Updates to alarm.txt---------------------------------------- Note: IC3.....pin 4 must be connected to pin 8, not shown on drawing....screwed up when I re-drew it :( Please note that this alarm currently can be disabled if one of the LED wires is cut, and then shorted to ground...it will not be disabled by just cutting the wires, though....this can be remedied fairly easily with an opto-coupler to drive the LED, but will result in about twice the power consumption...another fix would be to put a 50 to 100 mA fuse on the Anode(+) side of the LED, to blow if this line is shorted to ground...but this still leaves the Cathode(-) side of the LED open for tampering.. Another possibility is to use another NPN transistor to drive the LED, which, not as fail-safe as an opto-couple, will be better than just a fuse, and would not result in a lot more power consumption.... If you don't want the LED, simply leave it out of the circuit, it will still operate, and use an alarm sticker on the bike, or whatever... If you would like to know how to connect either of these circuits to fix this, please e-mail me....If I get enough requests, I shall draw a small GIF file to show this... For lower power consumption, R8 can be increased, to drop current through the LED, and there are also CMOS versions of the 555 timer available (usually called a 7555) I have usually used the mercury switch set up so that the contacts close when the bike is raised off it's side-stand, as I rarely use the centre-stand, and the knock needed to get a bike off the centre-stand has proved enough to disturb the mercury switch anyway.. I have mounted it surrounded in heat-shrink tubing, using a plastic cable-clamp that fits around it, under the seat or tank on an appropriate bolt.. Q1 and Q2 can be substituted to many different types of NPN transistor , the specs for the BC548 are: 30Vce, 6Veb, 100mA-Ic, 500mW, hFE(gain) 110minimum.. my book lists the USA equivalent as a 2N5818 or 2N5825 The missing capacitor designator across the relay contact is C7 (100nF) I recommend using a hidden siren, not just the horn...most bike horns are easy to unplug.... In the post-script file, the left-most capacitor has had the '1' chopped off, it should read 100uF. I have made a few of these on veroboard/breadboard, and put it in a small plastic zippy/jiffy box, seal around the wires and any holes in the box with silicone sealant, to prevent water getting in.. Hide your switch well , if you want to use a barrel key-switch, they are harder to hide, so ensure that the wires behind it are well protected. To set up the sensitivity (RV1): Turn your ignition _on_ Have all indicators, etc. _off_ Turn on the alarm By activating the tail-light with a brake lever, adjust RV1 so that the alarm is triggered... It should also, of course, be triggered if your ignition is switched on while the alarm is switched on... As can be seen from this, because of the voltage drop sensing, you can even leave the ignition on, and when brakes or indicators (or any other drop in the system) are used, the alarm will trigger. If you want ignition cut-out, find an appropriate point in the bike's electrical system, and use a double-pole switch, one pole for the alarm power, and one for the ignition cut-out.. *****The switch is the weak point, HIDE IT WELL!!! put it somewhere where it is not visible, and only your fingers can reach. Any exposed wiring, wrap in black tape or black tubing to match the wiring loom of your bike.. When building on veroboard/breadboard, some patience is required, especially if you have little elec. experience, it may not work the first time, so check over your connections very well before you apply power to it.. good luck! and again: don't blame me if it doesn't work :-) Thankyou to Michael Bain, and Ross Parker for putting it into post-script format, Stephen Andersen (sp?) for checking the first GIF, and of course, Bruce Tanner for the DoD archives! Marc Alexander maa@mullian.ee.mu.oz.au ------------------------------------------------------------------ Motorcycle Alarm Circuit: Parts List: resistors: 1 x 1K (R1) 2 x 100K (R2,R5) 4 x 10K (R3,R4,R7,R9) 1 x 4M7 (R6) 1 x 470ohm (R8) 1 x 100ohm (R10) 1 x 470K (R11) potentiometers: 1 x 10K trimpot (RV1) capacitors: 3 x 100nF (0.1uF) Disc Ceramic (C1,C2,C7) 3 x 10uF Electrolytic 25V (C3,C4,C6) 1 x 1uF Electrolytic 25V (C5) semiconductors: 3 x 555 IC (IC1,IC2,IC3) 2 x BC548 or DS548 (Q1,Q2) 2 x 1N914 (1N4148) Diode (D1,D2) 1 x Light Emitting Diode, with holder (LED1) 1 x 12V relay (RL1) note: L1 is simply 10 turns of say, 0.5mm thick enamelled wire, rolled on a thin pen, or whatever is handy... miscellaneous: PC board pins, PCB, enamelled wire, Zippy Box, hook-up wire, screws, washers, spacers, nuts, solder, terminal block, mercury switch, toggle switch, spaghetti tubing, piezo siren, heatshrink tubing, cable clamp.. HOW IT WORKS The alarm works by detecting a voltage drop anywhere in the motorcycle's electrical system. Its operating principle is rather complex but we trust can be followed if one reads this sectlon several times! All three ICs are 555 timers used for various functions. Pin 5 ot IC1 is the 2/3rd reference level- that is if the voltage on pin 6 exceeds that voltage on pin 5 the IC will be triggered. Potentiometer RV1, whlch is connected to pin 5,must be adjusted so that a voltage slightly lower than this appears on pins 6 and 7. These two pins are the upper threshold level and the internal discharge transistor of that IC. The lower threshold level is established by pin 2 which is connected to +12 volts via R4. Plns 6 and 7 are decoupled to the zero volt line by C3. If any load is placed on the motor-cycle's 12 volt supply to which of course the alarm system is connected - a voltage drop must occur even if only momentarily. This negative going signal will cause the 2/3rd voltage of pin 5 to fall relative to the upper threshold level voltage (whlch is maintained at a steady level by capacitor C3). If the 2/3rd voltage does fall below the upper threshold ievel then the output on pin 3 will drop to about 0.6 volts thus initiating the alarm sequence. IC3 is an osclllator running continuously at 1 Hz - this signal is also used to energise the instrument panel mounted LED to warn that the alarm is set. The 1 HZ signal drives the base of Q2 which in turn drives the output relay RL1. The emitter of Q2 is normally held at a level around 12 volts unless the alarm is activated- when, as described above -the output on pin 3 ot IC1 drops to about 0.6 volts taking the emitter of Q2 with it and thus allowing Q2 to pulse the relay. The timing circuit switches off and resets the alarm after (approximately) 45 seconds. Capacitor C4 is held at about 12 volts via D1 and R5 and as this voltage is applied to pins 2 and 6 ot IC2 the output ot that IC is 0V. When the alarm is triggered, C4 is allowed to discharge slowly via R6. When the voltage on pins 2 and 6 falls to about four volts (this takes about 45 seconds) the output ot IC2 goes high. This turns on Q1 thus resetting IC1 which in turn shuts off the alarm. Capacitor C4 then recharges and after three seconds or so the alarm is completely reset and if needed can be retriggered. The alarm sequence wlll also be initiated if the "EXTERNAL TRIGGER" point is connected to the zero volt line. maa@mullian.ee.mu.oz.au (Marc Alexander)