Automatic Crossing Signal Controller

// Basic crossing signal - alternating LEDs
const int LED1 = 2;
const int LED2 = 3;
const int SENSOR = 4;

void setup() {
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(SENSOR, INPUT);
}

void loop() {
  if (digitalRead(SENSOR) == LOW) {
    // Train detected - flash lights
    digitalWrite(LED1, HIGH);
    digitalWrite(LED2, LOW);
    delay(500);
    digitalWrite(LED1, LOW);
    digitalWrite(LED2, HIGH);
    delay(500);
  } else {
    // No train - lights off
    digitalWrite(LED1, LOW);
    digitalWrite(LED2, LOW);
  }
}