[chadaustin] has a favorite keyboard with a great ergonomic shape, key travel distance, and size, but after switching to Windows 10, the wireless connection introduced a terrible delay. Worse yet, the receiver is notoriously susceptible to interference from USB 3.0 hubs. To provide 128-bit AES encryption, the receiver is paired with the keyboard at the factory and cannot be replaced. If you lose that, you gain a highly ergonomic paper-weight. The solution for [chadaustin] was tethering the keyboard and receive several crash-courses in hardware hacking along the way. As evidenced by the responses to this project on ycombinator, many long-time fans of the Microsoft Sculpt Ergonomic Keyboard, introduced in 2013, suffer similar issues.

We really appreciate that [chadaustin] took an incremental approach, tackling one problem at a time and getting help from others along the way for first attempts at many complex steps. The proof-of-concept involved hand-soldering each lead from the keyboard matrix’s test pads to a QMK Proton C, which worked but couldn’t fit inside the keyboard’s case. For a more permanent and tidy solution, [chadaustin] tried a ribbon-cable breakout board and other microcontrollers, but none of those were compact enough to fit inside the case either. This required a custom PCB, another first for [chadaustin].

After a one-day intro to KiCad, [chadaustin] dug into the datasheets, completed a schematic for the board, and generously shared the process of choosing components and creating the layout. [chadaustin] ordered a board and found the mounting holes’ placement needed to be shifted.

With the full matrix mapped by [johnmilkspill], flashing QMK onto the AT90USB1286 controller went fairly smoothly. [chadaustin] chose to map both sides of the split spacebar back to the space key but did add a feature by repurposing the battery indicator LED to Caps Lock. And the results?

According to testing done with Is It Snappy?, the latency dropped from the wireless 78 ms down to 65 ms over USB. More importantly, this latency is now consistent, unaffected by USB hubs, and there is no receiver to lose. Of course, [chadaustin] has ideas for future improvement, including regaining the multimedia function keys, as these kinds of hacks are never really done; they are just in the current revision. No word on the fate of the detached number pad, but that likely needs its own tether and is a project for another day.

Thanks for the tip [Linus Söderlind]