#define PIN_RELAY  2 // the Arduino pin, which connects to the IN4 pin of relay module

// the setup function runs once when you press reset or power the board
void setup() {
  Serial.begin(9600);

  // initialize digital pin as an output.
  pinMode(PIN_RELAY, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  
  Serial.println("Turn on");
  digitalWrite(PIN_RELAY, HIGH);
  delay(1000);

  Serial.println("Turn off");
  digitalWrite(PIN_RELAY, LOW);
  delay(1000);
}