Blink LED

The classic \"Hello World\" of Arduino - make an LED blink on and off.

Circuit Diagram

Wire Connections & Pin Configuration

Wire Color Connections:

Yellow/Orange → Digital Pins 2–13 (signal to each LED anode)
Black → GND (common cathode connection)

Pin Configuration:

Arduino Digital Pin 2 → LED 1 anode
Arduino Digital Pin 3 → LED 2 anode
Arduino Digital Pin 4 → LED 3 anode
Arduino Digital Pin 5 → LED 4 anode
Arduino Digital Pin 6 → LED 5 anode
Arduino Digital Pin 7 → LED 6 anode
Arduino Digital Pin 8 → LED 7 anode
Arduino Digital Pin 9 → LED 8 anode
Arduino Digital Pin 10 → LED 9 anode
Arduino Digital Pin 11 → LED 10 anode
Arduino Digital Pin 12 → LED 11 anode
Arduino Digital Pin 13 → LED 12 anode
Arduino GND → All LED cathodes (common)

Arduino Code

Edit

// Total number of LEDs
int ledCount = 12;

// LED pins connected to Arduino
int ledPins[] = {2,3,4,5,6,7,8,9,10,11,12,13};

void setup() {
  // Set all LED pins as OUTPUT
  for(int i = 0; i < ledCount; i++){
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {

  // Turn LEDs ON one by one
  for(int i = 0; i < ledCount; i++){
    digitalWrite(ledPins[i], HIGH);
    delay(150);
    digitalWrite(ledPins[i], LOW);
  }

  // Reverse direction
  for(int i = ledCount-1; i >= 0; i--){
    digitalWrite(ledPins[i], HIGH);
    delay(150);
    digitalWrite(ledPins[i], LOW);
  }

}

Instruction Details

Wiring: Connect LED anode (long leg) to Digital Pin 2 via 220Ω resistor. Connect cathode (short leg) to GND. For multiple LEDs, connect each anode to Pins 2–13 via 220Ω and share common GND.
Library: Not required (built-in).
Upload Code: Tools → Board → Arduino Uno. Tools → Port → select your COM port. Click Upload button.
View Output: LEDs will chase in sequence from Pin 2 to 13 and back.

How to Use

Connect the required components as per the Pin Configuration above
Open Arduino IDE and create a new sketch
Copy and paste the code above
Select your Arduino board and COM port from Tools menu
Click the Upload button to upload the code to your Arduino
Open Serial Monitor (if applicable) to see the output

Components Required

Arduino Uno
12× LEDs
12× 220Ω Resistors
Breadboard
Jumper Wires

Category: Arduino Basics