Selective call system for door bells in block of flats - has receivers connected in parallel on reduced number of link conductors to caller

摘要

The system is used e.g. in a block of flats to enable remote control of visitor access and uses fewer cables to connect a greater number of room receivers to the transmitter, the receivers being parallel connected on the same conductors. The call is effected by action of a mechanical or static contact unique to each receiver. The contact signal is fed to a minimum of two conductors to which the receivers are connected, each being able to decode a signal from its associated contact only. The contact signal may be formed by a respective frequency signal or frequency combination to which a receiver can respond. Selection of calls may be realised by the association with the frequency or frequencies of one or more continued current voltages fed into the conductors.