CD4027B: The otput Q won't change

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

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?

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

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.

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

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.

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.

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.

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.

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.