proudova pojistka interfacing 3V and 5V logic
http://www.gizmology.net/LEDs.htm https://www.google.com/search?q=proudove+zrcadlo&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:cs-CZ:unofficial&client=iceweasel-a
http://www.forward.com.au/uCLedDriver/build_basic_uC_led_driver.html