| 摘要 |
A signal transmission circuit of a telephone system comprises a photo-transistor with its emitter and collector connected to telephone network lines, respectively. First and second relays are disposed, respectively, in the telephone network lines between a primary winding of a voice transformer and the collector and in a line between the base and the primary winding of the voice transformer. When a telephone call arises, the first relay connects the primary winding to the collector of the photo-transistor and disconnects a resistor, which is disposed between a junction of the primary winding and the second relay for connecting the base of the photo-transistor to the junction, from the primary winding so as to transmit voice signals through the voice transformer. When dialing is performed, the first relay is caused to disconnect the primary winding from the collector and connect the resistor to the primary winding, in a closed loop. The second relay disconnects the base from the junction so as to render the photo-transistor responsive to photo signals provided from the control means, thereby providing dial pulses the telephone network lines. |
