Happy Farming . com How to Grow Your Own Food
  • Soil Moisture Sensor Circuit Explained

    May 3 2009

    Update 2011-09-05: I have created a new blog about electronics only – check it out here: Electronic measurements, NSLU2 and soil moisture sensor

    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 the humidity sensor circuit 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.

Shops / Blog Sponsors


Amazon Products