I'm trying to come up with a simple, cheap thermostat control for cycling on a computer fan to keep my wine cooler at around 20*C. I could buy a house thermostat, but they are $15-$25 and big and bulky. I could use an arduino, a transistor, and some kind of temperature sensor, and write thermostat code, but that would be $20 in parts, just for a simple application.
I know you can buy snap switch thermostats like they use in thermoelectric coolers, but I have never seen one set to 20C; they are always for high temperatures...and I haven't found one under $10 anyway.
There must be a cheap, simple way to implement thermostat control. Maybe a diode temperature sensor and a comparator? I happen to have a PT100 I'm willing to use.