"Hedwig"-USB Powered Owl Head
This one I made for my future sister-in-law for Christmas. (She's a big Harry Potter fan.) It uses two CdS cells, Two AT Tiny 45s, two blue high-output LEDs and a single servo. The body is made from extruded PVC (Sintra/Komatex/etc.) and a PVC pipe joiner. I used an Arduino as ISP to program the AVRs. This project served as a demonstration of how sometimes it's actually easier to use microprocessors to achieve results normally associated with BEAM robotics. If you think about it, the component count is about half what you'd have for a bicore head and the number of solder joints is less than half, with the added benefit of not having to hack the servo. Also, trying to get a Schmidt Trigger cascade to function is such a crapshoot-you can go through a roll of chips and maybe have one work. Also, trying to get a 555 or a 741 to "breath" is more challenging than the available schema would predict.
Update-Pi day, 2013
I'm not just doing this for attention, I swear. There are a few other LMR members now interested in the ATTinies, so as a resource I thought I'd add some more goodies. For starters, here's the schematic:
The servo is just a regular old cheap eBay transluscent blue 9g (not even an official "Tower Pro."
I've also added the sketches. Remember this is Arduino as ISP with the HLT cores. The ATTinies are as far as I'm concerned not a great choice for servo control or small robots. If you want to work with an 8pin DIP micro, in my experience the PICAxes 08m(2)s are a better choice. The Tinies have their place, but they just don't have good enough timing (at least not through Arduino as ISP-I've never tried another AVR programmer or a crystal regulated ATTiny for example.) The servo control I acheived on Hedvig by all rights shouldn't work, and possibly was a fluke of combination of one individual chip and one individual servo just happening to be on the same "wavelength" as it were. I just found one PWM frequency that forced it all the way right, one all the way left and one that (unbelievably) centered it up.