6 ms·
The answer (excerpted from the linked article): The source of the problem was a homemade battery-operated device designed by a local resident to alert h
by nkurz 8y ago
The answer (excerpted from the linked article):
The source of the problem was a homemade battery-operated
device designed by a local resident to alert him if someone
was upstairs when he was working in his basement. It did so
by turning off a light.
“He has a fascination with electronics,” Mr. Glassburn said,
adding that the resident has special needs and would not be
identified to protect his privacy.
The inventor and other residents of his home had no idea
that the device was wreaking havoc on the neighborhood, he
said, until Mr. Glassburn and a volunteer with expertise in
radio frequencies knocked on the door.
“The way he designed it, it was persistently putting out a
315 megahertz signal,” Mr. Glassburn said. That is the
frequency many car fobs and garage door openers rely on.
“There was no malicious intent of the device,” he said in a
statement.
The battery on the device was removed and the signal
stopped. “It was a relief,” Mr. Glassburn said.
- argd678 8y agoWould be interesting to get a better understanding of how it worked. I’m assuming there was a motion sensor upstairs, though I don’t understand why it would send a constant signal.
- sokoloff 8y agoThere's a good chance the relevant code was running inside loop() in an Arduino sketch and "whohoo; it works!" represented the end of development on the project.
- SmellyGeekBoy 8y agoLike all the best projects.
- amingilani 8y agoI'm assuming he also didn't account for harmonics. It'd be interesting to see how dirty his transmissions made the spectrum.
- sokoloff 8y agoGiven that he took out 315MHz in a pretty wide area, I'm wagering he was using a specific 315MHz module and was just transmitting a near-constant signal. (A duty cycle issue rather than a harmonics issue.) Something like this: https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and-Receiver-superheterodyne-UHF-ASK-remote-control-Module-Kit-small-size-low-power/32665290214.html https://www.aliexpress.com/item/NEW315mhz-rf-Transmitter-and...
- riskable 8y agoAlso don't rule out an incredibly poorly made 315Mhz transmitter. Chinese companies will see lots of bad reviews on their 315Mhz breakout board like, "Terrible product! Only works from within like 3 feet from the transmitter." So management gets mad at the engineer (who likely has no formal training or knowledge of FCC regulations) and says, "fix it!" "OK OK I'll just crank up the power!" Version 1.1 of the board is released on AliExpress a week later ("New version of board. We fixed weak signal!"). End users start getting the new board and like magic they can pick up a signal from like a mile away!
- Cyph0n 8y agoThen the FCC comes knocking?
- colejohnson66 8y agoFCC can’t really do anything about a Chinese person selling from China
- cptskippy 8y agoWhy do you assume there was a microprocessor involved at all? Most PIR sensors come as modules that operate either with a normally open or normally closed trigger pin and a couple of pots for adjusting sensitivity and trigger duration. It would be easy to build a transmitter to blast out a constant high pulse and then just cut it off using a transistor or mosfet hooked up to the trigger on the PIR. Simple circuit with no microprocessor or coding required.
- jjoonathan 8y agoThis is probably how it worked: https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.. https://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-.... and how it also had unintended consequences. Note how many comments there are from people who don't seem to have understood the disclaimer. I'd bet our rogue dongle-jammer was in much the same boat :)
- sigmar 8y agoYou're probably right that they used a guide like that. It seems irresponsible to publish that blog post. 99% of Pi tinkerers will read that disclaimer in the third paragraph and either not understand that life critical devices _do_ can be interfered with or think their use-case is special/low-powered and won't do any harm.
- riskable 8y agoThe irresponsible part is that he says you "must use a filter" if you attach an antenna but does not describe what that would entail. There's not even a link anywhere that would describe how to make a filter or even what he's talking about ("I have a filter... There's no bad power going into this thing!") When you, "make something dangerous easy" you have a responsibility to be very specific in how to use your invention safely. Otherwise disaster seems inevitable.
- maxerickson 8y agoYou can buy razor blades almost everywhere for like a dollar. (Reviewing this comment later I see it can be read in sort of a nasty way; my meaning was that we don't really assign blame to providers of dangerous tools, the low price of razor blades reflects this)
- argd678 8y agoI see, so it was constantly broadcasting and then he’d encode some message in the signal to indicate if someone was up stairs, instead of only broadcasting when there was a message to send. That certainly would explain it.
- buttcoinslol 8y agoWireless activation for this is overkill, you could build this with some romex, a PIR sensor, a relay, a single-pole switch, and a light fixture for around $50, $75 if you don't have a fish stick to fish the romex through the walls.
- Dylan16807 8y agoOr I could hook the same sensor and relay up to a pair of $5 transceivers. Avoiding going into the wall isn't overkill, especially if it's cheaper and faster.
- epanchin 8y agoWithout verbatim: The source of the problem was a homemade battery-operated device designed by a local resident to alert him if someone was upstairs when he was working in his basement. It did so by turning off a light. “He has a fascination with electronics,” Mr. Glassburn said, adding that the resident has special needs and would not be identified to protect his privacy. The inventor and other residents of his home had no idea that the device was wreaking havoc on the neighborhood, he said, until Mr. Glassburn and a volunteer with expertise in radio frequencies knocked on the door. “The way he designed it, it was persistently putting out a 315 megahertz signal,” Mr. Glassburn said. That is the frequency many car fobs and garage door openers rely on. “There was no malicious intent of the device,” he said in a statement. The battery on the device was removed and the signal stopped. “It was a relief,” Mr. Glassburn said.
- colanderman 8y agoFYI: quoting material like that is impossible to read on mobile because it does not wrap. Please just use ">" as an quotation marker.
- nkurz 8y agoI'm aware, and consciously chose this because in this case I thought that preformatted was clearer. But perhaps I'm wrong. What percentage of people use mobile for HN? Is there a reasonable column width that works for 95% of them? Edit: OK, I just looked at it on a phone. Yes, it looks bad, and that the lines would have to be about half the length to be readable. Too late to edit this one, but I'll try to switch to italics or '>' in the future for everything except for code samples.
- mikeash 8y agoI’d wager it’s a pretty high percentage. HN works great on mobile aside from this. There’s no reasonable column width, just use quotes for quotes.
- Normal_gaussian 8y agoI get 26 characters portrait, 40 landscape. I almost exclusively read HN on mobile, occasionally emailing things to myself to do on a desktop/laptop later.
- giancarlostoro 8y agoOn the other hand reader mode for FireFox temporarily fixes the bug.
- hunter2_ 8y agoHard-wrapping to some column width only ever really works when you know the physical width of the screen/paper. Otherwise, dynamic soft wrapping.
- hollerith 8y agoI hate preformatted text in HN comments (and I never even read HN on mobile).
- erk__ 8y agoI really hope that someone who knows more about electronics could help the guy to get a better understanding of what he did wrong and how he could do it in a better way.
- deleted 8y ago[deleted]
- morpheuskafka 8y agoHe's lucky a local ham investigated and not the FCC.
- martimarkov 8y agoI think if it's a free frequency you can do whatever you want, no? I mean I use 433Mhz in my house to do some communications between devices and I think I don't need any authorization from someone. Or is it the power that is limited? (Which makes a lot of sense)
- krapht 8y agoEven if part of the spectrum is unlicensed, you're still bound by power limits.
- fegu 8y agoAnd duty cycle limits.
- wglb 8y agoAnd lack of interference to other services
- JeffGruszynski 8y agoNope. If it's an FCC class B, YOU must accept interference from otherwise approved class B compliant devices. Class B is a very low threshold for that. Mostly it's power limits and not much else. Key fobs, if you look at the fine print, are Class B. There are also exemptions for certain experimental or lab devices though you can't break power limits with those as narrowly defined by regulation. But if you happen to have your Class B device too close such a device, that's entirely your problem, the user of the Class B device. This is a common issue with ham radio: they actually are allowed to interfere with Class B but it's a political decision that drives most of ham radio to "play nice". Legally they have seniority when it comes to interference and the law when it comes to Class B devices. Basically you are screwed with Class B in most cases with little legal recourse. And Class B is such a low threshold that 99% of the time such interference is actually due to bad design or use of cheap components in the Class B device itself. In this case, the fobs. Same goes for TVs, broadcast radio receivers, etc. No one has a right to zero interference from other RF sources for the most part! Mostly because it's physically impossible to assure or deliver! There's merely a regulatory threshold for the extremely bad and summarily interfering levels of RF power.
- wheaties 8y agoIf you have ever wondered why they tell you to turn off electronic devices during take off and landing, here it is.
- stcredzero 8y agoWe're getting to the point where simple devices without the full range of security capabilities just aren't tenable anymore. Wireless devices should be securely keyed. The protocols cannot expose the key. They should be immune to replay attacks and eavesdropping. They should also be immune to simple jamming. It's like how people in the country in most cases can have a wood fire, and it's no problem. Get to the population density of the city, and backyard wood fires become the major source of particulate air pollution. It's like how in the early days of electricity, there were to GFCI safety devices and everything was just bare conductors on ceramic insulators nailed into wood. We're not in those days anymore.