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

LiquidCrystal_I2C lcd(0x27, 20, 1);  // Change the I2C address if needed

const int numSensors = 4;
const int triggerPin[numSensors] = {2, 3, 4, 5};   // Trigger pins of ultrasound sensors
const int echoPin[numSensors] = {6, 7, 8, 9};      // Echo pins of ultrasound sensors
const int stopDistance = 100;  // Distance in centimeters, below which "STOP" will be displayed

void setup() {
  lcd.init();
  lcd.backlight();
  
  for (int i = 0; i < numSensors; i++) {
    pinMode(triggerPin[i], OUTPUT);
    pinMode(echoPin[i], INPUT);
  }
  
  lcd.setCursor(0, 0);
  lcd.print("Reverse Mode");
}

void loop() {
  bool objectDetected = false;
  
  for (int i = 0; i < numSensors; i++) {
    long duration, distance;
    digitalWrite(triggerPin[i], LOW);
    delayMicroseconds(2);
    digitalWrite(triggerPin[i], HIGH);
    delayMicroseconds(10);
    digitalWrite(triggerPin[i], LOW);
    
    duration = pulseIn(echoPin[i], HIGH);
    distance = duration * 0.034 / 2;  // Calculate distance in centimeters
    
    if (distance < stopDistance) {
      objectDetected = true;
      break;  // Exit loop early if any object is detected
    }
  }
  
  lcd.setCursor(0, 1);
  if (objectDetected) {
    lcd.print("STOP");
  } else {
    lcd.print("SAFE");
  }
  
  delay(500);  // Delay for stability
}