I want to build a tachometer for my car using a AVR. I think I have no problem with the software, but I'm having trouble finding out how to get a signal to measure the revolutions.
So far I've found out that it is possible to read the ignition pulses from the coil by either connecting directly to the -ve terminal of the coil and the chassis of the car or by inductive coupling of the power wire of the coil. Is this right?
What i haven't found is detailed descriptions of what voltages and currents to expect from the approaches described.
My car is an old 3 cylinder Chevrolet sprint.
Thanks for any help you can give me.