kmk_firmware/docs/scanners.md

Scanners

Smaller boards and macro pads sometimes assign a GPIO pin to each key, rather than using a full matrix. Boards like this aren't compatible with the default matrix scanner, so you will need to swap it out with an alternative scanner.

Beside the default Matrix scanner, KMK includes the following:

keypad.Keys

The keypad.Keys scanner treats individual GPIO pins as discrete keys. To use this scanner, provide a sequence of pins that describes the layout of your board then include it in the initialisation sequence of your keyboard class.

Since the _init_sanity_check method in the KMKKeyboard class will attempt to validate a number of settings that are no longer needed, you need to override it with a modified version that doesn't fail when they aren't present.

import board
from kmk.kmk_keyboard import KMKKeyboard
from kmk.scanners.native_keypad_scanner import keys_scanner


# GPIO to key mapping - each line is a new row.
_KEY_CFG = [
    [board.SW3,  board.SW7,  board.SW11, board.SW15],
    [board.SW2,  board.SW6,  board.SW10, board.SW14],
    [board.SW1,  board.SW5,  board.SW9,  board.SW13],
    [board.SW0,  board.SW4,  board.SW8,  board.SW12],
]


# Keyboard implementation class
class MyKeyboard(KMKKeyboard):
    def __init__(self):
        # create and register the scanner
        self.matrix = keys_scanner(_KEY_CFG)

        # copy the key coordinates from the scanner
        self.coord_mapping = self.matrix.coord_mapping

    def _init_sanity_check(self):
        return self

keypad.KeyMatrix

The keypad.KeyMatrix scanner is an alternative implementation of the default matrix scanner using CircuitPython's builtin keypad objects. This is currently experimental and not recommended for use.

Using this scanner is similar to the keypad.Keys scanner. Create the scanner using keypad_matrix() instead of keys_scanner().

Scanner base class

If you require a different type of scanner, you can create your own by providing a subclass of Scanner. This is a very simple interface, it only contains a single method, scan_for_changes(self) which returns a key report if one exists, or None otherwise.