Mon Dieu! French Parent Kills Cell Service For An Entire Town To Stop Kids Surfing

It used to be that having technical skills meant that fixing the computer problems of elderly relatives was a regular occurrence. Over the last few years this has been joined by another request on our time; friends with teenage children requesting help configuring their routers such that Internet access is curtailed when the kids should sleeping. In France a desperate parent took more extreme measures, buying a wideband frequency jammer to ensure les petits anges can’t waste the night away on social media sites through their cellular connections. It had the intended effect, but sadly it also interrupted cellular coverage over a wide area The French spectrum regulator ANFR sent in their investigators (French, Google Translate link), and now the unfortunate parent faces the prospect of up to 6 months imprisonment and €30,000 fine for owning and using a device that’s illegal in France.

A cursory search of everybody’s favourite online electronics bazaars will find plenty of these devices, so perhaps what’s surprising is that we don’t see more of these devices even if it’s not the first tale of interference tracking that we’ve seen. Judging by the strategies our friends with kids take, we’d suggest meanwhile to the unfortunate French person, that they simply equip their kids with restricted data plans.

Interference Patterns Harnessed For Optical Logic Gates

The basics of digital logic are pretty easy to master, and figuring out how the ones and zeroes flow through various kinds of gates is often an interesting exercise. Taking things down a level and breaking the component AND, OR, and NOR gates down to their underlying analog circuits adds some complexity, but the flow of electrons is still pretty understandable. Substitute all that for photons, though, and you’ll enter a strange world indeed.

At least that’s our take on [Jeroen Vleggaar]’s latest project, which is making logic gates from purely optical components. As he himself admits in the video below, this isn’t exactly unexplored territory, but his method, which uses constructive and destructive interference, seems not to have been used before. The basic “circuit” consists of a generator, a pair of diffraction patterns etched into a quartz plate, and an evaluator, which is basically a pinhole in another plate positioned to coincide with the common focal point of the generator patterns. An OR gate is formed when the two generators are hit with in-phase monochromatic light. Making the two inputs out of phase by 180° results in an XOR gate, as destructive interference between the two inputs prevents any light from making it out of the evaluator.

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Duality Of Light Explored By Revisiting The Double-Slit Experiment

We’ve all seen recreations of the famous double-slit experiment, which showed that light can behave both as a wave and as a particle. Or rather, it’s likely that what we’ve seen is the results of the double-slit experiment, that barcode-looking pattern of light and dark stripes, accompanied by some handwaving about classical versus quantum mechanics. But if you’ve got 20 minutes to invest, this video of the whole double-slit experiment cuts through the handwaving and opens your eyes to the quantum world.

For anyone unfamiliar with the double-slit experiment,  [Huygens Optics] actually doesn’t spend that much time explaining the background. Our explainer does a great job on the topic, but suffice it to say that when coherent light passes through two closely spaced, extremely fine openings, a characteristic pattern of alternating light and dark bands can be observed. On the one hand, this demonstrates the wave nature of light, just as waves on the ocean or sound waves interfere constructively and destructively. On the other hand, the varying intensity across the interference pattern suggests a particle nature to light.

To resolve this conundrum, [Huygens] jumps right into the experiment, which he claims can be done with simple, easily sourced equipment. This is belied a little by the fact that he used photolithography to create his slits, but it should still be possible to reproduce with slits made in more traditional ways. The most fascinating bit of this for us was the demonstration of single-photon self-interference using nothing but neutral density filters and a CCD camera. The explanation that follows of how it can be that a single photon can pass through both slits at the same time is one of the most approachable expositions on quantum mechanics we’ve ever heard.

[Huygens Optics] has done some really fascinating stuff lately, from variable profile mirrors to precision spirit levels. This one, though, really helped scratch our quantum itch.

Wearable Cone Of Silence Protects You From Prying Ears

Careful,  the walls have ears. Or more specifically, the smart speaker on the table has ears, as does the phone in your pocket, the fitness band on your wrist, possibly the TV, the fridge, the toaster, and maybe even the toilet. Oh, and your car is listening to you too. Probably.

How does one fight this profusion of listening devices? Perhaps this wearable smart device audio jammer will do the trick. The idea is that the MEMS microphones that surround us are all vulnerable to jamming by ultrasonic waves, due to the fact that they have a non-linear response to ultrasonic signals. The upshot of that is when a MEMS hears ultrasound, it creates a broadband signal in the audible part of the spectrum. That creates a staticky noise that effectively drowns out any other sounds the microphone might be picking up.

By why a wearable? Granted, [Yuxin Chin] and colleagues from the University of Chicago have perhaps stretched the definition of that term a tad with their prototype, but it turns out that moving the jammer around does a better job of blocking sounds than a static jammer does. The bracelet jammer is studded with ultrasonic transducers that emit overlapping fields and result in zones of constructive and destructive interference; the wearer’s movements vary the location of the dead spots that result, improving jamming efficacy. Their paper (PDF link) goes into deeper detail, and a GitHub repository has everything you need to roll your own.

We saw something a bit like this before, but that build used white noise for masking, and was affixed to the smart speaker. We’re intrigued by a wearable, especially since they’ve shown it to be effective under clothing. And the effect of ultrasound on MEMS microphones is really interesting.

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Raspberry Pi 4 HDMI Is Jamming Its Own WiFi

Making upgrades to a popular product line might sound like a good idea, but adding bigger/better/faster parts to an existing product can cause unforeseen problems. For example, dropping a more powerful engine in an existing car platform might seem to work at first until people start reporting that the increased torque is bending the frame. In the Raspberry Pi world, it seems that the “upgraded engine” in the Pi 4 is causing the WiFi to stop working under specific circumstances.

[Enrico Zini] noticed this issue and attempted to reproduce exactly what was causing the WiFi to drop out, and after testing various Pi 4 boards, power supplies, operating system version, and a plethora of other variables, the cause was isolated to the screen resolution. Apparently at the 2560×1440 setting using HDMI, the WiFi drops out. While you could think that an SoC might not be able to handle a high resolution, WiFi, and everything else this tiny computer has to do at once. But the actual cause seems to be a little more interesting than a simple system resources issue.

[Mike Walters] on a Twitter post about this issue probed around with a HackRF and discovered a radio frequency issue. It turns out that at this screen resolution, the Pi 4 emits some RF noise which is exactly in the range of WiFi channel 1. It seems that the Pi 4 is acting as a WiFi jammer on itself.

This story is pretty new, so hopefully the Raspberry Pi Foundation is aware of the issue and working on a correction. For now, though, it might be best to run a slightly lower resolution if you’re encountering this problem.

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Hackaday Links: November 10, 2019

In the leafy suburbs of northern Virginia, a place ruled by homeowner’s associations with tremendous power to dictate everything from the color of one’s front door to the length of grass in the lawn, something as heinous as garage doors suddenly failing to open on command is sure to cause a kerfuffle. We’ve seen this sort of thing before, where errant RF emissions cause unintentional interference, and such stories aren’t terribly interesting because the FCC usually steps in and clears things up. But this story is a little spicier given the source of the interference: Warrenton Training Center, a classified US government communications station located adjacent to the afflicted neighborhood. WTC is known to be a CIA signals intelligence station, home to spooks doing spooky stuff, including running high-power numbers stations. The interference isn’t caused by anything as cloak-and-dagger as that, though; rather, it comes from new land-mobile radios that the Department of Defense is deploying. The new radios use the 380-400 MHz band, which is allocated to the Federal Government and unlicensed Part 15 devices, like garage door remotes. But Part 15 rules, which are clearly printed on every device covered by them, state that the devices have to accept unwanted interference, even when it causes a malfunction. So the HOA members who are up in arms and demanding that the government buy them new garage door openers are likely to be disappointed.

Speaking of spooks, if you’re tired of the prying electronic eyes of facial recognition cameras spoiling your illusion of anonymity, have we got a solution for you. The Opt-Out Cap is the low-tech way to instantly change your face for a better one, or at least one that’s tied to someone else. In a move which is sure not to arouse suspicion in public, doffing the baseball cap deploys a three-piece curtain of semi-opaque fabric, upon which is printed the visage of someone who totally doesn’t look creepy or sketchy in any way. Complete instructions are provided if you want to make one before your next trip to the ATM.

It’s always a great day when a new Ken Shirriff post pops up in our feed, and his latest post is no exception. In it, Ken goes into great detail about the history of the 80×24 (or 25) line standard for displays. While that may sound a bit dry, it’s anything but. After dispelling some of the myths and questionable theories of the format’s origin – sorry, it’s not just because punch cards had 80 columns – he discusses the transition from teletypes to CRTs, focusing on the very cool IBM 2260 Display Station. This interesting beast used an acoustic delay line made of 50′ (15 m) of nickel wire. It stored data as a train of sound pulses traveling down the wire, which worked well and was far cheaper than core memory, even if it was susceptible to vibrations from people walking by it and needed a two-hour warm-up period before use. It’s a fascinating bit of retrocomputing history.

A quick mention of a contest we just heard about that might be right up your alley: the Tech To Protect coding challenge is going on now. Focused on applications for public safety and first responders, the online coding challenge addresses ten different areas, such as mapping LTE network coverage to aid first responders or using augmented reality while extricating car crash victims. It’s interesting stuff, but if you’re interested you’ll have to hurry – the deadline is November 15.

And finally, Supercon starts this week! It’s going to be a blast, and the excitement to hack all the badges and see all the talks is building rapidly. We know not everyone can go, and if you’re going to miss it, we feel for you. Don’t forget that you can still participate vicariously through our livestream. We’ll also be tweet-storming and running a continuous chat on Hackaday.io to keep everyone looped in.

Building A Hardware Store Faraday Cage

Most Hackaday readers are no doubt familiar with the Faraday cage, at least in name, and nearly everyone owns one: if you’ve ever stood watching a bag of popcorn slowly revolve inside of a microwave, you’be seen Michael Faraday’s 1836 invention in action. Yet despite being such a well known device, the average hacker still doesn’t have one in their arsenal. But why?

It could be that there’s a certain mystique about Faraday cages, an assumption that their construction requires techniques or materials outside the realm of the home hacker. While it’s true that building a perfect Faraday cage for a given frequency involves math and careful attention to detail, putting together a simple model for general purpose use and experimentation turns out to be quick and easy.

As an exercise in minimalist hacking I recently built a basic Faraday cage out of materials sourced from Home Depot, and thought it would be interesting to not only describe its construction but give some ideas as to how one can put it to practical use in the home lab. While it’s hardly a perfect specimen, it clearly works, and it didn’t take anything that can’t be sourced locally pretty much anywhere in the world.

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