[HN Gopher] Show HN: AnyLeaf - PH Sensor for Microcontrollers
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Show HN: AnyLeaf - PH Sensor for Microcontrollers
Author : the__alchemist
Score : 49 points
Date : 2020-09-04 17:26 UTC (5 hours ago)
(HTM) web link (www.anyleaf.org)
(TXT) w3m dump (www.anyleaf.org)
| jonbronson wrote:
| How long do these probes last before oxidization destroy them?
| the__alchemist wrote:
| Unknown - I'm testing them, but can't provide data longer than
| the time since start. They're double-junction, which helps with
| logevity by slowing contamination of the internal KCl solution.
| My intent is to have them used for continuous immersion.
|
| The latest data: Comparing two probes manufactured in the same
| batch, one immersed in a hydroponic solution, and one with
| periodic measurements. 3 months in, the immersed one has
| drifted by about 0.3 pH after the first 2 months; fixed by
| calibration. Another 0.1 in the third month. I don't have a
| good answer for long-term life, but hope an immersed one will
| last at least a year, and one used for periodic measurements
| for several. Older probes require more frequent calibration,
| have slower response, and might experience jitter.
| xupybd wrote:
| Can someone explain the calibration code. They enter calibration
| points. Wouldn't you then need to calibrate the sensor with
| solutions at those PH levels?
|
| How would you do that with the example code?
| sovreign wrote:
| Typically with ph sensors like this you also get three ph
| packets(4.01, 6.86, 9.18) which when mixed with distilled water
| get you a baseline ph for calibration.
| ComputerGuru wrote:
| Inspired by the recently gone viral "digital pregnancy test just
| reads a pregnancy test strip," I wonder if you can get around the
| calibration issue via some sort of electromechanical pH strip
| autoloader and analyzer.
| pryelluw wrote:
| This is such a nice thing to market because you can laser focus
| on niches. However, the copy on this landing page reads like a
| technical specs sheet.
|
| I suggest you take the three benefits you have below the headline
| (affordable, precise, easy to use) and rewrite the copy by
| expanding on the benefits. Also use the examples listed. Like,
| how is this a great buy for a home brewer?
| the__alchemist wrote:
| Great idea - on it.
| quickthrower2 wrote:
| Another niche: swimming pool owners. Although it's only worth
| it if I can link it to an action eg add acid but that feels a
| bit dangerous for diy project! Maybe a sms to add he acid and
| how much is good enough
| bob29 wrote:
| A peristaltic pump is cheaper than the PH probe.
| pryelluw wrote:
| It sounds like a great idea on paper, but pools arent
| something people get really into when compared to sonething
| like home brewing or aquariums.
| adanto6840 wrote:
| FWIW, I purchased it for exactly this reason. My goal is to
| end up with a URL that I can hit on my LAN that tells me the
| PH of my pool.
|
| I don't need perfect accuracy, and checking it manually isn't
| overly time-consuming. It IS tedious enough that I only check
| it about once a week though, and I'd prefer to be checking it
| more often. And bonus points for being able to automatically
| track it & easily graph it, too!
| gregsadetsky wrote:
| Some more microcontroller-friendly pH sensors here --
| https://atlas-scientific.com/ph/
|
| Their datasheets are spectacularly well designed and clear!
| https://www.atlas-scientific.com/files/pH_EZO_Datasheet.pdf
| the__alchemist wrote:
| I love the formatting, pictures, and cautions. Good visual flow
| too. I'm a bit surprised it doesn't go into the technical
| aspects of what's going on with the transfer functions, which
| op-amps/ADC are used etc.
| SpikedCola wrote:
| Maybe someone with more experience than myself can chime in. At a
| previous startup we used regular pH sensors, from Atlas
| Scientific (exactly like the ones in the article), submerged in a
| tank of nutrient water. After a few days (a week tops) they would
| drift out of spec, and would need to be taken out, re-calibrated,
| and put back into the process.
|
| Short of a system that takes samples and feeds the probe, and can
| calibrate automatically, how do you measure pH in-system long
| term? Is there a special kind of probe that stays in calibration
| for longer?
| the__alchemist wrote:
| I don't think there's a way around periodic calibration if you
| want precise measurements. At least not with normal glass
| electrodes. If the precision requirements are loose, you could
| go months between calibration. If you're trying to get within
| 0.1pH, every few weeks or so. For anything that's going in a
| scientific paper, calibration before every use is important.
|
| There might be a clever way around this, like with a tech other
| than glass electrode, or some type of automation system with
| motors that raise and lower the probe into calibration
| solutions.
|
| Something interesting: pH electrode response is nearly linear,
| and you can make the transfer function using entirely 2 (or 3
| to compensate for non-linearity) calibration points. (voltage,
| pH, temp) No arbitrary coefficient required, other than maybe
| temp compensation.
|
| Edit: I wonder if your sampling idea could kill 2 birds with
| one stone, if implemented well: By sampling using a mechanical
| system, you could measure regularly, and calibrate. Auto
| calibration, and avoid the lifetime reduction from immersion.
| Eg some type of motor/pump system connected to the electrode.
| amerine wrote:
| What about the 1yr+ claim on https://atlas-
| scientific.com/probes/industrial-ph-probe/ ?
| ComputerGuru wrote:
| It may be suspended in water indefinitely, but the rated
| lifespan is four years. Hmmm..
| the__alchemist wrote:
| No idea. Sounds awesome. Might be a higher quality probe,
| or one designed with low drift rate in mind, given its
| marketed as an industrial probe. That length doesn't
| specify how much drift is expected, so it's unclear what
| tolerances that has in mind.
| brianhorakh wrote:
| At first glance this looks just like the one I bought on taobao
| for 120rmb (around 23usd) What is the difference?
| syntaxing wrote:
| Kind of excited for this because I wanted to get into hydroponics
| but a huge deterrent was an affordable and accurate PH sensor.
| Would be cool to see an example of this being pushed to some "IoT
| platform" like Adafruit IoT.
| coupdejarnac wrote:
| What's so hard about pushing this sensor reading to
| Adafruit/any other IoT dashboard? You're either sending a mqtt
| message or POST, regardless of where the sensor reading came
| from.
| syntaxing wrote:
| I should of clarified, it would of been nice to see an
| example using an ESP variant (since its cheaper and has wifi)
| pushing to an IoT dashboard. I haven't looked into the class
| file and how easy it is to port to micropython/cython.
| the__alchemist wrote:
| I'm working with the creator of
| [Mycodo](https://kizniche.github.io/Mycodo/) on a PR to get it
| added there. I don't have much experience with Mycodo, but it
| seems like a nice consolidated platform for measuring things
| and sending outputs from a Raspberry Pi server. It's an open-
| source project mainly run by one guy, who's very attentive to
| issues and PRs.
| syntaxing wrote:
| This is so awesome! I really love the nonsoldering setup
| (it's not hard to solder, just annoying in a small apartment
| with kids). I'm going to see if they're equivalent parts with
| Qwiic / STEMMA connectors instead of header breakout.
|
| Edit: Did not notice you were OP! Do you have more clarity on
| the calibration? Is there a buffer solution you can
| recommend?
| rohan1024 wrote:
| Thank you for sharing about hydroponics. New rabbit hole to be
| discovered!
| syntaxing wrote:
| I really enjoyed this book as a beginner[1]. I was seriously
| thinking about getting this [2]. For the price, it seemed
| very reasonable compared to making my own. I would of gotten
| it if I live in a more permanent location. I got an
| Aerogarden to try out but the light is so damn bright. I
| don't have any place in my apartment that fits it without
| blinding us throughout the night.
|
| [1] https://www.amazon.com/DIY-Hydroponic-Gardens-
| Inexpensive-Gr... [2] https://www.lettucegrow.com/
| bob29 wrote:
| Looks like the same stuff on Adafruit or ebay but more expensive.
| the__alchemist wrote:
| I was surprised that this doesn't seem to be the case - For
| example, I can't find any pH sensor on Adafruit. There is a
| model that's easy to find on eBay or Amazon, sold under various
| brands - I was unable to get this working, likely due to
| documentation or software issues.
| bob29 wrote:
| I'm using "Aquarium Hydroponic PH Electrode Probe/Liquid PH
| Value Detection Sensor" on ebay for $36 with probe. It even
| came with example code.
|
| I'm using it for a basic application and only roughly
| calibrated it with paper tests using tapwater and vinegar.
| I'm only measuring between ph 5-8 and my application doesn't
| really require precision.
| sokoloff wrote:
| I picked this sensor somewhat randomly on Aliexpress and it
| seems to work well (with calibration on both, tracks closely
| to my commercial Nutra-Dip Trimeter).
|
| For hydroponics (where 0.1 pH is plenty of precision and pH
| range should be inside 5-8), I was quite happy with the $14
| version below.
|
| https://www.aliexpress.com/item/32957428276.html?spm=a2g0s.9.
| ..
| gregsadetsky wrote:
| I only found one soil pH sensor on Adafruit, but it's
| currently sold out:
|
| https://www.adafruit.com/product/4026
| flaviu2 wrote:
| That's a capacitive moisture sensor. It is incapable of
| measuring pH.
| gregsadetsky wrote:
| Oof, you're right of course. My bad! Thanks
| fern856 wrote:
| Not open hardware? :(
|
| [1] https://github.com/anyleaf
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