even when the sun is invisible
Sunday, December 11 2005
I put a lot of effort today into cleaning up my solar sufficiency controller, which is finally working well enough for its first deployment actually controlling the pump that moves water from the panel down to the basement. Through the past weeks the circuitry has grown increasingly nuanced and complicated, able to handle such problems as the 60Hz hum picked up by the long wires connecting the basement to the solar deck (a hum that had tended to make switching erratic as the switchover threshold slowly arrived). Another task that has been occupying a lot of my time had been the making of a system allowing the digital thermometers to display temperatures being read by the same thermistors that are used to determine heat sufficiency. (The easiest solution would be to just buy a couple more digital oven thermometers, since they're only $16 each, but for debugging reasons I wanted to be able to see the actual temperatures being read by the control circuitry.) The problem with reading each thermistor with two different devices was that the readings would be wildly inaccurate for both readers if they both tried to do their reading at the same time. So I made an elaborate switching system using a momentary panel switch and dual 4PDT relays to electrically separate the thermistors' leads from the sufficiency circuitry whenever I wanted to take a visual reading of their temperatures on the digital displays. Of course, by doing so the sufficiency circuitry, suddenly reading a sharp increase in resistance across its thermistor leads, would then decide that night had fallen and turn off the pumps if they happened to be running. So I made the relays disable the reset lines to the flip flops whenever I was taking a digital reading, allowing the sufficiency states to stay frozen through the reading for both the hot water and slab "sufficiency zones."
It turned out that those thermistors are more complicated than I'd thought; instead of being simple heat-sensitive resistors, they actually have polarity and give completely different resistances when positive and negative power to them are reversed. This caused a maddening inaccuracy for me late in the afternoon today, but I eventually did the experiments necessary to discover the polarity effect. Another reading coming down the long wires from the solar panel seemed like a gross inaccuracy, that the panel had reached 82 degrees Fahrenheit despite overcast and air temperatures in the low 30s. So I climbed up to the panel and used my bare hand to grab the outgoing hydronic pipe. Sure enough, that bastard was warm! Evidently the panel can collect heat even when the sun is invisible behind the clouds.
This is the latest version of the solar sufficiency circuitry and you can click it to enlarge.
Note the addition of LEDs, which helped enormously with debugging the circuitry's behavior.
Most problems with noisy thermistor lines were solved by hysteresis-inducing resistors (R14, R15, R16, and R17) and the two capacitors C1 and C2, which ensure that signal changes happen slowly, over the course of a second instead of, say, a millisecond. I haven't included the relays and digital thermometers or the modifications necessary to accommodate them. Their effect on this circuitry is to isolate both thermistors and to simultaneously disconnect the RESET lines to both flip flops, thereby preserving their states while the thermistors are read by the digital readouts. Interestingly, due to the delay-inducing effects of C1 and C2, the thermistors are usually read as a very low temperature the moment I release the digital readout button, and this causes the sufficiency circuitry to momentarily order an insufficiency state. But it recovers quickly enough that the pump is never interrupted and the electrically-controlled valves never fall completely shut. (This only happens immediately after I conclude a deliberate reading - an infrequent event in a typical day.)
This evening Gretchen and I watched a DVD of a film called
What the Bleep Do We Know?, a strangely big-budget hybrid between a conventional movie, an animated kid's comedy, and a science/philosophy documentary. Much of its content wouldn't have been out of place in an episode of NOVA or something you might have been shown in high school when the teacher felt like kicking back, turning out the lights, and showing a film (I assume they still do this, but they're probably DVDs or MPEGs these days). That's why events seemed a little out of place when, about three quarters of the way into the film, its MPAA rating went from G to R in the space of about five minutes. I'm not complaining; jolting dynamics of any sort are always interesting for me, no matter the media.
The first part of What the Bleep Do We Know? was mostly about the strange world of particle physics, where nothing is more substantial than thin clouds of possibilities and disembodied information, interacting with each other through forces that produce all the illusions that we call the material world. I was following along up until a point, but then things started breaking down as the uncertainties and unpredictabilities of the microscopic quantum universe were gradually confused with the very predictable, very material world of the macroscopic. Then things suddenly took an unexpected turn for the fluffy pseudoscientific, with interviews of people who claimed that a gaggle of people meditating in Washington DC had managed to lower its crime rate by 25% and that blessings made over water have a predictable effect on the sorts of images you get when you photograph it using a scanning electron microscope.
It's hard for me to like a film after it sets off my bullshit detector so profoundly, but then the subject turned to religion and the nature of God and the talking heads snapped back to making sense again. The most interesting point they made about religion was that the absolute rules and the strong distinction between Creator and Creation reflect an anachronistic mindset. Here we are with our computers, iPods, jet planes, and assflossing thongs, but most of us are still following a religion that hasn't been fundamentally altered for three or four thousand years, one originally designed to coerce civil behavior out of ignorant people in hopes that they could be made to get along well enough to raise crops and families in the close proximity characteristic of early settlements.
Intersliced between documentary-style monologues by various quantum physicists, organic chemists, philosophers, and theologians, we follow a day in the life of a deaf woman. That day culminates at a raucous Polish wedding where she's the official photographer but nonetheless falls prey to the pleasure mechanisms of her body's unique chemistry. At this point we're treated to entirely too much computer-generated animation, as plump CGI cells and chemicals whirl among bridesmaids, gluttons, and guys on the make as they all succumb to their basic drives.
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