I've used the below information to built an external cooler for my "precious" laptop which constantly heats up badly. I bought a table-digital-clock-fan for three quid a while ago (It was on sale in BBQ). It runs on three AA size battery, which sums up to about 4.5 volts.
I know for a fact that USB have an output power of five volts. And with the table-fan I have, I can actually run it on my USB. Why do I want to run it on USB? I'm not very keen on batteries to be honest. They die out, and they are expensive to maintain. Connecting it to my USB means that I'll not have to pay for my AA batteries. Also, I get to turn on the fan anytime I want.
I have seen one of these USB fans (picture to the right) in some shops. Cool they are, the idea is actually very simple. Just plug in the right wires into the fan, and it'll run. USB cable outputs five volts DC. Which means, my fan will run. All I need, is a spare USB cable, and a fan. Of course you'll need some wires and a knife.
Now, how do I know which wires or which pin on the USB is what? A little search on the internet with appropriate keywords, I found what I needed (see information below). Certainly, there are more electronic hacks already done on exploiting USB. This particular information below is actually a charger for his own mobile phone. There's another one that exploits the USB for charging it's ninetendo game
Google is wonderful today.
But not tomorrow.
for the female usb connector, look down into the end of the connector so that it is oriented like so:
pin 1 is the positive (5v) terminal (which goes to the output of the 7805) and pin 4 is ground (which goes to the 7805 ground pin).
easiest way to test
several people were wondering how to tell if you are going to fry your device. here’s the easiest way to test when you are all done wiring:
- cut a standard usb cable in half.
- plug the male end into your usb battery.
- connect the positive and negative ends of your multimeter to the red and black usb wires respectively.
- if it reads something very close to 5v then you are wired correctly.
Reference: how-to: 'usb battery' v2 - hack a day - www.hackaday.com