Pro Micro Compatible MCU with USB-C

A (much) better Pro Micro

The Bit-C is a microcontroller daughterboard featuring the Atmel ATmega32U4, designed for DIY keyboard enthusiasts. It features a sturdy through-hole USB-C connector that is more rugged than a standard USB micro B. It's only 1mm thick, so it sits slim and low. The Bit-C ships with the Atmel DFU bootloader, which is smaller and less finicky than the default Caterina bootloader. 100% of Bit-C units are exhaustively tested before shipping, ensuring you're spending your time building, not debugging. Best of all, it comes in white!

100% Pro Micro compatible

The Bit-C is a drop-in replacement for any Pro Micro MCU, including the Elite-C. With 1-1 GPIO pin parity, firmware builds don't need to be changed in order to swap in a Bit-C. The Bit-C is shipped with the lightweight Atmel DFU bootloader, making flashing with QMK a breeze. VBUS detection & backdrive protection are implemented for split keyboards, and a 500mA resettable fuse is included for protection.

Tri-mode LED

The built in white LED shows power status by default, and can be set to 3 different brightnesses using GPIO controls. Don't like the built-in LED? Turn it off. Use it to show layer or caps lock status. Bright, dim, and off modes allow for maximum flexibility.

Bit-C Comparison Table

Bit-C PRO RP2040 Bit-C AVR 32U4
CPU architecture RP2040: ARM Cortex M0+ ATmega 32U4: AVR
CPU clock Dual core @ 133MHz Single core @ 16MHz
GPIO Voltage Level 3.3V 5V
Flash size (program storage) 4MB on-board 16kB on-chip
RAM size (variable and data storage) 264kB on-chip 2.5kB on-chip
QMK firmware support
Arduino IDE support 1
Micropython support
Circuitpython support
Electrically compatible with Bit-C PRO RP2040 2
Electrically compatible with Bit-C AVR 32U4 2

1 The Bit-C AVR 32U4 can be used with Arduino IDE, but requires flashing a new bootloader.
2 The Bit-C PRO RP2040 and Bit-C AVR 32U4 cannot be "mixed and matched", as they use two different electrical voltage levels. For example, if building a split keyboard such as the SNAP, both Bit-Cs must be the same model. Boards connected over TRRS must also use the same MCU.

See it in the wild

Check out community-posted images sourced from the nullbits Discord server, Reddit, and more.

Included in the box

  • Bit-C MCU

OS Compatibility

Supported by all major versions of Windows, MacOS, and Linux. Fully compatible with USB 2, USB 3, and USB-C. No driver installation required for MacOS and Linux; Windows 7/8/10/11 may require driver installation. See here for info.


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