| 摘要 |
<p>A telephone or intercom circuit in which the entry of a first line number by the caller locates the desired receiving terminal and after the ring signal commences, the subsequent entry of a secondary code number by the caller initiates a distinct preselected tone at the receiving terminal which identifies the desired recipient of the call or the identity of the caller in accordance with the secondary code number. The circuit may comprise a system of three relays (1), (3) and (7) and five electronic subsystems i.e. a ring detector circuit (2), a pulse counter (4), a remote on-hook detector (5), an acoustic signal generator (6) and a local off hook detector (8).</p> |
