Door annunciator

A door annunciator briefly sounds an alarm when a door opens but not when the door closes. When the door begins to open, a reed switch makes a connection so that an electrical current resulting from a change in the amount of electrical charge stored in a capacitor triggers an electronic alarm chip and thereby causes the alarm to sound. When the door closes the switch connects the capacitor to restore its original level of charge. The components are installed in a small self-contained enclosure adjacent the door, and a permanent magnet to operate the reed switch as the door opens and closes is installed on the door.

BACKGROUND OF THE INVENTION 
The present invention relates generally to alarm systems and more 
particularly to an annunciator which activates an alarm signal upon 
opening of a door. 
There are many instances in which there is a requirement for an alarm to 
sound automatically upon the opening of a door. For example, in retail 
establishments such an alarm is needed to alert a salesperson if someone 
enters. A simple alarm system which sounds upon the opening of a door 
includes a switch which is engaged by the door whenever the door is fully 
shut in its frame. As soon as the door begins to open it disengages from 
the switch and the switch contact is thereupon activated to sound the 
alarm. A disadvantage of such a system is that the alarm sounds 
continuously whenever the door is not fully shut, and if the door remains 
open for more than a few seconds the continuously-sounding alarm becomes 
highly annoying. 
To eliminate the annoyance of a continuously-sounding alarm, it has been 
proposed to utilize a switch which is momentarily activated by relative 
movement between the door and the switch. Thus, as the door is being 
opened it moves past the switch and momentarily sounds the alarm. However, 
as the door is being closed it again moves past the switch and again 
sounds the alarm, and this second sounding of the alarm has also been 
found to be annoying. 
This problem could be overcome by a switch mechanism which responds to 
movement of the door in only one direction, and such mechanisms have been 
proposed. However, these mechanisms tend to be relatively complex. They 
are also subject to damage because they frequently project out from the 
door frame and get in the way. Moreover, two such mechanisms are generally 
required if the door is of the kind that can open either in or out. 
It will be apparent from the foregoing that there is a need for a simple, 
economical door annunciator system which sounds an alarm briefly upon 
opening of a door but not upon a subsequent closing of the door. 
SUMMARY OF THE INVENTION 
The present invention provides a door annunciator which includes a switch 
operable to connect a capacitor or the like to provide electrical energy 
to briefly sound an alarm when a door is opened and to disconnect the 
capacitor when the door is closed, thereby providing an economical, 
mechanically simple annunciator system which sounds an alarm only when the 
door is being opened. 
A door annunciator according to the invention includes alarm means such as 
an electronic chime which provides a perceptible alarm signal in response 
to an energizing input signal; energizing means operable to provide an 
energizing input signal to the alarm means for a short time; a battery or 
other source of electrical energy; and switch means, operative to couple 
the energy source to the energizing means upon location of a door in a 
first position with respect to the switch means and to decouple the energy 
source from the energizing means upon location of the door in a second 
position whereby the alarm provides the alarm signal upon opening of the 
door but not upon closing thereof. 
In a preferred embodiment a door annunciator is housed in a pair of 
annunciator enclosures, the first adapted for installation on a door frame 
adjacent an edge of a door and the second adapted for installation on the 
door. The enclosures are located such that they are adjacent one another 
when the door is closed, the door being operative to carry the second 
enclosure away from the first while opening and toward the first while 
closing. A switch activation means is installed in one of the enclosures 
and the switch means is installed in the other. The alarm means, the 
energizing means and the energy source either are housed in the same 
enclosure as the switch means to provide a completely self-contained 
system or are remotely located if convenient. 
The energizing means comprises, for example, a capacitor operative to 
charge from the electrical energy source while the door is in the first 
position and to discharge while the door is in the second position. 
In a preferred embodiment the switch means comprises a reed switch and the 
switch activation means comprises a permanent magnet. The reed switch 
includes a switch contact which connects the capacitor to charge through 
the alarm means when the door opens, the charging current being sufficient 
to cause the alarm signal to be provided for a short time until the 
capacitor approaches full charge and the charging current diminishes. Then 
when the door closes, the connection is changed, and the capacitor 
discharges. 
In an alternate embodiment the capacitor is connected to charge while the 
door is closed and to discharge through the alarm means when the door 
opens. 
Other aspects and advantages of the present invention will become apparent 
from the following detailed description, taken in conjunction with the 
accompanying drawings, illustrating by way of example the principles of 
the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings for purposes of illustration, the invention is 
embodied in a novel door annunciator which briefly sounds an alarm when a 
door opens but not when the door closes. Existing door annunciators 
annoyingly sound the alarm continuously when the door is open or whenever 
the door either opens or closes, or rely on complex, damage-prone 
mechanical devices. 
In accordance with the invention, a door annunciator includes a switch 
operable to connect an energizing means to provide electrical energy to 
briefly sound an alarm when the door is opened and to disconnect the 
energizing means when the door is closed, thereby providing an economical, 
mechanically simple alarm system which sounds only when the door is being 
opened. 
More particularly, as shown in FIGS. 1 through 3 a door annunciator 
according to the invention includes alarm means 11, responsive to an 
energizing input signal at an input point 13 to provide a perceptible 
alarm signal at an output point 15; energizing means 17, operable to 
provide an energizing input signal to the alarm means 11 for a limited 
interval of time; a source 19 of electrical energy; and switch means 21, 
operative to couple the energy source 19 to the energizing means 17 upon 
location of a door 23 in a first position with respect to the switch means 
21 and to decouple the energy source 19 from the energizing means 17 upon 
location of the door 23 in a second position whereby the alarm means 11 
provides the alarm signal upon opening of the door 23 but not upon closing 
thereof. 
The energizing means 17 preferably comprises a capacitor 25 operative to 
charge from the energy source 19 while the door 23 is in the first 
position and to discharge while the door 23 is in the second position. 
In a preferred embodiment a door annunciator according to the invention is 
housed in a pair of annunciator enclosures 27 and 29, the first enclosure 
27 adapted for installation on a door frame 31 adjacent an edge of the 
door 23 and the second enclosure 29 adapted for installation on the door 
23 in a position which is adjacent the first enclosure 27 when the door 23 
is closed, the door being operative to carry the second enclosure 29 away 
from the first enclosure 27 while opening, as shown in broken lines in 
FIG. 1, and toward the first enclosure 27 while closing. 
Switch activation means 33 is located in one of the enclosures, for example 
the second enclosure 29 carried by the door, and the switch means 21 is 
located in the other enclosure. The alarm means 11, the energizing means 
17 and the energy source 19 are located in the same enclosure as the 
switch means 21 to provide a completely self-contained system or can be 
remotely located if desired. 
In the embodiment shown in FIG. 3 the switch means 21 comprises a single 
pole double throw reed switch 35 and the switch activation means 33 
comprises a permanent magnet 37. The switch means 21 includes a 
normally-closed contact 39 connected to a positive terminal (designated 
"V+") of the energy source 19, a normally-open contact 41 connected to 
ground, and a common contact 43 connected to a first plate of the 
capacitor 25. When the door 23 is closed, the reed switch 35 is located 
adjacent the magnet 37 and the magnet 37 exerts a force which moves the 
common contact 43 into connection with the normally-open contact 41. When 
the door 23 opens, the magnet 37 is moved away from the switch 35, 
releasing the common contact 43. This breaks the connection between the 
contact 43 and the normally-open contact 41 and establishes a connection 
between the common contact 43 and the normally-closed contact 39. 
The alarm means 11 comprises, for example, a melody chip 45 such as a type 
7920AT having an input pin #3 which receives the energizing input signal 
at the input point 13. The input point 13 is connected to a second plate 
of the capacitor 25. 
The chip 45 has an output pin #6 which provides the output signal at the 
output point 15. The output point 15 is connected to a base of a PNP 
transistor 47 such as a type 2N2709. An emitter of the transistor 47 is 
connected to V+ and a collector thereof is connected to a base of an NPN 
transistor 49 such as a type 2N222 through a resistor 51. An emitter of 
the transistor 49 is connected to ground and a collector thereof is 
connected to a first terminal of a loudspeaker 53. A second terminal of 
the loudspeaker 53 is connected to V+. 
Other circuit connections of the chip 45 include a pin #8 connected to V+, 
a pin #4 connected to ground, a pin #5 connected through a capacitor 55 to 
V+, and a pin #1 connected to a pin #2 through a resistor 57. 
The energy source 19 comprises a battery 59 having a negative terminal 
connected to ground and a positive terminal connected to a first contact 
of a power switch 61. A second terminal of the power switch 61 is 
connected to V+ to provide operating power to the circuit. A 9-volt 
transistor radio battery gives satisfactory results and ordinarily lasts 
for many months because virtually no current is drawn except while the 
door is open. 
The values of the components in this circuit are not critical. Satisfactory 
results are obtained by using a 3.3 microfarad capacitor for the capacitor 
25, a 33 microfarad capacitor for the capacitor 55, a 330 ohm resistor for 
the resistor 51, and a one megohm resistor for the resistor 57. 
As best shown in FIG. 2, all of the components of the annunciator (except 
the permanent magnet 37) are conveniently housed in the enclosure 27. The 
reed switch 35 is located adjacent a side of the enclosure 27 and the 
other components are mounted on a printed circuit board 63 or the like. A 
grille 65 covers and protects the loudspeaker 53 and provides an outlet 
for sound. 
When the door 23 is closed, the reed switch 35 is located near the magnet 
37 and the force exerted by the magnet 37 holds the common contact 43 in 
connection with the normally-open contact 41, grounding the capacitor 25. 
When the door 23 begins to open, the magnet 37 is carried away from the 
reed switch 35, releasing the common contact 43 from the normally-open 
contact 41. As the common contact 43 is released, it establishes a 
connection with the normally-closed contact 39 and allows a charging 
current to flow into the capacitor 25. This charging current flows through 
the capacitor 25 into the input pin #3 of the chip 45, triggering the chip 
45 to commence playing a musical tune. This tune is amplified by the 
transistors 47 and 49 and provided to the loudspeaker 53. 
Once the chip 45 has been triggered, it continues to play its tune until 
the tune has been completed. Meanwhile, the capacitor 25 approaches full 
charge and the charging current diminishes. By the time the chip 45 has 
finished playing its tune, the charging current has become too small to 
again trigger the chip 45, and the tune is not played again. 
When the door closes, the magnet 37 comes into proximity with the switch 
35, causing the common contact 43 to again establish a connection with the 
normally-open contact 41, grounding the capacitor and quickly discharging 
it. Then when the door opens again the entire cycle is repeated. 
From the above discussion it will be apparent that the chip 45 sounds its 
alarm one time for each opening of the door 23 but not when the door 23 
closes. 
From the foregoing it will be appreciated that the door annunciator system 
of the invention provides a mechanically simple, economical apparatus for 
briefly sounding an alarm each time a door opens but not when the door 
closes. The annunciator is conveniently mounted in an unobtrusive 
enclosure adjacent the door and is operable for extended periods of time 
from a self-contained battery. 
Although several specific embodiments of the invention have been described 
and illustrated, the invention is not to be limited to the specific forms 
or arrangements of parts so described and illustrated, and various 
modifications and changes can be made without departing from the scope and 
spirit of the invention. Within the scope of the appended claims, 
therefore, the invention may be practiced otherwise than as specifically 
described and illustrated.