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Pro Micro and compatible controllers

The classic keyboard controller footprint: 24 pins, 18 GPIOs. ATmega32U4 Pro Micro, RP2040 boards (KB2040, Elite-Pi) and the wireless nice!nano all fit.

What it does#

The SparkFun Pro Micro (ATmega32U4, 5 V, 16 MHz) became the standard socket for hobby keyboards; dozens of boards copy its pin layout:

Board Chip Firmware Notes
Pro Micro ATmega32U4 QMK micro-USB, fragile connector
KB2040 RP2040 QMK, KMK USB-C
Elite-Pi, Sea-Picro, Liatris RP2040 QMK, KMK USB-C
nice!nano v2 nRF52840 ZMK Bluetooth, battery pads B+/B−
Example circuit: A 1 × 2 matrix: ROW0 on D4, COL0/COL1 on D5/D6, diodes COL2ROW, a RESET button on RST. Unused pins have no-connect marks.
A 1 × 2 matrix: ROW0 on D4, COL0/COL1 on D5/D6, diodes COL2ROW, a RESET button on RST. Unused pins have no-connect marks. Open the promicro_keys example from this page in PCB Canvas: “Insert into my schematic”.

Power#

  • RAW: input (USB 5 V when plugged in) before the board’s regulator.
  • VCC: the board’s logic supply: 5 V on an AVR Pro Micro, 3.3 V on RP2040 and nRF boards. Feed LEDs and sensors from the right one.

Pitfalls#

  • Logic levels differ: an RP2040 board is not 5 V-tolerant, the AVR Pro Micro outputs 5 V. Check before mixing parts across them.
  • Mount on sockets (or low-profile machined pins) so the controller can be replaced; the micro-USB on the original Pro Micro breaks easily.
  • Orientation: components up or down changes which side the pins are on; PCB Canvas’s footprint is for components facing up.

Footprint#

PCBCanvas_Modules ProMicro (and the nice!nano version with extra pads). Hand-soldered.