Articles and whitepapers

No New Wires: Using Power Lines for Control (2/8/2004)

By Darren Sowerby

The demand for home control networks is growing at an ever-increasing rate, fuelled by a desire for the latest technology from a public with more excess cash than ever before.

So what do people want to control over a network around the home? Setting aside the A/V network, then what else is left to control? If we think of control in real terms as switching, then we can start to come up with some ideas. More often than not it involves turning something on or off such as security, irrigation, lighting, access control, projector screens etc.

There are many systems on the market offering a high degree of control around the home, but in this article we are concentrating on those systems that offer control over a home's existing mains wiring. Utilising power line (as they are known) systems as a control network offers us one major advantage, we already own the network!

Integrated control

Control of systems around the home has traditionally been achieved using proprietary control systems, so if you wanted heating control, you bought a heating control system and when you wanted to control the heating, you went to that system and made the changes. The problem with that route is that you end up with lots of control systems, each one independent from the other with no integration. People are beginning to favour a single control system for all systems around the home, and one user-friendly interface with which to become familiar.

So, what will drive your choice of system? Cost, level of control, disruption during installation, ease of use and degree of integration between systems are the usual criteria.

It would be fair to say that power line systems offer less control, integration and expansion than many of the hardwired system, but they have the major advantage of being easy to install and can quite often meet the requirements of the less demanding consumer.

How it works

Power line control is achieved over your existing home mains wiring by transmitting the control signal in harmony with the frequency of the supply, at the zero voltage crossover point. If that does not mean a lot to you, then do not worry, just accept the fact that it works and that it is easy to install.

For control via the power line, we need a method of getting signals into and out of the system and we also need something to control, such as a light switch or relay. Typical methods of input are via RF (radio frequency), infrared, contact closure or through integration with third party controllers such as the Comfort Home Control System.

Comfort Home Control Screen

Installation is normally very straightforward. For example, let us say that we want a system to control a light via a hand-held remote control. We could go for the following system from X-10:

The HR10 hand-held remote will control 16 lights via RF straight from the box.

The TM13 Transceiver plugs directly into any 13A mains socket in the house.

The LW11 Dimmer directly replaces your existing light switch.

The HR10 hand-held remote

The TM13 Transceiver

The LW11 Dimmer

And that's it! It can literally be fitted in 5 minutes without any real set-up being required. Each switch is given a unique number using a dial on the switch - and you're done.

Other applications

There is a wide range of modules available ranging from the popular ones such as lighting control and relays, to more specific products such as security panels, through to the more obscure such as barking dog alarms.

As another example, suppose we wanted to use X-10 to control an electric projector screen via a remote control. Again, we would need the HR10 or one of the other X-10 remotes, and the TM13 installed as above. We then connect an SW10G motor drive switch to the projector's electrics and calibrate the time to raise and lower the projector, and finally sit back and enjoy the film.

The SW10G motor drive switch

Limitations

There are limitations in using power line systems. The strength of the signal deteriorates over distance and is also affected by noisy mains. You should isolate your mains from others in the neighbourhood by fitting a filter to your incoming supply that will stop signals straying from your system to other peoples homes and vice versa. In addition, most of the modules available in the UK offer no status feedback from the network and so cannot be interrogated, for example to find out if a light is turned on or off. Nonetheless, in the future we can expect to see improvements that support a greater range and better addressing of units, and to see the choice of modules increase even further.

Conclusion

There is no doubt that power line control is quick, easy and cheap to install. It brings home control in an affordable package to the masses. However, for those people who require a higher degree of flexibility and control, a more professional dedicated system may be more suitable.

Darren Sowerby is the Managing Director of Easylife Automation Limited. Easylife Automation is a member of CEDIA and supplies and installs everything from basic A/V systems to full-blown automated homes.

www.easylifeautomation.com