Comu – $6 RISC-V board that fits inside a USB port

Comu is a $6 tiny CH32V203 RISC-V development board that fits inside a USB port - CNX Software

Over the years, we have seen several tiny “omu” USB boards that share this “fits-in-a-USB-port” form factor. It started with the Tomu, based on a Silicon Labs EFM32 Cortex-M0+, followed by the Fomu with a Lattice iCE40 FPGA, Qomu with an EOS S3 Cortex-M4F MCU and FPGA, and the Somu, a tiny FIDO2 security key.<br>Icy Electronics has now introduced Comu, another tiny development board based on the 144 MHz WCH CH32V203 RISC-V MCU. While measuring just 13 x 9.4 mm (slightly smaller than a microSD card), the board still packs two white LEDs, four capacitive touch buttons, and six GPIOs exposed through test pads. It is designed for bare-metal programming, custom USB HID projects, and USB packet experimentation.

Comu specifications:

MCU – WCH CH32V203V203F8

CPU – Single-core 32-bit RISC-V clocked at 144MHz

Memory – 20KB SRAM

Storage – 224KB Flash (64KB of 0-wait Flash and 160KB of normal Flash)

Package – QFN28

USB – 1x USB Type-A interface (Full Speed)

I/O

6x GPIOs broken out via test pads (PB14, PB15, PA1, PA2, PA3, PA8)

4x capacitive touch buttons with double-sided castellated edges (PA5, PA7, PB0, PB1)

12-bit ADC

Misc – 2x User LEDs (PB11, PA4)

Power

Input – 5V via USB port

Power consumption – 49.3 μA/MHz run, 19.4 μA/MHz sleep

Dimensions – 13 x 9.4 mm

Weight – 0.4 grams (0.2 grams without the 3D-printed case)

On the software side, the Comu development board is designed for lightweight bare-metal C/C++ development and works well with the ch32fun project. The developer says a basic blinky program can be as small as 40 bytes. It also comes with a custom 2KB USB bootloader, which leaves about 28KB of boot flash available for user applications. The CH32V203 can also be programmed with Rust (ch32-hal), the Arduino IDE (arduino_core_ch32), or WCH-HAL through the MounRiver Studio IDE.

PCB layout of the Comu USB board

The project is also fully open source, with the KiCad hardware files, custom bootloader, and several example programs available on its GitHub repository. The code samples cover features such as touch sensing, printf, and USB HID/MSC. Besides opening the project in KiCad, you can also check out the PCB layout directly on your web browser on the kicanvas website.<br>The Comu board is currently available on Tindie for $5.99, which includes the white 3D-printed case. Alternatively, you’ll also find it on Lectronz for $5.88.

Comu in its 3D printed case

Debashis Das<br>Debashis Das is a technical content writer and embedded engineer with over five years of experience in the industry. With expertise in Embedded C, PCB Design, and SEO optimization, he effectively blends difficult technical topics with clear communication

Comu – $6 RISC-V board that fits inside a USB port

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