Interphone network using two wire lines - has keyboards and memories with ultrasonic signalling and logic control

摘要

The equipment enables a number of users to communicate using equipment connected in a mesh or star network of two wire lines. Intercommunication between users having identical equipment is achieved by transmission and reception units housing a loudspeaker and microphone and with a keyboard for calling purposes. A memory circuit memorises the number formed by the keyboard in binary form and provides identification. The call signals are transmitted at ultrasonic frequency and decoded on reception, the called number being displayed. A logicspeak - listen switching circuit switches the microphone or loudspeaker into service depending on signals on the line and which user has priority. Call signals do not interfere with communication.