Sorry for the slightly blurry images, my camera isn't the best for close-ups.
These chargers power the battery inside your tooth brush wirelessly. How do they do this? It's all about induction. The dock sends out an alternating magnetic pulse that is harnessed by the toothbrush and stored in the batteries. Pretty cool. Oh, the wonders that surround us daily.
What we're doing is replacing the toothbrush with a coil and LED. I wrapped the little prong (I think that's the core, but if it isn't then at least it's circular) with enameled, or magnet copper wire. I didn't count turns, but I covered the prong and wrapped it several layers deep. Because the electricity that we receive from our makeshift transformer is AC, we must convert it! Using our diode, we can block half of the AC waves and make it DC. Just connect the diode to one end of the wire with the stripe on the other side. The opposing diode lead is now positive and the other end of your coil is negative. Unfortunately we only get half of the electricity that we can pull from the coil. If you use a bridge rectifier instead of a single diode you can harness it all! If any of this is confusing, just freshen up on how AC current works and what a diode does.
Now that you have "rectified" your current, you have a steady DC voltage of 4-5V! What are you going to do with it? The possibilities are endless.
I put an LED and a resistor in series and got that to work fantastically! I haven't tried it, but you have the power of the wall socket at your disposal--you can probably run a small motor if your magnet wire is thick enough.
You've done it! A simple and (maybe) free step-down, air-core transformer that took all of five minutes to make!
I think it's pretty cool. Feedback much appreciated. This is my first Instructable--I hope to make more soon!