Build your own microcontroller tree ornaments
These are ultra geeky tree ornaments which are assembled in a clever manner.
Here's an interesting microcontroller project that's appropriate for this time of year. Using an alphanumeric LED display, an Atmel AVR chip is cleverly soldered right onto the LED with a battery holder, thus creating an easily hung programmable "ornament". Your desired message is spelled-out one character at a time via the LED display, which can be tough to descramble, but it's sure to keep your holiday guests mesmerized as they attempt to decipher your witty humor or wise quips.
I can imagine that these would be useful in other situations, such as a pin that you could wear on your clothes (to a Star Trek convention? 
). You could also create a simple one or two wire interface between the units to have a coordinated multi-LED display. Even if that's not interesting, the assembly technique for the LED tree ornament units may be useful in the future.
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