Reading motorcycle RPM from coil signal

Using Arduino Project Guidance
1

Hello,

I'm making a project of motorcycle tachometer. I'd like to use coil negative side (signal) to measure RPM. Bike has TCI ignition. I came up with circuit as in attachment.

Opto Coupler will be LTV817,

D1 is Zener diode 5.1V, D2 is 1n4007, R1 and C1 works as low pass filter with 338Hz cut-off frequency.

Do You think it will work?

Regards

RPM_SENS.PNG
RPM_SENS.PNG908×456 3.74 KB

2

How much current are you expecting through the input of the opto?
How exactly do you expect to get a signal and what are you expecting to see from the negative side?

3

  1. With that circuit about 1.2mA.

  2. I'd like COIL_SIG wire to be connected in parellel to motorcycle ECU pin which is signal for one of ignition coils. I'm expecting to see 0-12V wave on ECU pin (of course some fluctuations at coil discharge, thats why I'm using LPF), and 0-5V wave on opto output.

4

Kamool:

  1. With that circuit about 1.2mA.

Can you show how you calculated that as I get a completely different value.

5

Just by using Ohm's Law.
So by Your post i assume that is incorrect.