daveh@solbourne.com (Dave Helms) (05/11/91)
Hello, I have an underground irrigation system in my yard and as a result cannot tell how wet different parts of the yard are. My question is does anybody know how I can buid some sort of moisture sensors to insert at different locations in my yard ? My neatest idea would be to have these moisture sensors placed a few inches under the ground and transmit into my house via telemetry. Wow, then I could hook this up to my mac and have a graphic representation of the moisture content in the yard. But I am problably being silly. Thanks for any responses. Dave
vbreault@rinhp825.gmr.com (Val Breault) (05/11/91)
In article <1991May10.173139.1371@solbourne.com>, daveh@solbourne.com (Dave Helms) writes: |> Hello, |> I have an underground irrigation system in my yard and |> as a result cannot tell how wet different parts of the yard are. My |> question is does anybody know how I can buid some sort of moisture |> sensors to insert at different locations in my yard ? My neatest idea |> would be to have these moisture sensors placed a few inches under the |> ground and transmit into my house via telemetry. Wow, then I could hook this |> up to my mac and have a graphic representation of the moisture content |> in the yard. But I am problably being silly. Thanks for any responses. |> Dave Not really silly, but you're complicating it a bit. If all you want is a relative idea of how much water is in one area or another, you can try this: Bury a grid of wires below the surface by slitting the sod and placing the wires in the slits. Use insulated wires, but strip the insulation off the wires where they overlap. Do not allow the bare wires to touch each other, but seperate them with an insulator of a known size. By measuring the resistance where any pair overlap, you can get an idea of how much moisture is in the ground at that point. More resistance = less water. Less resistance = greater water. You can use your computer, if you wish. You'll need a switching array, analog to digital converter, and voltage source. You'll have to handle things like electrical noise, switching times, and other things that plague high speed A/D conversion. I suppose an easier solution would be to wire up the grid to a rotary switch with an appropriate number of positions (example would use 9) and use whatever VOM you have handy. It wouldn't have the swell graphical display, and may take the better part of a minute to read and interpret the data, but it's do-able in one Saturday morning, leaving the afternoon free for loafing. | | | | | | -----+-----+-----+- | | | -----+-----+-----+- | | | -----+-----+-----+- | | | Simple problems should have simple solutions. ------------------------------------------- Val Breault - vbreault@gmr.com The opinions expressed by the author do not necessarily reflect the position of the General Motors Research Laboratories or the General Motors Corporation.
wllarso@sandia.UUCP (Bill Larson ) (05/15/91)
In article <1991May10.173139.1371@solbourne.com>, daveh@solbourne.com (Dave Helms) writes: |> does anybody know how I can buid some sort of moisture |> sensors to insert at different locations in my yard ? If you were to look back in Sunset Magazine three or four months, there was an article about soil moisture sensors and controller systems. The sensors they referred to were all commercial items, but from their description they are VERY simple. Using the resistance between two conductors with a water (solution) dielectric is quite common in chemistry. The problem is that this technique can be very difficult due to the possibility of various contaminants in the solution. If you were to bury wires directly in the soil and measure the resistance between them, the conductance would be provided by ions from salt, fertilizer, various organic acids, etc. I would suspect that this would make any attempt at a calibrated reading almost impossible. What the commercial sensors do is to in-case the conductors in gypsum, better known as Plaster of Paris. This way the sensors will absorb water until they are in equilibrium with the moisture in the soil and the conductors will have a much more controlled environment, just calcium and sulfate ions to provide the conductance. The normal technique in chemistry to measure resistance/conductance is by using an AC Wheatstone bridge to avoid polarization effects in the solution. With all of you brilliant EEs out there, do you have any cheap solutions to make a simple AC resistance/conductance measuring technique? Something that would use a six volt transformer to supply the current and/or voltage, and one or two op-amps to convert the conductance/resistance to a proportional output voltage.
fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) (05/17/91)
>In article <1991May10.173139.1371@solbourne.com>, daveh@solbourne.com (Dave >Helms) writes: > > does anybody know how I can buid some sort of moisture > sensors to insert at different locations in my yard ? > Greetings. I _know_ I saw an article on just such a project in BYTE. In fact, it was titled something like, "Build your own greenhouse controller" - or something like that. It had the theory, the facts, and the advice - what more can you want? :-) I don't have it with me but I can look it up. Take care. P.S. The original article expired and I couldn't "r"eply... -- _______________________________________________________________________________ "The Force will be with you, always." It _is_ with me and has been for 11 years Filip Gieszczykiewicz "... a Jedi does it with a mind trick... " ;-) FMGST@PITTVMS or fmgst@unix.cis.pitt.edu "My ideas. ALL MINE!!"