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

// Pin assignments
const int TRIG_PIN = 2;
const int ECHO_PIN = 3;

// Initialize LCD: Address 0x27, 16 columns, 2 rows
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  // Pin modes for sensor
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  
  // Initialize communication interfaces
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  
  // Print initial splash screen
  lcd.setCursor(0, 0);
  lcd.print("Distance Monitor");
  lcd.setCursor(0, 1);
  lcd.print("Initializing...");
  delay(1500);
  lcd.clear();
}

void loop() {
  // Clear trigger pin
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  
  // Send a 10-microsecond HIGH pulse to trigger the sensor
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  
  // Read the bounce-back travel time in microseconds
  long duration = pulseIn(ECHO_PIN, HIGH);
  
  // Calculate distance in centimeters
  // Speed of sound is ~343 m/s or 0.0343 cm/us. Divide by 2 for round-trip.
  int distance = duration * 0.0343 / 2;
  
  // Serial Monitor output for debugging
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // Update the visual display panel
  lcd.setCursor(0, 0);
  lcd.print("Target Status:  ");
  
  lcd.setCursor(0, 1);
  if (distance > 400 || distance <= 0) {
    lcd.print("Out of Range   ");
  } else {
    lcd.print("Dist: ");
    lcd.print(distance);
    lcd.print(" cm       "); // Extra spaces clear old characters
  }
  
  // Wait 200ms before taking the next reading to prevent echoing overlap
  delay(200);
}