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Light Up 7 segment display

  1. Dec 7, 2004 #1
    Hello all, you may remeber from past about the circuit I was working on to get a simple 7 segment display to work... we had to tangent from that for awhile but we are finally back...

    I got frustrated with problems in the 5 bread board circuit with around 100 led's so I streamlined the circuit with my partner and it now contains the integrated circuits on one board. I am trying to figure out how to get this stupid seven segment LED to light up

    Here is a diagram of what I currently have built- The 555 works and blinks the two leds, also the 8 other leds work and count... however the seven segment display does not work.

    I am not sure what to do with the final leads for the seven segment display

    the parts used are
    555-integrated circuit
    7490-integrated circuit *2
    7447-integrated circuit
    LN514rk seven segment display
    specs for seven segment display

    if link doesn't work just search www.alldatasheet.com for specific parts to get spec sheets

    I don't know what to do to make it work please help!!!!
  2. jcsd
  3. Dec 7, 2004 #2
    Do you have pins 3 and 4 of the 7447 tied high? I don't see it on the schematic. Look at the truth table for the 7447.

    Do you also have pins 3 and 14 of the display tied to gnd?
    Last edited: Dec 7, 2004
  4. Dec 7, 2004 #3
    Um no I don't ....I was just told to tie the other pins of the display to positive... hmm
  5. Dec 7, 2004 #4
    One thing I was also considering was making sure that the LN514rk 7 segmetn display is common anode as opposed to common cathode... becasue if its common cathode wouldn't I need the 7448 instead of the 7447?
  6. Dec 8, 2004 #5
    What I really need to know is the connections between the 7447 and ln514rk .... what goes ground what goes positive
  7. Dec 8, 2004 #6


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    Gold Member

    Your common cathodes (pins 3 & 14) should go to gnd.
  8. Dec 8, 2004 #7
    HAHAHAHAHA I got it!!!!!!!!!!!!!!

    I realized that the led was common cathode and so switched the 7447 with a 7448 and it worked

    thanks a lot for the help though guys... does anyone know of any free software taht streamlines circuits drawings?
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