Door telephone and remote unlocking system for flats - uses duplex communication system with individual wires to room units and common return wire

摘要

The equipment includes a door bell and provides door to room communication. It is also used for remote opening of doors. The device uses duplex communication. The equipment comprises a door unit connected to an electronic control and to room units. One wire is used for each room unit and a return wire is common to all room units. A door release device is located in the door. The door unit has a selector and a door bell push button. The door unit also has a microphone and a loudspeaker. The electronic control comprises a power unit and amplifiers for the communication system. Each room unit has a microphone, a loud-speaker and a door release push-button.