Analog Interfacing to Embedded Microprocessor Systems

335 Pages·2004·2.08 MB·English

by  Stuart Ball

Analog Interfacing to Embedded
Microprocessor Systems

Analog Interfacing to Embedded
Microprocessor Systems
Stuart R. Ball
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LibraryofCongressCataloging-in-PublicationData
Ball,StuartR.,1956–
Analoginterfacingtoembeddedmicroprocessorsystems/StuartR.Ball.—2nded.
p. cm.—(Embeddedtechnologyseries)
Rev.ed.of:Analoginter-facingtoembeddedmicroprocessors.2001.
Includesindex.
ISBN0-7506-7723-6
1. Embeddedcomputersystems—Designandconstruction. I.Ball,StuartR.,1956-
Analoginter-facingtoembeddedmicroprocessors.II.Title.III.Series.
TK7895.E42B332003
004.16—dc21 2003044211
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Contents
1 System Design 1
Dynamic Range 1
Calibration 2
Bandwidth 5
ProcessorThroughput 6
Avoiding Excess Speed 7
Other System Considerations 8
Sample Rate and Aliasing 11
2 Analog-to-Digital Converters 13
ADCs 15
Types of ADCs 17
ADC Comparison 25
Sample and Hold 26
Real Parts 29
MicroprocessorInterfacing 30
Clocked Interfaces 35
Serial Interfaces 36
MultichannelADCs 41
Internal Microcontroller ADCs 42
Codecs 43
Interrupt Rates 44
Dual-Function Pins on Microcontrollers 44
Design Checklist 46
v
3 Sensors 47
TemperatureSensors 47
Optical Sensors 59
CCDs 71
MagneticSensors 82
Motion/Acceleration Sensors 86
Strain Gauges 89
4 Time-Based Measurements 91
MeasuringPeriodversus Frequency 94
Mixing 96
Voltage-to-Frequency Converters 98
Clock Resolution and Range 100
Extending Accuracy with Limited Resolution 102
5 OutputControl Methods 107
Open-Loop Control 107
Negative Feedback and Control 107
Microprocessor-Based Systems 108
On-Off Control 109
Overshoot 112
Proportional Control 112
Proportional, Integral, Derivative Control 116
Motor Control 127
Predictive Control 133
Measuringand Analyzing Control Loops 134
PID Software Examples 138
Things toRemember in Control Design 143
6 Solenoids, Relays, and OtherAnalog Outputs 145
Solenoids 145
Heaters 149
Coolers 155
LEDs 157
DACs 162
Digital Potentiometers 163
Analog Switches 166
vi Contents
7 Motors 171
Stepper Motors 171
DC Motors 190
Tradeoffs between Motors 206
Power-Up Issues 207
Motor Torque 208
A Real-World StepperApplication 209
8 Electromagnetic Interference 215
Ground Loops 215
Electrostatic Discharge 220
9 High-Precision Applications 225
Input Offset Voltage 227
Input Resistance 228
FrequencyCharacteristics 229
Temperature Effects in Resistors 230
Voltage References 231
Temperature Effects in General 233
Noise and Grounding 234
Printed CircuitBoard Layout 236
Statistical Tolerancing 239
Supply-Based References 240
Summary 241
10 StandardInterfaces 243
IEEE 1451.2 243
4–20 ma Current Loop 244
Fieldbus 245
11 Analog Toolbox 247
Microcontroller Supply and Reference 247
ResistorNetworks 249
Multiple Input Control 250
ACControl 252
Voltage Monitorsand Supervisory Circuits 254
Contents vii
Driving Bipolar Transistors 254
Driving MOSFETs 257
ReadingNegative Voltages 261
Example Control System 262
Appendix AOpamp Basics 275
Opamp Configurations 275
GeneralOpamp Design Equations 279
Nonresistive Elements 280
Reversing the Inputs 281
Comparators 281
Hysteresis 283
Instrumentation Amplifiers 285
Appendix BPulse Width Modulation 287
WhyPWM? 287
Real Parts 292
FrequencyLimitations 292
Resolution Limitations 293
Power-Supply Considerations 294
PWM and EMI 294
Audio Applications 295
PWM Hardware 296
PWM Software 297
Appendix CUsefulURLs 299
Semiconductors 299
Motors 299
Other 300
Appendix DPython Code for Chapter 11; 301
Excel Data for Chapter4
Glossary 307
Index 311
viii Contents
Preface
Thereoftenseemstobeadivisionbetweentheanaloganddigitalworlds.Digital
designers usually do not like to delve into analog, and analog designers tend to
avoid the digital realm. The two groups often do not even use the same buzz-
words.
Even though microprocessors have become increasingly faster and more cap-
able,therealworldremainsanaloginnature.Thedigitaldesignerswhoattempt
tocontrolormeasuretherealworldmustsomehowconnectthisanalogenviron-
ment to their digital machines. There are books about analog design and books
about microprocessor design. This book attempts to get at the issues involvedin
connecting the two together.
Someone said about my firstbook, Embedded Microprocessor Systems: Real World
Design,thatitneededmoreanaloginterfacinginformation.Ifeltthataddingthis
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 tomicroprocessors could provevaluable.Thisbookistheresult.Ihopeit
provesuseful.
ix