Weirdness.
Having missed all my deadlines for the medal I can now relax and go back to the drawing board to get the stupid thing right. I have breadboarded the entire circuit to see where I went wrong.
I got the same sort of weird errors on the breadboard. That's good from a troubleshooting perspective. When I traced it back I came all the way to the MCU pins. Some of the MCU pins can't hold an Active High under any condition except open. The inputs to the ULN2803A are decently high impedance I think. But some of the MCU pins can do it. Others can.
I may have been mis-handling the MCUs the whole time and destroying outputs at random. That could explain what I've been seeing in all my prototypes. I'm going to swap MCUs tonight and see if the symptoms change.
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