Abstract:
A hush mode disabling device for a smoke alarm having a self-test function, a hush mode that engages upon activation of the self-test function to silence or desensitize the smoke alarm for a predetermined period of time, and a remote self-test controller. An improvement includes a hush mode disabler for determining whether the self-test function has presently been activated by the remote self-test controller and for disabling the hush mode if the self-test function has presently been activated by the remote self-test controller.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hush mode disabling circuit for a self contained smoke alarm that is connected to a remote fire alarm system. 
     BACKGROUND OF THE INVENTION 
     Smoke alarms often experience false alarms as a result of smoke produced from cooking, smoking and other non-threatening situations. Thus, it is desirable to be able to temporarily disable or desensitize a smoke alarm under such false-alarm conditions. 
     For this purpose, many modern smoke alarms include what is referred to as a silencing feature or hush mode. Typically, smoke alarms include a test button to allow a user to initiate a self-test function to assure the smoke alarm is working properly. In order to simplify smoke alarm construction and operation, many manufacturers have incorporated the hush mode into the test button. As such, when the test button is depressed, the smoke alarm will go into a silent or decreased sensitivity mode for a predetermined period of time, after which the smoke alarm will rearm itself in its normal operating mode. 
     FIG. 1 shows a typical photoelectric smoke alarm chip  100 , Model No. A5358CA or A5366CA manufactured by Allegro Microsystems, Inc., connected to external circuitry with which it would normally be used. The entire circuit is contained within a smoke alarm enclosure  102 . A power source  104  is provided to provide V DD  and V SS  (ground) for the circuit and the chip  100 . 
     The enclosure  102  is provided with a smoke chamber  106  in which a infrared emitting diode  108  and an infrared photo diode  110  are contained. The emitting diode  108  is connected between pin  6  of the chip  100  and V DD  of the circuit. The emitting diode  108  is driven by a oscillator and timing circuit  112  provided on the chip  100 . The detecting diode  110  is connected between pin  3  of the chip  100  and V DD  of the circuit. The output of the detecting diode  110  is amplified by a photoelectric amplifier  114  provided on the chip  100 . The output of the photo amp  114  is fed to a logic circuit  116  provided to the chip  100 . 
     When smoke particles enter the smoke chamber  106 , the particles cause the light emitted by the emitting diode  108  to be diffracted before it is received by the detecting diode  110 . The logic circuit  116  of the chip  100  detects this diffraction and, when appropriate, causes a horn driver  118  provided on the chip  100  to drive an external horn  120  which generates and audible alarm. 
     A momentary push button  122  connected between V DD  and pin  16  of the chip  100 , when pressed, causes the chip  100  to test the smoke alarm circuit and drive the horn  120  if the circuit is functioning properly. 
     To avoid false alarms, a hush mode is provided to the chip  100 . To utilize the hush mode, a voltage divider VD comprising two resistors R 1 , R 2  is connected between the power source  104  and pin  4  of the chip  100 . A ratio of the voltage provided by the voltage divider VD and V DD  sets a decreased sensitivity level of the smoke alarm circuit when hush mode is active. Whenever the push-button  122  is pressed, hush mode is activated for a predetermined period of time. To disable the hush mode entirely, the voltage VD provided to pin  15  of the chip  100  must be set to V SS . In this way, the hush mode is either permanently enabled or permanently disabled, depending upon the circuit configuration. 
     In recent years, there has been a need to provide inexpensive centralized fire alarm systems. In order to do this, many manufacturers have taken inexpensive individual smoke alarms and linked them together to form a centralized system. One of the features of these systems is the ability to perform a self-test of all of the smoke alarms in the system simultaneously from a centralized or remote location. 
     However, when smoke alarms having the hush mode described above enabled are used in such a network system, the activation of a remote self-test will engage the hush mode. As a result, all of the smoke alarms will be silenced or have reduced sensitivity for a period of time. During this time period, the areas protected by the smoke alarms will be at an increased risk of an undetected fire hazard. Further, the occupants of the individual areas may not be aware of the reduced sensitivity of the smoke alarm. Thus, it would be desirable to provide a means for selectively disabling and enabling the hush mode of this type of smoke alarm. 
     BRIEF SUMMARY OF THE INVENTION 
     To overcome the disadvantages of the prior described above, the present invention provides a circuit for disabling the hush mode of a smoke alarm during a remote test. According to an aspect of the present invention, a hush mode disabling device for a smoke alarm having a self-test function, a hush mode that engages upon activation of the self-test function to silence or desensitize the smoke alarm for a predetermined period of time, and a remote self-test controller is provided. An improvement comprises a hush mode disabler for determining whether the self-test function has presently been activated by the remote self-test controller and for disabling the hush mode only if the self-test function has presently been activated by the remote self-test controller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic view of a prior art integrated circuit smoke alarm chip and a typical circuit with which it may be used; 
     FIG. 2 is a schematic view of a network of integrated circuit smoke alarm; and 
     FIG. 3 is a schematic view of a hush mode disable circuit according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As mentioned above and shown in FIG. 1, smoke alarm circuits contained within a single integrated circuit package are readily available from a variety of manufacturers. 
     These integrated circuit smoke alarms, such as the Allegro A5358CA or A5366CA, are designed to be self sufficient. As shown in FIG. 2, however, due to their increasing economy, multiple integrated circuit smoke alarms  100  are sometimes networked together to form a economical multiple-point fire alarm system  124 . When used in such a configuration, the individual integrated circuit smoke alarms  100  are connected to a central remote station  126  where they can be monitored simultaneously and their self-test functions activated remotely. 
     Thus, when a smoke alarm is used in such a networked configuration and connected to a remote self test activation means, it would be useful to be able to selectively enable the hush mode. When a self test is activated remotely, it is desirable to not activate the hush mode of the smoke alarm so that the smoke alarm is not desensitized without local occupants being aware. However, it is also desirable for the hush mode to be available for local activation by pressing the test button, for situations such as false alarms when the hush mode would normally be used. 
     The present invention provides a remote hush disabling means for disabling the hush mode when the self-test is initiated be the remote station  126 . 
     As an embodiment of the present invention, FIG. 3 shows a hush mode disable circuit  10  designed to work with the Allegro A5358CA or A5366CA photoelectric smoke alarm integrated circuit  100 , that is connected in a network configuration as shown in FIG.  2 . The chip  100  and the hush mode disable circuit  10  are contained within the smoke alarm enclosure  102 . The remote station  126  is external to and remote from this enclosure  102 . 
     In order to function, the chip  100  requires additional circuitry which is well known in the prior art. One example of such circuitry is shown in FIG.  1 . 
     In operation, the chip  100  goes into a decreased sensitivity or hush mode for a period of ten minutes after a test button  122 , shown in FIG. 1, connected to self-test input pin  16  of the chip  100  is pressed, thereby shorting pin  16  to V DD , which is normally 9 VDC. The level of reduced sensitivity during hush mode is set externally to the chip  100  by connecting a hush mode sensitivity level configuration input pin  15  to the junction of a voltage divider network  20  of two resistors (R 1 , R 2 ) connected between V DD  and pin  4  of the chip  100 . When pin  15  of the chip  100  is connected directly to ground, the hush mode is set to function at the full sensitivity of the chip  100 , and thus the hush mode is effectively disabled. 
     In order to disable the hush mode of the chip  100  only during a remote activation of the test function, the hush mode disable circuit  10  is provided with a transistor Q 1  (FIG.  3 ). The base Q 1 B of the transistor Q 1  is connected through a diode D 1  to a remote test control circuit  30  contained within the remote station  126 . The collector Q 1 C is connected to pin  15  of the chip  100  and the emitter Q 1 E is connected to ground. 
     In order to remotely activate the test function of the chip  100 , a remote test function driver circuit  40  is provided. The driver circuit  40  comprises a transistor Q 2 . The base Q 2 B is connected to the remote test control circuit  30  through a diode D 2 . The collector Q 2 C is connected to V DD  and the emitter Q 2 E is connected to pin  16  of the chip  100 . 
     When the remote circuit  30  causes voltage at the cathode of the diode Dl of the hush mode disable circuit  10  to go from approximately 0 VDC to 9 VDC, the transistor Q 1  turns on and causes pin  15  of the chip  100  to be effectively shorted to ground, thereby disabling the hush mode. At the same time, the remote circuit  30  causes voltage at the cathode of the diode D 2  of the remote test function driver circuit  40  to go to approximately 9 VDC, turning the transistor Q 1  on, which causes pin  16  of the chip  100  to be effectively shorted to V DD , thereby activating the test function. 
     When the push-button  122  is pressed, pin  16  of the chip  100  is shorted to V DD , and the self test is activated without disabling the hush mode. In this way, the test function can be locally activated and the hush mode enabled for a period of ten minutes each time the push button is pressed. 
     As alternatives to the circuit  10  described above, the hush disabler of the present invention could comprise means such as an integrated circuit, one or more mechanical relays, diode logic gates, a silicon-controlled rectifier (SCR), an additional connection from the remote test control circuit  30 , or any other means that would be appreciated by one of ordinary skill in the art as sufficient to perform the described object of the present invention. Although particular embodiments of the invention have been described in detail, it is understood that the invention is not limited correspondingly in scope, but includes all changes and modifications coming within the spirit and terms of the claims appended hereto.