Furnace Monitor

SSzretter

I was considering if I might be able to buy a basic stamp and use it to hook the thermostat lines so the stamp can monitor their on/off state, and send this data to a computer (via serial or otherwise), thus allowing me to analyze the furnace run time, zone run times, etc.

Does this sound reasonable, and what might I start with - which stamp, what add-ons / type of circuit?

Thanks!

steve_b

Do you have a normal forced air gas furnace?
You'll want to verify what wires your thermostat uses....

I believe the lines run 24Volts AC...not totally sure (all that info is on my other laptop that just died!

Anyhow, look up a full wave rectifier circuit to convert AC to DC. Then look at 5volt rectifiers.
The DC voltage from the rectifier circuit will be about 20volts or so. you'll need to get this down to around 5volts (logic level) to keep the stamp happy.

You can use a BS2 stamp no problem. Download the "What's A Microcontroller" text from the parallax website (free download) and follow the examples to learn how to program it.

How might you log this on the computer? Hyperterminal? You'll want to time stamp the data somehow. you can either get a timing chip or use the PC's time.

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Roger Pierson

I think I would use the thermostat control lines to drive a 24 Vac relay, which in turn switches a 5 Vdc source. Check your Stamp I/O pin for a logic high to determine if the thermostat has ordered the furnace on.

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Roger Pierson
Senior Electronics Technicain
DTI Assoicates

KatyBri

Roger,

I would agree with your idea of driving 24vac relays. I am doing a similar project, and that is what I did.

Here is the relay hardware I used-hope it helps.

RELAYS: Porter-Brumfield KHAU-17A11-24. Socket: 27E166. Hold down spring: 20C217.

See attachment for relay connection pinouts.

alec

Hi

If you use a bridge rectifier and a 5 volt regulator on the thermostat line, you could read logic 0 for "on" and 1 for "off "- the thermostat just closes a switch and there'd be no voltage drop on the line.

This would be easier than a relay because you'd have to wire the relay in parallel with the funace control relay. Fewer parts, all solid state, and no fussing with the furnace controls.

Take care

Alec

steve_b

My thoughts were to keep solid state....but saying that...an SSR would work fine too.

Ultimately I'd like to control my furnace....well, I'd like to run the fan on a time schedule as opposed to during heat/cool cycles and when I manually set it on/off.

Another project on the list of "to be started" hehe...right beside the other list of "to be finished"

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."