery, which can be chargedthroughtheUSBport,hasabuilt inprotection IC,anda switching circuit used to detect if the vibration alertbraceletisconnectedtoUSBornot;ifconnectedtoUSB,then, the switching circuit enables the battery chargerat thesametimewithpassingthesupply to thepowerconverter.Fortheinputbutton,pull-upcircuitsareusedtodetectbuttonpressesontheGPIOpins.Duetohighcurrentdrawof themotor (whichGPIOcannotdirectlydrive)apowerFETisemployedtodrivethemotor.ThepowerFETandthebatteryweresimplyselectedbasedontheirvoltageratingsandavailability.Aspecialconsidera-tion in selecting thebatterywas its shapeandvolume,which needed to be as small as possible. More circuitdetails canbe seen in the circuit schematicof theVABunitshowninFigure 3.Themicrocontroller of theVAB is inside the Espressif

ESP8266System-on-ChipthatmountedonanAI-Thinker

breakoutboard.Althoughitsprimary intendedfunctionis that of an all-in-one WiFi receiver and controller, italsoprovidesI/OnecessarytointerfacewiththeParallax28821pagermotor,tocontroltheSunLEDXSMDK43MBnotification LED, and to poll the button for input. ThemotoritselfisconnectedtotheESP8266viaanInfineonBSL802SNH6327XTSA1 MOSFET. The Buck converter isprovidedwithbattery voltage via a TIBQ297-seriesbat-teryprotectionIC.TheBQ297isincludedforredundancyasthebatteryitselfhasinherentprotectioncircuitry.Thebattery’scurrentchargelevelisalsoreportedtothemicro-controllerforbatterylevelmonitoringpurposes.Thebat-tery is a Lithium-Ion polymer single cell and is directlycontrolledviathebatteryIC.Inordertofacilitatecharg-ing from a USB port, a Microchip MCP73811/2 chargemanagementcontrollerisintegratedintothedesign.AnAdafruitCP2104USB-to-serialchipisincludedtointerfacewith the Vibrating Alert Bracelet. The CP2104 allows ausertopushfirmwaretotheESP8266overUSB.TheusageoftheUSBstandardprovestobemostconvenientasitnotonlyprovides5Vcharginginput,butalsoallowsforeasycommunicationwiththeESP8266overitsUSBserialport.The schematic diagram was placed and routed with

EasyEDAPCBtoolandthenmanufacturedonaPCBwithtwolayers.ThePCBlayoutandphotographsoftheactualprototypepopulatedwiththecomponentsareshowninFigure 4.

2.1.3. 3D Printed EnclosureThevibrationbraceletiscasedinsideaprintedenclosure,designed tobeergonomic and tobe able to attachandwearonawristusingamilitarystylewatchstrap.The3DCADmodel of the enclosure and the actual 3DprintedenclosureareshowninFigure 5.

Figure 3:CircuitschematicoftheVABunit.

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TheenclosurewasdesignedusingSiemens’NX8.5CADprogramandwasprintedusingregularPLAplasticat60%infill. The Zenodo repository (discussed later) providesdesign files inDXF/DWG format, which can be openedwithfreeandopensourceCADprograms.

2.2. Software description2.2.1. Embedded SoftwareTheWiFiMCUrunsthemainembeddedprogramwhoseroleis:1)toreceivealertsignalsandturnonthevibrationmotorforaspecifieddurationoftime,2)todrivetolight-ontheLEDforthesameduration,and3)toreacttothebuttonbeingpressedbygeneratingandsendingviaWiFia distress signal. The flow-chart that describes the algo-rithmthatimplementsalltheabovetasksispresentedinFigure 6.TheESP8266operatesonasetloopoffunctionsthatallowsittofunctionproperly.Thefirstthingthatthebraceletunitdoesisconnecttothewirelessnetwork.Thisisonlydonewhentheunitstartsup.Theunitwill thenconnecttotheserverthatmanagesalltheunits.Onceaconnection to the server has been established, the unitwill send aMAC address that is used for identification.Theserverwillthensendaresponseeithertriggeringthealertontheunitorpassingon.Theunitwillthenalerttheserveriftheuserneedsassistanceoritwillsendanallclearresponse.Followingthis,theunitwillthendisconnectandlight-sleeptoconservebatteryenergy.Addingthissleeptimecandecreasethebatteryusagesignificantlyallowing

forlongertimesbetweencharging.Thereisaninterruptthatisnotshownintheflowchartthatallowsthebuttonpresstoberecordedevenwhilethebraceletissleeping.

2.2.2. Server-Side SoftwareTheserverbeginsitsoperationbyconnectingtoanetworkwhich will allow it to interact with the bracelet and theapplication(orapp).Oncetheserverhasconnectedto itsnetworkitwaitsfortheappandbraceletstocheckin.Whenadevicechecksinwiththeserver,itidentifiesitselfaseithertheapporabracelet.Ifabraceletconnects,theserverthenreceivesacheck inmessagethat includeswhetherornotthebracelethassentanalert.Followingthis,theserverthenreceivesaMACaddressfromthebraceletwhichisusedtoidentifythebracelet.Iftherewasanalert,thentheserversetsthealertstatusforthatbracelettohigh.Theserverthensends the bracelet an alert status that indicates whethertherehasbeenanalertfromtheadministration.Oncethisiscompleted,theserverthendisconnectsfromthebracelet.Iftheappconnectstotheserver,thentheserverwaitsforinstructionsfromtheappthateitherrequeststhestatusofthebraceletsonthenetworkorsendsanalerttooneorallbracelets.Iftheapprequestsanupdatetheserversendsanupdatedclientlisttotheapp.Ifanalertissentfromtheappthanthealertstatusissettohighforthenecessarybrace-lets.Oncethisiscompletedtheserverdisconnectsfromtheapp.Theflow-chartthatdescribesthealgorithmthatimple-mentsalltheabovetasksispresentedinFigure 7.

Figure 5:(a)3DCADmodelofcase.(b)3Dprintedcasewithattachedstrap.

Figure 4:(a)PCBlayoutoftheVABunitasrenderedbyEasyEDAPCBtool.(b)Prototypepopulatedwiththeelectroniccomponents.

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Figure 6:Flow-chartofthemainalgorithmexecutedonthebraceletmicrocontrollerunit.

Figure 7:Flow-chartofthealgorithmexecutedontheserver.

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2.2.3. Mobile ApplicationThecentralmanagerfromFigure 1consistsofanmobileapplicationor“app,”(calledVabApp),whoseroleis:1)tosend the alert signals to all users or selectedusers, and2)toreceivethedistresssignalssentbyanyofthebraceletunitsandhighlightona list-baseddashboardtheIDsofthecorrespondingunits.Theapplication’suserinterface(UI)isverysimpleanduserfriendlyasitprovidesessen-tiallytwobasicfeatures.The home-landing page (which shows also users that

sent out distress signals) and the send alert page areshowninFigure 8.Thecurrentlandingpageconsistsofadynamiclistofallthebraceletsthatareregisteredtothenetwork.Eachoftheselistitemsdisplaysthenameoftheclientthatthebraceletisregisteredtoaswellastheunitthatthatclientlivesin.Totherightofthisinformationisaradiobuttontodenotethestatusofthebracelet.Ifthebuttonisgreen,thebraceletisconnectedandhasnotsentoutanydistresscallswithinthelast15minutes.Aredbut-tonindicatesthattheclienthassignaledforhelpwiththebutton locatedon thedevice.Agrey icon indicates thatthebraceletisnotcurrentlyconnectedtothenetworkorisotherwiseunabletocommunicatewiththeserver.Thislistofconnecteddevicesisupdatedfrequentlytoensurethat the user of the app has a reliableway to view thestatusof thedifferentbracelets.Aside fromthe list, thelandingpagehas a button thatwill change the view toallowtheappusertosendoutalerts.Thesendalertscreen

isfairlysimple.Itessentiallyincludesonebuttonusedtosendthealertsignaltoalloronlytoselectedusers.Theotherprimaryfunctionalityoftheappwillbeits

abilitytoreceivealertsfromthebracelets.Thelistofcon-nected bracelets displays via the red radio buttons theunitswhichhaveissuedrequestsforhelp,theappalsoissuesanotificationonthephoneandcauseittovibrate.Thisistoreducetheriskthattheappuser(i.e.,thecen-tralmanager)willmiss any requests for help from theusers.

3. SafetyTheVABunit is suppliedwithpower fromabattery orviatheUSBinterface.Thevoltageandcurrentlevelsarelow enough for theVABunit not to present any safetyissues.Theenclosureisnotwaterproof.Itwouldbedesir-abletocheckmaterialsand3Dprintingtechniquesthatwouldallowtodevelopawaterproofcaseinthefuture.TheQuality-of-Service(QoS)ofthealertsystemdependsprimarily on: 1) the presence of the WiFi connectivity,whichenablestheconnectiontothecentralmanagerand2)thelevelofthebatterynecessarytoguaranteecorrectoperation.Because the proposed VAB system is connected via

WiFi, it is vulnerable to typical security threats thatanydevice or thing connected to the Internet suffers from[6–9]. Threats include interception of signal and gen-eration, redirection, or suppression of alerts. Currently,

Figure 8:Home-landingpageoftheApp’sUI(left).Pagetosendalertsignalstoselectorallusers(right).

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wehavenot includedanysecurityprovision inthealertsystem.Thereisaneedforimprovingthefirmwarecodeandtheserver-sidesoftwaretoprovideandenforcesecurenetwork connection, certifying both clients and servers.Potentialprivacyissuesmustbeexplainedtotheusersofthedevice:currently,oursystemdoesnotstoreorbroad-cast any type of sensible information, such as personal,medical,orfinancialinformation.However,locationinfor-mation can be obtained through a targeted maliciousattempt. To mitigate risks for any future deployment,transport and storage of information on the end usersmust be protected with strong encryption and propersecurityprovisions.Securitymeasuresareplannedforthefutureoftheprojectbutarenotprovidedinthisversionoftheprototype.

4. General testing4.1. Signal IntegrityThetwomost importantaspectsofthehardwaredesignare its voltage values at selected nodes and its signalintegrity,thelatterofwhichisabyproductofbothdesignandPCBlayout.Testingtheelectricalnoiseonkeynodeswithinthecircuitandmonitoringripplewasparamounttomaintainingahigh-qualitysignalforstableoperation,even in a low-power device like the VAB unit. Further-more,probingat these selectnodesenablesverificationofnodevoltages inaccordancewiththeirspecifications.Forexample,VBATmustsupply3.9–4.2Vwhenchargedtofullcapacity,VBAT_SCALEDmustcomplywiththeADCinput’sparametersandbeunder0.966V,USB5Vmustbe~5V,USB3.3Vmust be3.3V, and theremust benegligi-blevoltage rippleorelectricalnoise throughout thecir-cuitduringnormaloperation.Inordertotestthesignalintegrityofthefinalboard,keynodesinthecircuitweretested.Thesenodesincludedthefollowingvoltagenodes:USB5V,USB3.3V,Vcc,VBAT,VBAT_SCALED,CHARGE_EN,andBAT_CHECK.Theproceduretoverifythespecificationparametersofeachnodeisasfollows:

1. Turn bracelet hardware on under its own batterypower;

2. Locate test nodeonboard in accordancewith thespecific component circuit as per the PCB layoutschematic(VBATnodewithintheU3batterychargercircuit,forexample);

3. Usinganoscilloscope,applyprobesacrosstestpoint;4. Observe readoutvalueandconfirmthat themeas-

ured voltagematches the specification for the de-vice(5VforUSB5V,3.3VforVcc,4.2VandunderforVBAT,lessthan1VforVbatscaled/ADCinput);

5. Repeatmeasurementthreetimesacrosstwodiffer-entprototypes;

6. Recorddataandconfirmthatthevoltageiswithinspecificationandtolerance;Comparetosimulationresultsandconfirmexpectedfunctionality.

TheresultsreportedinthenextTable 1confirmproperoperation of all major voltage rails and current loopswithin the VAB’s circuitry while adhering to the devicespecificationsforeachcomponentusedinthedesign.

4.2. Battery Life and ChargingThemaindesignconsiderationoftheVABunitisthebat-tery life under normal operation.Given that theVAB isintended as a wearable alert system that is constantlyworn,batterylifeisexpectedtolastatleast24hoursonasinglechargethroughnormalusagewithminimalcharg-ingdowntime.Tolimitthisdowntimetwomeasurementsmustbeobserved, the time for thebattery todischargeand the time to charge as this controls the frequencyof thedowntimeand itsduration.Battery life testing isdonethroughascript thatallows forahighersamplingfrequencyandgreaterconsistencythanifapersonweretomanuallyrunthetests.ThescriptrunstheVABdeviceatfullpowerandeveryfivesecondsitreportsthevoltageacrossthebattery.Theproceduretoverifythebatterylifeisasfollows:

1. ChargethebatteryviaUSB;2. Uploadthebatterytestscript;3. Confirmthedeviceconnectstothenetworkand

isproperlyreportingtheVBATvoltage,itshouldreportvoltageonceevery5–6seconds;

4. DisconnecttheUSBpower;5. Allowthedevicetorununtilthebatterydies(i.e.,

completelydischarged);6. Checktherecordeddatavaluesandconfirmthe

runtime;7. Compareresultstosimulationsandestimations.8. Following theabove testprocedure, thebattery

life data reported in Figure 9 were collectedfor15 sec,30 sec, and60secwake/sleep inter-valcycles.Wecanobservethatthebatterylifeisabove20hourswhenthewake/sleepcycleis60sec.

Inorder to test thebatterychargingprocess,measuringsuppliedcurrentprovesmoreusefulthanvoltagecharge

Table 1: Resultsoftestingvoltageandcurrentsatselectedpoints.

Testpoint Voltage (V)

Current (mA)

Within Specification?

USB5V 5.04 – Yes

USB3.3V 3.5 – Yes

VCC(USBpower) 3.46 – Yes

VBAT 4.14 – Yes,within3.9–4.2V

VBAT_SCALED 0.932 – Yes,under0.966Vmax

BAT_CHECK 3.36 – Yes

RLED – 66.53 Yes

GLED – 66.9 Yes

R+GLED – 73.8 Yes

BaseCurrent – 61.8 Yes

Motor – 110.2 Yes

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duetothechargemethodologyappliedtolithiumionbat-terytechnology.Theproceduretoverifychargetimeisasfollows:

1. Dischargebattery;2. ConnectthebatteryuptothechargingIC;3. Setmultimeterprobesacrossbatteryterminals;4. Setupabenchpowersupplytosupply5V,turn

offoutput;5. ConnectVCCandgroundofthebreadboardtoa

benchpowersupplywhileoutputvoltageisoff;6. Turnonthepowersupply;7. Readmultimeter voltage and the power supply

currentvalue;8. Repeatonceevery5minutesuntilcurrentdrops

tonegligiblevalues;

The plot shown in Figure 10 shows that the battery’schargetimeislessthan30minutes.

5. Use caseThepotential applicationof theproposed alert systemis the typical retirement apartment community wheretheremay be users that are visually/hearing impaired.The role of theVABunit is to notify the user throughvibrationandlighting-upofthebracelet’sLEDofevents

that require their attention. In addition, the role ofthe bracelet unit is to provide the ability for the userto sendadistress signalupon thepressingof thebut-tononthebracelet.Wehaveprototypedasystemwithtwobracelets, as illustrated inFigure 1. Thehardwareand software componentsof theproposedVAB systemwere implemented successfully and they operated asintended. Setting up the hardware units is straightfor-ward, and themobile application is very user friendly.Thebatterylifeofthecurrentimplementationisabout22hours,which,whilesatisfactory,isalsothemainlimi-tationofthedevelopedsystem.ThisisbecausetheVABunitusesWiFiasawirelesstechnology,whichisknowntoconsumemoreenergy.Onewaytoaddressthisknownlimitationisdescribedinthenextsection.

6. Reuse potential and adaptabilityTheVABsystemiscompletelyreplicableandthehardwarecomponents are readily available from various vendors.Thedesigniscost-effective,replicable,andextendableaspresented. The proposed system could potentially havean importantmedical application, given that it offers asimpleandcost-effectalternativetoexistingcommercialdevices, discussed in the Introduction. The authors con-sideredcreatingastart-upcompanytocommercializetheproposed system,having as a specific target application

Figure 9:Batterylifeforwake/sleepcyclesof0,15,30,and60sec.

Figure 10:Characterizationofthebatterychargetime.

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the typical retirement apartment community. However,such a professional development is not pursued at thetimeofwritingthispaper.Thesimplicityoftheproposedsystemlendsitwelltoserveasaneducationalplatform.Theextensionsdiscussed inmoredetails in the “FutureWork” section later on could easily represent topics incapstoneprojectsforstudentsinelectricalengineeringorcomputersciencemajors.AnothereducationalpotentialoftheVABunitisthatitcouldbeusedfordemonstrationpurposesinmiddle-schoolsandhigh-schools inordertoattractstudentstoSTEMdisciplines.WhiletheproposedVABsystemcouldservemedical,

professional,andeducationalpurposes,wewouldliketo emphasize that we do notmake any claims abouttheusabilityofthedeviceformedicalordisastersitua-tions,whichwecannotguarantee.Thisprojectanditsdistributed software andhardware design files comeswith no warranties whatsoever. The system has notbeencertifiedasamedicaltechnologyandshouldnotbeusedformedicalpurposes.SincetheVABsystemhasnotbeentestednorcertifiedforreal-worldmedicalordisaster situations, it is presentedhereonly as apro-totypetobetested,extended,andcertifiedfor futureapplications.

7. Availability of materials and methodsThebillofmaterialsfortheVABunitislistedinTable 2.

8. Ease of buildCompletedesignfiles,bothhardwareandsoftware,anddocumentationaremadepubliclyavailableonZenodo.In the simplest scenario, one can simply duplicate theproposed system. The most challenging aspect in thisprocesswouldbe the solderingof all theSMDcompo-nentsonthePCBboard,becauseitrequirespriorexpe-rience and SMD soldering skills. Otherwise, everythingisrathersimpleandstraightforwardtoassembleandtoprogram.

9. Operating software and peripheralsSpecialsoftwareisonlyneededatthetimeofprogram-mingofthemicrocontrolleronthelogicboard.Specifi-cally, theArduno IDE is recommended to compile andprogramthemicrocontroller,butnotstrictlynecessary.For themobile application,Google’s Android Studio isrequired,which isavailable fordownload fromGoogle.Please note thatwhilewe have developed theVabAppmobile application with Android Studio, the VabAppstructure can be replicated in order to run with anyother mobile operating system (OS). None of the twosoftware tools thatweused (Arduino IDE andAndroidStudio)needmorediskspaceandmemorythantypicalprograms.

10. DependenciesTheentiredesignismadefreeandopensourcehardwareandsoftware. Itdoesnothaveanydependenciesandallcode (firmware, application) was written from scratch.However,itdoesrequirecodingframeworkssuchasGoog-le’sAndroidStudio.

11. Hardware documentation and files locationTheentiredesign ismadepubliclyavailableusingOpenHardware and Free Software licenses. The followingZenodorepositorycontainsbothhardwareandsoftwaredesign files, plus licensing information. A copy of thesamerepositorytreeisalsoavailableonGithubathttps://github.com/eigenpi/Vibrating-Alert-Bracelet. Finally,additional information, includingaprojectposterandashort video presentation is available at http://dejazzer.com/hardware.html

Name of repository:VibratingAlertBraceletPersistent identifier: https://zenodo.org/record/3406788License: Firmware,testingscripts,mobileapplication,and server-side files:GNUAGPLv3 license; PCBhard-wareandenclosuredesignfiles:CERNOHLv1.2license;Finalreport:CreativeCommonsCC-BY-SA,4.0licensePublisher: CristinelAbabeiDate published: 08/15/19

12. ConclusionsWe presented a completely open source design of avibration alert bracelet (VAB), intended to be used byvisual/hearing impaired people. We prototyped a com-pletesystemformedbytwobraceletsandcontrolledviatheapplication.Bothbraceletsareenclosedin3Dprintedcases that canbewornaswristwatches. Theprototypedsystemworkedasintendedandthecompletedesignfiles,bothhardwareandsoftware,aremadepubliclyavailable.Designed tobe simple, toprovide two-way communica-tion,andtobecost-effective,thebraceletunitprototypehasaformfactorthatismoresuitableforitsapplicationthantheexistingcommercialorhobbyistsolutions.

13. Future WorkTheproposedVABdesigncouldbeextendedandimprovedin severalways. To address the issue of high energy con-sumptionduetothecurrentlyusedWiFicommunication,thedesigncouldbeextendedbyreplacingtheWiFiwire-less technology with low energy Bluetooth (BT) technol-ogy.However,thissolutionwouldrequiretheadditionofagateway(stationaryandsuppliedwithpowerfromapoweradapter)whoserolewouldbetoreceivetheBTsignalandprovideconnectivity to the Internet.Essentially, thisgate-waywould be a Bluetooth toWiFi converter.While sucha systemwould guarantee longer battery lifetime for theVABunit,itwouldincreasetheoverallcostofthesystem,whichwouldneedtoincludethecostofthegatewayaswell.AnotherextensiontotheproposedVABdesigncouldbetheadditionofasimpleandlowenergyLCDdisplaythatwouldbeable todisplay simplemessagesalso transmitted fromthecentralmanagerwhenalertsaresent.Thisfeaturewouldnotnecessarilybehelpfultothevisionimpairedusersbutcouldbehelpfultoallotherusers–inthatshortmessageswithinformationdescribingthereasonforthealertcouldbeprovidedaswell.Toaddresstheissuethatwhentheuserisoutsidethedesignatedapartment(e.g.,commonroomsor similar) theprecise location isunknownbutneeded iftheuserpressedthedistressbuttonoftheVABunit,apos-

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siblemodificationistheintegrationofaGPS.Yetanotherenhancement could be the pairing of the VAB unit to asmartphone.Becausesmartphonesaresoprevalenttoday,suchpairingcouldunlockmanypossibilities.Oneexamplecouldbe todirect the attentionof theuser to additionalinformation provided on the smartphone in the form of

textandvideomessages,likeforinstancereminderstotakemedicineperiodically. Informationsecurityprovisionsandmedicalcertificationmustbedevelopedbeforetheprojectcanbedeployedandusedinreal-worldscenarios.Finally,itwouldbedesirabletoinvestigatematerialsand3Dprintingtechniquesthatcouldmaketheenclosurewaterproof.

Table 2: Billofmaterialsforthevibrationalertbraceletdesign.

Designator Component Part Number Manufacturer Material type

PCB PCB – LCSC Printedcircuitboard(PCB),Semiconductor

Battery Battery ASR00007 TinyCircuits NA

D4,D5 12/250V0402TVS PGB1010402KR Littelfuse NA

C9,C4,C5,C8 4.7uF0402Capacitor C1005X5R1A475K050BC TDK NA

R18 100KΩ0402Resistor ESR01MZPF1003 ROHMSemiconductor NA

C7 18pF0402Capacitor C0402C180J5HACTU KEMET NA

R5,R6,R8,R9,R12,R15,R23,R24,R1,R2,R19

10KΩ0402Resistor SFR01MZPF1002 ROHMSemiconductor NA

C10,C3,C1,C2,C11,C12

100nF0402Capacitor 0402YC104KAT2A AVX NA

R20,R21 100Ω0402Capacitor CRGP0402F100R TEConnectivity NA

R11 140Ω0402Resistor ERJ-2RKF1400X Panasonic NA

R13 110Ω0402Resistor ERJ-2RKF1100X Panasonic NA

R3 200KΩ0402Resistor SFR01MZPF2003 ROHMSemiconductor NA

R7 1KΩ0402Resistor SFR01MZPF1001 ROHMSemiconductor NA

R10 4.7KΩ0402Resistor SFR01MZPF4701 ROHMSemiconductor NA

R4 909KΩ0402Resistor AC0402FR-07909K YAEGO NA

R14 340KΩ0402Resistor RC0402FR-07340KL YAEGO NA

R16 5.5V0603Varistor V5.5MLA0603LNR Littlefuse NA

C6 10uF0603Capacitor EMK107BBJ106MA-T TAIYOYUDEN NA

F1 1.5A0603Fuse ERB-RE1R50V Panasonic NA

RESET,GPIO0 2.5×3×1.2mmSMDSwitch B3U-1000P OmronElectronics NA

BAT 2-PosMicroJSTHeader BM02B-SRSS-TB(LF)(SN) JSTSalesAmerica NA

U1 ESP8266Module ESP-12F Ai-Thinker PCB,Semiconductor

USB SMDMicroUSBHeader 47346-0001 MOLEX NA

ALERT 6×6×4.3mmSMDSwitch LL3301NF065QG E-Switch NA

U2 USBtoUARTIC CP2104-F03-GM SILICONLABS PCB,Semiconductor

L2 2.2uHSMDInductor VLS252015ET-2R2M TDK NA

D3,D1,D2 3A,10VSchottkeyDiode BAT60AE6327 Infineon NA

Q4,Q5 SmallSignalBJT MMBT2222AWT3G OnSemiconductor NA

U3 BatteryChargingIC MCP73811T-420I/OT MICROCHIP PCB,Semiconductor

Q2,Q1 7.5A,20VN-ChannelFET BSL802SNH6327XTSA1 Infineon NA

LED Red/GreenLED HLMP-4000 Broadcom NA

U5 BuckConverterIC NCP1522BSNT1G ONSemiconductor PCB,Semiconductor

Q3 4.6/3.2A,20VFETPair DMC2053UVT-7 DiodesIncorporated NA

M1 90mA,3VPagerMotor 28821 Parallax NA

Ababei et al: Vibration Alert Bracelet for Notification of the Visually and Hearing Impaired Art. 4, page 11 of 11

From a research perspective, one could envision theVABunitasaplatformtoenablegaitresearch.Theunitcanbeequippedwithanaccelerometersensortocollectuser-specificgaitdatathatcouldbeusedto implementalerts to prevent falls. The study of gait could involvemany ideas developed with machine learning basedtechniques.AnotherresearchideaistouseWiFisignalstolocatetheuserwithinapredefinedspace,suchasanapartmentoranentirebuildingsimilarlytothestudyin[10].Thedesignandsecurityextensionsdescribedhereare not within the scope of this paper and are left tofuturework.

AcknowledgementsThe authors would like to thank the generous supportfromtheDept.ofElectricalandComputerEngineeringinthe OPUS College of Engineering,Marquette University.Thethoroughtechnicalfeedbackandeditingsuggestionsfromthereviewersandtheeditorimprovedthequalityofthispresentationsignificantly.

Funding InformationThisworkwasnotfundedthroughresearchgrants.

Competing InterestsTheauthorshavenocompetingintereststodeclare.

Author Contributions1. Hardwaredesign,3Dprintedenclosure,andwriting;

KelseyConley.2. Androiddevelopment,server-sidecoding,andwrit-

ing;AlexFoyer.3. Firmwaredevelopmentandwriting;PatrickHara.4. Hardwaredesign,soldering,andwriting;TomJanik.5. Hardwaredesign,PCBlayout,soldering,andwriting;

JasonReichard.6. Hardwaredesignandwriting;JonD’Souza.7. Co-advisingandsomewriting;ChandanaTamma.8. Advisingandwriting;CristinelAbabei.

References 1. World Health Organization (WHO). “Deafness

andhearingloss,”2018,[Online].Available:http://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss.

2. Mike Price.“The5BestHearingImpairedAlertDevices,”2018. [Online]. Available: https://www.rehabmart.com/post/the-5-best-hearing-impaired-alert-devices.

3. SARA, Situational Awareness and Response Assistant.2019.[Online].Available:http://www.sta-tussolutions.com/technologies/automated-alerting.

4. DIY Emergency Buttons for the Elderly. 2019.[Online]. Available: https://www.medicalalertadvice.com/resources/diy-emergency-buttons-for-the-elderly/.

5. Emergency Button for 7$, Arduino, WIFI and ESP8266. 2019. [Online]. Available: https://www.instructables.com/id/Emergency-Button/.

6. Singh, S andSingh, N. “InternetofThings(IoT):Securitychallenges,businessopportunities&referencearchitec-tureforE-commerce,”International Conference on Green Computing and Internet of Things (ICGCIoT),2015.DOI:https://doi.org/10.1109/ICGCIoT.2015.7380718

7. Yi, S, Qin, Zand Li, Q.“Securityandprivacyissuesoffogcomputing:Asurvey,”International Conference on Wireless Algorithms, Systems, and Applications,2015.

8. Mahmoud, R, Yousuf, T, Aloul, FandZualkernan, I. “Internetof things (IoT)security:Currentstatus,challengesandprospectivemeasures,”International Conference for Internet Technology and Secured Transactions (ICITST),2015.

9. Conti, M, Dehghantanha, A, Franke, K and Wat son, S. “InternetofThingssecurityandforensics:Challengesandopportunities,”Future Generation Com-puter Systems,vol.78,no.2,pp.544–546,Jan.2018.DOI:https://doi.org/10.1016/j.future.2017.07.060

10. Sapiezynski, P, Stopczynski, A, Gatej, R andLehmann, S. “TrackinghumanmobilityusingWiFisignals,” PLOS One, July 2015. DOI: https://doi.org/10.1371/journal.pone.0130824

How to cite this article: Conley, K, Foyer, A, Hara, P, Janik, T, Reichard, J, D’Souza, J, Tamma, C and Ababei, C. 2019. Vibration Alert Bracelet for Notification of the Visually and Hearing Impaired. Journal of Open Hardware, 3(1): 4, pp. 1–11, DOI: https://doi.org/10.5334/joh.17

Published: 02 October 2019

Copyright: © 2019 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. See http://creativecommons.org/licenses/by/4.0/.

OPEN ACCESS Journal of Open Hardware is a peer-reviewed open access journal published by Ubiquity Press.