Oscillator Negativity Is A Good Thing

July 8, 2025 by 5 Comments

Many people who get analog electronics still struggle a bit to design oscillators. Even common simulators often need a trick to simulate some oscillating circuits. The Barkhausen criteria state that for stable oscillation, the loop gain must be one, and the phase shift around the feedback loop must be a multiple of 360 degrees. [All Electronics Channel] provides a thorough exploration of oscillators and, specifically, negative resistance, which is punctuated by practical measurements using a VNA. Check it out in the video below.

The video does have a little math and even mentions differential equations, but don’t worry. He points out that the universe solves the equation for you.

In an LC circuit, you can consider the losses in the circuit as a resistor. That makes sense. No component is perfect. But if you could provide a negative resistance, it would cancel out the parasitic resistance. With no loss, the inductor and capacitor will go back and forth, electrically, much like a pendulum.

So, how do you get a negative resistance? You’ll need an active device. He presents some example oscillator architectures and explains how they generate negative resistances.

Crystals are a great thing to look at with a VNA. That used to be a high-dollar piece of test gear, but not anymore.

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Hackaday Links: June 29, 2025

June 29, 2025 by 16 Comments

In today’s episode of “AI Is Why We Can’t Have Nice Things,” we feature the Hertz Corporation and its new AI-powered rental car damage scanners. Gone are the days when an overworked human in a snappy windbreaker would give your rental return a once-over with the old Mark Ones to make sure you hadn’t messed the car up too badly. Instead, Hertz is fielding up to 100 of these “MRI scanners for cars.” The “damage discovery tool” uses cameras to capture images of the car and compares them to a model that’s apparently been trained on nothing but showroom cars. Redditors who’ve had the displeasure of being subjected to this thing report being charged egregiously high damage fees for non-existent damage. To add insult to injury, if renters want to appeal those charges, they have to argue with a chatbot first, one that offers no path to speaking with a human. While this is likely to be quite a tidy profit center for Hertz, their customers still have a vote here, and backlash will likely lead the company to adjust the model to be a bit more lenient, if not outright scrapping the system.

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This Week In Security: The Localhost Bypass, Reflections, And X

June 13, 2025 by 26 Comments

Facebook and Yandex have been caught performing user-hostile tracking. This sort of makes today just another Friday, but this is a bit special. This time, it’s Local Mess. OK, it’s an attack with a dorky name, but very clever. The short explanation is that web sites can open connections to localhost. And on Android, apps can be listening to those ports, allowing web pages to talk to apps.

That may not sound too terrible, but there’s a couple things to be aware of. First, Android (and iOS) apps are sandboxed — intentionally making it difficult for one app to talk to another, except in ways approved by the OS maker. The browser is similarly sandboxed away from the apps. This is a security boundary, but it is especially an important security boundary when the user is in incognito mode.

The tracking Pixel is important to explain here. This is a snippet of code, that puts an invisible image on a website, and as a result allows the tracker to run JavaScript in your browser in the context of that site. Facebook is famous for this, but is not the only advertising service that tracks users in this way. If you’ve searched for an item on one site, and then suddenly been bombarded with ads for that item on other sites, you’ve been tracked by the pixel.

This is most useful when a user is logged in, but on a mobile device, the user is much more likely to be logged in on an app and not the browser. The constant pressure for more and better data led to a novel and completely unethical solution. On Android, applications with permission to access the Internet can listen on localhost (127.0.0.1) on unprivileged ports, those above 1024.

Facebook abused this quirk by opening a WebRTC connection to localhost, to one of the ports the Facebook app was listening on. This triggers an SDP connection to localhost, which starts by sending a STUN packet, a UDP tool for NAT traversal. Packed into that STUN packet is the contents of a Facebook Cookie, which the Facebook app happily forwards up to Facebook. The browser also sends that cookie to Facebook when loading the pixel, and boom Facebook knows what website you’re on. Even if you’re not logged in, or incognito mode is turned on.

Yandex has been doing something similar since 2017, though with a different, simpler mechanism. Rather than call localhost directly, Yandex just sets aside yandexmetrica.com for this purpose, with the domain pointing to 127.0.0.1. This was just used to open an HTTP connection to the native Yandex apps, which passed the data up to Yandex over HTTPS. Meta apps were first seen using this trick in September 2024, though it’s very possible it was in use earlier.

Both companies have ceased since this report was released. What’s interesting is that this is a flagrant violation of GDPR and CCPA, and will likely lead to record-setting fines, at least for Facebook.

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Hackaday Links: May 25, 2025

May 25, 2025 by 24 Comments

Have you heard that author Andy Weir has a new book coming out? Very exciting, we know, and according to a syndicated reading list for Summer 2025, it’s called The Last Algorithm, and it’s a tale of a programmer who discovers a dark and dangerous secret about artificial intelligence. If that seems a little out of sync with his usual space-hacking fare such as The Martian and Project Hail Mary, that’s because the book doesn’t exist, and neither do most of the other books on the list.

The list was published in a 64-page supplement that ran in major US newspapers like the Chicago Sun-Times and the Philadelphia Inquirer. The feature listed fifteen must-read books, only five of which exist, and it’s no surprise that AI is to behind the muck-up. Writer Marco Buscaglia took the blame, saying that he used an LLM to produce the list without checking the results. Nobody else in the editorial chain appears to have reviewed the list either, resulting in the hallucination getting published. Readers are understandably upset about this, but for our part, we’re just bummed that Andy doesn’t have a new book coming out.

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Hackaday Podcast Ep 322: Fake Hackaday Writers, New Retro Computers, And A Web Rant

May 23, 2025 by 1 Comment

We’re back in Europe for this week’s Hackaday podcast, as Elliot Williams is joined by Jenny List. In the news this week is the passing of Ed Smylie, the engineer who devised the famous improvised carbon dioxide filter that saved the Apollo 13 astronauts with duct tape.

Closer to home is the announcement of the call for participation for this year’s Hackaday Supercon; we know you will have some ideas and projects you’d like to share.

Interesting hacks this week include a new Mac Plus motherboard and Doom (just) running on an Atari ST, while a LoRa secure messenger and an astounding open-source Ethernet switch captivated us on the hardware front. We also take a dive into the Mouse programming language, a minimalist stack-based environment from the 1970s. Among the quick hacks are a semiconductor dopant you can safely make at home, and a beautiful Mac Mini based cyberdeck.

Finally, we wrap up with our colleague [Maya Posch] making the case for a graceful degradation of web standards, something which is now sadly missing from so much of the online world, and then with the discovery that ChatGPT can make a passable show of emulating a Hackaday scribe. Don’t worry folks, we’re still reassuringly meat-based.

Insert MP3 podcast link here.

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Hackaday Links: May 18, 2025

May 18, 2025 by 8 Comments

Say what you want about the wisdom of keeping a 50-year-old space mission going, but the dozen or so people still tasked with keeping the Voyager mission running are some major studs. That’s our conclusion anyway, after reading about the latest heroics that revived a set of thrusters on Voyager 1 that had been offline for over twenty years. The engineering aspects of this feat are interesting enough, but we’re more interested in the social engineering aspects of this exploit, which The Register goes into a bit. First of all, even though both Voyagers are long past their best-by dates, they are our only interstellar assets, and likely will be for centuries to come, or perhaps forever. Sure, the rigors of space travel and the ravages of time have slowly chipped away at what these machines can so, but while they’re still operating, they’re irreplaceable assets.

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Radio Apocalypse: Meteor Burst Communications

May 12, 2025 by 14 Comments

The world’s militaries have always been at the forefront of communications technology. From trumpets and drums to signal flags and semaphores, anything that allows a military commander to relay orders to troops in the field quickly or call for reinforcements was quickly seized upon and optimized. So once radio was invented, it’s little wonder how quickly military commanders capitalized on it for field communications.

Radiotelegraph systems began showing up as early as the First World War, but World War II was the first real radio war, with every belligerent taking full advantage of the latest radio technology. Chief among these developments was the ability of signals in the high-frequency (HF) bands to reflect off the ionosphere and propagate around the world, an important capability when prosecuting a global war.

But not long after, in the less kinetic but equally dangerous Cold War period, military planners began to see the need to move more information around than HF radio could support while still being able to do it over the horizon. What they needed was the higher bandwidth of the higher frequencies, but to somehow bend the signals around the curvature of the Earth. What they came up with was a fascinating application of practical physics: meteor burst communications.

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