JK-FF Problem

Discussion in 'Homework Help' started by ashourism, Mar 22, 2012.

  1. ashourism

    Thread Starter New Member

    Apr 2, 2011
    5
    0
    Hi
    i have a project in school to create a count by 16 counter, the problem is that i can't even get one JK-FF to work properly

    i'm using 4027b ic its a CMos ic and i couldn't find a ttl one , in school they had a built in kit with ttl and i had no problems with it.

    i connected the S and R of the first JK to ground, the J and K to high, also Vdd to high and Vss to ground am using a high voltage around 7v,

    the clock is connected to a 6 pin push button when pressed it inputs high when left it shorts the clock pin with the ground.

    then finall the Q pin is connected via a 270 ohm resistor to a Red Led anode and ofc its cathode is grounded.

    my problem is that i don't get constant effect. sometimes i press the push button and the state toggles sometimes it doesn't, i tried changing the ground wire several times and also the Vdd wire and they are perfect.

    i read that Cmos technology requires all input pins to be grounded so i grounded the pins of the second FF leaving only its Q and inverse Q without connection.

    please i need help with this as soon as possible.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    You are experiencing something called "switch bounce". Pushbuttons must be debounced in order for your circuit to behave properly.
     
  3. ashourism

    Thread Starter New Member

    Apr 2, 2011
    5
    0
    Thank you it was very helpful i did change the push button with an on-off-on switch and it did work perfectly,

    but i still like to do it with a push button i've tried the circuits mentioned here (hardware ones no mcu used)
    http://www.elexp.com/t_bounc.htm

    in the first circuit i used a cap of 100uf 16v and 10kohm i also changed the value till 80kohm but none gave a good output note i used an or gate in the output not a nand gate but i don't think it would make much difference

    the tried the second circuit with no luck, any other suggestions.

    thanks
     
  4. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
  5. ashourism

    Thread Starter New Member

    Apr 2, 2011
    5
    0
    Thank you very much guys, i've retired the frist method with a nand gate with its two inputs connected to the output of the RC circuit and it worked i just missed connecting the vcc to the nand gate node first time :S!

    it work perfectly but when i press the push button i notice that the illuminance of the led increase before it switches its state

    am going to try the SR-FF method and check if it would give a better result

    thank you again
     
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