Do-it-yourself room temperature controller. DIY temperature controller: power and load

To ensure the full development of plants in various greenhouses (especially with a year-round growing cycle), automated support is required. temperature regime at a certain level. Formation and adjustment external environment around the plants in the greenhouse is carried out simultaneously by several systems - ventilation, heating, humidifying the air and soil, evaporative cooling, etc. We will tell you how to make a thermostat in the greenhouse for all these systems in this article.

The control of these systems with subsequent adjustment is carried out using an air temperature controller, which is the most important detail to obtain a full-fledged harvest, since even minimal changes in data can adversely affect the development of plantings, not excluding their death.

Scrupulous adherence to the temperature regime is a guarantee of decent harvests

Customization thermostat allows you to control the temperature level throughout the day, stabilizing protective function boiler from overheating.

For most plantations, the most comfortable t is 16 - 25 ° C, any even slight deviations inhibit the development of plants, can lead to the development of diseases and wilting of plantings. Control is necessary not only for the air temperature of the greenhouse, but also for the t of the soil. These two indicators are dominant in creating conditions for the development of plants. The correct assimilation of nutrients in the soil depends on them, and they directly affect the growth and full development of plants.

For soil, one should adhere to the t range of 13 - 25 ° C, its exact indicators are determined depending on the variety of crop.

Please note! Changes in soil temperature are often more detrimental to plantings than a decrease in air temperature.

Fundamentals of the functioning of thermostatic devices

The principle of operation of structures of this type is straightforward: the control device receives a signal, after which different models installations can respond In a similar way:

• increase or decrease power heating system;
• turn on or off the ventilation of the room;
• open or close natural ventilation sashes;
• connect or completely turn off the heating of irrigation water and soil in the beds.

The appearance of signal pulses is carried out using a thermostat relay, which, in turn, receives data from sensors located in the greenhouse. As sensors, the following devices are most often used:

• Thermistor is often used as a temperature sensor. In home-made installations, a p-n junction of a semiconductor transistor or diode is often used as a temperature-sensitive element.
• A photoresistor is used as a light sensor, and in self-made designs, a p-n junction of a semiconductor transistor or diode can be used again, in which the reverse resistance directly depends on the illumination. To gain light access to the system, a cap is cut off from the transistor. metal case, and the paint is removed from the glass of the diode.

• Humidity parameters are regulated by industrial sensors, the indicators of which depend on the moisture permeability of the medium located between the capacitor plates. Changes in resistance during interaction with humidified air of aluminum oxide can also be taken into account. When adjusting air humidity, the result of a change in the length of a synthetic fiber or a human hair, etc. is also taken into account. For home-made devices, a similar sensor is a piece of foil fiberglass with cut grooves.

For your information! For small greenhouses personal use from the point of view of economy, it is absolutely unprofitable to purchase an expensive system of industrial design. In such situations, do-it-yourself thermostats for greenhouses are successfully introduced.

Do-it-yourself principles of a thermostat for a greenhouse

Self built temperature controller completely real challenge. But this will require elementary engineering knowledge and technical skills.

The main functioning of the system is carried out due to the introduction into the design of an 8-bit microcontroller of the PIC16F84A brand.

As a temperature sensor, a digital thermometer of the integral type DS18B20 is built in, which has an operating functionality in the range of t -55 - + 125 ° C. It is also possible to use a digital temperature sensor TCN75-5.0, which, in terms of parameters, compact size and relative lightness of design, is quite suitable for use in various automatic devices Oh.

Similar digital sensors essentially have minor measurement errors, so parallel application several types of sensors allows you to actually observe the heating temperature without errors.

The ability to control the degree of load is carried out using a small-sized type of relay K1, which corresponds to an operating voltage of 12 V. A load is connected to the relay through the contacts and this allows it to switch it. Indication is made using any four-digit LEDs.

The degree of temperature reaction is set: SB1-SB2 (microswitches). The memory of the microcontroller is energy autonomous and stores set parameters. Applying the operating mode on the indicator liquid crystal panel of the device, you can see the current indicators of the measured temperature.

On a note! Such electronic thermostats are becoming more and more popular as they have the ability to sense the temperature at any point inside the greenhouse, and the monitoring sensor can be placed between plants, in the soil substrate, or hung near the roof. Such an extensive range of placement allows the thermostat to have accurate data on the state of the internal environment of the greenhouse.

How to make a thermostat for a greenhouse with your own hands

Craftsmen make simplified thermostats for personal greenhouses with their own hands. Before choosing a greenhouse automation scheme, you must first set the control object data.

The photo shows a thermostat circuit with two transistors of the type VT1 and VT2. As output device relay RES-10 is activated. Temperature sensor - thermistor MMT-4.

One of the models of a do-it-yourself thermostat can be, for example, such a design. In it, as a temperature sensor, you can use a pointer thermometer that has undergone alteration:

• The design of the thermometer is completely disassembled.
• A hole of 2.5 mm is drilled in the regulation scale.
• On the contrary, a phototransistor is installed in a specially designed corner made of thin tin or sheet aluminum, in which holes 0 2.8 mm are pre-drilled. Glue is applied to the phototransistor along the edge and placed in the socket.
• A corner with a phototransistor is attached to the scale with Moment glue.
• A stop is attached below the hole.
• On the other side of the thermometer, a small 9 volt light bulb is installed. A lens is placed between the scale and the bulb - for a clear response of the device to the indicators.
• Thin wires of the phototransistor are laid through the central hole of the scale.
• For the light bulb wires, a hole is drilled in the plastic case. The tourniquet is threaded into a PVC tube and fixed with a clip.

In addition to the sensor, the thermostat must include a photo relay and a voltage stabilizer.

The stabilizer is assembled in the usual way. Photorelay is also not difficult to make. The GT109 transistor serves as a photocell.

A mechanism based on a converted factory relay is best suited. The work is carried out on the principle of an electromagnet, where the armature is drawn into the coil. The switch (2A, 220V) regulates the electrical magnetic switch to supply power to heating devices.

The photorelay and power supplies are placed in a common housing. A thermometer is attached to it. A toggle switch and a light bulb are attached to the front side, indicating the inclusion of heating elements.

Ventilation scheme

If the greenhouse is ventilated with an electric fan, two-position thermostats can be used. For creating desired mode operation of the fan, connect an intermediate relay.

If windows are built into the greenhouse, they must be provided with an electric drive (electromagnets or electric motor mechanisms).

But it is easier to solve the issue of greenhouse ventilation when using direct-acting thermostats. In them actuating mechanism and thermostat are in one device. However, for regulators of this type, the temperature variation can be up to 5 °C. To achieve a more precise adjustment, it is better to choose electronic regulators.

Humidity control

Ideal Solution- use of soil moisture sensors and adjustment of irrigation according to the specified moisture content. One of the principles of moisture measurement is based on taking into account changes in soil volume during moisture. Also often connected electronic regulator. As a humidity sensor, a depolarizer with 3336L battery rods is mounted. At relative humidity, the resistance values ​​​​are somewhere around 1500 ohms. Variable resistor R1 helps the regulator to operate at a certain level, resistor R2 helps to set the initial humidity.

Irrigation regulation

It is very tempting to control the irrigation system electronically, but it must be remembered that it turns out to be more reliable simple devices. Simplified irrigation arrangement is done by hand without the use of electronic circuits. This allows it to be used during power outages.

With electronic regulation of the water supply, an electric solenoid valve is used. The solenoid valve can be made independently. One of the designs can be seen in the photo.

1 - electromagnet; 2 - container; 3 - cargo; 4 - valve

Main disadvantage thermoregulation systems - complete subordination to the power supply source. Power outages can cause plant death. To avoid such misunderstandings, spare power sources are used: generator, solar or accumulator battery etc.

Also remember that all thermostats lose accuracy over time as they get older. Therefore, you need to check their accuracy every year. When checking the functioning of the thermostat, it is necessary to clean the sensors of the thermostat, carefully wipe all the leads and connections.

In everyday life and subsidiary farming, it is often necessary to maintain the temperature regime of a room. Previously, this required a rather huge circuit made on analog elements, we will consider one such circuit for general development. Today, everything is much simpler, if it becomes necessary to maintain the temperature in the range from -55 to + 125 ° C, then the programmable thermometer and thermostat DS1821 can perfectly cope with the goal.

The temperature threshold for switching on and off the thermostat is set by the values ​​TH and TL in the sensor's memory, which must be programmed into the DS1821. If the temperature exceeds the value recorded in the TH cell, the level of a logical unit will appear at the sensor output. For protection against possible interference, the load control circuit is implemented in such a way that the first transistor is locked into that half-wave of the mains voltage when it is equal to zero, thereby applying a bias voltage to the gate of the second field-effect transistor, which turns on the opto-triac, and it already opens the VS1 control load. The load can be any device, such as an electric motor or a heater. The reliability of locking the first transistor must be adjusted by selecting the desired value of the resistor R5.

The DS1820 temperature sensor is capable of detecting temperatures from -55 to 125 degrees and operating in thermostat mode.

If the temperature exceeds the upper threshold TH, then the output of the DS1820 will be a logical unit, the load will turn off the network. If the temperature drops below the lower programmed level TL, then a logical zero will appear at the output of the temperature sensor and the load will be turned on. If there were unclear moments, the home-made design was borrowed from No. 2 for 2006.

The signal from the sensor passes to the direct output of the comparator to operational amplifier CA3130. The inverting input of the same op-amp receives a reference voltage from the divider. variable resistance R4 set the required temperature.

If the potential at the direct input is lower than that set at pin 2, then at the output of the comparator we will have a level of about 0.65 volts, and if vice versa, then at the output of the comparator we will get a high level of about 2.2 volts. The signal from the output of the op-amp through transistors controls the operation of the electromagnetic relay. At high level it turns on, and when low, it turns off, switching the load with its contacts.

TL431 is a programmable zener diode. Used as a voltage reference and power supply for low power circuits. The required voltage level, at the control output of the TL431 microassembly, is set using a divider on resistors Rl, R2 and a negative TCR thermistor R3.

If the voltage on the TL431 control pin is higher than 2.5V, the microcircuit passes current and turns on the electromagnetic relay. The relay switches the control output of the triac and connects the load. As the temperature rises, the resistance of the thermistor and the potential at the control contact TL431 drops below 2.5V, the relay releases its front contacts and turns off the heater.

Using resistance R1, we adjust the level of the desired temperature to turn on the heater. This scheme capable of controlling a heating element up to 1500 watts. The relay is suitable for RES55A with an operating voltage of 10 ... 12 V or its equivalent.

The design of the analog thermostat is used to maintain the set temperature inside the incubator, or in a box on the balcony for storing vegetables in the winter. Meals are organized from car battery at 12 volts.

The design consists of a relay in the event of a temperature drop and turns off when the set threshold rises.

The temperature of the thermostat relay operation is set by the voltage level on pins 5 and 6 of the K561LE5 chip, and the relay off temperature is set by the potential at pins 1 and 21. The temperature difference is controlled by the voltage drop across the resistor R3. In the role of the temperature sensor R4, a thermistor with a negative TCR is used, i.e.

The design is small and consists of only two blocks - a measuring unit based on a comparator based on an op-amp 554CA3 and a load switch up to 1000 W built on a power regulator KR1182PM1.

The third direct input of the op amp receives constant pressure with a voltage divider consisting of resistances R3 and R4. The fourth inverted input is supplied with voltage from another divider at the resistance R1 and the thermistor MMT-4 R2.

The temperature sensor is a thermistor located in a glass flask with sand, which is placed in the aquarium. The main node of the design is the m / s K554SAZ - voltage comparator.

From the voltage divider, which also includes a thermistor, the control voltage goes to the direct input of the comparator. The other comparator input is used to adjust the desired temperature. A voltage divider is made of resistances R3, R4, R5, which form a bridge sensitive to temperature changes. When the temperature of the water in the aquarium changes, the resistance of the thermistor also changes. This creates a voltage imbalance at the comparator inputs.

Depending on the voltage difference at the inputs, the output state of the comparator will change. The heater is made in such a way that when the water temperature drops, the aquarium thermostat automatically starts, and when it rises, on the contrary, it turns off. The comparator has two outputs, collector and emitter. To control a field effect transistor, a positive voltage is required, therefore, it is the collector output of the comparator that is connected to the positive line of the circuit. The control signal is obtained from the emitter terminal. Resistors R6 and R7 are the load output of the comparator.

To turn on and off the heating element in the thermostat, use field-effect transistor IRF840. To discharge the gate of the transistor, there is a diode VD1.

The thermostat circuit uses a transformerless power supply. superfluous AC voltage decreases due to reactance capacity C4.

The basis of the first design of the thermostat is the PIC16F84A microcontroller with a DS1621 temperature sensor with an l2C interface. At the time of power-up, the microcontroller first initializes the internal registers of the temperature sensor, and then configures it. The thermostat on the microcontroller in the second case is already made on the PIC16F628 with the DS1820 sensor and controls the connected load using the relay contacts.

The dependence of the voltage drop on p-n junction semiconductors on temperature, is the best suited for creating our homemade sensor.

The Russian winter is distinguished by its severity and severe cold, which is known to everyone. Therefore, the premises in which people are located must be heated. Central heating is the most common option, and if this is not available, you can use an individual gas boiler. However, it often happens that neither one nor the other is available, for example, in an open field there is a small room of a water pumping station, in which machinists are on duty around the clock. It could be a room in some large uninhabited building or a guard tower. There are enough examples.

Way out

All these cases force the installation of electric heating. With a small room size, it is quite possible to get by with an ordinary electric oil radiator, and in rooms large sizes most often they arrange water heating using a radiator. If you do not monitor the temperature of the water, then sooner or later it may boil, which will cause the entire boiler to fail. To protect against such cases, thermostats are used.

Device Features

In functional terms, the device can be divided into several separate nodes: a comparator, as well as load control devices. All of these parts will be described next. This information is necessary in order to make a thermostat with your own hands. AT this case a design is proposed in which the temperature sensor is a conventional bipolar transistor, thanks to which it is possible to abandon the use of thermistors. This sensor works on the basis of the fact that the parameters of the transistors of all semiconductor devices largely depend on the temperature of the environment.

Important nuances

Creating a thermostat with your own hands should be carried out with the obligatory consideration of two points. First of all, we are talking about the propensity of automatic devices to auto-generation. In the event that too strong a connection is established between the actuator and the thermal relay sensor, after the relay is triggered, it immediately turns off and then turns on again. This will happen when the sensor is in close proximity to a cooler or heater. Secondly, for all sensors and electronic devices there is a certain amount of precision. For example, you can track a temperature of 1 degree, but it is much more difficult to track smaller values. In such a case, simple electronics often start to make mistakes and make mutually exclusive decisions, especially when the temperature is almost equal to that set for operation.

Process of creation

If we talk about how to make a thermostat with your own hands, then it is worth saying that the sensor here is a thermistor that reduces its resistance during the heating process. It is connected to a voltage divider circuit. R2 is also included in the circuit, through which the response temperature is set. From the divider, the voltage is supplied to the 2I-NOT element, which is switched on in the inverter mode, and then to the base of the transistor, which serves as a spark gap for the capacitor C1. It, in turn, is connected to the input (S) of the RS flip-flop, which is assembled on a pair of elements, as well as to the input of another 2I-NOT. From the divider, the voltage is supplied to the input 2I-NOT, which controls the second input (R) of the RS flip-flop.

How it works

So, we are considering how to create a simple thermostat with our own hands, so it is important to understand how it works in different situations. At high temperature thermistors are characterized by low voltage, so there is a voltage on the divider, perceived logic circuits like zero. In this case, the transistor is open, a logical zero is perceived at the input of the S-flip-flop, and the capacitor C1 is discharged. The output of the trigger is set to a logical unit. The relay is in the on mode, and the transistor VT2 is open. To understand exactly how to make a thermostat, it is worth noting that this particular implementation of the relay is focused on cooling the object, that is, it turns on the fan at a high temperature.

Temperature drop

When the temperature drops, the resistance of the thermistor increases, which leads to an increase in the voltage across the divider. At a certain moment, the transistor VT1 closes, after which the charging of the capacitor C1 through R5 begins. In the end, there comes a moment of reaching the level of a logical unit. It is she who enters one of the inputs D4, and the second input given element voltage is supplied from the divider. When logical ones are set at both inputs, and zero appears at the output of the element, the trigger will switch to the opposite state. In this case, the relay will be turned off, which will allow you to turn off the fan, if necessary, or turn on the heating. So you can make a thermostat so that it turns on and off the fan if necessary.

Temperature rise

So the temperature started to rise again. Zero on the divider will first appear at one of the inputs of D4, and it will remove zero at the input of the trigger, changing it to one. Further, as the temperature increases, zero will appear on the inverter. After changing it to one, the transistor will be opened, which will lead to the discharge of the C1 element and the setting of zero at the input of the trigger, which turns off the heating of the coolant in the water heating system or turns on the fan. These are handmade and work very well.

Blocks C1, R5 and VT1 are designed to eliminate autogeneration, due to the fact that they are set to turn off delay time. It can range from a few seconds to several minutes. We are considering a fairly simple thermostat, created with our own hands, so the above assembly also eliminates the bounce of the temperature sensor. Even with a very small very first pulse, the transistor opens and the capacitor is instantly discharged. Further chatter will be ignored. When the transistor closes, the situation repeats. Capacitor charging starts only after the end of the last bounce pulse. Thanks to the introduction of a trigger into the circuit, it is possible to ensure the maximum clarity of the relay operation. As you know, the trigger can have only two positions.

Assembly

To make a thermostat with your own hands, you can use a special circuit board, on which the entire circuit will be assembled in a hinged way. Can also be used printed circuit board. Power can be used any within 3-15 volts. The relay should be selected accordingly.

According to a similar scheme, you can make a thermostat for an aquarium with your own hands, however, it should be noted that it must be attached to the outside of the glass, then there will be no problems with its use.

The relay described above demonstrated a very high reliability during operation. The temperature is maintained to the nearest fraction of a degree. However, it is directly dependent on the time delay determined by the R5C1 circuit, as well as the response to operation, that is, the power of the cooler or heater. The temperature range and the accuracy of its setting is determined by the selection of the divider resistors. If you made such a thermostat with your own hands, then it does not need to be configured, but starts working immediately.

Considered simple design do-it-yourself thermostat to maintain the required temperature inside the cellar when storing vegetables in winter time of the year. The circuit is powered from a standard mains voltage of 220 volts.

This design is easiest to assemble with your own hands, as a temperature sensor is used digital module DS18B20 with measuring range from -55 to 125 °С. The self-made device has only two control buttons "+" and "-" for setting the required degrees, the setting step is 0.5 ° C. Arduino controls the operation of the DS18B20 module with a hysteresis of 0.5 ° C. If there is no temperature control within three seconds, the display will show the current temperature. The value of which is stored in non-volatile memory.

Sketch for programming arduino boards you can take, the connection diagram is shown in the figure below. The signet was not made, because I used a prototyping board for assembly.

The MAX6675 chip can measure the TEMF (Thermoelectromotive Force) of K-type thermocouples, the measurement result is displayed in degrees Fahrenheit and Celsius

Consider two homemade designs, one prototype (upper in the figure), peeped in the magazine modeler designer and its modernized version, just below

In the modernized version, a voltage divider is made on the resistances R1-R3, the Volts going through it are stabilized using the D814B zener diode. Resistance R3 is a 10 kiloohm KMT-12 thermistor, it can be replaced with MMT-1, MMT-9, MMT-12 or similar. In the upper arm of the divider there are two resistances: a variable value of 1.5-2.2 kOhm with a linear characteristic, its tuning knob is placed on front panel with graduation correction and tuning R2 with a resistance of 1.5-47 kOhm, for coarse tuning.

A clear dependence of the resistance of the thermistor on temperature makes it possible to use it as a sensor that changes the voltage level at inputs 1 and 2 of DD1.1 K561LA7. The knobs for setting the resistances R1 and R2 set the level of operation of the digital logic. Capacitance C1 eliminates the bounce DD1 at the time of switching. Thanks to the resistances R5 and R6, the K561LA7 output is galvanically linked to the KT972 transistor switch, in whose collector circuit the K1 relay is connected. It, through its front contacts, launches the K2 magnetic starter, which turns on the load of a conventional household heater with a built-in fan with a power of 1.5 kW or more.

The setting is carried out using the resistances R1 and R2, which set the temperature required to maintain in the cellar or storage vegetable. Initially, setting their handles to the middle position and placing the sensor in an environment with the required temperature, with a slow rotation of the handle, such an angle of rotation R2 is determined at which the relay is triggered.

The principle of operation of the circuit is extremely simple: if the voltage on the TL431 control electrode is 2.5 V (set by the internal reference voltage), the microassembly is open and current flows through the load. If the reference voltage level drops slightly, the TL431 closes and disconnects the load.

In this case, the zener diode microcircuit is used as a comparator, but with one input. This use of micro-assembly allows the design to be simplified as much as possible and the number of radio components to be reduced.

The voltage at the control electrode is formed using a divider across resistors R1, R2 and R4. A NTC thermistor is taken as resistance R4, i.e., with increasing temperature, its resistance decreases. If the voltage on the first pin of the zener diode is more than 2.5V, it is open, the relay is turned on, the triac D2 turns on the load. As the temperature rises, the resistance value of the thermistor decreases, the voltage drops below 2.5V - the relay turns off along with the load. With the help of resistance R1, the temperature of the thermostat operation is adjusted. You can take any relay for 12 volts, for example RES-55A.

The design is small and consists of only two blocks - a measuring unit based on a comparator based on an op-amp 554CA3 and a load switch up to 1000 W built on a power regulator KR1182PM1.

The third direct input of the op-amp receives a constant voltage from a voltage divider consisting of resistances R3 and R4. The fourth inverted input is supplied with voltage from another divider at the resistance R1 and the thermistor MMT-4 R2.

The device must be configured so that when the temperature in the cellar drops to three degrees Celsius, due to a decrease in the resistance of the MMT-4 thermistor, the voltage will be unbalanced at the output of the comparator and a logical zero will be set and the relay will operate, which switches the phase regulator on the KR1182PM1 chip with its contacts.

Trimmer R4 is used for fine tuning required temperature values. You can calibrate the cellar thermostat using a conventional mercury thermometer.

The relay must be a reed relay with a small current consumption. A more powerful relay cannot be used, because the relay is connected directly to the output of the op-amp, the load current should not exceed 50 mA.

The main advantage of this circuit is acceptable accuracy, without any calibration, with the maximum simplified design.

The main component of the thermostat circuit is a microcontroller. PIC12F629 from Microchip and a temperature sensor from Dallas. These are quite modern components capable of receiving and transmitting information digital code on one bus using 1-Wire interface.

The temperature range is stored in the EEPROM of the PIC12F629 microcontroller. It can be set with a resolution of 1 degree, from -55 to +125.

After the device is turned on, the microcontroller turns on the relay, and the HL1 LED starts to glow, indicating that the device is working. Then the value of the current temperature from the DS18B20 sensor and the set one is compared, and if the current temperature is below the lower threshold, the relay remains on, as well as the heater connected through the front contacts.

Next, the microcontroller compares the temperature in the cellar with a predetermined upper value. As soon as this limit is reached, the microcontroller generates a code and turns off the relay until the microcontroller detects a temperature drop below the lower set limit.

When you need to set the value of the upper (address 0x01) and lower (0x00) temperature thresholds. The firmware itself can be downloaded from the green link, just above.

Many of the useful things that will help increase the comfort in our lives can be easily assembled with your own hands. The same applies to the thermostat (it is also called a thermostat).

This appliance allows you to turn on or off the desired cooling or heating equipment, adjusting when certain changes in temperature occur where it is installed.

For example, in case of severe cold, he can independently turn on the heater located in the basement. Therefore, it is worth considering how you can independently make such a device.

How does it work

The principle of operation of the thermostat is quite simple, so many radio amateurs make home-made devices to hone their skills.

It is possible to use many various schemes, although the most popular is the comparator chip.

This element has multiple inputs but only one output. So, the so-called "Reference voltage" is supplied to the first output, which has the value set temperature. The second one receives voltage directly from the temperature sensor.

After that, the comparator compares these two values. If the voltage from the temperature sensor has a certain deviation from the “reference”, a signal is sent to the output, which should turn on the relay. After that, voltage is applied to the appropriate heating or cooling apparatus.

Manufacturing process

So let's look at the process self-manufacturing simple thermostat 12 V with an air temperature sensor.

Everything should go like this:

1. First you need to prepare the body. It is best to use an old electric meter in this capacity, such as Granit-1;
2. On the basis of the same counter, it is more optimal to assemble the circuit. To do this, you need to connect a potentiometer to the input of the comparator (it is usually marked with “+”), which makes it possible to set the temperature. The LM335 temperature sensor must be connected to the “-” sign, which indicates the inverse input. In this case, when the voltage at the "plus" is greater than at the "minus", the value 1 (that is, high) will be sent to the output of the comparator. After that, the regulator will send power to the relay, which in turn will turn on, for example, a heating boiler. When the voltage supplied to the "minus" is greater than the "plus", the output of the comparator will again be 0, after which the relay will turn off;
3. To ensure the temperature difference, in other words, for the operation of the thermostat, let's say it is turned on at 22, and turned off at 25, it is necessary, using a thermistor, to create a feedback between the "plus" of the comparator and its output;
4. To provide power, it is recommended to make a transformer from a coil. It can be taken, for example, from an old electric meter (it must be of an inductive type). The fact is that a secondary winding can be made on the coil. To obtain the desired voltage of 12 V, it will be enough to wind 540 turns. At the same time, in order for them to fit, the diameter of the wire should be no more than 0.4 mm.

Master's advice: to turn on the heater, it is best to use the meter terminal block.

Heater power and thermostat setting

Depending on the level of power withstand by the contacts of the relay used, the power of the heater itself will also depend.

In cases where the value is approximately 30 A (this is the level for which automotive relays are designed), a 6.6 kW heater can be used (based on 30x220).

But first, it is advisable to make sure that all wiring, as well as the machine, can withstand the desired load.

Its useful to note: homemade lovers can make an electronic thermostat with their own hands based on an electromagnetic relay with powerful contacts that can withstand currents up to 30 amperes. Such homemade device can be used for various household needs.

The installation of the thermostat must be carried out almost at the very bottom of the wall of the room, since it is there that cold air accumulates. Same important point is the absence of thermal interference that can affect the device and thereby confuse it.

For example, it will not function properly if it is installed in a drafty area or near some electrical appliance that emits intense heat.

Setting

To measure temperature, it is better to use a thermistor, in which the electrical resistance changes when the temperature changes.

It should be noted that the variant of the thermostat created from the LM335 sensor indicated in our article does not need to be configured.

It is enough to know the exact voltage that will be applied to the “plus” of the comparator. You can find it out with a voltmeter.

The values ​​required in specific cases can be calculated using a formula such as: V = (273 + T) x 0.01. In this case, T will indicate the desired temperature, indicated in Celsius. Therefore, for a temperature of 20 degrees, the value will be 2.93 V.

In all other cases, the voltage will need to be checked directly by experience. To do this, use digital thermometer such as TM-902S. To ensure maximum tuning accuracy, it is advisable to fix the sensors of both devices (meaning a thermometer and a temperature controller) to each other, after which measurements can be taken.

Watch a video that popularly explains how to make a thermostat with your own hands: