I have your standard twin cylinder lawnmower engine that I would like to build a tachometer for. I plan to use the wire you ground to shut the engine off as the input if possible. I don't know the values to expect is where the problem is as well as if it is even possible. If possible would something along the lines of megasquirt's circuit work? http://www.msextra.com/doc/general/ms1v3schems.html on the Tach Input drawing (third schematic from top) and referring to the opto isolator circuit.
I could also probably order up some hall effect sensors and try that instead, but I would kind of like to use up some things I've had laying around forever now.
I could also probably order up some hall effect sensors and try that instead, but I would kind of like to use up some things I've had laying around forever now.