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Homework Help: Using 2x 74LS47 to input binary 0-15

  1. Sep 23, 2009 #1
    is it possible to connect 2x 7447 IC's and 2x 7 segment and input binary 0-15?
  2. jcsd
  3. Sep 23, 2009 #2
    yes, that would be a fun project.

    one chip takes 9 as the highest number, so you would have to do some splicing and gating.

    but it's sort of redundant to use the second chip, 1 could be displayed with just one control line.
    Last edited: Sep 23, 2009
  4. Sep 24, 2009 #3
    can give me a schematics on this or maybe a link so i can implement this
  5. Sep 24, 2009 #4
    Hi Chris-
    Do you want to input binary 1111 and get output octal 17, or decimal 15 ?
    Bob S
  6. Sep 24, 2009 #5


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    The 7447 is a poor choice for this.

    Instead of using several chips to compensate for using the wrong decoder, you could look for a device like the Fairchild 9368 chip which decodes binary inputs of 10 to 15 as A, b, C, d, E and F which are the correct HEX outputs for these inputs.

    So, you would only need one of them and one 7 segment display.
  7. Sep 25, 2009 #6
    the decoder i have now is only 7447 ic so i have to make use of this.

    @Bob S
    in 1 of the 7447 ic you need to input 0000 upto 1111(15) so it should display the decimal equivalent in the 2x 7 segment. if its 15 the 1st 7 segment should display 1 and the other 5.
    this is what the cuircuit should look like.
    Last edited: Sep 25, 2009
  8. Sep 25, 2009 #7


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    the decoder i have now is only 7447 ic so i have to make use of this.

    If you can't make use of any other ICs, then I don't think you can do that.

    The second digit would always be a 1 or a 0, but the 7447 output on the right hand digit would be garbage for numbers greater than 9. It makes a series of letter "C"s oriented in different directions.

    If you can make use of any other IC's you should throw out the 7447s and use a suitable chip. These chips are very cheap.

    It is a simple job with a microprocessor and cost effective as well. You could have 8 bit binary pretty easily decoded to 3 displays.

    Is this a school assignment?
  9. Sep 25, 2009 #8

    not at all, i was thinking of using this 4 binary input as a count-up timer given the input was from a 555 ic and a 7490.
  10. Sep 25, 2009 #9


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    So, just use two 7490's. They only give BCD out anyway, but you can have one driving the next. Each 7490 can drive a 7447 which can then drive a 7 segment display.

    This would let you count up to 99 before it starts again.

    You would then have the beginnings of a frequency counter.
    Last edited: Sep 26, 2009
  11. Feb 19, 2010 #10
    You should put an AND gate on the counter with the inputs on QA and QD and the output connected to the reset of the counter

    or instead you can use a 4026 ic that has the outputs decoded for a 7- segment lcd display.
    if you are connecting them together then connect pin 5 of the first 4026 to pin 1 of the other

    second of all, you need to give a clock pulse to pin 1 of the first counter

    google: "integrated circuits by generic number"

    and click the first link. it has datasheets for every ic (except for a few)

    Attached Files:

    Last edited: Feb 19, 2010
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