Resistive Soil Moisture Sensing

I have a question, Does any one have any experience with soil sensing with any of the moisture sensors? I am waiting to receive a few Funduino moisture sensor but there is no spec from what I see out there for any of these type of sensors. I am concerned that they will corrode in the ground after an extended period of time. I was thinking about not keeping Vcc on continuously and just applying as needed when I take an ADC sample. Also will I need to sense the temperature of the soil as well? Are these types of sensors reliable or is there another approach?

Thanks, Tom

I was thinking about not keeping Vcc on continuously and just applying as needed when I take an ADC sample.

This is a good idea, you can use a 2N222 transistor for that.

Also will I need to sense the temperature of the soil as well? Are these types of sensors reliable or is there another approach?

Like you said they corrode pretty quickly especially with mineral water full of Ions.

-Standby That's exactly the transistor I was going to try. I wish I could accelerate the testing to see if my A/D reading become skewed because of corrosion, I did see another persons post where they did a read every 600 seconds and turned on the Vcc supply around 50ms before each read then off once the read was finished.

Thanks Tom.

How are you going to supply the Arduino. Batteries? Is there any connection to ground. Laptop/PC, internet, other sensors etc. There could be significantly more than 5volt between Arduino ground and the ground where the sensor is shoved into. If so, turning off the sensor could be a useless exercise for corrosion. Still ok to save power. A common transistor like the 2N2222 could have 0.5volt across when "on". That could upset the readings. Do you really need a transistor? Arduino pins can supply 20mA. That might be enough for some Kohms of ground resistance. Maybe switch polarity of the two electrodes after every sample you take. Should be possible with two digital pins and two analogue pins. Leo..

Theres a nice write-up about soil moisture sensors at http://www.vegetronix.com/TechInfo/Soil-Moisture-Sensor-Primer.phtml and some other information at http://zerocharactersleft.blogspot.com.au/2011/11/pcb-as-capacitive-soil-moisture-sensor.html.

You will get corrosion with and without power applied. More corrosion obviously with power on.

I have had good success with stainless steel electrodes with a "go no go" application. I used a relay to connect power to the sensor to take the readings.