MSefi.com read only forum (Jan.15,2018)

Lacking any sort of available sensor setup that would fit my engine and work with the MegaSquirt, I made my own crank position sensor using NTE3100's. (It's a long story, but trust me, it was necessary.)

Here's the result from the initial tests on the oscilloscope. Is this signal good enough to work reliably? I'm concerned that the voltage may not be falling off quickly enough to provide the MegaSquirt with a good tach signal. I'm troubleshooting a couple of items on this install, and would like to be sure that the sensor's waveform won't be a problem.

The red trace is the sensor's output. The blue trace is the signal from the Opto-Isolator to the processor.

Looks like the RPM it's picking up is a bit wavery. If it isn't reading a steady RPM, it should probably be OK.

That test was done using the starter to crank the engine. You're seeing the RPM's drop as each cylinder hits its compression stroke. So that part's normal, at least.

I thought about it some more, and it seems to me that the processor isn't going to look for a specific waveform. It's just going to look for a voltage above or below a set value. As long as the voltage off of the Opto isn't hovering around switch point for any length of time, the processor should be fine. Is that an accurate description of how the processor handles inputs?

Cheers,
Fred

The opto turns it into an abrupt on/off waveform anyway, so I wouldn't worry too much. May give a tiny bit of jitter but I don't expect a problem.

Well, the coils are making sparks when they're supposed to. So I'm going to operate on the assumption that it works.