Here's another i2c demo for the arduino.
This is a prototype of what will eventually become a digital sensor network, which will be comprised of i2c slaves which digitize sensors, i2c slaves which display data on gauges, and an i2c "orchestrator" which links the two together.
This milestone in development represents a two-member i2c network -- an orchestrator which generates a test pattern, and a gauge which displays it.
The orchestrator generates a sawtooth with a period of 2 seconds, and transmits i2c data 10 times per second. The slave receives the data and outputs it as PWM to a gauge. Both members toggle the pin 13 LED each time they send or receive an i2c "packet".
here's a descriptive video on youtube: http://www.youtube.com/watch?v=kKYJDkni5U4
here are the sketches:
here's the hex (for atmega168):