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Topic: How to build a non-corrosive soil moisture sensor? (Read 3 times) previous topic - next topic

marshalladam

Ive found a lot on how to build a moisture sensor, but not much on people using commercially available options such as http://www.dfrobot.com/index.php?route=product/product&product_id=599#.UhflOL-N_H0 that boasts a gold plating that protects it from the normal corrosion of a DC moisture sensor. I was wondering if anyone has had reliable, long term use of one of these, or if an AC set up might be more suitable. Thank you.

LarryD

Would you give more information on what your application is?
The way you have it in your schematic isn't the same as how you have it wired up!

jack wp

I have tried soil moisture sensors before, but not for an extended period of time (in my garden). You seem to be saying that a DC current will cause corrosion over a time, and effect the reading? But AC will not? Reversing the polarity reduceses the corrosion?

If that's the case, could we use two output pins to provide ground, and +5v to the voltage divider. Set them in the forward direction for 1/100 of a second, take our reading from the center tap. Switch the two outputs to provide a reverse voltage for a calculated time, then wait for 100 seconds, and do it again ? Now the probe is not seeing DC, it is seeing AC.  Just a thought.

Good luck, Jack

PeterH

I use a pair of stainless steel cooking skewers driven into the soil about 10mm apart. My measuring technique leaves the two probes unpowered except when I'm actively taking a reading, and powers them briefly to take the reading, them powers them with the reverse polarity for the same duration - the goal of the reverse polarity wasn't to do with corrosion but to stop electrolysis from moving ions around in the soil which I thought might affect the accuracy long-term.
I only provide help via the forum - please do not contact me for private consultancy.

jack wp

Interesting Peter.
How long have you been using that?
I really want to test the moisture down deeper than the top inch. I think maybe 6 inches down. Can I put on some heat shrink for the top 5 inches you recon? What do you think?
Good luck, Jack

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