#include <Wire.h>
#include <LiquidCrystal_I2C.h>
const int echopin = 2;
const int trigpin = 3;
const int led = 9;
long duration;
int distance;
LiquidCrystal_I2C lcd(0x27,16,2);

void setup(){
  pinMode(trigpin, OUTPUT);
  pinMode(echopin, INPUT);
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  digitalWrite(led, HIGH);
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Copyright @ ");
  lcd.setCursor(0, 1);
  lcd.print("Thanh 11A(0+1)");
  delay(1200);
  digitalWrite(led, LOW);
}

void loop(){
  digitalWrite(trigpin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigpin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigpin, LOW);
  duration = pulseIn(echopin, HIGH);  
  distance = duration * 0.0340 / 2; 
  lcd.setCursor(0,0);
  Serial.println(distance);
  lcd.print("Distance: ");
  lcd.print(distance);
  lcd.print(" cm");
  if (distance<=50){
    digitalWrite(led, HIGH);
  } else {
    digitalWrite(led, LOW);
  }
  delay(500);
}