# Tutte Coxeter 36k

![Partial Tutte-Coxeter Graph (26/30 vertices, 36/45 edges)](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvS5QfAl7YotptMtpu0nG8XOHOsqG2vocUFF2sRgrn_QwAcUQNhDkctHt_42rQor3Bb5tbAW6FiOsYqv2craP086HMTuAqWk9U0A4yOeEsQkhyphenhyphenUxoayJWf5e-N3_Jg1TC1p9YAiVPTK02pEVCUu3hl72REIk5BAjXgZGoF7T-NWQ28iRirwFs6yzFzAe0/w200-h194/Screenshot%202025-05-28%20at%2014.59.35.png)

This is firmware for a Raspberry Pi Pico PR2040 controller monoblock 36 key design
(split 3x5_3 - three rows of five, and three thumb keys, for each hand). This is a
*diode-free* design with a sparse 13 by 13 scanning matrix designed using a partial
[Tutte-Coxeter](https://en.wikipedia.org/wiki/Tutte%E2%80%93Coxeter_graph) graph
(using only 26 vertices or GPIO pins, with 36 edges or keys - see this
[blog post](https://astrobeano.blogspot.com/2025/05/ergo-mech-keyboard-wiring-using-tutte-coxeter-graph.html)
for background, although the final pin selection and trace routing changed):

| GP   | 11 | 10 | 3 | 4 | 7 | 26 | 27 | 28 | 15 | 21 | 19 | 20 | 16 |
|------|----|----|---|---|---|----|----|----|----|----|----|----|----|
| GP12 |  / |    |   |   |   |    |  F |    |    |    |    |    |    |
| GP8  |  P |  L |   |   |   |    |    |    |    |    |    |  A |    |
| GP9  |    |  . | , |   |   |    |    |    |    |    |    |    |    |
| GP1  |    |    | K | I |   |    |    |    |    |  E |    |    |    |
| GP6  |    |    |   | M | H |    |    |    |    |    |    |    |    |
| GP2  |    |  U |   |   | Y |  T |    |    |    |    |    |    |    |
| GP22 |    |    |   |   |   |  G |  B |    |    |    |    |    | L3 |
| GP0  |    |    | O |   |   |    |  W |  R |    |    |    |    |    |
| GP13 |    |    |   |   | N |    |    |  D | R2 |    |    |    |    |
| GP14 |  ; |    |   |   |   |    |    |    | R1 |  S |    |    |    |
| GP18 |    |    |   |   |   |  B |    |    |    |  X | L2 |    |    |
| GP17 |    |    |   |   |   |    |    |  C |    |    | L1 |  Z |    |
| GP5  |    |    |   | J |   |    |    |    |    |    |    |  Q | R3 |

The keys here are labeled as per Qwerty, with L1, L2, L3, R3, R2, and R1 for the thumbs:

| Q | W |  E |  R |  T |   |  Y |  I |  O | U | P |
|:-:|:-:|:--:|:--:|:--:|:-:|:--:|:--:|:--:|:-:|:-:|
| A | S |  D |  F |  G |   |  H |  J |  K | L | ; |
| Z | X |  C |  V |  B |   |  N |  M |  , | . | / |
|   |   | L1 | L2 | L3 |   | R3 | R2 | R1 |   |   |

The firmware follows the `LAYOUT_split_3x5_3` QMK community layout convention, making it much
easier to use with an existing layout like Miryoku.

The first physical PCB for this was designed using the [Gamma Omega
keyboard](https://github.com/unspecworks/gamma-omega) footprint from Ergogen.
This is intend use the same Raspberry Pi Pico YD-RP2040 microcontroller board
to fit the same 3D printed case, including reset button placement.

* Keyboard Maintainer: [Peter J. A. Cock](https://github.com/peterjc)
* Hardware Supported: Tutte Coxeter 36k (single PCB) with Raspberry Pi Pico
* Hardware Availability: https://github.com/unspecworks/gamma-omega/tree/main/tc36k

Make example for this keyboard (after setting up your build environment):

    make tutte_coxeter_36k:default

Flashing example for this keyboard:

    make tutte_coxetter_36k:default:flash

See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).

## Bootloader

Enter the bootloader in 3 ways:

* **Bootmagic reset**: Hold down the key at (0,0) in the matrix (bottom right key, Qwerty `/`) and plug in the keyboard
* **Physical reset button**: Briefly press the button on the back of the controller (if physically accessible)
* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available