A (friendly) open letter to Radio Shack

Posted on 2011-05-21 by M. Eric Carr

Dear Radio Shack,

Many of us who remember the “good old days” of going to Radio Shack for electronics parts, 100-in-one electronics kits, Forrest Mims’ books and the like were deeply disappointed when Radio Shack transformed itself from an electronics hobbyist’s one-stop-shop into a generic, consumer-centric cell phone and camera store. Its re-branding as “The Shack” seemed to be the final nail in the coffin of good old Radio Shack, and I was half-expecting to see the already meager selection of electronics components phased out completely.

Recently, though, Radio Shack seems to be making a sincere effort to win back do-it-yourselfers. This is great news! Although these days I do most of my electronics business with SparkFun, DigiKey, Jameco, MPJA, and Mouser, having an actual local electronics store available would be very welcome indeed. (Radio Shack hasn’t really been that since the late 80s or early 90s, unfortunately.) Radio Shack’s stock among many electronics hobbyists certainly isn’t what it once was. As one of my friends commented, “Radio Shack: You’ve Got Questions, We’ve Got Blank Stares™.”

As the great Jim Croce once said, “It doesn’t have to be that way.”

The trend towards selling cell phones and cameras is understandable. After all, Radio Shack is a business, and needs to make money to survive. It’s nice to see you trying to return to your roots among the DIY community, though. By doing so, you have an opportunity to not only generate a lot of goodwill among electronics hobbyists (who tend to spend significant amounts of money on equipment and components), but to help spread the DIY spirit and give a needed boost to our economy and the community’s education.

The most recent issue of Radio Shack’s DIY e-newsletter (that such a newsletter exists is itself encouraging) asked for suggestions for three products that we wished Radio Shack stocked locally. That’s a start, but there’s so much more potential out there! Here is a list of some suggestions that I think would really help Radio Shack not only rebuild some major “street cred” among DIYers, but help out the DIY community in a big way and even make some money in the bargain.

  • Get members of the DIY / hobbyist / geek / nerd community on board to provide advice. I’m sure Forrest Mims, Jeri Ellsworth, Chris Savage, Chris Gammell, Lady Ada, and many others would have plenty of good suggestions. If Radio Shack really wants to help out the DIY community, we’d love to help.
  • Consult with local hackerspaces, and consider sponsoring projects and contests with in-kind donations in return for publicity.
  • Expand the parts selection. Every DIYer will have different answers on what to focus on, but some things are universal. Here are some of the big ones that I would like to see…
    • 1k resistors (maybe a 100-pack for under $10)
    • 0.1uF or 1uF capacitors for decoupling
    • Larger packs of the reed relays (206-2478). These are great little parts!
    • DIP form factor PIC microcontrollers, especially the 12F683 / 16F88 / 16F887 / 18F4550 etc.
    • Arduinos. (If I saw one in Radio Shack for under $50, I’d buy it just to see what all the fuss was about. I bet others would, too.)
    • 830-pin solderless breadboards and wire kits
    • Better soldering irons (although this has improved, recently.)
    • Servo motors — at least something like the Futaba S3003
    • TTL oscillators (and lots of other DIP integrated circuits)
    • Lithium-Ion batteries (if the lawyers will let you carry them)
    • Better quality tools, especially small screwdrivers. Stock the cheap ones if you must, but have at least one or two decent sets (Xcelite, etc) on hand, too.
    • PC modding parts — power supplies, fans, etc.
    • Assorted small bolts, nuts, standoffs, etc.
    • A better selection of crimp connectors — maybe in bulk
    • A selection of higher-wattage (maybe 10W or 25W) resistors
  • Partner with SparkFun to offer some of their parts and kits locally in Radio Shack stores. SparkFun is a great example of an electronics company that truly “gets it.” Unfortunately, they’re in Boulder, CO — and even FedEx overnight is only so fast. Sometimes you need an accelerometer or LCD display — right now. Radio Shack could help with this! SparkFun-branded parts would certainly get me to stop by Radio Shack more often.
  • Bring back the “grab boxes” of mystery parts! Twenty years ago, one of the best parts of stopping by Radio Shack was the possibility that they would have one or two of these little boxes full of who-knows-what. One of these boxes, with capacitors, transformers, stepper motors, LEDs, resistors, and ICs could keep a hobbyist entertained for a week!
  • Provide datasheets for the parts you stock, at least online — and make sure a pinout and minimal data are available on the package. (Get someone knowledgeable about electronics to help with this.)
  • Designate at least one employee per store — and preferably one per shift, per store — as an electronics guru. He or she doesn’t have to know every detail about every part in stock, but should have a basic understanding of circuit theory and be able to recognize basic parts and read a datasheet etc. At a minimum, a hobbyist shouldn’t have to explain what an LED is.
  • Provide open-source plans for electronics projects, and put together the parts for these projects as kits, with suggested skill level ratings. (SparkFun could help out with this.) Hobbyists could start out by building a LED mood light, then progress to building a clock, or learning about microcontrollers and FPGAs and designing their own devices. DIYers get help learning more about electronics, Radio Shack gets more revenue, and the economy gets a boost when these folks decide to pursue engineering as a career and/or design the next big thing. Everybody wins!
  • Start a “Radio Shack University” to help people get started learning about electronics. Make video tutorials available free online, along with project plans, schematics, open source firmware, and parts lists (with Radio Shack part numbers helpfully provided as a subtle hint.) Start a forum for discussing these projects; DIYers are famous for helping each other out. Again, SparkFun is known for doing this sort of thing — it provides a service while creating a demand for components and equipment.
  • Phase out “The Shack” marketing. If nothing else, this is a slap in the face to the Amateur Radio community — and for me, represents all that is disappointing about Radio Shack these days (dumbed-down, consumer-centric, lowest-common-denominator marketing).
  • I see Radio Shack will be at Maker Faire. Great! Listen to what the Makers have to say. If Radio Shack is supportive of the Maker community, they will notice.
  • Get social networking involved. Create “achievements” based on knowledge, project creation, interaction with the DIY / hobbyist community, etc. (Make it so that these have more to do with learning, creating, and/or helping others than purchasing, and they will be a lot more meaningful to us.)
  • (This is kind of out-there but would be very cool if feasible) Consider offering in-store PC board prototyping services. If a laser-etch process could be developed, PC boards could be done locally, in-store, with a small equipment footprint. This would be a huge draw to the prototyping community!
  • Offer pick-up service for components. Customers order parts through the Web, pay online, and pick up a custom package at their local store. (Allow customers to make custom kits and share these lists with others, if they choose.)
  • Consider offering local delivery services for a fee, or partnering with local courier companies. This would be more for the professional community — but Radio Shack is in a great position to supply university research labs, small businesses, and the like with parts on a same-day basis.

I would love to see Radio Shack truly become a local electronics store once again. From the viewpoint of the hobbyist community, there is a huge need for such a store! Even in many large metropolitan areas (I live and work in Philadelphia), it’s difficult or impossible to find an actual electronics (parts) store locally — so hobbyists are forced to order parts online. This not only can cause big delays, but can deter purchases: why pay $6 shipping for a 50-cent part?

I bet that I would spend well upwards of $100 in a typical month in a good, local, open-source-friendly electronics store like Radio Shack could be — especially if enticed by interesting project ideas and ready-made parts lists. I know I’m not the only one, either.I used to love going to Radio Shack “back in the day,” and would love to have the good old Radio Shack back.

Let’s make it happen. (Please contact me if I can help with anything.)

Sincerely,

M. Eric Carr
Technologist, Computer Engineering grad student, and electronics tinkerer
eric@paleotechnologist.net

 

Posted in Current Events, Digital Citizenship, Electronics, Nostalgia, Toys | Tagged , , , , , , , | 4 Comments

Good (Geek) Books

Posted on 2011-05-20 by M. Eric Carr

Digital Design is fun and relatively easy, but nobody is born knowing this stuff. At some point, it’s helpful to have good reference materials. Here are links to several books, datasheets, websites, and other resources — both on Digital Design and on other interesting topics — that I’ve found helpful and/or fun to read over the years.

Disclaimer: The book URLs link to Amazon, and they offer me a small commission for purchases made through these links, but I do personally use (and recommend) each of these books — whether you buy them on Amazon, read them in the local library, find a copy at a local bookseller, or borrow them from a friend. Amazon has always seemed to provide good service for me, and I can recommend their services — and these books — without hesitation.

The Art of Electronics
(Horowitz & Hill) 

An excellent guide to introductory electronics, including both circuit theory and practical tips and tricks. Definitely recommended if you will be designing electronic circuits.
The C Programming Language
(Kernighan & Ritchie) 

This is the book on C programming. C geeks refer to it simply as “K&R”. (I actually have the first edition of this one, but plan on upgrading to the second edition shortly.)
Chaos
(James Gleick) 

This isn’t a book on engineering, but a fascinating discussion of the emerging science of chaos / dynamic systems. Chaos is (very roughly) the study of how small inputs to a system can end up having large-scale effects.
(link) The Z-80 Microcomputer Handbook
(William J. Barden) 

This is an excellent guide to both connecting and programming a Z80 CPU. It shows the various connections that need to be made to the address, data, and control busses, along with an explanation of how these control pins operate. In addition, it serves as a good introduction to Z80 assembly programming. I used this book almost exclusively when designing and programming the DrACo/Z80. It’s a great one-stop resource for getting started with Z80s.
The Road to Reality
(Roger Penrose, Ph.D) 

This book is essentially a complete college Physics curriculum in one book. It takes readers from a basic understanding of math (starting roughly with fractions), up through many of the concepts encountered in modern physics. It’s over 1,000 pages, the first 300 or so of which serve as a course in the mathematics that is needed for the rest of the book. The first hundred pages or so are relatively accessible (depending on your math background), and the material becomes more challenging and more interesting from there. It’s definitely a book to be read a few pages at a time.
BASIC Scientific Subroutines (Volumes I and II)
(F. R. Ruckdeschel) 

These books contain many useful scientific subroutines. Even if your language of choice isn’t BASIC, the programs are easy enough to read, and can be readily translated into more modern languages such as C/C++.
Programming and Customizing the PIC Microcontroller
(Myke Predko) 

This is a good introduction to PIC microcontroller programming. While Microchip’s freely-available datasheets do have pretty much everything you need to know — and are a good primary resource — in-depth, tutorial-oriented books like this make it much easier to get started with PIC programming.
Posted in C, Coding, Digital, Electronics, HOW-TO, Math, PIC Microcontrollers, Science | Leave a comment

What’s the frequency, PECO?

Posted on 2011-05-15 by M. Eric Carr

I’ve known for many years that standard AC power in the US has a nominal frequency of 60Hz. This may or may not be typical coffee-table conversation material, but it’s no secret, being stated on many electronic devices produced for US use. What I didn’t know until recently was just how central maintenance of the exact design frequency is to the distribution of power: apparently, when the load increases without a proportional increase in supply, the frequency drops. When load is removed from the network (or additional power is added), the frequency rises. In addition, synchronizing all of the power sources and loads on the network requires precise coordination of not only frequency, but phase.

This begs the question — how much does the power-network frequency vary? Could you use it as reference for a wall clock? If it were a musical note, would it be consistently on-key? Could you use it as a lab-quality timebase? This calls for an investigation!

The first obstacle to this, of course, is voltage. Standard household AC power in the U.S. is 120V RMS, or ~169.706V peak, or ~339.411V peak-to-peak. (So, as high as “120 volts” sounds, that’s actually quite an understatement!) Piping this directly in to sensitive modern electronic equipment is a guaranteed way to let all of the magic smoke out — and probably start a fire, for good measure. A way is needed to reduce this down to a reasonable level.

It would be straightforward to use a transformer, but that’s not really needed here. With some precautions, a simple voltage divider will do. A few considerations are important. First, the output voltage should be relatively low — say, less than 5V peak-to-peak. Second, since small 1/4-watt resistors will be used, current must be very low — specifically, under 1/480 amp (120V RMS, times this current, must be no more than 1/4 watt.)

The second requirement means that the total resistance must be no less than (120/(1/480)) = 57.6 kilohms. To satisfy the first (voltage) requirement, the ratio between the two resistors should be no more than 1:40 or so, preferably a bit more. I ended up going with a 1-megohm and a 1-kilohm resistor; this should result in RMS current of about 120uA and an output voltage of about 120mV RMS (~339mV peak-to-peak.)

Finally, the connection order matters — at least for safety. According to US code, AC wiring is done with black and white shrouded conductors (with green present as ground, on three-conductor cords.) White is neutral (which ideally should have a voltage near Earth ground and therefore be reasonably safe to expose), and black is “hot” — the active line, which should never be exposed outside a device. Consult your local electrical codes (or better yet, get a qualified professional to help you) if you’re not completely sure of what you’re doing. High-voltage AC power can kill.

The idea is to expose only the neutral line and the (slightly higher than ground, and still probably safe) voltage-divided line. Therefore, the large 1-megohm resistor is connected to AC “hot,” and the 1-kilohm is connected to the neutral. The two output wires are connected to the neutral line and the junction of the two resistors (see schematic below.)

A bare-bones circuit for reducing the AC voltage. "Ground" is really the Neutral line -- which should be the white wire in the US, if your electrical installation is compliant with current US code. Don't bet your life on this, though!

 

If I were going to do this right (to make it into a commercial product, or to use it on a regular basis etc), it would need a few more important features. I’d consider the following a minimal list — and even then, I’m not an expert in power electronics. It might be best to go with a transformer — but I was trying to avoid using any reactive components here. For safety, I’d add:

  • A fuse in the “hot” line, just after it comes from the plug;
  • 1K resistors (or perhaps higher) in series with the Vout and Ground lines;
  • A pair of back-to-back Zener diodes connected between Vout and Ground, to limit output voltage to a safe level.

Once the “quick-and-dirty” voltage divider circuit above was built (and carefully tested several ways), I was able to connect it to a frequency counter and log the frequency of the AC power over time. Here is a time-domain graph and a histogram of what I found, along with a graph showing a few strange anomalies in the raw data…

 

Frequency-vs-time graph (anomalies removed.) Click for larger.

 

Frequency histogram (anomalies removed.) Click for larger.

 

Frequency anomalies. Each was far outside the 60Hz spec, and lasted for a single sample. Click for larger.

So in conclusion, the frequency appears to be extremely stable — the average (excluding the three anomalies) was 59.99907Hz, with a standard deviation of 0.02569Hz. On average, the frequency was about 15.56ppm off. Two standard deviations corresponds to roughly an 0.0856% error, or 856 parts per million.

If you were to set a clock by the 60Hz timebase (and some mechanical clocks, at least, do use this method), it would probably gain or lose one second every 17 or 18 hours, if it were to have a low-pass filter to ignore the anomalies (and mechanical clocks would inherently be unaffected by these.)

The frequency ratio between two musical notes (in the chromatic scale common in Western music) is 2^(1/12). If 60Hz were the desired frequency of a musical note to be played, the next half-step up would be at ~63.567786Hz. This is about 138 standard deviations. (Assuming a Gaussian distribution, as suggested by the histogram above, this essentially means such a value would never happen in the expected lifetime of the Universe, and then some.) This also approximately corresponds to the “just-noticeable difference” between two pitches — meaning that the difference in frequency would have to be at least this much to be perceived by most people as different from 60Hz. In other words, the 60Hz of the AC power network is, musically, quite pure indeed.

The anomalies call for more investigation. About every eight thousand samples, a single sample appears with a count far outside the Gaussian distribution otherwise seen. To call these anomalies “outliers” would be a huge understatement; the smallest of these is hundreds of millions of standard deviations away from the mean. Clearly, another phenomenon is at work here. Could PECO be encoding periodic data in the power? If so, what are they saying??

 

 

Posted in Analog, Digital Citizenship, Electronics, Power, Science | 2 Comments

Core II, The Paleotech Way

Posted on 2011-04-18 by M. Eric Carr

At its core (pun intended), Paleotechnology is really about rediscovering old technological methods and documenting them for future use. Just as archaeologists and paleontologists might piece together the history of a forgotten village based on buried pottery shards and the remnants of old buildings, paleotechnology concerns itself with rediscovering the way engineers made things work, years ago.

A good example of one technology that is becoming increasingly difficult to find information on is magnetic-core memory. Since, with core memory, there is a more-or-less fixed amount of construction effort required per byte of capacity (I.E. someone has to thread all those wires through all those cores), Moore’s Law doesn’t apply. For that reason, core memory (with its relatively constant cost-per-byte) was long ago surpassed by RAM and later technologies such as Flash memory.

 

A 64-by-64 plane of core memory: half a kilobyte! (Click for larger)

Core memory stores bits in an array of ferrite cores — tiny rings made out of a ferromagnetic material which can be magnetized in one of two directions. Passing a large enough current through the core in one direction can record a “1”; passing a large enough current through the core in the opposite direction records a “0.”

The contents are read back via a destructive-read process: a “0” is written to the cell to be read. If the core was magnetized in the “1” direction, a small electrical pulse will appear on another wire passing through the core. If it was already a “0,” no pulse will appear (since writing a “0” didn’t change the magnetization of the core. What made core memory practical was an ingenious method of combining the currents from two different directions in order to select only one bit in an array.

The key observation is that a certain amount of current is needed to change the core’s magnetization. If only 60% of this current is used, the magnetic direction won’t change. Therefore, two wires can be passed through each core in an array: one for each row of bytes and one for each column. To write to a bit of memory, drive both the row and column lines in the correct direction, each with 60% of the critical current. Only the correct bit (at the intersection of those two wires) will be affected, since other bits will receive at most 60% of the critical current. (A third “sense” wire is threaded through many or all of the cores; the “sense pulse” that results when a “1” is converted back to a “0” is read out on this wire. This is the diagonally-threaded wire visible in the photo.)

This much theory is relatively easy to find online. The tricky part, I found, was in the details. How much current isthe right amount? Are we talking microamps, milliamps, or whole amps? I had found a plane of core memory (pictured above) on eBay a while ago and bought it with the intent of bringing it back online as a demonstration. What I didn’t want to do, though, was burn it out by using too much current.

Last quarter, I finally found the next few pieces of the puzzle. The professor teaching a course I was taking mentioned that the critical current was around 500mA.  He also provided the title of a book with more details on the workings of core memory. I’m not sure why core memory is still being discussed in computer engineering courses in 2011, but I’m not complaining!

So, with this new information, I am beginning “Project Core II.” (The II referring to a second career for this particular plane of core memory.) Here’s the plan:

  • Using an ohmmeter, test all 64 horizontal and 64 vertical wires, and the sense line for continuity. (DONE: everything seems fine!)
  • Pass a wire through one “bit” of core memory (I found a bag of ferrite cores on eBay, too.)
  • Pass increasing amounts of current pulses through it and see if I can sense pulses on a second wire.
  • Once the pulses are observed, characterize what amount of current is required to make this happen.
  • Try using a pair of wires to produce a combined current, and characterize what amount of current is required to drive the core using this method
  • Try the above with several cores on a wire in one direction and a separate select line for each.
  • Make a holder for the core memory plane, probably in the 3D printer. (I’d rather not solder directly to such a cool museum piece if I can help it.)
  • Try sending pulses through the actual plane of core memory, starting out with low current values, and characterize what drive current is needed.
  • Make a driver circuit (using a PIC and current-source circuitry) to store two or three bytes of information on a string of cores.
  • Expand the driver circuit to cover all of the lines in the plane of core memory
  • Design a nice interface for the thing and package it in acrylic as a demo piece.
  • Run automated test patterns to check for various error syndromes.
  • Perhaps design a simple PIC webserver, using the core as document-storage RAM!
Posted in Core Memory, Digital, Electronics, Nostalgia, Science | Tagged , , | 2 Comments