Polytechnic University of the Philippines
College of Engineering
Department of Computer Engineering
Score:
Blended Learning: Activity 3
CMPE 30094 – Logic Circuits and Design
1st Semester, AY 2022-2023
Student No.: ___________________ Name: __________________________________________
Yr./Sec.: ________
Teacher:______________________________ Date:_________________
Combinational Circuit Design
In this activity, you will be asked to design combinational logic circuit using the given
problem specification as worded problem and simplify the circuit using the Boolean Algebra
Postulates and Theorems. Two hours will be allotted for you to finish this activity.
Introduction
Creating logic systems from written specifications
Perhaps the most common application of switching logic is creating a logic system to meet a
given specification. Normally, by reading the specification carefully, the system designer can
almost ‘see’ the required logic system.
Worked example
A burglar alarm system is to sound if a master switch is on and either a light beam is broken or
a pressure pad is stood on.
Draw a logic diagram and a truth table for this system.
Read the specification carefully. You should notice that it has three inputs. These are:
•
•
•
a master switch (M)
a light sensor (L), and
a pressure pad (P).
It has one output, an alarm bell (B).
The bell should go to logic 1 if the master switch is at 1 and either the light beam goes to logic
0 or the pressure pad goes to logic 1. This can be written in Boolean as:
B
=
Blended Learning: Activity 3
CMPE 30094 – Logic Circuit and Design
1st Sem, AY 2022-2023
Prepared by: Engr. Julius S. Cansino, PCpE
M . (L + P )
Page | 1
Note: The alarm has to be triggered when the light beam is broken and so a NOT gate is
needed.
In other words, you need a two-input AND gate that is fed directly from M and also from a
two-input OR gate that is fed from L (through an inverter) and P. The logic diagram is shown
below.
M
B
P
L
L
The truth table for this system is shown below. Again, all you have to do is read the
specification carefully and then read across each row, one at a time, and decide whether the
bell should be ringing or not. There are some short cuts. For example, in the first four rows the
master switch is off; therefore the bell must be at logic 0 – even if there is a burglar in the
house.
Blended Learning: Activity 3
CMPE 30094 – Logic Circuit and Design
1st Sem, AY 2022-2023
Prepared by: Engr. Julius S. Cansino, PCpE
M
L
P
B
0
0
0
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
1
1
0
1
1
1
1
0
0
1
1
1
1
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Procedure:
Perform all required tasks.
Problem Set 1:
Two sensors A and B are used to control the paint mixing process at a local DIY store. Three
output valves control the flow of cyan, magenta, and yellow pigment. Valve V1 is the cyan,
Valve V2 is the magenta, and Valve V3 is the yellow. Mixing occurs according to the following
sequence. Logic 1 operates the valve.
•
•
•
a)
Valve 1 operates when input A is high and input B is high.
Valve 2 operates when input A is low and input B is low or when input A is high and
input B is low.
Valve 3 operates when input A is low and input B is high or when input A is low and
input B is low.
Complete the following truth table for the system.
Inputs
Outputs
A
B
0
0
0
1
1
0
1
1
V1
V2
V3
(cyan)
(magenta)
(yellow)
b)
Which type of gate will provide the V1 output?
c)
Write down an expression to describe V2 and V3 by comparing them with the
inputs.
V2 =
V3 =
Blended Learning: Activity 3
CMPE 30094 – Logic Circuit and Design
1st Sem, AY 2022-2023
Prepared by: Engr. Julius S. Cansino, PCpE
Page | 3
d)
Draw the circuit for the system
Problem Set 2:
The nation of Upper Slobovia has gained a missile defense capability governed by its Security
Council. The Council consists of four members: the U.S. (Upper Slobovia) President and three
Counselors (the Chiefs of Staff of the Army and Air Force plus the President’s Uncle Homer). The
missile system is to be activated by a device obeying these rules: each member of the Security
Council has a button to push; the missiles fire only if the President and at least one Counselor
push their buttons. Design the rocket firing circuitry. (Show the steps in designing a
combinational logic Circuit)
Blended Learning: Activity 3
CMPE 30094 – Logic Circuit and Design
1st Sem, AY 2022-2023
Prepared by: Engr. Julius S. Cansino, PCpE
Page | 4
Problem Set 3:
A hallway light is controlled by three switches. If the light is off, clicking any one of the three
switches turns it on. If the light is on, clicking any one of the three switches turns it off. A fourth
input variable is needed to register the current state of the light (1 = on, 0 = off). The output
variable should be 1 when the light is to be turned on and 0 when it is to be turned off. If two
switches are clicked at the same time then the state of the light remains unchanged.
Furthermore, if three switches are clicked at the same time then the state of the light does
change. Design a controller showing each step in designing a combinational logic circuit.
Grading Rubric
4 points
3 points
2 points
1 point
0 point
Rubric for Content and Organization
* Response is comprehensive, complete and accurate.
* Key ideas are clearly stated, explained, and well-supported.
* No evidence of misconception regarding the concept/s involved.
* Response is well-organized, coherently developed and easy-to-follow.
* Response is comprehensive or completely stated.
* Key ideas are addressed but not well-supported.
* No evidence of misconception regarding the concept/s involved
* Response is well-organized, coherently developed and easy-to-follow.
* Response is partial or incomplete
* Some key ideas are addressed but not well-supported.
* Contains minor inaccuracies and misconceptions regarding the concept/s
involved.
* Response is not that organized and developed.
* Response is partial or incomplete.
* Key points are not clear and not supported with theoretical evidences.
* There is/are evidence/s of misconception regarding the concept/s involved.
* Lacks organization and coherence.
* No attempt to respond.
References
http://www.electronics-tutorials.ws/combination/comb_1.html
https://learn.sparkfun.com/tutorials/digital-logic
http://www.electronics-tutorial.net/combinational-logic-circuits/index.html
https://www.electrical4u.com/digital-electronics/
http://electronics-course.com/combinational-logic-design
Blended Learning: Activity 3
CMPE 30094 – Logic Circuit and Design
1st Sem, AY 2022-2023
Prepared by: Engr. Julius S. Cansino, PCpE
Page | 5