Analog Interfacing to the embedded Microprocessors

284 Pages·2004·3.53 MB·English

Analog Interfacing to Embedded
Microprocessors
Real World Design

Analog Interfacing to Embedded
Microprocessors
Real World Design
Stuart Ball
Boston Oxford Auckland Johannesburg Melbourne New Delhi
Newnes is an imprint of Butterworth–Heinemann.
Copyright © 2001 by Butterworth–Heinemann
A member of the Reed Elsevier group
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in
any form or by any means, electronic, mechanical, photocopying, recording, or otherwise,
without the prior written permission of the publisher.
Recognizing the importance of preserving what has been written, Butterworth–Heinemann
prints its books on acid-free paper whenever possible.
Library of Congress Cataloging-in-Publication Data
Ball, Stuart R., 1956–
Analog interfacing to embedded microprocessors : real world design / Stuart Ball.
p. cm.
ISBN 0-7506-7339-7 (pbk. : alk. paper)
1. Embedded computer systems—Design and construction. 2. Microprocessors.
I. Title.
TK7895.E42 .B33 2001
004.16—dc21 00-051961
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
The publisher offers special discounts on bulk orders of this book.
For information, please contact:
Manager of Special Sales
Butterworth-Heinemann
225 Wildwood Avenue
Woburn, MA 01801-2041
Tel: [phone]
Fax: [phone]
For information on all Newnes publications available, contact our World Wide Web home page
at: http://www.newnespress.com
10 9 8 7 6 5 4 3 2 1
Printed in the United States of America
Contents
Preface ix
Introduction xi
1 System Design 1
Dynamic Range 1
Calibration 2
Bandwidth 5
Processor Throughput 6
Avoiding Excess Speed 7
Other System Considerations 8
Sample Rate and Aliasing 11
2 Digital-to-Analog Converters 13
Analog-to-Digital Converters 15
Types of ADCs 17
Sample and Hold 26
Real Parts 29
Microprocessor Interfacing 30
Serial Interfaces 36
Multichannel ADCs 41
Internal Microcontroller ADCs 41
Codecs 42
Interrupt Rate 43
Dual-Function Pins on Microcontrollers 43
Design Checklist 45
v
3 Sensors 47
Temperature Sensors 47
Optical Sensors 59
CCDs 72
Magnetic Sensors 82
Motion/Acceleration Sensors 86
Strain Gauge 90
4 Time-Based Measurements 93
Measuring Period versus Frequency 95
Mixing 97
Voltage-to-Frequency Converters 99
Clock Resolution 102
5 Output Control Methods 103
Open-Loop Control 103
Negative Feedback and Control 103
Microprocessor-Based Systems 104
On-Off Control 105
Proportional Control 108
PID Control 110
Motor Control 123
Measuring and Analyzing Control Loops 130
6 Solenoids,Relays,and Other Analog Outputs 137
Solenoids 137
Heaters 143
Coolers 148
Fans 149
LEDs 151
7 Motors 161
Stepper Motors 161
DC Motors 180
Brushless DC Motors 184
Tradeoffs between Motors 198
Motor Torque 201
vi Contents
8 EMI 203
Ground Loops 203
ESD 208
9 High-Precision Applications 213
Input Offset Voltage 215
Input Resistance 216
Frequency Characteristics 217
Temperature Effects in Resistors 218
Voltage References 219
Temperature Effects in General 221
Noise and Grounding 222
Supply-Based References 227
10 Standard Interfaces 229
IEEE 1451.2 229
4-20 ma Current Loop 231
Appendix A:Opamp Basics 233
Four Opamp Configurations 233
General Opamp Design Equations 237
Reversing the Inputs 238
Comparators 239
Instrumentation Amplifiers 243
Appendix B:PWM 245
Why PWM? 245
Real Parts 250
Audio Applications 252
Appendix C:Some Useful URLs 255
Glossary 257
Index 261
Contents vii

Preface
There often seems to be a division between the analog and digital worlds.
Digital designers usually do not like to delve into analog, and analog design-
ers tend to avoid the digital realm. The two groups often do not even use the
same buzzwords.
Even though microprocessors have become increasingly faster and more
capable, the real world remains analog in nature. The digital designers who
attempt to control or measure the real world must somehow connect this
analog environment to their digital machines. There are books about analog
design and books about microprocessor design. This book attempts to get at
the problems encountered in connecting the two together.
This book came about because of a comment made by someone about my
first book (Embedded Microprocessor Systems: Real World Design): “it needs more
analog interfacing information.” I felt that adding this material to that book
would cause the book to lose focus. However, the more I thought about it,
the more I thought that a book aimed at interfacing the real world to micro-
processors could prove valuable. This book is the result. I hope it proves
useful.
ix