Light Your First LED

• 1× Arduino Uno
• 1× USB programming cable
• 1× Breadboard
• 1× LED  (any colour)
• 1× 220Ω resistor  colour bands: red–red–brown
• 2× Male-to-male jumper wires

Build this circuit. Take your time — getting the LED facing the right way is the whole game.

Wire the circuit exactly as the table above. Nothing is powered yet — plug the USB cable into the Arduino only after you've checked the LED's long leg goes to the resistor side.

Open the Arduino IDE, type in this code, and upload it to your board:

// Define which pin the LED is connected to
#define LED_PIN 12

// setup() runs once when the board powers on
void setup() {
  pinMode(LED_PIN, OUTPUT);   // tell pin 12 it's an OUTPUT (it sends power out)
}

// loop() runs over and over, forever
void loop() {
  digitalWrite(LED_PIN, HIGH);  // turn the LED ON  (HIGH = 5 volts out)
  delay(500);                   // wait 500 ms (half a second)
  digitalWrite(LED_PIN, LOW);   // turn the LED OFF (LOW = 0 volts)
  delay(500);                   // wait another half a second
}

Once it uploads, your LED should blink on for half a second, off for half a second, forever. That's it — you just controlled the physical world with code.

Now make it yours. Try these before peeking at the answers:

1. Change the blink speed. Make it blink faster, then slower.
2. Move the LED to a different pin (like pin 2, 3, or 11) — and update the code to match.
3. Add a pattern. Make the LED blink three times quickly, then pause for a full second, then repeat.

The Arduino has a row of digital pins — little switches it can flip with code. When you wrote digitalWrite(LED_PIN, HIGH), you told pin 12 to push out 5 volts. That voltage pushes a tiny current through the resistor, through the LED, and out to GND — and a glowing LED is just what an LED does when current flows through it the right way. LOW sets the pin back to 0 volts, so no current flows and the light goes out. delay() simply makes the Arduino wait, so instead of switching millions of times a second (too fast to see), you get a visible blink.