#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2); 

// defines pins numbers
const int trigPin = 11;
const int echoPin = 12;

// defines variables
long duration;
double distanceCm;
double distanceM;

void setup() {
  lcd.init();
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
  pinMode(echoPin, INPUT); // Sets the echoPin as an Input
}

void loop() {
  // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(5);

  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(20);
  
  // Clears the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(5);
  

  // Reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);

  // Calculating the distance
 
      
  distanceCm = duration * 0.034 / 2;




  //correction
  if (distanceCm > 9) {
    if (distanceCm < 16) {
      distanceCm = distanceCm - 1;
    }
  }


  distanceM = round(distanceCm);
  distanceM = distanceM / 100;
  delay (10);
  lcd.backlight();
  lcd.setCursor(0,0); 
  lcd.print("D = "); 
  lcd.print(distanceM); 
  lcd.print(" m          ");
  lcd.setCursor(0,1); 
  
  if (distanceM > 2) {lcd.print("N/A          ");}
  
  if (distanceM < 2) {
    lcd.print("PE: ");
  if (distanceM > 0.8 && distanceM < 2) {lcd.print("+/- 5cm        ");}
  if (distanceM < 0.8 && distanceM > 0.2) {lcd.print("+/- 2cm      ");}
  if (distanceM < 0.2) {lcd.print("+/- 1cm       ");}
  }
  
  delay(500);
 
}