Jeff Lomicka's X10 MR26A Page
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This page contains information about the X10 MR26A RF wireless computer interface that I have discovered by taking it apart and poking at it with various tools. This page deals mostly with the electrical interface, and presents a method for interfacing the device to the Apple Macintosh serial port, and a failed attempt at increasing the range of service by interfacing multiple MR26A units to a single Macintosh serial port.
If you don't know why you might want to connect one of these units to your Macintosh computer, visit http://www.shed.com/ and find out about XTension. Using XTension, you can utilize the MR26A to remotely invoke scripts on your Macintosh to perform actions limited only by your imagination and ability to program in Applescript. The MR26A tutorial at shed.com has more details on this particular device. If you are wondering where to get one of these, try the MR26A page at the X10 web site.
This section describes how to take the unit apart, some facts about what is inside, and details about how the pins of the DB9 serial cable are used for signal and power. 
This section provides detailed instructions for adapting the DB9 interface cable attached to the MR26A to the MiniDIN 8 serial port of the Apple Macintosh. It compensates for the non standard electrical characteristics of the signal put out by the device. I have Email from users that have successfully used this cable when various off-the-shelf Mac to PC serial adaptors have not worked.
These are pictures of two antenna solutions. One is just a loop of wire, the other is a scanner antenna from Radio Shack. Both work pretty good, I'm currently using the scanner antenna. 
This section provides details of my failed attempt to build a hub that would allow many MR26A units to be placed in strategic places around a building, and attach them all simultaneously to a single serial port.
If you found any of the information on these pages useful, please let me know, it will encourage me to make more pages like these. (If you use the Email link, you will have to correct the obvious anti-spam measure in the Email address.)