Digital Tachometer for car

Panici:

PeterH:
Firstly, if you're using an MVR sensor the signal amplitude will be proportional to speed.

Not using a seperate MVR sensor. Using the tachometer pulse supplied to the gauge cluster.
Please read the first part of this thread for details. I 'scoped the tach pulse as well.

Signal frequency is proportional to RPM here.

Have you obtained a clean square wave at TTL levels, or are you still trying to clean up the signal in software?