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Epi controller

A new open-source controller with tiny footprint: Epi by u/rallekralle11.
Published December 8, 2022

Named after the Epipactis genus or orchids, the Epi by Rasmus (aka rallekralle11) is a tiny controller barely wider than the USB-C connector.

Announced and open sourced in late October, the first prototypes arrived and proved to be working fine.

This is something I've been working on for a while. It's based on the Atmega32U4 but is quite a lot smaller than a Pro Micro and has more pins broken out. The pin spacing is 1,27mm which lets the entire thing be tiny. You can see how it's barely wider than the USB-C port – rallekralle11.



  • Atmega32U4 chip
  • 23(?) GPIO pins
  • 1.27mm pin spacing
  • Dimensions: 23x12.5mm
  • castellated pins
  • Data line ESD protection
  • USB-C connector sunk into the board, and slightly protruding from the end for panel mounting
  • Holes where M2 bolts can be used to hold it in place


Despite the tiny footprint, it has most features of a classic Pro Micro:

Only thing it lacks are TX/RX LEDs, voltage regulators and a fuse. None of which should matter for a keyboard. Otherwise it's the same as a Pro Micro but smaller and with more usable pins.

So no integrated voltage regulator, only runs at 4.5-5.5V (down to 2.7 if you make it with an 8MHz crystal, or use the internal oscillator) which is totally fine for USB. No RX/TX/power LEDs either, only one on pin 13 for testing.


Published on Thu 8th Dec 2022. Featured in KBD #106 (source).

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