Not sure if I\'m oversimplifing this module ......

[Dan Purgert]

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Hash: SHA512

I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/


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[Don Y]

On 1/27/2023 12:36 PM, Dan Purgert wrote:

I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.

The role of the 555 is, as you say.

I would, however, question the whole idea of trying to convert
the \"capacitance\" into a voltage -- just because there\'s an A/DC
available doesn\'t mean that\'s the best way to acquire a signal.

Instead, you might consider letting the C be part of an RC
oscillator and \"counting\" frequency to determine capacitance.

Regardless, you will likely have variation from sensor to
sensor so plan on having a mechanism to \"calibrate\" them -- even
if only \"this is well watered\" and \"this is in need of water\".

 

[piglet]

On 27/01/2023 19:36, Dan Purgert wrote:

I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/

Correct. The RC filter and peak detector idea could use a PWM /square
wave output instead of the fixed frequency 555. The variable frequency
idea shown further down is probably better for accuracy. The peak
detector idea may be good enough, the temperature coefficient error of
the diode drop could be reduced by driving the PWM output steady high
during a calibration cycle but that may be gilding a donkey.

piglet

 

[Fred Bloggs]

On Friday, January 27, 2023 at 2:36:09 PM UTC-5, Dan Purgert wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/


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If you use the 555 multivibrator to trigger a oneshot of fixed pulse width, and then rc-filter that pulse train, you have a frequency-to-voltage converter obviously. Vout=PW x F x Vcc, where PW is oneshot pulsewidth, F is the 555 multivibrator moisture dependent frequency ( proportional to 1/C), and Vcc is supply voltage. Make output filter RC > 100/Fmin and use a second 555 to make a one shot, you should get workable results. If the sensor C is somehow proportional to soil moisture, then you\'ll have to run your F-to-V output voltage through a table look-up. No need to be super precise.

A peak detector is not a frequency-to-voltage converter. Any amplitude change they\'re seeing is due to a frequency dependent rectification efficiency of the diode in combination with a hyperbolic sine modulation of the stored charge with frequency in the 555 output driver. Pretty much unusable.

 

[piglet]

On 27/01/2023 22:53, Fred Bloggs wrote:
> A peak detector is not a frequency-to-voltage converter. Any amplitude change they\'re seeing is due to a frequency dependent rectification efficiency of the diode in combination with a hyperbolic sine modulation of the stored charge with frequency in the 555 output driver. Pretty much unusable.

What you wrote is true: A peak detector is not a F-V converter. But the
humidity sensor cap in the article is wired as an RC lowpass filter, so
the detected voltage does drop with increasing capacitance. Seems a
usable low cost way of doing things for uncritical apps?

piglet

 

[Arie de Muijnck]

On 2023-01-27 20:36, Dan Purgert wrote:

I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/

Regarding [2]: The design is flawed anyway. An electrode in moist earth should be DC free to prevent corrosion. Using an electrode with a solder mask over it is not a solution, the solder mask is not water proof.
It is much better to use the capacitance as the frequency determining element in the 555 oscillator instead of in the low pass filter. Place 100nF in series with the electrode to remove the DC component. Remove the detector and low pass filter completely, and measure (count) the frequency of the 555 digital output. You will get an enormous dynamic range, and less noise in the signal.

Arie

 

[Don Y]

On 1/28/2023 7:58 AM, Arie de Muijnck wrote:

Regarding [2]: The design is flawed anyway. An electrode in moist earth should
be DC free to prevent corrosion. Using an electrode with a solder mask over it
is not a solution, the solder mask is not water proof.

If located out-of-doors, you also have to contend with the ~50C change
in temperature expected over the course of a year; ~20C over the course
of a day.

And, if supplemental irrigation is used, the quality of the water
supply is an issue (e.g., we have high mineral content in our
domestic water; faucets have \"calcium growths\" in short order!)

It is much better to use the capacitance as the frequency determining element
in the 555 oscillator instead of in the low pass filter. Place 100nF in series
with the electrode to remove the DC component. Remove the detector and low pass
filter completely, and measure (count) the frequency of the 555 digital output.
You will get an enormous dynamic range, and less noise in the signal.

More importantly, you can trade time for resolution. As moisture
typically changes slowly, you can integrate the output over long
periods of time to get finer-grained data on the \"current\" level
of moisture.

And, you can dynamically adjust the integration period so you
can get \"coarse\" data more quickly (i.e., WHILE watering the
plant, you likely want to see frequent updates to help tell
you when to stop -- or, at least caution you as to when you
are approaching the desired moisture level).

[For frequency based acquisition over HUGE ranges, you can
also switch to measuring *period* as f approaches DC]

Timers are usually more effectively used than A/DCs on MCUs
(but people tend to naively think in terms of voltages)

 

[Fred Bloggs]

On Saturday, January 28, 2023 at 9:59:11 AM UTC-5, Arie de Muijnck wrote:

On 2023-01-27 20:36, Dan Purgert wrote:
I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/

Regarding [2]: The design is flawed anyway. An electrode in moist earth should be DC free to prevent corrosion.

Not necessary if the electrode is electrically insulated from the soil, air, water.

> Using an electrode with a solder mask over it is not a solution, the solder mask is not water proof.

What makes you think they only used solder mask. Advertising \"corrosion resistant\" implies a conformal coating with something like acrylic or urethane.. Enough of this product has been out there long enough and in large enough numbers to be satisfied with the corrosion resistance claim.

> It is much better to use the capacitance as the frequency determining element in the 555 oscillator instead of in the low pass filter. Place 100nF in series with the electrode to remove the DC component. Remove the detector and low pass filter completely, and measure (count) the frequency of the 555 digital output. You will get an enormous dynamic range, and less noise in the signal.

The product page schematic never made it clear which was the sensor capacitor. Looked like the 470p to me, 1u is pretty big for a sensor capacitor.
The peak detector scheme is a dud because even a 0.5V diode drop is 16% of the supply. The 1M bleed resistor pretty much guarantees a few uA continuous bleed, which must be conducted by the diode.

It\'s less trouble for the Arduino to read an A/D of a low pass voltage output than continually servicing a relatively high frequency interrupt to do a count.

Arie

 

[Fred Bloggs]

On Saturday, January 28, 2023 at 10:16:40 AM UTC-5, Don Y wrote:

On 1/28/2023 7:58 AM, Arie de Muijnck wrote:
Regarding [2]: The design is flawed anyway. An electrode in moist earth should
be DC free to prevent corrosion. Using an electrode with a solder mask over it
is not a solution, the solder mask is not water proof.
If located out-of-doors, you also have to contend with the ~50C change
in temperature expected over the course of a year; ~20C over the course
of a day.

You do understand plants do not require watering in subfreezing temperatures? Hmmm- well maybe you don\'t.

And, if supplemental irrigation is used, the quality of the water
supply is an issue (e.g., we have high mineral content in our
domestic water; faucets have \"calcium growths\" in short order!)
It is much better to use the capacitance as the frequency determining element
in the 555 oscillator instead of in the low pass filter. Place 100nF in series
with the electrode to remove the DC component. Remove the detector and low pass
filter completely, and measure (count) the frequency of the 555 digital output.
You will get an enormous dynamic range, and less noise in the signal.
More importantly, you can trade time for resolution. As moisture
typically changes slowly, you can integrate the output over long
periods of time to get finer-grained data on the \"current\" level
of moisture.

And, you can dynamically adjust the integration period so you
can get \"coarse\" data more quickly (i.e., WHILE watering the
plant, you likely want to see frequent updates to help tell
you when to stop -- or, at least caution you as to when you
are approaching the desired moisture level).

[For frequency based acquisition over HUGE ranges, you can
also switch to measuring *period* as f approaches DC]

Timers are usually more effectively used than A/DCs on MCUs
(but people tend to naively think in terms of voltages)

 

[John Larkin]

On Sat, 28 Jan 2023 15:58:52 +0100, Arie de Muijnck
<eternal.september@ademu.com> wrote:

On 2023-01-27 20:36, Dan Purgert wrote:
I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/


Regarding [2]: The design is flawed anyway. An electrode in moist earth should be DC free to prevent corrosion. Using an electrode with a solder mask over it is not a solution, the solder mask is not water proof.
It is much better to use the capacitance as the frequency determining element in the 555 oscillator instead of in the low pass filter. Place 100nF in series with the electrode to remove the DC component. Remove the detector and low pass filter completely, and measure (count) the frequency of the 555 digital output. You will get an enormous dynamic range, and less noise in the signal.

Arie

I wonder if that design actually measures capacitance. Or accurately
measures soil moisture content.

 

[Fred Bloggs]

On Saturday, January 28, 2023 at 7:40:41 AM UTC-5, erichp...@hotmail.com wrote:

On 27/01/2023 22:53, Fred Bloggs wrote:
A peak detector is not a frequency-to-voltage converter. Any amplitude change they\'re seeing is due to a frequency dependent rectification efficiency of the diode in combination with a hyperbolic sine modulation of the stored charge with frequency in the 555 output driver. Pretty much unusable.
What you wrote is true: A peak detector is not a F-V converter. But the
humidity sensor cap in the article is wired as an RC lowpass filter, so
the detected voltage does drop with increasing capacitance. Seems a
usable low cost way of doing things for uncritical apps?

piglet

Okay- I missed the 1u was the sensor, thought the 470p was it. He can calibrate with a conductivity probe. I\'ve used them extensively and consider them to be very reliable. Depending on what you\'re growing there are a few things to be kept in mind. The reading is highly dependent on soil compaction around the probe. If it\'s too loose, even a soil soaking wet with water will give you a dry reading. As for location the probe needs to be at significant root depth, not on the surface, usually 4-6 inches below the soil line, depends on what you\'re growing. That\'s why the conductivity probes are about 12\" long, and they\'re pointed for ease of insertion into the soil. You can get a perfectly good conductivity probe for about $10. They run off a PV cell and don\'t require batteries. They\'re also are capable of measuring soil pH and light level in addition to moisture, slide switch selectable. A lot of people don\'t pay attention to pH, but I can tell you it makes all the difference in the world. Most of the soil mixes come in at dead on 7.0, which most plants are satisfied with. But some are acid loving and really need a 6.0, so the meter can guide you in adding soil acidifier, usually a sulfur compound. So they pack a lot of bang for the buck. The moisture scale is three broad ranges of DRY-MOIST-WET- of equal angular extent on the analog needle movement. There\'s no need to measure every last plant in the plot, it\'s good enough to measure representatives. Water is not a nutrient, it merely dissolves soil nutrients to make them accessible to the plant.
This capacitance gizmo is pretty much an unusable gimmick. I wouldn\'t waste a dime on it.

 

[Fred Bloggs]

On Saturday, January 28, 2023 at 12:43:15 PM UTC-5, John Larkin wrote:

On Sat, 28 Jan 2023 15:58:52 +0100, Arie de Muijnck
eternal....@ademu.com> wrote:

On 2023-01-27 20:36, Dan Purgert wrote:
I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.



[1]https://www.amazon.com/AITRIP-Capacitive-Corrosion-Resistant-Electronic/dp/B094J8XD83

[2]https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/


Regarding [2]: The design is flawed anyway. An electrode in moist earth should be DC free to prevent corrosion. Using an electrode with a solder mask over it is not a solution, the solder mask is not water proof.
It is much better to use the capacitance as the frequency determining element in the 555 oscillator instead of in the low pass filter. Place 100nF in series with the electrode to remove the DC component. Remove the detector and low pass filter completely, and measure (count) the frequency of the 555 digital output. You will get an enormous dynamic range, and less noise in the signal.

Arie
I wonder if that design actually measures capacitance. Or accurately
measures soil moisture content.

Nobody actually trying to accomplish something gives a hoot about the gravimetric moisture content of the soil. The name of the game is repeatability of something related to the moisture content.

 

[Don Y]

On 1/28/2023 10:04 AM, Fred Bloggs wrote:

On Saturday, January 28, 2023 at 10:16:40 AM UTC-5, Don Y wrote:
On 1/28/2023 7:58 AM, Arie de Muijnck wrote:
Regarding [2]: The design is flawed anyway. An electrode in moist earth should
be DC free to prevent corrosion. Using an electrode with a solder mask over it
is not a solution, the solder mask is not water proof.
If located out-of-doors, you also have to contend with the ~50C change
in temperature expected over the course of a year; ~20C over the course
of a day.

You do understand plants do not require watering in subfreezing temperatures? Hmmm- well maybe you don\'t.

Actually, plants DO require watering in subfreezing temperatures
because water in the soil helps retain heat. This both hydrates
the plant to help it better fare against the cold and captures
heat in the soil to radiate into the plant during the colder overnight.

It\'s also important to note that the temperature within the immediate
confines of the tree can vary. The foliage can experience temperatures
COLDER than ambient.

Some folks apply a continuous \"mist\" to the trees to take advantage
of the heat given up by the water as it freezes. (The ice coating
that forms on the tree also serves as a crude insulator to buy a
*little* protection).

[Coming in from watering my 6 citrus trees because it has been 23-27F
for much of the last week]

Knowing that there is adequate moisture in the ground to protect them
(from such a sensor) would be a win.

But, *you* wouldn\'t know that now, would you?

Perfect D-K example. Its absolutely amazing how little you actually
know -- and how much you THINK you do! <plonk>

 

[Dan Purgert]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

On 2023-01-27, Don Y wrote:

On 1/27/2023 12:36 PM, Dan Purgert wrote:
I picked up a few \"capacitive soil moisture sensors\" from amazon[1] a while
back mainly to figure out how they worked, and to see if they could be
the basis for some data logging in the garden over the summer. Long
story short, I somewhat want to use the garden-data-logger as an excuse
to design my own board to do something useful; rather than cramming 4 or
5 different modules into a box.

In digging around the web, I came across \"The Cave Pearl Project\"[2],
who has already done, well, everything insofar as the
reverse-engineering, etc. And at this point, it seems to my (completely
inexperienced) eye that the whole purpose of the 555 (and the vreg, etc)
is just to make some product for the arduino crowd; and that one could
remove the vreg and 555, and just use a PWM output straight from a
microcontroller to feed directly into the RC filter.

The role of the 555 is, as you say.

I would, however, question the whole idea of trying to convert
the \"capacitance\" into a voltage -- just because there\'s an A/DC
available doesn\'t mean that\'s the best way to acquire a signal.

I mean the whole thing kinda seems a mess, and mainly aimed at the
Arduino crowd, where it\'s somewhat \"intentionally suboptimal\" such that
it\'s dead easy for non-EE-majors to make a \"thing\"

Instead, you might consider letting the C be part of an RC
oscillator and \"counting\" frequency to determine capacitance.

Regardless, you will likely have variation from sensor to
sensor so plan on having a mechanism to \"calibrate\" them -- even
if only \"this is well watered\" and \"this is in need of water\".

Not to mention the general difference in passives themselves, as with
the existing amazon modules (such as 10% resistors or the like).


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|O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1 E067 6D65 70E5 4CE7 2860

 

[Don Y]

On 1/28/2023 3:15 PM, Dan Purgert wrote:

Instead, you might consider letting the C be part of an RC
oscillator and \"counting\" frequency to determine capacitance.

Regardless, you will likely have variation from sensor to
sensor so plan on having a mechanism to \"calibrate\" them -- even
if only \"this is well watered\" and \"this is in need of water\".

Not to mention the general difference in passives themselves, as with
the existing amazon modules (such as 10% resistors or the like).

Yes. That was my point wrt temperature ranges. If you
expect a reading of X to mean <whatever>, you will be
disappointed when it *doesn\'t*! :>

It\'s often better (if your usage tolerates) to be able
to quickly/easily take a snapshot of \"this\" and then
treat it as having some particular significance:
- \"This is too dry\"
- \"This is properly wetted\"

If doing so is relatively easy, then you can capture
various conditions as the need arises.

E.g., here, in winter, we would want to know if the ground
immediately beneath our fruit trees was suitably wet to
weather a coming cold spell. Capturing a snapshot of
a known \"adequate\" level of watering (in winter) would act
as a reference for that. Anything \"less\" would simply be
\"not sufficient\"... we\'d never try to put a number on
HOW insufficient it was, we\'d just turn on the water!

And, the reading from one sensor in one location wouldn\'t
expect to correlate with the readings of any others in any
other locations. (because of variations in sensors as
well as variations in the microclimates for each tree;
a tree sheltered by a wall would fare the cold better
than one \"exposed\" in the middle of the yard)

Likewise, in summer, the roses would frequently need
to be watered so capturing the \"reading\" at a time when
they \"look like they need water\" would be the setpoint
for action.

Of course, as things grow and microclimates change, so
would these setpoints.

 

[Dan Purgert]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

On 2023-01-28, Don Y wrote:

On 1/28/2023 3:15 PM, Dan Purgert wrote:
Instead, you might consider letting the C be part of an RC
oscillator and \"counting\" frequency to determine capacitance.

Regardless, you will likely have variation from sensor to
sensor so plan on having a mechanism to \"calibrate\" them -- even
if only \"this is well watered\" and \"this is in need of water\".

Not to mention the general difference in passives themselves, as with
the existing amazon modules (such as 10% resistors or the like).

Yes. That was my point wrt temperature ranges. If you
expect a reading of X to mean <whatever>, you will be
disappointed when it *doesn\'t*! :

It\'s often better (if your usage tolerates) to be able
to quickly/easily take a snapshot of \"this\" and then
treat it as having some particular significance:
- \"This is too dry\"
- \"This is properly wetted\"

If doing so is relatively easy, then you can capture
various conditions as the need arises.

Yeah, I fully understand that the module is pretty well garbage (I mean,
they were like a dollar apiece...). The main thing here is more of a
\"huh, I wonder if I can get anything even remotely viable\" type of
tinkering.

[...]
Likewise, in summer, the roses would frequently need
to be watered so capturing the \"reading\" at a time when
they \"look like they need water\" would be the setpoint
for action.

Right, that\'s kinda what I\'m trying to do in a way. I mean, right now
it\'s \"ehhh, water things so they have an average of X water per week\",
based on the general instructions on the care labels.

Which is fine and all, and works (mostly); but why not throw a few of
these things together; see what 2 or 3 of them in the same general bed
area say the temperature / water / etc. was every hour for a few weeks
over the summer; hopefully catch a rainstorm or two, see what data I can
get.

Maybe this thing works out pretty okay, so then I make it better for
next year. Or maybe it doesn\'t work at all, but I built a thing, and
maybe gained a little insight as to why it was so useless.


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|_|O|_|
|_|_|O| Github: https://github.com/dpurgert
|O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1 E067 6D65 70E5 4CE7 2860

 

[Fred Bloggs]

On Saturday, January 28, 2023 at 2:10:08 PM UTC-5, Don Y wrote:

On 1/28/2023 10:04 AM, Fred Bloggs wrote:
On Saturday, January 28, 2023 at 10:16:40 AM UTC-5, Don Y wrote:
On 1/28/2023 7:58 AM, Arie de Muijnck wrote:
Regarding [2]: The design is flawed anyway. An electrode in moist earth should
be DC free to prevent corrosion. Using an electrode with a solder mask over it
is not a solution, the solder mask is not water proof.
If located out-of-doors, you also have to contend with the ~50C change
in temperature expected over the course of a year; ~20C over the course
of a day.

You do understand plants do not require watering in subfreezing temperatures? Hmmm- well maybe you don\'t.
Actually, plants DO require watering in subfreezing temperatures
because water in the soil helps retain heat. This both hydrates
the plant to help it better fare against the cold and captures
heat in the soil to radiate into the plant during the colder overnight.

It\'s also important to note that the temperature within the immediate
confines of the tree can vary. The foliage can experience temperatures
COLDER than ambient.

Some folks apply a continuous \"mist\" to the trees to take advantage
of the heat given up by the water as it freezes. (The ice coating
that forms on the tree also serves as a crude insulator to buy a
*little* protection).

[Coming in from watering my 6 citrus trees because it has been 23-27F
for much of the last week]

Knowing that there is adequate moisture in the ground to protect them
(from such a sensor) would be a win.

But, *you* wouldn\'t know that now, would you?

Perfect D-K example. Its absolutely amazing how little you actually
know -- and how much you THINK you do! <plonk

Plants don\'t \"require\" any such thing. You\'re talking about temporarily protecting a plant against a cold snap, not protecting it against an entire season of cold temperature aka a freeze.

From the last word on the subject:
..
Most of what you see in Arizona are just little temporary frosts, actual freezes occur from rare to never.
Freezes may last for several days. Attempts to protect trees are generally not very successful under these conditions.
Trees should be sprinkled with water throughout the
frost. As the water freezes around the leaves and branches,
it will liberate enough heat to maintain the tissue temperature at 32°F. This strategy will only be successful if the
water is flowing continuously throughout the frost, and if
it remains flowing until the air temperature is above 37°F.
Only the leaves that are sprinkled will not suffer freeze
damage, although there could be some limb breakage due
to accumulation of ice (Fig. 3).

So looks like you didn\'t even get that part right. You don\'t just one-time douse the tree with water. You subject it to a continuous misting until air temps recover to above 37oF.

Reference:
Protecting a Citrus Tree
from Cold

UAz College of Agriculture

https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1222..pdf

Your advice is half-assed.

 

[Don Y]

On 1/28/2023 5:06 PM, Dan Purgert wrote:

On 2023-01-28, Don Y wrote:
On 1/28/2023 3:15 PM, Dan Purgert wrote:
Instead, you might consider letting the C be part of an RC
oscillator and \"counting\" frequency to determine capacitance.

Regardless, you will likely have variation from sensor to
sensor so plan on having a mechanism to \"calibrate\" them -- even
if only \"this is well watered\" and \"this is in need of water\".

Not to mention the general difference in passives themselves, as with
the existing amazon modules (such as 10% resistors or the like).

Yes. That was my point wrt temperature ranges. If you
expect a reading of X to mean <whatever>, you will be
disappointed when it *doesn\'t*! :

It\'s often better (if your usage tolerates) to be able
to quickly/easily take a snapshot of \"this\" and then
treat it as having some particular significance:
- \"This is too dry\"
- \"This is properly wetted\"

If doing so is relatively easy, then you can capture
various conditions as the need arises.

Yeah, I fully understand that the module is pretty well garbage (I mean,
they were like a dollar apiece...). The main thing here is more of a
\"huh, I wonder if I can get anything even remotely viable\" type of
tinkering.

Using changes in capacitance is often a cheap, repeatable way
of sensing <something>. I used cast zinc plates (shaped to cup
the bottom of a test tube) to detect the introduction of blood
and reagents into that \"test tube\". Dirt cheap to manufacture.
Huge tolerances (that I could null out based on the application\'s
usage patterns)

Likewise, in summer, the roses would frequently need
to be watered so capturing the \"reading\" at a time when
they \"look like they need water\" would be the setpoint
for action.

Right, that\'s kinda what I\'m trying to do in a way. I mean, right now
it\'s \"ehhh, water things so they have an average of X water per week\",
based on the general instructions on the care labels.

Most irrigation systems, here, tend to be dumb, timer driven clockworks
(\"water this zone for 10 minutes every other day; this other zone for
15 minutes weekly; etc.\"). Some add an override when rainfall is
detected (but, that is so infrequent and seasonal that you can
just unplug the controller for those times).

But, we tend to plant (\"xeriscape\") with a reliance on low water
usage/drought tolerant plants so a shortage or abundance of water
beyond the norm isn\'t fatal to the flora.

[The citrus trees being notable exceptions]

Which is fine and all, and works (mostly); but why not throw a few of
these things together; see what 2 or 3 of them in the same general bed
area say the temperature / water / etc. was every hour for a few weeks
over the summer; hopefully catch a rainstorm or two, see what data I can
get.

Just plan on annotating your data collection with visual observations.
I.e., if something looks stressed/drooping, then THAT data value means
\"needs water\" for THAT planting.

Maybe this thing works out pretty okay, so then I make it better for
next year. Or maybe it doesn\'t work at all, but I built a thing, and
maybe gained a little insight as to why it was so useless.

You may try some controlled experiments, along the way. E.g., pour a
gallon of water on a plant and see where the data settles. Repeat
this a year later (similar environmental conditions) and see if things
have drifted.

Here, we have very high mineral content in our water. So, salts
accumulate in the soil requiring periodic \"deep\" waterings (to flush
the salts down below the roots). No idea how something like this might
affect your sensor.

You may also have to modify the sensor to allow it to be sited
deeper in the soil...