#include <LiquidCrystal_I2C.h>

#define TRIGGERPIN 5
#define ECHOPIN    4

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() 
{
  lcd.init();
  lcd.print("LCDisplay"); 
  lcd.setCursor(0, 1); 
  lcd.print("Test Program"); 
  delay(3000); 
  lcd.clear(); 

  pinMode(TRIGGERPIN, OUTPUT);
  pinMode(ECHOPIN, INPUT);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);

  lcd.setBacklight(255);
}

void loop() 
{
  lcd.clear();
  lcd.setCursor(1,0);
  lcd.print("Distance in cm");

  long duration, distance;
  digitalWrite(TRIGGERPIN, LOW);  
  delayMicroseconds(3); 
  digitalWrite(TRIGGERPIN, HIGH);
  delayMicroseconds(12); 
  digitalWrite(TRIGGERPIN, LOW);

  duration = pulseIn(ECHOPIN, HIGH);
  distance = (duration/2) / 29.1;

  Serial.print(distance);
  Serial.println("Cm");

  lcd.setCursor(2, 1);
  lcd.print(distance);
  
  if (distance < 20) {
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
  } else {
    digitalWrite(2, LOW);
    digitalWrite(3, HIGH);
  }
  
  delay(1000);
}