French telephone network line keyboard adaptor - has circuits to suppress listening control during numbering

摘要

An electrode and electromagnetic u nit is used to adapt a push-buttom keyboard to the French telephone network line with dialling call. The unit only requires four connections and has a circuit to suppress the listening control during numbering and a circuit to rapidly bring numbering to zero on cut-off. The listening control suppression circuit has a reed relay (R1) controlled by logic information from the keyboard (S2). No power is required during numbering. The zeroing circuit has two transistors (T2, T3) which can differentiate between the type of cut-off. It can sense numbering, exchange switching, brief cut-off by the caller, final cut-off. The circuit only reacts to brief or final cut-off by the caller.