ME3241 tokheim 8thed digital electronics principles and Applications(BookZZ org)
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\:h Learn
Succeed"'
DIGITAL ELECTRONICS: PRINCIPLES AND APPLICATIONS, EIGHTH EDITION
Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the
Americas, New York, NY, 10020. Copyright© 2014 by The McGraw-Hill Companies, Inc. All rights reserved.
Printed in the United States of America. Previous editions© 2008, 2003, and 1999. No part of this publication
may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system,
without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any
network or other electronic storage or transmission, or broadcast for distance learning.
Some ancillaries, including electronic and print components, may not be available to customers outside the
United States.
This book is printed on acid-free paper.
1234567890QVR/QVR109876543
ISBN 978-125-906092-2
MHID 125-906092-6
All credits appearing on page or at the end of the book are considered to be an extension of the copyright page.
The Internet addresses listed in the text were accurate at the time of publication. The inclusion of a website
does not indicate an endorsement by the authors or McGraw-Hill, and McGraw-Hill does not guarantee the
accuracy of the information presented at these sites.
www.mhhe.com
Contents
Editor's Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
Preface ..................................... ix
Acknowledgments ............................ xi
Walkthrough ................................. xii
About the Author ............................. xiv
Safety ...................................... xv
Chapter l
Digital Electronics
1-1
What Is a Digital Signal? . . . . . . . . . . . . . . . . . 2
1-2
Why Use Digital Circuits? ................ 4
1-3
Where Are Digital Circuits Used? .......... 7
1-4
How Do You Generate a Digital Signal? ..... 8
1-5
How Do You Test for a Digital Signal? ...... 15
1-6
Simple Instruments . . . . . . . . . . . . . . . . . . . . . 19
Summary ................................... 23
Chapter Review Questions. . . . . . . . . . . . . . . . . . . . . . 23
Critical Thinking Questions . . . . . . . . . . . . . . . . . . . . . 25
Answers to Self-Tests ......................... 26
Chapter 2
Numbers We Use in Digital Electronics 27
2-1
Counting in Decimal and Binary ..........
2-2
Place Value . . . . . . . . . . . . . . . . . . . . . . . . . . .
2-3
Binary to Decimal Conversion ............
2-4
Decimal to Binary Conversion ............
2-5
Electronic Translators ...................
2-6
Hexadecimal Numbers ..................
2-7
Octal Numbers ........................
2-8
Bits, Bytes, Nibbles and Word Size ........
Summary ...................................
Chapter Review Questions ......................
Critical Thinking Questions .....................
Answers to Self-Tests .........................
Chapter 3
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
Logic Gates
The AND Gate ........................
The OR Gate ..........................
The Inverter and Buffer. .................
The NAND Gate .......................
The NOR Gate ........................
The Exclusive OR Gate ..................
The Exclusive NOR Gate ................
The NAND Gate as a Universal Gate .......
Gates with More Than Two Inputs .........
27
28
30
30
31
34
36
37
39
39
40
42
43
43
46
48
50
51
53
54
56
57
3-10
3-11
3-12
3-13
3-14
3-15
3-16
Using Inverters to Convert Gates ..........
Practical TTL Logic Gates ...............
Practical CMOS Logic Gates .............
Troubleshooting Simple Gate Circuits ......
IEEE Logic Symbols ...................
Simple Logic Gate Applications ...........
Logic Functions Using Software
(BASIC Stamp Module) .................
Summary ...................................
Chapter Review Questions ......................
Critical Thinking Questions .....................
Answers to Self-Tests . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 4
59
62
65
69
72
73
77
82
83
86
89
90
Combining Logic Gates
4-1
Constructing Circuits from
Boolean Expressions .................... 91
4-2
Drawing a Circuit from a Maxterm
Boolean Expression .................... 92
4-3
Truth Tables and Boolean Expressions ...... 93
4-4
Sample Problem ....................... 97
4-5
Simplifying Boolean Expressions .......... 99
4-6
Karnaugh Maps. . . . . . . . . . . . . . . . . . . . . . . 100
4-7
Karnaugh Maps with Three Variables ...... 101
4-8
Kamaugh Maps with Four Variables . . . . . . 103
4-9
More Karnaugh Maps . . . . . . . . . . . . . . . . . . 104
4-10
A Five-Variable Karna ugh Map . . . . . . . . . . 105
4-11
Using NAND Logic ................... 106
4-12
Computer Simulations: Logic Converter ... 108
4-13
Solving Logic Problems: Data Selectors ... 112
4-14
Programmable Logic Devices (PLDs) ..... 116
4-15
Using De Morgan's Theorems ........... 124
4-16
Solving a Logic Problem (BASIC Stamp
Module) ............................. 126
Summary .................................. 131
Chapter Review Questions. . . . . . . . . . . . . . . . . . . . . 132
Critical Thinking Questions .................... 136
Answers to Self-Tests . . . . . . . . . . . . . . . . . . . . . . . . 136
Chapter 5
5-1
5-2
5-3
IC S~ecifications and Simple
Interfacing
141
Logic Levels and Noise Margin . . . . . . . . . . 141
Other Digital IC Specifications ........... 146
MOS and CMOS ICs .................. 150
Contents
v
5-4
5-5
5-6
5-7
Intetlacing TIL and CMOS with Switches ... 152
Intetlacing TTL and CMOS with LEDs .... 156
Intetlacing TTL and CMOS ICs .......... 160
Intetlacing with Buzzers, Relays,
Motors, and Solenoids ................... 164
5-8
Optoisolators ......................... 167
5-9
Intetlacing with Servo and Stepper Motors . . . 170
5-10 Using Hall-Effect Sensors ............... 178
5-11
Troubleshooting Simple Logic Circuits . . . . 185
5-12 Intetlacing the Servo (BASIC Stamp
Module) ............................. 186
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Chapter Review Questions. . . . . . . . . . . . . . . . . . . . . 190
Critical Thinking Questions . . . . . . . . . . . . . . . . . . . . 194
Answers to Self-Tests ........................ 194
Chapter 6
Encoding, Decoding, and
Seven-Segment Displays
6-1
The 8421 BCD Code. . . . . . . . . . . . . . . . . . .
6-2
The Excess-3 Code ....................
6-3
The Gray Code .......................
6-4
The ASCII Code . . . . . . . . . . . . . . . . . . . . . .
6-5
Encoders ............................
6-6
Seven-Segment LED Displays ............
6-7
Decoders . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-8
BCD-to-Seven-Segment Decoder/Drivers ..
6-9
Liquid-Crystal Displays ................
6-10 Using CMOS to Drive an LCD Display ....
6-11
Vacuum Fluorescent Displays ............
6-12 Driving a VF Display ..................
6-13
Troubleshooting a Decoding Circuit. ......
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
196
196
198
199
202
204
205
208
209
213
218
221
224
227
229
230
233
234
Chapter 8
Flip-Flops
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
The R-S Flip-Flop .....................
The Clocked R-S Flip-Flop ..............
The D Flip-Flop ......................
The J-K Flip-Flop .....................
IC Latches ...........................
Triggering Flip-Flops ..................
Schmitt Trigger .......................
IEEE Logic Symbols ..................
Application: Latched Encoder-Decoder
System ..............................
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
v1
Contents
236
236
239
241
243
247
249
251
252
254
257
258
259
260
262
8-1
8-2
8-3
8-4
8-5
8-6
8-7
8-8
8-9
8-10
8-11
Ripple Counters ...................... 262
Mod-10 Ripple Counters ............... 264
Synchronous Counters ................. 265
Down Counters . . . . . . . . . . . . . . . . . . . . . . . 267
Self-Stopping Counters ................. 269
Counters as Frequency Dividers .......... 270
TTL IC Counters ...................... 272
CMOS IC Counters .................... 276
A Three-Digit BCD Counter. ............ 280
Counting Real-World Events ............ 284
Using a CM OS Counter in an Electronic
Game ............................... 288
8-12
Using Counters-An Experimental
Tachometer . . . . . . . . . . . . . . . . . . . . . . . . . . 291
8-13
Troubleshooting a Counter .............. 295
Summary .................................. 298
Chapter Review Questions ..................... 298
Critical Thinking Questions .................... 302
Answers to Self-Tests ........................ 303
Chapter 9 Shift Registers
305
9-1
Serial-Load Shift Registers ..............
Parallel-Load Shift Registers ............
9-2
9-3
A Universal Shift Register ..............
9-4
Using the 74194 IC Shift Register ........
9-5
An 8-Bit CMOS Shift Register. ..........
9-6
Using Shift Registers: Digital Roulette .....
9-7
Troubleshooting a Simple Shift Register ...
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
307
308
311
313
315
318
323
325
325
327
328
Chapter l 0
Chapter 7
Counters
Arithmetic Circuits
Binary Addition .......................
Half Adders ..........................
Full Adders ..........................
3-Bit Adders .........................
Binary Subtraction ....................
Parallel Subtractors ....................
IC Adders ...........................
Binary Multiplication ..................
Binary Multipliers .....................
2s Complement Notation, Addition,
and Subtraction .......................
10-11 2s Complement Adders/Subtractors .......
10-12 Troubleshooting a Full Adder ............
Summary ..................................
Chapter Review Questions .....................
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
330
330
332
333
335
336
338
340
343
345
348
353
355
357
357
i2
Critical Thinking Questions .................... 358
Answers to Self-Tests ........................ 359
4
5
Chapter 11
7
Overview of Memory ..................
Random-Access Memory (RAM) .........
Static RAM ICs .......................
Using a SRAM .......................
Read-Only Memory (ROM) .............
Using a ROM ........................
Programmable Read-Only Memory
[PROM] .............................
11-8
Nonvolatile Read/Write Memory .........
11-9
Memory Packaging ....................
11-10 Computer Bulk Storage Devices ..........
11-11 Digital Potentiometer: Using NV Memory ...
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
Memories
11-1
11-2
11-3
11-4
11-5
11-6
11-7
Chapter 12
Simple Digital Systems
12-1
Elements of a System ..................
12-2 A Digital System on an IC ..............
Digital Games ........................
12-3
12-4 The Digital Clock .....................
12-5
The LSI Digital Clock ..................
12-6 The Frequency Counter. ................
12-7
An Experimental Frequency Counter ......
12-8
LCD Timer with Alarm .................
12-9 Simple Distance Sensing ...............
12-10 JTAG/Boundary Scan ..................
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
Chapter 13
13-1
13-2
13-3
Computer Systems
361
362
365
367
370
372
375
377
381
384
387
394
398
399
401
401
403
403
406
407
412
415
419
423
426
432
437
441
441
443
444
445
The Computer ........................ 445
The Microcomputer ................... 447
Microcomputer Operation ............... 450
Microcomputer Address Decoding ........
Data Transmission .....................
Detecting Errors in Data Transmissions ....
Data Transmission in a Computer System ...
Programmable Logic Controllers (PLCs) ...
Microcontrollers ......................
The BASIC Stamp Microcontroller
Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13-11 Digital Signal Processing ...............
13-12 DSP in a Digital Camera ................
13-13 Microcontroller: Photo Input and Servo
Motor Output ........................
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
13-4
13-5
13-6
13-7
13-8
13-9
13-10
Chapter 14
Connecting with Analog Devices
14-1
DIA Conversion . . . . . . . . . . . . . . . . . . . . . .
14-2 Operational Amplifiers .................
14-3
A Basic DIA Converter .................
14-4 Ladder-Type DIA Converters ............
14-5
An AID Converter .....................
14-6 Voltage Comparators ...................
14-7
An Elementary Digital Voltmeter .........
14-8
Other AID Converters . . . . . . . . . . . . . . . . . .
14-9
AID Converter Specifications ............
14-10 An AID Converter IC ..................
14-11 Digital Light Meter. ...................
14-12 Digitizing Temperature .................
Summary ..................................
Chapter Review Questions .....................
Critical Thinking Questions ....................
Answers to Self-Tests ........................
Appendix A
Appendix B
454
457
461
464
469
473
4 75
482
486
488
493
493
496
498
499
500
501
502
504
506
508
510
512
516
517
520
523
525
525
527
528
Solder and the Soldering Process .... 530
2s Complement Conversions ....... 535
l
Glossary of Terms and Symbols ................ 536
Credits .................................... 549
Index ..................................... 550
Contents
vu
''
Editor's Foreword
The McGraw-Hill Education Trade and Technology list
has been designed to provide entry-level competencies in
a wide range of occupations in the electrical and electronics fields. It consists of coordinated instructional materials designed especially for career-oriented students. A
textbook, an experiments manual, and online resources
support each major subject area covered in the series. All
of these focus on theory, practice, applications, and experiences necessary for those preparing to enter technical
careers.
There are two fundamental considerations in the preparation of a text like Digital Electronics: Principles and
Applications: the needs for the learner and the needs of
the employer. This text meets those needs in expert fashion. The authors and editors have drawn upon their broad
teaching and technical experiences to accurately interpret
and meet the needs of the student. The needs of business
and industry have been identified through personal interviews, industry publications, government occupational
trend reports, and reports by industry associations.
The processes used to produce and refine the series
have been ongoing. Technological change is rapid, and
the content has been revised to focus on current trends.
Refinements in pedagogy have been defined and implemented based on classroom testing and feedback from
students and instructors using the series. Every effort has
been made to offer the best possible learning materials.
These include animated PowerPoint presentations, circuit
files for simulation, a test generator with correlated test
banks, dedicated websites for both students and instructors, and basic instrumentation labs. All of these are well
coordinated and have been prepared by the author.
The widespread acceptance of Digital Electronics: Principles and Applications and the positive feedback from
users confirm the basic soundness in content and design of
all the components as well as their effectiveness as teaching and learning tools. Instructors will find the texts and
manuals in each of the subject areas logically structured,
well paced, and developed around a framework of modern
objectives. Students will find the materials to be readable,
lucidly illustrated, and interesting. They will also find a
generous amount of self-study materials, review items, and
examples to help them determine their own progress.
Both the initial and ongoing success of this text and
others with the McGraw-Hill Trade and Technology list
are due in large part to the wisdom and vision of Gordon
Rockmaker, who was a magical combination of editor,
writer, teacher, electrical engineer, and friend. The publisher and editor welcome comments and suggestions
from instructors and students using this series.
Charles A. Schuler, Project Editor
Basic Skills 1n EIBctricity and EIBctronics
Charles A Schuler, Project Editor
New Editions in This Series
Electricity: Principles and Applications, Eighth Edition, Richard J. Fowler
Electronics: Principles and Applications, Eighth Edition, Charles A. Schuler
VIII
Editor's Foreword
Preface
Digital Electronics: Principles and Applications, eighth
edition, is an easy-to-read introductory text for students new to the field of digital electronics. Providing
entry-level knowledge and skills for a wide range of
occupations is the goal of this textbook and its ancillary materials. Prerequisites are general math and introductory electricity/electronics. Binary math, Boolean
concepts, simple programming, and various codes are
introduced and explained as needed. Concepts are connected to practical applications, and a systems approach
is followed that reflects current practice in industry.
Earlier editions of the text have been used successfully
in a wide range of programs: electronic technology,
electrical trades and apprenticeship training, computer
repair, communications electronics, and computer science, to name a few. This concise and practical text can
be used in any program needing a quick and readable
overview of digital principles.
Chapter 5
• Information on low-voltage ICs.
• Added many application assignments on interfacing.
Chapter 6
• Updated applications of the Gray code, including
the shaft encoder, and new information on the
quadrature encoder.
• Updated information on display technologies.
Chapter7
• Application of an R-S latch.
• A new detailed application of a latched encoderdecoder system.
Chapter 8
• Expanded self-test questions.
Chapter 10
New to this Edition
Chapter 1
• Digital applications, including automotive fuel indicators, vehicle speed sensors, and engine control
module.
• A new section on where digital circuit applications
are used.
• Information on logic probe use in troubleshooting.
• A revised instruments section.
Chapter 2
• Subsection on applications of encoders and
decoders.
Chapter 3
• Updated information on practical chips including
lower voltage ICs.
• Expanded most self-test sections.
Chapter4
• Expanded several self-test sections.
• Revised material on data selectors.
• Expanded several self-tests.
• Updated binary subtraction section.
Chapter 11
•
•
•
•
Updated overview of memory section.
Updated nonvolatile read/write memory section
Updated memory packaging section.
Expanded bulk storage section, including more
information on USB flash drives.
• Internet research topics.
Chapter 12
• Expanded self-test and critical thinking questions.
• Information on distance sensing with coverage of
several sensor technologies.
• A DIY application demonstrating a distance sensor
triggering the timed operation of a stepper motor.
Chapter 13
• Updated microcomputer section.
• Updated data transmission section.
Preface
IX
• A revised microcontrollers section.
• Application of a microcontroller with photo input
and servo motor output.
Chapter 14
• Expanded self-test questions.
Additional Resources
An Experiments Manual for Digital Electronics contains
a comprehensive test, a variety of hands-on lab exercises
and experiments, and additional problems for each chapter in the textbook.
The Online Learning Center (OLC) at www.mhhe.
com/tokheim8e includes comprehensive Multisim files,
keyed to circuits found in the eighth edition, and a Multisim
primer (written by Patrick Hoppe of Gateway Technical
College), which provides a tutorial on the software for new
users. The Multisim program itself is not included on the
x
Preface
website, but the latest version, version 12, can be purchased
through McGraw-Hill at a discount when you adopt this
textbook. Visit www.mhhe.com/tokheim8e or contact your
McGraw-Hill sales representative for more information.
The OLC also features chapter study resources, links to
industry and association sites, and assignments and tests
for students. Instructors can access the instructor side of
the OLC to find a wide selection of information including:
• An Instructor's Manual that includes a list of the
parts and equipment needed to perform lab experiments, learning outcomes for each chapter, answers
to chapter review questions and problems, and more.
• PowerPoint presentations that correlate to all chapters and special PowerPoint presentations on breadboarding, soldering, circuit interrupters (GFCI and
AFCI), and instrumentation.
• A test generator, EZ Test, which includes a test
bank with questions for each chapter.
cknowledgments
Thanks to family members Marshall, Rachael, Dan, Jack,
Ben and Carrie for their help on this project. I would also
like to thank the reviewers who helped evaluate the textbook; I am grateful for their time and expertise.
Mike Carter
Mercedes-Benz Institute
Richard Fornes
Apollo Career Center Adult Education
J. C.Morrow
Hopkinsville Community College
Chrys Panayiotou
Indian River State College
G. Albert Popson
West Virginia Wesleyan College
Joseph Tront
Virginia Tech
Mark Winans
Central Texas College
Jillian Wooldridge
Erie Institute of Technology
Tom Neal
Southern Crescent Technical College
Randy Owens
State Fair Community College
Acknowledgments
x1
alkthrough
Digital Electronics: Principles and Applications, eighth
edition, is designed for a first course in digital electronics. It provides a concise, modern, and practical approach
that's suitable for a range of electricity and electronics
Digital Electronics
E~f~~~~;a~g~~f~~ ~it~~~~~~:io: ~~trSi~ii~
11
Learning Outcomes
Tflix chapter will hdp yo11 m:
1·1
fdr1u1/y ,,...,,er;tl dwr.ic1eri
/Ji{f<'mllit11eb.:t"ccndi~it~J
1·2
and;1n.1!oi;
.
op.:r~tion uf\Cvcr..11 !iq..,id·rnca.wrinJ,!
cin:ui1~ £11•frii1111hycomcninga0Jfog
1-3
fonn
Li.•f...:1·cr~I
I.
:;c-~r
c~n
Ix: u;:.:ful.
cununon pi~-.:.:.~ofclcctronic
1-4
information?
3. C;m the dc\•icc he programmed'!
4. C;in it he conncc!e
that .;on1ai11
f.i.1111lrcc typ<:-.• ofmulli\·ibr.llor.i.~nd
11<'.,.-rilJ<:how1hcyi.:encr.1letype•ofdigirnl
$ii;nakAml/_,·:e
1·5
A11a(1<:<"""circ\lit>. fll/rrprerlngie probe readings
durtns !~..,,1ing ofadii;ical circuit
If the answer to any one of the four questions is yes. then the product probably contains digital circuitry.
Digital circuitry is quickly hecoming
pe1vasive because of its ad1'antagc.1 over
analog including:
U11ders111mf1hcdefini!i(m;ofJ/fGlf.
(.O!V.Jndu111fr:ji11r:dwhcnoh>.ervingk1gic
1·5
Doe~ it have a disphiy that shows
numbers, letters. pictures, or video?
2. Docs it have a memory or can it More
thedemantlfoccomputerandelo::tronic>
!L-.:hnici~o•. and
opponunitics
Each chapter begins with a list of learning
outcomes that tell the reader what he or she
should expect to accomplish by the end of
the chapter. The outcomes are tied to the
chapter subsections.
What:iretheduesr.h;itnnelectronicproduct n111rai11.1· di&iWl drr.uirry? Signs that n
device contains digital circuitry indude:
inpol~fcum:n1<:1nJ,·ol!agts)from.<';Cll,Ots
todigi1~1
1
tal in nawre. Historically. most electronic
pnxlucls contained a.irnlog circuitry. Most
newly designed electronic devices rn111ain
digit:il circuitry. This chapter introduces
you to the world of digital electronics.
programs. With its easy-to-read style, numerous fullcolor illustrations, and accessible math level, the text is
ideal for readers who need to learn the essentials of digital
electronics and apply them to on-the-job situations.
I
Genernlly,
to Jesign using modern integrated
circuit~ (!Cs).
Information stornge is ca~ier to
level; in both TTl. ~nd CMOS digital
circuitry.
fJemmr.11wrethcu.cof><.'Vcr.1lM>
•
~:,l;~.~:e.~!:~~h~~;1i~a~·.,,,. ....., .....h! ..
2-8
Huadecimal
num!rersymm
Buel6system
He.aidecimi!
natatian
Key terms are carefully defined and explained
in the text and listed in the margins so students
can easily identify them.
S11/)/lfy1hrmi.ni11t-:u"mtfi11rach.1wtrmell/
!. Rc!erLo Fi!!.. 1·2. The +5-V li:vel of the
_ _ -(:rnalog,digita[J~ignalcould
:1ho be ca!k-U a logical ! or a _ __
i.\Onc that
hasa.~ignalwhichvariescon·
tinuouslyin~tepwith!hcinput.
3. Refer to Fig. l-4 The input to the
elecmmicblock iseta.~siliedasn(n)
_ _ _ (analog, digiiall signal.
4. Refert0Fig. l-4.Theo11tpmfromthe
efcetronic hlock i~ ctu.,silied a~ a(n)
_ _ _ (analog, digital) sign;iJ
5. An annlog circuit is one that procc~$C$
analogsignalswhileadigitalcircuit
proccsses _ _ ~ignals
OUTPUT
n__
_,,_
F.;t~Bi.Jcl<dag";rnricloc!nricorcut~a!ine"Ml'>'e'rt11a
XII
Walkthrough
Mii;ral'rucnstJr·
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Subscript!
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Hexadecimal Numbers
The he.111drd111u/ 1111m/1er .\\"Ht'/11 u~s the !6
symboh 0, I. 2. 3, 4, 5. 6, 7. 8. 9. A. B. C. D. E.
and F and is 1cfcrrcd to a~ the fxni• 16 .
hexadecimal representations for the decim;il
numbers 0 thmugh 17. The !cuer "A" slamh
for decimal IO. "B~ for decimal IL and ~o on.
The adv;inlage ut the hc:irndccimal sy,,tcm is it~
u1>
binary number. For instance. hexadcdm~! F
~tand~ for the -l·bit binary number l 11 ! He.w·
detima/ 11111Uti1111 is typically ug."d to repre~cnt
;i binary number. For in~tancc, the hexadecimal
number A6 y.uuld rcprc ...ent the 8·bit binary
number !UJUOl IU. Hexudcc1mal notatmn is
widely usi:d in micmprocc.uor-lm.1t:d f_Y\tt.'1111
to repre.\Cnt 4. 8-. !6-, 32·, or 6-1-·hit binary
numbers
The numhcr lO rt:prc).Cnh how many ob·
It can he oh~crved from the table ~hown
in Fig. 2-9 that the number IOcouldmc:m ten
ohjccts, two nhjt.-Cb. or ~ixtee11 objects depend·
ing on the ba~c of the number. Subsuipfl arc
~omctimes :iddcd to a number to indicate the
ba.~e of the numh-::r. U~ing \Ub?>Cripts, !he number 10"' repre,1,cnts ten object~. The subscript
{IOinthisexample) indic;itcsit isalwfc JO.or
decimal. number. U~ing ~uthcripl\, thc number
10, reprerent.~ two objects since this is in binary
(bi11e 2). Again u~ing suhscripls. the number
jcct~·!
The self-tests can either help students
identify areas that need further study or
serve as positive reinforcement for material
that students already know. After completing
a self-test, students may check their answers
in the Answers to Self-Tests sections at the
end of each chapter.
in comerting a more cump!katcd m;J.:tterm
c\prcs,ion to it' m11nem1 form. Conver..ion~
twm maxt1:rm-to·111intern1 or minterm-to-ma,.
lt:rmforin,u'l!co111u1onlyumkrt;ikentogc1rid
of Jong overh:1r~ in the Buoleln c'p1c~,io11.
rhe new e:umple iJlu,trated in Fi!!. 4-46 will
change the ma~tern1 e:tprc ....,ion (A + 8 + (;} ·
(;r:;:s-+c) = Yto i1~ mime1m equivalent :md
dim111;uethelongoverbar.Carcful!yfollow1he
comer:.ion procc...., in Fi!!- 4-~. The re~u!t of
thhcun\Cr.>itJn)iclJ,th<: iuinccnu IU1mA B
C + A B -C = Y.
which p.:rfonm C:.'
(...l. + B + 0 = Y. The re~ulting
rnm1ermcxpres.,ioncanhewrmen inconven·
t\lmJJ form :1.~A B · C +A· fl. C= Yu,\n!!
O\'t:r!iJr:. or in !he 'h\lftcncd kcybourd vefliio~
ABC+ A'B·c = Yu.,ing Jt mu~t hc undcr~too
grnm< that ""ould hc wird U'>ing the maxtern1
!A+B + Cl
Aphotographic hls!ory of the computer One ot the first computers was the Eniac (upper felt), devel·
oped in the 1940s. The 1970s marked the expanded use of the computer by busmesses. The mainframe computer (uppernght) was the 100101 the time. Jn the 1980s persona! computers such as the
Apple l!e (lower left) brought computers intn our homes and sehools. Today, perS-Onal computers can
goanywtiere,aslaptopcomputers(lowertighl}increaselnpopu!arity
if~~~~~~~!Jf~:2L. __________... -·~-AChanging Acid. E!ei:tmn!cs Is among Ille most exciting
a comhinati{ln of both. The to::chniciims
lxritd
weekly. lnterestiogly, m-OSt dtwelopments are based on the
fundamentals !earned in the first classes in elettrlcity, :ma1og
Why Use Digital Circuits?
Electronic~ Ue,ignct'i and technicians must
huvc a v.mldng knowledge of both analog and
digital \Y~tem~. The de~igncr mint
Digital Circuitry: Advontoges
and limitotions
ror
Some of the :idvanwgc\
u~ing dii;'1tal cir·
cuitry lnJ.!ead of anal0<,; arc nJ. !bllow':
l
J.
4.
5.
6
lnexpcn~ive IC~ can be u:-cd with few
extcrn;ilcomponent.\.
lnfounaci,1ncanbc\torcdfor,hort
pt!rioclsorinJelinitdy
Darn can he u~ for prt:cbe t:a!cubtion'
Systems can be de~igned more e:i..-ily
u,Jng conipaiihk digital logic familie.~
Systems cm1 be programmed and ~how
Mime manrr.:r ol "intclllgencc"
Al?hnnumeric,picture,and video
Electronics
George Boole was tiom 10 Lir;;:oln,
Eru]!and. on November 2, 1815.
He was a seU-taught matflemaucran wtc invented mooem
symbolic klgic and pioneered
thecaJculvsofaperat0
1850, Ge
thetheoryoflogrc.
;1
=~~~~ci~~~~,computertec
History of
mu~t
prototype (1r troublc)horJI and rcp;iir
digital. analog:, nnd combined ~y~tcm-..
Anulogd.:1111111ic 11·1t<:m\ haw been popular
in the ~1 ,1. Okkr TV>. telephones. and auiomo·
:ire as of technical s!udy. New developments are reported
~
in ~omc milit;iry applications such as tire con·
tro!oo.\hip.>.
Mo)t rcal·wnrld inforrnulion is mw/og in
nature. NJtural phenomena, ~uch a.> time,
temperature. lrnmidicy. wind ~peed. r;idiation. ani.J sound inten,ity. :ire :ma lug in nature
You proh;ib!y have ;ilrc;idy mea$1ircd voltage,
7. Digi1al dri:uib are !c~' uffix:ied by unwanted
de<.:uic:1tinteikn::ocet":l!b.J11(1i1e
connections encourage students to
do online research on certain topics.
~--;.:..-Internet
8. Suchcircuitsarecompaub!ewith the
lmern1:tnn
The limi/(/f/flll\ oj diir;1tal cirnii11y are
The features History of Electronics and
About Electronics add depth to the topics and
highlight new and interesting technologies or
facts.
:I.\
follow~:
! Mo.'l
re~!-WDfld
ewnl\ are ~na!n•3" in nature.
2 An;i!og pnlee~sing h U\u;1!!y 'impler and
fa.-ier.
Digital circuic~ a1e ;ipp.::aring in rnurc and
product.~ primarily bec;iu~ of low-co~t.
reliable digital JC~. Other n:a~on' for their
growing popularity arc ac1:uracy. added \tll·
hilitv. comouler commuibilitv. mcmocv, ea;.c
more
Critical facts and principles are reviewed in
the Summary and Review section at the end
of each chapter.
Chapter l Summary and Review
L Analog signals vary gradually and continuou~ly.
while digital ... ignah produce dhcrete \·oltngt:
lcveh commouly refcned to a\ HIGH and LOW.
2. Mo-.t modern electronic equipment contain.\ both
analoganddigitalcircuilry
3. Logic tcve!sJrediffen:nt forvariou,digital logic
fnmilics, such as 1TL and CMOS. These logic
lcvt'b an:: t'Qmmonly referred to as HIGH, LOW.
and undefined Figure 1-20 Uewih the;.c TIL nnd
6_
7
Digilalclectrooicsi~ a huge 3nd rapidly e.,p:in
ihelrn:lhoncofthe fnh:met
Bbt'1.ble, mono,1ah!c, 30d a.~table rnultivibrntors
Jn: ut.ed 10 !;!enerate digital ~ignah. Thc\C are
MHnctune~ca11ed la1che.~.onc·~ho1, ;ind Cree·
runningmultivibr.ito1Ji,rt:~peetively
8. Logic kvd indic:m}fs may toke the tv1m of ~imp!e
LE.D ;ind ~i,tor drcuits, ~ollmrten, or logic probes
f11181818181D!mR!E!llBRl:ll•••••1""'1-----!f- Chapter review questions are found at the end of
each chapter, as are critical thinking questions.
2-J I. Convert the bin;uy number.. in a to d 10
hexadecimal uumlx:r~:
OIOI !!JO
b. 00011!1 I
3.
c. 1101!01 I
d. 001 [()(XX)
2·12. Hexadecimal JE6""'
2-13. Decimal 4095 "" _ _ _ "
2-14. Octal 156
2-15. Decimal 391
2-16. A~lngleOor I
[bit, word).
2-17. An 8-bit g1oupof h:ind Os. which reprc::cm~;i
number. letter, or op code, b commonly cJIJed a
_ _ _ fbyte.nihbkJ.
= ___ ,,,
2-1. !(the digital circuiL~ in a computer only respond
to tiinary nuinher.;, why are ocrnl an
2-2. Jn a digital sy~tem .,uch a.' a mlCH\COmP'Jler, it
is common to consider an S-bit l!roup (called
2·18 A
nibbleisatermthatdei:cribe~a
_ _ _ (4-bit, 12-btt)datagroup.
2· 19.
Mieroptoce~~or-h3..ed ~yMems {~uch a.~ a
pulef) commonly identify the size
com-
or o d;ua
gT0Up3~---(fi!e.WOfd)!ength.
2·20. To encrypt data from a readable form (~uch
a~ alphanumeric) to m:ichinc code u.<.able by
digital r:in:uits is called _ _ _ (encoding,
interr~ing)
2-4. Al the op¢ ion of your instructor, U!>C circuit
slmu!;itioo ..art ware to (a) draw the logic dia·
gram of the binary-to-
(el dcrnonsuate the bin:iry·to-decirnal decoder
simufotiontoyourinstructor.
Walkthrough
XIII
bout the
Over several decades, Roger L. Tokheim has published
many textbooks and lab manuals in the areas of digital electronics and microprocessors. His books have
xiv
About the Author
uthor
been translated into nine languages. He taught technical
subjects including electronics for more than 35 years in
public schools.
Safety
Electric and electronic circuits can be dangerous. Safe
practices are necessary to prevent electrical shock, fires,
explosions, mechanical damage, and injuries resulting
from the improper use of tools.
Perhaps the greatest hazard is electrical shock. A current through the human body in excess of 10 milliamperes can paralyze the victim and make it impossible
to let go of a "live" conductor or component. Ten milliamperes is a rather small amount of current flow: It
is only ten one-thousandths of an ampere. An ordinary
flashlight can provide more than 100 times that amount
of current!
Flashlight cells and batteries are safe to handle because the resistance of human skin is normally high
enough to keep the current flow very small. For example, touching an ordinary 1.5-V cell produces a current
flow in the microampere range (a microampere is onemillionth of an ampere). The amount of current is too
small to be noticed.
High voltage, one the other hand, can force enough
current through the skin to produce a shock. If the current approaches 100 milliamperes or more, the shock can
be fatal. Thus, the danger of shock increases with voltage. Those who work with high voltage must be properly
trained and equipped.
When human skin is moist or cut, its resistance to the
flow of electricity can drop drastically. When this happens, even moderate voltages may cause a serious shock.
Experienced technicians know this, and they also know
that so-called low-voltage equipment may have a highvoltage section or two. In other words, they do not practice two methods of working with circuits: one for high
voltage and one for low voltage. They follow safe procedures at all times. They do not assume protective devices
are working. They do not assume a circuit is off even
though the switch is in the OFF position. They know the
switch could be defective.
Even a low-voltage, high-current-capacity system
like an automotive electrical system can be quite
dangerous. Short-circuiting such a system with a ring
or metal watchband can cause very severe burnsespecially when the ring or band welds to the points
being shorted.
As your knowledge and experience grow, you will
learn many specific safe procedures for dealing with electricity and electronics. In the meantime:
1. Always follow procedures.
2. Use service manuals as often as possible. They
often contain specific safety information. Read, and
comply with, all appropriate material safety data
sheets.
3. Investigate before you act.
4. When in doubt, do not act. Ask your instructor or
supervisor.
General Safety Rules for Electricity
and Electronics
Safe practices will protect you and your fellow workers.
Study the following rules. Discuss them with others, and
ask your instructor about any you do not understand.
1. Do not work when you are tired or taking medicine
that makes you drowsy.
2. Do not work in poor light.
3. Do not work in damp areas or with wet shoes or
clothing.
4. Use approved tools, equipment, and protective
devices.
5. Avoid wearing rings, bracelets, and similar metal
items when working around exposed electric
circuits.
6. Never assume that a circuit is off. Double-check it
with an instrument that you are sure is operational.
7. Some situations require a "buddy system" to guarantee that power will not be turned on while a technician is still working on a circuit.
8. Never tamper with or try to override safety devices
such as an interlock (a type of switch that automatically removes power when a door is opened or a
panel removed).
9. Keep tools and test equipment clean and in good
working condition. Replace insulated probes and
leads at the first sign of deterioration.
10. Some devices, such as capacitors, can store a lethal
charge. They may store this charge for long periods
Safety
xv
11.
12.
13.
14.
of time. You must be certain these devices are discharged before working around them.
Do not remove grounds and do note use adaptors
that defeat the equipment ground.
Use only an approved fire extinguisher for electrical
and electronic equipment. Water can conduct electricity and may severely damage equipment. Carbon
dioxide (C0 2 ) or halogenated-type extinguishers
are usually preferred. Form-type extinguishers may
also be desired in some cases. Commercial fire extinguishers are rated for the type of fires for which
they are effective. Use only those rated for the
proper working conditions.
Follow directions when using solvents and other
chemicals. They may be toxic, flammable, or may
damage certain materials such as plastics. Always
read and follow the appropriate material safety data
sheets.
A few materials used in electronic equipment are
toxic. Examples include tantalum capacitors and beryllium oxide transistor cases. These devices should
not be crushed or abraded, and you should wash
your hands thoroughly after handling them. Other
materials (such as heat shrink tubing) may produce
15.
16.
17.
18.
19.
irritating fumes if overheated. Always read and follow the appropriate material safety data sheets.
Certain circuit components affect the safe performance of equipment and systems. Use only exact or
approved replacement parts.
Use protective clothing and safety glasses when
handling high-vacuum devices such as picture tubes
and cathode-ray tubes.
Don't work on equipment before your know proper
procedures and area aware of any potential safety
hazards.
Many accidents have been caused by people rushing and cutting corners. Take the time required to
protect yourself and others. Running, horseplay, and
practical jokes are strictly forbidden in shops and
laboratories.
Never look directly into light-emitting diodes or
fiber-optic cables; some light sources, although invisible, can cause serious eye damage.
Circuits and equipment must be treated with respect.
Learn how they work and the proper way of working on
them. Always practice safety: your health and life depend
on it.
Electronics workers use specialized safety knowledge.
xvi
Safety
Digital Electronics
learning Outcomes
This chapter will help you to:
1-1
1-2
1-3
1-4
1-5
1-6
Identify several characteristics of digital
circuits as opposed to analog circuits.
Differentiate between digital and analog
signals, and identify the HIGH and LOW
portions of a digital waveform.
Classify the signals (analog or digital) in
several application circuits. Analyze the
operation of several liquid-measuring
circuits. Explain why converting analog
inputs (currents and voltages) from sensors
to digital form can be useful.
List several common pieces of electronic
gear that contain digital circuitry. Discuss
the demand for computer and electronics
technicians, and identify training
opportunities.
List three types of multivibrators, and
describe how they generate types of digital
signals. Analyze several multivibrator and
switch debouncing circuits.
Analyze several logic-level indicator
circuits. Interpret logic probe readings
during testing of a digital circuit.
Understand the definitions of HIGH,
LOW, and undefined when observing logic
levels in both TIL and CMOS digital
circuitry.
Demonstrate the use of several lab
instruments.
ngineers generally classify electronic
circuits as being either analog or digital in nature. Historically, most electronic
products contained analog circuitry. Most
newly designed electronic devices contain
digital circuitry. This chapter introduces
you to the world of digital electronics.
What are the clues that an electronic product contains digital circuitry? Signs that a
device contains digital circuitry include:
Identifying digital
products
1. Does it have a display that shows
numbers, letters, pictures, or video?
2. Does it have a memory or can it store
information?
3. Can the device be programmed?
4. Can it be connected to the Internet?
If the answer to any one of the four questions is yes, then the product probably contains digital circuitry.
Digital circuitry is quickly becoming
pervasive because of its advantages over
analog including:
1. Generally, digital circuits are easier
to design using modem integrated
circuits (ICs).
2. Information storage is easier to
implement with digital.
3. Devices can be made programmable
with digital.
4. More accuracy and precision are
possible.
5. Digital circuitry is less affected by
unwanted electrical interference called
noise.
All persons working in electronics must
have knowledge of digital electronic circuits. You will use simple integrated circuits
and displays to demonstrate the principles
of digital electronics.
Advantages af
digital
1-1
Analog signal
Volt-ohm-millimeter
HIGH and LOW
signals
Digital multimeter
Digital circuits
2
AJ
V\Jhat Is a Digital Signal?
In your experience with electricity and electronics you have probably used analog circuits. The
circuit in Fig. 1-l(a) puts out an analog signal
or voltage. As the wiper on the potentiometer is
moved upward, the voltage from points A to B
gradually increases. When the wiper is moved
downward, the voltage gradually decreases
from 5 to 0 volts (V). The waveform diagram
in Fig. 1-l(b) is a graph of the analog output. On
the left side the voltage from A to B is gradually
to 5 V; on the right side the voltacre
increasing
.
b
is gradually decreasing to 0 V. By stopping the
potentiometer wiper at any midpoint, we can
get an output voltage anywhere between O and
5 V. An analog device, then, is one that has a
signal which varies continuously in step with
the input.
A digital device operates with a digital signal.
Figure 1-2(a) pictures a square-wave generator.
The generator produces a square waveform that
is displayed on the oscilloscope. The digital signal is only at +5 V or at 0 V, as diagrammed in
Fig. l-2(b). The voltage at point A moves from
0 to 5 V. The voltage then stays at +5 V for a
time. At point B the voltage drops immediately
from +5 to 0 V. The voltage then stays at O V
for a time. Only two voltages are present in a
digital electronic circuit. In the waveform diagram in Fig. l-2(b) these voltages are labeled
HIGH and LOW The HIGH voltage is +5 V;
the LOW voltage is 0 V. Later we shall call the
HIGH voltage (+5 V) a logical 1 and the LOW
voltage (0 V) a logical 0. Circuits that handle
only HIGH and LOW signals are called digital
circuits.
The digital signal in Fig. 1-2(b) could also be
generated by a simple on-off switch. A digital
signal could also be generated by a transistor
turning on and off Digital electronic signals
are usually generated and processed by integrated circuits (ICs).
Both analog and digital signals are represented in graph form in Figs. 1-1 and 1-2. A
signal can be defined as useful information
transmitted within, to, or from electronic circuits. Signals are commonly represented as
a voltage varying with time, as they are in
Figs. 1-1 and 1-2. However, a signal could be
an electric current that either varies continuously (analog) or has an on-off (HIGH-LOW)
Chapter 1 Digital Electronics
-r\ .
+
sv-=...
(a)
6
5
4
(/)
g3
Wiper
moving
up
2
Wiper
moving
down
(b)
1-1 (a) Analog output from a potentiometer.
(b) Analog signal waveform.
characteristic (digital). Within most digital
circuits, it is customary to represent signals
in the voltage versus time format. When
digital circuits are interfaced with nondigital devices such as lamps and motors, then
the signal can be thought of as current versus
time.
The standard volt-ohm-millimeter (VOM)
shown in Fig. l-3(a) is an example of an analog measuring device. As the voltage, resistance, or current being measured by the VOM
increases, the needle gradually and continuously moves up the scale. A digital multimeter
(DMM) is shown in Fig. 1-3(b). This is an example of a digital measuring device. As the
8
Square-wave
1---_____,a
generator
(a)
~J
B
I
A
HIGH
I I I
Time
(b)
·1-2 (a) Digital signal displayed on scope.
(b) Digital signal waveform.
LOW
(a)
(b)
(a) Analog meter. (6) Digital multimeter (DMM). Courtesy Fluke Corporation. Reproduced with permission
current, resistance, or voltage being measured
by the DMM increases, the display jumps upward in small steps. The DMM is an example
of digital circuitry taking over tasks previously
Supply the missing word in each statement.
1. Refer to Fig. 1-2. The + 5-V level of the
_ _ _ _ (analog, digital) signal could
also be called a logical 1 or a _ _ __
(HIGH, LOW).
2. A(n)
(analog, digital) device
is one that has a signal which varies continuously in step with the input.
performed only by analog devices. This trend
toward digital circuitry is growing. Currently,
the modern technician's bench probably has
both a VOM and a DMM.
3. Refer to Fig. 1-4. The input to the
electronic block is classified as a(n)
_ _ _ _ (analog, digital) signal.
4. Refer to Fig. 1-4. The output from the
electronic block is classified as a(n)
_ _ _ _ (analog, digital) signal.
5. An analog circuit is one that processes
analog signals while a digital circuit
processes
signals.
INPUT
Lb-
Trend toward
digital circuitry
OUTPUT
Electronic
function
JL
Fig. 1-4 Block diagram of electronic circuit shaping a sine wave into a
square wave.
Digital Electronics
Chapter 1
3
History of
Electronics
A photographic history of the computer. One of the first computers was the Eniac (upper Jett), developed in the 1940s. The 1970s marked the expanded use of the computer by businesses. The mainframe computer (upper right) was the tool of the time. In the 1980s personal computers such as the
Apple lie (lower left) brought computers into our homes and schools. Today, personal computers can
go anywhere, as laptop computers (lower right) increase in popularity.
A Changing Field. Electronics is among the most exciting
areas of technical study. New developments are reported
weekly. Interestingly, most developments are based on the
fundamentals learned in the first classes in electricity, analog
and digital circuits, computer technology and robotics, and
communications.
1-2
l!1
Why Use Digital Circuits'?
Electronics designers and technicians must
have a working knowledge of both analog and
digital systems. The designer must decide if the
system will use analog or digital techniques or
4
Chapter 1 Digital Electronics
a combination of both. The technicians must
build a prototype or troubleshoot and repair
digital, analog, and combined systems.
Analog electronic systems have been popular
in the past. Older TVs, telephones, and automobiles featured analog circuits. Before modern
digital computers, analog computers were used
in some military applications such as fire control on ships.
Most real-world information is analog in
nature. Natural phenomena, such as time,
temperature, humidity, wind speed, radiation, and sound intensity, are analog in nature.
You probably have already measured voltage,
current, resistance, power, capacitance, inductance, and frequency in other electricity and
electronics courses. Other things to be measured include pressure, weight, oxygen (and
other gases), ultrasonic sound, acceleration
and tilt, vibration, direction (compass), global
positioning, proximity, magnetic fields, linear
distance, and angle of rotation (angular speed).
They are all analog in nature. Engineers and
technicians commonly use sensors to measure
these things. Many sensors emit an analog
signal.
A simple analog electronic system for measuring the amount of liquid in a tank is illustrated in Fig. 1-5. The input to the system is a
varying resistance. The processing proceeds
according to the Ohm's law formula, I = V/ R.
The output indicator is an ammeter which is
calibrated as a water tank gauge. In the analog
system in Fig. 1-5 as the water rises, the input
resistance drops. Decreasing the resistance R
causes an increase in current (/). Increased current causes the ammeter (water tank gauge) to
read higher.
The analog system in Fig. 1-5 is simple and
efficient. The gauge in Fig. 1-5 gives an indication of the water level in the tank. If more information is required about the water level, then a
digital system such as the one shown in Fig. 1-6
might be used.
Digital systems are required when data must
be stored, used for calculations, or displayed as
numbers and/or letters. A somewhat more complex arrangement for measuring the amount
of liquid in a water tank is the digital system
shown in Fig. 1-6. The input is still a variable
resistance as it was in the analog system. The
resistance is converted into numbers by the
analog-to-digital (AID) converter. The central
processing unit (CPU) of a computer can manipulate the input data, output the information,
store the information, calculate things such as
flow rates in and out, calculate the time until
the tank is full (or empty) based on flow rates,
and so forth. Digital systems are valuable when
calculations, data manipulations, data storage,
and alphanumeric or video outputs are required.
Data transfers via the Internet are common.
Analog-ta-digital
(A/D) converter
Central processing
unit (CPU)
Water tank
Analog
INPUT
Analog
PROCESSING
%
Analog
OUTPUT
1= .!::'._ (constant)
R
Fig. 1-S Analog system used to interpret float level in water tank
STORAGE
(memory)
Water tank
Analog
~
Digital
INPUT
AID
converter
PROCESSING
CPU
and
memory
I
OUTPUT
I
CRT or
other digital display
Fig. Hi Digital system used to interpret float level in water tank
Digital Electronics
Chapter 1
5
Application: Automobile
Fuel Indicators
shown in Fig. l-7(b), the instrumentation computer
module calculates the average-fuel-consumption
and miles-to-empty data. The driver sees this
information displayed on an LCD screen.
It will be noted that information from the
sensors in Fig. l-7(b) comes in various forms.
The fuel tank sending unit delivers a variablevoltage signal to the computer module. With
higher levels of fuel in the tank the sending unit
generates a higher positive voltage.
The vehicle speed sensor sends a variablefrequency signal. At lower vehicle speeds the
sensor emits a low-frequency signal. At higher
speeds a high-frequency signal is sent to the
computer module.
The engine control module sends several
digital signals to the instrument control module. The engine control module determines how
much fuel is injected into the cylinders of the
engine and the timing.
Older automobile circuitry was analog in nature. Consider the traditional fuel gauge system
sketched in Fig. l-7(a). The fuel tank sending unit
has a float that moves a wiper on a resistive material. Increasing the fuel level in the tank raises
the float, causing the wiper to move left on the
resistor. The resistor's value decreases. Decreased
circuit resistance causes an increase in current in
the series circuit (via Ohm's law, I= V/ R). The increased current causes the needle on the fuel gauge
(an ammeter) to move clockwise toward F on the
meter face. The older-style fuel gauge diagram in
Fig. l-7(a) is an example of an analog circuit.
Newer automobiles may use the information
from the fuel tank sending unit for several purposes. Figure l-7(b) shows the analog voltage
from the fuel tank sending unit entering the instrument panel module. The computer module
converts the analog input to digital information
(AID converter). The computer module also receives signals from the vehicle speed sensor,
engine control module (ECM). The input information is processed by the computer module. The instrument control module will drive
a traditional-looking fuel gauge located on the
instrument panel. A tachometer is probably also
located on the instrument panel. With the inputs
+12 v
Variable
resistor
Fuel tank
sending unit
I
I
.----4111'
~.I
/'/' I
f
I
rL~ ~~+-'--T-=----11-------'
...J~ ~ ,
; ( - !) Float
(a)
Fuel tank
sending unit
~
resistor
OUTPUTS
£~-=cRi,f=-J
·I . :.~.-.
I
Instrument
panel
.%.··.
·.·.
~.··~
0
LCD dash
display
INPUTS
Float -
Vehicle speed
sensor
Engine
control
module
(ECM)
(b)
Fig. 1-7 [al. A~tomobile fuel tank sending unit and fuel gauge. (b) Modern automobile fuel
1nd1cator system with computer module.
Ei
Chapter 1 Digital Electronics
Fuel gauge
(ammeter)
Automobile fuel tank
t"
Variable
+12V
1------1
Digital Circuitry: Advantages
and limitations
Some of the advantages for using digital circuitry instead of analog are as follows:
1. Inexpensive ICs can be used with few
2.
3.
4.
5.
6.
external components.
Information can be stored for short
periods or indefinitely.
Data can be used for precise calculations.
Systems can be designed more easily
using compatible digital logic families.
Systems can be programmed and show
some manner of "intelligence."
Alphanumeric, picture, and video
information can be viewed using a variety
of electronic displays.
Answer the following questions.
6. Generally, electronic circuits are classified as either analog o r - - - 7. Measurements of time, speed, weight,
pressure, light intensity, and position are
_ _ _ _ (analog, digital) in nature.
8. Refer to Fig. 1-5. As the water level
drops, the input resistance increases.
This causes the current I to - - - (decrease, increase) and the water level
gauge (ammeter) will read---(higher, lower).
9. Refer to Figs. 1-5 and 1-6. If this water
tank were part of the city water system,
where rates of water use are important,
the system in Fig.
(1-5, 1-6)
would be most appropriate.
1-3
Where Are Digital Circuits
Used'?
Digital electronics is a huge and rapidly expanding field. The global system of interconnected computer networks called the Internet
serves billions of users. Digital computers, in
7. Digital circuits are less affected by unwanted
electrical interference called noise.
8. Such circuits are compatible with the
Internet and computers.
The limitations of digital circuitry are as
follows:
1. Most real-world events are analog in nature.
2. Analog processing is usually simpler and
faster.
Internet
Connection
Search the web for
the following terms:
fuel tank sending
unit, vehicle speed
sensor. and engine
control module.
Digital circuits are appearing in more and
more products primarily because of low-cost,
reliable digital ICs. Other reasons for their
growing popularity are accuracy, added stability, computer compatibility, memory, ease
of use, simplicity of design, and compatibility
with a variety of displays.
10. True or false. The most important reason why digital circuitry is becoming
more popular is that digital circuits are
usually simpler and faster than analog
circuits.
11. Refer to Fig. 1-7(a). This traditional auto
fuel tank gauge assembly that senses and
indicates the fuel level is an example of
a(n)
(analog, digital) circuit.
12. Refer to Fig. l-7(b). The input voltage
from the fuel tank sending unit is a digital signal before it enters the instrument
panel module. (T or F)
13. Refer to Fig. l-7(b). The input from the
enaine
control module (ECM) having to
I:>
do with fuel flow and time is _ _ __
(analog, digital) in nature.
all their forms, serve as the backbone of the
Internet. The Internet consists of academic,
business, private, and government networks.
The Internet allows users to access huge
amounts of information using the World Wide
Web (WWW). The Internet also supports twoway communications with e-mail and social
Digital Electronics
Chapter 1
7
networking sites including Facebook. Huge
amounts of data are transferred via the Internet
by banks, manufacturers, the military, medical professions, security companies, governments, and businesses. The global economy
could hardly survive without the capabilities
of digital computers, huge memory banks, and
the Internet.
Millions of individual electronic devices
must be designed, manufactured, tested, and
repaired by technicians. Electronics technicians and engineers are in great demand. A
few applications of digital electronics are suggested by the images on the tablet sketched in
Fig. 1-8.
Laptops
Desktop
Tablets
iPhone
Auto electronics
Avionics
Automation
Cameras
Robots
TV-DVD
Instrumentation
Gaming
Financial
Security
GPS
Publishing
Internet
Search
Digital clock
Fig. 1-8 Applications of digital electronics.
B
Chapter 1 Digital Electronics
Jobs for technicians are available with most
high-technology businesses. Many government jobs call for some skills in computer
technology including electronics. Highly
skilled technicians work on extremely sophisticated military electronics. It is reported that
the half the cost of some military aircraft is
electronics in nature. The military has many
outstanding advanced electronics training
programs. Ask about these when you visit a
military recruiter.
The driving experience of a modern automobile has been greatly enhanced by electronics. Automobile engines have more power, run
smoother, and use less fuel due to precise electronic engine control. More automobiles contain entertainment systems that are outstanding.
Bluetooth for cell phones, GPS, and touch
screen displays are common. Assisted parking
and blind spot detection are standard on many
autos. Safety features like antiskid and traction
and stability control systems depend digital
electronics. Ask your school counselor about
opportunities in your area.
To cut down on thefts, the key to your automobile may contain a transmitter whose signal is picked up by a transponder ECM. The
transponder reads the wireless signal from the
key, allowing the engine to start. Some modern automobiles have more than 50 electronic
control modules (computers). Auto mechanics must be trained in modern electricity and
electronics. Check with your area technical
college to survey training openings. Auto
manufacturers also run outstanding training
classes.
Most measuring instruments you may use
at work in the lab will contain digital circuitry.
These might include a logic probe, digital multimeter (DMM), capacitance meter, frequency
counter, function generator (signal generator),
and programmable power supply. Modern
oscilloscopes may also feature some digital
circuitry.
Many hands-on lab activities will be provided. A updated Experiments Manual for
Digital Electronics is available that presents many hands-on lab activities chapter by
chapter.
Answer the following questions.
14. List at least four devices that use digital
circuitry.
15. Computer and electronics technicians are
in great demand. (T or F)
16. The military has excellent electronics
training schools. (T or F)
How Do You Generate a
Digital Signal'?
Digital signals are composed of two welldefined voltage levels. Most of the voltage
levels used in this class will be about + 3 V to
+5 V for HIGH and near 0 V (GND) for LOW.
These are commonly called TTL voltage levels because they are used with the transistortransistor logic family of ICs.
Generating a Digital Signal
A TTL digital signal could be made manually
by using a mechanical switch. Consider the
simple circuit shown in Fig. l-9(a). As the blade
of the single-pole, double-throw (SPOT) switch
is moved up and down, it produces the digital
waveform shown at the right. At time period t1,
the voltage is 0 V, or LOW. At t 2 the voltage is
+5 V, or HIGH. At t 3 , the voltage is again 0 V,
or LOW, and at t4 , it is again +5 V, or HIGH.
The action of the switch causing the LOW,
HIGH, LOW, HIGH waveform in Fig. 1-9(a)
is called toggling. By definition, to toggle (the
verb) means to switch over to an opposite state.
As an example in Fig. 1-9(a), if the switch moves
from LOW to HIGH we say the output has toggled. Again if the switch moves from HIGH to
LOW we say the output has again toggled.
One problem with a mechanical switch is
contact bounce. If we could look very carefully at a switch toggling from LOW to HIGH,
it might look like the waveform in Fig. 1-9(b).
The waveform first goes directly from LOW to
17. All auto mechanics that are specialists in
electronics are self-taught. (T or F)
18. List at least two measuring instruments
you will use as a technician and that
contain digital circuitry.
HIGH (see point A) but then, because of contact bounce, drops to LOW (see point B) and
then back to HIGH again. Although this happens in a very short time, digital circuits are
fast enough to see this as a LOW, HIGH, LOW,
HIGH waveform. Note that Fig. 1-9(b) shows
that there is actually a range of voltages that are
defined HIGH and LOW. The undefined region
between HIGH and LOW may cause trouble in
digital circuits and should be avoided.
To cure the problem illustrated in Fig. l-9(b),
mechanical switches are sometimes debounced.
A block diagram of a debounced logic switch is
shown in Fig. 1-9(c). Note the use of the debouncing circuit, or latch. Some of the mechanical logic
switches you will use on laboratory equipment
will have been debounced with latch circuits.
Latches are sometimes called flip-flops. Notice
in Fig. 1-9(c) that the output of the latch during
time period t 1 is LOW but not quite 0 V. During
t 2 the output of the latch is HIGH even though it
is something less than a full +5 V. Likewise t3 is
LOW and t4 is HIGH in Fig. 1-9(c).
It might be suggested that a push-button switch
be used to make a digital signal. If the button
is pressed, a HIGH should be generated. If the
push button is released, a LOW should be generated. Consider the simple circuit in Fig. 1-IO(a).
When the push button is pressed, a HIGH of
about +5 V is generated at the output. When the
push button is released, however, the voltage at
the output is undefined. There is an open circuit
between the power supply and the output. This
would not work properly as a logic switch.
Digital Electronics
TTL voltage levels
Transistor·
transistor lagic
Debaunced lagic
switch
Digital waveform
Latch (flip-flap)
Contact bounce
Chapter 1
9
