The Lazy Comparison Guide about Arduino UNO and Leonardo

Believe it or not, some people don’t enjoy making new things with Arduino boards. I used to hate it too because I lacked confidence.

It requires coding and skills. Once you start applying the right techniques and get a little confidence in using these microcontroller boards. You will get better by time and start to enjoy playing with the electronic toys.

The Arduino boards come in various shapes and sizes with different functionality and features. Just like Arduino Lillypad is specially designed for e-textile and It requires coding and skills. Once you start applying the right techniques and get a little confidence in using these microcontroller boards. You will get better by time and start to enjoy playing with the electronic toys wearable. Arduino UNO and Leonardo both work in the same way but there are a few reason why Arduino has made it separately:

A crucial difference is that a UNO has a replaceable microcontroller (Atmega328) which gives an additional advantage to the user. So you don’t have to buy the whole board again. On the contrast, Arduino Leonardo has a microcontroller (Atmega32u4) mounted on its surface which has a built-in support for USB.

Every other Arduino board is unique in its own way and has its own features and benefits. Are you still confused and don’t understand which one to buy Arduino Leonardo or UNO?

Let’s dive into the differences between LEO and UNO. So you don’t get trouble trying new things.

What are the differences between Arduino Leonardo and UNO?

There are many types of Arduino boards available in the market, and most of you spend a lot of time and research on the internet to buy the right type of board.

I recommend you to not go into so much technical details at first. You can just simply start your Arduino journey from the Arduino UNO or Leonardo. They both are the simplest and easiest among the arduino family. It has everything which you need to get started.

Both Arduino UNO and Leonardo are official Arduino boards, and it also works on the same software (Arduino IDE). Arduino software is free to use and you can download it from the website.

Before you waste your time on different types of microcontrollers boards; here are the differences between Arduino UNO and Leonardo which may help you in decision making.

Here is a quick tip: Don’t buy any second hand Arduino board.

There are pretty obvious differences that can be seen with our naked eyes.

    • Microcontroller – They both use the same series microcontroller but LEO uses a surface mounted Atmega32U4 which has a support for USB. At the same time, UNO uses a replaceable microcontroller Atmega328p which can be restored when you somehow burn its driver or microcontroller. You don’t need to buy the whole board again. You can re-use it after replacing the microcontroller. 
    • FTDI chip – There is no FTDI chip in UNO which is used to translate a USB signal into a serial communication. Microcontroller Atmega32U4 has serial ports and native USB.
    • USB B-class connector – They have also replaced the USB b-class connector with a micro USB connection.
    • Paint job – Leonardo has a smooth and dark paint so you can see clearly what has written on the board or the pin numbers.
    • Input/Output pins – Leonardo has more pins than UNO. Leonardo has 23 pins and each pin can be used as input or output. You can easily connect other compatible devices like drivers, sensors with the board and make your innovation into reality.
    • Price – Leonardo is 20% cheaper than the UNO board.
    • USB support – It gives an additional facility of USB in Arduino Leonardo board for the students and hobbyists who want to create more projects with USB.


Arduino UNO

Arduino Leonardo




Operating voltage



Recommended Input voltage



Digital I/O pins



PWM pins



Analog input channels



Flash Memory

32Kb (0.5 Kb used by bootloader)

32Kb (4 kb used by bootloader)

Clock Speed


16 Mhz





2 Kb

2.5 Kb



68.6 mm



53.3 mm



20 gm

DC current for 3.3V Pin


50 mA

DC current (Input/output pin)


40 mA

Pin Descriptions of Arduino UNO and Leonardo

Power Pins

You have now understood the most obvious difference between these boards. Now let’s dive into the power pin which could give you an advantage.

Power pins play an essential role in Arduino which power up the Arduino, sensors, motor drivers and shields. Power pins are pretty much the same in each type of arduino board.

There are two ways to power up the arduino boards:

  • AC-DC adaptor, from an external source supply that is battery.
  • You can also power up your Arduino with your laptop with the help of Printer Cable.
power pins of arduino Mega

VIN pin uses to power another Arduino, and can also be used to power other sensors and drivers. 
If you supply an external power source i-e a battery or power supply. GND and VIN can also start your board, but I would suggest you to use a battery (preferably 9 to12V battery) because of the voltage dropout. Maker of this board has already fixed a built-in regulator so it would only allow fixed 5V to the Arduino.Tip: You can use this pin to power other components, such as, motor drivers, shields, Arduino and sensors only if you supply power through a barrel jack or from a USB cable. 

5VMost of the time 5V pin is used to power up the drivers and shields like RFID, sensors, Bluetooth (5V pin is limited to 500mA current if you are using an Arduino with a USB cable). 

Moreover, the onboard voltage regulator is limited to 800mA but due to some power issues, you shouldn’t exceed more than 500mA. It might damage your board.

3.3VRegulated output, can be used to power up components which run at 3.3V.

GNDGround pin

Digital input and output pins can be used in both ways either input or output using pinmode(), digitalread(), digitalwrite() functions. Each of the pins operate at 5v, provide or receive the maximum amount of 40mA current.



Some pins are designed to perform specialized functions:

0(RX) and 1(TX)  – are used for receiving the data and transmitting data respectively.

SDA and SCL – SDA and SCL stands for serial data and serial clock respectively. They both support two-wire interface (TWI) communication using the wire library. Two wire interface TWI and I2C are quite similar.

PWM – 3, 5, 6, 9, 10, 11 and 13 analogWrite() function is used to provide 8 bit PWM output.

LED 13 – built-in LED is fixed at pin number 13.

Arduino is pretty famous among students, teachers and hobbyists because of its affordable price, easy to use hardware and software, but Arduino UNO gained much popularity among all the arduino boards. Here are a few points why UNO is popular:

  • Arduino UNO is famous because of its simple architecture and its pinout structure is quite easy to understand. 
  • Most of the UNO shields don’t support Leonardo. On the comparison, Arduino UNO is compatible with almost every driver and shield.
  • Tutorials of UNO are easily available on cyberspace while some of the uno code doesn’t support Leonardo.

So far, you have understood the difference between these two boards and it would help you to select the right one, but there are a few cool features which make arduino Leonardo unique:

  • Arduino Leonardo supports a microcontroller (Atmega32u4) which has a built-in support for USB. It also has a USB communication port which helps you to directly run your sketches. Since Leo doesn’t require an additional microcontroller for communication, but UNO requires one.
  • Arduino Leonardo has more number of digital and input output pins.

Arduino is an ongoing learning process and you get better by time when you start practicing daily. Here are a few more articles on arduino which might help you in gaining more knowledge about arduino and its family.

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