11-29-2020, 07:42 AM
I guess I should have been more clear, sorry. I have a MK2 Golf which I intend to engine swap with a VW ABF 16V engine, so that's why I started digging around trying to see how people may have sorted the original tach to work with the Speeduino/Mega and COP. I should have thought about that a lot earlier, but I am happy to admit that my electronics knowledge has expanded since opening this thread (Mostly thanks to you and all the info you share). I have ordered one of these Chinese scopes, but it says it's still in transit and I should expect it within a few days. When I get it, I will make sure to check out what kind of duty cycle, frequency and voltage level the ECU broadcasts on the tach line. I read on a forum thread about VQ swaps that a guy was trying to tap into the "RPM Output" wire of the ECU Going to the Power Steering control unit and posted a waveform that had 0-4V levels and the frequency corresponded with the amount of power strokes for the V6, so my guess is that the cause here will be similar. I'm Still kicking myself for not thinking about that earlier (well I did build that circuit with the arduino, but the "tone" library might not have sent the correct types of signals on the output pin).
I will try just the transistor with a current limiting resistor instead of the relay. If I understand correctly, the tach will be seeing a 12V signal, until the transistor is switched on by the "tach" wire on the J18 ECU, then it will pull the 12V to ground through the resistor and the tach will see 0V.
I will try just the transistor with a current limiting resistor instead of the relay. If I understand correctly, the tach will be seeing a 12V signal, until the transistor is switched on by the "tach" wire on the J18 ECU, then it will pull the 12V to ground through the resistor and the tach will see 0V.