X10 was developed in the 1970s in order to allow remote control of home devices and appliances. It allows up to 256 distinct devices on a home power system. It works by sending 120Khz control signal bursts superimposed on household power wiring at the zero crossing points in the AC power flow. All messages are sent twice to reduce false signaling. After allowing for retransmission, line control, etc, data rates are around 20 bps, Messages include an 8 bit address and 5 bit command. Obviously, X10 data transmission is so slow that the technology is confined to turning devices on and off or other very simple operations.
One Problem with X10 is excessive attenuation of signals between the two out of phase 110 volt lines used in much North American construction. This may come and go when 220 volt devices like stoves or dryers that bridge the two circuits are turned on or off. Other problems: TVs or wireless devices may cause spurious off or on signals. Noise filtering may help keep external noise out of X10 signals, but noise filters not designed for X10 may filter out X10 signals. X10 controls that use semicondutors rather than relays to control current flow may not work well or at all with low power devices (below 50 watts) or devices like fluorescent bulbs that do not present resistive loads.
Return To Index Copyright 1994-2002 by Donald Kenney.