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Homework Help: 7-seg display never works for me

  1. May 4, 2013 #1
    7-seg display never works for me:(

    Im flippin out. I always have this same problem with 7-segment-displays having only touched on theory stuff I don't know why this 7-seg display wont work. ive attached up probes and it shows all the right outputs.

    ive fiddled with common anode and cathode displays, I have used 7447N for the conversion.

    ive tried all combinations of EL EN BI and all I can get is it shows all segments lit up.

    most of the time I see current limiting resistors but im not sure how to apply them. there in nearly every example but nowhere is the theory for it.

    ive attached the multisim 11 file

    any help would be great. thanks.

    and if possible the theory behind any of it.

    Attached Files:

  2. jcsd
  3. May 4, 2013 #2


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    Staff: Mentor

    If you have some description of your IC, it would help if you could share it.

    Those AND/OR combinations look strange to me.
  4. May 4, 2013 #3
    It's bin-BCD Conv
    It's the "units" digit of what will be 3 digits. That's why the 5th output is left untouched.
  5. May 4, 2013 #4


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    Science Advisor
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    Gold Member

    What is the description of the ~EL input? The 7447 outputs are active low. Are you using a 7-segment display with active low inputs? Finally, what is with all the gates? Why don't you feed the switch outputs directly into the D inputs? Or is there more you haven't told us?
  6. May 4, 2013 #5
    Oh never mind. The screenshot I submitted is actually a 4511. And EL is enable latch. And it should be high.

    And the gates convert the binary inputs into the switch to BCD for the display. So I know binary and BCD are equal for 0-9 but now when binary 10-11-12-14-15 is on the switch it just displays the "units" digit.
  7. May 4, 2013 #6
    Actually it's right. EL should be high, but since its inverted it should be low. So it should still work.
  8. May 4, 2013 #7
    All fixed (:
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