Unicorn Hat HD errors - spontaneously switching on LEDs


When I connect my unicorn hat hd to a powered up pi, it immediately starts flashing a whole line of LEDs at a pretty high brightness, the unicorn hat board begins to heat up, and the pi resets. The line of LEDs flashes 3 or 4 times, and then everything stops, but the board keeps getting hotter.

This started to happen after I began to run the hat using individual jumpers (as specified here: https://pinout.xyz/pinout/unicorn_hat_hd, but with only one ground pin connected). This worked fine, but then after a while (an hour or so?), switched to the error I described above.

I’ve tried the same hat on both a pi 3B and 4B, with the same problem showing up. Even if I run any of the examples, or run the hat as designed, with all the GPIO connected, nothing changes and the error persists.
I was wondering if there is anything I can do to debug it, or if the problem is permanent?


Do not connect it to an already powered up Pi. You could damage the Hat or the Pi GPIO pins. Hats are not hot swappable. I’m not sure if that’s what your doing but I’m warn against it anyway.
If the pinout shows more than one ground used, you should hook up all the ones that are shown as used. On the Pi they are all one common ground, on a Hat they may not be, it may not be possible to route the tracks to do that.
Best guess is one of those missing grounds caused something on the Hat to fail.

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Ah I see - I assume there isn’t a way to recover the unicorn hat board itself?

If it was recoverable, plugging it right onto the Pi’s GPIO, with no jumpers should do it. If it still malfunctions that way it likely has a permanent hardware fault.

Yep - definitely a permanent fault then - I’ve tried plugging it right onto the Pi’s GPIO (without the jumpers) a few times and it hasn’t worked :(

Thanks for your help anyway! And your comment about the Hat probably not having a common ground - will keep that in mind :)

Don’t be surprised it that Pi also has issues. The GPIO circuitry can be a bit fragile some times, and it doesn’t take much to break things.