Automatic on=off power switching circuit for extension telephone - has second switch triggered by ringing signal to operate blocking circuit

摘要

The switching circuit has a switch for the power supply which closes when the telephone set's handset is lifted- or closes by means of another method of initiation- and allows current to flow from the exchange battery directly or indirectly. When the handset is replaced, the switch opens again & the current is discontinued. A second switch is triggered by the flow of ringing current and operates a blocking circuit that either blocks the supply or releases it. A delay circuit delays the supply's disconnection for a given time after the exchange battery's current has been interrupted.