Let’s go some more into home automation – the X10 power-line system in this case.

Here’s is a sketch which turns a remote appliance on and off every 3 seconds:

I used the Arduino X10 library (had to mess around with the use of headers to get rid of compile errors, and enable the pull-up on the zero-crossing input).

This sketch runs @ 3.3V on a JeeNode with some stuff attached to port 1:

It’s just a simple re-wiring to an RJ11 connector. This in turn, plugs into the XM10E opto-isolated interface:

There’s also a X10 receiver built into the XM10E, which I’m going to ignore for now.

X10, in its simplest and oldest form, is a power-line transmission system, i.e. the signals to control a switch are sent over the same wires as the AC power itself (using a 120 KHz signal injected at the zero crossings). Proper mains isolation is essential, of course – as built into the XM10E unit.

The result is that you can plug this device into any outlet in the house and it’ll switch on and off as defined in the above sketch:

It’s hard to miss – the relay built into that thing switches on and off with a very loud “clunk”!

The power consumption of this switch is 0.6 W off and 0.9 W when on, according to the Cost Control. Not bad, until you start installing many dozens of these switches around the house … then it will add up!