Second phone call. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Second phone call. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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This device will be useful for those who have several rooms in the apartment, and there is only one telephone set (TA) and its call can not be heard from the next room or kitchen. The easiest way out of the situation may be to connect in parallel to the TL another call in another room from an old broken phone. The bell is connected in series with a 1 uF capacitor for an operating voltage of 160 V. But in this case, when dialing a phone number on the phone (when impulses are generated by the interrupter in the line), an additional bell will ring. The same will happen if two SLTs are connected in parallel to the line.

This is inconvenient, as it creates unnecessary noise, and if there are two SLTs in the apartment, then you can mistakenly pick up the phone, mistaking the ringing for a call signal. To get rid of this problem, the addition of the telephone circuit shown in Fig. 2.12. Shown are two simple options for eliminating "ringing". The devices do not require explanations and allow using the same electromechanical bell that is installed in the SLT.

Rice. 2.12 (click to enlarge)

Second phone call
Rice. 2.13. PCB topology and layout of elements (C1 is located under the printed conductors and is not shown in the figure)

The circuit draws power from the telephone line only during ringing. When using the version with a reed relay, it can be of the type RES55A RS4.569.601 (RS4.569.606) or RES55B RS4.569.626 (RS4.569.631).

The board topology for this circuit is shown in fig. 2.13. Capacitor C2 type K50-29 for 63V.

The scheme in fig. 2.14 eliminates the need for an electromechanical telephone call. The call signal in the form of an intermittent sound signal is created by the BF1 piezoelectric emitter (any type). The circuit consists of two generators assembled on a D1 chip of the 561LE5 (or 561LA7) type, a signal amplifier based on the VT1 transistor of the KT940A (KT630B) type, and a ZGI piezoelectric emitter (or similar).

Fig.2.14 (click to enlarge)

The diode matrix VD1 can be replaced by four diodes of the KD102A type. Resistors and capacitors will fit any type.

Rice. 2.15 (click to enlarge)

Nowadays, many have phones with push-button dialing and a piezo call. A typical diagram of such a ringing device (bell) is shown in fig. 2.15. Using a small improvement shown in the figure will eliminate ringing when dialing a number on a parallel SLT.

With proper assembly and serviceable parts, all configuration schemes do not require.

Publication: cxem.net

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