12 stage ripple counter odd problems!

Discussion in 'Digital Circuit Design' started by PauloConstantino, Jan 9, 2017.

  1. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
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    It's a quad yes. So there are 4 gates but I'm only using 1 of them. I don't think that us affecting the signal because when I adjust the hold off on the scope the signal is showing correctly. What's going on ?
     
  2. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    266
    7
    I am uploading a video of what's happening. When I adjust the Hold Off option, the signal displays correctly. I cant tell whether adjusting the Hold Off is adjusting the scope or compensating for a problem in the circuit....
     
  3. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    266
    7

    The scope's signal quality is good, but that doesn't mean the logic states are correct. Watch the video again and see how the left side flikkers an d can't decide which voltage to be at.
     
  4. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    266
    7
    Here's a video of what happens when I adjust the Hold Off option, please let me know what you think.

     
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    At least two people have stated that unconnected pins could cause a problem. Maybe if you read it, you'll understand.

    http://www.sxlist.com/techref/logic/xtrapins.htm

    If I had something not working right, I would remediate ANYTHING that may cause problems.
     
  6. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    266
    7


    You said it right. "COULD". But they are not as I have tested MULTIPLE times.
     
  7. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    266
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    I have done some research on the net, and apparently the problem is the Hold Off Times.

    The output from the logic gate is not simple periodic but has two signals of different periods inside it and the scope doesn't know how to trigger correctly.

    When I adjust the hold off option, the signal is finally displayed correctly. EVEN WITH MY RATS NEST OF WIRES.
     
  8. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Hold-off adjustment on a scope affects *only * how the signal already inside the scope is displayed. It does not affect the actual circuit in any way. Rule #1 of test equipment - what you are seeing is a total strangers opinion of what you should be allowed to see, filtered through his opinion of how the circuit should be interpreted before it is displayed. In other words, all scopes lie, and all digital scopes lie more. If a scope adjustment shows you what you want to see, take the win.

    ak
     
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  9. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
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    Buddy, do you know how HoldOff works ? If you have two versions of a signal, one is good and the other is bad, which do you take?

    As I said, after adjusting hold off, the signal is perfect. Now how can you explain that ?
     
  10. OBW0549

    Well-Known Member

    Mar 2, 2015
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    I would explain it by pointing out the obvious: it means there never was any "problem" to begin with-- you just didn't have the scope set so the signal could be properly displayed. Adjusting the holdoff allowed the scope to properly synchronize with what's happening in your circuit, thereby giving you a stable display. This became very clear while viewing the video you posted in #44 above, which provides a good illustration of why oscilloscopes include a trigger holdoff function.

    NOTE: what you experienced is something that occurs fairly often when trying to view complex waveforms (especially data streams) on an oscilloscope; it often takes quite a bit of fiddling to get a coherent display, which is one of the main motivations for using a logic analyzer instead.
     
    Last edited: Jan 11, 2017
  11. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
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    Fantastic!!! Finally someone who is really interested in helping and clarifying rather than putting down someone who is learning. Thank you so much for that. Now I understand why it happened.... Indeed because the signal was complex and not the simplest periodic signal. I had no idea that holdoff was used for that. At the beginning I tried adjusting it but nothing happened so I thought it was useless. Then I tried again later and it took me a long time to find the right spot. Then I discovered that whenever the HoldOff time is a multiple of the signals period, then I get a stable display, and whenever it isnt't, the display is unstable.

    Many people have been telling me off saying that my circuit didn't work because of my jumper wires. Maybe they learn a few things as well today.


    And for those who have helped me, thank you indeed and best wishes :)
     
  12. ClassOfZero

    Member

    Dec 28, 2016
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    Paul, they weren't putting you down, you were receiving sage advice from experienced members. It is not meant as a personal slur. They were attempting to help you. It has been made a little more difficult by the absence of any circuit diagrams, a picture is worth a thousands words as they say.

    Paul, I would suggest that an apology to all that tried to help you may be the diplomatic thing to do. Not all the answers you receive here may be a 100% solution to your query, whatever the subject, but don't dismiss them out of hand because you don't like the answer or if you feel it is a critique of your workmanship. Don't forget you have many threads more or less relating to the same issue and many have attempted to help you along your way.

    I remember years ago reading something, though the context escapes me, that a CRO is not the be all & end all in test equipment, sometimes it can send you "up the garden path". But the good thing is you learned something regarding the use of the equipment at hand.

    Good luck and keep plugging away.
     
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  13. OBW0549

    Well-Known Member

    Mar 2, 2015
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    Ummm... I think more credit is due than that; many of us-- most of us, probably-- have long experience with solderless breadboards and have become acutely aware of how vexingly problematic they can be with regard to signal integrity, especially when used with high-speed clocked logic and/or analog circuits. The remarks made about jumper wires, etc. were quite on-point and should be taken seriously-- and those people most certainly WERE trying to help you.
     
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  14. OBW0549

    Well-Known Member

    Mar 2, 2015
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    And that goes double for digital scopes, which have some truly astonishing methods for misleading the unsuspecting engineer or technician.
     
  15. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    I'm vaguely aware of the concept. Do you know how an oscilloscope works?

    You can achieve a stable display without trigger holdoff, by taking the scope out of calibrated timebase mode and adjusting the variable timebase to be an integral sub-multiple of the complete waveform period. You won't be able to measure periods with the graticule, but you already know what they are from the schematic. gfy

    ak
     
    Last edited: Jan 11, 2017
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