OPEN HARDWARE · OPEN FIRMWARE

The Project.

Everything that goes into a Keeeyboard-Split
Schematics, board files, source code, STLs.
Take it, fork it, build your own.

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Files & links

GitHub CMK repository CMK (Custom Mechanical Keyboard) firmware.
Licence under GPLv2. [ github.com/AndreCusimano/CMK ] →
Soon available PCB KiCad project Full KiCad 10 source. Schematic and PCB layout.
Take it, change it, fab it. [ KiCad.zip ] →
Soon available Case Bambu Lab project Printable case (.3mf).
Pre-configured for Bambu Lab. [ BambuLab.zip ] →
Soon available Design STEP files Step file of the entire project.
Download, customize and it's yours! [ step.zip ] →
Soon available Production GERBER files Production-ready GERBER + drill, BOM & CPL files.
Drop straight into JLCPCB / PCBWay. [ gerber.zip ] →
Soon available 3D print STL files Ready to print.
Drop it into your 3D printer application. [ stl.zip ] →

Build log

From idea to Prototype.

FW Implementation
2026-11
  • LPM and BLE activity shared between the halves.
  • LIGHT/DEEP timeouts configurable at runtime.
  • Battery levels over BLE (left half, right half and mouse).
  • Split reconnection after waking from DEEP or after a staggered power-on.
  • Macros stored in EEPROM, and Unicode.
  • Volume, media and brightness keys (Consumer).
  • A fast roll with MT/LT reversed the key order.
  • Tapping term configurable at runtime.
  • FN no longer sends key data to the other half.
  • The halves didn't pair up after a staggered power-on.
  • The FN overlay blinked on the SLAVE with the LEDs off.
Test
2026-7/10
  • Tests.
FW Implementation
2026-06
  • Implemented the following features on the prototypes.
    • Implemented "core" features from QMK.
    • Multi-layer programmable keys.
    • Keyboard report HID.
    • Mouse report HID.
    • RGB effects.
    • BLE connections.
    • USB connections.
    • Battery recharge.
  • I2C connection between the two halves through the magnetic connector.
  • Split-Mode (the Central decides all the logic, so it is possible to use MO() buttons for the other half).
  • Live configurator on the site.
  • Flasher on the site for new releases.
  • Light and Deep Low Power Mode.
  • Transmission of the pressed keys to the other half in order to perform extended light effects.
HW Build & test
2026-05
  • Received all components and soldered 5 keeeyboard-split sets.
  • Hardware test on the v0.1.
  • Found 3 schematic problems and fixed them with external jumpers.
  • Fixed the schematics for the v1.0.
KeeeyBoard-Split
2026-04 late
  • Add 3-pin magnetic connector for dual-half recharging.
  • Migrate to 5-pin magnetic connector to support external Add-Ons.
  • Apply rubber pads to the case for grip and vibration damping.
  • Revise and upgrade the mechanical case.
  • Finalize PCB designs.
  • Order components and kick off first PCB batch.
Mockup
2026-04 early
  • Build a split prototype to validate the full functional stack.
  • Integrate hardware on/off switch.
  • Add USB-C connectivity.
  • Implement battery recharging over USB.
  • Install RGB LEDs on the prototype.
  • Confirm BLE as the required wireless communication method.
  • Design case with hot-swap support for both low-profile and standard switches.
  • 3D-print the mechanical case.
  • First working mockup complete.
CMK
2026-03
  • Start firmware rewrite with QMK-inspired features.
  • Rewrite core event loop and BLE manager from scratch.
  • Adopt stack: PicoSDK + FreeRTOS + BTStack + CYW43 + TinyUSB.
  • BLE chain supports up to 3 output devices and 1 input device.
  • Add HID reports for keyboard and mouse.
  • Test with BLE-Mouse and 2× BLE-3×3-Keyboard. Everything works.
  • Firmware complete. Hardware still missing.
Exploring
2026-02 late
  • Open direction toward a full custom mechanical keyboard.
  • Add EEPROM manager and test with external I2C EEPROM.
  • Implement addressable RGB LED support via PIO.
  • Test with an LED strip. Works correctly.
  • Research the existing custom keyboard market.
  • Evaluate QMK firmware. Not compatible with RP2350, discarded.
Improvement
2026-02 early
  • Prototype is stable and fully working.
  • Add BLE single-connection support.
  • Implement HID reports for joystick and keyboard.
Key-Pad 3x3
2026-01 late
  • Design a 3x3 keypad on Raspberry Pi Pico 2W.
  • 3D-print the case.
  • Data via micro-USB only (temporary).
  • Add LED status indicators.
  • Integrate a general on/off switch.
  • Device runs on USB power when connected, AAA batteries otherwise.
  • Implement a custom HID report.
The idea
2026-01 early
  • Identify the need: a dedicated device for sounds and macros.
  • Define requirements: mechanical switches for tactile feedback.
  • Device must be portable, expandable, and compact.
  • Choose a low-cost, easy-to-flash approach.