A friend of mine was wondering if I could build a simple device for=20
him.  He is looking for something that senses the outside and inside air=20
temperatures.  If the outside temperature is greater than ~70 and if the=20
inside temperature is 5 degrees greater than the outside temperature it=20
would enable an exhaust fan.  (We would probably need some hysteresis on=20
the temperatures to keep the fan from oscillating ON-OFF.)

I can see how this could be done easily with a small PIC, a couple of=20
thermistors, a FET & relay and a 5v power supply.
I could also do it with a few comparators, logic gates, FET & Relay,=20
thermistors and a power supply.

Both of these solutions seem overly complex for the problem.  Does=20
anyone have a more simplistically elegant solution?

   Thanks
-Phil-
--=20
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