Circuit board for telephone exchange - has interface circuit connected via lines to telephone sets and relays controlling connections of bus to line wires to call done generator

摘要

The circuit board (1) has several interface circuits (3,5,7) connected to lines (15,17,19) leading to telephone sets (9,11,13). A signal bus (21) on the board is connected via a first relay (kB) to at least one wire (a,b) of a line (15,17,19) and via a second relay (K3) to the call tone generator (23). A holder (31) on the board holds the signal generator (33) which is connected via a third relay (K5) to the signal bus. The board also has a relay control circuit (35) that controls the relay so as to connect the wires (a,b) to the signal bus (21) and to connect the bus to the call tone generator. ADVANTAGE - Simpler circuitry and few parts.