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July 8th, 2015, 06:07 AM  #1 
Newbie Joined: Jul 2015 From: London Posts: 6 Thanks: 0  Truth table AND THE Karnaugh Map
I have answered regarding I'm not sure if it is correct. I have done the truth table and done the Boolean expression. I need someone to check my answers and correct me if I made a mistake. Questions and scenario: The food dispenser will become active when the blue and green lights are on (irrespective of whether the red light is on or off); when the blue light is off and the green light is on (irrespective of whether the red light is on or off); and when only the blue light is on. All other combinations will not provide food. (a) Draw a truth table representing each light as a Boolean variable, showing all combinations of the variables and the output A which indicates whether the dispenser is active or not. (b) Using the truth table, write down a Boolean expression that will activate the dispenser when appropriate. (c) Use a Karnaugh Map to find the simplest representation of the expression. My answers: a) for the truth table click on the attachment b) The Boolean expression that I have written down were: Output = râ€™gb + râ€™gbâ€™ + râ€™gâ€™b + rgb + rgbâ€™ c) I'm struggling with the Karnaugh map. I need someone to explain it to me and show me how to do it. 
July 9th, 2015, 05:41 PM  #2 
Senior Member Joined: Dec 2007 Posts: 687 Thanks: 47 
I took a look at it, and it seems that you simply arrange a matrix $\displaystyle m$x$\displaystyle n$ with pairs of literals if m and n are both even, or with a single literal and its negation, say, in the column if n is odd. Example: you have a formula with A, B and C being literals, then \begin{array}{r  r  c  c } &&C&\sim\!C \\ \hline \\ &&0&1 \\ \hline \\ AB&11&& \\ \hline \\ \sim\!AB&01&& \\ \hline \\ A\sim\!B&10&& \\ \hline \\ \sim\!A\!\sim\!B&00&& \end{array} where $\displaystyle \sim\!AB$ means $\displaystyle \neg A\wedge B$, and the binary are the respective values. If you'd have got A, B, C and D, then your matrix would be: \begin{array}{r  r  c  c  c  c } &&CD&\sim\!CD&C\sim\!D&\sim\!C\sim\!D \\ \hline \\ &&11&01&10&00 \\ \hline \\ AB&11&&&& \\ \hline \\ \sim\!AB&01&&&& \\ \hline \\ A\sim\!B&10&&&& \\ \hline \\ \sim\!A\!\sim\!B&00&&&& \end{array} It is really just a scheme to ease visualization. 

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karnaugh, map, table, truth 
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