# 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):

|      | GP11 | GP10 | GP3 | GP4 | GP7 | GP26 | GP27 | GP28 | GP15 | GP21 | GP19 | GP20 | GP16 |
|------|------|------|-----|-----|-----|------|------|------|------|------|------|------|------|
| GP12 |   Z  |      |     |     |     |      |   J  |      |      |      |      |      |      |
| GP8  |   Q  |   S  |     |     |     |      |      |      |      |      |      |   ;  |      |
| GP9  |      |   X  |  C  |     |     |      |      |      |      |      |      |      |      |
| GP1  |      |      |  D  |  R  |     |      |      |      |      |   O  |      |      |      |
| GP6  |      |      |     |  V  |  G  |      |      |      |      |      |      |      |      |
| GP2  |      |   W  |     |     |  T  |   Y  |      |      |      |      |      |      |      |
| GP22 |      |      |     |     |     |   H  |   M  |      |      |      |      |      |  R3  |
| GP0  |      |      |  E  |     |     |      |   U  |   I  |      |      |      |      |      |
| GP13 |      |      |     |     |  B  |      |      |   K  |  L2  |      |      |      |      |
| GP14 |   A  |      |     |     |     |      |      |      |  L1  |   L  |      |      |      |
| GP18 |      |      |     |     |     |   N  |      |      |      |   .  |  R2  |      |      |
| GP17 |      |      |     |     |     |      |      |   ,  |      |      |  R1  |   /  |      |
| GP5  |      |      |     |  F  |     |      |      |      |      |      |      |   P  |  L3  |

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

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 left key, Qwerty `z`) 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