trouble with my jk flip flop

Discussion in 'General Electronics Chat' started by leonheard, Jul 15, 2013.

  1. leonheard

    Thread Starter Member

    Jan 8, 2013

    i bought today a SN74LS73AN - DUAL J-K FLIP-FLOPS WITH CLEAR
    i read the datasheet, it has 2 jk flip flop inside, so i just wanted to test it,
    i wired them as asynchronous counter something like this

    but only with 2 bits not 4 bits :p

    in the output Q 0 i put a led

    and in the output Q 1 i put another led

    more info:

    it makes randomes blinks, sometimes i have to press the button ( clock ) many times until it changes to another state 0-1 or 1-0 :(

    what could it be?, help me :/
  2. tshuck

    Well-Known Member

    Oct 18, 2012
    are you debouncing your inputs?

    My guess is no..
    leonheard likes this.
  3. crutschow


    Mar 14, 2008
    You need a debounce circuit for the button. Mechanical buttons generally put out several rapid pulse when pushed due to bouncing of the contacts. If it's an equal number of bounces, you may end up back at the same state you started. It switches so fast you don't see it changing.
    leonheard likes this.
  4. leonheard

    Thread Starter Member

    Jan 8, 2013
    maybe i try that debounce circuit later . I made an astable multivibrator with a ic555, the first led seems to blink fine, but still the second led doesnt turn on or off when it should, i dont know if i should add a NAND gate or a AND gate for this counter to work fine, ( i dont want to cheat :p )

    another solution is if you can give me a working counter binary circuit for my IC chip

  5. BobTPH

    Senior Member

    Jun 5, 2013
    Do you mean that the second flip-flop turns on and off, but not when you think it should? If so, you the ~Q output to go the second flip flop CLK. I am too lazy to look up the chip and see which edge it triggers on.

  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    The LED on Q0 may be loading the output such that it cannot provide good logic levels to the 2nd flip-flip.
    Do you have a current-limiting resistor in series with the LED? TTL cannot source a lot of current.
    You should probably connect the LED and its resistor to /Q.
    absf likes this.
  7. leonheard

    Thread Starter Member

    Jan 8, 2013
    the Q output is already in the second flip flop clock.

    example: if the rectangular signal from the IC555 IS 1 HERTZ, then the first flip flop should last 1 sec ON and 1 sec OFF

    the second flip flop should last 2 sec ON and 2 sec OFF

    the third flip flop should last 4 sec ON and 4 sec OFF

    and the fourth flip flop should last 8 sec ON and 8 sec OFF

    then it repeats.

    thats how the binary counter should work ( 4 bits )

    in my case i only have 2 bits so first flip flo 1 sec ON 1 OFF , second flip flop 2 sec ON 2 sec OFF. My first flip flop works OK, BUT the second flip flop doesnt follow the rules ( kind of random) :( am pretty sure i put the wires correctly.

    like i said, a binary counter mode schematics for my ic chip will help much more

    here is the datasheet site:

    ps. i made a 4bit binary counter from discrete components just for fun and it worked great,
    but it took much space and time, that why i bought this IC chip, but i see the IC is MUCH worst.
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    How is the Q0 LED connected? Post a schematic, if you can.
    Also, you need to have a 10uF (minimum) capacitor between pins 1 and 8 on the 555, and a 0.1uF capacitor between pins 4 and 11 (short leads) on the 74LS73.
    leonheard likes this.
  9. absf

    AAC Fanatic!

    Dec 29, 2010
    Did you follow what Ron said and connect the led on the /Q of the 74LS73? I simulated the circuit as Ron said and it worked fine...

    leonheard likes this.
  10. leonheard

    Thread Starter Member

    Jan 8, 2013
    wow! thank you so much! absf, allen.

    i watch you circuit schematic and i did it about 20 minutes ago, and it works great!

    but for some reason i didnt need to put that 100nf, if worked great without that capacitor also :p

    thank you so much again for the work u made, and your time!

    now i can make my digital clock :p
  11. WBahn


    Mar 31, 2012
    If you would, it could be helpful to others to post a sketch of the circuit as you had it wired up, including the LEDs and resistors (if you had them) and the 555 circuit as well. That way the issues can be pointed to and how the correct schematic deals with them.
    leonheard likes this.