TITLE
“BUS IDENTIFICATION SYSTEM
FOR VISION IMPAIRED”
Abstract
Many commercial products developed allow those with disabilities to substantially improve their quality of life.The use of these devices allows the user to experience the freedom of certain aspects of life such as mobility, communication and other fundamentaltasks. Examplesofsuchsolutionsincludecochlearimplants,prostheticlimbsand text-to-speechdevices. TheBEACONfollowsinthissamespirit,byprovidingvisuallyimpaired persons(VIPs)thefreedomtoindependentlycommuteviapublicbustransportation.
ThroughtheuseofBEACONtransmittersplacedonlocalbuses,VIPsareabletosafelycatch buses with the aid of a portable handheld device and an audio and tactile interface. The wireless communication system between the transmitter and the portable receiver can be achieved through a number of current technologies. With more exotic approaches like Bluetooth stillmaturing in termsof financialand performanceviability, thecheaperand more ubiquitousapproachofradiofrequencytechnologypointstowardsamorefeasiblesolutionthat canbeproducedatareasonablecostforeitherthedirectpurchasebyVIPsoragovernment subsidisedinitiative.
Withtheaidofthecurrentbustransportationsystem,theBEACONtransmitterisabletofilter existing vehicle identification information for retransmission to a nearby VIP. The BEACON receiveristhusabletoidentifybusesandtheircorrespondingroutes,andconsequentlyinform theVIPofthebus‘imminentarrival.
For the purposes of the BEACON prototype, communication is facilitated through FM transmissionsataround90MHz(withinthecommercialFMbroadcastrange). Inaddition,the solutionattemptstoresolvetheproblemthroughone-waycommunicationfrombustransmittertohandheldreceiver. Thisprojecthasthe potentialforvastimprovementbyimplementing a duplexcommunicationsystem,wherebythebusdriverisabletoidentifythepresenceofVIPs and vice versa. In this way, the process of catching a bus can be further streamlined for efficiency,convenienceandsafety.
Activites and goals
The proposed solution involves the development of a device which allows VIPs to detectthearrivalofparticularbuses. Toachievethis,eachbuswilltransmititsroute information, while a handheld receiver will be used to notifythe VIP through audio andtactileinterfaces.
Oncompletionofthisproject,VIPswillbeabletocatchpublicbuseswiththesame ease,convenienceandsafetyof theaveragecommuter. As visualcuesnolonger constrainthedistancerequiredtoidentifyabus,VIPswillbenefitfromtheadditional notificationtime. SuchasystemwilldirectlyinfluencethequalityoflifeofVIPs,by providingthefreedomtotravelindependently.
Thecompletescopeoftheprojectincludesthetasksofidentifying,catchingandde- boarding a bus; this thesis will only be involved in facilitating the communication required for bus identification
implementationOptions
StrategicOptionsforCommunication
In order to solve the problem in consideration, we must start with the user requirementofprovidingaudionotificationandthenworkbackwardsinanattemptto achievethedesiredoutcome. Thefivestagesofthedevelopmentprocessareshown
inFigure4-1.
It can be seen that the above situation involves the one-way transmission of data
frombustransmittertoVIPreceiver. Thisapproachhasbeenguidedbytheknown fact that BCC buses already transmit their details. However, this is not the only approachthatcanbetaken. Thethreeoptionsforcommunicationaredetailedbelow.
Stage1: Acquisitionof Bus Information
Stage2: Transmissionof Bus Information
Stage3: Receptionof Bus Information
Stage4: Processingof Bus Information
Stage5: AudioOutput for VIP Interaction
Figure4-1: StagesoftheActualDevelopment Process
Approach1: VIPCarriesaReceiverœBus Carriesa
Transmitter
¢Advantage: Anattractiveapproachifitispossibletoreceivethetransmitted
VITsignal.
¢Disadvantage: VIPswillneedtolocatethebusonceithasbeenidentified.
This becomes more difficult when there are multiple buses waiting at a commonbusstop.
Approach2: VIPCarriesaTransmitterœBusCarries
Receiver
¢Advantage: BusdriverswillknowifaVIPisinthevicinityandislookingto catch that particular bus. This approach solves the problem with multiple buses, as bus drivers can find a VIP even though a VIP cannot identify a particularbusfromagroupofpossiblebuses.
¢Disadvantage: VIPshavenoindicationofwhenandifthebusisarriving.
Approach3: VIP andBusCarryaTransceiver
¢Advantage: Inheritstheadvantagesandovercomesthedisadvantagesofthe firsttwoapproaches.
¢Disadvantage:Requires the development of two transceivers.This increasesthecostofproductionandmayaffectthefinancialfeasibilityofthe product. Italsosignificantlyincreasesthecomplexityoftheproject.
selectionofCommunicationApproach
Itcanbeseenthatthelastapproachinvolvingatransceiverpairwouldbethemost attractive option in terms of providing the best service to VIPs, whilst solving the
—multiple bus“ problem.Unfortunately, the development of such a product would require more time than is available for this particular project. The most suitable approachisthefirst,wherethebushasatransmitterandtheVIPhasareceiver. It provides better service to the VIP than the second approach, as the VIP is given someindicationofthearrivingbus.
Inallcommunicationapproaches,itcanbeseenthateitherthebusand/orVIPcarries
adevicewhichactsasabeacontotheother. Thesystemwillthereforebecalledthe
BEACONsystem.
Giventhechoiceof communicationapproach, itcan beseenthatthedevelopment stagesinFigure4-1stillapplies. Thisstructurecannowbeusedtoproducedifferent approachesforactualdevelopment.
VIT-Integration
stage1:AcquisitionofBusInformation
IfthesignaltransmittedbytheVITcanbereliablyreceivedbyaportabledeviceata distance of around 50 metres, then the acquisition and transmission stages willbe satisfiedinonefellswoop.
Stage2:TransmissionofBusInformation
Aspreviouslymentioned,thisparticularstagehasbeencoveredbytheVIT.
Stage3:ReceptionofBusInformation
ABEACONreceiverneedstobedevelopedwhichisabletoreceivethesignalthatis alreadybeingtransmitted. Detailsabouttheexistingtransmissionschemeisrequired.
Stage4:ProcessingofBusInformation
The received signal needs to be decoded according to the encoding method employedbytheexistingVIT. Thedecodedinformationmustthenbeprocessedfor audiooutputinthenextstage.
Stage5:AudioOutputforVIPInteraction
Oncethereceived signalhasbeendecoded,the datacan beusedto facilitate the audiointerface. Thisstageformsthescopeofaseparatethesisproject;hencethe designwillnotbeconsideredinthisreport. Tofacilitateautonomybetweenthetwo theses, a LCD displayor PC interface should be used to visually demonstrate the completionofStage4.
approach2: RetransmissionofInformation
Stage1:AcquisitionofBusInformation
If the VIT signal cannot be received, the data passed onto the VIT can still be intercepted through a RS-485 tap and processed for retransmission via a separate BEACONtransmitter.
Stage2:TransmissionofBusInformation
A BEACON transmitter needs to be developed which is able to send the bus informationtoaportablehandheldreceiver.
Stage3:ReceptionofBusInformation
A BEACON receiver needs to be designed in tandem with the newly designed transmitter.
Stage4:ProcessingofBusInformation
Thereceivedsignalneedstobeprocessedforaudiooutputinthenextstage.
VIT-IntegrationApproach
AnintegratedsystemusingbusVITsisahighlydesirablesolution. AstheBEACON receiver would be the only unit requiring development, the solution becomes technicallyandfinanciallyattractive. WiththeVITtransmittinga400kHzASKsignal
at4800baud,thereceivermusthavethefollowingattributes.
¢Asuitableantennatoreceivethesignal.
¢Afiltertosuppressunwantedsignals.
¢AnASKdecodertoconverttheanaloguedatatodigital.
¢Amicrocontrollertodecodethedigitaldata.
Figure5-1: DevelopmentBlocksfortheVIT-IntegrationApproach
AntennaFilterASKDecoderDataDecoder
During development, the success of each stage must be verified before the next
stagecanbeinvestigated. Thisparticularengineeringpracticeensuresthatproblems can be isolated and investigated without the influence of problems in other stages. Thedesignofeachdevelopmentblock(includingtestprocedures)isdiscussedbelow.
Stage1: AntennaDesign
ThemostcriticalstageintheVIT-IntegrationApproachinvolvesthereceptionofthe existing signal. The specifications in Chapter 3 indicated a maximum notification distanceof50metres.
Assumption:Itisassumed,fornow,thatthetimefromsignaltransmissiontoVIP notification is minimal.
ItisknownthattheVITshavebeendesignedtotransmittheirsignalviainduction. In fact,thesystemhasbeendesignedinsuchawaythatthetransmittedsignalcannot
bereceivedbyantennasinadjacentroadlanes;evenwiththetransmitterplaced20
feetabovetheroad.
It is possible that the VIT is also producing a propagated signal as a fringe effect. Althoughitishighlyunlikelythatthatthesignalcanbereceived50metresaway,the possilityiscertainlyworthinvestigating.
Figure5-2: Illustrationof ExistingVITSystem
RoadReceivers
SignalNot
DetectedIn
ThisLane
Signal
Detected
SignalNot
DetectedIn
ThisLane
BUS
TestProcedure: A loop antenna (eg. diameter of 8 cm, with an unwound length
equaltothesignal‘sfullwavelength)shouldbeusedtotestsignal reception with a spectrum analyser. If the VIT signal cannot be received bythe antenna, then the rest of the design for the VIT- Integrationapproachcanbeabandoned.
Stage2: FilterDesign
In order to extract the 400kHz signal from the entire collection of received transmissions,abandpassfiltermustbeconstructed. Asimpleconfigurationisthe seriesresonantcircuit;itreachesitsminimumimpedanceatresonanceandcanbe usedtoboostthevoltageofthe400kHzsignal.
Figure5-3: SeriesResonantCircuit
The quality factor (or simply the Q) determines the range and sharpness of the bandpassfilter,asseeninFigure5-4.
Figure5-4: FilterCharacteristicswitha VariedQFactor
Thevaluesfortheresistor(R),inductor(L)andcapacitor(C)determinetheresonant frequency(f)andtheQofthefilter. Thecalculationsareasfollows.
f =1
2pLC
Q=LC
RC
TestProcedure: Observe the frequency spectrum of the signal when a series
resonantfilterisconnectedtotheantenna. Ifthe400kHzsignalis clearly the dominant peak, then the next stage of design can be investigated.
Stage3: ASKDecoderDesign
ASK is presentationofdigitaldata. TheVIT transmitterusesavariationofASKcalledon-offkeying(OOK)..
ASK decoding can be achieved through the use of a simple diode detector. This
configurationworksbytakingananaloguesignal(representingalogiclevel),clipping thebottomhalftogenerateaDCsignal,andthensmoothingthetransitionswiththe helpofanRCfilter. Acomparatorcanthenbeusedtoachievethefixedvoltagefor theappropriatelogiclevel. Figure5-6illustratesthediodedetectorconfiguration.
Figure5-6: DiodeDetectorCircuit
Figure5-7showshowASKdatacanbeconvertedintodigitaldata. Thetopoutline
oftheASKdatashowstheoutputofthediodedetector. Thejaggedsignalcanbe passedthroughacomparatortoyieldthecorrespondingdigitaldata.
TestProcedure: Generatean400kHzASKsignalbyswitchingafunctiongenerator
onandoff. ConstructadiodedetectoranduseaCROtoobserve theoutputsignal. Ifthefixedvoltagelevelscorrespondtotheinput ASKsignal,thenthefinalstageofthedesigncanbeinvestigated.
Stage4: DataProcessorDesign
Thefinalstage of the VIT-Integration Approach involvesthe decoding of the digital data. Asthebusdetailsaretransmittedas8-bitASCIIcharacters,amicrocontroller needstobeusedtoconverttheincomingbitstream. Oncethedataisdecoded,it canthenbeusedtofeedtheaudiointerface. Themessageformatofthetransmitted signalcanbefoundinAppendixB.
TestProcedure: UseamicrocontrollertogenerateabitstreamrepresentingASCII characters. Receive the data through an input pin of another microcontroller and decode the received bit stream. If this is successful,thentheVIT-IntegrationApproachcanbeachieved.
RetransmissionApproach
If any of the stages in the VIT-Integration Approach cannot be achieved, then the entire transmitter-receiver communication link needs to be redesigned. Before the RetransmissionApproach canbe pursued, furtherresearchneedstobecompleted includingthegenerationofadditionalspecificationsandimplementationoptions.
SelectionofSignal Data Type
Thenextdecisiontobemadeisthetypeofsignalthatistobetransmitted. AudioDataTransmission
¢Advantage: Iftheaudiosignalbecomesdistorted,theinformationmaystillbe
understoodbytheVIP.
¢Disadvantage: Theaudiosignaltakestoolongtotransmit. Alsothesignal canbeeasilyinterceptedbyanyonelisteningatthatparticularfrequency.
DigitalDataTransmission
¢Advantage: Digitaldataisquickandeasytotransmit. Thegeneratedaudio
inthereceiverwillhavenodistortions.
¢Disadvantage:If a digital transmission is distorted, it is most likely unrecoverable. Anothertransmissionisthereforerequired.
Itcanbeseenthatdigitaldatatransmissionisthemoreattractiveoption,asittakes lesstimetotransmitthesignalandthegeneratedaudiowillbeperfectlyclear. The digital equivalent of FM is frequency shift keying (FSK), where bit levels are representedbytwodifferentfrequencies. Thelowerfrequencyiscalledthe—mark“, andthehigherfrequencyiscalledthe—space“. ThisisillustratedinFigure5-8.
DigitalData
FSK Data
Developement
ToachieveFSKcommunicationbetweenthetransmitterandreceiver,thefollowing developmentblocksarerequired.
¢Adataprocessortointerceptandfiltertheexistingbusinformation.
¢AnFSKencodertoconvertthedigitaldatatoanalogue.
¢AnFMtransmitterusedtomodulatethesignal.
¢Asuitableantennausedtotransmitthesignal.
¢Asuitableantennausedtoreceivethesignal.
¢AnFMreceiverusedtodemodulatethesignal.
¢AnFSKdecoderusedtoconverttheanaloguedatatodigital.
¢Adataprocessortodecodeandvalidatethedigitaldata.
Figure5-9: DevelopmentBlocksfortheRetransmissionApproach
dataocessorFSK EncoderFMTransmitterAntenna
Data ProcessorFSK DecoderFM ReceiverAntenna
Stage1: DataProcessorDesign(Transmitter)
AmicrocontrollerneedstobeusedtointerceptthedatabeingsenttotheVIT. Itcan
beseeninAppendixB,thatthereareatotalof19charactersthatarestoredinthe busVITs. Theonlyinformationthatisrequiredistheroutenumberandtheservice number,asthesetwovaluesprovideenoughinformationtoidentifytheroutethatthe bus follows and the direction the bus is travelling (inbound/outbound). If one characterisincludedforsynchronisation,thereareeightcharactersintotalthatneed
tobetransmitted.
¢3charœroutenumber
¢4charœservicenumber
¢1charœsynchronisation
Giventhatthereare8bitspercharacter(64bitsintotal),andthateachtransmission takes0.3seconds(asidentifiedinthepreliminaryspecifications),theminimumdata baudrateisapproximately215baud.
Astheelectronicbussystemisnotavailabletophysicallyinterceptthedata,thebus identificationmessagecanbeexplicitlystoredinamicrocontroller(asifithadbeen acquired).
TestProcedure: Use a microcontroller to hardcode the complete bus identification message. Extract the route and service numbers from the messageandconvertthedataintoasinglebitstream. Asatest, transmit a bit stream representing a square wave; use a CRO to checktheoutputofthemicrocontroller. Ifthisissuccessful,then thenextstageofdesigncanbeinvestigated.
Stage2: FSKEncoderDesign
InordertoconvertthedigitalbitstreamintoaFSKsignal,amicrocontrollercanbe used to generate the two square-wave frequencies. As the near-instantaneous transitionsofdigitaldatacannotbecorrectlyrepresentedbyaFourierSeries,square- wave frequencies cannot be used for frequency modulation. A simple RC configurationcanbeusedtosmooththetransitionsintoacurvedtrianglewave.
Figure5-10: RC SmoothingCircuit
TestProcedure: Use a microcontroller to convert logic levels to square waves of differentfrequencies. ConstructtheRCcircuit,showninFigure5-
10,andconnectittotheoutputofthemicrocontroller. Iftheoutput
resembles a triangle wave, then the next stage of design can be investigated.
Stage3: FM TransmitterAntennaDesign
TherearemanyFMtransmitterconfigurationswhichareusedinamateurkits. The basic structure of a three stage transmitter involves amplification, modulation and propagation of the signal. All three stages can be achieved with transistors. Amplificationisachievedusingavoltageamplifier,whilstmodulationisachievedby usingtheoutputoftheamplifiertochangethefrequencyofanLCoscillator. Thefinal stageinvolvesisolatingtheantennafromtheoscillatorinordertoimprovefrequency stabily.
Voltage LC
Amplifier oscillator anteena
TestProcedure: ReverseengineeranexistingaudioFMtransmitterkitbyreplacing
themicrophoneinputwiththeFSKencodeddata. Astheexisting transmitter kit will most likely operate in the commercial radio broadcastrange,anunoccupiedfrequencyrangemustbechosen. Construct a loop antenna, with the unwound length equal to the signal‘s full wavelength, and connect it to the output of the transmitter. Use a commercial radio receiver to receive the transmittedsignal;areceivershouldnotbeconstructedtotestthe transmitter as any encountered problems could be attributed to either the transmitter and/or receiver. In this way, the number of unknown variables is reduced and the task of problem solving becomes easier. Check the output of the receiver using a CRO connected to the receiver‘s earphone jack. If the received signal correspondstothetransmittedsignal,thenthenextstageofdesign canbeinvestigated.
Figure6-5: CircuitDiagramfortheOriginalFMTransmitterKit
Fromtheabovecircuitdiagram,itcanbeseenthattheinputisdrivenbyanelectret microphonethroughtheresistorR1. Theaudiosignalisthencoupledtoacommon emitter amplifier through an AC coupling capacitor. The voltage amplifier is self biasedthroughthefeedbackresistorR2; thepurposeoftheamplifieristoincrease the weak microphone signal (around 50mV to 100mV peak to peak). The second stageisaColpittsoscillatorwhichproducesthesinusoidsignal. L1,C4andC5are usedtogeneratethecarrierfrequency, whiletransistorQ2isusedtomodulatethe carrierwiththeaudiosignalreceivedthroughthetransistorbase. Theoutputsignal
of the modulator is AC coupled to a final transmitter stage which acts as a tuned collectorload. Thepurposeofthisstageistofilterthesignalfortransmissionandto isolate the antenna from the oscillator stage. This prevents instability of the modulator.
Stage4: FM ReceiverAntennaDesign
Demodulating FM signals issignificantlymorecomplicated thanFM modulation, as theprocessinvolvesrecognisingthedifferentfrequenciesinthesignalusingaphase lockloopconfiguration. MostFMreceiverkitsuseasingleICchipwhichachieves thedemodulationprocess;thisstageisusuallycascadedwithanaudioamplifierto driveanexternalspeaker.
TestProcedure: ConstructaFMreceiverkitandtesttheaudiooutputbytuninginto
a commercialradio station. Reverse engineer the receiver kit by removingtheaudiooutputstage. Thesameantennausedinthe transmittercanbeconstructedforthereceiver. Usethepreviously constructedBEACONtransmittertotestthereceivercircuit.
Stage5: FSKDecoderDesign
Decoding FSK signals also requires the precise recognition of the different frequencies. AsingleICchipcanbeusedtoperformtheFSKdecodingstage,with the data baud rate and the mark/space frequencies set by resistor and capacitor values.
TestProcedure: Construct the FSK decoding circuit using an appropriate IC chip.
Feed the signal from a function generator into the FSK chip and observe the output on a CRO. If the logic levels in the output correspondtothemarkandspacefrequencies,thenthefinalstage
ofdesigncanbeinvestigated.
Stage6: DataProcessorDesign(Receiver)
AmicrocontrollerneedstobeusedtoreceivethebitstreamfromtheFSKdecoder stage.The data can then be decoded into the required ASCII characters representing the route and services numbers. As this is the final stage in the RetransmissionApproach,aLCDdisplayorPCinterfacecanbeusedtodemonstrate thattheentiresystemoperatescorrectly.
TestProcedure: Use a microcontroller to poll the input pin that receives the FSK decodedbitstream. Convertthebitstreamintothecorresponding ASCIIcharactersandthenoutputtheinformationtoaLCDdisplay
orPCinterface.
DiscussionandConclusion
Theobjectiveoftheprojectwastoprovidevisionimpairedpersonswiththeabilityto safely and conveniently catch public buses. Through the use of transmitter and receiverdevices,communicationbetweenthebusesandVIPscouldbeestablished.
Uponreflectionof theprototype‘sdevelopmentaloutcomes,itcanbeseenthatthe project has made significant progress in terms of understanding and profiling the situation and the needs of VIPs. The resulting prototype was able to successfully demonstrate the concept of bus identification via a one-way communication link betweenaBEACONtransmitterandBEACONreceiver.
Throughananalysisoftheexperimentalresults,itcanbeseenthattheprototypehas many opportunities for improvement. These include the elimination of manual frequencytuning, thereductionof frequencydrift,andan improvementonthe data transmissionrate. Recommendationsforfurtherdevelopmentarecentredaroundthe prototypingofaduplexcommunicationlinkinvolvingatransceiverpair.
project would have contributed to the original goalofimprovingthequalityoflifeofthosewithvisionimpairments.