it sounds like you are going to build your own board. why not add a DC-DC chip like they use in the cigarette power adapter in cars ? you get 12v for all the external stuff and 500ma of 5vdc for the Arduino. then feed it as crossroads mentioned.
it sounds like you are going to build your own board. why not add a DC-DC chip like they use in the cigarette power adapter in cars ? you get 12v for all the external stuff and 500ma of 5vdc for the Arduino. then feed it as crossroads mentioned.