EEWebIssue 90

March 19, 2013

Electrical Engineering Community eeweb.com

Facing theCounterfeitIC Issue

TECHNICAL ARTICLE

Raspberry Pi -Part 2

FEATURED PROJECT

High Speed EngineeringManager, Samtec

JulianFerry

http://bit.ly/SJ9ugm

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Julian Ferry HIGH SPEED ENGINEERING MANAGER AT SAMTEC

A conversation with Samtec’s High Speed Engineering Manager about its differentiated connectors as well as some tips for choosing the right connector for your application.

“Fake” chips in the marketplace is a huge issue for manufacturing companies and distributers alike. Here is a solution to that problem.

RTZ - Return to Zero Comic

Featured Products

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Facing the Counterfeit IC Problem

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The Raspberry Pi - Part 2: Raspbian Wheezy

The daunting task of selecting the right components for your project made easy.

20Picking Components With Confidence

The second installment of this series outlines two different popular operating systems for the Raspberry Pi, Arch Linux ARM and Raspbian Wheezy.

BY KYLE OLIVE

BY ALAN LOWNE WITH SAELIG

& Arch Linux ARM

BY TAMARA SCHMITZ WITH INTERSIL

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FerryJulianSamtec is a service leader in the electronic interconnect industry. Its emphasis on customer satisfaction and service mixed with quality products solidifies its multinational status. We spoke with Julian Ferry, the High Speed En-gineering Manager at Samtec, about why customer service is key, how Samtec differntiates itself from other connector companies, and a few tips for choosing the right connector for your application.

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FerryJulian

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How did you get into Electrical Engineering?

I was always tearing stuff apart when I was a kid, and I eventually taught myself how to solder. I built antennas and fixed radios and amplifiers and stuff. When I was 16 or 17, I pulled an old oscilloscope out of the trash and fixed it up. I just thought it was fun. I didn’t think this interest might have some value in the real world.

I went to Penn State in the mid 1980’s, and started out as a chemical engineering major. I had some good chemistry and biology teachers in high school, and I think that influenced me at the time. But I did have some people telling me I should consider electronics. I switched majors to EE after my first Physics Electromagnetics class. Something just clicked. After that, I focused on Microwave and RF Design and Communications and took a lot of electives in those areas.

When I graduated, I started to work at what was then AMP Inc., which is now part of TE Connectivity and the former Tyco. They were the world’s largest connector company at the time. I worked in a product qualification test lab in a group that did microwave and RF testing of connectors and cables. Network Analyzers (VNA’s) had just made it into that industry, and we were testing to 26 GHz. This was also when high-speed computer designers were starting to run into microwave-like problems in their digital systems. Early in my career, I got involved in time domain and signal integrity work. One of my first projects as a test engineer was to build a differential TDR system, because they weren’t commercially available.

Later at AMP, I moved into a product development group where I focused on telecomm and data products, and eventually on Cat-5-type cabling

products. This was a combination mechanical and electrical engineering role, and I learned a lot of new skills there. I participated in developing the Cat-5 spec, which covers building wiring products for both data and telecom, and that was very educational. Around 1993, 6 or 7 years in to my career, I moved into a management role, which was way ahead of my planned timeline. But it worked out OK, and I eventually built up a test lab and EE design team of 6 engineers. I later moved into a pure R&D group in a Technical Staff role, where I focused on improving connector modeling and simulations. At the time we were moving from 2D field solvers, which had been the standard tool for 10-15 years, to 3D solvers.

From there, I worked a few years at Foxconn, where I designed high-speed cable assemblies and connectors. While I was at Foxconn, I got a call from Samtec. I knew Samtec didn’t offer many high-speed products—they were more focused on pin-headers and similar

connectors. But they were branching out into smaller, tighter pitch, SMT type connectors. Signal speeds were also increasing rapidly, and the combination of higher signal density and increased data rates was starting to make signal integrity problems more widespread. They were getting customer requests for things like SPICE models and insertion loss and crosstalk data, and they didn’t know how to respond.

At that point, Samtec was mostly mechanical engineering focused. They used consultants to help them with SI problems, but they realized they needed signal integrity engineers on staff, not only to help design high-speed products, but also to help their customers. Best-in-class customer support has always been a goal for Samtec. At the time (around 2000), signal integrity support was lacking in the connector industry. Samtec had decided to open an office near Harrisburg, PA, because of the number of SI connector engineers in the area, along with other local connector expertise.

“When we started our group, most companies

were providing good support to what we would

call Tier 1 companies, but they would pretty

much ignore the smaller businesses. At Samtec,

those smaller companies are a focus for us.”

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EEWeb PULSE INTERVIEW AMP had been headquartered in the area since the 1940’s, and many support industries had grown in the area. There were about 60 different connector manufactures located near Harrisburg. I was the first EE hired by Samtec, and part of my job was to build an SI engineering team. We’re still here with 18 engineers locally, and we’ve also added SI engineering groups in Taiwan, China, and Oregon.

Could you tell us a little about the design support that Samtec offers?

We try to differentiate ourselves from some of the larger connector companies with our level of support. When we started our group, most companies were providing good support to what we would call Tier 1 companies, but they would pretty much ignore the smaller businesses. At Samtec, those smaller companies are a focus for us—we have around 20,000 active customers today. Some of them don’t have engineers who are well versed in SI principles and problems. We’ve been willing to do a lot of work for them. One of our goals is to be “the easiest connector to design in.” Part of this requires very detailed characterization testing, and making this information easily available on the web. SI wise, connectors are poorly covered by industry standards, so test procedures are not well defined and data reporting is not standardized. We also do what we call “customer support R&D,” where we work to develop better test procedures. The end goal is to characterize our products fully so our customers can trust our data so they don’t have to do the characterization work themselves.

We take this same approach to modeling, where we provide connector models in most popular formats. This has changed over the years; SPICE was king and we

provided as many as eight various flavors such as PSPICE and HSPICE. We did a lot of post-processing work to convert our files so they were point-and-click usable by our customers. As the industry has moved to more microwave-type simulators, we’ve changed our modeling processes so we can provide S-parameter models. We also work with simulation tool vendors directly—we buy some tools for the sole purpose of making sure our models work easily and correctly in each tool.

What tools are the most popular?

In the last four or five years, there’s been a trend toward more S-Parameter based simulators, where simulation times are faster than SPICE at higher frequencies. Agilent’s ADS is probably the most popular currently, but it’s a dynamic situation, with a lot of players trying to carve out a niche as the industry shifts. Back to our large

customer base, we were fortunate because we could see the industry leaders in system design migrating towards ADS early on, as they’d ping us for certain types of models. That allows us to see over time where the industry is going as the newer tools progress and get cheaper, more user friendly ,and propagate through the industry. There are still many of our customers who use SPICE, so we can’t abandon SPICE models. We still provide backwards compatible and older format models for our less bleeding-edge customers.

What is the process of designing your connectors?

I’ve been designing connectors for more than 20 years, and in the past, connector design was primarily driven by mechanical issues. There was a lot of effort put into the physical interface design for robustness, reliability—those kinds of things. Of course, there have always been

Samtec’s Avanced Design System (ADS) Interface

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power and high current connectors, which have their own set of electrical issues. Even before SI issues were a factor, connectors were a challenging engineering problem. As signal speeds increased and form factors became smaller, the SI electrical side became much more important. Even as recently as two or three years ago, a lot of connectors were designed in an electrical vacuum, where there wasn’t much input provided by SI guys. Those days are ending.

We SI guys still lose many engineering tradeoff battles. We do 3D electrical and mechanical simulations of every connector we design. The

design process can be challenging, because many of the things we want to do from an EE perspective add cost and complexity, which makes the mechanical engineer’s job harder. Another challenge we face at Samtec is that, along with industry standard connectors, we offer many generic, non-standards based interfaces. Using PCI Express as an example, that interface is well defined, with things like signal and ground locations, shields, etc. The interface is defined, along with things like signal and ground locations, shields, etc. They also provide firm performance numbers that must be met. In a situation like that, we

could optimize things electrically to ensure we hit those specs. However, in generic connector applications, it’s more difficult because performance goals are often fuzzy. Some customers might use a connector in differential applications and some might use it single-ended. Many run differential and single-ended in the same connector. If we know it’s going to be purely differential, we can optimize it one direction, and vice versa if we know it’s single-ended only. But when we get into the mixed applications, it’s harder to optimize the electrical performance across all potential applications. Back to testing, this also requires us to characterize

“A few years ago, Samtec acquired an

optical engine design and fabrication

company. We’ve been working

on merging the two media

and developing a system

that allows customers to use fiber or copper, depending on their current

and future performance

requirements.“

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EEWeb PULSE INTERVIEW our connectors in many different configurations.

What are some tips for finding the best connectors for a particular application?

I’d say the biggest constraints are how much board space you have to work with, and how many signals you have to run. That drives everything. Once you have the general size nailed down and the configuration of the connector (whether it’s top entry, right angle, etc.), then you can start looking at which electrical parameter is most important in your particular application. In some cases, impedance performance might be important and in other cases, impedance might not matter much. The engineer needs to focus on which performance aspects are most critical in their application. Of course, if there is a spec in place, then it can be relatively easy to flip through a test report to see if the connector hits the specs. We also do quite a few system simulations on the front end, and publish those results in what we call an Application Note. For example, let’s take PCI express. A customer might have certain space requirement or a form factor in mind where a standard PCI express connector just won’t work, so they want to use one of our generic high speed connectors. What we do is take a system from the transceiver on one end to the transceiver on the other end, and then we add a certain amount of PCB trace in between. Then we add a connector pair in the middle and simulate that, and see if it meets the PCI spec requirements. We examine the eye patterns, and things like crosstalk and insertion loss. We might conclude something like, “With this pin out on this connector, you can operate PCI express at 4 Gb/sec with up to 12 inches of trace on each side”. We’ll typically publish multiple

scenarios like this in an App Note, and many customers have come to rely on this type of information. If they have a situation that’s just a bit different than a case covered in an App Note, we’ll often perform a simulation for them based on their particular requirements. Probably 20% of our current SI engineering effort at Samtec is spent doing system-type simulations like this.

What are some of Samtec’s new products?

One of our newest products is a combination of fiber optic and copper cables, called “FireFly.” A few years ago, Samtec acquired an optical engine design and fabrication company. We’ve been working on merging the two media and developing a system that allows customers to use fiber or copper, depending on their current and future performance requirements. Typically this is inside the box, so it’s somewhat like a high speed back plane replacement. The module mounts on the motherboard and operates with a copper cable assembly for short distances and lower speeds. If the speed, distance, or possibly EMI requirements, go up in the future, the copper can be replaced with a plug-in fiber optic assembly.

What other services does Samtec provide?

We provide what we call a “Final Inch,” where we step outside the connector and look at the PCB area around the connector. We develop an optimized

a PCB design for the breakout region in the area underneath the connector, including trace and via design and placement. We provide these designs in Gerber format along with SPICE models of the breakout region and traces. It makes sense for connector companies to do this because it’s basically the same for many applications. It doesn’t make sense to have to reinvent the wheel every time someone uses a connector. Similarly, we provide what we call intelligent PCB design libraries, which are libraries that a PCB designer can pull into his tool, which brings information on the footprint, pin numbering, schematic symbols, and sometimes information such as such as height and weight.

We’re also seeing some system design tools evolving to where one bill of materials contains models that are used for several different design tools. The BOM is basically a collection or database of models. There will be footprint info and symbols for use in layout; height, width, and window information for thermal/airflow simulations; SPICE or s-parameter models for SI simulations; weight and height information for pick and place optimization, etc. So this mega model is a one stop shop that contains all the information about the connector that’s needed from start to finish in the system design process. We work to stay abreast of such developments, and we often participate in industry efforts to develop standards for things like this. It’s all part of our goal of making our customer’s job easier. ■

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Low Input Current OptocouplersVishay Intertechnology, Inc. is broadening its optoelectronics portfolio with the release of two new series of 4-pin, low input current optocouplers with phototransistor output. The devices feature low DC input currents of 1 mA (VOS618A) and 5 mA (VOS617A) and are offered in the compact SSOP-4 mini-flat package, which saves more than 60 % of board space compared with a DIP-4 package. VOS618A and VOS617A series optocouplers are designed for isolated feedback loops, I/O isolation, and isolation in switch-mode power supplies, AC adapters, motor drives, solar inverters, networking switches, telecom line cards, and home appliances. For more information, please click here.

Compact Array AntennasMitsubishi Electric Corporation announced that 16 Atacama Compact Array (ACA) antennas delivered by the company under contract with the National Astronomical Observatory of Japan (NAOJ) were feted in an inauguration ceremony at the Operations Support Facility of the Atacama Large Millimeter/submillimeter Array (ALMA) Observatory in Chile. The Chilean President and numerous other guests celebrated the inauguration of the observatory, where the company-built ACA antennas comprising four 12-meter and 12 seven-meter antennas, will be used in astronomical observations as part of the 66 large radio telescopes being built in Chile’s Atacama Desert. For more information, please click here.

Thermistors Reduce Circuit FailuresAPI Technologies Corp. announced their latest development in NTC thermistors, Surge-Gard™ inrush current limiting devices. This new NTC thermistor is currently being showcased at Booth #907 at the 2013 Annual Applied Power Electronics Conference & Expo (APEC), which takes place in Long Beach, CA. APEC runs from March 17-21. Featuring steady state current ratings ranging from 1 to 36 amps and resistance values from 0.5Ω to 220Ω, Surge-Gard is manufactured using specially formulated metal oxide ceramic materials that allow the thermistors to suppress high inrush current surges. API offers fast prototyping of custom designs that utilize the new Surge-Gard as well as a wide variety of lead gauges and configuration. For more information, please click here.

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THE PROBLEM

ICs are not like hard-to-copy banknotes, and making fake “lookalike” parts which resemble real ones takes very little skill. Counterfeiting simply requires finding cheap parts in the same package and painting new marks on them. The problem of counterfeiting has arisen due to the high value of electronics parts, and the whole manufacturing chain, from assembly house to end-user, is vulnerable. The number of companies that have been duped by batches of fake devices is incalculable.

Counterfeiting semiconductors has been rapidly increasing, impacting a wide variety of electronics systems used by a wide gamut of involved parties – consumers, businesses, and military customers. The detection of counterfeit components has become an increasingly important priority, especially for electronics manufacturers and component suppliers worldwide.

Alan LowneCEO, Saelig Co.

Facing the

IssueCounterfeit

Alan LowneCEO, Saelig Co.

IC

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Alan LowneCEO, Saelig Co.

Facing the

IssueCounterfeit

Alan LowneCEO, Saelig Co.

IC

EEWeb PULSE TECH ARTICLE

14 EEWeb | Electrical Engineering Community

WHAT ARE COUNTERFEIT COMPONENTS?

The most prevalent counterfeiting technique is a re-badged product. It is a simple matter to remove the existing mark from a chip package and put on a new logo and part number, a different brand, or a different speed, and sell the semiconductor to an unsuspecting buyer who has no way of making sure that the product is “real”. Sometimes the purchased chip is only an empty package with no die inside. It is true that the finished system would fail before it left the factory – but this failure still requires expensive investigation and rework. With no part available to replace the bad one, such a failure can cause the dreaded exclamation “Line Down!” Worse, sometimes the failure of borderline ICs may not occur until the system is in the field, and field repairs can cost ten times as much to fix as those caught before they leave the factory.

Counterfeiting can also be from chips which are gleaned from discarded scrap boards. After being remarked with a different manufacturer’s logo, they are inserted into the supply chain and sold to innocent buyers – who naturally who assume that the products are genuine.

Usually, it is impossible to identify counterfeit components until they are fitted on a PCB and the first tests are made on the final product. Failure requires the costly identifica-tion of the components at fault and which then must be lifted from all boards in the production line. Complete

batches of finished products may need to be recalled to the factory – directly hurting a company’s bottom line.

There have been several technical measures to solve this problem in the past, including visual inspection of devices for marking errors – which needs a trained eye for all possible variations in marking. Electronically testing or x-raying every incoming batch is another technique. One more method, which is rather destructive, is to use a complex decapsulation system in order to visually inspect IC die sample. This method causes an immedi-ate loss of revenue due to the component’s destruction. Not only is this method expensive and time consuming, it requires complex training, skilled operators, and ex-pensive equipment.

SCREENING

Some distributors have advertised their screening ser-vices for verifying components, with a turnaround time of “as little as two days,” which is still unacceptable in many cases. These companies offer techniques such as: x-ray, x-ray fluorescence analysis (XRF), decapsulation, heated solvent testing, visual inspection, and solderability testing. These tests result in detailed reports when all that was really required was the simple question, “is it a good part?” In reality, this approach is only viable for military or large volume production runs.

What the electronics manufacturing industry really needs

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Counterfeiting accounts for more than8% of global merchandise trade and isequivalent to lost sales of as much as $600B and will grow to $1.2T by 2009US Dept of Commerce

Counterfeiting accounts for more than 8% of global merchandise trade, which is equivalent to lost sales of up to $600B and will grow to $1.2T by 2009US Dept. of Commerce

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Figure 2: Chip package markings can be made to look almost identical to the uncritical observer.

Can you tell which is the genuine

IC?

The outside package marking in this case does not match the die inside when the top cover is destructively removed.

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is a tool that can verify the identity of received ICs quickly and economically, using a statistically significant proce-dure. This tool would have to be suitable for all devices and packages, simple to use by any operator, and would need to give fast “good/suspect/fail” results.

In fact, there is such a commercially-available device – the ABI SENTRY Counterfeit IC Detector. SENTRY is a PC-driven product that uses a complex PinPrint™ Test Algorithm to check the validity of parts in sec-onds. The product is very simple to use and enables any receiving department to operate the equipment with minimal training. The analysis takes place in the background and the op-erator only sees a simple “Good Device”, “Blank Device” or “Fail Device” message, with the option to produce a detailed report to send to the supplier.

SENTRY contains a set of ZIF sockets accepting adapters for DIP, SOIC, BGA, SSOP, as well as discrete components. The system uses a comparative technique to rapidly analyze and learn new components, and then test the unknown parts. A known good component is locked into the ZIF socket while a test pattern is applied across all its pins. The component’s response to this test pattern, or PinPrint™,

is automatically measured and stored as a benchmark. SENTRY uses a combination of electronic parameter settings (voltage, frequency, source resistance, and wave-form) to generate the “signature” for each pin of the IC being checked. It then compares the unique electrical characteristics of known components and with suspect components. Testing between every possible pin com-bination is included, maximizing the chances of captur-

ing internal fault conditions. SENTRY can quickly detect missing or incorrect dies, lack of bond wires, inac-curate pin outs, and pin impedance variations. Simple pass or fail results are returned after testing, offering a high level of con-fidence in the authenticity of components.

As parts become increas-ingly complex, 100% testing becomes burdensome, but testing one or two pieces for, say, 200 pieces is man-ageable. Experience has shown that variations aris-ing from a suspect ship-ment will reveal themselves

well before such a test is complete. Nevertheless, if 100% non-destructive testing is required, using a SENTRY Counterfeit IC Detector is the ideal solution!

SENTRY is a unique solution for the quick and easy detection of counterfeit ICs and components. It is able to identify parts that have a different internal structure, or no structure at all, and even components originating from a different manufacturer. SENTRY is an easy to use instrument, capable of checking all types of components, ranging from simple two pin devices to more complex packages such as QFP and BGA.

Controlled via USB using the provided PC software, SEN-TRY’s device library can be built up by adding specific known good devices. Each device can have documents associated with it, such as photos of device markings, data sheets, and other documents, to further help in con-firming the integrity of a device. SENTRY contains all the hardware required to analyze the electrical characteristics of ICs with up to 256 pins. 256 pins+ devices can also be tested by rotating the device (BGA, QFP) to allow all pins

SENTRY is a practical and

affordable solution for solving the counterfeit IC issue, using its rapidly-built

dedicated library of component data

to cross-check each part tested.

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to be learned and compared. SENTRY is supplied with four 48 pin dual in line (DIL) zero insertion force (ZIF) sockets; these sockets can be used directly for older DIP components but can also be used to accommodate a variety of additional socket adapters available for different package types. The socket adapter can contain multiple IC sockets if required, to allow testing several ICs at the same time, or allow one IC to be compared to another. An expansion connector allows custom socket adapters with up to 256 pins to be attached.

Designed in Europe by ABI Electronics Ltd., a lead-ing manufacturer of PCB testing equipment, SENTRY has been conceived with component distributors and manufacturer Receiving Departments in mind for sample testing. Other application areas include electronics com-ponents suppliers using SENTRY to improve their quality assurance programs. Detailed reports can be saved to provide quality control traceability. SENTRY guards production facilities from the infiltration of counterfeit devices, identifying bad parts before they are mounted on PCBs; this protection saves time, money and frustra-tion, and SENTRY does not require any knowledge of electronics to use efficiently. After testing, the operator can just be presented with a simple “Good Device”, “Blank Device” or “Fail Device” message, but for in-depth analysis, PinPrints™ can be reviewed and full reports can be generated. In order to ensure consistency throughout the whole supply chain, SENTRY is designed to support data sharing – the PinPrints™ of a given component can be shared between users, from the OEM through to the distributor and end user.

ABI Sentry is housed in a sturdy metal box (10.6” x 10” x 3.6”) and weighs 8lbs, and can receive separate inter-changeable adapters for accepting various IC packages under test. With its large range of optional adapters, SENTRY can accommodate most types of IC packages, including DIP, SOIC, PLCC, QFP and even BGA. For simplicity of operation, SENTRY has no display or keypad, but is entirely controlled by a PC via USB using ABI’s custom designed free software.

SENTRY is a practical and affordable solution for solving the counterfeit IC issue, using its rapidly-built dedicated library of component data to cross-check each part tested. With lead-time issues making ICs harder to acquire to meet aggressive manufacturing schedules, identifying any parts that are not “real” before they enter production can potentially save every manufacturer a great deal of time and money – as well as that intangible but irretrievable quality – brand reputation.

Figure 3: SENTRY software screenshots.

For more information, visit:

www.saelig.com

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ep page master fp.indd 1 3/11/13 10:34:41 AM

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Confidence

PickingComponents

With

Tamara SchmitzIntersil ApplicationsManager for Optical Sensors

Confidence

PickingComponents

With

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Confidence

PickingComponents

With

Tamara SchmitzIntersil ApplicationsManager for Optical Sensors

Confidence

PickingComponents

With

So you have a circuit schematic you want to build. That seems simple enough. If you have a well-equipped lab at your disposal (possibly with a lab manager to guide you), then this article is not for you. However, if you will need to order electronic components for your project, this will offer some insight and advice.

So you have a circuit schematic you want to build. That seems simple enough. If you have a well-equipped lab at your disposal (possibly with a lab manager to guide you), then this article is not for you. However, if you will need to order electronic components for your project, this will offer some insight and advice.

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The two most popular places to order a wide range of electronic components are mouser.com and digikey.com. I’m going to reference Digikey since I’ve been to their headquarters in Thief River Falls, Minnesota and can vouch for the extent of their inventory and the efficiency of their factory.

To simplify our discussion, let’s choose one component to discuss: a resistor. If I ask Digikey’s search engine for a resistor, it returns a list with seven subheadings under “Resistor.” None of them are an obvious choice, such as “general purpose resistor.” Instead, they are categorized by the way they are mounted: surface mount, through hole, chassis mount, array, precision or accessories. Brute force dictates that you just start clicking and hope for pictures that can be deciphered. (Mouser categorizes the resistors by their composition material, by the way.)

Before choosing any component, you need to know about its function in the circuit. How much current travels through it? Is it in the power path? Is it in the signal path? How fast are the frequencies that must travel through it? If a component is in the power path, you might want to optimize its current carrying capability, heat dissipation, and charge storage (for capacitors). If a component is in the signal path, you have to consider the frequencies of the signals in the system. If it is a low frequency system, then there really aren’t any special requirements. Any component will work. If it is a high frequency system (hundreds of megahertz or higher), then you have to be more careful with your selection. The parasitics of a component can cause unwanted disturbances in your circuit. To first order, the smallest components are used in high frequency paths (like sports cars) and the largest components are needed in power systems (like tractor trailers or dump trucks).

Back to that list of choices under “Resistor.” “Through Hole” is the type of resistor that has been around for years, as shown in the figure to the right. This resistor is called “through hole” because the wires attached to each end go through plated holes in a printed circuit board (PCB). The value of the resistor is given in a color code of the first three bands. The fourth band designates the tolerance.

The second most typical choice is “Surface Mount.” Like the name suggests, these resistors do not penetrate through a PCB, they are soldered to pads on either side of it. Given the compact structure, this type of device is perfect for high frequency circuits. (They are also perfect for portable equipment.) Surface Mount Devices (SMDs) come in a variety of sizes. The largest size I’ve used is 1206 (about 0.12” x 0.06”). The next size to come along

was 0805 (about 0.08” x 0.05”). There is also 0603, 0402, 0201, and 01005. If you are going to solder these by hand, then I suggest sticking to the two largest values. When I was in graduate school and at the peak of my soldering skills, I could solder a 0402 component reliably and an 0201 component with about a 65% success rate. Fifteen years later, my clumsier fingers are much more comfort-able with 0805 and I groan when forced to deal with 0603.

The choices for resistors are less common. “Chassis mount” commonly refers to a type of resistor with a tab that allows you to mount it with a screw or bolt to a case. “Array” refers to a set of resistors in a chain like steps in a ladder. These are commonly used in simple conversion circuits. “Precision” refers to specially-trimmed compo-nents with values more exact than typical component values. (This type of precision costs, of course.)

Let’s assume you will choose a surface mount resistor and proceed to the selection page. Since there are more than 276,000 available, let’s narrow it down with the filters. I don’t usually limit myself to a particular manufacturer or series, since the component characteristics are far more important to me. Instead, let’s look at temperature coefficient. Temperature coefficient is the amount a com-ponent’s value will change as temperature changes. A smaller number is better. Next is tolerance. Tolerance is the allowed deviation from the predicted value. Tolerance is always plus or minus, so it is also the variability of the component. Again, a smaller number is better and will be more expensive.

For package and size, refer to the earlier discussion on attempting to solder different sizes of components. You can also specify a certain height for a package. (I assume there might be reasons why you would need to ensure the height does not exceed a certain value.) The packaging category refers to bulk orders and what type of automated machinery is being used to assemble electronic circuitry.

The filters I have skipped are the most important ones. Resistance value must guide your selection. Also, please

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pay attention to power dissipation. Once you know the DC and AC current through your component, you can calculate the power dissipation. For safety, order a com-ponent with more power capacity than is needed. (There could be shorts or surges and you don’t want the component to be destroyed.)

P = I2R.

A detailed discussion of resistor composi-tion is beyond the scope of this discussion. I don’t tend to limit this field when search-ing for a resistor, but I still like to have an idea of the options. Carbon resistors tend to be low wattage. Wire wound resistors, on the other hand, tend to have high watt-age capability.

The features add yet another flavor to this discussion. Military (and Automotive) qualified com-ponents have a wider temperature range and tougher qualifications. (Only pay for this if you need it.) Current sense resistors typically are small value resistors placed in series with the power supply to monitor it. Most of the other options are self-explanatory.

Most of the circuits I see on a daily basis are composed of surface mount components. For sensors, surface mount components are used exclusively. For an example, with a resistor, take a look at the ambient light and proximity sensor, the ISL29038, in the figure above. It is used in handheld devices, like smartphones. The ambient light sensor monitors the surrounding brightness to allow the backlight of the screen to dim and save power when appropriate. The proximity sensor senses when you are bringing the phone to your ear to talk on the phone and disables the screen.

In this case, surface mount components make sense because of their small size. (Smart phone makers, in fact, do prefer to use 0201 components around this part when possible.) For the eval board, which is hand assembled and most likely hand tested by the customer, 0805 com-ponents are friendlier. Compare the size of the R_EXT resistor to the standard paperclip in the figure. R_EXT sets the bias current for the device. It is not in a signal path. It has no high frequency signals through it. Still, it is good practice to keep it close to the sensor. Surface mount devices can be packed closely together.

As a matter of fact, in most situations, surface mount

components are my go-to package of choice. I would only choose through hole components if there was a high current supply, like 10 amps or more. This could still be handled with surface mount components, but would need good board layout with proper layers.

If you happen to be working on a board where you push connections together (no solder), then you’ll be happy to know that there are conversion boards available so that you can still prototype with surface mount components. However, the conversion board will add parasitics that may affect the performance of your prototype.

All in all, prototyping is a lot of fun. Don’t let the daunting task of ordering a component stop you from building that new idea or fun circuit you’ve wanted to try!

About the AuthorTamara Schmitz is a Senior Principal Applications En-gineer and Global Technical Training Coordinator at Intersil Corporation, where she has been employed since mid 2007. Tamara holds a BSEE and MSEE in electrical engineering and Ph.D. in RF CMOS Circuit Design from Stanford University. From August 1997 until August 2002 she was a lecturer in electrical engineering at Stanford; from August 2002 until August 2007, she served as assis-tant professor of electrical engineering at San Jose State University. Her interests include traveling, woodworking, dog training, playing guitar and accordion, and following major league baseball/college football.

To read more from this author, visit her EEWeb profile.

An example circuit with surface mount components. R_EXT is an 0805 surface mount resistor with a value of 499k ohms. The standard paperclip is for size reference.

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Kyle OliveComputer Engineering Student &

IEEE Student Branch ChairRaspberryRaspbian Wheezy(with Setup Guide),Arch Linux ARM

PART 2:

The

Pi

Raspberry Pi is a trademark of the Raspberry Pi Foundation

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Kyle OliveComputer Engineering Student &

IEEE Student Branch ChairRaspberryRaspbian Wheezy(with Setup Guide),Arch Linux ARM

PART 2:

The

Pi This is the second installment in my series on Raspberry Pi. If you haven’t worked with

Raspberry Pi before, please read my article “The Raspberry Pi: Intro-duction and Required Hardware“ to begin the series.

If you’re reading this article you’ve got your hands on a Raspberry Pi, and you’ve got all the hardware you’ll need to get yourself up and running. Unfortunately, until you’ve set up an operating system, you’re not going to get a whole lot of use out of it! This article will outline two different popular operating systems for the Raspberry Pi, Arch Linux ARM and Raspbian “Wheezy,” as well as go through a set-up guide for Raspbian.

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Operating System Comparison: Arch Linux ARM and Raspbian “Wheezy”

So, does it even make a difference as to which operating system you choose? In short, it depends. Depending on your skills and on your knowledge of Linux operating systems, the choice of operating system may not be an important one, but if you’re new to this realm of develop-ment, then there are some things to consider.

If you are new to Raspberry Pi, you might want to choose the recommended Raspbian “Wheezy” (http://www.rasp-bian.org/) operating system, which is based off of the popular Debian linux distri-bution, and is much friendlier to users who may not be too experienced with using Linux. Wheezy comes pre-packed with the LXDE (http://lxde.org/) desktop environment, a bunch of sample applications developed for the Raspberry Pi, and applications like Midori (a web browser) and Scratch (a graphical educational programming language). On top of that, it also has many of the standard require-ments for development (gcc, python, and more) pre-packaged and ready to go. If you want to be able to get started using your Raspberry Pi as quickly as possible and with minimal hassle, or if you wanted to be able to start using your Pi in an educational setting, your best bet is to go with this distribution.

On the other hand, you might want to choose Arch Linux ARM if you are a bit more experienced. Those familiar with the desktop-based Arch Linux will know that setting it up is a more involved process than other distributions, and Arch Linux ARM is no different. The base image for Arch Linux ARM is very light-weight, containing only the necessary software pack-ages to get your Pi running.

While this means a much longer, more involved setup process however, it also means that developers will be able to cut out a good portion of the software that they don’t need, resulting in a faster, more lightweight, operat-ing system.

Though there are more differences between the distribu-tions than discussed above, most users will probably want to use Raspbian “Wheezy”. It’s easier to set up, has a higher number of available software packages, and has a higher number of active users (in other words, you will have more people to ask for help from when something goes wrong). Raspbian “Wheezy” will generally be a better choice for random tinkering, while Arch Linux may be a better choice for an experi-enced developer with a well defined project.

This article will explain setting up Raspbian “Wheezy,” but

keep an eye out on EEWeb.com for a more in-depth discussion of Arch Linux ARM and a guide for how to set it up on a Raspberry Pi.

Setting up Raspbian “Wheezy”

To install Raspbian “Wheezy” on your Raspberry Pi, you’ll need the Rhaspbian image (available here) and an SD Card with at least 2GB of memory. If you plan on doing

Raspbian “Wheezy” is

easier to set up, has a higher

number of avail-able software

packages, and has a higher number of active users.

Figure 1: Win32 Disk Imager Tool being used to write the Rhaspbian image to SD Card

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something with your Pi that involves multimedia (videos, music, games, etc.) then you probably want to have a bigger SD Card (I’m currently running with an 8GB).

First we’ll have to transfer the image to the SD Card. Mount your SD card on your computer, and extract the .img file from the archive you downloaded into a folder on your computer. It’s important that you don’t just copy the image you downloaded to the SD Card, as that won’t actually format it in a way the Pi can read. The following steps will delete all data on the SD Card, so if you already have stuff on there you will want to back it up.

In Windows you’ll want to use a tool like Win32-Image-Writer. Extract the binary archive to a folder on your computer, and run Win32DiskImager.exe. Select the wheezy image you extracted as the image file, and the drive letter for your mounted SD card. Then press “write” and let the program do its thing. In a few minutes you should get a notice that the write was successful.

In Linux you’ll want to use the “dd” command. You first need to mount your sd card and then find its device name by running the “df -h” command. The device name will be something like /dev/sdb/ (note: if your SD card has multiple partitions (sdb1, sdb2, etc) you want to use all the partitions (sdb)). You then have to unmount the card in order to format it. You can do so using a graphical context menu in the file explorer of most Linux distros, or use the “umount” command.

Once you’ve gotten the device name of your SD card and you’re ready to setup the SD card use the command:

sudo dd bs=1M if=[WHEEZY IMG DIRECTORY] of=[SDCARD DEVICE PATH]

IMPORTANT:

This will format your SD card (output file) with your Wheezy image (input file) using 1MB blocks.

The command will take a few minutes to run, when it’s finished you can eject your newly imaged SD card and put it into your Raspberry Pi.

Start up your Raspberry Pi and in a minute or so you’ll be greeted with a blue screen and the Raspbi-config menu. This menu will help you go through the process of setting up your operating system. We’ll walk through the settings here in this article. Accepting the defaults will usually work fine, though you may want to fine tune some of the following settings.

Figure 2: Use “df” to get the correct drive path.

Figure 3: The dd command output. It can take a few minutes for the image to be written to the SD Card.

Ensure your SD Card is correctly pointing to your SD Card, oth-erwise you can wipe

your drive of all data.

Run df-h once before inserting your SD Card to see the current drives

Run df-h again after inserting your SD Card to see its filesystem path and mount location.

Run df-h once before inserting your SD Card to see the current drives

The SD Card will be the new addition. In this case, we will want to write our image to /dev/sdb.

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expand_rootfs – This setting will let you expand the root partition of Raspian Wheezy to fill the entire SD card. If you’re planning on using your SD card to store other data or want to manage partitions yourself, then don’t use this option. Otherwise, select it and it it expand the filesystem to use the entire SD card. After selecting it, you should be greeted with a message stating that the filesystem will expand on reboot.

overscan – This lets you enable or disable overscan. If you notice that your display isn’t filling your entire monitor, disabling overscan will usually fix that issue.

configure_keyboard – If you’re using an international keyboard, you can use this option to change keyboard settings.

change_pass – The default login and password for Rasp-bian Wheezy is pi : raspberry. If you would like to change this, you can do it here.

change_locale – This lets you change your locale, and sets languages and character sets appropriately. This defaults to British English.

change_timezone – Lets you set your timezone.

memory_split – This lets you set how much of the memory is dedicated to the graphics processing unit of your Raspberry Pi. The more graphically intensive applications you’ll be working with, the higher this value should be. The default of 64 should be fine for most applications.

overclock – This lets you change the clock rate and voltage levels of your Raspberry Pi to some pre-set de-faults. Note that overclocking can potentially lower the lifespan of your Pi and may lead to other issues. Only play with clock speeds if you know what you’re doing.

ssh – If you want to be able to ssh into your Raspberry Pi and use it remotely, enable this setting.

boot_behaviour – Lets you set up the Pi so the desktop environment starts automatically (otherwise you’ll have to use the command startx to start it)

update – Finally, update will check for updates to the config tool.

Once you’ve selected the settings you want, select “finish” and restart your Raspberry Pi (when prompted to login the default username is “pi” and the default password is “raspberry”). If everything went smoothly you should now be greeted by the desktop (if you have enabled it to start by default – you can run startx to have it launch otherwise). Hopefully you didn’t run into any issues. If you did, you can always try again by re-formatting the SD card with the original Wheezy image, or head over to the Raspberry Pi forums and FAQs to look for more pointers and tips.

Once you’ve got your Raspberry Pi set up with Rhaspbian, you’re ready to start developing.

To read Part 1 of this series, click the image below:

To find out more information about Raspberry Pi or to purchase Raspberry Pi products, visit their website at:

www.raspberrypi.org

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