The electronic thermostat for refrigerator will help in cases where your own (factory) thermostat is faulty or its operating accuracy is no longer sufficient. Older refrigerators use a mechanical temperature thermostat using a liquid or gas that fills a capillary.

When the temperature changes, the pressure inside the capillary also changes, which is transmitted to the membrane (bellows). As a result, the thermostat turns the refrigerator compressor on and off. Of course, such a temperature control system has low accuracy, and its parts wear out over time.

Description of the operation of the thermostat for the refrigerator

As you know, the temperature of food storage in the refrigerator should be +2...8 degrees Celsius. The operating temperature of the refrigerator is +5 degrees.

An electronic thermostat for a refrigerator is characterized by two parameters: the start and stop temperature (or the average temperature plus the hysteresis value) of the compressor. Hysteresis is necessary to prevent the refrigerator compressor from turning on too often.

This circuit provides a hysteresis of 2 degrees at an average temperature of 5 degrees. Thus, the refrigerator compressor turns on when the temperature reaches + 6 degrees and turns off when it drops to + 4 degrees.

This temperature range is sufficient to maintain optimal temperature storage of products, and at the same time it ensures comfortable operation of the compressor, preventing its excessive wear. This is especially important for older refrigerators that use a thermal relay to start the engine.

The electronic thermostat is a suitable replacement for the original thermostat. The thermostat reads the temperature using a sensor whose resistance changes depending on the temperature change. A thermistor (NTC) is often used for these purposes, but the problem is its low accuracy and the need for calibration.

To ensure accurate setting of the controlled temperature and eliminate the need for hours of calibration, in this version of the thermostat for the refrigerator, . It is an integrated circuit linearly calibrated in degrees Celsius, with a gain of 10 mV per degree Celsius. Due to the fact that the threshold temperature is close to zero, the relative change in output voltage is large. Therefore, the signal from the sensor output can be controlled using a simple circuit consisting of only two transistors.

Since the output voltage is too low to turn on transistor VT1, sensor LM35 is included as a current source. Its output is loaded by resistor R1 and therefore the current on it changes in proportion to the temperature. This current causes a drop across resistor R2. The voltage drop controls the operation of transistor VT1. If the voltage drop exceeds the threshold voltage of the base-emitter junction, transistors VT1 and VT2 open, relay K1 turns on, whose contacts are connected instead of the old thermostat contacts.

Resistor R3 creates positive feedback. This adds a small current to R2, which shifts the threshold and thereby provides hysteresis. Winding electromagnetic relay should be designed for 5...6 volts. The relay contact pair must withstand the required current and voltage.

The LM35 sensor is located inside the refrigerator in suitable place. Resistor R1 is soldered directly to the temperature sensor, which in turn allows you to connect the LM35 to the circuit board with just two wires.

The wires connecting the sensor can introduce noise into the circuit, so capacitor C2 is added to suppress interference. The circuit operates from a 5 volt power supply built by . Current consumption mainly depends on the type of relay used. must be reliably isolated from the network.

The big advantage of this circuit is that it starts working immediately upon first startup and does not require calibration or configuration. If there is a need to slightly change the temperature level, this can be done by selecting resistances R1 or R2. Resistance R3 determines the amount of hysteresis.

Portable USB oscilloscope, 2 channels, 40 MHz....

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

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

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

If the temperature exceeds the upper threshold TH, then the output of the DS1820 will be a logical one, the load will be disconnected from the network. If the temperature drops below the lower programmed level TL, a logical zero will appear at the output of the temperature sensor and the load will be turned on. If there are any unclear points, homemade design was borrowed from No. 2 for 2006.

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

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

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

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

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

The design of an analog thermostat is used to maintain a set temperature inside an incubator, or in a box on the balcony for storing vegetables in winter. Power is supplied from a 12 volt car battery.

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

The temperature at which the thermostat relay operates is set by the voltage level on pins 5 and 6 of the K561LE5 microcircuit, and the relay off temperature is set by the potential on pins 1 and 21. The temperature difference is controlled by the voltage drop across resistor R3. A thermistor with negative TCR is used as temperature sensor R4, i.e.

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

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

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

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

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

To turn on and off heating element The thermostat uses an IRF840 field-effect transistor. To discharge the transistor gate, there is a diode VD1.

The thermostat circuit uses a transformerless power supply. Excess alternating voltage is reduced due to the reactance of capacitance C4.

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

Dependence of voltage drop on p-n junction semiconductors on temperature, is perfect for creating our homemade sensor.

Many of the useful things that will help increase comfort in our lives can be assembled with your own hands without much difficulty. The same applies to the thermostat (it is also called a thermostat).

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

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

How does it work

The operating principle of a thermostat is quite simple, so many radio amateurs make homemade devices to hone their skills.

In this case, you can use many various schemes, although the most popular is the comparator chip.

This element has several inputs, but only one output. So, the first output receives the so-called “Reference voltage”, which has the value of the set temperature. The second one receives voltage directly from the temperature sensor.

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

Manufacturing process

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

Everything must happen in the following way:

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

Expert advice: To turn on the heater, it is best to use the meter terminal block.

Heater power and thermostat installation

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

In cases where the value is approximately 30 A (this is the level for which automotive relays are designed), it is possible to use a 6.6 kW heater (based on a 30x220 calculation).

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

It is worth noting: DIY enthusiasts can make an electronic thermostat with their own hands based on an electromagnetic relay with powerful contacts that can withstand currents of up to 30 amperes. This homemade device can be used for various household needs.

The thermostat must be installed almost at the very bottom of the room wall, since this is where cold air accumulates. Also important point is the absence of thermal interference that could affect the device and thereby confuse it.

For example, it will not function properly if it is installed in a draft or next to some electrical appliance that intensively emits heat.

Settings

To measure temperature, it is better to use a thermistor, whose electrical resistance changes as the temperature changes.

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

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

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

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

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

Autonomous heating of a private house allows you to choose individual temperature conditions, which is very comfortable and economical for residents. In order not to set a different mode indoors every time 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 , on gas boilers. But such, so to speak, luxury is not available in all areas and localities. The reasons for this are the most banal - the lack of thermal power plants or central boiler houses, as well as gas mains nearby.
• Have you ever visited a residential building, pumping station or weather station remote from densely populated areas in winter, when the only means of communication is a sleigh with a diesel engine? In such situations, very often they arrange heating with their own hands using electricity.

• For small rooms, for example, one duty room per pumping station, enough - it will be enough for the harshest winter, but for a larger area you will already need a heating boiler and a radiator system. To maintain the desired temperature in the boiler, we bring to your attention a homemade control device.

Temperature sensor

• This design does not require thermistors or various TCM type sensors, here an ordinary bipolar transistor is used instead. Like all semiconductor devices, its operation depends heavily on environment, more precisely, on its temperature. As the temperature rises, the collector current increases, and this negatively affects the operation of the amplifier 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 rising temperatures negatively affect them too. At t25⁰C, the “continuity” of a free silicon diode will show 700 mV, and for a permanent one - about 300 mV, but if the temperature rises, then the forward voltage of the device will decrease accordingly. So, when the temperature increases 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. The entire operation circuit of the thermostat is based on this negative cascade property with a fixed base current (diagram in the photo above).
• The temperature sensor is mounted on a transistor VT1 type KT835B, the cascade load is resistor R1, and the operating mode is DC The transistor is set by resistors R2 and R3. To ensure that the voltage at the transistor emitter at room temperature is 6.8V, a fixed bias is set by resistor R3.

Advice. For this reason, in the diagram R 3 is marked * and special accuracy should not be achieved here, just to avoid large differences. These measurements can be made relative to a transistor collector connected by a power source to a common drive.

• Transistor pnp KT835B specially selected, its collector is connected to a metal body plate that has a hole for attaching the semiconductor to the radiator. It is through this hole that the device is attached to the plate, to which the underwater wire is also 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 contact better.

Comparator

• Comparator, mounted on an operational amplifier OR1 type K140UD608, sets the temperature. The invertible input R5 is supplied with voltage from the emitter VT1, and through R6 the non-invertible input is supplied with voltage from the engine R7.
• This voltage determines the temperature for switching off the load. The upper and lower ranges for setting the threshold for triggering the comparator are set using R8 and R9. The required posteresis of the comparator is provided by R4.

Load management

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

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

power unit

• 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 current consumption of no more than 200mA. For this purpose, a transformer with a power of up to 5 W and an output of 15 to 17 V is suitable.
• The diode bridge is made using 1N4007 diodes, and the voltage stabilizer is based on an integrated type 7812. Due to the low power, it is not necessary to install a stabilizer on the battery.

Adjusting the thermostat

• To check the sensor, you can use the most ordinary table lamp with a metal lampshade. As noted above, room temperature allows you to withstand a voltage at the emitter of VT1 of about 6.8V, but if you increase it to 90⁰C, the voltage drops to 5.99V. For measurements, you can use a regular Chinese multimeter with a thermocouple type DT838.
• 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 equal to the voltage of the power source - this will be a logical one. 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 turning off and the relay turning off.
• At this time, no voltage is supplied to the boiler and the system begins to cool, which also entails the cooling of the VT1 sensor. This means that the voltage at the emitter increases and as soon as it crosses the limit set by R7, the relay starts again. This process will be repeated constantly.
• As you understand, the price of such a device is low, but it allows you to maintain the desired temperature in any weather conditions. This is very convenient in cases where there are no permanent residents in the room monitoring temperature conditions, or when people constantly replace each other and are also busy with work.

The operation of a gas or electric boiler can be optimized by using external control of the unit. Commercially available remote thermostats are designed for this purpose. This article will help you understand what these devices are and understand their varieties. It will also discuss the question of how to assemble a thermal relay with your own hands.

Purpose of thermostats

Any electric or gas boiler is equipped with an automation kit that monitors the heating of the coolant at the outlet of the unit and turns off the main burner when the set temperature is reached. Solid fuel boilers are also equipped with similar means. They allow you to maintain the water temperature within certain limits, but nothing more.

Wherein climatic conditions indoors or outdoors are not taken into account. This is not very convenient; the homeowner has to constantly select the appropriate operating mode for the boiler on his own. The weather can change during the day, then the rooms become hot or cool. It would be much more convenient if the boiler automation was oriented towards the air temperature in the rooms.

To control the operation of boilers depending on the actual temperature, various heating thermostats are used. Being connected to the boiler electronics, such a relay turns off and starts heating, maintaining the required temperature of the air, not the coolant.

Types of thermal relays

A conventional thermostat is a small electronic unit installed on the wall in a suitable location and connected to a heat source by wires. There is only a temperature regulator on the front panel; this is the cheapest type of device.

In addition to it, there are other types of thermal relays:

• programmable: they have a liquid crystal display, are connected using wires or use wireless communication with the boiler. The program allows you to set temperature changes at certain times of the day and by day during the week;
• the same device, only equipped with a GSM module;
• autonomous regulator powered by its own battery;
• wireless thermostat with remote sensor to control the heating process depending on the ambient temperature.

Note. A model where the sensor is located outside the building provides weather-dependent control of the operation of the boiler installation. The method is considered the most effective, since the heat source responds to changing weather conditions even before they affect the temperature inside the building.

Multifunctional thermal relays that can be programmed significantly save energy. During those hours of the day when no one is home, support high temperature the rooms don't make sense. Knowing his family's work schedule, the homeowner can always program the temperature switch so that at certain times the air temperature drops and the heating turns on an hour before people arrive.

Household thermostats equipped with a GSM module are capable of providing remote control boiler installation via cellular communication. A budget option– sending notifications and commands in the form of SMS messages with mobile phone. Advanced versions of devices have their own applications installed on a smartphone.

How to assemble a thermal relay yourself?

Heating control devices available for sale are quite reliable and do not cause any complaints. But at the same time, they cost money, and this does not suit those homeowners who have at least a little knowledge of electrical engineering or electronics. After all, understanding how such a thermal relay should function, you can assemble and connect it to the heat generator with your own hands.

Of course, not everyone can make a complex programmable device. In addition, to assemble such a model, it is necessary to purchase components, the same microcontroller, digital display and other parts. If you are new to this matter and have a superficial understanding of the issue, then you should start with some simple circuit, assemble it and put it into operation. Having reached positive result, you can aim at something more serious.

First, you need to have an idea of ​​what elements a thermostat with temperature control should consist of. The answer to the question is given circuit diagram, presented above and reflecting the algorithm of the device. According to the diagram, any thermostat must have an element that measures temperature and sends electrical impulse to the processing unit. The latter’s task is to amplify or convert this signal in such a way that it serves as a command to the actuator - the relay. Next we will present 2 simple circuits and explain their operation in accordance with this algorithm, without resorting to specific terms.

Circuit with zener diode

A zener diode is the same semiconductor diode that passes current only in one direction. The difference from a diode is that the zener diode has a control contact. As long as the set voltage is supplied to it, the element is open and current flows through the circuit. When its value falls below the limit, the chain breaks. The first option is a thermal relay circuit, where the zener diode plays the role of a logical control unit:

As you can see, the diagram is divided into two parts. On the left side is the part preceding the relay control contacts (designation K1). Here the measuring unit is a thermal resistor (R4), its resistance decreases with increasing ambient temperature. The manual temperature controller is a variable resistor R1, the power supply to the circuit is 12 V. In normal mode, a voltage of more than 2.5 V is present at the control contact of the zener diode, the circuit is closed, the relay is turned on.

Advice. Any inexpensive commercially available device can serve as a 12 V power supply. Relay – reed switch brand RES55A or RES47, thermal resistor – KMT, MMT or similar.

As soon as the temperature rises above the set limit, the resistance of R4 will drop, the voltage will become less than 2.5 V, and the zener diode will break the circuit. Then the relay will do the same, turning off the power part, whose diagram is shown on the right. Here, a simple thermal relay for the boiler is equipped with a triac D2, which, together with the closing contacts of the relay, serves as an executive unit. The boiler supply voltage of 220 V passes through it.

Circuit with logic chip

This circuit differs from the previous one in that instead of a zener diode, it uses a K561LA7 logic chip. The temperature sensor is still a thermistor (designation VDR1), only now the decision to close the circuit is made by the logical block of the microcircuit. By the way, the K561LA7 brand has been produced since Soviet times and costs mere pennies.

For intermediate amplification of pulses, the KT315 transistor is used; for the same purpose, a second transistor, KT815, is installed in the final stage. This diagram corresponds to the left side of the previous one; the power unit is not shown here. As you might guess, it may be similar - with the KU208G triac. The operation of such a homemade thermal relay has been tested on boilers ARISTON, BAXI, Don.

Conclusion

Connecting a thermostat to the boiler yourself is not a difficult task; there is a lot of material on this topic on the Internet. But making it yourself from scratch is not so easy; in addition, you need a voltage and current meter to make the settings. Buy ready product or take on making it yourself - the decision is up to you.

I present an electronic development - a homemade thermostat for electric heating. The temperature for the heating system is set automatically based on changes in outside temperature. The thermostat does not need to manually enter or change readings to maintain the temperature at heating system.

There are similar devices in the heating network. For them, the relationship between average daily temperatures and the diameter of the heating riser is clearly stated. Based on these data, the temperature for the heating system is set. I took this heating network table as a basis. Of course, some factors are unknown to me; the building may, for example, not be insulated. The heat loss of such a building will be large; the heating may be insufficient for normal heating of the premises. The thermostat has the ability to make adjustments for tabular data. (you can read more about the material at this link).

I planned to show a video of the thermostat in operation, with an eclectic boiler (25KW) connected to the heating system. But as it turned out, the building for which all this was done for a long time It was not residential; upon inspection, the heating system had almost completely fallen into disrepair. It is not known when everything will be restored; perhaps it will not be this year. Since in real conditions I cannot adjust the thermostat and observe the dynamics of changing temperature processes, both in heating and outside, I took a different route. For these purposes, I built a model of the heating system.

The role of an electric boiler is performed by a glass floor liter jar, the role of a heating element for water is a five hundred watt boiler. But with such a volume of water, this power was in excess. Therefore, the boiler was connected via a diode, reducing the heater power.

Connected in series, two aluminum flow radiator, they extract heat from the heating system, forming something like a battery. Using a cooler, I create dynamics of cooling of the heating system, since the program in the thermostat monitors the rate of increase and decrease in temperature in the heating system. On the return, there is a digital temperature sensor T1, based on the readings of which the set temperature in the heating system is maintained.

In order for the heating system to start working, it is necessary for the T2 (outdoor) sensor to record a temperature drop below +10C. To simulate changes in outside temperature, I designed a mini refrigerator using a Peltier element.

Describe the entire work homemade installation It makes no sense, I filmed everything on video.

Some points about assembling an electronic device:

Thermostat electronics, located on two printed circuit boards, to view and print you will need the SprintLaut program, at least version 6.0. The thermostat for heating is mounted on a DIN rail, thanks to the Z101 series housing, but nothing prevents you from placing all the electronics in another housing of suitable size, the main thing is that it suits you. The Z101 case does not have a window for the indicator, so you will have to mark and cut it yourself. The ratings of the radio components are indicated on the diagram, except for the terminal blocks. To connect the wires, I used terminal blocks of the WJ950-9.5-02P series (9 pcs.), but they can be replaced with others; when choosing, make sure that the pitch between the legs coincides, and the height of the terminal block does not interfere with the housing being closed. The thermostat uses a microcontroller that needs to be programmed; of course, I also provide the firmware for free access (it may have to be modified during operation). When flashing the microcontroller, set the internal clock generator of the microcontroller to 8 MHz.

Simple thermostat for refrigerator

Make a Simple Refrigerator Thermostat Circuit

Want to make an accurate electronic thermostat for your refrigerator? The solid state thermostat circuit described in this article will surprise you with its cool performance.

Introduction

The device, once built and integrated with any related device, will instantly begin to demonstrate improved system control, saving energy, as well as increasing the life of the device. Conventional refrigeration thermostats are expensive and not very accurate. Moreover, they are subject to wear and therefore are not permanent. A simple and effective electronic refrigerator thermostat is discussed here.
A thermostat, as we all know, is a device that is capable of sensing a certain set temperature level and turning off or switching the external load. Such devices may be electromechanical types or more complex electronic types.
Thermostats are usually associated with air conditioning, cooling and water heating devices. For such applications, the device becomes an important part of the system, without which the device can reach and operate under extreme conditions and ultimately become damaged.
Adjusting the control switch provided in the above devices ensures that the thermostat will cut off power to the unit once the temperature crosses the required limit and switches over once the temperature returns to the lower threshold.
In this way, the temperature inside the refrigerators or the room temperature through the air conditioner is maintained in favorable ranges.
The refrigeration thermostat circuit idea presented here can be used externally above a refrigerator or any similar device to control its operation.
Control of their operation can be accomplished by attaching the thermostat sensing element to an external heat sink typically located behind most cooling units that use freon.
The design is more flexible and wider than built-in thermostats and can provide better efficiency. The circuit can easily replace conventional low-tech designs and is also much cheaper in comparison.
Let's figure out how the scheme works:

Description of the scheme
Simple Refrigerator Thermostat Diagram

The diagram shows a simple circuit built around IC 741, which is basically configured as a voltage comparator. It uses a transformer with lower power consumption to make the circuit compact and solid state.
A bridge configuration containing R3, R2, P1 and NTC R1 at the input forms the main sensitive elements scheme.
The inverting input of IC is clamped to half the supply voltage using a voltage divider network of R3 and R4.
This eliminates the need to provide dual power to the IC, and the circuit can provide optimal results even with a single-pole supply voltage.
The reference voltage to the non-inverting input of the IC is fixed via a given P1 with respect to the NTC (Negative Temperature Coefficient).
In case the temperature under control tends to drift above the desired levels, the NTC resistance drops and the potential at the non-inverting input of the IC crosses the set point.
This instantly switches the IC's output, which in turn switches the output stage containing the transistor, the triax network, turning off the load (heating or cooling) until the temperature reaches a lower threshold.
Resistance feedback R5 helps to some extent to induce hysteresis in the circuit, important parameter, without which the circuit may spin rapidly in response to sudden temperature changes.

Once the assembly is complete, setting up the circuit is very simple and is done with the following points:

REMEMBER THE EXTERNAL CIRCUIT IS BASED ON A CONSTANT SOURCE POTENTIAL, CAUTION IS WARNED AGAINST TESTING AND INSTALLATION PROCEDURES. THE USE OF WOODEN BLANK OR ANY OTHER INSULATING MATERIAL ALONG YOUR FOOT IS STRICTLY RECOMMENDED; ALSO USE ELECTRICAL TOOLS, WHICH MUST BE INSULATED NEAR THE SITE.

How to Adjust This Electronic Refrigeration Circuit Thermostat You will need a sample heat source precisely adjusted to the desired thermostat circuit cutoff threshold level.
Turn on the circuit and introduce and attach the above heat source to the NTC.
Now set the preset so that the output simply switches (output LED lights up). Remove the heat source from the NTC, depending on the circuit hysteresis the output should turn off within a few seconds.
Repeat the procedure many times to confirm proper functioning.
This completes the setup of this refrigeration thermostat and is ready to integrate with any refrigerator or similar device to accurately and continuously regulate its operation.

Parts List

R2 = Preset 10KR3,

R9 = 56 OHM / 1watt

C1 = 105 / 400V

C2 = 100uF / 25V

Z1 = 12 V, 1 W Zener diode

*option via optocoupler, added a switch and a diode bridge to the power supply

How to Create an Automatic Refrigerator Temperature Controller Circuit

The idea of ​​this scheme was suggested to me by one of the keen readers of this blog, Mr. Gustavo. I have published one similar circuit for an automatic refrigerator thermostat, however the circuit was intended to determine more high level temperature available at the rear of the refrigerator grille.

Introduction

Mr. Gustavo didn't quite understand the idea and he asked me to design a refrigerator thermostat circuit that could sense cold temperatures inside the refrigerator rather than hot temperatures at the back of the refrigerator.
So with some effort I could find a real CIRCUIT DIAGRAM for a refrigerator temperature controller, let's explore this idea with the following points:
How circuits function
The concept is not very new nor unique, it is a common comparator concept that has been included here.

IC 741 was rigged in standard comparator mode and also as a circuit without an inverting amplifier.
The NTC thermistor becomes the main sensing component and is specifically responsible for sensitivity to cold temperatures.
NTC stands for Negative Temperature Coefficient, which means the thermistor's resistance will increase as the temperature around it drops.
It should be noted that the NTC must be rated according to these specifications, otherwise the system will not function properly.
The preset P1 is used to set the IC trip point.
When the temperature inside the refrigerator drops below a threshold level, the thermistor resistance becomes high enough to reduce the voltage at the inverting pin below the non-inverting pin voltage.
This instantly makes the IC pin high, activating the relay and turning off the refrigerator compressor.
P1 should be set such that the op amp output goes high at zero degrees Celsius.
The slight hysteresis introduced by the circuit comes as a boon, or rather a blessing in disguise, because it causes the circuit to not switch quickly at threshold levels, but to respond only after the temperature has risen about a couple of degrees above the shutdown level.
For example, suppose if the trip level is set to zero, the IC will turn off the relay at that point and the compressor of the refrigerator will also be turned off, the temperature inside the refrigerator will now start to rise, but the IC will not switch immediately, but maintains its position until the temperature will not rise to at least 3 degrees Celsius above zero.


If you have further questions regarding this automatic circuit refrigerator temperature controller, you can express the same through your comments

Regulation RP1, RP2 can be temperature control set points, 555 timing inverting Schmitt circuits using relays to achieve automatic control.