Mysterious Files PH

Would you like to make your own energy? Why, who doesn’t in this era of rising costs! A sterling engine always looks like a good fit for that: highly efficient, with no risk of a boiler explosion. A thermoacoustic sterling engine looks even better, since it has only one moving part at the output end. A thermoacoustic sterling engine you can 3D print yourself looks best of all, and that’s what [my engines] has on offer, now that even the burner and hot end of his thermoacoustic engine are designed for SLA metal printing.

We previously reported on the open-source engine, but there’ve been some improvements worth talking about. For one thing, he’s integrated a biogas/methane burner directly inside the 3D-printable hotend. For another, that 3D-printed design allows for an excellent heat exchange geometry that would be very hard to get any other way. The whole thing is open source with plans available at OwnEnergy.org, where you can find links to the apparently-mandatory Discord channel and now an old-style forum to actually collaborate on the design, which is open-source. The site is also now the home of all data and discussion about [my engines]’s homescale biogas plant, which is the power source for this little engine.

If you’d rather print a combustion engine, you can do that, too, but you’ll need more “vitamins” than this unit requires.

[Makestreme] had always wanted to own a nice telescope, but found that budget would not stretch to anything above a cheap model with a limited 50 mm aperture. Wanting a better view of the heavens, the way forward was obvious—it was time to build a better telescope, instead!

The build is based around a 114 mm diameter mirror sourced from Amazon. It’s assembled inside a length of 5-inch PVC pipe of just under a meter to suit the 900 mm focal length of the concave reflector. 3D printed components are used to mount the mirror and control its position for proper focus and collimation. Traditionally, a reflector based telescope would use a mirror and eyepiece to provide a view to the user. However, [Makestreme] built this as a smart telescope, instead integrating a Raspberry Pi Camera Module 3 at the focal point. It’s connected to a Raspberry Pi Zero 2W, running off an 18650 lithium-ion cell and a 5 V boost module for portability. The Pi runs a Python script that hosts a small web server allowing access to the live camera feed along with controls for brightness, exposure, and gain. [Makestreme] then uses apps like SkyMap and SkEye to help aim the telescope at astronomical elements of interest.

If you’ve ever wanted to explore the heavens from down on Earth, building your own telescope is a great way to start. A camera-based build like this one can be a bit simpler than traditional builds, too, without the fuss of having to install an eyepiece.

In this week’s episode, Hackaday Editors Elliot Williams and Tom Nardi start things off by getting excited about the recently announced 2026 Retrocomputing Challenge. From there the conversation will cover efforts to improve desktop 3D printing with lasers, an expensive grill with an ESP32 controller and an open source firmware, open source tools underground, and some impressive techniques to squeeze a bit more utility out of the common QR code.

You’ll also hear about turning PVC pipes into flat stock, old school Radio Shack electronic kits, and VR soldering demos. Stick around to the end of the episode learn about the latest developments in over-the-counter hearing aids and the 1-bit CPU that’s enjoying an unexpected fandom nearly 50 years after its release.

Check out the links if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download in DRM-free MP3.

Episode 383 Show Notes:

Mailbag:

• Alexander wrote in praise of buying ultrasonic knife guts. Donald Papp wrote up his experience with a hacked dental tool a few years back. Now you can get it over the counter.
• Joey wrote in asking if we can add video/visuals to the Podcast. We complain about how difficult that would be.  :)
• Mailbag still needs intro/outro music. Anyone want to whip something up? Send it to mailbag@hackaday.com.

News:

• Announcing The 2026 Hackaday Retrocomputing Challenge
• Using The Famicom Network System In 2026

Interesting Hacks of the Week:

• Laser Layers For (Almost) Isotropicly Strong Prints
  • 3D Print Smoothing, With Lasers
  • More On Wave Overhangs For 3D Printing
• Reverse Engineered Grill Controller Gets Open Firmware
• Hackaday Europe 2026: Open Source Hardware Goes Underground, Literally
  • GitHub – furbrain/STIC · GitHub
• Building Custom Backyard Solar Lights
  • PVC Pipe Transformed Into Handy Tool Box
• Compress Links For Optimal QR Codes
  • http://ha.mr#2)22
  • Store Tunes On Paper And Stream Them Over LoRA
• Radio Shack Toy Returns To Life

Quick Hacks:

• Elliot’s Picks:
  • Joy-Cons Plus WiiMotes Make For Switch 2 Wii-Cons
  • So, You Want To Fix An Old Camera
  • Watch Soldering Up Close And From Any Angle, In VR
  • May This Balloon Banjo Resonate With You
• Tom’s Picks:
  • Snooping Flume Water Monitor Data On The Wire
  • Smarting Up A Doorbell With Zigbee
  • Scanning For Lifesigns With ESP32 And Raspberry Pi

Can’t-Miss Articles:

• Smartphones And The Next Generation Of Hearing Aids
• Hackaday Europe 2026: The 1-Bit CPU That Ran Factories
  • Building An Industrial Control Unit With An Industrial Control Unit
  • A one-bit processor explained: reverse-engineering the vintage MC14500B
  • WDR-1-Bit-Computer
  • Too Cool For 8-bit Retro? Try 1-bit Gaming

These days, modems are pretty fancy bits of kit, what with to keep up with the speeds of cable, VDSL, and fiber connections. At lower speeds, though, it’s entirely possible to build a modem out of simple discrete components. [sv3ora] did just that, building a simple modem for the CB2 Micro.

The project takes advantage of the fact that the V1.54 firmware for the CB2 Micro enabled 75 baud serial communication. Thus, it made sense for [sv3ora] to build a 75 baud modem to suit. As was the way in the days of dial-up internet, the modem modulates data into audio, demodulates audio back into data, allowing the CB2 Micro to send and receive data over telephone lines, ham radio links, or to store and retrieve data via mediums like cassette tape.

The device is built out of good old BC547 transistors. along with a smattering of diodes, resistors, and capacitors as supporting hardware. That’s all you need to turn slow serial into audio and back again. [sv3ora] does a great job of demoing the hardware, using it to store a program on tape and retrieve it again later.

We love old school modems around these parts. We’ve even explored ways to build your own dial-up ISP in the past!

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.