[Bali]

I measured it using a PicoScope a few years back, but no longer have the log file from that session, sorry.
It was either 100 Hz or 200 Hz if I recall.
If I have time today, I will go take some samples and report back.

 

[Bali]

Set up and measuring now, waiting for electric fan to kick on.
Looks like 100 Hz, as the pulses are about 10ms each.
Voltage is around 1.6V peak-to-peak.

 

[Bali]

Interesting ... Which picoscope is that? Any recommendations for the low end of the pico market?

That model, the PicoScope 2203, is old and discontinued. I bought it about 15 years ago or so. Great little scope for low frequency stuff under 20V. The software is excellent and it has a data logger app, which is is great for intermittant signals.
Link to user’s guide: https://www.picotech.com/download/manuals/ps2203.en-4.pdf

All their stuff is well engineered and documented, and now like 1/3 the price they used to be. I spent nearly $400 for that one many years ago!

 

[Bali]

The waveform was so distorted; did the scope probe have a good ground to engine ground? It should be a nice square wave with clean corners. Did you use the dedicated scope probe with coaxial cable or just the simple IO lead for the signal?

I didn’t bother attaching the ground side of the probe. And I didn’t calibrate the probe. I’d guess the actual waveform is much closer to square.