#include <Arduino.h>

#define led_pin 26
#define echo_pin 33
#define trig_pin 27
#define buzzer_pin 25 
#define speed_sound 0.0343 //    in cm/microSeconds

long duration;
float distance_CM;

void setup()
{
  Serial.begin(115200);
  pinMode(buzzer_pin,OUTPUT);
  pinMode(led_pin,OUTPUT);
  pinMode(echo_pin,INPUT);
  pinMode(trig_pin,OUTPUT);
}

void loop()
{
  digitalWrite(trig_pin,LOW);
  delayMicroseconds(2);

  digitalWrite(trig_pin,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig_pin,LOW);

  duration=pulseIn(echo_pin,HIGH,30000);
  distance_CM=(speed_sound*duration)/2;

  if(distance_CM>100)
  {
    Serial.print("object is out of zone | detected at:- ");
    Serial.println(distance_CM);
  }

  distance_CM=constrain(distance_CM,0,100);

  uint8_t brightness = map(distance_CM,0,100,255,0);
  analogWrite(led_pin,brightness);

  if(distance_CM<20)
  {
    Serial.print("object is in red zone | detected at:- ");
    Serial.println(distance_CM);
    digitalWrite(buzzer_pin,HIGH);
  }
  else
  {
    digitalWrite(buzzer_pin,LOW);
  }

  if(20<distance_CM && distance_CM<100)
  {
    Serial.print("object is now inside 100cm range | detected at = ");
    Serial.println(distance_CM);
  }
  delay(1000);
}