The Arduino Leonardo is a microcontroller board based on the ATmega32u4 (datasheet). It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs) a 16 MHz crystal oscillator a micro USB connection a power jack an ICSP header and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a ACtoDC adapter or battery to get started.

The Leonardo differs from all preceding boards in that the ATmega32u4 has builtin USB communication eliminating the need for a secondary processor. This allows the Leonardo to appear to a connected computer as a mouse and keyboard in addition to a virtual (CDC) serial / COM port. It also has other implications for the behaviour of the board.

Microcontroller ATmega32u4
Operating Voltage 5V
Input Voltage (Recommended) 712V
Input Voltage (limits) 620V
Digital I/O Pins 20
PWM Channels 7
Analog Input Channels 12
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 32 KB (ATmega32u4) of which 4 KB used by bootloader
SRAM 2.5 KB (ATmega32u4)
EEPROM 1 KB (ATmega32u4)
Clock Speed 16 MHz
Lengh 68.6 mm
Width 53.3 mm
Weight 20 g