• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Newbi Alarmed by this site

Not open for further replies.


New Member
Hi All, just found this site and it looks great, load of info all most too much to look through, so appolgies if there is a circuit on here somewhere.

I am after some help my electronics is limited and is about 30 years old, however it looks as things don't change that much, looking at some of the circuits I have seen, anyway I am trying to build a simple car alarm for one of my sons car. Years ago I built one for myself using a couple of 555 timers. Now I have forgotten how I did it, to my amazement they are still around.

What I want to acheive is :-

To use the 12v from the door light switches to trigger the circuit, which will via a relay switch on the horns and lights for a predetermined (adjustable) time say 2-10 mins, then resets, irrespective of wheather the doors remain open or shut.

I want to be able to set and disable the alarm via a switch from inside the car so it needs to have an entry and exit timer (adjustable would be nice).

I have found this circuit which looks like it does what I want, but it looks like the relay stays on all the time until disarmed i.e no timer, but I am so rusty, is my undertanding correct, could someone just talk me through the circuit, and how to time the alarm on preiod or suggest something better..

So looking at this circuit, from memory R1 + C1 and R1 + C2 adjust the delays (but don't know how to calculate them)

Switch on alarm by closing S1
Open S2 to arm
timed delay for exit (R1 +C1)
(open and close door with no effect within the time delay)
Delay time elapsed
open doors
timed delay for entry (R1 +C2) starts
timed delay for entry ends
relay powers up (reains on until S2 is closed)
Close S2 disarmed

Thanks in anticipation Keith

PS: got another problem/project anyone know anything about CAN BUS's in cars, differnt car I hasten to add..



New Member
Hi Thanks for this I think (Micro-controllers) Hmm go on then point me somewhere, not oppossed to learning curve but this was just going to be a very quick cheap alarm .... not re engineered Cobra although it certainly do with it...


Most Helpful Member
Just have you son do what I did. Drive the oldest ugliest piece of junk around. No one will even think about stealing it or even breaking into it! :(

If it needs an alarm its to expensive or you have to much junk inside!:p

Plus having a eye sore car that stands out keeps him out of trouble simply because everybody will remember what vehicle was at the site of the crime!:eek:
Not open for further replies.

EE World Online Articles