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One winter evening I was walking around the Internet looking for a diagram of a soil moisture sensor, and I saw this diagram and I liked it because of its simplicity.

I modified it a little and this is what happened

I routed the tracks to " ", etched the board, soldered the parts and connected the power. I tried to touch contacts D1 D2, the relay clicked, turning the variable made sure that the sensitivity was changing. It seemed like everything needed to calm down, but I remembered that I once took apart a VCR and found what I thought were two resistances (I was not mistaken). Having dug up these resistors in a pile of radio components, I tried to connect one of them and see what happens. By rotating the variable, I made the circuit react to the steam coming from the mouth. You breathe on the sensor and the relay is activated, thus creating an air humidity sensor.

The circuit is very simple with available parts (except for the humidity resistance from the VCR). The device can be used to turn on ventilation in the bathroom, open a window in a greenhouse or greenhouse, and if you replace the resistance with two electrodes, you can automatically turn on watering of plants.

The following parts are used during assembly:

Variable resistor 100 kOhm type R3296; Capacitors 0.022 µF ceramic or film, 220 µF x 16V electrolyte, 470 µF x 25V electrolyte; Resistance 10 kOhm 0.125 W; Transistor KT315 with any letter indexor any analogue of it, for example BC847 ; Diode 1N4007 or any other similar diode; Voltage stabilizer LM7809 (9B) or any other similar; Relay LEG-12 or any other at 12V and the same pin arrangement; Microcircuit K176LA7 or K561LA7 or CD4011 or any of its analogues, the difference between the microcircuits is in the supply voltage;

When using K561LA7 and CD4011 microcircuits instead LM7809 need to install jumper and 12V relay.

If a microcircuit will be used K176LA7, then instead of a jumper (you can see the red jumper between the electrolytes in the photo), you need to solder a stabilizer according to the circuit, since the power supply for this microcircuit is a maximum of 9V. You also need to install a 9V relay instead of a 12V relay.

This is what happened to me

The circuit is adjusted by rotating the variable resistance R1 100 kOhm.

List of radioelements

16.04.2014

Determining quantitative indicators of the humidity of gaseous media, liquids, solids and granular bodies is a sought-after task for almost all areas of industry, economic and scientific activity, and various types of production. All methods for determining humidity indicators are divided into direct and indirect. The direct method involves the direct separation of dry matter in the material under study from moisture. The principle of indirect methods is to measure physical quantities that have a functional relationship with the moisture content of a substance or material.

The need to continuously measure, monitor and regulate the moisture content in various substances has contributed to the development and development of compact sensor devices - moisture sensors. They have greatly facilitated the process of round-the-clock detection of the concentration of water molecules in the analyzed material. Modern touch sensors must meet a number of requirements: in addition to high accuracy, sensitivity and speed of operations, these devices must have a wide measuring range, coverage of several orders of magnitude of the analyzed quantity, and stability of readings.

Sensor Applications

Measuring humidity indicators is necessary in such areas of activity as:

• chemical production;
• fuel transportation;
• pharmaceuticals;
• polymerization;
• livestock farming;
• product storage;
• maintenance of refrigeration and freezer chambers;
• timber processing industry;
• work of food shops;
• agricultural industry, etc.

Types of humidity sensors

Humidity sensors are classified according to various criteria, for example:

• state of aggregation and structural features of the material to be analyzed;
• conditions and mode of operation - there are sensors for continuous and discrete control and measurement activities;
• the method of taking measurements - the sensors are of flow-through and submersible types;
• method for determining humidity indicators.

The last criterion contributed to the identification of two large groups that are in high demand: sorption and sorption-impedance sensors.

Sorption humidity sensors

To determine and control minor moisture concentrations, sorption-type sensors are used, the measurement principle of which is based on piezosorption and sorption-impedance monitoring methods.

The main functional element of such sensors is a sorption layer, which, upon contact with the research environment, is capable of absorbing water vapor. Often this layer is played by a polymer film or material based on highly porous inorganic oxides.

The higher the dimensional characteristics of the internal cavities of the material, the more efficient the sensor based on it is. Therefore, the optimal analyzing elements are porous and mesoporous materials. It is important to note that an increase in the moisture sensitivity of sensors using such material may also be accompanied by an increase in the error of the measurements taken. In this regard, the development and production of humidity sensors requires special control and adherence to technologies for forming the sensitive element.

Sorption sensors used to monitor the humidity of various environments can have a “sandwich” structure. The sensor is manufactured on substrates made of glass-crystalline material or polycor filler. The electrodes are made of nickel with vanadium coating. The sensitive hydrophilic layer is represented by a special nanostructured film of polymers; its formation occurs using a special technique. A particularly thin gold coating is applied to the layer of the resulting dielectric film (the membranes of this film are capable of selectively transmitting water molecules), which takes on the functionality of the second electrode. The direct arrangement of contacts at the level of the lower electrode ensures reliable design. The time constant matters:

• for a relative humidity sensor – 1-2 s;
• for a microhumidity sensor - from 10 to 180 s, such a wide range is determined by the dependence on the level of the studied moisture concentration.

A special thermal treatment technology for the humidity sensor helps reduce the device error to 2%.

Sandwich type humidity sensor:

1. Sensor base;

2. Bottom electrodes;

3. Sorbent film;

4. Top electrode.

The operation of humidity sensors often involves the use of temperature meters. This helps improve the accuracy of environmental studies, ensure correct conversion of units of measurement and obtain the most accurate values ​​of absolute and relative humidity.

A special role is given to relative humidity sensors when monitoring the atmosphere, climate of industrial premises and residential buildings. Also, the operation of hydrometeorological equipment, including probes, is essential without these sensors.

Sensors used to monitor microhumidity parameters are in demand when studying extremely pure active gases and their media (an example is argon or oxygen). Therefore, electronics industries, laboratory buildings, etc. cannot do without such measuring equipment.

Sorption-impedance sensors

Sorption-impedance sensors help determine the moisture concentration in various environments. The advantages of these humidity monitoring devices are:

• high sensitivity rates;
• simple manufacturing technology;
• compactness of the product.

The operation of such a sensor is based on the dependence of the complex resistance of the sorption layer on the volume of moisture absorbed by it. Such humidity sensors can have two design options:

• the above-described “sandwich” structure;
• with planar placement of electrodes, often have a comb shape.

The calibration characteristics of sorption-impedance humidity measuring instruments depend on the sorption material. Initially, hygroscopic ion-forming additives in the form of salts (such as lithium chloride, beryllium fluoride, etc.) acted as a sorption layer. Measuring sensors of this type are characterized by shortcomings - low stability of indicators, less sensitivity and a high probability of errors.

Based on this, modern manufacturers rarely use ion-forming salts as an independent moisture-receptive agent. Hygroscopic salt has acquired an auxiliary role in the production of sensors - it is used as an impregnation material or additive to increase moisture sensitivity. The main application in various fields is impedance meters with polymer sorbents (both organic and inorganic) based on metal oxides. The coating can be thin-film or thick-film.

The process of improving humidity sensors

In both domestic and foreign production of humidity sensors, an effective direction of development is visible - the development of innovative moisture-sensitive compositions. In general, this industry is characterized by the following features:

• the inevitable transition to group planar microelectronic production technology (both thin-film and thick-film are used);
• creation of multitasking devices, for example, integrated temperature and humidity sensors. The operation of such sensors not only helps to increase the accuracy of the measurements taken, but also leads to a simplification of the process of their calibration;
• bringing to a unified design system of humidity sensors, as well as signal processing facilities against the backdrop of the widespread use of microprocessors.

The existence of a wide variety of models of humidity sensors can be explained by the fact that none of them is universal. Each type of sensor has its own specifics, has advantages and disadvantages, which means the choice of device should take into account the characteristics of its application.

Humidity monitoring with EXIS instrumentation

Based on manufactured humidity sensors, Ecological Sensors and Systems JSC develops automated multi-channel systems, as well as stationary and mobile versions of control and measuring instruments. The latter are used for monitoring relative humidity and temperature indicators (devices of the IVTM-7 line), in studies of microhumidity of gases (IVG-1 line).

It is worth noting that in publications for scientific research and technical purposes, the concept of a humidity sensor implies devices that contain a moisture-sensitive element (sensor) and an electrical circuit for receiving and converting the signal from the sensor into the required value. This is why monitoring devices are often called sensors.

The devices being developed are used in solving problems in production conditions, providing conditions for comfortable and safe work for workers in various industrial fields. An example is the use of measuring instruments in electronics, chemical plants, nuclear power plants, etc.

The manufactured devices have all the necessary characteristics for combining devices into a common measuring network. The configuration of such a network may include multi-channel and single-channel devices, network and portable models, and measuring transducers. The operation of innovative measuring systems is characterized by a distributed control scheme, remote control (including via the Internet) and other modern technologies for control and measurement activities.

This simple homemade device is used for water or other liquid, in various rooms or containers. For example, these sensors are very often used to detect possible flooding of the basement or cellar with melt water or in the kitchen under the sink, etc.

The role of the humidity sensor is performed by a piece of foil fiberglass with grooves cut into it, and as soon as water gets into them, the machine will disconnect the load from the network. Or if we use the rear contacts, the automatic relay will turn on the pump or the device we need.

We manufacture the sensor itself in exactly the same way as in the previous diagram. If liquid gets on the contacts of the F1 sensor, the sound alarm will begin to emit a constant sound signal, and the HL1 LED will also light up.

Using the SA1 toggle switch, you can change the order of the HL1 indication to a continuous LED glow in standby mode.

This humidity sensor circuit can be used as a rain detector, overflow of a liquid container, water leakage, etc. The circuit can be powered from any five-volt DC power source.

The source of the sound signal is a sound emitter with a built-in sound generator. The humidity sensor is made from a strip of foil PCB with a thin track in the foil. If the sensor is dry, the sound signal does not signal. If the sensor gets wet, we will immediately hear an intermittent alarm signal.

The design is powered by a Krona battery and will last for two years, because during standby mode, the circuit consumes almost zero current. Another bonus of the circuit is the fact that almost any number of sensors can be connected parallel to the input and thus cover the entire controlled area at a time. The detector circuit is built on two 2N2222 type transistors connected in a Darlington manner."

R1, R3 - 470K
SW1 - button
R2 - 15k
SW2 - switch
R4 - 22K
B1 - crown type battery
C1 - capacitor with a capacity of 0.022 µF
T1, T2 - input terminals
PB1 - (RS273-059) piezo buzzer
Q1, Q2 - 2N2222 type transistors

When the first transistor opens, it immediately unlocks the second, which turns on the piezo buzzer. In the absence of liquid, both transistors are securely off and very low current is consumed from the battery. When the buzzer is turned on, the current consumption increases to 5 mA. Sound emitters of type RS273-059 have a built-in generator. If a more powerful alarm is needed, connect several buzzers in parallel or use two batteries.

We manufacture printed circuit boards with dimensions of 3*5 cm.

The test toggle switch connects a 470 kOhm resistance to the input, simulating the action of a liquid, thereby checking the functionality of the circuit. Transistors can be replaced with domestic ones, such as KT315 or KT3102.

An automatic humidity sensor is designed to turn on forced ventilation of a room at high air humidity; it can be installed in the kitchen, bathroom, cellar, basement, garage. Its purpose is to turn on the fans for forced ventilation of the room when the humidity in it approaches 95... 100%.

The device is highly economical, reliable, and its simplicity of design makes it easy to modify its components to suit specific operating conditions. The diagram of the humidity sensor is shown in the figure below.

The scheme works as follows. When the air humidity in the room is normal, the resistance of the dew sensor - gas resistor B1 does not exceed 3 kOhm, transistor VT2 is open, the powerful high-voltage field-effect transistor VT1 is closed, the primary winding of transformer T1 is de-energized. The load connected to the XP1 connector will also be de-energized.

As soon as the air humidity approaches the point of dew, for example, a boil left unattended, the bathroom is filled with hot water, the cellar is flooded with melted water, groundwater, the thermostat of the water heater has failed, the resistance of the gas resistor B1, the sharp alternating current is removed from the secondary winding T1 and supplied to the bridge diode rectifier VD2. Rectified voltage ripples are smoothed out by a high-capacity oxide capacitor C2. The parametric DC voltage stabilizer is built on a composite transistor VT3 with a high base current transfer coefficient of the KT829B type, a zener diode VD5 and a ballast resistor R6.

Capacitors SZ, C4 reduce output voltage ripple. Fans with an operating voltage of 12...15V, for example, “computer” fans, can be connected to the output of the voltage stabilizer. Fans with a total power of up to 100 W, designed for a supply voltage of 220 VAC, can be connected to the XP1 socket. A bridge rectifier VD1 is installed in the open supply circuit of the step-down transformer T1 and the high-voltage load. A pulsating DC voltage is supplied to the drain of the field-effect transistor. The cascade on transistors VT1, VT2 is powered by a stabilized voltage of +11 V, set by the zener diode VD7. The voltage is supplied to this zener diode through the chain R2, R3, VD4, HL2. This circuit design allows the field-effect transistor to be opened completely, which significantly reduces the power dissipated on it.

Transistors VT1, VT2 are included as a Schmitt trigger, which prevents the field-effect transistor from being in an intermediate state, which prevents it from overheating. The sensitivity of the humidity sensor is set by trimming resistor R8, and, if necessary, by selecting the resistance of resistor R7. Varistors RU1 and RU2 protect device elements from damage by network voltage surges. The green LED HL2 indicates the presence of supply voltage, and the red LED HL1 signals high humidity and the device is switched to forced ventilation mode.

You can connect up to 8 low-voltage fans with a current consumption of up to 0.25 A each to the device and, or several fans with a supply voltage of 220 V. If using this device it is necessary to control a more powerful load with a supply voltage of 220 V, then to the output voltage stabilizer, you can connect electromagnetic relays, for example, type G2R-14-130, the contacts of which are designed for switching alternating current up to 10 A at a voltage of 250 V. In parallel with resistor R8, you can install a thermistor with negative TCR, resistance 3.3...4, 7 kOhm at 25°C, placed, for example, above a gas or electric stove, which will allow you to turn on the ventilation also when the air temperature rises above 45...50 °C, when the stove burners are operating at full power.

In place of transformer T1, you can install any step-down transformer with an overall power of at least 40 W, the secondary winding of which is designed for a current value not less than the current of the low-voltage load. Without rewinding the secondary winding “Yunost”, “Sapphire”. Unified transformers TPP40 or TN46-127/220-50 are also suitable. When making a transformer yourself, you can use an W-shaped magnetic core with a cross-section of 8.6 cm2. The primary winding contains 1330 turns of wire with a diameter of 0.27 mm.

Secondary winding 110 turns of winding wire with a diameter of 0.9 mm. Instead of the KT829B transistor, any of the KT829, KT827, BDW93C, 2SD1889, 2SD1414 series will do. This transistor is installed on a heat sink, the size of which will depend on the load current and the magnitude of the collector-emitter voltage drop VT3. It is advisable to choose a heat sink with which the temperature of the VT3 transistor body would not exceed 60°C.

If the voltage on the plates of capacitor C2 with a load connected to the output of the stabilizer is more than 20 V, then to reduce the power dissipated by VT3, you can unwind several turns from the secondary winding of the transformer. The field effect transistor IRF830 can be replaced with KP707V2, IRF422, IRF430, BUZ90A, BUZ216. When installing this transistor, it must be protected from breakdown by static electricity. Instead of SS9014, you can use any of the KT315, KT342, KT3102, KT645, 2SC1815 series. When replacing bipolar transistors, take into account the differences in pinouts.

KBU diode bridges can be replaced with similar ones KVR08, BR36, RS405, KBL06. Instead of 1N4006, you can use 1N4004 - 1N4007, KD243G, KD247V, KD105V. Zener diodes: 1N5352 - KS508B, KS515A, KS215Zh; 1N4737A - KS175A, KS175Zh, 2S483B; 1 N4741A - D814G, D814G1, 2S211ZH, KS221V.

LEDs can be of any general use, for example, AL307, KIPD40, L-63 series. Oxide capacitors are imported analogs of K50-35, K50-68. Varistors - any low or medium power for a classified operating voltage of 430 V, 470 V, for example, FNR-14K431, FNR-10K471. The gas resistor GZR-2B, sensitive to air humidity, was taken from an old domestic video recorder “Electronics VM-12”. A similar gas resistor can be found in other faulty domestic and imported VCRs or in old cassette video cameras. This gas resistor is usually bolted to the metal chassis of the tape drive. Its purpose is to block the operation of the device when the tape mechanism fogs up, which prevents the magnetic tape from wrapping and damaging. The device can be mounted on a printed circuit board measuring 105x60 mm. It is preferable to place the gas resistor in a separate box made of insulating material with holes, installed in a cooler place. It is also recommended to screw it to a small metal plate, perhaps through a thin mica insulating spacer. To protect the mounted board from moisture, the mounting and printed conductors are coated with several layers of FL-98, ML-92 varnish or tsaponlac.

There is no need to paint over the gas resistor. To check the device’s functionality, you can simply exhale air from your lungs onto the gas resistor or bring a container of boiling water closer. After a few seconds, the HL1 LED will flash and the fans connected as loads will begin to fight the increased humidity. In standby mode, the device consumes current from the network about 3 mA, which is very little. Since the device consumes less than 1 W of power in standby mode, it can be operated around the clock without worrying about power consumption. Since the device is partially galvanically connected to the 220 V AC mains voltage, appropriate precautions should be taken when setting up and operating the device.

As a result of numerous experiments, this soil sensor circuit appeared on one single chip. Any of the microcircuits will do: K176LE5, K561LE5 or CD4001A.

The air humidity sensor, the diagram and drawings of which are attached, makes it possible to fully automate the process of monitoring and managing the relative humidity of the air in any room. This humidity sensor circuit makes it possible to measure relative humidity in the range from 0–100%. With very high accuracy and stability of parameters

Light and sound alarm for water boiling. - Radio, 2004, No. 12, pp. 42, 43.
. - Circuitry, 2004, No. 4, pp. 30-31.
Constant" in the cellar. - CAM, 2005, No. 5, pp. 30, 31.

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.

Andrey Povny