Hi Phil,

My experience has shown that hysteresis is not necessary, but minimum on
and off times are absolutely required.

Cheerful regards,

Bob


On Sun, Jul 14, 2013, at 07:52 AM, Phil Keller wrote:
> 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.)
>=20
> 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.
>=20
> Both of these solutions seem overly complex for the problem.  Does=20
> anyone have a more simplistically elegant solution?
>=20
>    Thanks
> -Phil-
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