Small telephone PBX with two extensions - has band-pass filter recognising operation of dialling key in extension using multiple frequency key dialling

摘要

The extensions are equipped for multiple frequency key dialling and there is a connecting circuit between the two extensions (T1n1, T1n2). The connecting circuit has a bandpass filter (BP) recognising the operation of a dialling key at one of the extensions. It activates its output (bp). When the output (bP) is activated, a common clock pulse generator (TG) is connected to the other extension in order to make operative the call connecting element (2U).