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How to Turn on Arduino Uno's Internal LED

LED Internal Arduino

A. LED Internal Arduino

Controlling Arduino's Internal LEDs - This is an article made especially for those of you who are beginners in playing Arduino based on the ATMega328 microcontroller.

By default, Arduino boards have an internal LED. This LED is connected to PIN 13. So we will try to make this pin 13 output HIGH and LOW voltages for one second.

In theory, the voltage with a logic HIGH is 5 Volts and a logic LOW is 0 Volts.

But in practice, not all logic HIGH is 5 Volts, it could be 4, 4.5 or 4.8 Volts. But in the microcontroller, the logic still reads HIGH.

How to Turn on Arduino Uno's Internal LED
Arduino Uno LED Internal (gambar di ambil dari SparkFun Electronics - Juan Peña)

B. Internal LED Blink (1 Second On/Off)

Now please connect Arduino to your PC, then open Arduino IDE and follow these steps:
  • Go to menu File > Examples > 0.1 Basics > Blink
  • Then you will see a program like this:

      Turns an LED on for one second, then off for one second, repeatedly.
      Most Arduinos have an on-board LED you can control. On the UNO, MEGA and ZERO
      it is attached to digital pin 13, on MKR1000 on pin 6. LED_BUILTIN is set to
      the correct LED pin independent of which board is used.
      If you want to know what pin the on-board LED is connected to on your Arduino
      model, check the Technical Specs of your board at:
      modified 8 May 2014
      by Scott Fitzgerald
      modified 2 Sep 2016
      by Arturo Guadalupi
      modified 8 Sep 2016
      by Colby Newman
      This example code is in the public domain.
    // the setup function runs once when you press reset or power the board
    void setup() {
      // initialize digital pin LED_BUILTIN as an output.
      pinMode(LED_BUILTIN, 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

  • Please click the Tools menu > Board.
  • Select the Arduino/Genuino Uno list.
  • Select your Arduino USB Port.
  • Select AVRISP Programmer mkll.
  • Then return to the menu, click Upload as shown in the image below
  • .
  • How to Turn on Arduino Uno's Internal LED
  • If you have finished the upload process, pay attention to the LED on your Arduino, then you will see the LED turn on in approximately 1 second.
  • This 1 second timing is determined by the value of delay(1000). If you want the LEDs to flash alternately within 2 seconds, change delay to delay(2000).

B. LED External Blink

In real projects, we rarely use the internal LED. We will use the External LED more often, because we can change the position of the LED. For the circuit, please look at the following image.
How to Turn on Arduino Uno's Internal LED

We use a resistor with a value of 330 Ohms. Why do we use a resistor? For more, please read the article How to choose the correct Resistor For LED.

Please follow the steps from Turning on the Internal LED and upload the program to Arduino, then take a look at your Arduino. If the external LED is on, you have successfully assembled it. If it doesn't light up, check the circuit again.

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