#include <Servo.h> // include the Servo library

Servo myservo; // create a servo object

// define the pins for Ultrasonic Sensor HC-SR04
const int trigPin = 9;  // define the trigPin and trigPin for the Ultrasonic Sensor HC-SR04
const int echoPin = 10; // define the trigPin and echoPin for the Ultrasonic Sensor HC-SR04



void setup() {
  myservo.attach(8); // attach the servo to pin 8
  pinMode(trigPin, OUTPUT); // set the trigPin as an output
  pinMode(echoPin, INPUT); // set the echoPin as an input
 
  // start the serial communication
  Serial.begin(9600);

}

void loop() {
  long duration, distance; // create variables to store the duration and distance
  
  digitalWrite(trigPin, LOW); // set the trigPin low
  delayMicroseconds(2); // wait for 2 microseconds
  
  digitalWrite(trigPin, HIGH); // set the trigPin high
  delayMicroseconds(10); // wait for 10 microseconds
  
  digitalWrite(trigPin, LOW); // set the trigPin low
  
  duration = pulseIn(echoPin, HIGH); // read the duration of the pulse
  distance = (duration/2) / 29.1; // calculate the distance in centimeters
  
  if (distance < 100) { // if the distance is less than 20 cm
   digitalWrite(8, LOW); // set the trigPin low
    delay(1000); // wait for 1 second
   digitalWrite(8, HIGH); // set the trigPin low
  }
  else { // if the distance is greater than 20 cm
   digitalWrite(8, HIGH); // set the trigPin low
  }

}