Circuit Cellar July 2010

Why Specifications Matter, p. 14 | X10 Controller Design, p. 28 | Hexapod Robot Development, p. 44 THE MAGAZINE FOR ...

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Why Specifications Matter, p. 14 | X10 Controller Design, p. 28 | Hexapod Robot Development, p. 44

THE

MAGAZINE

FOR

COMPUTER

A P P L I C AT I O N S July 2010 Issue 240

Ubuntu Webcam Server C Language Rules and Assignments

PLUS The Professional Method: Research, Design, Write, Then Repeat

USB and Standard Device Descriptors A Look at Powerline Communication Chips Wireless Data Transmission

$7.50 U.S. ($8.50 Canada)

www.circuitcellar.com Personal Download for [email protected] I © Circuit Cellar

SSH Encrypted SERIAL TO ETHERNET SOLUTIONS Instantly network-enable any serial device Works out of the box no programming is required

Device P/N: SB70LC-100CR Kit P/N: NNDK-SB70LC-KIT

$47

Qty. 1000

Customize to suit any application with low-cost development kit

SB70LC

256-bit encryption protects data from unauthorized monitoring

2-port serial-to-Ethernet server

Features: 10/100 Ethernet TCP/UDP/SSH/SSL modes DHCP/Static IP Support Data rates up to 921.6kbps Web-based configuration

Device P/N: SB700-EX-100CR Kit P/N: NNDK-SB700EX-KIT

SB700EX

2-port serial-to-Ethernet server with RS-232 & RS-485/422 support

$129 Qty. 1000

Need a custom solution? NetBurner Serial to Ethernet Development Kits are available to customize any aspect of operation including web pages, data filtering, or custom network applications. All kits include platform hardware, ANSI C/C++ compiler, TCP/IP stack, web server, email protocols, RTOS, flash file system, Eclipse IDE, debugger, cables and power supply. The NetBurner Security Suite option includes SSH v1 & v2 support.

Device P/N: CB34-EX-100IR Kit P/N: NNDK-CB34EX-KIT

$149 Qty. 1000

CB34EX

industrial temperature grade

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2-port serial-to-Ethernet server with RS-232 & RS-485/422 support and terminal block connector

Personal Download for [email protected] I © Circuit Cellar




T

ASK MANAGER

July 2010 – Issue 240

I

THE MAGAZINE FOR COMPUTER APPLICATIONS

Circuit Cellar: The Next Iteration

FOUNDER/EDITORIAL DIRECTOR Steve Ciarcia

PUBLISHER Hugo Vanhaecke

EDITOR-IN-CHIEF C. J. Abate

have noted here before that Circuit Cellar’s on-going mission is to educate professional engineers and academics so they may design the next generation of embedded applications and systems. This month marks an important step forward in our endeavor to provide exciting new content and need-to-know information. As you’ll see, we’re using all of our resources to deliver readers a new monthly column, an informative interview section, easier access to essential content, and more. Let’s move in chronological order. I don’t usually reference ads here, but check out page 7 for an example of a new product we developed after reviewing feedback from readers. It’s an 8-GB waterproof flash drive with every issue of Circuit Cellar and all the associated code. We call the flash drive “CC Gold.” It’s a great example of delivering today’s engineers what they require—in this case, a portable storage drive holding literally “everything Circuit Cellar” in one small package. And with gigs of space to spare, it’s a great place to store future issues and personal project files. Turn to page 8 to read our new “Questions & Answers” section. There you’ll find my recent interview with Jan Axelson, author of the often-referenced USB Complete and seven Circuit Cellar articles. After meeting Jan at the 2010 Embedded Systems Conference in San Jose, CA, it occurred to me that she would be the perfect first interviewee for this new section, which is dedicated to giving readers insight into how talented professionals achieved their success, cultivated their skills, and contributed to the computer applications industry. In future issues, we’ll present interviews with other notable engineers. After learning about Jan’s background and considering her ideas regarding the future of USB technology, check out George Novacek’s new column titled “The Consummate Engineer” (p. 14). The purpose of the column is to provide readers with tips on becoming more well-rounded practitioners of their trade. Sure, all of our readers are soldering and coding pros. But what separates a workaday engineer from a go-to guru is an understanding of “robust design.” In this column, George will touch on topics such as proper spec development, system hazard analysis, reliability analysis, and more. With a background in engineering and management, George is an excellent resource for readers looking to take their designs and careers to the next level. The rest of the issue touches on some of the most intriguing subjects in the field of computer applications. Examples include server development (p. 16), mobile robotics (p. 44), and data transmission (Bluetooth on p. 36 and powerline communication on p. 66). Lastly, keep in mind that we are constantly updating and upgrading our digital magazine and website in an effort to meet our readers’ rapidly changing needs. Be assured: if you want it, we’ll deliver. Stay tuned. [email protected]

ASSOCIATE PUBLISHER Shannon Barraclough

WEST COAST EDITOR Tom Cantrell

CUSTOMER SERVICE Debbie Lavoie

CONTRIBUTING EDITORS Jeff Bachiochi Robert Lacoste George Martin Ed Nisley

CONTROLLER Jeff Yanco ART DIRECTOR KC Prescott GRAPHIC DESIGNERS Grace Chen Carey Penney

NEW PRODUCTS EDITOR John Gorsky PROJECT EDITORS Ken Davidson David Tweed

STAFF ENGINEER John Gorsky

ADVERTISING 800.454.3741 • 978.281.7708 • www.circuitcellar.com/advertise ADVERTISING REPRESENTATIVE Peter Wostrel Strategic Media Marketing, Inc. 1187 Washington St., Gloucester, MA 01930 USA 800.454.3741 • 978.281.7708 [email protected] • www.smmarketing.us Fax: 978.281.7706 ADVERTISING COORDINATOR Valerie Luster E-mail: [email protected] Cover photography by Chris Rakoczy—Rakoczy Photography www.rakoczyphoto.com PRINTED IN THE UNITED STATES CONTACTS SUBSCRIPTIONS Information: www.circuitcellar.com/subscribe, E-mail: [email protected] Subscribe: 800.269.6301, www.circuitcellar.com/subscribe, Circuit Cellar Subscriptions, P.O. Box 5650, Hanover, NH 03755-5650 Address Changes/Problems: E-mail: [email protected] GENERAL INFORMATION 860.875.2199, Fax: 860.871.0411, E-mail: [email protected] Editorial Office: Editor, Circuit Cellar, 4 Park St., Vernon, CT 06066, E-mail: [email protected] New Products: New Products, Circuit Cellar, 4 Park St., Vernon, CT 06066, E-mail: [email protected] AUTHORIZED REPRINTS INFORMATION 860.875.2199, E-mail: [email protected] AUTHORS Authors’ e-mail addresses (when available) are included at the end of each article.

CIRCUIT CELLAR®, THE MAGAZINE FOR COMPUTER APPLICATIONS (ISSN 1528-0608) is published monthly by Circuit Cellar Incorporated, 4 Park Street, Vernon, CT 06066. Periodical rates paid at Vernon, CT and additional offices. One-year (12 issues) subscription rate USA and possessions $45, Canada/Mexico $60, all other countries $63. Two-year (24 issues) subscription rate USA and possessions $80, Canada/Mexico $110, all other countries $116. All subscription orders payable in U.S. funds only via Visa, MasterCard, international postal money order, or check drawn on U.S. bank. Direct subscription orders and subscription-related questions to Circuit Cellar Subscriptions, P.O. Box 5650, Hanover, NH 03755-5650 or call 800.269.6301. Postmaster: Send address changes to Circuit Cellar, Circulation Dept., P.O. Box 5650, Hanover, NH 03755-5650.

Circuit Cellar® makes no warranties and assumes no responsibility or liability of any kind for errors in these programs or schematics or for the consequences of any such errors. Furthermore, because of possible variation in the quality and condition of materials and workmanship of reader-assembled projects, Circuit Cellar® disclaims any responsibility for the safe and proper function of reader-assembled projects based upon or from plans, descriptions, or information published by Circuit Cellar®. The information provided by Circuit Cellar® is for educational purposes. Circuit Cellar® makes no claims or warrants that readers have a right to build things based upon these ideas under patent or other relevant intellectual property law in their jurisdiction, or that readers have a right to construct or operate any of the devices described herein under the relevant patent or other intellectual property law of the reader’s jurisdiction. The reader assumes any risk of infringement liability for constructing or operating such devices. Entire contents copyright © 2010 by Circuit Cellar, Incorporated. All rights reserved. Circuit Cellar is a registered trademark of Circuit Cellar, Inc. Reproduction of this publication in whole or in part without written consent from Circuit Cellar Inc. is prohibited.

4

CIRCUIT CELLAR®


•

www.circuitcellar.com

Let your geek shine. Meet Leah Buechley, developer of LilyPad—a sew-able microcontroller—and fellow geek. Leah used SparkFun products and services while she developed her LilyPad prototype. The tools are out there, from LEDs to conductive thread, tutorials to affordable PCB fabrication, and of course Leah’s LilyPad. Find the resources you need to let your geek shine too.

»Sharing Ingenuity SP A R K F U N.C OM

©2010 SparkFun Electronics, Inc. All rights reserved.


240

INSIDE ISSUE July 2010

16 28 36 44

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Internet & Connectivity

Ubuntu Webcam Server Denny Lin

Webcam Server, p. 16

Build an X10 Controller (Part 1) Circuit Design Devlin Gualtieri Wireless Data Exchange Build a 2,700-lb. Bluetooth Headset Tom Struzik Hexapod Kinematics Motor Communication, Motion Planning, and Image Processing Matt Bunting & John Rogers

X10 Control, p. 28

Hexapod Robot, p. 44

14 54


58 66

THE CONSUMMATE ENGINEER It All Begins With a Spec George Novacek LESSONS FROM THE TRENCHES Put C Language to the Test (Part 3) Rules and Assignments George Martin FROM THE BENCH Application Communication with USB (Part 2) The Importance of Descriptors Jeff Bachiochi

TASK MANAGER Circuit Cellar: The Next Iteration C. J. Abate QUESTIONS & ANSWERS Research, Design, Write, Then Repeat An Interview With Jan Axelson C. J. Abate

6

10

TEST YOUR EQ

13

CROSSWORD

74

PRIORITY INTERRUPT 72 Flavors and More Steve Ciarcia CIRCUIT CELLAR®


8

NEW PRODUCT NEWS

INDEX OF ADVERTISERS August Preview

SILICON UPDATE Wall Whisperer A Fresh Take on Powerline Communication Tom Cantrell

4

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79 80



QUESTIONS & ANSWERS Research, Design, Write, Then Repeat An Interview With Jan Axelson Jan Axelson is the author of USB Complete (Lakeview Research, Fourth Edition, 2009), Serial Port Complete (Lakeview Research, Second Edition, 2007), and many other books and articles about hardware interfacing. Between 1997 and 2008, she wrote seven articles for Circuit Cellar. I met Jan Axelson at the April 2010 Embedded Systems Conference in San Jose, California. In a May 2010 interview, I asked Jan about topics ranging from her earliest design experiences to the future of USB technology. — C. J. Abate, Editor-in-Chief

CJ: Tell us about yourself. What’s your current occupation? JAN: I live in Wisconsin. When I’m not doing computer projects, I like to spend time outdoors. My favorite gadgets for outdoors are a GPS for navigating and an iPod with BirdJam software for identifying bird songs. I’m working on the design of a hand-held data logger that records the date, time, and GPS coordinates of sightings of target birds. With my books, articles, and website, I help developers use USB and other computer interfaces in their projects. CJ: How long have you been reading Circuit Cellar? JAN: I’ve subscribed to Circuit Cellar from the beginning. CJ: What was the first technology that really caught your attention and led you into the field of engineering?


JAN: I’ve long been interested in what’s outside the box—how PCs and embedded systems can talk to the world outside themselves. Early on, the options were parallel and serial ports, including RS-485 networks. From there, I expanded my horizons to USB and Ethernet.

8

JAN: I have a degree in electronics technology. What led me to writing was my frustration in trying to find useful information about the components and circuits I was interested in. To write about something, you have to understand it inside out, so writing is a good excuse to dig deep. CJ: Before writing books, what was your profession? JAN: In one job, I installed and maintained long-distance telephone circuits. Each channel extended anywhere from across town to across the state. Troubleshooting was a group effort, with one technician on each end and another in the middle. I also worked as a test technician for a manufacturer of computer-controlled scientific equipment. That job was my introduction to serial and parallel ports. CJ: You wrote seven articles for Circuit Cellar between 1997 and 2008. The main topics were connection (USB and parallel/serial ports) and memory (EEPROMs). What interests you about these two subjects?

CJ: How long have you been working with electronics and “embedded technologies”?

JAN: I like to work on projects where a computer monitors and controls the world outside itself, and to do that, you need an interface to provide the link. For me, EEPROMs are just a reason to explore synchronous serial interfaces such as SPI and I2C.

JAN: I have over 30 years experience with electronics and computers.

CJ: Give us a quick review. What are the main differences between USB from the late 1990s and USB of today?

CJ: What was your first MCU-based design?

JAN: The chips, speeds, and tools have all changed dramatically—in good ways—over the last decade. The number of silicon providers for USB host and device controllers has grown from a few to several dozen. You can find everything from bare-bones interface chips to intelligent controllers that handle many of the higher-level USB protocols for you. With the release of USB 3.0 in 2008, USB offers four bus speeds, though host computers are just beginning to support USB 3.0. Drives and video devices have been the first to

JAN: My first microcontroller project used an Intel 8052 microcontroller with a BASIC interpreter in ROM. An alphanumeric LCD displayed the temperature, maximum and minimum temperatures, and time. CJ: Describe your training. Are you trained as an electrical engineer, computer scientist, programmer, other?

CIRCUIT CELLAR®


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incorporate USB 3.0. Perhaps the best news for developers is that prices for debugging tools have plummeted. A bus analyzer captures, decodes, and displays USB traffic and is essential for debugging. You can buy a low/full-speed analyzer for one-tenth the price of a similar tool 10 years ago, and high-speed analyzers are available for under $1,000. (Expect to dig deep for USB 3.0 tools, however.)

International is another good source for modules.

CJ: Where is USB technology headed? Is there something beyond USB?

CJ: More advice. What would you say to a talented university student who asked you to suggest a topic to research for a dissertation?

CJ: Many Circuit Cellar authors and readers consider your book, USB Complete, a “go-to” reference. What about you? What books do you recommend on the subject? JAN: For anyone using the new Vinculum-II embedded host chip from FTDI, I recommend Embedded USB Design by Example by John Hyde, a free e-book from www.usb-byexample.com. The .NET Micro Framework is an underappreciated and now mostly open-source programming platform for small systems. A good programming guide is Expert .NET Micro Framework (Second Edition) by Jens Kühner. Programming 16-Bit PIC Microcontrollers in C: Learning to Fly the PIC 24 and Programming 32-Bit PIC Microcontrollers in C: Exploring the PIC32, both by Lucio Di Jasio, are great sources for useful code snippets and tips. CJ: I enjoyed meeting you at the Embedded Systems Conference 2010 in San Jose. How do you keep up with the latest technologies? By attending conferences? JAN: The expo at ESC is a great way to find out what’s new. There’s something about wandering the physical space and talking with real people that’s completely different from seeking out the same information on the web. I find web forums useful for finding out what technologies are catching the interest of developers (or causing them headaches). I’ve added a PORTS forum to my website (www.lvr.com) in part to replace the discontinued USB developer’s forum at usb.org. Of course, Circuit Cellar provides inspiration for projects. CJ: Did you see anything at ESC 2010 that really excited you? JAN: I got a look at some inexpensive Linux-capable modules for high-end USB host applications. The BeagleBoard (BeagleBoard.org) is based on a TI OMAP3530 processor and has a large and enthusiastic user community. Emac, Inc.’s iPac9302 board is based on a Cirrus EP9302 processor and comes with Linux installed and an Eclipse IDE. Digi www.circuitcellar.com

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JAN: My advice is to develop writing skills. Most jobs involve some writing, and the ability to produce useful documents can make you stand out.

JAN: The iPhone aside, so many devices still have difficult and frustrating user interfaces. I would like to see more research on how to improve that situation. CJ: If you were to research and write about something other than USB, what would be? JAN: I’m interested in wireless technologies, especially inexpensive ways to do remote, real-time monitoring. CJ: What projects are you currently working on? JAN: I’ve been looking at ways to add USB host capability to small systems. Because the USB host manages the bus, implementing a host is a much bigger job than implementing a device. Microchip and other vendors help by providing example code for their microcontrollers with embedded host-controller hardware. If you want host capability without messing with the low-level details, a variety of products can help. The USBwiz (see Photo 1) from GHI Electronics and the Vinculum from FTDI are host modules that handle the USB host protocols and communicate via commands sent over a UART, Photo 1—On this Microchip Explorer 16 development board, SPI, or other serial or parallel a PIC24FJ256GA110 microconinterface. For devices protroller is used with a USBwiz grammed using the .NET OEM module to access USB Micro Framework, GHI Elecdevices. tronics has modules with USB host support. Applications that require a major OS can use a module running Linux or one of the Windows editions for embedded systems. CJ: Are you planning any other projects for the near future? JAN: Watch for my book on USB hosts for embedded systems in 2011. Thank you for this chance to share my thoughts with the readers of Circuit Cellar! I

CIRCUIT CELLAR®



JAN: USB 3.0 promises data throughputs of up to 400 MBps, 900 mA of bus current per device, and new power-saving protocols. The interface adds a new 4-wire, 5-Gbps, dual simplex bus that is similar to PCI Express. Higher-level details such as the four transfer types and USB classes remain the same.

CJ: Advice time. Is there one thing that you think every electronics engineer needs to know? Why?

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S W E N CT DU R O EW P Edited by

John Gorsky

A MINI LINUX PC FOR UNIVERSAL USE


The PortuxG20 is a miniature Linux PC that’s energy-saving, compact, and comes with numerous interfaces. Its connection possibilities make it ideally suited for a wide variety of applications like data logging or computer interfacing. For instance, data can be recorded over time and periodically read into another device for additional processing as needed. In addition to the immediately available on-board interfaces, additional peripherals also can be connected. Depending on the multiplexing, up to four serial interfaces at TTL level, two SPIs, one I²C-compatible bus, an SSC, or up to 32 digital I/O ports are available. The SBC is equipped with an Atmel AT91SAM9G20 processor core running at 400 MHz and includes 64-MB SDRAM and 128-MB NAND Flash. The board measurements are 100 mm × 75 mm × 17 mm. It supports many common interfaces, including Ethernet, USART, USB 2.0 full speed, Micro SD card, JTAG, and the Portux Extension Bus (PXB). Additional interfaces such as SSC, SPI, TWI, an external SD card, a fourchannel 10-bit ADC, a 16-bit parallel bus, and up to 64 digital I/O ports are available via the PXB. Current consumption is 150 to 170 mA at 5 V (with an active Ethernet interface). Measurement, control, and regulation technologies are well-suited applications for the PortuxG20 compact single-board computer. The Linux operating system, the “U-Boot” boot loader, and the “JamVM” Java Virtual Machine with the “GNU Classpath” Java Class Library are all preinstalled. The board itself costs about $225. Several starter packages are also available.

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taskit GmbH www.Taskit.de

CIRCUIT CELLAR®


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CC430 PLATFORM FOR COMPLETE SOLUTIONS FOR WIRELESS NETWORKING The CC430F513x MCUs combine the world’s leading ultra-low-power MSP430 MCU with the high-performance, sub-1-GHz CC1101 RF transceiver. The CC430F513x devices offer up to 20-MIPS performance in a small package (7 mm × 7 mm) and support security options such as an integrated AES hardware module. Also available is the CC430F61xx series of LCD control devices, providing developers with more options to meet varying design needs. With the capability to support multiple protocols and a broad frequency range, the CC430 MCUs, along with the extensive third-party ecosystem, spur innovation in applications like home and building automation, smart metering, energy harvesting, asset tracking, and portable medical applications. Developers can also immediately jumpstart CC430 MCU-based designs with the EM430F6137RF900 and eZ430-Chronos wireless development tools that include all the hardware design information required to develop a complete wireless project. Eight devices offer non-LCD and LCD options, as well as a range of pin count, memory and high-performance analog integration to meet varying design needs. The devices draw low enough current to enable battery-operated wireless networking applications that operate without servicing for several years, reducing maintenance costs and overall BOM. Production quantities of the CC430F513x MCUs are immediately available and pricing starts at $4.15 (1,000 units). Sampling quantities of the CC430F61xx family with integrated LCD are also immediately available to order with pricing starting at $4.35 (1,000 units).

ICs AUTOMATICALLY AND SAFELY DISCHARGE X CAPACITORS CAPZero is a family of innovative, two-terminal, automatic X capacitor discharge ICs that eliminates power losses while allowing power supplies to comply with safety standards. CAPZero acts as a smart high-voltage switch when placed in series with discharge resistors. When AC voltage is applied, CAPZero blocks current flow in the X capacitor safety discharge resistors, reducing the power wasted in these components to zero at 230 VAC. When the AC voltage is disconnected, CAPZero automatically and safely discharges the X capacitor by closing the circuit through the bleed resistors and directing the energy away from the exposed AC plug. This approach provides engineers with total flexibility in their choice of the X capacitor used to optimize differential-mode EMI filtering without worrying about the effect of the required bleed resistors on system no-load and standby power budget. The innovative design inherently meets international safety standards for all open and short-circuit fault tests, allowing CAPZero to be used before or after the system input fuse. CAPZero is suitable for all AC-DC converters with X capacitors that require very low standby power. It’s offered with 825- or 1,000-V MOSFETs to support a variety of power supply design needs. It is ideal for a wide range of applications, including PCs, servers/workstations, monitors and TVs, printers and notebooks, and appliances requiring EuP Lot 6 compliance and adapters requiring ultra-low no-load consumption. CAPZero devices are available now in an SO-8 package at $0.40 each for 10,000piece quantities.

Power Integrations, Inc. www.powerint.com

Leading Embedded Development Tools...

Texas Instruments, Inc. www.ti.com

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For ARM Application Processors:

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NPN www.circuitcellar.com

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www.keil.com

1-800-348-8051

CIRCUIT CELLAR®



For Microcontroller:

11

OBD-II INTERPRETER MODULE IN A DIP-24 PACKAGE The microOBD 200 (#440101) is a complete OBD‐II interface in a vibration-resistant DIP-24 module. The only product of its kind, it offers engineers a simple and inexpensive way to add OBD-II support to any embedded project and tap into the wealth of information available on the vehicle’s communication bus. The interface is fully compatible with the popular ELM327 command set and supports all legislated OBD-II communication protocols, as well as the heavy-duty SAE J1939. It features automatic protocol detection, a large memory buffer, a UART interface capable of speeds of up to 10 Mbps, and a bootloader for easy firmware updates. The microOBD draws less than 1 mA in Standby mode, which makes it suitable for permanent in-vehicle installations. The host can force the module to enter the lowpower state by sending it an explicit “sleep” command or pulling the digital “host present” pin low. The module can also put itself in Standby automatically on UART inactivity or by sensing that the engine is off. Typical applications include diagnostic scan tools, code readers, data loggers, digital dashboards, fleet management, and vehicle tracking. Product documentation and volume pricing are available from www.microOBD.com. The module costs $49 in single-unit quantities.

ScanTool.net LLC www.scantool.net

NPN /,-

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CIRCUIT CELLAR®


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CIRCUIT CELLAR

Edited by David Tweed

Problem 1—Assuming that VP and VN are connected to voltage sources (negligible source impedance), what is the value of VOUT of the following circuit? The two RX have the same value, as do the two RY. Assume the op-amp is “ideal.”

EQ

Test Your

Problem 3—What kind of feedback circuit do you need in order to construct a switching regulator whose output is exactly half of its input voltage?

Problem 4—In the C programming language, name at least two ways in which the following structure for (expr1; expr2; expr3) { ... } is not precisely equivalent to this structure:

Problem 2—What is the significance of this circuit?

What’s your EQ?—The answers are posted at

expr1; while (expr2) { ... expr3; }

www.circuitcellar.com/eq/ Contributed by David Tweed


You may contact the quizmasters at [email protected]


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13

CIRCUIT CELLAR®


T

HE CONSUMMATE ENGINEER

by George Novacek (Canada)

It All Begins With a Spec Your goal is to become a well-rounded, multidisciplinary engineer who can address hardware and software issues alike, tackle difficult design problems, and deliver quality work on a consistent basis. But achieving this goal takes time, effort, and guidance. So let’s start with the basics.

E

ngineering is fun. Where else do we get to invent, create and play with such exciting toys—from iPhones to advanced military aircraft—and get paid for it? I know, I know, we also have to worry about schedules, budgets, and managers who are not engineers—but in the end, nothing beats the satisfaction of seeing our ideas become realities. The creative fun, however, goes hand in hand with a great deal of responsibility: to the end users, to our employers, to our colleagues, to our companies, and ultimately to ourselves in terms of professionalism and pride. Not only must we ensure our design will work as specified; we are equally responsible for making it reliable, ensuring that it’s safe to operate, making it environmentally friendly, and ensuring it can be manufactured consistently and economically. In future columns, I will address engineering activities and procedures to achieve those goals. The idea is simple: you want to become a well-rounded engineer. But that’s easier said than done. So, let’s begin with the basics.


WHAT’S IN A SPEC?

14

At the beginning of all our efforts has to be a good, concise specification defining in no uncertain terms what we, the engineers, are expected to deliver. Unfortunately, this is not always the case. Sometimes such a specification is impossible to develop, namely for systems and products with long life expectancy, where continuous technological improvement takes the product well beyond its original concept. The Internet is a good example. Let’s imagine what the Internet

could be, had its original creators had the benefit of knowledge of technological advances of the several following decades and developed the architecture and the protocols accordingly. Abuse of the Internet would be much harder today, although I don’t believe the Internet could be made bullet proof. Only a few of us will ever have the opportunity to be at the birth of a system with the impact and longevity of Internet, where inadequacies of the original specification could not be prevented. In the majority of development programs there is no excuse not to start with a specification cast in stone, with no detail left to a chance. It has been shown that most of product shortcomings are not the result of poor design, but poor, inadequate specification. Why is that? One excuse is economics. There were times when top-level system integrators, such as airframe manufacturers, had a team of experts specifying subsystems and their components as black boxes in minute detail. A specification for a simple embedded controller would have been a hundred or more pages long. For those not familiar with the concept, engineers like to talk about black and white box designs. These exist at all levels of a system. The black box design defines all the functions, interfaces and performance characteristics as viewed from the outside with no regard for how are those design goals achieved. White box design is the actual implementation, typically schematic diagrams and source code for an embedded controller. CIRCUIT CELLAR®


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SPEC AMBIGUITY Spec ambiguity is another pitfall we need to watch for. Engineers preparing a higher level specification may forget that while they understand the system well, engineers given the task to design to this spec may, without understanding the context, give it a different interpretation. Specifying the working environment of an equipment is one thing, but good engineer must also consider what extreme use and environments the equipment may be exposed to and take steps to ensure the equipment remains safe even outside its specified operating envelope. You must expect the unexpected. Once I worked on a controller where four sets of 380-V loads were connected to four separate MIL connectors, each about 4 inches in diameter. Because inserting a wrong plug into a wrong receptacle could result in catastrophic consequences, each connector set was color coded and keyed. We convinced ourselves that mismatching the connectors was impossible. Yet, it happened on the very first unit being installed. The fireworks, I was told, were spectacular. Fortunately, no one was injured, only the controller was destroyed and the customer extremely upset. Within hours an www.circuitcellar.com

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engineer was flying across the continent to investigate. He discovered that the installer, when the very first cable connector he touched didn’t mate with the receptacle, decided to take a monkey wrench to it, forced the plug into the wrong receptacle, breaking off the key in the process, then proceeded hammering the remaining three connectors in their wrong places. To prevent the “impossible” from happening again, we added monitors to the controller to stop the power from being turned on should someone invented another way to mate wrong connectors. While much of circuit design can be performed by junior engineers under supervision, the top-level spec development requires in addition to solid engineering knowledge something no school can give you—experience.

LOOKING AHEAD Moving forward, I’ll share my engineering experiences with you. Hopefully, they will help you to avoid learning the hard way from your own mistakes. I George Novacek ([email protected]) is a professional engineer with a degree in Cybernetics and Closed-Loop Control. Now retired, he was most recently president of a multinational manufacturer for embedded control systems for aerospace applications in Canada. George wrote 26 feature articles for Circuit Cellar between 1999 and 2004.

NEED-TO-KNOW INFO Knowledge is power. In the computer applications industry, informed engineers and programmers don’t just survive, they thrive and excel. To learn more about George Novacek’s design tips and projects, the Circuit Cellar editorial staff recommends the following: — Building an Electric Airplane by George Novacek Circuit Cellar 150, 2003 Many engineers see electric motor technology as the ticket to an energy-efficient, cost-effective future. With this in mind, George shows you how to design an electrically actuated system, with a focus on control and braking. Topics: Aeronautics, Actuator, PWM, Control, Braking, EMF, Fly-by-Wire Go to: www.circuitcellar.com/magazine/150toc.htm — Working with EMC by George Novacek Circuit Cellar 142, 2002 George explains differences between magnetic and electric emissions. You can design your next project to handle both. Topics: EMC, EMI, Electromagnetic Compatibility, EMI, Protection, Shielding Go to: www.circuitcellar.com/magazine/142toc.htm

CIRCUIT CELLAR®



To reduce non-recurring engineering costs, the burden to generate the black box definition of a sub-system, in other words the specification, was gradually shifted down the supply chain until it eventually ended up on the controller designer’s desk as perhaps a single paragraph of technical requirements, with a laconic statement “you are the experts, write your own spec”. Needless to say, expecting an electronics engineer, even though he may have designed similar controllers in the past, to be an expert on, say, aircraft dynamics is quite a stretch. What looked as a perfect way to save money to an accountant usually results in even higher cost of development, blown schedules and finger pointing. No better results come from a similar approach called “concurrent engineering,” where time and money should be saved by having the black and white boxes developed concurrently. This is an engineering version of the chicken or the egg dilemma. Several teams are second guessing each other, occasionally ending up in a dead end or having to do things the complicated way because the simple route had been blocked. Over-design, spaghetti code, less than optimum design, those are the results. Another cause of a poor up-front specification is that its importance is underestimated, its preparation considered boring. Many a hardware designer likes to start drawing schematics, just as a software designer likes to start by writing code without a previously developed and understood architecture and a set of requirements. This is a sure way to get in trouble. No engineer should start white box design before he has shown the black box to be correct, traceable to the top level spec and testable. In my experience the time spent up front developing a solid spec supported by black box description has always brought the best results.

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F EATURE

ARTICLE

by Denny Lin (USA)

Ubuntu Webcam Server Ready to take a look inside an Ubuntu webcam server? Once you finish this project, your viewers will have access to your streaming video via any modern browser (Internet Explorer, Firefox, Safari, Opera, or Chrome) and desktop OS platform (WindowsXP, MacOS, or Linux).

T

he Department of Mathematics and Computer Science at La Sierra University (Riverside, CA) where I work maintains a display area in which we showcase many of the cool gadgets we develop. One such design is a computer-controlled monkey we affectionately call Kiki, which users can control from any Internet connection and view via a LinkSys webcam (see Photo 1). The webcam originally had a serious shortcoming. It required the use of Internet Explorer, an ActiveX module, and a series of obscure procedures to enable the module. As a result, people using non-Microsoft browsers couldn’t see Kiki. We simply needed a video stream that was compatible with as many browsers as possible. Fortunately, I had a used IBM PC camera (which I’d bought


a)

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at a thrift store for less than $4) and a bunch of computer parts from a good friend. As a result, I decided to build a web camera server from the ground up, one that would offer broader browser compatibility. While assembling this server, I realized that displaying the inner workings of a functional server would effectively turn a video webcam server into useful, and educational, eye-candy. So, for $67, I bought a transparent computer case that came with three 80-mm fans illuminated by eye-catching blue LEDs (see Photo 2).

SYSTEM OVERVIEW The design features several key pieces of hardware: an Intel motherboard, a 1.70-GHz Intel processor, 256-MB memory, a

b)

Photo 1a—The Kiki computer-controlled monkey is located in a display case at the entrance to the Mathematics and Computer Science Department at La Sierra University where I work. My webcam server monitors Kiki. b—This is the Altera Nios web server controller board. It is the creation of Dr. Enoch Hwang at La Sierra University. CIRCUIT CELLAR®


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a)

b)

c)

Western Digital 6-GB hard drive, a BenQ DVD-ROM (16×), an NVIDIA GeForc video card, an Antec 300-W power supply, a Logisys Model CS888CL case, and an Xirlink IBM PC Camera KSX-X9903. Because I was building this system on the cheap, the next step was to find a free operating system. I chose the popular Linux distribution called Ubuntu, and downloaded the entire operating system as an image file to be burned onto a bootable CD-ROM (which can even run on a computer without a hard disk). Figure 1 shows the relationship between the Ubuntu webcam system I describe in this article and the Kiki Altera webserver displays. Figure 2 shows the components that make up the Ubuntu webcam system. Although there is a server edition of Ubuntu 9.04, I chose the desktop version because it’s easy to configure and provides a simple-to-learn graphical user interface (GUI). Many configuration steps still require the use of the command prompt; but fortunately, these simple commands can be documented in step-by-step instructions. This is how www.circuitcellar.com

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the idea for this article began! Building this Ubuntu webcam server involves three main steps. Let’s consider each one. The first step is to install Ubuntu onto the computer. This step is straightforward since the installation program on the Ubuntu CD-ROM includes a step-by-step “Wizard.” The second step is to install, configure, and update the servers. This configures the computer’s operating system to be used as a server and installs the two servers that run the webcam. Critical security updates are installed at the end of this step. The third step is to configure start-up scripts to automatically start the webcam server. Doing so loads the IBM PC camera driver that links the camera images to the computer’s video device, and it creates a start-up script for the webcam server. I added two additional steps. Although they’re optional, I recommend them. One, set up a remote desktop. Doing so makes it possible to manage the server from a remote computer. Next, set up a

firewall. This step disables all ports that are not essential for the functioning of the webcam server. While the hardware and software cost very little, considerable time and effort went into learning about and setting up the software. I found websites that contained bits and pieces of information needed to get my hardware and software to work. If your hardware or software differs significantly from mine, use common sense (and lots of patience) to troubleshoot any issues. The configuration files were created and modified by a text editor called Pico, which is included in this Ubuntu distribution. While Pico lacks a GUI, I found it easy to use. Context-sensitive commands, listed on the bottom of the screen, can be accessed by pressing a combination of CTRL and letter keys. For example, help (labeled ^G Get Help) is accessed by pressing CTRL-G.

INSTALLING UBUNTU To begin, find and download the 32-bit Desktop Ubuntu 9.04 disk image. Any computer with a browser connected to

CIRCUIT CELLAR®



Photo 2a—An IBM PC camera is pointed at Kiki. b—This is my completed webcam server housed in a transparent case. c—This is a close-up shot of the server. The system is pretty eye-catching, especially with its blue LEDs.

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Internet

Forwards off-campus requests for 192.156.214.81 to 10.1.31.24

Forwards off-campus requests for 192.156.214.80 to 10.1.31.23

IP Address forwarding firewall

Ethernet network traffic

Ethernet network traffic

Network switch

Local IP Address: 10.1.31.24

Local IP Address: 10.1.31.23

Video

IBM PC USB Camera

Drumming monkey

3-V DC

On/Off Relay

115-VAC to 3-VDC Adapter

Ubuntu webcam server: Host server’s main page, the webcam video, and embeds the Altera web server page

Altera web server and Kiki controller: Host embedded page containing the monkey on control button

Welcome to Kiki’s Webcam! Webcam video (Java applet)

Existing Altera controller monkey display by Dr. Enoch Hwang

Inline frame (iframe) tag embeds the Altera web server page within the Ubuntu webcam server’s main page The server’s index.html main page

Monkey On

Ubuntu webcam system display

Figure 1—This block diagram shows the relationship between the Ubuntu webcam system and the Kiki Altera web server displays. the Internet, equipped with a CDROM drive and burner software, can be used to create (burn) the CD-ROM. Using a Windows XP computer, I saved the image file, and right-clicked on its icon to burn an Ubuntu-bootable CDROM. I configured my computer’s ROM-BIOS to boot from the CD-ROM drive. I completed the installation using the steps noted in Figure 3.

IBM USB Camera

Sends video to

Supplies video feed to IBMCAM USB Driver module


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Runs on Configuration and maintenance tools

Executes

Configured and maintained by

Runs on

Webcam server

Starts

Loads driver

CONFIGURE SERVERS First, the computer is set to a static Internet protocol (IP) address and domain name server settings are configured. Second, the Apache web server is installed and configured to host the video stream produced by the webcam server. Third, an HTML file that serves the video stream from the webcam server is configured. The Update Manager must be allowed to download

users have a fixed target to connect to the webcam server. In addition, having a registered domain name makes it easier to access your server. If

critical security updates that have become available since Ubuntu was released. You need a static IP address so that

Startup modules, scripts, and symbolic links

Provides webcam video to Runs on

Ubuntu 9.04 operating system

Runs on Runs on

Sends web page to client via Network interface

Apache web server

Forward client request to

Get requests from and send images to

Internet

Figure 2—This is a context diagram of the components described in the article that make up the Ubuntu webcam system. CIRCUIT CELLAR®


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the computer is turned off and on. If you are creating a web server of any sort, I recommend purchasing a static IP address plan from your ISP and getting a domain name from a domain name registrar. Another alternative is to use a free domain name service that can translate your dynamic address to a fixed domain name that you choose. Since this webcam server is located at my university, I picked an IP address from a pool of static addresses reserved

1. Insert the Ubuntu 9.04 CD ROM and boot computer from the CD ROM 2. Select English 3. Select Install Ubuntu, press Enter a. Wizard Step 1: Select English, click Forward b. Wizard Step 2: Pick your region and city, click Forward c. Wizard Step 3: Pick a keyboard layout (I used Suggested option: USA), click Forward d. Wizard Step 4: Select Use the entire disk, click Forward e. Wizard Step 5: Enter your name, login and password, and computer information. i. Enter your full name: [administrator] ii. Pick a login name: [administrator] iii.Pick your password <enter this twice> iv. Name your computer: [administrator-desktop] v. Click Log In Automatically vi. Click Forward f. Wizard Step 6 is automatically skipped. In Wizard Step 7: Click Install 4. Restart computer: Click Restart Now 5. Remove CD ROM when prompted, and press Enter

Fi gure 3—The steps for installing Ubuntu

your ISP provides a dynamic IP address (using the dynamic host configuration protocol or DHCP), your server’s IP address could be different every time

by our campus network administrator. I also set up the domain search and name server (DNS) look-up information in the webcam server’s resolv.conf file. I received valuable help and advice from the university’s network administrator while setting up domain names for the webcam server. Next, I had to download and install servers. I used Donn Morrison’s webcam-server program to make the video stream available to the Apache web server. Morrison’s Sourceforge.net page provides the webcam_server (notice the underline in the name) program, but that did not recognize my webcam. The webcam-server (notice the hyphen in the name) program (also authored by Morrison) works well with my webcam, and it is the version that is available using the apt-get command in


1. Start Terminal: Go to Applications -> Accessories -> Terminal 2. Type sudo -i a. press Enter. b. enter the administrator’s password. 3. Define a static IP address: a. Go to the network directory. Type: cd /etc/network b. Type: pico interfaces c. Modify the interfaces network settings file so the contents of that file looks like listing 1. In our case, we set the static IP address to 10.1.31.241. You must use a different IP address, so consult your Internet Service Provider (ISP) or your network administrator for details about your particular environment. d. Exit pico: CTRL-X, Y(es) to save changes, press Enter to accept filename and exit. 4. Restart the computer. Type: reboot 5. Repeat steps 1 and 2 to use Terminal to get super user access 6. Configure the domain search and name server settings in the resolv.conf file. a. Go to the /etc directory. Type: cd /etc b. Type: pico resolv.conf c. Edit the resolv.conf file so the contents of this file looks like listing 2. In our case, the domain search is lasierra.edu, and our DNS server address is 192.156.214.14. You must use a different address, so consult your Internet Service Provider (ISP) or your network administrator for details about your particular environment. d. Exit pico: CTRL-X, Y(es) to save changes, press Enter to accept filename and exit. 7. Install webcam-server. Type: apt-get install webcam-server 8. Install apache2 server. Type: apt-get install apache2 a. Type Y to continue installation. 9. Install the Java browser plugin. Type: apt-get install icedtea6-plugin a. Type Y to continue installation. 10. Copy webcam server files to apache server directory. Type: cp /usr/share/doc/webcam-server/applet/* /var/www 11. Change to /var/www. Type: cd /var/www 12. Edit webcam.html and change the URL to your IP address; change the frames per second to 5, using listing 3 as reference: a. Type: pico webcam.html b. Look for the phrase http://localhost:88882 and replace “localhost” with the IP address you picked in step 3. For example, if your server’s IP address is 10.1.31.24, change this to http://10.1.31.24:8888 c. Look for the phrase FPS value= “1” and replace “1” with “5”. d. Exit pico: CTRL-X, Y(es) to save changes, press Enter to accept filename and exit. 13. Copy webcam.html to index.html. Type: cp webcam.html index.html 14. Go to the Update Manager a. Click Check to look for new updates. b. Enter the administrator password. c. Click Install Updates 15. Restart computer, click Restart Now

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1

The webcam server is actually located within a private sub-network; this is why I have a static IP address that starts with “10.” It is normally not possible for offcampus computers to directly connect to any devices in our private sub-network. So, a special public IP address “192.156.214.81” and a domain name of “cswebcam.lasierra.edu” were created by my network administrator to redirect traffic from off-campus machines to the webcam server in our private sub-network. On-campus users must either type the private IP address or use the private domain name “cswebcam.int.lasierra.edu” (notice the .int. in the domain name) to access the webcam server. 2 The webcam-server uses port number 8888 to send the video stream. If the client’s ISP blocks this port, they will get an “Error connecting to the video” message, though the rest of the web page will be visible.

Figure 4 —The steps for installing and configuring servers CIRCUIT CELLAR®


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Figure 4 (for installing and configuring servers). Morrison’s program provides a simple webcam_server.log file, in the /var/log directory, with connection statistics such as the date, time, and requestor IP address. Apache is used to serve the webcam page containing the video stream. This full-fledged web server is capable of hosting Java applets and even keeping track of website traffic. The access.log file can be used to analyze web traffic. It is found in the /var/log/apache2 directory and details every connection request (including IP address, operating system and version, browser and version, access date and time, which pages were visited) made to the web server during the current week. In addition, it is automatically rotated to access.log.1 at the end of each week.

Li sting 1—Contents of the interfaces file, found in /etc/network directory # File path and name: /etc/network/interfaces # Define the loopback interface lo auto lo iface lo inet loopback # Define the interface eth0 with static IP address auto eth0 iface eth0 inet static address 10.1.31.24 netmask 255.255.255.0 network 10.1.31.0 broadcast 10.1.31.255 gateway 10.1.31.1

L isti ng 2 —Contents of the resolv.conf file, found in the /etc directory # File path and name: /etc/resolv.conf search lasierra.edu # Search list for host-name lookup nameserver 192.156.214.14 # IP address of the campus name server


L isti ng 3 —Contents of the webcam.html and index.html files, found in the /var/www directory

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Kiki's Webcam <style type="text/css"> html, body, div, iframe { margin:0; padding:0; height:1020; } iframe { display:block; width:100%; border:none; } Welcome to Kiki's Webcam at La Sierra University!

<APPLET CODE = "WebCamApplet.class" archive="applet.jar" WIDTH = "352" HEIGHT = "240"> <param name=URL value="http://10.1.31.24:8888"> <param name=FPS value="5"> <param name=width value="352"> <param name=height value="240"> Kiki's Webcam runs on Linux Ubuntu 9.0.4, which can be downloaded for free here.
You can get step-by-step instructions to make an Ubuntu webcam, in MS-Word format and in PDF format.
The computer that runs Kiki's Webcam was donated by Craig Kinzer, alumnus of the Math & Computer Science department.
This webcam display, and the Ubuntu webcam setup instructions were created and written by Denny Lin, Assistant Professor of Computer Science.

<iframe src="http://10.1.31.23" height="1020" width="100%">
Kiki Cam

CIRCUIT CELLAR®


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What is the missing component? Electronics instructor Ollie Circuits planned to show his class of freshman electrical engineering students how to use a super capacitor as a memory back-up capacitor, but first he wanted to show how the students could make their own super capacitor and demonstrate its charge/discharge cycles with the simple circuit above. Most of the components were already on his workbench, the homemade super capacitor would be made from several layers of lemon juice-soaked paper towels interleaved between several layers of a mystery material to form a multi-layer stack.The stacked layers would then be sandwiched between the two copper-clad PC boards and held together with a rubber band. Ollie rushed to a nearby pet shop. What did he buy? Go to www.Jameco.com/teaser7 to see if you are correct and while you are there, sign-up for our free full-color catalog.

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1. Start Terminal: Go to Applications -> Accessories -> Terminal 2. Type sudo -i a. press Enter b. enter the administrator’s password. 3. Change to the etcetera directory. Type: cd /etc 4. Type: pico modules 5. Listing 4 is the /etc/modules file, which loads the ibmcam module. Make sure the contents of the options following ibmcam are on a single line. 6. Change to the startup directory. Type: cd /etc/init.d 7. Type: pico webcam_server 8. Create the startup script by typing the contents of listing 5. 9. Exit pico: CTRL-X, Y(es) to save changes, press Enter to accept filename and exit. 10. Grant execute permission to the file you created. Type: chmod 755 webcam_server 11. Define a symbolic link so the script is automatically executed when the computer starts. Type: update-rc.d webcam_server defaults 24 12. Restart the computer. Type: reboot


Fi gure 5 —The steps to configure automatic start-up scripts

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the word “localhost” with the server’s asked for the administrator’s password Older files are automatically comstatic IP address. Then, the frames per before updates were installed, and I was pressed and saved as access.log.n.gz, second (FPS) setting was increased from prompted to restart the computer for where the number n is two or larger for 1 to 5. I picked a value which would the updates to take effect. older files. not burden the server with a too-high Regarding the static IP address to Next, I downloaded and installed the frame rate, but would still allow the 10.1.31.24 in Figure 4, note that the Java browser plugin. (Windows and OS X user to observe the motion of Kiki beatwebcam server is actually located withcan run Java applets without this Java ing her drum. Finally, for testing, I in a private sub-network. This is why I plugin, so step 9 in Figure 4 for entered http://10.1.31.24/webcam.html have a static IP address that starts with installing and configuring servers is “10.” It is normally not possible for arguably optional.) The video stream into a browser running on a different hosted by the webcam server is a Java computer and modified the webcam.html off-campus computers to directly connect to any devices in our private subapplet that runs within the web browsfile on the server until I got the network. So, a special public IP address er. In order to view the video stream desired results. “192.156.214.81” and a domain name while using the server’s web browser, I Once I was satisfied with the webof “cswebcam.lasierra.edu” were creatinstalled the Iced Tea 6 Java plugin. cam.html file, I copied it to ed by my network administrator to This project aimed not only to show index.html, the default file that is redirect traffic from off-campus video images of Kiki, but also to allow automatically displayed whenever a machines to the webcam server in our users to control Kiki. The webcam-servuser types the IP address or the domain private sub-network. On-campus users er package provides a default web page name of the webcam server into a (named webcam.html) that serves a sim- browser: http://10.1.31.24 (notice there must either type the private IP ple video stream. I made several changes is no /index.html after the IP address). address, or use the private domain to this file so that it is seamlessly I then ran Update Manager. This tool name “cswebcam.int.lasierra.edu” linked to Kiki’s controller web page lists patches and updates that keep the (notice the .int. in the domain name) (served by a stand-alone Altera Nios server current and protected from vulto access the webcam server. board) while serving the video stream. I nerabilities. Ubuntu automatically runs As for the note regarding the phrase used inline frame tags to seamlessly the Update Manager to look for and http://localhost:8888 in Figure 4, the link Kiki’s controller web page to the install updates (step 14 in Figure 4 for webcam-server uses port number 8888 video stream in the webcam.html page, installing and configuring servers). I was to send the video stream. If the client’s so there are no wires that directly connect the webLi sting 4—Contents of the modules file, found in the /etc directory cam server to Kiki’s controller web page. Since I # File path and name: /etc/modules wanted to turn this webibmcam init_hue=96 init_color=250 init_brightness=48 init_contrast=110 lighting=0 site into a teaching tool, init_model2_yb=170 init_model2_sat=28 links to the step-by-step # Loads the ibmcam module (driver) upon startup instructions for creating # All of the numbers have a range from 0 to 255: # The initial hue set is 96 this webcam server were # The initial color is set to 250 posted in index.html. # The initial brightness is set to 48 Clearly, your circum# The initial contrast is set to 110 stances will vary, so # The lighting (photosensitivity of camera) is set to type 0 # The init_model2_yb parameter adjusts color balance, and is set to 170 adding inline frame tags, # The init_model2_sat parameter adusts the saturation, and is set to 28 for example, may not apply to your project. # More information about options for the ibmcam module can be found here: I first edited # http://www.mjmwired.net/kernel/Documentation/video4linux/ibmcam.txt webcam.html by replacing CIRCUIT CELLAR®


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Listi ng 5 —Contents of the webcam_server file, found in the /etc/init.d directory #!/bin/sh # File path and name: /etc/init.d/webcam_server # The first two characters in this file MUST be a number and an exclamation mark, because # they tell the operating system that this is a script, to be executed by the Bourne shell # interpreter found in /bin/sh webcam-server -s -c " Kiki The Monkey %D %H:%M:%S Viewers: %%v" # The -s option starts the webcam-server in daemon mode # The -c option defines the caption to be displayed: # %D inserts the system date # %H inserts the current hour from system time # %M inserts the current minute from system time # %S inserts the current seconds from system time # %%v inserts the number of connected viewers to the webcam-server

ISP blocks this port, they will get an “Error connecting to the video” message, although the rest of the webpage will be visible. Listing 1 shows the content of the interfaces file found in /etc/network directory. Listing 2 shows the content of the resolv.conf file found in the /etc directory. Listing 3 shows the content of the webcam.html and index.html files found in the /var/www directory.

This step lists the IBM PC camera driver in the modules file, so the driver is loaded when the server starts up. In addition, this step creates a startup script that launches the webcam server in daemon mode. Instructions to configure automatic startup scripts are listed in Figure 5. During start-up, Ubuntu loads drivers listed in the modules file. The ibmcam module allows the IBM PC camera to send its images to the /dev/video0 device. I found that when the module was loaded without any options, the images appeared overexposed; under minimal light, the image had a greenish tinge. I came across a website describing the options available for adjusting the video signal. I spent several hours of trial-and-error testing to figure out the best combination of settings for initial hue, color, brightness, contrast, and lighting. Subtle changes in lighting require different adjustments, so be patient while trying different settings. I named the webcam server startup script “webcam_server” in order to differentiate it from the executable file (which contains a hyphen instead of an www.circuitcellar.com

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CIRCUIT CELLAR®



START-UP SCRIPTS

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underline). All of the Li sting 6—Listings of the /etc/rc2.d and /etc/rc0.d directories options for the webcamserver program can be >ls /etc/rc2.d README S20hotkey-setup S50rsync S90binfmt-support viewed by typing “webS01policykit S24hal S50saned S91apache2 cam-server –h” in a termiS10acpid S24webcam_server S50system-tools-backends S98usplash nal window. I only needed S10apmd S25bluetooth S70bootlogs.sh S99acpi-support two options for my setup. S10sysklogd S30gdm S70dns-clean S99laptop-mode S11klogd S50avahi-daemon S70pppd-dns S99ondemand The -s option was used to S12dbus S50cups S89anacron S99rc.local launch the server in daeS16ssh S50NetworkManager S89atd S99rmnologin mon mode, so its execuS20apport S50pulseaudio S89cron S99stop-readahead tion is not tied to a termi>ls /etc/rc0.d nal session. The -c option K01gdm K63mountoverflowtmp S30urandom defined the caption that K02usplash K74bluetooth S31umountnfs.sh identifies the video and K09apache2 K99laptop-mode S35networking shows the date, time, and K20apport README S40umountfs K24webcam_server S01linux-restricted-modules-common S60umountroot number of users connected. K25hwclock.sh S15wpa-ifupdown S90halt The webcam_server K50alsa-utils S20sendsigs startup script is kept in the /etc/init.d directory; it’s made executable by using the chmod command in step sequence, remove the symbolic links. First, type: 10 in Figure 5 (for configuring automatic start-up scripts). It “update-rc.d - f webcam_server remove.” Then reissue the turns out that the order for executing this script is very update-rc.d command in step 11 from Figure 5 (for configurimportant. The Ubuntu Hardware Abstraction Layer must ing automatic start-up scripts) to establish a symbolic link. be started before the webcam_server script. Listing 4 shows the content of the modules file found in the Most users will run their Linux desktops at run level 2, 3, /etc directory. Listing 5 shows content of the webcam_server 4, or 5, which are multi-user modes. By default, Ubuntu uses file found in the /etc/init.d directory. Listing 6 shows the conrun level 2. Run levels 0 and 6 are used to kill processes durtent of the /etc/rc2.d and the /etc/rc0.d directories, produced ing system shutdown or reboot, while run level 1 is used by the ls command displayed at the top of each list. when Ubuntu is in single-user mode. Each run level has a Let’s move on to the topics of setting up the remote desktop matching control directory that contains executable symboland firewall. Both are optional. ic links to services that are started or ended during startup, shutdown, or reboot. Thus, for run level 2, the symbolic REMOTE DESKTOP SETUP links are in /etc/rc2.d, while the symbolic links for run level Remote Desktop is a virtual network computing (VNC) 0 are stored in /etc/rc0.d. These symbolic links are identified server program that runs on the webcam server, allowing by the initial letter S to start processes, or with the initial remote control of the server through a VNC client viewer. letter K to kill processes. The computer in our display case is not connected to a The number after the letter S of every symbolic link monitor, but VNC allows me to see what the webcam server denotes the order in which those services are started. Since is displaying. While I can and do use a secure shell terminal the webcam_server must be started after the hardware emulator program (PuTTY) to quickly access the server, abstraction layer (HAL), its number should be equal to or VNC provides access to Ubuntu’s GUI desktop environment. greater than the number for the HAL service (labeled as VNC is platform-independent, so any computer running a S24hal). There should be S24webcam_server links in the VNC client can be used to control your webcam server. You /etc/rc2.d, /etc/rc3.d, /etc/rc4.d, and /etc/rc5.d directories. For can download the “VNC Free Edition for Windows” if you wish to control the webcam server from a Windows PC. Try run levels 0, 1, and 6, there are symbolic links that start with “Chicken of the VNC” if you wish to control the webcam K, which kill processes during shutdown, single-user mode, server from a Macintosh. Refer to the resources listed at the or reboot. There should be K24webcam_server links in the end of this article for more information. /etc/rc0.d, /etc/rc1.d, and /etc/rc6.d directories. These startTo connect to your webcam server through the VNC up and shutdown symbolic links were created using the client, enter the IP address of the webcam server and the update-rc.d command in step 11 (for configuring automatic password chosen in step 2 of Figure 6 (to set up Remote startup scripts) shown in Figure 5. Desktop). Pick a secure password that is at least eight charIf you need to change the start-up or shutdown acters long. Set up the VNC server pro1. Start Remote Desktop. Go to System -> Preferences -> Remote Desktop 2. On the Remote Desktop Preferences dialog box: gram so that authorized users a. Check the “Allow other users to view your desktop” and “Allow other users to control your computer” checkboxes. can view and control your b. Un-check the “You must confirm each access to this machine” checkbox. c. Check the “Require the user to enter this password” checkbox, and enter a secure password. computer, and remove the d. Click Close requirement to confirm each Figure 6—The steps to set up Remote Desktop access to the webcam server. CIRCUIT CELLAR®


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1. Start Terminal: Go to Applications -> Accessories -> Terminal 2. Type: sudo -i a. press Enter b. enter the administrator’s password. 3. Check the ufw status. Type: ufw status (you should get a Status: inactive) 4. Set ufw to deny all connections by default. Type: ufw default deny 5. Allow browser traffic. Type: ufw allow 80 6. Allow secure shell traffic. Type: ufw allow ssh 7. Allow webcam traffic. Type: ufw allow 8888 8. Allow remote desktop traffic. Type: ufw allow 5900 9. Enable ufw. Type: ufw enable 10. View the status of the firewall, and list ports you have opened. Type ufw status 11. Restart the computer. Type: reboot

Figure 7—The steps to set up the firewall

D. Morrison, Webcam Server Project, http://webcamserver.sourceforge.net/. IBM C-it USB Camera Driver FAQ, www.linux-usb.org/ ibmcam/ibmcamFAQ.html. IBM C-it USB Camera Driver for Linux, www.linuxusb.org/ibmcam/. Official Ubuntu Documentation, https://help.ubuntu. com/. PuTTY: A Free Telnet/SSH Client, www.chiark.green end.org.uk/~sgtatham/putty/.

During set-up, I kept a monitor connected to the webcam server while connecting from a remote VNC client to make sure that my remote computer could display the same images as the webcam server’s monitor.

README for the Linux device driver for the IBM CIt USB Video Camera, www.mjmwired.net/kernel/ Documentation/video4linux/ibmcam.txt. RealVnc, www.realvnc.com.

Ubuntu’s uncomplicated firewall (ufw) front-end program easily removes avenues used by hackers to attack your server. I shut off all network ports to the webcam server and then reopened just the ports the server requires to provide its services. Port 80 must be open to serve web pages. Port 8888 must be open to allow the webcam-server software to stream video. I opened port 22 (ssh) to allow secure shell terminal emulator access. Port 5900 was opened to allow Remote Desktop (the VNC server) to connect. Figure 7 is a list of the steps associated with setting up the firewall.

DESIGN SUCCESS This project taught me a lot about setting up an Ubuntu server and interfacing it with a USB camera. And now it serves to inspire curiosity and excitement about computer technology in our department’s display case. Each day, curious students are lured to the display because of the attractive lights on the server and Kiki’s drumming. One student called his father, who lives several hundred miles away, to watch and control Kiki with the webcam server. You too can connect to the webcam server and control Kiki at http://cswebcam.lasierra.edu. I Denny Lin ([email protected]) has a BA in Music and a BS and an MSc in Computer Science. He is an Assistant Professor of Computer Science and a Senior Programmer/Systems Analyst at La Sierra University. Besides teaching C++ Programming, Software Engineering, and Systems Analysis courses, Denny also teaches Computer Music Synthesis courses in the Music Department and Electronics in the Physics Department.

Ubuntu 9.04 (Jaunty Jackalope), http://releases.ubuntu. com/jaunty/ubuntu-9.04-desktop-i386.iso.

SOURCES Nios embedded processor Altera | www.altera.com

NEED-TO-KNOW INFO Knowledge is power. In the computer applications industry, informed engineers and programmers don’t just survive, they thrive and excel. For more need-to-know information about topics covered in Denny Lin’s Issue 240 article, the Circuit Cellar editorial staff highly recommends the following content: — Build Your Own 8051 Web Server by Jim Brady Circuit Cellar 146, 2002 Building a web server doesn’t have to be difficult. Jim built an 8051 server and describes the project in this article. Topics: Web Server, TCP/IP, Ethernet

Chicken of the VNC, http://sourceforge.net/projects/cotvnc/.

Go to: www.circuitcellar.com/magazine/146toc.htm — Web Camera Design by Minas Kalarakis Circuit Cellar 228, 2009 This versatile web camera system can take pictures, pan a camera, and change its IP and gateway address to match a network. An Ethernet module transmits the packets over the Internet. Topics: Webcam, Servo, Ethernet, Packet Transmission

Dynamic Network Services, www.dyndns.com/.

Go to: www.circuitcellar.com/magazine/228.html

RESOURCES


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CIRCUIT CELLAR®



FIREWALL SETUP

27

F EATURE

ARTICLE

by Devlin Gualtieri (USA)

Build an X10 Controller (Part 1) Circuit Design This article series details the process of building an X10 controller from start to finish. Here you learn about the circuit design before moving on to the software.

B

ack in the 1980s, I combined my interest in carrier-current communication technology and embedded systems to design my first timed automatic control system. The design featured a Zilog Z80 microprocessor and a carrier-current transmitter that I built myself. Three decades later, I still find myself rethinking my first design. But now I have a lot more experience under my belt and new technologies to put into play. In this article series, I’ll describe my original X10 controller and then present my newest design. This article covers the circuitry (see Photo 1). Next month, I’ll describe the software side of the project.

When I went off to college, I saw that the same trick was used by the campus radio station. It had transmitters on the AM broadcast band coupled to the power lines in each of the dormitories. In that way, a low-power signal, legal under the FCC Part 15 rules, could reach a large audience. It was still done using vacuum tubes. Carrier-current communication didn’t enter my mind again until I was a homeowner in the early 1980s wrestling


CARRIER CURRENT

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When I was a grammar-school student, my parents had what I considered a magical device in their kitchen. It was an intercom that allowed them to talk with our next-door neighbor who had an identical unit. The amazing part about these intercoms was that there were no wires connecting the devices. They just plugged into an electrical outlet. Later, when I was in high school and more familiar with electronics, I realized that they were carrier-current devices. They had a low-frequency amplitude-modulated transmitter and a complementary AM receiver. The transmitter signals were injected into the power lines, and that’s how they traveled between houses. Everything was done using vacuum tubes because it was the 1960s at the time.

Photo 1—The finished controller. The ICSP connector is visible at the bottom of the board. The back-up lithium cell, in a home-built battery holder made from a small plastic bottle and some switch parts, is at the lower right. CIRCUIT CELLAR®


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CIRCUIT CELLAR®



with the unreliable mechanwith the zero crossings of the 8.333 ical timers I was using to AC line, they’re able to exam5.556 control the exterior lighting ine the proper time interval at my home. At about the to determine the presence or 2.778 same time, the X10 system absence of this signal. The 1 hit the stores. X10 is a carripresence of 120 kHz at the er-current system that appointed time is interpretallows control of lights and ed as a logical one, and its appliances. It’s a nicely inteabsence is a logical zero. 1 grated system of modules Only a single bit is trans2.778 that replaces the light mitted at each zero crossswitches and utility outlets ing. The data protocol calls 5.556 in your house. These modfor a 4-bit preamble, fol8.333 ules have the same function lowed by an 8-bit house as the switches and outlets code and a 10-bit device Figure 1 —Timing in milliseconds of the carrier-current signal for they replace, but they number or function code. X10 communication. The data is transmitted as 1-ms bursts of a include remote switching The 8-bit house code is actu120-kHz carrier synchronized with the zero crossings of the 60-Hz voltage sine wave. Each bit is transmitted redundantly three times circuitry. I was able to purally just four bits of informain a half cycle. chase these X10 devices tion, but each bit is followed with a companion control by its complement. If a logibox that injected carrier-current sigcal one is transmitted on one zero specifications, and I was able to build nals into the power lines to turn crossing, a logical zero is transmitted a reliable X10 controller using 1980slights on and off, brighten and dim on the next. The same is true for the era technology. lights, and turn appliances on and off. device number/function code. It’s just All this was nice when I was present five bits alternated with their compleTHE X10 SYSTEM to push the buttons on the control ments. Figure 2 summarizes the transThe X10 signal, as shown in Figure 1, box, but I wanted a timed automaticmission protocol. Table 1 shows the is a pulsed 120-kHz oscillator that’s control system. I was doing embedded binary values of the house codes and synchronized with the zero crossing systems work in the same period, so I device codes. Table 2 shows the binary of the AC power line. The X10 innohad the tools to roll my own concommand codes. The preamble, which vation, which made it a patentable troller. In those days, this was no sim- idea, was this synchronization of the is not interleaved with its complemenple task. An embedded system tary bits, is always 1110. Since it has datastream with the AC power line involved a Z80 microprocessor, a mul- zero crossings. The receiver modules three logical one bits in series, it can’t titude of peripheral chips, an ultraviobe confused with the home or know when to look for data, and this let-light-erasable EPROM burned with leads to noise immunity and device/function data. an assembly language program, and a enhanced reliability. The transmitter few kilobytes of static RAM with a accommodates the existence of INTO MODERNITY hefty NiCd battery backup. receivers on any of three possible My original X10 controller had an There was another problem. I needphases of the AC line by transmitting event table that was updated by a ed to design and build my own carriredundant signals at times where the serial data link, so it survived my er-current transmitter to mimic the zero crossings at these other phases transition from an early CP/M comX10 signals. These were the days would occur. puter system to an MS-DOS computbefore the Internet. But fortunately, The data signals are transmitted in er. After a time, computers became some hobby magazines published short bursts of the 120-kHz oscillator. ubiquitous enough for manufacturers information about the X10 signal Since the receivers are synchronized to notice, and an X10 controller with a similar serial access became available. This controller was the CP290, which came with a 1 2 3 4 5 6 7 8 9 10 11 simple DOS program for programming events and enough H1 * H1 H2 * H2 H4 * H4 H8 * H8 D1 * D1 D2 * D2 D4 * D4 D8 * D8 D16 * D16 Preamble information for programmers to 1 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 0 1 roll their own advanced serial interface. I purchased a CP290 “Start” code and retired my Z80 controller, Device code “7” House code “A” 1110 01010 0110 which was still operating after many years of service. More Figure 2—The data format of an X10 command. A command requires 11 full cycles of the power than ten years ago, I migrated line. After the transmission of the start code, the data bits and their complements are transmitted on successive half cycles of the AC voltage sine wave. from Windows computers to

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Code M N O P C D A B E F G H K L I J

H8 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1

H4 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1

H2 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1

H1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

Device 13 14 15 16 3 4 1 2 5 6 7 8 11 12 9 10

D16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

D8 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1

D4 0 0 0 1 0 1 1 1 0 0 0 0 1 1 1 1

D2 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1

D1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

Table 1—The house codes and device codes are listed in order of ascending binary values.

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Linux—first Red Hat, then Gentoo, and now Ubuntu. I happily migrated nearly all my tools to Linux, but I still needed to keep a DOS diskette with the CP290 control program on it. I dutifully booted from this diskette once each month to update the CP290 event table with new times. Several years ago, my CP290 started to do strange things. It started to turn on lights at odd times. A dump of the on-board memory showed that it was corrupted, a fact that I attributed to an exhausted back-up battery, which I replaced. The problems were solved for a few months, but they reappeared. The back-up battery was again exhausted, which led me to suspect that the CP290 power supply wasn’t putting out its rated voltage. As is usual for equipment that’s been operating continuously for many years, the electrolytic capacitor in the power supply had gone bad. It was a simple fix, but I started thinking of how I

would use today’s technology to build another X10 controller.

PL513 & EMBEDDED MCUs

Controlling X10 devices is simpler now, since you don’t need to build your own carrier-current transmitter. The PL513, shown in Photo 2, is an X10 carrier-current transmitter module that’s available from many sources for less than $20. The PL513 has circuitry that converts power line zero crossings to a logic signal, and it accepts a logic signal to activate a 120-kHz carrier-current transmitter. Using the PL513 lets you safely interface with the AC power line. It’s a well-designed circuit that has optical isolation between itself and your circuitry. One of its claimed benefits is that it enables you to use the X10 system commercially without infringing on any of the X10 patents. This may have been true in the past, but the fundamental X10 patents (4,200,862, 4,628,440, and 4,638,299) have now expired. However, it would be Command D16 D8 D4 D2 D1 hard to duplicate the All devices off 1 0 0 0 0 PL513 for $20, so Dim 1 0 0 1 0 that’s not recommendOn 1 0 1 0 0 ed. The only problem All lights off 1 0 1 1 0 with the PL513 is that All lights on 1 1 0 0 0 it’s supplied without a Bright 1 1 0 1 0 mating connector or Off 1 1 1 0 0 cable, but more on that later. There is a Table 2 —The command codes are listed in order of ascending similar X10 module, binary value. CIRCUIT CELLAR®


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appealing to hobbyists because of the availability of free software tools and the fact that these tools will run under Linux. I’ve been using the PIC microcontrollers with the PICBasic Pro compiler for many years, so I used what was familiar. PICBasic Pro has built-in statements for X10 control, which makes for easy programming.

CONTROLLER HARDWARE

Photo 2 —The PL513 X10 carrier-current transmitter module the TW523, which both sends and receives X10 signals. This would be useful for an alarm-type system, but it wasn’t needed in my home system. It might be worthwhile buying the TW523 instead of the PL513, since it contains the PL513 circuitry and it would allow a future alarm system

feature. The TW523 is just a little more expensive. Today’s designer has a choice of many microcontrollers, most of which are more than adequate for a simple task such as an X10 controller. The Arduino system, which uses an Atmel chip, is especially

Figure 3 and Figure 4 are schematics of the X10 controller. A PCB layout and parts placement guide are available online. Since I often etch my own circuit boards, this board is laid out as single-sided with a few necessary jumper wires. Through-hole parts are used, since surface-mounted components don’t make sense for a one-off board built by a hobbyist. The Microchip Technology PIC16F877 microcontroller I used has a built-in hardware USART for the serial interface, another feature that makes the programming easier. The PIC16F877 is a 40-pin DIP package, which might appear overkill for this application.

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CIRCUIT CELLAR®



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Figure 3 —This is a schematic of the X10 controller showing the PIC16F877 microcontroller and most of the peripheral circuitry.

I had a few of them in my surplus parts drawer—a design decision known to all designers. The PIC16F877A is slightly different from the PIC16F877. It has a

comparator option for some input pins, but this feature is disabled at power up to make it code-compatible with the PIC16F877. I used a 20-MHz chip, since high clock speeds are


Aside from its hardware USART feature, it has other redeeming features. There are its 256 bytes of EEPROM for storing events, a large data and code memory, and, most importantly,

32

CIRCUIT CELLAR®


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always good when doing serial communication. The clock signal in this design is derived from an oscillator, not a crystal or ceramic resonator, but those can be used instead since the precision of the timebase is not that important. The processor configuration data needs to specify the timebase type when programming the device. There’s an in-circuit serial programming (ICSP) connector on board, which is nearly essential for program development when high-pincount chips are used. Repeatedly removing such chips to program them in an external programmer would be possible only if a zeroinsertion-force (ZIF) socket is used. Such sockets are expensive and they take up a lot of board space. Every controller for real-time events needs a real-time clock. The PIC16F877 has enough horsepower to act as its own real-time clock, and the AC power line zero-crossing signal from the PL513 would make an excellent timebase. However, battery backup for timekeeping during power outages would be a problem, so I chose a standalone real-time clock chip, the Maxim DS1307. The DS1307 is inexpensive, it communicates using an I2C serial connection, and PICBasic Pro has built-in I2C commands. The clock chip handles its own battery back-up with a 3-V lithium cell. The serial data link is buffered by the usual MAX232 chip that provides the bipolar voltage signals that an RS-232 serial port expects. Of course, many computers now eschew such serial ports, but there are many USB-to-RS232 converters on the market that

2

3

solve this problem. I use a few transistors for driving external LEDs and the PL513. The PL513 driver circuitry is similar to that

4

Figure 5—The connections to the PL513 X10 carrier-current transmitter module www.circuitcellar.com

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CIRCUIT CELLAR®



1

Figure 4—This schematic of the X10 controller shows the MAX232 serial interface and the voltage regulator. Although the voltage regulator accepts a 12-V input, a 9-V input is acceptable, and it allows for greater energy efficiency. The controller draws about 35 mA in its quiescent state, about 70 mA when an X10 command is being sent, and a maximum current of less than 100 mA.

recommended by the manufacturer. I made a small change to preserve signal polarity on the output driver to maintain compatibility with the PICBasic Pro X10 commands. The output driver as published by the manufacturer inverts the data signal. The drivers have diode protection circuitry to prevent damage from voltage spikes. It is possible to drive LEDs directly from the PIC pins, but I never like that approach. I like bright LEDs, which translates to a lot of drive current, and a microcontroller shouldn’t be too abused. One LED is used to indicate whenever an X10 signal is being transmitted, and the other indicates that the back-up battery is still good. Either or both of these LEDs and their associated components can be eliminated at no real loss of functionality, although there’s another function of the transmit LED. If the connection from the controller to the PL513 is broken, the LED will remain lit when a command is attempted but no power line zero crossings are detected. One

33

advantage of the PIC microcontroller is the availability of analog-to-digital conversion on some pins. For the PIC16F877, this is a 10-bit conversion that has plenty of resolution for most applications. The PICBasic Pro compiler has commands that simplify handling analog input. Since I had an overabundance of input pins, I decided to use one of them to monitor the back-up battery voltage. The Maxim datasheet specifies a nominal 3-V lithium cell and recommends a backup battery voltage of between 2.0 and 3.5 V. It would be nice to continually monitor the battery voltage to give an indication of when the backup battery is reaching its end of life, but there’s a problem here. Maxim says that a back-up battery will last for 10 years, so attempts to monitor the battery voltage will actually reduce the battery lifetime, even if the monitor impedance is several megohms! I’ve taken the approach of using a removable jumper to one of the PIC analog inputs so the battery can be checked occasionally without a voltmeter. In normal operation, the jumper is removed so that the battery is not unnecessarily drained. A front panel push button can be used instead of the jumper, and a push button with an integrated LED would be ideal. Because of the availability of many input pins, I used jumpers to set the house code. The house code also can be set with software at the loss of one event location in the event table in EEPROM. However, the house code is rarely changed once it’s set, so the jumper approach is not a problem. One house code allows control of 16 devices. If you have a large house that needs more devices, you could modify the software to include different house codes in the event table, but the number of possible events in the table would be reduced because of the extra storage requirement. Photo 1 is the finished circuit. The ICSP connector is visible at the bottom of the board. The power source is a regulated 9-V wall transformer. It’s one that stands vertically, so it can be plugged into the same outlet as the PL513. You could probably build the PL513 and power supply into your controller box so it can use a single plug connection to a wall outlet.


CONNECTIONS

34

The connector on the PL513 mates with those old telephone and modem cables you have at the bottom of a drawer somewhere, but they’re not going to work. Although the connectors have four pins, inexpensive telephone cables typically contain just two or three wires. The PL513 requires four wires. I found that handset cords, the coiled cords that connect old-style telephone handsets to the telephone body, use all four wires. Telephone cables purchased at home improvement stores usually have four wires, and I used one of these for connection to the PL513. The mating jack for the controller side is available at nearly every home improvement store. Figure 5 shows the PL513 connections. The TW523 connections are the same, except that pin 3 is an open-collector output for received signals. If you aren’t using this signal,

this pin can be grounded to maintain compatibility with the PL513 connection at the controller.

THE PROGRAM AHEAD In Part 2 of this article series, I’ll review the controller program and a utility I wrote to convert a human-readable event file to the serial data the X10 controller understands. The utility is written in ANSI C, so it compiles and executes under both Linux and Windows. Executables will be provided for those of you without compilers. I Devlin Gualtieri received a PhD in Solid-State Science from Syracuse University in 1974 and worked for many years doing research for a major aerospace company. Now retired, he spends his time doing various embedded systems projects. He can be reached at [email protected].

PROJECT FILES To download the code, go to ftp://ftp.circuitcellar.com/ pub/Circuit_Cellar/2010/240.

SOURCES PIC16F877 Microcontroller Microchip Technology, Inc. | www.microchip.com PL513 X10 Module X-10 (USA), Inc. | www.x10.com

NEED-TO-KNOW INFO Knowledge is power. In the computer applications industry, informed engineers and programmers don’t just survive, they thrive and excel. For more need-to-know information about topics covered in Devlin Gualtieri’s Issue 240 article, the Circuit Cellar editorial staff highly recommends the following content: — XTstat A Portable Wireless X10 Thermostat by Henry Jacobs Circuit Cellar 175, 2005 Henry’s XTstat wireless thermostat allows you to adjust a room’s temperature. The PIC-based device is a great starting point for wireless temperature control projects. Topics: X10, Wireless Communication, RF Go to: www.circuitcellar.com/magazine/175toc.htm — Radio Riot by Tom Cantrell Circuit Cellar 167, 2004 Going wireless doesn’t need to be difficult. Tom has the scoop on several essential wireless solutions. Topics: Wireless, RFID, ZigBee, Bluetooth, IEEE 802.15.4, Spread Spectrum Go to: www.circuitcellar.com/magazine/167toc.htm

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F EATURE

ARTICLE

by Tom Struzik (USA)

Wireless Data Exchange Build a 2,700-lb. Bluetooth Headset Building a Bluetooth-enabled device can be difficult if you don’t have any experience with the technology. Finding the right module can greatly simplify the process. The Bluegiga WT32 is a highly integrated Bluetooth module that fits the bill. Here you learn how to put Bluetooth to good use.


E

36

nvy is a strong motivator. My wife bought a new Toyota Prius and it had one exceptionally “geekworthy” feature: a built-in Bluetooth interface. As if by magic, when you start the car, it automatically connects to her Palm Treo. She answers incoming calls by simply pressing a button on the steering wheel. The audio, which comes in over the car’s stereo speakers, automatically mutes whatever is playing when a call is received. All in all, it’s a slick, simple interface. Unfortunately, instead of a Prius, I have an old (2,700-lb. tare weight) Acura, and its only upgrade is a radio with an auxiliary input. My thought was that I should be able to build a Bluetooth-to-aux-in adapter that functions much like the Prius’s Bluetooth interface. However, I figured I should be able to support playing MP3s from my smart phone with a custom adapter. Plus, if I could access the phone’s voice command functionality, I thought I would really “out geek” the Prius! Thus, I started my project to construct a “2,700-lb. Bluetooth headset.” I had three goals for the project. The first was to learn something about Bluetooth. The second was to find a Bluetooth module I could use for this Bluetooth project and others. My third goal was to one-up the Prius’s Bluetooth functionality!

to be a very DIY-friendly shop. They provide breakout boards for their SMD parts, manuals, user guides, and even a support forum. They’re also one of the few parts sources that offer low-cost U.S. Postal Service shipping, so you don’t have to pay a $10 shipping fee for a $2 part! So, off to SparkFun I went, and they had several different Bluetooth modules in stock (all with breakout boards).

FINDING A MODULE

Fi gure 1—The Bluegiga WT32 is a highly integrated device. In addition to the radio, it contains multiple digital and analog I/O sources, a programmable MCU, and a DSP.

When I look for small-quantity parts, I tend to start searching at SparkFun (www.sparkfun.com). I find them

USART/USB Flash

PIO

RAM

Antenna

2.4GHz Radio

DSP

I/O

Audio in/out

MCU PCM, I2S, SPDIF XTAL

RESET

SPI

CIRCUIT CELLAR®


•


of the WT32 datasheet, the iWRAP user guide, and the circuit diagram for the WT32 breakout board. With this in hand, I thought I should be able to power up and begin interacting with the WT32 device. One thing I noticed while working on powering up the WT32 was that the SparkFun breakout board has differences in the pin nomenclature and c) d) wiring between it and the actual WT32 device. For example, the breakout board has VDDIO and VDD_BAT wired together and AGND and DGND have a solder jumper. With power to the board, the next step was to gain access to the UART. The UART has CMOS input/outputs, so a MAX3232 line driver chip was required for interfacing to my PC serial port. With the UART connected, I confirmed the basics were working by Photo 1a—A WT32 module without its cover. The heart of the WT32 is a Cambridge Silicon running HyperTerminal on my PC Radio BlueCore 5 Multimedia chip. b—The underside of the WT32 module. Don’t place bare copper on your board underneath the WT32! See the WT32 datasheet for board layout recand connecting at 115,200 bps, 8N1 to ommendations. c—The SparkFun WT32 breakout board with the cover intact on its WT32. I the WT32 UART interface. When I added the legs on the breakout board in order to facilitate easy breadboard experimentation. applied power to the WT32, HyperTerd—This is the breadboard with the breakout board on the left. minal displayed the iWRAP boot screen (see Figure 2). Success! Now, with a live connection to the Only one, however, the Bluegiga WT32, build a complete Bluetooth applicaWT32’s iWRAP firmware, the fun supported anything more than simple tion using nothing more than the really began. The next logical step was WT32 and its UART or USB inter“serial cable replacement.” to create an hands-free profile (HFP) face. It appeared that the Bluegiga Further investigation revealed that link between the WT32 and my smart WT32 was an almost-perfect candithe WT32 was quite a find. Per the phone. With this link, I could explore date for my project. datasheet, it has one of just about the basics of Bluetooth link setup and Figure 1 and Photo 1 show the everything. On the analog audio side, how the iWRAP firmware operated. WT32 module’s details. Photo 1c it supports stereo input and output The iWRAP user guide was a bit light with differential signal levels. On the shows the SparkFun breakout board. on how to actually set up an HFP link, digital audio side, it has an integratso I went over to the Bluegiga website ed DSP with stereo codec and supGETTING STARTED and signed up for their tech support port for multiple digital audio forMy initial goal for working with the forum. This move turned out to be mats (PCM, I2S, and SPDIF). The digWT32 was to breadboard the simplest excellent, as the tech support forum possible configuration and validate ital I/O interface has support for had not only firmware updates and PC that I could indeed make a Bluetooth USB, RS-232, and SPI—and on top of tools, but also WT32 application notes connection to my phone. I also felt that, 10 individually programmable like the “Hands-Free and Headset Prothat I needed to gain some experience I/O pins. Most importantly, in the files” iWRAP application note. From with how the WT32, iWRAP, and area of Bluetooth, it supports multithis, there were two main things ple Bluetooth profiles (A2DP, AVRCP, phone interact. I started by reviewing the documenHFP, HFP-AG, SPP, OPP, and HID) required to configure an HFP link. The tation that SparkFun had available on and has an integrated antenna, giving first was to enable the required Blueits website. This information consisted tooth profile. The second was to define the device a 30-m range. And if all that wasn’t enough, throw in a the Class-of-Device (CoD). built-in LiPo battery charger! Enabling and disabling profiles WRAP THOR AI (3.0.0 build 165) On top of this massive hardwas straightforward. The Copyright (c) 2003-2008 Bluegiga Technologies Inc. ware feature list, Bluegiga iWRAP command was SET READY. loaded the WT32 with its PROFILE {profile_name} iWRAP firmware. The program[SDP_name]. Note that leaving Figure 2—When I applied power to the WT32, HyperTermiming language provided by this out the SDP_name disables the nal displayed the iWRAP boot screen. Success! (Source: Bluegiga Technologies) firmware makes it possible to specified profile. For my simple www.circuitcellar.com

•

CIRCUIT CELLAR®



b)

a)

37

WRAP THOR AI (3.0.0 build 165) Copyright (c) 2003-2008 Bluegiga Technologies Inc. READY. HFP 1 CONNECT 0 HFP 2 00:17:e8:3f:d9:e2 P[OHOVZ[VMTVK\SLZZ[HUKHSVUL Gateways

HKHW[LYZ07LUHISLKNH[L^H`ZHUKP+PNPKH[HZLY]PJLZ+PNPOHZ[OL[VVSZ[VZLL`V\YWYVQLJ[ [OYV\NOMYVTILNPUUPUN[VLUK

Modules

Get started today with an XBee Development Kit Digi International Tel. 1-877-912-3444

Adapters

www.digi.com/getXBee Personal Download for [email protected] I © Circuit Cellar


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