Hardware Button - sblantipodi/firefly_luciferin GitHub Wiki

The pull-up resistor is very common in digital circuits.
It is simply a resistor connected from an input pin to VCC (the positive supply of the circuit).

Pull-up resistors are used to ensure a HIGH state on the input pin when a button is not pressed.
Without a pull-up, the input pin would float, and the signal could randomly switch between HIGH and LOW due to noise or interference.

Luciferin uses GPIO0 as the default INPUT_PULLUP for the hardware button.