gsm

81 Articles

Texting With A Teletype

April 23, 2019 by 13 Comments

How do you get the kids interested in old technology? By connecting it to a phone, obviously. Those kids and their phones. When [Marek] got his hands on an old-school teletype, he hooked it up to a GSM network, with all the bells and whistles including a 40mA current loop running at an impressive 50 baud.

The teletype in question here is a vintage T100 teletype manufactured in Czechoslovakia sometime in the ’70s. This was a gift to [Marek]’s workplace, the museum of Urban Engineering in Cracow, and this project is effectively an experiment to investigate the possibility of running this teletype as an interactive exhibit rather than an artefact from the age of current loops and phone systems.

The current loop is, or was, the standard way of connecting a teletype to anything, so all [Marek] had to do was construct a box that translated the signals from a GSM modem to this current loop. For the prototype, the microcontroller in question is an old AT89C2051 (as that’s what was sitting in the parts drawer). This was moved over to a PIC32 microcontroller and a SIM800 GSM module. This is housed in a two-part enclosure, with the GSM interfaced housed in one half, with the current loop generator consisting of a simple DC power supply housed int the other half.

This interface is capable of receiving and sending messages from the keyboard to a GSM network, so it is theoretically possible you could text your friends using an old-school teletype. This functionality hasn’t been implemented yet, but it is just about the coolest thing you could possibly imagine. You can check out a video of the teletype in action below. Continue reading “Texting With A Teletype” →

This Vintage Phone Goes Cellular

February 5, 2019 by 8 Comments

Way back in the good old days, life ran at a slower pace. It took us almost a decade to get to the moon, and dialling the phone was a lazy affair which required the user to wait for the rotary mechanism to rewind after selecting each digit. Eager to bring a taste of retro telephony into the modern era, [Marek] retrofitted this vintage Polish telephone with a GSM upgrade.

The phone [Marek] salvaged had already been largely gutted, so there was little to lose in the transformation. A Motorola D15 GSM module was sourced from an alarm system to provide a network connection to the project. An Atmega328 was then used to translate the rotary dial mechanics into something more usable by the cellular module.

Attention to detail can really make a project shine, and [Marek] didn’t skimp in this area. The original ringer was rewound to operate with a half H-bridge at a lower voltage more suitable to the modern electronics inside. The microcontroller also helped out by using its PWM hardware to simulate a dialtone and the characteristic sound of pulse dialling.

It’s always nice to see retro hardware given a new lease on life. Unfortunately, GSM networks aren’t long for this world, so a further update may be required before long. These old phones have plenty of potential, as we’ve seen before.

SENSEation Shows The Importance Of Good Physical Design

October 4, 2018 by 1 Comment

Sensor network projects often focus primarily on electronic design elements, such as architecture and wireless transmission methods for sensors and gateways. Equally important, however, are physical and practical design elements such as installation, usability, and maintainability. The SENSEation project by [Mario Frei] is a sensor network intended for use indoors in a variety of buildings, and it showcases the deep importance of physical design elements in order to create hardware that is easy to install, easy to maintain, and effective. The project logs have an excellent overview of past versions and an analysis of what worked well, and where they fell short.

One example is the power supply for the sensor nodes. Past designs used wall adapters to provide constant and reliable power, but there are practical considerations around doing so. Not only do power adapters mean each sensor requires some amount of cable management, but one never really knows what one will find when installing a node somewhere in a building; a power outlet may not be nearby, or it may not have any unoccupied sockets. [Mario] found that installations could take up to 45 minutes per node as a result of these issues. The solution was to move to battery power for the sensor nodes. With careful power management, a node can operate for almost a year before needing a recharge, and removing any cable management or power adapter meant that installation time dropped to an average of only seven minutes.

That’s just one example of the practical issues discovered in the deployment of a sensor network in a real-world situation, and the positive impact of some thoughtful design changes in response. The GitHub repository for SENSEation has all the details needed to reproduce the modular design, so check it out.

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GSM Phone Network At EMF Camp Built On Raspberry Pi And LimeSDR

August 30, 2018 by 22 Comments

The Electromagnetic Field 2018 hacker camp in the UK will have its own GSM phone network, and as we have already covered its badge will be a fully-functional GSM phone. This is as far as we are aware a first in the world of badges, and though it may not be a first in hacker camp connectivity it is still no mean achievement at the base station side. To find out more we talked to two of the people behind the network, on the radio side Lime Microsystems‘ [Andrew Back], and on the network side Nexmo‘s developer advocate, [Sam Machin].

There are sixteen base stations spread around the site, of which each one is a Raspberry Pi 3 B+ with a LimeSDR Mini. Development of the system was undertaken prior to the release of the Raspberry Pi Foundation’s PoE board, so they take a separate 24V supply which powers the Pi through a DC-to-DC converter. This arrangement allows for a significant voltage drop should any long cable runs be required.

On the software side the base stations all run the Osmocom (Open Source Mobile Communications) cellular base station infrastructure package. It was a fine decision between the all-in-one Osmocom NITB package and the fully modular Osmocom, going for the former for its reliability. It was commented that this would not necessarily be the case at a future event but that it made sense in the present. It appears on the network as a SIP phone system, meaning that it can easily integrate with the existing DECT network. Let’s take a look at how the network operates from the user side, and the licencing loophole that makes everything possible.

Continue reading “GSM Phone Network At EMF Camp Built On Raspberry Pi And LimeSDR” →

Classic American Dial Phone Gets A GSM Makeover

April 18, 2018 by 14 Comments

For sturdy utilitarianism, there were few designs better than the Western Electric Model 500 desk phone. The 500 did one thing and did it well, and remained essentially unchanged from the mid-1940s until Touch Tone phones started appearing in the early 70s. That doesn’t mean it can’t have a place in the modern phone system, though, as long as you’re willing to convert it into a cellphone.

Luckily for [bicapitate], the Model 500 has plenty of room inside the case once the network interface is removed, because the new electronics take up a fair bit of space. There’s no build log per se, but the photo album makes it clear what’s going on. An Arduino reads the hook switch and dial pulses, while a Fona GSM module takes care of the cellular side of things. It looks like a small electret mic and a speaker replace the original transmitter and receiver. As a nice touch, the original ringer is used, but instead of trying to drive it electrically, [bicapitate] came up with a simple cam mechanism on a small motor. Driven at the right speed, the cam hooks the clapper arm, rings one bell, then releases it to let the clapper spring back to hit the other bell. Everything is powered by a LiPo, so it could be taken to the local coffee shop for some hipster hijinks.

We’ve seen similar retro-mods like this before using phones from all over the world; here’s a British take and one from Belgium, both using phones with equally classic lines.

[via r/arduino]

Inside An Amateur Bugging Device

November 12, 2017 by 32 Comments

[Mitch] got interested in the S8 “data line locator” so he did the work to tear into its hardware and software. If you haven’t seen these, they appear to be a USB cable. However, inside the USB plug is a small GSM radio that allows you to query the device for its location, listen on a tiny microphone, or even have it call you back when it hears something. The idea is that you plug the cable into your car charger and a thief would never know it was a tracking device. Of course, you can probably think of less savory uses despite the warning on Banggood:

Please strictly abide by the relevant laws of the state, shall not be used for any illegal use of this product, the consequences of the use of self conceit.

We aren’t sure what the last part means, but we are pretty sure people can and will use these for no good, so it is interesting to see what they contain.

Continue reading “Inside An Amateur Bugging Device” →

Accidental Satellite Hijacks Can Rebroadcast Cell Towers

October 2, 2017 by 21 Comments

A lot of us will use satellite communications without thinking much about the satellite itself. It’s tempting to imagine that up there in orbit is a communications hub and distribution node of breathtaking complexity and ingenuity, but it might come as a surprise to some people that most communications satellites are simple transponders. They listen on one frequency band, and shift what they hear to another upon which they rebroadcast it.

This simplicity is not without weakness, for example the phenomenon of satellite hijacking has a history stretching back decades. In the 1980s for example there were stories abroad of illicit trans-atlantic serial links nestling as unobtrusive single carriers among the broad swathe of a broadcast satellite TX carrier.

Just sometimes, this phenomenon happens unintentionally. Our attention was drawn to a piece by [Harald Welte] on the unintended rebroadcast of GSM base station traffic over a satellite transponder, and of particular interest is the presentation from a conference in 2012 that it links to. The engineers show how they identified their interference as GSM by its timing frames, and then how they narrowed down its source to Nigeria. This didn’t give them the uplink in question though, for that they had to make a downconverter from an LNB, the output of which they coupled to an aged Nokia mobile phone with a wire antenna placed into an RF connector. The Nokia was able to decode the cell tower identification data, allowing them to home in on the culprit.

There was no fault on the part of the GSM operator, instead an unterminated port on the uplink equipment was enough to pick up the GSM signal and introduce it into the transponder as a parasitic signal for the whole of Europe and Africa to hear. Meanwhile the tale of how the engineers identified it contains enough detective work and outright hardware hacking that we’re sure the Hackaday readership will find it of interest.

If satellite hacks interest you, how about reading our thread of posts on the recapture of ISEE-3, or maybe you’d like to listen for a lost satellite from the 1960s.

Thanks [Kia] for the tip.