RPM input

[z0tya]

What kind of protection have the rpm input pin?
Can I put on signal from the ignition coil primary side, or just 0-12v rpm signal from ecu or from ignition module?

Thanks

[rob@vems.co.uk]

I'm not sure about the protection, never having seen the schematics for the gauge.
As a matter of course I would use a Zener diode to block any spikes from the ignition coil.

[z0tya]

The webshop 18V unidirectional transient diode will be good? How put am I into the circuit?

[rob@vems.co.uk]

I think a plain 18v Zener would be best - mounted with the stripe facing the coil

Coil(-) -------|<----- RPM input

[z0tya]

Thanx

[kristjan]

I have a bit different problem about rpm input, but I thought I won't start a new thread for it. The problem is that the rpm signal is very bumpy at both Megatune and in the gauge. I took the rpm signal form the coil directly to pin 10 on the 15 pin connector. But on idle the rpm gauge jumps a great deal (from 500-2000rpm, occasionally higer and lower too). It's jumping while cruising too.

That's how the rpm signal shows in the logviewer.


What could be causing this problem? I have the RPM settings set to 8 (4 teeth per camrot, stock distributar hall sensor on mk2 golf) teeth and the multiplier is 229. I don't know what firmware is on the gauge, it's borrowed from a friend.

Edit: My stock tacho is working in perfect order from the same source.

[kristjan]

Anybody?? Got the multimeter and measerd the values from pin 10 (RPM input) and 11 (RPM reference). The RPM input measures around 12.2V and the RPM reference 2.80-2.87V. It's a cheap multimeter so there might be some variations in the measurements. AFAIK the 2.8V in the reference pin is ok and no pull-up nor pull-down resistor is needed. Why is the RPM reading so bumpy then?

[ranz]

Take the signal to the gauge from cable to original tacho. I had almoust the same problem, I taked the signal directly from RMP sensor and the signal was jumpy, now I connected it to the cable from ECU to tacho and the reading is almoust OK (it has some random spikes, but I have not seen anybody finding cure for that).

[kristjan]

Well, I don't have an ecu and I have already tried to take the signal from the tacho, but it has the same problem because it's the same signal. I quess I'll just have to live without the tacho reading.

Tnx for your reply though.