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latch circuit

Discussion in 'Electronic Basics' started by GLM590620, Sep 30, 2003.

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  1. GLM590620

    GLM590620 Guest

    I'm looking for a latch IC or a sutable circuit for use with a 4X4 keypad,
    something that will keep only one key on untill another one is pressed.


  2. John Fields

    John Fields Guest

    I'm not sure I understand what you're asking for , but it sounds like
    what you want is something like this:

    Let's say you have a 4X4 keypad and 16 relays, and when you press key #1
    relay #1 comes on and stays on until you press another key. When you
    do, relay #1 will drop out and the relay corresponding to the new key
    you pressed will come on and stay on until you press another key, and so

    Is that what you want?
  3. ----------------------------
    Simple, 16 buttons to ground, each other pole with a guide diode toward
    each button. Then pull-ups on the data lines, and pull them down as
    needed by wiring the right button to the right bits to encode it in

    Also bring together diodes from each button to one pullup, which
    becomes the latch strobe, then use that to latch the value to a
    latch, like a 74xx574 or such.

    To do two digits, simply debounce the strobe and run it to a 74747
    as a divide by two counter, that changes states to enable whichever
    of the two digits, back and forth.

    You COULD do some clock-driven polled circuit, but this is more elegant
    actually. Run the latch outputs to two 7447's and two 7-segment LED

  4. Dana Raymond

    Dana Raymond Guest

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