Grand 1 article on Arduino Leonardo Pinout and their functions read now

The Arduino Leonardo is one of the best boards provided by the Arduino platform.

It comes with the  ATmega32u4 controller that has built-in USB support.

The Arduino Leonardo contains everything that is needed to support the microcontrollers just connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started. Arduino Leonardo is very much similar to Arduino UNO try Arduino Leonardo vs Uno comparison and comment down. There is a mini version of Arduino Leonardo available name Arduino, micro.

How does Arduino Leonardo work?

The ATmega32u4 is a high-performance, low-power AVR 8-bit microchip. It has 32 kilobytes of memory (of which 4 KB is used by the bootloader), 2.5 KB of SRAM, and 1 KB of EEPROM. Arduino Leonardo uses ATmega32u4 controllers for function.

Arduino Leonardo on board components

Crystal Oscillator

The Crystal oscillator inside the board has a frequency of 16MHz, which generates the clock signal in the microcontroller. Its basic function is to provide basic timing and control to the board.


The Arduino Leonardo specifications are as follows

Operating Voltage5V
Input Voltage (Recommended)7-12V
Input Voltage (limits)6-20V
Digital I/O Pins20
PWM Channels7
Analog Input Channels12
DC Current per I/O Pin40 mA
DC Current for 3.3V Pin50 mA
Flash Memory32 KB (of which 4 KB is taken by the bootloader)
SRAM2.5 KB (ATmega32u4)
EEPROM1 KB (ATmega32u4)
Clock Speed16 MHz
Length68.6 mm
Width53.3 mm
Weight20 g

Arduino Leonardo Pinout

arduino leonardo pinout

The Pinout diagram of Arduino Leonardo is given below

Pin categoryRepresentationDescription
Power pins5V, RESET, 3.3V, GND (3), Vin, AREF, IOREFPins used to deliver power to the device connected with Arduino
Digital pins0 to 13Pins used for digital input and outputs of Arduino
PWM pins13,11,10, 9, 6, 5, 3Pins used to generate the pulsating signal
Analog pinsA0 to A5 (A5 for SCL and A4 for SDA)Pins used for analog inputs and outputs of Arduino
Miscellaneous pinsAdditional pins for SCL and SDA SCL is the clock pin, and the SDA is the data pin for I2C and TWI communication devices
6 header pinsICSPPins used to program the controller

For communication purposes in Arduino Leonardo SCA and SDL, pins are given. We use pins A5 and A4 for the SCL and SDA respectively.

Arduino Leonardo IO pins

Digital Pins of the Arduino Leonardo

For connecting the digital devices with the Leonardo the Arduino has provided 14 pins from which Pin 0 and Pin 1 are used for transmitting and receiving of the data and are also called the communication pins. 

arduino leonardo digital pins

As the word digital suggests it is associated with the data. According to this, the data will be in the form of 0 and 1. 

For the generation of the input and output in the form of pulses, you can use pins 13,11,10, 9, 6, 5, and 3 of the Leonardo as they are dedicated pins of Pulse Width Modulation(PWM) and the duty cycle of the pulse is from 0 to 255.

Analog Pins of Arduino Leonardo:-

There are 6 Pins provided in Arduino Leonardo which are used to connect analog devices having resolutions ranging from 0 – 1024. In terms of voltage, it will be 5Volts for 1024.

arduino leonardo Analoug pins

The Arduino Leonardo has provided two dedicated pins next to the AREF pin which is used for the data line and clock of the I2C devices.

However, we can use pins A4 and A5 as the SDA and SCL pins respectively for the devices that used I2C and TWI (Two Wire Interface) communication protocols

The SDA pin is the data line for the connected devices while SCL is the clock pin of the connected devices. 

Power Pins Of Arduino Leonardo

There are three pins of ground are present, the first pin is for 5 volts, another pin is for 3.3 volts and the two pins are for giving the reference voltage for analog and digital devices.

There is also a reset pin available on the Arduino Leonardo board to RESET the Leonardo using an external button, however, a dedicated reset pin is provided on the Arduino Leonardo board.

For connecting the Arduino Leonardo board with the supply voltage there is one built-in USB port provided while for power supply purposes a jack is also provided.

arduino leonardo power pins for supply

The USB port can be used for power as well as to upload the code to the Arduino.

Arduino Leonardo Communication pins

ICSP header pins of the Arduino Leonardo

There are 6 header pins provided on the Arduino Leonardo board that is dedicated to in-circuit system programming (ICSP).

arduino leonardo ICSP pins

SPI Pins

SPI stands for Serial Peripheral Interface. 

These pins are used by the microcontroller for communicating with one or more peripheral devices efficiently. 

The Serial Peripheral Pins in Arduino Leonardo are present in the ICSP header, these pins SPI communication using SPI libraries.

arduino leonardo communication pins

Two-Wire Interface (TWI)/I2C

I2C stands for Inter-Integrated Circuits. The I2C uses two lines to send and transmit data: a serial clock (SCL) pin and a serial data (SDA) pin. 

Other Pins

AREF: Reference voltage for the analog inputs.

LED 13: In the board, there is a built-in LED connected to digital pin 13. When this pin is set to  HIGH or 1, the LED is switched on, when this pin is set to LOW or 0, it’s switched off.

IOREF: This pin represents the voltage at which the I/O pins of the board are operating

Connection and Firmware of Arduino Leonardo

Connecting the device requires a USB data cable that is connected to a PC or a  power supply from an external source.

For installing the Arduino Leonardo Driver

Following are the steps required to install the Arduino Leonardo driver:-

  • connecting the device to the PC
  • Waiting for the start of the software installation wizard (if there is no start, manually go to the hardware section, select the Arduino Leonardo line, and press update);
  • searching for the drivers on the PC and clicking “Next”;
  • In the folder with the software, select the required driver;
  • accepting the installation.

For flashing the device, it is needed to press the Upload button to load the software into the memory of the device automatically.

Then, the controller’s reset is initiated, which leads to the bootloader start which is responsible for receiving, saving, and starting the new software. For elevated steps, you can refer to this article.

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