Boolean Algebra

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Activity 2.1.4 Circuit Simplification:
Boolean Algebra
Introduction
Have you ever had an idea that you thought was so unique that when you told someone else
about it, you simply could not believe they thought you were wasting your time with it? If so,
you know how the mathematician George Boole felt in the 1800s when he designed a math
system that, at the time, had no practical application. Today, however, his math system is the
most important mathematical tool used in the design of digital logic circuits. Boole introduced
the world to Boolean algebra when he published his work called “An Investigation of the Laws
of Thought, on Which Are Founded the Mathematical Theories of Logic and Probabilities.”
In the same way that normal algebra has rules that allow you to simplify algebraic
expressions, Boolean algebra has theorems and laws that allow you to simplify expressions
used to create logic circuits.
By simplifying the logic expression, we can convert a logic circuit into a simpler version that
performs the same function. The advantage of a simpler circuit is that it will contain fewer
gates, will be easier to build, and will cost less to manufacture.
In this activity you will learn how to apply the theorems and laws of Boolean algebra to
simplify logic expressions and digital logic circuits.
The moral of the story is to keep dreaming. Someday your grandchildren may be using
something that you’re thinking about right now. When your grandparents were kids, do you
think that they imagined someday that we would all have 10,000 songs in our pockets or a
telephone in our backpacks?
© 2014 Project Lead The Way, Inc.
Digital Electronics Activity 2.1.4 Circuit Simplification: Boolean Algebra – Page 1
Procedure
Using the theorems and laws of Boolean algebra, simplify the following logic expressions.
Note the Boolean theorem/law used at each simplification step. Be sure to put your answer in
Sum-Of-Products (SOP) form.


1.
F1  A A  A B
2.
F2  X Y Z  X Y Z  X Y Z
3.
F3  J K  J K
4.
F4  B  B A B  A B C
5.
F5  X  Y X  Y 
6.
F6  J K  J  K L  J K
F=AB
F=J





F=X

F= X’Z+XZ
F=AB’

F= JK+J’L+K’L
7.
F7  R S  R S  T  S S  U
F= RS+RT+S’U
8.



F8  N  N M N  N M N  M
F=NM+M
© 2014 Project Lead The Way, Inc.
Digital Electronics Activity 2.1.4 Circuit Simplification: Boolean Algebra – Page 2
Almost as important as being able to use the laws of Boolean algebra (i.e., associative,
commutative, or distributive) to simplify logic expressions, it is also critical that you are
able to identify them. Identify the law of Boolean algebra upon which the following
equalities are based.
9.
AB A CBC A CBC AB
Commutative
10.
D EF G  D E F G
Associative
11.
R  S  T  U  R  S  T  U
Associative
12.
J  KL  M  J L  J M  K L  K M
Distributive
13.


R ST  S V RST RS V
Distributive
Now that you’ve practiced simplifying logic expressions, apply your knowledge to simplifying
an actual circuit.
14. Shown below is a VERY poorly designed AOI circuit that is part of a coffee vending
machine. Write the UN-SIMPLIFIED logic expression for the output Brew Cut Off.
“If the temperature is too high or the pressure is not below the safe value with water present,
the brew sensor cuts off the brew process.”
(TP+W)P’+T+TP’
© 2014 Project Lead The Way, Inc.
Digital Electronics Activity 2.1.4 Circuit Simplification: Boolean Algebra – Page 3
15. Using the theorems and laws of Boolean algebra, simplify the logic expression
Brew Cut Off. Be sure to put your answer in Sum-Of-Products (SOP) form.
T+T’P’W
T
P
W
F
0
0
0
0
0
0
1
1
0
1
0
0
0
1
1
0
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
1
16. In the space provided, draw an AOI circuit that implements the simplified logic
expression Brew Cut Off. For your implement, assume that only 2-input AND gates
(74LS08), 2-input OR gates (74LS32), and inverters (74LS04) are available. Draw this
circuit in the space provided.
© 2014 Project Lead The Way, Inc.
Digital Electronics Activity 2.1.4 Circuit Simplification: Boolean Algebra – Page 4
Brew Cut Off Circuit
Conclusion
1. Describe the process that you would use to simplify a logic expression using Boolean
algebra.
Using different of the Laws and theorems you will go along the process simplifying the
expression and every step you made make the expression simpler.
2. How do you know when you are finished simplifying and have arrived at the simplest
equation?
I the expression explains the truth of the circuit correctly and is a very simple way then the
expression in the simplest.
3. Other than using Boolean algebra, how could you prove that two circuits are
equivalent?
By comparing the truth tables.
4. If you worked for a company that manufactured the coffee vending machine that used
the poorly designed circuit, how much money would your new design save the
company annually if each GATE cost 15¢ and the company made 500,000 vending
machines per year?
150,000.oo *saving 1,000,000 gates per year
© 2014 Project Lead The Way, Inc.
Digital Electronics Activity 2.1.4 Circuit Simplification: Boolean Algebra – Page 5
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