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555 w/ 4017 7-segment LED Question

  1. Jul 10, 2012 #1
    I have a 555 and a 4017. My question is that there seems to be a bunch of 7-segment LED controllers for BCD outputting decade counters but I don't see (or know what to Google) for a non-binary coded decimal output.

    The 4017 outputs single digital pulses on a given terminal which indicates which number the count is on. There are 10 pin outputs for values 0-9. The problem is how to take these outputs and control a 7-segment LED with them. I do not want to hand wire a bunch of connections to the LED if at all possible.

    Could you guys help with either the IC number that handles the 4017 to LED control or perhaps give a better solution than hand wiring the LED myself?

    Thanks.

    4017 link: http://www.doctronics.co.uk/4017.htm#pins [Broken]
    555 link: http://electroschematics.com/wp-content/uploads/2008/11/lm555.pdf

    Edit: If you guys look here: http://www.youtube.com/watch?feature=endscreen&v=2PBSOLG4n08&NR=1 you will see what I mean about the intermediate controller IC. The problem is that the IC this guy uses expects BCD inputs and the 4017, at least by default, doesn't code its output in binary.
     
    Last edited by a moderator: May 6, 2017
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  3. Jul 10, 2012 #2

    vk6kro

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  4. Jul 10, 2012 #3
    So that's really close to what I need but I don't think it will quite work.

    The binary outputs are going to be:

    0000 (0)
    0001 (1)
    .....
    .....
    .....
    1001 (9)

    If I map these out to the LED I'm really saying that any number that has a common bit set (one's bit for instance) has a shared circuit in the LED. This isn't true; overlaying 1 with 4 doesn't make a 5 on the LED if you get what I'm saying.

    If you can find something great, if not I was thinking of rolling one using a microcontroller, since there doesn't seem to be anything for this rather ordinary task. Could be this IC would work I'm just not seeing it. Brain's a bit thick these days. :-) Thanks BTW.
     
  5. Jul 10, 2012 #4

    vk6kro

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    I don't understand what the problem is, but the chip is available if you want it. It seems to do what you asked for.

    I would use a micro and convert directly to 7 segment output. skipping the BCD stage.
     
  6. Jul 10, 2012 #5
    The problem is that I don't want to code a bunch of specialized circuits, one for each digit, duplicated for each LED on a tiny protoboard.

    I would have 10 outputs, one for each decimal digit, which in turn have between 2 and 7 additional outputs going to the LED. Imagine how ugly that protoboard is going to look, just for a single LED. Now what if I want like 5 or 6 LEDs for something nice?

    Now imagine I just wire the 10 outputs to 10 inputs on an IC that does all that for me? And then you run the connections from it to the LED. When the first IC increments the second IC updates its internal circuitry which updates the LED.

    Unless someone else finds the IC it looks like I will either have to make the micro or move to a BCD setup. Neither is a great option IMHO.

    Edit: if you were asking what the problem was with your IC I'd ask you to think carefully about how you'd wire the BCD outputs to the LED. You'd still need to run basically individual circuits for each digit. The visual representation on the LED and the binary outputs don't correspond usefully. '0001' and '0011', even though they share a common 'on' (the one's bit) bit cannot be meaningfully combined, at the level of circuitry, thus the original problem of having to wire each output-to-LED circuit manually remains. Again, you can't overlay the circuitry for '1' on top of any number that's odd, right? '5' has a piece missing on the right, whereas '1' does not.
     
    Last edited: Jul 10, 2012
  7. Jul 10, 2012 #6

    vk6kro

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    You might be able to use multiplexing with the BCD outputs.

    Briefly, you would connect all the 7 segment LEDs anodes in parallel, (ie all the "a" segments in parallel etc) but turn them on one at a time using the common cathode connection for each display. Thus only one display turns on at a time.
    If you do it fast enough, it looks like they are all on and giving different displays.

    You could use any one of many counter chips which give a BCD output, so maybe you could rethink the use of 4017s, because I doubt that 40147s are all that commonly available.
     
  8. Jul 10, 2012 #7
    Not sure we're still on the same page, but thanks for looking. Yeah the 40147 was a good guess but may have to end up with custom IC for this.
     
  9. Jul 10, 2012 #8

    vk6kro

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    If you watch that video, notice he takes the 7490 BCD outputs to a 7447 BCD to 7 segment decoder.

    You would have to do this to get a meaningful output on the display.

    Your original problem was getting a BCD output from a 4017 which would only give a 1 of 10 output. The 40147 would do this, but you would still need a BCD to 7 segment decoder and you would need multiplexing if you wanted to drive multiple LEDs from one decoder.
     
  10. Jul 10, 2012 #9

    jim hardy

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    Last edited: Jul 10, 2012
  11. Jul 11, 2012 #10
    Thanks Jim. That'll do nicely.
     
  12. Jul 11, 2012 #11

    jim hardy

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    i think you and V6 were headed there, credit belongs to you guys.
     
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