Wireless door intercom

Details Wireless door intercom Wireless door intercom

1997-12-19

2001-07-03

Vo, Nguyen T. (Department: 2682)

Telecommunications

Transmitter and receiver at same station

With transmitter-receiver switching or interaction prevention

C455S410000

Reexamination Certificate

active

06256479

ABSTRACT:

The present invention relates to a door intercom for a dwelling, the intercom being of the type comprising a street panel designed to be used by a visitor and an indoor set designed to be used by an occupier of the dwelling, the street panel being provided with a call button and being connected to an electric latch fitted to a door of the dwelling, the street panel and the indoor set including means enabling a sound link to be established between them, and the indoor set including a button for causing the latch to open.
BACKGROUND OF THE INVENTION
Numerous door intercoms for dwellings of that type are known in which sound and data are conveyed between the street panel and the indoor set by one or more electric cables.
The electrical power consumed by the electric circuit of the latch is relatively large and it is typically greater than about 10 watts.
Manufacturers of electric latches therefore propose powering them from a transformer whose primary is connected to the mains supply, and whose secondary is capable of delivering about 20 watts of power.
Laying electric cables between the street panel and the indoor set and for powering the electric latch constitutes a problem when no provision was made therefor in the initial construction of the dwelling.
A similar problem is encountered when a cable needs to be laid between a call button and a doorbell located inside the dwelling. Devices, sometimes known as “wireless chimes”, have been available for a long time, in which the traditional wire link between the call button and the doorbell is replaced by a radio link.
However, in a wireless chime the information transmitted by radio is one-way and very simple since all that is required is to trigger the doorbell under remote control, whereas with a door intercom information must travel in both directions, and the information concerned is more complex since it must not only enable dialog to be established between the visitor and the occupier, but it must also enable the latch to be remotely controlled when the occupier seeks to let the visitor in.
So far as the Applicant is aware, no wireless intercom has yet been made available.
Known techniques such as those implemented in wireless chimes provide no solution to the problem of electricity consumption by the street panel, and would require the use of batteries of large capacity and of high cost, or else battery replacement that is so frequent, or a number of batteries that is so large, as to remove any practical advantage in having a wireless link.
In addition, apart from the problem of street panel battery life, known wireless telephony techniques do not provide a solution to the problem of transmitting information such as a latch-opening command, since such transmission must be insensitive to interference in order to avoid any untimely opening of the latch which could jeopardize the security of the dwelling.
Finally, the wireless link between the street panel and the indoor set must be a long-range link in that it must work through the walls of the dwelling.
Unfortunately, the known solution of increasing the range of a transmitter by increasing its power is incompatible both with the requirement for battery lifetime in the street panel and with complying with transmission standards laid down by the authorities which put a severe limit on maximum authorized power.
French patent application No. FR-A-2 593 339 and German patent DE-C-44 08972 describe door intercoms in accordance with the precharacterizing portion of claim
1
, and capable of controlling a latch by radio waves.
Nevertheless, in those known devices, the latch is not powered by an stand-alone power supply contained in the street panel and it is necessary to use a power supply cord to connect the latch or the street panel to the electricity mains supply, with all the drawbacks associated with installing such a cord unless installation thereof was planned at the time the dwelling was built.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to propose a wireless door intercom for a dwelling in which the electricity consumption of the street panel is small enough to enable it to be powered by a small number of low cost batteries that do not require frequent replacement, and which also provides a sound link of good quality together with reliable control of latch opening.
The invention achieves this by the fact that the street panel further includes a radio transmitter and receiver and means for recognizing a latch-opening code received by said receiver, a stand-alone electrical power supply, means for activating the electric circuit of the latch, and means for controlling electricity consumption, firstly to put the street panel in a standby state where its electricity consumption is practically zero while waiting for the call button to be pressed, and secondly to put the panel in an active state enabling a sound link to be established with the indoor set, and enabling the electric circuit of the latch to be activated when the latch-opening code is recognized and the means for activating the electric circuit of the latch have the necessary amount of electrical energy.
In making the invention, the inventors have overcome the prejudice whereby the electricity consumption of a door intercom for a dwelling could not be decreased sufficiently to make it an attractive proposition to power it from a small number of low cost batteries, and that explains why no wireless door intercom for a dwelling has been available in the past in spite of the ever-present need for such a device and the large number of wireless telephones and chimes that have been available for a long time.
In a particular embodiment of the invention, the means for activating the electric circuit of the latch comprise a capacitor whose nominal capacitance is selected so that in the charged state, said capacitor is capable, on being discharged into the electric circuit of the latch, of activating it to enable the door to be opened.
Preferably, the latch-opening code recognition means are organized to trigger charging of said capacitor via a charging current limiter resistor when the latch-opening code has been recognized, and the means for activating the electric circuit of the latch comprise means for monitoring the potential on said capacitor and, when said potential exceeds a predetermined value, for causing it to discharge through the electric circuit of the latch.
Thus, because of the invention, the batteries constituting the stand-alone electrical power supply never deliver a current greater than a predetermined value, even when it is necessary to excite the latch, and the predetermined maximum current value can be selected to ensure long battery lifetime.
In a particular embodiment of the invention, the street panel includes means for causing a coded signal to be transmitted after a visitor has pressed the call button in order to cause a call signal to be issued by the indoor set, with the coded signal depending on the state of the stand-alone electrical power supply. The indoor set includes means for decoding said code signal and for issuing, when a predetermined code signal is recognized, a signal for informing the occupier that the stand-alone electrical power supply of the street panel is in a low state.
Thus, the occupier is informed that the batteries need replacing without any need to provide an indicator lamp on the street panel concerning the state of the batteries, which lamp would itself consume electricity and decrease the lifetime of the street panel batteries.
In a particular embodiment of the invention, said means for controlling the electricity consumption of the street panel include a timer triggered by depressing the call button, said timer causing the street panel to be maintained in the active state for a predetermined duration.
In a particular embodiment of the invention, the street panel includes a radio duplexer.
In a particular embodiment of the invention, the transmitter and the receiver of the street panel operate by frequency modulation (FM) and in duplex using two

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