Intercommunications system for apartment block - uses number selection by binary coded signal and interconnection by one pair of wire between flats and main door

摘要

The terminals in each flat (40-52) are all connected in parallel on a single pair of wires (56,62,58) and are also in parallel with the terminal (10) at the main door. Each terminal has a transmit-receive circuit. The unit at the main door has a set of push buttons (12-26), one for each flat. By pressing a button, a binary coded pulse train is transmitted which is only acted upon by the circuit coded for its receipt, giving an audible signal in the flat. The person answering in the flat can then carry on a two-way conversation with the person at the door. By means of the binary code signalling facility the person in the flat can unlock the main door and also, for example, put on the hall and staircase lights.