I know the tachometer question has been asked a million times, but I don't need help building a circuit for interpreting a conditioned input signal and displaying RPM's, which is what most of the threads were about when I did a search.
I just want to know a little about interfacing a circuit with the ignition coil in my car. I heard the typical way is the negative terminal. The question I have is what kind of signal am I going to see there?
what kind of voltage is going to be present? how noisy is it? is it going to look somewhat like a square wave (if a bit messy)?
Basically I just need to know a little about it so I can build a simple circuit to interface that signal with a PIC. Obviously I don't want my PIC directly connected to it if it's putting out hundreds or thousands of volts. I can't get to my car with an oscilloscope, so I just want a starting point for a prototype circuit to try out on it.
would a resistor voltage divider, some caps to smooth out the signal, and a comparator be sufficient?
or how about a large-value resistor in series with the input, and a reverse-biased zener (5v or so?) to ground, with some caps thrown in for good measure?
thanks