Inside Automation Systems

By Amir Majidimehr
AMX NI-3000

As we explained in the article on the need for automation in your home, an automation controller is a device which receives input due to some event occurring (e.g. hitting the pause on your remote) and creating a set of response to it (e.g. pausing the DVD player and turning the lights on).

In its simplest form then, an automation controller is nothing but a specialized computer. After all, what is a computer than a device which receives input (e.g. what you type on your computer) to something output (e.g. going to some web page and displaying its content).

In the case of a general purpose computer, you run an operating system such as Windows or MacOS. On top of that, you run a set of applications such as the web browser and email. Our automation "controller" also comes with a pre-loaded operating system (usually a customized version of Linux). So in this regard, it is very similar to a personal computer. Where it deviates is that it does not run an application you buy or download. But rather, companies like us write a custom “control” program for it which gets embedded in it to teach it how to manage the functions of your home from showing a user interface on a touch screen, to turning your lights and audio/video system on and off.

Let's now dive in and examine the hardware that lives inside these opaque boxes. The best way to do that is to look at an example such as the AMX NI-3100.
AMX NI-3000 Back

Not much to look at, right? Now you know why we install it in a rack in a closet rather than showcasing it in your entertainment center! Well, it turns out the "business end" is the back:
AMX NI-3000 Back

Still makes no sense to you? Well, it will once we take out the jargon out of the specification mentioned by AMX for this controller:

(7) Configurable RS-232 / RS-422 / RS-485 Serial Ports

A “serial port” is a type of electrical connection that is used to communicate with other devices. The connection is called “serial” because a single wire is used to either transmit or receive data. Computer data tends to be in “8 bit” chunks (which we call a "byte") so to use a serial port, that data is “serialized” or sent out one bit at a time and hence the terminology used here.

“RS-232/RS-422/RS-485” designations are the various standards that specify how the bits look on the wire electrically. In other words, how you represent a "1" or "0." That in turn determines how far the signals can travel (in feet over certain quality cable). The details are beyond the scope of this article and frankly rather boring. If you are curious to learn about them anyway, you can refer to the articles in Wikipedia:
RS-232: http://en.wikipedia.org/wiki/RS-232
RS-422: http://en.wikipedia.org/wiki/RS-422
RS-485: http://en.wikipedia.org/wiki/RS-485

Of the three, RS-232 is the most common but it also has the shortest reach. The implementation in this AMX controller is quite nice in that the same physical port can be configured to behave as any of the above formats. Such is not the case for many devices this controller manages. As such, the port needs to be set up correctly in the control software to match the device being controlled. For example, LG LCD TVs have an RS-232 port for control (see picture below) so unless the AMX controller is instructed to use the same electrical signals, proper communication cannot be established.

By the way, in the past your PC also had RS-232 ports but they have long been replaced with the much faster USB ports. That might make you think that serial ports are yesterday’s news and not very useful but that would be wrong. A PC needs to move a lot of data as it for example communicates with a printer or flash memory over that USB port. In our situation, we only need to send a handful of bits to make something happen such as turning on a TV or changing the light level in a room. So even though RS-232 is much slower than USB, it is still plenty fast for the types of things we use with it. That said, there are poorly designed control systems where the designer did not understand the speed limitations of this connection and as a result, you have a system where you push a button, and you visibly see things happen one at a time instead of all at once.

Cable length restrictions is also another reason we use slower links like RS-232. The automation controller may sit a hundred feet away from where your TV might be installed. USB has a maximum range of 16 feet (5 meters) so it would not work in this situation without some kind of extra hardware to boost its range. RS-232 on the other hand can easily reach 200 feet and if you use it at slower speeds, as far as 3000 feet! Now you see why there is such a strong preference in the automation world for this flavor of communication over USB connection in your PC.

That said, there are occasions where a faster interface might be handy. For example, driving a touch panel user interface requires that the controller output a lot of data such as pictures of buttons and music cover art. In that scenario, the speed of the serial port would become a serious bottleneck. For these applications, we can use the much faster Ethernet network interface explained below.

8 Relays

A relay is an electrical switch which can be turned on or off under software control. By connecting the output of the relay to some other device, we can instruct it to do something when relay contacts open or close. And example may be opening a gate when you hit a button on your touch screen. The relay output would be connected to the motor controller in the gate, telling it to open or close.

As the example above shows, relays are useful when we just want to send a "binary" message to some other device: either do something or not. Serial ports are more sophisticated in that we can send longer messages such as telling a TV to change is volume to 25%. Alas, it costs more money to implement a serial port on a device so we are stuck with a simple relay control in them.

8 IR / Serial ports

IR stands for Infrared and is the type of communication mechanism used in most remote controls and their corresponding receiver such as a TV or Blu-ray player.

If you look at the front of typical remote control, you see little round domes (sometimes hidden behind dark red glass). These are Infrared “LEDs” which while invisible, create a beam of “light” which is modulated (varied) to send a message to a receiving device. Think of IR as a wireless one-way serial port (i.e. output only). In the aforementioned LG TV example, we could have instructed it to turn on using an IR port instead of serial same way as if you had used the remote control for it. So if there is a button to change channels, the control system can emulate the same function but now, under the control of the custom software we write for it. This allows us for example to give you a touch screen and have you hit buttons on that to change functions of your TV.

In general IR communication tends to be less reliable than serial. The communication is one way by nature, making it much more difficult to know what the device is doing before telling it to do something. For example, if we don’t know if the TV is on, sending it the “on” command again might just turn it off as the power switch is sometimes a "toggle" meaning the same button turns things on if off, and on if off. While there are work-around for such limitations, it is much better to avoid the problem if possible by utilizing a device that has serial ports. So all else being equal, you want to buy a TV or Blu-ray player which has a serial port rather than resorting to controlling it with IR.

8 Digital I/O ports

“I/O” stands for Input or Output. In this context, it means a wire connection from/to the controller. Being a single wire, an I/O port can only transmit or receive a “binary” message of 1 or 0. Hence the use of the term “Digital” by AMX.

Unlike serial ports where a single wire transmits entire messages, these ports communicate simply whether something is on or off. In output mode, this is similar to using relays as above. However, electrically they look different and so they are not always compatible with other devices that expect relay (“dry”) contacts.

The input mode is useful for example to receive data from simple devices. Let’s say you have a door sensor in a closet and you like the light in there to come on when someone opens that door and turn off the light when it is closed. To do this we would install a simple mechanical switch in the door mechanism and then “watch” for it changing in the controller (software) by connecting it to one of these input lines on the controller. Once we see the input going from zero to one -- meaning the door is open -- we send a command to the lighting subsystem to turn on the closet light. When the door is closed, the value on the input port changes back to zero and we use that to turn off the light. The beauty of this is that it costs very little to implement. The input device is just a simple switch as opposed to a small computer with a serial port.

(2) Communication Networks: AxLink and Ethernet (TCP/IP)

Ethernet communication is the same as what you have in your PC. It is a high-speed serial port which is used to communicate with other devices. The Ethernet port usually runs at a speed of 100 Mbit/sec which is about 500 to 1000 times faster than a serial port enabling it to move large amounts of data in less time.

Ethernet connections can be used to "talk" to other devices as long as they sport the same connection. One example would be connecting the AMX controller to your lighting system using this single cable. The the two devices can then communicate back and forth and at high speed. While serial ports can and very often is used in this situation, Ethernet provides better performance in certain situation where a lot of lighting data needs to be communicated.

Yet another use is for remote diagnostic, and updating of the control software in the system. By connecting the AMX controller to your home network, our system designers can connect to your system remotely and update its software. This is saves travel time and expense. The same thing can be done using the serial port but that would require a phone line but as you can slow down the work substantially and require proximity and availability of the phone line.

Processor Speed 404 MIPS

This is the speed of the microprocessor that runs the control software. No, MIPS is not another name for Gigahertz that you might be familiar with from your PC spec sheet. Old time computer geeks might remember this term being an acronym for Millions of Instructions Per Second. In reality, it doesn’t really mean that. To understand the true meaning requires a bit of history.

A now defunct minicomputer company called Digital Equipment Corporation (DEC) used to be the leading provider of mid-tier computers to businesses. In 1977, DEC introduced a new machine called the VAX 780. That machine was thought to be able to run at speed of one million instructions per second (this was later shown to be incorrect but the history was left written as it was).

Fast forward a few years later and a benchmark called Dhrystone was written to measure performance of computer systems. The benchmark outputs a number which is the number of “Dhrystones” the computer is able to compute in the predetermined time. To arrive at a MIPS rating for a different computer, the same benchmark is run and then its Dhrystone rating divided by the value produced by VAX 780. Since the later is assumed to be “one MIPS,” then whatever that ratio is will give you the overall MIPS rating of the computer in question.

Putting what we just learned to practice, the microprocessor used in this AMX controller is 404 times faster than VAX 780. Typical VAX computer of the time costs hundreds of thousands of dollars and was the size of multiple refrigerators. So achieving such performance in such a tiny package (similar to a DVD player) shows how far we have come!

But then again maybe not. Let’s translate the MIPS rating into something we might be more familiar with: a personal computer. As of this writing (2010) the Intel Core i5 powering many PCs is rated at over 5500 MIPS. That is one heck of a speed difference!

Fear not. Control software requires very little CPU horsepower to do its job. We get an event, run through some logic and decide to take some action. This is a fraction of code that for example your web browser uses to display this web page. So proportionally, we need far fewer MIPS in our application than your PC.

64 MB RAM

OK, another let down from the PC world. We have 64 Megabytes of memory instead of 4+ Gigabytes (thousand megabyte) of memory in a modern PC. Fortunately, our control programs are very efficient and small so this is plenty of space to get the job done even in complex scenarios.

256 MB Compact Flash (upgradeable to 1 G)

Normal computer memory loses its content when you turn it off (whether it is in your PC or this controller). Flash memory as in the type you use in your camera or USB thumb drives, retains its data even when turned off. That is quite useful as you can store permanent data as if you had a little hard disk.

This controller has an expandable flash memory of 256 megabytes which is plenty to hold control software and any data it needs to store in case of power failure.

1 MB Non-Volatile Memory

This just another name for flash memory. It holds the software that is loaded into the device from the factory and in some cases, the control software written by your system integrator.

Summary

So there you have it. You now know more about the heart of the automation system than most people including some who install them!

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