A simple telephone. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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The telephone set (see figure) contains only one calling chip and two transistors (compare with the devices described in the article by S. Derevyanko "Repair of imported telephone sets" in Radio, 1999, No. 2, pp. 38, 39). When a call signal is received, an alternating voltage is supplied through the capacitor C1 to the diode bridge, composed of VD1 - VD4. The rectified voltage is supplied to the parametric stabilizer R1VD5, which feeds the DA1 chip. As a result, the BQ1 piezoelectric transducer emits a variable pitch sound.
As soon as the handset is picked up, contacts SA1 are closed and the conversational amplifier on transistors VT1, VT2 is connected to the line.
If you want to make a call, pick up the handset and dial the number with a rotary dialer. The SA2 contacts that open at the same time send pulses to the line.
The operating mode of the transistors is selected (using resistor R4) so that when the tube is raised, their collectors have a voltage of 8 ... 10 V relative to the common wire.
From the BM1 electret microphone, which contains a built-in amplifying stage, the signal is fed to the input of the conversational amplifier. It is heard in the BF1 telephone capsule, but is much quieter than the interlocutor's voice. The operation of the amplifier is signaled by the HL1 LED.
Diodes 1N4004 can be replaced with 1N4007 or KD102A. Zener diode VD5 - any for stabilization voltage 25 ... 29 V, LED - any of the AL307 series. Instead of the specified microcircuit, any other specialized for calling devices, for example, DBL5002, is suitable. KA2410, KA2411. KIA6410P. ML8205. FT2040. When using these microcircuits, it must be remembered that if there is no ringing signal generation, a resistor with a resistance of about 1 kOhm should be connected between pins 2 and 220.
Transistors - any of the KT3102 series. KT315. Capacitor C1 - K73-17 or another for a rated voltage of at least 250 V. Oxide capacitors - K50-6. K50-35. K53-14, K53-20 or others, for a voltage not lower than that indicated in the diagram; the remaining capacitors - any small ones for a voltage of at least 50 V. Resistors - MLT-0,125 or MLT-0,25.
Piezoelectric emitter BQ1 - any, for example, ЗП-19. capsule BF1 - low-impedance dynamic, microphone BM1 - electret domestic or imported with a built-in amplifier. If there is a microphone with two outputs, then the left output of the resistor R5 according to the diagram must be connected to the upper output of the microphone.
It is desirable to place the details of the device in the case of a non-working telephone set with a working rotary dialer. A telephone receiver is used from it, inside which a conversational amplifier is mounted. The handset is connected with a two-wire cord to terminals X1 and X2 located inside the device.
The only operation when setting up the apparatus is setting the above transistor mode. If desired, you can change the duration of the ringing tones by selecting parts R2. C3, as well as the tones themselves - by selecting the details of R3. C4.
Author: A. Genno, st. Zelenchukskaya, Karachay-Cherkessia
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