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What are all the little resistors for...

Discussion in 'Electronic Basics' started by Russ, Jul 8, 2005.

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  1. Russ

    Russ Guest

    Real beginerers question: I was looking at a control board for my vending
    machine and there are the ususal number of IC's and next to every IC there
    are resistors, rows and rows of them. There are also rows of diodes. Why
    do they need to add so many resistors to each IC? what do they do? If they
    drop the voltage shouldn't they just come in with less voltage and save all
    of those resistors? Can someone explain how and why these resistors and
    diodes are used in this way?
    Thank you very much
  2. Bob Myers

    Bob Myers Guest

    What you're calling "resistors" are very likely bypass capacitors; these
    are used to provide a distributed capacitance across the board, and
    one which will respond well to rapid transients, so as to reduce the
    effect of noise on the power supply causes by the digital circuits
    On the other hand, there are very often cases in which resistors really
    are used in series with the outputs of digital logic ICs, especially when
    these outputs are being used to drive long lines or traces. In this case,
    the resistors are there for "damping," reducing the amplitude of overshoot,
    undershoot, and "ringing" on these lines.

    Diodes might be for any of a number of reasons. One possibility is
    for protection against electrostatic discharges (ESD).

    Bob M.
  3. me

    me Guest

    resistors and diodes are often used to form circuitry. How they are
    connected, to what they are connected, and their values determine the
    properties of the circuitry. To sum up the answer, we'd need to know how
    they are connected, to what they are connected, and their values to tell
    you anything of any value.

    (except those who are familiar with the circuitry in question, then they
    would just need the machine model number)
  4. Bob Masta

    Bob Masta Guest

    Hmm. Since this is from a vending machine, I wonder
    if it is the input lines from all the pushbuttons, each
    with a pull-up resistor. The diodes might be for some
    sort of multiplexing, so that they can be read as rows
    and columns by a central processor instead of the
    chip needing a dedicated line for each switch.
    Just a thought...

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  5. TokaMundo

    TokaMundo Guest

    Wow... this could almost be a computer bot response! ;-]

    You should be sure to make a few mistakes in spelling or grammar,
    such that we know the source is really human! Hehehehe...

    Anyway... good job. The short answer... Parts is parts...
  6. Kitchen Man

    Kitchen Man Guest

    My guess is along similar lines. I'm thinking the diodes are zeners,
    and the resistors the complementary current control for the zeners.
    The total design will take electro-mechanical impulses from coins,
    buttons, etc., and convert these to logic levels.
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