Differential readings can reduce this problem because that doubles the ADCs impedance. TomGeorge: I tried multiple Arduino uno boards, and tried both 5v and 3.3v. The following may help with everyone's sanity. https://so-now.com/electronics/capsense.php, Powered by Discourse, best viewed with JavaScript enabled, Capacitive Soil Moisture Sensor barely drops Values, Capacitive_Soil_Moisture_Sensor_SKU_SEN0193-DFRobot, Adafruit STEMMA Soil Sensor - I2C Capacitive Moisture Sensor : ID 4026 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits, How to fix faulty Capacitive soil moisture humidity sensor v1.2 - YouTube, https://how2electronics.com/interface-capacitive-soil-moisture-sensor-arduino/. This patches the frequency output to AOUT. The thing is, I had it running for a few days now and the values barely drop. Maybe the board is faulty, but I ordered 5 of them, will all 5 be broken? This segment shows daily drawdown by vegetation during the hottest/driest month of the year followed by several rainfall events starting on 9/4 . What voltage are you applying to the sensor? So you have to use a voltage divider at the output of the sensor. The tricky part is that you probably need to use a metal tube for cutting your sample (and for the oven drying) but you dont want metal near a capacitance probe later on so you would want to transfer your soil plugs into a PVC pipe with the same internal volume using some kind of plunger before the final measurements. We ran several of these sensors in our back yard this summer. Traditional soil moisture sensors are prone to corrosion with a limited lifespan regardless of measures taken. We have some northern projects waiting in the wings and I want to see how well the unregulated student builds stand up to the cold. I remove the regulator & bridge the Vin to Vout pads. To fix this, I temporarily ground the VIN pin of the sensor which causes it to function normally for a few seconds until it reverts to a faulty state. 
Weather/environmental sealing of the capacitive soil mooisture sensor: https://thecavepearlproject.org/2020/10/27/hacking-a-capacitive-soil-moisture-sensor-for-frequency-output/ (see image below). So Im sailing pretty close to the wind here: it would be much wiser to just leave the original C5/6 caps in place and skip pin powering all together. Perhaps stump up the money and (if you are in the USA.)
Older NE555 based probes run at 370khz but the V1.2 probes with the TLC555 run at a higher 1.5Mhz frequency with a 34% duty cycle. This is kind of obvious if you think about how differently sand behaves with respect to water infiltration & retention compared to a soil high in clay content but the low level details get quite complex. A third alternative is to use hot glue inside regular heat shrink tubing squashing it into full contact with the circuits while the glue is still warm & pliable. The only information I get from the serial monitor, after setting it to 9600, is 1023. Here Im using Loctite E30-CL.
This might be true, but even tested with a multimeter the output only changes when using a arduinoUNO Are you able to get a decent reading out of that? When I touch the resistors with my finger the value jump up, but then slowly goes to zero again. Hi Everyone. When I swapped to a baud rate of 115200, I got values ranging from 833 (dry in air) to 520 (wet in water). First post to this forum, so please excuse any etiquette errors. Move the10k R1 to the R3 pads, and the 1Meg ohm R4 to the R2 pads. The wet sample must be allowed to drain under gravity until water is no longer actively dripping from it. 3.3v operation is out-of-spec for the NE and 1/2 the NEs Ive tried didnt even work in their default analog config at 5v. When powered at 3.3v, the default config outputs a range of ~3.0v dry to 1.5v fully submerged in water.
3.3v ProMini ADC readings from an analog soil moisture sensor at ~8cm depth (vertical insertion) with DS18b20 temp from the same depth. @TimMJN Yes, I double checked, with multiple Arduino's and used different analog ports. ranges between 8% to 35% in beans, 5% to 25% in corn. Hey Edward, Im looking into using machine learning to detect anomalies or patterns in soil moisture data, which may only be detectable in post processing. After testing some naked boards ( where I had removed all the components) I realized that the bare traces fell within a workable capacitance range for the same astable configuration the timer was already configured for: Get the regulated boards with the CMOS TLC555 chip rather than the NE555. Try using A0 as the pin address. Once pull out into air the response is in seconds going back to the max value. We reviewed those in the Adding Sensors to an Arduino Datalogger but the short version of that is: Tillarts TSL235R example works, or you could try PJRCs FreqCount Library. Cut PCBs can absorb several % water if edges are left exposed. When the new R2 exceeds is more than 10x the new R3 resistor you approach a 50% duty cycle on the FM output. When I looked into the frequency of commercial sensors, they were running at least 100 kHz, and most were in the 10s of MHz range. Here Ive combined two of the four wires to carry the output. It can also be pushed to 2 MHz in astable mode, though youd need a more advanced counter to keep up. Denes Senes Simple Kalman filter is also fun to play with, though in this case thats killing flies with a sledge hammer. (use gloves so you dont burn your fingers!) At its heart, this is just a variation of standard RC rise-time methods with the 555 converting that into pulsed output. thijsb: This humble sensor was less affected by daily temperature cycles than I was expecting but if you use field capacity as your starting point the delta was only ~200 raw ADC counts. (with the possible exception of neutron probes) Another issue with this method is drilling the hole necessarily cuts any moisture pulling roots away from the probe, creating offsets relative to the root-permeated soil nearby. I found you cant push that combination past the 4.096V gain setting or the 1115s low input impedance starts draining the output capacitor. The voltage on the Analog signal pin can be measured by an analog pin on the Arduino which represents the humidity in the soil. Here is a very nice article, how this person has done the percentage calculated using the map function: https://how2electronics.com/interface-capacitive-soil-moisture-sensor-arduino/. Once you go down that rabbit hole you discover a surprising number of those cheap boards can be improved with other alterations. While much faster to prepare: the heat-shrink (shown in the photo above) & hot glue methods willpull away from the smooth sensor surface after about 1 year in service epoxy encapsulation lasts for the lifetime of the probe. With a water/air dielectric difference of about 80:1 even unmodified soil probes do that job well if you put in a little calibration time. Are you able to get a decent reading out of that? Vendors on eBay have started listing 3.3-5v compatibility, and even posting the schematic showing the regulated TLC555 circuit, and then shipping the 5v only NE555 sensors. Since Ive already switched over to using the Input Capture Unit to read thermistors, I started with Reply #12, on Nicks Timers & Counters page. This logger was running unregulated from 2x lithium AA cells and the regulator was also removed from the soil sensor. I am hoping some of you guys have a tip. adding different relative %-volumes of water to each, distance between the centers of the electrodes. The Hack: (click images to enlarge). As a rule of thumb, the field usually has a penetration distance of between 0.5-1x the distance between the centers of the electrodes. The analog soil sensor from the start of the post is still chugging away, but (with the exception of a few rainy days) after leaf-fall the soil sensor has basically leveled out at field capacity. This reduces error and lets you approach frequencies to about 1/2 your uC clock speed (depending on the interrupt handling). For example, in your addendum, detecting some sort of a pattern after the two heavy rain events compared to the expected daily stair-step drying cycles you mentioned earlier. I will be installing a number of these next spring in a more organized way as part of a new tree monitoring experiment, but wont really have data consistent enough for a decent training set till next winter. You want at least 2-3 monitoring locations due to the spatial variability of infiltration pathways, and then 2-3 sampling depths at each spot for a complete profile. Pingback: El ampermetro vintage se convierte en varios medidores de humedad - la-tecnologia.com, Pingback: Bodenfeuchtesensor mit ESP8266 | theloxleyfiles, removing the usual load of redundant pullups and those ubiquitous, bringing $1 DS3231 modules from ~0.1 mA down to less than 3A sleep current which is quite useful if you want to, Another easily modified board is the soil moisture probe I flagged in, 3.3v ProMini ADC readings from an analog soil moisture sensor at ~8cm depth, (Note: After checking batches from MANY different suppliers Ive now started adding a 1Meg ohm resistor across the output of any sensors that output ~95% of their supply voltage in free air. A bit more fiddling and i discovered that the output when in water (low) takes a couple of minutes to get to the minimum value. I tried pin powering anyway because the TLC555 is so much better than the the old NE555s which would surely destroy any IO pin used to supply it. Capacitive measuring basically measures the dielectric that is formed by the soil and the water is the most important factor that affects the dielectric. GENTLE heating compresses the tubing from the bottom up. Officially, as little as 0.1uF needs a limit resistor to protect I/O pins, but unofficially pin-powering dodgey circuits with AVR pins is surprisingly robust. Bytesize = 8, stopbits = 1 and parity = NONE are other values displayed by the IDE. One can then measure this voltage by use of an Analog to Digital Converter (ADC), which produces a number that we can then interpret as soil moisture.
I still consider the soil sensor work as mid-experiment, which means that what I have are a bunch of different runs with various hardware and software hacks applied, that dramatically change the sensor response (in some cases negatively). Connect bottom plug wire (AOUT) to an analogue port on the Arduino board (e.g.
You have variety of options to read pulsed signals with an Arduino. Do you have a DMM to measure the output voltage of the sensor? I expect those events will register as extremely dry due to the reduced dielectric of ice. although I do not have exactly the same setup as in the tutorial you mentioned, I did stumble across that one as well while trying to get my sensor to work. What Arduino board are you using? The Arduino analog input voltage is max. 1V and the output voltage of the capacitive sensor is about 3V (if you use it from 3.3V power supply). The result is a much more robust sensor without corrosion worries. Agricultural applications usually install two sensors, with one shallow sensor at 25-30% of the root zone depth and one deep at 65-80% of the root zone depth. However the readings plateau as you approach 10 mS/cm so its not much use in the kind of brackish coastal environments we play in. Linking the other T4 pad to C3 replaces puts the probes capacitance in its place. On both units i receive a value of around 330. Consequently, there is a smaller reactance to the square wave, thus lowering the voltage on the signal line. The reward can be substantial, with our low power RTC mod bringing $1 DS3231 modules from ~0.1 mA down to less than 3A sleep current which is quite useful if you want to power the entire logger from a coin cell. I am having issues trying to calibrate this moist sensor: https://wiki.dfrobot.com/Capacitive_Soil_Moisture_Sensor_SKU_SEN0193, Which suggests me to calibrate it with this code. @TimMJN Yes, I double checked, with multiple Arduino's and used different analog ports, thijsb: Sensor use and calibration: https://how2electronics.com/interface-capacitive-soil-moisture-sensor-arduino/, Theory and calibration: https://makersportal.com/blog/2020/5/26/capacitive-soil-moisture-calibration-with-arduino. Remove the T4 diode, C3 & C4 caps and R2& R3 resistors as shown. The idea is you want to keep the relative density of the sample similar to the original soil insitu. Rain event on 9/5 reset the probe to normal for a few days. Rain events would reset back to normal behavior, but eventually the rising curve would happen again. The final output value is affected by probe insertion depth and how tight the soil packed around it is. The square wave generated is then fed to the sensor like a capacitor. But at first bounce, with parts I already had, the 1M&10K combination seemed workable. there is something odd. Sparkfun boards usually have leaner trim, but with all the cheap PCB services available now Im tempted to just roll my own.
Im envisioning an SMD quad in the middle, and a few layers of elegantly designed traces & well labeled through-holes for population with resistors & caps. The sensors I tested stabilize at power on after ~1 second but take more than 35 seconds to discharge down if you suddenly move the probe from air to water this behavior indicates the boards are missing the R4 ground connection. An Arduino can be used to read the analog signal from the capacitive sensor, which can be calibrated to volumetric soil moisture content via gravimetric methods (using volume and weight of dry and wet soil). How Does a Capacitive Moisture Sensor Work? I also tried to measure the electrical conductivity of solutions with this hacked probe. Accurate measurement of soil water content is essential for applications in agronomy and botany - where the under- and over-watering of soil can result in ineffective or wasted resources. A positive plate, a negative plate and the space in-between the plates, known as the dielectric. In this case I estimate the useful sensing distance is less, say 3-6 millimeters from the probes surface, so you have to take care there are no air gaps near the sensor surface during the calibration, and when you deploy. Two heavy rain events in this record. Gadget Reboot gives a good overview of how the basic configuration works, feeding the RC filtered 555 output into a simple peak detector. Have you tried replacing your sensor with a potentiometer? We have 6 months of continuous operation on these probes so far but with only that thin ink-mask protecting the copper traces Id be surprised if they go more than a year. Its important to leave the C1 bypass in place but I havent had problems pin-powering other sensor boards with similar caps. Value_1 is the value for dry soil and Value_2 is the value for saturated soil.For example: Value_1 = 520; Value_2 = 260.The range will be divided into three sections: dry, wet, water. These things are cheap enough that Ive started noodling around with them for other tasks like measuring water level. But it might be possible with readings from multiple sensors and some kind of a heavily averaged approach to deal with the inconsistencies from all the air gaps. Unfortunately, the serial output was an underwhelming "3". I Followed the same tutorial (Capacitive_Soil_Moisture_Sensor_SKU_SEN0193-DFRobot) but the output of the analog output remains 0.
Would it be possible for you to share your raw (soil moisture and temperature) sensor data? Then theres all the factors related to your sampling technique. also a more comprehensive summary on his web page (note is page certs are not up to date so you may get warnings). I have had the same issues as described throughout this thread. Have you tried replacing your sensor with a potentiometer? I also changed power from 3.3 to 5v but nothing changed. Capacitive soil moisture sensors exploit the dielectric contrast between water and soil, where dry soils have a relative permittivity between 2-6 and water has a value of roughly 80. What voltage are you applying to the sensor? The capacitance of the sensor is measured by means of a555based circuit that produces a voltage proportional to the capacitor inserted in the soil.
the amount of salt dissolved in the pore water. Otherwise the Aout pin outputs absolutely no voltage. Has somebody a tip for me which I can try, or that I can check that the board(s) are not broken. 
Could you please assist? You still have to treat the edges of the PCB, but that can also be done with nail polish. So there wont be much going on over winter but, I will be leaving most of the loggers outside anyway. Extract two samples with a tubular cutter whos volume is large enough to cover your sensor and weigh them (you can back-calculate the gravimetric % moisture for those in-situ readings later from the sample you dry out ). Essentially using the circuit as a cheap resistance to frequency converter. At first, uPyCraft set the baud rate to 9600 by default (and as suggested in the tutorial). Women in Science: Don't get stuck in the GIRL box! So I just started replacing the NE555 chips myself, since TLC555s are only about 50 each: The Touchstone TS3002 timer IC could be another interesting 555 replacement option as its specd to draw only 1A from a 1.8-V supply. 
The model itself would not be relevant to me since my soil is different, but having actual, historic raw data, as opposed to creating a set of random data points, would give me a better idea if its possible or not. . Then weigh both samples again & take readings with your sensor embedded in the wet & dry soil samples packed back into their original sampling volume. A capacitive moisture sensor works by measuring the changes in capacitance caused by the changes in the dielectric.
Pingback: Sensor de tierra con capacidad de pirateo para suministros de tensor inferior - la-tecnologia.com, Can we use that like grain moisture meter? 
There isnt much left after the mod. The output frequency is controlled by the time constant when charging/discharging C3 through R2/R3. 3/4(18mm) to 1(24mm), 2:1 heat-shrink forms a container around the circuits, with smaller adhesive lined 3:1 at the cable to provide a seal to hold the liquid epoxy. And since the TL555 doesnt draw more than 5mA (after settling), you can supply it from a digital I/O pin to save power provided you give the sensor a couple of seconds to charge the output capacitor after power on. (modified from: https://www.switchdoc.com/2020/06/tutorial-capacitive-moisture-sensor-grove/). I tried two sensors, both the same result. This capacitive soil moisture sensor features no exposed plating and uses capacitive sensing to detect soil moisture. It does not measure moisture directly (pure water does not conduct electricity well), instead it measures the ions that are dissolved in the moisture These ions and their concentration can be affected by a number of factors, for example adding fertilizer for instance will decrease the resistance of the soil. If the distance between interdigital coplanar electrodes is comparable to the smallest dimension of each electrode, then fringe fields are significant. At that point I might as well get out the hack-saw, because Im really just using the top section of the board as a TLC555 breakout that I can mount under epoxy. And up to four of those $1 ADC could be hung off the same bus though Ive learned the hard way not to put too many sensors on one logger because it risks more data loss if you have a point failure due to battery leaks, critters, or vandalism. get a better product? Only fill to about 15% of the volume with epoxy. Jim HaseloffDept of Plant SciencesUniversity of Cambridge, +44-1223-766546biomaker@engbio.cam.ac.ukcoordinator@engbio.cam.ac.uk, Projects to promote interdisciplinarity and open innovation. As usual, I pretty much ignored all the calibration homework and simply stuck the thing in the ground for a couple of weeks to see what Id get. I found a youtube video with the title "How to fix faulty Capacitive soil moisture humidity sensor v1.2" (How to fix faulty Capacitive soil moisture humidity sensor v1.2 - YouTube) so maybe i am able to fix it. Sensors with the 1meg already connected the way its supposed to be on the board usually output ~85% of their supply voltage with the sensor in air & about 35% of their supply when completely submerged in water.). However at lower frequencies the precision suffers, so measuring the elapsed time during a single cycle is better. There is a fixed frequency oscillator that is built with a 555 Timer IC. Aref moves in step with the supply voltage so we didnt have interference from battery variation. This forces the epoxy over the components.
The physical form and construction of practical capacitors vary widely and manycapacitor typesare in common use. This epoxy takes 24 hours to fully cure. This will give you grief with almost all of the soil measuring sensors on the market. Trying to read the sensors output with my EX330 when the sensor was running brought the output voltage down by about 0.33v and its got 10M internal impedance similar to the ADS so a cheaper voltmeter will knock the output from this sensor around even more. I was having a similar problem where i thought it was not responding and why i found this thread. Thanks Tom.. Hello, Perhaps that was because the water was leaving, but the ions were being held on the probe surface? It does not display any different information when I dip it in water. Are you measuring from the right pin? So we still use a lot ofeBay modules after removing the usual load of redundant pullups and those ubiquitous 662k regulators. (Even in clay the %volume of water at field capacity is usually lessthan 50%.) A drain that low brings these soil sensors within the power budget of our 2-Part falcon tube loggers that run for a year on a coin cell. Be interesting to see if the soil sensor can withstand being frozen right into the soil. Its worth mentioning that the 555s notorious supply-current spikes during output transitions might give you bad reads or weird voltage spikes. To get a complete response curve you would use 5-10 jars of dry soil, adding different relative %-volumes of water to each pot from 5 to 50%. (& add a series limiter if pin powering). While my attempts with the 1M&10K pair didnt deliver much, the parrot aint dead yet. An old USB or phone cable works for light duty sensor applications. This works with these hacked soil sensors, though it will occasionally throw a spurious High/Low outlier with those rounded trapezoidal pulses. Comparison of soil sensors and some tips: https://arduinodiy.wordpress.com/2020/08/, Dr. Steph NorwoodProf. Theres something of a cultural divide between the OpAmp/555 crowd and Arduino users. The Soil is still at 100% moisture What am I doing wrong? NodeMCU and Wemos D1 Mini seem to work sporadically. While the heat shrink/epoxy method is our gold standard for sensor encapsulation, adhesive lined 3:1 heat-shrink can do a reasonable job on these sensors if you make sure the surfaces are super-clean with isopropyl alcohol & take time to carefully push out any air bubbles. Reply #12, on Nicks Timers & Counters page. I use a NodeMCU, the capacitive soil moisture sensor v1.2 and uPyCraft IDE (MicroPython). Changing that R2/R3 resistor combination to boost frequencies to much higher frequencies when the probe is in dry soil might reduce that polarization problem. Or you could drop in your own resistor combination to tune the output. Since the contacts (the plus plate and the minus plate of the capacitor) are not exposed to the soil, there is no corrosion of the sensor itself. So it would be tricky to get good readings because of irregular packing of the grain/corn against the sensing surface -and this would also be shifting over time. The capacitance is converted into voltage level basically from 1.2V to 3.0V maximum.
It is recommended that 3.3V power be used if available, to maximise resolution of the ADC. I also note you can check the output from the sensor with a DMM it ranges around 1.8 v in water to 3 volts in air. there is always the possibility of a bad sensor, funny, but does it pass the smell test ? Did anyone make them work? @Paul__B Thanks, I think I will buy those sensors then, Now I just have to find a webshop which has those sensors (Adafruit STEMMA Soil Sensor - I2C Capacitive Moisture Sensor : ID 4026 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits) on stock.