The latest build of the perpetually-in-beta XTension adds direct, simple support for Arduino (or similar) microcontrollers. You simply add your Arduino (or Raspberry Pi, etc) as a serial or IP interface, then define units for which the device will provide values. On the Arduino side, it's very simple for your sketch to send CR-terminated data directly to XTension. You can even send info for the XTension log. A very handy feature, and I'm pleased to see it! For details see the Mac Home Automation wiki.