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X10 Principles
By
Whome
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X10 works by carrying control signals over the domestic mains power wiring. Because most houses are wired so that all power and lighting circuits originate from the same point, a control device in one part of the house can control appliances in another part. This means that controllers do not have to be wired directly to appliances.
Control signals can be generated by various sources, including plug-in controllers, radio and infra-red receivers, and computer interfaces. These signals are detected by appliance and lamp controllers, among other things. The X10 protocol also provides for a controller to determine the status (on or off) of an appliance, although many appliance modules don't support this.
As all controllers and appliances are connected to the same mains wiring system, how does the X10 system determine which device a particular control signal should be directed to? Embedded in each X10 signal are a `house code' and a `unit code'. Both of these can take values between 1 and 16. Each appliance or lamp is set to respond to a single house code/unit code combination. The house code was originally intended to allow adjacent houses to use X10 without interfering with each other; this is necessary in theory because houses in the same neighbourhood may share a connection to the power distribution system, so that control signals can `bleed' from one to another. In the UK, where uptake of X10 has not been widespread, the house code and unit code can both be used to select which device to control. This means that a total of 256 devices can be controlled independently in a given property.
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