The device and circuit intercom

Technical means of restricting the penetration of unwanted persons into the protected area are increasingly being used to improve the safety of homes and industrial premises. Among them, intercom systems that allow you to remotely control visitors and control their access are popular, and their designs are constantly being improved.

The device and the intercom operation scheme are created for specific consumer requests. They differ in the principles of construction, elemental base, installation, maintenance, operation technologies.

Features of building intercom systems

The following principles are used in the work of doorphone circuits that control and manage people's access:

1. the creation of a closed territory with the possibility of restricting the passage of visitors by technical means based on automatic locking devices;

2. organization of communication points for providing information between the entrance to the protected area and the person controlling the territory in the mode of a regular telephone conversation or video communication;

3. the ability of the manager to remotely, at his discretion, unlock the locking device for visitors to access;

4. the implementation of a simplified procedure for the passage of proxies by providing them with special keys or cards;

5. quick automatic unlocking of the access system in case of fires and accidents in buildings for safe emergency evacuation of people.

Each of these five principles can be created in different technical ways and have varieties, work for an individual private house or a multi-story residential building. Manufacturers deal with these issues on their own. State standardization of such equipment does not yet exist.

Currently, intercom systems are being intensively operated:

• buildings of the old construction, working on an analog or digital telephone base;

• new buildings, providing the exchange of information on video tools.

Building intercom device with telephone equipment

Organization of admission of unauthorized visitors

At the entrance to the controlled territory, for example, the entrance of a multi-story building, an anti-vandal barrier is installed - a metal door, which is constantly in the locked position with an electromagnetic lock.

A call center has been mounted on its outside from the street, through which visitors call the owner of the apartment to talk.

To do this, they dial the number of the apartment on the keypad, where the call goes in the same way as on a regular landline phone. During the conversation, the owner of the living room can unlock the electromagnetic lock and let the visitor into the staircase.

For this purpose, in his apartment there is a stationary unit with a handset on which the button for opening the door is located.

The tube in daily condition is hung on a plastic tongue and fixed on a stationary unit. At the same time, a micro switch is located on the inside of the unit, which controls the operation of the handset. He puts it in one of two modes:

1. conducting a telephone conversation;

2. Waiting for a call from the intercom.

Modern intercoms allow you to negotiate in duplex mode. Devices by which communication was carried out alternately in a simplex order are almost obsolete.

Scheme of construction and operation of audio doorphone logic

The basis of the system used is a miniature telephone exchange, which can function due to:

1. analog signals using standard equipment of similar coordinate-matrix automatic telephone exchanges;

2. digital coding packages based on the use of microprocessor technologies.

Installation and operation of digital intercoms is somewhat simpler, and their cost is gradually reduced.

To connect the subscribers of the apartments, the input button, the call station, a conventional two-wire telephone wire is used, which is laid together with the high-voltage circuits of the building.

The PBX is powered by a special unit from building standard power network. All commands to open the door from the apartment tubes, as well as the buttons of the front door and the call panel, come through the mini-automatic telephone exchange, where they are processed and redirected to the executive electric circuit for controlling the lock.

Design features of intercom system elements

Entry doorphone call station

It is usually performed with:

• buttons for dialing the apartment number and canceling erroneous input with backlight;

• information board indicating entered numbers;

• nests with contacts for installing the electronic key by permanent residents;

• built-in microphone and speaker.

Access control door on the inside

There is already a limited space zone in which only trusted visitors can enter. There are less requirements for anti-vandal protection.

To exit the entrance through a closed door, just press the usual button located at the optimum height for adults and children. It is made in an open way with free access and LED backlighting, which is clearly visible even in the half-dusk of the entrance.

The control wires of the intercom system and the electric power cable of the electromagnetic lock are mounted discreetly, and the exposed areas are protected by a metal sleeve. Mini-automatic telephone exchange and other equipment are placed in an airtight closed box.

Electromagnetic lock

Its design consists of a coil winding, powered by voltage from a power supply (usually 12 volts) and a magnetic drive having two separate contact pads:

1. stationary, fixed to the door frame;

2. movable, mounted in the door leaf.

When closing the sash, their surfaces are in close contact, holding the door in the locked position with an force exceeding a hundred kilograms. It is impossible to overcome it with human hands.

An electric current constantly flows through the winding of the electromagnet, which ensures the attraction of the sash in the closed position. Voltage relief is carried out from the PBX teams for a certain time necessary for the visitor to go through. After its completion, the voltage is again applied to the coil winding.

In the event of an accident inside the building, electricity is cut off by automatic protections and the coil is de-energized. Due to this, free evacuation of people from the building is organized.

In addition to the electromagnetic principle, the lock on the front door can operate on the basis of an electromechanical design, representing a deadbolt, moved by an electromagnet or an electric motor with reverse.

The design of the door lock is selected based on its weight and the required operating conditions.

Mechanical door closer

This is one of the necessary elements of the intercom system, working automatically to bring the door to the closed position after the visitor passes through it in any direction.

It is installed in two parts at once:

1. a wall or door frame;

2. movable sash.

At the location of the closers are:

• top located above the door;

• outdoor;

• hidden in the door frame.

For the convenience of carrying large-sized and heavy objects through the door, the mechanical closer is equipped with a convenient detachable mechanism that is easily opened by the human hand.

Doorphone Key

It is based on one of three technologies:

1. resistive models with an accurate resistance rating due to a resistor built into their housing;

2. programmable devices with non-volatile memory, providing connection via a single-wire interface with a capacitor that provides power when connected;

3. contactless devices in the form of a card or key fob.

Doorphone Electrical Protection

Power Supply and power circuits of the intercom system must be protected by a circuit breaker to prevent the effects of short circuits and overloads in the circuit.

Given the large area of ​​exposed metal surfaces and the possibility of leakage currents passing through them in emergency situations, it is recommended that visitors prevent electrical injuries apply RCD in the power scheme of the house.

Building video intercom device

Intercom systems using video transmission between the visitor and the owner have the same principles as the equipment with telephone exchanges. An access restriction zone and a controlled checkpoint with a door are also organized.

The difference lies in the use of a video camera at the input and replacement of the PBX with newer devices for exchanging video information. In this case, various video network configuration schemes can be created.

Simple video intercom scheme

The most affordable option is created by connecting the video doorphone monitor directly to the door station located near the front door. But, with this system, you can only negotiate between the visitor and the owner. For remote control of the door lock, an additional system must be created.

To power the equipment you need to connect a single-phase network voltage of 220 volts. Communication between the monitor and the call panel is carried out via a low-current cable with twisted pair cores:

• audio information;

• land;

• +12 volt supply;

• video information.

Their connection is carried out according to the wiring diagram in strict sequence. To facilitate installation, digital or color marking is performed. But on the equipment of different manufacturers, it may differ. Therefore, each time the circuit must be called by electrical methods.

When the door station refers to a significant distance from the monitor of the video intercom, the resistance of the twisted pair begins to affect the quality of signal transmission. In such situations, they use a special combination cable that simultaneously transmits audio and video signals while providing power.

For high-quality transmission of video information over long distances, a coaxial cable with a wave impedance of 75 ohms is best suited.

Connection scheme for video intercom with controller

More complex configurations of video networks can be created through the use of specially designed controllers for these purposes, which allow several or all subscribers of the apartments of the entrance to work, rather than one separate one.

The electronic controller processes information coming from the call panel, exit buttons and the owner of the apartment. Based on the embedded algorithms, a command is issued to unlock the front door lock.

Here, in most schemes, an additional video lens can be connected, which improves visibility by viewing from a favorable point.

When installing a video intercom inside the entrance of a multi-storey building, video signal splitters of various designs are used to connect video monitors.

Special features

The video doorphone controller can be equipped with additional functions. For example, in the absence of the owner of the house, the visitor is given the opportunity to leave him a message in the form of a voice or video message or vice versa: when leaving the premises, the owner can warn the expected visitor about certain actions.

Certain types of controllers can notify the owner with an additional signal about each opening of the door with electronic keys or the exit button or have other specific functions.

Wireless intercoms

The logic of such devices is based on the reception and transmission of signals and commands via radio channels without laying telephone and video wire channels.

The main communication unit is connected to them for power from the mains, and information is exchanged via Wi-Fi at a constant frequency.

They require more sophisticated equipment, cost more. In addition, they have a limited radius of action, which is influenced by thick walls, metal structures, shielding signals, as well as extraneous radio interference.

GSM intercom

Manufacturers have launched the release of new models that provide not only the typical functions of conventional intercoms, but also communication from the call panel through the owner’s mobile phone.

For this, the mobile number is entered into the device’s memory. Such an opportunity allows the owner to use the subscriber's handset of the intercom system when he is at home, and during his absence to have complete information about all visitors and keep in touch with them for communication.