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Im trying to design an embedded system that detects when a plant needs more water (mostly the kind of plants you have in at home in a pot) What kind of sensors would you recommend?

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    \$\begingroup\$ You could put the plant on a scale. Whenever part of the water is used up, the pot should be lighter indicating more water needs to be added. The scale could be rigged to an Arduino, and when it reads below a certain, pre-programmed plant weight, a bell rings. \$\endgroup\$
    – Josh
    Jun 20, 2013 at 19:28
  • \$\begingroup\$ There are plenty of off-the-shelf commercial sensors available, so you could start with one of those and modify for your needs. There's an indiegogo project called Wimoto Motes that's working on a bluetooth sensor that you can access from any bluetooth device (they will have models for plants, security, and temperature) \$\endgroup\$
    – Johnny
    Jun 20, 2013 at 19:32
  • \$\begingroup\$ You could use an off the shelf sensor: there are a bunch of these on eBay \$\endgroup\$
    – mikeY
    Jun 20, 2013 at 19:36
  • \$\begingroup\$ Thx, I don't plan on buying electronics from china..especilly unknown sources but i like how they show the electronic schematic (Also nice to see they're using a TI chip) \$\endgroup\$
    – Iancovici
    Jun 21, 2013 at 1:57
  • \$\begingroup\$ @echad You should buy or build what you are comfortable with. I have purchased Chinese made things like this without any problems. I don't know anything about that particular eBay seller or that particular product. I can say that there are a number of similar products available at different prices, that you might be surprised at the quality for price that is available (I was), and that I wouldn't dismiss the source so quickly. Best of luck with your project. \$\endgroup\$
    – mikeY
    Jun 21, 2013 at 5:29

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If you use two probes, made of different material, and they're in the moist environment, you'll have a battery. You can measure this tension to know how dry /wet the soil is.

That's how those soil moisture work, without batteries. You can attach it to any eletronic device (like automatic watering, or something like that).

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  • \$\begingroup\$ Bottom line I need a soil moisture sensor right? If i use this soil moisture sensor and a dsPIC, should i use analog signal conditioning by an external circuit or can i just implement it in the software? \$\endgroup\$
    – Iancovici
    Jun 21, 2013 at 2:02
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    \$\begingroup\$ that sensor has an analog outpur, and since PIC can deal with it, I would go to a software-only approach. Why bother with more circuits? :) \$\endgroup\$ Jun 21, 2013 at 13:46
  • \$\begingroup\$ Haha thanks, that's what I'd like to hear. Last thing is safety, do you know if can i attach these sensors to 6 different plants and wire them directly to the pic? Last thing we want is for electricity and water to interact when watering the plants \$\endgroup\$
    – Iancovici
    Jun 21, 2013 at 13:52
  • \$\begingroup\$ For that voltage and current, don't worry. It's too low to cause problems, even if you're with your hand inside the soil. \$\endgroup\$ Jun 21, 2013 at 14:34
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I would recommend taking 2 nails and driving them into the dirt relatively close to each other, then solder a wire to each nail and these wires each become the end of a variable resistor that changes resistance depending on how dry or moist the soil is. Using this variable resistance you can wire up a voltage divider with a known voltage, and another known resistance. You can then read from the voltage divider into a microcontroller and sense how dry or moist the dirt is.

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  • \$\begingroup\$ Quite the clever idea \$\endgroup\$ Jun 20, 2013 at 19:47
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    \$\begingroup\$ Have you tested it? Won't nails erode because of current and humidity and change their resistance? \$\endgroup\$
    – Voitcus
    Jun 20, 2013 at 21:21
  • \$\begingroup\$ Im sure they will some eventually, but with something that changes as slowly as soil moisture you only have to sample once or twice a day, and only long enough to get a reading. Without there being a constant current, for the year I have been using this setup I have seen no erosion. Also I believe with using DC and not AC you should never get erosion. \$\endgroup\$ Jun 20, 2013 at 21:29

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