Thursday, July 12, 2007

Measuring Soil Moisture

One of the linchpins of our early prototype will be soil moisture sensing. We're still figure out how exactly we're going to do this although we are making progress. A big problem with almost all of the soil moisture sensors available is that they are industrial grade. They're big, waterproof, require all sorts of elaborate accessories, and are very expensive. I found a company that creates kits for educational settings, but it comes with one expensive soil moisture sensor and proprietary software that won't work for our application. A couple weeks ago we were just about to purchase some pricey sensors only to discover at the last minute that it required an additional expensive piece of equipment that would not provide a real time data feed without he addition of yet another piece of equipment. So we had to start from the drawing board again.

The only significant body of hobbyists dabbling with moisture sensors seem to be weather geeks who are specifically interested in "leaf wetness sensors" to measure dew. It does seem, however, that much of the hardware and software appropriate for that is also appropriate for soil moisture sensors.

Marcel has volunteered to make the sensors himself based partially on a schematic that Bryant found. It turns out to be pretty easy to make a soil moisture sensor with a bit of electrical engineering know-how and a few dollars. We already have a data acquisition and control device from LabJack. Of course the hard part is getting everything to work together! Now we just have to decided if we're going to go with the homemade set up or with the Watermark sensor. Probably the decision will be made tomorrow. We also have to decide whether to use the moisture meter from
Hobby Boards. We weren't sure if the Hobby Board moisture meter set would work for us, but I found this paper Intelligent Plant Monitoring System online today by Ya-Shian Li. Ya-Shin may have used the moisture meter in conjunction with a home made sensor. Might be some useful clues here how to set up our system and how to write the API at least. As the soil moisture sensing is a means to an end for us, I'm hoping that we will get this part of the system up and running ASAP.

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