Embedded Control Systems Design/Home and Building Automation

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This application chapter discusses the use of embedded control systems in home and building automation systems, sometimes called domotics and immotics. A short introduction to home automation systems and their components is followed by an analysis of the evolution of embedded systems in domotics.

Introduction

Home automation is a form of building automation, only on a smaller scale and (most of the time) of a lower complexity degree. Both types of systems try to fill in the specific automation requirements of private homes and buildings, hereby increasing the comfort and security of the users and improving on overall energy efficiency. Not all home automation systems posses these characteristics, simpler (cheaper) systems only focus on comfort or security.

Home automation systems come from the need of automating processes in the house of e.g. an immobile elderly person, a handicapped person,... Building automation systems originate from the simple fact that it is easier to control lots of systems remotely from one place instead of running around, controlling each of these systems manually. (HVAC and chilled / hot water systems come to mind)

Now that electronics are becoming more affordable and implemented in people's houses, the urge for electronic comfort is increasing by the day. Hence the growth of the domotics market.

Tasks

Home and building automation systems can perform a magnitude of tasks. Nowadays there is almost no limit to the tasks such an automation system can perform. As long as the task itself is not impossible to perform with current mechanical/electronic systems, the only limit is the customers budget.

Some applications of home automation systems include but are not limited to:

Since this document discusses embedded control systems in home and building automation systems, it is not necessary to give an accurate view of the tasks than can be completed by such an automation system. More information can be found here: Home automation and building automation.

Component functions

Home automation systems commonly exist of several components, which are all part of the complete system. Each of these components can perform a function, some components are multifunctional.

Most components functions can be categorized into 3 categories:

Some components can be used for input, output and control. A multimedia terminal for example can be used for:

In the early days of home automation, a system could be nothing more than a central switching box with timers and some logic modules, with switches wired throughout the house to be used as input and relays / actuators to be used as output.

At the time of writing this document, there is no simple way of categorizing the components of an automation system into input/output/control, since most components incorporate all three functions. Later on in this document this will be the baseline for an analysis of the evolution of home automation systems.

Input Functions

Input functions are mostly performed by components called sensors. Sensors can be anything from a simple on/off switch to a capacitive proximity switch to a complex audio/video recognition system.

Some examples of sensors:

A lot of the more complex sensors need some electronics to condition the sensor signal and transform it into a signal suitable for the home automation system.

Output functions

Output functions are mostly performed by components called actuators. Actuators use a signal from the automation system to change the state of an object in the controlled environment (e.g. switching AC power to the circuit feeding the light bulbs, moving an object).

Some examples of actuators:

To get an actuator to do something useful in an automation system, most of the time it has to be equipped with extra mechanical/electric systems. A stepper motor e.g. won’t do much unless it’s attached to something, a fluid control valve for example. The output function is thus being performed by a combination of a basic actuator in conjunction with some additional systems.

Control functions

Control functions are somewhat different than input/output functions in that their functionality itself is not so easy to describe. Control functions can be a lot of things, including but not limited to:

Control functions are performed by a control unit, but since there are so many different forms of systems and again due to the changing nature of home automation systems in time, it is difficult to describe the system that performs these control functions. Systems performing control functions can be as simple as a few logical gates or as complex as a full-blown mainframe.

Communication

Evidently, there is a need for a communication system between all these components. Since the birth of home and building automation systems, a multitude of standards has popped up.

In the early days of home automation systems, communication occurred over simple copper wiring. There was no need for high data speed or interference shielding. At the time of writing a lot more possibilities exist for communication in such systems.

For example:

All these communication means have their own characteristics, discussing them falls out of the scope of this document. Which standard uses which communication method can be found on the general Wiki page about Home automation.

Embedded control systems in Home / Building automation systems

Design characteristics

First of all a short list of embedded control system design characteristics and their application to the current subject of home/building automation systems. These are the characteristics a design engineer has to keep in mind when designing such an automation system:


High importance characteristics:


Medium importance characteristics:

We discuss watchdogs more in Embedded Control Systems Design/Design Patterns#Watchdog timer.

Low importance characteristics:

System complexity

Since there has been a large evolution in home/building automation systems it follows that there has also been an evolution in the technologies used in these systems.

Home/building automation systems span a few decades already and the available technologies evolved over time. Categorizing home/building automation systems in general is very difficult thanks to the change in used technologies.

Therefore an analysis of these systems during their evolution seems in place. On the whole these automation systems can be said to belong to one of following three categories:

The trend that can be seen in the evolution of home/building automation system is that they evolve from category 1 to 3 throughout their existence.

More general information concerning the categories can be found in the section Categories of system complexity.

Category 1: Centralized hardware – centralized software

picture schematically describing the centralized/centralized character

The first category is also the one that occurred most in the early days of home/building automation systems. Due to available technologies (the beginning of the semiconductor era) it seemed logical to have a centralized hardware/software setup. This consisted of 1 rack or machine which contained nearly all the necessary hardware and, if applicable, software parts of the system.

A simple switching box with some timers and logical circuits would be sufficient if provided with e.g. switches as inputs and relays as outputs. Later on, when PLC’s were getting into play, systems got a little more complicated, but it was still of the same centralized type.

Pro/con
Abstraction level

The user abstraction level of this type of systems is rather low. This means that for the simplest of these systems the user directly controls the outputs with one input or a logical combination of inputs, the more complex using multiple inputs and timers to set the outputs. For example a user switches a zone of lighting on or off, sets the house to night mode (close the curtains, switch off all the lights except the one outside by the door, …).

In systems with a higher abstraction level the user could, for example, switch the living room to ‘Romantic mode’ or ‘Movie mode’. These kind of abstractions are difficult to program on the simpler category 1 systems (since they are quite inflexible), going up in system complexity eases the task of implementing higher abstraction levels.

Communication

This type of system mostly uses standard electrical wiring (low voltage for the inputs, low/high voltage for the outputs). Since there is no communication between different components of the system other than a voltage difference used for inputs/outputs, there is no need for a specific communication protocol.

Category 2: Distributed hardware – centralized software

picture schematically describing the distributed/centralized character

The second category consists of the type of systems found in most lower to middle class home/building automation systems of today and the high end systems of earlier.

They consist of a central controller (mostly an embedded processor or a PC type controller) which runs specific software on an operating system (specific or generic, depends on the implementation). This central controller is then connected to a field bus or busses, which connect it to its hardware peripherals.

The hardware peripherals can also have an embedded processor, but they do not run an operating system. The software can be found only on the central controller, which uses the field bus to communicate with its peripherals and gather inputs / set outputs.

Pro/con

The hardware peripherals are not very sophisticated, they only consist of a hardware layer, no software involved. This is benificient for the robustness of the hardware peripherals but compromises the system’s flexibility.

Abstraction level

In comparison with category 1 systems, a higher abstraction level can be achieved. It’s easier to implement on the more powerful central controller, but still the software is quite problem specific and the ‘abstraction levels’ need to be programmed into the software. This does not make for a user-friendly input for these ‘abstraction levels’ since the user needs to update the software of the central controller manually to implement them.

In systems of category 3, if implemented, the user can setup his or her own ‘abstraction levels’ at user interfaces throughout the house, without having to meddle with the central controller’s software. This is not possible for category 2 systems (in a strict sense) because there is no bi-directional communication between central controller and hardware peripherals.

Communication

A multitude of field busses have been developed for the sole purpose of serving in home/building automation systems, including e.g. Batibus. Naming all field busses ever used for these systems and describing them is beyond the scope of this document.

Also it would not be correct to list domotic standards here since most of these standards use multiple means of communication, mixing category 2 and 3 communication methods.

Category 3: Distributed hardware – distributed software

picture schematically describing the distributed/distributed character

The third type of systems is found in the newest home/building automation systems and some of the most expensive older systems. Here a total home/building automation system consists of multiple sub-systems of category 1 or 2, linked together using a software and communication layer. Communication between these sub-systems can occur via a lot of different networking technologies (RF, wireless, optical, …).

While systems of category 1 or 2 were synchronous, most category 3 systems work in an asynchronous way, due to every subsystem having its own controller (with or without an operating system).

For example: every room in a house is a sub-system of category 2, controlling the lighting, the curtains, the multi-media content, the temperature, … Every room has its own controller used for setting inputs or outputting music/video/security info/… Each room is controlled by the room’s controller while there are controllers which can control a room’s controller.

For example when going on a vacation, every room has to switch off the power as to save as much energy possible, but it might come in handy to have a light on in a random room every night as to give the impression somebody’s home. The room’s controller must then have some priority scheme to decide which command to listen to.

Pro/con
Abstraction level

With systems of category 3, the highest degree of abstraction can be attained due to their high processing power and extensive software flexibility. The hardware is more of a generic kind while the software makes up for the functionality of the different components.

picture of a high abstraction level interface for home automation systems

A highly user-friendly interface which can control different abstraction layers aids the user greatly to implement his or her custom ‘abstraction levels’. If the user likes soft jazzy music, dimmed lights, the curtains closed, the hearth lit etc. when he’s having a romantic evening, he could program a ‘Romantic’ abstraction program which, when called, closes the curtains, switches off television, puts on some soft jazzy music, dims the lights and lights the hearth.

This type of system is very suitable for high level automation control, but this also means that the software has to be flexible and robust, even more than in categories 2 and 1. This doesn’t get any better since the user will have a lot more interaction with this kind of system than with simpler types of systems.

Communication

These systems use a mix of different communication technologies, including twisted pair, electrical wiring, radio frequency, coaxial, optical, …

An overview of these different communication technologies and which standard uses which technology is out of the scope of this document, but information about these can be found on their respective Wikipedia page or on the general home automation page.

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