VFETs Are (Almost) Solid State Tubes

October 26, 2025 by 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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Hackaday Links: October 26, 2025

October 26, 2025 by 11 Comments

There was a bit of a kerfuffle this week with the news that an airliner had been hit by space junk. The plane, a United Airlines 737, was operating at 36,000 feet on a flight between Denver and Los Angeles when the right windscreen was completely shattered by the impact, peppering the arm of one pilot with bits of glass. Luckily, the heavily reinforced laminated glass stayed intact, but the flight immediately diverted to Salt Lake City and landed safely with no further injuries. The “space junk” report apparently got started by the captain, who reported that they saw what hit them and that “it looked like space debris.”

We were a little skeptical of this initial assessment, mainly because the pilots and everyone aboard the flight were still alive, which we’d assume would be spectacularly untrue had the plane been hit by anything beyond the smallest bit of space junk. As it turns out, our suspicions were justified when Silicon Valley startup WindBorne Systems admitted that one of its high-altitude balloons hit the flight. The company, which uses HABs to gather weather data for paying customers, seems to have complied with all the pertinent regulations, like filing a NOTAM, so why the collision happened is a bit of a mystery.

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Examining The First Mechanical Calculator

October 26, 2025 by 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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A 2D simple regression analysis.

Making Math Less Stressful With A Python Super-Calculator

October 26, 2025 by 15 Comments

In a recent write-up, [David Delony] explains how he built a Wolfram Mathematica-like engine with Python.

Core to the system is SymPy for symbolic math support. [David] said being able to work with symbolic math easily has helped his understanding of calculus and linear algebra. For statistics support he includes NumPy, pandas, and SciPy. NumPy is useful for creating multidimensional arrays and supports basic descriptive statistics such as mean, median, and standard deviation; pandas is a library for operating on tabular data arranged into “DataFrames”, it can load data from spreadsheets (including Excel) and relational databases; and SciPy is a “grab bag” of operations designed for scientific computing, it includes some useful statistics operations, including common probability distributions, such as the binomial, normal, and Student’s t-distribution.

For regression analysis [David] includes statsmodels and Pingouin. If you’re not familiar with the term “regression analysis” it basically refers to the process of curve fitting. When your data is two-dimensional, with one dependent variable, the simple linear regression algorithm will generate a function that fits the data as y = mx + b, including the slope (m) and the y-intercept (b); this can be extrapolated to higher dimensional data and other types of regression.

If you have an interest in symbolic math you might enjoy learning about Mathematica And Wolfram On The Raspberry Pi.

Spreadsheets Apple ][ Style

October 26, 2025 by 9 Comments

It is hard to remember a time when no one had a spreadsheet. Sure, you had big paper ledgers if you were an accountant. But most people just scribbled their math on note paper or, maybe, an engineering pad. [Christopher Drum] wanted to look at what the state of the art in 1978 spreadsheet technology could do. So he ran VisiCalc.

Surprisingly, VisiCalc got a lot of things right that we still use today. One thing we don’t see much of is the text-based menu. As [Christopher] puts it, when you press the slash key, “what first appears to be ‘the entire alphabet’ pops up at the top of the screen.” In reality, it is a menu of letters that each correspond to some command. For example, C will clear the sheet (after prompting you, of course).

Interestingly, VisiCalc of the day didn’t do a natural order of evaluation. It would process by rows or by columns, your choice. So if cell A1 depended on cell B5, you’d probably get a wrong answer since A1 would always be computed before B5. Interestingly, the old Apple didn’t have up and down keys, so you had to toggle what the right and left keys did using the space bar. Different times!

This is a great look into a very influential piece of software and its tutorials. If you have old VisiCalc files you want to drag into the 21st century, [Christopher] explains the convoluted process to get mostly there.

We’ve been known to abuse spreadsheets pretty badly, although we’ve seen worse.

HRV Gets Home Automation Upgrades

October 26, 2025 by 5 Comments

In our modern semi-dystopia, it seems like most companies add automation features to their products to lock them down and get consumers to buy even more proprietary, locked-down components. The few things that are still user-upgradable are getting fewer and farther between, but there are still a few things that can be modified and improved to our own liking like this control panel for a heat recovery ventilator (HRV).

HRVs are systems that exchange fresh, outside air with stale, inside air while passing them both through a heat exchanger to keep from wasting energy. Many systems run continuously but they aren’t always needed, so some automation is beneficial. This upgrade from [vincentmakes] improves the default display for a Zehnder Comfoair Q350 HRV with a color display as well as adding it in to a home automation system, letting a user control fan speeds remotely as well as alerting the user when it’s time for filter replacements and providing up-to-date information from all the sensors in the HRV.

The project builds on a previous project which adapted an ESP32 to interact with the CAN bus used on these devices. With these upgrades the user can forgo the $300 proprietary upgrade that would be needed to get the same functionality otherwise. It’s also fully open-source so all that’s needed is to flash the firmware, replace the display, and enjoy the fresh air. There’s other modern HVAC equipment that can benefit from new controllers and a bit of automation as well.

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Windows 95, With Just A Floppy Drive

October 26, 2025 by 45 Comments

It’s something of a shock to be reminded that Microsoft’s Windows 95 is now 30 years old — but the PC operating system that brought 32-bit computing to the masses and left behind a graphical interface legacy which persists to this day, is now old enough that many in the community have never actually seen it. The original requirements were a 386 or better, 4 megabytes of memory, and a hard drive. [Robert’s Retro] is exploding one of those requirements, creating a full Windows 95 install using only a floppy drive.

As you might imagine, even if you had one of the super-rare 2.88 megabyte drives, such a feat would require a few tricks. In this case the biggest trick is the FlashPath, a curious 1990s peripheral that allows a SmartMedia card to be used in a floppy drive. With a special DOS driver it allows what is in effect a 32 megabyte floppy disk, but even that’s not enough for ’95. In come a couple of further tricks, installing Windows 95 to a compressed DriveSpace volume which is copied to the FlashPath, and copying the Drivespace volume to a RAM drive and mounting it, on boot. It needs a conventional floppy to boot before swapping to the FlashPath and it seems the copying process is extremely slow, but we’d expect Windows 95 from RAM to be very quick indeed.

There have been other minimalist Windows 95s over the years, but what makes this one unusual is that it’s a full install. Five years ago at the OS’s quarter century we took a look at it with 2020 eyes, and tried gauge its effect on modern desktops.

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