This was my entry for the 2005 Microchip Start-Now contest. It won first place, and I got a PicKit-2 and some other miscellania. I bought all the parts to build it, but never got around to it.
The Beowulf collar is comprised of 12 to 31 PIC10F220 'node' processors, each with a bi-color red/green high-brightness LED attached, whose intensity can be controlled with software PWM.
The node processors are connected serially to each other, and managed by a PIC12F510 master processor (used for it's larger program space). At reset, the master performs a discovery of the number of attached node processors. Each node then becomes individually addressable, and be commanded to enable or disable the red and/or green LED at varying brightnesses. The master can either run 'canned' display patterns (cycling, alternating, chaser, etc), or use one or more of its ADC inputs to generate random patterns.
Devices connected to the ADC may include a microphone, MCP9700 temperature sensor, accelerometer, or photocell. The master can also adjust the brightness of the nodes either to maximize battery life or visibility.
The collar is built on a flexible PCB, and is designed to either be sewn into a canvas collar, or bonded to a stiff plastic carrier. Power is supplied by 3 1.5V AA cells (conventional, or lithium, for reduced weight).
With the Beowulf collar, the dog has both high visibility for safety or location at night, and can particpate as an active Christmas ornament during the holidays.