DIY Temperature Controlled Window Fan

[jdurand]

If you ever need to do something like that tiny and cheap, you can use two silicon diodes (1N4148) as sensors along with an 8-pin comparator chip and two resistors. You probably need a transistor to help the comparator drive a DC fan directly or a relay for an AC fan. Won't give any readout but will switch fan on/off based on which sensor is hotter.