#include <ESP32Servo.h>

const int TRIG_PIN  = 2;  
const int ECHO_PIN  = 4;  
const int SERVO_PIN = 18; 
const int DISTANCE_THRESHOLD = 50; 
Servo servo;

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;

  if(distance_cm < 10)
    {
      servo.write(90);  
      delay(2000);     
    }
  else
    {
      servo.write(0);    
    }
  
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  delay(500);
}