#include <Servo.h>
int SERVO_PIN = 11;
Servo servo;

int TRIG_PIN = 8;
int ECHO_PIN = 7;
float duration_us, distance_cm;

void setup() {
  Serial.begin(9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);

  servo.attach(SERVO_PIN);
  servo.write(0);

}

void loop() {
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  duration_us = pulseIn(ECHO_PIN, HIGH);
  distance_cm = 0.017 * duration_us;

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

   delay(500);

    if (distance_cm<=50){
        servo.write(90);
  delay(500);
    }
    else{
             servo.write(0);
  delay(500);
    }


}