#define TRIG_PIN 26 // ESP32 pin GIOP23 connected to Ultrasonic Sensor's TRIG pin
#define ECHO_PIN 25
#define LED_PIN 18
#define DISTANCE_THRESHOLD 100
#define DISTANCE_THRESHOLD1 120

float duration_us, distance_cm;

void setup() {
  // begin serial port
  Serial.begin (9600);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, OUTPUT);
  pinMode(LED_PIN , OUTPUT);
}

void loop() {
  // generate 10-microsecond pulse to TRIG pin
  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>DISTANCE_THRESHOLD & distance_cm<DISTANCE_THRESHOLD1)
    digitalWrite(LED_PIN, HIGH);
  else
    digitalWrite(LED_PIN, LOW);
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  delay(500);
}