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uC economic keyboard

Discussion in 'Electronic Design' started by mdavid, Mar 6, 2007.

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  1. mdavid

    mdavid Guest

  2. Guest

    mdavid escreveu:
    ya, i know how that works, where u wante conmect that?
  3. Joel Kolstad

    Joel Kolstad Guest

    It's nice... what he's doing is energizing one column of keys at a time
    (1/4/7/*, 2/5/8/0, or 3/6/9/#), and then using the four pins to read back
    which (if any) button is pressed. But... since he uses one of those same four
    pins to energize a column, he needs two ways to energize each column: When the
    leftmost diode is driven, the 3/6/9/# column is energized, but he can't read
    back "#" since it's already high. Hence, he'll next drive the 2nd to leftmost
    diode, which still powers up the 3/6/9/# column, and now he can read # (but
    not 6 -- but he already checked that last time).

    The pin driving the LED is an input while he's "scanning" the keys, although
    it'll light up if 1, 2, or 3 are pressed. If the duty cycle of scanning is
    low, this probably won't be visible. (He could add a largish resistor between
    the top row and the input pin to reduce this effect, if it is noticed.) When
    he's not scanning he can use it to flash the LED or whatever.

  4. mdavid

    mdavid Guest

    Thanks, Joel.
    I took another look to that schematic. Your explanations it's ok, but
    i think he does the "scanning" on rows
    (Make one row "0" logic), and then use the other 3 (connected to
    columns now through corresponding diodes)
    to see what key was pressed.

  5. jasen

    jasen Guest

    you mean the 3x4 matrix is controlled by 4 IO pins,

    I expect what they do is turn on the pullups on those pins and then take
    them low one at a time and see which others follow,

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