Julian Ferry - EEWeb

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Julian Ferry - EEWeb

Julian

Ferry

High Speed Engineering

Manager, Samtec

FEATURED PROJECT

Raspberry Pi -

Part 2

TECHNICAL ARTICLE

Facing the

Counterfeit

IC Issue

EEWeb

Issue 90

March 19, 2013

Electrical Engineering Community eeweb.com


EEWeb PULSE TABLE OF CONTENTS

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.

Featured Products

Facing the Counterfeit IC Problem

BY ALAN LOWNE WITH SAELIG

“Fake” chips in the marketplace is a huge issue for manufacturing companies and distributers

alike. Here is a solution to that problem.

Picking Components With Confidence

BY TAMARA SCHMITZ WITH INTERSIL

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

The Raspberry Pi - Part 2: Raspbian Wheezy

& Arch Linux ARM

BY KYLE OLIVE

The second installment of this series outlines two different popular operating systems for the

Raspberry Pi, Arch Linux ARM and Raspbian Wheezy.

RTZ - Return to Zero Comic

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EEWeb PULSE INTERVIEW

Julian

Ferry

Samtec 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 Engineering

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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EEWeb PULSE INTERVIEW

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 highspeed

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.”

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

Samtec’s Avanced Design System (ADS) Interface

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 pointand-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

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EEWeb PULSE INTERVIEW

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

“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.“

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

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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EEWeb PULSE TECH ARTICLE

Facing the

Counterfeit

Alan Lowne

CEO, Saelig Co.

IC

THE PROBLEM

Issue

Alan Lowne

CEO, Saelig Co.

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.

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EEWeb PULSE TECH ARTICLE

Reports

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Counterfeiting accounts for more than

8% of global merchandise trade, trade which and is

equivalent is equivalent to to lost lost sales of of as up much to as

$600B and will grow to to $1.2T by by 2009

US Dept Dept. of Commerce

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WHAT ARE COUNTERFEIT COMPONENTS?

The most prevalent counterfeiting technique is a rebadged

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 identification

of the components at fault and which then must be

lifted from all boards in the production line. Complete

Year

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 immediate

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 expensive

equipment.

SCREENING

Some distributors have advertised their screening services

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

Figure 2: Chip package markings can be made to look almost identical

to the uncritical observer.

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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.

15


EEWeb PULSE TECH ARTICLE

is a tool that can verify the identity of received ICs quickly

and economically, using a statistically significant procedure.

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 seconds.

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 operator

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,

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.

is automatically measured and stored as a benchmark.

SENTRY uses a combination of electronic parameter

settings (voltage, frequency, source resistance, and waveform)

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 combination

is included, maximizing the chances of capturing

internal fault conditions.

SENTRY can quickly detect

missing or incorrect dies,

lack of bond wires, inaccurate

pin outs, and pin

impedance variations.

Simple pass or fail results

are returned after testing,

offering a high level of confidence

in the authenticity of

components.

As parts become increasingly

complex, 100% testing

becomes burdensome, but

testing one or two pieces

for, say, 200 pieces is manageable.

Experience has

shown that variations arising

from a suspect shipment

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 confirming

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

Figure 3: SENTRY software screenshots.

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 leading

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 components

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 frustration,

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 interchangeable

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.

For more information, visit:

www.saelig.com

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EEWeb PULSE TECH ARTICLE

Picking

Components

Tamara Schmitz

Intersil Applications

Manager for Optical Sensors

With

Confidence

So So you you have a a circuit schematic you you want to to build. That

seems simple enough. If If you you have a a well-equipped lab lab at at

your disposal (possibly with a a lab lab manager to to guide you),

then this this article is is not not for for you. However, if if you you will will need to to

order electronic components for for your project, this this will will offer

some insight and and advice.

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EEWeb PULSE TECH ARTICLE

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 comfortable

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 components

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 component’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

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 component

with more power capacity than is

needed. (There could be shorts or surges

and you don’t want the component to be

destroyed.)

22 EEWeb | Electrical Engineering Community

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P = I 2 R.

A detailed discussion of resistor composition

is beyond the scope of this discussion.

I don’t tend to limit this field when searching

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 wattage

capability.

The features add yet another flavor to this

discussion. Military (and Automotive) qualified components

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 components

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

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.

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 Author

Tamara Schmitz is a Senior Principal Applications Engineer

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 assistant

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.

23


EEWeb PULSE PROJECT

The

Raspberry

Pi PART 2:

Kyle Olive

Computer Engineering Student &

IEEE Student Branch Chair

Raspberry Pi is a trademark of the Raspberry Pi Foundation

Raspbian Wheezy

(with Setup Guide),

Arch Linux ARM

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: Introduction

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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25


EEWeb PULSE PROJECT

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 development,

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.raspbian.org/)

operating system,

which is based off of the

popular Debian linux distribution,

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 requirements

for development (gcc, python, and more) prepackaged

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 desktopbased

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 lightweight,

containing only the

necessary software packages

to get your Pi running.

Raspbian

“Wheezy” is

easier to set up,

has a higher

number of available

software

packages, and has

a higher number

of active users.

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, operating

system.

Though there are more differences between the distributions

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 experienced

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

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

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

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.

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.

The SD Card will be the new addition. In

this case, we will want to write our image

to /dev/sdb.

Run df-h once before inserting your SD Card

to see the current drives

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

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:

Ensure your SD Card

is correctly pointing

to your SD Card, otherwise

you can wipe

your drive of all data.

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.

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Making Wireless

Truly Wireless:

Need For Universal

Wireless Power

Solution

Dave Baarman

Director Of

Advanced Technologies

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eaque ipsa quae ab illo inventore

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minima veniam, quis nostrum exercitationem ullam corporis suscipit

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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 Raspbian

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 defaults.

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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