I am planning to make a tachometer for my classic car with no ECU from where I could get a signal. I am going to use the pulses coming from the primary side of the ignition coil. I was planning to use an optocoupler in a simple way (see schematics below), but I came across other schematics using another optocoupler, diode and adding a capacitor.
If there is something I don't quite understand in electronics, it is definitely inductors. So, I think the variants I found on this forum will work better than what I was planning to use but which one would work better, I don't know.
For the optocoupleurs chosen, I think the H11L1M is better, thanks to its Schmitt trigger, but I did not find any explanation for the choice of this precise one.
Here is the schematics I've made and the ones I've found:
And here is what the signal from the coil primary looks like (I don't have access to an oscilloscope unfortunately but it should look like this):
Can you help me choose the most suitable circuit?