Technical Audacity And The Phone Book

I often think we — or maybe the people who control our money — lack the audacity to take on really big projects. It is hard to imagine laying the transatlantic cable for the first time today, for example. When I want a good example of this effect, I usually say something like: “Can you imagine going to a boardroom of a major company today and saying, ‘We plan to run wire to every house and business in the world and connect them all together.'” Yet that’s what the phone company did. But it turns out, running copper wire everywhere was only one major challenge for the phone company. The other was printing phone directories. In today’s world, it is easy to imagine a computer system that keeps track of all the phone numbers that can spit out a printed version for duplication. But that’s a relatively recent innovation. How did big city phonebooks work before the advent of the computer?

Turns out, the Saturday Evening Post talked about how it all worked in a 1954 article. We aren’t sure there weren’t some computerized records by 1954, but the whole process was still largely manual. By that year, an estimated 60,000,000 directories went out each year in the United States alone. Some of these were small, but the Chicago directory — not including suburban directories — had over 2,100 pages. In New York City, the solution was to print a separate book for each borough. Even then. the Manhattan book was three inches thick and projected to grow to five inches by 1975.

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Affordable Transilluminator Helps Visualize DNA

If you want to examine the results of gel electrophoresis — and who doesn’t — you need a transilluminator. These devices can be quite pricey, though, so you might want to check out [Gabriel St-Pierre’s] plans to make an affordable blue-light version. You can see a video about the device below.

Using a UV filter, an Arduino Nano, an LED strip, 3D printing, and some mechanical items, it looks like this is a very easy project if you need such a device. There are a few miscellaneous parts like a hinge and some mirror material, but nothing looks too exotic.

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Portable Drill Press

We aren’t sure that [John Heisz’s] build is really what we think of as a drill press, but it is a very portable way to convert a regular drill into something like a drill press. Your drill will probably be different, but you can follow along with his build in the video below.

On the face of it, it doesn’t seem like this would be very hard, but there are a few tricks. Finding the exact center of the drill axis on the back of the drill takes a bit of effort.

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One Instruction To Rule Them All: C Compiler Emits Only MOV

How many instructions do you need to successfully compile C code? Let’s see, you’d need some jump instructions, some arithmetic functions, and — of course — move instructions, right? Turns out you only need the move instruction, which — on x86, at least — is Turing complete.

While the effort is a bit tongue-in-cheek, we have to admit that if you were trying to create your own CPU, this would make for a simple architecture and might have power or complexity advantages, so maybe someone will find a practical use for it after all. If you wanted a C compiler for a simple CPU, this wouldn’t require much to emulate at a byte-code level, either.

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Reading Floppies With An Oscilloscope

There’s a lot of data on magnetic media that will soon be lost forever, as floppies weren’t really made to sit in attics and basements for decades and still work. [Chris Evans] and [Phil Pemberton] needed to read some disks that reportedly contained source code for several BBC Micro games, including Repton 3. They turned to Greaseweazle, an interface board that can dump just about any kind of floppy disk if it is attached to the right drive. The problem is that Greaseweazle couldn’t read the disks due to CRC errors. Time to break out the oscilloscope and read the disk manually, which is what they did.

Greaseweazle provides a nice display of read sectors and shows timing coming from the floppy read head. The disk in question looked good with reasonably clean timing clocks except in the area of one sector. At that point, the clocks degenerated into noise. Looking on the disk, it was easy to see why. The actual media had a small dent in it.

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Project Starline Realizes Asimov’s 3D Vision

Issac Asimov wrote Caves of Steel in 1953. In it, he mentions something called trimensional personification. In an age before WebEx and Zoom, imagining that people would have remote meetings replete with 3D holograms was pretty far-sighted. We don’t know if any Google engineers read the book, but they are trying to create a very similar experience with project Starline.

The system is one of those that seems simple on the face of it, but we are sure the implementation isn’t easy. You sit facing something that looks like a window. The other person shows up in 3D as though they were on the other side of the window. Think prison visitation without the phone handset. The camera is mounted such that you look naturally at the other person through your virtual window.

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Practical Sensors: The Hall Effect

Measuring a magnetic field can be very easy with some pretty low tech, or it can be very high tech. It just depends on what kind of measurement you need and how much effort you want to expend. The very simplest magnetic sensors are reed switches. These are basically relays with no coil. Instead of a coil, an external magnet gets close enough to make or break the contacts in the reed. You see these a lot in, for example, door alarm sensors.

Then again, there’s no real finesse to a reed. It changes state when it sees enough of a magnetic field and that’s about all. You could use a compass with some sort of detection on the needle to get some more information about the field, but not much more. That was, however, how early magnetometers worked. Today, you have lots of options, including the nearly ubiquitous Hall effect sensor.

You might use a Hall effect to measure the magnetic button on a keyboard key coming down when you press it or the open and closed state of a valve. A lot of Hall effects see service as current monitors. Since a coil generates a magnetic field proportional to the current through it, a magnetic sensor can estimate the current in a coil of wire without any physical contact. Hall effects can also watch a magnet go by in a linear motion system or a rotating system to get an idea of position or speed. For example, check out this brushless motor controller that uses three sensors to understand the motor’s position.

History

Edwin Hall identified the effect in 1879. The basic idea is simple: an electrical conductor carrying current will exhibit changes due to an external magnetic field nearby. These changes show up as voltage you measure across the conductor. Normally, the voltage across a conductor will be nearly zero, but with a magnetic field, you’ll get a non-zero reading in proportion to the magnetic field strength in a particular plane, as we’ll see shortly.

Hall effect sensors are just one type of modern magnetometer. There are many different kinds including those that use inductive pickup coils that may or may not rotate or a fluxgate, which is a special type of coil. Some use a scale or a spring to measure force against another magnet — sometimes microscopically. You can even detect a magnetic field using optical properties like the Kerr effect or Faraday rotation.

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