Unchat keeb

Overview

This repository contains the design materials, firmware, and related docs for two iterations (2023 and 2024) of the "Unchat" keyboard. Highlights of this design include:

• An ergonomic, split form keyboard with 40 keys (2024) or 42 keys (2023)
• Custom Rust firmware supporting QMK JSON keymaps using a limited feature set
• Hardware chatter mitigation through Hall Effect magnetic switches (2024) or hardware debouncing circuitry (2023)
• Diode-free using a 6-bit bus (2023) or 4-bit analog muxes (2024)

Here are some photos.

The Unchat-42 (2023):

Designing the PCB in Kicad and the results:

The Unchat-40 (2024) (assembly still WIP):

Why design a custom keyboard?

This project was motivated in small part by wanting to solve frustrating key chatter on my main keyboard and in larger part as a way to kill free time during holiday seasons. It was an awesome way to learn several new skills. I recommend this sort of project if any of these interest you as well:

• PCB design in Kicad
• Mechanical design in OpenSCAD
• Electronic assembly and debugging
• Embedded Rust

Free to use and share

Designs and code in this repository are covered by the CC0 license, allowing anyone to freely copy, modify, or distribute these materials. Attribution not required.

That said, there are some known issues with the original designs. These are documented below, along with my workarounds. In some cases, these issues are corrected in the latest design files, but corrections have not been tested. You may discover other issues that I have not personally encountered. Use at your own risk!

Unchat-40 (2024)

Design overview

Summary of design features:

• Two reversible PCBs connected via RJ45
• Controlled by an Adafruit QT Py RP2040
• Hall-effect switches queried via analog muxes
• Acrylic and/or aluminum plate and frame

The 2023 design was fairly successful at reducing key chatter without software debouncing, but I still experienced occasional chatter (see below). Unfortunately, this was on timescales far above the filtering provided by the hardware debouncing, likely due to corrosion and mechanical deformation in the switches due to my terrible assembly process.

With this new 2024 design, I entirely circumvented using electrical contacts by moving to a Hall Effect magnetic switch design. This is also used in some "gaming-friendly" keyboards because it allows very rapid triggering, but from the perspective of this design the main advantage is that we can apply hysteresis to completely eliminate chatter. The cheap DRV5055 sensor fit the design perfectly. Unfortunately, magnetic switches are still fairly rare and a bit more pricey, but the overall cost was still manageable.

Electronic design

Mechanical design

Cost breakdown

Unchat-42 (2023)

More design info and post-mortem coming soon!