Furnace: September 2010 Archives

Bench space reclaimed!

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Furnace monitor 

Well, that only took a little over 9 months and 25 days. Way back in December 2009 I started a project to monitor the runtime of my furnace and compare that against the outside temperature. Over the past 10 months, I have added monitoring of the air conditioner and temperature of the upstairs and downstairs of my house. Today, I finished the (essentially) final mounting of the hardware. No more prototype boards and loose wires precariously strewn across my work bench. It is all mounted, tied up and hanging on the wall out of the way.

I used a black painted particle board stand from a large picture frame as the board to mount the circuits onto. This is screwed to the little shelf made from 2x4 cut offs. The circuit boards are mounted with standoffs unceremoniously ripped from dead computer power supplies.

The blue wire is from the furnace and carries:
  • 24AC power
  • W / Y - heat and cool signals from the thermostat
  • DS1822 one-wire data from a sensor in the cold-air return upstairs, directly above the furnace.
The brown wire is from a DS1822 one-wire temperature probe in the cold air return in my shop, which is in the basement - this provides the basement temperature.

The two yellow / light green wires are DB-9 to 1/8" 3 conductor patch cables harvested from a couple of Barbie Cameras I purchased years ago from XS-cargo (I might still have a camera or two kicking around). The cameras were cheaper then serial cables from any computer store.

The top circuit board is power conversion, PC / stamp/pic interface.
Next is the BasicStamp.
A large high voltage capacitor is used to filter the raw AC before the 7805 voltage regulator.
Finally a project box containing the opto-isolators and wire busses to connect the external lines.

For those interested in details, I have the following files available for download:
  • cron_list.txt
     - List of crontab jobs to keep this all running
  • MAY19201.BAS
     - BasicStamp code that monitors the thermostat (effectively the furnace / AC)
  • furnace.txt
     - script which pokes the stamp and records the status that is returned. A large number of batch scripts then process this raw data into pretty graphs.
  • gettemp.txt
     - Script to scrape Environment Canada's Winnipeg current conditions page
  • getonewiretemp.txt
     - Script to interface with the one-wire controller from P. Anderson which reads one-wire temperature probes I picked up from the Gray-E TGIMBOEJ.
So, all this results in a daily update to these graphs which record the temperature outside, inside upstairs, inside downstairs, kWh used to heat and kWh used to cool my house. The past 7 days looks like this:

Moving off the breadboard....

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My tweeting furnace project took a step forward these past few weeks. I took this mess (24VAC to 5VDC power supply and Serial port adapter):

5VDC prototype power supply

And soldered it up to look like this:

Finished 5VDC from 24VAC

I have since added a RS-232 to TTL conversion circuit and plan to wire in a One-Wire management circuit.

DIY Dehumidifier / RV battery maintainer

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What does a dehumidifier and an RV deep cycle battery have in common? Not much. Except that I'm using the periodic nature of the dehumidistat to cycle a trickle charger. Last year I posted a description of a real cheap dehumidifier that is available to everyone! Well, certainly cheaper then a 'proper' dehumidifier.

The only real problem with my setup was lack of humidity control. Air conditioners work on temperature, not humidity. This meant I either had to turn to max and let it run 24 hours a day / 7 days a week until I was parched, or guess what temperature setting might get close to the proper humidity level.

Well, last week I realized that there must be dehumidistats on the market - controls that turn a circuit on when the humidity is too high. Ideally these would be line voltage capable (and not some 24v control voltage rating) and so I went to the local hardware store. It took some searching - McDiarmid Lumber, Canadian Tire and even HomeDepot did not have DEhumidistats (some had 24v humidistats, but that would be too much work). Rona had them and for only $20! and they are rated for 10A / 120V - perfect for the A/C unit. I wired it into an extension cord so I could also power a 12VDC adapter for the bilge / fountain pump. The setup works like a charm with the unit nicely maintaining 50%.

So, what about the battery? Summer is over and I have a deep cycle battery from my camper I need to store. Trouble is, the charge needs to be maintained over the next 5 months without over charging. I could buy an expensive charge maintainer, or - and I love this part - since the 12VDC adapter isn't quite strong enough to run the bilge pump, I could have it charge the RV battery and use the battery to run the pump. The pump is on a float switch, so it only runs for about a minute every few days, while the charger will trickle charge for a couple hours every day and keep the battery healthy!

How sweet is that!

Anyway - here's my new setup:

Dehumidistat Charger