Who doesn't need a wirelessly-controlled fermentation fridge? Figured it'd be the bee's knees for automated temperature ramps when lagering.
This logs data to and can be controlled from my Linux server (Debian). Records ambient air, ambient fridge air, and carboy temps (carboy sensor taped and insulated against outside of carboy). Serial XBee input is read by a 13KB C-based Linux daemon that parses, validates, and publishes the XBee packets to interested clients via TCP/IP. A PHP-based logger script "subscribes" to the stream, only listens for packets from the fridge, and shoves them in a MySQL database where it can be graphed through a web browser (facilitated with PHP and JPGraph).
Temperature control is based on carboy temps. Cold stage controls fridge power, hot stage controls Flex-Watt heat tape. Built-in time protection for shortcycle delays.
I used an RGB LCD display so it turns blue when cooling, red when heating, green when temp is within setpoint, and a weird purplish color when off.
In this graph, the setpoint (orange line) was changed to 45F and control turned on. The dark blue line indicates when the fridge was being powered. Tested with a can of paint thinner ("carboy" temp is bright green line). Kept temps to +/- 1 degree. After the last power cycle, it was turned off. The light blue line is the ambient air swing of my shop heater; you can see at the end of the fridge power that the ambient air swung to 50F - had to open the shop door to vent engine fumes. Door was closed and the ambient swung back up, then gradually declined. Hard to see in the compressed graph, sorry.
Will be testing with a real carboy and heat tape possibly this evening. Will be interesting to see how well it controls it.
I know it's only a matter of time before someone says that I could have used a Fermtroller.
Before you do: I don't care.