Most thermostats are passive. No electronic parts inside. There's usually a two
circuit mercury bulb that will turn the heat/ac on or off. There's also an
anticipator resistor circuit that works on the current flowing through the
heat/ac relay circuit. This keeps the unit from cycling to quickly. No micro or
anything fancy unless you get one of those that have a clock and timer circuit
in them with remote controls. There is also an additional position on the
switch. The "cool/off/heat/em heat". The em meaning emergency heat that
bypasses the heat pump and kicks in the resistance heating that drains your
wallet. Check out:
http://www.howstuffworks.com/home-thermostat.htm
for a simple description.
Rick

Wagner Lipnharski wrote:

> Thinking to build a home made temperature control for the "home AC".
> Any hint where I can find some description of the wiring coming to the
> actual thermostate box?
>
> It seems to be the most common type of controls, COOL-OFF-HEAT  AUTO-FAN-ON
> and the temperature lever that changes the thermostate mercury switches.
> Coming 9 wires from the cable, 8 used.  There is a name "TRANE" printed on
> front panel.
>
> I guess we may have power in some wire that can be regulated to feed some
> uC.
> Small relays and temp sensors could be a good job in saving energy during
> the non-necessary time of the day, including remote programming via phone
> DTMF (on/off, set temp, etc).
>
> I also noticed that there is a variable resistor inside, probably to set up
> the auto-fan timer.
>
> Any hint will be appreciated.
> VV46NER.
>
> --

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