Pro Micro pinout

The Arduino Pro Micro is cheap (~3$) and perfect for small boards (less than 81 keys). With a little hack though, it can drive a keyboard with up to 100 keys.

Using 24 inputs of an Arduino Micro? - Microcontrollers - Arduino Forum

Pro-Micro – Mechboards

Bit-C PRO

RP2040 Pro Micro 16MB/128Mbit USB-C Controller – Keebio

Pro Micro: Arduino Pinout - tinkerBOY

Arduino Pro Micro 32U4 - A2D Electronics

Pro Micro 5V/16MHz Arduino Compatible Microcontroller - RobotShop

40% Keyboards: Pro Micros

RP2040 Pro Micro MCU

Arduino Pro micro - micro usb connector detached - IDE 1.x - Arduino Forum

Quickpin

Pro Micro - 5V/16MHz - DEV-12640 - SparkFun Electronics

STeMCell - STM32 based pro micro pinout : r/ErgoMechKeyboards

Fixing an Arduino Pro Micro: the USB Port Came Off !! : 17 Steps - Instructables