#include <Servo.h>
Servo servo1;
int pos;

void setup() {
  // put your setup code here, to run once:
servo1.attach (3);
}

void loop() {
 for(pos = 0; pos <= 180; pos += 20)
 {
  servo1.write(pos); 
  delay(1000);                
 }

 for(pos = 180; pos >= 0; pos -= 20)
 {
  servo1.write(pos); 
  delay(1000);                
 }
}