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- เผยแพร่เมื่อ 4 ต.ค. 2024
- Unfortunately, most soil moisture sensors used in our Arduino, ESP8266, or ESP32 projects destroy themselves after a short while. We need a better solution.
Today we will test different sensors, and I will show you, how they work and why most sensors from China destroy themselves. And of course, we will find a solution to the problem.
Links:
Good (capacitive) moisture sensors: s.click.aliexpr...
bit.ly/2t4xd1Q
(Mostly) bad moisture sensors: s.click.aliexpr...
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I always had doubts on which one of these sensors to use. Thanks for explaining so well and solving my dilemma.
Glad to help
Hi Andreas! You can not imagine how valuable this video is for me! I know programming but almost nothing about electronics. I have started about a month ago and your videos are helping me a lot (I still don't understand a lot but it's a way to know what to study). I will try to reproduce your sensor and connect it in an esp32! Again thanks a lot!
Thank you for your feedback and good luck with your build!
As we don't live on the surface of the sun the moisture does not need to be measured multiple times per second. Limiting measurements even to once every 5-10minutes increases the lifespan of the cheap sensor drastically as the lack of constant dc current means the copper corrodes much slower. Of course the time frame between measurements could be increased even more for a longer lifespan.
Water and other things in the soil will react with the metal even when no current is flowing, so a capacitive sensor is a much better option as it is 'non contact'. But you are correct the lifespan can be increased.
And the capacitive sensors are like 3$, so it's not that bad
There are a lot of Arduino sketches out there where a digital pin is used to power the sensor only when needed.
WKD:
what you say is right but to be sure to stop the galvanic corrosion you should electrically disconnect the sensor when you do not take the measurement, this should be done using another Arduino channel and maybe a bipolar relay
why make things complicated, one should try to keep sketches small, so one can add usefull code when neeeded
the quality of your content is unmatched!
a comprehensive walk through the circuit diagrams and a solution -- what more could you ask for
Glad you liked the video!
After a heck of a lot of failed tests, I went to an AC drive detection scheme initially seen from National Semiconductor in the later '70s. My version drives a Ti electrode at around 100khz and 12v peak to peak capacitor coupled (a 555) - neither value is too critical - and senses via a voltage doubler (or a few of them for water level in a tank) consisting of two diodes and two .1uf caps loaded by 100k and directly driving an arduino or ESP logic input for water level, or with different loading to suit your electrodes, an a/d converter. Water has a dielectric constant around 80 - so here we are using the capacity change as water is more or less present between the electrodes. I'm using titanium wire for those (pure) as in most cases it wouldn't corrode even electrolytically, and have had one system (for cistern water level) in continuous use for around 10 years now with no maintenance required. Nothing else ever survived even a whole year - floats stick, optics cloud up, any DC stuff corrodes and so on.
Sadly, I didn't do a full documentation on this yet - it's so simple I just remember it, maybe I should and share it - or maybe Andreas can, he'd do a nicer job. Nice pics/plots of what I did do are here: www.coultersmithing.com/forums/viewtopic.php?f=59&t=904&p=5584&hilit=water+level#p5584
Sounds like an alternative concept. It would be good if you document it one to be used by others.
I will. Your skills in explaining would probably be superior re telling people how to tune the parameters for a given task...
Here you go, folks. Let's bug Andreas to do this up right!
www.coultersmithing.com/forums/viewtopic.php?f=7&t=1098&p=6438#p6438
@@DCFusor Great article - thanks for writing that up, and sharing it here. One point that I'm not clear on: You use alternating current (ac) to drive your "water tank capacitors", and you use titanium wire as the "conductive plates" of those capacitors. The ac will stop electrolysis - as long as the driving current has no dc component. Does the titanium stop some other from of corrosion that is unrelated to electrolysis?
@@seamusdemora5598 Yes, it's nearly immune to pretty much all corrosion from water based chemistry. It's widely used in things like salt water for that reason. FWIW, while mine grows a little fuzz (algae?) now and then, it's good as new after more than a decade. Nothing else ever came close to that level of reliable longevity.
Totally unbiased analysis showing which of the sensors really work. Thanks for the improved content.
You are welcome!
I know it's one of your old videos, but this is incredibly helpful. Thank you again Andreas!
Glad it was helpful! This video still gets lots of views.
Dear Andreas, your study is priceless. Saved me tons of work and some money (and I'm afraid a friend of mine is not going to receive any payment of a device he was going to build me...)
Thanks for this.
A Venezuelan exiled in Lima, looking to come back soon to my country, once freed. Cheers!
Glad to help! And sorry for your colleague.
As expected, another superb exposition! Thank you Andreas.
To extend the lifespan of the cheap sensors, you can use 2 analog pins one as a digital output to power the sensor and one as analog input, you take the reading and then turn off the output pin. On the next measurement you just swap the pins. This way you are simulating an AC behavior. The copper will eventually corrode for chemical reactions over time, but it will not be accelerated by flowing current.
Good idea!
thesimbon - The copper (plus the other metal that's plated onto the copper, if you're lucky it's tin, if not, it's nickel and there's a much greater chance for the latter) will not only corrode, but also leach into the soil. Sounds like just the right thing to make your plants happy....
CoolKoon I only suggested how to extend the life of sensor, I am not a chemist or a biologists so I don't know what will happen to the plant 😁
thesimbon - Well, soil moisture sensors are usually used in order to be able to water plants properly. Which kinda presumes that the goal is to make the plants thrive and avoid poisoning them as much as possible, don't you think? I mean what else would you use a soil moisture sensor for?
Use AC-driven stainless steel probes. I´ve seen that used on a water tank level sensor, and it seems to work.
I didn’t know there was a non-rusting sensor solution. Thanks for sharing
You are welcome!
An informative video that points out the short comings of the different types of commercial sensors that can be purchased. It would of course be easy enough to elongate the life of these but because they rely on conductivity, they do need to be exposed to the soil, whereas a capacitive sensor, does not so can be coated to protect it. 2 nails would suffice to replace the copper electrodes if you wanted longevity, or because of the price of these types you could just replace them every year.
Thanks for the video, it gives people insight into the different types to use
You are right. There are many other comments on the different solutions and suggestions...
capacitive sensing is a good idea. Also: Don't forget to protect the whole sensor, including the electronic components with lacquer, not only the sensing part.
You are right!
That is if you stick the components in the ground, which you do not do :) Also don't water the components!
This is just what i needed. Now i can start my garden without flying blind. Thank you Andreas!
You are welcome!
Nice video Andreas.
Thank you!
Perfect timing... I couldn’t understand why my plants were being over watered. I’ve ordered the recommended sensor. Thanks again.
You are welcome!
Resistive measurement works perfectly fine. I use two Stainless steel rods that are sampled for 1ms every hour. Inbetween sampling there is no voltage. It is running for 5 years now without issue.
In analytical chemistry for cunductometry this whole issue is managed by the use of alternateing current (and platina electrodes but stainless steel, copper or graphite should be fine for this). I don't know a damn about eletronics but why don't they just use alternating current, it reverses every chemical changes it makes? Sorry for the spelling.
I to did the same thing. Using Stainless steel rods have worked in my soil for years now. I also did not want add more circuity (even though I like the capacitive approach) to my project design. I have my Microcontroller pulse for a few milliseconds make a ADC read then average these raw reads, off the rest of the time. No electrolysis effect.
I also use stainless steel rods, the only issue I have with resistive measure is the dependence from temperature, anyway I don't know if the capacitive have same issue
Hello Andreas, this is an excellent video. I am Electronic Engineer but never had the opportunity to practice it. I love how you explain the principle with the electronic schema. This video has been very useful for me since I was doing the same type of research as you by comparing different probes. I am typing to make a wifi watering system (possibly solar) and this was very helpful.
Now, I have heard that the consumption of this device was abnormally high and that better solutions should be found (unless you don't mind about consumption).
I do no more remember the consumption. But maybe a small solar panel can help. And you do not need it on the whole time. One or two measurements a day should be ok.
I laugh when you said "this is not a channel about good looks and makeup" at 8:42 . Brilliant and informative video as always Andreas!
Thank you!
Great job, Andreas. I love the detail you've gone into, even finding the schematics for these unknown models.
I wanted to understand how they work myself!
@@AndreasSpiess can you help me in my Arduino project
@@abdulrahmanismailali1064 i am a TH-camr and do not do consulting.
Thanks for the video. I ordered a capacitive sensor and will add it to my projects queue.
damm this channel is good. Might not have millions of views but honestly guys who are just starting electronic this is gold...👌👌👌👌
Thank you for your nice words!
One more minute to see the finished protected sensor with the material you mentioned would have been a nice touch. Overall it was a very interesting and informative video. Thank you.
Unfortunately I do not have the material at hand. But one of my trusted colleagues gave me the tip.
what about nail varnish?
I also thought about that. But I do not have it in my lab ;-) Maybe somebody tried?
Big Clive proposed Nail varnish. (Tip from a Patreon)
Another thing that should be considered is how long these suggested protective coatings will last. And if they will release toxic substances in the long run. I doubt this would matter for decorative plants but if used for edible plants/vegetables it might. Of course this applies for the stuff that would be released from the exposed PCB also.
Dear sir, I exactly understood what you meant. No electrical current as it will do electrolysis function, within different metal, different electrolyte, or even different potential differences in a circuit. The capacitive way is I will always like. Thank you for this enlightment. Thought it was just that simple to measure soil moisture. Thanks again.
:-)
Your Swiss Guy intro convinced me!! 😅😁😁😁 Great video!!
Thank you!
Well explained. I have made various moisture sensors, including resistive sensors and capacitive sensors. Both have their pro' s and cons.
You already mentioned most of the disadvantages of the resistive sensors. Those can be minimized by interrupting the power to the sensor and only switch it on for a few milisec when you measure and that can be done say 4-6 times/day. More than enough.
I also do not use copper, but Iron. This way sensors last several seasons
I found the capacitive sensors (made with 555 or HC14) a bit sensitive to surroundings, apparently their wires pick up stray capacitance.
I was surprised about your sensor working with a plastic bag around it, it will, but probably not well with so much airspac around it. I tried with heat shrink.... that didnt really work. Lacquer and plastidip (expensive) do.
One more thing about that various resistive models. If you use the analog output, the 'module' that comes with it is usually superfluous,as it connects directly to the sensor
I thought iron starts to rust. No problem with that? Or do you use stainless steel? Concerning the plastic bag: Plastidip arrived too late for the video:-( But as you saw, it worked with the bag.
Usually galvanized I use. Yes it builds up some corrosion, but I just wipe it down end of season, doesn't really influence the reading throughout the season. Yes I saw it worked. I used a plastic bag too during some tests, but I never expected it to still work with so much air in between :-) My bad
I've been using 316 SS threaded rod. No problem with corrosion that I can detect.
You got the same solution I found. Cool someone else thinks like me.
Electrolytic corrosion is the death of almost all electronics. That is the reason why it is important to block direct current. Those cheap moisture sensors are actually a nice learning tool and included in almost all arduino-kits. And the rapid electrolytic destruction is a feature, it shows beginners the importance to think about these problems and how to avoid them. :)
The naive approach is, to add a resistor to make a voltage divider and put them between Vcc and GND and measure the voltage drop with the built-in ADC. This makes them corrode away in no time. The next less naive approach is to put the voltage divider between a port-pin and GND and enable them only a few times to measure the value. This slows it down but doesn't solve the problem. Third approach is, putting it between two port-pins and to take measurements they are driven with alternating current ( alternate between high and low on those two port-pins, always one pin high and the other low and taking measurements in between). This remove almost all direct current, but some direct current might be still present if the program takes longer when one specific pin is high (i.e. when taking a sample only in one code path). Then you can fix the program, maybe add a capacitor in series with the voltage divider and so on. Then you might introduce the capacitive sensor. It is a learning tool. :)
And when all flowers are dried up, you can build electric neon flowers: th-cam.com/video/rbrjkzMEpPU/w-d-xo.html www.bigclive.com/nixie.htm (and they don't need water)
Edit:
The other thing I wanted to mention is: Conformal coating helps a lot and it is extremely easy to retrofit, just get a spray bottle of kontaktchemie plastik 70 (or similar product), clean the PCB, and spray it (be careful with connectors). Conformal coating could be done in the factory, it is very cheap but it isn't done to increase the chance for water damage. Water damage means no warranty and the customer has to buy a new product and that is what some vendors of some products want (Especially the vendor of particularly hard to repair laptops that get turned into a PC when a corroded trace or pad is replaced with a wire).
The easy way to make your own, and more robust, moisture sensor is a screw terminal with two nails in it. I mean the screw terminals used to install light fixtures (They are called Lüsterklemme in German, this should give good results in google image search).
Thank you for summarizing all connection methods. Maybe I should have mentioned it.
Now I have mentioned it. Maybe it helps some readers. :)
I also edited the comment and mentioned conformal coating that can cheaply added. You mentioned it too, but isn't that plasti dip stuff really thick? That is why I mentioned a product that is especially made for conformal coating and it is old, very old, I know that I used the kontakt chemie stuff almost 20 years ago. ;)
My second choice „Tropenlack“ seems to be a conformal coating. But not easily available. Thanks for your proposal.
Wow. That big yellow/blue can with its big letters worked perfectly. It kept the better suited, but less prominently presented, product under the perception threshold...
Somebody should tell this to the marketing people from electrolube. ;)
making the learning curve steeper, while this is not needed ? i think these subjects are some of the basics of electronics, making a battery, galvanic properties, etc...
Muchas gracias profe, muy educativo e interesante el video, para este tipo de sensores tan útiles. El sensor de patas delgadas y macizas es útil para una ecualización del riego en la fase de diseño, por su características físicas, permiten una fácil penetración a la tierra, pero no dejarlo expuesto por periodos prolongados, debido a lo que usted expone en el video, y el sensor recubierto si sera útil para dejarlo en la tierra, claro incluyendo la mejora que usted menciona, recubriendo el borde, para así garantizar un riego proporcional a la humedad del suelo en todo momento. Saludos.
Yes, you can use the simple sensors for a short time and for tests.
You could also just switch the power to the sensor on for just a splitsecond fir a measurement
You are right.
A channel named "Flaura - Smart Plant Pot" has a video titled "Capacitive Soil Moisture Sensors don't work correctly" that you might find interesting. He includes video clips directly from your tests, and mentions the need for a 3V regulator in-circuit to get reliable, repeatable readings. Some boards exclude that regulator (shunting that connection with a 0-ohm resistor, for example, if the regulator's footprint is actually on the board).
I think I once was contacted by the creator of this board. Stable voltages are important for most sensors, BTW.
It is always a pleasure to learn something from you sir.
Keep it up :)
:-)
I used the striped sensor as christmas tree water sensor, it corroded in only 2 weeks totally. Thanks for the video, really concise and clear information here!
Fortunately, Christmas was over till then ;-) You are welcome!
Just bury an ESP8266, the water will change the signal strength. 😎
:o)
Make sure you add a LiPo battery so it's self drying. Bonus is that the plant will add to the "heating" effect (read: fire!)
😆😜😂
Interesting tangent opportunity here, doesn't the ESP32 offer onboard capacitance sensing intended for touch detection? I imagine it wouldn't be too much of a rework this for a buried soil probe along the lines of what Andreas came up with. I might give this a shot when mine arrives!
@Andrew Sanjanwala Yeah, that should be possible. I believe the working principle is the same, except that with a capacitative touch sensor, one of the plates of the capacitor is your finger (or whatever you're touching the sensor with), and with soil moisture sensors, you have to put another plate.
I did something like this a while ago. I only measured every 15 minutes, using the AC measuring method with an arduino. The sensor itself was very reliable and basic, just two stainless steel rods stuck into a pair of screwable wire connectors. The system was running for a year with no loss of accuracy and absolutely no damage to the rods. The rods were 4mm diameter and 10cm in length.
Thank you for sharing your experience!
Just switch polarity every time you check moisture. Second thing - buy only gold plated sensors.
They ll corrode anyways but a little bit slower and switching wont help until you saturate the soil with copper salts. Additionally platinium would be a much better choive then gold.
Decreasing sampling frequency and reducing sampling time would improve cheap sensors lifespan considerably.
Thanks Andreas! If I'm studying to develop a lora connected watering system for my plants is only because of you. Thank you for inspiring and explaining things in a way that is both fascinating and simple!
Glad you like the content of the channel!
Great video! Ive learnt new things. Anyway, instead of using capacitive sensors, what about using graphite as sensor probes? Graphite are used in many electrolytic cells as electrodes so they won't corrode away like copper does. Plus, i think graphite can be cheap too as it can be found in pencils.
Graphite was suggested also by other viewers. It is a good idea.
yes it is good... but electrolysis will still take place.
Thank You! I went through EXACTLY the same problem. There is an ON-OFF trick how to slow down the unavoidable corosion, but all attepmts will lead "everyone" to capacitive sensors. Thank You again and more, more, more videos.
You are right, I should have mentioned this trick.
The green stuff should be copper oxide, which is classified as a hazard to the environment. Considering though, that there are a lot of copper pipes out there that also oxidize, I guess it's not all to bad. Fun fact: the statue of liberty is made of copper and oxidized over the years, that's what gives it its distinctive green color
You are right.
@@AndreasSpiess
CuO = black
CuCO3 = green
Cu(OH)2 = bluish green
Great video! For those of you that wanna know more about the topic there's a good overview of various soil moisture sensors in elektor magazine that was just recently uploaded. It's called 'Moisture Sensors for Watering Systems' by Peter Tschulik and is pretty instructive
Thank you for the link. Unfortunately, he also does not provide data. So far, I never saw a study showing how good or bad the different sensors are.
@@AndreasSpiess There are a bunch of scientific papers comparing different soil moisture sensors, for example 'assessing the applicability of low-cost soil moisture sensors' from April 2020 by Abdulla Alshahri
of course i believe you master! and i proved it
did not really ever thought about getting a moisture sensor... But after watching this advise I got an capacitive one :D
I hope it works.
the green stuff is probably mostly oxidized copper.
You are right!
I don't really know plant biology. But I think some copper ions dissolved in the soil will be harmless or even necessary/beneficial.
Although too much coppper in the soil will change the pH or reach toxic levels. And some species may be more sensitive than others (for better or for worse).
I dont think so, because copperoxide(s) are not green. The copper somehow goes into some kind of copper-salts, maybe copperchloride/carbonate/hydroxide... they are all nice greenish colors
@@paulg.3067 tap water would have some chlorine so copper chloride, and hydroxide would be likely. the plating will probably be tin so you might get some stannous chloride as well (not sure if you can get tin hydroxides, not a chemist).
Thanks for the analysis. I am about to install moisture sensor in my home garden (30-40 of them) and waned to understand the difference between all types of moisture sensors available in the market before i place the bulk order. This 10 min video saved me from going through all of their datasheets. One info missing from this video is the resolution of these sensors.
I just saw a longtime study of the capacitive sensors. Pay attention your protect them with and additional layer. Especially the side which is completery unprotected
@@AndreasSpiess True. There are several concerns around directly inserting these sensors in soil. The best solution i could find is to put these sensors in plastic zip lock bags. This will not only protect the sensor but also prevent any toxic chemical from sensors eroding into the soil and then sucked in by the plant. It will probably reduce sensor's resolution but since its just a astable NE555, I should be able to fix it.
10:32
I love like he talks to us like we are computers, and he is the software running us.
Finally someone who speaks my language 💜🤖
Relationship goals
Where is the else condition. Where is the ELSE
I just bought 3 of these on Aliexpress, then I found this video... Gotta love Andreas :D
Good choice!
I though this was a channel about beauty and make-up
Sorry for not declaring it in the „small print“ ;-)
Plants are beautiful for the make-up of a house :)
yes
To avoid corrosion I used two stainless screws for probing, and alternating current for measuring. That means instead of connecting them to VCC/GND they-re connected between two GPIO analogue pins, and switch polarity 10 times/second. That also allows keep both "legs" at same gnd voltage between measurements. It needs no circuitry, one gpio pin is configured input-pullup the other as output low so there is a measurable voltage on the input pin. In a few ms program swaps them and averages last 10 read values.
Thank you for your feedback!
Hi,
I really like your videos. But this time I am a little bit disappointed. I thought you will bring a "real" solution. I got the same problem like you and I found a way to solve the problem forever without any toxic stuff (plastics, softener, etc). And without having any materials that can corrode.
I took two graphite electrodes, printed a holder for them and connected them to a controller of the cheap china sensor. To prevent any way of electrolysis it changes the polarity of the electrodes every 24h. I take data once every 10minutes.
To get perfect values I did the following:
I took 500g soil and put it in a compartment dryer about 48h around 60°C that it is 100% dry.
In the next step I took 30g of the soil and put water in it. After it was saturated I took the values from the 100% wet and the 100% dry soil - each with 30g of soil. Then it was time to get some values between these measurements because it does not change linear.
Here are my resultes (6cm dipped electrodes, 5mm diameter) :
Moisture // Value
0% // 1024
20% // 634
40% // 339
60% // 321
80% // 307
100% // 260
It shows, that I need to repeat this measurement with moisture values between 0% and 50% in smaller intervals. But if we think about the resilience of nature it isn't so important.
Anyway: Thank you for your great videos and explainations.
Good work! Maybe you follow the interesting link in Craig’s comment (above). The studies there suggest it is hard to get reliable measurements from resistive and capacitive sensors. This is what I experienced and why I gave up to increase accuracy. I accepted the results because to keep home plants healthy it should be ok. But it seems you got pretty good results with your sensor.
Andreas Spiess I cannot find that comment, at least here from the smartphone. What's his username?
I have this setup in use for 3 months now for my peppermint. I have tested it with soil from it and the values are nearly the same (+/-1% - condition: same temperature, same water, etc.). The main reason for this is that the surface of the electrodes does not change. No corrosion etc...
In addition: the problem with metal electrodes is, that they solve in postitiv ions under electrolyse. This changes the conductivity of the soil and the result is: BAD measurements. So just use inert electrodes like graphite (quiet expensive, but for food, its a better choice)
What i understand of Adreas's test, is that the galvanic/resistive "way" may be not the correct "road" to travel on, (somebody already tried aluminium electrodes ?) due to corrosion, maybe one should use silver electrodes because silver oxide is a conductor :) (hence use on switch contacts) in theory copper oxide stops oxygen from further corrosion, but will be a isolator, doing it the capacitive way seems a better solution, otherwise ultrasone ? the sound travels faster through water, i can't think of a better way then Andeas found in this test. and doubt if there is.
Eric-Jan van den Bogaard what about platinum or gold plating the electrodes?
I know this has been awhile. But I came up with a probe that works really well, is super cheap, and easy to make. I simple put three long pieces of coax cable snugly into a 1/2" pvc pipe. The probe is sealed with simple pipe caps. I found that putting a bolt through the bottom for grounding made it more stable. All this stuff is super cheap and easy to work with.
Interesting concept!
What about using AC to measure the moisture? I would expect that the simple sensors should life much longer. Also a pulsed current, only measuring the moisture a few milliseconds every hour or so should help. It is not neccessary to measure all the time. What do you think?
AC is the best way to do it. It avoids a problem - electrode polarisation and allowes for even electrode aging
You are right. There is a comment summarizing the different possibilities with their advantages and disadvantages.
AC will not remove the corrosion which the metal electrodes will experience in the soil. The DC current only accelerates this degradation - even without DC current a copper trace in soil with or without tin plating will be gone after a very short while.
And copper salts - while an essential micronutricient - will kill your plants quickly.
Uwe: I was thinking the same thing. Copper in high concentrations is bad. And coming from a PCB, that is probably high enough concentration to weaken the plant. Especially if you replace the sensor every month.
Frank: Pulsed DC is exactly what Andreas showed in his example with the last sensor and the signal generator. It create a capacitance effect. Pretty neat in how that works considering there isn't any touching parts.
Actually copper is a fungicide won't hurt the plant.
Great video! I've had this problem a few years ago with water level detectors. Even with small voltages the electrodes disappeared after a few days. I tried replacing them with stainless steel electrodes, it appeared it didn't corrode, at least not as fast, but I now realize it might create even more toxic waste as a result because of chromium. I wish I knew about the capacitive sensors back then.
Thank you for sharing your experience!
Straight to the point. Thank you for protecting us customers against this cheap China sensors! Thumbs up!
Thank you!
LetsBuildSomething - Actually the capacitive moisture sensor is also a Chinese product....
Thank you for taking the time and effort to make and publish this. I was looking for a soil moisture sensor and this was very helpful I'm the decision making process.
Glad the video was helpful!
Yea, just pulse the sensor every couple seconds
According to other commenters this works for some time.
Thank you Andreas for those explanations !
My pleasure!
Du darfst kein grünes Uranglas für Deine Experimente verwenden, dann löst sich auch das Kupfer nicht ab .. ;o)
Die Farbe habe ich zufällig genommen. Es hat am Schluss aber noch etwas „giftiger“ ausgesehen. So hat es mindestens den Effekt optisch verstärkt.
Very useful. I'm glad that I was lucky by purchasing the last model.
Thank you!
What if you use the first type but switch the polarity regularly?
You find many other comments about that principle.
Works well for me.
Great video. I'm doing a lot with this sensors. At first i was using the crappy cheap ones. Now i replaced them all with the capacitive sensors.
Thanks for sharing your experience.
If I try one of these I am just going to buy a couple stainless bolts and connect them to the sensor. Pot the rest. Bam
Should work.
Fetid Tuna ok Erin brockovich, I suppose I'll die as the massive current going through stainless bolts erodes them entirely. And leaches into my tomatoes 🍅. Cool
I have here a few self destructing moisture sensors, never put them to use because of that. Now I shall buy the capacitive version and forget about the other one! Thanks mate!
If they don't contain electronics, only bare traces. Keep them. If they contain electronics that can only drive them with direct current, keep them and maybe remove the electronics. You can drive them with alternating current to minimize electrolytic corrosion or maybe try to convert them into capacitive sensors. Or destroy them by using them to observe the effects of electrolytic corrosion or teach someone else about electrolytic corrosion. :)
By the way, the easiest sensor is a screw terminal with two nails in them. I mean the screw terminals used to install light fixtures (They are called Lüsterklemme in German, this should give good results in google image search).
by removing the electronics, one can also DIY some electrodes :)
I thought about driving them with AC, but I feel like the payoff doesn't justify the work required to modify them. Especially if there's a better version off the shelf!
Dear Andreas, we make a fabric able to sense humidity. It's resistive sensing element is made of stainless steel. We think its main advantage is to be able to measure humidity right in between the plant roots and not only in the surface of the vase. Let me know in case you want to test it.
So far I have no plans for a additional video on this topic. Did you make scientific tests to prove that it works? Because so far, nobody was able to show a correlation between real and measured humidity of such sensors (resistive or capacitive)
All the sensors I use for soil profile moisture sensing rely on frequency or time domain reflectometry. They last forever. However, I know there are also capacitive sensors on the market suitable for science or agricultural use...now I know how they work. Thanks very much.
It wold be interesting to compare these sensors with the TDM ones.
The "chemistry" that happens when one leg of your humidity sensor dissolves, is the oxidation of your anode. To prevent this, you can combine the following two strategies: (1) use metals that form a stable anode (gold, platinum, titanium, nickel, carbon) which means that when using PCB technology, your limited to ENIG and more advanced plating technologies, and (2) apply as little as possible voltage between the legs of the sensor, which means use as little current as possible to measure the resistance and amplify the voltage with e.g. an instrumentation amplifier. I agree that the capacitive sensor is a much more elegant and robust approach though! The working principle reminds me of the good old Theremin :)
I used a relay to cut off the sensor when not in use. You only need to use the sensor once an hour or so for a second.
Just bought it for my pi pico garden project, thank you so much!
Have fun!
This is brilliant... thanks! Love the circuits you separate to understand what it actually does! Kind regards from Croatia!
Glad it was helpful!
Very interesting. I’m not that versed with hydration systems but work on a lot of automation systems dealing mostly with HVAC. I like your simplified explanation and appreciated field data.
I am certain that this technology will become more apparent as people are continually looking to automate processes. Keep up the good work.
Thank you! I think water will become more and more important.
I love all your videos. But especially the ESP & sensor ones 😁. Thx for all the effort you put in your videos.
You are welcome!
The green stuff is Copper.
I just took 2 big steel nails put them into an 2 wide luster terminal strip (Lüsterklemme).
The trick to avoid electrolysis is to not connect to DC but to an arduino output and just give it power while reading the sensor for a millisecond.
There are many discussions in the comments about this method.
@@AndreasSpiess don't want to read all comments since I'm building a circuit right now.
Were they positive about this method? For me it works perfectly.
Years back I built an analogue system to water my plants. I found that my mild steel nails used as sensors would just rust away. I then used graphite rods from a lab supply shop. They are more fragile than the nails, but they don't corrode and don't give off any toxic oxides.
Your observations are shared by a few other commentators
Thanks! That is informative. Bought some of the bad sensors, didn't thought about it, but it totally makes sense.
You are welcome!
8:12 "The Sensor anyway works if we do not understand these calculations" - Uncle Andreas The Badass 😂👍❤
:-))
thank you Andreas. Yet another phenomenal video. I will be purchasing a few of those moisture sensors soon.
You are welcome!
thank you very much
very useful information
regards from colombia
Glad it was helpful!
Nice work! I need to measure the moisture content of the floor material in my beehives, so this was useful.
Would be interesting to know if it works.
Phil Chandler May I ask why only the floor level?
Or do you mean, the floor for each tray in the hive box?
For aired environment, you might want to try other methods than what Andreas has presented. An humidity and temperature sensor arrangement might work better, providing the bees are not sensitive to sensor RFI and will not block the sensor's probes.
Got to ask... Why are your beehive floors wet? Solid floors should be built with a slope to the entrance (usually double sided). The hives should be off the ground (no plant contact either) and most hives today use a Varroa screen (Stainless Steel mesh) and so there is little wood in the floor. If you have water running through your hives, they probably need maintenance ;) Timber, where possible, should be red cedar which is light and naturally anti fungal, although painted wood is fine. Other than that, the bees will be maintaining temperature, humidity and air flow.
It will be difficult to measure the wetness of wood with the capacitive probe (as shown), you will probably want something with pointed probes, like those sold at your local DIY shop.
Nice little video Andreas, as ever! In the past I have used both Stainless and carbon probes working with a reversing sensor (AC) for commercial greenhouse watering. Those capacitive units are very nice. The ones that I have used were already sealed at the edges.
@@DougHanchard A bee hive only has one floor, although from time to time one may use something like a Snelgrove board to separate the hive in two, as in swarm control, queen production etc.
Technically, a floor is not needed, but adds additional protection from the elements, robbing from other colonies, wasps etc. ingress of slugs, snails, mice etc. In addition to the floor, the entrance size (part of the floor in most hive types) can also be manipulated.
Having a floor and the ability to close the entrance is useful when moving colonies too ;)
Very valuable information through this very clear explained test ! A must know for everybody who wants to do this kind of moisture measurements ! Thankyou !
Thank you. This was my goal.
It also proves one should be selective at what you buy, and not always go for the cheap stuff, if one is seriuos with the hobby, getting good results, with projects that last.
Dear Andreas,
Take a look at the Irrometer 200SS app note. It uses a pseudo AC current with muxes for multiple sensors. If you are only using one of this or even a leaf wetness sensor, you can connect it in series with a known resistor and connect both ends to two digital output pins. Of course you connect an analog input in between. By running a small sketch pulling the pins HIGH and LOW and then LOW and HIGH, you generate an AC from the sensors point of view. That way you do not have galvanic current corroding the plates. Cheers Namensvetter!
This procedure was described by a few other viewers and you are right, it seems to prolong the life of the electrodes.
Very good, yeah i remember that copper will oxidized if get amoerage and put in the water
Thank you.
Likely someone already explained the green foam in the water, but to keep it fresh, a brief explanation.
The green "gunk" is the de-plated copper from the sensor. Copper turns green when combined with oxygen, forming copper-oxide. (The Statue of Liberty was once copper colored, but exposure to the environment turned her "skin" green.)
Wow, that one was staring me right in the face and I should have realized these cheapo bare copper sensors simply won't work!
I know what's happening because I use a similar method to extract gold from computer electronics. The method I use eats away the copper holding the gold on the surface of a chip. The copper underneath the gold is dissolved by acid, leaving nothing for the gold to bond to. The gold then floats away for collection. The bath I use turns exactly the same color of what's floating in your glass.
And here is the silly thing staring me right in the face. You don't put copper in a moist environment that contains acids and salts and then run a current through it. (AKA soil.) That is an anode and a cathode. All that's needed is even the slightest bit of juice and some O2 in the environment and out goes the copper! Do that in reverse with a bit of acid and you can plate things to copper- that's how the gold gets deposited on electronics. The "teeth" in a stick of memory are copper underneath. Run that through an anode cathode setup and your memory comes out golden. (Fun fact- the ancient Egyptians figured this out! MANY of the "solid gold" trinkets dug up by archeologist are gold plated lead.)
As to toxicity...
Copper oxide is seriously poisonous. Best throw that cup away.
But it does exist in dirt. (Never eat dirt.) Plants need trace amounts of copper in the form of copper oxide. You actually consume copper when you eat plants- but it is bound up in no toxic forms. With the plant in the way to filter the copper, I would guess there is no real harm. You touch copper oxide all the time on coins.
But as to the what else is on those sensors? God himself knows.
The people who make these devices live in the single most polluted country in the world. If it were coming out of Europe or the US, the chemical purity of the copper would be assured. And the strata that the copper bonded to would be food grade- because this is going into gardens you might be eating from. But somehow money makes that go away. Maybe it is safe, but i would only use these as a demonstration sensor.
I hate to be mean, but this is the same place that "recycles" human hair from barber shops to make sure the dog food we buy meets certain levels of biotin and other biological tests. And let's not forget the "plastic baby milk" incident... Babies all over Europe came down with kidney stones and some may have died because the company located in in the same country where these sensors are made was putting melamine, the chemical that makes plastic flexible, into baby formula to fool the regulatory testing agencies in Europe. The people doing this made millions of course. (Melamine is not dangerous if it is in plastic. But in food? Gives you massive kidney stones...)
Point is, most things are worth what they cost. If it is a super good deal, you should ask wise.
Thank you for bringing this to my attention- before I bought any.
Thank you for your explanation. Indeed, in the many comments the copper-oxide was mentioned.
Green stuff is copper carbonate which is caused by corosion and electrolysis speeds up the corrosion process on your electrodes. Same thing when people remove rust using electrolysis but the object that needs derusting is grounded.
Good video. Been too busy lately. At least I found time to catch this one.
Busy is always good if it produces either fund or money ;-)
I have solved this problem years ago by using a capasitor in series with the sensor and using alternating current for measurement. The capasitor eliminates the DC component and prevents corrosion.
Using AC was mentioned several times in other comments. Some also mentioned it will not completely remove oxidation.
This actually seems like a great idea for multiple plants, so I will try to use this with my Cannabis plants... Awesome Video ;)
Maybe you build it before you smoke the plants ;-)
that's where it went wrong ;)
Super simplified explanation: Even without any "power" at all, "dissimilar" (different) metals give up their electronic charges at different rates, as metal gives up its electronic charge, it completely breaks down (corrodes). Even without any power, when you connect dissimilar metals with a conductor (e.g. - wire or water or humidity), the electronic charges move from the weaker metal (anode) to the stronger metal (cathode). When you add electricity, it increases the flow and causes the process to speed up rapidly. Even without electricity, even the tiniest bit of humidity in the air allows this process to happen naturally which is why you when you calibrate the device, you will never see a "zero" reading.
When you calibrate it, you're testing for *your* environment with *your* water (and your water's electrolytes, metals, etc.) to see how much voltage is conducted when "dry" versus "completely submerged in water" to estimate a range in between. That's why these must be calibrated on site with the same water that is used to water a yard.
Bonus info 1: Since boats sit in water and are full of humidity (both are conductors), we try very hard to make sure all metals are similar (e.g. - all the same steel with similar compositions). As a "fail safe", we attach a plate of zinc underneath the boat because zinc is an extremely weak metal and will usually give up its charges to other metals so that it rusts instead. Then we replace the zinc plate as needed.
Bonus info 2: This process is the entire basis for how a batter works - one cell is loaded with a cathodic (+) material and the other is loaded with an anodic (-) material.
pomametals.com/wp-content/uploads/2018/03/galvanic-series-chart-metals.png
Very interesting explanation for an non-chemist. Thank you! It created some memories from way back when I was in school.
Awesome video! I was about to order some cheap moisture sensors from Banggood, when I suddenly though to myself "Hmm, some weeks ago there was a video I wanted to watch about these... Time to watch it before ordering!" So you actually saved me a few bucks and some headache, thanks! :)
Always good to know!
Great Andreas always the number one. just in these days, I'm approaching these arguments. I have to test the leakage in the cooking room. Actually, I solved it using a couple of steel electrodes mounted on a homemade 3d printed box. Your video has been a great help because I was waiting for the capacitive sensor for testing it. It already works and I send an allarm message on telegram when the water gets wet on the floor. Now in my agenda are some projects refer to your works. All the best, I rest waiting for your next video.
Glad to see that my videos help to solve real problems!
As a proponent of KISS, I simply don't use any of those sensors.
It's just an ESP that opens/closes a solenoid and starts/stops a pump according to a schedule. The schedule can be changed in a web interface hosted on the ESP. Look how much water you use with watering cans and the output of your pump. Then you know how to match your schedule.
I also write the schedule to the ESP and time gets synched. So if power loss happens, everything will keep working like nothing happened.
I think this will also work. You even could combine it with Google calendar as I did in one of my videos. Then the user interface is also quite simple and the ESP has no data stored.
Really Cool Andreas. I'm using those sensors in a project with attiny85 and sending the info via RF433Mhz to a arduino nano connected to a raspberry pi.
Those sensors have a short lifespan indeed, but i think that humidity doesn't change that often or that quickly, we don't need to be always reading, nor always powering that sensor. So i have used powergating and the sensors last way longer now! :) I have one Capacitive soil sensor, but i still need to test this.
All the best!
There were many comments about switching these sensors on and off. I think I should have mentioned it in the video...
Nice and cheap idea with the 433 MHz
An AC Bridge might reduce corrosion and can be used to reduce noise. So I used two optocouplers with the transistors configured as a half bridge to drive one electrode with a square wave. The LEDs of the couplers are connected anti parallel and connected on one side to a voltage divider, which also limits the LED current. Connecting the other side to GND or the supply voltage one or the other LED are switched on, but never both. This circuit also minimizes crosstalk and noise. The other electrode of the moisture sensor is connected to a second voltage divider and an analog input. For the measurement a digital output controls the LEDs and the analog input is measured with the values being reversed if the digital output is high. At the end I average over many cycles (e.g. 16) This way a very basic synchronous detection is implemented greatly reducing noise. Not bad for a circuit with 4 resistors and 2 couplers.
I use stainless steel wires for the sensor to further reduce corrosion and a gypsum cast around them to measure soil water tension which allows for different soil types, rather than moisture
If there is interest, I will create a github page with schematics etc. What do you think about this circuit?
There are quite a few comments about hat methods already.
You could treat the sensor like you do an LCD screen and ensure there is never a DC offset to prevent electrolysis. Maybe with an H-bridge to flip the polarity and therefore drive it with AC.
Hugely overcomplicated, and you'd still get normal corrosion, but at least it wouldn't be accelerated by electrolysis. Sounds like a fun project!
Btw, not dangerous chemically if used in a non confined space. The amount of hydrogen coming off is tiny and it will quickly disperse and float away. Confined and sealed space... Not good
There are many suggestions about that topic in the comments. There is a simple solution with just using 2 processor pins. But it seems not to be the solution.
By maintaining the polarity of the legs and having a constant current running through them you are literally deplating the metals from the positive electrode (anode) and inefficiently plating on the negative electrode (cathode). There are at least 2 things you can do to greatly improve the sensor life. Only turn the power on to the sensor long enough to make your measurement, and change the polarity of the sensor each time. It is a little more complicated, but your sensors should last a very long time. Thanks for the video!
There were quite a few proposals in the comments to avoid a fast dead of the sensor. Changing polarity was one of them. But it dis not help everywhere...
@@AndreasSpiess
Well, of course, you should start out with good sensors. Perhaps 200 microinches of electroplated watts semi-bright nickel, plated after etching to ensure all exposed copper is covered. Any exposed copper at all is going to go away in fairly short order with or without electric current. :-)
Still, I suspect the capacitive sensing has the potential to last longer if you coat the entire assembly in a good thin conformal coating. Except for the connectors of course, to which I would apply a generous helping of silicone dielectric grease.
Have a great day!
Coolest one. So we can make our own capacitive sensor using 555 timer.
Yes!
You can solder some stiff copper wire onto the legs of the cheap sensors so the PCB tracks are not in the damp soil, but this is only a partial fix.
I noticed that when the temperature drops at night the conductivity of the soil changes and of course this makes it difficult to set accurate limits. Another problem is that when you add liquid fertilizer like "Miracle Gro" the conductivity of the soil increases as does the chemical reaction on the wires.
Basically then Andreas' suggestion with the capacitive sensors and waterproof dip is the only reliable way to go.
Thank you for sharing your experience!
google knows what i am wondering about and Andeas seems to have lots of videos explaining it. thanks!
:-)
Danke Herr Spiess, wieder mol sehr lehrrich :-)
Bitte, gern geschehen!
Good video for anyone planning to use moisture sensors! Btw,with reactive components the correct terminology is 'impedance' not 'resistance'.
Thanks for the correction!
Thank you for this informative video. I am happy that I have opted for the capacitive sensor on Ali. Now, I also understand why it works without corrosion :)
You are welcome!
Useful and interesting. Great video. I like these kinds of videos a lot. One just need to watch a single video and everything is said.
Thank you for your nice words!
What I also experienced with these cheap sensors is that they supply the soil with a small voltage all the time. I observed two things happening to the plants near these sensors: 1.- Their growth stopped or slowed down dramatically. 2.- All plagues were gone.
Good to know. Thanks!