Apress - Smart Home Automation with Linux (2010)- P27 pptx

CHAPTER 3 ■ MEDIA SYSTEMS 108 If you are wanting to distribute high-definition images around your house, then you currently have to consider the more expensive options, such as matrix switchers, because the current crop is focused around RCA sockets. Switching The cheapest piece of necessary equipment is an AV switch box, or AV source selector box. This provides multiple inputs for your various devices, DVD, PVR, VCR, and so on, and routes one of these to the TV output. Most equipment give you the option of using either S-Video, RCA, or SCART inputs. This naturally requires that the TV is always set to receive the input from the box, not its internal tuner. There are many switch boxes available, so the features to consider are as follows. Infrared remote control: This is a necessity, really. Since this box is now taking the place of your TV channel changer, it must have the functionality you’d expect from the TV which at a bare minimum is a remote control. Active or passive devices: Active units have a small amplifier in them and therefore need power. These ensure a strong signal but at the expense of a lower quality on the cheaper models, since their internal amplifier isn’t as good as the ones on the DVD player or on a TV. Passive devices have no such amplification and are more likely to lack an IR remote. Input connections: Although some boxes provide S-Video, RCA, and SCART, for each input they might not be interconnected. That is, the RCA input socket might only be connected to the RCA output socket, and not to the S-Video or SCART. Since you only have one output to the TV, this requires you to compensate for adapting your interconnects to the most common form factor and to convert every other input into the same type of plug (there are converters available in most electronic shops). You then use the equivalent output. This part of the specification isn’t usually well documented, so check the shops return policy first. Number of inputs: Count the devices you have, add to this the number of devices you want to buy, and add two more for good measure! Once this limit has been exceeded, you have no real choice but to buy a bigger switch box. You can chain them, which is troublesome and lowers quality, or you can use a separate EXT input on the TV for each switch box, which is equally annoying but has fewer electronics in the signal chain. The biggest omission on the entry-level switch boxes is the facility to switch between stereo audio and 5.1 surround. Consequently, you will need a separate set of cables from the 5.1 output of the DVD (controlling the 5.1 speakers) and the stereo output of the DVD connected to your switch box. Splitting and Merging Once you have the AV signal ready, you might want to split it so that the video part of the signal goes the TV, while the audio makes its way into the line-input on a HiFi. There are two main ways of achieving this. The first is the easy way and works if your TV has its own stereo-out sockets, since they can be connected from the TV to the HiFi directly without a problem. The other way is to split the signal coming out the switch box into two (or more) outputs—one for the TV and one for the HiFi. This approach CHAPTER 3 ■ MEDIA SYSTEMS 109 means you won’t be able to use the HiFi to amplify any stations selected using the TV’s internal tuner, but this can be rectified by watching the TV solely through a receiver (such as a cable tuner or digibox) or VCR, which has been plugged into the switch box. This can be done in a variety of ways. The cheapest is the use two Y-cables (aka Y-adapters), one each for the left and right audio signals. These provide two identical outputs from one input and require no power. These work well when splitting audio signals but can be less than satisfactory when used on video signals because of impedance problems. If the quality isn’t good enough, then you need a more involved splitter box. A splitter box acts like its Y-cable counterpart but usually has an amplifier in it to stop signal degradation. This also allows it to provide more outputs for very little extra cost, allowing you to run a separate pair of cables into the kitchen and dining room, say. If neither of these is suitable, you can split the output after the amplifier stage by running multiple speaker cables. Wiring Looms Wiring looms is where cables carry a powerful signal (pun intended!) to drive various passive speakers around your house. Consequently we call this passive distribution. You should create one loom for each area of the house where the same audio content is likely to be heard, because local control here is more difficult (unless you get speakers with a volume control or want to hack one yourself). In a room layout as shown in Figure 3-1, you have little privacy between the living room and the dining area, so these would be on the same loom, as would the kitchen since you probably want to pop in and out of the kitchen without missing the music or TV output. If an extension, such as a sun room or den, were added to the rear of the house, on the other hand, it would be considered a separate area with a different lifestyle purpose and would not be on the same loom. Instead, any music in there should be provided over IP. Figure 3-1. A standard downstairs plan CHAPTER 3 ■ MEDIA SYSTEMS 110 The first component in a wiring loom is the main power amplifier, taking its input from the switch box we covered previously. Normally, this will drive one set of speakers, although some amplifiers provide extra outputs for additional sets. It’s rare to have more than two and even rarer to have more than a couple of rooms on the same loom, so you don’t often need any more equipment. In those cases where you need more outputs, you can add a speaker control box into the chain. This takes a single speaker output and splits it into many. These additional speaker cables can be run into the other rooms and wired directly into other speakers without the need for power. This is the main advantage of this approach; namely, the cables are easier to run (the holes are smaller because there are no bulky plugs on the end), and there’s no need for power sockets nearby, enabling you to add music to the bathroom where media players would not be practical or possible. ■ Note Special waterproof speakers are necessary for bathroom use, which have sealed cones and baskets so they can cope with water and humidity. Various models exist, including flush-mounting ones that can be placed in the ceiling. Provided you use a reasonable quality of speaker cable, the signal will not dissipate over the distances involved. ■ Note If you have two outputs on your amplifier but want to control three sets of speakers, then connect the control box to the second of the outputs and your primary speakers (on which you’re more likely to do critical listening) on the first. There’s no point in adding a step in the chain if you don’t need to do so. Wireless AV Distribution Running cables is not difficult but should be done with care to avoid drilling through power cables, water, and gas pipes. With this in mind, there are a few pieces of hardware now available, such as the AV video senders you saw in Chapter 1, built to solely wirelessly distribute audio signals. For the most part, they offer a solution of convenience, but landscape speakers, which are built to exist outside and made to look like rocks (for example), provide the only practical solution. They must also be powered from batteries. Matrix Switchers For most home applications, a standard switch box is enough to control your AV setup. If you have a Blu- ray player or other high-definition equipment, you will generally plug it straight into the TV using HDMI CHAPTER 3 ■ MEDIA SYSTEMS 111 because this eliminates all other components from the signal chain. And, alas, none of the reasonably priced switch boxes I’ve seen support HDMI. 8 Furthermore, if you want to distribute two of your input devices (such as PVR or DVD) to two different places, then you’ll find that you can’t, because the switch only provides a single output. Both of these limitations can be overcome with matrix switchers. They have a broader range of inputs (often including VGA) and can send the input signal from any one of (say) eight inputs to any (or all) of the outputs, which often number four or more. This allows the most powerful AV control method possible, with all your hardware being located in a single place and the results carried by cable to each room in the house. Also, since this is professional-level equipment, it usually comes with a serial port, making it easy for a computer to control it directly. Utilizing a matrix switcher in your setup is a big step, not just financially. To make full use of the device, you will need to keep your AV equipment in close proximity to the switcher. Furthermore, not only will you have the usual mess of cables entering the switcher, but you’ll have an additional mess of cables leaving it—one set to every room. And for the most part, matrix switchers are not small. Consequently, it is impractical to have them in the living room. Instead, you need to consider a room or a hidden cabinet into which the switcher and AV equipment can be placed. With the equipment now hidden away, the purchase of an IR relay or gateway to retransmit IR signals to the devices inside the cabinet is essential. It will be needed for the matrix switcher and may come as part of the package, so buy it second! The output connectors vary between matrix switchers. Some provide the output as an AV signal, like S-Video or other domestic formats, making it very simple to connect other receivers into your home and have it work. Others are intended for hotels and conference centers and encode each input into a proprietary protocol so the output can be transmitted over Ethernet. This case requires an additional receiver unit for each room, thus saving the effort of running specific AV cables around your house. And because the data is traveling over your existing Cat5 cables, you can usually send the IR control data back the same way, saving you on the IR relays that are so often necessary. ■ Note If the majority of your source media is stored on a hard drive, then you probably won’t need a matrix switcher at all, since it can be transmitted by Cat5 to small Linux-based head units using software-streaming solutions such as VLC. For those evil geniuses living in an underground volcano, a matrix switcher provides a mission- control room scenario for very little extra cost! After all, you can connect one set of outputs to a row of small, cheap TV sets and watch multiple sources at the same time. 8 There are a few HDMI switch boxes now appearing on the market, but these contain only HDMI switching such as the one shown at http://www.tvcables.co.uk/cgi-bin/tvcables/hdmi-matrix-switch-4x2.html. They are still hugely expensive, so realistically the choice now is either to have local processing of data or to distribute only a standard-definition version of the picture around the house. CHAPTER 3 ■ MEDIA SYSTEMS 112 Control Having the ability to play music in every room is one thing. Being able to control from every room is something else. This is the next step in the chain but one that is not always necessary. Imagine the house layout shown in Figure 3-1. This needs no complex control systems since the living room is controlled locally, and the kitchen audio stream is usually switched on when you start preparing dinner and switched off once you’ve finished. Consequently, being forced to control the AV from the living room is not an issue. Nor is it an effort to wire several rooms together (for example, the master bedroom, bathroom, and den) with a speaker control box and leave them on all the time. In this case, it is likely that although two of the three rooms may be unoccupied for most of the day, when one of them is in use, it is at the exclusion of the others, making it unnecessary to apply the cost or effort in providing separate controls for each room. Local Control Being able to control the device (such as a speaker or stereo amplifier) from the device itself is the most logical solution, and fortunately most head units provide this automatically. A local amplifier or set of powered (active) speakers, for example, will have a volume control on its front and a means to change the source input. Therefore, any distribution system using AV or Cat5 cables will have control built in. To affect the volume of a passive speaker (maybe one fed from a remote speaker control box), you need an attenuator placed in series with the speaker. For low-power solutions, it is possible to mount a double logarithmic potentiometer directly into the speaker mountings. (You need logarithmic because this is the way volume works, and you want double for stereo volume control.) This won’t give you particularly good fidelity, since the two tracks inside the device won’t be well matched with each other and some frequencies made be lost, but it will be cheap. For a better solution, there are custom attenuators that come in a basic wall unit and provide a better-looking control mechanism, with improved quality. If your speakers are not wall-mounted, then you will have to run an extra set of cables either inside the wall cavity or in external tracks. Consequently, the cable runs from the speaker control box to the switch and then to the speaker. It is better to consider this approach before laying other cables. Apart from the bathroom (where such attenuators need to be waterproof), this method of control is usually impractical and better served with active head units or no form of local control at all. Remote-Control Methods Your house will come alive with the sound of music. Until you’ve lived with music in every room, you cannot underestimate the difference it makes. Being able to change the volume is nice, but not necessary, because each album is normalized to be consistent within itself. However, if you’re randomizing the tracks, then the volume can vary wildly, necessitating a local volume control. And if you’re introducing such functionality, you’ll often want more involved local control to skip those random tracks you don’t want to hear. Such functionality requires more hardware. Direct Control Standard HiFi equipment is invariably supplied with an IR remote, making it possible to place an IR relay receiver in each room and line up its transmitter with the receiver eye on the device. Small receivers can be mounted in-wall alongside, or instead of, a light switch and be powered by batteries. . http://www.tvcables.co.uk/cgi-bin/tvcables/hdmi-matrix-switch-4x2.html. They are still hugely expensive, so realistically the choice now is either to have local processing of data or to distribute only a standard-definition. Cat5 to small Linux- based head units using software-streaming solutions such as VLC. For those evil geniuses living in an underground volcano, a matrix switcher provides a mission- control room. and better served with active head units or no form of local control at all. Remote-Control Methods Your house will come alive with the sound of music. Until you’ve lived with music in every