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 AC-to-DC adapter or battery to get started.

The Leonardo differs from all preceding boards in that the ATmega32u4 has built-in 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.

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	Microcontroller ATmega32u4 Operating Voltage 5V Input Voltage (Recommended) 7-12V Input Voltage (limits) 6-20V 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