LED Blink and Two-LED Patterns

Lesson 1 · Blink a single LED with delay()

Build with the USB cable unplugged. Use one 220–330 Ω resistor for each LED. The long LED leg is usually the anode; the short leg and flat edge mark the cathode.

const int led1 = 8;
void setup() {
  pinMode(led1, OUTPUT);
}
void loop() {
  digitalWrite(led1, HIGH);
  delay(1000);
  digitalWrite(led1, LOW);
  delay(1000);
}

setup() runs once. loop() repeats. HIGH turns the LED on; LOW turns it off. delay(1000) waits one second.

Lesson 2 · Alternate two LEDs

const int led1 = 8;
const int led2 = 9;
void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
}
void loop() {
  digitalWrite(led1, HIGH);
  digitalWrite(led2, LOW);
  delay(500);
  digitalWrite(led1, LOW);
  digitalWrite(led2, HIGH);
  delay(500);
}

Practise the patterns

1. Change both delays to 200 ms, then 1000 ms. Predict which version looks fastest before uploading.
2. Make LED 1 flash twice quickly, then LED 2 stay on for one second. Write the HIGH, LOW and delay steps in order before coding.
3. Create a short–short–long flash pattern, followed by a pause. Check that neither LED is connected without a resistor.