Temperature Control System - LBM4

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Tuesday 3 September 2019

Temperature Control System

Temperature Control System

A Temperature Controlled System is a type of control system that automatically controls the temperature of an object or an area.

Have you ever wondered how your Air Conditioner or Heater or Refrigerator adjusts its temperature automatically? The answer is a Temperature Control System. In this post we are going to learn how to build a model of such temperature control system using minimum components and without any complex circuit.

Depending upon the feedback control system are of two types:
1. Open loop control system
2. Closed loop control system

Now we are going to learn closed loop control system

Components Required:

          1. Temperature Sensor LM35
          2. Op-Amp IC (LM324/741)
          3. Motor Driver IC L293D
          4. Potentiometer-10k
          5. DC Toy motor
          6. Propeller
          7. 7805 Voltage Regulator
          8. 100uF Capacitor
          9. Multi-meter (Digital one is Preferred)
         10. A Breadboard


Basically the circuit switches ON a toy motor fan connected to the motor driver whenever heat is applied to the temperature sensor unit using say a burning matchstick. The wind from the motor fan would blow off the matchstick and switches OFF itself automatically.
block diagram for temperature control system

Here the Temperature is the output to be controlled. A feedback is generated using the sensor which is fed into comparator which acts as a controller here. And the power is the input. The Temperature sensor LM35 is very accurate whose output is directly proportional to its surrounding temperature. For every 1°C of rise/fall in temperature, the output voltage of the sensor varies by 10mV

 Setup Instructions

  • At room temperature, the output of the sensor would be a stable value. Connect the sensor to the +5V and GND and then measure the voltage at the output pin using a multi-meter. Note down the value as V1 for further use. In my case I got 0.28 Volts. It is not necessary that you get the same readings since the value depends on Temperature of your room, Quality of the sensor, multi-meter, etc.
  •  Now apply power to the potentiometer and take readings from the output of it. Adjust the potentiometer using a screw-driver in such a way that it’s output voltage is slightly higher than that of the voltage readings obtained from the temperature sensor output pin. This is your reference voltage V2
 (Note: The higher you set the pot voltage, the lesser sensitive you system would be. I set it to 0.35 Volts so that I get a quite sensitive system i.e. a system with quicker response to the temperature variation. If you set it with lesser variation from V1 voltage then the system would respond even for small temperature changes also and would switch ON or OFF the fan faster.)
  •  Now assemble the other components as per the given circuit. Connect the propeller to the motor axle to make the fan.
  • Mount the fan firmly on a small plastic or carton box to so that it can rotate freely.
setup diagram

Here used electrical tape is to attach it to the box since it was a cardboard box. Position the fan in such a way that when turned ON, it directly blows wind onto the LM35 IC


real working diagram

Power ON the circuit and bring a heat source (burning matchstick in my case) close to the temperature sensor. Now the temperature close to the sensor is increased and thus it sends a feedback to the comparator.

If everything is done right then the motor would start spinning within few seconds and would blow heavy air on matchstick, extinguishing the fire. After a few second the motor will automatically stop spinning.


  1. Make sure you keep away from the propeller blades while the fan is in ON state. It may be weak normally but while revolving at high speed, the propeller can hurt you easily.
  2. Since we’ll be using a burning matchstick to apply heat to the sensor so care should be taken. Isolate the temperature sensor away from any wires or any other components and take some precautionary measures
  Do it in a well-ventilated room.


Initially, at room temperature, V1 < V2 and hence the output of the comparator is low so the motor is in OFF state.

When heat is applied on the temperature sensor using a burning matchstick, the output voltage of the sensor V1 gradually increases. This generates a feedback signal. When the output voltage of sensor V1 exceeds the reference voltage V2 set by the pot, the comparator’s output goes high and hence turns ON the motor through the motor driver.

When the motor turns ON, It produces high velocity wind and blows off the matchstick. Now since the heat source is turned OFF, the temperature sensor starts cooling and there by its output voltage V1 reduces gradually. When V1 falls below the reference voltage V2, the comparator’s output again goes low and hence turns off the motor. No matter how many times you try, the fire on matchstick put near the sensor will be blown off.


         1. No complex circuitry.
         2. Cheap
         3. No need of any advanced programming or Microcontrollers.

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