#include <LiquidCrystal_I2C.h>

#define TRIG_PIN   4  // The Arduino Nano pin connected to TRIG pin of ultrasonic sensor
#define ECHO_PIN   3  // The Arduino Nano pin connected to ECHO pin of ultrasonic sensor

LiquidCrystal_I2C lcd(0x27, 16, 2); // I2C address 0x27 (from DIYables LCD), 16 column and 2 rows

float duration_us, distance_cm;

void setup() {
  lcd.init();               // Initialize the LCD I2C display
  lcd.backlight();          // open the backlight
  pinMode(TRIG_PIN, OUTPUT); // config trigger pin to output mode
  pinMode(ECHO_PIN, INPUT);  // config echo pin to input mode
}

void loop() {
  // Produce a 10-microsecond pulse to the TRIG pin.
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure the pulse duration from the ECHO pin
  duration_us = pulseIn(ECHO_PIN, HIGH);

  // calculate the distance
  distance_cm = 0.017 * duration_us;

  lcd.clear();
  lcd.setCursor(0, 0); // start to print at the first row
  lcd.print("Distance: ");
  lcd.print(distance_cm);

  delay(500);
}