gsm

81 Articles

Open-Source Cell Phone Based On ESP32

August 3, 2023 by 40 Comments

Over the past decade or so, smartphones have exploded in popularity and seamlessly integrated themselves into nearly every aspect of most people’s lives. Although that comes with a few downsides as well, with plenty of people feeling that the smart phone makes it a little too easy to waste time and looking to switch to something simpler, like an older-style flip phone. If this style of phone is more your speed, take a look at this DIY cell phone which takes care of everything a phone really needs to do. (Google Translate from French)

The phone uses an ESP32 at its core, with a SIM800L GSM modem to interact with the cell network, including retrieving the system time. A small battery is included as well as all of the support circuitry for charging it as well as a USB interface that can communicate to a PC. The operating system for the phone is built from the ground up as well, with a touch screen interface allowing the user to make phone calls, send text messages, store contacts, and a few other basic features. There’s also a GPS application though, allowing the phone to know basic location information.

Another perk of this device is that its creator, [Gabriel], made the design schematics, print files for the case, and the operating system software completely open source for anyone to build this phone on their own. Everything is available on the project’s GitHub page. It’s a fairly remarkable achievement, especially considering [Gabriel] is only 16. And, if you’re not one to eschew modern smart phone technology there are some DIY smart phones available to build as well.

Thanks to [come2] for the tip!

A ginger cat, wearing a blue harness with a brass and wooden box on its back

Handmade GPS Tracker Keeps An Eye On Adventurous Cats

January 31, 2023 by 29 Comments

One of the most convenient things about having cats is their independent lifestyle: most are happy to enjoy themselves outside all day, only coming back home when it’s time for dinner and a nap. What your cat gets up to during the day remains a mystery, unless you fit it with a GPS collar. When [Sahas Chitlange] went searching for a GPS tracker for his beloved Pumpkin, he found that none were exactly to his liking: too slow, too big, or simply unreliable. This led him to design and build his own, called Find My Cat.

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Here’s How Those Battery-Free Flashing Phone Stickers Worked

February 26, 2022 by 27 Comments

The late 90s and early 2000s were a breakout time for mobile phones, with cheap GSM handsets ushering in the era in which pretty much everybody had a phone. Back then, a popular way to customize one’s phone was to install a sticker that would flash when the phone rang. These required no batteries or any other connection to the phone, and [Big Clive] has dived in to explain how they worked. 

The simple schematic of the flashing sticker circuit. The flashing was generated by the pulses of RF energy from the smartphone.

It’s an old-fashioned teardown that requires a bit of cutting to get inside the sticker itself. A typical example had three LEDs in series for a total voltage drop of around 7V, hooked up to two diodes and a PCB trace antenna. A later evolution used raw unpackaged components bonded to the PCB. Future versions went down to a single diode, using the LEDs to serve as the second. The basic theory was that the PCB traces would pick up RF transmitted by the phone when a call was coming in, lighting the LEDs.

In the 2G era, the freuqencies used were on the order of 300 MHz to 1.9GHz. A combination of the change in frequencies used by modern phone technology and the lower transmit powers used by handsets means that the stickers don’t work properly with modern phones according to [Big Clive].

Incidentally, you might like to consider running your own old-school cellphone network. Video after the break.

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UnifiedWater Finds Potable Water And Stops Polluters

August 29, 2020 by 16 Comments

Millions of people all over the world don’t have access to clean drinking water, and it’s largely because of pollution by corporations and individuals. Solving this problem requires an affordable, scalable way to quickly judge water quality, package the data, and present it to an authority that can crack down on the polluters before the evidence dissipates. Ideally, the solution would be open source and easy to replicate. The more citizen scientists, the better.

[Andrei Florian]’s UnifiedWater flows directly from this line of thinking. Dip this small handheld device below the surface, and it quickly takes a bunch of water quality and atmospheric readings, averages them, and sends the data to a web dashboard using an Arduino MKR GSM.

UnifiedWater judges quality by testing the pH and the turbidity of the water, which gauges the amount of impurities. Commercial turbidity sensors work by measuring the amount of light scattered by the solids present in a liquid, so [Andrei] made a DIY version with an LED pointed at a photocell. UnifiedWater also reads the air temperature and humidity, and reports its location along with a timestamp.

This device can run in one of two modes, depending on the application. The enterprise mode is designed for a fleet of devices placed strategically about a body of water. In this mode, the devices sample continuously, taking readings every 15 minutes, and can send notifications that trigger on predefined thresholds. There’s also a one-and-done individual mode for hikers and campers who need to find potable water. Once UnifiedWater takes the readings, the NeoPixel ring provides instant color-coded judgment. Check out the demo after the break.

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A Mobile Phone For The Pulse Dial Generation

July 29, 2020 by 7 Comments

One of the useful side effects of the ubiquitous availability of cellular network data modules is that they can be used to create custom mobile phones. It’s surprising in a way that we don’t see as many of these projects as we’d expect, but by way of redressing that deficiency we’re pleased to see the work of [Proton Gamer], who has taken a vintage rotary dial phone and upgraded it with an Arduino and GSM shield to make a very unexpected mobile phone project.

It’s not entirely certain from the write-up which manufacturer produced the donor phone or for which country’s network it was produced, but it seems typical of the type you might have found the world over in the 1960s. We’re given a breakdown of the various components and how to interface to them, the ringer for example is run using a motor driver board. There are comprehensive instructions for the conversion, though sadly they involve gutting the phone and removing the original hardware. The result can be seen in the video below the break, and the finished project makes a mobile phone call from the unlikeliest of hardware.

This certainly isn’t the first rotary dial mobile phone we’ve featured, including one based on a conference badge.

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GSM Module Does More Than Advertised

March 25, 2020 by 13 Comments

For many projects, a WiFi connection is overkill, too complicated, or too far away to work properly. Even though it’s relatively ubiquitous, sometimes the best choice for getting data to or from the real world is a connection to the cellular network, which can be done with the M590 module for about a dollar each. For that price, lots of people have had the opportunity to explore the module itself, and [marcrbarker] shows some of the extra, unadvertised, features it has.

Acting as a GSM module that can send and receive SMS messages is just the tip of the iceberg for this tiny device which we saw once before for a DIY GPS tracker. With a USB TTL serial data module, a lot more is on the table including answering voice calls and responding with DTMF tones, operate as a dial-up modem, connect with TCP, and even has some FTP capabilities. [marcrbarker] also suggests that it could do “call pranking” where it can send signals without being charged for a call.

There are a lot of details on the project site about all of this newfound functionality, and it reminds us of a time when it was discovered that not only was the ESP8266 a cheap WiFi module, but it could also run custom programs on its own. While the M590 probably can’t do all of that, it does seem to have a lot more locked away than most of us had thought before.

36C3: SIM Card Technology From A To Z

December 30, 2019 by 1 Comment

SIM cards are all around us, and with the continuing growth of the Internet of Things, spawning technologies like NB-IoT, this might as well be very literal soon. But what do we really know about them, their internal structure, and their communication protocols? And by extension, their security? To shine some light on these questions, open source and mobile device titan [LaForge] gave an introductory talk about SIM card technologies at the 36C3 in Leipzig, Germany.

Starting with a brief history lesson on the early days of cellular networks based on the German C-Netz, and the origin of the SIM card itself, [LaForge] goes through the main specification and technology parts of each following generation from 2G to 5G. Covering the physical basics, I/O interfaces, communication protocols, and the file system located on the SIM card, you’ll get the answer to “what on Earth is PIN2 for?” along the way.

Of course, a talk like this, on a CCC event, wouldn’t be complete without a deep and critical look at the security side as well. Considering how over-the-air updates on both software and — thanks to mostly running Java nowadays — feature side are more and more common, there certainly is something to look at.

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