// Define the pins for the LEDs
const int onboardLED = 13;
const int redLED = 12;
const int greenLED = 11;

// Variables to control timing
unsigned long previousMillis = 0;
const long interval = 1000; // 1 second interval between LED changes
int ledState = 0; // 0 for onboard, 1 for red, 2 for green

void setup() {
  // Set the LED pins as outputs
  pinMode(onboardLED, OUTPUT);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
}

void loop() {
  unsigned long currentMillis = millis();

  // Check if it's time to change the LED
  if (currentMillis - previousMillis >= interval) {
    // Save the last time we changed the LED
    previousMillis = currentMillis;

    // Turn off all LEDs
    digitalWrite(onboardLED, LOW);
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, LOW);

    // Turn on the next LED in the cycle
    if (ledState == 0) {
      digitalWrite(onboardLED, HIGH); // Turn on onboard LED
      ledState = 1; // Next LED is red
    } else if (ledState == 1) {
      digitalWrite(redLED, HIGH); // Turn on red LED
      ledState = 2; // Next LED is green
    } else if (ledState == 2) {
      digitalWrite(greenLED, HIGH); // Turn on green LED
      ledState = 0; // Next LED is onboard
    }
  }
}