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input to PC parallel port

Discussion in 'Electronic Design' started by yoavshe, Oct 10, 2006.

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  1. yoavshe

    yoavshe Guest

    I've been trying to read a signal by a parallel port.
    The signal is the output of a comparator LM339, by a 21k resistor
    connected to 30V, and then 10k connected to ground.
    The problem is - whenever I connect the parallel port - the signal dies
    (0V read).
    What am i doing wrong?
    What should I check?
    Can anyone refer me to an example circuit where data is read by a
    parallel port?
  2. linnix

    linnix Guest

    Not knowing the details. Here is my guess: You are comparing against
    a 10V signal (21K,10K divider). So, your LM339 is at least 10V VCC,
    and the output is almost 10V.
    Check if you parallel port is still working (not smoking).
  3. yoavshe

    yoavshe Guest

    linnix כתב:
    I tried it with a 5k-25k voltage divider as well - no good. And it's
    not smoking...
    How do I check whether the comparator is "strong" enough to raise the
    pin to '1'?
  4. Leon

    Leon Guest

    Try it without the comparator, by connecting the pin to +5V and ground
    and checking that you can read the values with your software. Then
    check that the comparator is working by testing the output with a DVM
    or scope.

  5. yoavshe

    yoavshe Guest

    Without the comparator (Directly from a power source ) it reads ok,
    although only from about 7V.
    I was thinking maybe the 20k and 10k resistors are too large. could
    this be a reason?
  6. "yoavshe" <> schreef in bericht

    linnix ???:
    \I tried it with a 5k-25k voltage divider as well - no good. And it's
    \not smoking...
    \How do I check whether the comparator is "strong" enough to raise the
    \pin to '1'?

    If you tried to push 10V onto a parallelport pin it might as well been
    blown. What pin did you use anyway? What mode is the parallel port suppose
    to work in? For a comprehensive treatment of PC ports see:
  7. Sjouke Burry

    Sjouke Burry Guest

    Fisrt, you should select in your bios setup
    SPP for the printer port.
    thats short for Standard Parallel Port.
    That ensures that the outputs and inputs
    behave like standard TTL .
    Then if you want some software and info to
    horse around with, get
    Source code included.
    That software uses a cable between printerports,
    to send /receive computer files.
  8. The LM339 is opencollector and requires a pull up resistor to +5 volts.

    +5------2K resistor ------output of LM339 and input pin to port.

  9. Si Ballenger

    Si Ballenger Guest

    A simple setup below.
  10. Leon

    Leon Guest

    Looks like you have a problem with that input. It should respond to TTL

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