3D Printing A Self-cleaning Water Filter

August 14, 2025 by Al Williams 22 Comments

No one likes cleaning out water spouts. [NeedItMakeIt] wanted to collect rainwater and was interested in using a Coanda filter that those used on hydroelectric plants to separate out debris. Ultimately, he decided to design his own and 3D print it.

The design uses a sloping surface with teeth on it to coax water to go in one direction and debris to go in another. It fits into a typical spout, and seems like it works well enough. Some commenters note that varying volumes of rain and different types of debris behave differently, which is probably true. However, there are similar commercial products, so you’d guess there would be some value to using the technique.

The water pushes the debris off the slope, so you end up losing a little water with the debris. So as always, there’s a trade-off. You can see in the video that if the water flow isn’t substantial, the debris tends to stall on the slope. Could the filter be improved? That was the point in trying a second design.

It wasn’t a big improvement. That’s where there’s a plot twist. Well, actually, a literal twist. Instead of making a flat slope, the new design is a conic shape with a spiral channel. That improved flow quite a bit. We weren’t clear from the video of exactly where the debris was going with the last version.

Usually, when we think of the Coanda effect, we are thinking aerodynamics. It can be quite uplifting.

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Flyback Converter Revealed

August 13, 2025 by Al Williams 10 Comments

As [Sam Ben-Yaakov] points out in a recent video, you don’t often see flyback converters these days. That’s because there are smarter ways to get the same effect, which is to convert between two voltages. If you work on old gear, you’ll see plenty of these, and going through the analysis is educational, even if you’ll never actually work with the circuit. That’s what the video below shows: [Sam’s] analysis of why this circuit works.

The circuit in question uses a bridge rectifier to get a high-voltage DC voltage directly from the wall. Of course, you could just use a transformer to convert the AC to a lower AC voltage first, but then you probably need a regulator afterwards to get a stable voltage.

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The World’s First Podcaster?

August 13, 2025 by Al Williams 12 Comments

When do you think the first podcast occurred? Did you guess in the 1890s? That’s not a typo. Telefonhírmondó was possibly the world’s first true “telephone newspaper.” People in Budapest could dial a phone number and listen to what we would think of now as radio content. Surprisingly, the service lasted until 1944, although after 1925, it was rebroadcasting a radio station’s programming.

Tivadar Puskás, the founder of Budapest’s “Telephone Newspaper” (public domain)

The whole thing was the brainchild of Tivadar Puskás, an engineer who had worked with Thomas Edison. At first, the service had about 60 subscribers, but Puskás envisioned the service one day spanning the globe. Of course, he wasn’t wrong. There was a market for worldwide audio programs, but they were not going to travel over phone lines to the customer.

The Hungarian government kept tight control over newspapers in those days. However, as we see in modern times, new media often slips through the cracks. After two weeks of proving the concept out, Puskás asked for formal approval and for a 50-year exclusive franchise for the city of Budapest. They would eventually approve the former, but not the latter.

Unfortunately, a month into the new venture, Puskás died. His brother Albert took over and continued talks with the government. The phone company wanted a piece of the action, as did the government. Before anything was settled, Albert sold the company to István Popper. He finalized the deal, which included rules requiring signed copies of the news reports to be sent to the police three times a day. The affair must have been lucrative. The company would eventually construct its own telephone network independent of the normal phone system. By 1907, they boasted 15,000 subscribers, including notable politicians and businesses, including hotels. Continue reading “The World’s First Podcaster?” →

That’s No Moon, Er, Selectric

August 12, 2025 by Al Williams 5 Comments

If you learned to type anytime in the mid-part of the 20th century, you probably either had or wanted an IBM Selectric. These were workhorses and changed typing by moving from typebars to a replaceable element. They were expensive, though worth it since many of them still work (including mine). But few of us could afford the $1,000 or more that these machines cost back in the day, especially when you consider that $1,000 was enough to buy a nice car for most of that time. [Tech Tangents] looks at something different: a clone Selectric from the sewing machine and printer company Juki.

The typewriter was the brainchild of [Thomas O’Reilly]. He sold typewriters and knew that a $500 compatible machine would sell. He took the prototype to Juki, which was manufacturing typewriters for Olivetti at the time.

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Current Source Mixes Old School And New

August 12, 2025 by Al Williams 4 Comments

At first glance, [RobBest]’s constant current source looks old school. The box is somewhat old-fashioned, featuring switches and binding posts. Most importantly, there’s a large analog meter dominating the front panel. Then you notice the OLED display, and you know something’s up.

The device can source or sink a constant current. In addition, it features a timer that calculates milliamp-hours and automatically turns off when not in use. The brain is a PIC 16F1765, which controls the screen, the buttons, and a few relays. While that might seem an odd choice for the processor, it is actually smart. The device has both a DAC and an ADC, plus an internal op amp. The analog output and a single pass transistor control the current flow, while the two relays flip it between a source and a sink.

Without that op amp, the DAC can’t produce much current. However, by passing it through the onboard amplifier, the output can drive about 100 mA, which is sufficient for this project.

This is a classic circuit, but the addition of a CPU and a display gives it capabilities that would have been very difficult to build back in the day. Want to dive into the theory behind constant current sources? Or just the practical use of a voltage regulator to make one?

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Calipers: Do You Get What You Pay For?

August 11, 2025 by Al Williams 53 Comments

Generally, you think that if you pay more for something, it must be better, right? But that’s not always true. Even if it is true at the lower end, sometimes premium brands are just barely better than the midrange. [Project Farm] looks at a bunch of different calipers — a constant fixture around the shop if you do any machining, 3D printing, or PCB layout. The price range spans from less than $10 for some Harbor Freight specials to brands like Mitutoyo, which cost well over $100. Where’s the sweet spot? See the video below to find out.

The first part of the video covers how much the units weigh, how smooth the action is, and how much force it takes to push it down. However, those are not what you probably care most about. The real questions are how accurate and repeatable they are.

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Neon Bulbs? They’re A Gas!

August 11, 2025 by Al Williams 39 Comments

When you think of neon, you might think of neon signs or the tenth element, a noble gas. But there was a time when neon bulbs like the venerable NE-2 were the 555 of their day, with a seemingly endless number of clever circuits. What made this little device so versatile? And why do we see so few of them today?

Neon’s brilliant glow was noted when William Ramsay and Morris Travers discovered it in 1898. It would be 1910 before a practical lighting device using neon appeared. It was 1915 when the developer, Georges Claude, of Air Liquide fame, received a patent on the unique electrodes suitable for lighting and, thus, had a monopoly on the technology he sold through his company Claude Neon Lights.

However, Daniel Moore in 1917 developed a different kind of neon bulb while working for General Electric. These bulbs used coronal discharge to produce a red glow or, with argon, a blue glow. This was different enough to earn another patent, and neon bulbs found use primarily as indicator lamps before the advent of the LED. However, it would also find many other uses.

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