I'm trying to figure out a way to make a ground signal last longer on my car. I'll explain what is happening and what needs to be done.

I'm hooking up an factory alarm on my car. It uses a negative trigger to trip the locks, I got everything working like it should, you hit lock button on the key fob, it locks and hit the unlock button and it unlocks. The only thing I'm trying to figure out is how to arm the theft system with the door closed..it only arms with the door open, then you have to shut the door.

Everything is tied in with the door switch...

The lock button has 12v constant but when you hit the lock button on the key fob it sends a negative trigger and drops the voltage to 0V for half a second which locks the car.

Door switch-When the door is open it is grounded..when the door is closed it gets 12V constant.

I tried tricking the car into thinking the door was open when I hit the lock button when the door is closed but the ground signal only last half a second and I need it to last about 3 seconds.

I ran a jumper wire from the lock wire to the door switch and placed a 1n4001 diode in the jumper wire to only let the ground signal pass to the door switch when I hit the lock button but it only last half a second. In order to arm the theft system I need the door switch to be grounded for atleast 2-3 seconds then get the 12V back.

To make this long story short, when I hit the lock button it sends a very short half second ground signal to the door switch but jumps back up to 12V..I need it to last about 3 seconds, then jump back up to 12V.

Remember the lock has 12V constant power when you hit the button it sends a negative trigger and drops voltage to 0V for a quick half second..just need it to last 2-3 seconds then return back to 12V.

What can I use to accomplish this? I was thinking a time delay relay but it needs to be triggered by a ground signal using the lock button.


1 Answer 1


You can use RC-circuit with logic elements: short "0" impulse should charge some capacitor then while this capacitor did not disharged to "zero" logic level, you should invert it's logical voltage.


simulate this circuit – Schematic created using CircuitLab

The greather R3 resistance is, the longer delay you'll get. V2 is logic-levelvoltage source.


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