Split Keyboard Mk. I

hermod-thumbnail This is my very first split keyboard build ever, and while it’s far from perfect, it was an amazing learning experience.

Disclaimer:
This DIY split keyboard PCB was designed for personal use and is shared as-is. While it works well for me, it’s not a professionally validated design—there may be imperfections or quirks. If you decide to build it, please do so at your own risk. Double-check everything, and make modifications as needed. Happy building!

Instructions

Specs

  • Split, Columnar Staggered Layout
  • 2x1.5u and 2x1u Thumb Keys per side
  • Magnetically Detachable Numpad
  • STM23F072CBT6 MCU
  • Kailh Choc Brown Switches
  • Two 2.2” LCD’s
  • Per-Key RGB Lighting

Inspiration

The inspiration for this build came from two other keyboards, and I wanted to make sure to give credit early and often!

  • Tzarc Djinn Rev2
    • The 2.2” displays instantly struck a cord in me and I knew I had to find a way to incorporate them into this design.
    • Also Tzarc directly helped me get this board working on Discord, so again, huge shoutout to him!
  • ZSA Voyager
    • The overall look and feel of my keyboard was largely influenced by the ZSA voyager, with it’s low profile choc switches, per-key RGB lighting and thumb clusters. If I hadn’t had the insane idea to build my own keyboard from scratch, I would have bought the voyager.

Post-mortem

Mistakes

  • No 5.1kΩ resistor on the Split USB Communication lines
    • This meant the two halves literally couldn’t communicate
    • Fixed by soldering an SMD 5.1kΩ resistor to the USB port pins and bridging with solder
  • Pin selection was sub-par
    • Not necessarily a mistake, but it make the firmware much harder to write.

Pros

  • Absolutely Love the arrow keys being tucked in under my right palm. I never accidentally press them and they are always right there, easy to access when I need them.
  • The thumb clusters are awesome, having quicker access to Cmd, Ctrl, Layer changes, and other custom behavior with my thumbs has resulted in a huge productivity boost!
  • The 2.2” displays are amazing. I don’t have any legends on my keycaps, so having a place to quickly determine which key is where at a glance is super handy.
  • The magnetically detachable numpad is great for when I’m at my desk and find myself needing to type lots of numbers, but if I’m on the road or a smaller desk, I can pop it off and free up some real estate.
    • Also, being able to add another numpad to the other side of my keyboard and map it to more custom macros is a huge bonus!

Cons

  • The STM32F072 was a poor choice.
    • It’s a good choice for entry level boards, but this board required too much from it. A beefier MCU would have been very handy when it came to time to write the firmware.
    • I am experimenting with the STM32G474CETx - Datasheet Here
  • Thumb clusters are a little too far away from my other fingers
    • Not quite my thumbs natural resting position, so sometimes I feel like I’m manually holding my thumbs out too much.
  • Didn’t use a “handedness” pin
    • This means I have to compile and flash separate firmwares for Left/Right

Resources

Absolute TOP resources:

Everything else

Below is a list of every single link I saved during the building of this keyboard. It might not be complete, and it might actually be a little bit overwhelming, but they were each helpful to me in some way, so I figured better safe than sorry and included them all!

Table of contents