04 : Process
Iterations
Each revision existed to answer one question. The point of printing quickly is that a wrong answer costs an evening instead of a month.
September 2023
A first test case, all 42 keys
Iteration one was a case I printed as a test, still holding every key of the full Corne. It needed printed supports for the component leads under the PCB, plus standoffs and retaining C rings to hold it together. Living with it for a few days convinced me I could go even smaller.
Four days later
Cutting to 36
The outer columns came off the PCB, the three keys on the left of the photo, and the next case was modelled in Fusion 360 around what was left: a base with standoffs for the PCB and a separate tray underneath.
October 2023
Tenting and support
The constraint that really shaped the case. Two legs sit flush in recesses on the underside and swing out to tent the half. The case stays thin enough to hold in one hand with everything folded away.
The first underside used a printed TPU foot across the whole base. It did not give enough grip, so it was replaced with rubber feet at the corners.
Today
Adding the trackpad
On the right half the TPS43 sits at the inner top corner, where the left half has its controller window, under a walnut veneer that sits flush with the edges of its holder. It took about three mounts to get right, and it is still a work in progress.
I wanted the trackpad to be removable at first. After a few attempts at stripping a six pin ribbon cable I gave up and soldered it straight to the pads on the trackpad. Since then the work has been on tracking performance and battery drain.
Firmware
Electronics and firmware
Switches, diodes, controller, and the trackpad on its own bus. ZMK handles the split link and the keymap; getting a pointing device to behave alongside it is where the configuration work lives.
Each half runs a Nice!Nano v2. The TPS43 is soldered straight to the right Nano's pads and talks over I2C. I moved to a fork of the Azoteq driver that ties the trackpad into ZMK's sleep states, because the original kept the pad awake and drained the right half's battery. A small custom input processor adds laptop style tap and tap to drag.
Layout
Designing the layout
36 keys means every symbol, number, and modifier lives on a layer. This is interface design with the same rules as any other: frequency drives placement, and anything you have to think about is in the wrong spot.
The letters start from Colemak, then I moved a few of them. Before moving any letter I checked why Colemak put it there, so a change would not undo something that was optimized. The moves put the most important hotkeys back where QWERTY has them. Z, X, C and V sit exactly where every program expects undo, cut, copy and paste, and S is back under the ring finger for save.
Common edits are home row combos. S and R together is Backspace, R and T is Delete, and S and T is Tab, so fixing a typo never means reaching. The S and R backspace is one of my favorite optimizations in the whole layout.
Holding R or T mirrors the right half onto the left hand, so with the right hand on the mouse the left can still type any letter. The thumbs carry Shift, Ctrl, Alt and Win, which covers every modifier combination from the same hand.
Gaming needed its own answer. A home row built for typing puts WASD in the wrong place, so two layers can be switched on for games. Pressing A, S and T together toggles a layer that puts the keys back in their QWERTY spots shifted one column in, with WASD under the fingers and Shift and Ctrl under the pinky. Holding Q on that layer brings up the numbers.
