Real-Time Car Speed Detection Project with Speed Alarm & LCD Display

/*
 * Project: Real-Time Car Speed Detection & Speed Alarm System
 * Author: ElectronLab STEM Curriculum
 * Target: Arduino Uno / Nano
 * Description: Calculates speed from dual IR beam break timestamps
 */

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

// Initialize 16x2 LCD with I2C address 0x27 (or 0x3F)
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Hardware Pin Definitions
const int SENSOR_ENTRY_PIN = 2; // IR Sensor 1 (Start Gate)
const int SENSOR_EXIT_PIN  = 3; // IR Sensor 2 (Stop Gate)
const int BUZZER_PIN       = 4; // Active Alert Buzzer
const int ALERT_LED_PIN    = 5; // Red Warning LED

// Physical Configuration (in meters)
const float SENSOR_DISTANCE_METERS = 0.15; // 15 cm distance between sensors
const float SPEED_LIMIT_KMH        = 30.0; // Over-speed alert threshold in km/h

// State variables
unsigned long timeEntry = 0;
unsigned long timeExit  = 0;
bool isCarDetected      = false;

void setup() {
  Serial.begin(9600);
  
  // Configure input sensor pins with internal pullups if required
  pinMode(SENSOR_ENTRY_PIN, INPUT);
  pinMode(SENSOR_EXIT_PIN, INPUT);
  
  // Configure output alarm pins
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(ALERT_LED_PIN, OUTPUT);
  digitalWrite(BUZZER_PIN, LOW);
  digitalWrite(ALERT_LED_PIN, LOW);
  
  // Initialize LCD
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("ElectronLab Radar");
  lcd.setCursor(0, 1);
  lcd.print("Ready for Cars..");
  delay(2000);
  lcd.clear();
  lcd.print("Speed Trap: Active");
}

void loop() {
  // Read digital state from optical sensors (Active LOW when beam occluded)
  int entryState = digitalRead(SENSOR_ENTRY_PIN);
  int exitState  = digitalRead(SENSOR_EXIT_PIN);

  // Step 1: Detect car entering Sensor 1
  if (entryState == LOW && !isCarDetected) {
    timeEntry = millis();
    isCarDetected = true;
    
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Car Detected...");
    lcd.setCursor(0, 1);
    lcd.print("Timing Speed...");
    
    // Wait for the car to clear the first sensor
    while (digitalRead(SENSOR_ENTRY_PIN) == LOW) {
      delay(1);
    }
  }

  // Step 2: Detect car reaching Sensor 2
  if (exitState == LOW && isCarDetected) {
    timeExit = millis();
    isCarDetected = false;
    
    // Calculate elapsed time in seconds
    unsigned long timeElapsedMillis = timeExit - timeEntry;
    
    if (timeElapsedMillis > 10) { // Reject accidental noise
      float timeSeconds = (float)timeElapsedMillis / 1000.0;
      
      // Calculate speed: Speed = Distance (m) / Time (s)
      float speedMps = SENSOR_DISTANCE_METERS / timeSeconds;
      
      // Convert Meters/Sec to Kilometers/Hour (1 m/s = 3.6 km/h)
      float speedKmh = speedMps * 3.6;

      // Print metrics to Serial Monitor
      Serial.print("Elapsed Time (ms): ");
      Serial.print(timeElapsedMillis);
      Serial.print(" | Speed: ");
      Serial.print(speedKmh, 2);
      Serial.println(" km/h");

      // Display metrics on 16x2 LCD
      lcd.clear();
      lcd.setCursor(0, 0);
      lcd.print("Speed: ");
      lcd.print(speedKmh, 1);
      lcd.print(" km/h");

      // Step 3: Trigger Speed Alarm if Limit Exceeded
      lcd.setCursor(0, 1);
      if (speedKmh > SPEED_LIMIT_KMH) {
        lcd.print("OVER LIMIT! SLOW");
        triggerSpeedAlarm();
      } else {
        lcd.print("Status: NORMAL");
        delay(3000);
      }
    }
    
    // Reset display for next vehicle
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Speed Trap: Active");
    lcd.setCursor(0, 1);
    lcd.print("Limit: ");
    lcd.print(SPEED_LIMIT_KMH, 0);
    lcd.print(" km/h");
  }
}

// Function to sound buzzer alarm and flash LED
void triggerSpeedAlarm() {
  for (int i = 0; i < 5; i++) {
    digitalWrite(BUZZER_PIN, HIGH);
    digitalWrite(ALERT_LED_PIN, HIGH);
    delay(200);
    digitalWrite(BUZZER_PIN, LOW);
    digitalWrite(ALERT_LED_PIN, LOW);
    delay(200);
  }
}