#define Relay_pin 3
void setup(){
 // put your setup code here, to run once:
 pinMode(Relay_pin, OUTPUT);
 Serial.begin(9600);
}
void loop() {
 // put your main code here, to run repeatedly:
 digitalWrite(Relay_pin, HIGH);
 Serial.println("Relay ON");
 delay(3000);
 digitalWrite(Relay_pin, LOW); 
 Serial.println("Relay OFF");
 delay(3000);
}