I have been designing a pcb for a car dash board for a while now, and one of the last bugs on my list is working out how to read the tacho signal from my new engine ECU. Since the engine is still in a box, I can't test the signal to see what it's doing, but I was imagining I would be looking at a 12v square wave for my tacho input.
I've just read the manual for the ECU and while it doesn't state the output type, it does state that the input to the dash should need a pull-up resistor of around 5k between the input line and 12v ignition. Doing a bit of Google research, it must be that the ECU pulses to ground so with the pull-up resistor, the dash input will see 12v or ground. Right??
If that's the case then would this be an appropriate circuit to connect to the tach signal?
Also, if this is the case, I would like to test the setup using another Arduino on a bread board to simulate the ground pulse from the ECU. What's the best component to use to do this? N-Channel MOSFET?