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Question about design of clocking circuit

Discussion in 'Electronic Basics' started by usao, Aug 2, 2004.

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  1. usao

    usao Guest

    Disclaimer: I am not a student, but a home hobbyist trying to work out
    a problem.

    Here's the situation. I have a 1Mhz osc which I want to switch on-off.
    The issue is that I don't want the on-time of the clock to change
    depending on when the switch is thrown.
    Im looking not for answers, but for pointers or suggestions on how I
    should work this problem. The angle I have tried so-far is to use a
    edge triggered flip-flop to catch the output of the input osc ANDed
    with the switch input. The idea here is that if I catch the edge, and
    it's active, then I can send this through a one-shot, or somthing else
    to keep the width of the pulse the same size.
    However, this seems kind of complicated, and may require a debounce on
    the switch as well...
    Is there some simpler approach im missing?
    Ron (rwatkins at dssolutions dot com)
  2. Yes, you just have to synchronize your on/off with the clock with a FF.

  3. Activ8

    Activ8 Guest

    HArd to say without more osc circuit details but I'm quessing this
    osc is made with inverters (?) Why not use a SPDT or dpdt switch
    with one side to turn on the OSC supply and the other (when off) to
    ground out the timing cap to return it's initial condition to 0V?
  4. Ken Smith

    Ken Smith Guest

    Clk in
    ! NOR -------- Output
    ! ---
    ! DBSW !--------! !
    ! ----------!D ! !
    ------------!Clk ! !
    ! Q/ !----------

    DBSW = debounced switch

    You can use the other section of a dual FF to debounce the switch.
  5. it can be done even simpler with a latch,

    ____ ___
    gatesignal --------|D Q|--------| |
    | | | & |---- CLKout
    | | +---|___|
    CLK ---------+----o|LE | |
    | |____| |

  6. its even simpler with a latch

    ____ ___
    gatingsignal ---------|D Q|------| |
    | | | & |---- Gated CLK
    CLK --------------+--o|LE | +--|___|
    | |____| |

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