infrared remote control switch 405 Method Not Allowed

7/30/2019 infrared remote control switch 405 Method Not Allowed

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RemoteControlsRadioFrequencyorInfraredWhitepaperbyMartinGotschlich,InfineonTechnologiesAG,2010

ContentRemoteControlsRadioFrequencyorInfrared....................................................................................1

Introduction.............................................................................................................................................

2

JointAspectsofIR andRFRemoteControls..........................................................................................2

IRdatacommunication...........................................................................................................................3

IRprotocols.............................................................................................................................................5

RFdatacommunication..........................................................................................................................8

BidirectionalRFRemoteControls......................................................................................................9

RFprotocols...........................................................................................................................................10

DifferencesbetweenIRandRF.............................................................................................................11

ThingstobeaddedgoingfromIRtoRF................................................................................................12

Receiver

wake

up

..............................................................................................................................

12

Synchronizationofreceiverwithincomingdataclock......................................................................13

Coding................................................................................................................................................13

UniqueIDandPairing........................................................................................................................13

RF2irExampleRFtoIRconverter.......................................................................................................15

RF2ir RoomforImprovement.........................................................................................................17

SummaryandConclusion......................................................................................................................18

Links.......................................................................................................................................................18

IRRemoteControls...........................................................................................................................18

RFtransmittersandreceivers...........................................................................................................18

RF2ir...................................................................................................................................................18


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IntroductionDoyourememberthosetimeswhenyouneededtostandupandsteptoyourtelevisionsetto

changechannelsortunethevolume?Orareyouyoungenoughandalreadygrownupwithan

infraredremotecontrolinyourhands?Nodoubt,thecomfortprovidedbyremotecontrolsis

essentialinoureverydaylife.Infrared(IR)remotecontrolshaveprovenbeingacostefficientsolution

forcontrollingmanykindsofelectronicdevices:Homeentertainment,aircondition,homelighting.

Buttherearesomelimitationsanddisadvantagesusinginfraredlightasthemedium.Duringrecent

yearsthereisastrongtrendtowardsradiofrequency(RF)remotecontrols.Deliveringevenmore

comfortfortheuser,thebillofmaterialscouldbeshrunktoacompetitivelevelandnowbeing

competitivewithIR.

InthispaperyouwillreadaboutthedifferencesbetweenIRandRFremotecontrolsnotonlyfrom

theusersviewbutalsofromtheengineersviewwhohastodesignsuchremotecontrolsystems.

JointAspects

of

IR

and

RF

Remote

Controls

Theremotecontrolleritself,alsocalledtransmitter,isamobiledeviceandhastoprovidegood

usabilityinhumanshand.Theonlyreasonablepowersourceisbatteries.Regardlessofusing

disposalorrechargeablebatteries,AAcell,AAAcell,9VPP3blockorbuttoncellbatteries,minimum

powerconsumptionisoneofthemostimportantrequirements.Notonlytheactivemodesupply

currentdirectlyfollowingabuttonpressisofinterest(upto500mApeakcurrentinIRemitting

diodes).Evenmorechallengingisalowidlecurrentduringtimeswhennobuttonispressed.

Theactivecurrentisbasicallydefinedbytheoutputpowerofthetransmitterandthedurationof

sucharemotecommand.DifferentprotocolsforIRandRFareestablished,someofthemare

standardsoratleastdefactostandards.Allofthemshowadifferentnumberofinformationbits,

differentmodulationandcoding,anddifferentdatarates.Whilesingleeventcommandsarerather

short(e.g.poweronorchannelup)therearealsotuningcommandswhereabuttonishelddown

foralongerperiod(e.g.volumeup).Whenselectingordefiningsuchaprotocoltheengineerhasto

findatradeofftakingthefollowingparametersintoaccount:

Bitlengthofcommanddataframe:Thelowerthenumberofbitsinaframe,thelowertheenergyconsumption.Ontheotherhand,longerframesallowlongersynchronization

patternsandmorepayloadinformationcontent.

Bitrate:Higherbitratesresultinshorterdurationoftransmission.Ontheotherhand,higherbitratesrequirefasterreceiverhardwareandhigherbandwidthforradioremotecontrols.

Reliability:Stabilityofthelinkmaybeincreasedbyadditionalerrordetectionbitsinthedataframe(e.g.CRC).

Receiverarchitecture:Dependingonthereceiverandmodulationconcept,theprotocolpossiblymustbyfreeofDCcomponents(seeManchesterCoding)andmustprovidea

suitableruninsequencegivingthereceiverthechancetoadapttochangingmedia

conditions.


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Thepowerdowncurrentisdefinedbythemicrocontrollerdesignwaitingforawakeuptriggeredby

abuttonpress.Highendremotecontrollersmayofferadditionalfeatureswhichfurthercontribute

totheoverallpowerconsumption:Illuminationofthepushbuttons,LCDs,selflearningfeaturesand

manymore.

Oneinteresting

topic

is

the

need

for

security.

Depending

on

the

application

there

may

be

the

requirementforasecurelinktoavoidmisuseofthecontrolleddevice(e.g.remotekeylessentryfor

automotiveorgaragedooropeners).Suitableencryptionalgorithms(e.g.AES,XTEA,..)and rolling

codemechanismschangingthetransmittedbitpatterneachbuttonpressarecommonlyusedfor

securityrelevantremotecontrollers.Theexchangeofencryptionkeysintroducessomeadditional

complexitytothesecuresystem.Furthermore,encryptionanddecryptionareconsumingadditional

powerregardlessofbeingimplementedinahardwareengineorinmicrocontrollerfirmware.

Incontrasttothemobileremotecontroller,thecontrolleddevice(e.g.TVset)istypicallymains

supplied.Butthisfactdoesnotrelaxthedemandforlowestpowerconsumption.Beingreadyto

receivecommands

at

any

time

during

stand

by

(waiting

for

power

on

command)

this

is

an

essential

contributortotheelectricalenergyconsumptioninhouseholds.Thiswasteofenergyisnotcaused

bythereceivercircuititselfbutmainlybybadefficiencyofpowersuppliesespeciallywhenoperated

atcurrentconsumptionmuchlowerthanitsnominalvaluesrequiredforpoweronoperation.The

EuropeanUnionhasissuedregulationslimitingthestandbypowerconsumptionofelectrical

equipmentto2Watt(1Wattfrom2014onwards).

IRdatacommunicationInfraredremotecontrolsuseinvisiblelightpulsesbelowthevisiblewavelengthspectrum(approx.

950nm).In

terms

of

its

radiation

behavior

it

is

like

any

other

visible

source

of

light:

There

must

be

a

lineofsightbetweenthetransmitter(lightsource)andthereceiver(lightdetector).Anyobstacles

betweentransmitterandreceiverwillpreventfromcorrectreception.Undergoodconditions

scatteredlightorlightreflectedfromwallsmaykeepthesystemworking.Havingwallsbetweenthe

remotecontrollerandthereceivingdevicewilldefinitelydisabletheremotecontrol.Thisobvious

disadvantageofIRremotecontrolssimplifiestheprotocolatthesametime.Allremotecontrolsfor

thesamedevicemodelmayuseidenticalcoding.Thereisnoneedforexplicitpairingbetween

transmitterandreceiverwithdedicateduniquecodesasthedifferentiationisguaranteedbyoptical

separationofidenticaldevices.

Practicallythere

is

no

legal

regulation

of

the

maximum

emitted

light

power.

This

is

more

limited

by

powerconsumption(batterylifetime)andrange.Upto10metersisthetypicalrangeofinfrared

remotecontrolsassumingperfectconditions(controllerphysicallyorientedtowardsthereceiver,no

obstacles,andnodisturbanceofotherlightsources).Tomaketheinfraredconnectionmorerobust

againstanyotherinfraredlightsources(e.g.electronicballastsoffluorescentlamps)theremote

controlsignalisonoffpulsedatafrequencyofapprox.38kHz.Thedatainformationismodulated

onthis38kHzcarrierusingonoffkeying.Thebitinformationisrepresentedwithpulsedistance

codingorBiPhase(Manchester)coding.

Theadvantagesofinfraredremotesystemsareobvious:Withaverylowbillofmaterialsonboth,

thetransmitter

and

receiver

side,

they

are

widely

used

in

many

lowest

cost

applications.

On


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transmitsidethereisjusttheneedforaverysimplemicrocontroller.Thenumberofrequiredinput

andoutputpinsisbasicallydefinedbythenumberofbuttonsonthecontroller.TheIRLEDissimply

connectedtooneoftheoutputpinsofthemicrocontrollerdirectlyor insomecasesdrivenbyan

additionaltransistorstage.Asatimebaseacrystalisratheroverengineered;mostdesignsrelyona

cheapceramicresonatororevenaRCoscillatorwithratherpoorfrequencystability(upto+/5%

maybetoleratedbythereceiver).Disposalbatteriesarethefirstchoiceforthepowersupply.Asthe

dimensionsoftheremotecontrollercasearemainlydefinedbythenumberofbuttonsand

ergonomicaspectsthereisenoughspaceforcheapestAA orAAAcells.

Figure1:Blockdiagramofatypicalinfraredremotecontroller

Onthereceivesidethebillofmaterialsisbasicallydefinedbytheinfraredsensitivetransistor.

Today,manydesignsuseanintegratedinfraredreceivercomponentwhichnotonlyincludestheIR

transistorbutalsoademodulatorandanautomaticgaincircuit(e.g.TSOP1838,TSOP11xx,SFH506,

SFH5110).

Its

output

is

already

adigital

signal

with

clean

edges

for

easy

protocol

handling

by

a

microcontroller. Asthedatarateoninfraredisratherlow(approximately500to1000bitper

second)amicrocontrollerwhichisanywayinthereceivingdevicemayhandletheIRreceptionasa

sidetaskbysimplymeasuringthetimedistancebetweenedgesusingatimer.Therealdesign

challengeisthepowersupplyconceptsincetheremotecontrolreceivermustremainactiveevenin

standbymodeofthesystem.


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IRprotocolsMostIRprotocolscontainthefollowinginformation:Adeviceaddresswhichisthesameforall

devicesofthesamemodeltypeandacommand(e.g.volumeup).Simplestrategiesimprovingthe

linkrobustnessarecommonlyused:Forexampleresendingofthesamebitpatterninaninverse

manner.Comparingthepayloadreceivedindifferentversionsenablesthereceiverdetectingerrors

inthereceivedbitstream.Suchframesaresimplyignored.SomeextendedfeaturesinIRprotocols

are:

Togglebitschangingtheirstatewitheachbuttonpressenablingthereceivertodistinguishcontinuousbuttonpressesfromrepresseseasily.

Batterydownbits:Assoonasthebatterycharginglevelofthetransmitterfallsunderacertainthresholdthisbitwillbeset.Thereceiverwillsignalizethistotheuserwhohasthe

chancetochangebatteriesbeforeasuddenbreakdown.

MostIRprotocolsuseoneofthefollowingmodulationtechniquesrepresentingone andzerobits

onthe38kHzcarrier:

Pulsedistancecoding:Thebitinformationisrepresentedinthedistanceofedges.Typically,thiscodingisnotfreeofDCcomponents.ButthisisnorealissueforIRreceivers.Itisrather

simpletodecodetheinformationinthereceiversmicrocontrollerbymeasuringthepulse

durationsusingatimer.

Manchestercoding:TheadvantageofManchesterCodingisthatitisfreeofDCcomponents.This

enables

receivers

to

perfectly

adjust

the

decision

threshold

between

incoming

high

and

lowlevels.Decodingisslightlymoredifficultinthereceiversmicrocontrollersincethe

directionoftheedgeinthemiddleofeachdatabithastobedetected(risingorfalling).

Findbelowthetimingdiagramsoftwotypicalinfraredprotocols.TheRC5protocolwasinitially

definedbyPhilipsandSIRCwasintroducedbySony.Botharewidelyusedforhomeentertainment

equipmenttoday.


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Figure2:PhilipsRC5infraredprotocol

Figure3:SonySIRCinfraredprotocol(12bitversion)


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Thesetwoprotocolexamples,RC5andSIRCdemonstratethetypicaldifferencesbetweencommon

IRprotocols.WhileRC5isusingManchesterCoding,SIRCisusingPulseDistancecoding.RC5

transmitsmostsignificantbits(MSBs)first;SIRCLSBsfirst.SIRCisusingareservedstartbitsymbol

foreasieridentificationofframestartbythereceiver.RC5providesatogglebitwhichenablesthe

receiverdistinguishingrepetitivebuttonpressesfromcontinuousbuttonpresses.Witheachnew

buttonpressthestateofthetogglebitwillbesimplyreversed.

AgoodsourceforfindingmoreinformationaboutinfraredprotocolsistheLinuxInfraredRemote

Controlproject(LIRC):http://www.lirc.org.LIRCdefinesadescriptionformatforallkindsofinfrared

protocols.Actually,theformatsofallIRprotocolsonthemarketcanbefoundontheinternetin

LIRCconfigfilerepresentation(seehttp://lirc.sourceforge.net/remotes).


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RFdatacommunicationRadiofrequencycommunicationuseselectromagneticwavesastransmissionmedium.Their

propagationpropertiesallowconnectionsofextremelyhighdistances.Electromagneticwavespass

throughnonshieldingmaterialstosomeextent(e.g.concretewalls).Thisattractivenessdemands

somelimitationenforcedbyworldwideregulationsdefinedbystandardizationgroups(e.g.ETSI,

FCC,).Forallregionsoftheworldthereexistbindingregulationscoveringfollowingaspects:

Frequencybands(spectrum) Maximalpowerofemittedradiowaves Bandwidthofemittedsignal Durationofemissions(dutycycle) Purposeofemission(e.g.TVbroadcast,mobilephonenetworks,authorityscommunication,

generalpurpose)

LicensefeesForremotecontrolapplicationstherearesomelicensefreebandsavailable,thesocalledISMbands

(industrial,scientificandmedicalbands).ForRegion1(Europe,Africa,formerSovietUnion)themost

attractivefrequencybandisat434MHz,forNorthandSouthAmericaat902928MHz.

Additionally,inEuropetheSRDband(shortrangedeviceband)at868MHzandintheUSthe

frequencybandat315MHziscommonlyusedforremotecontrols.Analternativewithworldwide

compatibilityisISMbandat2.4GHz.Unfortunately2.4GHzrequireshigherpowerconsumptionat

comparablerangeandthereforehighercost.Practically,RFremotecontrolsuse315,434or868MHz

asRFcarrierfrequency.

ThepayloaddataneedstobemodulatedontheRFcarrier.Basically,therearetworathersimple

modulationtechniquespopular:AmplitudeShiftKeying(ASK)andFrequencyShiftKeying(FSK).For

powerconsumptionreasons,ASKismostlyimplementedasOnOffKeying(OOK).Thatmeans,the

carrierissimplyturnedonandoff(asthisisdoneforinfraredcommunicationdescribedabove).

Transmittersforbothtechniques,OOKandFSK,maybeimplementedasClassCpoweramplifiers

resultinginhighpowerefficiency.WithOOKthereisnoneedtochangethecarrierfrequencyatall.

Inthiscase,SAWbasedtransmittersarethefirstchoiceifsomefrequencytoleranceisaccepted.

UsingcrystalstabilizedPLLsynthesizersallowhigheroutputpowerastheydonotneedanysafety

marginsintermsoftheregulationslimits.ForFSK,SAWbasedtransmittersmaybeusedonlywith

somelimitationsandtricksastheoutputfrequencymustalternatecontinuously.Therefore,FSKis

preferablyimplementedwithPLLsynthesizerswhichallowexactgenerationofbothfrequenciesby

digitallyswitchingthedividerfactorofthePLL.Generally,FSKprovidesbetterrobustnessagainst

disturbersatthepriceofhigherhardwarecomplexityandslightlyincreasedpowerconsumption.

Someknowhowandeffortmustbespentforthedesignoftheantennaitselfandthematching

networkbetweenantennaandTx orRxIC.Modernsoftwaretoolssimplifythedesignerslifein

doingthisimportantdesignstep.Thechallengeisfindinganantennadesignorconceptwhich


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representsaperfectcompromisebetweencostandperformance.Furthermore,acleanRFdesignis

essentialformeetingtheradioregulations.

BidirectionalRFRemoteControls

HighendremotecontrolsmaybebasedonbidirectionalRFlinks.Inadditiontothelinkfromthe

remotecontrollertothecontrolleddevicethereisanadditionallinksbackwardsfromthedeviceto

thecontroller.Thisbackwardslinkmaybeusedforseveralpurposes:

Securingtherobustnessoftheremotelinkbyusinghandshakeprotocols:Thecontrolleriswaitingforapositiveacknowledgethatthecommandwassuccessfullyreceived.Otherwise,

itwillstartanewtransmissionattempt(maybewithhigheroutputpoweroronadifferent

RFchannel).

Givingfeedbacktotheuser:Adisplayontheremotecontrollermayvisualizeinformationfromthecontrolleddevice(e.g.devicestatus).Thismaybeofspecialattractivenesswhen

thereis

no

line

of

sight

between

the

user

and

the

remote

controlled

device.

BidirectionalRFlinksareimplementedusingsocalledRFtransceiverICswhichincludeanRFreceiver

andRFtransmittersharingonesinglePLLandusingonesingleantenna.InfineonsTDA7255Visa

typicalexampleofsuchaRFtransceiverIC:http://www.infineon.com/TDA7255V.


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RFprotocolsBasically,RFremotecontrolprotocolshavetorepresentthesameinformationasIRremotecontrol

protocols:Deviceaddressandcommand.But,communicationviaRFdemandssomeadditional

measures(seechapterThingstobeaddedgoingfromIRtoRFbelow).Thepowerconsumptionofa

RFtransmitterisnotashighasofanIRLEDandmaximumdataratesofaRFlinkarehigherresulting

inframeswithshorterduration.Asaconsequence,frameswithahighernumberofbitsandmore

informationcontentarepossibleusingRFwhilesavingbatterylifetimeatthesametime.Thisfact

enablessomemorefancyfeaturesforRFremotecontrols.

EachRFremotecontrolrequiresauniqueID.ThismaybecomparedwiththedeviceaddressofIR

remotes.TheonlydifferenceisthatIRusesthesameaddressforthewholeseriesofdevicesofthe

samemodeltypewhereasRFremotesuserealuniqueIDsmeaningthateachtransmitterworldwide

hasanotherID.Therefore,thebitlengthreservedforRFIDsislonger(e.g.3240bit).

Asmentioned

above

some

IR

protocols

provide

atoggle

bit

for

identification

of

successive

button

presses.SomeRFprotocolsevenimplementacountersignalizinghowoftenabuttonwaspressed

repeatedly.

ForimprovedrobustnessoftheRFlinkCRCvalues(cyclicredundancycheck)areoftengeneratedand

transmittedaspartoftheframe(e.g.8bit).Thereceivermayclearlyidentifyanybiterrorsby

recalculatingtheCRCvalueofthereceiveddataframeandcomparingitwiththeonegenerated

beforetransmission.

Thetransmittersbatterycharginglevelmaybesignalizednotonlybyasinglebit(batterylowbit)but

evenwith

acomplete

4bit

or

8bit

data

field

representing

the

measured

battery

voltage.

Additionalsecuritymaybeintroducedbyrollingcodeschangingsomebitswitheachbuttonpress

(e.g.simple16bitcounter)andencryptionofthecompleteoratleastapartofthepayload(e.g.AES

orXTEA).

FindbelowatypicalexampleofRFremotecontrolprotocolasimplementedinInfineonsPMAfob

applicationexample(seehttp://www.infineon.com/PMAfob):


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Figure4:PMAfobRFremotecontrolprotocol(XTEAencryptionmode)

DifferencesbetweenIRandRFFollowingtablesummarizesthegeneraldifferencesbetweenIRandRFremotecontrols:

Infrared RadioFrequency

Powerconsumption

transmitter(activeduring

transmit)

20150mA(sometimesupto

500mApeak)dependingon

numberof

LEDs

and

range

520mA

Powerconsumption

transmitter(standby)Dependingonmicrocontrolleridlecurrent(


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BitlengthofframeRestrictedbybatterylifetime

(typicallymax.40bitperframe)

Typically,80140bitpossible.

Forextendedfeatureslike

security,robustnessand

additionalstatusinformation

(e.g.batteryvoltagestatus).

Datarate Typ.500bit/s1kbit/s Upto100kbit/s

Regulation Nolimitations

Regulatedinworldwide

standards(ETSI,FCC,).

Needforcompliancetests.

Expecteddesigneffort Low

Low(usingRFmodules),higher

whenimplementingoptimized

antennaandmatching

ThingstobeaddedgoingfromIRtoRFThemanifoldadvantagesofRFoverIRmotivateengineerstoconvertexistingremotecontrol

systemsfromIRtoRF.

ReplacinganIRLEDbyaRFtransmitter(module)andanIRreceiverbyaRFreceiver(module)is

notabigdeal.Behindthissimplesentencethereissomeconsiderabledesigneffortbehind.While

theIR

hardware

is

rather

simple

(an

IR

diode

as

transmitter

and

an

integrated

IR

receiver

component

withadigitaloutputsignalasareceiver),RFhardwareismorecomplex.Asimplesolutionmaybe

theuseofRFmoduleswhichcompriseallnecessarycomponentsonasmallPCB.Theoptimal

solutionisadedicatedtransmitterandreceiverdesign.Thisgivesthechancetousespecificantenna

designsandasuitableantennamatchingdesign.

Anyway,inmanycasestheeffortshallbeaslowaspossibleandthechangesontransmitterand

receiversideshallinterferewiththerestofthesystemtoaminimalextentonly.Thenaiveideato

keeptheIRprotocolbasicallyunchangedandtomodulatethesamedataframeonaRFcarrier

seemsbeingasmartsolution.Unfortunately,thiswillnotworkforthefollowingreasons:

Receiverwakeup

Asmentionedabove,lowstandbypowerconsumptionofthereceiverisanessentialrequirement.

WhileanIRreceivermayremainpoweredatconsiderablelowconsumption(approx.1mA),anRF

receiverisconsuming5mAorevenmore.Toovercomethisissueasuitablepollingschememaybe

applied.Duringpollingthereceiverisswitchedonforashorttimeperiodtocheckwhetherthereisa

validsignalavailable.Ifnot,thereceiverfallsbackinpowerdownmodeimmediately.Dependingon

thepollingintervalasuitableRFprotocolhastobedesigned.Afterpressingabuttonontheremote

controllerapredefinedruninsequencebeinglongenoughmustbesentgivingthereceiverthe

chancetowakeupaftertheendofthepollinginterval.


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Synchronizationofreceiverwithincomingdataclock

Infraredprotocolsareveryrobustintermsoftimingaccuracy.Evenwithconsiderablehighclock

instabilitiesitispossibletodistinguishzero andonebits.RFcommunicationismuchmoresensitive

onclockerrors.Therefore,thereceiverhastomeasuretheincomingdataframeclockbeforestarting

payloaddecoding.

Long

enough

preamble

(run

in

and

sync

patterns)

with

fixed

content

(e.g.

0000001)intheprotocolenabletheRFreceivertosynchronizewiththeincomingsignalsclock.

Coding

Infraredcommunicationisratherrobustagainstdisturbers(e.g.sunlight)usinga38kHzonoff

modulation.Incontrast,RFismuchmoresensitivetonoise.Therefore,RFreceiversautomatically

adjusttheirzeroonedecisionthreshold(dataslicer)basedontheincomingdatasignal.Inorderto

haveawellpositioneddecisionlevel,zero andonebitsmustbedeployedinabalancedoccurrence.

ThisisimplementedbycodingtheactualpayloadwithcodesbeingfreeofDCcomponents.Oneof

thecommonlyusedcodesforthispurposeisManchestercodingwhichrepresentseachbitofthe

payloadwithtwoconsecutiveunequalchips.Theactualbitinformationisrepresentedbythecenter

edgeinthemiddleofthetwochips. Arisingedgerelatestoaonebitafallingedgerelatestoazero

bit(orviceversa).

Figure5:

Manchester

Coding

(DC

free)

OnedisadvantageofManchestercodingisobvious:Actually,thenumberofbitsonthechannel

(calledchips)istwiceashightheninthepayloadaseachpayloadbitisrepresentedbytwochips.

Thatmeansthattheactualbitrateandbandwidthrequirementsaretwiceashighasforuncoded

data.

UniqueIDandPairing

AsIRcommunicationisrestrictedonalineofsightbetweentransmitterandreceiverthereislowrisk

thatidenticalsystemsintheneighborhoodareinfluencedunintentionally.Allmodelsofagiven

equipmenttype

are

using

the

same

identification

and

their

remote

controllers

are

exchangeable.

In

thissensethehigherrangeofradioremotecontrolsgoingeventhroughwallsturnsoutbeingkindof

aproblem.Thereishighprobabilitythatsomebodycontrolstheequipmentinanearbyroomwithout

intention.Asasolutiontothisproblem,RFtransmitterandRFreceiverhavetobepairedusinga

uniquecodeembeddedinthedataframe.Usually,eachRFtransmitterprovidesahardcodedunique

identifier.Thereceiverhastobepairedtoeachoftheassignedtransmittersduringapairing

procedurewherethereceiverlearnstheuniqueIDofagiventransmitter.Typically,thepairing

processisintroducedbypressingadedicatedbuttononthereceiverunit.ThenextreceivedIDwill

beaddedtothelistofpaireddevices.Innormaloperationthereceiverwillacceptonlydataframes

withIDcodesbeinglearnedduringpairingprocedurebefore.Allotherframeswithmismatching


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codesaresimplyignored.Asaconsequence,thereceiverrequiresnonvolatilememory(e.g.

EEPROM,Flash,)tokeepthepairinglistevenduringpowerdown.


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RF2irExampleRFtoIRconverterFollowingdesignexamplenamedRF2irperfectlyillustratesthedifferencesbetweenIRandRF

remotecontrolsystems.

Figure6:RF2irblockdiagram

Itrepresentsaconverterbetweenthetwoworlds:ReceivingRFcommandsandtransmittingrelated

IRcommands.OntheRFsideitiscompatiblewithInfineonsPMAfobremotecontroller.More

informationaboutthiskeyfobdesign,itsinternalhardwarebasedontheSmartLEWISMCU

PMA5105,thefirmwareandtheprotocolisavailablehere:http://www.infineon.com/PMAfob

Figure7:

PMAfob

fotos

of

housing

and

PCB

ForthisRFtoIRconverterthereisnotanyspecialencryptionforthedataframeimplementedasthis

isnotrequiredfortypicalhomeentertainmentsystems.InfineonsnewTDA7210Vsuperhetreceiver

demodulatestheincomingRFcommands.Thisrobustreceiverprovidesexcellentperformance

(sensitivityupto 118dBm),doesnotrequireanydigitalregisterconfigurationandisperfectlysuited

forconsumerapplicationswithitslowsizeVQFNpackage.MoreinformationabouttheTDA7210Vis

availablehere:http://www.infineon.com/TDA7210V


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AnAtmelAVRATtiny44microcontrollerisusedtoreconstructthereceivedRFdataframe(clock

recovery,datasliceranddecoder),extracttheremotecontrolcommandandtobuildupanIRdata

framewithanequivalentcommandforbeingsentoutviaIR.TheAVRseriesiswellknowninthe

worldwideembeddedsystemscommunity.Powerfulsoftwaredevelopmenttoolsareavailablefor

free.ThefirmwareforthisdesignexamplewasdevelopedusingAtmelsAVRStudio4withGNUs

avrgcccompiler.AllsoftwareusedanddevelopedfortheRFtoIRconverterisfreeunderGNU

GeneralPublicLicense.

OntheRFsidetheRF2irfirmwareincludesaveryrobustandconfigurablealgorithmwhich

implementsthefollowingtasks:

RFcarrierdetection Clockrecoveryandsynchronization Manchesterdecodingofpayloaddata Payloadbitframeextraction

TheRFreceivealgorithmispurelybasedontimedistancemeasurementsbetweenedgesofthe

receiveddigitalsignalusinga16bittimerofthemicrocontroller.

OntheIRsidetheconverteremitscommandswhichcanbechosenoutofabroadvarietyof

protocolsdefinedbyvariousmanufacturers.AcomprehensivesoftwarelibraryforIRtransmission

waspublishedbyFrankMeyerundertheGNUGeneralPublicLicenseandisreusedfortheRFtoIR

converter.ThehomepageoftheIRSNDprojectislocatedhere:

http://www.mikrocontroller.net/articles/IRMP#SourceCode_IRSND(Germanonly).

ThisRF2ir

firmware

was

implemented

and

verified

using

ageneric

ATmega

16

evaluation

board

connectedtoaTDA7210Vevaluationboard.Withminimalchangesitwillbecompatibletothe

ATtiny44asproposedabove. ThesourcecodeispublishedundertheGNUGeneralPublicLicense

availablefordownload:http://www.infineon.com/RF2ir.

Followingmicrocontrollerfeaturesareutilized:

8bittimerforgenerationofthe38kHzinfraredcarrier 16bittimerfortimedistancemeasurementsbetweenedgesofthereceivedRFdatasignal

andalternativelyas10kHzclockforgenerationoftheIRdataframeoutput

Themicrocontrollersoscillatorwithan8MHzcrystalprovidetheclocksource.DependingontheconfiguredIRprotocol,theRF2irfirmwareexamplerequiresacodesizeof

approximately3300bytesandusesabout110bytesofrandomaccessmemory.


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RF2ir RoomforImprovement

FocusduringdevelopmentoftheRF2irdesignwastheillustrationofdifferencesbetweenRFandIR.

Ifitcomestoamoreproductfocuseddesignthereshouldbesomeoptimizationtakeninto

consideration:

TheRF2irexampleusestwoseparatedcrystaloscillatorsfortheTDA7210Vreceiverandthe

microcontroller.FortheTDA7210Vtheclockaccuracyandstabilityofacrystalisabsolutely

mandatorybutforthemicrocontrolleraninternalRCoscillatormaybesufficient.Unfortunately,

thereisnowaytoderiveamicrocontrollerclockfromtheRFreceiversoscillator.

TheinfraredLEDisdirectlyconnectedtooneofthemicrocontrollersgeneralpurposeIOpins.The

availablecurrentissufficientforshortdistancesofafewmeters.Butforamorepowerfullight

sourceandawiderrangeadriverstage(onetransistor)fortheLEDisrecommended.

Intheexistingdesigntherewasnofocusonpowerconsumption.Oneideamaybeadaptingthe

designtotherequirementsofabatterypowersource.ThatmeansmakinguseoftheTDA7210V

powerdownmodeandapollingstrategytowakeupandsynchronizetheconverterjustintime

beforethepayloaddataiscomingin.ForsuchapollingschemeanadaptationoftheRFprotocoland

theruninsequenceshouldbetakenintoconsideration.

InthisinitialversionofRF2irtheuniqueidentifierofthetransmitterisnotevaluated.Thereceiver

reactsonanyreceivedframesignoringthetransmittersidentificationcode.Inaproductiveversiona

pairingfunctionneedstobeaddedandnonassignedIDcodeshavetobeignored.

ThebasicimplementationofRF2irdoesnotcareaboutimprovedcommunicationrobustnessand

security.A

better

version

of

RF2ir

may

check

the

consistency

of

the

8bit

CRC

transmitted

by

the

PMAfobtransmitterembeddedinthedataframebydefault.Furthermore,encryptionofthe

communicatedpackage(e.g.AES)andarollingcodemaypreventfrommisuse.


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SummaryandConclusionRFremotecontrolsprovidemultipleadvantagesfortheusercomparedtoIRremotes.Most

importantistheRFrangesincetheradiosignalsevenpassconcretewalls.Thereisnoneedforthe

usertotargetatthereceiver.HighrobustnessofRFlinksresultinincreasedusabilityandcomfort.

OntopofthatRFcommunicationenablesthedesignertoimplementnewfeaturesandsecurity.

LowerpowerconsumptionforRFtransmitterallowsforsmallerbatterieswhichdonthavetobe

replacedformanyyearsofuse.

DesigneffortandbillofmaterialsforRFremotecontrolsisalreadyintherangeofIRremotessince

integratedtransmitter andreceiverICssimplifytheschematicatoptimalperformance.

Comprehensivedocumentation,toolingandexampledesignsreducethedesignineffort,especially

whenusingcomponentsfromInfineonTechnologies.

Links

IRRemoteControls

Collectionofwwwlinksaboutinfraredremotecontrol:

http://www.epanorama.net/links/irremote.html

LinuxInfraredRemoteControlproject(LIRC):

http://www.lirc.org

LIRCconfigfilesofmanydevices:

http://lirc.sourceforge.net/remotes

RFtransmittersandreceivers

GeneraloverviewofInfineonsWirelessControlproductportfolio:

http://www.infineon.com/wirelesscontrol

IntegratedmicrocontrollerandRFtransmitterSmartLEWISMCUPMA71xx:

http://www.infineon.com/PMA

PMAfob DesignexampleofanRFremotecontrolbasedonPMA7105:

http://www.infineon.com/PMAfob

TDA7210V ASK/FSKSingleConversionRFReceiverIC:

http://www.infineon.com/TDA7210V

RF2ir

SourceCodeandHWdesignexampleincludingschematicandPCBlayout:

http://www.infineon.com/RF2ir

infrared remote control switch 405 Method Not Allowed

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