#include <LiquidCrystal.h>

#define trig_PIN 2
#define echo_PIN 3

const int buzzer_PIN = 10;

const int rs = 4;
const int en = 5;
const int d4 = 6;
const int d5 = 7;
const int d6 = 8;
const int d7 = 9;

LiquidCrystal lcd (rs, en, d4, d5, d6, d7);

long int duration;
long int distance;

void setup() 
{
  lcd.begin(16, 2);
  pinMode(trig_PIN, OUTPUT);
  pinMode(echo_PIN, INPUT);
  pinMode(buzzer_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() 
{
  digitalWrite(trig_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(trig_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig_PIN, LOW);

  duration = pulseIn(echo_PIN, HIGH);
  distance = duration / 58;

  lcd.setCursor(0,0);
  lcd.print("Distance: ");
  lcd.print(distance);
  lcd.print(" cm   ");

  Serial.println(distance);

  if (distance > 100) {
    noTone(buzzer_PIN);
    delay(500);
  } 
  else if (distance > 20) {
    tone(buzzer_PIN, 1000);
    delay(400);
    noTone(buzzer_PIN);
    delay(400);
  } 
  else if (distance > 10) {
    tone(buzzer_PIN, 1000);
    delay(200);
    noTone(buzzer_PIN);
    delay(200);
  } 
  else if (distance > 5) {
    tone(buzzer_PIN, 1000);
    delay(80);
    noTone(buzzer_PIN);
    delay(80);
  } 
  else {
    tone(buzzer_PIN, 1000);
  }
}