A soil moisture sensor will help you get rid of monotonous repetitive work, and a soil moisture sensor will help you avoid excess water - it’s not that difficult to assemble such a device with your own hands. The laws of physics come to the aid of the gardener: moisture in the soil becomes a conductor of electrical impulses, and the more there is, the lower the resistance. As humidity drops, resistance increases and this helps track optimal time glaze.
The design of the soil moisture sensor consists of two conductors that are connected to a weak energy source; a resistor must be present in the circuit. As the amount of moisture in the space between the electrodes increases, the resistance decreases and the current increases.
The moisture dries - the resistance increases, the current decreases.
Since the electrodes will be in a humid environment, it is recommended to turn them on via a key to reduce the destructive effects of corrosion. During normal times, the system is turned off and only starts up to check the humidity by pressing a button.
Soil moisture sensors of this type can be installed in greenhouses - they provide control over automatic watering, so the system can function without human intervention at all. In this case, the system will always be in working condition, but the condition of the electrodes will have to be monitored so that they do not become unusable due to corrosion. Similar devices can be installed on garden beds and lawns in the open air - they will allow you to instantly obtain the necessary information.
In this case, the system turns out to be much more accurate than simple tactile sensation. If a person considers the soil to be completely dry, the sensor will show up to 100 units of soil moisture (when assessed in the decimal system), immediately after watering this value increases to 600-700 units.
After this, the sensor will allow you to monitor changes in moisture content in the soil.
If the sensor is intended to be used outdoors, it is advisable to carefully seal its upper part to prevent information distortion. To do this, it can be coated with waterproof epoxy resin.
The sensor design is assembled as follows:
- The main part is two electrodes, the diameter of which is 3-4 mm, they are attached to a base made of textolite or other material protected from corrosion.
- At one end of the electrodes you need to cut a thread, on the other side they are made pointed for more comfortable diving into the ground.
- Holes are drilled in the PCB plate into which the electrodes are screwed; they need to be secured with nuts and washers.
- Outgoing wires need to be placed under the washers, after which the electrodes are insulated. The length of the electrodes that will be immersed in the ground is about 4-10 cm, depending on the container or open bed used.
- To operate the sensor, a current source of 35 mA is required; the system requires a voltage of 5V. Depending on the amount of moisture in the soil, the range of the returned signal will be 0-4.2 V. Resistance losses will demonstrate the amount of water in the soil.
- The soil moisture sensor is connected via 3 wires to the microprocessor; for this purpose, you can purchase, for example, Arduino. The controller will allow you to connect the system to a buzzer to sound a signal when soil moisture decreases excessively, or to an LED, the brightness of the lighting will change with changes in the operation of the sensor.
This homemade device can become part of automatic watering in the Smart Home system, for example, using the MegD-328 Ethernet controller. The web interface shows the humidity level in a 10-bit system: the range from 0 to 300 indicates that the ground is completely dry, 300-700 - there is enough moisture in the soil, more than 700 - the ground is wet and no watering is required.
The design, consisting of a controller, relay and battery, is removed into any suitable housing, for which any plastic box can be adapted.
At home, using such a humidity sensor will be very simple and at the same time reliable.
The application of a soil moisture sensor can be very diverse. They are most often used in automatic watering systems and manual watering of plants:
- They can be installed in flower pots, if plants are sensitive to the water level in the soil. When it comes to succulents, such as cacti, it is necessary to select long electrodes that will respond to changes in humidity levels directly at the roots. They can also be used for other fragile plants. Connecting to an LED will allow you to accurately determine when it is time to carry out.
- They are indispensable for organizing watering of plants. Using a similar principle, air humidity sensors are also assembled, which are needed to put the plant spraying system into operation. All this will allow you to automatically water the plants and normal level atmospheric humidity.
- At the dacha, the use of sensors will allow you not to remember the time of watering each bed; electrical engineering itself will tell you about the amount of water in the soil. This will prevent overwatering if it has recently rained.
- The use of sensors is very convenient in some other cases. For example, they will allow you to control soil moisture in the basement and under the house near the foundation. In an apartment, it can be installed under the sink: if the pipe starts to drip, the automation will immediately report this, and flooding of neighbors and subsequent repairs can be avoided.
- A simple sensor device will allow you to fully equip everything with a warning system in just a few days. problem areas home and garden. If the electrodes are long enough, they can be used to control the water level, for example, in an artificial small reservoir.
Making your own sensor will help you equip your home automatic system control at minimal cost.
Factory-made components can be easily purchased via the Internet or in a specialized store; most of the devices can be assembled from materials that can always be found in the home of an electrical engineering enthusiast.
More information can be found in the video.
Arduino Soil Moisture Sensor designed to determine the moisture content of the soil in which it is immersed. It allows you to find out about insufficient or excessive watering of your household or garden plants. Connecting this module to the controller allows you to automate the process of watering your plants, garden or plantation (a kind of “smart watering”).
The module consists of two parts: a YL-69 contact probe and a YL-38 sensor, wires for connection are included. A small voltage is created between the two electrodes of the YL-69 probe. If the soil is dry, the resistance is high and the current will be less. If the ground is wet, the resistance is less, the current is a little more. According to the final analog signal you can judge the degree of humidity. The YL-69 probe is connected to the YL-38 sensor via two wires. In addition to the contacts for connecting to the probe, the YL-38 sensor has four contacts for connecting to the controller.
- Vcc – sensor power supply;
- GND – ground;
- A0 - analog value;
- D0 – digital value of the humidity level.
Module Specifications
- Supply voltage: 3.3-5 V;
- Current consumption 35 mA;
- Output: digital and analog;
- Module size: 16×30 mm;
- Probe size: 20×60 mm;
- Total weight: 7.5 g.
Usage example
Let's consider connecting a soil moisture sensor to Arduino. Let's create a project for soil moisture level indicator for indoor plant(your favorite flower that you sometimes forget to water). To indicate the level of soil moisture we will use 8 LEDs. For the project we will need the following parts:- Arduino Uno board
- Soil moisture sensor
- 8 LEDs
- Bread board
- Connecting wires.
Let's launch the Arduino IDE. Let's create a new sketch and add the following lines to it: // Soil moisture sensor // http://site // contact for connecting the analog output of the sensor int aPin=A0; // contacts for connecting indication LEDs int ledPins=(4,5,6,7,8,9,10,11); // variable to save the sensor value int avalue=0; // variable for the number of glowing LEDs int counted=8; // value of full watering int minvalue=220; // critical dryness value int maxvalue=600; void setup() ( // initializing the serial port Serial.begin(9600); // setting up the LED indication pins // to OUTPUT mode for(int i=0;i<8;i++) { pinMode(ledPins[i],OUTPUT); } } void loop() { // получение значения с аналогового вывода датчика avalue=analogRead(aPin); // вывод значения в монитор последовательного порта Arduino Serial.print("avalue=";Serial.println(avalue); // scale the value by 8 LEDs counted=map(avalue,maxvalue,minvalue,0.7); // indication of the humidity level for(int i=0;i<8;i++) ( if(i<=countled) digitalWrite(ledPins[i],HIGH); //light the LED else digitalWrite(ledPins[i],LOW) ; // turn off the LED ) // pause before the next value is received 1000 ms delay(1000); ) The analog output of the sensor is connected to the analog input of the Arduino, which is an analog-to-digital converter (ADC) with a resolution of 10 bits, which allows the output to obtain values from 0 to 1023. The value of the variables for complete watering (minvalue) and severe dry soil (maxvalue ) we obtain experimentally. Greater soil dryness corresponds to a larger analog signal value. Using the map function, we scale the analog value of the sensor to the value of our LED indicator. The higher the soil moisture, the higher the LED indicator value (number of lit LEDs). By connecting this indicator to a flower, we can see the degree of humidity on the indicator from a distance and determine the need for watering.
Frequently asked questions FAQ
1. Power LED does not light up- Check the presence and polarity of the power supplied to the YL-38 sensor (3.3 - 5 V).
- Adjust the response threshold using the potentiometer. Check the connection of the YL-38 sensor with the YL-69 probe.
- Check the connection of the YL-38 sensor with the YL-69 probe.
- Check for the presence of a probe in the ground.
The device that measures humidity levels is called a hygrometer or simply a humidity sensor. In everyday life, humidity is an important parameter, and often not only for ordinary life itself, but also for various equipment, and for agriculture (soil moisture) and much more.
In particular, our well-being depends a lot on the degree of air humidity. Particularly sensitive to humidity are weather-dependent people, as well as people suffering from hypertension, bronchial asthma, and diseases of the cardiovascular system.
When the air is very dry, even healthy people feel discomfort, drowsiness, itching and irritation of the skin. Often, dry air can provoke diseases of the respiratory system, starting with acute respiratory infections and acute respiratory viral infections, and even ending with pneumonia.
In enterprises, air humidity can influence the safety of products and equipment, and in agriculture, the influence of soil moisture on fertility, etc. is clear. This is where the use of humidity sensors - hygrometers.
Some technical devices are initially calibrated to a strictly required value, and sometimes in order to fine-tune the device, it is important to have the exact value of humidity in the environment.
Humidity can be measured by several of the possible quantities:
To determine the humidity of both air and other gases, measurements are carried out in grams per cubic meter when talking about the absolute value of humidity, or in RH units when talking about relative humidity.
For measuring the humidity of solids or liquids, measurements as a percentage of the mass of the test samples are suitable.
To determine the moisture content of poorly mixed liquids, the units of measurement will be ppm (how many parts of water are in 1,000,000 parts of the weight of the sample).
According to the principle of operation, hygrometers are divided into:
capacitive;
resistive;
thermistor;
optical;
electronic.
Capacitive hygrometers, in their simplest form, are capacitors with air as a dielectric in the gap. It is known that the dielectric constant of air is directly related to humidity, and changes in the humidity of the dielectric lead to changes in the capacitance of the air capacitor.
A more complex version of the capacitive humidity sensor in the air gap contains a dielectric with a dielectric constant that can vary greatly under the influence of humidity. This approach makes the sensor quality better than simply having air between the capacitor plates.
The second option is well suited for making measurements regarding the water content of solids. The object under study is placed between the plates of such a capacitor, for example, the object can be a tablet, and the capacitor itself is connected to an oscillatory circuit and to an electronic generator, while the natural frequency of the resulting circuit is measured, and from the measured frequency the capacitance obtained by introducing the test sample is “calculated.”
Of course, this method also has some disadvantages, for example, if the sample humidity is below 0.5%, it will be inaccurate, in addition, the sample being measured must be cleared of particles with high dielectric constant, and the shape of the sample is also important during the measurement process; it should not change during the course of the study.
The third type of capacitive humidity sensor is the capacitive thin film hygrometer. It includes a substrate on which two comb electrodes are applied. In this case, comb electrodes play the role of plates. For the purpose of temperature compensation, two additional temperature sensors are additionally introduced into the sensor.
Such a sensor includes two electrodes that are deposited on a substrate, and on top of the electrodes themselves is applied a layer of material that has a fairly low resistance, which, however, varies greatly depending on humidity.
Aluminum oxide may be a suitable material for the device. This oxide absorbs water well from the external environment, while its resistivity changes noticeably. As a result, the total resistance of the measurement circuit of such a sensor will depend significantly on humidity. Thus, the level of humidity will be indicated by the amount of current flowing. The advantage of sensors of this type is their low price.
A thermistor hygrometer consists of a pair of identical thermistors. By the way, let us recall that this is a nonlinear electronic component, the resistance of which strongly depends on its temperature.
One of the thermistors included in the circuit is placed in a sealed chamber with dry air. And the other is in a chamber with holes through which air with characteristic humidity enters it, the value of which needs to be measured. The thermistors are connected in a bridge circuit, voltage is applied to one of the diagonals of the bridge, and readings are taken from the other diagonal.
In the case when the voltage at the output terminals is zero, the temperatures of both components are equal, therefore the humidity is the same. If a non-zero voltage is obtained at the output, this indicates the presence of a humidity difference in the chambers. Thus, the humidity is determined from the value of the voltage obtained during measurements.
An inexperienced researcher may have a fair question: why does the temperature of the thermistor change when it interacts with moist air? The thing is that as humidity increases, water begins to evaporate from the thermistor body, while the temperature of the body decreases, and the higher the humidity, the more intense the evaporation occurs, and the faster the thermistor cools.
4) Optical (condensation) humidity sensor
This type of sensor is the most accurate. The operation of an optical humidity sensor is based on a phenomenon related to the concept of “dew point”. At the moment the temperature reaches the dew point, the gaseous and liquid phases are in thermodynamic equilibrium.
So, if you take glass and install it in a gaseous environment, where the temperature at the time of research is above the dew point, and then begin the process of cooling this glass, then at a specific temperature value, water condensation will begin to form on the surface of the glass, this water vapor will begin to transform into the liquid phase . This temperature will be the dew point.
So, the dew point temperature is inextricably linked and depends on parameters such as humidity and pressure in the environment. As a result, having the ability to measure pressure and dew point temperature, it will be easy to determine humidity. This principle serves as the basis for the functioning of optical humidity sensors.
The simplest circuit of such a sensor consists of an LED shining on a mirror surface. The mirror reflects the light, changing its direction, and directing it to the photodetector. In this case, the mirror can be heated or cooled using a special high-precision temperature control device. Often such a device is a thermoelectric pump. Of course, a sensor is installed on the mirror to measure temperature.
Before starting measurements, the mirror temperature is set to a value that is obviously higher than the dew point temperature. Next, the mirror is gradually cooled. At the moment when the temperature begins to cross the dew point, drops of water will immediately begin to condense on the surface of the mirror, and the light beam from the diode will break due to them, dissipate, and this will lead to a decrease in the current in the photodetector circuit. Through feedback, the photodetector interacts with the mirror temperature controller.
So, based on the information received in the form of signals from the photodetector, the temperature controller will keep the temperature on the surface of the mirror exactly equal to the dew point, and the temperature sensor will indicate the temperature accordingly. Thus, with known pressure and temperature, the main humidity indicators can be accurately determined.
The optical humidity sensor has the highest accuracy, unattainable by other types of sensors, plus the absence of hysteresis. The disadvantage is the highest price of all, plus high energy consumption. In addition, it is necessary to ensure that the mirror is clean.
The operating principle of an electronic air humidity sensor is based on changing the concentration of electrolyte covering any electrical insulating material. There are devices with automatic heating linked to the dew point.
Often the dew point is measured over a concentrated solution of lithium chloride, which is very sensitive to minimal changes in humidity. For maximum convenience, such a hygrometer is often additionally equipped with a thermometer. This device has high accuracy and low error. It is capable of measuring humidity regardless of the ambient temperature.
Simple electronic hygrometers are also popular in the form of two electrodes, which are simply stuck into the soil, controlling its humidity according to the degree of conductivity depending on this very humidity. Such sensors are popular among fans because you can easily set up automatic watering of a garden bed or flower in a pot, in case you don’t have time to water manually or it’s not convenient.
Before you buy a sensor, consider what you will need to measure, relative or absolute humidity, air or soil, what the expected measurement range is, whether hysteresis is important, and what accuracy is needed. The most accurate sensor is optical. Pay attention to the IP protection class, the operating temperature range, depending on the specific conditions where the sensor will be used, and whether the parameters are suitable for you.
The poet Andrei Voznesensky once said: “laziness is the engine of progress.” It is perhaps difficult to disagree with this phrase, because most electronic devices are created precisely for the purpose of making our daily lives easier, full of worries and all sorts of hectic affairs.
If you are reading this article now, then you are probably very tired of the process of watering flowers. After all, flowers are delicate creatures, you overwater them a little, you’re unhappy, you forget to water them for a day, that’s it, they’re about to fade. And how many flowers in the world have died just because their owners went on vacation for a week, leaving the poor green creatures to wither in a dry pot! Scary to imagine.
It is to prevent such terrible situations that automatic watering systems were invented. A sensor is installed on the pot that measures soil moisture - it consists of stainless steel metal rods stuck into the ground at a distance of a centimeter from each other.
They are connected via wires to a circuit whose task is to open the relay only when the humidity drops below the set value and close the relay at the moment when the soil is saturated with moisture again. The relay, in turn, controls the pump, which pumps water from the reservoir directly to the root of the plant.
Sensor circuit
As is known, the electrical conductivity of dry and wet soil differs quite significantly; it is this fact that underlies the operation of the sensor. A 10 kOhm resistor and a section of soil between the rods form a voltage divider; their midpoint is connected directly to the input of the op-amp. The voltage is supplied to the other input of the op-amp from the midpoint of the variable resistor, i.e. it can be adjusted from zero to supply voltage. With its help, the switching threshold of the comparator, in the role of which the op-amp operates, is set. As soon as the voltage at one of its inputs exceeds the voltage at the other, the output will be logical “1”, the LED will light up, the transistor will open and turn on the relay. You can use any transistor, PNP structure, suitable for current and voltage, for example, KT3107 or KT814. Operational amplifier TL072 or any similar one, for example RC4558. A low-power diode, for example, 1n4148, should be placed in parallel with the relay winding. The supply voltage of the circuit is 12 volts.
Due to the long wires from the pot to the board itself, a situation may arise that the relay does not switch clearly, but begins to click at the frequency of the alternating current in the network, and only after some time is set in the open position. To eliminate this bad phenomenon, you should place an electrolytic capacitor with a capacity of 10-100 μF in parallel with the sensor. Archive with the board. Happy building! Author - Dmitry S.
Discuss the article SOIL MOISTURE SENSOR DIAGRAM
Many gardeners and gardeners are deprived of the opportunity to daily care for planted vegetables, berries, and fruit trees due to work pressure or during vacation. However, plants need timely watering. With the help of simple automated systems, you can ensure that the soil on your site maintains the necessary and stable moisture throughout your absence. To build a garden automatic watering system, you will need a main control element - a soil moisture sensor.
Humidity sensor
Humidity sensors are also sometimes called moisture meters or humidity sensors. Almost all soil moisture meters on the market measure moisture using a resistive method. This is not a completely accurate method because it does not take into account the electrolysis properties of the object being measured. The readings of the device may be different at the same soil moisture, but with different acidity or salt content. But for experimental gardeners, the absolute readings of the instruments are not as important as the relative ones, which can be adjusted for the water supply actuator under certain conditions.
The essence of the resistive method is that the device measures the resistance between two conductors placed in the ground at a distance of 2-3 cm from each other. This is normal ohmmeter, which is included in any digital or analog tester. Previously, such instruments were called avometers.
There are also devices with a built-in or remote indicator for operational monitoring of soil conditions.
It is easy to measure the difference in electrical current conductivity before watering and after watering using the example of a pot with a house aloe plant. Readings before watering 101.0 kOhm.
Readings after watering after 5 minutes 12.65 kOhm.
But a regular tester will only show the resistance of the soil between the electrodes, but will not be able to help with automatic watering.
Automation operating principle
In automatic watering systems, the rule is usually “water it or don’t water it.” As a rule, no one needs to regulate the water pressure. This is due to the use of expensive controlled valves and other unnecessary, technologically complex devices.
Almost all humidity sensors on the market, in addition to two electrodes, have a comparator in their design. This is the simplest analog-to-digital device that converts the incoming signal into digital form. That is, at a set humidity level, you will receive one or zero (0 or 5 volts) at its output. This signal will become the source for the subsequent actuator.
For automatic watering, the most rational option would be to use a solenoid valve as an actuator. It is included in the pipe break and can also be used in micro-drip irrigation systems. Turned on by supplying 12 V.
For simple systems operating on the principle “the sensor is triggered - the water flows”, it is sufficient to use the LM393 comparator. The microcircuit is a dual operational amplifier with the ability to receive a command signal at the output at an adjustable input level. The chip has an additional analog output that can be connected to a programmable controller or tester. An approximate Soviet analogue of the LM393 dual comparator is the 521CA3 microcircuit.
The figure shows a ready-made humidity relay along with a Chinese-made sensor for only $1.
Below is a reinforced version, with an output current of 10A at an alternating voltage of up to 250 V, for $3-4.
Irrigation automation systems
If you are interested in a full-fledged automatic watering system, then you need to think about purchasing a programmable controller. If the area is small, then it is enough to install 3-4 humidity sensors for different types of irrigation. For example, a garden needs less watering, raspberries love moisture, and melons need enough water from the soil, except during excessively dry periods.
Based on your own observations and measurements of humidity sensors, you can approximately calculate the cost-effectiveness and efficiency of water supply in areas. Processors allow you to make seasonal adjustments, can use the readings of humidity meters, and take into account precipitation and the time of year.
Some soil moisture sensors are equipped with an RJ-45 interface for network connection. The processor firmware allows you to configure the system so that it will notify you about the need for watering via social networks or SMS messages. This is convenient in cases where it is impossible to connect an automated watering system, for example, for indoor plants.
Convenient to use for irrigation automation system controllers with analog and contact inputs that connect all sensors and transmit their readings via a single bus to a computer, tablet or mobile phone. The actuators are controlled via a WEB interface. The most common universal controllers are:
- MegaD-328;
- Arduino;
- Hunter;
- Toro.
These are flexible devices that allow you to fine-tune your automatic watering system and entrust it with complete control over your garden.
A simple irrigation automation scheme
The simplest irrigation automation system consists of a humidity sensor and a control device. You can make a soil moisture sensor with your own hands. You will need two nails, a 10 kOhm resistor and a power source with an output voltage of 5 V. Suitable from a mobile phone.
A microcircuit can be used as a device that will issue a command for watering LM393. You can purchase a ready-made unit or assemble it yourself, then you will need:
- 10 kOhm resistors – 2 pcs;
- 1 kOhm resistors – 2 pcs;
- 2 kOhm resistors – 3 pcs;
- variable resistor 51-100 kOhm – 1 pc.;
- LEDs – 2 pcs;
- any diode, not powerful - 1 pc.;
- transistor, any average power PNP (for example, KT3107G) – 1 pc.;
- capacitors 0.1 μ – 2 pcs.;
- microcircuit LM393 – 1 piece;
- relay with an operating threshold of 4 V;
- circuit board.
The assembly diagram is presented below.
After assembly, connect the module to the power supply and soil moisture level sensor. Connect a tester to the output of the comparator LM393. Using a construction resistor, set the response threshold. Over time, it will need to be adjusted, perhaps more than once.
The circuit diagram and pinout of the LM393 comparator is presented below.
The simplest automation is ready. It is enough to connect an actuator to the closing terminals, for example, an electromagnetic valve that turns the water supply on and off.
Irrigation automation actuators
The main actuator for irrigation automation is an electronic valve with and without water flow control. The latter are cheaper, easier to maintain and manage.
There are many controlled cranes and other manufacturers.
If there are problems with water supply in your area, purchase solenoid valves with a flow sensor. This will prevent the solenoid from burning out if the water pressure drops or the water supply is cut off.
Disadvantages of automatic irrigation systems
The soil is heterogeneous and differs in its composition, so one moisture sensor can show different data in neighboring areas. In addition, some areas are shaded by trees and are wetter than those located in sunny areas. The proximity of groundwater and its level relative to the horizon also have a significant impact.
When using an automated irrigation system, the terrain of the area should be taken into account. The site can be divided into sectors. Install one or more humidity sensors in each sector and calculate its own operating algorithm for each. This will significantly complicate the system and it will hardly be possible to do without a controller, but subsequently it will almost completely save you from wasting time awkwardly standing with a hose in your hands under the hot sun. The soil will be filled with moisture without your participation.
Building an effective automated irrigation system cannot be based only on the readings of soil moisture sensors. It is imperative to additionally use temperature and light sensors and take into account the physiological need for water of plants of different species. Seasonal changes must also be taken into account. Many companies producing irrigation automation systems offer flexible software for different regions, areas and crops grown.
When purchasing a system with a humidity sensor, do not fall for stupid marketing slogans: our electrodes are coated with gold. Even if this is so, then you will only enrich the soil with noble metal in the process of electrolysis of plates and the wallets of not very honest businessmen.
Conclusion
This article talked about soil moisture sensors, which are the main control element of automatic irrigation. The principle of operation of an irrigation automation system, which can be purchased ready-made or assembled yourself, was also discussed. The simplest system consists of a humidity sensor and a control device, the DIY assembly diagram of which was also presented in this article.