//Initializing Servo Pin
int servo_pin = 4;
void setup() {
  //Declaring Servo pin as output
  pinMode(servo_pin, OUTPUT);
}
void loop() {
  for(int i=0; i<255; i++){
    analogWrite(servo_pin, i);
    delay(5);
  }
  for(int i=255; i>0; i--){
    analogWrite(servo_pin, i);
    delay(5);
  }
}