3 digit 7 segment display help

Discussion in 'General Electronics Chat' started by ddickey, Feb 12, 2012.

  1. ddickey

    Thread Starter Member

    Sep 28, 2011
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  2. Wendy

    Moderator

    Mar 24, 2008
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    Sorry, the link you used required a password. Not a good thing.

    You can attach documents and pictures to this site directly. We even have an albums section.

    You can upload and attach files to your post using the paper clip icon above the text window, between the font-select "A" and the undo arrow. Please see our FAQ on attachments for more details.

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  3. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    See if this works. Thanks
     
  4. crutschow

    Expert

    Mar 14, 2008
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    If you have an open collector type driver (output logic active-low) then you use the common anode version of the display (anodes go to V+) as shown in the bottom schematic. If you have an output logic active-high driver then you use the common cathode version (cathodes go to ground) as shown in the top schematic.

    In either case, unless the driver is a constant-current type, you need a resistor in series with each segment driver to limit the LED current to the proper value.
     
  5. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
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    Here is part of the schematic I'm trying to copy. I'm using BC 547 instead of the BC 557.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    You can't use a BC 547 in that circuit since it is an NPN which requires the opposite signal polarity from the BC 547 which is a PNP. You need a PNP. Just about any small signal PNP will work.
     
  7. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    Oh yes, of course. Thanks for pointing that out. I should of checked. I forgot to order them so used the 547 which i had laying around.
    I'm confused on the led display. It has 5 pins one one side and 6 on the other. I don't inderstand the led schematic.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    The numbers on the schematic correspond to the pin numbers. Normally pin 1 is on the top right, looking at the bottom, with the numbering going clockwise from there.

    For your circuit you need the display shown in the bottom schematic.
     
  9. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    According to the drawing, pin 1 is labeled
    on the lower left when viewed from the front.

    The pins should be in order 1-12 going counter
    clockwise.

    Oddly, from what I gather from the drawing, there is
    no pin 6. If the bottom row has 5 pins the numbers
    would be 1-5 (starting from the left) on the bottom row,
    and the top row would be 7-12 (starting from the right).
    Without seeing it that would be my guess.

    Do you have the other specs (Vf, If, Reverse voltage, etc.)?
    If you wish to verify pin numbers by applying
    power, through the appropriate resistor of course,
    be careful not to exceed the maximum reverse voltage
    in case you accidentally apply power the wrong way.
     
    Last edited: Feb 13, 2012
  10. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    Yes I think iv'e Damaged it. My teacher just helped me and we can't get the third display to come on.
     
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