Category Archives: Engineering and Design

Try *this* with your fancy new iPhone 4S camera!

Many have written about the new iPhone4S’s camera, and how it might displace quite a few point-and-shoot models.  Still, there are some things it can’t do, or you wouldn’t want to do with it.  This is one.

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An Interview with Woz and Jobs — from 1979

UPDATE (Nov 19th): The IEEE newsletter can now be found here, and the article begins on page 21.  Many thanks to the authors and the interviewer, Robin Bradbeer.

In the most recent issue of IEEE Consumer Electronics Society Newsletter (Fall 2011) you’ll find two articles from Practical Computing April & May 1979: one is an interview with Steve Wozniak and the other with Steve Jobs.  I believe this issue of the newsletter went to press before the announcement of Steve’s death.

The articles are quite interesting as they tell a story so common to the companies that MindTribe encounters.  For those of us who’ve been in or around the computing industry since the 1970’s, it’s especially interesting to see how certain technical decisions took form, and how they led to the predominant architectures we work with today.

Reach out to your IEEE member friends for a copy of the newsletter, or your local geek hoarder for a copy of the 1979 magazines.  I encourage all to read the two articles for a perspective on the men and the technology that affects us all to this day.

– Tim Prachar

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Clamping, Bounding, and Pease moments

Here’s a great article with more from analog guru Bob Pease.  The collection of analog circuits for diode clamps and ideal zeners are all pretty useful.

And the photos of Pease are classic!

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What’s All This Electrosmog Stuff, Anyhow?


From time to time new words are coined in the tech world, and some stick like glue while others evaporate like old political jokes. And often these terms are formed not by the tech community, but by those outside of it. Enter Electrosmog.

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Do Engineers Fear the Known More Than the Unknown?

They say that we fear what we don’t understand, but I wonder whether engineers have this flip-flopped, as many of us seem to fear what we do understand.

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Thinking Outside the Digi-Key Box

Earlier today, I recalled a prescient conversation of the mid-1990’s that I had with a procurement person about how engineers select components. There in our San Jose R&D office on Brokaw, deep in the belly of Silicon Valley, she felt that engineers she worked with would only design in a component if they could order it from Digi-Key. With such a rich world of options out there, why, she asked, would otherwise good engineers trap themselves in the Digi-Key box?


Well here we are over 15 years later, and the answer is obvious. Digi-Key realized that the fastest way to get engineers to use them was to make the selection and ordering process easy. Digi-Key provided engineers with the links they need, and the late-in-the-day shipping deadline allowed them to design during Happy Hour and still have presents by 8am the next morning from the friendly brown truck.

The problem, though, is that we begin to have a monoculture in our designs. Like eating wheat, corn, and oats, we ignore kamut, quinoa, and millet. All are perfectly good, and some of those less common ones might actually be a smarter choice. But when we as engineers can go the easy path (nearly one-click shopping at Digi-Key), it’s easy to ignore the other options out there.

My challenge to the design community is to think outside the Digi-Key box. I know you’re all in love with Atmel, Microchip, NXP, TI, and a number of ARM-based processors for your embedded designs, but let’s not forget the broader landscape. Heard of Holtek for example? Yes, they’re on Digi-Key, but their processor line is not, so you might not even know about it.

If you search for “microcontroller” on Digi-Key’s site, they return 29,867 options from 27 different companies. Whoa. Ask yourself, how many of these companies have you actually considered for a design? How many do you have in your toolkit of tricks right now? Missing anything?

Maybe the kamut of processors out there has just what you need in your next design.

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EE Loses Two Heroes

There’s been a huge upset in the force. The two great EE legends of circuit design are no more, with the second one passing Saturday as he left the memorial for the first. A sad time in Silicon Valley to be sure.

Jim Williams and Bob Pease represented the core of great electrical engineers, and their many articles endeavored to spread that deep knowledge outward for all to share. Bob in particular was quite diverse and presented interesting points-of-view on numerous topics ranging from VW repair to hiking in Nepal to measuring femtoamperes. His works are worthy of reading to all EE types. Look here and other places for his writings.

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Name that Diode

In a recent interview, one of the tasks for the candidate was to give the diode names for various schematic symbols. Some were easy and others were a bit more obscure. And to make matters more interesting, there are multiple symbols for some. Below are a few examples, but know that there are many more not mentioned here.

In Baby’s First Diode Book you just get one diode, this one:

All it does is conduct one way and not the other. That’s easy. And to a first order this gets one through a lot of design problems. In the discipline, we call this the “ideal diode”. Alas, that’s vastly oversimplified and overly limiting. And you can’t buy one.

Turns out that the diode world is quite rich and complicated. Let’s introduce some of the family members, roughly in order of reverse obscurity. First off is what we already know:

This can be a switching diode, fast switching diode, or rectifier. And it comes in silicon (mostly) or germanium (rarely nowadays). The point is, this diode symbol tells you a little bit, but not everything you need to know. This diode’s little secret? It’s light sensitive if you get it in a glass package. The most common flavor is the 1N914 of old and the 1N4148 of today. In the diode family tree, switching diodes are often the lowest cost.

If you need something faster or lower forward voltage drop (Vf), then try this Schottky diode:

For simplicity, sometimes the last tail of the curls is dropped, but the above symbol is best. Schottky diodes are blazingly fast switchers and have lower Vf than the typical switching diodes, but they are generally more expensive and have higher reverse leakage currents. High-current flavors of this part include the 1N5817.

Maybe switching isn’t your goal, but rather regulation. Enter the zener diode:

This one is all about conducting backward, the mode that diodes aren’t supposed to go into. Normall,y. current flows in the A –> K direction, but in reverse (K –> A) the idea is that the diode blocks current flow until the voltage exceeds a certain level. Thus they make excellent voltage regulators, holding the voltage at a set level. Or they work well at protecting processor input pins as they can clamp the voltage at levels safe for downstream circuits. Unfortunately, these are not ideal, and the voltage where they begin to conduct is mushy. This means that they start conducting a little bit at first and then conduct progressively more as the voltage increases. Oh, and their knee voltage is temperature dependent, but with one little secret: for some parts the voltage goes up with temperature, and for some the voltage goes down. But for a few magic values, the temperature coefficient (Tc) is near zero. Pick these values if your application needs stability across temperature.

A special variant of zener diodes is the transient voltage suppression (TVS) diode. These are built for speed and for power. Many of these can absorb pulses of 1500W and turn on in a mere picosecond – the perfect solution for crushing ESD impulses.

Okay, these were the common ones, but let’s get into some more interesting examples. Need a variable capacitor? A diode’s your part for the job, though it needs to be a varactor diode:

Vary the bias voltage and the capacitance changes. Look for these in tuning circuits of radio receivers. These poor diodes are almost always operated reverse-biased so they never get to forward conduct as their non-zener brethren generally do.

Need a double-zener that avalanches? Try a DIAC:

This is not really a diode in that it doesn’t conduct differently in different directions. It’s actually a member of the thyristor family, another rich family of semiconductors that many electrical engineers rarely use in their designs. DIACs stay mostly off until the voltage reaches a threshold, then the device becomes conductive, passing current indefinitely until the current drops below a specified holding current. The most common place to find these components is in conjunction with TRIACs in lamp dimmers.

Read more about the family here. Engineers should know about SCRs and TRIACs at a minimum if they ever need to control AC currents.

As mentioned at the start, there are many other members of the broad diode family. Not even covered here are the diodes designed to emit light, or be sensitive to light, or those made from cat whiskers.

Still, my favorite diode has to be this one released by Signetics, the Noise Emitting Diode (NED). This device is designed to be connected to +1000VDC and emit a noise. Once.

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Is My Cell Phone Giving Me Cancer?

Much noise has been made in the press recently about the WHO’s addition of “mobile phone use” to its list of things which it considers can possibly cause cancer. Lawmakers in San Francisco are likely excited by this as the city has been trying to pass ordinances requiring cancer warning stickers on cell phones.

But do they cause cancer? And what did the WHO really say?


Let’s start with what the WHO actually did and said.

There were no new studies performed, but rather this was the result of a 31-person team’s review of past studies. The category they added mobile phone use into is called “possibly carcinogenic to humans”. Note the use of the weasel-word “possibly”. Also, pay attention to the other items on this list, which includes 266 items (Group 2B) such as coffee, nickel, and talc-based body powder.

On their “known carcinogen” list (Group 1) is alcoholic drinks, wood and leather dust, salted fish (Chinese-style), and 104 other agents. Less fearful, their “probably carcinogen” list (Group 2A) includes night shift work, fried food, and 57 other entries. Read the whole list here.

Right now there are five billion cell phone users. That’s right, three-quarters of the world’s population uses cell phones. One might expect that with all these people using cell phones, and if that phone use increases the risk of brain cancer, we’d see an increase in the rate of brain cancer. After all, five billion is a lot of test cases. And the answer? No. There’s been no notable increase in the observed rate of brain cancer. But I’d bet there has been a detectable increase in the rate of people walking into parking meters.

What is happening, though, is groups are talking about the amount of radiation emitted by phones that is subsequently absorbed by your body. CNN published this article listing the ten highest and ten lowest radiators.

What’s not mentioned in this article, however, is that for that coveted piece of technology to perform its function, it must emit radiation – that’s how it communicates with the cell tower. So, if you select a model that’s low on this list for radiation, such as the LG Quantum (AT&T), it’s likely that it won’t connect nearly as well to the network as the Motorola Bravo (AT&T), which generates more than four times as much radiation. The lower performance of the Quantum is confirmed by reviewers here and here, and the higher performance of the Bravo here by the same folks that panned the Quantum.

In short, RF emissions are what a wireless device is all about. Less emissions, less range. Should you worry about cancer? So far the studies don’t support this connection, but if you’re worried, I do have a nice Princess Phone I can make you a deal on.

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Is Lawrence Expressway the Geek Center of the Universe?

Palo Alto generally lays claim to the birthplace of Silicon Valley: the famous garage where Hewlett and Packard started their oscillator business.  Having walked by that garage nearly every day for seven years, I have to say it certainly doesn’t stand out in this present day. Perhaps that’s because the center of the Valley has moved south to Sunnyvale.  More specifically, to Lawrence Expressway.

When I moved to the Valley about 16 years ago, I knew the giants of National, Intel, and the like, but not the secret spots where “my kind” would gather away from the office.  These had to be learned from the locals as there were no wiki sites to list them, or stone markers to show the way.

Fast forward to today, and one can find geek paradise all along Lawrence Distressway – enough to declare it the Geek Center of the Universe.

Exit for Geek Central on SB101


Hidden in the cloverleaf of Central Expressway is Halted, (HALL-ted), officially named HSC Electronic Supply, though I’ve never heard it called by that name.  Picture a giant warehouse chock-full of every electronic component imaginable, but with a strong bias toward things that have been out of production for decades, and are happy to live in open-face cardboard boxes with a sharpie-written price on the front.  Need a 36V round muffin fan?  It’s here.  Need a 100ft of braided copper wire?  It’s here.  Picture a whole grocery store aisle of wall-warts for your every need.  And of course, there’s always the daily sale rack out front with a promise of anything for a dollar.

Not into the surplus scene?  Go a couple blocks north and drop in on HRO, Ham Radio Outlet.  In this world of ubiquitous mobile phones many believe that the world of amateur radio has long since gone the way of the eight-track, but a step into this shop will reveal otherwise.  Here is a world where everyone can be an RF engineer, designing their own special tweak on a proven antenna design.  Stop in for a little yammering with the locals, those who might still own eight-tracks, or to take in the latest in high-end RF transceivers that will allow you to talk around the globe even after the zombie apocalypse.

In the same building with HRO is another place that shouldn’t be missed: St. John’s Grill.  This place seems to have not changed a bit in the fifteen years I’ve known it, and if you go at lunchtime, expect to see a 50ft long line of people waiting to order their signature burger and fries.  Don’t let the line scare you though, as these folks have mastered the art of the assembly line and mass-production.  Perhaps the proximity of Applied Materials has something to do with that. This is a place where you’re as likely to hear arguments over alternative gate topologies in deep sub-micron design as you are a discussion of the latest Sci-Fi movie.

Now that you’re fed, you’re ready to adventure into Weird Stuff, at the very north end of Lawrence after it turns into Caribbean.  This pit trap for pack rats is much like Halted, jammed to the walls with the surplus and the obsolete.  Their take is different though, as they are like a museum of every product every made in the PC industry with an emphasis on weird.  Looking for that B&W tank game from the 70’s on a CRT?  It’s there.  Need a replacement 1200baud modem?  Yep, it’s right there next to about 50 other types of modems.  Scared to visit?  Then check out their web cam where you watch people navigate one of the more modern parts of the store.

And lastly, no talk of geek-land in the Valley would be complete without at least a nod to Fry’s Electronics, more or less across the street from HRO and St. Johns.  Fry’s has come to be the poster-child store for the geek world, celebrating it with every remodel of their store.  If one knows of any geek gathering ground, it’s Fry’s.

So, the next time you’re traveling to the San Francisco Bay Area and are looking to find the essence of Silicon Valley, don’t opt for SFO and the Palo Alto garage.  Instead, fly into SJC and take the short trip up to Lawrence Expressway where your every geek need will be indulged.  Word of warning, though:  Either leave your wallet at home, or plan for boxes full of souvenirs that’ll likely cause the rolling of eyes from 99% of the world — and big knowing smiles from the rest of us as we contemplate our next trip to geek corridor that is Lawrence.

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