Video communications system for main entrance and flats - has simple semiconductor switches replacing electromechanical switches

摘要

The communications system has each indoor unit, e.g. located in flats, provided with an electronic switch containing a capacitor which, when charged, switches the indoor unit on and when discharged switches it off. The outdoor unit e.g. at the main entrance to the block of flats, has a device to charge the capacitor when a call button is pressed associated with the desired indoor unit. After the call button has been released the capacitor's charge remains for a given time above the level required to switch on the indoor unit concerned. When another call button is operated this capacitor is discharged or maintained at its discharged level if it has not in the meantime discharged by natural leakage.