How to Use Arduino Leonardo (Rev3b): Examples, Pinouts, and Specs

The Arduino Leonardo (Rev3b), manufactured by Arduino (Part ID: A000057), is a microcontroller board based on the ATmega32u4. Unlike other Arduino boards, the Leonardo features built-in USB communication, enabling it to emulate a keyboard, mouse, or other HID (Human Interface Device). This unique capability makes it ideal for projects requiring direct interaction with a computer, such as custom input devices, automation tools, or creative installations.

• Custom keyboards and mice
• Game controllers
• Automation scripts for repetitive tasks
• Data logging and communication with a PC
• Interactive art installations

The Arduino Leonardo has a total of 26 pins, including digital, analog, and power pins. Below is a detailed breakdown:

1. Powering the Board:

   • Connect the board to your computer via a USB cable for both power and programming.
   • Alternatively, use an external power supply (7-12V) connected to the VIN pin or the DC power jack.

2. Programming the Board:

   • Open the Arduino IDE on your computer.
   • Select Arduino Leonardo under Tools > Board.
   • Choose the correct COM port under Tools > Port.
   • Write or load your sketch and click the Upload button.

3. Using the USB HID Feature:

   • The Leonardo can emulate a keyboard or mouse. Use the Keyboard or Mouse libraries in the Arduino IDE to send keystrokes or mouse movements to your computer.

4. Connecting Components:

   • Use the digital and analog pins to connect sensors, actuators, and other peripherals.
   • Ensure that the total current drawn by all components does not exceed the board's limits (40 mA per pin).

The following example demonstrates how to use the Arduino Leonardo to send a keystroke to your computer when a button is pressed.

#include <Keyboard.h> // Include the Keyboard library

const int buttonPin = 2; // Pin connected to the button
int buttonState = 0;     // Variable to store the button state

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // Set button pin as input with pull-up resistor
  Keyboard.begin();                // Initialize the Keyboard library
}

void loop() {
  buttonState = digitalRead(buttonPin); // Read the button state

  if (buttonState == LOW) { // Check if the button is pressed
    Keyboard.print("Hello, World!"); // Send "Hello, World!" to the computer
    delay(500); // Add a delay to prevent multiple keystrokes
  }
}

• USB HID Behavior: When using the USB HID feature, the Leonardo may appear as a keyboard or mouse to your computer. Be cautious when uploading sketches that send continuous keystrokes or mouse movements, as they can make your computer difficult to control.
• Power Supply: Avoid exceeding the recommended input voltage (7-12V) to prevent damage to the board.
• Pin Current Limits: Ensure that no single pin draws more than 40 mA, and the total current does not exceed 500 mA when powered via USB.

1. The board is not recognized by the computer:

   • Ensure the USB cable is properly connected and functional.
   • Check that the correct COM port is selected in the Arduino IDE.
   • Try pressing the reset button on the board before uploading a sketch.

2. Sketch upload fails:

   • Verify that the correct board and port are selected in the Arduino IDE.
   • Ensure no other program is using the COM port.
   • Double-tap the reset button to enter the bootloader mode and try uploading again.

3. USB HID functionality is unresponsive:

   • Ensure the Keyboard or Mouse library is included in your sketch.
   • Check that the board is properly powered and connected to the computer.

Q: Can the Leonardo be powered via USB and an external power supply simultaneously?
A: Yes, the board automatically selects the appropriate power source.

Q: How do I reset the Leonardo if it becomes unresponsive?
A: Press the reset button on the board. If the issue persists, double-tap the reset button to enter bootloader mode.

Q: Can I use the Leonardo with shields designed for other Arduino boards?
A: Yes, the Leonardo is compatible with most Arduino shields, but ensure the shield does not rely on specific pins used differently on the Leonardo.

Q: How do I stop a sketch that continuously sends keystrokes?
A: Disconnect the board, press and hold the reset button, reconnect it, and upload a new sketch without USB HID functionality.

This concludes the documentation for the Arduino Leonardo (Rev3b).