VFETs Are (Almost) Solid State Tubes

October 26, 2025 by Al Williams 9 Comments

We always enjoy videos from [w2aew]. His recent entry looks at vertical or VFETs, which are, as he puts it, a JFET that thinks it is a triode. He clearly explains how the transistor works as a conductor unless you bias the gate to form a depletion zone.

The transistors have a short channel, which means they conduct quite well. The low gate resistance and capacitance mean the devices can also switch very quickly. These devices were once in vogue for audio applications. However, they’d fallen out of favor until recently. The reason is that they work quite well in switching power supplies.

How good is the on resistance? So good that his meter reported the probes were shorted instead of measuring the resistance. Pretty good. We’ve seen these VFET transistors used as switches to drive magnetic field coils many years ago and they replaced much more complex circuitry.

The curve tracer in the video is a beautiful instrument of its own. The digital displays give it a high tech yet retro look. A curve tracer, if you haven’t used one, plots stepped voltages against current flowing, and is very useful for examining semiconductor devices. While not as fancy, it is possible to make one to connect to a scope quite easily.

We are pretty sure that it is a Tektronix 576. We watched a repair of a similar unit, the 577, if you’d like to see some (probably) similar insides.

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Examining The First Mechanical Calculator

October 26, 2025 by Al Williams 9 Comments

Blaise Pascal is known for a number of things, but we remember him best for the Pascaline, an early mechanical calculator. [Chris Staecker] got a chance to take a close look at one, which is quite a feat since there were only about 20 made, and today we only know where nine of them wound up.

This Pascaline was lost for many years, and turned up in an antique store, where they thought it was a music box of some kind. The recent owner passed away, and now this machine is going to go up for auction, probably for more than we can afford. While he wasn’t able to handle the antique, he has plenty of knock-offs that were made back when people actually used them, which wasn’t that long ago. One of these is transparent, so you can see the mechanism inside.

The idea is to use the wheels like an old-fashioned phone dial to add counts to an output wheel. A linkage moves the next input wheel every time the current output wheel passes nine. Of course, if you have a multi-digit carry, it might take a little more elbow grease than just flipping the dial one normal position.

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Making WiFi Sound Like Dial-Up Internet

October 24, 2025 by Lewin Day 24 Comments

Dial-up modems had a distinctive sound when connecting, with the glittering, screeching song becoming a familiar melody to those jumping online in the early days of the Internet. Modern digital connections don’t really have an analog to this, by virtue of being entirely digital. And yet, [Nick Bild] decided to make WiFi audible in a pleasing tribute to the modems of yore.

The reason you could hear your dial-up modem is because it was actually communicating in audio over old-fashioned telephone lines. The initialization process happened at a low enough speed that you could hear individual sections of the handshake that sounded quite unique. Ultimately, though, once a connection was established at higher speed, particularly 33.6 k or 56 k, the sound of transmission became hard to discern from static.

Modern communication methods like Ethernet, DSL, and WiFi all occur purely digitally — and in frequencies far above the audible range. Thus, you can’t really “listen” to a Wi-Fi signal any more than you can listen to the rays of light beaming out from the sun. However, [Nick] found an anachronistic way to make a sound out of WiFi signals that sounds vaguely reminiscent of old-school modems. He used a Raspberry Pi 3 equipped with a WiFi adapter, which sniffs network traffic, honing in on data going to one computer. The packet data is then sent to an Adafruit QT Py microcontroller, which uses the data to vary the amplitude of a sound wave that’s then fed to a speaker through a digital-to-analog converter. [Nick] notes this mostly just sounds like static, so he adds some adjustments to the amplitude and frequency to make it more reminiscent of old modem sounds, but it’s all still driven by the WiFi data itself.

It’s basically WiFi driven synthesis, rather than listening to WiFi itself, but it’s a fun reference to the past. We’ve talked a lot about dial-up of late; from the advanced technology that made 56 k possible, to the downfall of AOL’s long-lived service. Video after the break.

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A Deep Dive Into The Coolness That Was CRT Projectors

October 11, 2025 by Donald Papp 22 Comments

CRT monitors: there’s nothing quite like ’em. But did you know that video projectors used to use CRTs? A trio of monochrome CRTs, in fact: one for each color; red, green, and blue. By their powers combined, these monsters were capable of fantastic resolution and image quality. Despite being nowhere near as bright as modern projectors, after being properly set up, [Technology Connections] says it’s still one of the best projected images he has seen outside of a movie theatre.

After a twenty-minute startup to reach thermal equilibrium, one can settle down with a chunky service manual for a ponderous calibration process involving an enormous remote control. The reward is a fantastic (albeit brightness-limited) picture.

Still, these projectors had drawbacks. They were limited in brightness, of course. But they were also complex, labor-intensive beasts to set up and calibrate. On the other hand, at least they were heavy.

[Technology Connections] gives us a good look at the Sony VPH-D50HT Mark II CRT Projector in its tri-lobed, liquid-cooled glory. This model is a relic by today’s standards, but natively supports 1080i via component video input and even preserves image quality and resolution by reshaping the image in each CRT to perform things like keystone correction, thus compensating for projection angle right at the source. Being an analog device, there is no hint of screen door effect or any other digital artifact. The picture is just there, limited only by the specks of phosphor on the face of each tube.

Converging and calibrating three separate projectors really was a nontrivial undertaking. There are some similarities to the big screen rear-projection TVs of the 90s and early 2000s (which were then displaced by plasma and flat-panel LCD displays). Unlike enclosed rear-projection TVs, the screen for projectors was not fixed, which meant all that calibration needed to be done on-site. A walkthrough of what that process was like — done with the help of many test patterns and a remote control that is as monstrous as it is confusing — starts at 15:35 in the video below.

Like rear-projection TVs, these projectors were displaced by newer technologies that were lighter, brighter, and easier to use. Still, just like other CRT displays, there was nothing quite like them. And if you find esoteric projector technologies intriguing, we have a feeling you will love the Eidophor.

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A Function Generator From The Past

October 10, 2025 by Jenny List 11 Comments

It’s always a pleasure to find a hardware hacker who you haven’t seen before, and page back through their work. [Bettina Neumryr]’s niche comes in building projects from old electronics magazines, and her latest, a function generator from the British Everyday Electronics magazine in April 1983, is a typical build.

The project uses the XR2206 function generator chip, a favourite of the time. It contains a current controlled oscillator and waveform shaper, and can easily produce square, triangle, and sine waves. It was always a puzzle back in the day why this chip existed as surely the global market for function generators can’t have been that large, however a little bit of background reading for this write-up reveals that its intended application was for producing frequency-shift-keyed sinusoidal tones.

The two PCBs on the bench, with a multimeter — Yellow-stained boards for the win!

The EE project pairs the XR2206 with an op-amp current generator to control the frequency, and another op-amp as an amplifier and signal conditioner. The power supply is typical of the time too, a mains transformer, rectifier, and linear regulators. There are a pair of very period PCBs supplied as print-outs in the magazine for home etching. This she duly does, though with toner transfer which would have been unheard of in 1983. After a few issues with faulty pots and a miswired switch, she has a working function generator which she puts in a very period project box.

It’s interesting to look at this and muse on what’s changed in electronic construction at our level in the last four decades. The PCB is single sided and has that characteristic yellow of ferric chloride etching, it takes up several times the space achievable with the same parts on the professionally-made dual-sided board designed using a modern PCB CAD package we’d use today. A modern take on the same project would probably use a microcontroller and a DAC, and a small switch-mode supply for less money than that transformer would provide the power. But we like the 1983 approach, and we commend [Bettina] for taking it on. The full video is below the break.

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Colorful parachutes at different levels of expansion

Holy Parachute Out Of Kirigami

October 9, 2025 by Ian Bos 15 Comments

If you have a fear of heights and find yourself falling out of an airplane, you probably don’t want to look up to find your parachute full of holes. However, if the designer took inspiration from kirigami in the same way researchers have, you may be in better shape than you would think. This is because properly designed kirigami can function as a simple and effective parachute.

Kirigami, for those unfamiliar, is a cousin of origami where, instead of folding, you cut slits into paper. In this case, the paper effectively folds itself after being dropped, which allows the structure to create drag in ways similar to traditional parachute designs. Importantly, however, the stereotypical designs of parachutes have some more severe drawbacks than they appear. Some major issues include more obvious things, such as having to fold and unpack before and after dropping. What may be less obvious are the large eddies that traditional parachutes create or their ease at being disturbed by the surrounding wind.

The kirigami chutes fix these issues while being easier to manufacture and apply. While these are not likely to be quite as effective for human skydiving, more durable applications may benefit. Quoted applications, including drone delivery or disaster relief, worry more about accuracy and scalability rather than the fragile bones of its passenger.

Clever and simple designs are always fun to try to apply to your own projects, so if you want to have your own hand, make sure to check out the paper itself here. For those more interested in clever drone design to take inspiration from, look no further than this maple seed-inspired drone.

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Can A Coin Cell Make 27 Volts?

October 7, 2025 by Jenny List 8 Comments

We have all no doubt at some point released the magic smoke from a piece of electronics, it’s part of what we do. But sometimes it’s a piece of electronics we’re not quite ready to let go, and something has to be fixed. [Chris Greening] had a board just like that, a 27 volt generator from an LCD panel, and he crafted a new circuit for it.

The original circuit, which we think he may have drawn incorrectly, uses a small boost converter IC with the expected inductor and diode. His replacement is the tried and tested joule thief, but with a much higher base resistor than its normal application in simply maintaining a battery voltage. It sucks 10 mA from the battery and is regulated with a Zener diode, but there’s still further room for improvement. Adding an extra transistor and using the Zener as a feedback component causes the oscillator to shut off as the voltage increases, something which in this application is fine.

It’s interesting to see a joule thief pushed into a higher voltage application like this, but we sense perhaps it could be made more efficient by seeking out an equivalent to the boost converter chip. Or even a flyback converter.