Relay Computing FTW?

So we finally got around to getting a new humidifier to replace one that had died. Three times. (Hint: If you get the chance to put in a Honeywell humidifier? Don't. They suck.) The new one is an Aprilaire 700. Very nice, digital controls, outside temperature sensor, and the works.

We put it in ourselves.

Now, this doesn't seem like a big deal on the face of it. We had to cut the duct work a bit, and putting up the outdoor temp sensor was a joy, but by and large these are straightforward processes.

Wiring the thing into the furnace? That's where it got interesting. Our furnace is probably a decade and a half old. Unlike modern furnaces, where you open them and find yourself face to face with a printed circuit board (which, in fairness, I'd have been a lot more leery of working with), our contains relays and interrupt switches, and that's pretty much it. Working through the schematic has been interesting. Heaven forbid the HVAC industry should use electronics industry schematic symbols or anything. Once I figured out that those two vertical lines are contactor (relay) contacts and not a capacitor, the thing made more sense.

Once I sorted out which circuit did what, it dawned on me that I was looking on a string of and gates, effectively. If the white wire is at 24v, turn on the ventilator motor. If the flue pressure is correct (ventilator motor is running, flue is not blocked), turn on the ignitor and the gas. If the flame sensor indicates there's flame, turn the ignitor off. If the rollout sensor is off (that is, flame and/or gas are NOT coming out the back of the burners into the body of the furnace - yikes) keep the gas on. If the manifold temperature is above temperature x and the manifold temperature is below temperature y, turn on the blower. OR if the green wire is on, turn on the blower by itself, and bypass all the furnace start sequence logic. OR if the yellow wire is on, throw the relay to turn on the AC compressor. (note that these two ORs are not exclusive, and in fact the thermostat turns on both lines for AC.) It's all pretty straightforward. Theoretically.

Practically, I got the motor relay line plugged in the wrong place (on the yellow wire's terminal instead of the green) and it has been giving me bizarre results since yesterday for anything except heat. Now that that's straightened out, I just have to find out from Aprilaire how exactly I keep the humidifier from coming on when the call for heat comes down, humidifying the return plenum, switching itself off, then switching itself back on when the humidity in the plenum drops down, then switching off three or four times while the furnace goes through its startup sequence for heating. I don't even know if it's bad that it does this.

But it did amuse me once I realized that the furnace /does/ have a computer of sorts in it, and one of the more ancient types imaginable, at that. Flagging this post steampunk, since telegraphic relays most certainly did exist in the era, and you could do some interesting computing with them if you were so inclined.

-JRS

Some thoughts about Steampunk

As I dig more and more into Brass and Steel: Inferno (or whatever it finally winds up being called,) I'm forced to try to really understand the Steampunk esthetic in a way I can articulate it. While by no means does the esthetic define the movement, it does give an insight into what steampunk is and how steampunkers (steampunks?) think.

75 years ago, the hot trend was to streamline everything. Hide all the fussy mechanical bits under a smooth, sleek exterior. Sure, it made those machines (e.g. steam locomotives) a monstrous pain in the rear to service, but they certainly looked cool, at least to the esthetic of the day.

Radio underwent this transformation as well, from the Atwater Kent breadboards of the 20s, where they went out of their way not only to leave the guts of the radio out where you could see them, but also made those guts /pretty/. An Atwater Kent breadboard is a radio for the steampunk esthetic. these were finished radios, as you'd take home and use. By 1926, however, the tubes all went inside a wooden box or a metal can,like this and by 1929, they needed to, since your radio was now plugged into the wall and had voltage and current enough to kill you.

Fast forward to the computer revolution. If you were around at the beginning of the personal computer revolution, as friend Jeff was, your first computer might have been a Cosmac Elf, IMSAI or Altair, or perhaps an Apple I. These machines came as kits. You knew how they worked, because you put them together yourself, and you put them in a case for one specific reason: to keep dust, RF interference, and the cat out of them. Nowadays, they look like this or this.

Steampunk inverts this trend. More than that. Steampunk says this trend is a lie, and that it's used to cheat you by hiding an inferior machine inside, or worse, that the machine is up to something and you don't know what that is.. Steampunk embraces mechanical complexity that isn't afraid to show off its construction. Steampunk is about the construction. It's about the complexity. It's about being honest and showing you how things work, even if they don't do anything especially useful. To whit, this art 'bot, archived at Make Magazine. Watch the video. It's worth it. Steampunk, at its best, is about that kind of mechanical grace, where your eye can take the object apart at the same time as watching the whole thing move.

At least, that's my take on it.

It could just be about cool hats. :)

-JRS