Introduction to Arduino Micro - The Engineering Projects
Amazon.com: AITRIP Pro Micro ATmega32U4 5V/16MHz Module Board with 2 Row pin Header Compatible with arduino Leonardo Replace ATmega328 Pro Mini (1 PCS) : Electronics
Arduino Pro Micro pin mapping - iCircuit
Amazon.com: ACEIRMC Pro Micro for Atmega32U4 5V 16MHz Bootloadered IDE Micro USB Pro Micro Development Board Microcontroller Compatible for Pro Micro Serial Connection with arduino Pin Header (3pcs) : Electronics