Asi som nasiel primarnu pricinu. http://electronics.stackexchange.com/questions/66992/pin-13-do-i-need-a-resistor "Only the very early boards had a resistor on pin 13." https://www.arduino.cc/en/uploads/Main/arduino_NG_schematic.png No a prve tutorialy boli prave pripojit LED priamo k pinu 13 a blikat... wek