Price - Stock No 510




Constructing the PCB

  1. Check  the  P.C.Board  for  damage to tracks.  Any breaks can be soldered over.  Check with a multimeter or electronic circuit tester.
  2. There are eleven resistors, identify them and their locations using the Resistors page and the PCB Placement diagram above.
  3. Solder in place - see Soldering Technique.
  4. Insert the two 1N914 diodes, care needs to be taken to ensure the correct polarity - see  Diodes.  Solder in place.
  5. The three IC sockets can be soldered in place.  While orientation is not critical, it is a good idea to insert them so their notches match the orientation of the IC's in the PCB Placement diagram. 
  6. Identify the three ceramic capacitors marked 104 - see  Capacitors , insert in the correct positions and solder in place.
  7. The 7 PCB pins can be inserted and soldered.
  8. Insert the trimpot and solder.
  9. The electrolytic capacitors are polarised and must be inserted in the correct orientation.  There are 3 x 10uF and 1 x 1uF electrolytic capacitors, ensure the location and orientation is correct and solder in place.
  10. The BC548 Transistors need to be orientated correctly.  Check the PCB Placement diagram and solder.
  11. Insert the relay and solder.
  12. The coil is made from the length of enamelled copper wire wrapped thirty times around a 5mm former (5mm drill bit shaft).  The enamelling insulates the inner copper wire when wound into the coil.  Once the coil is wound, trim excess wire allowing about 10mm for soldering.  The enamelling is to be removed on these 10mm leads to allow solder to take to the copper wire.  Scraping with a sharp knife or light sand paper will suffice.  Insert the coil in the PCB and solder.



  1. Tin all the PCB pins - similar to Tinning wire.
  2. The fig 8 wire and a LED bezel are included to remotely mount the LED.  Take the Fig 8 wire and strip about 5mm of insulation - tin the ends of the wire - refer Tinning wire
  3. Solder one end to the PCB pins at the LED location.  The other end of the fig 8 wire is to be soldered to the LED legs - ensure polarisation is correct - see  Diodes.
  4. The black wire is for 0V or electrical earth of the car.  An eye terminal is supplied so this wire can be attached directly to the vehicle chassis.
  5. The switch needs to be located in a descrite position accessable from the outside of the vehicle.  This allows the alarm to be disabled before entering the vehicle.
  6. 12V is supplied via the switch.  The red wire is for +12 V and this should remain at 12 V even if the key is turned off and removed.  A wire tap is supplied to tap into a suitable wire.
  7. The relay output could be used to sound the vehicle's horn or other attention attracting device.

The cuircuit should not be connected directly to the battery as this will inhibit the voltage drop sense/trigger.


Operation and Testing

  1. Before inserting the IC's, connect 12V to the circuit and turn the switch on.  use a multimeter to check that each IC socket has 0V at pin 1 and 12 V at pin 8.
  2. Turn the power off and insert the IC's.
  3. Set the sensitivity trimpot to a central position.
  4. Turn the power on - observe the LED - flashing about 1 Hz.
  5. Turn the trimpot anti-clockwise until the alarm triggers.
  6. Turn the power off and turn the trimpot clockwise a small amount.
  7. Turn the power on and operate something electrical on the vehicle (interior light, parkers ...) and observe the alarm trigger.  The alarm will trigger for about 43s and reset.
  8. If you experience false triggers, turn the sensitivity trimpot a small amount clockwise and re-test.
  9. The External Trigger is activated when this pin is taken to 0V - possible uses could be a boot or bonnet switch activated on opening.

Trouble shooting

Troubleshooting,  if necessary will involve careful checking of locations and polarity of components - IC's, transistors, diodes and capacitors. Re-solder all joints and check to make  sure  you  have  not  bridged across  between  any  two adjacent component legs.  The end  of  a  broken  hacksaw  blade  sharpened  on  an  emery wheel is a good tool for cleaning between soldered joints.

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