My plan is to make RPM counter to my motorcycle. I'm planing to read ignition box signal with arduino. I think that ignition box gives 0-12V (or 14.5V max) square wave signal to coil. I was wondering if I can read that signal with something like this:
Does my design work at all with NPN transistor? Why? And if it does can I have some advice with that transistor model and resistor sizes. It have been while since last transistor calculations. Also is there any danger with coils recoil?