Setup BMW(E30) Tachometer

[wazzu70]

I am sure this is an easy question, but I am not sure which type of output to use for the tachometer signal for the factory BMW E30 cluster.

Is it a push/pull with divider 16? That is where I assume I would start to find out, but I do not want to risk damaging the circuit if I guess incorrectly :)

Any help appreciated!

[mattias]

Yes, one of the stepper outputs will do nicely. Or the low current output (P259) on EC36-pin4 which has a +12V pull-up (1K).

[wazzu70]

Thank you!

[wazzu70]

I used the P259 ch.0 (EC36-pin4) with no luck. I am using the normal divider of 16, is this correct?

If this is the correct setting, then I will check the cluster to verify its working properly.

Thanks!

[mattias]

If you measure the voltage on that pin towards ground, what do you get?

[wazzu70]

I was not able to measure any voltage at the pin.

Is this pin grounding when activated or providing power? The 12v 1k pullup confuses me as I'm not exactly sure what that means.

Maybe I misunderstood what you meant and I should use a known 12+V source and connect the ground to the pin and see if I get voltage when its activated.

[mattias]

Pretty much all ECUs have always been equipped with a resistor that internally connects +12V to this pin. The ouput is grounding when active, so it should measure +12V when it's not. 

If you have no voltage, apply that yourself externally. 1kOhm resistor between a +12V source and this pin.

[wazzu70]

Thank you for the help and explination. I will report back after some more testing :)

I took on this project to learn more about electronics and ECU logic. So far its been a great learning tool with all the help I have recieved here!

[wazzu70]

Well I solved my tachometer problem and it was user error  ::)

The VEMS unit itself worked perfectly at the pin. +12V and then grounding when activated. I traced the wire in the harness to realize it connected the wrong thing! Unfortunately I got two wires mixed up that had the same color/stripe scheme.

Thanks for the help!