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Distributed control systems at home

posted Sep 8, 2008, 11:33 PM by Daniel Berenguer

Distributed control is a concept originated along the 70's to cover the needs of a growing industry in terms of automation. Before that, centralized automation systems, where a main computer did all the measurements and controls, were the only valid model at those times. The need of distributing the intelligence along an industrial plant and avoiding complex cable layouts made some companies think about a way of providing a communication method for their controllers. That was the genesis of the field buses. The overall solution was then progressively adopted by the industry so that nobody questions nowadays the advantages of the distributed control model.

Distributed control systems are typically found in the manufacturing industry and also in buildings, vehicles, planes and vessels. Nevertheless, is the distributed model really suitable for home automation applications? At the beginning of our current century Microsoft tried to impose a centralized model based on a PC running Windows. Microsoft knew that no distributed control system could compete against a PC in terms of flexibility, power and price. Moreover, most of the home automation manufacturers already provided drivers and applications for controlling their systems from a Windows machine. Other companies as HomeSeer Technologies or Home Automated Living have been providing very good tools for transforming a simple PC into a programmable home controller with lots of functionalities at very competitive prices. Under this panorama, the professional distributed systems found an important adversary in the home environment. Only Lonworks and EIB seemed to gain some part of the market to the PC-based system. Other distributed systems as CBUS or InstallBus also got some success but only in some localized markets. These distributed systems are commonly installed in large houses so that they provide important savings in cable runs. But the small and medium houses are still dominated by the centralized systems. Home automation devices rarely are as powerful as any industrial controller. Moreover, they usually emphasize on the low complexity of installation rather than on other aspects, most of them vital in other environment (speed of communication, robustness, programming capabilities, etc). Moreover, most pure home controllers (not building controllers) often delegate in the external PC the responsibility of taking the most complex decisions. As result, implementing a PC-based home automation network in a medium-size house or apartment is often less expensive than using distributed systems. As result, distributed systems are usually economically advantageous in large installations, where the costs of installing complex cable runs are not justified.

Ok, so could we state that PC-based central systems are less expensive than distributed systems for the home? But what about other aspects? Is then the PC-based model the best for home automation applications? This is also a very personal point of view, but I think that distributed systems are less error-prone, as every controller does a different job, in contrast to the PC-based system, where a computer maintains a number of tasks and the complexity of the system is sometimes exponentially proportional to the amount of endpoints to control. Hence the popular phrase: "when the computer gets halted, the whole installation gets useless".

Thus, must we live with that dilemma? low cost against robustness? As a home automation enthusiast and developer of embedded controllers I began thinking about a way of breaking that rule. First I thought that Linux and low cost 32-bit platforms could be a good starting point. Then I discovered some good open-source resources that perfectly complemented the idea that I had in mind. After more than two years of work the opnode project is taking shape...