#include <Servo.h>
Servo myservo;
void setup() {
  myservo.attach(D1);  // ATTACH SERVEO TO D1 PIN
}

void loop() {
  int pos;

  for (pos = 0; pos <= 180; pos += 1) { // it goes from 0 degrees to 180 degrees
    // in steps of 1 degree
    myservo.write(pos);    
    delay(15);                    
  }
  for (pos = 180; pos >= 0; pos -= 1) { // it goes from 180 degrees to 0 degrees
    myservo.write(pos);     
    delay(15);                     
  }
}