// hd44780 library see https://github.com/duinoWitchery/hd44780
// thehd44780 library is available through the IDE library manager
#include <Wire.h>
#include <hd44780.h>                       // main hd44780 header
#include <hd44780ioClass/hd44780_I2Cexp.h> // i2c expander i/o class header

// if there should be an additional I2C-devices on the I2C-Bus 
// which has a lower I2C-adress it might happen that this other devices I2C-adress 
// will be chosen as the I2C-adress of the LCD
// if this happends add the I2C-adress to the constructor of the HD44780
// example instead of writing hd44780_I2Cexp lcd;
// add the I2C-adress hd44780_I2Cexp (0x27);
hd44780_I2Cexp lcd; // declare lcd object: auto locate & auto config expander chip

// LCD geometry
const int LCD_COLS = 16;
const int LCD_ROWS = 2;

void setup() {
   lcd.begin(LCD_COLS, LCD_ROWS);
   lcd.clear();
   lcd.print("Hello World");
   lcd.setCursor(0, 1);
   lcd.print("Millis ");
}

void loop() {
   updateLCD();
}

void updateLCD() {
   static unsigned long lcdTimer = 0;

   if ( TimePeriodIsOver(lcdTimer,500) ) { // check if more than 500 milliseconds have passed by
      // if 500 milliseconds HAVE passed by
      lcd.setCursor(8, 1);
      lcd.print("       "); // overwrite old data
      lcd.setCursor(8, 1);  // reset the cursor
      lcd.print(millis());
   }
}


// easy to use helper-function for non-blocking timing
boolean TimePeriodIsOver (unsigned long & startOfPeriod, unsigned long TimePeriod) {
  unsigned long currentMillis  = millis();
  if ( currentMillis - startOfPeriod >= TimePeriod ) {
    // more time than TimePeriod has elapsed since last time if-condition was true
    startOfPeriod = currentMillis; // a new period starts right here so set new starttime
    return true;
  }
  else return false;            // actual TimePeriod is NOT yet over
}