Temperature Sensor using LM35 & Opamp

Temperature Sensor circuit using LM35 & IC741

The Opamp IC 741 is used here as non-inverting non-zero reference comparator. Its inverting terminal is connected to variable voltage which can be adjusted with the help of variable resistor VR1.

The non inverting terminal is connected to the output of temperature sensor LM35.

The prototype works very effectively and responds to quick changes in temperature of LM35.

Temperature Sensor circuit using LM35 & IC741

Prototype of Temperature Sensor using IC741 & LM35
(Click to enlarge)

Circuit Details

  1. Pin 1 and pin 5 of IC 741 are left open.
  2. Pin 2 is connected to voltage divider using one fixed resistor of 2.2k and one variable resistor of 10k.
  3. Pin 3 is connected to the output pin i.e. middle pin of IC LM35.
  4. Pin 7 and pin are connected to +ve and ground supply of 6V, single power supply.

The circuit is fully tested in our laboratory and works very nicely to measure the temperature from room temperature value to maximum of hot soldering iron temperature.

Please note that the circuit works only on single power supply. Don’t try it on dual power supply as the output of the IC gets saturated and both LEDs remain ON, if you connect dual power supply.

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  • If any technique is there please say that sir.

  • sir,I have a doubt.
    can we monitor the baby using any image processing techniques?

    • This is really a novel idea, Satyapriya.
      I never thought about it.
      When I received the comment since I was working on its framework.
      Of course, we can monitor a baby using image processing technique.
      But it needs quite a good thinking.
      I’m working on it.
      Well, have you come up with something regarding this? I mean have you worked out this idea?