I am attempting to build a digital dashboard for my car (a 1998 honda civic), I have run into a bit of trouble, wherein the tachometer signal is quite hairy. I was wondering if someone would lend me a hand in cleaning it up so that I can feed it to a microcontroller (an arduino uno, just to keep things simple).
I have an oscilloscope and have scoped the tach signal. Here is an image of it:
This is at 50v per division vertical and 5 milliseconds per division horizontal. Unfortunately just an analog scope.
There is a pretty serious spike in voltage, (presumably) when the ignition coil is charging, then it drops down to around 40v, and then further down to about 14v for the long wait until it discharged and is grounded out. There is ringing on each of these transitions that will have to be dealt with to the tune of 50khz as well.
I would greatly appreciate any suggestions as to how to clean this up.