Original Arduino® Leonardo

Original Arduino® Leonardo

Arduino® Leonardo is a microcontroller board based on the ATmega32u4. It has 20 digital input/output pins (7 of which can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal, micro USB socket, power jack, ICSP connector, and reset button. The board includes everything required for the microcontroller to operate. It can be easily connected to a computer via a USB cable or powered with an adapter or battery.

If you are new to Arduino®, you can check out our Lessons for Arduino® series on our blog site.

The biggest feature that distinguishes Leonardo from many other Arduino® models is that the ATmega32u4 has built-in USB communication capability. This means there is no need for a second USB-to-serial converter processor such as the 16u2. Thanks to this, in addition to the virtual COM port (CDC), Leonardo can be connected to the computer and used like a mouse or keyboard.

Original Arduino® Leonardo Technical Specifications:

• Microcontroller: ATmega32u4
• Operating Voltage: 5V
• Input Voltage (recommended): 7-12V
• Input Voltage (limit): 6-20V
• Digital I/O Pins: 20 (7 PWM outputs, 12 analog inputs)
• Analog Input Pins: 12
• Current per I/O Pin: 40 mA
• Current for 3.3V Output: 50 mA
• Flash Memory: 32 KB (ATmega32u4), 4 KB of which is used by the bootloader
• SRAM: 2.5 KB (ATmega32u4)
• EEPROM: 1 KB (ATmega32u4)
• Clock Speed: 16 MHz
• Length: 68.6 mm
• Width: 53.4 mm
• Weight: 20 g

Arduino® Leonardo can be powered via USB or an external power supply. The external power supply can be an AC-DC adapter or a battery. The adapter can be connected through the 2.1 mm center-positive power jack on the board. The battery can be connected through the GND and Vin pins on the board. USB does not have to be connected continuously for the board to operate. The board can be operated only with an adapter or battery. In this way, the board can work independently from the computer. An external power supply between 6-20V can be used. However, these values are limit values. The recommended external supply for the board is between 7-12V. This is because the regulator on the board may not operate stably at values below 7V and may overheat at values above 12V. The operating voltage of the microcontroller on the Leonardo board is 5V. The 7-12V voltage supplied through the Vin pin or power jack is reduced to 5V by the voltage regulator on the board and distributed to the board.

The power pins are as follows:

• VIN: Voltage input pin between 7-12V when using an external power supply.
• 5V: This pin provides the 5V output from the regulator. If the board is powered only via USB (5V), the 5V coming from USB is directly provided as output through this pin. If the board is powered through Vin (7-12V) or the power jack (7-12V), the 5V from the regulator is directly provided as output through this pin.
• 3V3: This is the output pin of the 3.3V regulator on the board. It can provide a maximum output of 50mA.
• GND: These are the ground pins.

Original Arduino® Leonardo Memory:

The ATmega32u4 has 32 KB of flash memory (4 KB of which is used by the bootloader). It has 2.5 KB SRAM and 1 KB EEPROM.

Original Arduino® Leonardo Input and Output:

All 20 digital pins on the Leonardo can be used as input or output. The logic level of all these pins is 5V. Each pin operates with a maximum input and output current of 40mA. In addition, some pins have different features. The special pins are listed below.

• Serial Communication, 0 (RX) and 1 (TX): Used to receive (RX) and transmit (TX) TTL serial data. The important point to note is that the Serial class is used for USB (CDC) communication on the Leonardo. The Serial1 class should be used for serial communication on pins 0 and 1.
• External Interrupts, 3 (interrupt 0), 2 (interrupt 1), 0 (interrupt 2), 1 (interrupt 3), 7 (interrupt 4): These pins can be used as rising edge, falling edge, or change interrupt pins. For detailed information, you can review the attachInterrupt() function page.
• PWM, 3,5,6,9,10,11 and 13: Can be used as PWM output pins with 8-bit resolution.
• SPI, on the ICSP Header: These pins are used for SPI communication. The point to note is that the SPI pins on the ICSP header are not connected to any other pin on the board. In other words, unlike the Uno, these pins are not connected to pins 10, 11, 12, and 13. If you are going to use a shield that communicates via SPI, this shield must have a 3x2 pin ICSP header. Otherwise, this shield cannot be used with Leonardo.
• LED, 13: There is a built-in LED connected to pin 13 on the Leonardo. When the pin is set HIGH, the LED will turn on; when set LOW, the LED will turn off.
• Analog, A0-A5 and A6-A11 (also digital pins 4, 6, 8, 9, 10, and 12): Leonardo has 12 analog input pins with 10-bit resolution. A0-A5 are in the analog pin section, as on the Uno. A6-A11 are in the digital pin section and are connected respectively to digital pins 4, 6, 8, 9, 10, and 12. These pins are indicated on the underside of the board. All analog pins can also be used as digital inputs and outputs. The measurement range of the pins is 0-5V. By using the AREF pin and the analogReference() function, the lower limit can be raised and the upper limit can be lowered.
  
• I2C, pin 2 or SDA pin and pin 3 or SCL pin: These pins are used for I2C communication. On the Uno, these pins were connected to A4 and A5. On the Leonardo, they are connected to pins 2 and 3.
• AREF: Reference pin for analog input.
• Reset: When the microcontroller needs to be reset, this pin is set LOW. Resetting can also be performed using the Reset Button on the board.

You can review the pin mapping page between Arduino® Leonardo and ATmega32u4.

Original Arduino® Leonardo Communication:

Arduino® Leonardo has several different options for communicating with a computer, another Arduino® board, or a microcontroller. The ATmega32u4 offers UART TTL (5V) serial communication through pins 0 (RX) and 1 (TX). The 32u4 connects to the computer via USB, opens a virtual COM port, and enables serial (CDC) communication. The serial monitor included in the Arduino® computer program allows text-based information to be sent and received between Arduino and the computer. When communication between Leonardo and the computer occurs over USB, the RX and TX LEDs on the board will light up.

Leonardo has one hardware serial port. However, this number can be increased through software with the SoftwareSerial library.

The ATmega32u4 also provides I2C and SPI ports. The Arduino® computer program includes the Wire library for I2C usage, while the SPI library is used to enable SPI communication.

Leonardo can be recognized by the computer as a mouse or keyboard and can be used with the Keyboard and Mouse classes.

Original Arduino® Leonardo Programming:

The Arduino® Leonardo board is programmed with the Arduino® computer program (Arduino® IDE). In the program, you can select Arduino Leonardo under the Tools > Board tab and start programming. For detailed information, you can review the reference and basic functions pages. The ATmega32u4 on the Arduino® Leonardo comes with special software called a bootloader installed. Thanks to this, you do not need to use an extra programmer while programming the board. Communication is provided with the original AVR109 protocol.

Bypassing the bootloader software, the board can be programmed directly through the microcontroller’s ICSP header with an ISP programmer (Reference).

Original Arduino® Leonardo USB Overcurrent Protection:

The resettable fuse on the Arduino® Leonardo protects the computer’s USB port from short circuits or overcurrent consumption. When the board draws more than 500mA from the computer’s USB port, it automatically cuts off the power it receives from USB for protection. When the overcurrent condition or short circuit is removed, the fuse returns to normal and the connection is re-established.