Momentary contact during power On and Off.

Thread Starter


Joined May 27, 2009
I am new to this forum and my knowledge about electronics is very basic. I am planning to add a laptop in my car which will be used as a carputer.

My requirement is to make momentary contacts for the power switch both during the power (12 VDC) ON and OFF (to switch on and switch off the laptop).

I am able to find some circuit diagram which gives momentary contact during power on in the following link

But not able to find something which also gives momentary contact during power OFF.

Any help will be really appreciated.
Last edited:


Joined Dec 19, 2007
Sure. That's just what I had used to get a long pulse period. The length of the pulse depends on the size of the capacitor and the resistance of the relay coil...mostly. About C (in farads) x R (in ohms) = T (in seconds).