Your First Arduino Program: Blink the Built-In LED (No Wiring Needed)

Arduino Basics Course · Exercise 1 of 5

Every Arduino journey starts the same way: no breadboard, no wires, no external parts. Just the board, a USB cable, and one blinking light. This is the “hello world” of electronics — the first thing every beginner builds.

The LED is already on the board

Look closely at your Arduino Uno and you’ll spot a tiny LED labeled “L” sitting right next to pin 13. It’s wired permanently to that pin, which means you can control it with code alone — no circuit building required.

The code

Open the Arduino IDE, paste this in, and you’re ready to upload:

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
  delay(1000);
}

LED_BUILTIN is a built-in shortcut that always points to the correct onboard LED pin — on an Uno, that’s pin 13. pinMode tells the board that pin is an output. The loop then turns it on, waits one second, turns it off, waits one second, and repeats forever.

Upload it

1. Plug in your Uno via USB
2. Select Tools > Board > Arduino Uno
3. Select Tools > Port and pick your board’s port
4. Click Upload (the arrow icon in the toolbar)

1. Select your board

Go to Tools > Board > Arduino AVR Boards, then choose Arduino Uno. This tells the IDE which chip to compile for — pick the wrong board and the upload will fail or behave oddly.

2. Select the port

Go to Tools > Port and pick the port your Uno is connected to — it’s usually labeled with “usbmodem” or “usbserial” and often shows “(Arduino Uno)” right next to it, like in the screenshot below.

3. Paste the code, then click Upload

Open the Arduino IDE, select all the default placeholder code, and paste in the sketch from above. The checkmark icon compiles your code (good to catch typos early); the arrow icon next to it — circled below — uploads it to the board.

Within a few seconds, the “L” LED on your board should start blinking once per second. If it does — congratulations, you just wrote and ran your first Arduino program.

If the upload fails

On Mac, clone Uno boards often need a USB driver installed before the port even shows up in the Tools menu — that’s a separate, very common issue and not something wrong with this code.

That’s lesson one. Every project we build at Volt Vidya — from a line-follower robot to a remote-control car — starts from this exact same loop: pinMode, digitalWrite, delay. Once this blinks, you’re ready for the next step.

In this course

1. Exercise 1: Blink the Built-In LED (No Wiring Needed) — you are here
2. Exercise 2: Breadboards and Blinking an External LED — live now
3. Exercise 3: Reading a Pushbutton — coming soon
4. Exercise 4: Understanding Arduino Variables — coming soon
5. Exercise 5: Binary Numbers and an LED Binary Counter — coming soon

Course Index • Next: Exercise 2 →