Subscriber appts. controller switching between types of communication - deactivates calling signal generator when loop is closed and loop current monitored for presence of DC

摘要

The controller includes a loop current detector circuit (S1) connected (A2) to a power supply transformer (U) to determine whether a DC component is present in a calling signal. Its AC component is shorted out by a capacitor (C) leaving 50 Hz pulsed DC to be detected by an opto-coupler (OK). When the loop is closed no calling signal can be heard via the speech circuit if the telephone set is lifted from its hook. USE/ADVANTAGE - Esp. in speech, facsimile and text communication. Improved appts. with less complex circuitry for reliable switching. No particular combination of terminating equipment, or no auxiliary equipment required.