A while back I discusssed how my freezer uses power; it's relatively efficient except for one item, the defroster <link>. A freezer's defroster is a combination of a timer, a heater, and a thermostat to monitor the temperature of the evaporator. What bothered me was the timing of the defrost cycle. Every 11 hours or so, it would defrost, and this meant that the heater would be on during peak usage period. Since I pay a lot for peak usage it would be nice to have better control of the timing of the defrost cycle. So, an examination of the defrost circuitry showed a clear opportunity for an accurate timer and a simple SPDT relay as a replacement for the conventional method.
So, since I had a couple of arduinos that weren't doing anything, I got one of these: