Electronics projects Alarm circuit Home Julian Rogers Home

The car alarm I developed for my TR7 lies within what appears to be a bit of a mess of circuits and wiring seen in the picture left. The actual circuit is under the buzzer near the middle.

The system and the other bits and pieces are located in a tray which I have made to fit under the dash on the driver’s side (the car is LHD by the way). The original idea was to tidy up the messy collection of odometer and clock reset controls, the bonnet release and the choke which hang under the dash in a rather un-designed, after-thought sort of way on the original car. This had consequences which led to the usual complications!

However, the story behind the alarm system is quite straight forward. A soft top is a very insecure car and I felt a few security measures were justified. For example the door buttons are so easy to access by just un-popping a popper and just reaching in a few inches. I removed the buttons and fitted an electric lock was needed but I just felt something that beeped and flashed if a person leant into the car might be helpful.

The system uses an Arduino linked to an ultrasonic alarm module. I also use the same Arduino to operate the flashers and hazards so it was no problem to link in the alarm. I also fitted a remote switching module utilising a key-fob transmitter so the alarm could be set and unset remotely and linked in the lock motors to give remote locking if required.

The original reason for converting to electronics for the flashers and hazards was that I wanted to change the existing switch gear for old-school Lucas-type toggle switches. I couldn’t find a switch of this type which would do for the flashers so I had to complicate things. However, using electronic flashers means that the number or type of lamps does not affect the flash rate. (I have a combination of filament and LED lamps installed - I cant find an LED which is bright enough for the rear lights as the lamp is fitted sideways.

Circuit diagram and software is next.

Car Alarm