stopwatch circuit

Discussion in 'Homework Help' started by ernestpanda, Nov 23, 2014.

  1. ernestpanda

    Thread Starter New Member

    Nov 23, 2014
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    hi so i need to do a mod 60 counter which counts from 00 t0 59 and it has to have a start/stop button and a reset button. im not really sure how to do it. can anyone send me a multisim file of it at <SNIP>. please help me!

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    Last edited by a moderator: Nov 23, 2014
  2. ernestpanda

    Thread Starter New Member

    Nov 23, 2014
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    i made a circuit and it dosent seem to work. can someone help me see why it does not work?
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    You're making one of the classic mistakes of trying to solve the entire problem and then hoping that it will work and being stuck with a complicated mess when it doesn't.

    Step back and approach things methodically. Break the problem into smaller tasks and get each task to work first before building upon it to get closer and closer to the end goal. You also need to come up with a clear strategy and plan. Looking at your schematic, it appears that you have chosen to use a counter IC for the least-significant digit and a FF based approach for the most-significant digit. Why? It's fine to do it that way, but it might help us help you if we understood why you are going this route. Also, information like that should be included along with your schematics and also simulation results when you ask for assistance. Otherwise, you are asking us to take a set of schematics, which presumably have problems, and figure out what you intended to do and also what you wanted it to do and also what it is actually doing. Sounds pretty unreasonable to expect strangers offering free assistance to jump through those kinds of hoops, doesn't it?

    There are several reasonable ways to break a project like this down. The obvious tasks would include:

    Getting a mod-60 counter working (no start/stop and no reset and no display).
    Getting a display working
    Getting the reset working
    Getting the start/stop working

    If you have a scope (which, in simulation, you should) you can hold off on the displays until the end. Or, it might make sense to get the display working right away as it might make further development and troubleshooting easier.

    It is often very helpful to simply the problem considerably into a toy problem that you can play with first. For instance, make a mod-10 counter with start/stop, reset, and a display. That way you only have to work with a single digit. Using a decade counter IC, the first part is pretty easy. So get a display working on it and then focus on the start/stop and then focus on the reset. Then modify the design so that it is a mod-6 counter. Now you have a working design for a mod-6 and a mod-10 counter that you can meld together to make you final counter.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    If you want to see the changes on the display, you should lower the clock frequency.
    400 Hz as given in your drawing will take the 60 counts in about .15 seconds.

    Bertus
     
  5. absf

    Senior Member

    Dec 29, 2010
    1,493
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    Another mistake is that the 7 segment decoder chip was wrong. It should be 74LS47 in stead of LS48. LS48 is for driving common Cathode LEDs.

    Allen
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I agree with WBahn, you need to break this down to individual blocks and then start working on each block individually.

    I see your project as a CLOCK (if you don't use just a signal generator), a Modulo 60 counter, a display unit with a decoder.

    The human interface (switches) to start, stop, and reset are the last things on the list.

    I'm starting to wonder if they teach block diagrams these days. With the whole function in one chip, it may be counter productive to teach block diagrams .... or so might be the thinking.
     
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I agree with WBahn, in that I would further break the mod60 counter into two simpler functions: a mod10 counter and a mod6 counter. Developing the second counter after the first should be a trivial exercise.
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Well ... I will wait till the OP or TS returns and reworks his diagram in bite size chunks. Till then ....

    And yes, I like the modulo 10 and modulo 6 counters as well.

    If the OP or TS is looking for a quick "victory" in this circuit, start with the display ... inputs are BCD ... less than five minutes worth of work, from beginning to testing. Then move onward to another section.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    I agree with getting the quick victory with the display, particularly in simulation. In the real circuit, the number of wiring connections that are needed can deter some people looking for instant gratification (and, hey, we all do to some degree, especially when starting something new).
     
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