The default key scanner in KMK assumes a garden variety switch matrix, with one diode per switch to prevent ghosting. This doesn't cover all hardware designs though. With macro pads, for example, it is very common to not have a matrix topology at all. Boards like this aren't compatible with the default matrix scanner, so you will need to swap it out with an alternative scanner.
The scanners in kmk.scanners.keypad wrap the keypad module that ships with
CircuitPython and support the same configuration and tuning options as their
upstream. You can find out more in the CircuitPython
documentation.
This is the default scanner used by KMK.
It uses the CircuitPython builtin keypad.KeyMatrix.
from kmk.scanners.keypad import MatrixScanner
class MyKeyboard(KMKKeyboard):
def __init__(self):
# create and register the scanner
self.matrix = MatrixScanner(
# required arguments:
column_pins=self.col_pins,
row_pins=self.row_pins,
# optional arguments with defaults:
columns_to_anodes=DiodeOrientation.COL2ROW,
interval=0.02, # Debounce time in floating point seconds
max_events=64
)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 initialization sequence of your keyboard class.
import board
from kmk.kmk_keyboard import KMKKeyboard
from kmk.scanners.keypad import KeysScanner
# 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 = KeysScanner(
# require argument:
pins=_KEY_CFG,
# optional arguments with defaults:
value_when_pressed=False,
pull=True,
interval=0.02, # Debounce time in floating point seconds
max_events=64
)This scanner can read keys attached to a parallel-in serial-out shift register like the 74HC165 or CD4021. Note that you may chain shift registers to load in as many values as you need.
from kmk.scanners.keypad import ShiftRegisterKeys
class MyKeyboard(KMKKeyboard):
def __init__(self):
# create and register the scanner
self.matrix = ShiftRegisterKeys(
# require arguments:
clock=board.GP0,
data=board.GP1,
latch=board.GP2,
key_count=8,
# optional arguments with defaults:
value_to_latch=True, # 74HC165: True, CD4021: False
value_when_pressed=False,
interval=0.02, # Debounce time in floating point seconds
max_events=64
)The digitalio Matrix can scan over, as the name implies, digitalio.DigitalInOut
objects. That is especially useful if a matrix is build with IO-expanders.
from kmk.scanners.digitalio import MatrixScanner
class MyKeyboard(KMKKeyboard):
def __init__(self):
# create and register the scanner
self.matrix = MatrixScanner(
cols=self.col_pins,
rows=self.row_pins,
diode_orientation=self.diode_orientation,
pull=digitalio.Pull.DOWN,
rollover_cols_every_rows=None, # optional
)Matrix events from a quadrature ("rotary") encoder?
from kmk.scanners.encoder import RotaryioEncoder
class MyKeyboard(KMKKeyboard):
def __init__(self):
# create and register the scanner
self.matrix = RotaryioEncoder(
pin_a=board.GP0,
pin_b=board.GP1,
# optional
divisor=4,
)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.
Sometimes a single scanner doesn't cover all hardware configurations. For
example: The bulk of the keyboard may be scanned with a matrix scanner, but a
couple of additional keys are directly connected to GPIOs.
In that case KMK allows you to define multiple scanners. The KMKKeyboard.matrix attribute can either be assigned a single scanner, or a list of scanners.
KMK assumes that successive scanner keys are consecutive, and populates
KMKKeyboard.coord_mapping accordingly; for convenience you may have to supply a coord_mapping that resembles your physical layout more closely (expanded below).
Example:
class MyKeyboard(KMKKeyboard):
self.matrix = [
MatrixScanner(...),
KeysScanner(...),
# etc...
]To add more scanners you need to add onto your coord_mapping.
Example:
coord_mapping with just one MatrixScanner on a 58 key split keyboard:
coord_mapping = [
0, 1, 2, 3, 4, 5, 35, 34, 33, 32, 31, 30,
6, 7, 8, 9, 10, 11, 41, 40, 39, 38, 37, 36,
12, 13, 14, 15, 16, 17, 47, 46, 45, 44, 43, 42,
18, 19, 20, 21, 22, 23, 29, 59, 53, 52, 51, 50, 49, 48,
25, 26, 27, 28, 58, 57, 56, 55,
]coord_mapping using MatrixScanner and RotaryioEncoder on the same 58 key split keyboard with an encoder on each half:
coord_mapping = [
0, 1, 2, 3, 4, 5, 37, 36, 35, 34, 33, 32,
6, 7, 8, 9, 10, 11, 43, 42, 41, 40, 39, 38,
12, 13, 14, 15, 16, 17, 49, 48, 47, 46, 45, 44,
18, 19, 20, 21, 22, 23, 29, 61, 55, 54, 53, 52, 51, 50,
25, 26, 27, 28, 60, 59, 58, 57,
30, 31, 62, 63
]On the top left side of a standard split keyboard coord_mapping, right below that you see a split keyboard where RotaryioEncoder and MatrixScanner (the default scanner) are used.
In the single scanner example, we used to count from 0 to 29 while the top right side starts at 30.
With the addition of the encoder scanner, the left side has 2 additional keys making it count up to 31 and the right side would then start at 32 and count to 63.
This means that keys 30, 31, 62, and 63 are for encoders.
Notice that all of the encoders are at the end of the array, because we put the encoder scanner after the matrix scanner in keyboard.matrix.
Therefore, we need to add 4 more key codes in the corresponding places of our keyboard.keymap, they will be used for the encoders.