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High perforinance design has special SOMCCAR This ultrasonic movement detector can be added to your house or car alarm system, or can be used as a selfcontained ultrasonic car burglar alarm. By BRANCO JUSTIC The unit to be described here is a proven performer. It's easy to build, does not require any alignment, and has been field tested in several cars. It's also extremely sensitive and will instantly respond to the opening of doors, glass breakage or movement anywhere in the vehicle. Unlike other ultrasonic alarms published in the past, this unit includes special circuitry to guard against false triggering. We'll talk about that feature a little later on. There is also full provision for back- up battery operation, a flashing dashboard light and two separate instant trigger inputs which can be wired to bonnet and boot switches. A single control line is used to enable and disable the circuit. This line can be controlled by a simple mechanical switch, by relay contacts, or by digital logic circuitry. If you wish, you can easily add the UHF Remote Switch described in the March issue of SILICON CHIP. This will let you switch your ultrasonic alarm on and off simply by pressing the button on a small keyring transmitter. Another possibility is to use the ultrasonic movement detector as a sensor for the Protector Car Burglar Alarm. In that case, you would simply feed the output of the ultrasonic movement detector to one of the inputs on the Protector, instead of to an external siren circuit. By combining the two units in this way, you will end up with a comprehensive car burglar alarm with features to rival any commercial unit. Crystal control All ultrasonic movement detectors include an oscillator circuit which drives an ultrasonic transducer element, generally at 40kHz. Many designs use freerunning RC oscillators but these can lead to all sorts of problems, in- This version includes the optional lamp flasher/battery back-up circuit and can be used as a self-contained car burglar alarm. The two transducers are fitted with rubber spark plug covers and spring steel clips which attach to the windscreen pillar trim. 62 SILICON CHIP circuitry to stop false triggering BURGLAR ALARM eluding loss of sensitivity as the oscillator drifts and false triggering due to amplitude and phase changes. The design described here solves those problems by employing a crystal locked oscillator. This allows extremely high sensitivity settings without false triggering problems. As a bonus, it eliminates the need for critical frequency adjustments during construction. We'll talk more about the crystal oscillator later on in the circuit description. How it works Fig.1 shows the circuit details. In brief, it works like this: oscillator IC2a-IC2d provides a 40kHz drive signal to the transmitter transducer (Tx) which generates the ultrasonic output signal. This signal is picked up by the receiver transducer (Rx) and undergoes two stages of amplification (ICla and IClb) before being detected by Dl. In a still environment, a steady DC signal appears at the output of the detector. When movement occurs, the detector output varies accordingly and these amplitude variations are coupled to low frequency amplifier stage IClc which then triggers a monostable consisting of ICZe and ICZf. The monostable then drives switching transistor Ql which can be used to activate an external alarm circuit or to trigger an external relay. Let's now look at the circuit in more detail. The transmitter section employs four inverters (IC2aIC2d) in a 4049 hex inverter package. ICZd is biased in the linear mode by the 270k0 resistor and its output also biases ICZc in the linear mode. Thus, ICZd and ICZc form a linear amplifier with an overall phase shift of 360°. The 40kHz crystal forms part of the If you wish, you can build the circuit and transducers into a plastic case for installation on the dashboard or the rear parcel shelf. This version can be used as a movement detector for an existing car or house alarm. The two transducers can be soldered directly to PC stakes on the PCB or connected via shielded cables. The LED turns on when movement is detected. feedback path between input and output and so the circuit oscillates at the crystal's resonant frequency - ie, 40kHz. Note the lOOkO a nd 27k0 resistors on pin 13 of ICZc. These form an attenuator circuit which prevents excessive drive voltage from being applied to the crystal. Inverters ICZb and ICZa buffer the oscillator output and produce complementary 40kHz output signals (ie, signals that are 180° out of phase with each other). These complementary signals are then used to drive the 40kHz transducer. MAY 1988 63 .,. + 1M +9V +12V .,. 100+- 0.11 LINK D3 1N4148 +12V 08 1N4004 t + 10M 1+ 27k D6 1N4148 100k OUTPUT TO RELAY/ALARM -:- -:- D4 1N4148 220!l + TO DISABLE -:- B t SEE TEXT 1NOouT EOc GNO VIEWED FROM BELOW ULTRASONIC MOVEMENT DETECTOR/ALARM Fig.1: 40kHz signals from the transmitter (IC2a-lC2d) are picked up by the receiver, amplified by ICla and IClb and detected by D1. When movement occurs, the output of IClc swings high and triggers an output monostable (IC2e and IC2f). Because the drive signals are out of phase, the peak-to-peak transducer drive voltage is approximately twice the rail voltage; ie, 18V p-p. Receiver The 40kHz signal from the transmitter is picked up by the receiver transducer and applied to a low pass filter (lkQ and 680pF). From there, the signal is fed to sensitivity control VRl before being AC-coupled to the inverting input of op amp stage ICla. ICla and ICl b form two identical amplifier stages with each stage having a gain of 37, or 31dB. Thus, 64 SILICON CHIP the overall gain of these two stages is 62dB. The 2.2pF capacitors across the lMQ feedback resistors roll off the gain of each op amp stage above 70kHz. The amplified output from ICl b appears at pin 4 and is fed to diode detector Dl. Dl 's output, in turn, is fed to a low pass filter stage consisting of the lOkQ and lO0kQ resistors and a 0.1µ,F capacitor. This detector/filter circuit produces a varying output voltage when movement is detected and this signal is AC-coupled to lowfrequency amplifier stage IClc. IClc also has a gain of approx- imately 30dB and a bandwidth of approximately 230Hz. Its output, which is normally biased low, is fed to a "charge accumulator circuit" consisting of a lOkQ resistor, diode DZ, a 1µ,F capacitor and a lMQ resistor. This circuit allows rapid charging of the 1µ,F capacitor (via the 10kQ resistor) when IClc's output swings high (ie, when movement is detected), with the lMQ resistor then discharging the capacitor over a much longer period of time. Because it takes a relatively long time for the capacitor to discharge, the inclusion of this circuitry prevents the alarm from false trig- + 0-/41+-'W,h-il_ _ _ _....,._....,....._...---.--......--......--O.ULt moTN~C FROM ALARM VEHICLE 100 + SUPPLY 16VW _ D2 22 {1 1N4004 -.i 1W BACK UP BATTERY + +12V VIA IGNITION SWITCH GNi ., B ELJc VIEWED FROM BELOW Fig.2: this is the optional lamp flasher/battery back-up circuit. When the ignition is off, 555 timer ICl drives Q2 and the lamp at a lHz rate. When the ignition is turned on, Q2 turns on and disables the 555 timer. gering on noise or other brief disturbances. At the same time, it has no affect on the unit's sensitivity in a practical situation. Inverters IC2e and IC2f and their associated components form the output monostable circuit. This circuit monitors the voltage across the lµF capacitor via diode D3. Here's what happens: Normally, pin 7 of IC2e is low and pin 6 is high and so both sides of the 22µF capacitor are at + 9V. This means that the output of the monostable (pin 4 of IC2f) is low and thus Ql is off. If movement is detected, the output of IClc swings high and charges the lµF capacitor via DZ and the 1okn resistor. When the voltage across the lµF capacitor reaches approximately + 5V, pin 6 of IC2e goes low and this pulls pin 5 of IC2f low via the 22µF capacitor. Pin ·4 thus switches high and turns on Ql and indicator LED 1. At the same time, the monostable latches up via diode D4 which connects the output (pin 4) back to the input, pin 7. The monostable timing period now commences, with the 22µF capacitor charging towards the + 9V rail via the 10Mn timing resistor. After about two minutes, the voltage on the capacitor reaches + 4.5V and pin 4 of IC2f switches low again, thus turning off Ql and the indicator LED. Alternatively, if the link is installed, the monostable timing period is PARTS LIST 1 PCB, code OE102, 129 x 62mm 1 pair of 40kHz ultrasonic transducers 1 40kHz crystal 1 6-way PC-mounting terminal block 4 PC stakes 1 plastic case to suit Semiconauctors 1 CA3401 quad Norton op amp 1 4049 hex inverter IC 1 BC337 NPN transistor 1 78L05 3-terminal regulator 1 1N4004 silicon diode 7 1N41 48 silicon diodes 1 5mm red LED Capacitors 2 100µF 16VW PC electrolytics 2 22µF 16VW LL electrolytics 4 1µF 1 6VW LL electrolytics 2 0. 1µF ceramic 7 680pF ceramic 2 2.2pF ceramic cut to one second, as set by the 10okn resistor. The link should be installed during testing, or if the ultrasonic movement detector is to be used as a sensor for another alarm circuit. There are a couple of other details in this part of the circuit that remain to be discussed. First, when Ql turns on, it quickly discharges the lµF capacitor via Resistors (0.25W, 5%) 4 x 1 oMn , 5 x 1 Mn, 1 x 21okn , 5 x 1 00kn, 5 x 27 kn, 7 x 1 0kn, 1 x 1kn, 2 x 220n, 1 x 150n , 1 x 4. ?kn horizontal trimpot Lamp Flasher/Backup Battery Circuit 1 1 . 2Ah gel battery 1 '8-way PC-mounting terminal block 1 1 2V bezel lamp Semiconductors 1 555 timer IC 1 BC327 PNP transistor 1 BC548 NPN transistor 1 15V 1W zener diode 2 1N4004 silicon diodes Capacitors 1 100µF 16VW electrolytic 1 22µ,F 16VW electrolytic 1 .01 µ,F ceramic Resistors (0 .25W, 5 %) 2 x 22kn, 2 x 1 0kn, 2 x 1kn, 1 x 22n (1W), 1 x 4.7n (1W) D5 and its series lOkn resistor. This effectively resets the trigger circuit. Second, if a voltage of 6V or more is applied via diode D7, the output of IC2f remains low and the alarm is unable to respond to received signals. This is the DISABLE input. In practice, the anode of D7 can be switched to the + 12V rail to disable the alarm. This is made MAY 1988 65 ... w ,z ~ 3: "' et 12V o ~ s ~ CUT PCB HERE IF REQUIRED I= - + + s z t LINK FOR DETECTOR (1 s). OMIT FOR ALARM (2m). i 40kHz TRANSMITTER Fig.3: the PCB layout includes both the alarm circuit and the lamp flasher/battery back-up circuit. The transmitter is wired using twin-core shielded cable while the receiver is connected with single-core shielded cable. possible by the inclusion of D6 which clamps the input of IC2f to the + 9V rail. Protection for the bonnet and boot is provided by the two instant trip inputs. These inputs are each coupled via a lµF capacitor and a common low pass filter network to the inverting input of IClc. Shorting either input to ground briefly pulls pin 11 of IClc low and instantly triggers the alarm. Power for the circuit is derived from the vehicle's battery via a 78L05 3-terminal regulator (which is the low power version of the familiar 7805). The combination of the two resistors associated with the 78L05 jacks its output up to + 9V. The associated lOOµF and 0.lµF capacitors provide supply line decoupling. Lamp flasher circuit Fig.2 shows the optional lamp flasher and battery back-up circuit. In this case, power from the vehicle's battery is derived via isolation diode D1 and a 4.7n resistor. Diode D2 isolates the optional back-up Where to buy the parts Parts for this project are available from Oatley Electronics, 5 Lansdowne Pde (PO Box 89), Oatley, NSW 2223 . Telephone (02) 579 4 985 . Prices are as follows: · PCB plus on-board parts fpr ultrasonic movement detector section only (excludes ultrasonic se nsors) ...... .... ........ .. .. .. ..... $2 5 .90 On-board parts plus bezel lamp (no PCB) for the lamp flasher/battery backup circuit ...... .. .. .... .. ...... .. .. .. .. .. .. .. .... .. .... .. . $ 7. 50 40kHz ultrasonic transducers (pair) .... .. .... .. ...... .. .. ...... .... .. .... . $ 1 3 .50 Pair of transducer covers plus spring steel wire .. .......... ..... ... ... .. $2. 50 12V 1.2Ah gel battery ........ ... .. .. .......... .. .. .. ..... .. .... .. .. .......... $24 .90 Relay kit (includes PCB, relay and standoffs ) .. .. .. .. ...... .... ...... .. .. $3 .80 Note: copyright for the PCB artwork associated with this project is retained by Oatley Electronics. 66 SILICON CHIP battery, while zener diode ZDl protects the lamp flasher circuitry from spikes on the supply rail. Normally, D2 is reverse biased and the back-up battery is charged via the 220 resistor across D2. However, if the vehicle's supply is disconnected, D2 is forward biased and power is supplied to the alarm circuit from the back-up battery. ICl, Ql and Q2 form the lamp flasher circuit. It operates quite independently of the ultrasonic movement detector circuitry. When the ignition is off, the lamp flashes; when the ignition is on, the flasher circuit is disabled. ICl is a 555 timer wired in astable mode and oscillates at a frequency of approximately lHz (ignition off). Its pin 3 output drives PNP transistor Q2 which switches the lamp on and off. Alternatively, a high-intensity LED and a current limiting resistor could be used instead of the lamp. When the ignition is turned on, Ql saturates and pulls pins 2 and 6 of the 555 timer low. This immediately disables the 555, with pin 3 remaining high and Q2 and the lamp off. WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS .. . WOOD FOR CHIPS .. . WOOD FOR C LED DISPLAY SPECIALS SYDNEY'S MOST COMPREHENSIVE RANGE OF DIN41612 CONNECTORS? ~ ~ (t 0 "Cl 0 ~ ~ c It 0 "Cl 0 ~ ~ :t (.) It 0 "- Cl 0 ~ Geoff is now stocking most of the DI N41612 :E::::Et?S:5=2:i:iES:i::i:i:$~:iE:ii:: range of plugs and sockets . The coding for '!'"_ -_..,....._........,........,_ _ _ _ __ _........,__..l!i the uninitiated is as follows •· "" · There are three rows of pin locations A,B and C. £ indicates even pins only . The body size and number of pins is quoted SOCKETS each time thus 96/32 is a 96 hole body fitted BODY/PINS CONNECTION PRICE with 32 pins S64/32 A STR PCB $8.00 STR = straight connection RIA = Right S64/64 A+B STR PCB $13.65 angled S96/96 ALL STR PCB $16.35 PCB = circuit board mounting WW = Wire S96/32 A STR PCB $8 .00 Wrap S96/64 A+C STR PCB $12.55 PLUGS S96/32 A+CE STR PCB $8.00 BODY/PINS CONNECTION PRICE P64/32 A STR PCB $8.00 S64/32 A RIA PCB $8.00 P64/64 A+B STR PCB $12.55 S96/96 ALL RIA PCB $18.40 P96/32 A STR PCB $8.65 S96/64 A+C RIA PCB $13 .55 P96/32 A+CE STR PCB $8.65 S96/32 A+CE RIA PCB $8 .65 P96/64 A+C STR PCB $13 .55 S96/32 A RIA PCB $8.65 P96/96 ALL STR PCB $11 .45 S64/32 A STR PCB $8.00 A P64/32 RIA PCB $5.90 S96/32 A STR PCB $8 .65 P64/64 RIA $8.40 A+B PCB S96/32 A+CE STR PCB $8.00 P96/96 ALL RIA PCB $12.55 S64/64 ALL $13.55 STR PCB P96/32 A RIA $5.85 PCB S96/64 A+C STR PCB $11.45 P96/64 RIA $8.40 A+C PCB P96/32 A RIA PCB $6.40 S32/32 A STR WW $8.65 P96/32 A+CE RIA PCB $6.40 S64/32 A STR WW $8.65 P96/64 A +G RIA PCB $8.40 S96/32 A STR WW $8.65 S96/32 A+CE STR WW $8.65 P64/32 A $8.65 STR WW S96/64 A+C STR WW $11 .45 P64/64 STR WW $13.65 A+B S96/96 ALL STR WW $18.35 P96/32 A STR WW $10.65 S96/96 ALL STR WW $18.35 P96/32 A+CE STR WW $10.65 S96/32 A STR WW $8.65 P96/64 A+C STR WW $11.45 S96/64 A+C STR WW $13.65 P96/96 ALL STR WW $13.55 S96/32 A+CE STR WW $8 .65 Don't just ask Geoff for DIN41612... You'll find one of the widest ranges of HEADER PLUGS leading brands of connectors - ex stock - at 0.1" PITCH IDC CARD EDGE CONNECTORS 40way $11.55 50way $13 .95 $8.50 $9.40 IDC "D" CONNECTORS ~ It 0 "Cl 0 10way RIA 14way RIA STR 16way RIA STR 20way RIA 26way RIA 34way RIA STR 40way RIA STR SOway RIA 60way RIA Geoff Wood's . So call in and discuss your requirements! 26 way 34 way ~ Plug $6.40 Socket $6.40 1Spin Plug $7.60 Socket $7.60 25pin Plug $8.40 Socket $8.90 37 pin Plug $20.40 ~ 0.8" GREEN DISPLAYS 7 segment common cathode with R&L hand decimal points. Peak wavelength is 565µm If is lOmA (25mA max) Only a few available LTS3403 $4 .50 1.02" GREEN DISPLAYS 7 segment common cathode with R hand decimal point. Peak wavelength is 565µm If is 10mA (25mA max) Only a few available LTS1723 $5.50 $6.90 $7.65 $5.90 $4.20 $4.20 $7.65 $4.90 $6.20 $5.40 $8.55 $9.80 $10.60 $11.70 10way $3.55 14way $4.75 16way $4.70 26way $5.20 34way $5.70 40way $7.80 50 way $7.40 64way $14 .85 ~ 0 0 ..,, 0 J:) () :i: ~ 1.02" RED DOT-MATRIX DISPLAYS Anode column by cathode row dot matrix display with 35 leds . Peak wavelength is 655µrn If is 10mA (25mA max) Only a few ava ilable LTP1057 $7.50 10 POINT BAR GRAPH DISPLAYS Red, light red, green and yellow Extremely limited quantity only LTA1000 $4.50 ~~, 11 TRANSITION SOCKETS 9pin ~ ~ FND500 REPLACEMENT So many projects have used the popu lar FNDS00 led display . Alas the FNDS00 is no longer available. But Geoff has found a direct replacement - the LTS543 from Liton . And they're only B0cents each if you buy ten of 'em . But hurry I LTS543 $8.00/ten $1 .20 each. ~ j 11~ . f□OO~~O~ ',' 5mm SQUARE LEDS Parallel sides for easy stackability . Ch oice of three colours - red , light red and gree n - all at the same low price of 30c each ($2 .70 for ten all the same colour) And if you 're after 3mm Yellow leds they're just 20c each 1 PHOTO INTERRUPTER A real handy gadget for anyone into robotics . Consi sts of a LED(Max If 60mA ) and 30V phototransistor faci ng each other acro ss a 3mm x7mm gap. Any object in the gap stops the light and switch es the transistor off. Very fa st (5µs ). Easy to mount. Use in counting , position sens ing , tacho , opto ignition etc. \ You could pay more \ than twice Geoff's price of $4.00 each. ~ 0 0 ..,, 0 J:) () :i: 'i; (/) :"i: a 0 0 GEOFF WOOD ELECTRONICS PTY LTD ..,, 229 Burns Bay Road , (Corner Beatrice St.) INC IN Nsw Lane Cove West, N .S.W . P.O . Box 671 , Lane Cove N .S .W. 2066 0 0 Telephone: (02) 427 1676, Fax: (02) 428 5198. () Cl 8.30am to 5.00pm Monday to Friday , 8.30am to 12 noon Saturday. Mail Orders add $5.00 to cover postal charges . Next day d elivery in Sydney add $5.00. It "0 ~ All prices INCLUDE sales tax. Tax exemption certificates accepted if line value e xceeds $10.00. J:) :i: r"'=""°' ="= --,~,, --'S=-T -,1 TO I~ BANKCARD. MAS TE RCA RD. VISA. CHEQUES OR CASH CHEERFULLY ACCEPTED ~ BONNET 12V RELAY BOOT :.:5 +12 GROUND....,...._.-. +12V FROM BACK.UP BATTERY....;f--_;;;3A~l<N•L:::IN::JE~FU::SE_..;,+~----• cur• LINK• +12V VIA IGIITIOH SWITCH . FLASHER LAMP +12V TO ALARM CIRCUIT~ GROUND eg BA - ··· ·· · 0---+12V IGNITION SWITCH ~DASHBOARD • CHASSIS 1 ,e/ FLff~~R Fig.4: here's how to wire the unit as a self-contained car burglar alarm. In practice it would be best to delete the disable switch and use the UHF Remote Switch described in the March issue instead. The optional lamp flasher/back-up battery circuit has been deleted from this movement detector version. Angle the transducers away from each other as shown if they are soldered to the PCB. Construction All the parts are mounted on a printed circuit board (PCB) coded OE102 and measuring 129 x 62mm. The optional lamp flasher circuit is accommodated at one end of the PCB and this section may be separated from the main part of the board if not required. Two versions of the circmt can be built up: (1). An ultrasonic movement detector only, without the lamp flasher circuit. This version could serve as 68 SILICON CHIP a sensor for a house or car alarm (eg, the Protector Car Burglar Alarm described in the February 1988 issue of SILICON CHIP). The ultrasonic sensors could either be soldered directly to the PCB (eg, for use in a house) or connected to the PCB via shielded cables [for use in a car). (2). An ultrasonic detector/alarm for use as a self-contained car burglar alarm. In this version, the lamp flasher circuit would typically be retained and the alarm output used to trigger a relay to sound a siren horn. Both the above versions are shown in the accompanying photographs. Follow the parts layout diagram shown in Fig.3 when wiring up the unit. No special procedure need be followed here but make sure that all diodes, transistors, ICs and electrolytic capacitors are correctly oriented. Also, be sure to use the correct part at each location. Regardless of which version you build, the link in series with the lOOkO resistor should initially be installed. This will set the monostable period to about one second and make the unit much easier to test later on. If you are going to use the unit as a free-standing alarm, the link can be cut later on to extend the alarm time to around two minutes. Leave the link in circuit if you intend using the ultrasonic movement detector to trigger another alarm circuit. PC stakes are used to terminate the connections from the transducers, while PC-mounting terminal blocks terminate the remainder of the external wiring connections. Don't confuse the two transducers. The transmitter will be marked with and an "S" or a '·'-T" while the receiver will be marked • PROTECTOR CAR BURGLAR ALARM •• • +12V ;• ••• •• • • • • •9 INSTANT •10 DELAYED __-1 CHASSIS~ ' r - T O DISABLE OUTPUT OF UHF REMOTE SWITCH •• ~~Cl>Wf- ~::1~~~ ~~=+~= ULTRASONIC MOVEMENT omcTOR t INSTALL 6 LINK Fig.5: the ultrasonic movement detector can be used as a sensor for the Protector Car Alarm. Just follow the wiring diagram shown here. with an "R" or an "M". Damage may result if the transducers are interchanged. Note that the transmitter should be connected using twincore shielded cable. Rubber spark plug covers are used to cover the transducers as shown in one of the photographs. These are pushed over the transducers which are fitted inside coiled pieces of spring steel wire. The other ends of wires are shaped to clip onto the windscreen pillar trim. Testing This step is straightforward since no adjustment of the transmitter frequency is required. To test the unit, set the sensitivity control midway and connect up a 12V DC power supply. The unit should now be operational; ie, the LED should light for about one second whenever movement occurs. You can now check the alarm output by connecting your DMM between the OUTPUT terminal and The lamp flasher/battery back-up circuit can be used separately if required. ground ( - ve ). Set the DMM to the 20V range and check that the OUTPUT terminal switches from + 12V (nominal) to less than 1V whenever movement occurs . Installation Once assembly has been completed, the PCB can be installed in a suitable plastic case. We mounted the detector version in a plastic jiffy case, with cutouts to clear the LED and the two transducers. Alternatively, you can wrap the PCB in foam rubber and then "poke" the assembly into a suitable spot behind the dashboard. Use plastic cable ties to secure the assembly behind the dashboard. In many cars, you can gain access behind the dash panel by temporarily removing a loudspeaker grille and the loudspeaker. Fig.4 shows how to wire the unit as a self-contained car burglar alarm. Note that the disable switch will have to be mounted externally since the unit has no exit and entry delays. · A far better scheme would be to get rid of the disable switch altogether and substitute the UHF Remote Switch described in March 1988. It's really quite easy - just connect the disable output of the remote switch to the disable input of the ultrasonic alarm (see Fig.5). Fig.5 shows how to use the ultrasonic movement detector as a sensor for the Protector Car Burglar Alarm. In this case, the optional lamp flasher circuit is deleted from the movement detector and the + 12V supply is derived from terminal 7 or 8 on the Protector PCB. Connections to the remaining terminals on the Protector PCB are as shown in Fig.5, p.25 of the February issue. Fig.12, p33 of the March issue shows how to use the UHF Remote Switch to control the Protector alarm, instead of the original on/off switches. Finally, make sure that you install the alarm in a professional manner. Hide the back-up battery in the boot or some other inaccessible location, and use a crimp connector kit to correctly terminate the wiring leads. ~ MAY 1988 69