Real World Instrumentation with Python: Automated Data Acquisition and Control Systems

622 Pages·2010·9.88 MB·English

by  John M. Hughes

Real World Instrumentation with Python

Real World Instrumentation
with Python
J. M. Hughes
Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo
Real World Instrumentation with Python
by J. M. Hughes
Copyright © 2011 John M. Hughes. All rights reserved.
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November 2010: First Edition.
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ISBN: 978-0-596-80956-0
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Table of Contents
Preface .................................................................... xiii
1. Introduction to Instrumentation .......................................... 1
Data Acquisition 2
Control Output 4
Open-Loop Control 5
Closed-Loop Control 6
Sequential Control 9
Applications Overview 9
Electronics Test Instrumentation 9
Laboratory Instrumentation 11
Process Control 13
Summary 13
2. Essential Electronics .................................................... 15
Electrical Charge 15
Electric Current 17
Basic Circuit Theory 19
Circuit Schematics 20
DC Circuit Characteristics 24
Ohm’s Law 25
Sinking and Sourcing 27
More About Resistors 27
AC Circuits 30
Sine Waves 30
Capacitors 32
Inductors 36
Other Waveforms: Square, Ramp, Triangle, Pulse 38
Interfaces 39
Discrete Digital I/O 40
Analog I/O 44
v
Counters and Timers 49
PWM 50
Serial I/O 51
Parallel I/O 54
Summary 55
Suggested Reading 56
3. The Python Programming Language ...................................... 59
Installing Python 60
The Python Programming Language 61
The Python Command Line 61
Command-Line Options and Environment 63
Objects in Python 64
Data Types in Python 65
Expressions 77
Operators 78
Statements 84
Strings 91
Program Organization 96
Importing Modules 106
Loading and Running a Python Program 108
Basic Input and Output 110
Hints and Tips 115
Python Development Tools 117
Editors and IDEs 117
Debuggers 120
Summary 120
Suggested Reading 120
4. The C Programming Language .......................................... 123
Installing C 123
Developing Software in C 124
A Simple C Program 125
Preprocessor Directives 128
Standard Data Types 132
User-Defined Types 133
Operators 134
Expressions 143
Statements 143
Arrays and Pointers 150
Structures 153
Functions 156
The Standard Library 158
vi | Table of Contents
Building C Programs 159
C Language Wrap-Up 163
C Development Tools 163
Summary 164
Suggested Reading 164
5. Python Extensions .................................................... 167
Creating Python Extensions in C 168
Python’s C Extension API 169
Extension Source Module Organization 169
Python API Types and Functions 171
The Method Table 172
Method Flags 172
Passing Data 174
Using the Python C Extension API 175
Generic Discrete I/O API 175
Generic Wrapper Example 178
Calling the Extension 181
Python’s ctypes Foreign Function Library 184
Loading External DLLs with ctypes 184
Basic Data Types in ctypes 186
Using ctypes 187
Summary 188
Suggested Reading 188
6. Hardware: Tools and Supplies ........................................... 189
The Essentials 189
Hand Tools 190
Digital Multimeter 192
Soldering Tools 195
Nice-to-Have Tools 197
Advanced Tools 198
The Oscilloscope 198
Logic Analyzers 199
Test Equipment Caveats 202
Supplies 203
New Versus Used 204
Summary 204
Suggested Reading 205
7. Physical Interfaces .................................................... 207
Connectors 208
DB-Type Connectors 208
Table of Contents | vii
USB Connectors 210
Circular Connectors 212
Terminal Blocks 213
Wiring 215
Connector Failures 218
Serial Interfaces 218
RS-232/EIA-232 219
RS-485/EIA-485 225
USB 231
Windows Virtual Serial Ports 235
GPIB/IEEE-488 237
GPIB/IEEE-488 Signals 238
GPIB Connections 239
GPIB via USB 239
PC Bus Interface Hardware 241
Pros and Cons of Bus-Based Interfaces 242
Data Acquisition Cards 244
GPIB Interface Cards 244
Old Doesn’t Mean Bad 245
Summary 246
Suggested Reading 246
8. Getting Started ....................................................... 249
Defining the Project 250
Requirements-Driven Design 251
Stating the Need 252
Project Objectives 253
Requirements 253
Why Requirements Matter 255
Well-Formed Requirements 256
The Big Picture 257
Requirement Types 257
Use Cases 258
Traceability 261
Capturing Requirements 264
Designing the Software 265
The Software Design Description 265
Graphics in the SDD 266
Pseudocode 270
Divide and Conquer 270
Handling Errors and Faults 272
Functional Testing 273
Testing to the Requirements 274
viii | Table of Contents