Automatic recording of a telephone conversation. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Automatic recording of a telephone conversation. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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If you need to record a telephone conversation, then do not rush to send a signal from the telephone line (TL) directly to the input of the tape recorder. This will lead to the appearance of a background with a frequency of 50 Hz in the line (due to the penetration of ripple from the mains power supply of the tape recorder), which will affect the intelligibility of speech and the quality of the recording of the conversation, and the subscriber with whom the conversation is in progress may suspect illegal eavesdropping TL. In addition, such a connection can damage the input stage of the tape recorder and disrupt the operation of the TL.

At the time of calling the subscriber, the voltage amplitude in the line exceeds 120 V.

Rice. 2.19 (click to enlarge)

On fig. 2.19 shows a device diagram that eliminates all these problems and, if necessary, can be used to automatically record any telephone conversations.

The device is powered by a network of 220V. In standby mode, it consumes minimal energy - the no-load current of the transformer T1. The tape recorder turns on only when the handset is lifted after 1 second and turns off after the handset is put on the SLT. The delay is necessary so that the circuit does not operate from short-term power surges that occur when dialing a number on the SLT.

For these purposes, it is better to use a tape recorder with an electromagnetic pressure of the sound head to the tape, for example, YaUZA-220. If you use a portable tape recorder with a mechanical clamp, then it will have to be constantly in the recording mode (without turning on the power), which will lead to the punching of the rubber roller pulling the magnetic tape, as well as the tape sticking to it, which can damage it (the effect of "chewing" ribbons).

The circuit is connected to a telephone line in any convenient place, observing the polarity indicated on the diagram. The device consists of an off-hook indicator (VT1 ... VT3, their operation is described in the article above), an optocoupler switch (U1), transistor switches (VT4, VT5), a relay for switching circuits K1, K2 and a power supply unit (T1, VD2 .. .VD5).

The use of an optocoupler LED pair U1 makes it possible to obtain electrical isolation of the TL from the control circuit and the 220 V network. Capacitors C1 and C2 provide decoupling of the tape recorder circuits from the constant component in the TL; C3 - delays the activation of relays K1 and K2.

For the convenience of using the device, the SA1 power switch is set to three-position. This allows you to turn on the tape recorder without turning on the circuit of the machine when listening to the recording.

Automatic call recording
Fig. 2.20

The circuit uses resistors of type C2-23; capacitors C1, C2 type K73-16V for 100 V, C3 - K52-1 for 6 V, C4 - K50-24 for 63 V; relay K1, K2 type RES9 RS4.524.200; switch SA1 type PG2-18-ZP4N. X1 plug - standard telephone, X2 - widely used in household radio equipment for transmitting audio signals, X4 - any type of mains plug, sockets X5, X4,0 type GXNUMX or similar.

As a transformer T1, you can use any small-sized one that provides a voltage sufficient for the operation of the relay (16 ... 25 V) in the secondary winding.

When setting up the circuit, it may be necessary to select the resistor R6. To control the operation of the machine, the HL1 LED is used, which glows when the machine is turned on and goes out when the handset is picked up from the phone (in this case, the network power of the tape recorder is turned on by the contacts of relay K1.2).

The external view of the housing structure is shown in Fig. 2.20.

Publication: cxem.net

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