Blink 2 LEDs Program | IoT Project Code & Circuit Explained

Q. Write a program to blink 2 LEDs with a delay of 2 seconds.

This is the important program in O Level Module 4 — IOT Practical — that makes two LEDs blink alternately. One LED is connected to pin 12, and the other to pin 8 of the Arduino board. Each LED stays ON for 2 seconds, then turns OFF as the other turns ON.

So, let’s start this program. Here is the image what we want to make

Variable Declaration

//
int led1 = 12;
int led2 = 11;

• Define Both LEDs with name e.g led1 and led2
• Pins are integer data type values, so we have added int.

Setup Function

//
void setup()
{
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
}

• The setup() function runs once when the Arduino starts or resets.
• pinMode(pin, OUTPUT) configures a pin so that it can send voltage (to light up an LED).
• led1 and led2 are set as OUTPUT.

Also Read: Write a program to blink 5 LEDs in serial mode with a delay of 2 seconds.

Loop Function

//
void loop()
{
  digitalWrite(led1, HIGH);   // Turn ON LED connected to pin 12
  delay(2000);              // Wait for 2 seconds (2000 milliseconds)
  
  digitalWrite(led1, LOW);    // Turn OFF LED on pin 12
  digitalWrite(led2, HIGH);    // Turn ON LED on pin 11
  delay(2000);              // Wait for 2 seconds

  digitalWrite(led2, LOW);     // Turn OFF LED on pin 11
}

CODE

//
int led1 = 12;
int led2 = 11;
void setup()
{
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
}
void loop()
{
  digitalWrite(led1, HIGH);
  delay(2000);
  digitalWrite(led1, LOW);
  digitalWrite(led2, HIGH);
  delay(2000);
  digitalWrite(led2, LOW);
}

• The loop() function runs continuously after setup().
• digitalWrite(pin, HIGH) turns the LED ON by sending 5V to the pin.
• digitalWrite(pin, LOW) turns the LED OFF.
• delay(2000) pauses the program for 2 seconds.

How It Works in Steps:

• LED 1 ON (Pin 12) → wait 2 seconds
• LED 1 OFF, LED 2 ON (Pin 11) → wait 2 seconds
• LED 2 OFF
• Loop back to step 1