FLEX Pager Protocol in Depth

We love pager hacks. One of our earliest head-slappers was completely reverse-engineering a restaurant pager’s protocol, only to find out that it was industry-standard POCSAG. Doh!

[Corn] apparently scratches the same itch, but in the Netherlands where the FLEX protocol is more common. In addition to walking us through all of the details of the FLEX system, he bought a FLEX pager, gutted it, and soldered on an ATMega328 board and an ESP8266. The former does the FLEX decoding, and the latter posts whatever it hears on his local network.

These days, we’re sure that you could do the same thing with a Raspberry Pi and SDR, but we love the old-school approach of buying a pager and tapping into its signals. And it makes a better stand-alone device with a lot lower power budget. If you find yourself in possession of some old POCSAG pagers, you should check out [Corn]’s previous work: an OpenWRT router that sends pages.

A Haptic Bracelet for Physical Computing

[Tinkermax] has been reading about the Internet of Things and wearable computing and decided it was time for him to have a go at building a device that turned computing physical. The result is a vibrating wristband that connects his sense of touch to the Internet.

The electronics for this haptic wristband are a mix of old and new technology. The radio and microcontroller come from an ESP-8266 module that was programmed with [Mikhail Grigorev]’s unofficial SDK. The mechanics for the wrist-mounted computer consist of six pager motors mounted around the wrist. These are driven somewhat ingeniously by a TLC5917 LED driver chip. This meant the ESP would only need to use two of its GPIOs to control six motors.

Right now the software is simple enough; just a web page, a few buttons, and the ability to buzz any of the pager motors on the wrist band over the Internet. Now it’s just a question of making this wearable useful, but connecting each pager motor to different notifications – a new email, a new SMS, or some emergency on the Internet – should be pretty easy.

Video below.

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Bringing A Legacy Pager Network Back to Life

[Jelmer] recently found his old pager in the middle of a move, and decided to fire it up to relive his fond memories of receiving a page. He soon discovered that the pager’s number was no longer active and the pager’s network was completely shut down. To bring his pager back to life, [Jelmer] built his own OpenWRT-based pager base station that emulates the POCSAG RF pager protocol.

[Jelmer] opened up his pager and started probing signals to determine what protocol the pager used. Soon he found the RF receiver and decoder IC which implements the POCSAG pager protocol. [Jelmer] began going through the sparse POCSAG documentation and assembled enough information to implement the protocol himself.

[Jelmer] used a HLK-RM04 WiFi router module for the brains of his build, which talks to an ATMega that controls a SI4432 RF transceiver. The router runs OpenWRT and generates POCSAG control signals that are transmitted by the SI4432 IC. [Jelmer] successfully used this setup to send control signals to several pagers he had on hand, and plans on using the setup to send customizable alerts in the future. [Jelmer] does note that operating this device may be illegal in many countries, so as always, check local frequency allocations and laws before tackling this project. Check out the video after the break where a pager is initialized by [Jelmer]’s transmitter.

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Pager message sniffing with RPi and SDR


The 1990’s called, they want you to use modern technology to listen in on your friends’ pager messages. Seriously, how many people are still using pagers these days? We guess you can find out by building your own Software-Define Radio pager message decoder.

[Sonny_Jim] bought an RTL2832 based USB dongle to listen in on ADS-B airplane communications only to find out the hardware wasn’t capable of communicating in that bandwidth range. So he set out to find a project the hardware was suited for and ended up exploring the POCSAG protocol used by paging devices. It turns out it’s not just used for person-to-person communications. There are still many automated systems that use the technology.

Setting things up is not all that hard. Reading the comments on the project log show some folks are having dependency issues, but these sound rather banal and will be a good chance for you to brush up on your Linux-fu. Once all the packages are installed you’re simply working with text which can be displayed in a myriad of ways. [Sonny] set up a text files on the Pi’s webserver so that he can check out the latest captures from a smartphone.

[Image Source]

‘Vortex-drive’ for underwater ROV propulsion

This is [Lee von Kraus’] new experimental propulsion system for an underwater ROV. He developed the concept when considering how one might adapt the Bristlebot, which uses vibration to shimmy across a solid surface, for use under water.

As with its dry-land relative, this technique uses a tiny pager motor. The device is designed to vibrate when the motor spins, thanks to an off-center weight attached to the spindle. [Lee’s] first experiment was to shove the motor in a centrifuge tube and give it an underwater whirl. He could see waves emanating from the motor and travelling outward, but the thing didn’t go anywhere. What he needed were some toothbrush bristles. He started thinking about how those bristles actually work. They allow the device to move in one direction more easily than in another. The aquatic equivalent of this is an angled platform that has more drag in one direction. He grabbed a bendy straw, using the flexible portion to provide the needed surface.

Check out the demo video after the break. He hasn’t got it connected to a vessel, but there is definitely movement.

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Paging system for your TV remote

[Matt] brought together a TV remote and cordless phone to add a locator system to the remote control. One of the best features of a cordless phone is the pager button on the base. When you press it the handset beeps until found. Matt gutted one and got rid of the unnecessary parts. He then cracked open his TV remote housing and inserted the telephone handset’s circuit board, speaker, and battery. The base station is used just like normal to locate the phone/remote combo, and has been modified with a charging cable to top-off the telephone battery which powers everything in the newly hacked unit. [Matt’s] demonstration video is embedded after the break.

It’s too bad that he got rid of the microphone. It would be interesting to take calls on this thing.

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25C3: Cheap swarm robotics


The Formica project was our favorite presentation at 25C3. The goal is to build open source swarm robots as cheaply as possible. The team ended up building 25 robots in an assembly line fashion. With enough lead time, the price could get as low as £15 each. Each bot has two direct drive cellphone vibration motors with tiny neoprene wheels. They’re controlled by an MSP430 microcontroller. The only really specialized chip is a charge controller so the bots can charge without any intervention. They have copper skis on the front that touch the ground plane plus antennas to contact Vcc. On top of the bot are three IR detectors for both navigation and for transferring firmware updates between bots. A reflective sensor is on the underside for detecting “food”. It looks like a great design and any easy way for anyone to start researching swarm robotics.