Mysterious Files PH

The Peripheral Component Interconnect (PCI) bus was first introduced all the way back in 1992. It quickly became the standard way to interface add-on cards on the PC platform, supplanting earlier buses like ISA and various other oddball standards. You wouldn’t expect to see a PCI bus on a Motorola-based machine, but [maniek86]’s homebrew rig offers just that. 

This computer is a beautiful piece of homebrew engineering, constructed out of protoboard and loose wires rather than any fancy PCB. At the heart of the build lies a Motorola 68000 running at 10 MHz. It’s got 1 MB of SRAM, 4 KB of ROM, and a MC68681P acting as a UART, timer source, and I/O controller. Where things get special, though, is in the inclusion of a Xilinx Spartan II FPGA (XC2S100), which acts as a PCI bridge. It provides the machine with two 32-bit 5-volt PCI slots which are interrupt capable, albeit with no bus mastering. A XC95144XL CPLD also sits present to act as glue logic to help lace everything together.

[maniek86] does a great job of explaining exactly why the PCI bus was hard to implement, and how it was pulled off in the end. The guide also covers how the system was able to interface various cards, from a PCI serial expansion to a Cirrus VGA adapter. It’s all good stuff.

We’ve featured other work from [maniek86] before, too, like this brilliant 486-based single-board computer. Video after the break.

Much like Apple’s once vaunted super-slim butterfly keyboard, today’s range of portable devices featuring flexible OLED displays – which can fold said display into a much smaller form factor – are a marvel of engineering.

Unfortunately engineering can only do so much against fundamental flaws. In the case of both these flexible OLEDs and butterfly keyboards the main issue is that of dust intrusion, with a recent teardown by [iFixit] going over the reasons for this.

As test subject we got a Galaxy Z Fold 8, as an example of a modern-day foldable smartphone-tablet hybrid. This phone has an IP48 rating, meaning that it’s water-resistant, but not dust-resistant for particles smaller than 1 mm. To test this, [iFixit] used UV-reactive dust particles, making sure that they got literally everywhere inside the phone’s hinge mechanism.

After this treatment, trying to fold the phone caused the hinge mechanism to make absolutely horrific crunching noises, confirming that it’s reached dust-under-butterfly-keycap levels of unusable. During the subsequent teardown a quick pass with the UV lamp showed that not much of the dust had penetrated into the two halves of the device at least, but the hinge mechanism wasn’t as lucky.

Getting to the hinge is sadly rather destructive, as it involves removing the flexible OLED. Once the hinge was exposed and subjected to UV light the spectacle was something to marvel at, as can be seen in the above screenshot. With the dust caking literally every part of the mechanism, it was little wonder that the hinge had ceased to work.

Although this was obviously an extreme case of dust exposure, and the average flexible OLED screen’s hinge won’t see nearly as much dust, one can’t help but feel slightly disconcerted at that crunching noise, knowing that it’s just one big dust exposure away.

Over the years poly(lactic acid) (PLA) – also known as polylactide – has become a popular thermoplastic for a variety of reasons. One of these reasons is that it’s easily produced from a renewable resource, i.e. lactic acid, with the resulting polymer even being compostable if you assume that your compost pile hits a steady 65°C or more, well above the polymer’s glass transition temperature (Tg).

That said, PLA by itself is a pretty crummy material, being exceedingly brittle and inferior to common alternatives like PET(G) in many metrics. Over the decades much research has gone into figuring out this material, its amorphous and crystalline states, as well as how to use plasticizers, copolymers, mechanical manipulation and PLLA/PDLA blends to produce more useful variants of PLA.

Today’s spools of thermoplastic filament that gets marketed as ‘PLA’ are the result of such engineering, though with plenty of remaining issues, as anyone who has struggled through a spool of brittle PLA filament can attest to. Although you can find plenty of tips online about how you should ‘just’ toss said spool into an filament dryer, oven or similar to bake it – with accusing fingers pointed at moisture intrusion, hydrolysis and kin – it helps to understand the fundamentals of how PLA works, and how it degrades.

Stereoisomer

Although we use the generic acronym of ‘PLA’, there are actually two chiral forms of poly(lactic acid). Generally the one that we most commonly find in our spools of consumer-grade PLA filament is poly(L-lactide) (PLLA), while its more rare chiral form is poly(D-lactide) (PDLA). These match their chiral lactic acid forms, being L-lactic acid and D-lactic acid.

If both PLLA and PDLA are combined into a single polymer chain you thus get another type of material with its own set of properties. Overall this PDLLA polymer is quite stable, preferring to stay amorphous while still resisting hydrolysis better than its other polymer forms.

While industrial production of D-lactic acid is possible, most production is in the form of cheaper L-lactic acid, with correspondingly FDM printer filament thus having a high chance of being PLLA. This, along with factors like the ratio of crystallinity versus amorphous areas determines the initial state of the material.

These two states, of crystalline versus amorphous are defined by the state of the polymers, with the crystallized state being the most stable form that is most resistant to degradation through hydrolysis, yet this state is also the most rigid and thus most brittle. This is of course just the beginning of all the fascinating materials science.

Polymer Types

While just the basic PLLA and PDLA polymers already provide a lot of fascinating materials science, there is a whole world of things you can do with these polymers. We already touched on blending PLLA and PDLA, whereby both types of polymers support each other. This same blending can be done with other types of polymers as well, to further modify the properties of PLA, with many of the essentials covered by Vincent DeStefano et al. in this 2020 paper.

In addition to blending polymers, we can also create copolymers, whereby PLA monomers are mixed with other monomers to create a new polymer type with certain desirable properties, like enhanced flexibility. This already gets us right in the territory of the countless additives for PLA to modify its plasticity, nucleation and other characteristics.

Of note are the different crystallinities of PLA, as also covered by DeStefano et al., starting with ɑ and ɑ’-crystallinity as the most common types, and a PLLA/PDLA blend being fully amorphic if it contains more than 10% of PDLA. Since most PLA blends tend to have less PDLA than this we generally classify PLA filament as semi-crystalline.

Plasticizing

Unsurprisingly, most of the additives and modifications to PLA focus on plasticizing it, which can be done through a number of methods in addition to modifying the amount of PDLA in the blend. A good overview of these methods can be found in this 2024 paper in Polymers by Elena E. Mastalygina et al..

Beyond PDLA/PLLA blends we can also blend in other polymers, including a range of flexible polyesters, though it’s essential to determine intermolecular compatibility. Common here are polycaprolactone (PCL), polybutylene adipate terephthalate (PBAT) and polybutylene succinate (PBSA), which like PLA are biodegradable polyesters.

Where things get interesting is with copolymers, which can also involve the aforementioned PCL, PBAT, etc., as well as polyethylene glycol (PEG), with a wide range of combinations possible. Some of these combinations are summarized in the graphic to the right from said paper by Mastalygina et al. using data from cited papers.

Although these methods, along with the more experimental structural modification approach, make the base PLA polymer more flexible, it’s also possible to introduce oligomeric and low-molecular-weight plasticizers which essentially wriggle into the PLA polymer matrix, thus increasing its mobility.

Another focus of such additives can be to act as nucleation agents for nano-crystallization, creating small spherulites that do not impact plasticity nearly as much as naturally forming large spherulites.

Plasticizer

The aforementioned paper covers a range of these plasticizers, such as PEG. Here a problem is that although PEG as a plasticizer additive does promote PLA ductility, PEG tends to migrate out of the polymer. Fortunately there is a dizzying amount of possible plasticizers here, ranging from lactic acid oligomers to epoxidized sunflower oil, as well as linseed, cottonseed, soybean, castor, and other oils.

In a 2025 paper in Polymers by D’Amico et al. the use of used sunflower oil (USOP) as PLA plasticizer is compared with the conventional plasticizer tributyrin (TB). Both show a very similar effect on the plasticity of the final product, though long-term stability of the plasticizer was not tested.

Of course, determining which plasticizer was used in any off-the-shelf spool of PLA filament is effectively impossible. A quick look at a number of commercial PLA filament options, ranging from Prusa to Bambu Lab, shows that their material safety data sheet (MSDS) lists the material only as ‘PLA with additives’.

In a way this makes even ‘regular’ PLA about as much of a mystery filament as so-called ‘PLA+’, with its arbitrary additives such as calcium carbonate.

Degradation

As for how that spool of filament degrades, we can thus draw a number of conclusions. The first is that hydrolysis is the primary degradation mechanism, gradually shortening the backbones of the polymer chains. Yet the other type is one that happens regardless of whether the PLA is fully dried and stored in a container of some sort. A good example of this can be found in e.g. a 2021 Polymers research paper by Tien-Wei Shyr et al. in which many variations of additive-free PLA samples were stored for multiple years.

One set of samples was put into zipper bags and stored in a vacuum-free desiccator, while the other set was stored in vacuum-sealed bags. Both sets were stored like this at room temperature for three years, after which their crystallization and hydrolysis levels were checked.

For the vacuum-sealed samples there was no significant degradation compared to the received samples, while the three-year old samples in the zipper bags had degraded significantly, suffering hydrolysis, nucleation and corresponding crystallization and thus brittleness.

Brittleness

When I recently did some FDM printing for a comparison article series with SLA resin printing, I had dug up a spool of white Sunlu PLA filament that I had left kicking around for probably around three years. This spool had seen itself stuck exposed to room conditions for at least a year when I noticed that after letting it sit fed into the extruder for a number of hours would result in it snapping.

Although I could still print with this filament if I didn’t let it sit too long, it was clear that not only was the PLA rather brittle at this point, it also had assumed a very strong preference for staying in the shape that it was in while on the spool.

What this suggests is thus two things: significant hydrolysis had weakened the filament, and increased crystallization had resulted in both rigidity and brittleness.

Unknown is whether something like a PEG plasticizer was used with this filament, with it having left the building somewhere in the past few years. If the plasticizer is no longer present that would obviously pose somewhat of a conundrum with any attempts to revive the filament.

Ultimately what one can do here is to heat the filament above its T_g for a number of hours, so at least 65 °C for the average PLA blend. This should restore the semi-crystalline state somewhat, although if enough damage has been wreaked by hydrolysis all bets are off. For this particular spool of PLA I did toss it into a Chitu Filapartner filament dryer as it allows you to set the temperature and time, but without a good way to measure the internal material temperature it may not have gotten hot enough.

Considering that this old spool of PLA was fully dried about a year prior in a Sunlu filament dryer using its PLA preset, followed by it being stuffed into a vacuum bag and into an ‘airtight’ container, it’s likely that most of the damage was indeed done by 1-2 years of exposure to room air.

I have saved a few samples of this old filament for later study, but in light of the research covered in this article it highlights just how hard the materials science is, even when it comes to a material as mundane as PLA. Ultimately the best you can do is keep it in that nice vacuum-sealed bag when not printing and pray to the 3D printer gods that you didn’t overlook something important and that maybe one day the filament manufacturers will bless us with details on what these ‘additives’ are.

For as popular as Atari was in their heyday, it wasn’t until well after they were on their famous decline that they released their first handheld, the Atari Lynx. In retrospect, competing with the Game Boy was not going to be a recipe for success even without considering their other problems as a company, and as a result was their penultimate console before exiting the market completely. But [Nick]’s most recent project asks what the world would have been like with an Atari handheld from their golden era, and has been working on this miniaturized version of the 2600.

Unlike any modern emulators which can easily handle Atari 2600 games in almost any form factor today, this console is doing it all with as much original hardware as possible. It uses much smaller switches and buttons compared to the original, and omits some other unnecessary hardware for today’s world like the RF modulator. [Nick] has also designed a custom PCB that reduces the overall footprint considerably as well, and has relocated the cartridge port in preparation for its eventual handheld shape. The result is a console using original hardware that’s less than half the footprint of the original.

Although there were around 30 million Atari 2600 consoles sold and the system is unlikely to be a real collector’s item anytime soon, [Nick] makes sure to note that no real 2600 hardware was harmed in this build. And, as far as its handheld nature, this is a stepping stone on the path to that eventual goal. We’ll look forward to an eventual system that integrates a screen and controller as well as a port for the original cartridges. In the meantime, here’s another handheld 2600 that fits completely inside one of those cartridges.

[Ayushmaan] states up front that most of his free time is spent “building things that probably didn’t need to exist”. Well, this one might be an anomaly, because it seems pretty useful to us.

HYDR8, as it says on the tin, is a wearable that knows when it’s time to hydrate. The impetus for this one was something we all chase: the flow state. [Ayushmaan] would sit down, get deep into work, and look up hours later to to find that he had a headache and a full water bottle. Phone reminders were soon swiped away in annoyance.

This wearable is based on a XIAO ESP32-C3. It reads heart rate, oxygenation, skin temperature, and both the ambient temperature and humidity. It also learns your personal resting numbers range.

Taking all of this into consideration, it generates a heat/hydration stress score between 0-100. The thing is, HYDR8 tells you specifically what to do; sometimes it’s ‘drink water’ and other times, it’s ‘find shade’.

The wearable itself, while somewhat chunky, is pretty simple: it only shows the time and a message when it matters. The ESP32 hosts a full dashboard on your phone.

Keep in mind that this is not a medical device, it’s an experiment, a prototype. It can’t measure how hydrated you are. Instead, it measure hydration stress.

If you don’t want to wear anything, here’s a smart straw that uses a tiny turbine flowmeter and a Hall effect sensor to record the volume sipped, and detect whether the sipper is low on fluids. And if you find yourself under the hot lights of a wet bulb event, here’s how to survive it.

Your desk or bench is a work area, so why not make it look the part? That’s the idea behind the miniature blinking traffic barrels that [Glen Akins] recently put together. Of course, just a single blinking light doesn’t really sell the idea of a busy construction zone, so he spent a somewhat surprising amount of time and effort optimizing the design for small-scale production.

The end result is a fascinating write-up that dives into the design decisions [Glen] made. Every aspect of this project, from the overhang of the “handle” on the 3D printed barrel to the number of passive components on the PCB was carefully considered. Critics may say [Glen] put too much thought into something that didn’t need to be so complex, but projects like these are an excellent way to keep your skills sharp — there’s no such thing as practicing too much.

Starting with the design of the barrel itself, we appreciate that [Glen] kept the capabilities of his desktop 3D printer in mind. By breaking the design up into multiple pieces and avoiding overly steep angles, he produced a design that prints cleanly without the need for support material. His step-by-step documentation and screenshots also serve as a great introduction to designing parts in Fusion if that’s something you’re interested in.

From there, things switch over to the electronics. Some in the audience will bemoan that he’s using a PIC12F1612 microcontroller to blink a single LED instead of a 555, but [Glen] brought the receipts on this one. Not only does the PIC offer more flexibility in terms of getting the blinking to look the way he wants, but it requires fewer passive components on the board and is considerably more energy efficient than the iconic timer IC. Even if you ignore all the other advantages, he calculates that going with a 555 would have cut the battery life of the finished product by approximately 15%.

This is one of those projects that’s difficult to summarize in such a terse format, as every time you think the write-up must be about over it takes a new turn on you. We were mildly bemused when the second iteration of the PCB popped up, but by the time he introduced the custom programming adapter board, we knew [Glen] wasn’t messing around.

Unsurprisingly, this isn’t the first time we’ve seen [Glen]’s handiwork. You may recall seeing his RP2040-powered sound board earlier this year, but his name has been popping up on these pages for more than a decade now.

Here’s a historical hack for you: you have a big, rolling pressurized kettle, also known as a steam locomotive. It needs water to make up for the steam constantly chuff-chuff-chuffing away, or bad things happen. How do you get water from an unpressurized tender into a high pressure boiler with no moving parts? What you need is a some way to inject steam with no moving parts — a steam injector, if you will. [Marc Flint] found that the steam injectors were the hardest part of a loco to understand, so he made a video for all of us once he’d figured it out.

The steam injector isn’t a new idea. [Henri Griffard] came up with it back in the 1850s to replace expensive and maintenance-hungry pumps. It’s rather ingenious and uses the fluid mechanics uncovered by another European bloke by the name of Bernoulli. First, the high-pressure steam from the boiler goes through a converging-diverging nozzle to drop its pressure and speed its flow up, just as you’d guess if you’ve seen Bernoulli’s laws. Even more vacuum-inducing is the presence of water: the steam, already cooled by its expansion, hits the water in the pipe open to the tender, and condenses into it, shrinking a couple of orders of magnitude, creating a vacuum that draws in no small quantity of feed water. That one we did not expect from Bernoulli, but it makes sense. So how to get from below atmospheric pressure to the 180-odd PSI or more in the boiler?

Well, the water is now moving at a good clip, between the Venturi effect and the momentum gained from absorbing that steam, so another converging nozzle is the trick. Bernoulli’s law, once more! A one-way valve lets the now-pressurized water into the boiler, with a gap in between to dump water while the pressure builds up. It’s a clever trick, and since the steam coming from the boiler makes it back inside along with at least some of its heat energy, it’s much more efficient in both coal and water than running a pump. It’s also a bit of a head scratcher how it works unless someone sits you down to explain it, so we’re glad [Marc] did.

Not many of us are likely to use this knowledge directly — unless we’re firing up a 90 year old boiler or building a new steam locomotive — but seeing how great engineers of years past made use of basic physical laws can serve both as education and inspiration.