Hexadecimal to 7-segment decoder

Discussion in 'Homework Help' started by xdone, Jun 16, 2010.

  1. xdone

    Thread Starter New Member

    Jun 16, 2010
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    0
    As mention i am given 4 Inputs D C B A and the decoder for outputs for common cathode a b c d e f g.
    I need to obtain from 0-9, A-F
    So the truth table which i obtained is
    D C B A| a b c d e f g
    0 0 0 0 |1 1 1 1 1 1 0
    ....
    ....


    So i made a k map for each segment and how am i suppose to implement the circuit using only basic gates?
    this is what i obtain
    a = BA'+ DC'B'+DA'+D'B+CB+D'CA+C'B'A' (' means invert)
    b = D'C'+D'B'A'+C'B'+D'BA+C'BA'+DB'A
    c = ....
    d= ....
     
  2. Georacer

    Moderator

    Nov 25, 2009
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    I take it your question is about the sheer number of the materials used. Do the restrictions of your exercise prohibit you from using a ready-made bin-to-7seg decoder? If so, consider using groups of gates more than once, ie construct the CB combination needed for a and invert it to use it for the b segment. Or try to find suitable factorizations among the sum elements that can be used by multiple segments.
     
  3. xdone

    Thread Starter New Member

    Jun 16, 2010
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    Do i combine the segments a b c d e f g together?
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Just take a look at the datasheet of the 7447 how it works.

    Bertus
     
  5. xdone

    Thread Starter New Member

    Jun 16, 2010
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    so sorry, i dont get what u mean by the 7447.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Read the attached PDF in my last post.
    It says sn54ls47, but it equals the 7447.

    Bertus
     
  7. xdone

    Thread Starter New Member

    Jun 16, 2010
    9
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    sorry bertus for asking again, so after getting all the segments individually, do i combine them first? i used K-map method to simplify them already.
     
  8. xdone

    Thread Starter New Member

    Jun 16, 2010
    9
    0
    Sorry guys, after getting each segment, must i combine them together? i need help urgently sorry.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you look at the data sheet for any 7 segment display, you will see that the above signals control individual segment illumination.
     
  10. xdone

    Thread Starter New Member

    Jun 16, 2010
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    so i dont combine them? then how am i suppose to implement the circuit?
     
  11. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    Think of your circuit as a black box that has 4 inputs and 7 outputs. There's no combining of the segment outputs.

    Look at the pdf that Bertus linked to above. They have the internal logic diagram for the 74ls47, which is a bcd-7seg decoder. You just need to change it a bit to display a-f instead of the random symbols it does now.
    /mike
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
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    Try looking at a display and the segment control lines. It becomes very obvious how the decoder/driver and the display function together.
     
  13. xdone

    Thread Starter New Member

    Jun 16, 2010
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    In other words, i implement the circuit seperately then later combine them? Wow, it will be messy hahas
     
  14. beenthere

    Retired Moderator

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    As an exercise, just draw up a schematic that shows the various connections.
     
  15. xdone

    Thread Starter New Member

    Jun 16, 2010
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    sorry, what do u mean?
     
  16. beenthere

    Retired Moderator

    Apr 20, 2004
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  17. xdone

    Thread Starter New Member

    Jun 16, 2010
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    but i am required to draw the digram with basic gates =/
     
  18. Georacer

    Moderator

    Nov 25, 2009
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    Exactly! The datasheet of the 7447 contains a schematic wich is down to the gate level. You could duplicate the exact behaviour of the IC by constructing the gate circuit given. If you want to display A, B, C, etc for numbers larger than 9 however, you need to modify this circuit, wich, I imagine, will require some work, but isn't impossible by any means.
     
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