4.0 Specifications: ATMEGA32u4-Based Boards
The ATMEGA32u4 microcontroller introduces a key differentiator to the Arduino family: native USB support. This built-in capability allows boards like the Arduino Leonardo to directly emulate a computer keyboard or mouse. This opens up unique possibilities for Human Interface Device (HID) projects that can interact seamlessly with a host computer without requiring additional drivers or software.
| Board Name | Operating Voltage | Clock Speed | Digital I/O Pins | Analog Inputs | PWM Outputs | UARTs | Programming Interface |
| Arduino Leonardo | 5V | 16MHz | 20 | 12 | 7 | 1 | Native USB |
| Pro micro 5V/16MHz | 5V | 16MHz | 14 | 6 | 6 | 1 | Native USB |
| Pro micro 3.3V/8MHz | 3.3V | 8MHz | 14 | 6 | 6 | 1 | Native USB |
| LilyPad Arduino USB | 3.3V | 8MHz | 14 | 6 | 6 | 1 | Native USB |
The specification now transitions to the more powerful ATMEGA2560 family, designed for more demanding applications.