Please help me draw a circuit for expression (A + B) * C + A'*B

Discussion in 'Homework Help' started by luka0309, Dec 20, 2014.

  1. luka0309

    Thread Starter New Member

    Dec 20, 2014
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  2. anhnha

    Active Member

    Apr 19, 2012
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    - To create A' you need to use a NOT gate.
    - To create A'*B you use an AND gate with two inputs
    - Finally, use an OR gate for (A + B)*C + A'*B
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    You should only post one problem per thread. You will invariably get some posts that are addressing one problem, some posts that are addressing the other, some that are addressing both, and most posts won't indicate which they are addressing. It will become chaos quickly.

    To develop a circuit that directly implements a Boolean expression, just evaluate the expression according to rules of Boolean algebra. It can help to use parens to make the ordering explicit until you get comfortable with it. It can also help to define new signals the represent internal signals in the expression. For instance:

    F = (A + B)*C + A'*B
    F = ((A + B)*C) + ((A')*B)

    This is of the form
    F = Y + Z
    where
    Y = (A + B)*C
    Z = (A')*B

    Similarly
    Y = X*C
    where
    X = A+B

    and
    Z = W*B
    where
    W = A'

    In your logic schematic, you should be able to label the signals that correspond to W, X, Y, and Z.

    Your second one appears correct.
     
  4. luka0309

    Thread Starter New Member

    Dec 20, 2014
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  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    832
    You can post your images directly on the forum. I mention this because the link you included tried to install software on my device and resulted in a popup or two. I am very suspicious of sites that behave in this manner

    Where you type your post, look in the lower right corner for the button labelled "Upload a File"...
    Untitled.png
    After the file is uploaded, you are given the option to insert it into your post. You can either insert the full image, or if it is large, insert a thumbnail. With this latter option, a reader can click on the thumbnail to view the entire image. The full image looks like this:
    Untitled-2.png
    The thumbnail looks like this...
    Untitled-2.png
    The end result looks like this post!
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    Good, clear directions, djfantasi.

    And if it is too large to reasonably view when inserted, it is almost certainly too large to post at all. Most cameras these day produce huge images that are about 100x as large as is needed. You can usually just use Paint (or some similar program) to adjust the picture size to be between 300 and 400 pixels wide and the result will fit nicely in most browsers. If it is a line drawing or similar art, you typically get superior compression using PNG over JPG, but for picture images the reverse is generally true.

    Posting images directly in the forum is the much preferred route. Not only does it mean that people don't have to jump through hoops to access your images, but it also means that the images are archived as part of the site instead of relying on some third-party site, which may be here today and gone tomorrow.
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    You've got a number of problems.

    You have two signals in the diagram that are not labeled, including one input signal.

    You have three signals, B, Z and W, in the equations that are not in the diagram.

    The signal B pretty much has to be the other input to the OR gate.

    But W and Z are mysteries. Since you say that W=A', this also implies that A=W' which means that W would be the signal going into the inverter. But the real mystery is the other AND gate because you show a gate with one input and two outputs -- what's up with that?
     
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