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Op Amp Follower Question

Discussion in 'Beginner Electronics' started by Noone, Nov 30, 2004.

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  1. Noone

    Noone Guest

    I am very new to this newsgroup scene, so I am hoping that someone will have
    some tips for me. The issue is that I am using a a PIC16F877 to do an adc
    and I am getting floating inputs (The voltage is very stable, but the PIC
    reading is very unstable). My circuit consists of a pressure sensor that
    goes into a difference amp with a gain of 100. The output resistance from
    all of that is very high (>10MOhm, my Multimeter cant read it, it is so
    high). From googling around I learned that I need a voltage follower to
    lower the resistance at the PIC analog input. The problem that I have is
    that no matter what op amp I use, it doesn't lower the resistance. I have
    tried several:

    LM324N (Quad Op Amp)

    LM741CN

    LF347N (Quad Jfet Op Amp)

    LM837N (Quad Op Amp)

    All with the same result, my voltage is stable, but my PIC reading is
    unstable. And my resistance at the pic input is still very high. So my
    question is:

    Are there only certain types of op amps that work as voltage followers
    (buffers)??

    And if so, what is a good (preferrably somewhat cheap) op amp to use?

    TIA to anyone that can help me out. If anyone wants more information to help
    me diagnose the problem I have a graphic of my circuit drawn and I can give
    part numbers for my other components too.

    Steve
     
  2. Is your op-amp circuit sharing the same ground (0v) as your PIC?
     
  3. loedown

    loedown Guest

    Do you have the manual for the PIC chip?

    I am using PIC 12F675 at the moment and they have circuits for the ADC in
    them, if not, grab it from microchip's website

    Paul
     
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