Automotive tachometer signal interpretation
You need to debounce your signal, counting only instances when the signal remains above a certain level for a certain time.

If your microcontroller has analog pins, you can implement both the threshold comparison and the debouncing in software. If you only have digital pins, I'd still recommend to make debouncing in software, producing a digital signal using a comparator IC. Of course, it's possible to debounce the comparator output in hardware (using a low-pass filter and a Schmitt trigger), but I see no compelling reason to do so, if you'll use a microcontroller anyway.