Electrical Gremlins

Imagine my dread when I woke up to this message from John:

“Are you around tomorrow? I could do with some advice. I’m having an issue with the propeller board which is resetting itself randomly when the motors run at any speed. I think its an electrical problem rather than software, but really struggling to figure out what’s going on.”

The usual advice here – add decoupling capacitors everywhere!

After lots of hunting around, adding new 0.1uF caps to suppress the motors (one cap between the terminals, one from each terminal to the case), John eventually figured it out:

“I’ve been probing around with my ‘scope this morning and the power supply looks dead smooth, so my latest theory is that the reset line is the culprit and is picking up spikes from the motor. ”

And sure enough – a cap on the reset line to our propellor hat fixed it! ¬†Phew…

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