Haven't seen the answer anywhere else, so I hope I'm not posting an oft repeated stupid question.
I want to build a binary clock into a PC drive bay. I also want it powered via USB.
I intend to use this parts kit. http://www.oomlout.co.uk/component-bundle-for-arduino-compatible-arcb-p-227.html
and some strip board.
I will be using the circuit from the playground shift out example, with 4 LEDs for hours and 6 for minutes, running from two shift registers. Perhaps 3 if I get carried away,and add seconds. And acouple of buttons to set the time. http://www.arduino.cc/en/Tutorial/ShiftOut
Everything works fine when my Duemilanove is powered from USB.
I want the Arduino and clock powered on all the time, which the USB connections can handle as I want. I think... And I have a few spare internal sockets on my motherboard. Problem.
USB provides 5 volts. But after going through a 7805, it will be way too low to power anything. I tried just now with the same regulator, and only got 2.something with no load.
Would it be safe to bypass the regulator, and power the Arduino and all directly from the 5 volt USB connection,with a capacitor to smooth out any bumps? And would the USB supply be smooth enough for the job? Especially during boot?
Or would this be a really really stupid idea that may damage my PC and my Arduino?
Any advice would be greatly appreciated.