μS V3 reading rpm from cdi tach wire or pickup sensor

[Vili]

Hello

I have Suzuki DR 800 with fuel control only. Microsquirt V3 with stock code (3.77) inside.

I was originally planning to read rpm from tach signal wires of CDI ignition box. When cranking, tach signal is 0 to 2V once per rev. When tach wire is connected to optoin + and grounding optoin (-) there was no rpm reading. How should it be connected, or is the signal voltage too small?

I have also tried connecting vr in 1 to bike's cdi pickup sensor wires. It is a VR sensor generating one pulse per rev I suppose. Then I get rpm reading, but it has errors showing from 0 to 10k rpm when turning engine with starter. It may show approximately correct information in tunerstudio and data logs (~300 rpm) for some seconds, but there is always "not cranking" in tunerstudio screen.

Any advice which option for reading rpm would be better to use and how to get it working correctly?

Thanks in advance

[Matt Cramer]

If it's only putting out 2 volts, I'd feed the signal in through VR1+ and connect VR1- to some sort of 1 volt source, possibly made with a voltage divider on VREF.