Tach input from spark voltage (BEWARE!!!)

[tom cloud]

>I know that's what we were taught in school, but I have never been able to
>"scope" anything near that high out of a simple points and coil system with
>a cap to ground on each post of the coil. I also don't understand the line
>below about the resister and zener bit. He wanted to use an inductive
>pickup to sense the ignition on the primary side, not attach to it
>directly.

The spikes will be fast and severe -- but limited by the cap.  The cap
absorbs the energy of the coil temporarily, thereby extending the
length of the spark -- and protecting the points from burning.


Tom Cloud <cloud at peaches.ph.utexas.edu>