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rangefinder cap
Saturday, March 5 2011
Some days ago I decided to pursue multiple approaches in making my solar controller capable of measuring the level in the household fuel oil tank. One of those approaches arrived today in the form of an SRF08 ultrasonic range finder. It looked to be more useful for measuring fuel than a similar, though Christianist-manufactured, rangefinder sold by SparkFun because it provided for several possible measurement systems (microseconds, inches, or centimeters). Also, it was capable of talking on an I2C bus. Earlier I'd thought that I2C buses could only communicate across a few inches, but subsequent research confirmed that ranges measureable in meters are possible. I needed a range of about ten feet.
The first thing I did with the new rangefinder was to solder a row of pins to its connectors and then attach it to my desktop Atmega168 (which, for software purposes, acts like an Arduino. I accidentally hooked it up backwards the first time but, somewhat surprisingly, it survived. I found I was able to use the ranger across about 12 feet of CAT-3 wire, although this arrangement was very sensitive to noise and communications would crap if I simply put my foot down on the insulated jacket of the CAT-3 cable. I was able to improved the quality of the I2C connection by pairing all of the signals in the wire with a ground. This probably wasn't the best approach from an electrical engineering standpoint in that it probably increased cable capacitance, which is the chief enemy of I2C connections, but I wasn't going to argue with success.
Next I began assembling a two inch PVC cap into which the range finder could sit, pointing downward, at the top of the oil tank. I'd already established that I had an extra cap hole on the tank that I could use for this purpose and I'd bought a bunch of reducing adapters to neck down the two inch hole to the 9/16 inch size of the rangefinder's piezoelectric transducer. But when I had all these adapters stacked up into a pyramid, the rangefinder proved useless. Evidently the sides of the pyramid were too close to the soundbeam, causing premature echoes. So I built a second cap using a two inch fitting into which I mounted a wooden board for holding the rangefinder near its center. This seemed to work okay, so I sealed all the gaps with plumbers glue. I also sealed away the rangefinder board itself beneath a layer of epoxy, making it so the only thing protruding were the four pins of the I2C interface. For this project I've been extra-vigilante with testing every aspect of the system before employing it, and the tank cap range finder was no different. I made a mock up of the fuel tank using a five gallon bucket and a piece of cardboard to confirm that range values changed predictable as fluid was added. (It could have easily been the case that echoes in the tank proved too chaotic for ranges to be measured.)
Getting my new range-finder cap to screw into the top of the tank proved difficult because the threads in the hole had been mangled. I tried fixing the threads with the tip of a screw driver, but they were too solid to alter. I have an NPT tap set, but it doesn't include a two inch tap, which is massive and costs $50 minimum (at Amazon). Somehow, though, I was eventually able to get the new cap screwed somewhat into the hole. I don't know if the seal between the cap and the tank is leak proof, but that's not going to be an issue until the tank is refilled.
There's a small bore hole through the concrete wall separating the garage from the boiler room (which is a partial story lower) and the boiler fuel line and a wire for the long-abandoned security system pass through it. As I was trying to fish the I2C wire through this same hole, there was great barking of dogs and then, unannounced, Mark showed up. Ray was off at work and he'd grown bored with the women folk and their endless card games.
So I put Mark to work helping me fish the cable through the wall. We had a few false starts but eventually we did it and it was Miller Time, which we celebrated with Wolaver's IPAs. Mark isn't much of fancy beer kind of guy, but that was all I had. Meanwhile Gretchen had driven down to the City to hang out with Mary P., who had flown in from Seattle.
Mark's visit hadn't been on my social calendar, but the monthly art opening down at KMOCA had been. Mark and carpooled down there together. Since Michæl at KMOCA always brings interesting IPAs to the openings and shares them with me, I'd thought ahead and bought my own IPAs, which was perfect because this was the first time in recent memory when he hadn't brought any.
Openings at KMOCA are always a good time even when (as this time) the art isn't anything special. One of the artists featured today had produced little models of cows with crosses protruding from their backs and scattered them on astroturf around churchlike structures that would normally have been crowned with those crosses. There were also some photographs where plastic animals were depicted in scenes alongside the animals they represented. I spent most of my time talking to Paul, the guy who owns his own church in the Rondout and drives a bus to places where news recently happened in order to follow up in depth.
During the opening we'd added Nancy, Mark's wife Lynne, his five year old daughter Vivienne, and some unknown adult woman to our contingent. All of us, with the addition of Deborah, reconvened over at New World Home Cooking some 25 minutes away (it's close enough to Saugerties to make it sort of convenient for Deborah) so we could be served by Ray during tonight's big Mardi-Gras-themed event. (Ray hasn't been working long, having only just recovered enough from heart surgery to spend his entire evenings on his feet.)
I ordered a Hurricane Kitty and the special vegan gumbo, which looked really good. Somehow, though, it ended up costing $23, which is not what a vegan pot dish should ever cost. By this point I was kind of drunk from all the IPAs I'd been drinking, and I said a few sexually demented (though comic) things at the table that others found shocking, mostly because there was a five year old with us. But the thing about Vivienne is that she's completely nonverbal in such situations and it's easy to forget that she's a bright kid likely to repeat the crazy shit I say on the playground when playing hopscotch or Wii (or whatever) with peers. Vivienne's involvement with our table consisted mostly of dragging us sequentially out to the dance floor, where a competent multiracial roots-rock band cranked out such classics as "We Got to Get Out of This Place." Vivienne also test drove everybody's eyeglasses on forays through the restaurant; I thought she look particularly stylish in mine, which made me feel good about the way I probably look in them. It's interesting that eyeglasses are the sort of thing that can fit almost equally-well on a five year old and forty three year old head.
For linking purposes this article's URL is:
http://asecular.com/blog.php?110305 feedback
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