Arduino Uno vs Leonardo: Key Differences and When to Use Each

The Arduino Uno uses the ATmega328P microcontroller and has a standard USB-to-serial converter, while the Arduino Leonardo uses the ATmega32u4 microcontroller with built-in USB communication, allowing it to act as a keyboard or mouse. This makes the Leonardo better for projects needing direct USB device control.

Quick Comparison

Here is a quick side-by-side comparison of the Arduino Uno and Leonardo boards highlighting their main features.

Feature	Arduino Uno	Arduino Leonardo
Microcontroller	ATmega328P	ATmega32u4
USB Interface	Separate USB-to-serial chip	Built-in USB controller
Can act as USB device (keyboard/mouse)	No	Yes
Digital I/O Pins	14 (6 PWM)	20 (7 PWM)
Analog Input Pins	6	12
Operating Voltage	5V	5V

Key Differences

The Arduino Uno uses the ATmega328P microcontroller and relies on an external USB-to-serial converter chip to communicate with the computer. This means it appears as a serial COM port and cannot directly emulate USB devices like keyboards or mice.

In contrast, the Arduino Leonardo uses the ATmega32u4 microcontroller, which has built-in USB communication capabilities. This allows the Leonardo to appear as a native USB device, enabling it to act as a keyboard, mouse, or other USB device without extra hardware.

Additionally, the Leonardo offers more digital and analog pins, giving more flexibility for complex projects. The Uno is simpler and more common, making it a great choice for beginners or basic projects.

Code Comparison

Here is a simple example to blink the onboard LED on the Arduino Uno.

arduino

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
  delay(1000);
}

Output

The onboard LED blinks on and off every second.

Arduino Leonardo Equivalent

The same LED blink code works on the Arduino Leonardo since it also has an onboard LED connected to LED_BUILTIN.

arduino

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
  delay(1000);
}

Output

The onboard LED blinks on and off every second.

When to Use Which

Choose Arduino Uno if you want a simple, widely supported board for basic projects and learning. It is great for beginners and general-purpose use.

Choose Arduino Leonardo if your project needs to emulate USB devices like keyboards or mice, or if you need more input pins. It is ideal for custom USB controllers or advanced input devices.

Key Takeaways

Arduino Uno uses ATmega328P with external USB-to-serial; Leonardo uses ATmega32u4 with built-in USB.

Leonardo can act as a USB keyboard or mouse; Uno cannot.

Leonardo has more digital and analog pins than Uno.

Use Uno for simple projects and beginners; use Leonardo for USB device emulation and advanced inputs.