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using PIC to act as button push

Discussion in 'Electronic Design' started by [email protected], Dec 22, 2005.

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  1. Guest

    I've got a little device that has some pushbuttons on it, and an LCD
    that lights up. The PCB has some room on it, and I want to add a PIC
    that I can use to "push" the buttons on this. Once I do that, I'll
    have the PIC cycle through button pushes in order to automatically show
    the functionality of the device.

    Any ideas on how I can do this?

    The button traces are a standard two traces that interlock, but do not
    touch. The conductive rubber button is pressed, and touches both
    traces to complete the circuit.

    How can I get the PIC to do that for me?
  2. Donald

    Donald Guest

    Easily done.

    But a little more information please.

    Does one side of each switch go to ground ?

    How many buttons are there ?

    Is this "little device" publicly available ??

  3. Guest


    Yes, I think so. One side of each switch is connected to the same
    trace which ends up in a place known as Vss. The other side of each
    switch goes to a place underneath the epoxy, it would appear each to a
    different place. I checked the resistance between the common switch
    traces and the negative terminal of the battery clip and there was
    virtually no resistance.

    There are 3 buttons.

    Publicly available, yes, but no schematics or circuit diagrams or
    anything like that.


  4. Dan Hollands

    Dan Hollands Guest

    With the PIC ground and the pcb ground connected you can probably just
    connect the output of the PIC to ungrounded trace that goes to the

    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
  5. Guest

    I see, so that when the output pin is off, the switch is open (that
    means button not pushed, right?), and when the output pin is on, then
    that pushes the button? Is that the idea?


  6. Donald

    Donald Guest

    Yes, thats it. But "ON" mean logic LOW and "OFF" means logic HIGH.

    So tell us:
    What is it ??

  7. Guest

  8. Guest

    You know, now that I'm at it, I just imagined that getting my PIC to
    output IR inside an enclosure to the IR input of the 2nd device would
    be more of a pain than just manipulating the buttons.

    BUT, perhaps in the long run, assembly might be a lot easier, because
    there would be no buttons to remove from the PCB. Just connect, glue
    and go.

    If the level of difficulty of "pushing the buttons" is 1 on a scale of
    1 - 10, how hard would it be to rig the IR output? I assumed I would
    have to:

    1) Decode the output of the original device's IR
    2) Replicate that in code of PIC
    3) Find the circuitry in some PIC publication and "steal" it so that
    the hardware would work
    4) Find the proper positioning of the IR output device so that the
    communications would work reliably

    There's probably more, but I thought those were the major milestones.

    What would that difficulty level be? And how hard would it be to find
    somebody who could do it?


  9. Daniel Pitts

    Daniel Pitts Guest

    if the level of difficulty of "pushing the buttons" is 1 on a scale of
    I don't know the answer, but I do know that usually you start at 5, not
    one, in case IR would be easier. :)
  10. Donald

    Donald Guest

    OK, now that we know what the target is.

    Do you understand that the "ON" state will need to be low for many
    milliseconds, and "OFF" for many milliseconds before you "press" the
    next button ??

    The speed of each key press will be many times slower than the PIC runs.

  11. Guest

    Oh Danny-Boy, the pipes, the pipes are callin' :)

    Although I just could not imagine it being so, POINT TAKEN! You are
    so right!


  12. Guest

    Yes, I do realize that, I would imagine because of their debouncing
    routines, I will need to wait it out...

    Still, if that is 50 milliseconds ON to recognize a button press, and
    say 50 to establish the OFF, that's 5 chars per second, plus a the 3
    second wait, is about 5 seconds to establish and display the messages I
    want to display.

    I remember from my IBM-PC days that can seem like an eternity.

    I will have to get the IR kit and see if those times can be improved


  13. Rob

    Rob Guest

    I'm not sure about this, but it may be useful to have on="output low" and
    off="pin set as input". That way the buttons can still be used without them
    having to forcibly pull the pic out hi level down.
  14. Donald

    Donald Guest

    So, if I understand this new specification:

    The first display will send a command to the slave display,
    maybe to sync the displays together.

    Or are you thinking of replacing the "PC to IR Programming kit" ??

  15. Donald

    Donald Guest

    Thanks Rob,

    You are correct. That would be a better design.

    But he would running the PIC from the same battery as the display. So
    it should not really matter.


  16. 4066 quad analog switch

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
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