#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define TRIG 19
#define ECHO 18

#define RED_LED 17
#define YELLOW_LED 16
#define GREEN_LED 4
#define BUZZER 0

LiquidCrystal_I2C lcd(0x27, 16, 2);

long duration;
float distance;

void setup() {
  Serial.begin(115200);

  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);

  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(BUZZER, OUTPUT);

  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Distance Meter");
  delay(2000);
  lcd.clear();
}

void loop() {

  // Trigger ultrasonic pulse
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  // Read echo
  duration = pulseIn(ECHO, HIGH);

  // Calculate distance
  distance = duration * 0.034 / 2;

  Serial.print("Distance: ");
  Serial.println(distance);

  // Display on LCD
  lcd.setCursor(0, 0);
  lcd.print("Distance:      ");
  lcd.setCursor(0, 1);
  lcd.print(distance);
  lcd.print(" cm");

  // LED + Buzzer logic
  if (distance < 100) {
    digitalWrite(RED_LED, HIGH);
    digitalWrite(YELLOW_LED, LOW);
    digitalWrite(GREEN_LED, LOW);
    digitalWrite(BUZZER, HIGH);
  }
  else if (distance >= 100 && distance < 200) {
    digitalWrite(RED_LED, LOW);
    digitalWrite(YELLOW_LED, HIGH);
    digitalWrite(GREEN_LED, LOW);
    digitalWrite(BUZZER, LOW);
  }
  else {
    digitalWrite(RED_LED, LOW);
    digitalWrite(YELLOW_LED, LOW);
    digitalWrite(GREEN_LED, HIGH);
    digitalWrite(BUZZER, LOW);
  }

  delay(500);
}