Arduino Basic Knowledge

Arduino Leonardo Specifications/Functions

In this article, we will explain in detail the specifications and functions of Arduino Leonardo.

Compared to Arduino Uno, Arduino Leonardo does not require a USB-serial conversion chip, has more I/O ports, and the USB terminal has been changed to Micro-B.

Arduino Leonardo Specifications

Tech Specs Arduino Leonardo
Board Size 74.9×53.3mm
Clock Speed
(Main Memory)
Flash Memory 32kB
Operating Voltage +5V
Input Voltage (recommended) +7~+12V
Output Voltage +5V, +3.3V
Digital I/O Pins 20
PWM Digital I/O Pins 7
Analog Input Pins 12
Analog Output Pins
Rated Current per Pin 40mA/Pin
Program Writing Pins Micro USB Type-B
Interface UART

For the specifications of Arduino boards other than Arduino Leonardo, see the following article.

Arduino Leonardo Functions

Arduino Leonardo Appearance

Socket Header Placement(Pin Header Placement)/LED Placement

Arduino Leonardo Pin Header LED Placement

↑Click to enlarge.


The Arduino Leonardo Microcontroller(Microcomputer) uses “ATmega32U4” from Microchip Technology(USA).

A microcontroller(microcomputer) is a very important component in controlling electronic devices that correspond to the human “brain”.

In addition, various memories such as SRAM, Flash memory, and EEPROM are also built into the microcontroller.

②USB Port

You can communicate between Arduino Leonardo and PC by connecting it to the USB port of Arduino Leonardo and PC with a USB cable.

You can write a program(sketch) created on your PC to Arduino Leonardo, and control Arduino Leonardo from your PC by serial communication.

You can also power the Arduino Leonardo via USB instead of the power jack.

③Power Jack

You can connect an AC adapter(outer diameter 5.5mm, inner diameter 2.1mm) to power the Arduino Leonardo.

④Reset Button

You can restart the Arduino Leonardo by pressing the reset button. Use this when you want to restart the program from the beginning or when the Arduino Leonardo behaves strangely.

⑤I/O Port・Power

Digital I/O・PWM

Digital I/O・PWM Explanation
D0-D13/D18-D23 Digital input/output(0-13, 18-23)
PWM 0 to +5V analog output
Analog output by switching between 0V and +5V at high speed

PWM and serial communication are shared with digital I/O. You can specify which one to use in the program.

Analog Input

Analog Input Explanation
A0-A11 Analog input(0-11)
10-bit A/D converter(1step change every 4.8mV)


Communication Explanation
(Serial communication)
TX Serial data transmission
RX Serial data reception
I2C SCL Serial clock
SDA Serial data transmission/reception
SPI SS Select device to control
SCK Serial clock
MOSI Master ⇒ Slave data transfer
MISO Slave ⇒ Master data transfer


Power Explanation
Vin The voltage of “③Power jack” is output,
Power can be supplied from “Vin” without using the power jack.
GND Ground/Reference point
+5V +5V voltage output
+3.3V +3.3V voltage output


Other Explanation
GND Ground/Reference point
AREF Analog input reference voltage (0 to +5V input),
Not normally used
(Same function as “④Reset Button”)
IOREF +5V voltage output


LED Explanation
ON Lights up when the Arduino Leonardo is powered
TX Blinks when sending via serial communication
RX Blinks when receiving via serial communication
L Connect to digital I/O No.13

Arduino Leonardo has 4 LEDs(chip parts). The “L” of LED is connected to the 13th digital I/O, and can be lighted up by setting the 13th pin to HIGH (5V) in the program.

⑦ICSP(For ATmega32U4)

By connecting an ICSP-compatible writer(program writing device), you can write programs(sketches) directly to the “ATmega32U4”, which is an Arduino Leonardo microcontroller(microcomputer).

However, since you can usually write programs(sketches) via the USB port, I think that it is rarely used for writing purposes.

In addition, it can also be used as an SPI terminal.

How to get technical data for Arduino Leonardo

Various technical materials of Arduino Leonardo can be obtained from the official Arduino website.

Arduino Leonardo Technical Data

Arduino Leonardo DOCUMENTATION



Arduino Leonardo EAGLE FILES SCHEMATICS Download

Click each icon to download the “EAGLE FILES” and “SCHEMATICS”.

The Arduino Leonardo has the same board size as the Arduino Uno. Arduino Uno board size data(DXF format) can be downloaded from the link below.

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