#include <Servo.h>
Servo servo; 
void setup() {
  servo.attach(9);  
  servo.write(0);   
}
void loop() {
  for (int pos = 0; pos <= 180; pos += 1) { 
    servo.write(pos);  
    delay(10);         
  }

  for (int pos = 180; pos >= 0; pos -= 1) {  
    servo.write(pos);                        
    delay(10);                               
  }
}