CircuitPython (7.x.x and above) code for a TADA-68 style keyboard with a Raspberry Pi Pico controller.

code.py

# Copyright wulfboy_95 2022, 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 keypad
import struct
import usb_hid

from adafruit_hid.keyboard 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")

matrix = keypad.KeyMatrix(
    row_pins = (
        board.GP6, board.GP7, board.GP8, board.GP9, board.GP10
    ),
    column_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
    ),
    columns_to_anodes=True
)

# Key list to convert key_number from KeyMatrix events to the corresponding keycode.
keys_list = [
    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.HOME, 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.END, 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
] # TODO: use a dictionary instead of a list so that unused buttons do not need placeholders.

keys_pressed = []
modifiers_pressed = []
report_array = [0x00] * 8

while True:
    while matrix.events: # Run when there are events queued.
        event = matrix.events.get()
        key = keys_list[event.key_number]
        if event.pressed:
            if key >= 0xE0: # Check if modifier is pressed.
                modifiers_pressed.append(key) # Add to modifiers_pressed list.
            else: # Check if a key is pressed.
                keys_pressed.append(key)
        if event.released:
            if key in keys_pressed:
                keys_pressed.remove(key)
            if key in modifiers_pressed:
                modifiers_pressed.remove(key)
    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 modifiers_pressed:
            report_array[0] |= Keycode.modifier_bit(i) # Add modifiers to report.
        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