LOUD SPEAKING COMMUNICATION SYSTEM Russian patent published in 1994 - IPC

FIELD: communication engineering. SUBSTANCE: intercommunication system has user's phone sets 1, terminals of call button disposed in the sets, diode connected in series to call button, sonic frequency amplifiers 8, dynamic heads 12, mode of operation switches 10 connected with central point by means of two-wire lines 2 and 3. Central point has call indicating units 4, calling device 6, dynamic head 38, power supply 7, user's switches 21 and mode of operation switches 37. Central point is provided with call indicating relay 26, which has one end of the winding connected with positive terminal of power supply 7, the other end of winding is connected to communication wire 3 and to anode of diode 27 through terminals 24, 25 of user's switch. Cathode of diode 27 is connected with negative terminal of power supply 7 through break contact 28 of call indicating relay 26. Diode 19 and additional terminals 17 and 18 are connected in series to communication line 2, 3 from the side each user. Additional terminals 17 and 18 of operation mode switch 10 play role of call buttons. Cathode of diode 19 is connected with anode of de-coupling diode 11. Control input of calling device 6 is connected to common points of relay 26 of call indicating units 4 and to terminal of corresponding user's switches 21 through de-coupling diodes 31. Such a design widens functional capabilities because the operator doesn't need to carry out additional manual operations for indicating and rejecting call signals. EFFECT: simplified operation of turning users to user's line; simplified power supply circuit. 2 cl, 2 dwg