Mysterious Files PH

Although it can be hard to tell from looking at the often placid waters of the Earth’s oceans, their currents carry immense amounts of water around the globe on a daily basis, underlying a dynamic system that – much like the Earth’s atmosphere – plays a major role in everything from weather systems to local climates and ecosystems.

Of all these ocean currents the Atlantic meridional overturning circulation (AMOC) is perhaps the most famous, as it is basically the sole reason why Europe has the mild climate that it does today, courtesy of it carrying thermal energy from the equator all the way to the coast off Scandinavia.

Although collapsing an ocean current seems as improbable as stopping the jet streams in the upper atmosphere, it’s actually significantly easier due to how much ocean currents rely on factors that we can fairly easily influence. Over the past decades we have seen worrying signs that the AMOC is indeed weakening, with the million-dollar question being what scenario we’ll be looking at.

While collapsing the AMOC within a decade may be theoretically possible, current models seem to point towards a weakening by about half by the end of this century, with a recent research article by Valentin Portmann et al. in Science Advances going over the various statistical models to come to this conclusion.

The AMOC

Differences in temperature and salinity drive the ocean currents, causing the transport of water from one area to another as the system seeks to equalize itself. While this may bring to mind the atmosphere’s unrelenting jet streams, or the precarious and harrowing traversal of the area near the Cape of Good Hope where the Agulhas and Benguela currents meet, the AMOC is rather slow and ponderous, taking centuries to circulate.

Although it’s obviously a circular system, you can put its beginning at the point of energy input, which for the AMOC is the warm water of the Gulf of Mexico, from where the Gulf Stream flows through the Straits of Florida, following the coast line until it splits up into various smaller currents. The largest of these is the North Atlantic Current (NAC) that provides Europe with warmth and nutrients, while another significant branch is the Canary Current which brushes along the west coast of Africa as part of the North Atlantic Gyre.

As the warmer water travels along the surface of the ocean, it will gradually lose heat to the cooler air, especially once it reaches the North Atlantic. This thermohaline circulation (THC) follows the same pattern around the world’s oceans, with AMOC and the Southern Ocean overturning circulation (SOOC) forming its two main components, distributing heat and nutrients from the equatorial regions to the rest of the world’s oceans.

When the cooling water reaches the limits, the cooling water undergoes a density change that results in it sinking. This is caused by the process of brine rejection, which is the phenomenon where the freezing of saltwater rejects the salts from the forming ice matrix. This produces very salty brine, which is more dense than the surrounding ocean water, ergo it will sink and thereby terminate its branch of the THC.

Salinity Changes

An obvious conclusion one can draw from this brine rejection mechanism is that it can conceivably be interrupted, such as when enough freshwater slows down or disturbs the process. This collapse of the AMOC by freshwater forcing has been the topic of many studies over the years, with a 2024 article in Oceanography by René van Westen et al. investigating evidence that the AMOC is indeed on course for such an event.

At the core of this research are coupled models such as those of the Coupled Model Intercomparison Project (CMIP), which has been developed in phases since 1995. This a cooperative project in which researchers from around the world attempt to create the most complete climate model possible, in order to improve our understanding of the current climate and to make projections about what effects certain changes would have.

The Community Earth System Model (CESM)  is one of the contributing models to the CMIP5, using which Van Westen et al. tried to find evidence of a so-called tipping event in the AMOC. What’s notable about their study is that they didn’t attempt freshwater forcing using very large volumes of said freshwater, but still saw a gradual weakening over centuries.

With freshwater forcing consistently reducing the amount of salinity transferred via the NAC, this weakens the effect of brine rejection, thus weakening the AMOC until it eventually collapses. The balance here is the freshwater budget of the Atlantic Ocean, with rivers and melt-off from glaciers and such affecting said budget.

This is where we run into the conundrum that the analysis done by Portmann et al. on the CMIP6 predictions suggest a consistent weakening of the AMOC of about 50% by the year 2100, whereas Van Westen et al. observed a tipping point and rapid collapse of the AMOC to effectively zero using the CESM and a gradual freshwater forcing until said tipping point in the Atlantic freshwater budget is reached.

While a gradual weakening of the AMOC would obviously be bad, a full-blown collapse would obviously be significantly worse, potentially occurring over the span of a few decades and with any recovery deemed either unlikely or taking multiple millennia, as modelled by e.g. Curtis et al. in a 2024 study (free access PDF).

Implications

Whether the AMOC merely weakens by about half or collapses completely, the implications will be severe, with the same 2024 paper by Van Westen et al. providing a good overview, including a summary graphic:

Europe in particular would be hit, experiencing far colder seasons along with a sharp drop-off in precipitation. Yet other regions would not be left untouched either, with the Amazon region in particular experiencing a big shift in its climate patterns. In particular the periods when it’d experience cooler, wet weather and vice versa would be flipped, while even Africa and Australia would see a shift in precipitation levels.

In effect, there would likely be severe consequences for the ecosystems in South-America, while Europe would largely turn into a significantly more arid and colder region, similar to e.g. parts of Canada that are on the same latitude. With most of Canada’s population doing its utmost to avoid its more northern latitudes for rather reasonable reasons, it seems fair to say that a full-blown collapse of the AMOC would spell disaster for most European nations.

Keeping The AMOC Healthy

Now that we know the mechanism behind the AMOC and other parts of the THC, the solution to its weakening seems rather obvious: all we have to do is prevent excess freshwater forcing that risks diminishing the Atlantic Ocean’s freshwater budget and we should be golden. Doing so requires identifying the sources of this excess forcing, with a recent study by Oliver Mehling et al. making clear that where the freshwater forcing occurs matters a lot, with many models overestimating the time that we have left until an AMOC tipping point for this reason.

We can also look back on historical climate data courtesy of Antarctic ice cores that go back about a million years, though the Greenland ice cores are the golden standard for e.g. the Dansgaard-Oeschger event that occurred at the end of the last ice age. Since a warming climate naturally results in more freshwater forcing due to meltwater run-off into the oceans, we might be able to find some historical data that shows how the AMOC fared over the past millennia.

What we know is that the AMOC first formed about 34 million years ago when the continents shifted sufficiently to create the THC that we know today began to form. Since then the AMOC has apparently operated continuously, including the repeated glacial periods of the Pleistocene (2.58 million – 11,700 years ago) which ended around the time when the Dansgaard-Oeschger event occurred with an influx of freshwater into the Atlantic.

Of course, much of this historical data is reconstructed from proxies as part of paleoclimatology, so everything has to be taken with a grain of salt. Even so, we can for a large period directly measure aspects such as CO₂ concentration in the atmosphere before we have to resort to proxies. This shows us that to get similar atmospheric levels of that gas in Earth’s history we have to look all the way back to ~16 million years ago during the middle Miocene after atmospheric CO₂ levels had gradually come down from 1,600 ppm.

Even as some of us are contemplating direct weather modification, it might thus be an idea to consider the impact of anthropogenic greenhouse gases, as they clearly cause a very rapid increase in the global surface temperature. This warming then increases the melting of glaciers and similar, which in turn increases freshwater forcing into the THC, which thus could result in a sudden AMOC collapse.

Of course, the fun thing about such climate models is that they are only a projection based on our current knowledge. Only in hindsight will we know just how far off the mark we were, but when the stakes are this high, it might not be a terrible idea to err on the side of caution.

Featured image: Illustration of the Atlantic Meridional Overturning Circulation (AMOC).  Eric S. Taylor, Woods Hole Oceanographic Institution

Back in the 80s, buying a home computer could easily mean an inflation-adjusted cost of thousands of dollars (or your equivalent currency unit of choice), and all for an 8-bit machine that might not have a hard drive and almost certainly didn’t connect to a network. Here in the future it’s easy to get spoiled by all the computing power and inexpensive devices practically falling into our laps, but using some modern low-cost microcontrollers can connect us to our early computing roots like [Joe]’s latest Arduino-based computer.

Taking design an engineering cues from computers like the Timex Sinclair 1000, Commodore PET, and TRS-80 MC-10, this computer uses a trio of Arduinos to accomplish what the best computer manufacturers once did with tons of integrated circuits. An Arduino Due handles all of the processing and traditional computing tasks, including a somewhat customized BASIC implementation, while an Uno performs audio processing duties. Taking care of the video processing is the much more capable Arduino Mega, outputting 40×25 monochrome NTSC composite video at 8×8 character resolution. There’s even WiFi courtesy of an ESP32 — certainly an upgrade compared to the source material.

After booting it up, the user gets a Commodore-like experience that replicates the 80s computing era quite well, and is even built inside its own keyboard case just like that era of computers usually were. [Joe] plans to release all three firmware images and the Python script used to get files onto the faux-retro machine, so keep an eye out for that.

In the event that you used rubles instead of dollars to pay for your expensive 8-bit machines back in the 80s, this computer might be more up your alley instead.

The Honeywell X2S Smart Thermostat is a Wi-Fi-enabled thermostat that is meant to integrate with your typical ‘smart home’ setup, with mobile app control available as well. Of course, just using it as-is would be extremely boring, so fortunately we have [author0] to take it apart and reverse-engineer its encrypted firmware.

Of the two brains in this thermostat the first is a succinctly named Renesas R7FA6M4AF3CFP MCU containing a 200 MHz Cortex-M33 core with TrustZone features to theoretically keep out any firmware hackers. Handling the wireless side is a Realtek RTL8721DM Wi-Fi/BLE 5.0 SoC. There are also two Winbond Flash chips connected to these two main chips, with their contents of course encrypted.

Fortunately there are plenty of test points to connect to, for which a custom pogo-pin equipped breakout board was created. Cracking the encryption for the Realtek turned out to be as simple as using its RSIP decrypt-on-the-fly feature. From there exploring the firmware was the next step, with a TLS issue pertaining to certificates found to make man-in-the-middle attacks easy, along with a seeding bug that makes recovering session keys possible.

Although the Renesas MCU firmware still has to be decrypted and the full wireless handshake reverse-engineered, these do seem to be solid steps towards fully reverse-engineering this thermostat. It also makes it very clear once again that the ‘S’ in IoT absolutely stands for ‘security’. Maybe that’s why the smart home bubble popped.

The Commodore 64 has, by modern standards, the interesting power requirement of needing both 5 VDC and 9 VAC. Traditionally, one would use an iron-core transformer to step-down the wall current — be it 220 V or 115 V, 50 Hz or 60 Hz — to produce the low-voltage AC.

That’s how Commodore did it, and that’s how most of the aftermarket replacements do it, too. That iron-core transformer is bulky, though, and [Side Projects Lab] decided that in this day and age of switching supplies and USB-PD he could surely do better. Which he did, with the diminutive PD-64.

As you can see, it just covers the power port of the C64, and not much else. Partly that small size comes from offloading some of the hard work onto a USB-PD wall wart. The PD-64 requests 12 VDC, which it then steps down to 5 VDC with the usual buck converter, and inverts to 9 VAC in a circuit that is the most interesting part of the project.

There are various ways one could do this, after all, and we’re sure some of you will have different ideas than [Side Projects Lab], but his method seems sound. In order to provide galvanic isolation between the two outputs, the 12 VDC line is first chopped into a 500 kHz signal, and run through a tiny 5:6 ferrite transformer. That output gets rectified to 13.6 VDC, a voltage that is used to run a class-D audio amplifier to produce the 9 V peak-to-peak, zero-DC-offset signal the C64 needs.

[Side Projects Lab] has released both FreeCAD files for the case and STLs as BY-CC-ND 4.0, and a circuit diagram is available for the electrical side. If you don’t want to design your own PCB, [sideprojectslab] will be selling finished versions.

If you’re interested in further dragging your C64 into the modern era, check out the HDMI output that [Side Projects Lab] hacked together for the iconic computer last year.

There’s a line in a [Weird Al] (no relation) song that says, “I upgrade my system at least twice a day…” I know how that is. I primarily use a rolling distro, OpenSuse Tumbleweed, and if I’m having a problem that I’m too lazy to run down, it is extremely tempting to do an upgrade and see if it just happens to fix the problem.

Of course, the problem is often caused by a previous upgrade. Recently, I’ve been having a lot of trouble with the NVIDIA proprietary drivers, so I updated them yet again. After a huge amount of effort to sort out the video problems, I found that the latest kernel didn’t like my MediaTek Bluetooth adapter, which is built into the motherboard’s WiFi chipset.

This post isn’t about how to fix your Bluetooth problem. You probably don’t have the same setup I do, and even if you do, it will be sorted out in a week or two anyway. But how I temporarily fixed this issue is worth documenting. The details are going to apply to Tumbleweed and this particular adapter, but the general approach should work anywhere with any sort of kernel module problem.

My Own Fault

Part of my problem is my own fault, of course. I have a complex disk setup and do not use the recommended btrfs root file system. That means I can’t do the snapshot thing where I can just undo a bad upgrade. If I did, then sure, I should just roll back and wait for an upstream fix.

I do have “normal” backups, but they are not always totally up to date. Worse, I have found that for things like NVIDIA, the user stuff and the kernel module stuff have to match up. That makes it very hard to roll back a kernel with older modules. The modules themselves live with the kernel, but the user space stuff gets pushed out. Or, if you uninstall things, it uninstalls it for all kernels.

Truthfully, NVIDIA and others like that should keep all the user space stuff in a kernel-specific place, and then symlink it at boot to /usr/bin or wherever. But they don’t. In the end, I didn’t want to go through the trouble of rolling things back and decided to push ahead.

Modular

I did a quick search and found a four-day-old post that had the same error message I was getting and mentioned a patch to the kernel module source — literally just two lines needed changing in the btmtk module.

Of course, the trick is how to do that. If you’ve done kernel module development, you are probably all set up for it. If not, how to proceed will vary by distro. For Tumbleweed, something like:

sudo zypper in -t pattern devel_kernel
sudo zypper in kernel-source kernel-default-devel kernel-syms gcc make bc flex bison openssl-devel dwarves

For other distros, you need the current kernel’s source code and the same sort of build tools. For example, for Ubuntu and probably other Debian-based distros:

sudo apt update
sudo apt install build-essential linux-headers-$(uname -r) linux-source bc flex bison libssl-dev libelf-dev dwarves rsync

Then you’d still need to unpack the source tarball.

For Tumbleweed, you don’t need to unpack, but I did want to get it somewhere in my user directory:

mkdir -p ~/kernel-local
# Note: trailing slashes matter here!
rsync -a --delete /usr/src/linux/ ~/kernel-local/linux-btmtk/
cd ~/kernel-local/linux-btmtk

Either way, you need to get the running kernel’s configurations into the linux-btmtk directory:

cp /lib/modules/$(uname -r)/build/.config .
cp /lib/modules/$(uname -r)/build/Module.symvers . 2>/dev/null || true

The Patch

The next step is to find the btmtk.c file and patch it. In my case, I needed to find this code: case BTMTK_WMT_FUNC_CTRL: if (!skb_pull_data(data->evt_skb, sizeof(wmt_evt_funcc->status))) { err = -EINVAL; goto err_free_skb; }

and replace the error return/goto with:

status = BTMTK_WMT_ON_UNDONE;
break;

The Build

Now you just have to build and install the module:

make olddefconfig
make modules_prepare
make M=drivers/bluetooth modules

If you want to use multiple CPUs, put a -j=X line on make (e.g,. -j=8 to use eight cores). This will take a minute.

You’ll wind up with a drivers/bluetooth/btmtk.ko file. Your first instinct will be to simply copy it over the old one. Resist that urge. Instead, try this:

sudo mkdir -p /lib/modules/$(uname -r)/updates/drivers/bluetooth
sudo cp drivers/bluetooth/btmtk.ko /lib/modules/$(uname -r)/updates/drivers/bluetooth/
sudo depmod -a

Run It!

If you want to verify things, try:

modinfo -n btmtk

It should show your module and not the stock one. You could try to avoid rebooting by stopping the Bluetooth service, tearing down btusb and btmtk, and then reloading them along with the service. But, yeah, just reboot.

If your distro is different, you might have to modify these instructions a bit. Of course, you also need to know how to fix the bad module, too. Naturally, if you update the kernel, you might have to repeat it all unless your problem has been fixed. Then again, you could set up the module in DKMS to rebuild every time, but I wouldn’t unless you really thought this was going to be a long-term problem.

Once you have all this set up, you could also build your own kernel. That’s another set of headaches, but it can be worth it if you need special setups. Want to write your own modules? We’ve done that.

Zinc air batteries have been a familiar sight for decades in the world of photography, where they provided an environmentally less dangerous alternative to mercury cells. They operate by the oxidation of metallic zinc using air, and the zinc comes in the form of a paste spread between two electrodes. Can their astounding energy density be harnessed for something useful? [ZollerLab] has designed a zinc air battery to find out, and is using it to power a rudimentary model car.

The video below is in German so you’ll have to enable translated subtitles if you’re an Anglophone, and it’s very long. But it goes into extreme detail on the chemistry, construction, and constraints of a zinc-air battery, and describes the system in this design. It’s a stack arrangement, in which the cells are held together on threaded rods, and pushed into each other with springs.

We think the car model is intended to demonstrate that this battery chemistry might one day be used in automotive applications. It’s not such a far-fetched idea given the low cost, relatively low environmental footprint, and high energy density, indeed we’ve heard of similar experiments with aluminium primary cells. But in this case we can see it provides the hacker with another route for their experiments, and that’s no bad thing.

Glass-based substrates are slowly beginning to push out organic substrates commonly used in PCBs due to often superior material properties. One area where glass substrates have however struggled is with through-hole vias and providing the conductive copper path through them. A 2024 article by [Keith Best] gives a good overview of the topic, with recent news showing how much companies like Intel are pushing for glass substrates, specifically for the packaging of dies.

One major advantage with vias in glass substrates is that they can be much smaller, enabling smaller than 0.1 mm diameter holes with far finer pitch. The challenge here is to make perfect holes with a laser that are defect-free, as well as have the intended diameter.

After that this through-glass via (TGV) has to be coated or filled with copper, much like their organic equivalent. Said TGV can be fully filled with copper, or use plating and add dielectric filler. Detecting flaws in such a finished TGV is important.

In a 2025 review article of glass substrate technologies by [Pratik Nimbalkar] et al. published in Chips the state of the art at the time was covered. The need for ever higher-density integration options with ASICs is highlight here, especially now that many chips today consist of multiple interconnected dies inside a single package.

The complications of creating TGVs with femtosecond laser pulses in Borofloat 33 glass are highlighted by [Daniel Franz] et al. in a 2025 research article, with microcracks and backside ablation observed without proper precautions, something which previously was often resolved by an etching step following said laser drilling. The main issue here is the post-drilling residual stress from the thermal shock, which the authors demonstrate can be largely prevented with careful tweaking of the laser drilling parameters.

As pointed out in a 2024 review article by [Chen Yu] et al. glass substrates are useful for far more than just high-density chip packaging. Glass substrates are also chemically resistant, have a higher heat resistance, are largely transparent to RF and can be hermetically sealed against outside influences. This makes them great for various advanced sensors and communication devices.

Meanwhile, if you wanted to do some metal-depositing on glass at home, we covered this recently.