Help! 7 Segment led driver circuit...

Discussion in 'The Projects Forum' started by b1gb0y2013, Feb 15, 2010.

  1. b1gb0y2013

    Thread Starter New Member

    May 10, 2009
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    Well im kind of new to electronics, and I tried making this circuit here:
    http://www.allaboutcircuits.com/vol_6/chpt_7/9.html
    but since I didnt have a 4511, I replaced it with a 7447, using this datasheet here:
    http://pdf1.alldatasheet.com/datasheet-pdf/view/80216/NSC/7447.html
    to replace all the wires correctly. However, it didnt have an (LE)latch enable, but an (RBI)Ripple blanking input instead... Its also TTL, not cmos, but i figured it would still work... Is there ANYTHING im doing wrong? I made sure all the connections are right, tested the led display, (Which is the exact one the tutorial used), and already tried 5 different 7447s... And by the way, the problem is nothing lights up unless I put the Lamp Test on low and the Blanking input on low, then everything lights up...
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    The outputs on the 4511 are active high (source current), and the outputs on the 7447 are active low (sink current).

    So, for the 4511, you use common cathode displays; for the 7447 you use common anode displays.

    Does that make sense to you?
     
  3. b1gb0y2013

    Thread Starter New Member

    May 10, 2009
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    Yeah that makes plenty of sense... I wondered if that was a problem... Just for testing purposes, could I connect all the outputs to inverters?
     
  4. b1gb0y2013

    Thread Starter New Member

    May 10, 2009
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    Actually now I just took all the inputs to the dip switch and put them to ground, and the leds light up opposite of what they should... so I think inverters should work, thanks for the help.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    It's going to be a bit goofy.

    You'll need to use PNP transistors to invert the 7447 outputs. Connect the emitters to +5v, 1k resistors from the bases to the 7447 a-g outputs, and the current limiting resistors from the collectors to the a-g inputs of the LED.

    The 7447 has high sink current capability compared to typical TTL/CMOS IC's. Regular inverters aren't going to work well; they won't source enough current.
     
  6. b1gb0y2013

    Thread Starter New Member

    May 10, 2009
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    I have the WIERDEST problem when I make circuits... I make it exactly but with a TTL, it doesnt work, so I put inputs to ground instead of power, so then the output is in reverse... So, next I put all outputs to inverters, but then its STILL BACKWARDS!! Then I take off the inverters and reconnected it all back to normal, and it works fine... Why does this happen?
     
  7. b1gb0y2013

    Thread Starter New Member

    May 10, 2009
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    And I just used a 2 hex NOT gate ics instead.
     
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