Can anyone help me clean up this layout

Discussion in 'General Electronics Chat' started by mnunez021, Feb 28, 2009.

  1. mnunez021

    Thread Starter Member

    Feb 27, 2009
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    When I test this layout everything works fine except the decimal. The decimal has to work by itself but when I turn it on, other parts turn on also
     
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  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's not a layout - it's a schematic with no parts/pins labeled. How did you get it to work with no labeling?
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What conditions should cause the decimal to be on? Are there more digits to the left or right?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I replied to your post in the Homework Help forum.

    Sorry it takes awhile; this forum isn't interactive and I have several things going on.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    This site is asleep.
    It takes many minutes for the attachement to load. It takes many minutes for my reply to work.
    The attachment is not a schematic. It is a fuzzy JPG file type that is covered with chicken-pox dots.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    It shows no voltage pin to the 7 segment display, nor does the logic have current limiting resistors. I question the working part.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    I was wondering about those same issues.
    So, I downloaded Logisim, available for free here:
    http://sourceforge.net/projects/circuit
    No limitations.

    The quirky thing about the library 7-segment display is that it's common-cathode (and automatically "grounded"), whereas most 7-segment display drivers are common-anode.
    It also appears to have a "built in" current limiting circuit; just supply a logic '1' to a segment, and it lights up.
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    Is the decimal point being turned on by I3 only?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    No, it's supposed to be turned on if the input is not a valid BCD number.

    DecimalPoint = I3 AND (I2 OR I1).

    They need some additional logic to accomplish what they need to do; if the input is not a valid BCD number, then none of the segments should be lit except for the decimal point.
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    He has to check his truth table and his connections carefully.


    Decimal point=I3 I2' I1 I0' + I3 I2' I1 I0 + I3 I2 I1' I0' + I3 I2 I1' I0 +
    I3 I2 I1 I0' + I3 I2 I1 I0
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    Your truth table is not very helpful for you.

    Put each signal for each segment of the display on the table and derive boolean equations according to the table.
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    At the end but during the building stage make a more useful one which will make your life easier.
     
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