The Internet Power Line Adapter - University of Queensland

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Home Automation, Power Lines and the Internet Quenten Alick Power lines communications offers a slightly different set of options to the other cabling methods. There is no need to install additional cable since every home has power lines. Outlets are also conveniently placed close to where appliances will exist in the home. However, power lines communications suffers from interference problems due to the fact that power is being transmitted as well as communications, and that the power lines are unshielded and can act like antennas. Several standards already exist in the home automation industry and some of these will be discussed next. The topics that will be discussed are the X-10 power line communications protocol, the LONWorks standard and the CEBus (Consumer Electronics BUS) home automation standard. 2.2 X-10 Power Lines Home Automation Standard The X-10 standard is the oldest standard that was considered, being first introduced in 1978. It is purely a power line communications standard. Due to it being the first standard on the market it does have widespread support. However, it originally did not have any support for two-way communication between devices. Devices capable of two-way communication have only been developed relatively recently. 2.2.1 X-10 Network Layout The X-10 network specification allows for up to 256 devices which consists of 16 house codes and 16 unit codes. It also defines X-10 devices as being either receivers or transmitters. This means that a single transmitter would be able to control 16 devices. In order to control more devices, new transmitters would need to be added with each transmitter using a different house code. Receivers ignore any signal that is not sent to their assigned house code. Two-way transceivers fit into the same pattern except that they can both receive and - 6 -
Home Automation, Power Lines and the Internet Quenten Alick transmit. In this manner, is should be possible to chain transceivers together to have a single controller controlling more than 16 devices. 2.2.2 X-10 Transmission Protocol The X-10 transmission protocol is concerned only with sending pure digital data. Therefore the only two signals which can be sent are a logical one and a logical zero. This information is transmitted at the zero crossing point of the 50Hz power signal. Logic one is represented by the presence of a 120kHz PCM (Pulse Code Modulation) burst 1ms in length at the zero crossing point. Logic zero is represented by the absence of this burst. Bursts are transmitted three times per AC cycle to allow the receiver to gather the data even if it is located on a different phase to the transmitter. The transmission points are highlighted in figure 2-1. Of course for this to work coupling between phases is required but devices that can perform this are commercially available. Transmission points Figure 2-1 X-10 transmission signal 1ms 120kHz burst - 7 -
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