Updated April 2023: v2 'alpha' is reduced to around the size of a quarter (note: code in this repository is still for v1): https://youtu.be/KFr5jRC6k0c
A 59-key USB HID open hardware PC keyboard using a Raspberry Pi Pico microcontroller and CircuitPython for the key matrix decoder. This might be the smallest PC keyboard -- it fits within the outline of the Pico for direct soldering.
Build video: YouTube
Code explanation video: YouTube
This code requires the CircuitPython interpreter installed on your Raspberry Pi Pico: https://circuitpython.org/board/raspberry_pi_pico/ (just copy the UF2 file to the Pico)
This code also requires the Adafruit HID keyboard and keycode files in your library: https://github.com/adafruit/Adafruit_CircuitPython_HID/releases/ (download the Adafruit library that matches your CircuitPython version and copy the /lib/adafruit_hid/ files into your Pico's /lib folder)
key matrix logical layout (rows/columns) <--> pin layout <--> Pico pin names in CircuitPython <--> physical layout/silkscreen
var c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14
pin 1 2 4 5 6 7 9 10 11 12 14 15 16 17 19
name GP0 GP1 GP2 GP3 GP4 GP5 GP6 GP7 GP8 GP9 GP10 GP11 GP12 GP13 GP14
r0 20 GP15 ESC `~ 1 2 3 4 5 6 7 8 9 0 -_ =+ BACKSPACE
r1 21 GP16 TAB Q W E R T Y U I null O P [{ ]} \|
r2 22 GP17 A S D F G H J null K L ;: UP '" DOWN ENTER
r3 27 GP21 Z X C V B N M SPACE ,< .> /? LEFT null null RIGHT
same for modifier keys
var alt ctrl shift
pin 34 32 31
name GP28 GP27 GP26
modifiers 29 GP22 ALT CTRL SHIFT
There is no ctrl+alt+del due to no delete key; if you want this, I suggest implementing delete via shift+backspace as a special case such that ctrl+alt+shift+backspace sends the ctrl+alt+del combination
