Chuck

Charlieflex Keyboard

Features

• 30-32 key wireless ergo keyboard with aggressive pinky stagger and splay
• central rotary encoder can be used by either hand
• designed for the Seeed Studio XIAO BLE wireless microcontroller
  • also works with the XIAO RP2040 for a lower-cost wired board
• Choc v1 or v2 low profile hotswap switches to allow a wider range of keycap choices
• Unique tiered low-profile "snug sandwich" case with no exposed electrical components
• RGB LED status visible on the top of the case
• Wireless-first design using ZMK firmware (including ZMK Studio)
• Internal space (5.5 x 27 x 32 mm) for a "large" 502530 300mAh battery
• PCB designed with ergogen for easy modification
• Licensed under the CERN Open Hardware License v2
• All source files available, so you can tweak the design if needed

Design goals

• Low cost wireless
  • xiao ble is only $10 per controller compared to $25 for the nice!nano
  • Big battery and an option for a dongle, so you can run for months without recharging
  • xiao rp2040 is under $5 with no need to purchase a battery or power switch if you want a wired board
• Ergonomic unibody design for the ultimate comfort and easy portability
  • each half is angled to match the angle of the hands on the board
  • keys are placed where fingers naturally fall, with no excessive stretching
    • 1DFH: no finger has to move farther than 1 key's distance from its home row position
    • when fingers extend, they splay, so the keys also splay outward to follow the fingers
    • the pinky is shorter than the other fingers, so the pinky keys are placed lower to match, and the top pinky key is traded for a ring finger key
    • the inner column of each hand is reduced to two keys to eliminate the need for index finger stretching
    • each thumb gets a single key, with an option for a secondary thumb key if your thumbs are smarter than mine
  • centrally located rotary encoder knob for easy ambidextrous access to scrolling and volume control
  • includes all source files, so if your fingers are slightly different, with a little work you can adjust the keyboard to fit you exactly

• Low profile 3D printable case
  • wireless case is only about 7mm high in front and 15mm high in the back, and comes in three separate pieces, each largely flat on one side for easy FDM printing with minimal fuss
  • for those who don't want or need the extra space required for a battery, a separate wired case is provided, which comes in two pieces and is just under 7mm tall
  • options for 1 or 2 thumb keys on each hand so you can go minimal if desired
  • smaller versions are included for smaller print beds
  • a few different knobs are included so you can get the height that works best for you
  • bumpons are inset into the case 1mm to minimize their height; they add only 1/2mm in height
• Hotswappable
  • keycaps and switches can be easily removed and exchanged so you can fine-tune the feel
  • ability to move back and forth between or even mix and match choc v1 and choc v2
• Electrostatic mitigation
  • unlike many other ultra-low-profile cases, no electronics are left exposed
  • usb port and power switch are on the back, reset switch is recessed into the bottom of the case

Build Guide

Interested in building a Charlieflex of your own? Check out the Build Guide for details.

Ancestry

I designed the Lintilla keyboard before the Charlieflex, but over time I realized that I didn't actually like split keyboards with separate halves, because I move around a bit as I type so I either have to keep adjusting the position of each half, or I end up contorting my wrists to align with the keyboard.

I also came to the conclusion that I would be better off with fewer pinky keys, due to the strain of reaching with the pinky, and my thumbs aren't actually smart enough for three keys each.

However, the basic layout of the remaining keys didn't change much from what I had before, so if you want a split layout and more keys than the Charlieflex offers, maybe the Lintilla is for you.

Descendants

I found some issues with running a charlieplex matrix on a wireless board where battery levels can impact the performance of the diodes, which need very precise cutoffs to interpret the keys being pressed; it made some of my 3-key combos a little unreliable in practice.

So I went back to the drawing board and discovered an extra two usable pins on the xiao ble. Using those allowed me to build the Patagona gigas, with 32 keys and a five-way switch, along with the Patagona chaski, with 42 keys, the same number of keys used by the Lintilla.

Builds

My Charlieflex, in the Twentyone Chuck Street layout, with 2 keys for the left thumb and one key for the right. I'm using Lofree Hades Choc v2 switches and Nuphy Shiokaze nSA keycaps.

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I also built a pink Charlieflex for the office, this time with LDSA keycaps on Bokeh Ambient Choc v1 switches.

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An alternate snap-fit case that uses fewer screws and is a bit more stable if you tend to use the keyboard directly on your lap.