How to use PC parallel port as a power supply for any device (similar to charging Mobile Phones). Actually I have to powrer my circuit based on parallel port. Which pin of parallel port can supply at least 5 volts without cause any change(sending signals) to the pc.
The PC parallel port is not designed to power external equipment.
While it xcan be used for his the power levels obtainable are low.
Better, if available, is USB.
Even a serial port MAY have greater power capability.
I provide several pages as, when you are trying to do something non standard, seeing what various people say can help.
Below is a typical pinout table.
Any one of the output pins may supply some current.
If you take all outputs, connect a 1N4148 diode from each facing "outwards" (Anode to port, cathode to output) , connect all Cathodes and add a capacitor o ground (say 10 uF) you will get some voltage. How much and at what level is to be determined.
This page reports that Linksys, who should know better [tm] have drawn power from some pins for some of their equipmenty. eg
"Another area that might be of interest in your document would be some comment on the parallel port extenders. I have a xmit/rcv pair from LinkSys that I bought from Fry's Electronics for about $70. They convert the parallel signal to a serial data stream, using the signal and control lines for power. My set was working fine until I added a hardware dongle for an expensive Windows application. Then, printing ceased to work reliably. I took the transmitter apart and partially traced the schematic.
They have used 7 diodes to suck power from pins 13, 14, 15, 17, 1, 2, and 3.
Also, they connected pins 15 (ERR) to 16 (INIT). The strobe line is coupled in to a flip-flop, which starts clocking the parallel loaded data."
How much current do you need?
The parallel port only has logic outputs. You might get 50 mA out of it, by setting pins high and connecting them together. You probably won't get 5V. I'd forget about it.
The parallel pinout specifications that I've found in brief Google-fu indicate that the port does not have a constant high logic-level pin, and certainly not one for VCC (supply voltage). You can do some more research into the Wikipedia version of the IEEE spec here: http://en.wikipedia.org/wiki/IEEE_1284 and then the pinout for a connector here: http://en.wikipedia.org/wiki/Parallel_port. I don't see anything that looks promising for you, but I'll submit that I have no practical evidence that you can't do it. Perhaps use the USB port for juice?