Thanks!

I was hoping to test it out a lot sooner and now I guess the ground is going to be frozen in a couple of months so it was now or never! It seems to be very useable from preliminary testing.

Thank you very much for the tip about epoxy. Gonna order that from something closer to home!

Yeah I learned a lot when researching this sensor. Now that spring is here, maybe I will have more projects with it coming up.

@@GadgetReboot Maybe I find the time to integrate this sensor into RIOT OS :) Would make it simpler. So that I can use CoAP over 6LoWPAN. Creating a nice app to get all sensor data combined into one application.

I am actually going to be doing a 555 video sometime soon, not sure exactly when it might take a couple of weeks because I’m going to mix it in with some other things like a hex inverter oscillator and maybe a few other logic circuits with individual gates and a 4017 counter etc. Getting back to the pre-Arduino days.

There is a 555 oscillator that feeds signal to voltage divider formed by a 10 k resistor and the reactance of the probe arduinodiy.wordpress.com/2020/08/24/soil-moisture-sensors/ And arduinodiy.wordpress.com/2018/06/28/a-capacitive-soil-humidity-sensor-part-4/

Yeah I could use epoxy but I also wondered if I could use something else that can be removed with a solvent if I ever needed to access the components for some reason but for the cost of the probe I probably don’t need to worry about that.

hot glue then... easy removable... lifehacker.com/5676237/use-rubbing-alcohol-to-remove-hot-glue-from-nearly-anything

Yeah exposed copper is probably not going to do well in the long run. This was overall more of a first experience with the sensor to get an idea how to use it. even within the same environment, maybe the sensor needs to be observed for the most dry and most wet conditions a certain section of a garden may experience with various sun and shade conditions. There’s a lot of variables so it just needs to be characterized for every unique installation.

Why? You can do this on the side of the mcu. :)

If the sensor is already powered, it is always giving out an analog voltage that can be read immediately but if the sensor is going to be powered up only when it’s time to take a reading, that would have to be measured. If I can remember, I’ll see how long it takes to stabilize when powered on.

5 times the output rc time constant to reach 98% the value. Should be good after 5 seconds of powering the sensor.

Reading the analog signal with an op amp comparator configuration would convert it to digital where the output changes low to high when a certain analog input threshold is reached. Using hysteresis gives even better results (noise immunity). www.ti.com/lit/ug/tidu020a/tidu020a.pdf

Yes because water can get in so I used epoxy

I haven’t tested it with long cables from the output to the Arduino input but it’s possible there could be some noise pick up if it works at shorter lengths. Three things I might try are 1.Twist the signal wire with the ground wire - A spare ethernet cable would have several twisted pairs in it so a certain pair could be used for signal and ground. 2. Try a cable that has an extra ground shield, certain audio cables or maybe even an old coax cable might work, connect the signal on the normal conductor and connect the outer shield to ground only on the measuring ESP side. If the shielded cable has two conductors inside plus the shield wire, run signal and ground through it and connect the shield only to ESP side ground. 3. Maybe a simple RC filter on the receiving signal input would help filter. No specific values in mind but maybe a few tens or hundreds of ohms in series with the signal line coming in and then a capacitor to ground after the resistor, right at the ESP input. Maybe 1 nano to 1 uF experimentally. If I can find some long wires here, maybe I can try to duplicate the set up and see if I get a difference between long and short wires and if I can fix it.

@@GadgetReboot Thanks, will try different cables, and will keep testing.

If I wanted a low power design I would design a load switch circuit whether it’s just a MOSFET high side driver or an actual IC load switch that I can come out of sleep mode occasionally and power on this sensor, take the reading, then power it off and go back to sleep. I don’t need to constantly know what the moisture is, maybe once per hour or less often is good enough. Even just once per day if I plan to do watering only at a specific time like early in the morning or just when the sun is going down take the reading and then choose if I need to water, and maybe one or two readings throughout the day when the sun is supposed to be out just to make sure what happens between the day and the night.

I used an n-mosfet for such as a load switch contolling the ground by the Gate of the mosfet controlled by the MCU ( esp32 ). Thanks for the verification.

Thank you for asking about the low power application. This channel has lots of good plans.

You would switch the supply on to the probe just before you take the ADC sample, say 5s on, 3595s off, sample the ADC after 4s. Sample the soil moisture 24 times a day.

I might do some testing to check different ways of waterproofing later but I’m not sure if there’s any adverse effects in terms of chemical interaction with the components or issues with thermal dissipation and all of that. When I get into researching that I’m sure there’s going to be a lot of info to look at.

Gadget Reboot tx and tx in advance.

Experimenting would be best, it would depend how it holds moisture, if it's uniform enough and stays distributed similar to soil. Since the sensor can detect levels for completely dry air and a wet glass of water, as long as there's some amount of moisture around it, it could work after some observation of the output levels between wet and dry material it's in.

The capacitive sensor operates on the dielectric properties of the medium rather than the electrical conductivity but similarly I’m sure the dielectric of soil is going to be different from air or water so the sensor would need to be calibrated probably even in different sections of a landscape where some might have clay soil and some might be store-bought potted soil mix. Now that it is summer here again I plan to continue the experiments so hopefully more will be learned.

@@GadgetReboot Thank you for your answer. May I ask something else? I tried to understand how the capacitive sensor works but I really can't make it; if it deppends on the medium, how putting a plastic bag around doesn't prevent it from obtaining the humidity? When I search for capacitors I get the classic picture of 2 plates with a dieletric in between, but this sensor has only one probe. Shouldn't the soil be somewhere between the plates?

The electric field between the two plates consists of two sections. The first is directly side-by-side flat on the board which is what you are familiar with, you just have the two copper strips beside each other and there is air in between and whatever coating on the circuitboard, but then there’s the other electric field radiating actually out of the board from one conductor in a semi circle coming back to the other, similar to the lines of flux on a magnetic field diagram radiating out in circles away from one part of the structure and coming back to another part of the system. And that’s where the soil gets to interfere with that portion of the electric field radiating out from one plate and being obstructed as it tries to return to the other plate, changing the dielectric properties.

The sensor output can go to the 5 V Arduino analog input.

Using DuPont jumpers and alligator clips, I had the meter on the analog sensor output and ground and taped it so it wouldn’t fall apart while transporting.

@@GadgetReboot thank you too much

the 555 has all kinds of different variations from different manufacturers and they all may have different maximum frequencies, and the frequency on the PCB version of a circuit might be better performing than a breadboard version in general as frequencies increase, so it’s hard to say if there’s anything that can be done on the bread Board to match the PCB performance even if the same version of 555 chip is used. www.quora.com/What-is-the-range-of-output-frequency-for-a-555-timer-IC

Gadget Reboot Thank you for your answer!

The sensor has a 3.3 V regulator so it takes 5 V in but then runs lower.

@@GadgetReboot Yes i see, but how much lower? The regular output it 3.3v volt ,and the output 555 in leg 3 also 3.3v ,so it should be little higher

With 5 V power, the 555 power is 3.3, output dry is 2.8, output wet is 1.5.

In case I still wanted to be able to probe any of the components while testing and evaluating. I’m going to be using that probe again soon actually and I plan to enclose the electronics in another container that might also have a battery and other things like ESP 8266 and that should be sealed to protect everything that is above ground for the experiment.

Yeah it may not be linear but I just look for empirical thresholds that work in different settings such as indoor potted vs outdoor in ground and trigger a watering session. I am planning more follow-up experiments, this one was just more getting started with using the sensor.