LED Throwie casing with auto-on

thingiverse

"Electronic graffiti", it's simply a magnet, LED, and small button battery. You toss them is on some metal surface and they turn on, and last for a few days: https://www.youtube.com/watch?v=AX7jA4NJV8s&feature=youtu.be Instructions I made about a hundred of these for burning man one year. BESt made with PLA. Simply requires: led (just about any will do, though as a general rule red ones will last the longest) CR2032 Button cell battery 8mmx1mm rare earth magnet (http://www.ebay.com/itm/like/400674419094?lpid=82) Just thread the led leads through the holes like you see in the picture. The key to the "auto on" feature is to have a little hook at the bottom where the lead comes into contact with the magnet. When it sticks to a surgace, the lead is forced into contact and the led turns on (can be finiky though). When I bought in bulk (2 years ago), i think i got the unit price down to ~ 50 cents