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THE FUTURE IS NOW

Wireless Internet-Based Remote Control Using a Pager Interface
by Bob Brown

Start ý CreataLink Hardware ý FLEX Stack Firmware ý Selecting a Microcontroller ý Putting it All Together ý Sources and PDF

Itýs all set. Youýve taken Friday off for a three-day weekend at your country place. You get on your Internet connection to tell your country home that it should go on its Friday schedule on Thursday to be ready for your arrival Thursday night. When you get there, the driveway and garage lights are on and the house is a comfortable 68ý.

A few years ago, that scenario was thought of as futuristic. These days, with embedded Internet connectivity constantly hyped in the press, you would think that every house will soon be wired to the Internet. But the fact is, for these few simple control functions, a fully Internet-enabled house would be a bit of overkill (and over cost). In this article, Iýll describe a much simpler manner of remote control over the Internet using some technologies that have been around for a while, which are stable, inexpensive, and do not require that your house be wired to the Internet.

Alphanumeric pagers have been around for a few years now, and you can send e-mail messages to most pagers by sending a message to <the pager number>@skytel.com. For simple control tasks like turning on lights, a short message is plenty. If you add a pager receiver to a microcontroller and X10 interface, you have the hardware for a controller that can be directed remotely via the Internet. For a simple web-based interface, you only need an HTML form that, when submitted, calls a CGI script that sends the form data as an e-mail message to the controllerýs pager.

Several manufacturers make pager receivers that are suitable for embedding in the home controller. The one that Iýll focus on is Motorolaýs CreataLink FLX receiver, which Motorola is coincidentally promoting as a solution for control links. It uses Motorolaýs industry standard 900-MHz FLEX system for pager data transmission.

Motorola has created an API (provided through a block of software written in C) through what it calls the FLEX Stack that provides a standard interface for a microcontroller to the CreataLink receiver. Surprisingly, the FLEX Stack has only been ported to Toshiba and Hitachi microcontrollers, not Motorolaýs own. And at this time, Toshiba seems to be more active in supporting the FLEX Stack in the U.S. Figure 1 shows a block diagram of the basic controller system.

Figure 1ýThe two major components of the controller are the CreataLink receiver and a processor with the FLEX Stack and application firmware.

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