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A radio based transport is also defined. X10 was developed in 1975 by Pico Electronics of Glenrothes, Scotland, in order to allow remote control of home devices and appliances. It was the first domotic technology and remains the most widely available. Although a number of higher bandwidth alternatives exist including INSTEON, BACnet, and LonWorks, X10 remains popular in the home environment with millions of units in use worldwide. Power-line carrier control overviewHousehold electrical wiring is used to send digital data between X10 devices. This digital data is encoded onto a 120 kHz carrier which is transmitted as bursts during the relatively quiet zero crossings of the 50 or 60 Hz AC alternating current waveform. One bit is transmitted at each zero crossing. The digital data consists of an address and a command sent from a controller to a controlled device. More advanced controllers can also query equally advanced devices to respond with their status. This status may be as simple as "off" or "on", or the current dimming level, or even the temperature or other sensor reading. Devices usually plug into the wall where a lamp, television, or other household appliance plugs in; however some built-in controllers are also available for wall switches and ceiling fixtures. The relatively high-frequency carrier frequency carrying the signal cannot pass through a power transformer or across the phases of a multiphase system. In addition, because the signals are timed to coincide with the zero crossings of the voltage waveform, they would not be timed correctly to be coupled from phase-to-phase in a three-phase power system. For split phase systems, the signal can be passively coupled from phase-to-phase using a passive capacitor, but for three phase systems or where the capacitor provides insufficient coupling, an active X10 repeater is sometimes used. It may also be desirable to block X10 signals from leaving the local area so, for example, the X10 controls in one house don't interfere with the X10 controls in a neighboring house. In this situation, inductive filters can be used to attenuate the X10 signals coming into or going out of the local area.
X10 protocolWhether using powerline or radio communications, packets transmitted using the X10 control protocol consist of a four bit "house code" followed by one or more four bit "unit codes", finally followed by a four bit "command". For the convenience of the users setting up the system, the four bit house code is labeled as one of the letters A through P while the four bit unit code is label as a numbers 1 through 16.
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