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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 behavior of the board;
these are detailed on the getting started page.
EAGLE files: arduino-leonardo-reference-design.zip
The Arduino Leonardo can be powered via the micro USB connection or
External (non-USB) power can come either from
The board can operate on an external supply of 6
The power pins are as follows:
The ATmega32u4 has 32 KB (with 4 KB
Each of the 20 digital i/o pins on the Uno can be used as an input or output, using pinMode(), digitalWrite(), and digitalRead()
There are a couple of other pins on the board:
See also the mapping between Arduino pins and ATmega32u4 ports.
The Leonardo has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega32U4
A SoftwareSerial library allows for serial communication on any of the Leonardo's digital pins.
The ATmega32U4 also supports I2C (TWI) and SPI communication. The Arduino software includes a Wire library to simplify use of the I2C bus; see the documentation for details. For SPI communication, use the SPI library.
The Leonardo appears as a generic keyboard and mouse, and can be programmed to control these input devices using the Keyboard and Mouse classes.
The Leonardo can be programmed with the Arduino software (download). Select "Arduino Leonardo from the Tools > Board menu (according to the microcontroller on your board). For details, see the reference and tutorials.
The ATmega32U4 on the Arduino Leonardo comes preburned with a bootloader that allows you to upload new code to it without the use of an external hardware programmer. It communicates using the AVR109 protocol.
You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header; see these instructions for details.
Rather than requiring a physical press of the reset button before an
Because of the way the Leonardo handles reset
The Leonardo has a resettable polyfuse that protects your computer's
The maximum length and width of the Leonardo PCB are 2.7 and 2.1
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