Soil Water Sensor Method & Chemistry

[spec]

Hy all,

As usual, a recent question on ETO got me wondering; this time about soil water content sensors: https://www.electro-tech-online.com...n-submersion-suggestions.148195/#post-1265284. While there are tons of cheap sensors to interface to an Arduino for example, nearly all corrode rapidly if left in the soil. This is the OPs problem.

There is a corrosion resistant sensor which uses capacitance rather than resistance: https://www.dfrobot.com/index.php?ro...385&search=soil&description=true#.V0anYL5V0uM But I suspect even this will fail in the end.

There are many professional soil sensors, some even using radio transmitters and solar cells for the power, but these are relatively expensive.

I had the idea of using bright stainless steel (not original) or gold (not original and expensive) or carbon rods as the sensors and encasing the joints to the connecting wires in epoxy or similar, so that the whole sensor assembly could be buried in the soil and left.

Of course, it is not as simple as that because of the electrochemistry. Has anyone got any information about this?

spec

 

[granddad]

A length of string ..... seriously... string ( hemp ) is shorter when dry,, longer if moist , connect one end to strain gauge... fix other ( say inside a porous tube ) and bury .

Remember the little couple in a weather house ... wet or dry ? can't remember who comes out in the wet ...

 

[spec]

A length of string ..... seriously... string ( hemp ) is shorter when dry,, longer if moist , connect one end to strain gauge... fix other ( say inside a porous tube ) and bury .

Remember the little couple in a weather house ... wet or dry ? can't remember who comes out in the wet ...

Hmm Interesting approach granddad.

spec

 

[alec_t]

The capacitive sensor method should be usable with electrodes totally covered in impervious material, e.g. plastic, glass, or multiple paint layers.

 

[SPDCHK]

I used this design by Audioguru "Soil moisture reader"
I used two 10" nails, placed them 1" apart, and put the ends (wire side) in some resin epoxy (thinking that the nails would not last long).
But! to my surprise, my sensor has now been up and running for I think 4-5 years already?
I placed the probes in a flower pot filled just with dirt. The pot is placed on top of an outside wall. I use this sensor to determine when to switch on my irrigation system. Till this day it has served me well for the purpose I intended it to perform.

 

[MikeMl]

This seems to be the standard for grape growers (wine makers). Ignore the price, but read the description. There are some instructions to DIY Gypsum-encased sensors on the web. These sensors have have been researched by university students and results published as a Thesis...

Because nothing changes very fast in the soil, you could sample DC-excited sensors so infrequently (duty cycle like 0.0001) that electrolysis could be minimal...