Grandma’s Phone, DSL, And The Copper They Share

February 5, 2016 by Rud Merriam 79 Comments

My DSL line downloads at 6 megabits per second. I just ran the test. This is over a pair of copper twisted wires, the same Plain Old Telephone Service (POTS) twisted pair that connected your Grandmother’s phone to the rest of the world. In fact, if you had that phone you could connect and use it today.

I can remember the old 110 bps acoustic coupler modems. Maybe some of you can also. Do you remember upgrading to 300 bps? Wow! Triple the speed. Gradually the speed increased through 1200 to 2400, and then finally, 56.6k. All over the same of wires. Now we feel short changed if were not getting multiple megabits from DSL over that same POTS line. How can we get such speeds over a system that still allows your grandmother’s phone to be connected and dialed? How did the engineers know these increased speeds were possible?

shannon_maze_hr — Claude Shannon with his maze running mechanical mouse

The answer lies back in 1948 with Dr. Claude Shannon who wrote a seminal paper, “A Mathematical Theory of Communication”. In that paper he laid the groundwork for Information Theory. Shannon also is recognized for applying Boolean algebra, developed by George Boole, to electrical circuits. Shannon recognized that switches, at that time, and today’s logic circuits followed the rules of Boolean Algebra. This was his Master’s Thesis written in 1937.

Shannon’s Theory of Communications explains how much information you can send through a communications channel at a specified error rate. In summary, the theory says:

There is a maximum channel capacity, C,
If the rate of transmission, R, is less than C, information can be transferred at a selected small error probability using smart coding techniques,
The coding techniques require intelligent encoding techniques with longer blocks of signal data.

What the theory doesn’t provide is information on the smart coding techniques. The theory says you can do it, but not how.

In this article I’m going to describe this work without getting into the mathematics of the derivations. In another article I’ll discuss some of the smart coding techniques used to approach channel capacity. If you can understand the mathematics, here is the first part of the paper as published in the Bell System Technical Journal in July 1948 and the remainder published later that year. To walk though the system used to fit so much information on a twisted copper pair, keep reading.

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A Better Way To Plug A CPLD Into A Breadboard

February 4, 2016 by Bil Herd 63 Comments

If you read my first post about a simple CPLD do-it-yourself project you may remember that I seriously wiffed when I made the footprint 1” wide, which was a bit too wide for common solderless breadboards. Since then I started over, having fixed the width problem, and ended up with a module that looks decidedly… cuter.

To back up a little bit, a Complex Programmable Logic Device (CPLD) is a cool piece of hardware to have in your repertoire and it can be used to learn logic or a high level design language or replace obsolete functions or chips. But a CPLD needs a little bit of support infrastructure to become usable, and that’s what I’ll be walking you through here. So if you’re interested in learning CPLDs, or just designing boards for them, read on!

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High Energy Gardening Means Nuking Plants

February 3, 2016 by Bryan Cockfield 45 Comments

We live in a world transformed by our ability to manipulate the nucleus of atoms. Nuclear power plants provide abundant energy without polluting the air, yet on the other hand thousands of nuclear warheads sit in multiple countries ready to annihilate everything, even if it’s not on purpose. There are an uncountable number of other ways that humanity’s dive into nuclear chemistry has impacted the lives of people across the world, from medical imaging equipment to smoke detectors and even, surprisingly, to some of the food that we eat.

After World War 2, there was a push to find peaceful uses for atomic energy. After all, dropping two nuclear weapons on a civilian population isn’t great PR and there’s still a debate on whether or not their use was justified. Either way, however, the search was on to find other uses for atomic energy besides bombs. While most scientists turned their attention to creating a viable nuclear power station (the first of which would only come online in 1954, almost ten years after the end of World War 2), a few scientists turned their attention to something much less obvious: plants.

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One Hoss Shay And Our Society Of Obsolescence

February 1, 2016 by Kristina Panos 86 Comments

Legend has it that Henry Ford would send engineers out to junkyards all over the US looking for Fords. They were supposed to study each one they found and make note of any parts that had not failed. But it wasn’t so that he could start making all of those parts stronger. Instead, Ford allegedly used this data to determine where he could cut corners in future production runs so as not to waste money by making any part last longer than any other part.

Most things tend to break down rather than completely giving out. Usually it’s only one or two components that stop working and the rest of it is still serviceable. And this is a good thing. It’s what lets us repair PCBs or scavenge parts off them, drive our cars longer, and help save each other’s lives through organ donor programs. Can you imagine how different life would be if each part of every thing failed at the same time?

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A Hackers Guide To Arts, Crafts, Food, And Music In Shenzhen

February 1, 2016 by Mike Szczys 18 Comments

When you mention Shenzhen, many people think about electronic gadgets, cheap components, manufacturing, and technology. I’m there quite often and find that all of the technology and manufacturing related stress can be overwhelming at times. Sometimes I feel the need to escape it all so I go to markets and places that aren’t traditionally associated with technology so I can clear my head as well as expose myself to something different. It provides me with a constant source of new design ideas and also allows me to escape the persistent tech treadmill that Shenzhen runs on. There are a lot of places in Shenzhen that I consider hidden gems that don’t get a lot of press since mainstream media associates Shenzhen with either factories or technology. Here are my favorite places to window shop and de-stress in Shenzhen.

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VGA In Memoriam

January 29, 2016 by Brian Benchoff 118 Comments

The reports of the death of the VGA connector are greatly exaggerated. Rumors of the demise of the VGA connector has been going around for a decade now, but VGA has been remarkably resiliant in the face of its impending doom; this post was written on a nine-month old laptop connected to an external monitor through the very familiar thick cable with two blue ends. VGA is a port that can still be found on the back of millions of TVs and monitors that will be shipped this year.

This year is, however, the year that VGA finally dies. After 30 years, after being depreciated by several technologies, and after it became easy to put a VGA output on everything from an eight-pin microcontroller to a Raspberry Pi, VGA has died. It’s not supported by the latest Intel chips, and it’s hard to find a motherboard with the very familiar VGA connector.

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Beautiful And Bizarre Boards

January 28, 2016 by Nava Whiteford 49 Comments

weirdboard — An odd board (piezo coupler), fabbed by OSHPark.

Recently I’ve been getting curious about interesting PCB shapes. In the past I’ve always used simple Polygons, perhaps rounding out the corners to make the design a little more aesthetically pleasing. The board to the right was my introduction to the possibilities of oddly shaped boards. It’s designed to couple with a piezo buzzer (used as an actuator). I’ve been planning to have it fabricated out of FPC (Flexible Printed Circuits), but with fabrication being so cheap I sent it to OSHPark to see what they’d make of it. OSHPark doesn’t have hard specs around internal routing, but in my experience they’re up to try anything (and they’re quality is always great). The width of the prongs on the PCB shown is 5mm. I figured it was a risk, and that it was likely the FR4 could break, but it came back great!

This has led me to the realization that my boards could look much more exciting than they do currently, and that our highly optimized modern PCB fabrication process provides a lot of room for experimentation. This article will discuss some of the options available when creating non-traditional PCBs.

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