Generating 12V output signal when car alarm is disabled

[mikebigball]

Hello forum ! I want to create a circuit, that will produce a 12v output signal, when my car alarm in NOT armed..

So, what i have :
An aftermarket alarm system, that only has a GND output, when the system IS armed..
Also, it produces 12v square pulse, when the systems is arming/de-arming for the doors to lock/unlock

What i want :
To have a 12v signal (that will be used to drive some relays maybe) ,when the car alarm is not armed.
And the whole circuit should not be consuming any current at all, when the car alarm is armed...

 

[AnalogKid]

An aftermarket alarm system, that only has a GND output, when the system IS armed..
Also, it produces 12v square pulse, when the systems is arming/de-arming for the doors to lock/unlock

Are these two separate signals, or the same one?

ak

 

[dougy83]

Hello forum ! I want to create a circuit, that will produce a 12v output signal, when my car alarm in NOT armed..
An aftermarket alarm system, that only has a GND output, when the system IS armed..

Is there any reason you can't connect a relay between 12V and the "GND output"?

 

[Pommie]

The only way to not consume any current is with a latching relay. Use the ground (or lock) signal to turn it on and the unlock to turn it off.

 

[AnalogKid]

Not the only way. The alarm system output is at GND when armed, so a circuit with an NPN BJT or n-channel MOSFET as the first stage would be completely off.

ak

 

[KeepItSimpleStupid]

A dual coil magnetic latching relay would work for you. **broken link removed** Nothing easy to connect to though.

Here, the polarity of the coils matters. One is called set and one reset. With a pulse of the polarity marked, the relay moves to that position. These can be connected to lock/unlock and you'll get an isolated contact. Do, put diodes across the coils opposite the direction of current flow. (band to plus).