Controlling servos with an arduino
From what I have read, the signal line should only draw a few milliamps at most. However, as Arduino can safely sink or source up to 40mA on it's pins, if you want to limit the draw to say half that just use say a 270 ohm resistor in series with the signal pin to provide a current limit. On a 5V line no more than 18mA should be able to flow in or out per pin.