Electronic Thermostat Circuit and Working

The popular techniques to control temperature consist of the Nose-Hoover thermostat, Anderson thermostat, Berendsen thermostat, and Langevin (stochastic) thermostat. A thermostat is so important for ensuring that the HVAC system installed in your house works optimally. This gadget is set to turn on or off an air conditioning, balances the heat of a system, and also allows you to dictate what the temperature should be set. This article discusses electronic thermostat circuit working, types and its applications

What is a Thermostat?

A thermostat basically switches the heating system on and off accordingly. It detects by sensing the air temperature, switches on when the heating of air temperature falls below the thermostat setting and switches off when the set temperature has reached. By spinning a room thermostat to a higher setting which will not build the heat in the room. How speedily the room heats up depending on the design of a heating system. For example, the size of a boiler and radiators. Rotating a room thermostat to a lower setting will result, the room can be controlled at a lower temperature and saves energy. The heating system doesn’t work if the time switch or programmer switch is off.

Electronic Thermostat Circuit and Working

The simple circuit of the electronic thermostat using IC LM356 is shown below. This IC is a simple, low power, dual output, and precise thermostat The IC LM56 has a variety of useful features such as interior temperature sensor, two internal voltage comparators, internal voltage reference, etc. Here VT1 and VT2 are two stable temperature-trip points that are formed by separating the IC LM356.

Electronic Thermostat Circuit
Electronic Thermostat Circuit

Three external resistors like R1, R2, and R3 are used for internal reference voltage 1.250V. There are two outputs for IC LM356 namely output1 and output2, Whenever the temperature increases above T1 then the output goes low. Similarly, the temperature decreases below T1 then the output goes high. In the same way, the output2 also becomes high when the temperature goes below T2 and becomes lower when the temperature goes high T2. Here, by connecting the loads’ heater and cooler relays L1 and L2 we can build a simple electronic thermostat circuit that can be constructed.

The values of three resistors R1, R2 and R3 for the necessary trip points VT1 & VT2 can be calculated using the following equations.

VT1= 1.250V X R1/R1+R2+R3


VT2= 1.250V X (R1+R2)/R1+R2+R3


R1 +R2 +R3 = 27 kilo-ohms

T2 or VT1 = = 395 mV therefore

R1 = VT1/ (1.25V) X 27 k Ohms

R2= VT2/ (1.25V) X 27 k Ohms –R1

R3= 27 k Ohms –R1-R2

How Thermostats Works

A Temperature sensor in a mechanical thermostat is made up of the two pieces of metal that are covered together. Every kind of metal has a different rate of growth when heated and cooled, which is what controls the thermostat temperature. When you set the temperature on a mechanical thermostat, the heat is controlled when the power of awaiting temperature reaches the set point, then the heater will be turned off. The heater will turn reverse once again when the room temperature drops below the set temperature and the cycle repeats. Because the mechanical thermostats are exact within 2 and 5 degrees, depending on a model, that translates to be temperature swings of a few degrees.

Indifference, electronic thermostats include digital sensors that are much more precise and reactive. The temperature swings with electronic thermostats are much smaller. Many of them are within 1 degree of the temperature, which can be set on the thermostat.

Types of Thermostats

Thermostats are available in five basic types

  • Linear-voltage
  • Low-voltage thermostats
  • Programmable Thermostats
  • Mechanical Thermostats
  • Electronic Thermostat

Line-Voltage Thermostats

These thermostats are used in single heating systems, as well as radiator systems and baseboards. Line-voltage thermostats are installed in the series with heaters, generally at 240V. In this type of connection, the current flows throughout the thermostat and into the heater. Unfortunately, the thermostat itself has to achieve the set room temperature, causing it to shut off till before the heater has to bring the whole room to set temperature.

Line-Voltage Thermostats
Line-Voltage Thermostats

Low-Line-Voltage Thermostats

Low-voltage thermostats are more capable of controlling the current of air. These thermostats are used in several central HVAC systems that use electricity, gas, and oil. They may be also used in water heating systems, particularly in zone valves, and in electric unitary systems. With a low-voltage thermostat, you will not only be able to precisely control the current, but also have an easier time using programmable controls. This happens regularly because they operate between 50V and 24V, as opposed to the 240V used for line-voltage thermostats.

Low-Line-Voltage Thermostats
Low-Line-Voltage Thermostats
Programmable Thermostats
Programmable Thermostats

If you have installed a programmable thermostat, you can have the temperature of your own in your house automatically attuned according to preset times. This means that you will maintain the time conserving energy because you can allow the gadget to decrease the temperature in your house in the absence and increase the heat when you require it. Programmable thermostats can be purchased in several models. The simpler ones let you program, day time and night time temperature settings, while the extra complicated ones can be programmed toward adjusting temperature differently for different days and times of the week.

Mechanical Thermostats

These are possibly the cheapest and easiest thermostats that you can install. They feature moreover vapor-filled bellows or bi-metallic strips, which react to variations in the temperature. Mechanical thermostats are careful, unreliable, particularly the cheapest models that produce the use of bimetallic strips. The main letdown you will possibly experience with these thermostats is, it has to act with the slow response of the bi-metallic strip, which may be resulting in major temperature variations moreover above or below the preferred set points.

Mechanical Thermostats
Mechanical Thermostats

Electronic Thermostats

Dissimilar mechanical thermostats, these are thermostats build which uses electronic gadgets to detect the temperatures and subsequently start control for your heating system. They are faster in responding to the temperature variations. You can have electronic thermostats moreover for line-voltage or the low-voltage purposes. These gadgets will present you with much expediency with features similar to programmability and the automatic setback. For these reasons, electronic thermostats will price you more than the mechanical alternatives.

Electronic Thermostats
Electronic Thermostats

Applications of the Thermostat

Thermostats are used to monitor and control the temperature of an inside area. An electronic thermostat will sense the temperature, such as with a thermistor or thermocouple, and returns an electrical signal to the rest of the heating, aeration, and air conditioning (HVAC) system, representative functions (e.g. Heating, cooling, etc.) must be enabled. Lacking some form of a thermostat, an HVAC system would have no feedback or control, building it costly, wasteful, and unable to preserve a steady temperature. Electronic thermostats that stay track of the limited time and the day of the week can be programmed with temperature profiles that help reduce energy expenses and maximize comfort. Thermostats are used in wireless devices.

In the above article, we have discussed what is a thermostat and how the thermostats work and their principle involved in it. The 5 types of thermostats are Linear-voltage, Low- voltage thermostats, Programmable thermostats, Mechanical thermostats finally Electronic thermostats are explained in detail. These all types of thermostats working, mechanism and operating systems are discussed in the article and real-time applications of the thermostats too. Furthermore, any queries regarding electrical and electronics projects please give your valuable suggestions by commenting in the comment section below.

Photo Credits:

  • Low-voltage thermostats shopthermostats
  • Programmable Thermostats emersonclimate
  • Mechanical Thermostats wundatrade
  • Electronic Thermostats conrad
  • Electroni thermostat Circuit  circuitswiring


  1. Sam Moses says:

    Thank you for the information am currently working on this project so called, temperature control circuit and i appreciate the information you gave on this
    Thank you

    1. Tarun Agarwal says:

      Hi Sam
      My pleasure. I hope it helps a lot

  2. Charles Ndung'u says:

    Great information on types of thermostats and circuit. I am currently working on a project and this will be of great assistance

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