There are countless gadgets that serve no useful purpose, yet draw power from USB ports to do something. ( http://www.thinkgeek.com/gadgets/lights/7825/ )
These gadgets don't have any meaningful connection to or interaction with a computer they are attached to, they only use the USB port as a power source.
I have a 92mm internal PC case fan with a 3-pin fan connector, and also an adapter cable to plug the fan's 3-pin connector in to a standard molex 4-pin connector (like what you plug in to desktop hard drives or optical drives.
I *WANT* to fabricate a wire that would connect to the fan on one end, and plug into a standard USB port at the other end, to supply power to the fan.
This seems to me like it should be simple. BUT, a couple of nights ago I cut off the end of a standard USB cable, and attached the red & balck wires from the USB cable to the red & black wires on the fan. I plugged the USB end into the sole USB port on the back of a very old laptop, and of course the fan did not power up. I then tested the wires with my multimeter, and no power was on the line. In hindsight, I probably was testing the line improperly.
Surprisingly to me, I can only find one hit via Google for a cable that does what I'm talking about - http://groovygamegear.com/webstore/i...roducts_id=299
Questions:
1) Has anybody heard of GroovyGameGear.com ?
2) Does anybody know how I could make a cable like this myself?
3) How could I test the cable for the presence of power? I should be able to draw the 5v from the USB jack. I believe it's 500milliamps, but I'm not sure.
My multimeter has two separate pair of jacks to connect the probes, and did not come with any substantive instructions, so I've always sort of muddled through figuring things out as I go, and I really have no idea when/why/how to use one of the pairs of probe jacks. The pair of jacks I ordinarily use to test voltage are labelled with a + & -, with a lightning bolt between the two. Of the other two jacks, one is labelled 10A, and states 'Unfused' below it. The other is labelled AΩ. Between the two is the warning '10A MAX'.
The multimeter has ranges for AC-V (voltage), DC-V (voltage), AC-A (assuming amps), DC-A (again, assuming amps), hFE (transistor testing I think), OHMS, and 'F'.
As stated above, I don't know how or when to use the probe inputs labelled 10A and AΩ. I also don't know what the 'F' range is for. It's values are labelled with the 'micro' symbol or a lower-case n.
Thanks for any info that may help.