Arduino Pro Micro Atmega32u4, USB, 5V, 16MHz, Sparkfun design
Pro Micro Atmega32u4 is an Arduino compatible, very small and powerful micro controller development board. The integrated USB transceiver makes an additional USB-TTL bridge IC obsolete. Together with the micro USB port, Pro Micro Atmega32u4 is only 4 mm high. With dimensions of 34 x 18 mm is Pro Mic