One thing to watch out for is the hysteresis in these devices. The device
I pointed out will turn the fan on at 30 degrees, but it won't go off
again until the temperature drops to 20. If your room is warmer than that
it will never turn off!


Gareth.



Could build something. I recall seeing some temperature controller circuits
that used a diode as the sensing element. Should be easy to adjust the
hysteresis by selecting component values.