#include <LiquidCrystal.h>

// LCD pins
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

// IR sensor pins
const int IR1 = 8;
const int IR2 = 9;

// Variables for time and velocity calculation
unsigned long t1 = 0;
unsigned long t2 = 0;
float velocity = 0.0;

void setup() {
  // Initialize LCD
  lcd.begin(16, 2); // Initialize LCD: 16 columns, 2 rows
  lcd.clear();      // Clear LCD screen
  lcd.setCursor(0, 0); // Set cursor to first column of first row
  lcd.print("Vehicle Speed"); // Print initial message on LCD

  // Initialize IR sensor pins
  pinMode(IR1, INPUT);
  pinMode(IR2, INPUT);

  // Initialize Serial communication for debugging
  Serial.begin(9600);
}

void loop() {
  // Check if IR1 is triggered
  if (digitalRead(IR1) == HIGH && t1 == 0) {
    t1 = millis(); // Record time when IR1 is triggered for the first time
  }

  // Check if IR2 is triggered after IR1
  if (digitalRead(IR2) == HIGH && t1 != 0 && t2 == 0) {
    t2 = millis(); // Record time when IR2 is triggered after IR1
  }

  // Calculate velocity if both t1 and t2 are recorded
  if (t1 != 0 && t2 != 0) {
    unsigned long timeDifference = t2 - t1;
    float timeSeconds = timeDifference / 1000.0; // Convert milliseconds to seconds
    
    // Calculate velocity in km/hr
    velocity = (0.2 / timeSeconds) * 3.6;

    // Display velocity on LCD
    lcd.clear(); // Clear LCD screen
    lcd.setCursor(0, 0); // Set cursor to first column of first row
    lcd.print("Vehicle Speed"); // Print initial message on LCD

    lcd.setCursor(0, 1); // Set cursor to first column of second row
    lcd.print(velocity); // Print velocity
    lcd.print(" Km/hr"); // Print unit

    // Print velocity to Serial Monitor for debugging
    Serial.print("Velocity: ");
    Serial.print(velocity);
    Serial.println(" Km/hr");

    // Reset values for next calculation
    t1 = 0;
    t2 = 0;

    delay(500); // Delay for readability
  }
}