A Lorenz Teletype Shows Us Its Secrets

When we use the command line on Linux, we often refer to it as a terminal. It’s a word with a past invoking images of serial terminals, rows of green-screened machines hooked up to a central computer somewhere. Those in turn were electronic versions of mechanical teletypes, and it’s one of these machines we’re bringing you today. [DipDoT] has a Lorenz teletype from the 1950s, and he’s taking us through servicing and cleaning it, eventually showing us its inner workings.

The machine in question had been in storage for many years, but remained in good condition. To be this long out of use though meant it needed a thorough clean, so he sets about oiling the many hundreds of maintenance points listed in a Lorenz manual. It’s a pleasant surprise for us to see keyboard and printer unit come away from the chassis for servicing so easily, and by stepping it through its operation step by step we can see how it works in detail. It even incorporates an identifier key — think of it as a mechanical ROM that stores a sequence of letters — which leads him to believe it may have come from a New York news office. The video is below the break, and makes for an interesting watch.

He’s going to use it with a relay computer, but if you don’t have one of those there are more modern ways to do it.

Continue reading “A Lorenz Teletype Shows Us Its Secrets”

A New Cartridge For An Old Computer

Although largely recognizable to anyone who had a video game console in the 80s or 90s, cartridges have long since disappeared from the computing world. These squares of plastic with a few ROM modules were a major route to get software for a time, not only for consoles but for PCs as well. Perhaps most famously, the Commodore VIC-20 and Commodore 64 had cartridge slots for both gaming and other software packages. As part of the Chip Hall of Fame created by IEEE Spectrum, [James] found himself building a Commodore cartridge more than three decades after last working in front of one of these computers.

[James] points out that even by the standards of the early 80s the Commodore cartridges were pretty low on specs. They’re limited to 16 kB, which means programming in assembly and doing things like interacting with video hardware directly. Luckily there’s a treasure trove of documentation about the C64 nowadays as well as a number of modern programming tools for them, in contrast to the 80s when tools and documentation were scarce or nonexistent. Hardware these days is cheap as well; the cartridge PCB and other hardware cost only a few dollars, and the case for it can easily be 3D printed.

Burning the software to the $3 ROM chip was straightforward as well with a TL866 programmer, although [James] left a piece of memory management code in the first pass which caused the C64 to lock up. Removing this code and flashing the chip again got the demo up and running though, and it’ll be on display at their travelling “Chips that Changed the World” exhibit. If you find yourself in the opposite situation, though, we’ve also seen projects that cleverly pull the data off of ancient C64 ROM chips for preservation.

Google Confirms Non-ADB APK Installs Will Require Developer Registration

After the news cycle recently exploded with the announcement that Google would require every single Android app to be from a registered and verified developer, while killing third-party app stores and sideloading in the process, Google has now tried to put out some of the fires with a new Q&A blog post and a video discussion (also embedded below).

When we first covered the news, all that was known for certain was the schedule, with the first trials beginning in October of 2025 before a larger rollout the next year. One of the main questions pertained to installing apps from sources that are not the Google Play Store. The answer here is that the only way to install an app without requiring one to go through the developer verification process is by installing the app with the Android Debug Bridge, or adb for short.

The upcoming major release of Android 16 will feature a new process called the Android Developer Verifier, which will maintain a local cache of popular verified apps. The remaining ones will require a call back to the Google mothership where the full database will be maintained. In order to be a verified Android developer you must have a Google Play account, pay the $25 fee and send Google a scan of your government-provided ID. This doesn’t mean that you cannot also distribute your app also via F-Droid, it does however mean that you need to be a registered Play Store developer, negating many of the benefits of those third-party app stores.

Although Google states that they will also introduce a ‘free developer account type’, this will only allow your app to be installed on a limited number of devices, without providing an exact number so far. Effectively this would leave having users install unsigned APKs via the adb tool as the sole way to circumvent the new system once it is fully rolled out by 2027. On an unrelated note, Google’s blog post also is soliciting feedback from the public on these changes.

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A magnifying glass is seen behind a small tea candle. The magnifying image is projecting the shadow of a column of heated air.

Finding Simpler Schlieren Imaging Systems

Perhaps the most surprising thing about shadowgraphs is how simple they are: you simply take a point source of light, pass the light through a the volume of air to be imaged, and record the pattern projected on a screen; as light passes through the transition between areas with different refractive indices, it gets bent in a different direction, creating shadows on the viewing screen. [Degree of Freedom] started with these simple shadowgraphs, moved on to the more advanced schlieren photography, and eventually came up with a technique sensitive enough to register the body heat from his hand.

The most basic component in a shadowgraph is a point light source, such as the sun, which in experiments was enough to project the image of an escaping stream of butane onto a sheet of white paper. Better point sources make the imaging work over a wider range of distances from the source and projection screen, and a magnifying lens makes the image brighter and sharper, but smaller. To move from shadowgraphy to schlieren imaging, [Degree of Freedom] positioned a razor blade in the focal plane of the magnifying lens, so that it cut off light refracted by air disturbances, making their shadows darker. Interestingly, if the light source is small and point-like enough, adding the razor blade makes almost no difference in contrast.

With this basic setup under his belt, [Degree of Freedom] moved on to more unique schlieren setups. One of these replaced the magnifying lens with a standard camera lens in which the aperture diaphragm replaced the razor blade, and another replaced the light source and razor with a high-contrast black-and-white pattern on a screen. The most sensitive technique was what he called double-pinhole schlieren photography, which used a pinhole for the light source and another pinhole in place of the razor blade. This could image the heated air rising from his hand, even at room temperature.

The high-contrast background imaging system is reminiscent of this technique, which uses a camera and a known background to compute schlieren images. If you’re interested in a more detailed look, we’ve covered schlieren photography in depth before.

Thanks to [kooshi] for the tip!

2G Gone? Bring It Back Yourself!

Some parts of the world still have ample 2G coverage; for those of in North America, 2G is long gone and 3G has either faded into dusk or beginning its sunset. The legendary [dosdude1] shows us it need not be so, however: Building a Custom 2G GSM Cellular Base Station is not out of reach, if you are willing to pay for it. His latest videos show us how.

Before you start worrying about the FCC or its equivalents, the power here is low enough not to penetrate [dosdude]’s walls, but technically this does rely in flying under the radar. The key component is a Nuand BladeRF x40 full-duplex Software Defined Radio, which is a lovely bit of open-source hardware, but not exactly cheap. Aside from that, all you need is a half-decent PC (it at least needs USB-3.0 to communicate with the SDR, the “YateBTS”  software (which [dosdude1] promises to provide a setup guide for in a subsequent video) and a sim card reader. Plus some old phones, of course, which is rather the whole point of this exercise.

The 2G sunset, especially when followed by 3G, wiped out whole generations of handhelds — devices with unique industrial design and forgotten internet protocols that are worth remembering and keeping alive. By the end of the video, he has his own little network, with the phones able to call and text one another on the numbers he set up, and even (slowly) access the internet through the miniPC’s network connection.

Unlike most of the hacks we’ve featured from [dosdude1], you won’t even need a soldering iron, never mind a reflow oven for BGA. 

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Logitech POP Buttons Are About To Go Pop

For those who missed out on the past few years of ‘smart home’ gadgets, the Logitech POP buttons were introduced in 2018 as a way to control smart home devices using these buttons and a central hub. After a few years of Logitech gradually turning off features on this $100+ system, it seems that Logitech will turn off the lights in two weeks from now. Remaining POP Button users are getting emails from Logitech in which they are informed of the shutdown on October 15 of 2025, along with a 15% off coupon code for the Logitech store.

Along with this coupon code only being usable for US-based customers, this move appears to disable the hub and with it any interactions with smart home systems like Apple HomeKit, Sonos, IFTTT and Philips Hue. If Logitech’s claim in the email that the buttons and connected hub will ‘lose all functionality’, then it’d shatter the hopes for those who had hoped to keep using these buttons in a local fashion.

Suffice it to say that this is a sudden and rather customer-hostile move by Logitech. Whether the hub can be made to work in a local fashion remains to be seen. At first glance there don’t seem to be any options for this, and it’s rather frustrating that Logitech doesn’t seem to be interested in the goodwill that it would generate to enable this option.

Know Audio: Distortion Part Two

It’s been a while since the last installment in our Know Audio series, in which we investigated distortion as it applies to Hi-Fi audio. Now it’s time to return with part two of our look at distortion, and attempt some real-world distortion measurements on the bench.

Last time, we examined distortion from a theoretical perspective, as the introduction of unwanted harmonics as a result of non-linearities in the signal path. Sometimes that’s a desired result, as with a guitar pedal, but in a Hi-Fi system where the intention is to reproduce as faithfully as possible a piece of music from a recording, the aim is to make any signal path components as linear as possible. When we measure the distortion, usually expressed as THD, for Total Harmonic Distortion, of a piece of equipment we are measuring the ratio of those unwanted harmonics in the output to the frequencies we want,  and the resulting figure is commonly expressed in dB, or as a percentage. Continue reading “Know Audio: Distortion Part Two”