#include <LiquidCrystal.h>

#define PIN_TRIG 4
#define PIN_ECHO 3
#define RED_LED 13
#define BUZZ 10
#define LEVEL_1 32 
#define LEVEL_2 22 
long duration, cm;
LiquidCrystal lcd(12,11,9,8,7,6);

void setup() {
  Serial.begin(9600);
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT);
  pinMode(RED_LED, OUTPUT);
  pinMode(BUZZ, OUTPUT);

  lcd.begin(16,2);
  lcd.print("Duration:");
}

void loop() {
  digitalWrite(PIN_TRIG, LOW);
  delayMicroseconds(5);
  digitalWrite(PIN_TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG, LOW);
  duration = pulseIn(PIN_ECHO, HIGH);
  cm = (duration / 2) / 29.1;
  
  lcd.setCursor(0, 1);
  lcd.print(cm);
  lcd.print(" cm    ");
  
  if (cm <= LEVEL_2) {
    lcd.setCursor(0, 0);
    lcd.print("Warning! Object");
    
    digitalWrite(RED_LED, HIGH);
    tone(BUZZ, 1000); 

  } 
  
  else if (cm <= LEVEL_1) {
        lcd.setCursor(0, 0);
    lcd.print("Duration:       ");
    
    digitalWrite(RED_LED, LOW);
    
    int frequency = map(cm, LEVEL_2, LEVEL_1, 2000, 500);
    tone(BUZZ, frequency, 100); 
    delay(200 - (cm - LEVEL_2) * 5); 
  } 
  
  else {
    lcd.setCursor(0, 0);
    lcd.print("Duration:       ");
    
    digitalWrite(RED_LED, LOW);
    noTone(BUZZ);
  }

  delay(250);
}