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  • Soil Moisture Sensor Circuit Explained

    May 3

    The 1-wire soil moisture sensor circuit I use in my garden is designed by Eric Vickery from http://www.hobby-boards.com.

    (c) 2006 Hobby Boards  Designed by Eric Vickery
    Title: Moisture Meter 3
    Rev: 3
    Date: 10/27/2006 06:11:30p

    (Click the picture for a larger version.)

    Here’s a bit of explanation on how it works.

    The circuit is connected like this:

    and the circuit works like this:

    1. Watermark sensor gets wet
    2. The time constant of oscillator IC 555 changes
    3. 555 IC oscillates faster and its supply current goes up
    4. Current in resistor R2 goes up causing the voltage across R2 to go up too
    5. The value of the current register of IC DS2760 changes
    6. Current register of IC DS2760 is read via 1-wire network

    In my case I got the following values during calibration. I let the Watermark sensor dry in the wind and recorded the current register value, and afterwards the sensor was soaked in a bucket of water:

    Dry = -0.2368
    Wet = -1.400

    These numbers form the 0 and 100 % limits of my soil moisture readings.

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    4 Responses to “Soil Moisture Sensor Circuit Explained”

    1. Dennis Hall said on July 13th, 2009 at 11:13 pm

      Quick question. What type of data is provided for the output? Is it serial or a square wave? Please let me know, I want to send the output to a transducer or a pizzo for a simple alarm when the saturation point is reached. Thank you for your time and consideration in reviewing my request.

      Sincerely,

      Dennis Hall
      technician1965@hotmail.com

    2. Thomas W. said on July 14th, 2009 at 1:48 pm

      @Dennis: As I see it the “output” of the circuit is a software register.
      I think what you need is an OpAmp Schmitt-trigger measuring the voltage across R2, and removing U1, R1, C3 and D1, but I’m not sure if that’s what you want?…

    3. braulio said on March 9th, 2010 at 4:51 am

      Hi, I want to do this circuit, but in dallas website, the ds2760 is no loger available, I could change the ds2760 to ds2762? thanks, best regards

    4. Thomas W. said on March 9th, 2010 at 1:29 pm

      @Braulio: I think you can use DS2762 instead as the manufacturer Maxim states, “DS2762 is an update to DS2760″.

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