My First Arduino Project — Breathing LED!

Today I uploaded my very first Arduino program! 🎉

The best part? I didn’t even need a breadboard or extra components. The Arduino UNO R4 WiFi has a built-in LED right on the board, connected to pin 13.

What does the project do?

The LED slowly fades in and fades out, like a calm breathing light. It uses something called PWM (Pulse Width Modulation) — a fancy way of turning the LED on and off very fast so our eyes see it as dimming.

What you need

• Arduino UNO R4 WiFi (or any Arduino with a built-in LED on pin 13)
• A USB cable to connect it to your computer

That’s it! 🙌

The code

/*
  Breathing LED for Arduino UNO R4 WiFi
  Fades the built-in LED on pin 13 smoothly in and out.
*/

const int LED_PIN = 13;  // Built-in LED on Arduino R4

void setup() {
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Breathing LED started!");
}

void loop() {
  // Fade in: brightness 0 to 255
  for (int brightness = 0; brightness <= 255; brightness += 5) {
    analogWrite(LED_PIN, brightness);
    delay(20);
  }

  // Fade out: brightness 255 to 0
  for (int brightness = 255; brightness >= 0; brightness -= 5) {
    analogWrite(LED_PIN, brightness);
    delay(20);
  }

  // Small pause at the bottom of each breath
  delay(200);
}

How I uploaded it

I used the Arduino CLI from my computer. These were the commands:

# Check that the board is connected
arduino-cli board list

# Compile the sketch
arduino-cli compile --fqbn arduino:renesas_uno:unor4wifi BreathingLED

# Upload it to the board
arduino-cli upload -p /dev/cu.usbmodem9888E00970202 --fqbn arduino:renesas_uno:unor4wifi BreathingLED

If you’re on Windows, your port will look something like COM3 instead of /dev/cu.usbmodem....

How it works

1. pinMode(LED_PIN, OUTPUT); tells the Arduino that pin 13 is an output.
2. analogWrite(LED_PIN, brightness); sets the LED brightness from 0 (off) to 255 (full brightness).
3. The first for loop increases brightness step by step → the LED fades in.
4. The second for loop decreases brightness step by step → the LED fades out.
5. delay(20) makes each step last 20 milliseconds, so the fade looks smooth.

Try changing it!

• Make it breathe faster by changing delay(20) to delay(10).
• Make it breathe slower by changing it to delay(50).
• Remove the final delay(200) if you don’t want a pause.

What’s next?

Next, I want to:

• Wire my own external LED with a resistor.
• Make the LED blink in patterns like an ambulance or heartbeat.
• Use the RGB LED on the R4 WiFi to make colourful lights!

Have fun making your Arduino glow! 💡

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