/diy/ - Do It Yourself

>>2725172
Let's see if I can actually describe my problem, I am software guy, hardware is new to me. But I've gotten a pretty good grasp of it.

To finalize my project I need to measure the RPM on a gokart engine (single cylinder), I have already tested this circuit, and it works by creating a capacitive load from the ignition cables then triggering an octocoupler on each pulse.
All that works fine.

Problem: I'm trying to copy the commercial solutions available for kart racing, the commercial dashboard are entirely water sealed, and for the tachometer, you simply placed the wire in a half loop on a specific part of the case.

How the fuck does that work? That's beyond my dum dum software brain.

I bought some mag wire, made a shitty coil (28awg, 15~wraps, 5 layers) based on 0 math and just throwing shit at the wall.

My kart is at the track, but I'm not trying to entirely waste time, is this fucking idea going to work?

1: wrap lead around ignition wire 5-8times
2: place other end in a half loop over my shitty coil

If it's not clear I have zero idea what I'm doing
I managed to figure everything else out to build a prototype, but I can't figure out this magical coupling method they used. And I'm too dumb to know what to Google.

I don't know if it's going to generate enough flux or any at all for a hall effect sensor, maybe that would work??
At least tell me what to Google, in so lost