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Blink an LED with Arduino Uno

The classic first Arduino project: make an LED turn on and off once per second. Learn digital output, pinMode, and the loop.

Beginner10 min

What you need

Wiring

Arduino Uno
LED

Hover a pin or a wire to trace the connection.

Code

blink.ino
// Blink an LED on pin 13 once per second.
// Pin 13 (LED_BUILTIN) also drives the Uno's onboard LED.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);   // set pin 13 as an output
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH); // LED on
  delay(1000);                     // wait 1 second
  digitalWrite(LED_BUILTIN, LOW);  // LED off
  delay(1000);                     // wait 1 second
}

Steps

  1. Push the LED into the breadboard. The long leg is the anode (+).
  2. Connect Arduino D13 to the LED's anode through the 220Ω resistor.
  3. Connect the LED's short leg (cathode) to an Arduino GND pin.
  4. Upload the sketch. The LED blinks once per second.