If you’re looking for a low cost thermostat for keeping bees warm or maybe even for an incubator, here’s a simple hardware only based solution that might work for you.
I just built and tested the following thermostat to control a heater in a bumble bee hive. It looks like it works pretty good. Why heat a BB house you’re probably asking… I’m doing that so I can observe the BBs in a hive without having to fill the BB hive with any hair/cotton/fluff to keep them warm. This will allow me to easily observe them thru a plexiglass cover.
I tested this thermostat in a BB hive in the basement. The basement is pretty much a constant 65F. I set this thermostat circuit to about 85F and stuck a commercial thermometer in there to see how good the system maintained temp. I didn’t sit there and watch the thing all day, but it looked like as the hive lost a tad bit of heat, the thermostat would kick on at 84.6F. Due to the large thermal mass of my heaters, the heat doesn’t start pouring out instantly so what I saw happening was the BB hive would keep dropping in temp until it hit 84.1F. At that point the heat from the heaters would build up enough to start pushing the hive temps back up. When the temps pushed back thru 84.6F, the thermostat would turn off the heater. However due to heat stored into the cement heater, the hive temp would keep rising and overshoot to 85.5F before the cycle would repeat over and over. So with my setup the best I can control is about +/- 1F. That is certainly good enough for some bumble bees or keeping nucs warm.
My guess is if I reduced the thermal mass of my bee heater I could get a tighter control system using this hardware only approach. For tighter control, a micro controller would likely work best. With a micro you could drive the heater with a PWM signal and tune the heat output from the heater to exactly match the heat loss from hive.
To see photos of this hardware based thermostat, see my photobucket album here:http://s1082.photobucket.com/albums/j365/MichiganBee/Thermostat/