Dual 7-Segment Common Anode Display

Discussion in 'General Electronics Chat' started by hondabones, Mar 25, 2010.

  1. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    Does anyone know how I can use each digit separately for this dual 7-segment?

    [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Sure. Just supply +V to the anode of the side you want to display.

    Note that you will need current limiting resistors on the cathodes. I suggest that you don't exceed 15mA. See the datasheet for the display for more info.
     
  3. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    o.k. let's say I want to use both digits. For example counting from 0 - 99. When I hook up both anodes the display counts 00, 11, 22 etc. because they are wired parallel.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I guess you haven't heard about multiplexing.

    With multiplexing, just one display is turned on for a period of time, then turned off, and the next display is turned on.

    The displays are cycled through so quickly that it looks like they are all on constantly.

    The basic procedure is:
    1) All displays off.
    2) Prepare to sink current from the segments desired to be lit.
    3) Apply current to the desired display for a period of time.
    4) Turn off the current to the display.
    5) Go back to step 2.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    That is because you are suppose to apply the voltage to anode of interest. You are not intended to supply both anodes at the same time. The term for this is multiplexing.

    hgmjr
     
  6. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    I have heard of multiplexing but I don't quite understand it. I will have to look into it more. I wasn't aware that these displays were like this when I bought them. Now I want to use them for something.
    Thanks for the help.
     
  7. hondabones

    Thread Starter Active Member

    Sep 29, 2009
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    I like these "5 Easy Steps to Multiplexing Virtually Useless Dual 7-Segments to a 4th Quarter Electronics Student":D

    I could use transistors to do such a thing, correct?

    They could somehow switch back and fourth rapidly and it wouldn't be noticeable to the human eye because of the "persistent eye" I have seen you talk about.

    There are also chips designed for this:

    MAX6950 (5-digit)
    MAX6951 (8-digit)
    MM74C925 (4-digit)
    MM74C926 (4-digit)
    MM74C927 (4-digit)
    MM74C928 (4-digit)

    Are there any 10-digit?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Why so many digits?

    See the attached for a simple 3-digit counter I was going to build to count windings for solenoids and inductors. I used a $1 step counter with a 5-digit LCD display instead (cheap and easy) but that's besides the point.

    I'd thrown it together in a hurry, so it has some mistakes in it. Using the 2N3904's as voltage followers wasn't a great idea.

    The 4553 is a 3-digit BCD up-counter with digit select outputs. These 4553 ICs can be cascaded, to get 6, 9, 12, or more digits.

    The 4543 is a BCD to 7-segment display driver.

    If you decided to use 4553's, you would need one 4543 per 4553. Each digit in the 3-digit group would be on for roughly 33% of the time.
     
  9. hondabones

    Thread Starter Active Member

    Sep 29, 2009
    123
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    I was referring to counting with one decimal digit. 0 - 9

    I misunderstood the data sheets. The chips are designed to count (for example) 4 7-segment displays, NOT 4 decimal digits on one display.

    Your attachment made that apparent, Thank You.
     
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