The current prototype is based on an Adafruit Feather 32u4 board which has the Atmel ATmega32u4 micro. I've soldered pins A0 and GND to that board and used the internal pull-up resistor of the ATmega32u4 on pin A0. When you hit the button, a sequence of keystrokes is sent over a USB HID interface to the computer. The keystrokes depend on the operating system so when I compile the firmware, it's OS dependent.