Temperature controlled door opener?

[Patches]

My house has an atrium that can get nice and warm for a few hours in the winter on sunny days - but is quite cold the rest of the time.

I'd like to rig something up that uses two temperature gauges, one inside the atrium and one inside the house, and when the atrium is hotter than the house the door get opened so the heat flows into the house. It doesn't have to open very far, maybe a foot or so.

Anyone know a source for such a device, or ideas on where to cobble parts from?

[Sinecure]

PM or email me. My old ski lease landlord rigged something like that except it used two thermostats to turn on/off a fan that blew heat from the downstairs to the upstairs of the house (house in Tahoe Donner so you could probably go look at his setup). He also had a cool thing that was like an answering machine except that when it answered and you punched in the correct code, it turned on the heat by switching from one thermostat to the other (not the same thermos as the ones controlling the fan unit thingy). Anyway, get in touch and I'll give you his details so you can call him.

[Jukes]

A decent greenhouse supply store should have temperature or timer activated window/roof panel openers you may be able to use on a door. As far as I know, they are a pretty common way to regulate temperature in and ventilate a greenhouse. . .

Do you have much of an electronics background? I think you could rig something up reasonably easily with a relay, two temperature sensors, a really simple microcontroller and some sort of door opening device (a motor or a solenoid, I guess). Temp sensors send temperatures to microcontroller, microcontroller does a simple subtraction to see which temperature is higher, microcontroller turns on or off output that triggers relay, which in turn controls the door opening device. You would also want a delay in the program to prevent your relay from flipping on and off too fast and burning out your motor (shouldn't need to open and close the door more than once every 5 minutes, I would think).

Maxim-ic.com has some nice temperature sensors that send their data serially to a microcontroller (you don't even have to do any analog->digital conversion) and in my experience, Maxim is really good for giving out free samples.

[Big E]

Temp sensors send temperatures to microcontroller, microcontroller does a simple subtraction to see which temperature is higher, microcontroller turns on or off output that triggers relay, which in turn controls the door opening device.

No need for a microcontroller, this is exactly what a comparator does. You only need one, so you could get that for free as a sample.

You would also want a delay in the program to prevent your relay from flipping on and off too fast and burning out your motor (shouldn't need to open and close the door more than once every 5 minutes, I would think).

That would be called hysteresis. No need for a separate device, just proper design of the comparator circuit.

[Patches]

Sinecure, PM sent.

Thanks for the info guys. The microcontroller route sounds attractive - my electronics skills are minimal but I'm good at coding, and it seems pretty straightforward if I went that route. I've not used a microcontroller before but it shouldn't be too hard.

Jukes, would this be enough to do what I want?

http://www.parallax.com/Store/Microc...5/Default.aspx

I already have a nice linear actuator I can use, so I think all I would need would be that kit, a pair of relays and temperature sensors, plus power supplies.

Fun project. I think the heat from the atrium will meet 1/4 to 1/3 of my heating needs if I can capture it.

[jondrums]

The comparator circuit that BigE mentioned would actually be a lot simpler, but you need to know about analog circuits. The microcontroller route is more intuitive for folks these days, but you'll spend more time fiddling with bugs.

biggest problem is probably going to be rigging up the linear actuator in a way that doesn't look like shit, and so that you can still use the door as a door.