Rolling Code

7/28/2019 Rolling Code

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Constructional Project

10 Everyday Practical Electronics, August 2009

eectronic sys-tes have now been deveoped for

keyess entry. hese incude systesthat require a coded eectronic keysuch as and infrared transitters2&)$S2ADIO&REQUENCY)DENTIÚCATIONevices keypads and swipe cards.here are aso units that do not require acoded eectronic key and these incudeÚNGERPRINTFACEANDIRISRECOGNITION

2EGARDLESSOFFORMATELECTRONICKEYSusuay coprise a sa keyfob-styeTRANSMITTER ANDA RECEIVER THAT GOES

with the door ock echanis. heTRANSMITTERSENDSASTRINGOFDATATHATis unique to each individua ock andthis data ust atch the data storedin the receiver before the ock wi beRELEASED4HECONCEPTISROUGHLYSIMI-ar to a standard eta key which hasAPATTERNOFPEAKSANDVALLEYSALONGITSLENGTH4HESEPEAKSANDVALLEYSMUSTatch the tubers within the ock in

order for the ock to open.ith any type of ock there is awaysa probe of security. eys can easiy

be copied whie any conventiona and infrared transitters are far frotaper-proof. ne technique is to usea specia receiver to intercept and copythe transitted code. nce copied theSIGNALCANTHENBERETRANSMITTEDTOTHE

DOORLOCKTOGAINUNAUTHORISEDENTRYn fact this technique was co-ony used by car thieves in carparksANDPROVEDVERYEFFECTIVEAGAINSTEARLYELECTRONIC LOCKING SYSTEMS )T COULDALSOBEUSEDTOOPENAUTOMATICGARAGEDOORSANDGAINACCESSTOBUILDINGS

oig code securityodern transitters now circu-

VENTTHISPROBLEMBYCHANGINGTHEIRCODEEACHTIMETHEYSENDASIGNAL3Oif an unauthorised person capturesTHETRANSMITTEDCODERESENDINGTHIS

code wi not unock the door. his is because the door ock is now expect-INGANEWCODEBASEDONANALGORITHM

dea for keyess etry for doors i cars, hoesad idustry, this eyess try yste featuresa roig code to esure high security. t asohas two door-strike outputs, a aar syste

ad provisio to use up to 6 separate keyfobtrasitters with the sae receiver.

Rolling Code KeylessEntry System

Versatile IR unit also

functions as an alarmPart.1: By JOHN CLARKE




Everyday Practical Electronics, August 2009 11

that both the transitter and receiverhave in coon.

his code changing technique iscoony caed a ‘roing code’athough it is soeties aso caed‘code hopping’. t renders copyinguseess and thus provides a very higheve of security. t is aso virtuay i-possibe to send a correct code withouthaving a vaid roing code transitter.his is because of the huge nuber of code variations possibe.

ecause of its security advantages aroing code transitter fors the basisof the oing ode eyess ntry ys-te described here. n fact the odds of picking a correct code at rando forour roing code transitter are one

in 1. triion or roughy one in 11

.f you want to know ore aboutroing code transissions refer to theseparate pane esewhere in this artice.

ai featuresur new oing ode eyess ntry

yste coprises a sa keyfob-styetransitter and a separate receiver.he transitter is sa enough to

be attached to a keyring and has twopushbutton switches each capabe of sending a separate code. ach tieone of the switches is pressed a sa

INDICATOR,%$ÛASHESTOINDICATETHATthe transitter has sent its code.

he arger of the two switchesactivates the aar functions of thereceiver. t ars the unit so that itwi sound an aar shoud there beunauthorised access.

he aar functions incude an eec-tric door strike contro (this aows thedoor to be opened two aar inputs(eg to onitor doors windows or othersensors and an ar/disar output.he door strike can optionay be set tooperate on aring on disaring or both.

n addition an aar output isprovided to sound a siren if required.

he second saer pushbuttonswitch on the transitter is independ-ent of the aar. t can be used tooperate a separate door strike or soeother device connected to the receiver.uch devices can incude a ight or asiren that can be used as a panic aar.his can be optionay set to operateoentariy or can be togged on andoff with each switch pressing.

he door strike outputs can be set to

operate fro between to 6 secondswhie the inputs can incude deayedoperation fro to 6 seconds. hese

deayed inputs aow the aar to beared whie giving the user enough

tie to exit the door without setting off the aar. n identica deay period a-ows the aar to be disared on entry.

uring the exit deay period the INDICATOR,%$INTHERECEIVERUNITÛASHESon and off at a one second rate. t theend of the exit deay this indicatesTHATTHEUNITISARMEDBYÛASHINGBRIEÛYonce every second. his conservespower and increases its effectivenesswhen it coes to attracting attention.

n cknowedge/ower is asoincuded in the receiver. his norayÛASHES WITHAVERY SHORT DUTYCYCLEowever when the receiver picks upa signa fro the transitter the ck/0OWER,%$ÛASHESATAVERYHIGHRATE)Taso shows if the received code is invaid

by oentariy binking off and on.f the code is correct the receiver

responds to the signa. he transis-sion range is about which shoud

BESUFÚCIENTFORMOSTPURPOSESote,however, that it wi ot work if the receiver is i direct suight.

ettig it up

efore using the nfrared oingode ar both the transitter andthe receiver ust be set up correcty.

irst each transitter ust be given aseparate identity ranging fro 1 to 16.

his is seected using ink options onthe transitter board but note that notwo transitters shoud be given thesae identity.

econd the transitter ust berandoised. his changes the initiaroing code and agorith paraetersto ensure that the transitter code isgoing to be unique.

he third step invoves synchronisingthe transitter and receiver. his proc-ess invoves sending the roing codeparaeters to the receiver as describednext onth. ou can synchronise fro1 to 16 transitters provided each hasa different identity.

so incuded is a faciity to preventany or a transitters fro operatingthe receiver once they have been syn-chronised. his ‘ockout’ feature can beusefu if a transitter has been ost andyou no onger want it to work with youraar syste.

transitter identity can beocked out individuay but if youdon’t know the identity of a osttransitter a identities can be

ocked out. he transitters that areto be used with the receiver are thenre-synchronised.

Features

Transmitter

s Rolling code infrared transmission

s Small keyfob style case

s Dual function buttons

s Randomisation of code parameters feature

s Synchronising of parameters feature

s Up to 16 identifications

Receiver

s 12V operation

s Up to 16 separate transmitters can be synchronised

s Dual function with an independent output

s Two alarm inputs with exit and entry delays

s Two door strike outputs

s Alarm output

s Arm/disarm output and LED indicator

s IR receive acknowledge LED

s Strike 1 operates on arm, disarm or both

s Strike 2 operates independently with momentary operation or toggleoutput

s Arm output invert option

s Adjustable door strike, entry/exit delay and alarm periods

s 200-code look ahead feature

s Transmitter lockout feature





rasitter circuit so uch for the background

detais. et’s now take a ook at howthe circuit works starting with thetransitter – see ig.1.

1 a 1668 icrocontroer

fors the heart of the transittercircuit. he circuit ight ook quitesipe but there are a ot of ‘sarts’

hidden inside the icro incudingthe software necessary to generate theroing code.

nder nora conditions switches1 and are open circuit and transis-tor is off so no power is appied.

his is done to ensure ong battery ife.f power were continuousy appiedthe current drawn fro the battery

woud be around because of thequiescent current of the 5 reguator.

onversey pressing either 1 or connects the 1 battery to theinput of reguator 1 via diode1 or . Ω resistor is incudedin series between the battery and theswitches to iit the initia chargingcurrent into the 1μ bypass capacitorat 1’s input. his iniises wearon the switch contacts.

hen power is appied to 1’sinput its output deivers a reguated+5 rai to 1. s a resut the icropowers up and runs its interna soft-ware progra.

witch check

NEOFTHEÚRSTTHINGSTHEPROGRAMdoes is check which switch waspressed (this happens after a shortdeay to ake sure the switch is fuycosed. n operation the progra candecide if 1 or is pressed because of the 1kΩ resistor connected between and the icro’s input.

t works ike this. nitiay isset ow by the progra. his pin isthen ade open circuit so that it can

be pued high if switch was cosed.owever if 1 was cosed instead the pin wi stay at . y checking

the votage on the progra canthus deterine which switch waspressed and initiate the correct func-tion codes for that switch.

he 1kΩ resistor is necessary toiit the current into the internacaping diodes at when iscosed. n practice the positive capdiode wi conduct caping the input to .6 above the +5 suppy.his protects the input fro daage.

iodes 1 and protect the regu-ator fro reverse poarity shoud the

battery be inserted the wrong wayaround. hese diodes aso isoate theswitch outputs fro each other so thatthe input wi ony go high if is pressed. f 1 is pressed the 1 at1’s input reverse biases and sois bocked fro reaching .

ext the progra sets at pin 1of the icro high. his output drivesthe base ( of NPN transistor 1via a 1kΩ resistor. s a resut 1switches on and this in turn switcheson transistor .

his action atches the suppy to

reguator 1 even if switch 1 or is reeased. his is necessary to aowtie for the roing code cacuations to

Parts List – Rolling Code Keyless Entry System

Receiver

ᗂ1 PC board, code 721, size61mm × 122mm

1 UB3-type plastic box, size130mm × 68mm × 44mm

5 2-way PC-mount screwterminal blocks (5mm or 5.08mm pin spacing)

1 SPST vertical mount microtactile switch, with 0.7mmactuator (S1)

3 3-way pin header terminalstrips (2.54mm spacing)

4 2.54mm jumper shunts3 PC stakes

1 25mm length of 0.8mm tinnedcopper wire

Semiconductors

1 PIC16F88-I/P microcontroller programmed with irrcroll.hex(IC1)

1 78L05 low-power 5V regulator (REG1)

1 38kHz infrared receiver (IRD1)2 BD681 Darlington NPN

transistors (Q1,Q2)2 BC337 NPN transistors (Q3,Q4)1 16V 1W Zener diode (ZD1)

4 1N4004 1A diodes (D1-D4)1 1N5404 3A diode (D5)2 3mm red LEDs (LED1,LED2)

Capacitors5 100μF 16V PC electrolytic3 100nF MKT polyester 3 10nF MKT polyester 1 1nF MKT polyester

Resistors (0.25W, 1%)4 10kΩ 1 220Ω2 2.2kΩ 2 100Ω

2 1kΩ 1 10Ω2 680Ω

Test Components4 red LEDs4 2.2kΩ 0.25W 1% resistors

Transmitter

ᗂ1 PC board, code 722,measuring 30 × 36mm

1 keyfob remote controlcase (Jaycar HB-5605 or equivalent)

1 12V A23 car alarm battery (9.5diameter × 27mm)

2 SPST SMD tactile switches 6 ×6 × 3.85mm (S1,S2)

1 TO-3P transistor siliconeinsulating washer, cut to 20 ×24mm

5 PC stakes1 25mm length of 0.8mm tinned

copper wire1 ICSP 5-pin connector (CON1)

Semiconductors1 PIC16F628A-20/SO

18-lead SOIC microcontroller,programmed with irxmroll.hex(IC1)

1 MC78M05 DPAK 5V regulator (REG1)

1 MMBT100 SOT-23 SMD NPN

transistor (Q1)1 MMBT200 SOT-23 SMD PNP

transistor (Q2)

2 1N4148 diodes (D1,D2)1 3mm infrared emitting LED

(LED1)1 green gull wing style surface

mount LED (2.2 × 2.2mm)(LED2)

Capacitors2 1μF monolithic ceramic1 100nF monolithic ceramic

Resistors (0.25W, 1%)2 10kΩ 2 22Ω

3 1kΩ2 10kΩ horizontal trimpots

(VR1,VR2)

ᗂ Printed circuit boards availablefrom the EPE PCB Service





be ade and stored without interrup-tion otherwise the code ay becoecorrupted. t aso ensures that the ro-ing code is transitted in its entirety.

he next stage in the progra in-voves cacuating the code and storingthe vaues. his cacuation is basedon the previousy transitted codeand uses an interna agorith. ncecacuated the new code appears atoutputs to 5 which in turndrive an infrared (1. he Ω resistor in series with 1 iits thecurrent to a safe vaue.

n operation 1 is driven using1 puses at a rate of 8.6kz.

high (or a ‘1’ is transitted as a 51μs burst of 8.6kz signa foowed by51μs of no transission. onversey aow (or a ‘’ consists of a 51μs periodof no transission foowed by a 51μs

burst of 8.6kz signa. is the ransit and is

driven by output during codetransission. asicay goes higheach tie there is a ‘1’ in the transit-ted code and ow each tie there is alm!SARESULT,%$ÛASHESTOMIMICthe transission code.

rasitter idetityransitter identity is seected usingthe 1 to ink connections to 1

7 and 6. s shown eachindividua input can be connected toeither the +5 suppy or the ground (

suppy but to both or the suppywi be shorted. he nuber of possibecobinations is 16.

ach of these inputs is initiay tiedto +5 on the board (via thin tracks and this seection is identity 1.he other 15 identities are seected by

breaking one or ore of these connec-tions to the +5 rai and connectingthe instead to an adjacent rai.

e’ tak ore about this in theconstruction.

-circuit prograigive-pin header 1 is provided

on the circuit to aow for n-ircuiteria rograing ( of 1 us-ing a prograer. ternativeywe have deveoped a surface-ountconverter board that wi aow 1 to

be prograed directy using a prograer. e’ pubish the detaison this next onth.

he connections on thetransitter are aso used to run therandoisation and synchronisationfunctions using a bridge between pins

and 5 and and respectivey.1 runs at a noina z asprovided by an interna osciator.

his osciator has a 1 toeranceANDITSACCURACYISSUFÚCIENTFORTHISappication (ie there’s no need for a

crysta osciator. owever becausethe osciator frequency can varywith teperature we have incudeda eans for the receiver to ock ontothe transitter’s cock rate so thatvariations over a ong tie period donot atter.

y the way the transitter usessevera surface-ount coponentsSOTHATTHECIRCUITWILLÚTINTOASMALLkeyfob case. hese surface-ountparts incude 1 1 1 1 and . he reaining parts

are standard through-hoe coponentTYPESTHATARESMALLENOUGHTOÚTONTOthe board.

eceiver circuitefer now to ig. which shows

the receiver circuit. t’s buit aroundinfrared receiver 1 and i-crocontroer 1 the atter operatingat z to atch the transitter’sfrequency. nce again uch of thecopexity is hidden by the softwareprograed into the icrocontroer.

1 ony has three eads but inside

it coprises a copete infrared de-tector and processor. irst it receivesthe 8kz infrared puse signa fro

+5V

INFRARED ROLLING CODE TRANSMITTER

ig.: a 6628 icrocotroer fors the heart of the trasitter circuit. t cotais a the software ecessaryto geerate the roig code ad drives a ifrared (.





THETRANSMITTERANDAMPLIÚESTHISTOACONSTANTLEVEL4HISSIGNALISTHENFEDTO

AKZBANDPASSÚLTERTOREMOVEANYZORZMAINSSIGNALANDOTHERNOISE)TTHENDEMODULATESTHESIGNALTOPRODUCEASERIALDATABURSTAT)2$mSPINOUTPUT

4HISSERIALDATASIGNALFROM)2$ISFEDTOTHE2"INPUTOF)#VIAAΩ RESISTOR!N&CAPACITORÚLTERSOUTANYTRANSIENTS

)2$ISPOWEREDFROMTHERECEIVERmSSUPPLYRAIL!ΩRESISTORANDAμ&CAPACITORPROVIDESUPPLYDE-COUPLINGANDÚLTERINGTOPREVENTTHERECEIVERFROMPRODUCINGFALSESIGNALS

DUETOPOWERLINECHANGES!S WELL AS THE )2 RECEIVER THERE

ARE TWO OTHER INPUTS TO THE 0)#

MICROCONTROLLER 4HESE ARE ALARMSENSOR INPUTS )NPUT AND )NPUT

ANDTHESECONNECTTOTHE2"AND2"INPUTSOF)#VIAKΩRESISTORS%ACHINPUTISALSOBYPASSEDUSINGAN&CAPACITORTOÚLTEROUTTRANSIENTSAND THUS PREVENT FALSE TRIGGERINGOFTHEALARM

HENTHESEINPUTSAREOPENBOTH2" AND 2" ARE HELD HIGH IE AT VIA INTERNAL PULLUP RESISTORS)NPRACTICETHISMEANSTHATYOUCANUSENORMALLYOPENORNORMALLYCLOSEDREEDSWITCHANDMAGNETASSEM-

BLIESTOTRIGGERTHEINPUTS)FYOUUSEANSWITCHTHEINPUT

WILLNORMALLYBEHIGHANDTHESYSTEMWILLTRIGGERIFASWITCHISCLOSED#ON-VERSELYIFAN#SWITCHISUSEDTHE

INPUTWILLNORMALLYBEPULLEDLOWBUTWILLGOHIGHIFTHESWITCHISOPENED

"ASICALLYANYCHANGEINLEVELWHENAREEDSWITCHOPENSORCLOSESWILLBEDETECTEDANDSOUNDTHEALARMATTHE

END OF THE ENTRYPERIOD PROVIDEDTHATTHERECEIVERISINITSARMEDSTATEOTEHOWEVERTHATTHEALARMWILLNOTSOUNDIFTHERECEIVERISSTILLWITHINITSEXITDELAYPERIOD

oor strike outputsHEN AN )2 SIGNAL TRANSMISSION

ISRECEIVEDTHEOUTPUTFROM)2$ISPROCESSED BY )# 4HIS THEN DRIVES$ARLINGTONTRANSISTORSANDASAPPROPRIATETOCONTROLTHEDOORSTRIKEOUTPUTSIE3TRIKEAND3TRIKE

!SSHOWNANDAREDRIVENVIAΩRESISTORSFROM)#mS2"AND2!OUTPUTSRESPECTIVELY$IODES$AND$CLAMPTHEVOLTAGEPRODUCED

BY THE DOOR STRIKE SOLENOID TO THESUPPLY RAIL WHEN THE TRANSISTOR ISSWITCHEDOFF

4RANSISTORS AND ARE BOTH"$ $ARLINGTON TYPES ANDCANBEUSED TO DRIVE LOADS UP TO ! !TYPICALELECTRICDOORSTRIKEONLYDRAWSABOUTM!AT

4HEOTHERTWOOUTPUTSARETHE!LARMAND!RMOUTPUTSANDTHESEARECON-

TROLLEDBYTRANSISTORSANDBOTH"#RESPECTIVELYISDRIVENBY)#mS2"OUTPUTVIAAΩCURRENTLIMITINGRESISTOROWEVERTHEBASECURRENTISSUFÚCIENTFORTHETRANSISTORTOREMAINFULLYSATURATEDFORAM!LOADANDTHISISIDEALFORMANYPIEZOSIRENS

3IMILARLYTRANSISTORISDRIVENVIAAKΩRESISTORFROM)#mS2"OUTPUTmSCOLLECTORPROVIDESTHE!RMOUTPUTANDTHISCANBEUSEDASATOGGLEOUTPUTTOSETASECONDALARMSYSTEM

4YPICALLY YOU WOULD USE A KΩ

PULLUP RESISTOR BETWEEN THE !RMOUTPUTANDTHERAILSOTHATTHELEVELCANSWINGBETWEENAND!LTERNATIVELYmSCOLLECTORCOULDBEUSEDTODRIVEARELAYCOIL)NTHISCASETHEKΩBASERESISTORWILLNEEDTOBEREDUCEDTOKΩSOTHATTHETRANSISTORCANREMAININSATURATIONWHILEDRIVINGa 85ΩRELAYCOIL

4HEUNITCANBEOPTIONALLYCONÚG-UREDWITHEITHERONOROFFWHENARMED4HISISSETUSINGLINK,

HEN,ISINTHElmPOSITIONISONWHENTHEUNITISARMEDANDOFF

WHENDISARMED)NTHISCASETHE2"INPUTISHELDATVIAANINTERNALPULLUPRESISTORWITHIN)#

Specifications

Transmitter

Standby current: 0mATotal transmit current: rolling code transmission = 35mA for 80ms;synchronise = 35mA for 100ms; randomisation = 10mA.

Infrared transmit frequency: 38.46kHz

Code transmission rate: 1.024ms

Encoding: a high (or a 1 bit) is transmitted as a 512μs burst of 38.46kHzinfrared signal, followed by 512μs of no transmission. A low (or 0 bit) istransmitted by a 512μs period of no transmission, followed by a 512μsburst of 38.46kHz infrared signal.

Rolling code: sends four start bits, an 8-bit identifier, the 48-bit code plusfour stop bits. The start bits include a 16.4ms gap between the secondstart bit and the third start bit.

Synchronise code: sent as two blocks. Block 1 sends four start bits, the8-bit identifier, a 32-bit seed code and four stop bits. Block 2 sends four start bits, a 24-bit multiplier, the 8-bit increment and 8-bit scramble values,and four stop bits. The start bits include a 16.4ms gap between the secondstart bit and the third start bit.

Code randomisation: alters the multiplier values, the increment value, thescramble value and the seed code at a 40μs rate.

Infrared transmission range: 4m

Receiver

Supply Current: 7.6mA typical when armed and with no external devicespowered.

Strike 1 period: adjustable from 0-64 seconds in 0.25s steps

approximately.Strike 2 period: adjustable from 0-64 seconds in 0.25s stepsapproximately.

Input 1 delay: adjustable from 0-64 seconds in 0.25s steps approximatelyfor exit and entry delays.

Input 2 delay: adjustable from 0-64 seconds in 0.25s steps approximatelyfor exit and entry delays.

Alarm period: adjustable from 0-128 seconds in 0.50s stepsapproximately





INFRARED ROLLING CODE RECEIVER

SYNCHRONISE

oving to the ‘–’ position pus to ground and changes the senseof the r output. n this case is off when the unit is ared and on

when disared. indicates the state of the unit.t’s driven fro the output of 1via a 1kΩRESISTORANDÛASHESWHENthe unit is ared.

4HEREARETWODIFFERENTÛASHSTYLES$URINGTHEENTRYANDEXITDELAYPERI-ODSTHE,%$ÛASHESWITHADUTYCYCLEIEITISONFORHALFTHETIMEANDoff for haf the tie. owever at theENDOFTHEDELAYPERIODITÛASHESONFORONLYOFTHEDUTYCYCLEIEEACHÛASHISVERYBRIEF

ther ik optiosinks 1 and are in-cuded to provide further options.

&OR EXAMPLE , CAN BE TIED TOEITHERTHERAILORTOORITCAN

BE LEFT OPEN 4HESE THREE OPTIONSdeterine how the trike1 output

OPERATES"ASICALLY3TRIKECANBESETto operate when the unit is aredWHENITISDISARMEDORONBOTHARM-ing and disaring.

n operation the software pro-graed into the icro decidesWHERETHELINKISINSERTEDBYRUNNINGAfew tests. irst it takes the 7 outputHIGHANDTHENSETSTHE2!PINASan input to read the votage. f the vot-AGEISNOWLOWTHENTHELINKMUSTBEINthe ‘–’ position. owever if the inputreains high then the ink is eitherin the ‘+’ position or is open circuit

ITREMAINSHIGHWHENTHELINKISOPEN BECAUSEOFTHECHARGEONTHEASSOCIATEDN&CAPACITORTOGROUND

o test if the ink is in the ‘+’ positionor open the 7 pin is ade an outputAGAINANDISDRIVENLOWTO4HE7 pin is then changed to an input

and the eve checked again. f the vot-AGEISNOWHIGHTHENTHELINKMUSTBEINTHElmPOSITION#ONVERSELYIFTHEvotage is ow then the ink is open.

4HEKΩ resistor in series with 7is there to prevent shorting when thispin is taken high and ow with a inkin position.

sets trike’s operation forEITHER MOMENTARY OPERATION OR FORtogge operation. his ink pus the2!INPUTEITHERTOWHENITISINTHElmPOSITIONMOMENTARYORTOWHENITISINTHElmPOSITIONTOGGLE

OTETHATTHISLINKCANNOTBELEFTOPEN BECAUSETHE2!PINCANONLYBEUSEDas an input.

ig.2: ifrared receiver ad icrocotroer are the ai parts i the receiver. picks up addeoduates the ifrared trasissios, whie decodes the data ad drives the various outputs.





addition if 1 is cosed during power-up it seects the transitter identityockout function.

ower suppyower for the circuit is fro a

1 suppy such as a battery or pugpack. iode 5 provides reversepoarity protection and is rated at so that it can hande the currents thatay be drawn by an eectric door strikeand siren.

he 1Ω resistor and ener diode

1 provide transient protection withthe ener caping votages over 16.he 1Ω resistor iits the currentthrough 1 to a safe eve.

&OLLOWING:$THESUPPLYISÚLTEREDusing a 1μ capacitor and appiedto the -terina reguator 1. heresuting reguated +5 rai is then

Resistor Colour Codes (Transmitter)

❏ No. Value 4-Band Code (1%) 5-Band Code (1%)

❏ 2 10kΩ brown black orange brown brown black black red brown

❏ 3 1kΩ brown black red brown brown black black brown brown

❏ 2 22Ω red red black brown red red black gold brown

Capacitor Codes

Value μF Code IEC Code EIA Code

100nF 0.1μF 100n 104

10nF .01μF 10n 103

1nF .001μF 1n0 102

is used in conjunction withtripots 1 and to set the varioustie periods. hese incude the trike1and trike oentary on periods theentry and exit deays for nput1 andnput and the aar period.

s shown in ig. tripots 1 and are connected across the 5 sup-py and their wipers (oving contactconnect to anaogue inputs and1 respectivey. he votage appied

to each anaogue input is converted toa digita vaue within the software andit is these vaues that deterine thetieout periods.

ychroise switchwitch 1 is the ynchronise switch

and this connects to the 7 input.his input is noray hed high viaan interna pu-up resistor but when1 is cosed it pus 7 to .

asicay1 is used to

synchronisethe receiverw i t h t h etransitter.t is aso usedwhen set-ting the tieperiods. n

Note: transistor Q2mounts under 10kΩresistor

hese two arger-tha-ife-size photos ceary show how the parts are outed o the trasitter board. ou wi eed alNETIPPEDªSOLDERINGªIRONªMMªDIAMETERªORªLESSªANDªAªMAGNIFYINGªGLASSªTOªDOªTHEªASSEMBLY

ig.: foow these parts ayout diagras to buid the trasitter board. oteTHATªYOUªHAVEªTOªSETªTHEªTRANSMITTERSªIDENTITYªBEFOREªINSTALLINGª)#ªSEEªTEXTªANDªDONTªFORGETªTRANSISTORª1ªnªITªGOESªUNDERªAªKΩªRESISTORªJUSTªBELOWª3

&IGªTHISªENLARGEDªTRACKªSECTIONªSHOWSªTHEªLOCATIONSªOFªLINKSª++ªONªTHEªtrasitter board. he trasitterIDENTITYªISªCHANGEDªBYªBREAKINGªONEªORªMOREªOFª THEª THINNEDª LINKªCONNECTIONSªTOªTHEªªRAILªANDªBRIDGINGªTHEMªWITHªSOLDERªTOªTHEªADJACENTªªRAILªINSTEAD





he keyfob case is suppied withthe key switch covers outed asshow here. his asseby ust bereoved.

ig.5: oce the switch covers have BEENªREMOVEDªTHEªmANGESªAREªGROUNDªdow usig 80-grit sadpaper, sothat oy the tops reai (see text.

bove: the fiished trasitter board iside its keyfob-stye pasticcase. ower coes fro a 2 2car aar battery. ote how thekeyswitch covers are outed othe id, usig a 20 × 24 siicoewasher – see text.

ight: the two keyswitchcovers are attached to the20 × 24 siicoe washeras show here. se siicoeseaat to ‘gue’ the i

pace. he keyfob id ca beused as a tepate to positiothe correcty.

breaks in the copper or shorts betweentracks. epair any fauts that you doÚNDRARETHESEDAYSTHENCHECKTHE

shape of the board. t shoud have acurved front edge and a sa circuarCUTOUTATTHEOTHEREND)NADDITIONthere shoud be two sots for the bat-tery cips.

EXTCHECKTHATTHE 0#BOARDÚTSneaty into the base of the keyfob case.)FITDOESNOTÚTITmSJUSTAMATTEROFÚLINGit neaty aong the edges unti it does.

ettig the idetityefore outig ay of the

PARTSª ITSª lRSTª NECESSARYª TOª SETª THEª

trasitter’s idetity – but oy if oretha oe trasitter is to be used. f ore tha oe trasitter is used, the

each wi require a uique idetity.!S SUPPLIED THE 0# BOARD INI-

tiay ties inks 1 to to the SUPPLYRAIL 4HIS IS)DENTITYor 1. f ony one transitter is to

BEUSED THEN YOUDONmTHAVE TODOATHINGJUSTLEAVEITATTHEDEFAULTIDENTITY)$

f you do wish to change the iden-TITYITmSJUSTAMATTEROFALTERINGONEORore of the inks as shown in abe9OUDOTHATBYBREAKINGTHELINKmSthinned connection to the +5 track

USED TOPOWER )# AND THE INFRAREDRECEIVER)2$

0OWERONOFFINDICATIONISPROVIDED BY ,%$ WHICH ALSO ACKNOWLEDGESTHE INFRARED SIGNALORMALLY ,%$ÛASHES WITH ADUTYCYCLEABOUTTWICEPERSECONDOWEVERWHENANINFRAREDSIGNALISRECEIVEDITÛASHESat the infrared reception rate.

,%$ALSOÛASHESWITHANEVENDUTYcyce for a short tie at the end of synchronisation and if the infraredsigna is incorrect.

ostructio4HE 2OLLING #ODE EYLESS

%NTRY3YSTEMISBUILTONTWO0# BOARDSA2ECEIVERBOARDCODE ANDA 4RANSMITTER BOARDcode 7. oth boards are avai-abe fro the EPE PCB Service.

EmLLSTARTWITHTHETRANSMITTERASSEMBLYWHICHISTHETRICKIEROFTHE

TWO)NORDERTOÚTINTHEKEYFOBCASETHETRANSMITTERBOARDMEASURESJUST¯MMANDUSESLOTSOFSURFACEMOUNTcoponents.

OWEVERTHESEARENOTTOODIFÚCULTTO SOLDER IN PROVIDED YOU HAVE ASOLDERINGIRONTIPTHATISJUSTMMINDIAMETERORÚNER!MAGNIFYINGGLASSOR PREFERABLY A lMAGGIE LAMPm ISALSOREQUIREDTOCHECKYOURSOLDERINGwhie a ength of 1.5 de-sodering

BRAID3OLDERWICKWOULDALSOBEUSE-fu for ceaning up any excess soderTHATMAYÛOWBETWEENCONNECTIONS

&IGSHOWSTHECOMPONENTLAYOUTONTHE0#BOARD4HEÚRSTSTEPISTOCHECKTHE0#BOARDCAREFULLYFORANY

Table 1: Transmitter Identity

Iden-tity

LK1 LK2 LK3 LK4

1 + + + +

2 + + + -

3 + + - +

4 + + - -

5 + - + +

6 + - + -

7 + - - +

8 + - - -

9 - + + +

10 - + + -

11 - + - +

12 - + -

13 - - + +

14 - - + -

15 - - - +

16 - - - -

eproduced by arrangeentWITH3),)##)0

MAGAZINEwww.siiconchip.co.au





and connecting it to the adjacent track instead via a sa soder bridge.

ake sure however that a ink con-nection is not ade to both the +5 and tracks. e have abeed the +5connection with a pus (+ sign and the connection with a inus (– sign.

t is iportat to seect the idetityow because the 5 track sectiocaot be accessed whe is i

pace. he +5 connections shoudony be broken with a sharp craftknife and once broken shoud not beresodered. hat’s because 1 woudno onger sit propery on the boardMAKINGITDIFÚCULTTOSOLDERITSPINS

he seected identity shoud bearked on the back of the boardusing a arker pen. or exape if the identity is write on the

board. his nuber can aso be writtenon the back of the keyfob transittercase in the indentation provided.

oftwaref you are buiding the unit froa kit then 1 wi be suppied pre-prograed. f not you wi have

to progra the yoursef using asuitabe prograer. s previousyentioned we have provided two pro-GRAMMINGOPTIONSTHEÚRSTOFWHICHis to use the in-circuit prograingconnector on the board.

ternativey you can buid and usethe surface ount adaptor board to bedescribed next onth so that 1 can

be prograed out of circuit.

4HESOFWAREÚLESWILLBEAVAILABLEvia the EPE ibrary site accessed viawww.epeag.co. re-prograeds wi aso be avaiabe fro a-genta ectronics – see their advert inthe issue for contact detais.

arts assebyxcept for a singe wire ink a

parts for the transitter ount onthe copper side of the board. on’tinsta the ink yet though – that stepcoes after you insta 1.

o insta 1 position it on the

board with its pin 1 at top right – seeig. (pin 1 is indicated by a saadjacent dot in the body of the .arefuy adjust it so that its pins ine

up with the tracks and use a cothespeg (or soe other sa spring-capto hod it in position.

hat done soder a coupe of di-agonay opposite pins check thateverything is correct then reove thepeg and carefuy soder the reain-ing pins.

he ain thing to watch out for hereis unwanted soder bridges betweenadjacent copper tracks. f this doeshappen use soe soder wick to drawup the excess soder to cear the short. agnifying gass wi be handy hereto inspect your work.

ote that pins 6 to and 1 and11 are connected together anyway sosoder between these pins is .

nce the is in you can insta theink beneath it on the other side of the

BOARD4HIS LINKMUST SITÛATAGAINSTthe board otherwise the board wi notsit down in the case correcty.

he reaining surface ount

coponents – 1 and1 – can now be sodered in pace.rasistor Q has a abe o itstop, whie Q2 has a 2 abe istead.

Resistor Colour Codes (Receiver)

❏ No. Value 4-Band Code (1%) 5-Band Code (1%)

❏ 4 10kΩ brown black orange brown brown black black red brown

❏ 2 2.2kΩ red red red brown red red black brown brown

❏ 2 1kΩ brown black red brown brown black black brown brown

❏ 2 680Ω blue grey brown brown blue grey black black brown

❏ 1 220Ω red red brown brown red red black black brown

❏ 2 100Ω brown black brown brown brown black black black brown

❏ 1 10Ω brown black black brown brown black black gold brown

ig.6: foow this diagra to out the parts o the receiver board. se a socket for the icrocotroer adtake care to esure that a poarised parts are correcty orietated. he ifrared receiver odue ( ca either

be outed o the board (as i the prototype or coected via shieded cabe (see diagra ext oth.





hese nubers reate to the 1and types respectivey.on’t get the ixed up.

staig the seicoductorshe orientation of the two transistors

is obvious – they have one pin on oneside of the body and two on the otherside. 1 has a tab pus and pins that ust be sodered to the

board. he centra pin between the and pins is eft unconnected.e carefu with the orietatio of

2 – its cathode ead is the ogerof the two.

ext soder in switches 1 and THENINSTALLÚVE0#STAKESFORTHE)#30header. hese pins are inserted frothe non-copper side of the boardand sodered in position. he pinsare then tried on the copper sideto in height. n the undersideTHEYARETRIMMEDANDÚLEDTOMM

he standard coponents can now

be instaed. hese ust be ountedÛATAGAINSTTHE0#BOARDORASCLOSETOITASPOSSIBLEINTHECASEOFTHEKΩ RESISTORTHATSTRADDLES4AKECAREwith the orientation of diodes 1 and and note that the tops of the threeonoithic capacitors ust be no orethan above the board.

n particuar the two capacitors near2%'CANBELAIDOVERATABOUTWHILEthe one adjacent to 1 needs to have itseads adjusted so it can be pushed downonto the board far enough to eet the height requireent.

ut a the eads beneath the BOARDIEONTHENONCOPPERSIDEÛUSHwith the surface.

1 can go in next. ts anode eadISTHELONGEROFTHETWOUNLIKE,%$and this ead ust go towards 1. oMOUNTITÚRSTBENDITSLEADSDOWNBYEXACTLYMMFROMITSBODYTHENinsert the eads into the board. i-nay push the a the way downonto the board soder the eadsANDCUTTHEMÛUSHWITHTHEUNDERSIDE

ote that a sa circuar notch isREQUIREDINTHERIMOFTHEKEYFOBBASEfor the to sit in. his can be adeUSINGASMALLRATTAILÚLEHENTHISNOTCHHASBEENMADEÚLEAMATCHINGNOTCHINTHETOPHALFOFTHEKEYFOBCASE

attery teriashe battery terinas are instaed

BYÚRSTPLACINGTHE0#BOARDINTHEBASEof the case. hat done the terinasare sid into position and sodered.AKESURETHATTHETERMINALWITHTHEspring is ocated as shown in ig..

3WITCHªCOVERªMODIlCATIONS4HEKEYSWITCHCOVERSTHATARESUP-PLIEDWITHTHEKEYFOBCASEHAVETOBEMODIÚEDTOSUITTHETWOSWITCHESONthe board.

s suppied the two switch coversAREALREADYSECUREDINPLACEINTHEKEY-fob id. his asseby ust be reovedand the covers carefuy ground downTOMMTHICKSEE&IG4HISISDONE

by pacing soe 18-grit sandpaperONTOAÛATBENCHANDSANDINGTHESWITCHCOVERSUNTILTHEYAREÛATONTHEIRBASE

hat done cut out a ×

rectanguar piece fro a siicone -WASHER ¯MMTOMAKEANEWswitch cover asseby. t’s then sipy

a atter of attaching the switch coversto this washer using siicone seaant –SEEPHOTOSETHEKEYFOBLIDASATEM-pate to position the covers correcty.

eceiver assebyow for the receiver – see ig.6.

!S USUAL START BY CHECKING THE 0# BOARDFORANYDEFECTS#HECKALSOTHATthe hoe sizes for the screw terina

BLOCKSARECORRECTANDENLARGETHEMIFnecessary.4HATDONECHECKTHATTHE0#BOARD

ÚTSINSIDE THESPECIÚEDUTILITYCASE&ILETHEBOARDEDGESTOGETITTOÚTIFNECESSARYBUTDONmTÚLETHEMTOOMUCHOTHERWISETHEBOARDWILLNOTLOCKCOR-recty into the wa sots.

ig.6 shows the asseby detais.)NSTALLTHEWIRELINKÚRSTTHENINSTALLthe resistors. he accopanying tabeshows the resistor coour codes butYOUSHOULDALSOCHECKTHEMUSINGAdigita utieter.

4HEDIODESANDTHE)#SOCKETCANGOINNEXTTAKINGCARETOORIENTEACHWITHthe correct poarity. oow these withTHECAPACITORSAGAINMAKINGSURETHATthe eectroytics go in correcty. heTHREE0#STAKESFOR4040AND40'can then be instaed.

epending on your requireentss 1 and can either be ounteddirecty on the board or ountedexternay and connected using wireeads. e sure to ount each with its cathode ead (the shorter of the two towards the ower edge of

the board.iiary 1 can either be ounted

directy on the board or connected

he assebed board cips eaty ito a stadardpastic utiity case. he fu istaatio ad settig up

detais for the receiver wi be i art 2 ext oth.





using twin-core shieded cabe (seediagra in art next onth.

ripots 1 and and the-way and -way pin headers for 1- are next on the ist. hat done

insta 1 and transistors 1 to-.1 and ust be instaed with theireta faces towards 1.

inay copete the board asseby by instaing switch 1 and thescrew terina bocks. ote that the6-way terinas at the righthand edgeof the board are ade up using

three -way bocks. hese are joined by siding their dovetai joints together before instaing the on the board.

hat’s a we have space for thisonth. ext onth we’ copete theconstruction and describe the instaa-tion and setting-up procedures incud-ing setting the entry and exit deays.

e’ aso describe the optiona adapator board so that you can prograthe icrocontroer out of circuit.

One question that’s often asked

about rolling code systems is what

happens if the transmitter is outof range and one of the transmit

switches is pressed? Will the receiver

still work when the transmitter is later

brought within range and the button

pressed again?

This question is asked because the

code the receiver was expecting has

already been sent and the transmit-

ter has rolled over to a new code. So

how does the system get around this

problem?

The answer to this is that the receiver

will acknowledge a signal that is the

correct length and data rate, but it willnot trigger unless it receives the correct

code. So if the signal format is correct

but the code is incorrect, the receiver

then calculates the next code that it

would expect, and checks this against

the received code. If the code is now

correct the receiver will unlock the door.

If the code is still incorrect, the

receiver calculates the next expected

code and will do this up to 200 times.

If none of these are correct, the re-

ceiver keeps its original code, but it

will not trigger. In fact, the only way

to trigger the receiver after this is to

re-synchronise it to the transmitter.

Of course, a second transmitter will

still operate the receiver (provided

they have been synchronised in the

first place). That’s because this trans-

mitter has a different identity and a

different code to the other transmitter.

Automatic synchronisationSome rolling code transmitters sys-

tems offer automatic synchronisation

if the transmitter and receiver lose

sync. In these systems, the receiver includes a code ‘look-ahead’ feature,

as described above, but the number

of look-ahead codes is usually limited

to fewer than 200. What happens is

that if the code is not recognised after

all the look-ahead calculations have

been made, the receiver changes its

synchronisation method.

Basically, the receiver requires twoseparate transmission codes before

restoring correct operation. On the

first transmission, it calculates the

next code it should receive using this

received code as the basis for calcu-

lation. If the second code sent by the

transmitter is the same as the code that

was calculated, the receiver operates.

The drawback of this latter scheme

is somewhat less security since, in

theory, two successive transmission

codes could be intercepted and re-

corded. These codes could then be

re-transmitted to synchronise andthus trigger the receiver.

Calculating the codeAnother question that’s often

asked is how does the receiver know

which code to expect from the trans-

mitter, since this changes each time?

The answer to this is that the trans-

mitter and the receiver both use the

same calculation to determine the

next code. They also both use the

same variables in the calculation and

these variables tend to be unique

values that no other transmitter uses.

For example, if the calculation for

consecutive codes requires the origi-

nal calculated code to be multiplied

by 100 and the number 7 added to it,

then both the transmitter and receiver

will use these numbers to perform

the calculation.

Without knowing both the mul-

tiplier and the increment value, it

would be very difficult to predict the

next code. This is particularly true

because of the very large numbers

involved. The values quoted for themultiplier and increment value are not

as simple as 100 and 7 but are 24 bits

and eight bits respectively in length.

In addition, the code length is 48 bits

with as many as 2.8 x 1014 combina-

tions. This reduces by a factor of 200

because of the look ahead feature to a 1

in 1.4 × 1012 chance of striking the cor-

rect code – still impossibly long odds.

Code scramblingA further complication with the

transmitted code is that the code is not

necessarily sent in sequence. There

are also 32 possible scrambling vari-

ations that can be applied to the code.

What if the transmitter sends two

consecutive codes that are the same

and the code is intercepted and re-

transmitted to open the lock? This is

highly improbable and our rolling code

transmitter has safeguards to prevent

the same code appearing twice in suc-cession. For each code calculation,

a comparison is made between the

current and last code. If the code is the

same, the code is recalculated after an

increment of the code value to ensure

successive code calculations diverge.

It is this new code that is transmitted.

The receiver performs the same

recalculation so that the new code

will be accepted.

Another question concerns the use

of different transmitters. Does each

transmitter use the same rolling code

calculation and if so, wouldn’t the

receiver lose its synchronisation if

several transmitters were used? The

answer is that the receiver will not

lose synchronisation, even if one of

the transmitters is not generally used.

This is because each transmitter op-

erates independently from the others.

Only 16 transmitters can be used

with a given receiver and each must

have its own different identity from

1 to 16. The identity is built into each

transmitter and synchronisation is

required for each transmitter.The codes sent by each transmitter

are different and the code includes the

transmitter identity value. The receiver

has 16 different rolling code and

calculation parameters, and so each

transmitter is treated independently.

Frequently Asked Questions




24 Everyday Practical Electronics, September 2009

H copleted the receiver board assebly as described last

onth it can be housed in a -sizedplastic box s shown in the photo lastonth it siply clips into place butÚRSTYOUWILLNEEDTODRILLAHOLEINONEend for 1 plus a hole in the otherend for the external wiring

ou will also have to drill atching

holes in the lid for the ckower andr s (1 and 2)

ow for the initial set-up irstinstall a juper link in the inus

Last month, we described the circuitry andgave the PC board assembly details forour Rolling Code Keyless Entry System.This month, we cover the installation andsetting-up procedures and describe an

optional SOIC adaptor board, so that youcan program the PIC micro out of circuit.

(–) position for 2 his will set thetrike2 output to toggle ode (note:2 ust always have a juper con-nection either to the ‘+’ or ‘–’ posi-tion) eave jupers 1 and out for now

ext set tripots 1 and 2 toid-range hese tripots are laterused to set the various tie periods

Transmitter set-upt this stage the transitter is

already partially set up because its

identity is selected during construc-tion f the transitter’s icro-controller has not been prograedthen progra it now via the connection his connection can beMADEBYSOLDERING ÚVE LEADS TOTHEtransitter’s pins and then con-necting the other ends of these leads

to a 5-way socket to plug into the prograer

fter the has been prograedclip in the 12 battery and check thatthe green acknowledge lightswhen a switch is pressed

f course if you buy a copletekit the icrocontroller (and the in the receiver) will be suppliedpre-prograed so you won’t haveto worry about that last step

Testing the receiverhe receiver can now be tested irst

with 1 out of its socket connect a 12power source that can supply at least60 hat done switch on and checkthat there is 5 between pins 1 and 5

Rolling Code KeylessEntry System

Versatile IR unit also

functions as an alarm

art2: y J




Everyday Practical Electronics, September 2009 25

of the socket f this is within 10 of 5 (5 to 55) switch off and plug1 into its socket aking sure that it

is correctly orientatedext wire up the test s as shownin ig6 hese are all wired in serieswith 22kΩ current-liiting resistorsnce the s are wired up applypower and check that the receiver’sPOWER,%$ÛASHESBRIEÛYATABOUTONCEper second f it does then so far so good

4HETRANSMITTERMUSTNOWBERAN-doised and then synchronised withthe receiver et’s now take a look atthese two procedures

Randomising

andoisation of the transitterensures that it uses a unique set of pa-raeters to calculate the rolling code4HISPROCEDUREISIMPORTANTBECAUSEthe original paraeters prograedin are the sae for every transitter

asically you need to personalise theparaeters to prevent another trans-itter that has the sae identity frooperating your receiver f randoisa-tion is not done there is the real riskthat soeone else’s transitter that has

ALSONOTBEENRANDOMISEDWILLOPERATEyour receiver

o randoise a transitter siply

connect pins and 5 of its con-nector together and then press switch34HETRANSMIT,%$WILLÛASHATAone-second rate for the duration e-lease the switch when you are readyAFTER BETWEEN SEVERAL SECONDS ANDseveral inutes)

he paraeters are all altered every0μs (that’s 25000 ties a second) soTHEYWILLBEDIFFERENTFOREACHTRANSMIT-ter after even short presses

Synchronisingfter randoising the transitter

MUSTTHENBESYNCHRONISEDWITHTHEreceiver o do this disconnect pins and 5 of the header and connectpins and together instead hatdone press and hold down 1 on thereceiver and then press one of theswitches on the transitter

4HE TRANSMIT,%$ WILL NOW ÛASHtwice oentarily and the receiver’sACKNOWLEDGE,%$WILL ÛASH ONANDoff at a one-second rate until switch1 on the receiver is released

olling ode rotection: eeping t ecret As previously noted, the Rolling Code Keyless Entry System provides a high

level of security because the transmitted code changes each time it is sent.

However, to further improve security, we have also included code protection for

both the transmitter and receiver.

Basically, code protection prevents the program and data within the PIC micro-

controllers from being read by a PIC programmer. As a result, the parameters used

to calculate successive rolling codes are kept safe within the microcontrollers.

In particular, this effectively prevents a transmitter from being ‘interrogated’, in

order to make a duplicate transmitter that will operate the door lock.

So, while the hex files can be used to program the microcontrollers, they can-

not be read back once programming has been verified. The parameters used

for calculating the rolling code are then randomised in the transmitter using the

set-up procedure already described. It is these parameter and the rolling code

seed values that are hidden by the code protection.

Fig.6: the test LEDs are connected to the receiver as shown here. Follow theprocedure in the text to synchronise the transmitters and test the receiver.

.OWREMOVETHELINKBETWEENPINSand on the transitter’s header/NCETHATmSDONEYOUSHOULDNOWÚNDthat the transitter operates the receiv-

er f it doesn’t try synchronising againand ake sure that the receiver hasa clear ‘view’ of the transitting

4HEABOVERANDOMISATIONANDSYN-CHRONISATIONPROCEDURESMUSTBEDONEfor each new transitter ote that aTRANSMITTERTHATHASNOTBEENSYNCHRO-NISEDWILLNOT BEABLE TOOPERATE ITSreceiver even if their rolling codes arethe sae ote also that synchronisinga new transitter prevents the use of a previously synchronised transitterthat has the sae identity

ext press the ain switch on the

transitter and check that the receiver’s3TRIKE,%$LIGHTSFORABOUTÚVESEC-onds he external r shouldALSOLIGHTWHILETHERECEIVERmSONBOARD!RM,%$SHOULDÛASHWITHANEVENONOFFDUTYCYCLE4HISÛASHINGSHOWSthe exit delay

!FTER ABOUT S THE EXIT DELAYshould expire and the r shouldTHENÛASHBRIEÛYONCEPERSECOND

ow check the operation of thesecond (saller) switch which is onthe transitter his switch should

toggle the trike2 on and off withsuccessive pressings

Testing the alarmo test the alar ar the unit and

short nput1 on the receiver to ground(0) using a clip lead he externalalar () should light after20s and should then stay on for 60s

ou can check the operation of THEDELAYEDEXITBYARMINGTHEUNITand oentarily shorting nput1 ornput2 to 0 during the exit periodhe alar should not light after

the exit period has expired

Receiver options4HERECEIVERCANBEPOWEREDFROM

A$#PLUGPACKORABATTERY7HENPOWEREDBYAPLUGPACKMAKEsure it can supply the necessary cur-rent for the electric striker and anALARM SIREN IF ÚTTED ANY ELECTRICstrikes draw around 800 so a 1PLUGPACKWILLBEREQUIRED

ote that the ared status is storedin case the power goes off; the aredORDISARMEDMODE WILL BE RETURNEDwhen power is reconnected o if the receiver was ared when powerwas lost then the ared ode will BERESTOREDWHENPOWERISRETURNED





hen powering fro a 12 batterya charger should also be connected toaintain battery charge – see ig 12 50 charger for sealed lead-acid batteries would be suitable hese charg-ers are fully autoatic – they charge the battery when required and aintain fullcharge with a trickle current

epending on your applicationtrike1 can be optioned to operate onaring on disaring or on both aringand disaring hese options are selected

using link 1 able 1 shows what eachlink connection does ou ay also wishto place a sall buzzer across the doorstrike connection to give an audible in-dication of door strike operation

he trike2 output can be oentar-ily activated whenever the secondaryswitch on the transitter is pressedlternatively it can be toggled on oroff with each switch pressing ink 2selects these options

Receiver time periodsripots 1 and 2 are used to set

the tie periods for trike1 and trike2the exit and entry delays for nput1 andnput2 and the alar period ink provides the eans to set each tieperiod – see able

ith in the ‘+’ position 1 and2 set the strike period for trike1 andtrike2 respectively able shows thevarious voltages that 1 and 2 canprovide to set the strike periods hesevoltages can be easured at 1 for1 and at 2 for 2

o set the strike periods siply adjust1 and 2 to the voltage settings re-quired and press the synchronise switch(1) on the receiver board

he delayed inputs (ie the entry

delays for nput1 and nput2) are setwhen is in the ‘–’ position nceagain it’s siply a atter of setting thevoltages at 1 and 2 and pressing1 to set the values

inally when is out 1 sets thealar period (2’s setting is ignored) Just set the required voltage at 1 andpress 1 to progra the period in

ote that because pressing switch 1progras in the tiing adjustentssynchronisation will also alter thetiing his eans that if you syn-chronise a transitter to the receiver

at a later date you will have to akesure that 1 and 2 are inthe correct positions for the option selected beforepressing 1

Table 1: Strike1 operation (LK1)

LK1 + – Open

Strike1

operateson

Arm OnlyDisarmOnly

Arm andDisarm

Table 2: Strike2 operation (LK2)

LK2 + – Open

Strike2

operation

Momen-

taryToggle Not valid

Table 3: LK3, VR1 and VR2 settings

LK3 + – Open

Operates whenS1 pressed

VR1 sets Strike1periodVR2 sets Strike2period

VR1 sets Input1 delayVR2 sets Input2 delay

VR1 sets alarm period

Notes

5V sets 64s2.5V sets 32s1.25V sets 16s0.625V sets 8s0.313V sets 4s0.156Vsets 2s



here o et he itsSuitable reed switch assemblies, door strikes and sirens are

available from Jaycar electronics. They can also supply kits

for this project.

The parts available from Jaycar include: (1) the LA-5072

normally closed (NC) reed switch magnet assembly;

(2) the LA-5078 door strike; and (3) the LA-5255 and

LA-5256 piezo sirens.

Above right: door strike available from Jaycar.

n practice this just eans leavingAND,INTHEIRÚNALPOSITIONSAFTERYOUÚNISHTHETIMINGADUSTMENTShat way if you synchronise a transit-

ter later on the last set tiing values aresiply reset to the sae values

Arm output optionink sets the ar output option

– see able hen is in the ‘+’position the r output is low on arand open on disar onversely when is in the ‘–’ position the r outputis open on ar and low on disar t alldepends on how you intend to use thisoutput as to which option you choose

Receiver lockoutny transitter that has been syn-

chronised can later be locked out frooperating the receiver his is done bysetting links 1 2 and in the receiver and pressing switch 1during power up

able 5 shows the link options foreach transitter identity ote thatthese link settings correspond exactlyto the links used in the transitter toset the transitter identity

hen lockout is perfored thePOWER,%$ÛASHESTHEIDENTITYNUMBER

to indicate that the procedure has been successfully copleted o forexaple if you lock-out an identity TRANSMITTERTHEPOWER,%$WILLÛASHthree ties at a noinal 1s rate beforea s break until 1 is released

hen 1 is released the receiverthen operates norally but with theselected transitter now locked out

f 1 is held closed the cycle of ,%$ÛASHINGCONTINUES!TTHEENDOFthe third cycle all identities will belocked out and the power will staylit until 1 is released his feature is

included as a short cut to locking outall identities

f one transitter is locked out and asecond one also needs to be lockedout then the power will have to be

switched off and links 1- repo-sitioned for that transitter identityhe power ust then be re-applied

with 1 pressedOnce the lockout procedure has

been completed, you must relocatelinks LK1-LK4 to their correct posi-tions for the receiver functions thatyou wish to select. t is then best to testthat everything is correct by pressingthe switches on another (non-locked-out) transitter and verifying that thereceiver operates as expected




Everyday Practical Electronics, September 2009 2

Undoing lockoutt’s easy to get a locked out transit-

ter to operate the receiver again (ie tounlock it) Just synchronise the trans-itter with the receiver and all will be back to noral

The rolling code for the infrared

transmitter comprises four start bits,a 48-bit code and four stop bits.

A calculation comprising a multi-

plier and an increment value is usedto generate the 48-bit code. First, youstart with a number (called the seed),

then you multiply this seed by themultiplier and then add the increment.

The result becomes the next value forrandom code.

Normally, if the calculation is con-tinued, the random code will become

larger and larger as we multiply andthen add the increment value. How-

ever, this is prevented by limiting theseed value used in the calculation to

a certain width; 32 bits in this case.In practice then, the 24-bit multiplier

multiplies the 32-bit seed. The 8-bitincrement value is then added and the

result is limited to 48-bits by eliminatingthe more significant bits. This resulting

48-bit code is the code used for the roll-ing code transmission. In addition, the

order of transmission for these bits isjumbled using an 8-bit scramble code

with 32 possible combinations.

The calculations do not necessarilyproduce random numbers, but they doproduce variations from one transmis-

sion to the next. However, in somecases, the result could converge to

settle at the same value, so it is impor-

tant to check this and make sure thecalculations do give diverging values

each time.To do this, the result of each calcula-

tion is compared to the last value toensure it is not repeated. If the result is

the same as before, the duplicate codeis not transmitted and a new calcula-tion is made after incrementing the

result. Subsequent calculations willthen begin to diverge again.

andoisationTo avoid conflict, each transmitter

must have a unique set of parameters

for making the rolling code calcula-tions. As a result, we have included

a ‘randomisation’ function, wherebythe multiplier value, the increment

value, the scramble value and theseed value are all changed in a rela-

tively random way.There are 16.7 million multipliers

available and 54 possible incrementvalues. Together with the 32 scramble

variations, these provide 29 billion dif-ferent combinations. In addition, the

minimum multiplier value is 8192 toensure a significant change in value

with each calculation.Even if two transmitters do end up

with the same parameter values, the

fact that the seed value is a part of

the calculation means that you needto be within 200 values of the correct

value in order to unlock someoneelse’s lock. The probability of this is

224 divided by 200, or one in 83,000.

This is in addition to the one in 29billion chance of having the same

parameter values!There are up to 16 different trans-

mitters that can be used with the onereceiver, and each transmitter uses

a different set of seed, multiplier,increment and scramble values. The

transmitter sends out its identificationcode that is embedded in the rolling

code, so the receiver knows which setof values it must use in the calculationfor each transmitter.

When the transmitter is sendingsynchronising code to the receiver,

it sends the 8-bit identifier, the 24-bitseed, the 24-bit multiplier, the 8-bit

increment value and the 8-bit scram-ble values. The identifier value is also

stored, so that the receiver knows thatthis identity has been synchronised.

An identity that has not been synchro-

nised will not operate the receiver.Once the receiver has these param-eters, the transmitter and receiver will

remain in lock because they use thesame calculation values.

alculating he olling ode

Installationhe olling ode eyless ntry

yste is suitable for use in hoesfactories and cars ig showshow to wire the unit for a typicalinstallation. Note that IRD1 must

be shielded from direct sunlight,otherwise the reception range will

be severely affected.n soe cases it ay be necessary

to connect the infrared receiver (1)via extended leads using twin-core

Fig.7: here’s how to connect the receiver in a typical installation. Note that you can use both NO (normally open) and NC(normally closed) sensors on the alarm inputs (Input1 and Input2). The battery charger keeps the battery topped up.





shielded cable (eg if the receiver isounted on one side of a wall but in-frared reception is needed on the otherside) ig8 shows how this is done

he two alar inputs (nput1 andnput2) can be used in conjunctionwith reed switch agnet assebliesthat change state when a door orwindow is opened or closed oucan use either norally closed ()or norally open () types (eelast onth’s weather station projectfor the lowdown on reed switches)

s shown in ig9 types areconnected in series while typesare connected in parallel oweverfor best security use only one sensorper input

lternatively you can use a de-tector or a glass breakage detector onone or both of the inputs EPE

Table 5: Receiver lockoutselections

LockoutIdentity

LK1 LK2 LK3 LK4

1 + + + +

2 + + + –

3 + + – +

4 + + – –

5 + – + +

6 + – + -

7 + – – +

8 + – – –

9 – + + +

10 – + + –

11 – + – +

12 – + – –

13 – – + +

14 – – + –

15 – – – +

16 – – – –

Table 4: Arm output (LK4)

LK4 + –

Arm output low

on arm, open ondisarm

Arm output open

on arm, low ondisarm

Fig.8: the IR receiver (IRD1) can be connected via twin-core shielded cable as shown here.

Above: you can buy both NO andNC reed switchassemblies.

Fig.9: here’s how to wire the two different sensor types (NO and NC) to thealarm inputs on the receiver board.

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