Why Won’t This Darn Thing Charge?

What is more fun than plugging in your phone and coming back to find your battery on empty? Stepping on a LEGO block with bare feet or arriving hungry at a restaurant after closing probably qualify. [Alex Sidorenko] won’t clean your floors or order you a pizza, but he can help you understand why cheap chargers won’t always power expensive devices. He also shows how to build an adapter to make them work despite themselves.

The cheapest smart device chargers take electricity from your home or car and convert it to five volts of direct current. That voltage sits on the power rails of a USB socket until you plug in a cable. If you’re fortunate, you might get a measly fuse.

Smart device manufacturers don’t make money when you buy an off-brand charger, and they can’t speak to the current protection of them, so they started to add features on their own chargers to protect their components and profit margins. In the case of dedicated chargers, a simple resistor across the data lines tells your phone it is acceptable power. Other devices are more finicky, but [Alex Sidorenko] shows how they work and provides Eagle files to build whatever flavor you want. Just be positive that your power supply is worthy of the reliability these boards promise to the device.

Now you know why connecting a homemade benchtop power supply to a USB cable seems good on paper but doesn’t always get the job done. Always be safe when you make your own power supplies.

Making Software Defined Radio Portable

While most smartphones can receive at least some radio, transmitting radio signals is an entirely different matter. But, if you have an Android phone and a few antennas (and a ham radio license) it turns out that it is possible to get a respectable software-defined radio on your handset.

[Adrian] set this up to be fully portable as well, so he is running both the transceiver and the Android phone from a rechargeable battery bank. The transceiver is also an interesting miniaturized version of the LimeSDR, the Lime SDR Mini, a crowdfunded Open Source radio platform intended for applications where space is at a premium. It operates on the 10 MHz to 3.5 GHz bands, has two channels, and has a decent price tag too at under $100.

For someone looking for an SDR project or who needs something very portable and self-contained, this could be a great option. The code, firmware, and board layout files are all also open source, which is always a great feature. If you’re new to SDR though, there’s a classic project that will get you off the ground for even less effort.

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Easy Time-lapse Video via Phone and Command Line

A good time-lapse video can be useful visual documentation, and since [Tommy]’s phone is the best camera he owns he created two simple shell scripts to grab time-lapse images and assemble them into a video. [Tommy]’s work is just the glue between two other things: an app that turns the phone into an IP camera with a web server on the local network, and the ability to grab a still image from that server on demand.

The app he uses for his iPhone normally serves video but has an undocumented feature that allows single frames to be downloaded by adding ‘/photo’ to the end of the URL, but the ability to get a still image is a common feature on IP camera apps for smartphones. His capture script (GitHub repository here) should therefore need only minor changes to work with just about any IP camera app.

Perching a phone over a workspace and using it to create a time-lapse with a couple of shell scripts is a great example of combining simple tools to get better functionality. It could be a good way to get additional use out of an older smartphone, too. Heck, even older dumbphones can still get some use out of them; Shmoocon 2017 brought us details on rolling your own 1G network.

Emergency Cell Tower on a Budget

Cell phone towers are something we miss when we’re out of range, but imagine how we’d miss them if they had been destroyed by disastrous weather. In such emergencies it is more important than ever to call loved ones, and tell them we’re safe. [Matthew May] and [Brendan Harlow] aimed to make their own secure and open-source cellular network antenna for those occasions. It currently supports calling between connected phones, text messaging, and if the base station has a hard-wired internet connection, users can get online.

This was a senior project for a security class, and it seems that the bulk of their work was in following the best practices set by the Center for Internet Security. They adopted a model intended for the Debian 8 operating system which wasn’t a perfect fit. According to Motherboard their work scored an A+, and we agree with the professors on this one.

Last year, the same SDR board, the bladeRF, was featured in a GSM tower hack with a more sinister edge, and of course Hackaday is rife with SDR projects.

Thank you [Alfredo Garza] for the tip.

Cluephone for Partiers

[Sam Horne] adapted an old school landline phone to deliver clues to birthday party guests. When guests find a numerical clue, they type it into the keypad to hear  the next clue, which involves decoding some Morse code.

The phone consists of an Arduino Pro Mini, a MP3/WAV trigger, and the phone itself, of which the earpiece and keypad have been reused. [Sam] had to map out the keypad and solder leads connecting the various contact points of the phone’s PCB to the Arduino’s digital pins. He used a digitally-generated voice to generate the audio files, and employed the Keypad and Password Arduino libraries to deliver the audio clues.

This seems like a great project to do for a party of any age of attendee, though the keying speed is quick. Hopefully [Sam]’s guests have a high Morse WPM or are quick with the pen! For more keypad projects check out this custom shortcut keyboard and printing a flexible keyboard.

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Automatic Phone Dialer Illuminates Inner Workings

The invention of the transistor ushered in a lot of technologies that we now take for granted, and one of the less-thought-about areas that it improved living conditions worldwide was by making the touch-tone phone possible. No longer would the world have to fuss with dials to make phone calls, they could simply push some buttons. This technology is still in use today, and it is possible to build external phone dialers that use these tones to make phone calls, as [SunFounder] demonstrates with his latest project.

The tones that a phone makes when a button is pressed correlate with specific frequencies for each number. Automatic dialers like this one help when there are multiple carriers (like different long-distance carriers, for example) where different prefixes can be used to make calls cheaper depending on the destination of the call. A preprogrammed dialer can take all of this complication out of making phone calls. [SunFounder] is able to make a simple dialer from scratch, using an Arduino, its “tone” library, and a speaker that is simply held up to the phone that the call will be placed on.

[SunFounder] points out that he built this more because he’s interested in the inner workings of phones, and not because he needed a purpose-built dialer. It’s a good demonstration of how phones continue to use DTMF though, and how easy it is to interface with such a system. It might also suit a beginner as an introduction to the world of phreaking.

Exposing Dinosaur Phone Insecurity With Software Defined Radio

Long before everyone had a smartphone or two, the implementation of a telephone was much stranger than today. Most telephones had real, physical buttons. Even more bizarrely, these phones were connected to other phones through physical wires. Weird, right? These were called “landlines”, a technology that shuffled off this mortal coil three or four years ago.

It gets even more bizarre. some phones were wireless — just like your smartphone — but they couldn’t get a signal more than a few hundred feet away from your house for some reason. These were ‘cordless telephones’. [Corrosive] has been working on deconstructing the security behind these cordless phones for a few years now and found these cordless phones aren’t secure at all.

The phone in question for this exploit is a standard 5.8 GHz cordless phone from Vtech. Conventional wisdom says these phones are reasonably secure — at least more so than the cordless phones from the 80s and 90s — because very few people have a duplex microwave transceiver sitting around. The HackRF is just that, and it only costs $300. This was bound to happen eventually.

This is really just an exploration of the radio system inside these cordless phones. After taking a HackRF to a cordless phone, [Corrosive] found the phone technically didn’t operate in the 5.8 GHz band. Control signals, such as pairing a handset to a base station, happened at 900 MHz. Here, a simple replay attack is enough to get the handset to ring. It gets worse: simply by looking at the 5.8 GHz band with a HackRF, [Corrosive] found an FM-modulated voice channel when the handset was on. That’s right: this phone transmits your voice without any encryption whatsoever.

This isn’t the first time [Corrosive] found a complete lack of security in cordless phones. A while ago, he was exploring the DECT 6.0 standard, a European cordless phone standard for PBX and VOIP. There was no security here, either. It would be chilling if landlines existed anymore.

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