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Power Button

Discussion in 'Electronic Basics' started by Kit, May 1, 2007.

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  1. Kit

    Kit Guest

    Hi all,
    I am making a battery powered device that uses a Single board computer
    running Linux. The problem is that because I am using a CF Card
    mounted read/write I cannot just cut the power to the SBC. So I need
    to have some system by which the SBC can shutdown properly before it
    cuts the power. I am thinking of something like the power button on a
    So does anyone know how I could go about this?
    A circuit would be great.
  2. Some idea of the SBC you are using would be helpful, but it must have some
    kind of i/o capability. Either a serial port, I2C or some kind of GPIO
    ports must be present regardless of the SBC type. You should be able to
    read from one of these in software and then initiate a "shutdown -h now"
  3. Kit

    Kit Guest

    Sure, I am using a Technologic Systems TS-7200.

    Yes, I can do that, but once the SBC is shutdown I need to turn off
    the power.
  4. You could use an output pin on the SBC to trigger a one-shot. The falling
    edge of the one-shot output could then reset a flip-flop that drives the
    power relay. To start the system, apply power directly to the relay and
    to the 'set' input of that flip-flop.
  5. Ok, I think I get it now. ;-) Looks like you have a serial port on there.
    After you do a "shutdown -h now", see if the DTR (or any other status) pin
    changes state. If so, that could be used as the signal to an external
    device to turn it off.

    Or you could possibly use one of the i/o pins to start a timer that would
    power off the computer after a predetermined delay. The i/o pin would be
    toggle from a script that executes during shutdown.
  6. BTW, how do you like that board? Is the Linux distro stable (as in runs for
    months without issue)? I'm looking to use something like as a central
    controller for a bunch of home automation junk I've come up with. Mostly
    just to do a bunch of long term logging, yet be accessible over the network.
  7. jasen

    jasen Guest

    in linux the shutdown process is controlled by the symlinks in


    (got questions? read up on sysv-init and/or ask again in a linux newsgroup.)
    after it turns off, how is it supposed to turn on ?

    does the board have a shutdown mode, if so what happens on DIO1 pin 16?
    and or the USB power terminals, serial port outputs etc...

  8. Epictitus

    Epictitus Guest

  9. Kit

    Kit Guest

    So far the board has been great. As for stability, I can't really say.
    Because I haven't had it for very long, and it hasn't been running for
    most of the time (I have been trying to get the rest of my project
    going :).

    I figured out what I needed. I just needed a SCR.
    Thanks for the help anyway.

    This isn't related, but I was wondering if anyone has used the
    Propeller from Parallax? If so what is it like, how well dose it work?

    Thanks again
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