Building a KMK Split Keyboard with RP2040 Dactyl Minidox (36-Key). 🡆 How to do stuff

This guide provides step-by-step instructions for hand-wiring a split-keyboard. A 36-key Dactyl Minidox keyboard using Raspberry Pi Picos(RP2040 ) and KMK Firmware. This build uses a “Visual Flow” wiring technique, The right half of keyboard is wired as the left half flipped around. See the visual wiring matrix under. This allows the firmware to remain simple and identical on both sides.

Prerequisites

Materials

Product	Variant	Quantity
3D Printed Case	Dactyl Minidox	1 Left, 1 Right
Raspberry Pi Pico Board RP2040	TYPE-C/MICRO with pins	2 pcs
Switches	Type MX. Brown, blue or your choice	40 pcs
Keycaps	Type MX	40 pcs
USB M-F Extension Cable	5 cm, male TYPE-C/ MICRO	2 pcs
Audio Jack Socket	PJ392A 3.5MM	2 pcs
4 Pole TRRS Male to Male	3.5MM	1 pcs
1N4148 Switching Diodes		100 pcs
Dupont Jumper Wires	40 cm, female to female	20 wires
High Temperature Heat Tape	15 mm	1 roll

Tools

Soldering iron and solder
Glue gun and glue sticks
Wire strippers/cutters
Tweezers
Multimeter (optional, for debugging)

Testing and preparing your Pi Picos(controllers)

Before you begin, I recommend to get your Pi Picos ready to rock. Follow the instruction on the KMK get started page to make sure you controllers are tested and up and running. Do the same procedure on both controllers before you start the assembly

Hardware Assembly

1. Wiring the Matrix

You will wire a 5-column x 4-row matrix on each side.

The Golden Rule of this Build: Wire the right half as the left half flipped around.

Wiring Steps

Rows: Solder the diodes to the right pin of every switch. Connect the other end of the diodes horizontally. I hope the picture under clarify more than this simple words.

Diode Direction

The black band (cathode) must point away from the switch and towards the controller row wire.

Here the rows consist of diodes soldered together(Don’t do as mee. It is easier to solder the “diode” rows before the columns)

Columns: Solder wires connecting the left pin of every switch vertically(Red, orange, yellow, green and blue colored wires on picture)

The rules for soldering rows and columns to switches, are the same for both sides of keyboard(The pictures shows the left side of the keyboard)
- Rows: solder always on left pin of switch
- Columns: solder always on right pin of switch

2. Connecting the Controller

Look at the picture above and under, the columns and rows are prepared with female DuPont wires, that makes it easy to connect to to a controller with pins. That makes it easy to reconnect rows/cols to controller if you do some mistakes. It also makes it easy to switch controller later on for an upgrade.

Connect the matrix rows and columns to the Raspberry Pi Pico using the following pinout.

Note

This pinout applies to BOTH the Left and Right controller.

Function	Visual Position	Pico Pin
Col 1	Pinky	GP2
Col 2	Ring	GP3
Col 3	Fuck you	GP4
Col 4	Pointer	GP5
Col 5	Inner Column	GP28
Row 1	Top Row	GP6
Row 2	Home Row	GP7
Row 3	Bottom Row	GP8
Row 4	Thumb Cluster	GP9

3. Split Communication (TRRS)

Connect the TRRS breakout boards to establish communication between the halves. We use a single-wire data connection (PIO).

Note

This pinout applies to BOTH the Left and Right TRRS connector/controller.

Tip (T): Connect to VBUS (any VBUS pin).
Ring 1 (R1): Connect to GP1 (Pin 2).
Sleeve (S): Connect to GND (any GND pin).

If these terms on the TRRS connectors does not say nothing to you, just connect them on TRRS connectors that are the same on both sides of keyboard.

Electrical Hazard

NEVER plug or unplug the TRRS cable while the USB is connected to the computer. This can short the power pin to the data pin and permanently destroy your Pico. Always unplug USB first.

4. Identity Jumper (Right Side Only)

To allow the code to automatically detect which side is which, you must add a physical “jumper” wire to the Right Controller only.

Right Pico: Connect a female to female DuPont cable connecting GP21 directly to a GND pin of choice.
Left Pico: Nothing to do here.

In the documentation for KMK split keyboards, there is described that you have to rename the drives for Circuit python, for both sides. That is not necessary with this build.

Firmware Configuration

1. Installing Circuit Python and KMK

I assume that you have done this already.

Follow the instruction on the KMK get started page to make sure your Pi Picos are tested and up and running. Do the same procedure on both Pi Picos

2. The Code (`code.py`)

Copy the code below into the file named code.py, overriding the test code you made in the previous step. Do it on BOTH drives, Left and right. When using and testing the full keyboard. The USB cable could always be connected to the left keyboard half.

print("--- STARTING KEYBOARD ---")
 
import board
import digitalio
 
from kmk.kmk_keyboard import KMKKeyboard
from kmk.keys import KC
from kmk.scanners import DiodeOrientation
from kmk.modules.split import Split, SplitType, SplitSide
from kmk.modules.layers import Layers
 
 
# --- 0. PIN DEFINITIONS ---
# All GPIO pins are defined here as constants for readability and easy maintenance.
# If you change the wiring, you only need to update the values in this section.
 
# General Pins
SIDE_DETECTION_PIN = board.GP21  # Jumper to GND on the right side to identify it.
SPLIT_UART_PIN = board.GP1       # Pin used for UART communication between halves.
 
# Column Pins (based on finger hints, from outside to inside)
PINKY_COL_PIN         = board.GP2   # Col 1
RING_FINGER_COL_PIN   = board.GP3   # Col 2
MIDDLE_FINGER_COL_PIN = board.GP4   # Col 3
INDEX_FINGER_COL_PIN  = board.GP5   # Col 4
INDEX_INNER_COL_PIN   = board.GP28  # Col 5
 
# Row Pins (from top to bottom)
TOP_ROW_PIN    = board.GP6   # Row 1
HOME_ROW_PIN   = board.GP7   # Row 2
BOTTOM_ROW_PIN = board.GP8   # Row 3
THUMB_ROW_PIN  = board.GP9   # Row 4
 
 
 
# --- INITIAL SETUP ---
keyboard = KMKKeyboard()
keyboard.modules.append(Layers())
 
# --- 1. JUMPER DETECTION ---
jumper = digitalio.DigitalInOut(SIDE_DETECTION_PIN)
jumper.direction = digitalio.Direction.INPUT
jumper.pull = digitalio.Pull.UP
 
is_right = False
if not jumper.value:
    is_right = True
 
 
# --- 2. SPLIT CONFIGURATION ---
split = Split(
    split_type=SplitType.UART,
    data_pin=SPLIT_UART_PIN,
    use_pio=True,
    uart_flip=True
)
 
if is_right:
    split.split_side = SplitSide.RIGHT
else:
    split.split_side = SplitSide.LEFT
 
keyboard.modules.append(split)
 
# --- 3. PINS & MATRIX (The Fix) ---
# We use the SAME pin order for both sides.
# Order: GP2 -> GP3 -> GP4 -> GP5 -> GP28
col_pins = (
    PINKY_COL_PIN,
    RING_FINGER_COL_PIN,
    MIDDLE_FINGER_COL_PIN,
    INDEX_FINGER_COL_PIN,
    INDEX_INNER_COL_PIN,
)
row_pins = (
    TOP_ROW_PIN,
    HOME_ROW_PIN,
    BOTTOM_ROW_PIN,
    THUMB_ROW_PIN,
)
# Matrix
keyboard.col_pins = col_pins
keyboard.row_pins = row_pins
keyboard.diode_orientation = DiodeOrientation.COL2ROW
 
# --- 4. KEYMAP ---
keyboard.keymap = [
    [
        # Left Hand (Cols 1-5)                     # Right Hand (Cols 1-5)
        KC.Q,  KC.W,  KC.E,    KC.R,    KC.T,      KC.Y,   KC.U,    KC.I,    KC.O,   KC.P,    # Row 1
        KC.A,  KC.S,  KC.D,    KC.F,    KC.G,      KC.H,   KC.J,    KC.K,    KC.L,   KC.SCLN, # Row 2
        KC.Z,  KC.X,  KC.C,    KC.V,    KC.B,      KC.N,   KC.M,    KC.COMM, KC.DOT, KC.SLSH, # Row 3
        
        # Thumbs (Row 4)
        KC.NO, KC.NO, KC.LCTL, KC.LSFT, KC.SPC,    KC.ENT, KC.BSPC, KC.LALT, KC.NO,  KC.NO,
    ]
]
 
if __name__ == '__main__':
    keyboard.go()

How to do stuff

Explorer

Building a KMK Split Keyboard with RP2040 Dactyl Minidox (36-Key).