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Foot pedal for CTRL key

Discussion in 'Electronic Design' started by George, Dec 21, 2003.

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  1. George

    George Guest

    I would like to modify my PC keyboard so that some of the keys may
    be "depressed" with a foot switch. At the moment I need the Control
    key to work that way.

    There's a 40-pin encoder chip in the keyboard, and with my voltmeter
    I found that one of the pins goes from near gound to near +5V when
    either Control key is depressed. Is it possible that I could just
    connect lines to that pin and the Vcc pin, and bring them out to the
    momentary foot switch? Or would that likely make the keyboard
    release it's captive smoke?

    It's not obvious to me how the key matrix works, but it almost has
    to be some kind of polling operation.

    The keyboard is your average Keytronic.
  2. George

    George Guest

    Never mind. I found the row and column, and installed the momentary
    foot switch across them. Works fine.
  3. Jim Nagy

    Jim Nagy Guest

    But be careful of static discharges that could damage the chip.
    Personally, I'd put two 220 ohm resistors at the keyboard, each one in
    series with one of the wires that goes to the footswitch. If it still
    works bigger resistors, all the better.
  4. George

    George Guest

    Yes, I've got a 1K on each line, and it still works, which
    kinda surprised me. I was also thinking of putting a cap
    across the pair on the switch side of the resistors, but
    don't know if that really helps anything, or what value to
  5. Jim Nagy

    Jim Nagy Guest

    Personally, I would just leave it exactly as you have it. I really
    think the cap might cause more grief than help.
  6. YD

    YD Guest

    Sounds like a great idea for speed typists. Make a pedal board for
    Shift, Control, Alt and Esc keys, frees up the fingers for the actual

    - YD.
  7. N. Thornton

    N. Thornton Guest

    No sooner is a concepts shown to work, than someone tries to take it
    to the max. How could we do that?

    Perhaps an additional set of nose operated number keys, along with
    elbowed control keys? We could put escape and shift on the eyebrows,
    and space on the tongue to save a bit more time. Maybe put some of the
    most common letters on toes...

    I'm trying to picture our typist of the future :) Perhaps sticking
    with the OP's more conservative plan would be best.

    Regards, NT
  8. I read in that N. Thornton <>
    Nah! Unimaginative. Think of a five-manual pipe organ, with a pedal
    board of course. Specifically designed for multitasking!
  9. TSmith1315

    TSmith1315 Guest

    No sooner is a concepts shown to work, than someone tries to take it
    Escape should be linked to the pucker string!

    The mouse gets in *my* way, gotta let go of the keyboard to reach for it...
    So, how 'bout an Apache-helicopter-style helmet that monitors eye position to
    control the pointer, and blink the R/L eye for the corresponding mouse click?

  10. Jim Thompson

    Jim Thompson Guest

    I've used a shift register inserted in series with the keyboard
    cabling to capture certain keystrokes to operate monitor switching.

    You might modify such an approach to accomplish what you want.

    Or simply wire a switch in parallel with the appropriate key?

    ...Jim Thompson
  11. N. Thornton

    N. Thornton Guest

    I assume thats what will happen one day, more or less.

    Regards, NT
  12. George

    George Guest

    Upon reflection, I think the school-approved solution here
    would be to install a 5V zener diode from each line to
    ground. That would prevent any excursion outside the range
    of -0.6V to +5.1V, and should prevent any static damage
    without affecting normal operation at all.
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