Bit of a noob question.
How would I figure out which resistor to use to bring the arduino's 5V down to 2V?
Thanks in advance.
The answer depends on what you are trying to do with that 2V.
How would I figure out which resistor
sp. "resistors"
I'm Trying to make some sort of iPhone Charger, with 5V and Ground on USB as standard, and D+ and D- as 2V
Good luck!
Newer iPods and iPhones seem to make charging as difficult as possible.
Make sure you find instructions for your exact phone model, as they all seem to be different.
But yes, you need a potential divider to give the 'mode' voltage to turn charging on.
You don't want an iPod breakout connector do you? Its yours for a small fee 
Sounds Interesting?
How much we talking here?
You don't want an iPod breakout connector do you? Its yours for a small fee
Don't do it! He's not really there, he's just in your imagination! ;D
You probably want to review this information. iPod/iPhones use the USB lines to determine what charger is connected (to help determine how much current they can safely draw). It isn't necessarily as simple as a Voltage Divider.