Designed a simple immobiliser

[Vinci]

Hey, for you solder junkies I thought it would be interesting to post a simple immobiliser schematic which I designed a while ago.

I used this in several of my cars and found them a few times with a broken door lock, broken tupperware around the steering wheel and broken lock/stripped and cut wiring...BUT at least it was still there!!!

The schematic at the bottom proposes a bypass in the connection between the crankshaft sensor and engine control unit pins 47 and 48, which is a good choice for a car with a red top engine. Do keep in mind this connection is made with shielded wire though... Whatever connection you want to cut between your engine and the control unit is up to you off course, that makes it harder to figure it out for any regular car thieve. To test your choice just pull some plugs under the bonnet and see which one prevents the engine from being started. Or as a professional... Just keep in mind the current rating of the relay contacts... As an activate/deactivate button you can even place hidden or combined switches which are impossible to figure out for those who don't know. You could even use coded switches or key lock switches, hidden magnetical reed contacts...whatever, I'd say BE CREATIVE!!

The system could work as follows:

You turn the ignition key to make contact, then you need to operate the switch which will connect any bypassed connections between the engine and control unit. The engine starts.... Then I have incorporated a time delay which will keep the connections in tact for a few minutes so if you want to make a short quick stop (to adjust your GPS or whatever, write an SMS..) you don't need to re-activate it, engine still starts..

If you are going to leave the car for longer anyway and want to activate the immobiliser right away then press the same button with the ignition key off and the system will activate right away, without delay...

I have included an LED which will be lit for as long as the delay is activated, it will only be lit when the ignition key is off. After the delay time when the light is out the car won't start until the button is pressed...

The circuit draws no power when the car is parked and the delay time is passed, when the button is pressed it'll draw just 160mA!!

Car thieves, eat that!!!

Here's the schematic:

[Paul]

Good info. Thread title changed as per PM

Paul

[scooby-KILLER]

at it again wish i learnt more about this sort of stuff but think i would struggle to pick it up now

good work vinci

[Nemesis]

Nice system but it won't stop Paul, his flatbed and his Dudley crew.

[scooby-KILLER]

Nice system but it won't stop Paul, his flatbed and his Dudley crew.

[Vinci]

Nice system but it won't stop Paul, his flatbed and his Dudley crew.

I figured that, hence the pedal lock and me always parking it in tight between other cars.... It's a barrier, and as it is invented by a human there will always be humans knowing their way around it....

Been using it for about two years now in my Astra by the way and it's still going strong! Had it in previous cars as well, but don't own them any more....

[Vinci]

This I can build for anyone interested as well by the way... It'll be:

-A simple small box with some screw connectors to be the wire in/outputs for any sensor wiring (or if you like to keep it simple take a single wire to the ignition coil or the switched live to the starter. The latter will be much easier to figure out though....)

-A connector for any type of momentary switch (you can use window up/down switches, tank cap opening switches etc. etc. from Vauxhall so it will blend in with the interior nicely) I recommend a magnetic reed contact, easily glued behind a plastic panel and then just as easily flicked by wiping a small magnet past it...

-An LED connector to give indication of the time delay. This will only be on when the ignition is switched off and also be off after the time delay has passed...

So the simple functional description is:

Starting
-Get in car, turn ignition key, press secret button and start.
-When stopping shortly you can just start, no hassle.

Stopping
-Just turn ignition off and the delay time will start, I can make this adjustable to set any desired range of delay times.
-When stopping for longer and in a creepy place you can deactivate the delay by simply pressing the secret button with the ignition switched off.

[MSG]

Clever coont!

[Dom]

Just some constructive critisism .......

C1/S1 could be a little tricky long term as inrush currents could cause the S1 contacts to arc on larger capacitors, a small(ish) resistor in series with S1 will help a lot.

Replace T2 with a darlington and you can reduce C1 significantly.

You could also do with some pulldown resistors for all the bases of the transistors - just in case as you have diodes in line with all the base drives effectively leaving the bases floating when there is no drive to them.

[Vinci]

Just some constructive critisism .......

C1/S1 could be a little tricky long term as inrush currents could cause the S1 contacts to arc on larger capacitors, a small(ish) resistor in series with S1 will help a lot.

Replace T2 with a darlington and you can reduce C1 significantly.

You could also do with some pulldown resistors for all the bases of the transistors - just in case as you have diodes in line with all the base drives effectively leaving the bases floating when there is no drive to them.

Thanks for the info Dom, the arching has crossed my mind and the darlington as well, but this was just built and tested with some parts I had in the drawer. Pulldowns were added, just not drawn, this was sort of a preliminary schematic....

I should probably edit it for the community's sake....