Logitech Harmony Wireless Extender

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Logitech Harmony Wireless Extender

If you are lucky enough to own a Logitech Harmony remote including a wireless extender (like the Harmony 890), you can connect it directly to your serial port via a special cable. This has the benefits of being able to control your MythTV box through walls, doors, and cabinets, and doesn't require the intermediate step of transitioning to Infra-Red.


I guess you could find something off the shelf, but I thought it would be cheaper and more fun to build it myself. So, here's what you need:

  1. An RS-232 DB9 female serial plug. I was able to scrounge one from an old external modem cable.
  2. A 3.5mm (a.k.a. 1/8") headphone plug...preferably mono (i.e. just two contacts and wires instead of 3)
  3. Some 2-conductor, small gauge wire (or you can just use whatever is already attached to the plugs you've scrounged).
  4. Skills with a soldering iron or splicing wires.
  5. A serial port on your MythTV box.

How to do it

Ultimately, you only need to make two connections:

  1. Connect the "tip" of the 3.5mm plug to pin 1 (DCD) on your DB9 plug...the pins should be labeled, but pinout diagrams are all over the Internet if you need help figuring out what's what.
  2. Connect the "base" of the 3.5mm plug to pin 5 (ground). Connect the middle of the 3.5mm plug as well if you're recycling a stereo plug.

Along the way, I'd suggest you test the continuity of your connections to ensure they're hooked up correctly and completely. Also, be sure to check for short circuits.


Plug the 3.5mm jack to the back of the wireless extender, and the DB9 female into your serial port and proceed with Logitech_Harmony_Generic_Setup. It should work just like any other LIRC device, but without the added hassle!