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The Arduino Leonardo is based on the ATmega32u4 micro-controller board. It has a total of 20 digital I/O pins (of which seven could be used as PWM outputs and 12 for analog input purposes), a 16-MHz crystal oscillator, a micro USB connection, a power jack, an ICSP header, and a reset button. It contains everything that is required to support the micro-controller’s operation and connects it to a PC with a USB cable / power it up with an AC-DC adapter / battery to get started.
All above boards Arduino Leonardo is different however the ATmega32u4 has a built-in USB communication process, eliminating the need for a secondary processor. This allows the board to appear to be a connected computer that can be operated by a mouse and keyboard, in addition to a virtual (CDC) serial / COM port.

1 x Arduino Leonardo R3 Board.