For automatic maintenance temperature regime You can create a thermostat with your own hands. A high-quality homemade product will perform its functions no worse than its factory counterpart. After carefully studying the assembly process, upgrading and repairing will not be difficult.
From the examples given, the basic requirements for accuracy that a suitable thermostat circuit must provide are clear. In some situations it is necessary to maintain a given level no lower than ±1C°. To monitor operating parameters, an operational indication is needed. Load capacity is essential.
The listed features explain the purpose of typical functional units:
For your information. In addition to the parts discussed, the thermal relay circuit may contain additional components to supply power to an electric heater or other powerful load.
Any thermostat circuit operates on the same principles. The temperature information is compared with the set value. Crossing a certain level activates the actuator to correct the controlled parameter as required.
In the simplest version (refrigerator relay), a mechanical switch is used. For more precise adjustment (engine speed), not only microelectronics are used, but also specialized software.
To make a simple thermostat with your own hands, the circuit for the power supply of a personal computer is better than other options.
The thermistor measures the temperature at the control point. The potentiometer sets the optimal value for turning on the fan. This circuit is not capable of changing speed. Connects an inductive load MOSFET transistor. It is acceptable to use an analogue with suitable power characteristics.
You can make your own temperature controller as part of a project to modernize an old boiler. The type of fuel does not matter, although it is easier to provide good result using gas equipment.
In this example, the developers created a device for maintaining temperature conditions in a fruit (vegetable) storage facility. To analyze incoming data, a chip with the following blocks was selected:
When the switches are in the appropriate position, the LED matrix shows the current temperature value or reference level. Buttons in step by step mode set the desired response threshold.
Creating a functional thermostat with your own hands is not too difficult. However, you need to be realistic about your own capabilities. The following instructions will help you make the right decision.
To eliminate unnecessary difficulties, use a circuit with a power supply without a transformer. To rectify the supply voltage, a conventional diode bridge is used. The required level of the constant component is maintained by a zener diode. The capacitor eliminates surges.
A typical divider is suitable for voltage control. A resistor is installed in one arm, which responds to temperature changes. A relay is suitable to control the actuator.
This device can be used to maintain temperature conditions in a mini-greenhouse or other limited volume. The main element is an operational amplifier chip, which is turned on in voltage comparison mode. Fine and coarse adjustment of the response threshold is performed using resistors R5 and R4, respectively.
This option is intended for connecting electrical heated floors, other powerful loads. You should pay attention to the increased reliability of the product, which is ensured by galvanic isolation of circuits with weak and strong currents.
In some situations, you will need skills in making complex printed circuit board. The simplest circuits can be assembled in a few minutes using a soldering iron and technology wall-mounted. Before performing work operations, you must purchase:
The shopping list is compiled based on the selected electrical diagram. To protect your device from adverse external influences and improvements appearance create a corresponding body.
The pros and cons of individual schemes are assessed taking into account actual operating conditions. Sometimes it is profitable to spend time and money at the stage of implementing an idea in order to extend the service life finished product. There is no point in creating a homemade product if a factory equivalent with official guarantees costs less.
To extend the life of the thermostat, use the following recommendations:
It is not difficult to restore a homemade temperature sensor with your own hands, since the testing (adjustment) technology is known. Instructions for repairing factory products can be found on the manufacturer's official website.
Thermostats are widely used in modern household appliances, automobiles, heating and air conditioning systems, manufacturing, refrigeration and furnace applications. The operating principle of any thermostat is based on turning on or off various devices after reaching certain temperature values.
Modern digital thermostats are controlled using buttons: touch or regular. Many models also come 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 temperature changes hourly or set the required mode for a week in advance. The device can be controlled remotely: via a smartphone or computer.
For 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 any home craftsman can assemble a small device for a cooler or incubator.
In order to understand how a temperature controller works, consider a simple device that is used to open and close the damper of a mine boiler and is activated when the air is heated.
To operate the device, 2 aluminum pipes, 2 levers, a return spring, a chain that goes to the boiler, and an adjustment unit in the form of a faucet axle box were used. All components were installed on the boiler.
As is known, 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, causing the levers to shift and the damper to close. 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 response threshold of the thermostat. Today, preference is given to devices based on electronic elements.
Typically, relay-based circuits are used to maintain a set temperature. The main elements included in this equipment, are:
Semiconductor elements, thermistors, resistance thermometers, thermocouples and bimetallic thermal relays can be used as sensors.
The thermostat circuit reacts when the parameter exceeds a given level and turns on the actuator. The most simple option Such a device is an element based on bipolar transistors. The thermal relay is based on a Schmidt trigger. A 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 thermistor R2 and potentiometer R3. 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 surges, 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 correspond to each other. Sometimes the pictures may simply show other devices. Therefore, production can begin only after carefully studying all the information.
Before starting work, you should decide on the power of the future thermostat and the temperature range in which it will operate. The refrigerator will require some elements, and the heating will require others.
One of the elementary devices, using an 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 pin, then you can use a solderless board.
The thermostat circuit in this case consists of only three elements:
The temperature sensor reacts to an increase in degrees, due to which the entire circuit is activated and the fan turns on.
Now let's move on to the setup. To do this, turn on the computer and adjust the potentiometer, setting the value for the fan turned off. At the moment when the temperature approaches critical, we reduce the resistance as much as possible before the blades rotate very slowly. It is better to do the setup several times to make sure the equipment is working effectively.
The modern electronics industry offers elements and microcircuits that differ significantly in appearance and technical specifications. Each resistance or relay has several analogues. It is not necessary to use only those elements that are indicated in the diagram; you can take others that match the parameters of the samples.
When adjusting heating systems It is important to accurately calibrate the device. To do this you will need a voltage and current meter. To create a working system, you can use the following diagram.
Using this scheme, you can create external equipment for monitoring 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 a thermistor to reduce resistance when heated. The resistor is connected to the electricity voltage divider network. The required temperature can be set using variable resistor R2. The voltage is supplied to the 2I-NOT inverter. The resulting current is supplied 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 proceeds according to the following scheme:
It is better to solder on a mole rat. As a battery, you can take any device operating within 3-15 V.
Carefully! Installation homemade devices any purpose on heating systems can lead to equipment failure. Moreover, the use of such devices may be prohibited at the level of services providing communications in your home.
In order to create a fully functioning thermostat with accurate calibration, you cannot do without digital elements. Consider a device for monitoring temperatures in a small storage area for vegetables.
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, CCP comparison modules and USART data transfer exchange modules.
When the thermostat is operating, the value of the existing and set temperature is supplied to MT30361 - a three-digit indicator with a common cathode. To ask required temperature, the following buttons are used: SB1 – to decrease and SB2 – to increase. If you carry out the adjustment while simultaneously pressing the SB3 button, you can set the hysteresis values. The minimum hysteresis value for this circuit is 1 degree. Detailed drawing can be seen on the plan.
When creating any of the devices, it is important not only to correctly solder the circuit itself, but also to think about how best to place the equipment. It is necessary that the board itself is protected from moisture and dust, otherwise a short circuit and failure cannot be avoided individual elements. You should also take care to insulate all contacts.
The need to adjust the temperature regime arises when using various systems heating or refrigeration equipment. There are many options, and they all require a control device, without which the systems can operate 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 influence the system through a temperature sensor and turn it on or off as needed. Using ready-made kits equipment, control units are included in the delivery set, but for homemade systems you have to assemble the thermostat yourself. The task is not the easiest, but quite solvable. Let's take a closer look at it.
A thermostat is a device that can respond to changes in temperature. Based on the type of action, a distinction is made between trigger-type thermostats, which turn off or turn on heating when a specified limit is reached, or smooth-action devices with the ability to fine-tune and accurately adjust, capable of controlling temperature changes in the range of fractions of a degree.
There are two types of thermostats:
Mechanical devices do not allow high precision settings. They are both a temperature sensor and an actuator, combined into a single unit. Bimetallic strip used in heating devices, is a two-metal thermocouple with different coefficient thermal expansion.
The main purpose of the thermostat is automatic maintenance 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.
The chamber with the gas mixture is a sensitive element of the refrigerator thermostat or heating thermostat. When temperature changes, the volume of gas changes, which causes movement of the surface of the membrane connected to the lever of the contact group.
The thermostat for heating uses a chamber with a gas mixture that works according to Gay-Lussac's law - when the temperature changes, the volume of gas changes
Mechanical thermostats are reliable and provide stable operation, but the operating mode is adjusted with a large error, almost “by eye”. If fine tuning is necessary, providing adjustment within a few degrees (or even finer), electronic circuits are used. The temperature sensor for them is a thermistor, which is capable of distinguishing the smallest changes in the heating mode in the system. For electronic circuits, the situation is the opposite - 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 a change in the resistance of the sensor caused by fluctuations in the temperature of the controlled environment. The circuit reacts to changes in signal parameters and increases/decreases heating in the system until another signal is received. The capabilities of electronic control units are much higher and allow you to obtain temperature settings of any accuracy. The sensitivity of such thermostats is even excessive, since heating and cooling are processes with high inertia, which slow down the reaction time to changing commands.
Manufacturing mechanical thermostat at home is quite difficult and irrational, since the result will work in too wide range and will not be able to provide the required tuning accuracy. Most often they collect homemade electronic thermostats, which allow you to support optimal mode temperature of the heated floor, incubator, ensure the desired water temperature in the pool, heating the steam room in the sauna, etc. There can be as many options for using a homemade thermostat as there are systems in the house that need to be configured and adjusted. For rough adjustments using mechanical devices, it is easier to purchase ready-made elements; they are inexpensive and quite accessible.
A homemade thermostat has certain advantages and disadvantages. The advantages of the device are:
The disadvantages include:
The main problem is the need for training or, at a minimum, the participation of a specialist in the process of creating the device.
The manufacture of a thermostat occurs in stages:
The manufacturing stages of the device have their own characteristics, so they should be considered in more detail.
Materials required for assembly include:
Other tools or materials may be needed during the process, so this list should not be considered exhaustive or definitive.
The choice of scheme is determined by the capabilities and level of training of the master. How more complicated scheme, the more nuances will arise when assembling and configuring the device. At the same time the most simple circuits make it possible to obtain only the most primitive instruments operating with a high error.
Let's 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 is the relay block that turns on the load. The temperature sensor is resistor R4, and R1 is a variable resistor used to adjust the heating mode. The control element is a zener diode TL431, which is open as long as there is a load on its control electrode above 2.5 V. Heating of the thermistor causes a decrease in resistance, causing the voltage on the control electrode to drop, the zener diode closes, cutting off the load.
The other 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 for adjusting the temperature of a heated floor.
Any change in voltage caused by an increase or decrease in the resistance of the thermistor creates a difference between the standard 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 turn on or off. Such schemes, in particular, are used to regulate the operating mode of heated floors.
The assembly procedure for each device has its own characteristics, but some general steps can be identified. Let's look at the build progress:
To configure the device, you must either have a reference device or know the voltage rating corresponding to a particular temperature of the controlled environment. Individual devices have their own formulas showing 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 required temperature in Celsius.
In other schemes, adjustment is made by selecting the values of adjusting resistors when creating a certain, known temperature. In each specific case, our own methods can be used, optimally suited to the existing conditions or equipment used. The requirements for the accuracy of the device also differ from each other, so in principle there is no single adjustment technology.
The most common malfunction of homemade thermostats is instability of the thermistor readings caused by poor quality parts. In addition, there are often difficulties with setting modes caused by mismatches in ratings or changes in the composition of parts required for proper operation devices. Majority possible problems directly depend on the level of training of the technician who assembles and configures the device, since skills and experience in this matter mean a lot. However, experts say that making a thermostat with your own hands is a useful practical task that gives good experience in creating electronic devices.
If you don’t have confidence in your abilities, it’s better to use a ready-made device, of which there are plenty on sale. It must be taken into account that a regulator failure 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 options.
Among the various useful gizmos that can add comfort to our lives, there are many that can easily be made independently.
This category also includes a thermostat, also called a thermostat, a device that turns on and off the heating or refrigeration equipment according to 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 extreme cold weather. From our article you will learn 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 design of the thermostat is not particularly complicated, so many novice radio amateurs hone their skills in the manufacture of this device. A variety of circuits are offered, but the most widely used option is the use of a special microcircuit called a comparator.
This element has two inputs and one output. One input is supplied with a certain reference voltage, which corresponds to the required temperature, and the second input is supplied with voltage from the temperature sensor.
Thermostat circuit for heated floors
The comparator compares the incoming data and, at a certain ratio, generates an output signal that opens a transistor or turns on a relay. In this case, current is supplied to the heater or refrigeration unit.
The temperature sensor is usually a thermistor - an element whose electrical resistance changes depending on the temperature. Semiconductor elements are also used - transistors and diodes, the characteristics of which are also influenced by temperature: when heated, the collector current (for transistors) increases, while a shift in the operating point is observed and the transistor stops working, not 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 homemade thermostat leaves much to be desired.
Meanwhile, the industry has long mastered the production of inexpensive temperature sensors, the calibration of which is carried out during the manufacturing process.
These include the LM335 device from National Semiconductor, which we recommend using. This analog temperature sensor costs only $1.
“Troika” in the first position of the digital row in the marking means that the device is intended for use in household appliances. Modifications LM235 and LM135 are intended for use in industry and military applications, respectively.
Having 16 transistors, this sensor works like a zener diode. Moreover, its stabilization voltage depends on temperature.
The dependence is as follows: for every degree on the absolute scale (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 is from -40 to +100 degrees Celsius.
Thus, when assembling a thermostat based on LM335, the user is freed from 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 will need a comparator (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 – an integral part of autonomous heating. will help maintain the temperature in the house at a comfortable level.
The operating principle of the thermostat for infrared heater Let's sort it out.
Is it worth installing a thermostat for a heating radiator? In this article we will consider the purpose of the device and the types and features of installation.
Temperature sensor LM335 is connected in series with 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.
The thermostat can be powered from a standard 12 V power supply or from a manufactured one on our own transformer.
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.
Let us recall that the current in the temperature sensor circuit does not exceed 5 mA, so to connect the relay you need to use a transistor with higher 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 a transistor will not be needed.
Let's look at how thermostats (thermal relays) with a 12 V air temperature sensor are made with your own hands. The device is assembled in the following sequence:
Simple homemade thermostat
To turn on the heater, it is convenient to use the meter terminal block.
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 (a car relay is designed for this current), then the heater can have a power of up to 30 x 220 = 6.6 kW. You just need to first make sure that the wiring and the circuit breaker in the panel are able to withstand such a load.
The thermostat should be installed in the lower part of the room where cold air accumulates.
It is important to prevent exposure to thermal noise, which could confuse the instrument.
For example, you should not place the thermostat in a draft or near electrical equipment that emits heat.
As already mentioned, a thermostat based on the LM335 sensor does not need adjustment. It is enough to know the voltage supplied by the potentiometer to the direct input of the comparator.
It can be measured using a voltmeter. The required voltage value is determined by the above formula.
If you need, 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 checked experimentally. To do this, you need to use a digital thermometer, for example, TM-902S. For precise adjustment, the thermometer and thermostat sensors can be connected using electrical tape, after which they are placed in an environment with different temperatures.
Thermostat made from scrap materials
The potentiometer knob must be rotated smoothly until the thermostat operates. At this moment, 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 determine extreme points, for example, for temperatures of 8 and 40 degrees, and mark intermediate values by dividing the range into equal parts.
If you don’t have a digital thermometer at hand, the extreme points can be determined by water with ice floating in it (0 degrees) or boiling water (100 degrees).
