here is a tiny bit of avr code used in an interactive belt buckle based on an attiny13 avr microcontroller.
for some pictures of the belt buckle and a little bit more rambling, look at: http://wiki.acemonstertoys.org/Heart_On_Buckle
this code uses the attiny arduino core from the core13 project. you can find the core13 project here: http://sourceforge.net/projects/ard-core13/