Author: Rud Merriam

85 Articles

New Angle On Raspberry Pi Zero Hub

February 6, 2016 by 48 Comments

Collectively, the Hackaday readers sigh, “Not another Pi Zero hub!!!”. But [Sean Hodgins’] hub is different. It has a new angle, literally. Besides, it’s an entry in the Hackaday and Adafruit Pi Zero Contest .

1514291454445337873[Sean Hodgins’] acute approach is orthogonal to most of the other hubs we’ve seen. He’s mating the hub at right angles to the Zero. The hub plugs into both the on-the-go USB port and the USB power port. No extra cables or wiring needed. [Sean] plans to release the design on GitHub after his Kickstarter campaign ends. He’s supplying bare boards for those who like the smell of solder paste.

This project nicely triangulates the issues of adding a hub to the Zero. The physical connection is solid with the boards connecting via the USB connectors. Power is supplied through the hub the way the Pi expects, which means all the protections the Pi Foundation built into the onboard conditioning are left in place. This also reduces surge problems that might occur when back powering through a hub and hot swapping USB devices. Another neat feature is the notched corner leaving the HDMI port accessible. Similarly, the Pi’s GPIO pins are free of encumbrance. One drawback is the hub is fused at 2 amps, just like the Pi. It would be nice to have a little more headroom for power hungry USB devices. Maybe another 0.5 amp to allow for the Zero’s usage.

[Sean] snaps the two together after the break.

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

February 5, 2016 by 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.

18zbmki8n3xgkjpgI 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?

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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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Code Craft: Cross Compiling For The Raspberry Pi

February 3, 2016 by 48 Comments

Sometimes there’s just no place like your desktop. You’ve already got your favorite development tools and references setup or installed and it’s a pain when you’re trying to work on an unfamiliar, or simply uncustomized, system. On your desktop everything is at your fingertips. If you want to search the web, the browser is just an alt-tab away. If you need a calculator, it’s right there to run. Your editor highlights syntax in your favorite colors already.

When developing on a Raspberry Pi, you leave all these creature comforts behind unless you spend the time to configure the Pi to your liking. Then it all gets wiped when you install a new distribution, like the recent change from Wheezy to Jessie. Even then it’s frustrating to switch back and forth between the desktop and the Pi because there is always something on the other system that you need. My usual comment is, “dirty word”, literally.

Cross-developing on your desktop is a very workable solution. We’re going to walk through setting up your desktop and a Pi to do this. This means loading a Pi ARM toolchain on your desktop and a debugging server on the Pi. This’ll let you develop and debug from in the comfort of your desktop. An added advantage is when you put that Pi in a robot you can debug over a wireless link.

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This Is My 3D Printed Brain!

January 30, 2016 by 25 Comments

This hack is a strange mixture of awesome and ghoulish. [Andrew Sink] created a 3D printed version of his brain. He received a CD from an MRI session that contained the data obtained by the scan. Not knowing what to do with it he created a model of his brain.


Out of a number of images, some missing various parts of his head, he selected the one that was most complete. This image he brought into OisriX, a Mac program for handling DICOM files. He worked on the image for an hour dissecting away his own eyes, skull, and skin. An STL file containing his brain was brought over to NetFabb to see how it looked. There was still more dissection needed so [Andrew] turned to Blender. More bits and pieces of his skull’s anatomy were dissected to pare it down to just the brain. But there were some lesions at the base of the brain that needed to be filled. With the help of [Cindy Raggio] these were filled in to complete the 3D image.

The usual steps sent it to the 3D printer to be produced at 0.2 mm resolution. It only took 49 hours to print at full-size. This brain was printed for fun, but we’ve seen other 3D printed brain hacks which were used to save lives. How many people do you know that have a spare brain sitting around?

The Flowing Pixels Of Time Wait For No Man

January 28, 2016 by 14 Comments

The hourglass dramatically depicts the flow of time; gravity pulling grains of sand inevitably downward. So it is with the Bits of Time project by [Frank Andre]. The pixels drop, stopping only when the battery dies. Or, when your eggs are ready. (Pssst, it’s also on Hackaday.io.)

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Look, Ma! No GIF!

The project starts with a couple of [Frank’s] PixBlocks. A processor is added to one PixBlock to serve as the controller for both after they are connected via the serial bus. A tilt switch, with a debouncing circuit, is connected to an IO pin. This tells the processor the orientation of the box and therefore which way the pixels should flow.

Two  switches set the duration of the timer in 15 second increments. A third starts the timer. When the box is rotated the pixels start flowing in the opposite direction. With code available on GitHub the system can be programmed for other effects such as changing colors, flickering, or even text display.

You’ll agree this is a bit less intimidating than the MacGyver-ish kitchen timer we covered last year.

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Whiskey Tango Foxtrot Is The Phonetic Alphabet?

January 26, 2016 by 98 Comments

Sometimes words just have to be spelled for others. I’ve been on phone conversations where the person on the other end is spelling for me and it’s painful. “Was that a ‘b’ or a ‘p’?” Sometimes they’ll try on the fly to use words with the beginning letter trying to convey the letter: “B as in boy”. Then they’ll get stumped mumbling while they think desperately for ‘k’ words… ‘ketchup’. Okay, but is that really ketchup or catsup? Now think how much easier spelling is on a phone than over a poor quality radio channel. What we say, and how we say it is the key to our brain’s ability to error correct human speech. It’s a solved problem that was built into radio etiquette long ago.

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