What Is X10
Home Automation has been standardized with the open industry X10 standard which is a communications protocol used among various controller devices. These devices are used to control practically anything that uses your home electrical power.
X10 primarily transmits it’s radio signal along the home electrical power wires within the home. It’s basically sending digital information by way of brief radio frequency bursts. Within X10, there is also a wireless protocol establish to transmit signals to x10 remotes.
X10 has been around since about 1975 so it is a long established and recognized protocol. Because of it’s age and wide acceptance, it’s considered the defacto standard in home automation.
Home Electrical Control Protocol Explained
Your home electrical wiring, the same which is used to supply power to your home electrical recepticals, lights and the such, is the primary medium used to transmit digital signals between X10 devices. Digital data is imposed into a 120kHz carrier which is sent in bursts during the quiet zero voltage crossings of the 50 or 60 hertz alternating voltage waveform. Exactly one bit is transmitted at each zero crossing.
The data that is sent contains an address and the command to be sent to the address. The controlled device with the matching address will receive the command and act upon it. Commands can consist of simple ‘turn on’ or ‘turn off’ or change your light dimming level to more advanced commands that request temperature or general sensor readings.
Controlled devices typically plug into the wall electrical socket and the device being controlled is plugged into the x10 controller. You will plug in things like lamps. Other controller devices can be built right into a light switches to hide their true functionality.
X10 protocol
Whether using power line 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 code, finally followed by a four bit command. For the convenience of users configuring a system, the four bit house code is selected as a letter from A through P while the four bit unit code is a number 1 through 16.
When the system is installed, each controlled device is configured to respond to one of the 256 possible addresses (16 house codes × 16 unit codes); each device reacts to commands specifically addressed to it, or possibly to several broadcast commands.
The protocol may transmit a message that says “select code A3″, followed by “turn on”, which commands unit “A3″ to turn on its device. Several units can be addressed before giving the command, allowing a command to affect several units simultaneously. For example, “select A3″, “select A15″, “select A4″, and finally, “turn on”, causes units A3, A4, and A15 to all turn on.
Note that there is no restriction (except possibly consideration of the neighbors) that prevents using more than one house code within a single house. The “all lights on” command and “all units off” commands will only affect a single house code, so an installation using multiple house codes effectively has the devices divided into separate zones.
