Hardware Reference
In-Depth Information
CHAPTER 1
Appliance Control: Making
Things Do Stuff
For most people, home automation begins and ends with the principle of appliance control. When any household device
such as a video or TV is controlled by something other than a button on its front panel or its original remote control, it is
deemed somewhat magical and a topic of further inquiry, particularly if the control is done remotely. Lights and toasters
don't need to be controlled by a wall switch, and your TV doesn't need to be fed signals from your PVR, DVD player, or
satellite receiver. Each device has its own idiosyncrasies and control methods, and each has specific functionality that
cannot easily be abstracted into any general-purpose form of control interface. However, it is possible to control the vast
majority of them using one of two basic methods:
u
Mains line-powered control (light bulbs, toasters, electric teakettles)
u
Infrared (IR) remote control (TV, video)
Although modern set-top boxes might have a serial, USB, or network socket on the back, these are in addition
to the previous two methods, not exclusive of them. Therefore, being able to control IR signals and the power lines
covers the majority of devices in the modern home. Even relatively unsophisticated appliances such as teakettles,
which were built without any intention of them being controlled by another means, can be controlled remotely if
you know how to control their power source. After all, if you ensure the teakettle is full of water and plugged into a
wall-switched socket and the teakettle itself is switched on, then the only necessary task to start the water boiling is
to flick the switch on the wall socket—something that can be governed by mains control. And it is these methods of
controlling the mains power that I'll cover first.
X10
X10 is one of the methods I'll cover that allows you to remotely control the power of any device plugged into the
standard ring main in your home. The lights, electric teakettle, and toaster are all examples of existing devices in
this category. Additionally, I'll cover devices that were originally invented to be controlled by X10 such as motorized
curtain rails. X10 achieved its market penetration by being fairly cheap and very easy to install.
About X10
X10 is a control protocol that sends data packets along the mains power line with messages such as “turn device on”
or “dim to 50 percent.” The data packets are applied to the power lines by a transmitter such as a computer interface or
a custom-built remote control, and they're processed by a much simpler receiver device, such as a light switch, which
in turn controls the power to the local device.
