threeboard.dev

What It Is

threeboard is an open-source software and open-hardware project: it turns a “mechanical USB keyboard with only three keys” into a fully usable computer keyboard. It is not a conventional productivity peripheral, but more of a teaching reference for embedded systems, USB HID, keyboard firmware, and hardware design. The project implements everything from the USB stack to the PCB hardware design from scratch, all in a single repository.

Core Features and Technical Implementation

threeboard uses combinations of three keys to specify keycodes and modifier keycodes, with two built-in 8-bit LED binary indicators providing feedback on the current input state, ultimately sending USB keycodes to the host. It supports multi-layer programmable layouts, and users can write macros into threeboard’s storage for quick access. The firmware is written in C++, with a design goal that emphasizes readability rather than reliance on complex external frameworks.

Open Source, DIY, and Debugging Experience

The project is explicitly both open source and open hardware. Users can read the source code and hardware designs, or build the physical device themselves; however, building the hardware requires a PCB, soldering tools, components, and some electronics and soldering knowledge. For users without the required hardware setup, the project provides a terminal-based graphical firmware simulator built on simavr. It runs the same firmware file as the physical hardware and supports GDB remote debugging, which is highly valuable for learning and troubleshooting firmware issues.

Documentation, Pricing, and Ecosystem

Documentation is one of threeboard’s major strengths. The project includes firmware comments, detailed Markdown documentation, a user manual, firmware design and build instructions, simulator documentation, hardware design and build instructions, a bill of materials, and a 41-page PDF design document. No commercial pricing is provided; as a GitHub open-source project, it can be obtained for free. However, DIY hardware will still involve costs for PCBs, components, and tools. In terms of ecosystem integration, it mainly revolves around the USB keyboard protocol, simavr, and GDB, with no direct integration shown with existing keyboard firmware ecosystems such as QMK or ZMK.

Pros, Cons, and Best-Fit Users

Its strengths are that it is self-contained, has few dependencies, is highly readable, and comes with comprehensive documentation, while also covering simulation, testing, and physical hardware construction. Its drawbacks are that the three-key input method is clearly not suitable for most everyday office users, and the learning curve is steep. Information on commercial support, finished-product purchases, and after-sales service is also not disclosed. It is best suited to embedded development learners, keyboard firmware enthusiasts, open-hardware researchers, and anyone who wants to understand the full path of a USB keyboard from hardware to firmware.

Access in China

The source text does not provide information on access regions, mirrors, or payment. If the project mainly relies on GitHub, access stability in mainland China may vary depending on network conditions. There is also no commercial purchase information for payments. Alternative directions worth considering include QMK, ZMK, KMK, or other Arduino/AVR USB HID keyboard projects.