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A simple do-it-yourself temperature sensor. How to make a thermostat with your own hands. Self assembly costs

A simple do-it-yourself electronic thermostat. I propose a method for making a homemade thermostat to maintain a comfortable temperature in the room in cold weather. The thermostat allows you to switch power up to 3.6 kW. The most important part of any amateur radio design is the enclosure. A beautiful and reliable case will ensure a long life for any home-made device. In the version of the thermostat shown below, a convenient small-sized case and all power electronics are used from an electronic timer sold in stores. The self-made electronic part is built on the LM311 comparator chip.

Description of the scheme

The temperature sensor is a thermistor R1 with a nominal value of 150k of the MMT-1 type. Sensor R1 together with resistors R2, R3, R4 and R5 form a measuring bridge. Capacitors C1-C3 are installed to suppress interference. The variable resistor R3 balances the bridge, that is, it sets the temperature.

If the temperature of the temperature sensor R1 drops below the set value, then its resistance will increase. The voltage at input 2 of the LM311 chip will become greater than at input 3. The comparator will work and a high level will be set at its output 4, the voltage applied to the timer electronic circuit through the HL1 LED will trigger the relay and turn on the heating device. At the same time, the HL1 LED will light up, indicating that the heating is on. Resistance R6 creates negative feedback between output 7 and input 2. This allows you to set a hysteresis, that is, the heating turns on at a temperature lower than it turns off. The board is powered by the electronic timer circuit. Resistor R1 placed outside requires careful insulation, since the power supply of the thermostat is transformerless and does not have galvanic isolation from the network, that is dangerous mains voltage is present on the elements of the device. The manufacturing procedure for the thermostat and how the thermistor is insulated is shown below.

How to make a thermostat with your own hands

1. The donor of the case and the power circuit is opened - the electronic timer CDT-1G. A timer microcontroller is installed on a gray three-wire cable. Unsolder the cable from the board. The holes for the loop wires are marked (+) - +5 Volt power supply, (O) - control signal supply, (-) - power minus. The load will be switched by an electromagnetic relay.

2. Since the power supply of the circuit from the power unit does not have galvanic isolation from the network, we carry out all work on checking and configuring the circuit from a safe 5 volt power source. First, at the stand, we check the performance of the circuit elements.

3. After checking the circuit elements, the design is assembled on the board. The board for the device was not developed and assembled on a piece of a breadboard. After assembly, a performance test is also carried out on the stand.

4. Temperature sensor R1 is installed on the outside on the side surface of the block socket housing, the conductors are insulated with a heat shrink tube. To prevent contact with the sensor, but also to maintain the access of outside air to the sensor, a protective tube is installed on top. The tube is made from the middle part of a ballpoint pen. A hole is cut in the tube for installation on the sensor. The tube is glued to the body.

5. The variable resistor R3 is installed on the top cover of the housing, a hole for the LED is also made there. It is useful to cover the resistor case with a layer of electrical tape for safety.

6. The adjustment knob for the R3 resistor is homemade and made by hand from an old toothbrush of a suitable shape :).

Before installing the device, it is better to get acquainted with the principle of its operation. The Russian market offers an impressive number of models from different companies, almost all of them operate according to the same scheme, regardless of their purpose.

According to this plan, devices are made to maintain the atmosphere in the aquarium, incubator, floor, etc. It allows you to maintain the thermal regime with an accuracy of ± 0.5 0 С.

The device includes a bellows for the liquid composition, a spool, a stem and an adjustable valve.

simple thermostat circuit diagram
thermostat diagram for incubator

Assembly instructions

Required materials, parts and tools:

  • magnifier;
  • pliers;
  • insulating tape;
  • several screwdrivers;
  • copper wires;
  • semiconductors;
  • standard red LEDs;
  • pay;
  • forged textolite;
  • lamps;
  • zener diode;
  • thermistor;
  • thyristor.
  • a display and an internal-type generator with a capacity of 4Mgu (for creating digital devices on a microcontroller);

Step-by-step instruction:

  1. Primarily, an appropriate microcircuit is required, for example, K561LA7, CD4011
  2. fee must be prepared for the laying of paths.
  3. For similar schemes thermistors with a power of 1 kOm to 15 kOm are well suited, and it must be located inside the object itself.
  4. heating device must be included in the resistor circuit, due to the fact that the change in power, which is directly dependent on the decrease in degrees, affects the transistors.
  5. Subsequently, such a mechanism will warm the system until the power inside the thermal sensor returns to its original value.
  6. Regulator sensors of a similar plan need setting. During significant fluctuations in the surrounding atmosphere, it is necessary to control the heating inside the object.

Assembling the digital instrument:

  1. microcontroller should be connected together with a temperature sensor. It must have port outputs, which are required to install standard LEDs that work in conjunction with the generator.
  2. After connecting the device to the network with a voltage of 220V, the LEDs will automatically turn on. This will indicate that the device is in working condition.
  3. The design of the microcontroller contains memory. If the device settings are lost, the memory automatically returns them to the originally specified parameters.

Assembling the design, we must not forget about safety. During the use of the temperature sensor in a watery or humid atmosphere, its outputs must be hermetically sealed. The value of the thermistor R5 can be designated from 10 to 51 kOhm. In this case, the resistance of the resistor R5 must have a similar value.

Instead of the indicated K140UD6 microcircuits, you can use K140UD7, K140UD8, K140UD12, K153UD2. In the role of the zener diode VD1, you can implement any tool with a stabilization power of 11 ... 13 V.

In the case when the heater exceeds the voltage of 100 W, then VD3-VD6 must exceed in power (for example, KD246 or their analogues, with a reverse power of at least 400V), while the trinistor must be mounted on small radiators.

The value of FU1 should also be made larger. The control of the device is reduced to the selection of the resistor R2, R6 in order to safely close and open the trinistor.

Device


 diagram of a mechanical thermostat

The temperature always remains at the same level due to the turning on and off of the heating device (TEN). A similar control principle is used on all simple structures.

It may seem that the thermostat circuit is very simple, but as soon as it comes to assembling the device, a lot of questions appear related to the technical part.

The thermostat device includes:

  1. Temperature sensor- is created on the basis of the comparator DD1.
  2. Key circuit thermostat is a comparator DA1, made on an operational amplifier.
  3. Desired temperature indicator set by resistor R2, which is connected to the inverting input 2 of the DA1 board.
  4. As a temperature sensor the thermistor R5 (type MMT-4) connected to the input of the 3rd device acts.
  5. Construction scheme does not have galvanic isolation from the network, and takes energy from a parametric stabilizer on the details of R10, VD1.
  6. As a power supply for the device you can take a cheap network adapter. During its connection, you must be guided by the rules and requirements for new wiring, since the conditions of the room can be electrically dangerous.

A small margin of capacitor C1 contributes to a gradual increase in power, which leads to a smooth (no more than 2 seconds) switching on of electric lamps.

Self assembly costs

Today, any such gadget can be purchased at the store. The price range is quite large, and the cost of many models is over 1000 rubles. In terms of financial investment, this is rather unprofitable, so it is much cheaper to do it yourself.

Self-assembly costs are several times lower, namely:

  • board K561LA7 will cost no more than 50 rubles;
  • thermistor with a power of 1 kOm to 15 kOm - about 5 rubles;
  • LED (2 pcs) - 10 rubles;
  • zener diode - 50 rubles;
  • thyristor - 20 rubles;
  • display - 200 rubles (for creating digital devices on a microcontroller);

The purchase of lamps, foil and other materials will take no more than 100 rubles. It turns out that the cost of self-assembly will have to spend no more than 430 rubles and a little personal time. The owner can fully adapt the device to his needs, using a simple scheme for this.

Operating principle


The thermostat circuit is multifunctional. Based on its foundation, you can create any adapted device that will be as convenient and simple as possible. The power supply is selected according to the available relay coil voltage.

The principle of operation of the adjusting device is the feature of gases and liquids to contract or expand during cooling or heating. Therefore, the basis of the action of water and gas equipment is the same essence.

Between themselves, they differ only in the speed of reaction to changes in temperature in the house.

The principle of operation of the device is based on the following steps:

  1. As a result of a change in the temperature of the heated object, there is a change in the operation of the coolant in the heating mechanism.
  2. Together with that, this causes the siphon to increase or decrease its dimensions.
  3. After that, the spool is displaced, which balances the coolant inlet.
  4. The inside of the siphon filled with gas, contributing to uniform temperature control. The built-in temperature sensor monitors the outside temperature.
  5. Each value of heat level the specific value of the pressure force of the working atmosphere inside the siphon is equated. The missing pressure is compensated by a spring that controls the operation of the stem.
  6. As a result of rising degrees the valve cone begins to move in the direction of closing until the level of working pressure in the siphon becomes balanced due to the forces of the spring.
  7. In case of lowering degrees, spring action is reversed.

The result of the work depends on the type and functionality of the control valve, which is directly subordinate to the heating circuit and the diameter of the supply pipe.

Kinds


Manufacturers offer customers 3 types of thermostats, each of which has different internal signals. They control the process of heating the coolant and align the temperature order.

Ways to expand signals:

  1. directly from the coolant. It is considered insufficiently effective, therefore it is used infrequently. Its operation is based on a submersible sensor or similar mechanisms. Compared to other types, it is one of the most expensive.
  2. internal air waves. It is the most reliable and economical option. It balances the air during its fluctuations, and not the level of water heating. Easily installed in the apartment. It communicates with heating communications using a cable through which a signal is transmitted. Thermoregulators of this type are continuously supplemented with new functions and are quite convenient to use.
  3. external air waves. High efficiency is achieved by giving an immediate response to any weather changes. Signs in the form of a signal sent by a diaphragm give the system a command to open or close a pipe with a heater.

In addition, devices can be electrical and electronic.

According to the scheme and option for receiving a signal, the devices are divided into semi-automatic and automatic, which, in turn, can:

  1. Control the heating level of the radiator and the line branch.
  2. Track for boiler power.

Overview of thermostats on the market


 Thermostat IWarm 710

The most popular models today are E 51.716 and IWarm 710. Their non-flammable, plastic-polymer case is small in size, but has a large number of useful tasks and a built-in battery. It has a fairly large built-in display that displays the relevant temperature characteristics.

The cost of these models is presented within 2700 thousand rubles.

The features of E 51.716 include the fact that it has a 3 m long cable, is able to balance the temperature simultaneously from the floor itself, and that the device can be built into the wall in any position.

The only thing to think about before installing it is how exactly it will be located so that the switch buttons are not covered by foreign objects and are easily accessible.

The disadvantages of the thermostat include an insignificant set of functions, however, similar devices perform them quite easily. In operation, this can cause discomfort. Also, in the memory of E 51.716 and IWarm 710 there is no automatic heating function, so you have to do it yourself.

Electronic regulators with a mechanical principle of operation:

  1. Work regulation based on automation, and are carried out using the buttons located on the panel.
  2. include display, which indicates the previous and given degrees.
  3. It is possible to configure the device yourself: number, operating time, heating cycles while maintaining a specific mode, you can also specify the degree of heating.
  4. Compared to mechanical counterparts, the temperature of electric models can be easily adjusted by approximately 0.5 degrees.

The purchase of such a model will take no more than 4 thousand.

Electronic kits:

  1. independently control the temperature.
  2. Just one device can control the atmosphere for several days ahead and separately for each room.
  3. Allows you to set the "absent" mode, and do not spend extra money on it if no one is at home.
  4. The system automatically analyzes the quality of work devices in every room. The owner does not have to guess about possible malfunctions in the work, since the system will issue all the shortcomings on its own.
  5. Manufacturers of expensive models provided the ability to control modes while away from home. Adjustment is carried out using the built-in Wi-Fi router.

The cost of such devices depends on the set of built-in functions, so it varies from 6,000 to 10,000 thousand rubles and more.

Among the various useful gizmos that can add comfort to our lives, there are many that you can easily do yourself.

This category also includes a thermostat, also called a thermostat, a device that turns on and off heating or refrigeration equipment in accordance with the temperature of the environment in which it is installed.

Such a device can, for example, turn on a heater in the basement where vegetables are stored during severe cold weather. From our article you will learn about how you can make a thermostat with your own hands (for a heating boiler, refrigerator and other systems) and what parts are best suited for this.

The thermostat device is not particularly difficult, so many novice radio amateurs hone their skills in the manufacture of this device. The schemes are offered in a variety of ways, but the most common option is using a special microcircuit called a comparator.

This element has two inputs and one output. A certain reference voltage is applied to one input, which corresponds to the required temperature, and the voltage from the temperature sensor is applied to the second.


Scheme of a thermostat for underfloor heating

The comparator compares the incoming data and, at a certain ratio, generates a signal at the output that opens the transistor or turns on the relay. In this case, current is supplied to the heater or refrigeration unit.

DIY temperature controller details

The temperature sensor is usually a thermistor - an element whose electrical resistance changes depending on temperature. Semiconductor elements are also used - transistors and diodes, the characteristics of which are also affected by temperature: when heated, the collector current (for transistors) increases, while a shift in the operating point is observed and the transistor stops working without responding to the input signal.

But such sensors have a significant drawback: they are quite difficult to calibrate, that is, “bind” to certain temperature values, which is why the accuracy of a home-made thermostat leaves much to be desired.

Meanwhile, the industry has long mastered the production of inexpensive thermal sensors, the calibration of which is carried out in the manufacturing process.

These include the LM335 brand device from National Semiconductor, which we recommend using. The cost of this analog thermal sensor is only $1.

"Three" in the first position of the digital row in the marking means that the device is focused on use in household appliances. Modifications LM235 and LM135 are intended for use in industry and in the military, respectively.

With 16 transistors, this sensor works like a zener diode. Moreover, its stabilization voltage depends on temperature.

The dependence is as follows: for each degree on an absolute scale (in Kelvin), there is 0.01 V of voltage, that is, at zero Celsius (273 Kelvin), the stabilization voltage at the output will be 2.73 V. The manufacturer calibrates the sensor at a temperature of 25C (298K ). The operating range lies in the range from -40 to +100 degrees Celsius.

Thus, when assembling a thermostat based on the LM335, the user gets rid of the need to select, by trial and error, the reference voltage at which the device will provide the required temperature.

V = (273 + T) x 0.01,

Where T is the temperature of interest to the user on the Celsius scale.

In addition to the temperature sensor, we need a comparator (an LM311 brand from the same manufacturer is suitable), a potentiometer for generating a reference voltage (setting the required temperature), an output device for connecting a load (relay), indicators and a power supply.

Thermostat power supply

The temperature sensor LM335 is connected in series with the resistor R1. So, the resistance of this resistor and the supply voltage must be selected in such a way that the value of the current flowing through the temperature sensor is in the range from 0.45 to 5 mA.

The maximum value of this range should not be exceeded, as the sensor characteristics will be distorted due to overheating.

You can power the thermostat from a standard 12 V power supply or from a transformer made in-house.

Turning on the load

An automotive relay can be used as an actuator that supplies power to the heater. It is designed for a voltage of 12 V, while a current of 100 mA must flow through the coil.

Recall that the current in the temperature sensor circuit does not exceed 5 mA, therefore, to connect the relay, you need to use a transistor with more power, for example, KT814.

You can use a relay with a lower turn-on current, such as SRA-12VDC-L or SRD-12VDC-SL-C - then the transistor is not needed.

How to make a thermostat with your own hands: step by step instructions

Consider how thermostats (thermostats) are made with a do-it-yourself 12 V air temperature sensor. The device is assembled in the following sequence:

  1. First of all, you need to prepare the body. A counter that has served its purpose, for example, "Granit-1", will do.
  2. The circuit can be assembled on the board from the same counter. A potentiometer is connected to the direct input of the comparator (marked with a “+” sign), which allows you to set the temperature. To the inverse input ("-" sign) - LM335 temperature sensor. If the voltage at the direct input turns out to be higher than at the inverse one, a high level (one) will be set at the output of the comparator and the transistor will energize the relay, and it will power the heater. As soon as the voltage at the inverted input is greater than the direct one, the level at the output of the comparator will become low (zero) and the relay will turn off.
  3. In order to ensure the temperature difference, that is, the operation of the thermostat, for example, at 23 degrees, and shutdown at 25 degrees, it is necessary to create a negative feedback between the output and the direct input of the comparator using a resistor.
  4. The transformer for powering the thermostat can be made from a coil from an old induction-type electric meter. It has a place for a secondary winding. To get a voltage of 12 V, it is necessary to wind 540 turns. They can fit if you use a wire with a diameter of 0.4 mm.

A simple homemade thermostat

To turn on the heater, it is convenient to use the meter terminal block.

What should be the heater?

The power of the heater depends on how much current the contacts of the relay used can withstand. If this value is, for example, 30 A (an automobile relay is designed for such a current), then the heater can have a power of up to 30 x 220 = 6.6 kW. It is only necessary to first make sure that the wiring and the machine in the shield are able to withstand such a load.

Mounting

Consider how the device should be installed correctly.

The thermostat should be installed in the lower part of the room where cold air accumulates.

It is important to prevent the effects of thermal noise, which can confuse the instrument.

So, for example, you should not place the thermostat in a draft or near electrical equipment that radiates heat.

Setting the thermostat

As already mentioned, the thermostat based on the LM335 sensor does not need to be configured. It is enough to know the voltage supplied by the potentiometer to the direct input of the comparator.

You can measure it with a voltmeter. The required voltage value is determined by the above formula.

If it is necessary, for example, for the device to operate at a temperature of 20 degrees, it should be 2.93 V.

If any other element is used as a temperature sensor, the reference voltage will have to be verified empirically. To do this, you must use a digital thermometer, for example, TM-902C. For precise adjustment, the sensors of the thermometer and thermostat can be connected with electrical tape, after which they are placed in an environment with different temperatures.


Thermostat from improvised materials

The potentiometer knob must be rotated smoothly until the thermostat works. At this point, you should look at the scale of the digital thermometer and apply the temperature displayed on it to the scale of the thermostat. You can define extreme points, for example, for temperatures of 8 and 40 degrees, and mark intermediate values ​​by dividing the range into equal parts.

If there is no digital thermometer at hand, extreme points can be determined by water with ice floating in it (0 degrees) or by boiling water (100 degrees).

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microclimat.pro

A simple do-it-yourself thermostat


Sometimes at home you have to have a household incubator or a vegetable dryer. Often, cheap equipment of this kind has a very poor quality thermal relay, the contacts of which quickly burn out or it does not have a good smoothness of adjustment. And so, today we have a simple do-it-yourself thermostat on the agenda, we will assemble the circuit and demonstrate its operation.

A simple do-it-yourself thermostat - a diagram

The thermostat circuit is powered by a transformerless power supply, it consists of a quenching capacitor C1 and a diode bridge D1. Parallel to the bridge, a zener diode ZD1 is included, which stabilizes the voltage within 14V. If desired, you can also add a 12V stabilizer.

The basis of the circuit is a controlled zener diode TL431. The TL431 is controlled using a voltage divider R4, R5 and R6. The air temperature sensor is an NTC thermistor R4 with a nominal value of 10 kOhm. As the temperature rises, it reduces its resistance.

With a voltage of more than 2.5V at the TL431 control contact, this microcircuit opens, then the relay operates, closing the contacts and turning on the load.

When the temperature of the R4 sensor rises, its resistance will begin to fall. When the voltage at the TL431 control contact drops below 2.5V, the microcircuit will close and turn off the relay with the load.

By selecting resistors R5 and R6, it is necessary to achieve the required temperature control range. The R5 rating is responsible for the maximum temperature, and R6 for the minimum.

To eliminate the effect of rattling of the relay contacts when turning on or off, it is necessary to connect the capacitor C4 in parallel with the terminals A1 and A2 of the relay contacts. Relay K1 must be used with as little holding current as possible.

When using used TL431 and NTC thermistors, it is important to check their performance. To do this, it is advisable to familiarize yourself with the materials on the topic: how to check the TL431 and how to check the thermistor.

Here we have such a simple thermostat with our own hands.

Photo of the reverse side of the board.

Such a do-it-yourself device can be safely used as a thermostat for an incubator or drying. When using a sealed thermistor (temperature sensor), its scope is already expanding, it will play a good role as an aquarium thermostat.

A simple do-it-yourself thermostat in action

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diodnik.com

Do-it-yourself thermostats - instructions and connection diagram

Automatic control of the coolant supply is used in many technological processes, including domestic heating systems. The factor determining the operation of the thermostat is the outside temperature, the value of which is analyzed and when the set limit is reached, the flow rate is reduced or increased.

Temperature controllers come in various designs and today there are a lot of industrial versions on sale that work according to different principles and are intended for use in different areas. Also available are the simplest electronic circuits, which anyone can assemble with the appropriate knowledge of electronics.

Description

The thermostat is a device installed in power supply systems and allows you to optimize the energy consumption for heating. The main elements of the thermostat:

  1. Temperature sensors - control the temperature level by generating electrical impulses of the appropriate size.
  2. Analytical unit - processes the electrical signals coming from the sensors and converts the temperature value into a value that characterizes the position of the executive body.
  3. Executive body - regulates the flow, by the amount indicated by the analytical unit.
A modern thermostat is a microcircuit based on diodes, triodes or a zener diode that can convert heat energy into electrical energy. Both in industrial and home-made versions, this is a single unit to which a thermocouple is connected, remote or located here. The thermostat is connected in series to the power supply circuit of the executing body, thus reducing or increasing the value of the supply voltage.

Principle of operation

The temperature sensor delivers electrical impulses, the current value of which depends on the temperature level. The inherent ratio of these values ​​​​allows the device to very accurately determine the temperature threshold and decide, for example, how many degrees the air supply damper to the solid fuel boiler should be opened, or the hot water supply damper should be open. The essence of the operation of the thermostat is to convert one value to another and correlate the result with the current level.

Simple home-made regulators, as a rule, have a mechanical control in the form of a resistor, by moving which, the user sets the required temperature threshold, that is, indicating at what outside temperature it will be necessary to increase the supply. With more advanced functionality, industrial devices can be programmed to wider limits, using a controller, depending on various temperature ranges. They do not have mechanical controls, which contributes to long work.

How to DIY

Self-made regulators are widely used in domestic conditions, especially since the necessary electronic parts and circuits can always be found. Heating the water in the aquarium, turning on the ventilation of the room when the temperature rises, and many other simple technological operations can be completely shifted to such automation.

Schemes of autoregulators

Currently, among fans of homemade electronics, two automatic control schemes are popular:

  1. Based on an adjustable zener diode type TL431 - the principle of operation is to fix the excess voltage threshold of 2.5 volts. When it is broken on the control electrode, the zener diode comes into the open position and a load current passes through it. In the event that the voltage does not break through the threshold of 2.5 volts, the circuit comes into the closed position and disconnects the load. The advantage of the circuit is its extreme simplicity and high reliability, since the zener diode is equipped with only one input for supplying an adjustable voltage.
  2. A thyristor microcircuit of the K561LA7 type, or its modern foreign counterpart CD4011B - the main element is the thyristor T122 or KU202, which acts as a powerful switching link. The current consumed by the circuit in normal mode does not exceed 5 mA, at a resistor temperature of 60 to 70 degrees. The transistor comes into the open position when pulses are received, which in turn is a signal to open the thyristor. In the absence of a radiator, the latter acquires a bandwidth of up to 200 watts. To increase this threshold, you will need to install a more powerful thyristor, or equip an existing radiator, which will increase the switching capacity to 1 kW.

Necessary materials and tools

Assembling it yourself will not take much time, but some knowledge in the field of electronics and electrical engineering, as well as experience with a soldering iron, will definitely be required. To work, you need the following:

  • Soldering iron pulse or conventional with a thin heating element.
  • Printed circuit board.
  • Solder and flux.
  • Acid for etching tracks.
  • Electronic parts according to the selected scheme.

Walkthrough

  1. Electronic elements must be placed on the board in such a way that they can be easily mounted without hitting the neighboring ones with a soldering iron, near the parts that actively generate heat, the distance is made somewhat larger.
  2. The tracks between the elements are etched according to the drawing, if there is none, then a sketch is first made on paper.
  3. It is imperative to check the performance of each element with a multimeter, and only after that is it landed on the board, followed by soldering to the tracks.
  4. It is necessary to check the polarity of diodes, triodes and other parts in accordance with the diagram.
  5. It is not recommended to use acid for soldering radio components, since it can short-circuit nearby adjacent tracks, for insulation, rosin is added to the space between them.
  6. After assembly, the device is adjusted by selecting the optimal resistor for the most accurate threshold for opening and closing the thyristor.

Scope of homemade thermostats

In everyday life, the use of a thermostat is most often found among summer residents who operate home-made incubators, and as practice shows, they are no less effective than factory models. In fact, such a device can be used wherever it is necessary to perform some actions depending on the temperature readings. Similarly, it is possible to equip the lawn spraying or watering system, the extension of light-shielding structures, or simply sound or light alarms that warn of something with automation.

DIY repair

Assembled by hand, these devices last a long time, but there are several standard situations when repairs may be required:

  • Failure of the adjusting resistor - happens most often, since the copper tracks wear out, inside the element along which the electrode slides, it is solved by replacing the part.
  • Overheating of the thyristor or triode - the power was incorrectly selected or the device is located in a poorly ventilated area of ​​\u200b\u200bthe room. In order to avoid this in the future, thyristors are equipped with radiators, or the thermostat should be moved to a zone with a neutral microclimate, which is especially important for wet rooms.
  • Incorrect temperature control - possible damage to the thermistor, corrosion or dirt on the measuring electrodes.

Advantages and disadvantages

Undoubtedly, the use of automatic control is already an advantage in itself, since the energy consumer receives such opportunities:

  • Saving energy resources.
  • Constant comfortable room temperature.
  • No human involvement required.
Automatic control has found particularly great application in the heating systems of apartment buildings. Inlet valves equipped with thermostats automatically control the supply of heat carrier, thanks to which residents receive significantly lower bills.

The disadvantage of such a device can be considered its cost, which, however, does not apply to those that are made by hand. Only industrial devices designed to control the supply of liquid and gaseous media are expensive, since the actuator includes a special motor and other valves.

Although the device itself is quite undemanding to operating conditions, the accuracy of response depends on the quality of the primary signal, and this especially applies to automation operating in conditions of high humidity or in contact with aggressive media. Thermal sensors in such cases should not come into direct contact with the coolant.

The leads are placed in a brass sleeve and hermetically sealed with epoxy glue. You can leave the end of the thermistor on the surface, which will contribute to greater sensitivity.

househill.com

How to make a thermostat yourself?

Before installing the device, it is better to get acquainted with the principle of its operation. The Russian market offers an impressive number of models from different companies, almost all of them operate according to the same scheme, regardless of their purpose.

According to this plan, devices are made to maintain the atmosphere in the aquarium, incubator, floor, etc. It allows you to maintain the thermal regime with an accuracy of ± 0.5 0С.

The device includes a bellows for the liquid composition, a spool, a stem and an adjustable valve.


simple thermostat circuit diagram


thermostat diagram for incubator

Assembly instructions

Required materials, parts and tools:

  • magnifier;
  • pliers;
  • soldering iron;
  • insulating tape;
  • several screwdrivers;
  • copper wires;
  • semiconductors;
  • standard red LEDs;
  • pay;
  • forged textolite;
  • lamps;
  • zener diode;
  • thermistor;
  • thyristor.
  • a display and an internal-type generator with a capacity of 4Mgu (for creating digital devices on a microcontroller);

Step-by-step instruction:

  1. First of all, you need an appropriate microcircuit, for example, K561LA7, CD4011
  2. The board must be prepared for laying the tracks.
  3. Thermistors with a power of 1 kOm to 15 kOm are well suited to such circuits, and it must be located inside the object itself.
  4. The heating device must be included in the resistor circuit, due to the fact that the change in power, which is directly dependent on the decrease in degrees, affects the transistors.
  5. Subsequently, such a mechanism will warm the system until the power inside the temperature sensor returns to its original value.
  6. Regulator sensors of a similar plan need to be adjusted. During significant fluctuations in the surrounding atmosphere, it is necessary to control the heating inside the object.

Assembling the digital instrument:

  1. The microcontroller should be connected together with a temperature sensor. It must have port outputs, which are required to install standard LEDs that work in conjunction with the generator.
  2. After connecting the device to a network with a voltage of 220V, the LEDs will automatically turn on. This will indicate that the device is in working condition.
  3. The design of the microcontroller contains memory. If the device settings are lost, the memory automatically returns them to the originally specified parameters.

Assembling the design, we must not forget about safety. During the use of the temperature sensor in a watery or humid atmosphere, its outputs must be hermetically sealed. The value of the thermistor R5 can be designated from 10 to 51 kOhm. In this case, the resistance of the resistor R5 must have a similar value.

Instead of the indicated K140UD6 microcircuits, you can use K140UD7, K140UD8, K140UD12, K153UD2. In the role of the zener diode VD1, you can implement any tool with a stabilization power of 11 ... 13 V.

In the case when the heater exceeds the voltage of 100 W, then the VD3-VD6 diodes must exceed in power (for example, KD246 or their analogues, with a reverse power of at least 400 V), while the trinistor must be mounted on small radiators.

The value of FU1 should also be made larger. The control of the device is reduced to the selection of the resistor R2, R6 in order to safely close and open the trinistor.

Device


diagram of a mechanical thermostat

The temperature always remains at the same level due to the turning on and off of the heating device (TEN). A similar control principle is used on all simple structures.

It may seem that the thermostat circuit is very simple, but as soon as it comes to assembling the device, a lot of questions appear related to the technical part.

The thermostat device includes:

  1. Temperature sensor - is created on the basis of the comparator DD1.
  2. The key circuit of the thermostat is the comparator DA1, made on an operational amplifier.
  3. The desired temperature indicator is set by resistor R2, which is connected to the inverting input 2 of the DA1 board.
  4. The thermistor R5 (type MMT-4) connected to the input of the 3rd device acts as a temperature sensor.
  5. The design scheme does not have galvanic isolation from the network, and takes energy from a parametric stabilizer on the details of R10, VD1.
  6. As a power supply for the device, you can take a cheap network adapter. During its connection, you must be guided by the rules and requirements for new wiring, since the conditions of the room can be electrically dangerous.

A small margin of capacitor C1 contributes to a gradual increase in power, which leads to a smooth (no more than 2 seconds) switching on of electric lamps.

Self assembly costs

Today, any such gadget can be purchased at the store. The price range is quite large, and the cost of many models is over 1000 rubles. In terms of financial investment, this is rather unprofitable, so it is much cheaper to do it yourself.

Self-assembly costs are several times lower, namely:

  • board K561LA7 will cost no more than 50 rubles;
  • thermistor with a power of 1 kOm to 15 kOm - about 5 rubles;
  • LED (2 pcs) - 10 rubles;
  • zener diode - 50 rubles;
  • thyristor - 20 rubles;
  • display - 200 rubles (for creating digital devices on a microcontroller);

The purchase of lamps, foil and other materials will take no more than 100 rubles. It turns out that the cost of self-assembly will have to spend no more than 430 rubles and a little personal time. The owner can fully adapt the device to his needs, using a simple scheme for this.

Operating principle

The thermostat circuit is multifunctional. Based on its foundation, you can create any adapted device that will be as convenient and simple as possible. The power supply is selected according to the available relay coil voltage.

The principle of operation of the adjusting device is the feature of gases and liquids to contract or expand during cooling or heating. Therefore, the basis of the action of water and gas equipment is the same essence.

Between themselves, they differ only in the speed of reaction to changes in temperature in the house.

The principle of operation of the device is based on the following steps:

  1. As a result of a change in the temperature of the heated object, there is a change in the operation of the coolant in the heating mechanism.
  2. Along with this, this causes the siphon to increase or decrease its dimensions.
  3. After that, the spool is displaced, which balances the coolant inlet.
  4. The inside of the siphon is filled with gas, helping to regulate the temperature evenly. The built-in temperature sensor monitors the outside temperature.
  5. Each value of the heat level is equated with a specific value of the pressure force of the working atmosphere inside the siphon. The missing pressure is compensated by a spring that controls the operation of the stem.
  6. As a result of increasing degrees, the valve cone begins to move towards closing until the level of working pressure in the siphon becomes balanced due to the forces of the spring.
  7. In the case of a decrease in degrees, the work of the spring is reversed.

The result of the work depends on the type and functionality of the control valve, which is directly subordinate to the heating circuit and the diameter of the supply pipe.

Kinds

Manufacturers offer customers 3 types of thermostats, each of which has different internal signals. They control the process of heating the coolant and align the temperature order.

Ways to expand signals:

  1. directly from the coolant. It is considered insufficiently effective, therefore it is used infrequently. Its operation is based on a submersible sensor or similar mechanisms. Compared to other types, it is one of the most expensive.
  2. internal air waves. It is the most reliable and economical option. It balances the air during its fluctuations, and not the level of water heating. Easily installed in the apartment. It communicates with heating communications using a cable through which a signal is transmitted. Thermoregulators of this type are continuously supplemented with new functions and are quite convenient to use.
  3. external air waves. High efficiency is achieved by an outdoor sensor, giving an immediate response to any weather changes. Signs in the form of a signal sent by a diaphragm give the system a command to open or close a pipe with a heater.

In addition, devices can be electrical and electronic.

According to the scheme and option for receiving a signal, the devices are divided into semi-automatic and automatic, which, in turn, can:

  1. Control the heating level of the radiator and the line branch.
  2. Monitor the power of the boiler.

Overview of thermostats on the market

Thermostat IWarm 710

The E 51.716 and IWarm 710 are among the most popular models today. Their non-flammable, plastic-polymer case is small in size, but has a large number of useful tasks and a built-in battery. It has a fairly large built-in display that displays the relevant temperature characteristics.

The cost of these models is presented within 2700 thousand rubles.

The features of E 51.716 include the fact that it has a 3 m long cable, is able to balance the temperature simultaneously from the floor itself, and that the device can be built into the wall in any position.

The only thing to think about before installing it is how exactly it will be located so that the switch buttons are not covered by foreign objects and are easily accessible.

The disadvantages of the thermostat include an insignificant set of functions, however, similar devices perform them quite easily. In operation, this can cause discomfort. Also, in the memory of E 51.716 and IWarm 710 there is no automatic heating function, so you have to do it yourself.

Electronic regulators with a mechanical principle of operation:

  1. The regulation of work is based on automation, and is carried out using the buttons located on the panel.
  2. Includes a display that shows the previous and set degrees.
  3. It is possible to configure the device yourself: the number, operating time, heating cycles while maintaining a specific mode, you can also specify the degree of heating.
  4. Compared to mechanical counterparts, the temperature of electrical models is easily adjustable by approximately 0.5 degrees.

The purchase of such a model will take no more than 4 thousand.

Electronic kits:

  1. independently control the temperature.
  2. Only one device can control the atmosphere for several days ahead and separately for each room.
  3. They allow you to set the “absence” mode and not spend extra money on it if no one is at home.
  4. The system automatically analyzes the quality of the device in each room. The owner does not have to guess about possible malfunctions in the work, since the system will issue all the shortcomings on its own.
  5. Manufacturers of expensive models have provided the ability to control modes while away from home. Adjustment is carried out using the built-in Wi-Fi router.

The cost of such devices depends on the set of built-in functions, so it varies from 6,000 to 10,000 thousand rubles and more.

slarkenergy.ru


Temperature controllers are widely used in modern household appliances, automobiles, heating and air conditioning systems, manufacturing, refrigeration equipment and ovens. The principle of operation of any thermostat is based on turning on or off various devices after reaching certain temperature values.

Modern digital thermostats are controlled by buttons: touch or conventional. Many models are also equipped with a digital panel that displays the set temperature. The group of programmable thermostats is the most expensive. Using the device, you can provide for a change in temperature by the hour or set the desired mode for a week in advance. You can control the device remotely: via smartphone or computer.

For a complex technological process, for example, a steel-smelting furnace, making a thermostat with your own hands is a rather difficult task that requires serious knowledge. But to assemble a small device for a cooler or an incubator is within the power of any home master.

In order to understand how a temperature controller works, consider a simple device that is used to open and close the damper of a shaft boiler and is activated when the air is heated.

For the operation of the device, 2 aluminum pipes, 2 levers, a return spring, a chain that goes to the boiler, and an adjusting unit in the form of a crane box were used. All components were mounted on the boiler.

As you know, the coefficient of linear thermal expansion of aluminum is 22x10-6 0C. When an aluminum pipe with a length of one and a half meters, a width of 0.02 m and a thickness of 0.01 m is heated to 130 degrees Celsius, an elongation of 4.29 mm occurs. When heated, the pipes expand, due to this, the levers are shifted, and the damper closes. When cooling, the pipes decrease in length, and the levers open the damper. The main problem when using this scheme is that it is very difficult to accurately determine the threshold for the operation of a thermostat. Today, preference is given to devices based on electronic elements.

Scheme of operation of a simple thermostat

Typically, relay-based circuits are used to maintain the set temperature. The main elements included in this equipment are:

  • temperature sensor;
  • threshold scheme;
  • actuating or indicating device.

As a sensor, you can use semiconductor elements, thermistors, resistance thermometers, thermocouples and bimetallic thermal relays.

The thermostat circuit reacts to the excess of the parameter above the set level and turns on the actuator. The simplest version of such a device is an element on bipolar transistors. The thermal relay is based on the Schmidt trigger. The thermistor acts as a temperature sensor - an element whose resistance changes depending on the increase or decrease in degrees.

R1 is a potentiometer that sets the initial offset on R2 thermistor and R3 potentiometer. Due to the adjustment, the actuator is activated and relay K1 is switched when the resistance of the thermistor changes. In this case, the operating voltage of the relay must correspond to the operating power supply of the equipment. To protect the output transistor from voltage pulses, a semiconductor diode is connected in parallel. The load value of the connected element depends on the maximum current of the electromagnetic relay.

Attention! On the Internet, you can see pictures with thermostat drawings for various equipment. But quite often the image and description do not match. Sometimes the illustrations may simply represent other devices. Therefore, production can only begin after a thorough study of all the information.

Before starting work, you should decide on the power of the future thermostat and the temperature range in which it will work. For the refrigerator, some elements will be required, and for heating, others.

Thermostat on three elements

One of the elementary devices, on the example of which you can assemble and understand the principle of operation, is a simple do-it-yourself thermostat designed for a fan in a PC. All work is done on a breadboard. If there are problems with the palnik, then you can take a solderless board.

The thermostat circuit in this case consists of only three elements:

  • power transistor MOSFET (N channel), you can use IRFZ24N MOSFET 12V and 10A or IFR510 Power MOSFET;
  • potentiometer 10 kOhm;
  • NTC thermistor in 10 kOhm, which will act as a temperature sensor.

The temperature sensor reacts to an increase in degrees, due to which the whole circuit is triggered, and the fan turns on.

Now let's move on to the settings. To do this, turn on the computer and adjust the potentiometer, setting the value for the off fan. At that moment, when the temperature approaches the critical one, we reduce the resistance as much as possible before the blades rotate very slowly. It is better to make the adjustment several times to make sure the equipment is working efficiently.

The modern electronics industry offers elements and microcircuits that differ significantly in appearance and technical characteristics. Each resistance or relay has several analogues. It is not necessary to use only those elements that are indicated in the scheme, you can take others that match the parameters with the samples.

Temperature controllers for heating boilers

When adjusting heating systems, it is important to accurately calibrate the device. This will require a voltage and current meter. To create a working system, you can use the following scheme.

Using this scheme, you can create outdoor equipment for controlling a solid fuel boiler. The role of the zener diode here is performed by the K561LA7 microcircuit. The operation of the device is based on the ability of the thermistor to reduce resistance when heated. The resistor is connected to the electricity voltage divider network. The required temperature can be set using a variable resistor R2. The voltage is supplied to the inverter 2I-NOT. The resulting current is fed to capacitor C1. A capacitor is connected to 2I-NOT, which controls the operation of one trigger. The latter is connected to the second trigger.

Temperature control is as follows:

  • when the degrees decrease, the voltage in the relay increases;
  • when a certain value is reached, the fan, which is connected to the relay, turns off.

Soldering is best done on a mole rat. As a battery, you can take any device that operates within 3-15 V.

Carefully! Installing home-made appliances for any purpose on heating systems can lead to equipment failure. Moreover, the use of such devices may be prohibited at the level of services that provide communications in your home.

Digital thermostat

In order to create a fully functioning thermostat with accurate calibration, digital elements are indispensable. Consider a temperature control device for a small vegetable store.

The main element here is the PIC16F628A microcontroller. This chip provides control of various electronic devices. The PIC16F628A microcontroller contains 2 analog comparators, an internal oscillator, 3 timers, SSR comparison and USART data exchange modules.

When the thermostat is operating, the value of the existing and set temperature is fed to the MT30361 - a three-digit indicator with a common cathode. In order to set the required temperature, the buttons are used: SB1 - to decrease and SB2 - to increase. If you carry out tuning while pressing the SB3 button, you can set the hysteresis values. The minimum hysteresis value for this circuit is 1 degree. A detailed drawing can be seen on the plan.

When creating any of the devices, it is important not only to solder the circuit itself correctly, but also to think about how best to place the equipment. It is necessary that the board itself be protected from moisture and dust, otherwise a short circuit and failure of individual elements cannot be avoided. You should also take care to isolate all contacts.

Video

The need to adjust the temperature regime arises when using various systems of thermal or refrigeration equipment. There are many options, and all of them require a control device, without which the operation of systems is possible either in maximum power mode or at a complete minimum of capabilities. Control and adjustment are carried out using a thermostat - a device that can act on the system through a temperature sensor and turn it on or off as needed. When using ready-made sets of equipment, control units are included in the package, but for home-made systems, you have to assemble the thermostat yourself. The task is not the easiest, but quite solvable. Let's consider it more carefully.

The principle of operation of the thermostat

A thermostat is a device that can respond to changes in temperature. According to the type of action, trigger-type thermostats are distinguished, which turn off or turn on heating when a predetermined limit is reached, or smooth action devices with the possibility of fine and fine tuning, capable of controlling temperature changes in the range of fractions of a degree.

There are two types of thermostats:

  1. Mechanical. It is a device that uses the principle of expanding gases with a change in temperature, or bimetallic plates that change their shape from heating or cooling.
  2. Electronic. It consists of a main unit and a temperature sensor that signals an increase or decrease in the set temperature in the system. Used in systems requiring high sensitivity and fine adjustment.

Mechanical devices do not allow for high tuning accuracy. They are both a temperature sensor and an executive body, combined into a single unit. The bimetallic plate used in heating devices is a thermocouple made of two metals with different coefficients of thermal expansion.

The main purpose of the thermostat is to automatically maintain the required temperature.

When heated, one of them becomes larger than the other, causing the plate to bend. The contacts installed on it open and stop heating. When cooled, the plate returns to its original shape, the contacts close again and heating resumes.

A chamber with a gas mixture is a sensitive element of a refrigerator thermostat or a heating thermostat. With temperature changes, the volume of gas changes, which causes the surface of the membrane connected to the lever of the contact group to move.

The thermostat for heating uses a chamber with a gas mixture that works according to the Gay-Lussac law - when the temperature changes, the volume of gas changes

Mechanical thermostats are reliable and provide stable operation, but the setting of the operating mode occurs with a large error, almost “by eye”. When fine-tuning is required, providing adjustment within a few degrees (or even finer), electronic circuits are used. The temperature sensor for them is a thermistor that can distinguish the smallest changes in the heating mode in the system. For electronic circuits, the situation is reversed - the sensitivity of the sensor is too high and it is artificially coarsened, bringing it to the limits of reason. The principle of operation is to change the resistance of the sensor, caused by fluctuations in the temperature of the controlled medium. The circuit reacts to the change of the signal parameters and increases / decreases the heating in the system until another signal is received. The capabilities of electronic control units are much higher and allow you to get the temperature setting of any accuracy. The sensitivity of such thermostats is even excessive, since heating and cooling are processes with a high inertia, which slow down the response time to command changes.

Scope of a homemade device

Making a mechanical thermostat at home is quite difficult and irrational, since the result will work in a too wide range and will not be able to provide the required tuning accuracy. Most often, self-made electronic thermostats are assembled, which allow you to maintain the optimal temperature of the heated floor, the incubator, provide the desired water temperature in the pool, heat the steam room in the sauna, etc. There can be as many options for using a home-made thermostat as there are systems in the house that need to be set up and adjusted. For rough tuning using mechanical devices, it is easier to purchase ready-made elements, they are inexpensive and quite affordable.

Advantages and disadvantages

Homemade thermostat has certain advantages and disadvantages. The advantages of the device are:

  • High maintainability. A self-made thermostat is easy to repair, since its design and principle of operation are known to the smallest detail.
  • The cost of creating a regulator is much lower than when buying a ready-made block.
  • It is possible to change the operating parameters to obtain a more suitable result.

The disadvantages include:

  • The assembly of such a device is available only to people who have sufficient training and certain skills in working with electronic circuits and a soldering iron.
  • The performance of the device depends to a large extent on the condition of the parts used.
  • The assembled circuit requires tuning and alignment on the control stand or using a reference sample. It is impossible to get a ready-made version of the device right away.

The main problem is the need for training or, at least, the participation of a specialist in the process of creating a device.

How to make a simple thermostat

The manufacture of the thermostat takes place in stages:

  • Select the type and scheme of the device.
  • Acquisition of necessary materials, tools and parts.
  • Assembly of the device, configuration, commissioning.

The stages of manufacturing the device have their own characteristics, so they should be considered in more detail.

Necessary materials

Materials needed for assembly include:

  • Foil getinax or circuit board;
  • Soldering iron with solder and rosin, ideally a soldering station;
  • Tweezers;
  • pliers;
  • magnifying glass;
  • wire cutters;
  • Insulating tape;
  • Copper connecting wire;
  • Necessary details according to the wiring diagram.

In the process, other tools or materials may be needed, so this list should not be considered exhaustive and definitive.

Device diagrams

The choice of scheme is determined by the capabilities and level of training of the master. The more complex the circuit, the more nuances will arise when assembling and configuring the device. At the same time, the simplest circuits make it possible to obtain only the most primitive devices operating with a high error.

Consider one of the simple schemes.

In this circuit, a zener diode is used as a comparator.

The figure on the left shows the regulator circuit, and on the right - the relay block that turns on the load. The temperature sensor is resistor R4 and R1 is a variable resistor used to set the heating mode. The control element is the TL431 zener diode, which is open as long as there is a load on its control electrode above 2.5 V. Heating the thermistor causes a decrease in resistance, causing the voltage on the control electrode to drop, the zener diode closes, cutting off the load.

Another scheme is somewhat more complicated. It uses a comparator - an element that compares the readings of a temperature sensor and a reference voltage source.

A similar circuit with a comparator is applicable to adjust the temperature of a warm floor

Any change in voltage caused by an increase or decrease in the resistance of the thermistor creates a difference between the reference and the operating line of the circuit, as a result of which a signal is generated at the output of the device, causing the heating to be turned on or off. Similar schemes, in particular, are used to adjust the operating mode of a warm floor.

Step-by-step instruction

The assembly order of each device has its own characteristics, but some general steps can be distinguished. Consider the build progress:

  1. We prepare the body of the device. This is important because you cannot leave the board unprotected.
  2. We are preparing a payment. If foil-coated getinax is used, the tracks will have to be etched using electrolytic methods, having previously painted them with paint insoluble in the electrolyte. The circuit board with prefabricated contacts greatly simplifies and speeds up the assembly process.
  3. We check the performance of the parts with a multimeter, if necessary, replace them with serviceable samples.
  4. According to the scheme, we collect and connect all the necessary parts. It is necessary to monitor the connection accuracy, correct polarity and installation direction of diodes or microcircuits. Any mistake can lead to the failure of important parts that will have to be purchased again.
  5. After the assembly is completed, it is recommended to carefully examine the board again, check the accuracy of the connections, the quality of the soldering and other important points.
  6. The board is placed in the case, a test run and configuration of the device is performed.

How to setup

To set up the device, you must either have a reference device, or know the voltage rating corresponding to a particular temperature of the controlled environment. For individual devices, there are own formulas that show the dependence of the voltage on the comparator on temperature. For example, for the LM335 sensor, this formula looks like:

V = (273 + T) 0.01,

where T is the desired temperature in Celsius.

In other circuits, tuning is done by selecting the values ​​​​of control resistors when creating a certain, known temperature. In each specific case, own methods can be used, optimally suited to the existing conditions or the equipment used. The requirements for the accuracy of the device also differ from each other, so there is no single tuning technology in principle.

Main malfunctions

The most common malfunction of homemade thermostats is the instability of the thermistor readings caused by poor quality parts. In addition, there are often difficulties with setting the modes, caused by a mismatch in ratings or a change in the composition of the parts necessary for the correct operation of the device. Most of the possible problems directly depend on the level of training of the master who assembles and configures the device, since skills and experience in this matter mean a lot. Nevertheless, experts say that making a thermostat with your own hands is a useful practical task that gives good experience in creating electronic devices.

If there is no self-confidence, it is better to use a ready-made device, of which there are enough on sale. It must be taken into account that the failure of the regulator at the most inopportune moment can cause serious troubles, the elimination of which will require effort, time and money. Therefore, when deciding on self-assembly, you should approach the issue as responsibly as possible and carefully weigh your capabilities.