Help with 2 digit BCD counter

Discussion in 'Homework Help' started by Allain Dominique Borno, Nov 13, 2015.

  1. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
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    1
    I need someone to explain this to me. I have attached pictures showing what is needed to be done, but basically I need to make a circuit that connects to 2 7 segment displays to make a counter that can count from 00-99. This counter can also count down, and it can be parallel loaded. We are using a 74157 multiplexer and two 4510 up/down binary counters.

    Right now I don't really understand where some of the extra inpus/outputs of these chips go. On the 74157 chip, I don't know what to do with "strobe" or "select" (which are pins 15 and 1 shown in the picture). With the 4510 chip, I don't know where to put clock, up/down, reset, preset enable, carry in or carry out.

    Any help, guidance, tips are much appreciated.

    20151113_130115_706x600.jpg

    20151113_130127_001_694x1024.jpg
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Well, have you read the data sheets for those chips so that you can understand what those pins do?
     
  3. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    I have. It's listed in one of the pictures I posted. I still don't understand too well though.

    Looking at it now, I guess up/down is simply connected to a switch so that if the person wants to count up they'll deactivate/activate it, and vice versa. I'm wondering if the clocks should be connected together too? Other than that, I am still very lost.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    A pinout diagram is NOT a data sheet. It tells you nothing about what the Strobe signal is, just which pin it is. You need to look at the datasheet for the part.
     
  5. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    In that case, I'm pretty sure no data sheet was given. Is this something that I should look up?
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    The files you attached was too big, I was compressed it from 1.87 Mb to 117Kb, it was about 16:1, and another one from 4.3Mb compressed to 72Kb, it was about 60:1, when you attach the files on next times, please compress to 800x600 or 1024x768, almost files using 800x600 is enough, thanks.
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,649
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    Hello,

    As Wbahn said, have a look at the real datasheets.
    It is also not a very good practice to mix TTL and CMOS chips.
    For the 74LS157 I would take a CD74HC157 to stay in the CMOS family.

    Bertus
     
  8. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    I'm still not getting it. This project is due by the 25th of november, so I have some time. The teacher isn't really that helpful. Is there a way that someone can walk through it with me?
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
    834
    So you're still not getting it. Apparently, we can lead... Have you read the datasheets? What does the select pin do? I know if you do your homework, you can answer that question.

    Notice that we are trying to walk you through this!
     
  10. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    Have you looked at the data sheet yet? What does it say those pins do?

    If you aren't willing to look up and read the data sheet, then you have zero chance making it in this field.
     
  11. absf

    Senior Member

    Dec 29, 2010
    1,493
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    That's why you have to read the datasheet. In the DS, the up/down is shown as UP/DOWN (where the underscore is on the top of DOWN). That would mean if the pin is on logic high (1), it would count up and count down if it is on logic low (0).

    If I were you, I would try redraw the diagram in the conventional way so it is much easier to understand.

    Allen
     
  12. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    Ok so select has something to do with A'B (A not B), but I don't really understand.

    The up/down counter should just be connected to each other, then also connected to one of my switches. Sounds simple enough.
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    Do you understand what a multiplexer is? If not, what have you done to try to understand it?

    What does the word "select" imply?

    What does the function table tell you about how Select affects the output relative to the A and B inputs?

    What does the equivalent logic diagram tell you about how Select affects the output relative to the A and B inputs?
     
  14. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    I'm also looking and I think that the carry in/outs of the 4510 chips can be connected to each other in some way, so that when the least significant digit is done counting from 0-9, the second 4510 will know to change the number so the first one can count all over again, if that makes sense
     
  15. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    Yea a multiplexer in my understanding, is basically traffic control. A bunch of lines of data can be coming in at once, and the multiplexer tells each set where to go.

    So in that case, would select have something to do with the transition from 9s to 10s? like if the counter is going 1 2 3 4 5 6 7 8 9 then the select thing will tell it to add a 1 so that it can continue with 10 11 12 13 14 15 blah blah.
     
  16. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    Forget what I just said. So am looking now, and select basically determines the outputs. There is one select signal, and when it's 0, the output is the same as input A. When it's 1, the output is the same as input B.
     
  17. absf

    Senior Member

    Dec 29, 2010
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    Yes, that's correct. If you just take one of the 4 muxes inside 74157 and study it carefully. It is not that hard to understand how it works. 'Strobe' is like 'enable' in this chip.

    SINGLE MUX.PNG
     
  18. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    I actually think teach goofed. You need to learn how to read a datasheet.

    this one has the "truth table"
    0
    1
    X
    rising edge (this is important)

    The bar above means not; so. This UP/~DOWN would mean that a 1 is needed to count up and 0 is needed to count down.

    many times CE is written as ~CE or Not chip enable. You can talk about CE as Chip Enable is Active Low.

    Implicit meaning are used a lot.
     
  19. Allain Dominique Borno

    Thread Starter Member

    Oct 13, 2015
    35
    1
    Ok I have been studying this a little more. I am trying to figure out how to make one 4510 chip count in 10s while the other counts in 1s. Using the reset pins on the chips may do it. I was thinking that when one counter's ABCD = 1001 (or 9), so that it goes 123456789 then 0 and starts again. Is that the right idea? And basically I should do that with both counters?

    But with the 4510 chip that represents the 10s, I don't understand how to make it count for every rotation of the other chip, meaning only change when 0-9 have been completed.

    I get the thing with the up/down counter now. Thank you.
     
  20. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Have you read the datasheet?
    Have you read the datasheet?
    Have you read the datasheet?

    Have you read the datasheet? It includes a circuit that does exactly what you want it to! See figure 18. And explains the pins that make it work.
     
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