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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Three prefixes to telephone sets. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony The devices, which will be discussed below, are designed to expand the functionality of telephone sets, improve the convenience of using them. All set-top boxes work together with devices of public telephone networks (urban or rural automatic telephone exchanges); with appropriate settings, set-top boxes can also be used to work with devices of home-made telephone communication devices [1]. The principle of operation of all set-top boxes is based on the registration of ringing signals coming to the telephone set and the corresponding processing of these signals. The prefixes are made in the form of a stand for a telephone set and have an inductive connection with the bell winding. Their operation does not contradict the requirements of the State Telecommunications Inspectorate, since there is no galvanic connection between the set-top boxes and the telephone network.
The block diagram of the attachment is shown in fig. 1. The signal from the ID inductive sensor, located in the magnetic field of the bell coil of the TA telephone set, is amplified by the amplifier U and fed to the shaper F. From the shaper, the signal goes to the LB logic unit, and then to the IU actuating device. Call indicator light It is designed for people with hearing loss and provides the appearance of a light signal when a call is received by the subscriber (Fig. 2).
The inductive sensor L1 is placed in the magnetic field of the ringer coil of the telephone. The alternating voltage that occurs on the coil L1, through the decoupling capacitor C1, is supplied to the amplifier, made on the logic element DD1.1. In this case, the digital microcircuit element operates in the analog (linear) mode [3]. This is achieved by introducing negative DC feedback through resistor R2. The signal amplified ten times through the isolation capacitor C2 is fed to the input of the shaper - the Schmitt trigger on the logic elements DD1.2, DD1.3. Capacitor C2 is necessary in order to exclude the flow of a constant component from the output of the amplifier on the logic element DD1.1 to the input of the Schmitt trigger. In the absence of an input signal, the constant voltage at the output of the logic element DD1.1 is approximately half the supply voltage (this is ensured by negative feedback through the resistor R2). The Schmitt trigger threshold is also about half the supply voltage, so if the amplifier output is directly connected to the input of the Schmitt trigger, spontaneous switching of the latter could be observed (in the absence of a signal on the L1 coil). Resistor R3 provides a low-level voltage supply to the trigger input in the absence of an input signal, and also ensures that capacitor C2 is discharged. From the output of the Schmitt trigger, the signal goes to the high-voltage transistor VT1, which operates in the control electrode circuit of the trinistor VS1. A feature of this method of turning on the transistor is the insignificant power that is dissipated on it. This is due to the fact that after opening the trinistor, the voltage between the collector and emitter of the transistor decreases to 1 ... 2 V, and the current through it stops. The trinistor controls the load - the lighting lamp HA1, which signals an incoming call to the subscriber. Capacitor C4 smooths out the ripple of the ringing voltage and eliminates the flickering of the signal lamp HA1. The microcircuit is powered by a parametric stabilizer, in which the elements R10, VD1, C3 work. The K561LN2 chip can be replaced with K561LN1, K561LA7, K561LA9 or the corresponding analogues from the K 176 series. Transistor VT1 - KT605, KT940 with any letters. Trinistor VS1 - KU201K(L), KU202(K-N). Capacitor - KM-6, K10-7 (C1, C2), K50-6, K50-16, K50-12 (C3). As a sensor L1, a coil from an electromagnetic relay PC13, passport RS4.523.026, was used. The coil contains 28 turns of PEL-000 wire 1 mm and has a resistance of 0,05 kOhm. Coil length - 8 mm. Coils from similar relays are also suitable - RKN, RKM. You can also use homemade coils. The magnetic core in them should be made of a steel bar with a diameter of 40 .... 5 mm (for example, an ordinary nail). The telephone light signaling device is assembled on a board made of foil fiberglass, and the board is mounted in a case measuring 210x140x40 mm, made in the form of a stand for a telephone. The sensor coil L1 must be located at a distance of no more than 40 ... 50 mm from the bell winding. Establishing the device consists in selecting the resistance of the resistor R1 to provide the necessary sensitivity. The power of the HA1 incandescent lamp can be from 25 to 150 watts. Sound signaling device This prefix allows you to replace the sharp sound of a call with a pleasant melodic nightingale trill. Let's go back to the concept it can be taken here. The input part of the signaling device (sensor, amplifier and shaper) is similar to the corresponding cascades of the previous one. On the elements R6, R7, VD1, C3, a filter is made that converts the pulsating voltage into a constant one. On the logic elements DD1.4 and DD2.1, DD1.5 and DD2.2, DD1.6 and DD2.3, generators are made that generate frequencies of 1000, 10, 500 Hz, respectively (approximately). The total signal imitates the singing of a nightingale. From the output of the logic element DD3.2, the sound signal is fed to the key amplifier in which the transistor VT1 operates. The load of the latter is a variable resistor R12, from which a signal is taken to the sound emitter HA1. The elements of the signaling device are powered from the mains through the capacitor C8, which performs the function of a ballast resistance (the capacitance of this capacitor to alternating current with a frequency of 50 Hz is about 10 kOhm). Resistor R13 ensures the discharge of the capacitor after the device is turned off from the network. The voltages for powering the microcircuits and the sound emitter are taken from the zener diodes VD3 and VD2; capacitors C7 and C10 smooth out the ripple of the rectified voltage; capacitor C9 increases the noise immunity of the signaling device. The sound emitter VP-1 (NA1) can be replaced by DEMSh-1A, TK-47 or any other with a DC winding resistance of 60 ... 200 Ohm. The remaining types of elements and their possible replacements are the same as in the previous device. Signaling device with selection of the number of calls Such a signaling device, in contrast to the one described above, does not start emitting an audible signal immediately after the sending of calling parcels (for simplicity, calls), but only starting from a certain number of them. In other words, the signaling device, as it were, misses a certain number of calls, without responding to them with a sound, but only recording them in memory. It is obvious that the ringing of the telephone set must be muffled. This device can be used, for example, to exclude calls from unwanted subscribers. It is known that, on average, the subscriber holds the handset for 4 ... 5 rings (this is quite enough for the called subscriber to come to the phone and answer), and then hangs up, returning the handset to the device lever. If the signaling device is set to ignore this number of calls, then only those subscribers who have been informed of the "secret" and who will hold the phone for 6 or more rings will be able to get through. Another possible case of using such a device is to set priorities in the operation of two parallel-connected telephones located in different rooms, in this case one of the two telephones works together with the signaling device. When ringing messages appear on the line, at first only the first telephone responds to them - a bell rings in it. Employees in this room pick up the phone. If there is no one in the room where the first telephone is located or no one wants to pick up the phone, then after some time the signaling device installed next to the second telephone begins to sound. The employees of the second room pick up the phone. It is convenient to use the signaling device when the boss is in the first room and, by agreement, should pick up the phone first, and his subordinates in the second room. If a call came into the second room, it means that the boss is not in place, and you need to pick up the phone. At the same time, part of the calls goes unnoticed by employees in the second room and does not distract them from work. Other areas of application of the signaling device are also possible. circuit diagram can be taken here. The input stages, audio signal generator and power supply are exactly the same as in the previous device. When the device is connected to the network and in the absence of a signal at the sensor L1, a high-level voltage appears at the output of the logic element DD1.2. Capacitor C4 starts charging through resistor R9. After 10 ... 15 s, the voltage on the capacitor will reach the switching threshold of the logic element (about 5 V). Entering the input R of the counter DD3, this voltage will set the counter to its initial state, in which all counter outputs have a low voltage. The low-level voltage supplied to pin 4 of the logic element DD4.1 prohibits the sound signal to the input of the element DD4.2. The signaling device is in standby mode. When an alternating magnetic field appears in the immediate vicinity of the sensor L1, rectangular pulses appear at the output of the logic element DD1.3. Capacitor C4 quickly discharges through resistor R8 and diode VD2, and a low-level voltage appears at the input R of the counter, which switches the DD3 microcircuit to the counting mode. During the pause between two calls (4 ... 5 s), the capacitor C4 does not have time to charge through the resistor R9 to the switching voltage, so the DD3 chip operates in the counting mode all the time while the calls are being made. Resistors R6, R7, capacitor C3, diode VDl work in an integrating circuit that converts bursts of rectangular pulses taken from the output of the logic element DD1.3 into a single pulse. Diode VD1 provides fast charging of the capacitor C3 with a high voltage level from the output of the logic element DD1.3. Thus, when a call is made, a high-level voltage acts at the input of the logical element DD1.4, and a low-level voltage acts at the output of this element. Since the meter is switched by a positive voltage drop at the SR input, the meter state will change at the end of the first ring. At the first output of the counter (pin 2), a high level voltage will be established. When a high-level voltage appears at the output of the meter, to which the movable contact of the SA1 switch is connected, the same voltage will be set at the CN input of the counter. This will set the counter to storage mode, i.e. pulses at the CP input will no longer lead to a change in the state of the counter. At pin 3 of the DD4 microcircuit, a high-level voltage will be established, and when subsequent calls appear, the HA1 sounder of the device will sound. The beeps will sound until the called party picks up their handset or until the calling party stops ringing. In this case, the device will return to its original state. The device is assembled on a printed circuit board. The housing is exactly the same as for the light signaling device. The handle of the variable resistor R14 and the handle of the biscuit switch SA1 are displayed on the side wall (the MPN-1 switch with 11 positions was used). In the manufacture of set-top boxes, it should be remembered that they have a galvanic connection with the network, therefore, careful isolation of the axes of variable resistors and biscuit switching is necessary. Enclosures must always be made of non-conductive material. When setting up devices, it is advisable to use a 9 ... 10 V power source that does not have a galvanic connection with the network, or use an isolation transformer. Literature
Publication: cxem.net
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