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SN74LVC1G74: A circuit that /Q would keep high(or low) after release the button

daniel
Genius 5095 points
Part Number: SN74LVC1G74

Hi Team,

We want to design a circuit that /Q would keep high(or low) after release the button

(First press→/Q high→release→/Q keep high→Next press→/Q low→release→/Q keep low→....)

But below circuit, /Q would not stay the status after release the button.

Please kindly help on the circuit revise or any other TI parts suggestions.

Thanks

  • 0
    TI__Guru* 97046 points
    Hi Daniel,
    The circuit shown above is intended to have the output at Q, and it should achieve what you are describing. This is essentially a state machine:

    State 0: Q = 0 (Q\ = 1), button is not pressed.
    State 1: Q = 1 (Q\ = 0), button is pressed.
    State 2: Q = 1 (Q\ = 0), button is not pressed.
    State 3: Q = 0 (Q\ = 1), button is pressed.

    And the state diagram looks something like this:

    State 0 --> State 1 --> State 2 --> State 3 --\
    ^-----------------------------------------------------/

    Forgive my poor artwork -- that should look like a loop. The states just cycle through with every button press.

    If you're having trouble with your implementation, I would recommend posting your full circuit, and the i/o scope shots for each stage of the device.
  • 0 in reply to Emrys Maier
    Genius 5095 points

    Hi Emrys,

    Thanks for your support.

    Attached the schematic and the scope waveform. (CH1- The CLK pulse is each button pressed)

    As you can see from the waveform, /Q behave normal at the first button press, but abnormal after that.

    We expect the second button pressed would change /Q status to high. But as the button is not pressed(release the button), /Q go back to low.

    And we sometimes got detect issue as the last CLK pulse in the waveform.


    Please kindly help to review our schematic, give us some modify suggestions to get below loop:

    State 0 --> State 1 --> State 2 --> State 3 --\
    ^-----------------------------------------------------/

    State 0: Q = 0 (Q\ = 1), button is not pressed.
    State 1: Q = 1 (Q\ = 0), button is pressed.
    State 2: Q = 1 (Q\ = 0), button is not pressed.
    State 3: Q = 0 (Q\ = 1), button is pressed.

    Many Thanks

  • 0 in reply to daniel
    TI__Guru* 97046 points
    The time scale is absolutely huge on your scope shot -- please zoom in on the edges so we can see what is happening. These devices respond in nanoseconds!