FPGA Brings UNIX V1 To The DEC J-11

August 30, 2025 by 13 Comments

If you’ve never used a PDP-11 before it’s probably because you simply weren’t around in the 70s and 80s. Although they started as expensive machines only in research labs and industry, they eventually became much more accessible. They’re a bit of a landmark in computing history, too, being largely responsible for the development of things like UNIX and the C programming language. [ryomuk] is using an FPGA in combination with an original DEC J-11 to bring us a new take on this machine. (Google Translate from Japanese)

The FPGA used in this build is a Tang Nano 20k, notable for its relatively low cost. The FPGA emulates the memory system and UART of a PDP-11 system down to the instruction set, while the original, unmodified DEC chip is left to its own devices. After some initial testing [ryomuk] built a PC11 paper tape emulator to ensure the system was working which runs a version of BASIC from the era. The next thing up was to emulate some disk drives and co-processors so that the machine can run the first version of UNIX. 

[ryomuk] also developed a PCB for the DEC microprocessor and the FPGA to sit on together, and it includes all of the jumpers and wiring needed to allow the computer to run UNIX, as well as handling other miscellaneous tasks like power. It’s an interesting build that gets to the heart of the early days of computer science. PDP-11 computers did eventually get smaller and more accessible, and if you want to build a modern version this build fits a complete system into an ATX case.

Thanks to [RetepV] for the tip!

A 3D-printed case encloses a number of electronic components. In the top left of the case, a laser diode is mounted. In the top right, the laser beam is shining into a cuvette, which is glowing red from scattered light. In the bottom right, a small breadboard has an integrated circuit and a few parts mounted. In the bottom left is a large red circuit board marked “Rich UNO R3.”

Measuring Nanoparticles By Scattering A Laser

August 30, 2025 by 6 Comments

A fundamental difficulty of working with nanoparticles is that your objects of study are too small for an optical microscope to resolve, and thus measuring their size can be quite a challenge. Of course, if you have a scanning electron microscope, measuring particle size is straightforward. But for less well-equipped labs, a dynamic light scattering system, such as [Etienne]’s OpenDLS, fits the bill.

Dynamic light scattering works by shining a laser beam into a suspension of fine particles, then using a light sensor to measure the intensity of light scattered onto a certain point. As the particles undergo Brownian motion, the intensity of the scattered light changes. Based on the speed with which the scattered light varies, it’s possible to calculate the speed of the moving particles, and thus their size.

The OpenDLS uses a 3D printed and laser-cut frame to hold a small laser diode, which shines into a cuvette, on the side of which is the light sensor. [Etienne] tried a few different options, including a photoresistor and a light sensor designed for Arduino, but eventually chose a photodiode with a two-stage transimpedance amplifier. An Arduino samples the data at 67 kHz, then sends it over serial to a host computer, which uses SciPy and NumPy to analyse the data. Unfortunately, we were about six years late in getting to this story, and the Python program is a bit out of date by now (it was written in Python 2). It shouldn’t, however, be too hard for a motivated hacker to update.

With a standard 188 nm polystyrene dispersion, the OpenDLS calculated a size of 167 nm. Such underestimation seemed to be a persistent issue, probably caused by light being scattered multiple times. More dilution of the suspension would help, but it would also make the signal harder to measure, and the system’s already running near the limits of the hardware.

This isn’t the only creative way to measure the size of small particles, nor even the only way to investigate small particles optically. Of course, if you do have an electron microscope, nanoparticles make a good test target.

NFC Hidden In Floppy Disk For Retro-Themed PC

August 29, 2025 by 13 Comments

As we all look across a sea of lifeless, nearly identically-styled consumer goods, a few of us have become nostalgic for a time when products like stereo equipment, phones, appliances, homes, cars, and furniture didn’t all look indistinguishable. Computers suffered a similar fate, with nearly everything designed to be flat and minimalist with very little character. To be sure there are plenty of retro computing projects to recapture nostalgia, but to get useful modern hardware in a fun retro-themed case check out this desktop build from [Mar] that hides a few unique extras.

The PC itself is a modern build with an up-to-date operating system, but hidden in a 386-era case with early-90s styling. The real gem of this build though is the floppy disk drive, which looks unaltered on the surface. But its core functionality has been removed and in its place an Arduino sits, looking for NFC devices. The floppy disks similarly had NFC tags installed so that when they interact with the Arduino, it can send a command to the computer to launch a corresponding game. To the user it looks as though the game loads from a floppy disk, much like it would have in the 90s albeit with much more speed and much less noise.

Modern industrial design is something that we’ve generally bemoaned as of late, and it’s great to see some of us rebelling by building unique machines like this, not to mention repurposing hardware like floppy drives for fun new uses (which [Mar] has also open-sourced on a GitHub page). It’s not the first build to toss modern hardware in a cool PC case from days of yore, either. This Hot Wheels desktop is one of our favorites.

An image of a pigeon on the left and a breakdown of six of the different kind of feathers on the bird. The bird's right wing is white with black dots and has an arrow pointing to it saying, "Developing wing with feather buds." The left wing is grey with one feather highlighted in pink with the text "Adult wing with feathers" at the end of an arrow pointing to it. The six feather types on the right side of the image are flight feathers, illustrated in pink with the text "enable flight, support aerodynamic loads, morph depending on flying style, building blocks for wing planaform." In green, we have tail feathers and the text "Maneuverability and controlability." In blue are the contour feathers, accompanied by the text, "streamline, camouflage, and sexual display. Found above filoplumes and semiplumes." A black floofy branched structure shows us the downy feathers next to the text "thermal insulation." Filoplumes and semiplumes look to be both thin and bushy feathers in black with the text "Sense underlying feathers, found above downy feathers." Finally, we have a black, stick-like bristle feather with the text "Protect face and eyes, sense surroundings."

Feathers Are Fantastic, But Flummoxing For Engineers

August 29, 2025 by 7 Comments

Birds are pretty amazing creatures, and one of the most amazing things about them and their non-avian predecessors are feathers. Engineers and scientists are finding inspiration from them in surprising ways.

The light weight and high strength of feathers has inspired those who look to soar the skies, dating back at least as far as Ancient Greece, but the multifunctional nature of these marvels has led to advancements in photonics, thermal regulation, and acoustics. The water repellency of feathers has also led to interesting new applications in both food safety and water desalination beyond the obvious water repellent clothing.

Sebastian Hendrickx-Rodriguez, the lead researcher on a new paper about the structure of bird feathers states, “Our first instinct as engineers is often to change the material chemistry,” but feathers are made in thousands of varieties to achieve different advantageous outcomes from a single material, keratin. Being biological in nature also means feathers have a degree of self repair that human-made materials can only dream of. For now, some researchers are building biohybrid devices with real bird feathers, but as we continue our march toward manufacturing at smaller and smaller scales, perhaps our robots will sprout wings of their own. Evolution has a several billion year head start, so we may need to be a little patient with researchers.

Some birds really don’t appreciate Big Brother any more than we do. If you’re looking for some feathery inspiration for your next flying machine, how about covert feathers. And we’d be remiss not to look back at the Take Flight With Feather Contest that focused on the Adafruit board with the same name.

The Confusing World Of Wood Preservation Treatments

August 29, 2025 by 19 Comments

Wood is an amazing material to use around the house, both for its green credentials and the way it looks and feels. That said, as a natural product there are a lot of microorganisms and insects around that would love to take a few good nibbles out of said wood, no matter whether it’s used for fencing, garden furniture or something else. For fencing in particular wood treatments are therefore applied that seek to deter or actively inhibit these organisms, but as the UK bloke over at the [Rag ‘n’ Bone Brown] YouTube channel found out last year, merely slapping on a coating of wood preserver may actually make things worse.

For the experiment three tests were set up, each with an untreated, self-treated and two pressure treated (tanalized) sections. Of the pressure treated wood one had a fresh cut on the exposed side, with each of the three tests focusing on a different scenario.

After three years of these wood cuts having been exposed to being either partially buried in soil, laid on the long side or tossed in a bucket, all while soaking up the splendid wonders of British weather, the results were rather surprising and somewhat confusing. The self-treated wood actually fared worse than the untreated wood, while the pressure treated wood did much better, but as a comment by [davidwx9285] on the video notes, there are many questions regarding how well the pressure treatment is performed.

While the self-treatment gets you generally only a surface coating of the – usually copper-based – compound, the vacuum pressure treatment’s effectiveness depends on how deep the preservative has penetrated, which renders some treated wood unsuitable for being buried in the ground. Along with these factors the video correctly identifies the issue of grain density, which is why hardwoods resist decay much better than e.g. pine. Ultimately it’s quite clear that ‘simply put on a wood preserver’ isn’t quite the magical bullet that it may have seemed to some.

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The (RF) Sniff Test

August 29, 2025 by 11 Comments

Sometimes the old tricks are the best. [Kevin] learned an old trick about using a ‘scope to sniff RF noise and pays it forward by sharing it in a recent video. He uses an oscilloscope. But does he need some special probe setup? Nope. He quickly makes a little RF pickup probe, and if you have a ‘scope, we’re pretty sure you can make one in a few seconds, too.

Of course, you can get probes made for that, and there are advantages to using them. But the quick trick of quickly and non-destructively modifying the existing probe to pick up RF means you always have a way to make these measurements.

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Illustration of a Gemini B reentry vehicle separating from the Manned Orbiting Laboratory (MOL). (Source: US Air Force)

The Advanced Project Gemini Concepts That Could Have Been

August 29, 2025 by 7 Comments

Looking back on the trajectory leading to Project Apollo and the resulting Moon missions, one can be forgiven for thinking that this was a strict and well-defined plan that was being executed, especially considering the absolute time crunch. The reality is that much of this trajectory was in flux, with the earlier Project Gemini seeing developments towards supplying manned space stations and even its own Moon missions. [Spaceflight Histories] recently examined some of these Advanced Gemini concepts that never came to pass.

In retrospect, some of these seem like an obvious evolution of the program. Given both NASA and the US Air Force’s interest in space stations at the time, the fact that a up-sized “Big Gemini” was proposed as a resupply craft makes sense. Not to be confused with the Gemini B, which was a version of the spacecraft that featured an attached laboratory module. Other concepts, like the paraglider landing feature, were found to be too complex and failure prone.

The circumlunar, lunar landing and Apollo rescue concepts were decidedly more ambitious and included a range of alternatives to the Project Apollo missions, which were anything but certain especially after the Apollo 1 disaster. Although little of Advanced Gemini made it even into a prototype stage, it’s still a fascinating glimpse at an alternate reality.

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