I threw together some pretty basic control software this weekend to try and get a feel for how fancy I would need to get with it in order to maintain a steady temp, and also to get an idea for how much longer I could go on a single round of ice. It's been going for about 19 hours now and the ice and carboy of test water have held very nicely. The test water is showing some bumps that I currently think are because I still don't have a good insulated seal around the sensor on the outside of the carboy. I think that's getting influenced by the air temp, so I need to do a better job there still. Regardless, the first attempt at a software based thermostat is pretty promising at this point.