#include <Servo.h>

const int trigPin = 9;  // Pin for the trig pin of the HC-SR04
const int echoPin = 10; // Pin for the echo pin of the HC-SR04
const int servoPin = 11; // Pin for the servo signal

Servo myServo; // Create a servo object
const int distanceThreshold = 20; // Distance threshold in cm

void setup() {
  Serial.begin(9600); // Start the serial communication
    pinMode(trigPin, OUTPUT); // Set the trigPin as an output
      pinMode(echoPin, INPUT); // Set the echoPin as an input
        myServo.attach(servoPin); // Attach the servo to the servoPin
          myServo.write(0); // Initial position of the servo
          }

          void loop() {
            long duration, distance;
              digitalWrite(trigPin, LOW); 
                delayMicroseconds(2);
                  digitalWrite(trigPin, HIGH);
                    delayMicroseconds(10);
                      digitalWrite(trigPin, LOW);
                        duration = pulseIn(echoPin, HIGH);
                          distance = duration * 0.034 / 2;

                            if (distance <= distanceThreshold) {
                                myServo.write(90); // Rotate servo to 90 degrees
                                  } else {
                                      myServo.write(0); // Rotate servo back to 0 degrees
                                        }

                                          delay(500); // Wait for half a second before the next loop
                                          }