Tuesday, August 24, 2010

DZ 3.6.3 Release Is Out

Changes since 3.6.2

  • Fixed the Cold Start bug;
  • Improved XBee device handling upon late arrivals.

Dilbert Creator Weighs In

Scott Adams wrote an article called How I (Almost) Saved the Earth.

If you care to read and see through the usual Dilbert language, there are quite a few good advices on what and how to do (and not to do).

(Image: Wall Street Journal)

Monday, August 23, 2010

Correction: HVAC Controller Setup

"HVAC Controllers" section of the Configuration Guide was missing a slide - thanks to KF for pointing that out.


Wednesday, August 18, 2010

SO Override HOWTO

Since I started eating my own dog food (but more about that later), I've met with the same problem many of other DZ users already have: the fact that system is not quite that accessible. Easy to control, yes, but not accessible. You can't just push a button passing by the thermostat in the hallway.

And the worst situation you may find yourself in is when you're asleep or away, and someone in the house wants things warmer or colder. Oh no, you don't want that (yeah, and that tooth had to be removed anyway).

But there is a solution.


Granted, totally ugly, but totally dependable.

How It Works

When you connect the relay board, you connect it not directly to HVAC cable or the unit itself, but as a piggyback to an existing thermostat. Let's consider RTH7500 (above) as an example.

Determine Wiring Scheme

Find the manual for your thermostat (here's a link to RTH7500 manual). Find the diagram for your specific installation (mine is on page 10, "Connect wires: Heat Pump").

Thus, you now know what wires to connect. For the example above I needed red, orange, yellow and green.
Careful! your HVAC installer may have used different colors, you have to look at the markings, not at the wire color!
Get yourself a piece of thermostat cable, or just find appropriate wires.

Connect the relay board

Red wire is the common wire, connect it to all "common" contacts. Connect other wires as appropriate.


There are two common thermostat connection schemes - (white and yellow) vs. (yellow or white and orange) or (yellow or white and blue). Orange and blue wires are mode selectors - you need to know which exactly is the scheme your thermostat uses. For example, RTH7500 uses yellow plus orange ("energize to cool") and I connected it to NC contacts, since most of the year the thermostat is in cooling mode. Your mileage may vary.

Congratulations, you're done

So how does all this help you? Simple.

First of all, you set the thermostat much higher (assuming cooling mode) than it is necessary (if you take a look at the big picture, you'll see that the thermostat is set to 90°F) and set it to permanent hold. Then when you're not around and there is a desperate need to change settings, all that needs to be done is
  • Press the "Use Schedule" button (or the equivalent);
  • (optional) Disconnect the power to the relay board.
Added benefit is that whenever anyone is compelled to do so, the home climate will return to abominable state it was before, and the temptation will disappear for a long time.

PS: I am working on a more permanent solution, right now.

Monday, August 16, 2010

DZ 3.6.2 Release Is Out

Changes since 3.6.1

This is a maintenance release.
  • Many objects' reflections in JMX are now less cryptic and more usable;
  • XBeeDeviceFactory now properly reflects in JMX;
  • XBee deices not present at startup will now be discovered as they arrive;
  • XBee sensors departing will be discovered within a specified timeout and corrective action will be taken.

Monday, August 9, 2010

Honeywell RTH7500: Long Term Verdict

Surprisingly, the most annoying feature of this thermostat turned out to be lack of programmable hysteresis, a.k.a. deadband.

This particular one, installed in this particular location, allows runtimes as short as three bleeping minutes - whereas the time required to get into more or less efficient operating mode is no less than about five minutes for furnaces and about fifteen minutes for an A/C or a heatpump.

Likewise, there is no minimum run time protection (sometimes called short cycling protection).

In other words, this thermostat will make your unit work much less efficiently than it is designed to, and the only way to prevent that is to put the thermostat in a place where the temperature changes very, very slowly - like a closet or a thermally insulated box. Which is not quite that practical.

So, thumbs down, no go.

Likewise, if I ever have to select a thermostat again, I will pay particular attention to presence of programmable hysteresis and minimum run time.

Friday, August 6, 2010

DZ 3.6.1 Release Is Out

Changes since 3.6

New Features

Thursday, August 5, 2010

Early Access: XBee Analog Sensors

Subversion contains the driver for XBee ZB based temperature, humidity, pressure and any other imaginable kinds of analog sensors. Scaling is also supported, so different hardware sensors can be used.

Read the article on making the wireless sensor for more details on sensor design. Configuration guide is coming soon (there are caveats, hint: take a look at ConvertingSensor).