circuit sudden spike in signal. help

Discussion in 'Homework Help' started by allhuber, Nov 9, 2011.

  1. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    Hi AAC community,


    I need help for my circuit. This questions may be stupid but try to bare with me. My question is:

    I have a up/down counter and some logic gate to detect the "HIGH" signal when number 9(1001) appears. I will push the up counter button to count up till it reaches 9(1001), then push the down counter button till it reaches 0(0000). I noticed a small spike when the counter down from 8 to 7(1000). Is there a way to filter this out. I am new to electronics so if anyone can give me step-by-step advice?


    Here is the picture:
    http://farm7.static.flickr.com/6041/6328324154_eb7da565a4_b.jpg


    Thanks :)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome to AAC.

    First try to put a 100nf ceramic cap across supply pins of all the logic IC's. As close as possible to the IC's
     
  3. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    Hi Rifaa,

    thanks for replying. The logic gate in multisim has no vcc and ground as you can see in the pic. do i connect at the outputs of the counter(Q0-Q3)?
     
  4. R!f@@

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    Apr 2, 2009
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    I believe it's a synchronous counter, right?
     
  5. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    Hi,

    Got this from the data sheet. So i guess it is.
    "LS192 and LS193 are Asynchronously Presettable Decade and 4-Bit Binary Synchronous UP/DOWN (Reversable) Counters."

    thanks
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You have to use Asyn counter to avoid that glitch Mate
     
  7. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    the problem is i can't change the 193 ic so they expect me to fix the glitch myself. :[
     
  8. R!f@@

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    Apr 2, 2009
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    I thought you had made the circuit.

    It's a home work right ?
     
  9. t06afre

    AAC Fanatic!

    May 11, 2009
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    Are you sure. I think it should be opesite. Synchronous operation is having all flip-flops clocked simultaneously. So that the outputs
    change together when so instructed by the steering logic. With asynchronous (rippleclock) counters. You will have output counting
    spikes normally. ​
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    The problem you are observing is caused by "race". The way to avoid this is to draw a Karnaugh map. Then you will find that the simplest solution is one AND gate with QA and QD as inputs.
     
  11. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    kind of. I designed the circuit but I am only give the 74LS193 and logic gates.
     
  12. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    hi Mr Chips,

    I tried that at the start but got the "small spike" while counting up and down, [9 to 8 spike] [8 to 7 spike appear],

    Then I did the circuit above and got a "small spike" when counting down [9 to 8 - no spike] [8 to 7 spike appear].

    I use the oscilloscope to check and gates U1A and U2B. The spike source was from and gate U1A. So I was wondering if there is a way to filter out the slight delay.

    Thanks
     
  13. MrChips

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    Oct 2, 2009
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    Is this a real circuit or a simulator?
    On another note, there is another thread going similar to this. You must debounce your clock push buttons.
     
  14. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    I plan to test on simulator then move to actual circuit. similar thread. I cant find the thread. May I know the title so I can relate the solution to my question. Did you mean the up and down push button.

    Thanks
     
  15. t06afre

    AAC Fanatic!

    May 11, 2009
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    You could try this. Swap around the signals. So both the inverted inputs end up on the same gate. Then replace this gate and the inverters on the input with a NOR gate.
     
  16. allhuber

    Thread Starter New Member

    Nov 5, 2011
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    I just tested the real circuitry it out and it works. Strange? Should not trust simulators... haha. Thanks guys any way.
     
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