Problem discovered

I posted about my problem on reddit yesterday and got a lot of very helpful suggestions. The top voted answer was that switching all those LEDs caused a current transient that shows up in my hall effect line. It probably doesn’t help that I have a long thing Vcc line to the hall effect sensor and that I have a long thin output line from the hall effect sensor running directly under the LEDs and a huge Vcc plane (which is only there due to my poor board design).

I proved this theory by first lifting Vcc from the LED driver, preventing it from pulling current, but keeping everything else the same. This eliminated the problem! Then I realized I didn’t really need to do that–I could have just as well initialized the LED driver to turn all the LEDs off. But finally I realized that probably switching 2 LEDs (turning 1 on and one off) wouldn’t draw too much current, so I soldered Vcc back on and gave that a try:

Hall effect sensor works exactly as expected now with no glitches!

Hall effect sensor works exactly as expected now with no glitches!

Works perfectly, thus providing even more evidence that’s what the problem is.

Now I just need to find a way to get some more caps added on there…

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