9-0 seven segment counter

Discussion in 'The Projects Forum' started by Sparky49, Mar 1, 2012.

  1. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Hi everyone.

    I'm looking into seven segment displays, and I think I've got a reasonable idea of how they work.

    However, I cannot seem to find anything which allows a countdown. Clearly this is possible, and I probably missing something obvious, but can someone point me in the right direction?

    Nothing complicated, something like 9-0 would be great, without PICs that is.;)

    Thank you very much for your time, I really appreciate it. :)

    Sparky
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    You have the 74xx190 circuit. It may do what you want. It is others also. Google "up down BCD counters"
     
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  3. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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  4. crutschow

    Expert

    Mar 14, 2008
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    A CD40110 is an up/down counter that directly drives a 7-segment display.
     
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  5. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    That's spot on crutschow! Thanks.:)

    Just to confirm some things:

    http://www.jameco.com/Jameco/Products/ProdDS/676502-DS01.pdf

    1. As I'm counting from 9 to 0, can I just leave pin 9 floating or shall I tie it to ground?

    2. For pin 7, should I use a monostable input to avoid 'bounce'? If so, what would be a good time period?

    3. If I'm not needing to reset, can I leave pin 5 floating?

    4. What does latch enable do?

    5. I need to use borrow. How does this connect within the circuit? Also, what should I do with carry?


    Thanks for taking a look, I think I just need a bit more confidence and re-assurance that I'm doing things correctly.:)

    Sparky
     
  6. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    I've had a go at the connections.

    How does this look?

    I will add resistors for the display later, but are the other connections correct?

    Thankyou.:)

    Sparky
     
  7. crutschow

    Expert

    Mar 14, 2008
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    If you look at the schematic of the chip you will see that borrow and carry are outputs so you want to leave them open, not tied to Vcc or ground as you show.

    For your purposes you can just tie the Latch Enable to ground although connecting it to the clock will work also. If the Latch Enable is high then the display value is held constant, independent of any change of the counter value.

    You need a one-short or other type of debounce circuit if the clock is coming from a mechanical switch. The period should be at least 100ms.
     
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  8. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Thanks again Crutschow.:)

    I will complete the schematic tomorrow. Would you mind giving it a quick check again?

    Sparky

    P.S. Wally is my favourite character too!
     
  9. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Phew, the hardest part was stretching the canvas for paint. It took me longer than drawing the circuit!

    Does this look reasonable? I think the values of components are correct, but I'm not 100% sure.

    Sparky
     
  10. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    Sometimes I take a 0.1uF cap from pin 5 to gnd on the 555. Not sure if you need it. :rolleyes:
     
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