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LM 35

Discussion in 'General Electronics Discussion' started by vick5821, Apr 28, 2012.

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  1. vick5821

    vick5821

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    Jan 22, 2012
    Anyone here have experince using LM 35 Temperature sensor ? How does it able to sense heat ?

    Can I use it without microcontroller ?

    Thank you
     
  2. TedA

    TedA

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    Sep 26, 2011
    vick5821,

    The LM35 is an analog part. It does not require any microcontroller.

    Have you looked at the data sheet?

    http://www.datasheetarchive.com/dl/Datasheets-22/DSA-423890.pdf

    "The LM35 series are precision integrated-circuit temperature
    sensors, whose output voltage is linearly proportional to the
    Celsius (Centigrade) temperature."

    You can hook a voltmeter to the LM35 output and read off the temperature.

    If you should want to use it with a microcontroller, you will need to involve an ADC or one or more voltage comparators.

    The temperature is sensed using a special sort of band-gap voltage regulator circuit that is designed to have a very linear and predictable response to the temperature of the chip.

    Ted
     
  3. vick5821

    vick5821

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    Jan 22, 2012
    Then can it performs the function like thermister or it just sense heat and display it ?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It doesn't do any displaying, but in some sense it is like a thermistor.

    An output voltage on the LM35 changes as temperature changes.

    A thermistor, if supplied with a constant current will do a similar thing.

    HOWEVER, the LM35 is far more linear and has an output voltage which is more tightly specified than a thermistor's change in resistance.
     
  5. vick5821

    vick5821

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    Jan 22, 2012
    So I can do a heat detector circuit using LM 35?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You can do a TEMPERATURE detector using an LM35 (a thermometer). Heat is a totally different thing.
     
  7. vick5821

    vick5821

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    Jan 22, 2012
    if heat i need to use thermister? but got heat the temperature increases right? so interelated?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, thermistors and other things detect temperature.

    Heat is the total amount of thermal energy, temperature is the average thermal energy.

    For example, consider a hot cup of tea and a warm bath. The first has a higher temperature, but the latter contains more heat.

    I'm not sure there's a way to directly measure heat.
     
  9. vick5821

    vick5821

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    Jan 22, 2012
    i want to do a heat detector circuit, so can use LM35?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You can do a TEMPERATURE detector using an LM35 (a thermometer). Heat is a totally different thing.
     
  11. vick5821

    vick5821

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    Jan 22, 2012
    I am doing a circuit that can detect open burning.When someone do open burning, it will sense the temperature rise and buzer will sounds. So is it apporpiate to use LM 35?
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It will only work if the temperature of the LM35 is increased by the radiated, convected, or conducted heat.

    So if the hot air from the combustion is directed toward the LM35, it will detect it.

    However, if you're wanting to detect temperature remotely then you may need a different device.
     
  13. vick5821

    vick5821

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    Jan 22, 2012
    You mean I have to bring the heated thing near to LM 35 ? Or else it won detect the rise in temperature from a distance ?
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, it reports its own temperature. Just like a thermometer.

    This will tell you how to detect heat at a distance. Note that you're detecting black-body radiation, and not temperature directly. The temperature is related to the distribution of the wavelengths emitted.

    Perhaps you should also read this.
     
    Last edited: Apr 29, 2012
  15. vick5821

    vick5821

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    Jan 22, 2012
    OMG..just like a thermometer..means have to bring quite near to the heat source to have a significant change i voltage :(
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Check my edits :)
     
  17. vick5821

    vick5821

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    Jan 22, 2012
    Using PIR sensor ? Isnt that it is used as to detect motion ?
     
  18. vick5821

    vick5821

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    Jan 22, 2012
    What other sensor that can be used to detect heat ?
     
  19. davenn

    davenn Moderator

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    Last edited: Apr 29, 2012
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yes, but:

     
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