Could I just put a button on each one to 3.3V without further hardware and do the rest in software
Yes! GND or VCC will work, but GND is probably more readily available as you can just scratch away at the solder resist almost anywhere on the PCB and get to the ground plane.
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That's looking great @devsnd!
Yes! GND or VCC will work, but GND is probably more readily available as you can just scratch away at the solder resist almost anywhere on the PCB and get to the ground plane.