#include <LiquidCrystal.h>
#include <Ultrasonic.h>

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

const int trigPin = 8; // HC-SR04 trigger pin
const int echoPin = 9; // HC-SR04 echo pin
Ultrasonic ultrasonic(trigPin, echoPin);

float prevDistance = 0; // Declare and initialize prevDistance as a global variable

void setup() {
  lcd.begin(16, 2);
  lcd.print("Velocity (m/s):");
  Serial.begin(9600);
}

void loop() {
  float distance = ultrasonic.distanceRead();
  
  // Calculate velocity assuming constant time interval between measurements
  static unsigned long prevTime = millis();
  unsigned long currentTime = millis();
  unsigned long deltaTime = currentTime - prevTime;
  float velocity = (distance - prevDistance) / (deltaTime / 1000.0);
  prevTime = currentTime;
  prevDistance = distance;

  // Print velocity to Serial monitor for debugging
  Serial.print("Velocity: ");
  Serial.print(velocity);
  Serial.println(" m/s");

  // Display velocity on LCD
  lcd.setCursor(0, 1); // Set cursor to the second row
  lcd.print("          "); // Clear previous velocity value
  lcd.setCursor(0, 1); // Set cursor to the second row
  lcd.print(velocity, 2); // Display velocity with 2 decimal places

  delay(100); 
}