// Define the GPIO pins for the LEDs
const int ledPin1 = 21; // GPIO 21
const int ledPin2 = 22; // GPIO 22
const int ledPin3 = 23; // GPIO 23

void setup() {
  // Initialize the GPIO pins as outputs
    pinMode(ledPin1, OUTPUT);
      pinMode(ledPin2, OUTPUT);
        pinMode(ledPin3, OUTPUT);
        }

        void loop() {
          // Turn all three LEDs on
            digitalWrite(ledPin1, HIGH);
              digitalWrite(ledPin2, HIGH);
                digitalWrite(ledPin3, HIGH);
                  delay(1000); // Wait for a second

                    // Turn all three LEDs off
                      digitalWrite(ledPin1, LOW);
                        digitalWrite(ledPin2, LOW);
                          digitalWrite(ledPin3, LOW);
                            delay(1000); // Wait for a second
                            }