| 摘要 |
PURPOSE:To detect station voltage without causing speaking transmission loss, by inserting a detection circuit of parallel connection using two photocouplers to a speaking line, and also by providing a means to control the continuity state of the light receiving element. CONSTITUTION:If a handset is picked up, hook switches HS1 and HS2 are closed. Due to this, station current I1 is supplied, and also part I1' of the station current runs through a light receiving element P1(B) and light emitting element P2(A) of a photocoupler. The light emitting element P2(A) emits light accordingly. When the P2(A) emits light, a corresponding light receiving element P2(B) becomes conductive to set an FF1, and an output terminal -Q lowers to level L. Therefore, current running in the light emitting element P1(A) disappears, and the corresponding P1(B) becomes nonconductive. If a telephone being called responds to reverse the polarity of the station current, part I2' of the station current runs through a light emitting element P4(A) and light receiving element P3(B) to make the P4(A) emit light, and the P3(B) becomes nonconductive in the same manner as the previous case. |
