How to Use Arduino Leonardo: Examples, Pinouts, and Specs

The Arduino Leonardo is a versatile microcontroller board based on the ATmega32u4. It is a member of the Arduino family and is notable for its built-in USB communication, eliminating the need for a secondary processor. This feature allows the Leonardo to appear as a mouse or keyboard to a connected computer, in addition to a virtual (CDC) serial / COM port. It is widely used in hobbyist and educational environments for creating interactive projects such as automation systems, robotics, and custom gaming controllers.

• Human Interface Device (HID) projects
• Robotics and automation
• Educational purposes and DIY projects
• Prototyping IoT devices
• Custom keyboard or mouse

• Microcontroller: ATmega32u4
• Operating Voltage: 5V
• Input Voltage (recommended): 7-12V
• Input Voltage (limits): 6-20V
• Digital I/O Pins: 20 (of which 7 can be used as PWM outputs)
• Analog Input Pins: 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)
• Clock Speed: 16 MHz

1. Powering the Board:

   • Connect a 7-12V power supply to the VIN and GND pins, or plug a USB cable into the board's USB port for power and communication.

2. Connecting I/O Devices:

   • Digital devices can be connected to digital pins 0-20.
   • Analog sensors can be connected to analog pins A0-A11.
   • PWM devices can be connected to pins 3, 5, 6, 9, 10, 11, and 13.

3. Programming the Board:

   • Connect the board to a computer using a USB cable.
   • Use the Arduino IDE to write and upload sketches to the board.

• Ensure that the power supply voltage does not exceed the recommended limits to prevent damage.
• When using PWM outputs, ensure that the connected devices are compatible with the 5V logic level.
• Use appropriate resistors or current-limiting devices to protect the I/O pins from excessive current.
• Avoid connecting devices that draw more than 40 mA from a single I/O pin.
• Always disconnect the power source before making or altering connections on the board.

• Board not recognized by the computer:

  • Check the USB cable and port.
  • Ensure the correct drivers are installed.
  • Try resetting the board using the RST pin.

• Sketch not uploading:

  • Verify the correct board and port are selected in the Arduino IDE.
  • Check for errors in the code.
  • Ensure the bootloader is functioning correctly.

• Unexpected behavior in circuits:

  • Double-check wiring and connections.
  • Ensure power supply is stable and within the recommended range.
  • Verify that the code corresponds to the connected hardware.

• Use the onboard LED connected to pin 13 to test basic sketches and ensure the board is functioning.
• Consult the Arduino forums and community for support and advice on specific issues.
• Review the official Arduino Leonardo documentation for additional troubleshooting tips.

Here is a simple example of blinking an LED connected to pin 13 on the Arduino Leonardo:

// Define the LED pin
const int ledPin = 13;

// the setup routine runs once when you press reset:
void setup() {
  // initialize the digital pin as an output.
  pinMode(ledPin, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(ledPin, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                  // wait for a second
  digitalWrite(ledPin, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                  // wait for a second
}

This code will blink the onboard LED on the Arduino Leonardo, which is a great way to test if your setup is working correctly. Remember to select "Arduino Leonardo" from the Tools > Board menu in the Arduino IDE before uploading the sketch.