resistors: 5V USB = 9V battery?

hi,

I've built some small prototypes powered by usb so far. I've two questions:

I) As they are stand alone-objects, I'm going to power the board by a 9v-battery (connecting to 9v + gnd pin).

Do I need to change the resistors ore does the arduino board "calculate inside" everything on a 5V base? (does the board "turn down" the voltage to 5V if the power comes from the 9V-pin). [sorry for my bad explanation]

II) Do I need to change the Jumper to "external", even if the power doesn't come from the dc power jack, (but from the 9v-pin as I connect the battery to the pin)?

Thanks a lot for your help, bluma*

Yes, to use a 9V battery, you need to switch the jumper to "external", and connect + to the 9V terminal, - to the GND terminal. The board has a built-in voltage regulator that converts down to exactly 5V, so long as the input is above 6.5V or so. In fact, I hate buying expensive 9V batteries, so I power mine using 6 AA rechargeable Ni-MH batteries.

great thanks for your help and the tip :) bluma*