Things I (re) learnt today: don't be lazy and put sockets in when you're prototyping with a microcontroller module. "Never trust the footprint" extends to keycaps.
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Also: test the microcontroller module before you install it into something. Somehow this Teensy has no 3.3V on it's internal regulator and I have no idea if it was like that before I soldered it in or whether my board is shorting something somewhere. These are all things that I did know once, but it's been a while and I've filled by brains with other things since then :/
And finally: just because you have something in your parts drawer that you'd like to use doesn't mean it's the right design choice >_<