Blink an LED

Part of the First Circuits section of Coddy's Arduino journey. Lesson 1 of 22.

An Arduino Uno is a small computer called a microcontroller. You write a program for it, called a sketch, and the board runs it on its own, again and again, as long as it has power.

Every sketch has two parts:

void setup() {
  // runs once, when the board starts
}

void loop() {
  // runs again and again, forever
}

The board talks to the world through its pins. Pin 13 has an LED wired to it. To light it, make the pin an output in setup(), then set it HIGH (5 volts, on) or LOW (0 volts, off):

pinMode(13, OUTPUT);
digitalWrite(13, HIGH);

delay(1000) pauses the sketch for 1000 milliseconds, one second. Put an on, a wait, an off and another wait in loop(), and the LED blinks forever.

Challenge

Easy

The board has an LED on pin 13. This sketch makes it blink: setup() makes pin 13 an output, and loop() turns the LED on, waits a second, turns it off and waits again, over and over.

Press Run on the board to watch it blink, then press Check.

Try it yourself

void setup() {
  pinMode(13, OUTPUT);  // pin 13 is an output
}

void loop() {
  digitalWrite(13, HIGH);  // LED on
  delay(1000);             // wait one second
  digitalWrite(13, LOW);   // LED off
  delay(1000);             // wait one second
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LEDSetup and Loop Change the Blink Speed An LED of Your Own Two LEDs Taking Turns Comments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing Values Combining Conditions Read a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground