This is my version of the LED Throwie. The design isn't mine, this is just my mod of it. In the original design, the LED Throwie is on from the moment you put it together. This can be annoying if you're planning to make tons of these, or if you want to make them ahead of time but not have the battery run out. Someone has already posted a mod that adds an on/off tab to the throwie, however I've taken it one step further: in this design the throwie automatically turns on when it sticks to something, and turns off as soon as you remove it! It's just as simple to make as normal throwies, and doesn't require any extra materials either! These also work great as simple LED pinch lights. Credit goes to everythingdigital for the idea (it was mentioned in a comment), but the implementation is mine.
I'll point out that though this instructable may seem long or complicated at first, it's only because I wanted to make sure it was well documented. It is actually VERY easy and VERY quick to do. Making these throwies should be just as easy, and take no longer than the original design. Once you've done one and you understand how it works, you'll be whipping these out in no time.
From the original throwie:
Developed by the Graffiti Research Lab a division of the Eyebeam R&D OpenLab, LED Throwies are an inexpensive way to add color to any ferromagnetic surface in your neighborhood. A Throwie consists of a lithium battery, a 10mm diffused LED and a rare-earth magnet taped together. Throw it up high and in quantity to impress your friends and city officials.
Step 1: Parts and Materials
If you only intend to make a few of these, or just want to try them out, you can get all the parts you need at Radioshack. However if you plan to make a large quantity, you should buy all your parts in bulk online, as Radioshack would get kinda pricey for more than a few of these. You can go to the original throwie article (http://www.instructables.com/id/LED-Throwies) for info on where to buy the parts.
What You Need:
-5mm Diffused LED (the original uses 10mm, but these were cheap in an assorted pack at Radioshack, so I got them)
-CR2032 3V Button Cell
-3/8" x 1/16" Neodymium Disc Magnet
-Scotch Tape, or Strapping Tape (Strapping is better, but Scotch works fine)
-Double sided tape, or just about any glue
-Leftover cardboard from battery package/other packaging
Note: The magnets I used were 3/16" diameter (that's all Radioshack had at the time). They seem plenty strong for just sticking the throwie to things, however if you wanted to actually throw it at something, I think you'd want something a little stronger so that it would actually stick. I'd recommend 3/8" diameter by 1/16" thick, though you can try other sizes and see what works best. What is important is the magnet has to be smaller than the battery - half the size should work fine, two-thirds is too large. You'll see what I mean when you see how the design works.
As of March 2011, if you purchase all the parts at Radioshack, one throwie would cost you about $7 ($5.50 of that is the battery).
According to the original throwie article, if you purchase all your items bulk online, you can get the cost down to about a doller per throwie.