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The goal of the QMK software project is to develop a completely customizable, powerful, and enjoyable firmware experience for any project - keyboard or otherwise - and to provide helpful, encouraging, and kind support and feedback for people with any software development experience.

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Proton C

The Proton C is an Arm STM32F303xC based drop-in replacement for the Pro Micro. It uses the same chip as the Planck rev6 boards, and Skullydazed’s Arm Clueboards.

Rev 2 made the following changes:

You can find the Proton C for purchase at:


If you want to know why you should choose the Proton C for your next product, here is a comparison of the chips:

  ATmega32U4 AT90USB1286 STM32F303xC
Speed 16MHz 16MHz 72MHz
Voltage 5V 5V 3.3V with some 5V capable pins
Flash size 32kB (28kB usable) 128kB (120kB usable) 256kB (248kB usable)
EEPROM size 1kB 4kB 4kB (emulated in flash)
Memory 2.5kB 8kB 48kB
Timers 4 total 4 total 10 total
Digital IO 25 pins 46 pins 37 pins

The STM32F303 has 9 times the usable storage space that the ATmega32U4 has. You could enable a bunch of features and still have plenty of room left. For instance, the Planck EZ, which has audio and RGB matrix fully enabled (no sub-features disabled), and has the Link Time Optimization option turned off uses 45kB of firmware, leaving 200kB+ free, still. Plenty of room for most anything you want to do.


Some of the PCBs compatible with Pro Micro have VCC (3.3V) and RAW (5V) pins connected (shorted) on the pcb. Using the Proton C will short 5V power from USB and regulated 3.3V which is connected directly to the MCU. Shorting those pins may damage the MCU on the Proton C.

So far, it appears that this is only an issue on the Gherkin PCBs, but other PCBs may be affected in this way.

In this case, you may want to not hook up the RAW pin at all.