The Different Smart Home Technologies

In this report I am going to explain the different smart home technologies EIB also known as KNX and CBUS. I will be giving a full explanation about what each system is capable of and a little about their company background. I will also be comparing both system with the advantages and disadvantages for each system. (Add more)

EIB (KNX) System

EIB (KNX) is the only worldwide bus system which offers a complete range of transmission media for building control systems, including Twisted Pair, Power line, Radio Frequency (RF), infrared (IR), Coaxial cable and Ethernet IP. This smart home network is designed to work independently on any particular hardware platform. It can be controlled through a network of 8 bit micro controller to a PC.

EIB (European Installation Bus) uses the twisted pair functioning which uses a cable with two pairs, using only one pair from the twisted cable for communication. The line voltage for these cables is 36v DC. Each device has a bus coupling unit which is used to connect sensors and actuators to the bus for example a NIC card on a PC. EIB is a field bus technology which is maintained by the Konnex Association. Its topology is the same as the CBUS system.

EIB (KNX) has over 176 members and manufacturers in 29 different countries some of which include Ardan smart home, ABB, Armour Home Electronics Ltd, Bosch, Basalte BVBA, CIAT, and many other companies based around the world. You can find the full list of members and manufacturers at:

http://www.knx.org/

“A “field bus” is a special form of Local Area Network that implements, not computers but sensors and actuators at its nodes and is optimised for short point to point communication of status and command messages” (M C-Wonders).

The field bus system is built up in 7 OSI layers (as shown below) which is also known as the protocol stack. However the EIB system does not use all 7 layers it only uses 5 layers (See diagram below) this shows the difference between an OSI Model and the EIB Model.

OSI Protocol Stack
EIB Protocol Stack

Layer 1

The physical layer in the EIB protocol stack defines both the bit by bit transmission of data and the physical media type (how the bits are transmitted depends on the media type)

Here is a specification of the twisted pair which is used in the EIB system:

RS485 bit communications
Twisted pair cable
9.6 kbps
1000m range
64 end devices per line

Layer 2

The data link layer defines the device addressing mechanism, making sure each device has its own unique address. It also defines the method of access to the bus arbitration as there must be a control mechanism which has to stop devices from communicating on the bus at the same time. The device address is as follows:

Device number: 0 – 63
Line number: 0 – 11
Zone number: 0 – 14

An EIB twisted pair system can only have 15 zones, 12 lines per zone and 64 devices per line.

Layer 3

On the Network layer there can only be device to device communications as this allows data packet transmission between devices and connectionless communications. This layer also uses Unicast and Group addressing.

Unicast addressing is only used during device installation (system access mode) also using the physical device address.

Group address is equivalent of multicast and broadcast addressing as it has normal bus operation mode and allows an input device to control many other grouped output devices. The group address consists of a main group, middle group and a sub group e.g. 2.4.2

Layer 4

The transport layer is responsible for reliable communications as it creates a connection between both the sender and the receiver using positive acknowledgment with retransmission (PAR).

The PAR sequence is as follows:

A connection between sender and receiver is set up
Sender sends data with sequence number
Sender waits a set period of time for an Acknowledgment from receiver. If none data is sent again. After 3 attempts to send the data have failed the operation will terminate its connection
If the receiver suspects an error at any point it will send and (Nack), which terminates the connection.

2. When all telegrams have been transmitted the connection is terminated.

Layer 7

This is the application layer in the EIB protocol. This layer is based around the concept of communication objects. Each device on the networks paired with a software application which has the relevant functions it needs. The application associates objects to particular devices as these objects are the communication methods for EIB which use the group address within the device. Each application on each device stores an association table, this association table links to the group address table and a communication object table for example:

CBUS System

Clipsal BUS (CBUS) is a microprocessor control and management system for homes and buildings. This system is used to control electrical services such as lighting, audio visual devices, motors, etc. Either a simple on/off control for lighting or variable (analogue) type control for example dimmers. CBUS is easily controlled through virtually any type of electrical load.

CBUS certifies each of its products has its own built-in microprocessor for reliability and fast operation allowing each unit to be programmed individually. CBUS uses a unique method of updating each unit which involves a method which can not involve a central computer or controller. Each unit device is assigned a specific time frame in which it broadcasts its status which is then synchronised by a self generated system clock pulse. This allows great quantities of data to be passed on in small time frames in low overheads and bandwidth requirements.

CBUS is an interconnected system of inputs (sensors) and outputs (controllers) used to allow automatic operation and control of machinery or processes such as environments that can make and execute decisions with or without human interface (MC-Wonders). CBUS uses a UTP cat 5 cable which allows each of its devices to interconnect within the system.

The maximum total cable length per network cannot exceed more than 1000 meters with a system voltage of 15v D.C – 36v D.C (across any node in a network). Its data rate is 3500 bits/second with 64 byte frames. Its bus contention method uses CSMA/CD with CA.

CBUS transmit units and dimmers units connect to the main power supply and other switches/sensors which are used to control a buildings electrical service. The network is electrically isolated from the mains supply operating at a safe extra low voltage level of 36v DC.

The CBUS system is develops continuously therefore making it practically unlimited. Networks of 100 units are larger installations which have been divided allowing the system to be managed in sections, up to 1000 meters of cables may be in installed in each network.

The CBUS system can be as large or as small as a user prefers it to be and it does not only simplify the design of automations needed but limits potential faults which makes trouble shooting easier.

CBUS responds too many of the following devices:

Home entertainment – audio visual, lighting control
Security – integrated security, lighting
Comfort – scene setting, dimming
Convenience – central point control from touch screens, automated time based control, multiple point control, automated messages

CBUS is suitable for many different applications for example:

Residential Automation
Home entertainment – audio visual, lighting control
Security – integrated security, lighting
Comfort – scene setting, dimming
Convenience – central point control from touch screens, automated time based control, multiple point control, automated messages
Standalone room lighting control
Via a touch screen user interface becomes automated for conference rooms and home theatres
Many different scene and mood setting are available
Commercial light control
In a warehouse high bay control is used for energy saving costs
Energy saving costs in high rise buildings is brought to minimum by using fluorescent lighting.
For retails and restraints mood lighting is used to set a scene
Flexible control of lighting and audio visual used in boardrooms
For hotel foyers, ballrooms, etc architectural lighting control is used

CBUS supports all multi room audio visuals with a full range of amplifiers and ceiling speakers which are all controlled by switches and touch screens. As all electrics have to return to one central panel it is very expensive to convert existing houses to use CBUS unless renovations are being made allowing reconfiguration.

A switch which is placed in the boardroom is programmed with the CBUS group address. When the light switch is pressed an on command is sent to the group address of the CBUS.

The command which was sent to the group address from the input switch is then sent on to the CBUS network or all units throughout the network. Only the programmed units respond to the command form the group address. Other units which have not been programmed to respond the message will ignore the command as it was not intended for them. This is only an overview of the flexibility and power of the CBUS system.

When using a CBUS system each device has to have a CBUS connection including devices such as the mains power will obviously need connection to the mains. Wiring for the mains and CBUS do not need to be adjoining as the mains can be connected to a different phase or completely different system.

Field bus system

The advantages of a system include:

Less complex installation: this means less hassle with wiring as it can be done through a bus that carries the messages
Total ownership cost becomes less: reduced cabling and installation time, easy modification and upgrade and easy to fault find means reduced costs.

Offers more flexibility: Each node is a micro controller which is programmable. Each node has its own intelligence making no 1 point of failure.

CBUS can have a maximum of 255 sub networks, within each sub network there is a combination of input and output units a sub network allows a maximum of 100 units which can connect to a single sub network.

When sub networks contain units it is essential to be able to give each unit a address, there are 4 main levels of addressing which are available for these units these are:

1. Network address

This is assigned to each sub network with a 2 digit HEX value

2. Unit address

This unit address identifies the individual unit for example light switch

3. Area address

Allows division of a sub network, it also enable messages to be sent to areas by the units

4. Group address

Really a less specific area addressing scheme, only allows maximum of 255 groups on a sub network.

There are two main devices which are needed in order to set up a CBUS system. These are a power supply and a PC interface which is used for programming the units.

Some of the advantages of CBUS system are:

CBUS can forcefully and reliably control all the different systems with low costs per node.
There are many different tools which are used to allow 3rd party companies to interface with both PC and embedded systems.
One CBUS connection controls a unlimited number of devices
CBUS is very flexible for switching and controlling, for example functions may be removed, changed, added or reprogrammed at any time without bulky hard-wiring through the network itself.
Simple installation process
CBUS is able to control all different types of load including load, digital and analogue.

Some of the disadvantages of the CBUS system are:

it can have only one distribution panel
does not allow loop topologies
each device has to return to one central panel
each device has to have a CBUS connection

CBUS and EIB Compared

CBUS and EIB systems are used to control electrical devices in home and building environments for example both home systems can control lighting, dimmers, audio visuals and many other electrics. They also have the same topologies available which includes the bus topology, star topology and the hybrid topology. Neither of these systems can form loop topologies as this does not allow the system to have a valid distribution panel.

The EIB system can only uses device to device communications as this allows data packet transmission between devices making connectionless communication whereas the CBUS system uses a network connection which is set up on each node through each sub network mask. This also means that the CBUS system can have as many devices linked to one distribution panel making it an unlimited as an EIB system can only have up to 64 devices on each line within each zone available.

Each CBUS product has its own built-in microprocessor which allows each unit to be programmed individually. As each unit device is assigned a specific time frame great quantities of data can be passed in small frames. In an EIB system there can only be device to device communication as this allows data packet transmission between devices and connectionless communications, within the transport layer is creates a connection between both sender and receiver.

Both EIB and CBUS systems have a maximum cable length per network which cannot exceed more than 1000 meters with system voltage of 15v DC – 36v DC. CBUS has a maximum of 255 sub networks within which there is a combination of input and output units. Within sub network a maximum of 100 units can be connected to a single network. In an EIB system the twisted pair system can only have 15 zones within those zones there can only be a maximum of 12 lines. There can only be a maximum of 64 devices per line on a zone meaning there is limited space on the system.

A typical scene situation:

There are two lighting strips within an office. Lighting strip 1 is located by the window, lighting strip 2 by the wall. These lights can be switched on and off manually. If there is sufficient ambient light, the lighting strips are switched off and are locked (i.e., they cannot be switched back on again) automatic switching on again when darkness falls is not required but is manually possible. Before the start of a working day a timer automatically switches lighting strip 2 on to guarantee sufficient light level.

This is the layout of the office with strip lights and touch switches and actuators

A solution to this problem would be to get bus devices including 1 touch sensor to fold, 1 bus coupling module which will have a brightness sensor and timer (1 channel) which is din rail mounted, 1 controller again it should be din rail mounted, 1switchin actuator 2 fold and a din rail mounted devices installed in the distribution panel

When an outside has sufficient light, the brightness sensor will automatically switch off lighting and lock it. In order for this operation to succeed the brightness sensor telegram (address 1/0/3) is AND (gate) linked with the touch sensor telegram (address 1/0/1). The output of the AND gate sends a message (address 1/0/6) to the switching actuator (1.1.4) which will switch lighting strip 1. To avoid the brightness automatically switching the light back on when it is darker the result of the linking (1/0/6), this is why when the sensor is switched off both inputs in the AND gate are set to “0”.

These are the parameter blocks which are used in the programming of the system:

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