24-bit ADC recommendations for 3-wire sensor

Other Hardware Sensors
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Hi, I'm developing some installations that are trying to track micro-fluctuations in some analog sensors, specifically for detecting changes in mycelium signals, using a resistive soil moisture sensor.

I'm trying to figure out a recommended ADC for this purpose. I've been working with the ADS-1232 but no luck getting any readings from this — the documentation examples seems scant and out-of-date and more importantly, it seems designed for load cells.

Same with the HX711 with Load Cells.

There seem to be some breakouts on Adafruit that might support this with 16-bit to 18-bit resolution (might be okay), but perhaps some problems with the sample rate. Right now, I'm using 20 SPS in my installation.

Anyhow, if anyone here has some advice for me the check out, that'd be appreciated.

Thanks,
Scott

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Either of the linked ADCs is worth trying. Especially with the 18 bit sensor, you will need to take great care with shielded wiring and shielded sample enclosures, in order to reduce external noise pickup. 24 bit resolution is probably out of the question.

It will be no problem with either to sample at 20 SPS. The stated rate figures are the maximum achievable.

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thanks for the guidance here, I'll check out that one.

And will need to do more research on shielded wiring + sample enclosures. Ultimately, I'll be making my own circuit boards for these, so there's that.

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Please, provide a link to the sensor.

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The sensor I'm using at the moment is this one:

HD-38

I may end up being my own or finding something else, but you get the idea. It's a straight-up analog sensor.

I would like to find an ADC that can handle a variety of other analog sensors, with just one SIG line.

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Forget about adding external A/Ds. A 4-bit A/D is already overkill for those toy sensors.
The sensor is nothing more than two metal sticks in the ground. It will react/drift with soil nutrients and corrosion of the sticks. Basically useless to measure soil moisture.
A capacitive soil moisture sensor will do better than that resistive one.
Leo..

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I agree with @Wawa that you do not have the slightest chance of getting useful signals from those junk electrodes, and Arduino hobby ADCs.

Take a look at the techniques in this Open Access Nature paper to see how professionals approach the problem.

Reference: Electrical integrity and week-long oscillation in fungal mycelia
Yu Fukasawa, Daisuke Akai, Takayuki Takehi, Yutaka Osada, Nature, Scientific Reports 14, Article number: 15601 (2024)

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Thanks for the response.

Really my question is more about the ADC than the sensor.

** Do you have advice on the high-resolution ADC that I could try to use to work towards better results? **

I've been reading the Adamantsky study (here):
https://royalsocietypublishing.org/doi/10.1098/rsos.211926

And he uses the ADC-24, which is, unfortunately, a data-logger and can't do the live data processing in software code, which is what I aim to improve with my artwork & experiments.

ADC-24 specs here:

I do know these resistive sensors aren't the best ones to ultimately to use, for a more pure scientific approach, and I'm hoping to transition to some of the electrodes in the paper that you sent — thanks for this, haven't read this material, which looks like it's the similar sensor setup that Adamantsky used for his studies.

It takes me awhile to wade through the science papers, since I'm an artist-coder rather than a scientist, but there are the best source materials to work from.

My idea is to solidify the higher-resolution / better ADC first, and move towards a solid circuit with other sensors installation that I'm making and then tackle a better mycelium sensor.

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Thanks, any advice on the capacitive soil moisture sensor that I should be looking at? Happy to do more research here!

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Which is completely Irrelevant if the sensor and associated wiring are environmentally noisy.

Even with a 16 bit ADC, great care in shielding and grounding is required to obtain useful information in the lowest significant bits.

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