adc and lm35: do i need opamp?

Discussion in 'The Projects Forum' started by efm, Oct 26, 2006.

  1. efm

    Thread Starter Member

    Sep 14, 2006
    i'm an electronic newbie, so a help would be really appreciated here :)

    i'm making a project that includes a lm35d and a adc0808,
    from articles on the net, i read that the lm35d needs opamp before the output goes to adc0808's input,

    my questions are:

    1. is it possible to do it without opamp?
    2. can i connect the lm35d's output to adc0808's input?
    3. if i set the vref of the adc to 2.5 v, can it be possible to connect lm35d without opamp?
    4. or, do you guys have any suggestion?

    thank you,
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    National's big claim for the LM35 is a low output impedance, so yes, you can attach it to the A to D directly.

    There is always the matter of scaling though. If you want to get the full range of the LM35 into the A to D, then you may need to add an op amp for some tailored amplification.

    Without any idead of what accuracy you need, or range of temperatures to respond to, it's pretty hard to get more specific.
  3. efm

    Thread Starter Member

    Sep 14, 2006
    Hi, beenthere, thanks for the reply,

    so, I still can use LM35 without A/D? but perhaps the output I get by doing it is around 1 V only (as
    100 Celcius is 1 V)?

    anyway, I've decided to use an OpAmp. I'm going to use three LM35s, is a LM324 (quad operational
    amplifier) suitable enough for it instead of LM358 (three LM358s?)

    thank you,
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004

    the lm324 will do better than 3 lm358. temperature effect on the lm324 will illicit practically the same reaction, while the individual lm358 will react to temperature not in the same way as the lm324.

  5. shashi21all

    New Member

    Jan 16, 2007
    please i need info abt the signal conditioning ckt of lm35