Arduino Pro Mini Atmega328 3.3v 8MHz Microcontroller ATmega328P-MU Operating Voltage 3.3V Input Voltage 2.7** -15 V*** Digital I/O Pins 20 Analog Input Pins 8 Clock Speed 8 MHz ** below 2.7V unable to work *** below 5V able to connect with VCC pins above 5V must connect with RAW pins Dimensions:33.3 * 18.0 (mm)