Originally Posted By: tfabris
With it powered by the Pololu like that, can I still safely hook up a USB cable to the computer simultaneously?

I don't think so -- the two PSUs (Pololu and the computer) will fight each other and Bad Things(tm) will happen!

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I think that long-term, if the Arduino Mega board is going to be my 3.3v source, then I need a 7v power supply instead of a 5v power supply.

Just use 5V through the USB connector. It is simpler for probably everyone, since most cars have more 5V sources than 12V sources these days, and those that don't can be updated with a simple plug-in dual 5V thingie.

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Would another option be to get a small linear regulator that takes 5v in from the existing pololu and puts out 3.3v

You already have this. It is on the Arduino board. smile