Intercoms provide telephone communication between two subscribers. The call is made through the bell available on the telephone. In such intercoms, you can use telephone sets in which only the handset, bell and lever switch are working.
Telephone sets E1 and E2 (Fig. 1) are connected by a three-wire line into which AC and DC voltages are supplied. The alternating voltage is removed from the winding II of the network transformer T1, the constant voltage is removed from the parametric voltage stabilizer (R1, VD2, CD of the full-wave rectifier (VD1), which is powered from the winding III of the transformer.
If the first subscriber (he has an E1 telephone set) wants to call the second subscriber, he must press the SB1 switch button. In this case, alternating voltage from winding II of the transformer is supplied to the telephone E2, and the bell rings. When both telephone sets are off-hook, the DC voltage source is switched on in series with the devices - you can carry on a conversation. The second subscriber presses the SB2 switch button to call the first. The rectifier diode bridge VD1 can be any of the KTs402, KTs405, KTs407 series. It can also be assembled using four diodes of the D7, D9, D220, D223, D311 series. Capacitor C1 - K50-6, K50-16, K50-24. Push-button switches - KM-1, P2K, power switch - toggle switch TV2-1. The network transformer is made on a strip magnetic core ШЛ 16х25. Winding I contains 2200 turns of PEV-2 0.08 wire, winding II - 400 turns PEV-2 0.10, winding III - 100 turns PEV-2 0.19.
Telephone sets can be of types TA-68, TAN-66, TAN-70. In the same case, if devices with faulty dialers are used, you should disconnect the conductors from the dialers and connect them to a lever switch so that when the handset is off-hook, a bell is connected to the line through a 1-μF capacitor (it is in the device), and when the handset is off-hook ? series-connected microphone and telephone handset.
The transformer and rectifier parts are mounted in the housing of the E1 device. A power switch is installed on its back wall, and a power cord with a plug at the end is brought out through a hole in the wall. Switches are installed on telephone bodies. For the line, use single-core or multi-core telephone or installation wire with a core diameter of less than 0.5 mm for long distances (up to 1 km) and less than 0.2 mm for short distances (up to 200 m). The diameter of the wire is determined mainly by considerations of its mechanical strength.
Despite its simplicity, such an intercom has a drawback: the communication line contains three wires. By slightly complicating the device, the number of wires in the line can be reduced to two, as is the case in city telephone networks.
Types of Commax intercoms
Such diversity allows you to choose the best solution for any object. The most widely used Commax intercoms in Moscow are used to equip:
Why Commax?
Today, Commax (South Korea), founded in 1968, is one of the recognized world leaders in the production of intercoms, intercoms and other electronic equipment for video surveillance and access control. The brand's products are sold in more than 100 countries, with Commax playing a leading role in its market segment in most of them. Intercoms of this brand are distinguished by well-thought-out functionality, are certified in UL and TUV systems, and their reliability is confirmed by many years of experience in use.
Commax intercoms in the catalog of the Rossi online store
The Rossi catalog is an opportunity to buy Commax intercoms in Moscow with the opportunity to choose the best solutions among dozens of unique options. On the pages of the online store and during a telephone consultation, you can order kits and additional system elements in any quantity, in strict accordance with the characteristics of the object and the task at hand. Call now!
A simple intercom can be assembled from two subscriber loudspeakers. Its use can be different, at the dacha, in the house, in the apartment, etc. In some cases, the use of a radio channel or mobile communication is unjustified, and often not possible. Especially if constant 24/7 communication is required. This is why this design was developed. The main advantage of the intercom is that the speakers BA1 and BA2 are both microphones and a loudspeaker. There are two possible options for manufacturing the device. The first option uses only one amplifier.The device consists of a pre-amplifier on VT1 and a power amplifier assembled on the K174UN7 IC. Switching between reception and transmission modes occurs using switch S1; only one subscriber has the switch, with which you can connect speakers one by one to the input or output of the amplifier. A simplified diagram of the second version of the intercom is shown in the following figure.
In this case, amplifiers M and switches S are installed in each loudspeaker. Switching from reception to transmission can be done for each subscriber. When switch S is pressed, the loudspeaker is used as a microphone and is connected to the preamplifier input via coupling capacitor C1. The pre-amplifier is assembled on transistor VT1. Variable resistor R1 determines the feedback level and sensitivity at the input of the cascade. From the output of the pre-amplifier, through variable resistor R5, the signal is supplied to a power amplifier assembled on the DA1 chip.
Using resistor R5, the output power is regulated. From the output of the amplifier, the signal enters the line and, through the pressed S2 button, goes to the loudspeaker, which in this case is used for its intended purpose. It is necessary to pay attention to the fact that the line can be either two-wire or single-wire, if grounding is used as the second wire. Grounding can be water pipes, heating pipes, or simply a metal rod driven into the ground.
The intercom is powered from a network nine-volt power source or galvanic elements. A correctly assembled device begins to work immediately; if necessary, you can adjust the sensitivity using resistor R1, and use resistor R5 to adjust the output power. I used miniature loudspeakers in which the step-down transformers were removed, instead of volume controls, buttons S1, 2 of the P2K type without fixing were installed. Author: Valery Ivanov.
A simple diagram for connecting two old telephone sets to organize a two-way communication line. It turned out that after the exchange of an apartment, two simple rotary telephone sets became redundant. There was no telephone point in the new apartment, and no one regretted it - everyone had cell phones.
The devices remained in the storage room for several years, until it was necessary to organize two-way communication between the garage and the country house (both objects are on the same site).
And so, the diagram of a typical telephone set is shown in Figure 1. B1 and M1 are the components of the telephone handset - a carbon microphone and an electromagnetic capsule. F1 - call. S1, S2 - dialer until it is touched S1 is closed and S2 is open.
And when a number is dialed, S2 closes, and S1 opens the circuit as many times as there are units for the dialed digit, for example, turning “9” opens the line nine times. S3 is a lever switch.
Rice. 1. Schematic diagram of a typical telephone set.
When the receiver hangs in the position as in the diagram, that is, it connects a bell to the line. And when we pick up the phone, instead of calling, he connects the receiver. The challenge is how to connect these two circuits to each other.
After searching on the Internet, I found several options, but all of them with additional calling buttons. Or complex circuits on digital microcircuits - individual mini-PBXs.
In a simplified form, a telephone line is a direct current source with a voltage of about 60 V with an internal resistance of about 1000 Ohms.
When a call signal comes in, it turns into an alternating voltage source of about 100V with the same internal resistance. That is, in principle, in order to “talk” you need to connect telephone sets as in Figure 2.
Rice. 2. The simplest diagram of connecting two telephone sets.
But now comes the challenge after the challenge. In principle, it can be solved even in such a scheme, especially with some simple models of telephone sets equipped with electronic calls. Remember what happens if you pick up the handset of one of the parallel telephones - the bell of the second device will ring or squeak.
And if you start dialing a number, this ringing or beeping will continue the entire time the number is being dialed. So, here’s your call signal: pick up the handset and dial “0”. The second device will ring ten times. There is also a drawback, firstly, not all telephones behave this way - it depends on the design of the particular ringing device.
Secondly, even if there is sound, it is not as loud as a regular call. It turns out that for a full call you need an AC voltage source.
The easiest way is to supply alternating voltage via a separate wire. This does not create a big problem, because now it is easy to buy a three-wire cable - it is used for electrical wiring with grounding and is sold in any electrical goods store. In addition, its wires are multi-colored, which prevents confusion when connecting.
The result is a circuit shown in Figure 3. The power source is a ready-made transformer T1 with an output voltage of 42V. The voltage through the rectifier on diode VD2 is supplied to capacitor C1.
Where a constant voltage of about 60V is generated. It is supplied through diode VD1 and resistor R1 to telephone sets TA1 and TA2.
Rice. 3. Schematic diagram of connecting telephone sets with calling capabilities.
The alternating voltage is removed before the rectifier and supplied to telephone sets through switch buttons S1 and S2. If we press S1, alternating voltage is supplied to TA2, which is in a hung-up state and therefore rings.
If we press S2, the alternating voltage is now supplied to TA2, which is on-hook and ringing. Thus, to call subscriber TA2, subscriber TA1 presses the S1 button, releases it and listens for the answer. To call subscriber TA1, subscriber TA2 does the same, but presses the S2 button.
Buttons S1 and S2 can be installed in telephone cases - there is usually a lot of free space there. Transformer T1 is ready, you can use any transformer with a secondary voltage from 36 to 50V. The transformer can even be the lowest power - the load current in this circuit is no more than 50 mA.
Content:Sometimes situations arise when communication is required between just two apartments, garages, cottages and other objects for various purposes. In this case, using a telephone switch is impractical, so an intercom for two subscribers can solve the problem.
Such systems have a significant limitation in line resistance, reaching 1-2 kOhm. The copper wire used with a diameter of 0.5 mm provides a communication range of several tens to several hundred meters, and when using an amplifier - up to 5-10 km. If you increase the length of the lines or the cross-section of the wire, the inductance will begin to increase and the capacitance of the line will increase, which will cause significant attenuation during signal transmission.
The main components of intercoms are two remote controls installed at sites and a two-wire communication line connecting these remote controls. Each remote control is a communication device with an amplifier and a dynamic head. The last element can be dual purpose. During the transmission of messages, the dynamic head acts as a microphone, and during reception it is used for its intended purpose - to convert an electrical signal of audio frequency into sound.
In most intercoms, the signal amplified by the head travels from one device to the dynamic head of another via a direct communication line. Due to the low resistance of the head, losses occur in the communication lines: the sound volume begins to fall as the distance increases. Therefore, the operation of these systems is limited by distance depending on the scheme used.
It is quite possible to avoid losses on the line if the output signal from one remote control is supplied not to the dynamic head, but to the amplifier of another device, which has a significantly higher resistance. It is this connection that allows signal reception and transmission to reach several kilometers, without any significant losses. A significant advantage of such intercoms is the ability to be powered from a low voltage source.
The circuit diagram proposed for consideration includes two remote controls A1 and A2 and two communication lines connecting the sockets of the XS1 and XS2 remote controls to each other. Since the remote control amplifiers have the same circuits, only one of them will be considered - from device A1.
Transistors VT2, VT3 and VT4 were used for the audio amplifier. The negative feedback voltage is supplied from the collector VT4 to the base VT2 through resistor R8. Feedback helps stabilize the operating mode of the transistors and the cascade gain. Its action reduces sound distortion.
When the transmit-receive switch SB1 is in the closed position, the input signal from the communication line is supplied to the emitter circuit VT2 through C1. Thanks to the small capacitance of capacitor C1, the characteristics of the head are equalized for use as a microphone. Capacitor C2 protects the amplifier input from high-frequency interference, and resistor R2 maintains the component of the emitter current VT2 at a constant value.
The cascade on VT1 is an electronic switch that supplies voltage to the first stage of the amplifier. This key is located in the load circuit (R3) of transistor VT2. In the indicated diagram, switches SB1 are in standby mode, and in the closed position. At this time, the devices' current consumption from the power source is very small. Therefore, the remote controls do not require separate power switches.
After pressing the SB1 button, the BA1 dynamic head is connected to the amplifier input. In this case, the wire connected to the XS2 socket will be connected to the amplifier output. Next, from G1, power is supplied through R10 to the input of the amplifier of the second device along its line. Transistor VT1 opens in the second remote control, supply voltage is supplied to VT2 and the amplifier of the second remote control is turned on. At the same time, the amplifier is also turned on in the first remote control due to the opening of the transistor VT1 by the current flowing through the dynamic head BA1 along the base circuit. During a conversation, the voltage in front of the head increases, which is generated in its voice coil and enters the communication line through capacitor C5. Next, the signal weakened in the communication line is amplified, after which it goes to the dynamic head.
Thus, when you press the SB1 button, both remote controls are turned on simultaneously. However, in the transmitting apparatus, the amplifier acts as a microphone and its current consumption is only about 3.5 mA. In receiving equipment, it performs its direct function, consuming approximately 100 mA at the loudest sound. The conversation between subscribers is carried out one by one. The button is pressed after receiving the message and released when the transmission is complete.
The intercom circuit is simplified by the absence of a volume control. Therefore, in order to prevent significant sound distortion, certain rules must be followed. If the line is short, up to 2 km, then you should talk quietly, keeping a distance of 40-50 cm from the remote control. In the case when the devices are located at a maximum distance of 5-10 km, it is recommended to talk loudly, keeping a distance of 10-20 cm from the remote control.
To mount amplifier parts, one-sided foil-coated PCB is used as a board. The installation itself can be performed not only by printed methods, but also by a hinged method, when special copper pins are attached to the pins of the parts on the board.
The remote control body is made of steel, 0.5 mm thick. The board is attached to the rear wall of the case so that the switch button protrudes outward.
In order to finally install the intercom for two subscribers, it is necessary to determine the location of the sockets XS1 and XS2. Instead, you can use a small-sized connector from a tape recorder. All that remains is to secure the dynamic head, install the power source and check the functionality of the device.
