Very very electrical question., Tachometer waveform Options

[sgomes]

Ok, I don't expect to get an answer to this question but here goes nothing:

I've got this fancy tacometer drive thingy that is supposed (IMG:style_emoticons/default/unsure.gif)

Assumptions about the tach:

It expects at least +5V pulses more is ok.
It assumes a four cylinder engine.

My assumption on how tachs work:

You get one pulse for every spark. So.....

assume 6000rpm for the sake of argument
6000rpm= 100 revs per second * 60 seconds
4 sparks per revolution.
4 * 100 = 400 pulses per second.

I've got something close to 200 pulses per second comming out of my sender at about +10V.
The tach isn't moving.

[mightyohm]

5V square wave will NOT work with anything but the 911 CDI type tachs.

The tach wants a square-ish type waveform, but with voltage peaks at the edges of at least several tens of volts. This is due to the inductive kickback a stock coil will cause - the tach triggers off of the voltage peaks. I think the tach is pretty picky. I was planning to reverse engineer a tach and convert it for 5V use but I haven't gotten around to it yet. The early tachs (pre 74) are full of germanium transistors and stuff. (IMG:style_emoticons/default/icon8.gif)