Temperature controlled on off relay circuit using LM393

A guest who visit my site would like to create a project about the control on/off the fans with based on temperature automatically or Simple fan on off controller by temperature sensor.
I would like to introduce the concept of the temperature controlled on off relay circuit. You probably know that, Useful fan when the weather is hot. But cold weather, fans are not very useful. If we turn the fan on sleep then at night is cold. We get fan the whole night still feel unwell certainly.

If you use a timer, may not be exact. Sometimes the time been exhausted. But the weather is hot. Need to turn the fan again, Cumbersome and not really the point. Lets we use the temperatures to control a fan better.

Temperature controlled on off relay circuit using LM393

Figure 1 The Fan controller circuit diagram.

How this circuit works (in short style)
As shown in the figure circuit below. It has main ideals is the thermistor R4 will be charged its resistance with a temperature. And the IC1-LM393 (Low power dual voltage comparator) is a comparator between voltage from the thermistor and Reference voltage (R3 voltage) The results of compare out to be bias current of transistor Q1 and Q2 that both is darlington to drive relay RY1 works.

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Customization is not as difficult as you think.

If you want to tune easily. If you want to tune easily, should have an air conditioning and a thermometer.

First, bring this circuit placed in the room, away from the ventilator of the air conditioning be fitted. Then adjust the temperature to a high cool to look at the thermometer reads about 24 degrees Celsius, Adjust VR1 to wait up to two minutes to see LED1 off to indicates that the relay RY1 running.

Next, you want the temperature of the circuit work, such as the temperature is 26 degrees Celsius. Now the relay stops working. You adjust the thermostat in the airs, until temperature increased to 26 degrees Celsius. Then adjust VR1 until LED1 light or relay work. Concluded that temperatures above 26 ° C, the relay to works and also the fan rotate, if the temperature low down so the fan stops rotate. You may Tune many times. until definitely a worked-up.

Note: Because this circuit is just a design concept only. If you try build with own. May have to modify the equipment properly, such as resistors, transistors and other. However, I think this circuit is useful for who looking at the automatic fan on-off circuit with temperature easily.

Other circuits involved.

Note: You can see various Temperature circuits below:

  1. Measurements temperature by diode 1N4148
  2. Digital temperature meter using LM335 or LM135
  3. Opto-Thermo Control Relay Switch with IC 741
  4. Temperature detector circuit


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7 thoughts on “Temperature controlled on off relay circuit using LM393”

  1. Hi every one, here every person is sharing these kinds of know-how, so it’s pleasant
    to read this webpage, and I used to visit this websjte everyday.

  2. is it possible to add a capacitor somewhere to give it a minimum ‘on’ duration, so that for example, if i want to use this for air conditioning switch, it will not turn on and off every minute, but at some predetermined minimum period of say 30mins or 60 mins such that the air conditioner does not burn out?

    thank you in advance

  3. Please can any one help us we are not getting output for this project temperature control on off relay using Lm393 did any one got this project if any changes forward us .


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