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Originally Posted by Joe Johnson
It depends on how much power you are trying to pull. I think you can get away with small power needs but power hogs are another matter.
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I just did a bit of digging. The parallel port doesn't seem to have a power pin. You will have to steal power from an I/O pin. The spec on the port is 12mAmps at 2.5V. This is not a lot to work with. You may get more on a particular implementation, but you can't count on it.
This Book gives a great example of how to steal power from the parallel port (I recommend the book too by the way, but it is sort of a specialty product).
They recommend a MAX756 step up DC-DC converter. For what it is worth.
To me it seems like a lot of bother. I would just steal power from a nearby USB port which has a nice juicy 5V pipe ready to supply your current hungry needs!
Finally, have you thought about data rates? How fast are you trying to do things (or how fast is the signal you need to service?) ? This matters because Windows can be more or less counted on to insert random 60-100msec delays at times when you need them least.
Think about it before you get too far down this path.
Joe J.