#include <Servo.h>

#define TRIG_PIN  23  // ESP32 pin GPIO23 connected to Ultrasonic Sensor's TRIG pin
#define ECHO_PIN  22  // ESP32 pin GPIO22 connected to Ultrasonic Sensor's ECHO pin
#define SERVO_PIN 26  // ESP32 pin GPIO26 connected to Servo Motor's pin
#define DISTANCE_THRESHOLD  50 // centimeters

Servo servo; // create servo object to control a servo

// variables will change:
float duration_us, distance_cm;

void setup() {
  Serial.begin (9600);       // initialize serial port
  pinMode(TRIG_PIN, OUTPUT); // set ESP32 pin to output mode
  pinMode(ECHO_PIN, INPUT);  // set ESP32 pin to input mode
  servo.attach(SERVO_PIN);   // attaches the servo on pin 9 to the servo object
  servo.write(0);
}

void loop() {
  // generate 10-microsecond pulse to TRIG pin
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // measure duration of pulse from ECHO pin
  duration_us = pulseIn(ECHO_PIN, HIGH);
  // calculate the distance
  distance_cm = 0.017 * duration_us;

  if (distance_cm < DISTANCE_THRESHOLD)
    servo.write(90); // rotate servo motor to 90 degree
  else
    servo.write(0);  // rotate servo motor to 0 degree

  // print the value to Serial Monitor
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  delay(500);
}