How to Blink an LED with Arduino

This Article tells the simplest thing you can do with an Arduino  Uno or Genuino Uno to see the physical output: it blinks the onboard LED.

Hardware Required:

  1. Arduino UNO
  2. LED


This  Article uses the blinking an LED by Arduino UNO/Nano. This LED is connected to a digital pin and its number may vary from board type to board type.

If you want to lit an external LED with this sketch, you need to build this circuit, where you connect one end of the resistor to the digital pin correspondent to the LED_BUILTIN constant. Connect the long leg of the LED (the positive leg, called the anode) to the other end of the resistor. Connect the short leg of the LED (the negative leg, called the cathode) to the GND. In the diagram below we show a UNO board that has D13 as the LED_BUILTIN value.

The value of the resistor in series with the LED may be of a different value than 220 ohms; the LED will lit up also with values up to 1K ohm.



After you build the circuit plug your Arduino Uno or Genuino Uno board into your computer, start the Arduino Software (IDE) and enter the code below.
You may also load it from the menu File/Examples/01.Basics/Blink.
The first thing you do is to initialize LED_BUILTIN pin as an output pin with the line.


In the main loop, you turn the LED on with the line:


This supplies 5 volts to the LED anode. That creates a voltage difference across the pins of the LED, and lights it up. Then you turn it off with the line:


That takes the LED_BUILTIN pin back to 0 volts and turns the LED off. In between the on and the off, you want enough time for a person to see the change, so the delay() commands tell the board to do nothing for 1000 milliseconds, or one second. When you use the delay() command, nothing else happens for that amount of time.

// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin LED_BUILTIN as an output.

// the loop function runs over and over again forever
void loop() {
digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
delay(1000); // wait for a second
digitalWrite(LED_BUILTIN, LOW); // turn the LED off by making the voltage LOW
delay(1000); // wait for a second

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