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12 Hour Digital Clock Circuit

Discussion in 'General Electronics Chat' started by 46robbie46, Jun 15, 2010.

  1. 46robbie46

    46robbie46 New Member

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    Hi everyone,

    I am having some problems trying to create a circuit for a 12 Hour digital clock circuit using 74LS90 IC's and 6x 7 segment displays to show the hours, minutes and seconds. I need the clock to have a start / stop and a reset function. Attached to this post is a screen shot of the circuit that I have so far, using the 7490 IC's.

    Any help with this would be very much appreciated, as I am having real trouble in understanding how to make it work at the moment.

    Thanks!
     

    Attached Files:

  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    You cannot really clock all of the 7490's with a 1hZ clock.
    You connect them as a ripple counter, that is the secs units clocks the secs tens and the sec tens clock the units minutes and so on.
    Do you have any 7492 IC's.?

    EDIT:
    Look at this circuit posted by a fellow member some time ago.
     

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    Last edited: Jun 15, 2010
  3. 46robbie46

    46robbie46 New Member

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    Hi, no i'm afraid I will have to make the circuit using 7490's. Thank you for the reply, and the circuit diagram, i'm sure that will be of use to me.

    In that circuit, what are the 7447 IC's used for?

    Again, thank you very much!
     
  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The 7447 are BCD to 7segment LED drivers, you need them to convert the BCD count of the 7490 into signals to drive LED's.
    As you can seem, the designer used the mains to get 1 hZ signal.
     
  6. ljcox

    ljcox Well-Known Member

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    The 74LS90 IC has reset gating that can be used to convert it into a modulo 6 counter for the seconds & minutes tens digit counting.

    Here is the basic idea.

    I'll leave you to do the rest.
     

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    Last edited: Jun 15, 2010
  7. Dean Huster

    Dean Huster Well-Known Member

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    A 24-hour clock is much easier to design because the count goes from 00:00 to 23:59. A 12-hour clock is a bear to design, especially with non-parallel-load ripple counters because you never start at zero on the hours going from 12:59 to 1:00.

    It's likely that the original schematic with all the clocks tied together was intended to use synchronous counters such as the 74160-series and the 7490 was mistakenly specified.

    Designing clock circuits from scratch is wonderful practice in digital design to get the correct modulus, start count, final count, etc. without glitches sliding in invisibly to cause nagging problems.

    Dean
     
  8. x_name41

    x_name41 New Member

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    Last edited: Sep 29, 2010
  9. x_name41

    x_name41 New Member

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    [​IMG] My 6-Digits Multiplexing LED Clock schematic v.2(edited)!
     
    Last edited: Oct 5, 2010
  10. wajijh_zoya30

    wajijh_zoya30 New Member

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    Can anyone plz help me I m supposed to make a 12 hour digital clock by using 74LS160 decade counter. But I couldn't find a circuit diagram using this IC. Help
     
  11. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The data sheet I looked at was hard to understand. It seems like you can detect 5 using gates and then set it up such that the clock loads a 0. It might be easier than trying to reset the counter. That edge also needs to be gated to th next stage.

    I'd look for a couple of manufacturer's data sheets to see if any are any better.
     
  12. wajijh_zoya30

    wajijh_zoya30 New Member

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    I might be able to make it. But this ic is giving me a problem. Can u recommend me any book for it?
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  14. wajijh_zoya30

    wajijh_zoya30 New Member

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    Ok thank u so much:)
     

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