Intercom customer-cashier

In a whole series of life situations, for example, when a client and a cashier communicate at a station, at a bank, at a gas station, etc., an intercom helps them. Indeed, in these cases it is unlikely to be able to talk without such a technical intermediary. In addition, at the factory or in the office, there is always the need for remote communication between the director and the secretary, the boss and subordinates, which is also provided by similar devices called intercoms or interphones abroad.

Intercom: general description

The first thing to note is the assignment of all intercoms of the class in question to wired communication devices. Microphones and speakers on either side of the dividing speaking partition are connected by electrical wires. Even if such a device is called "wireless" (the English term wireless is used abroad), this is a very conditional name, because the wires of the power supply network with voltage of 220 V are used to transmit the audio signal.

If a voice message is reproduced by a stationary speaker, then such a speakerphone is usually called an intercom. If there are subscribers instead of the usual handsets there is an interphone.

A typical intercom is a simplex device, that is, subscribers cannot talk at the same time. Interphones are always duplex intercoms, like a regular telephone.

Both types of devices can be both single- (for two subscribers) and multi-channel.

The latter can be built either according to the radial scheme with one central and multiple subscriber units, or according to the “common bus” scheme with an arbitrary number of subscriber units at the same level.

Two-wire communication lines of intercoms and interphones

When industrial production of equipment for wired intercom systems began in the early 70s, it required the development of a single standard, a description of the electrical and logical properties of the communication channel included in any intercom for compatibility of equipment from different manufacturers.

Soon, such a standard appeared that described a three-wire communication line, in which the sound signal itself is transmitted through two wires , and the third wire is the “plus” of the line power (the common wire is one of the sound wires). Such a communication line played the role of a “common bus”, to which all equal subscribers were connected, that is, everyone was hearing the speaker at the moment. Unofficially, this type of intercom organization was called a party line, which means “shared line”.

However, another name has taken root better - a two-wire line (two wire, TW). It is due to the fact that in a three-wire line, only two wires are used directly for sound transmission. It should be emphasized that the term party line does not define the applicable communication standard, but only means the principle of its organization - “all with everyone”. But any two-wire intercom could work only on this principle. As a result, they began to associate it only with them, although the party line can be organized using any (for example, four-wire) connected standard.

Modern modifications of TW-lines of intercoms and interphones

Despite their considerable age, two-wire (more precisely, three-wire) communication lines continue to be widely used in modern devices. As a rule, they are found in three versions.

Thus, the well-known manufacturer Clear Com uses in its equipment a line with one common wire for power and audio signal, one signal wire and one power wire.

The second modification used by Audiocom includes a pair of audio wires, each of which is powered, and a common wire.

And finally, the third modification - with one common power wire, one wire for the first signal and power and a wire for another signal.

Four wire communication lines

In some modern intercoms and interphones for organizing noise-free duplex communication, the received and transmitted audio signals are galvanically isolated from each other, i.e., there are two separate signal wires and two common wires in the communication line. In such a four-channel line, power is transmitted via signal wires. At the same time, the power sources of modern devices are characterized by a very low level of (their own) interference created by them.

Components of intercoms and interphones

These include power sources, central consoles (for multichannel intercoms with a radial organization), subscriber kits (consoles, calling panels), connecting cables, etc.

The constant voltage power supply is usually centralized. However, some subscriber consoles (especially remote over a considerable distance) may have their own power sources. Many intercoms are connected to the mains, but there are devices powered by two or three series-connected 9-volt batteries.

Subscriber kits are mainly available in three versions:

- with a microphone headset;

- in the form of a calling panel "speaker-microphone";

- with a combination of a headset and speaker;

- in the form of a telephone receiver.

Their construct can also be represented by wall or desktop options. Typically, subscriber kits are equipped with a microphone button (switch) (“Transfer” button), sometimes combined with a “Call” indicator, and a volume control for phones (in the version with a headset). The subscriber set in the form of a calling panel (option "speaker-microphone") usually does not contain controls.

Intercom customer-cashier

In order to provide communication between the client and the employee of the enterprise (manager, cashier, administrator), a special type of client-cashier communicators has been created, since they are most widely used at the cash desks of banks, cultural facilities, air, bus and railway stations. Such loud-speaking intercoms occupy an intermediate position between intercoms and interphones, since they are usually duplex, but may be able to switch to simplex communication mode from the cashier. This is necessary, for example, so that he can consult with his management about the problems of the client, without passing this conversation to his side. At the same time, the client himself can be heard at the box office.

Features of voice transmission in client-cashier devices

The cashier’s workplace is usually soundproofed from the premises where clients are located. Therefore, for such devices it is important to transmit the client’s speech with maximum filtering of extraneous noise.

Manufacturers specifically narrow the spectrum of the transmitted signal to a frequency band from 100 Hz to 8.2 (sometimes 9.5) kHz, into which any human voice is known to fall. Sounds of a higher frequency only distort speech, interfering with its understanding.

Usually, special algorithms for digital signal processing, implemented by electronic microchips of audio processors, for example, Motorola, are used to isolate the client’s voice from the total noise. Due to the accuracy and speed of signal processing, such a digital intercom transmits even the first phrase distinctly, without “swallowing” the first sounds.

Single channel intercoms

Such an intercom has the main electronic equipment in the console on the side of the cashier. Only a remote panel with a speaker and a microphone is mounted on the client side. To protect against vandals, the speaker is covered with a metal (usually aluminum) cover. Depending on the operating conditions, the client panel can also be in wind and moisture-proof versions with a call button, usually made in the form of a membrane, which prevents moisture from flowing inside.

If several cashiers work simultaneously at the cash desk, it is preferable to equip their workstations with client-cashier systems with headphones or a headset. At the same time, the speech of colleagues will not distract the attention of any of the cashiers focused only on their customers.

Multichannel devices

The cashier of the gas station (or the central security post of the enterprise) must be connected to several anti-vandal client panels located in different places on the fuel dispensers (or peripheral posts). Therefore, the central console must be multi-channel, and at the gas station - also provide dispatch functions by transmitting high-profile announcements. To do this, it must have a linear output connected to a sound amplifier connected to the speakers.

A multi-channel client-cashier intercom, including communication lines with fuel dispensers and a speakerphone subsystem controlled from a single central gas station console, significantly speeds up customer service and also allows the cashier to inform the refueling station of the necessary information.

Organization of multi-channel intercom

So, what kind of equipment, in addition to the central console and calling panels, includes a multi-channel intercom? Its circuit contains the switch unit included in the kit. It is connected by a four-wire cable line to the central console. Each calling panel is connected to the switch unit with a separate wire.

The central control panel of the device contains a set of digital buttons for selecting call panels. To ensure that the cashier’s messages are clearly audible in gas station conditions, these panels provide for his voice output to the speakerphone through an external amplifier and loudspeakers made in the 2nd performance category - “Work under a canopy”.

Features of intercoms with speakerphone

The hands-free intercom (for gas stations and other facilities) is designed with some design features in order to simplify the cashier’s communication with customers and refuelers. To ensure the cashier’s communication with interlocutors at a distance of several tens (or even hundreds) meters from the desk, the microphone of his desk must be highly sensitive and have wind protection for voice transmission with high intelligibility regardless of the source of wind noise (for example, from fans). To confidently disassemble the interlocutors' speech at a high level of noise, the central console and calling panels are equipped with high-volume speakers from Mylar, which have a high specific area of ​​the diffusers.

Popular Commax Intercoms

The Commax VTA-2D single-channel intercom, the client-cashier type, provides duplex communication (without the need to press the Transfer buttons). Consists of two identical subscriber sets in the form of “speaker-microphone” calling panels in gray plastic cases. There are wall and tabletop panels. It is powered by a 12 V DC source with a maximum consumption of 3.5 watts. Its cost is about 1700 rubles.

Also, the Commax DD-205 single-channel client-cashier duplex device contains a cashier console with flexible microphone mount, electronic adjustment of its sensitivity, and light and sound indication of adjustments. The package includes a vandal-proof client panel. The device is controlled by a Motorola audio processor. Its cost is about 6000 rubles.