#include <Servo.h> // Include Servo library
// Create Servo object
Servo myservo ;

// Variables
// pins
int servopin = 10;
// timers
long timer = 0;
int offset = 15;
// servo angle
int angle = 0;
int servodir = 1;

// Setup
void setup(){
  Serial.begin(9600);
  pinMode(servopin,OUTPUT);
  myservo.attach(servopin);
  myservo.write(angle);
}

// Das Loop
void loop() {
  // Check the timer
  if(timer + offset < millis()) {
    // if the timer has passed, do the swing
    doSwing();
    // reset the timer
    timer = millis();
  }
}

void doSwing() {
  //Serial.println(angle);
  if(angle == 180) { servodir = -1; }
  if(angle == 0) { servodir = 1;  }
  myservo.write(angle);
  angle = angle + servodir;
}