#include <Servo.h>

Servo myServo;

int trigPin = 9;
int echoPin = 10;

int buzzer = 5;

long duration;
int distance;

void setup() {

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  pinMode(buzzer, OUTPUT);

  myServo.attach(6);

  myServo.write(0);

  Serial.begin(9600);
}

void loop() {

  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);

  digitalWrite(trigPin, LOW);

  // Read echo
  duration = pulseIn(echoPin, HIGH);

  // Calculate distance
  distance = duration * 0.034 / 2;

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Hand detected
  if (distance < 20) {

    myServo.write(90);

    tone(buzzer, 1000);

    delay(3000);
  }

  else {

    myServo.write(0);

    noTone(buzzer);
  }

  delay(500);
}