Tach input from spark voltage (BEWARE!!!)

[Johnny]

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.

> wow ! don't try it unless U wish to fry a few components
> the good 'ol points & coil sys the primary runs up to 3-400 volts
> the spikes are MUCH higher so BEWARE !
> if you wish to use some impulse use a hall sensor it's smaller than a
> teardrop
> or cut the pulses with a big resistor and zener diodes but it can affect
> the ignition
> 
> bye
> charley