Speech, ringing and opening system

摘要

Speech, ringing and opening system between at least one external station (A) and at least one internal station (I) with the aid of only two wires. The problem here is to implement a system of this type by means of a single circuit. For this purpose, three DC voltage sources are provided in the internal station (I) for a low (1 V), a medium (6 V) and a high voltage (15 V), the low voltage being applied to the external station when the handset is on-hook, the medium voltage being applied for the simplex or duplex operation when the handset is off-hook, and the high voltage being applied to the door opener (TÖ) when the door-opening button is pressed. <IMAGE>