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Counting circuit problems

Discussion in 'General Electronics Discussion' started by kong, Nov 22, 2013.

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  1. kong

    kong

    122
    2
    Sep 26, 2010
    I built a counter circuit that I want to count down from :30 to :00.

    It is composed entirely of 4000 series logic. I'm using two 4510 chips and two 4511 chips.

    I built an astable that works but not when connected to the circuit.

    These counting circuits work when on the breadboard but not when soldered together.

    I use wire lengths to connect everything together. I just bought new chips and installed them.

    When I turn it on random digits come on the display each time I connect and disconnect power.

    The preset input which I have tied to a 10k pulldown resistor doesn't preset the display when I take it high.

    I'm thoroughly confused and would welcome any advice.
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009
    hi kong

    it would probably be a great idea if you showed us your circuit
    that way design errors may be seen and solved

    Dave
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    I would suspect a wiring error.

    With such a rat's nest of wires, it would be almost impossible to trace the wiring from a photo.

    Can you show us the other side of the board? You may have shorts on that side which could affect things.

    Do you have the reset logic used? If not, what happens if you wire a reset line and reset both chips?
     
  4. kong

    kong

    122
    2
    Sep 26, 2010
    I have discovered that one lamp test pin was floating on one 4511 the other was wired properly and pin 4 on both 4511's was floating. I fixed that and it counts and presets correctly, however I still think I might have a wiring error with the first 7 segment display because my 6's 5's and 2's are not displaying correctly. Could also be a bum chip. Thank you both for your advice and i'm sorry I do not have a schematic handy.

    I can post the other side and will, I did not utilize the reset pin it's permanently soldered to ground on both chips
     
  5. kong

    kong

    122
    2
    Sep 26, 2010
    Here is the back

    Good luck lol.....I need to start etching
     

    Attached Files:

    • back.jpg
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  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    For the amount of wiring you have there it's actually pretty tidy.

    But really hard to see much from a photo as so much is obscured.

    It sounds like you have significant progress though. Maybe if it is counting down you can write down how each digit displays. Maybe there's just a simple transposition of segments to the display?
     
  7. kong

    kong

    122
    2
    Sep 26, 2010
    Here is how the digits show on the 'ones' display. All the others work fine
     

    Attached Files:

  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    Are all segments of equal intensity for all digits?

    Just a thought, make sure you have wired up the power correctly to the 7 segment driver chip.
     
  9. kong

    kong

    122
    2
    Sep 26, 2010
    It's not terribly noticeable but the segments that aren't supposed to light up might be a bit fainter than the others....everything else works perfectly so I don't think it's a power issue...I have it connected to a wall adapter instead of a battery it can only supply 150mA though....you think that is enough current?
     
  10. kong

    kong

    122
    2
    Sep 26, 2010
    Continuity is solid to VCC and ground on the 4511. Curious if it could just be a bum 7 segment. It's definitely possible I made another error somewhere but I've swapped out the chips and double-checked the wiring.
     
  11. kong

    kong

    122
    2
    Sep 26, 2010
    I think I might have located the source of the problem. I was testing the backside of the 7 segment display with my continuity meter and I got a signal between the "b" and "c" pin of the 7 segment.

    I ordered some new displays and am going to swap the one out. Will report back in a couple of days.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,477
    2,820
    Jan 21, 2010
    I'd be very carefully checking for a solder bridge too...
     
  13. kong

    kong

    122
    2
    Sep 26, 2010
    Ah, after further investigation this proves true!

    There was a simple connection between pins 11 and 12 of the 4511, which correspond to 'c' and 'b' respectively. Thank you so much for your help. Everything is working perfectly. Sometimes those bridges are so inconspicuous. It was impossible to tell from the naked eye but the continuity meter caught it.
     
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