#include <Servo.h>
Servo myservo;
int angle=0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  myservo.attach(9);
}

void loop() {
  // put your main code here, to run repeatedly:
  for(angle=0;angle<180;angle++){
    myservo.write(angle);
    delay(20);
  }
  for(angle=180;angle>=1;angle--){
    myservo.write(angle);
    delay(20);
  }
}