Telephone communication between two subscribers. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Telephone communication between two subscribers. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In everyday life, you may need a telephone connection between two subscribers (with relatives, a garage, workshops). This problem can be solved without creating complex electronic devices, but taking ordinary telephones as a basis.

The proposed device consists of two standard telephone sets (TA) - basic and subscriber. Details are added to the base one that ensure the making of calls and the power of conversational nodes. The basic TA is powered by AC power. The communication line is two-wire. The communication range is several kilometers.

The circuit (see figure) is drawn up in relation to the Bulgarian telephone set TA-4100, from which the dialer, capacitor C1, resistor R1 (marked on the TA board) are removed. The arrows in the diagram show which points of the base TA are connected to additional parts.

Telephone communication between two subscribers

The principle of operation of the device is as follows: when the handset is picked up by a remote subscriber, a circuit is formed: "+" C2 of the rectifier, relay winding K1, the third terminal of the ZN dialer, the conversational node of the base telephone PC, the contacts of the lever switch S1.1, the second linear terminal 2L, the line, the ZL terminal , freed bell terminal Zv, "-" C2. Relay K1 will work. The bell is ringing, powered by the circuit: the secondary winding of the transformer T1, contacts 7-8 of the relay K2, contacts S1.2, the bell HA1, contacts 6-7 K1.2, T1 The call is continuous. The handset is removed during a call, and in contacts S1.2 the ringing circuit is opened. Contacts 4-5 K2.1 duplicate S1.1, so that when the handset is removed, the power circuit of the conversational nodes of both phones is preserved.

When a call is made, the base unit goes off-hook. In this case, alternating current from T1 passes through contacts 7-8 of relay K2, S1.2, LED HL1, R1, contacts 3-4 K1.1, 2N, 2L, TA, ZL, Zv, T1. The subscriber's bell rings. Through contacts S1.1, the multivibrator starts, relay K2 through contacts 7-8 of group K2.2 periodically connects the ringing current to the line or through 4-5 of group K2.1 constant voltage. When the subscriber's TA handset is removed, at the moment of closing contacts 4-5 of relay K2, relay K1 will work and communication is established. The line voltage drops to a few volts and the multivibrator stops. Call progress is controlled by LED HL1.

If we make it a little more difficult to make a call from the base SLT, then a multivibrator is not needed. In this case, a few seconds after going off-hook (during which the call is in progress), the hook switch is pressed and a ringback is expected.

Details: T1 - power transformer, magnetic circuit Ш16х16 mm. The primary winding contains 4000 turns of PEL wire 0,08; secondary - 750 turns of wire PEL 0,2. T1 may be different, with an output voltage of 38 ... 43 V. K 1, K2 - relay RES9, nacnopi RS4.524.205. The relay can be different, with a winding resistance of 2 ... 3 kOhm and corresponding contacts. Transistors KT315I can be replaced with KT503G - KT503E, and KT502G - with KT50ZD, KT502E. Diodes - series KD105, D226B-D226G Capacitors of any type, suitable in terms of capacitance and operating voltage. Capacitor C1 can be replaced with ceramic or metal-paper

The base can be replaced by a different type of telephone. Both groups of contacts S1 must be changeover.

When the dialer is removed, additional parts are placed inside the case; the transformer is attached to the base, and the circuit board is attached to the dialer stand. If the parts are not placed in the housing, then the transformer is placed in a separate unit.

The phone can work as a simple burglar alarm. Closing the contacts of the microswitch SB1 (MP1) is equivalent to picking up the handset, which causes a call. Such an alarm does not control line breaks. The addition of a third wire-loop and a slight complication of the circuit eliminate this drawback. When SB2 (MP1) is triggered, the loop or common wire is broken through resistor R5, the trinistor VS1 opens and relay K1 is activated, including contacts 6-7 of the bell. At the same time, the trinistor opens the VT3 transistor, through which the multivibrator is launched, and the call becomes intermittent. This is different from calling. The power is turned off to end the call. If self-blocking of the call in the burglar alarm mode is not desirable, then the trinistor is replaced by the KT315I (KT503V) transistor. If the microswitches SB1 and SB2 are installed in different places, then by the nature of the call, you can determine which one worked. It was checked (within the house) the possibility of using heating pipes as a common wire - pickups are insignificant, which allows using a two-wire line in the alarm circuit

In telephones, when the handset is on-hook, the conversational circuit is shunted by contacts. In this circuit, shunting can be done by connecting terminal 1H to contact 8 of relay K1 through a capacitor (1 - 3 microfarads for an operating voltage of 63 - 100 V).

Author: P. Sevastyanov, Tashkent Uzbekistan

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