LABORATORY11: Digital Logic Circuits

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LABORATORY11Digital Logic Circuits

• General Engineering
• Polytechnic University

2
Overview

• Objectives
• Logic Functions
• Sample Problem
• Truth Table
• Boolean Equation
• Karnaugh Maps (K-maps)
• Simplified Boolean Equation
• Combinational Logic Circuit

• Integrated Circuits (ICs)
• IC Identification
• Digital Logic Trainer
• Materials for Lab
• Problem Statement
• Procedure
• Written Assignment
• Written Topics
• Recitation Topics
• Closing

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Objectives

• Understand the functions of logic gates
• Become familiar with digital circuits Use you new
  knowledge to design implement a combinational
  logic circuit using the digital trainer

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Logic Functions

• AND - The all or nothing operator
• Output is high (1) only when ALL inputs are high
  (1)
• OR gate - The any or all operator
• Output is high (1) when at least ONE input is
  high (1)
• NOT (INVERTER) operator
• Output is opposite of input
• Only one input and one output

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Logic Functions
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Sample Problem

• An ATM machine has three options, Print
  statement, Withdraw money, or Deposit Money
• The ATM machine will charge you 1.00 if you
• Want to withdraw
• Only want to print out your statement (no
  transactions at all)

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Truth Table

• A truth table is a table
• that displays all possible
• input combinations and
• the resulting outputs.
• INPUT OUTPUT
• P print C charge
• W withdraw
• D deposit
• 0 do not 0 0.00
• 1 do 1 1.00

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Boolean Equation
Outputs with a value of ONE are kept
C

• PWD

PWD
PWD
PWD
PWD
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Karnaugh Maps (K-maps)
Place output ONE in corresponding boxes. Circle
neighboring ONES in multiples of 2, try to find
the greatest amount of neighbors Only overlap
circles as a last resort

• C PWD PWD PWD PWD PWD

PWD
PWD
PWD
0
0
1
1
1
1
0
0
W
P
P
P
P
W
W
W
1
1
1
D
0
1
1
1
D

_ Why cant you switch PW and PW?
Why cant you loop the three adjacent 1s in the
top row together?
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Karnaugh Maps (K-maps)

• C PWD PWD PWD PWD PWD

NOTECircle neighboring ONES in multiples of 2.
Try to find the greatest amount of neighbors.
Only overlap circles as a last resort
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Simplified Boolean Equation
Opposite values cancel out
W

• C

_ PD
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Simplified Boolean Equation
Opposite values in circles cancel out

• C W PD

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Combinational Logic Circuit
W
W
P
_ PD
P
_ D
D
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Integrated Circuits (ICs)

• Used to implement combinational logic circuits
• We use the TTL family (transistor transistor
  logic)

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IC Identification
7404 Inverter Chip
7408 AND Chip
7432 OR Chip
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Digital Logic Trainer

• Complete diagram on page 98
• Breadboard
• Points with a line through them represent the
  same connection line

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Materials for Lab

• Digital/Analog Trainer
• 7432 2-Input OR gate IC
• 7408 2-Input AND gate IC
• 7404 Hex Inverter (NOT gate) IC
• Hook-up Wire
• Computer equipped with LabVIEW

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Problem Statement

• A farmer has two barns
• A hen is free to move about.
• A supply of corn is moved periodically from one
  barn to the other.
• He wants to protect the hen from a predator fox,
  and also prevent the hen from eating the supply
  of corn.
• An engineering student is hired to design an
  alarm system, using digital electronics. It will
  activate under the following conditions
• The fox and the hen are in the same barn.
• The hen and the corn supply are in the same barn.

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Problem Statement

• Design a combination logic circuit that will
  accomplish this task.
• The design should be cost effective, using the
  least amount of gates and input variables.
• The logical output of the circuit should be
  connected to a lamp.
• The lamp being on indicates alarm activation
• The lamp being off indicates alarm
  deactivation.
• The fox and hen and corn must be present in
  either barn 1 or barn 2
• Presence in barn 11
• Presence in barn 20

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Procedure

• Truth Table
• Determine what are the input variables and the
  output variable
• Decide how many combinations there should be
• Create and complete the truth table on a sheet of
  paper

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• Boolean Expression
• Gather all the combinations that produced a 1
  for the output
• Create a Boolean expression from these smaller
  expressions

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• K-Map
• Create a K-Map table
• Be sure to only have one variable change states
  at a time from one box to another
• Use the Boolean expression to fill in the 1s

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• Simplified Boolean Expression
• Use the K-Map to circle the pairs of 1s
• The 1s may only be circled in multiples of 2,
  starting from the largest possible combination
  and working its way down
• Write down the new simplified expression

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• Logic Circuit Diagram
• Use the new simplified expression to design a
  logic circuit
• Have your instructor check your work

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• Digital Trainer
• Do NOT plug anything in until your instructor has
  looked over your work
• Use the logic circuit and IC chip diagram to
  create the actual circuit on the breadboard
• Be sure to connect each of the ICs to Ground and
  VCC - 5V

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Procedure

• LabVIEW Simulation
• With the use of your logic circuit diagram -
  recreate the circuit in LabVIEW
• The front panel should have three control
  switches representing the variables and one
  Boolean indicator to represent the output
• HINT LabVIEW has the following built in
  comparison functions

• Truth Table
• Boolean Expression
• K-Map
• Simplified Boolean Expression
• Logic Circuit
• Digital Trainer
• LabVIEW Simulation

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Written Assignment

• Full Team Report (one report per team)
• Use the guidelines on page 5 for help
• Include original data with instructors initials
• Original tables and work should be re-written so
  it is legible
• Include a printout of the LabVIEW front and
  diagram panel
• Include the topics found on the next slide
• Remember to create a title page

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Written Topics

• Each of the following topics must be addressed in
  the full report and should be placed in the
  proper sections
• What are possible applications of digital
  electronics?
• Account for any error made during the lab
• Compare the problem before and after it was
  simplified
• What are some advantages of minimization using
  digital logic?

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Recitation Topics

• If your design did not work the first time,
  discuss why
• Discuss how the digital circuit and its design
  would be affected if barn one had an alarm bell
  and barn two has an alarm horn

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Closing

• Return all the equipment back to your instructor