Russian winter is distinguished by its severity and severe cold, which is known to all. Therefore, the premises in which people are located must be heated. Central heating is the most common option, and if it is unavailable, you can use an individual gas boiler. However, it often happens that neither one nor the other is unavailable, for example, in a clean field there is a small room of a pumping waterworks station, in which drivers are on duty around the clock. It can be a room in some large uninhabited building or a guard tower. There are enough examples.
Way out
All these cases force the implementation of an electric heating device. With the small size of the room, it is quite possible to do with a conventional electric oil radiator, and in large rooms most often arrange water heating using a radiator. If you do not monitor the temperature of the water, then sooner or later it can boil, because of which the entire boiler will fail. To protect against such cases, temperature controllers are used.
Device features
In functional terms, the device can be divided into several separate nodes: temperature sensor, comparator, as well as load control devices. All of these parts will be described below. This information is necessary in order to make a thermostat with your own hands. In this case, a design is proposed in which a conventional bipolar transistor serves as a temperature sensor, so that you can refuse to use thermistors. This sensor works on the basis that the parameters of the transistors of all semiconductor devices are more dependent on the temperature of the medium.
Important Nuances
Creating a thermostat with your own hands should be carried out with the obligatory consideration of two points. Firstly, we are talking about the tendency of automatic devices to auto-generation. In the case when the connection between the actuator and the thermal relay sensor is too strong, after the relay is activated, it immediately turns off and then turns on again. This will occur when the sensor is in close proximity to the cooler or heater. Secondly, all sensors and electronic devices have a certain accuracy. For example, you can track the temperature at 1 degree, but lower values are much more difficult to track. In this case, simple electronics often begin to make mistakes and make mutually exclusive decisions, especially when the temperature is almost equal to the temperature set for operation.
Process of creation
If we talk about how to make a thermostat with your own hands, then it is worth saying that the sensor here is a thermistor that reduces its resistance during heating. It is included in the voltage divider circuit. The variable resistor R2 is also included in the circuit , through which the response temperature is set. From the divider, the voltage is supplied to the 2I-NOT element, which is turned on in the inverter mode, and then to the base of the transistor, which serves as a spark gap for the capacitor C1. He, in turn, is connected to the input (S) of the RS-trigger, which is assembled on a pair of elements, as well as to the input of another 2I-NOT. From the divider, the voltage is supplied to the input 2I-NOT, which controls the second input (R) of the RS-trigger.
How it works
So, we are considering how to create a simple thermostat with your own hands, so it is important to understand how it works in different situations. At high temperatures, the thermistors are characterized by a low voltage, so there is voltage on the divider, which is perceived by logic circuits as zero. In this case, the transistor is open, a logical zero is perceived at the input of the S-trigger, and the capacitor C1 is discharged. At the output of the trigger, a logical unit is set. The relay is on, and the transistor VT2 is open. In order to understand exactly how to make a thermostat, it is worth noting that this particular implementation of the relay is focused on cooling the object, that is, it turns on the fan at high temperature.
Temperature reduction
When the temperature decreases, the resistance of the thermistor increases, which leads to an increase in the voltage on the divider. At a certain moment, the transistor VT1 closes, after which the charging of the capacitor C1 through R5 begins. In the end, there comes a moment of reaching the level of a logical unit. It is she who comes to one of the inputs of D4, and the voltage from the divider is applied to the second input of this element. When logical units are established at both inputs, and zero appears at the output of the element, the trigger will switch to the opposite state. In this case, the relay will be turned off, which will turn off the fan, if necessary, or turn on the heating. So you can make a thermostat for the cellar with your own hands, so that it turns on and off the fan if necessary.
Temperature rise
So, the temperature began to increase again. Zero on the divider will appear first on one of the inputs of D4, it will remove zero at the input of the trigger, changing it to one. Further, as the temperature rises, zero will appear on the inverter. After it is changed to unity, the transistor will open, which will lead to the discharge of the C1 element and zeroing at the input of the trigger, which turns off the heating of the coolant in the water heating system or turns on the fan. Such self-made temperature controllers for heating work quite efficiently.
Blocks C1, R5 and VT1 are designed to eliminate auto-generated, due to the fact that they set the time delay off. It can range from a few seconds to several minutes. We are considering a fairly simple thermostat that we have created ourselves, so the above node also eliminates the chatter of the temperature sensor. Even with a very small first pulse, the transistor opens and the capacitor discharges instantly. Further, bounce will be ignored. When the transistor closes, the situation repeats. Capacitor charging starts only after the completion of the last bounce pulse. Thanks to the introduction of a trigger into the circuit, it is possible to ensure maximum clarity of the relay. As you know, a trigger can have only two positions.
Assembly
To make the thermostat yourself, you can use a special circuit board on which the entire circuit will be assembled in a hinged way. You can use a printed circuit board. Power can be used any within 3-15 volts. Relays should be selected in accordance with this.
By a similar scheme, you can make a temperature controller for the aquarium with your own hands, however, it should be noted that it must be mounted externally to the glass, then there will be no problems with its use.
The relay described above demonstrated very high reliability during operation. The temperature is maintained accurate to fractions of a degree. However, it is directly dependent on the time delay determined by the R5C1 circuit, as well as the response to operation, that is, the power of the cooler or heater. The temperature range and the accuracy of its installation is determined by the selection of resistors of the divider. If you made such a thermostat with your own hands, then it does not need to be configured, but starts working immediately.