Detecting Mobile Phone Transmissions With a Sound Card

Anyone who had a cheap set of computer speakers in the early 2000s has heard it – the rhythmic dit-da-dit-dit of a GSM phone pinging a cell tower once an hour or so. [153armstrong] has a write up on how to capture this on your computer. 

It’s incredibly simple to do – simply plug in a set of headphone to the sound card’s microphone jack, leave a mobile phone nearby, hit record, and wait. The headphone wire acts as an antenna, and when the phone transmits, it induces a current in the wire, which is picked up by the soundcard.

[153armstrong] notes that their setup only seems to pick up signals from 2G phones, likely using GSM. It doesn’t seem to pick up anything from 3G or 4G phones. We’d wager this is due to the difference in the way different cellular technologies transmit – let us know what you think in the comments.

This system is useful as a way to detect a transmitting phone at close range, however due to the limited bandwidth of a computer soundcard, it is in no way capable of actually decoding the transmissions. As far as other experiments go, why not use your soundcard to detect lightning?

Tearing Down the Boss Phone

Poke around enough on AliExpress, Alibaba, and especially Taobao—the Chinese facing site that’s increasingly being used by Westerners to find hard to source parts—and you’ll come across some interesting things. The Long-CZ J8 is one of those, it’s 2.67 inch long and weighs just 0.63 ounces, and it’s built in the form factor of a Bluetooth headset.

A couple of months ago Cory Doctorow highlighted this tiny phone, he’d picked up on it because of the marketing. The lozenge-shaped phone was being explicitly marketed that it could “beat the boss”. The boss in question here being the B.O.S.S chair—a scanning technology that has been widely deployed across prisons in the U.K. in an attempt to put a halt to smuggling of mobile phones to inmates.

The Long-CZ J8 is just 2.67 inch (6.8cm) long.

I wasn’t particularly interested in whether it could make it through a body scanner, or the built-in voice changer which was another clue as to the target market for the phone. However just the size of the thing was intriguing enough that I thought I’d pick one up and take a look inside. So I ordered one from Amazon.

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Nexus 5X Phone Resurrected By The Oven

Warranty shmarranty — toss the phone in the oven! There’s apparently a problem with the assembly of the Nexus 5X smartphones, and it looks like it is due to faulty BGA chip soldering. LG USA has had enough problems with the phone that they may not even have enough parts or new units to fix it, so they’re offering a refund. But we all know how it is to get attached to a device, right?

So [Alex] disassembled his beloved phone, pulled out the board in question, and gave it the XBox Red Ring Of Death treatment. He placed the board on some insulating aluminum foil, and baked it for six and a half minutes. Season with lemon and pepper, and serve! We’re honestly surprised that sticking the affected board into the oven at 195° C / 390° F for a few minutes would work at all. Isn’t that a low temperature for soldering, especially with a lead-free mix? Could it have been a problem with humidity after all? Continue reading “Nexus 5X Phone Resurrected By The Oven”

Building Beautiful Cell Phones Out Of FR4

Over on Hackaday.io, [bobricius] took this technology and designed something great. It’s a GSM cell phone with a case made out of FR4. It’s beautiful, and if you’re ever in need of a beautifully crafted burner phone, this is the one to build.

The components, libraries, and toolchains to build a cellphone from scratch have been around for a very long time. Several years ago, the MIT Media Lab prototyped a very simple cellphone on a single piece of FR4. It made calls, but not much else. It was ugly, but it worked. [Bobricius] took the idea and ran with it.

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Phone-To-Phone Power Thievery

Once again, [Rulof]’s putting his considerable hacking abilities to good use, his good use that is. By modding a few simple parts he’s put together something that he can carry around on his keychain that’ll allow him to steal power from his friend’s phones to charge his own phone.

He starts by cutting away the motor from an iPhone fan to isolate the Micro USB connector. He then removes the charging circuit board from a cheap Chinese USB power bank, and solders wires from the Micro USB connector to one side of the board. Lastly, he cuts away the Lightning connector from a Lightning-to-USB cable and solders that connector to the other side of the circuit board. For longevity and cosmetics, he puts it all in a small wood block and connects a key ring. The result is a small, neat looking box with a Micro USB connector on one side and a Lightning connector on the other. You can see him make it, and then use it to steal power from his friends in the video after the break.

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Retrotechtacular: Whatever Happened To The Paper Mobile Phone

It was one of the more interesting consumer tech stories floating around at the turn of the century, a disposable cell phone manufactured using a multi-layer folded paper circuit board with tracks printed in conductive ink. Its feature set was basic even by the standards of the day in that it had no display and its only function was to make calls, but with a target price of only $10 that didn’t matter. It was the brainchild of a prolific New Jersey based inventor, and it was intended to be the first in a series of paper electronic devices using the same technology including phones with built-in credit card payment ability and a basic laptop model.

The idea of a $10 mobile phone does not seem remarkable today, it’s possible that sum might now secure you something with features far in excess of the Nokias and similar that were the order of the day at that time. But when you consider that those Nokias could have prices well into three figures without a contract, and that the new features people considered exciting were things like integrated antennas or swappable coloured plastic covers rather than the multicore processors or high-res cameras we’re used to today, a phone so cheap as to be disposable promised to be very disruptive.

The web site publicity shot for the disposable paper phone.
The web site publicity shot for the disposable paper phone.

The product’s wonderfully dated website (Wayback Machine link, we’ve skipped the Flash intro for you) has pictures of the device, and the video below the break features shots of it in use as its inventor is interviewed. But by the end of 2002 the Wayback Machine was retrieving 404 errors from the server, and little more was heard of the product. No sign of one ever came our way; did any make it to market, and did you have one?

With the benefit of fifteen years hindsight, why did we not have paper mobile phones as part of the ephemera of the early years of the last decade? It was not a product without promise; a ten-dollar phone might have been a great success. And the description of a cheap laptop that talks to a remote server for its software sounds not unlike today’s Chromebooks.

Some of you might claim the product was vapourware, but given that they demonstrated a working prototype we’d hesitate to go that far. The likelihood is that it did not find the required combination of component price and manufacturing ease to exploit its intended market segment before its competition improved to the point that it could no longer compete. If you have ever taken apart a typical mobile phone of the period you’ll have some idea of why they were not cheap devices, for example the RF filter modules of the day were individually adjusted precision components. And paper-and-ink printed circuit boards are still a technology with a way to go even now, perhaps the idea was simply too far ahead of its time. Meanwhile within a relatively short period of time the price of simple candybar phones dropped to the point at which they would tempt the $10 buyer to spend more for a better product, so the window of opportunity had passed.

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Amazon Dash Button Finds Your Phone

This scene replays quite often in our house: my wife has misplaced her cell phone so she asks me to call her. But where did I leave my cell phone? And the race is on! Who will find their phone first to call the other?

[Zapta] solves this problem with his Phone Finder. The system comes in two parts: a base station with WiFi that’s also connected to the house’s phone line, and an arbitrary number of Amazon Dash buttons that trigger dialing commands.

[Zapta] presses a Dash button, which connects over WiFi to the base station. The base station recognizes the MAC address of the button, looks up and dials the corresponding missing cell phone. This solves the need-a-phone-to-find-a-phone problem very neatly, and since Dash buttons are dirt cheap they can be scattered liberally around the house. They’re clearly marked “his” and “hers” suggesting a similar domestic dynamic.

If we were implementing the base station from scratch, we’d probably try to figure out how a single ESP8266 could do all of the heavy lifting, but browsing through [Zapta]’s GitHub and the included circuit diagram (PDF) demystifies the phone-line interface.

In the early days of cordless phones, we used to joke that a solution to losing them would be to attach a string and tie them to the wall. (Luddites!) We’re glad to see [Zapta] take this project in the opposite direction — using technological overkill to solve the unintended problems that arise from technological progress.