Two alternating LEDs

Goal

Alternate two LEDs (pins 12 and 13) like a level crossing.

Why it matters

You learn to drive several independent outputs inside the same loop.

Steps

1. 01Add a second LED + resistor on pin 12.
2. 02Declare both pins as OUTPUT.
3. 03In loop(), set one HIGH while the other is LOW, then swap.

Next tutorials

• Blink an LED

  Turn an LED on pin 13 on and off every second.

• 5-LED chaser

  Run a light across 5 LEDs using a for loop and an array.

• SOS message in Morse code

  Send ··· ––– ··· on the LED with exact timings.

• Blink without delay() (millis)

  Replace delay() with a time comparison based on millis().