/* Ultrasonic HC-SR04 + LCD 16x2 display */

/* Used pins  */
int echoPin = 11;
int triggerPin = 12;

long tps_echo;
float distance;

/* LCD 16x2 with I2C interface */
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2);

void setup()
{
  pinMode(triggerPin, OUTPUT);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);
  /* LCD 16x2 */
  lcd.init();
  lcd.backlight();
  lcd.clear();
}

void loop()
{
  /* measure for 10 micro seconds */
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  
  /* measure time for the echo */
  tps_echo = pulseIn(echoPin, HIGH);
  
  /* distance calculation */
  distance = tps_echo*0.034/2;

  /* display on LCD */
  if (distance > 20) //if measured distance is more than 20cm
    {
      lcd.setCursor(0,0);
      lcd.print("                "); // erase line
      lcd.setCursor(0,0);
      lcd.print("Too far away!");
      delay(300);
    } 
  else
    {
      lcd.setCursor(0,0);
      lcd.print("                "); // erase line
      lcd.setCursor(0,0);
      lcd.print("Distance:");
      lcd.print(distance,1);
      lcd.print("cm");
      delay(300);
    }
}