Telephone exchange crosspoint switching marker - uses relay and transistor to mark crosspoints and prevent double switching

摘要

The control circuit is for busy and marker circuitry for crosspoint switching in a telephone exchange. The system uses decoupling rectifiers and switching transistors as auxiliaries to the crosspoint relay. The system reduces power requirements to a third. Each crosspoint has a marker relay at the inlet/outlet. When one relay is operated by the earth on an outlet and battery on the inlet, all other crosspoints are then barred by switching on the auxiliary transistors in the other crosspoint circuits due to the current flow through the decoupling rectifiers providing the bias conditions to emitter, base and collector circuit resistors.