oh i thought that NPN with 0.5A collector current will be ok because we r using only 0.2A. so i gusse the bigger the margin the better.
- and yes, by the link i posted (http://arduino.cc/en/Main/Standalone) the r using an 7805 regulator for power supply.
CrossRoads Thank you very much, you helped me a lot and i learned a lot ! thanks for the patience