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Decrementing a four digit counter?

Discussion in 'Electronic Basics' started by Zucker, Aug 6, 2004.

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  1. Zucker

    Zucker Guest

    I have built a four digit counter using an Allen Bradley photoswitch which
    clocks four 74190s (Up/Down Decade Counters). When the beam from the
    photoswitch is interrupted, the counter counts up.

    I would like to be able to decrement the counter manually with a single
    switch and have it act independently from the photoswitch (when
    decrementing, the switch should be the clocking device, not the
    photoswitch). This switch would have to drive the up/down pin AND the clock
    pin of the 74190s at the same time. It doesn't seem like you would be able
    to control both up/down and clocking operations at the same time due to the
    propagation delays of the 190s.

    Does anyone have any ideas on how I can decrement these 74190s with a single

  2. I beleive you have to use a delay circuit. The button itself must be
    conected to the up/down pin on the counter directly (no delay circuit
    The delay circuit must stay between the button and the clock-input of the

  3. John Fields

    John Fields Guest

    You might be able to get away with something like this:

    | +-----+
    |<--+----|D/U- |
    | | | |
    +---O [R] | |
    | S1A | | |
    | | | |
    | |<--+----|>CLK |
    | | | +-----+
    IN--------O [C]
    | S1B |

    if you used a DPST NC switch and you could assure that S1B opened
    first and closed last, but I'm pretty sure bounce would kill you no
    matter what.

    Plus, you haven't mentioned anything about what the photoswitch
    outputs look like and how you've got them connected to the counter
  4. Randy Day

    Randy Day Guest

    John Fields wrote:


    Something like this? If I read the 74190 data
    right, the clock line is positive-edge
    triggered, and D/U=1 counts down. The switch
    is SPST, normally closed.

    | |R
    | |
    | .-----.
    +------+--------------|D/U |
    | | | |
    | .-. | |
    | | |R | |
    | | | | |
    | '-' | |
    o| | __ | |
    | +-------\ \ | |
    --| | | |--|CLK |
    | --- +-/__/ '-----'
    o| --- C | OR
    | | |
    | | |
    === === in from photoswitch cct

    created by Andy´s ASCII-Circuit v1.24.140803 Beta
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