software engineers shouldn’t use soldiering irons…

After a brief hiatus of 15 years, I picked up a new soldiering iron and I am actually building hardware again. I’m slowly rebuilding my lab from scratch.  The new house is going to come in handy because I actually want space for a workbench and some decent magnifying glasses, and the usual crap.

As a reflexive problem, I figured out my first new project, because I need a lab, because of the new house, oh whatever…

I’m going to try my hand at building a wireless internet thermostat for the SF house.
As it turns out, good thermostats are more complicated than one would expect.  We want hysteresis in the system so it isn’t firing and shutting down the heating/cooling units, plus, with multi-stage equipment (small and large furnace burners and small and large air conditioning) we want to intelligently maximize the use of the small (eco-friendly) stage, but kick on the big stage when the energy differential between the desired and current temperatures is high.

I just want to be able to turn off the damn heat when I’m out of the house for a few days.. or turn it on when I’m driving up from the Peninsula so it’s not freezing when I get there.

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2 thoughts on “software engineers shouldn’t use soldiering irons…

  1. How about something like this:

    http://www.hometech.com/hts/products/automation/hvac/index.html#RO-300202

    From the description:

    This gorgeous thermostat has an extra pair of connections, and two
    temperature settings. When you short the extra contacts together,
    the thermostat uses the ‘night’ setting (which could also be an
    ‘away’ or ‘anti-freeze’ setting.) Run an extra pair of wires from
    the thermostat to something that can connect the wires via remote
    control, and you have a remotely controllable thermostat!

    There are two basic ways to hook up this thermostat: Run the two
    wires to a Universal Module. Plug in the Universal Module and you
    can send X-10 commands from any X-10 controller (including a telephone
    transponder) to operate the thermostat. This mode is quite popular
    with the ‘mountain cabin’ folks. Imagine calling your cabin from
    your cell-phone while on the way to tell it to warm up the place!
    And always being assured that, when away, the thermostat will not
    let the pipes freeze.

    1. I thought about that, but I figure if I’m going to the trouble, it would be just as much fun and the same amount of work to build my own. It’s not like thermostats are like writing a routing protocol. In fact, I was going to use a PID controller to figure out when to kick on the second stage, and then I realized it’s really quite simple. If the temp is > 5 degrees below target, or if the stage one heater has been running for more than 10 minutes, fire the stage 2 up.

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