Author: Al Williams

4460 Articles

Fourier, The Animated Series

June 5, 2024 by 7 Comments

We’ve seen many graphical and animated explainers for the Fourier series. We suppose it is because it is so much fun to create the little moving pictures, and, as a bonus, it really helps explain this important concept. Even if you already understand it, there’s something beautiful and elegant about watching a mathematical formula tracing out waveforms.

[Andrei Ciobanu] has added his own take to the body of animations out there — or, at least, part one of a series — and we were impressed with the scope of it. The post starts with the basics, but doesn’t shy away from more advanced math where needed. Don’t worry, it’s not all dull. There’s mathematical flowers, and even a brief mention of Pink Floyd.

The Fourier series is the basis for much of digital signal processing, allowing you to build a signal from the sum of many sinusoids. You can also go in reverse and break a signal up into its constituent waves.

We were impressed with [Andrei’s] sinusoid Tetris, and it appears here, too. We’ve seen many visualizers for this before, but each one is a little different.

Mechanic Prince Of Tides

June 5, 2024 by 2 Comments

Lord Kelvin’s name comes up anytime you start looking at the history of science and technology. In addition to working on transatlantic cables and thermodynamics, he also built an early computing device to predict tides. Kelvin, whose real name was William Thomson, became interested in tides in a roundabout way, as explained in a recent IEEE Spectrum article.

He’d made plenty of money on his patents related to the telegraph cable, but his wife died, so he decided to buy a yacht, the Lalla Rookh. He used it as a summer home. If you live on a boat, the tides are an important part of your day.

Today, you could just ask your favorite search engine or AI about the tides, but in 1870, that wasn’t possible. Also, in a day when sea power made or broke empires, tide charts were often top secret. Not that the tides were a total mystery. Newton explained what was happening back in 1687. Laplace realized they were tied to oscillations almost a century later. Thomson made a machine that could do the math Laplace envisioned.

We know today that the tides depend on hundreds of different motions, but many of them have relatively insignificant contributions, and we only track 37 of them, according to the post. Kelvin’s machine — an intricate mesh of gears and cranks — tracked only 10 components.

In operation, the user turned a crank, and a pen traced a curve on a roll of paper. A small mark showed the hour with a special mark for noon. You could process a year’s worth of tides in about 4 hours. While Kelvin received credit for the machine’s creation, he acknowledged the help of many others in his paper, from craftsmen to his brother.

We actually did a deep dive into tides, including Kelvin’s machine, a few years ago. He shows up a number of times in our posts.

Ham Busts The Myth Of Ground

June 4, 2024 by 21 Comments

Everyone who deals with electronics knows that grounding is important. Your house has a copper rod in the ground. But [Kristen K6WX] has news: the idea of ground is kind of a myth. She explained at a talk at the recent ARRL National Convention, and if you didn’t make it, you can watch it in the video below.

The problem is analogous to finding something that is standing still. You really can only talk about something standing still relative to something else. Sure, you might be standing still outside a building, but seen from the moon, you and the building are spinning around at about one revolution per day. If you were sitting on the sun and not burning up, you’d see lots of motion of everything, and, of course, the sun itself is moving in the right frame of reference.

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Tunneling TCP By File Server

June 4, 2024 by 15 Comments

You want to pass TCP traffic from one computer to another, but there’s a doggone firewall in the way. Can they both see a shared file? Turns out, that’s all you need. Well, that and some software from [fiddyschmitt].

If you think about it, it makes sense. Unix treats most things as a file, so it is pretty easy to listen on a local TCP port and dump the data into a shared file. The other side reads the file and dumps the same data to the desired TCP port on its side. Another file handles data in the other direction. Of course, the details are a bit more than that, but that’s the basic idea.

Performance isn’t going to be wonderful, and the files keep growing until the program detects that they are bigger than 10 megabytes. When that happens, the program purges the file.

The code is written in C# and there are binaries for Windows and Linux on the release page. The examples show using shared files via Windows share and RDP, but we imagine any sort of filesystem that both computers can see would work. Having your traffic stuffed into a shared file is probably not great for security but, you know, you are already jumping a firewall, so…

Of course, no firewall can beat an air gap. Unless you can control the fans or an LED.

Tech In Plain Sight: Theodolites

June 3, 2024 by 23 Comments

We take it for granted that you can look at your phone and tell exactly where you are. At least, as exact as the GPS satellites will allow. But throughout human history, there has been a tremendous desire to know where here is, exactly. Where does my farm end and yours start? Where is the border of my city or country? Suppose you have a flagpole directly in the center of town and a clock tower at the edge of town. You know where they are precisely on a map. You also know how tall they are. What you need is a theodolite, which is an instrument that measures angles very precisely.

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Can You Hear Me Now? Try These Headphones

May 29, 2024 by 12 Comments

When you are young, you take it for granted that you can pick out a voice in a crowded room or a factory floor. But as you get older, your hearing often gets to the point where a noisy room merges into a mishmash of sounds. University of Washington researchers have developed what they call Target Speech Hearing. In plain English, it is an AI-powered headphone that lets you look at someone and pull their voice out of the chatter. For best results, however, have to enroll their voice first, so it wouldn’t make a great eavesdropping device.

If you want to dive into the technical details, their paper goes into how it works. The prototype uses a Sony noise-cancelling headset. However, the system requires binaural microphones so additional microphones attach to the outside of the headphones.

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The 6809 Lives On In An FPGA

May 28, 2024 by 40 Comments

At one point, the Motorola 6809 seemed like a great CPU. At the time it was a modern 8-bit CPU and was capable of hosting position-independent code and re-entrant code. Sure, it was pricey back in 1981 (about four times the price of a Z80), but it did boast many features. However, the price probably prevented it from being in more computers. There were a handful, including the Radio Shack Color Computer, but for the most part, the cheaper Z80 and the even cheaper 6502 ruled the roost. Thanks to the [turbo9team], however, you can now host one of these CPUs — maybe even a better version — in an FPGA using Verilog.

The CPU may be old-fashioned on the outside, but inside, it is a pipeline architecture with a standard Wishbone bus to incorporate other cores to add peripherals. The GitHub page explains that while the 6809 is technically CISC, it’s so simple that it’s possible to translate to a RISC-like architecture internally. There are also a few enhanced instructions not present on the 6809.

In addition to the source code, you’ll find a thesis and some presentations about the CPU in the repository. While the 6809 might not be the most modern choice, it has the advantage of having plenty of development tools available and is easy enough to learn. Code for the 6800 should run on it, too.

Even using through-hole parts, you can make a 6809 computer fit in a tiny space.You can also break out a breadboard.