Home Control Protocols
Home automation has roots dating back to the 1950s. I recently read an article titled "Push Button Manor" published in Popular Mechanics magazine. This article takes a look into the home of Emil Mathias of Jackson, MI. The article discusses many of the reasons for home automation, complete with illustrations.
But back in the 1950s, Emil was not using fancy electronics. He was simply using push button switches, motors, pulleys and other mechanical devices of that era to automate things such as raising and lowering windows.
It was in the mid 1970s that Home Automation started becoming widely available with the developement of the X10 system by Scottish engineers. By 1978, these products were being sold in retail stores across the country.
Today, X10 is still in wide use by many DIY home automation enthusiasts and has paved the way for many of today's modern protocols. Let's take a closer look at how X10 works.
X10 is a PLC protocol with devices having an identifier code made up of a House Code and a Unit Code. House Codes are designated with letters A through P and Unit Codes are designated with numbers 1 through 16. These two identifiers together make up the Device Code (for example, A10).
There are a total of 256 unique possible device codes. By setting multiple devices to the same code, you are able to control them at the same time. For example, setting a motion sensor and lights with X10 modules both set to Device Code A1 (Figure 4) essentially links them together. When the motion sensor is activated, it sends a signal on the powerline telling all the other A1 devices to activate.
Figure 4: Dials to set X10 Device Code A1
Special interfaces allow X10 signals to be sent and received over a computer's serial port, which allows more complicated sequences to be performed.