Multi-room video audio system. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Disagreements in the family when using one video-audio complex (VCR, TV, CD player, AV-pe-sever, etc.) can be avoided if the apartment is equipped with a radio-frequency distribution network and a remote control system. Additionally, at a minimum, you will need another TV and a speaker system. How to do this is described in the published article.

In recent years, the so-called multi-room systems (MULTI-ROOM) have found distribution abroad, providing the operation of one set of video and audio equipment for several residential premises. For example, having a TV set (TV), a VCR (VCR), an AV receiver and a CD player (CD player) in one room, you can get the opportunity to watch a football match in this room by the head of the family, a movie with a rented video cassette by the hostess of the house in the kitchen and listening to CDs by young people in the children's room. And all this at the same time. The necessary requirements for providing the complex are the presence of a second TV in the kitchen (it is possible to have a third TV in the children's room) and a simple acoustic system (AC) in the children's room.

How to organize a simple multi-room complex and will be discussed. One of the options for placing its components is shown in Fig. 1. The complex consists of a distribution system for audio and video signals and a remote control device (RC).

The most simple implementation is to supply sound signals from an AV receiver (or UMZCH) to speakers in room 3. The connecting cable can be a regular wire used for electrical wiring, with a core cross section of at least 0,75 mm2 (of course, we are not talking about Hi systems -Fi). Before laying the wire, it is necessary to mark one of the wires with some kind of icon, for example, "+", at both ends, then it will be difficult to do this. It is necessary to connect the speakers with the correct polarity, otherwise the stereo panorama will be distorted. In cases where the AV receiver (or UMZCH) does not have "B" outputs for the second pair of speakers, you will need to install an external switch, which can be used as toggle switches for high-current (more than 6 A) circuits. They use reliable silver-plated contacts.

TV in rooms 2 and 3 is connected via high frequency coaxial TV cable. When purchasing it, you need to pay attention to the quality of the braid. It should be dense, without gaps, with copper, possibly tinned, conductors. The connection diagram is shown in fig. 2 and the placement of high-frequency elements - in fig. 2b.

To implement such a network, you will need broadband splitters 1, 3-5 and an adder 2. You can buy them at any radio market or in stores selling radio components. They are made on ferrite rings and have low losses. Structurally, they are most often assembled in a box with three standard TV jacks. When buying, you must choose products of broadband (MB - UHF) performance. You will need to make four cables for internal connections (Vn) on your own, that is, solder the plugs to the cable sections of the required length. On sale there are the same splitters with a cable segment and a plug at the input, which can be used in positions 3-5. In this case, you only need to make the cable Vn1 yourself.

The design of the device can be very different, up to the placement of all elements inside the equipment cabinet or behind it. It is most convenient and simple to use a plastic box of suitable dimensions for this purpose. It is only necessary to glue splitters and an adder to its bottom, having previously drilled holes for the connectors. All connectors must be labelled.

A few words about operation. Since VCRs usually have a UHF RF output, you should set the frequency of its internal oscillator so that the VCR signal does not interfere with the reception of local UHF stations. Tuning is usually possible within the range from the 36th to the 42nd channels (the tuning procedure is described in the instructions for the VCR).

Television and VHF FM signals to the input of the device come from the "antenna". It is written in quotation marks because in each case there may be either a broadband antenna, or two or three or more antennas, or a cable from the house network in the entrance, or others. Often, VHF FM signals are fed to an AV receiver or tuner from a separate antenna. In this case, the splitter 4 and the VnZ cable are not needed. And if there are only two TVs, both the splitter 5 and the Vn4 cable are not needed. There may be many options.

Let's move on to the consideration of the main component of a multi-room complex - a remote control device for video-audio components (see Fig. 1), consisting of photodetectors in rooms 2, 3 and a transmitter in room 1. The principle of operation of the device is very simple. Infrared photodetectors located in rooms 2 and 3 react to the commands of the remote control and form impulse signals transmitted by wire to the transmitter in room 1, which generates infrared flashes that control all components of the complex.

To use the VCR in room 2, it is only necessary to insert the required cassette into it, and then the VM remote control will implement any VM control commands. Similarly, the respective remotes control the components in the main room and from room 3.

The easiest way for the practical implementation of a multi-room remote control device is the use of modern industrial photodetectors, which are an integrated microcircuit of small size with three leads. Such photodetectors are reliably protected from external illumination and interference, and this circumstance is very important, since it is not easy to ensure high noise immunity when manufacturing a photodiode signal amplifier on your own. In this case, radio amateurs of average qualification can use the recommendations in the book by I. A. Remezantsev, A. V. Atsyukovsky "Remote controls for household equipment" (M .: Mark Print & Publisher, 1999, pp. 108-116), where schemes of photodetectors are given and advice on their use.

Foreign firms produce a large number of integrated photodetectors. Unfortunately, the author does not have complete reference information on them, therefore, the further presentation is based on information obtained experimentally.

The RPM675CBRX10 photodetector is used in many MATSUSHITA (PANASONIC) VCRs. Its appearance, pinout and oscillogram of the output signal are shown in fig. 3, a and b. This miniature photodetector does not respond to various interferences from sources of visible light of fairly high intensity (tested in a small room with two lamps of 150 W each). It is therefore extremely easy to install, right down to sticking it to a wall, skirting board, etc. with adhesive tape. No other elements are required. Connection to the transmitter is possible with any wire up to 5 m long. For longer distances, a twisted-pair output signal may be required.

An important question is where to buy such a device. They can now be bought from radio markets, specialty stores and by mail through specialized mail order companies. Prices for photodetectors at parcel agencies are within 2 ... 10 US dollars.

An alternative option is to use the photodetectors located in the TVs themselves in rooms 2 and 3. In this case, you will need to do a little "research" work, for which you need an oscilloscope. The purpose of the work is to determine the polarity of the output pulses of the photodetector. They need to be removed through a buffer cascade. The easiest way to do it is on the DTC143TS transistor. Its pinout, parameters and switching circuit are shown in fig. 3, c and d. The transistor (price ≈ 0,25 US dollars) can be replaced by a transistor of the KT315 series, etc. with an external resistor in the base circuit with a resistance of 47 kOhm. Moreover, the resistor R1, shown in Fig. 3,d, can be placed outside the TV.

The schematic diagram of the entire remote control is shown in fig. 4. Photodetectors Pr1, Pr2 are located in rooms 2 and 3, respectively. Blocking capacitors C1 and C2 are soldered to the terminals of the photodetectors.

The photodetectors are powered by a battery of galvanic cells located in the transmitter (316, 343, etc.). The mains power supply can also be used instead of the GB1 battery. It should be noted that the entire device in standby mode (in the absence of remote control commands) consumes practically no energy, i.e. the battery will last a long time.

When a command is given from the remote controls of the equipment through photodetectors and connecting lines, pulses with a swing of about 1 V arrive at the inputs of the DD1 microcircuit (pins 2, 4,5), as shown in Fig. 3,6. In the microcircuit, they are inverted and pass through the emitter follower on the transistor VT1 to the power amplifier on the transistor VT2, the load of which is the IR emitting diode VD1. Its radiation controls the video and audio equipment in room 1. It should be noted that if you simultaneously press the buttons on the remote controls in rooms 2 and 3, the device will not work. However, such a situation is unlikely.

It is necessary to dwell on some aspects of practical implementation. First of all, this concerns the choice of photodetectors Pr1 and Pr2. Not every radio amateur will be able to purchase exactly the photodetector, which is indicated in Fig. 3 and 4. But this is not a big problem. You can use most of the other, more affordable ones. They are usually made in a small metal box with three leads and a "peephole" for a phototransistor. Usually sellers in the radio markets can not say anything about the parameters of photodetectors.

Therefore, you will need to deal with this issue yourself, which will require an oscilloscope, a 5 V power supply and any remote control

First of all, you need to determine the pinout of the acquired photodetector. The output of the common wire (case) in it is usually connected to the screen. Connecting to it the negative conductor of the power source and the case (total) of the oscilloscope, apply a voltage of +5 V to any of the remaining outputs of the photodetector through a 1 kΩ resistor. The input of the oscilloscope is connected to another output and, having directed the emitter of the remote control to the "peephole" of the photodetector, any command is given. If at the same time pulses appear on the oscilloscope screen, the pinout (output and power output) is determined, if not, the conductors of the positive output of the power source and the oscilloscope input are interchanged.

In practice, of course, there may be other situations, for example, in the case of building the output stage of a photodetector according to an open collector (drain) scheme. In this case, they do the same, but apply a voltage of +5 V to the input of the oscilloscope through a resistor with a resistance of 5-10 kOhm.

During operation, the polarity of the output pulses of the photodetector is also observed. If it does not correspond to that shown in Fig. 3b, then into the transmitter path according to the scheme in Fig. 4, you need to add an additional inverter from the DD1 chip (for example, with an input from closed pins 5, 6 and an output - pin 4).

In the course of further "research" determine the sensitivity of the photodetector to external illumination, as well as the sensitivity to the signal at different positions of the remote control. Based on the results obtained, the most convenient location of photodetectors in the rooms is found. Similar actions are carried out when placing the transmitter in room 1.

Before installing the system, the operability of the entire device with the required length of connecting lines is checked. In the presence of particularly strong external interference, it is necessary to use a shielded wire for signal circuits.

To increase the IR radiation zone, it is possible to connect a second IR emitting diode VD2 through the transistor VT3, as shown by the dashed line in Fig. 4.

The KT646A transistor (VT2, VT3) can be replaced with 2SC1956Y 2SD1616, 2SD1781, 2SD1328, and the AL 107A (VD1, VD2) diode can be replaced with an IR emitting diode from the AL 156 or EL-1L2, TS1P7700, LN66A series.

In conclusion, it should be noted that such systems can be used for remote control of many other household appliances, lighting, etc.

Author: Yu.Petropavlovsky, Taganrog

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