Novice level Multisim software / general voltage level input questions

Discussion in 'General Electronics Chat' started by Fieldinator89, Apr 15, 2014.

  1. Fieldinator89

    Thread Starter New Member

    Apr 8, 2014
    5
    0
    Hello everybody,

    I am currently a student enrolled in a 100 level circuits class, "Digital Design Fundamentals". Throughout the semester we have been implementing circuits using the LogicWorks software... Anyway, I will cut to the chase. I have constructed several circuits through the LW and this being the only software I had used I felt the need to check into others out of curiosity and wanting to explore. I recently (2 days ago) purchased NI Multisim and have been doing tutorials and playing around with and have run into an issue that I have tried to find an answer to and have come up empty (probably asking the wrong questions). Basically I am trying to rebuild everything we have created thus far in LW in the Multisim software. BUT, in LW we have only used binary switches to test / control the circuits.

    Actual question post rambling:
    Here are my pictures to help with my question:

    [​IMG]

    (Left is Multisim, Right is LogicWorks)

    As seen here, I set up the full adder with the Vcc and GRND, and hooked them up to switches which I believe would similarly mimic the same thing a binary switch in LW achieves. But for some reason, which is what I'm trying to figure out, I am never able to get the 'Sum' output probe to light up. I then noticed after setting up voltage test probes that going into the first XOR gate (probe 3), the lower(S2) input was registering 5.00pV ~~ .000000000005V. I figured this was why at probe 4, right after the XOR gate, I was getting a LOW reading because there was actually a small hint of voltage causing the XOR gate to get two HIGH inputs. (Not sure if this is a correct assumption). So I then dug a little more to see if there were available inputs more similar to the binary switch in LW...

    [​IMG]

    Arriving at this stage I had found switches that had a closer 'look' to the switches in LW (I found a video where another guy had used these instead and figured I would try them). Also, the voltage on probe 3 which was previously 5.00pV was now registering at a flat 0V. So now, going into the XOR gate I had 5V and 0V.. Which I thought would set the output (probe 4) to HIGH. But, as seen here it did not.

    [​IMG]

    Lastly, as seen in this final picture the Cout probe does function and light up when A = 1 and B = 1 as it should.. The Cout also works when Cin = 1 as it should, but again in this case, the sum does not..

    I am having a time trying to the answer as to why this issue is occurring and having very little luck so I figured it would be beneficial to talk to an actual person with more experience and have direct input. I hope this post is in the correct sub-forum (seemed the best fit), as this is my first post I am not completely familiar with the site although I have frequented the reading materials section.

    Thank you very much for looking over my question and I sincerely appreciate any help or advice you have.

    Jeremy
     
    Last edited by a moderator: Apr 15, 2014
  2. Fieldinator89

    Thread Starter New Member

    Apr 8, 2014
    5
    0
    Hopefully this isn't against the rules, but i'm going to refresh this post one time because a bunch of people have looked at it and I'm still stuck! Haha. Even if the answer doesn't specifically apply to the software I'm assuming the answer has to be due to the voltage inputs in general.. At a loss here. I will only refresh the thread one time :) Thanks again everyone! Really enjoying the forums thus far, lots of really helpful and friendly people.
     
Loading...