Help building my logic clock

Discussion in 'The Projects Forum' started by Rocky_circuits, Nov 23, 2011.

  1. Rocky_circuits

    Thread Starter Member

    Nov 1, 2011
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    I've been trying to solder my clock together. I ran into a problem with my first attempt and gave up and started again. This time it appears to work fine except one very aggravating problem. I've only been able to get to the seconds, haven't gotten any more of the clock done cause I keep running into problems.

    So the problem now is that using a NAND gate going into the CLK of IC2 74161 and LOAD of IC1 74161. Works fantastic in my simulation in multisim 5.1. But when I tested it in real life, turns out that my "1" seconds work fine. Counts over to 0 after it goes to 9.
    My "10" seconds however, count up 1 right after the IC1 counts 8. It then works fine counting to 9..

    So... Like this: 00, 01, 02, 03, 04, 05, 06, 07, 08, 19, 30, 31, 32, 33, 34, 35, 36, 37, 38, 49, 60.

    Very annoying and not a clue why it happens. Here's pictures if you like but the bread bored is quite wild. My circuit is difficult to see some areas but the NAND gate part of it isn't


    Edit: editing pictures they didn't upload full resolution

    [​IMG]


    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    No bypass capacitors on the IC's, no current limiting resistors on the LEDs, long looping wires running everywhere - it's a wonder it works at all.

    Try fixing those things, and then see what happens.
     
  3. Rocky_circuits

    Thread Starter Member

    Nov 1, 2011
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    I don't need the bypass capacitors for something like this. I know it is proper and professional but is not needed for this to work. I don't need current limiting resistors for this short testing on the LED's. But I appreciate the concern. The bread board is temporary but just to test that it works. I just realized something that I completely forgot... that was the whole purpose of this. My A-D is not connected to my Qa-Qd
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You are incorrect.

    You're still wrong.

    It's bad practice; you stress both the IC and the LEDs, but mostly the IC.

    Why is there never time to do it right in the first place, but always time to do it over again?
     
  5. Rocky_circuits

    Thread Starter Member

    Nov 1, 2011
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    Because I'm cranky... :p I'll throw some resistors in. I don't have any capacitors sadly and no access to them in the manhasset area while I'm away from my dorm.

    The reason I disagree about not needing those bypass capacitors is because the 70 people in my Intro to digital and analogue electronics class are all building their similar version of this clock. None of them are using bypass capacitors, primarily because they have never been taught it. When I asked my TA about it after I heard about it from a previous post from you, he said they don't teach it till the beginning of your junior or 2nd sem. of sophomore year at this university.. And it is one of the top engineering schools in the country.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    If you don't want to listen to sound advice then you don't need this forum.
     
  7. Rocky_circuits

    Thread Starter Member

    Nov 1, 2011
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    I apologize if it sounded rude.. It's more that I have no access to capacitors of the sort for the rest of the week. I guess I'll give the project a rest till I can get those capacitors.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    That's a much better reason.

    Just because they are uninformed doesn't mean that you have to be uninformed.

    Now THAT is simply absurd. It would take perhaps 15 minutes of lecture time to cover it in detail, and it is one of the basic requirements of using integrated circuits - that is, if you want them to be relatively quiet and trouble-free.

    You might just get away with it with (very) low-speed analog circuits, but it's not recommended. With digital circuits, you can wind up with ringing on the power rails, which may make your circuit seem to change states at random anytime some gate changes states. These types of problems can be very difficult to track down. By using a 0.1uF/100nF poly metal film or ceramic cap on each and every IC's power pins, you avoid that type of problem from the start.

    Yeah, I know - it sounds very excessive. It did to me as well, when I heard it many years ago. But if you omit them, you are inviting big problems to visit you.

    0.1uF/100nF caps are used so frequently, you might as well order a few hundred of them from someplace like Avnet Express, Mouser, or Digikey.
    Mouser has these:
    http://www.mouser.com/ProductDetail...EpiMZZMuMW9TJLBQkXrq%2bH4l5OQZlquv%2b6dd4dTQ=
    $0.04/ea if you buy 100 at a time. That's four lousy bucks plus shipping. You can hardly buy a cup of coffee in Manhattan that cheap. You might as well get 200, as the shipping won't go up for that small of a package.
     
  9. Georacer

    Moderator

    Nov 25, 2009
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  10. bwack

    Active Member

    Nov 15, 2011
    109
    10
    Hi I'm new to this forum.
    I just want to say, that there are some pit-falls that I can remember that you might have fallen into. First, since there is some fail in the sequence, check the logic circuitry. Are you sure there are no "glitch" incomming on the LOAD input of the bottom left flipflop(?) on your cirtcuit? When I see like three stage logic on a load/enable/flange input, I would check for glitches.. Hook the LOAD line up to your scope and trigger and look if there are no unwanted "loading". I must admit I have'nt looked so well at the schematic, but do check this please, and I also support the comments above (currentlimitting those resistors (I had one microcontroller fail its operation once because of similar (connected a bipolar base directly to the output of the mcu).. (sorry the language, I'm not english. .)
     
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