/*
   Project:       Ultrasonic Alarm
   Description:   Lights an LED if an object gets too close.
   Creation date: 5/15/23
   Author:        AnonEngineering

   License:       Beerware

   Originally from:

   This ESP32 code is created by esp32io.com
   This ESP32 code is released in the public domain
   For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-ultrasonic-sensor
*/

#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 LED_PIN  21 // ESP32 pin GPIO21 connected to LED

const int ALARM_DISTANCE = 200; // set alarm distance in cm here

unsigned long duration_us = 0;
float distance_cm = 0.0;
float last_distance_cm = 0.0;

void setup()
{
  // begin serial port
  Serial.begin (9600);
  pinMode(LED_PIN, OUTPUT);
  // configure the trigger pin to output mode
  pinMode(TRIG_PIN, OUTPUT);
  // make sure trigger is LOW
  digitalWrite(TRIG_PIN, LOW);
  // configure the echo pin to input mode
  pinMode(ECHO_PIN, INPUT);
}

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;

  // print - if the distance has changed
  if (distance_cm != last_distance_cm)  {
    last_distance_cm = distance_cm; // save the current distance

    // print the value to Serial Monitor
    Serial.print("Distance is now ");
    Serial.print(distance_cm, 1); // print only 1 decimal place
    Serial.println(" cm.      ");

    // light up led if distance under limit
    if (distance_cm < ALARM_DISTANCE - 1)
    {
      digitalWrite(LED_PIN, HIGH);
      Serial.print("Distance < ");
    }
    else
    {
      digitalWrite(LED_PIN, LOW);
      Serial.print("Distance > ");
    }
    Serial.print(ALARM_DISTANCE);
    Serial.println(" cm.");
    Serial.println();
  }
  delay(50); // slow measurements a little
}