LM2937 is a good regulator for the the automotive environment, along with
heavy filtering (bypass caps).  You should use a schottky optoisolator to
isolate the pic input from the distributor.

Regards,
Bob

On 11/30/06, Dumitru Stama <list@mirosat.com> wrote:
>
>
> Hi Guys,
> I want to make a small board-computer for an old car (1965 model) i
> own and i have a short question. I want to use a wire connected to the
> distributor/ignition to get pulses to a pic and count the rpms.
> Since this car has a 4 cylinders 4 strokes motor i will have to divide
> that number by 2 and get the real rpm.
> The question i have though is the folowing : What precautions i will
> have to take in order to have an usable product which does not crash
> when the voltage varies a lot ? I mean should i use a special 12v to
> 5v converter instead of 7805 ?
> Also i think about using the schematics for a simple zener regulator
> to get the signals from the ignition to the controller :
> http://www.asm.ro/schema.gif
> I was thinking that this way i can be sure i get a 5v max and i can
> safely use a microcontroller digital pin for this. Do you think there
> is a much better solution to this ?
>
> Thank you very much for your time
>
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