// Relay Module -> digital pin 7
const uint8_t RELAY_PIN = 7;

void setup() {
  Serial.begin(9600);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW); // start OFF (change if your module is active LOW)
}

void loop() {
  digitalWrite(RELAY_PIN, HIGH); // turn relay ON
  Serial.println("ON");
  delay(5000);                    // ON for 5 seconds

  digitalWrite(RELAY_PIN, LOW);  // turn relay OFF
  Serial.println("OFF");
  delay(5000);                    // OFF for 5 seconds
}