Polymath-Studio One-Handed Keyboard (PS-OHK)

Overview

The Polymath-Studio One-Handed Keyboard, or PS-OHK (pronounced “psawk”), is a specialized input device designed to provide a high-performance typing experience using only one hand. Unlike many one-handed solutions that rely on complex layers or non-standard key counts, the PS-OHK utilizes a standard key count and a layout optimized for the natural shape and movement of the human hand.

Design Philosophy

The project is built around four core pillars to ensure that the transition from a standard QWERTY keyboard is as seamless as possible while maximizing efficiency:

1. Common Letter Frequency: The layout prioritizes the most frequently used letters in the English language, placing them in the most accessible positions.
2. Phonetic Relationships: Keys are organized based on the relationships between sounds, aiding in muscle memory retention.
3. Ergonomics: The physical design and key mapping are tailored specifically to the shape and reach of a left hand.
4. Practicality: It maintains a standard key count to ensure it can function as a primary input device without requiring specialized modifiers for basic characters.

Technical Implementation

The PS-OHK firmware is designed for the CH55x series of microcontrollers, which are popular 8051-based chips known for their built-in USB capabilities. The development environment is managed through a Nix shell, ensuring reproducible builds across different systems.

Build System and Toolchain

The project utilizes a robust open-source toolchain:

• SDCC (Small Device C Compiler): Used to compile the C-based firmware for the 8051 architecture.
• ch55xtool: A Python-based utility used for flashing the compiled binary to the microcontroller.
• GNU Make: Orchestrates the build and upload process.
• Arduino-CLI: Included in the dependencies for auxiliary tasks or potential framework compatibility.

Hardware and Enclosure

Beyond the firmware, the repository includes comprehensive design files for the physical hardware. This includes:

• PCB Designs: Breakout boards for components like the PCA9505DGGY.
• Enclosure: 3D-printable or manufacturable housing designs located in the enclosure directory.
• Hand-Specific Layouts: Dedicated configurations for left-handed use, with deprecated right-hand versions available for reference.

Getting Started

To build the firmware, users typically navigate to the firmware directory and run make. The flashing process involves a specific hardware sequence: holding the program button while plugging the device into a USB port, then executing the upload command within a three-second window. This bootloader entry method is characteristic of the CH55x family’s factory bootloader.