I'm wondering about the longevity of the soil contacting elements. The usual generic soil moisture probes typically have a high failure rate, IIRC due to galvanic corrosion.
That's correct in my experience. Galvanic corrosion was never a problem for the capacitive sensors I developed a few years back (unlike the resistive sensors linked by the parent). However you typically want them more rugged than a bare PCB for industrial settings and since the capacitive field can pass through plastic I had them in a plastic housing filled with resin. Perfectly isolated from the outside environment and hard as a rock.
I can see how your prototype defends against corrosion, not so much this b-parasite toy.
What I don't see anyone talking about is the impact of dielectric moisture absorption[1], which is typically around 0.3-0.5% over 24 hours exposure for cheaper FR-4 on the market, let alone how this product intends to maintain sensor calibration over time.
I'd expect to see external corrosion impact at the solder joints first, especially around the battery terminals, but corrosion creep may happen alot sooner than that: vias in the b-parasite prototype are clearly tented[2], but that masking is superficial and won't protect against hygroscopic exposure from the inside; being open source certainly doesn't preclude hobbyists from making even worse material decisions either.
Wow, I must have been way too slow thinking about how to word this remark[1] that I completely missed your post. Thanks for the design intuition confirmation.
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This is cool. wonder if conformal coating over this would be enough to survive the outdoors
I'm wondering about the longevity of the soil contacting elements. The usual generic soil moisture probes typically have a high failure rate, IIRC due to galvanic corrosion.
https://www.digikey.com/en/products/detail/seeed-technology-...
It is my understanding that capacitive moister sensors don't have this problem.
Can anyone confirm?
That's correct in my experience. Galvanic corrosion was never a problem for the capacitive sensors I developed a few years back (unlike the resistive sensors linked by the parent). However you typically want them more rugged than a bare PCB for industrial settings and since the capacitive field can pass through plastic I had them in a plastic housing filled with resin. Perfectly isolated from the outside environment and hard as a rock.
Here's a prototype: https://imgur.com/9yO28CY
I can see how your prototype defends against corrosion, not so much this b-parasite toy.
What I don't see anyone talking about is the impact of dielectric moisture absorption[1], which is typically around 0.3-0.5% over 24 hours exposure for cheaper FR-4 on the market, let alone how this product intends to maintain sensor calibration over time.
I'd expect to see external corrosion impact at the solder joints first, especially around the battery terminals, but corrosion creep may happen alot sooner than that: vias in the b-parasite prototype are clearly tented[2], but that masking is superficial and won't protect against hygroscopic exposure from the inside; being open source certainly doesn't preclude hobbyists from making even worse material decisions either.
[1] https://www.ipc.org/sites/default/files/test_methods_docs/2....
[2] https://github.com/rbaron/b-parasite/blob/main/img/resized/i...
I think that this twitter thread describes the horror show in trying to build such a sensor. TL;DR It ain't easy.
https://twitter.com/rbaron_/status/1491467468996431873
Wow, I must have been way too slow thinking about how to word this remark[1] that I completely missed your post. Thanks for the design intuition confirmation.
[1] https://news.ycombinator.com/item?id=33284221