Small-sized intercom. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Telephony

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Despite the fact that many descriptions of intercoms have been published on the pages of the Radio magazine, another design is proposed that contains interesting solutions.

The intercom (PU) provides communication from the front door to the remote control located in the house or apartment. The dialogue between subscribers occurs by switching modes (reception - transmission) with the button on the remote control.

In contrast to the PU, similar in purpose, published in [1), the proposed device has some advantages. Firstly, it provides loudspeaker communication at a distance of 100 m or more over a two-wire line. Secondly, its output power reaches 0,4W. And besides, there are no microphones in the device - their role is played by dynamic heads.

The basis of the device (Fig. 1) is a universal AF amplifier based on an operational amplifier (op-amp) K157UD1, developed in the laboratory of the Radio magazine [2]. To switch the electrical circuits of the device, a small-sized relay RES-60 (K1) with two groups of switching contacts (K1.1 and K1.2) was used.

(click to enlarge)

The control panel is always in the "Receive" mode when the relay is de-energized and the contacts of its groups occupy the position shown in the diagram. As soon as a sound is heard outside the door, it is converted by the dynamic head BA2 into an electrical signal that passes through the closed contacts of group K1.2 and capacitor C1 to the input of the DA1 microcircuit (pin 9). Then the signal is amplified "and from the output of the op-amp (pin 6) through the circuit capacitor C5 - group contacts K1.1 - clamp XT1 - wire L1 of the communication line enters the pools, where through the closed contacts of the button SB1 and capacitor C1 it reaches the head BA1 reproducing sound {of course, the signal transmission involves the circuit common wire - clamp XT2 - wire L2).

In the "Transfer" mode, the PU is transferred by pressing the SB 1 button. This creates the following DC circuit: plus the power source - resistor R1 - winding of the relay K1 - terminal XT1 - wire L1 - closed button contacts - collector-emitter section of the transistor - wire L2 - terminal XT2 - minus the power source. Through this circuit, power is supplied to the transistor cascade of the remote control, the relay is activated. switching contacts of groups K1.1 and K1,2, the circuits are switched: the output of the amplifier is connected to the head of the VAZ, and its input is connected to the remote control via the wires of the communication line.

Now we can speak. The signal 34 from the head VD1 through the capacitor C1 enters the base of the transistor VT1, is amplified by it and is allocated to the load of the cascade - the relay winding. Further, the signal passes through the closed contacts KTJ, a divider of resistors R2-R4 and an isolation capacitor to the input of the main amplifier. From the output of the amplifier, the signal enters through the capacitor C6 and the closed contacts of the K1.2 group to the head BA2, from which the visitor hears the answer. The sound volume is adjusted in advance by a variable resistor R4. By pressing and releasing the button on the remote control, they are talking with the visitor.

The device is powered by a rectifier or ready-made adapter with an output voltage of 9 8 and a load current of at least 100 mA. In standby mode, the device consumes no more than 4 mA, and in the "Transfer" mode, the current increases to 100 mA.

The length of the communication line wires, as mentioned above, can reach 100 m or more without affecting the sound quality. This is achieved by pre-amplifying the signal 34 by a transistor stage directly in the console, which reduces the effect of pickups and allows the use of even unshielded wires. In order to be able to negotiate, say, from different rooms, in each of them you will have to install clamps or sockets and connect a portable remote control to them. Or, in general, make two remotes, place them in the right places and connect them in parallel.

In the device, it is permissible to use any transistor of the KTZ15 series with a base current transfer coefficient of at least 30, Relay K1 - RES60, passport RS4,5b9D35-02 or RS4,569,435-07 with a winding with a resistance of 230 ... 310 Ohm and a trip current of 22,5 mA. Of course, another small-sized relay with similar parameters will do, but then you will have to change the drawing of the printed circuit board.

Dynamic head VA1 - small-sized (0,25GDSH-2: 0,1GD13-50) with a voice coil with a resistance of 50 Ohms, VAZ - 1 GD8-A with a coil with a resistance of 8 Ohms, Diode VD1 - any of the series VD521, VD522. Oxide capacitors - K50-6, K53-1; C2 - MBM, KM-6; the rest - ceramic types KM, KD, All resistors - MYAT-0,125, button - KM1.

The details of the main amplifier are mounted on a printed circuit board (Fig. 2) with dimensions of 50x60 mm from one-sided foil fiberglass. The board is installed in a separate housing, for example, from a subscriber loudspeaker. Here you can install the power supply.

Details of the console are placed in a box with dimensions of 30x60x80 mm. A dynamic head is installed on its front side. opposite the diffuser of which holes are pre-drilled. A button is attached to the side wall. The remote control is connected to the amplifier terminals with a stranded wire (MGSHV, MTV, etc.).

The PU nodes are located in different ways. Here is one of the options, the VD2 dynamic head is fixed on the inside of the front door above the viewing eye. Opposite the diffuser, holes with a diameter of 4 ... 6 mm should be drilled in the door. The main amplifier is placed near the door 8 in the corridor, which is connected to the head with a flexible (better shielded) wire with a so-called compensation loop - it eliminates the wire break when the door is opened.

Establishing PU comes down to matching the transistor cascade of the remote control with the relay used. It consists in selecting the resistor R1 of the main amplifier of such resistance that when the button is pressed, the relay is activated (at a current of 22 ...

Literature

1. Prokoltsev Yu. Intercom "Who's there?" - Radio, 1992 / No. 9, p. 52.
2. Polyakov V. Universal amplifier ZCH.-Radio, 1994, No. 12, p. 34,35.

Author: Yu. Ivanov, Omsk; Publication: cxem.net

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