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9.1. X-10

The X-10 technology was invented about 25 years ago by engineers with a Scotland company. Pico Electronics Ltd. of Glenrothes, Scot-land, was founded in the early 1970s for the growing electronic calculator market. Every time Pico began a new project, it was given an experiment number. Experiments 1 through 8 were increasingly more complex calculator Integrated Circuits (ICs). Experiment 9 was a project for a programmable record changer. This work was done for BSR (British Sound Reproduction). Experiment 10, therefore the name of X-10, was also requested by BSR to provide a wireless method of remote control for its equipment. It was determined that wireless over existing electrical wiring was better than other alternatives such as RF or Infrared. X 10 devices were first introduced to the U.S. market in early 1979 by a New York mail order electronics company. X-10 devices were also later available from Radio Shack (as Plug 'n' Power) and Sears. Today, many companies make X-10-based home automation devices, such as switch and lamp modules, available over Web sites and in electronics stores.

An X-10 switch module sends signals over existing electrical wiring to a lamp module. X-10 modules can be either adapters that plug into wall outlets or units that replace conventional manual devices. X-10 power line technology transmits binary data in 1-ms bursts of 120 kHz during these zero-voltage crossing points of the 60 Hz AC sine wave between positive or negative transitions. The zero-crossing point was considered as having the least noise and interference from other devices on the power line. For robustness, X-10 requires two zero crossings to transmit either a zero or one bit. Every bit requires a full 60-Hz cycle; therefore, the X-10 transmission rate is limited to only 60 bps. A complete X-10 command consists of two packets with a three-cycle gap between each packet. Each packet contains two identical messages of 11 bits (or 11 cycles) each. Therefore, a complete X-10 command consumes 47 cycles, which yields a transmission time of about 0.7833 seconds. Because signal bursts are operating in a relatively low frequency of 120 kHz, a capacitive coupling bridge between different phases of an in-house electrical wiring system might be necessary to minimize attenuations.


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