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 He soon discovered that the pager’s number was no longer active and the pager’s network was completely shut down.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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I2S Audio And SPI Display With An Ethernet Module

LCD[kgsws] is working on a small project that requires some audio and a display of some sort. While this project can be easily completed with a bigish microcontroller or ARM board, he’s taking a much simpler route: the entire project is built around a cheap router module, giving this project amazing expandability for a very meager price.

The router module in question is the HLK-RM04 from Hi-Link, commonly found via the usual Chinese resellers for about $25. On board this module is a UART, Ethernet, and a WiFi adapter along with a few GPIO pins for interfacing with the outside world.

[kgsws] is using the native SPI pins on this module to control the clock and data lines for the tiny LCD, with a GPIO pin toggling the chip select. I2S audio is also implemented, decoded with an 8-bit DAC, the MCP4801.

It’s an extremely inexpensive solution for putting audio and video in a project, and since this board has Ethernet, WiFi, and a few more GPIO pins, it’s can do much more than whatever [kgsws] is planning next.