This is just to hold some pics for now ... more deets later!
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This is just to hold some pics for now ... more deets later!
And a great study of capacitive depth measurements is here: http://www.umbc.edu/cuere/BaltimoreWTB/pdf/TM_2009_003.pdf
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Hey Don -- How well does the depth feature work? @stevie and I were just talking about it, and are needing a reminder. :)
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Hi @gretchengehrke :)
I'd never really testing it very thoroughly, and I haven't done sufficient background research to know if the 555 approach I was using would be particularly robust in the field. Could be a fun project for folks to look into with us -- if it works well enough for a someone's particular use case, it'd be a pretty inexpensive way of getting water depth ...
Don have you described somewhere how in the world this thing measures water depth? I need this and I discovered today that my spring house up in the woods is within range of the home wi-fi signal.
This sounds like it might prompt a PVOS research trip up to Bernie Country ...
I need to write up a research note, but here's the basic idea (courtesy of a hacking session with Dan Beavers and Scott Eustis a while back): we're exploiting the fact that a capacitor placed in a dielectric will have an enhanced capacitance. We can make a capacitor out of a long extension cord, or another two-wire cable; the measured capacitance in the extension cord increases as more of it is placed in water (a dielectric). So, if we can measure the capacitance, we might be able to correlate it with water depth. Here's what I'd tried, in more detail:
Do you have power in that spring house?
Why does this work when the two wires (the extension cord) are insulated? It must be that the electric field extends outside the wires into the water. Electricity is weird.
There is no power at the spring house. There is a constant flow of water like a little waterfall, so we could fix up a turbine generator.
It might not be an important project because I already get data on the water level at the house -- when it gets low enough nothing comes out of the faucet.
Exactly. Was confusing for me, too, as I'd been nursing a rather fixed mental picture of a parallel plate capacitor with a dielectric slab sandwiched in-between the plates. But for long, parallel wires, I guess there is fringing of the field lines into the water.
The trick here is whether the measurements are repeatable and stable; the link I referenced in my initial comment on the note is a study of capacitive depth sensors, and tries to assess how conductivity biofilms affect the measurements.
That said, if you want to measure "is the water level above X feet or not", I would think you could fairly reliably measure that with this system by placing the end of the wire at the threshold of interest -- the difference between water being present, or not, should be fairly dramatic.
That said, in such a "binary" case you could just use two wires directly, perhaps -- no special circuitry needed.
Regarding power, I suspect that this won't do the trick (insufficient pressure?), but it looks pretty neat anyway -- a little hydro-generator, with internal battery.
(Aside: if you could: please refrain from voicing the "... but if I needed to check that environmental parameter, I could just walk over and look at the ..." critique in a public forum? You'll blow my entire gig.)
That hydro generator says it needs 3 liters per minute, which we have.
Sorry about revealing your irrelevance. Also, we wouldn't need the internet if you would visit more often. Only 20 more days of winter for SNOWFEST to happen (assuming the snow part is non-essential).
Oh, exciting ... it'd be fun to demonstrate anything powered by moving water. Maybe this thingy should be ordered immediately.
A visit ASAP sounds very much in order.
For $25 that hydro generator has got to be a good thing. It is an impartial solution for my spring house because it can't freeze (operating range 4° to 80° C).
The thingy has a 700 mAh battery, and it charges that battery, so it does not have to be running all the time to supply power. So it can be inserted into plumbing where the water flows intermittently and power a microcontroller continuously. The only plumbing I have where I also have heat in the winter is in the house where I also have power and therefore don't need to generate my own.
It might be fun to experiment with a long hose in a mountain stream to see how far upstream (how far uphill) you have to put the inlet for the pressure to be sufficient to run the generator. Or we could ask an engineer who understands the Bernoulli and Darcy–Weisbach equations. I'm guessing you would need a couple hundred feet of garden hose and 20 feet of head to run the generator (that's a steep stream). Solar power will probably be more widely applicable, but if someone wants to power Riffles in a shady mountain stream, this might be a solution.
Or you could just walk over to the stream and see if it looks okay.
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