#include <Servo.h>

Servo myservo;
int servo_pin = 9;

void setup() {
  // put your setup code here, to run once:
  myservo.attach(servo_pin);
}

void loop() {
  // put your main code here, to run repeatedly:
  int pos = 0;
  int dtwait = 15;

  for(pos = 0; pos < 180; pos += 1){
    myservo.write(pos);
    delay(dtwait);
  }
  for(pos = 180; pos > 0; pos -= 1){
    myservo.write(pos);
    delay(dtwait);
  }
}