The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 30, 2003
Filed:
Sep. 24, 2001
Aiphone Co., Ltd., , JP;
Abstract
An intercom system for a building or apartment house includes at least one main entrance station which is installed at an entrance or the like of a building or an apartment house, a plurality of residential master stations which are respectively installed inside a plurality of residences in the building or apartment house for receiving calls and talking with the main entrance station , a common line which connects the main entrance station and respective residential master stations in parallel, a line power supply which supplies direct current power, for example, DC 24 V to the main entrance station and respective residential master stations through the common line , an electronic door lock which is connected to the main entrance station for locking and releasing an entrance door of a main entrance, and a plurality of call switches connected to respective residential master stations and mounted on front doors of respective residences for operation by a visitor. A series resistance and capacitance forming a frequency response leveling circuit is connected across a choke circuit in the line power supply to eliminate frequency dependent impedance differences found to interfere with feedback cancellation and howling control.