CircuitPython code for a TADA-68 style keyboard with a Raspberry Pi Pico controller.

code.py

# Copyright wulfboy_95 2021, All Rights Reserved.

# Copying and distribution of this file, with or without modification,
# are permitted in any medium without royalty provided the copyright
# notice and this notice are preserved.  This file is offered as-is,
# without any warranty.

import board
import digitalio
import struct
import usb_hid

#from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode

# Create and init keyboard USB HID device.
keeb = None
for dev in list(usb_hid.devices):
    if ((dev.usage == 0x06) and
        (dev.usage_page == 0x01) and
        hasattr(dev, "send_report")):
        keeb = dev
if keeb == None:
    raise Exception("Device cannot be found")

# 2D list to convert keyboard matrix to keycode
matrix = [
    [
        Keycode.ESCAPE, Keycode.ONE, Keycode.TWO, Keycode.THREE, Keycode.FOUR,
        Keycode.FIVE, Keycode.SIX, Keycode.SEVEN, Keycode.EIGHT, Keycode.NINE,
        Keycode.ZERO, Keycode.MINUS, Keycode.EQUALS, Keycode.BACKSPACE,
        Keycode.GRAVE_ACCENT
    ],
    [
        Keycode.TAB, Keycode.Q, Keycode.W, Keycode.E, Keycode.R, Keycode.T,
        Keycode.Y, Keycode.U, Keycode.I, Keycode.O, Keycode.P,
        Keycode.LEFT_BRACKET, Keycode.RIGHT_BRACKET, Keycode.BACKSLASH,
        Keycode.DELETE
    ],
    [
        Keycode.CAPS_LOCK, Keycode.A, Keycode.S, Keycode.D, Keycode.F,
        Keycode.G, Keycode.H, Keycode.J, Keycode.K, Keycode.L,
        Keycode.SEMICOLON, Keycode.QUOTE, Keycode.RETURN, Keycode.ENTER,
        Keycode.PAGE_UP
    ],
    [
        Keycode.LEFT_SHIFT, Keycode.SHIFT, Keycode.Z, Keycode.X, Keycode.C,
        Keycode.V, Keycode.B, Keycode.N, Keycode.M, Keycode.COMMA,
        Keycode.PERIOD, Keycode.FORWARD_SLASH, Keycode.RIGHT_SHIFT,
        Keycode.UP_ARROW, Keycode.PAGE_DOWN
    ],
    [
        Keycode.LEFT_CONTROL, Keycode.LEFT_GUI, Keycode.LEFT_ALT,
        Keycode.SPACE, Keycode.SPACE, Keycode.SPACE, Keycode.SPACEBAR,
        Keycode.SPACE, Keycode.SPACE, Keycode.RIGHT_ALT, Keycode.RIGHT_GUI,
        Keycode.RIGHT_CONTROL, Keycode.LEFT_ARROW, Keycode.DOWN_ARROW,
        Keycode.RIGHT_ARROW
    ],
] # matrix[row][col]

input_pins = (board.GP6, board.GP7, board.GP8, board.GP9,board.GP10) # 5 input rows

input_pin_array = [] # DigitalIO array for inputs.

output_pins = (
    board.GP11, board.GP12, board.GP13, board.GP14, board.GP15,
    board.GP16, board.GP17, board.GP18, board.GP19, board.GP20,
    board.GP21, board.GP22, board.GP26, board.GP27, board.GP28
) # 15 output columns

output_pin_array = [] # DigitalIO array for outputs.

# Initialise DigitalIO pins.
for pin in input_pins:
    key_pin = digitalio.DigitalInOut(pin)
    key_pin.direction = digitalio.Direction.INPUT
    key_pin.pull = digitalio.Pull.DOWN
    input_pin_array.append(key_pin)

for pin in output_pins:
    key_pin = digitalio.DigitalInOut(pin)
    key_pin.direction = digitalio.Direction.OUTPUT
    key_pin.drive_mode = digitalio.DriveMode.PUSH_PULL
    output_pin_array.append(key_pin)
           
keys_pressed = [] # list for possible n-key rollover upgrade in the future.
report_array = [0x00] * 8

while True:
    for col in range(len(output_pin_array)):
        output_pin_array[col].value = True # Turn on column pin.
        for row in range(len(input_pin_array)):
            if (matrix[row][col] >= 0xE0) and (input_pin_array[row].value): # Check if modifier is pressed
                report_array[0] |= Keycode.modifier_bit(matrix[row][col]) # Add modifier bit to report.
            elif input_pin_array[row].value: # Check if key is pressed.
                keys_pressed.append(matrix[row][col])
        output_pin_array[col].value = False # Turn off column pin.
    if len(keys_pressed) > 6: # Check for Rollover Error
        for i in range(2,8):
            report_array[i] = 0x01 # Add Rollover Error keycode*6 to report.
    else:
        for i in range(6):
            report_array[i+2] = keys_pressed[i] if i < len(keys_pressed) else 0 # Add keycode to report.
    keeb.send_report(struct.pack("8B",*report_array))
    report_array = [0x00] * 8
    keys_pressed = []

@wulfboy-95 The keypad.KeyMatrix module added in recent versions of CircuitPython does matrix scanning, which you are doing "by hand" now. See https://learn.adafruit.com/key-pad-matrix-scanning-in-circuitpython/keymatrix. You'll want to read the whole guide for background.

(Referred here by a mention of your code in https://forums.adafruit.com/viewtopic.php?f=60&t=193075&p=934045#p934029)

@dhalbert Thanks! I'll check it out.

I've written a new version of this code which uses the keypad.KeyMatrix module and has fewer lines of code. Make sure you've flashed CircuitPython 7.x.x (or newer) on your Pico before using it.