I remember I used to have a magic 8 ball key-chain as a kid. I loved asking it the stupidest questions and seeing it magically divine the answer. Either that or it just repeatedly responded with an anti-climatic ask again later. One day the magic just dried up … literally, the purple fluid in the cavity evaporated! Randomly remembering this device, I decided on the spur of the moment, after learning how to seed and use the rand() function in the standard c library, to make my very own digital magic 8 ball (which would be impervious to drying up, but still vulnerable to releasing its magic smoke).
Digital Magic 8 Ball - [Link]
As soon as I heard about the 555 timer contest, I knew I had to come up with something inspiring! My buddy Jay recently introduced me to Nixie Tubes, and I thought… hmm, how can I use a tube and the 555 timer? I noodled on it for a while, and ultimately came up with the notion of a KEYCHAIN! Simple really, take the smallest Nixie Tube that displays digits, and make it display a ’5′ in the smallest package possible and put it on a keychain. That was the idea… and it took quite a journey to complete.
A Nixie Tube Keychain – [Link]
This is a simple description (some kind of engineering reversing ) of cheap KeyChain Lasers that are sold for 5 bucks or so.The laser diode head has three pins labeled: LDC (Laser Diode Cathode), PDA (Photo Diode Anode) and COM+ (common Positive Terminal).Inside the laser diode head we find the laser diode itself and a photodiode, used to regulate the laser diode current with an external feedback loop. [via]
Keychain LASER driver circuit - [Link]