I'm sure this has been asked and answered before but for some reason searching didn't find it.
I made a shield at one point that worked well enough that I wanted to make a dedicated board of the thing with a permanent Arduino-loaded 328. But it's only a "serial device to USB hardware driver"--ie it'll only be connected to a FTDI cable for programming and USB port for use, so power will always come from the USB +5v line. Am I safe to just wire the 5V lines together and drop the voltage regulator entirely? (I would think so, since one would hope the USB 5V out was pretty regulated, but I wanted a warm fuzzy before trying it).
Am I safe to just wire the 5V lines together and drop the voltage regulator entirely?
Yes, as long as your total +5vdc current demand is 500ma or less. The Uno board uses a thermofuse to keep that limit enforced, but your simple design may not, which could risk damage to your PC's USB port if you try and draw more then that much current or you cause a short circuit by mistake sometime.
Thanks; that's what I was hoping and had figured. Thermofuse, eh? Probably not necessary given that the only things I'll be attaching are an old serial device or an FTDI friend, but I'll keep it in mind just in case (and look one up; probably good practice in case I ever sell this as a kit).