Romu Puts an RP2350 on Your Keychain

If you’re the sort of person who is always hacking on hardware, you probably keep a stash of Raspberry Pi boards ready to go in your workshop. That’s good enough to keep most people happy, but what if you are away from home when inspiration strikes? Even if you’re just across town, your workshop might as well be a thousand miles away.

Fortunately, you no longer need to rush home to bring your ideas to life. A tiny development board called Romu that is smaller than a coin puts an RP2354A microcontroller right in your pocket or on your keychain for whenever you need it. Simply plug it into a USB port (into which it almost entirely disappears) and start hacking with all of the user-friendly development tools that you are accustomed to using at home.

Romu takes inspiration from earlier ultra-compact boards but pushes the concept forward with better performance and built-in interactivity. The board is designed around a dual-core Arm Cortex-M33 processor running at 150 MHz, paired with 264 KB of SRAM and 4 MB of flash storage. That might not sound massive compared to full single-board computers, but for embedded work, it’s more than enough to build responsive, feature-rich projects.

There’s no need for cables, external programmers, or carrier boards. Power and data are handled directly through its USB Type-A connector, letting it behave almost like a flash drive for development. With support for MicroPython, users can write and deploy code quickly, making it approachable for beginners while still being powerful enough for experienced developers prototyping ideas on the fly.

Despite its size, Romu doesn’t skimp on interactivity. It includes an onboard RGB LED for visual feedback and a capacitive touch input that can be used for simple user interaction. These built-in features make it easy to create demos, test interfaces, or build small standalone gadgets without additional components.

For those who want to go deeper, Romu also supports more advanced workflows. A dedicated programming and debugging jig expands the board’s capabilities by exposing interfaces like SWD for low-level debugging and UART for serial communication. The jig uses pogo pins to make temporary contact with the board’s test points, allowing developers to access professional-grade debugging tools without permanently modifying the tiny device.

The project is fully open hardware, with plans to release schematics, PCB layouts, and example code in the future. Romu will be launching soon on Crowd Supply, so be sure to sign up for notifications if you’d like to pick one up.