The Leonardo is Arduino?s first development board to use one microcontroller with built-in USB. Using the ATmega32U4 as its sole microcontroller allows it to be cheaper and simpler. Also, because the 32U4 is handling the USB directly, code libraries are available which allow the board to emulate a computer keyboard, mouse, and more using the USB-HID protocol!
? ATmega32u4 Microcontroller
? Input Voltage: 7-12V
? 20 Digital I/O Pins
? 7 PWM Channels
? 12 ADCs
? 16MHz Clock Speed
? 32 KB Flash Memory
The Arduino Leonardo is a microcontroller board based on the?ATmega32u4?(). 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.
|Input Voltage (recommended)||7-12V|
|Input Voltage (limits)||6-20V|
|Digital I/O Pins||20|
|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)|
The Arduino Leonardo can be powered via the micro USB connection or with an external power supply. The power source is selected automatically.
External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board’s power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector.
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.
The power pins are as follows:
The?ATmega32u4?has 32 KB (with 4 KB used for the bootloader). It also has 2.5 KB of SRAM and 1 KB of EEPROM (which can be read and written with the?).
Each of the 20 digital i/o pins on the Leonardo can be used as an input or output, using?,?, and?functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions:
There are a couple of other pins on the board:
See also the?.
The Leonardo has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The?ATmega32U4?provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). The 32U4 also allows for serial (CDC) communication over USB and appears as a virtual com port to software on the computer. The chip also acts as a full speed USB 2.0 device, using standard USB COM drivers.?. The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the Arduino board. The RX and TX?LEDs?on the board will flash when data is being transmitted via the USB connection to the computer (but not for serial communication on pins 0 and 1).
A??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??for details. For SPI communication, use the?.
The Leonardo appears as a generic keyboard and mouse, and can be programmed to control these input devices using the??classes.
The Leonardo can be programmed with the Arduino software (). Select “Arduino Leonardo from the?Tools > Board?menu (according to the microcontroller on your board). For details, see the??and?.
The?ATmega32U4?on the Arduino Leonardo comes preburned with a??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??for details.
Rather than requiring a physical press of the reset button before an upload, the Leonardo is designed in a way that allows it to be reset by software running on a connected computer. The reset is triggered when the Leonardo’s virtual (CDC) serial / COM port is opened at 1200 baud and then closed. When this happens, the processor will reset, breaking the USB connection to the computer (meaning that the virtual serial / COM port will disappear). After the processor resets, the bootloader starts, remaining active for about 8 seconds. The bootloader can also be initiated by pressing the reset button on the Leonardo. Note that when the board first powers up, it will jump straight to the user sketch, if present, rather than initiating the bootloader.
Because of the way the Leonardo handles reset it’s best to let the Arduino software try to initiate the reset before uploading, especially if you are in the habit of pressing the reset button before uploading on other boards. If the software can’t reset the board you can always start the bootloader by pressing the reset button on the board.
The Leonardo has a resettable polyfuse that protects your computer’s USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.
The maximum length and width of the Leonardo PCB are 2.7 and 2.1 inches respectively, with the USB connector and power jack extending beyond the former dimension. Four screw holes allow the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8 is 160 mil (0.16″), not an even multiple of the 100 mil spacing of the other pins.