Hello!! 
Just a quick question! I'm using an Arduino along with one servo (HS-635HB) and I need to use an external power supply for my project. Can I simply split the supply so that 6v goes straight to the servo with servo's ground and signal connected to Arduino while the Arduino is also connected to the 6v supply? The servo isn't actually moving any weight but if it was.................? Thanks Goatboy
Should work...you don't just want to try it? 
I simply split the supply so that 6v goes straight to the servo with servo's ground and signal connected to Arduino while the Arduino is also connected to the 6v supply?
Well, 6V is a little low for the Arduino's regulator, and if it gets pulled any lower when the servo is operating, you may run into problems.
Cool! Then if I operate from 9volts is there a simple circuit to that I can add to keep the servo operating under 6volts?
Actually the MC33269 regulator has a dropout voltage of 1V so 6V in should be enough to get 5V out.
Thanks RuggedCircuits!
Actually the MC33269 regulator has a dropout voltage of 1V so 6V in should be enough to get 5V out.
What about the series reverse polarity protection diode between the regulator input and the external power input? Wouldn't this then require at least 6.7vdc for external input voltage to insure that there is at least 6 vdc to the regulator input pin? If so then 6.7 vdc might be a little to high to wire to a servo's power pin unless it also included a series diode.
Lefty
In that case what are my best options considering I want to use the same external power supply for both the Arduino and a servo? :)Thanks, Goatboy
Yes, but I was counting on not needing exactly 5V throughout the board. The ATmega328 should be OK at 4.3V and 16 MHz, and the FT232 is fine at that voltage.