Apress - Smart Home Automation with Linux (2010)- P10 potx

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C-Bus
Although there are several well-known protocols for appliance control, X10 is the best known by a long
shot with members of the general public being aware of it, primarily because of its low barrier to entry.
Within the HA community, however, it is the ownership of a Clipsal C-Bus system, which becomes
the goal.
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About C-Bus
The C-Bus system was developed by an Australian company, Clipsal, as a means of controlling various
light systems remotely. Clipsal’s original intention wasn’t in the field of HA but in stadium lighting rigs
and commercial arena and conference centers. This meant the system had to support much longer cable
runs than would be utilized in a home setup and a larger address space. It succeeded on both counts,
with cable lengths of 1km being possible with 100 appliances on a subnet—with each subnet being
capable of connections to another six through basic bridges or considerably more through the now
available Ethernet bridges.
Differences Between X10 and C-Bus
C-Bus’s primary difference is with its installation. Although X10 transmits its data along existing power
cables, C-Bus devices are controlled by utilizing a proprietary protocol that travels along a separate Cat-
5 cable. Consequently, such installations can be carried out only by qualified Clipsal-approved staff,
pushing up the initial cost. However, once all the cables have been laid, one achieves the benefit of a
near-zero level of maintenance since the interconnects will always exist and remain future-proof. It also
provides two-way communication between the switch and a computer, making it trivial to query the
state of the light dimmer or appliance. Furthermore, since the signal speed is not limited by the zero-
crossings in the power line, all light changes happen instantaneously—a benefit that only those with
many years of experience with X10 systems can truly appreciate.
To lower this initial overhead, Clipsal has recently introduced a wireless version of C-Bus, which
eliminates the need for costly installations, so it is this subset of devices on which I’ll concentrate. This

optionally supports 128-bit encryption of its data stream, making it more secure than an (unfiltered) X10
wireless solution, although it’s still hackable by the determined. Its wireless range is no better than the
RF-X10 combinations covered previously, with a 5 to 20 meter range according to material.
Unfortunately, there is a maximum of 30 devices on a C-Bus wireless subnet, making it less capable than
an X10 system using two house codes. The generally adopted approach to C-Bus installations is that a
wired version is used for the initial house configuration, with wireless being added later as a cheap
upgrade path.
For the geek, the primary difference is in the software because the protocol is closed, making Linux
tools impossible. To reclaim this market, Clipsal has released an RPM containing a binary-only driver
that is available for zero cost on its website.


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C-Bus is used mostly in the United Kingdom and Australia, with the U.S. equivalent known as SquareD Clipsal. This
is to avoid confusion with a similar technology called CEBus/EIA-600 utilizing the consumer electronics bus (CEBus).
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■ Note A Red Hat package manager (RPM) can be utilized on non–Red Hat platforms such as SUSE or converted
using tools such as Alien. The biggest problem with drivers packaged in this way, however, is its level of
compatibility with the Linux kernel. Any change in the driver API, or similar breakage between kernel version
numbers, will render the driver (and therefore your C-Bus system) useless. In these situations, when there is no
more open solution available, it is always best to keep a low-level legacy system available and be prepared to
migrate other software away from the box when necessary.
Unlike X10, each C-Bus device contains a microprocessor that makes it possible to control other
devices remotely, without a computer. This is provided by switching the device into one of its five
modes, which break down roughly as follows:
• Normal, stand-alone, switch
• Basic peer-to-peer switch control

• Networked switch control
• Networked switch control, with remote
• Interfacing with a wired C-Bus install
The adscititious computer is of benefit to smaller HA installations and those concerned about
complex lighting UI. But for those of us intending to control other devices, the inclusion of a PC is not an
issue.
Devices
Like X10 devices, C-Bus has the ability to dim lights and control appliances that are attached to it. Where
they differ is the ability of a C-Bus light switch to control one or more other devices straight out of the
box and with minimal on-device configuration.
■ Note I’ll consider only the wireless devices here, for the reasons given previously.
Controlling Lights
There are two designs of light switch, Neo and Saturn, which fall in the 5850 and 5880 product ranges,
respectively, and differ by their decorative styles only, although within each group you have the choice of
two-, four-, six-, and eight-button versions. They are always paired, with the first two buttons controlling
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the dim function of the connected lightbulb. Each subsequent pair is required to transmit the button
press information (wireless) to another device,
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or devices. Because of the built-in microcontroller, these
switches can be configured as a dimmer switch, an on/off pair, a remote trigger, or a scene trigger (the
latter being the C-Bus term for macro programming, where several state changes can occur on several
devices at the same time). Scene programming can also occur through the C-Bus Toolkit Software,
although this is currently available only for Microsoft Windows.
There are several devices in each family, capable of various support loads and characteristics, but
generally speaking a C-Bus dimmer will support incandescent and halogen lamps between 25W to 500W
(up to 2A), along with fan motors (up to 2A).

These two series also provide basic switch units. These appear the same as their lamp-controlling
counterparts, except that they lack the dim functionality. By way of compensation, they can support a
much greater range of devices (up to 2KW, and 8A in places) including fluorescent lights.
■ Note There appear to be no in-wall units for sale, meaning you cannot use wireless C-Bus electronics with your
own style of face plate.
Controlling Appliances
Like X10, C-Bus provides an appliance module that plugs into the wall and controls the flow of current to
its corresponding socket. These are known as the 5812 series plug adapters and look like their X10
counterparts, with the exception that they too support dimming and switch versions.
Since every C-Bus device includes a microcontroller and the C-Bus protocol supports the remote
programming of other devices, any of the light switches mentioned earlier can also be used to control an
appliance switch by programming an “association” on the switch, equivalent to a Linux symbolic link.
Controllers
The Series Wireless remote control 5888 is the main device here. It is an RF transmitter (operating at
433.92MHz) supporting ten devices up to 70 meters away (although 25 is more likely inside a building).
Because of the unified design of all C-Bus modules, it is technically possible to control more than the
allotted ten devices by using the remote to control one switch, which in turn controls another two
through the use of a scene. Furthermore, no RF gateway is required to use this remote, since the C-Bus
wireless network is already operating on RF. This also means that multiple remotes can control any
individual device, and any individual button can control multiple devices.
Like X10, it also supports an “all off” message.


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Provided they are configured in a networking mode.
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Gateways

With so much emphasis on the wireless network, it is sometimes necessary to revert to wires. This is
where the Wireless Gateway C-Bus 5800 Series comes in. This is a necessary feature and the only way
that the wired and wireless versions of C-Bus can be connected together. Also, through the use of
software such as C-Bus Toolkit, it can be connected to a computer for remote, sequenced, and intelligent
control. Consequently, this device is also necessary for a wireless-only network that needs to feature PC
control since the 802.11 wireless protocol used by commercial routers is not suitable as a C-Bus wireless
gateway.
Networked Devices
Although X10 and C-Bus both provide a good means of sending simple controls to simple devices, more
complex communication requires something better. More specifically, it requires something with more
bandwidth. When the command is “play this song,” it needs significantly more bandwidth. The most
accessible way of supplying this is through a local Ethernet network, because it can send commands and
data at high speeds without the distance limitations of USB, RS-232, or parallel cables. And unlike X10,
two-way communication is provided for free as part of the specification.
Ethernet Devices
There are many devices that support communication through Ethernet, either to control it or to supply it
with data. Some can work on their own without additional hardware, such as personal video recorders
(PVRs) and media enclosures. Both consist of a method of storing the media and the technology for
playback. Others require a server to supply it with data. The functionality of the device, and its use
within an automated home, is always improved by utilizing networked capabilities. This means you will
need a server, of some kind, for most future appliances. This elicits the distinction of two necessary
parts—a front end and a back end—connected by a local area network, be it wired or wireless.
The front end, or head unit, will generally consist of a device connected to a nearby HiFi or TV in
order to play media located on a physically remote machine. Because such a unit is placed in the living
room or bedroom, it should be small, silent, and attractive. Preferably, it should also be fairly cheap,
because one front-end unit is needed for every room in the house that wants to participate in streamed
media.
The back end, by contrast, is stored away from the main living areas (since it’s generally a big PC
with a noisy fan) but able to supply media streams to all the head units within the house via the network.
I’ll cover various media-oriented head units in Chapter 3, although most of those shown could be

re-created with a Linux machine running the appropriate software. However, the power usage, noise,
and cost will generally be larger than a custom-built embedded device, even though many of those
devices may be running Linux themselves! To connect the units, however, you need to know how to set
up a network.
Networking Primer
To best utilize the devices here, you will need to configure a Linux machine as a suitable server. Most
computer science books will begin their networking section by describing the OSI seven-layer model of
networking I won’t! Instead, you’ll learn only the necessary, practical steps of providing and
configuring a suitable home network for automation.
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■ Note Each Linux example here, and throughout the book, is based around Debian and the packages within it.
This is not advocacy on my part, merely practicality, because it’s what I use. Some distributions may place the
files in slightly different places or have slightly different names, but the principles are always the same, and the
equivalents are easy to find.
Concepts
A home network is a way for each computer in the house to share a set of common resources such as
printers, scanners, and storage space. In this sense, it’s very much like an office network. Where the
home differs is in the level of technology and, consequently, the expertise needed to run it. One of the
main bugbears in office IT systems is the issue of security. With a home network, the relationships
between the people using it are very much different, and social mores are brought to bear.
The standard network configuration has two parts—internal and external. The internal part is a
network that connects all the house computers together, along with their peripherals, and makes them
invisible to the outside world. These devices may be networked together through cables or wireless.
The external network is everything else! The big, wide Internet is generally unavailable the
computers at home; it is available only by connecting to an ISP through a modem, broadband
connection, 3G card, or similar device.
To connect these two sides of the network together, you need a router. Sometimes the router is a

small box that comes as part of your DSL/cable/broadband package and automatically separates the
internal and external traffic. Sometimes you’ll need to buy one. They have one RJ-45 socket carrying the
external network traffic, into which you plug the network cable from the broadband modem, and one or
more outputs to the internal network.
Alternatively, you can use a PC with two network cards—one configured to talk to the external
network and one for the internal. If you have a 3G card, then this acts like your externally configured
network card.
With the router existing in both internal and external networks, it is able to automatically keep both
sets of traffic separate and block any data or software you don’t want moving between the two. Most
routers are configured, by default, to allow all outgoing traffic but block all incoming traffic, except those
on specific ports. The port is the route by which traffic protocols flow and is dereferenced by a number.
All web pages, for example, are requested on port 80. So if your router is blocking incoming traffic on
port 80, you won’t be able to access your internal web server from outside your home’s internal network.
Depending on the number of machines on your network, you might also need a switch that provides
additional network sockets, into which you can plug more computers. Although it is unlikely that many
people will fill eight sockets with computers, it is not uncommon to have noncomputer devices that also
use Ethernet to transmit data, thereby exhausting the available sockets.
Addressing
Every device on the network must have a unique address. There are two current forms of addressing,
IPv4 and IPv6. IPv4 was the original form of describing addresses by means of a dotted quad, such as
89.16.172.66, and is used by virtually every machine and home device on the planet. IPv6 was introduced
in 1998 by the Internet Engineering Task Force to overcome the various problems with IPv4, such as
address exhaustion. However, its adoption is less than widespread, and many of the small, home-
oriented devices do not use it, so I’ll be concentrating on IPv4.