#include <Wire.h> 
#include <LiquidCrystal_I2C.h> // muss installiert werden

// I2C Adresse meist 0x27 oder 0x3F
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Verbindung:
// GND -> GND
// VCC -> 5V
// SDA -> A4
// SCL -> A5

// Button	Pin 7
// Button	GND
const int buttonPin = 7;   // Button input pin

void setup() {

  pinMode(buttonPin, INPUT_PULLUP); // internal pull-up resistor

  lcd.init();        // initialize I2C display
  lcd.backlight();   // turn on backlight

  lcd.setCursor(0,0);
  lcd.print("Reaction Timer!");
  delay(2000);
  lcd.clear();
}

void loop() {

  lcd.setCursor(0,0);
  lcd.print("Get Ready...");

  delay(random(3000,6000));   // random wait 3-6 s

  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("NOW!");

  long startTime = millis();

  while (digitalRead(buttonPin) == HIGH) {
    // wait for button press
  }

  long reactionTime = millis() - startTime;

  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("Reaction time:");
  
  lcd.setCursor(0,1);
  lcd.print(reactionTime);
  lcd.print(" ms");

  delay(2000);
  lcd.clear();
}