int relay_in = 25;

void setup() {
  pinMode(relay_in, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(relay_in, HIGH);
  Serial.println("ดับ");
  delay(1000);
  digitalWrite(relay_in, LOW);
  Serial.println("สว่าง");
  delay(1000);
  Serial.print("Relay pin is = ");
  Serial.println(relay_in) ;
  delay(500);
}