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  • TI Thinks Resolved

CD4027B: The otput Q won't change

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Replies: 11

Views: 382

Part Number: CD4027B

Dear *,

I attached my schematic with CD4027B. I have connected toggle button on P2 and when press the button the 14V comes to K1, J1 and through R10 10Ohm C8 100n to CLK1 but the Q1 is always 12V and Q1_n always 0V

please can you help?

BR.

TOGGLE-BUTTON.pdf 

  • What is the purpose of the circuit? What do you expect to happen?

  • In reply to Clemens Ladisch:

    When I press the button I want to toggle the output Q on the rising edge of the CLK.

    Upon press the J and K are 1 and the CLK is rising.

    is it possible that the RC circuit are the problem?

  • In reply to ZeroD:

    Just connect J and K directly to VDD; their state is relevant only during a rising edge.

  • In reply to Clemens Ladisch:

    Dear Clemens,

    i connected the J and K direct to VDD=12V, and now when i press the button the Q output changes but when i release the button then it changes back to previous state?

    J=1, K=1 -> button press CLK from 0->1 -> Q from 1->0, release the button Q from 0->1

    i also removed C7 and C8 but i get the same thing.

    ( one observation when i unplug the board, the capacitors have some charge left, and then when i press the button the Q changes and stays in the state to another button press ??)

    Br.

  • In reply to ZeroD:

    I'd guess that the RC filter is too weak, and the button is still bouncing. Check with an oscilloscope.

  • In reply to Clemens Ladisch:

    Hey Br,

    Could you provide some scope shots of the operation with the issue you are experiencing. Also make sure to zoom in on the button press to verify if the button is still bouncing. The RC may be too small.

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  • In reply to Dylan Hubbard:

    Dear Dylan,

    for some season after the CLK input goes from high to low the Q,Q_N changes again

    a) regarding button press denouncing RC

    I have first RC then the buffer CD4050BE and then the button press signal goes to CD4027BE JK bistabil CLK input.

    I don't see any bouncing of the button:

    Blue button signal

    Yellow after the RC

    Green on the CD4050BE = CLK in of the CD4027BE 

    b)  when i release the button the clk goes from high to low and then the output changes ??

    Br,

    David.

  • In reply to ZeroD:

    Hi David,

    Could you zoom in on the falling edge green signal. As much as you can while keeping the whole edge on screen. I think I might know whats going on here.

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  • In reply to Dylan Hubbard:

    Dear Dylan,

    i will do that but currently i don't have the oscilloscope by hand. i will do it ASAP

    please can you explain what do you think that is going on?

    Br.

  • In reply to Dylan Hubbard:

    Dear Dylan,

    here are the oscilloscope shots:

    yellow: button

    blue: after RC button -> buffer input

    purple: buffer output -> J-K CLK input

    green: j-k output Q and QN

    whole ***:

    zoomed rising edge

    zoomed falling edge

    Br.

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