Compliance with the temperature regime is a very important technological condition not only in production, but also in everyday life. Being so important, this parameter must be regulated and controlled by something. A huge number of such devices are produced, which have many features and parameters. But making a thermostat with your own hands is sometimes much more profitable than buying a ready-made factory analogue.

Create your own thermostat

General concept of temperature controllers

Devices that fix and simultaneously regulate the set temperature value are found to a greater extent in production. But they also found their place in everyday life. To maintain the required microclimate in the house, water thermostats are often used. With their own hands they make such devices for drying vegetables or heating an incubator. A similar system can find its place anywhere.

In this video, we will find out what a temperature controller is:

In reality, most thermostats are only part of general scheme, which consists of the following components:

1. A temperature sensor that measures and records, as well as transfers the received information to the controller. This happens due to the conversion of thermal energy into electrical signals recognized by the device. The sensor can be a resistance thermometer or thermocouple, which in their design have a metal that reacts to temperature changes and changes its resistance under its influence.
2. The analytical unit is the regulator itself. It receives electronic signals and reacts depending on its functions, after which it transmits the signal to the actuator.
3. An actuator is a kind of mechanical or electronic device that, when receiving a signal from the unit, behaves in a certain way. For example, when the set temperature is reached, the valve will shut off the coolant supply. Conversely, as soon as the readings fall below the preset values, the analytical unit will give the command to open the valve.

These are the three main parts of the temperature control system. Although, in addition to them, other parts like an intermediate relay can participate in the circuit. But they perform only an additional function.

Principle of operation

The principle by which all regulators work is to take a physical quantity (temperature), transfer data to the control unit circuit, which decides what needs to be done in a particular case.

If you make a thermal relay, then the simplest option will have a mechanical control circuit. Here, with the help of a resistor, a certain threshold is set, upon reaching which a signal will be given to the actuator.

To get additional functionality and the ability to work with a wider temperature range, you will have to integrate the controller. This will also help increase the life of the device.

In this video you can see how to make your own thermostat for electric heating:

Homemade temperature controller

There are actually a lot of schemes for making a thermostat yourself. It all depends on the area in which such a product will be used. Of course, creating something that is too complex and multifunctional is extremely difficult. But a thermostat that can be used to heat an aquarium or dry vegetables for the winter can be created with a minimum of knowledge.

The simplest scheme

The most simple circuit the thermostat with its own hands has a transformerless power supply, which consists of a diode bridge with a parallel connected zener diode, which stabilizes the voltage within 14 volts, and a quenching capacitor. You can also add a 12 volt stabilizer here if you wish.

The creation of a thermostat does not require much effort and money investment

The whole circuit will be based on a TL431 zener diode, which is controlled by a divider consisting of a 47 kΩ resistor, a 10 kΩ resistor and a 10 kΩ thermistor acting as a temperature sensor. Its resistance decreases with increasing temperature. Resistor and resistance are best matched to achieve the best response accuracy.

The process itself looks like this: when a voltage of more than 2.5 volts is formed on the control contact of the microcircuit, it will open, which will turn on the relay, supplying a load to the actuator.

How to make a thermostat for an incubator with your own hands, you can see in the video presented:

Conversely, when the voltage drops, the microcircuit will close and the relay will turn off.

To avoid rattling of the relay contacts, it is necessary to select it with a minimum holding current. And parallel to the inputs, you need to solder a 470 × 25 V capacitor.

When using an NTC thermistor and a microcircuit that has already been in use, it is worth first checking their performance and accuracy.

In this way, the simplest device turns outregulating the temperature. But with the right ingredients, it performs excellently in a wide range of applications.

Indoor device

Such thermostats with a do-it-yourself air temperature sensor are optimal for maintaining the specified microclimate parameters in rooms and containers. It is fully capable of automating the process and controlling any heat radiator from hot water and ending with teni. At the same time, the thermal switch has excellent performance data. And the sensor can be either built-in or remote.

Here, a thermistor, indicated in the diagram R1, acts as a thermal sensor. The voltage divider includes R1, R2, R3 and R6, the signal from which goes to the fourth pin of the operational amplifier microcircuit. A signal from the divider R3, R4, R7 and R8 is applied to the fifth contact of DA1.

The resistances of the resistors must be selected in such a way that at the lowest low temperature of the measured medium, when the resistance of the thermistor is maximum, the comparator is positively saturated.

The comparator output voltage is 11.5 volts. At this time, the transistor VT1 is in the open position, and the relay K1 turns on the executive or intermediate mechanism, as a result of which heating begins. As a result, the ambient temperature rises, which lowers the resistance of the sensor. At the input 4 of the microcircuit, the voltage begins to rise and as a result exceeds the voltage at pin 5. As a result, the comparator enters the phase of negative saturation. At the tenth output of the microcircuit, the voltage becomes approximately 0.7 volts, which is a logical zero. As a result, the transistor VT1 closes, and the relay turns off and turns off the actuator.

On the LM 311 chip

Such a do-it-yourself thermocontroller is designed to work with heating elements and is able to maintain the specified temperature parameters within 20-100 degrees. This is the safest and most reliable option, since it uses a galvanic isolation of the temperature sensor and control circuits, and this completely eliminates the possibility of electric shock.

Like most similar circuits, it is based on a DC bridge, in one arm of which a comparator is connected, and in the other - a temperature sensor. The comparator monitors the mismatch of the circuit and reacts to the state of the bridge when it crosses the balance point. At the same time, he tries to balance the bridge using a thermistor, changing its temperature. And thermal stabilization can occur only at a certain value.

Resistor R6 sets the point at which balance should be formed. And depending on the temperature of the environment, the thermistor R8 can enter into this balance, which allows you to regulate the temperature.

In the video you can see an analysis of a simple thermostat circuit:

If the temperature set by R6 is lower than the required one, then the resistance on R8 is too large, which lowers the current on the comparator. This will cause current to flow and open the semistor VS1.which will turn on the heating element. This will be signaled by the LED.

As the temperature rises, the resistance of R8 will begin to decrease. The bridge will tend to the balance point. On the comparator, the potential of the inverse input gradually decreases, and on the direct one, it increases. At some point, the situation changes, and the process takes place in the opposite direction. Thus, the thermocontroller with its own hands will turn on or off the actuator depending on the resistance R8.

If LM311 is not available, then it can be replaced with the domestic KR554SA301 microcircuit. It turns out a simple do-it-yourself thermostat with minimal costs, high accuracy and reliability.

Required materials and tools

By itself, the assembly of any circuit of an electric temperature controller does not take much time and effort. But to make a thermostat, minimal knowledge of electronics is required, set of parts according to the diagram and tool:

1. Pulse soldering iron. You can use a regular one, but with a thin sting.
2. Solder and flux.
3. Printed circuit board.
4. Acid to etch the tracks.

Advantages and disadvantages

Even a simple do-it-yourself thermostat has a lot of advantages and positive aspects. There is no need to talk about factory multifunctional devices.

Temperature controllers allow:

1. Maintain a comfortable temperature.
2. Save energy resources.
3. Do not involve a person in the process.
4. Observe the technological process, increasing the quality.

The disadvantages include the high cost of factory models. Of course, homemade appliances it doesn't apply. But the production ones, which are required when working with liquid, gaseous, alkaline and other similar media, have a high cost. Especially if the device must have many functions and capabilities.

Autonomous heating of a private house allows you to select individual temperature modes, which is very comfortable and economical for residents. In order not to set a different mode in the room every time when the weather changes outside, you can use a thermostat or thermostat for heating, which can be installed on both radiators and the boiler.

Automatic room heat regulation

What is it for

• The most common in the territory Russian Federation is an , on gas boilers. But such, if I may say so, luxury is not available in all regions and localities. The reasons for this are the most commonplace - the absence of a CHP or central boiler houses, as well as gas pipelines nearby.
• Have you ever visited a residential building, pumping station or weather station far from densely populated areas during the winter season, when the only means of communication is a sled with a diesel engine? In such situations, they very often arrange heating with their own hands using electricity.

• For small rooms, for example, one room of the duty officer at a pumping station is enough - it is enough for the most severe winter, but for a larger area, a heating boiler and a radiator system will already be required. To maintain the desired temperature in the boiler, we bring to your attention a homemade regulator.

Temperature sensor

• This design does not require thermistors or various sensors of the TCM type., here instead of them, a bipolar ordinary transistor is involved. Like all semiconductor devices, its operation is highly dependent on the environment, more precisely, on its temperature. As the temperature rises, the collector current increases, and this negatively affects the operation of the amplifying stage - the operating point shifts until the signal is distorted and the transistor simply does not respond to the input signal, that is, it stops working.

• Diodes are also semiconductors., and an increase in temperature has a negative effect on them. At t25⁰C, the "continuity" of a free silicon diode will show 700mV, and for a permanent one - about 300mV, but if the temperature rises, then it will decrease accordingly forward voltage device. So, when the temperature rises by 1⁰C, the voltage will decrease by 2mV, that is, -2mV / 1⁰C.

• This dependence of semiconductor devices allows them to be used as temperature sensors. On such a negative cascade property with a fixed base current, the whole circuit of the thermostat operation is based (diagram in the photo above).
• The temperature sensor is mounted on a VT1 transistor of the KT835B type, the load of the stage is resistor R1, and the mode of operation for direct current of the transistor is set by resistors R2 and R3. To keep the voltage across the transistor emitter at 6.8V at room temperature, the fixed bias is set by the resistor R3.

Council. For this reason, R 3 is marked with a * on the diagram, and you should not achieve special accuracy here, as long as there are no large drops. These measurements can be made with respect to a transistor collector connected by a power supply to a common drive.

• Transistor p-n-p KT835B specially selected, its collector is connected to a metal case plate with a hole for attaching the semiconductor to the radiator. It is for this hole that the device is attached to the plate to which the underwater wire is still attached.
• The assembled sensor is attached to the heating pipe using metal clamps, and the structure does not need to be insulated with any gasket from the heating pipe. The fact is that the collector is connected by one wire to the power source - this greatly simplifies the entire sensor and makes the contact better.

Comparator

• Comparator, mounted on an OP1 operational amplifier of the K140UD608 type, sets the temperature. The inverted input R5 is supplied with voltage from the emitter VT1, and through R6, the voltage from the engine R7 is supplied to the non-inverted input.
• This voltage determines the temperature to disconnect the load. The upper and lower ranges for setting the threshold for the operation of the comparator are set using R8 and R9. The required postresis of the comparator operation is provided by R4.

Load management

• On VT2 and Rel1 a load control device has been made and the indicator of the operating mode of the thermostat is also here - red when heating, and green - reaching the required temperature. A diode VD1 is connected in parallel with the winding Rel1 to protect VT2 from the voltage caused by self-induction on the Rel1 coil when disconnected.

Council. The figure above shows that the permissible switching current of the relay is 16A, which means that it allows control of the load up to 3kW. Use a device with a power of 2-2.5kW to lighten the load.

Power Supply

• An arbitrary instruction allows for a real thermostat, due to its low power, to use a cheap Chinese adapter as a power supply. You can also assemble a 12V rectifier yourself, with a circuit consumption current of no more than 200mA. For this purpose, a transformer with a power of up to 5W and an output from 15 to 17V will fit.
• The diode bridge is made on 1N4007 diodes, and the voltage regulator on the integral type 7812. Due to the low power, it is not required to install the stabilizer on the battery.

Adjusting the thermostat

• To test the sensor, you can use the most ordinary table lamp with a metal shade. As noted above, room temperature allows withstanding the voltage at the emitter VT1 of about 6.8V, but if you increase it to 90⁰C, then the voltage drops to 5.99V. For measurements, you can use an ordinary Chinese multimeter with a DT838 thermocouple.
• The comparator works as follows: if the voltage of the temperature sensor at the inverting input is higher than the voltage at the non-inverting input, then at the output it will be equivalent to the voltage of the power supply - it will be a logical unit. Therefore VT2 opens and the relay turns on, moving the relay contacts to heating mode.
• Temperature sensor VT1 heats up as the heating circuit heats up and as the temperature rises, the voltage at the emitter decreases. At the moment when it drops slightly below the voltage that is set on the R7 engine, a logical zero is obtained, which leads to the transistor being locked and the relay turned off.
• At this time, the voltage is not supplied to the boiler and the system begins to cool down, which also entails the cooling of the VT1 sensor. This means that the voltage at the emitter rises and as soon as it crosses the border set by R7, the relay starts up again. This process will be repeated constantly.
• As you can imagine, the price of such a device is not high, but it allows it to withstand the required temperature under any weather conditions. This is very convenient in cases where there are no permanent residents in the room who monitor the temperature regime, or when people are constantly replacing each other and, moreover, are busy with work.

It is used in many technological processes, including household heating systems. The factor that determines the action of the thermostat is the outside temperature, the value of which is analyzed and when the set limit is reached, the flow rate decreases or increases.

Thermostats come in various designs and today there are quite a few industrial versions on sale that work according to different principles and are intended for use in different areas. The simplest electronic circuits are also available, which can be assembled by anyone, with the appropriate knowledge in electronics.

Description

A thermostat is a device installed in power supply systems that optimizes energy consumption for heating. The main elements of the thermostat:

1. Temperature sensors - control the temperature level by generating electrical impulses of the appropriate magnitude.
2. Analytical unit - processes electrical signals from the sensors and converts the temperature value into a value characterizing the position of the executive body.
3. Executive agency - regulates the flow, by the value 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 electric power circuit of the executing organ, thus decreasing or increasing the value of the supply voltage.

Principle of operation

The temperature sensor generates electrical impulses, the current value of which depends on the temperature level. The built-in ratio of these values \u200b\u200ballows the device to very accurately determine the temperature threshold and make a decision, for example, by how many degrees the air supply damper to the solid fuel boiler should be opened, or the hot water supply valve should be open. The essence 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 mechanical control in the form of a resistor, by moving which, the user sets the required temperature threshold for operation, that is, indicating at what outside temperature it will be necessary to increase the flow. With more advanced functionality, industrial devices can be programmed to wider limits, using a controller, depending on different temperature ranges. They have no mechanical controls, which contributes to long-term operation.

How to do it yourself

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 easily shifted to such automation.

Autoregulator circuits

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

1. Based on an adjustable zener diode type TL431 - the principle of operation consists in fixing the excess of the voltage threshold of 2.5 volts. When it is broken on the control electrode, the Zener diode comes to the open position and the load current passes through it. In the event that the voltage does not break through the 2.5 volt threshold, the circuit comes to 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 analogue CD4011B - the main element is a T122 or KU202 thyristor, 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 to the open position when pulses arrive, which in turn is a signal to open the thyristor. In the absence of a radiator, the latter acquires throughput up to 200 watts. To increase this threshold, you will need to install a more powerful thyristor, or equip an existing heatsink, which will bring the switching capacity to 1 kW.

Required materials and tools

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

• Pulse or ordinary soldering iron with a thin heating element.
• Printed circuit board.
• Solder and flux.
• Acid for etching tracks.
• Electronic parts according to the chosen scheme.

Thermostat circuit

Step by step guide

1. Electronic elements must be placed on the board in such a way that they can be easily mounted without touching the neighboring ones with the soldering iron, near the parts actively generating heat, the distance is made somewhat large.
2. The paths between the elements are etched according to the drawing, if there is none, then a sketch on paper is first performed.
3. It is imperative to check the performance of each element and only after that the landing on the board is carried out, 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 closely adjacent tracks; for isolation, 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 homemade 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 action depending on the temperature readings. Similarly, you can equip the lawn spraying or irrigation system with automation, the extension of light-shielding structures, or just a sound or light alarm warning about something.

DIY repair

Assembled with our own hands, these devices serve for a long time, however, there are several standard situations when repairs may be required:

• Failure of the regulating resistor - it happens most often, since the copper tracks wear out, inside the element on which the electrode slides 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. To avoid this in the future, thyristors are equipped with radiators, or else the thermostat should be moved to an area with a neutral microclimate, which is especially important for wet rooms.
• Incorrect temperature adjustment - the thermistor may be damaged, corrosion or dirt on the measuring electrodes.

Advantages and disadvantages

Undoubtedly using automatic regulation, in itself is an advantage, since the energy consumer gets the following opportunities:

• Saving energy resources.
• Constant comfortable room temperature.
• No human involvement required.

Automatic control is especially used in heating systems for apartment buildings. The inlet valves equipped with thermostats automatically control the supply of the heating medium, 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 made by hand. Only industrial devices designed to regulate the supply of liquid and gaseous media are expensive, since the actuator includes a special motor and other shut-off valves.

Although the device itself is quite undemanding to the operating conditions, the accuracy of the response depends on the quality of the primary signal, and especially this 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 sealed with epoxy glue. You can leave the end of the thermistor on the surface, which will contribute to greater sensitivity.

The thermostat in everyday life is used in a wide variety of devices, from a refrigerator to irons and soldering irons. Probably, there is no such radio amateur who would bypass such a scheme. Most often, thermistors, transistors or diodes are used as a temperature sensor or sensor in various amateur designs. The operation of such thermostats is quite simple, the operation algorithm is primitive, and, as a consequence, a simple electrical circuit.

The preset temperature is maintained by turning on and off the heating element (TEN): as soon as the temperature reaches the set value, the comparator (comparator) is triggered and the TEN is turned off. This principle of regulation is implemented in all simple regulators. It would seem that everything is simple and understandable, but this is only to the point, until it comes to practical experiments.

The most difficult and time-consuming process in the manufacture of "simple" thermostats is setting to the required temperature. To determine the characteristic points of the temperature scale, it is proposed to first immerse the sensor in a vessel with melting ice (this is zero degrees Celsius), and then in boiling water (100 degrees).

After this "calibration" by trial and error using a thermometer and voltmeter, the required response temperature is set. After such experiments, the result is not the best.

Nowadays, various companies produce many temperature sensors that are already calibrated during the production process. These are mainly sensors designed to work with microcontrollers. The information at the output of these sensors is digital, transmitted via a single-wire bidirectional 1-wire interface, which allows you to create entire networks based on such devices. In other words, it is very easy to create a multipoint thermometer, to control the temperature, for example, in the room and outside the window, and not even in the same room.

Against the background of such an abundance of intelligent digital sensors, the modest LM335 device and its varieties 235, 135 look good. The first number in the marking indicates the purpose of the device: 1 corresponds to military acceptance, 2 to industrial use, and the three indicates the use of the component in household appliances.

By the way, the same harmonious designation system is characteristic of many imported parts, for example, operational amplifiers, comparators and many others. The domestic analogue of such designations was the marking of transistors, for example, 2T and KT. The former were intended for the military, and the latter for widespread use. But it's time to return to the already familiar LM335.

Outwardly, this sensor looks like a low-power transistor in a TO-92 plastic case, but inside it there are 16 transistors. Also, this sensor can be in the SO - 8 package, but there are no differences between them. Appearance The sensor is shown in Figure 1.

Figure 1. External view of the LM335 sensor

According to the principle of operation, the LM335 sensor is a zener diode, in which the stabilization voltage depends on the temperature. When the temperature rises by one degree Kelvin, the stabilization voltage increases by 10 millivolts. Typical scheme inclusion is shown in Figure 2.

Figure 2. Typical connection diagram of the LM335 sensor

When looking at this figure, you can immediately ask what is the resistance of the resistor R1 and what is the supply voltage with such a switching scheme. The answer is contained in the technical documentation, which says that the normal operation of the product is guaranteed in the current range of 0.45 ... 5.00 milliamperes. Note that the 5mA limit should not be exceeded as the sensor will overheat and measure its own temperature.

What will the LM335 sensor show

According to the documentation (Data Sheet) the sensor is calibrated according to the absolute Kelvin scale. If we assume that the indoor temperature is -273.15 ° C, and this is an absolute zero in Kelvin, then the sensor in question should show zero voltage. As the temperature rises for each degree, the output voltage of the zener diode will increase by as much as 10mV or 0.010V.

To convert the temperature from the usual Celsius scale to the Kelvin scale, just add 273.15. Well, about 0.15 is always forgotten, so just 273, and it turns out that 0 ° C is 0 + 273 \u003d 273 ° K.

In physics textbooks, 25 ° C is considered normal temperature, and according to Kelvin, 25 + 273 \u003d 298, or rather 298.15. This point is mentioned in the datasheet as the only calibration point for the sensor. Thus, at a temperature of 25 ° C, the output of the sensor should be 298.15 * 0.010 \u003d 2.9815V.

The operating range of the sensor is in the range -40 ... 100 ° C and in the entire range the sensor characteristic is very linear, which makes it easy to calculate the sensor readings at any temperature: first, you need to convert the temperature from Celsius to Kelvin degrees. Then multiply the resulting temperature by 0.010V. The last zero in this number indicates that the voltage in Volts is indicated with an accuracy of 1 mV.

All these considerations and calculations should suggest that when making a thermostat, you will not have to calibrate anything by dipping the sensor into boiling water and melting ice. It is enough to simply calculate the voltage at the output of the LM335, after which it remains only to set this voltage as a master at the input of the comparator (comparator).

Another reason for using the LM335 in its design is its low price. In the online store, you can buy it for about $ 1. Probably, delivery will cost more. After all these theoretical considerations, you can proceed to the development electrical circuit thermostat. In this case, for the cellar.

Schematic diagram of the thermostat for the cellar

To design a cellar thermostat based on the LM335 analog temperature sensor, you don't need to invent anything new. It is enough to refer to the technical documentation (Data Sheet) for this component. The datasheet contains all methods of using the sensor, including the actual thermostat.

But this scheme can be considered as functional, according to which the principle of operation can be studied. In practice, you will have to supplement it with an output device that allows you to turn on a heater of a given power and, of course, a power supply unit and, possibly, operation indicators. We will talk about these nodes a little later, but for now let's see what the proprietary documentation offers, it's datasheet. The circuit as it is is shown in Figure 3.

Figure 3. Wiring diagram for LM335 sensor

How Comparator Works

The basis of the proposed circuit is the LM311 comparator, aka 211 or 111. Like all comparators, the 311th has two inputs and an output. One of the inputs (2) is direct and is marked with a + sign. Another input - inverse (3) is marked with a minus sign. The output of the comparator is pin 7.

The logic of the comparator is quite simple. When the voltage at the direct input (2) is greater than at the inverse (3), the output of the comparator is set to a high level. The transistor opens and connects the load. In Figure 1, this is just a heater, but this is a functional diagram. A potentiometer is connected to the direct input, which sets the threshold for the comparator, i.e. temperature setpoint.

When the voltage at the inverse input is greater than the direct voltage, the comparator output will go low. The LM335 temperature sensor is connected to the inverse input, therefore, when the temperature rises (the heater is already on), the voltage at the inverse input will increase.

When the sensor voltage reaches the threshold set by the potentiometer, the comparator switches to low level, the transistor closes and turns off the heater. Then the whole cycle will be repeated.

There is absolutely nothing left - on the basis of the considered functional diagram, develop a practical diagram, as simple as possible and accessible for repetition by novice radio amateurs. Possible variant a practical circuit is shown in Figure 4.

Figure 4.

A few explanations for the schematic diagram

As you can see, the basic schema has changed a bit. First of all, instead of a heater, the transistor will turn on the relay, and what will turn on the relay about this a little later. An electrolytic capacitor C1 has also appeared, the purpose of which is to smooth out the voltage ripples on the Zener diode 4568. But let's talk about the purpose of the details in a little more detail.

The power supply of the temperature sensor and voltage divider of the temperature setpoint R2, R3, R4 is stabilized by the parametric stabilizer R1, 1N4568, C1 with a stabilization voltage of 6.4V. Even if the entire device will be powered from a stabilized source, an additional stabilizer will not hurt.

This solution allows the entire device to be powered from a source, the voltage of which can be selected depending on the voltage of the relay coil available. Most likely it will be 12 or 24V. The power supply can even be unregulated, just a diode bridge with a capacitor. But it’s better not to be stingy and put the 7812 integral stabilizer in the power supply unit, which will also provide protection against short circuit.

If the conversation turned to the relay, what can be used in this case? First of all, these are modern small-sized relays, like those used in washing machines... The external view of the relay is shown in Figure 5.

Figure 5. Small relay

Despite their miniature size, such relays can switch current up to 10A, which allows switching a load of up to 2 kW. This is if for all 10A, but this is not necessary. The most that you can turn on such a relay is a heater with a power of no more than 1 kW, because there must be at least some kind of "safety margin"!

It is very good if the relay with its contacts turns on the magnetic starter of the PME series, and let it turn on the heater. This is one of the most reliable load switching options. A possible implementation of this option is shown in Figure 6.

Figure 6.

Thermostat power supply

The device's power supply is unstabilized, and since the thermostat itself (one microcircuit and one transistor) consumes practically no power, any Chinese-made network adapter is quite suitable as a power source.

If you make a power supply, as shown in the diagram, then a small power transformer from a cassette recorder, calculator or something else is quite suitable. The main thing is that the voltage on the secondary winding should not exceed 12..14V. With a lower voltage, the relay will not work, and with a higher voltage, it can simply burn out.

If the output voltage of the transformer is within 17 ... 19V, then you cannot do without a stabilizer. This should not be scary, because modern integrated stabilizers have only 3 pins, it is not so difficult to solder them.

Turning on the load

An open transistor VT1 turns on relay K1, which, with its contact K1.1, turns on the magnetic starter K2. Contacts of the magnetic starter K2.1 and K2.2 connect the heater to the mains. It should be noted that the heater is switched on by two contacts at once. This solution ensures that when the starter is off, there will be no phase left on the load, if, of course, everything is in order.

Since the cellar room is humid, sometimes very damp, and very dangerous in terms of electrical safety, it is best to connect the entire device using an RCD in accordance with all the requirements for modern wiring.

What should be the heater

A lot of temperature control schemes for the cellar have been published. Once they were printed by the magazine "Modelist-constructor" and other printed publications, but now all this abundance has migrated to the Internet. These articles give recommendations on how the heater should be.

Someone offers ordinary hundred-watt incandescent lamps, tubular heaters of the TEN brand, oil radiators (it is even possible with a faulty bimetallic regulator). It is also suggested to use household heaters with a built-in fan. The main thing is that there is no direct access to live parts. Therefore, the old electric cookers with an open spiral and home-made heaters of the "goat" type should never be used.

Check the installation first

If the device is assembled without errors from serviceable parts, then special adjustments are not required. But in any case, before switching on for the first time, be sure to check the quality of the installation: whether there are any non-soldering or, on the contrary, closed tracks on printed circuit board... And do not forget to do these actions, just take it as a rule. This is especially true for structures connected to the electrical network.

Setting the thermostat

If the first switching on of the structure happened without smoke and explosions, then the only thing that needs to be done is to set the reference voltage at the direct input of the comparator (pin 2), according to the desired temperature. This requires several calculations.

Suppose that the temperature in the cellar should be kept at +2 degrees Celsius. Then first we translate it into Kelvin degrees, then we multiply the result by 0.010V, as a result, a reference voltage is obtained, it is also the temperature setpoint.

(273.15 + 2) * 0.010 \u003d 2.7515 (B)

If it is assumed that the thermostat must maintain the temperature, for example, +4 degrees, then the following result will be obtained: (273.15 + 4) * 0.010 \u003d 2.7715 (V)

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

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

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

simple thermostat circuit
incubator thermostat circuit

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.
• display and generator of internal type 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 needs to be prepared for making paths.
3. To similar schemes thermistors with a power of 1 kOm to 15 kOm are not bad, 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 up the system until the power inside the temperature sensor returns to its original value.
6. Regulator sensors of a similar plan need customization. During significant changes in the surrounding atmosphere, it is necessary to control the heating inside the object.

Assembling a digital device:

1. Microcontroller should be connected together with the temperature sensor. It must have port outputs that 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 be an indication that the device is in working order.
3. The microcontroller contains memory. If the device settings go wrong, the memory automatically returns them to the originally specified parameters.

When assembling the structure, one must not forget about safety precautions. During the use of the temperature sensor in a watery or humid atmosphere, its terminals must be hermetically sealed. The value of thermistor R5 can be indicated from 10 to 51 kOhm. In this case, the resistance of the resistor R5 must have the same value.

Instead of the designated K140UD6 microcircuits, you can use K140UD7, K140UD8, K140UD12, K153UD2. In the role of the VD1 Zener diode, any instrument with a stabilization power of 11 ... 13 V can be introduced.

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

The FU1 value 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 SCR.

Device

mechanical thermostat circuit

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

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

The thermostat device includes:

1. Temperature sensor - created on the basis of the comparator DD1.
2. Key thermostat circuit 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 thermal sensor there is a thermistor R5 (type MMT-4), connected to the input of the third device.
5. Construction diagram does not have galvanic isolation from the mains, and takes energy from the parametric stabilizer on the R10, VD1 parts.
6. As a power supply for the device you can take a cheap network adapter. During its connection, you need to be guided by the rules and requirements for new wiring, since the conditions of the room can be electrical hazard.

An insignificant reserve of capacitor C1 contributes to a gradual increase in power, which leads to a smooth (no more than 2 seconds) turning on of electric lamps.

Self-assembly costs

Today, any similar 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 investments, this is not quite profitable, therefore it is much cheaper to do it yourself.

The costs for self-assembly are several times lower, namely:

• board K561LA7 will cost no more than 50 rubles;
• a thermistor with a capacity of 1 kOm up 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 costs of self-assembly will have to be spent no more than 430 rubles and a little personal time. The owner can fully adapt the device for his needs, using a simple scheme for this.

Operating principle

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

The principle of operation of the regulator is the feature of gases and liquids to contract or expand during cooling or heating. Therefore, the operation of the water and gas configurations is based on the same essence.

They differ from each other 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 stages:

1. As a result of a change in the temperature of the heated object, there is a change in the work of the coolant in the heating mechanism.
2. Together with that, this makes the siphon increase or decrease in size.
3. After that, the spool is displaced, which balances the coolant inlet.
4. Inside of the siphon filled with gas, facilitating uniform temperature control. A built-in thermal sensor monitors the external temperature.
5. Each heat level value the specific value of the pressure force of the working atmosphere inside the siphon is equated. The lack of 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 towards the closing side until the level of the working pressure in the siphon becomes balanced due to the forces of the spring.
7. In case of lowering 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.

Views

Manufacturing companies offer customers 3 types of thermostats, each with different internal signals. They control the process of heating the coolant and equalize the temperature order.

Signal extension methods:

1. Directly from the coolant. It is considered insufficiently effective, therefore it is used infrequently. Its work is based on an immersion sensor or similar mechanisms. In comparison with 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 changes, and not the level of water heating. Easy to install in the apartment. It communicates with heating communications using a cable through which a signal is transmitted. Thermostats 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 the diaphragm give the system a command to open or close a pipe with a heating device.

In addition, devices can be electrical or electronic.

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

1. To control the heating level of the radiator and the branch line.
2. Follow for the boiler power.

Overview of thermostats on the market

Thermostat IWarm 710

The most popular models today are the E 51.716 and IWarm 710. Their non-combustible plastic housing 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 corresponding temperature characteristics.

The cost of these models is presented within 2,700 thousand rubles.

The features of the E 51.716 include the fact that it has a 3 m cable, is able to balance the temperature simultaneously from the floor itself, and the fact 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. This can cause discomfort in operation. Also, the memory of E 51.716 and IWarm 710 does not have an automatic heating function, so you have to do it yourself.

Electronic regulators with a mechanical principle of operation:

1. Regulation of work based on automation, and carried out using the buttons located on the panel.
2. Include display, which indicates the previous and specified degrees.
3. It is possible to configure the device yourself: number, operating time, heating cycle while maintaining a specific mode, you can also specify the degree of heating.
4. Compared to mechanical counterparts, the temperature of the electric models is easily adjustable by about 0.5 values.

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

Electronic configurations:

1. They independently control the temperature.
2. Just one device can control the atmosphere for several days in advance and separately for each room.
3. Allows 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 work devices in every room. The owner will 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 far from home. The adjustment is carried out using the built-in Wi-Fi router.

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