Telephone intercom system

Abstract

An intercom system which requires neither a common control nor specially-designed telephone instruments. A station module is connected to a two-line telephone outlet wherever an intercom station is desired, and a conventional telephone instrument is plugged into the module. The module includes a single push-button for setting up or joining an intercom call. Dialing is accomplished using the tone pad of the telephone instrument, with a DIP switch being provided in each station module for assigning an address to the module. When the handset of a telephone instrument is first placed off-hook, the instrument is automatically connected to the telephone line. To switch back from an intercom call (after the intercom button has been operated so that the instrument is connected to the intercom line), all that the user must do is momentarily depress the switch-hook of his telephone instrument. The system is designed to be fool-proof in the sense that the user really has to remember only two things: the intercom button is operated momentarily to originate or to join an intercom call, and the switch-hook is operated momentarily to transfer from an intercom call to the telephone line. Everything else is automatic, for example, each telephone instrument being connected automatically to the telephone line when the handset is placed on-hook.