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Soil Moisture Sensor Circuit Explained
May 3The 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:
- Watermark soil moisture sensor: Pin 4 and 5
- 1-wire network: Pin 1 and 2
- 12 volts power supply: Pin 1 and 3
and the circuit works like this:
- Watermark sensor gets wet
- The time constant of oscillator IC 555 changes
- 555 IC oscillates faster and its supply current goes up
- Current in resistor R2 goes up causing the voltage across R2 to go up too
- The value of the current register of IC DS2760 changes
- 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 = -1.400These numbers form the 0 and 100 % limits of my soil moisture readings.
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6 Responses to “Soil Moisture Sensor Circuit Explained”
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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 -
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?… -
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
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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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RD Pawar said on July 27th, 2010 at 11:46 am
I require to measure water content at root zone of plants. What material shall be used as a probe. whether still wires will work.
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Thomas W. said on July 27th, 2010 at 2:02 pm
@RD Pawar: Please take a look at this post: http://happyfarming.com/2008/12/23/soil-moisture-sensor/
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