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Description  |
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FIELD OF THE INVENTION
The present invention generally relates to security systems, and more
specifically to electronic security systems used in retail stores,
offices, hotels and other establishments to prevent the theft of
merchandise.
BACKGROUND OF THE INVENTION
Various types of security systems to protect retail goods on display in a
store are known throughout the trade. The basic components of the system
include a sensor which is attached to each item of merchandise intended to
be protected, a switch within the sensor which generates an alarm signal,
splitter boxes or similar modular connecting units for receiving signals
from the sensors, and an alarm box which is connected to the splitter
boxes through various conducting cables and which houses an alarm and
related circuitry.
Merchandise security systems can be broadly classified into two groups,
closed loop and open loop systems. In a closed loop security system,
current constantly flows from the alarm box to the sensor. The sensor
switch is in a normally open state, i.e., a non-conducting state.
Depressing the actuator of the switch would place the switch in a closed
state, i.e., a conducting state. The sensor is attached to the article
through the use of two-sided tape or a similar means. With the sensor
flush against the item of merchandise, the actuator of the switch is
depressed, placing the switch in its closed state, i.e. the contacts of
the switch make or are electrically connected. After a sensor is attached
to each item of merchandise, the alarm circuit is armed or set. When
armed, the alarm box circuitry sends out a continuous current through the
splitter boxes and sensor switches; the current then returns to the alarm
box circuitry. As long as no cables are cut and the actuator remains
depressed, the security system remains in this armed state.
During an unauthorized removal of the sensor, the actuator is distended,
which opens the switch contacts and which breaks the closed loop circuit.
Similarly, if a cable is cut the continuous current to the sensor is
interrupted. The alarm box circuitry detects that the current has been
interrupted and an alarm will sound. The alarm notifies store personnel
that there has been a security breach.
A typical closed loop alarm system is disclosed in U.S. Pat. No. 5,172,098,
issued Dec. 15, 1992 (the '098 patent). This alarm system includes an
alarm box, multiple splitter boxes, shunt plugs for the splitter boxes,
sensors, light emitting diodes (LEDs) on the sensors, switches in each
sensor, and a power supply. The power supply provides power to the alarm
circuitry and the LEDs. The LEDs located on the sensors are two-terminal
bi-color LEDs. When the sensor is properly affixed to the merchandise, the
actuator of the switch is depressed and the current flows from the alarm
circuit to the detector circuit in the splitter box, through the connector
cables and finally through the sensor switches. This forms a first circuit
loop or a switch loop.
The detector circuit determines if the switch is closed and therefore
whether the merchandise is secured. When in the armed or secured state,
current flows through a second loop (the LED loop) to power the LED a
first color, e.g., red. This second loop doubles the number of wires and
connections requiring a total of four wires for this alarm system sensor.
The increase in the number of wires and connections increases the costs
associated with these alarm systems. In addition, the increased number of
loops or circuits, means that there is a greater likelihood of improper
installation since inaccurate feedback may be given to the person
installing the system. For example, the sensor may be improperly attached
to the merchandise, but the LED may indicate an armed condition. This may
occur when one loop has been damaged or when there is a faulty connection
in one of the loops.
When the sensor is removed from the merchandise, the sensor switch is
opened and the detector circuit determines that a security breach has
occurred. The detector circuit sends a signal to the alarm circuit
activating the alarm and also sends a control signal through the second
loop to change the color of the sensor LED to indicate an unsecured state,
e.g., green.
The '098 patent's splitter boxes typically have connections for up to six
items of merchandise. The splitter boxes can be strung together to
increase the number of items secured. When the number of pieces of
merchandise needed to be secured is not a multiple of six, shunt plugs are
required to be inserted into all open connections, to keep the sensor loop
closed.
The assignee of the '098 patent has developed several security systems
which operate similar to the '098 patent, for example its Kord
Kontrol.RTM. strip alarm system. The assignee's variations from the '098
patent have substantially the same drawbacks as the '098 patent.
A drawback of all closed loop security systems is that current must
constantly flow. Accordingly, power must be supplied to the sensor switch
at all times. This presents a problem during power outages. Also, many
stores turn off all power to the retail floor space at night or when the
store is closed.
Battery backups have been designed to supply the necessary current;
however, the current draw on the batteries is often too great to supply
current for extended periods of time. This leaves the merchandise
unprotected from unscrupulous security guards and support personnel
(janitors, stock boys, etc.). In addition, batteries would need to be
checked and replaced on a regular basis, increasing the maintenance of the
security system. Recently, the situation has become more acute with the
use of light emitting diodes (LEDs) on the splitter boxes and on the
sensors. The LEDs add to the current drain making a battery back-up system
an even less viable option.
Another drawback to many closed loop security systems is that they require
shunt plugs on the splitter box connections which are not connected to
merchandise. The shunt plugs form an electrical connection to prevent the
alarm from sounding when the system is armed. Shunt plugs increase the
cost of the system and are also a source of misconnections if improperly
installed. Further, shunt plugs must constantly be installed and removed
as the items of merchandise are sold or as stock is replaced. Accordingly,
the shunt plugs increase the amount of time store personnel must spend
attending to the security system. In addition, if the required shunt plugs
are lost or not installed properly the security system is inoperable since
the alarm will sound continuously.
An open loop security system operates in a similar fashion to a closed loop
system. However, the sensor switch would be normally closed, i.e. when the
actuator is distended. When the sensor is properly attached to the
merchandise, the actuator is depressed and the circuit is open. If there
is a tampering of the sensor switch, the actuator distends, the switch
contacts close and current flows through the sensor switch. A circuit is
completed when the sensor switch closes, activating the alarm.
In an open loop security system, the alarm does not sound unless a circuit
is completed. Normally, the only way to complete the circuit is to remove
the sensor from the article. Therefore, an open loop security system may
be circumvented by cutting the sensor cable or removing the sensor cable
plug from its jack. In this manner, the article may be stolen without the
alarm sounding. Since open loop systems are easier to circumvent, they are
not as popular as closed loop systems.
In both, closed loop and open loop systems, the use of alarm modules or
splitter boxes increases the maintenance of the security system. Extra
connections are required to incorporate these splitter boxes; these extra
connections are a weak link that can be attacked by a thief. Further,
splitter boxes are unsightly to look at, and are a source of
misconnections and false alarms.
SUMMARY OF THE INVENTION
It is an object of the instant invention to provide an improved security
system to protect merchandise and the like.
The present invention is a fully integrated security device and system to
protect articles of merchandise within a retail store. All alarm and
detection circuitry and all connections to the sensors are located in one
housing, making it an integrated or completely self-contained unit. The
instant security device and system includes a plurality of sensors
attached to the items which are to be protected. Item cords connect the
sensors directly to an alarm circuit. Separate alarm modules or splitter
boxes are not required.
The alarm circuit is housed in a single unit or strip and is usually
remotely located from the protected items of merchandise. A bi-color LED
is associated with each sensor circuit and is located on the housing next
to the item cord connector. In its secure or non-alarm state, the LED
displays a first color, e.g. green, indicating that the system is armed
and the item of merchandise is protected. Upon the unauthorized removal of
the sensor, the cutting of the item cable, or upon a similar security
breach, the alarm will sound and the LED will change from its first color
to a second or alarm color (green to red).
After a security breach, the store personnel goes to the alarm system to
turn the alarm off. After viewing the LEDs on the housing, the store
personnel can immediately see the alarm color displayed by the housing LED
(red), and will be informed of the exact location in which the security
breach took place.
Bi-color LEDs may also be placed within the sensor housing to provide a
visual warning to a potential thief that the item of merchandise is
protected by a security system. The colors of the sensor LEDs may match
the colors of the strip LEDs. When the system is armed and the sensor
properly attached to the item, the sensor LED indicates a first or secure
color (green). Upon the unauthorized removal of the sensor from the item,
the sensor LED turns from green to red.
The instant invention is a closed system when drawing power from its AC
adapter. However, during a power outage or when the power is turned off in
the stores at night, the system switches to an energy conservation mode in
which a battery supplies the power. In the energy conservation mode,
current does not continuously flow to the sensors but is pulsed. The
current is sent through the circuit in microsecond bursts, thus conserving
energy. The strip LEDs are turned off during battery operation and are
only lit during a security breach, further conserving the battery power.
The sensor LEDs will pulsate during the microsecond bursts, which further
conserves the battery. The pulsating sensor LEDs are still visible to
store personnel.
If there is a security breach during the energy conservation mode, the
alarm will sound and the strip LED which corresponds to the sensor which
was breached will indicate the alarm color. If the security breach is the
unauthorized separation of the sensor from the merchandise, then the
sensor LED will also indicate the alarm color.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become apparent
from the following detailed description, when taken in conjunction with
the accompanying drawings, wherein:
FIG. 1 is a perspective view of the security system according to the
present invention;
FIG. 2 is a perspective top view of a sensor for hard goods, utilizing a
bi-color LED;
FIG. 3 is a cross-sectional view of the sensor of FIG. 2 along lines 3--3;
FIG. 4 is a perspective bottom view of the sensor of FIG. 2;
FIG. 5 is a schematic diagram of the sensor of FIG. 2, shown in
cross-section;
FIG. 6 is a block diagram of the security system according to the present
invention;
FIG. 7 is a schematic diagram of the sensor circuitry which is a section of
the security system indicated by 31A of FIG. 6;
FIG. 8 is a schematic diagram of the detector circuitry which is a section
of the security system indicated by 33A in FIG. 6;
FIG. 9 is a schematic diagram of the strip LED drive circuitry which is a
section of the security system indicated by 35A in FIG. 6;
FIG. 10 is a schematic diagram of the sampling circuitry which is a section
of the security system indicated by 37 in FIG. 6;
FIG. 11 is a schematic diagram of the low battery detect circuitry which is
a section of the security system indicated by 39 in FIG. 6;
FIG. 12 is a schematic diagram of the alarm circuitry which is a section of
the security system indicated by 41 in FIG. 6;
FIG. 13 is a cross-sectional view of a sensor for hard goods utilizing a
single color LED;
FIG. 14 is a bottom plan view of a plug and a jack having two slider
switches which are activated upon the insertion and removal of the plug;
FIG. 15A is a cross-sectional view of the jack of FIG. 14 along lines
15A--15A;
FIG. 15B is a cross-sectional view of the jack of FIG. 14 along lines
15A--15A when the plug is fully inserted into the jack; and
FIG. 15C is an enlarged cross-sectional view of the slider switches of the
jack shown in FIG. 15A, when the slider switches are in their intermediate
position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The security system of the present invention is particularly adapted for
use in protecting merchandise displayed in a retail store. Referring now
to the drawings, a security system, according to the instant invention,
includes at least one sensor along with an alarm circuit; one such
security system being designated in its entirety by reference numeral 10.
Referring to FIG. 1, a twelve jack security system 10 is shown which can
protect twelve items of merchandise. One skilled in the art could
replicate the circuitry to make a security system to protect any number of
items. The preferred embodiments envision a twelve or twenty-four jack
security system.
A strip or housing 12 contains the majority of the circuitry. This
self-contained or integrated approach eliminates the need for splitter
boxes. Accordingly, the number of wire connections is reduced.
Under normal operation, strip 12 is mounted in a location remote from the
merchandise, and preferably near an AC outlet. Although the strip 12 is
shown in a vertical orientation, it may be mounted in any orientation,
including horizontally, without affecting its operation.
Power to the security system 10 is supplied by an AC adapter 14. AC voltage
is converted by AC adapter 14 to nine volts DC and is supplied to the
system circuitry via power cord 16.
Power cord 16 may be hard-wired to the security system. However, for
flexibility and maintenance reasons, a two-wire plug 18 is attached to the
end of the power cord 16 for connection to the alarm circuit. A jack 20 on
the housing 12 receives plug 18. The wires connected to jack 20 carry the
voltage to the circuitry.
Whenever plug 18 is inserted into jack 20 and adapter 14 is being supplied
AC power from an outlet, power indicator light 42 is lit. If power is
interrupted (e.g., plug 18 is removed from jack 20 or there is an AC power
failure) power LED 42 is turned off. The power indicator light 42 may be a
one color LED, and is preferably a green LED. The illumination of power
indicator 42 is independent of the position of key switch 38.
The jack 20 and power LED 42 may be located anywhere on the strip 12. The
positions of jack 20 and power LED 42 are dictated by design constraints,
the location of the circuitry inside strip 12 or for aesthetic reasons.
Store personnel decide which articles of merchandise 22 are to be
protected. In this embodiment, up to twelve items of merchandise 22 may be
selected for protection since a twelve-item security system 10 is used.
Hard goods, including TV's, VCRs, computers, telephones, etc., are
commonly displayed in stores. A variety of sensors may be used to attach
to the merchandise to be protected. For purposes of illustration, hard
goods sensor 24, as seen in FIGS. 2-4 will be used to describe the
operation of the security system. However, one skilled in the art would
readily understand that this system would work with any sensor that had a
two-state element (off/on); for example clips, conductive loops, and
specially adapted computer plugs and RCA-type plugs.
Hard goods sensor 24, including a sensor housing 23, is attached to the
article 22 by double-backed tape 26, as seen in FIG. 4, or by a similar
means (plastic straps, clamps, etc.). Protective backing 27 is removed
from the tape 26 and the sensor 24 is pressed against article 22
depressing actuator 48.
Item cord 28 is of sufficient length to connect the sensor 24 to the alarm
circuitry in strip 12. In the preferred embodiment, item cord 28 is coiled
to allow for a longer length while minimizing entanglement.
Any connection means can be used to connect the sensor 24 to the security
system circuit. In the preferred embodiment, when utilizing three terminal
bi-color LEDs 46 on the sensor 24, three-contact sensor plugs 34 are used
with two contacts shorted together (see FIGS. 5 and 7). Sensor plugs 34
are illustrated as being straight, however any style of plug may be used
including right-angle plugs.
A dual-switch mating jack 36 is mounted in the housing 12. The sensor plugs
34 and its corresponding mating jack 36 are off-the-shelf items.
The security system 10 is activated by a switch means. For increased
security, the preferred switch is a key switch 38. Key switch 38 is a
double-pole double-throw switch, and switches the security system from a
SET-UP mode to the armed or ON mode. Key 40 activates key switch 38 and
can be customized for each security system 10. Only authorized personnel
should have access to key 40 to prevent the circumvention of the security
system.
The basic circuit operation will now be described. FIG. 6 is a block
diagram of the security system 10. A single alarm circuit will be
described, however one skilled in the art would understand that this
circuit can be readily replicated to form a custom security system to
protect any number of items of merchandise. In the preferred embodiment,
the present security system is designed having either twelve or
twenty-four jacks 36 on the strip 12.
Referring to FIG. 3, sensor 24 is shown in cross-section. A single-pole
single-throw switch 50 is the principal alarm signal generation means and
is secured to the interior of the sensor housing 23. Actuator 48 of switch
50 is biased in a distended position and switch 50 is normally open. The
backing 27 of the annular piece of double-sided tape 26 is removed,
exposing a security sticky surface. As the sensor 24 is brought into
contact with the article 22, the actuator 48 is depressed and sensor
switch 50 is closed. The sensor 24 is held in place by the double-sided
tape 26 which is sufficiently strong to keep actuator 48 depressed and to
prevent the accidental separation of sensor 24 with the article of
merchandise 22 when handled by prospective buyers.
Referring now to FIGS. 5 and 7, when the actuator 48 is depressed, closing
switch 50, current flows from the alarm circuit through plug 34, wire 30,
switch 50, green LED 56, and wire 32 back to the alarm circuit. The green
LED 56 of the bi-colored LED 46 is turned on, as is the corresponding
green LED 111 of strip LED 44. (See FIGS. 1 and 9.)
If there is a security breach, for example when there is an unauthorized
removal of the sensor 24 from the article 22, the actuator 48 distends
opening switch 50. Accordingly, the current flows through wire 30,
resistor 52 and the red LED 54 of the bi-colored LED 46, and returns, via
wire 32, to the alarm circuit. The value of resistor 52 is determined
primarily by the design of the alarm circuit and is typically a one kilohm
(K.OMEGA.) resistor.
Other sensors may be used with the present security system having an
operation similar to sensor 24. The LED 46 is not required, however a
two-state element similar to switch 50 is needed.
In FIG. 13, a sensor 24' is shown which is also used to protect hard goods.
A two-terminal single color LED 46' is utilized instead of the three
terminal bi-color LED 46. One terminal of the single color LED 46' is
connected to wire 30', and the remaining terminal is connected to one side
of switch 50. The other connector of switch 50 is connected to wire 32'.
Plug 34 is connected to wires 30' and 32' in the normal manner.
If sensor 24' is used, the first or non-alarm color may be green; a
security breach is indicated when the LED 46' is not illuminated.
In a twelve-item security system, shown in FIG. 6, the sensors are divided
into three groups of four sensors each 31A, 31B, 31C for the purpose of
discussion. FIG. 7 is a schematic diagram of sensor 31A. The operation of
each group of sensors 31A, 31B, 31C is generally identical to the other
groups, however, as explained previously, different sensors may be used.
Also, twelve sensors are not required for the proper operation of the
security system. It may be operated with one sensor plug 34 inserted into
a sensor jack 36.
Wires 30 and 32 are connected to the alarm circuit through sensor plug 34.
Plug 34 is a three conductor plug having two of its conductors 62,63
shorted together. Wire 30 is connected to the shorted conductors 62,63.
Wire 32 is connected to the remaining conductor 61 of plug 34. Wires 30,32
are connected to plug 34 in the normal manner, however, FIG. 5 provides a
visual of the connections showing the three separate conductive areas of
plug 34.
Detector and latch circuits 33A, 33B and 33C of a twelve item security
system are shown in FIG. 6. The circuitry and operation of each detector
circuit 33A, 33B, 33C is substantially identical. The schematic diagram of
detector circuit 33A is shown in FIG. 8. Jack 36 having conductors 71, 72,
73 is shown. When plug 34 is inserted into jack 36, conductor 61 makes
electrical contact with conductor 71, conductor 62 makes contact with
conductor 72 and conductor 63 makes contact with conductor 73. Conductor
71 is grounded and is also connected to contact 81. Conductor 73 is
connected to contact 83. Connector 72 is connected to resistor 74,
typically a 560 ohm resistor; the other end of resistor 74 is connected to
the collector terminal 76 of transistor 78. The emitter terminal 80 is
attached to the supply voltage V1 which is nominally nine volts DC. The
base terminal 86 of transistor 78 is connected so that transistor 78 is
normally ON. Transistor 78 is a PNP transistor, for example a 2N2907. The
voltage at the collector terminal 76 is designated V2 and is nominally
nine volts.
With switch 50 closed, i.e. sensor 24 properly attached to the merchandise
22, and with the sensor plug 34 plugged into strip jack 36, the voltage
appearing at conductors 72, 73, with respect to ground, is approximately 2
to 2.2 volts, which is the forward voltage drop of the green LED 56 of the
sensor 24. Note that when using the hard goods sensor 24, the voltage at
conductor 72 is equal to the voltage at conductor 73 since plug conductors
62 and 63 are shorted at sensor plug 34. The voltage to sensor LEDs 54, 56
is provided through resistor 74. Terminal 73 of jack 36 is connected to
the junction of pull-up resistor 88 and resistor 90. Resistor 88 is
typically a 6.2 megaohm (M.OMEGA.) resistor and resistor 90 is a 10 kilohm
(K.OMEGA.) resistor.
The connection of terminal 73 with resistors 88 and 90 is made through
contacts 83 and 84 of a double-pole double-throw slide switch 85. Slide
switch 85 is integrated into jack 36 and co-acts with jack 36 when plug 34
is inserted into and removed from jack 36. Contact 84 is the common
contact. When the sensor plug 34 is inserted into the jack 36, the slide
switch contacts 83 and 84 are shorted together and contacts 81 and 84 are
open. When sensor plug 34 is removed from jack 36, the slide switch
contacts 81 and 84 are shorted together and contacts 84 and 83 are open.
Resistor 88 provides a pull-up voltage V1 (9 volts in this embodiment) to
the input of the cross-coupled NOR set/reset latch 100. Resistor 90
provides input protection to the set input 240 of latch 100. Various
set/reset latches can be used; for example CD4043B is a common integrated
circuit chip 115 which contains four set/reset latches 100. Chip 115 is
connected in a normal manner including a filtering capacitor 101.
When the voltage appearing at the input to the latch 100 is less than 1/3
of the V1 supply voltage (a non-alarm condition), the output of the latch
100 will be low. If the voltage appearing at the input to latch 100 is
greater than 1/3 of the V1 supply voltage (a security breach), the output
of the latch 100 will go high.
The output of the latch 100 drives the input of a true/complement buffer
106 via line 102. (See FIGS. 8 and 9.) Buffer 106 is a typical buffer and
may be found for example on semiconductor chip CD4041UB designated by
reference numeral 107.
The latch circuitry 100 ensures that the removal and reinsertion of plug
34, or the removal and reapplication of sensor 24, will not reset the
alarm circuitry. Accordingly, once a breach of security condition is
detected, the alarm horn 126 will sound Until key switch 38 is turned from
the 0N position to the SET position. The latching circuits also prevent
tampering of the strip 12. If a new plug 34 or a foreign object is
inserted into jack 36, an alarm will be initiated.
The LED drive circuitry is designated by reference numerals 35A, 35B and
35C. The circuitry and operation of each module 35A, 35B and 35C is
substantially identical. Buffer 106 drives the bi-colored strip LED 44.
The true output 109 of buffer 106 drives the anode of the red LED 110 of
bi-colored strip LED 44; the complement output 113 of buffer 106, drives
the anode of the green LED 111 of the strip LED 44 through a tri-state
non-inverting buffer 112. When the output of the latch 100 is low (a
secure or non-alarm condition), the complement output 113 will be high,
which forces the output of the tri-state buffer 112 to be high. This high
voltage will forward bias the green LED 111 on the strip causing it to
light. The true output 109 of the buffer 106 will be low thereby reverse
biasing the red LED 110 on the strip, keeping the red LED 110 off.
The tri-state non-inverting buffer 112 may be part of a common integrated
circuit chip CD4503. In a twelve-item security system, two CD4503 chips
will be needed.
The cathodes of the red LED 110 and the green LED 111 of the bi-color strip
LED 44 are connected together and attached to resistor 114. Resistor 114
limits the current through the bi-colored strip LED 44 and is typically 1
K.OMEGA.. The other end of resistor 114 is connected to the common
terminal 94 of a second slide switch 116 contained within strip jack 36.
Slide switch 116 is activated upon the insertion and removal of sensor
plug 34 from jack 36. The purpose of slide switch 116 is to provide the
proper bias voltages for strip LED 44.
The connections between terminals 91, 93 and 94 are similar to terminals
81, 83 and 84. These terminals 91, 93 and 94 are part of a double-pole
double-throw slide switch 116. Terminal 94 is the common terminal.
Connections are made between the common terminal 94 and the connecting
terminals 91 and 93 depending on whether a plug 34 is inserted into jack
36. When plug 34 is inserted into jack 36, terminal 94 is shorted to
terminal 93. Terminal 93 is connected to ground. When plug 34 is removed
from jack 36, terminal 94 is shorted to terminal 91. Terminal 91 is
connected to the complement output 113 of the true/complement buffer 106.
It should be noted that both slide switches 85 and 116 are integral to jack
36. Slide switches 85 and 116 are break-before-make switches. The slide
switches 85,116 are activated with the insertion and removal of plug 34.
When no plug 34 is inserted into jack 36, the input 240 of latch 100 is
grounded because common terminal 84 is connected to terminal 81. Since
input 240 is less than 1/3 of the V1 supply voltage, the output. 102 of
latch 100 remains low. Therefore, whenever jacks 36 are not being used
(i.e., when less than twelve items of merchandise are being protected)
shunt plugs or jumpers do not have to be inserted into the unused jacks
36.
The output 102 of latch 100 is also connected to an eight input. OR gate
120 as shown in FIG. 6. OR gate 120 may be integrated circuit chip CD4078.
The output 121 of OR gate 120, drives transistor 122 through resistor 124.
(See FIG. 12). Transistor 122 is an NPN transistor, e.g. 2N2222
transistor. Resistor 124 is nominally a 2 K.OMEGA. resistor. The emitter
of transistor 122 is connected to ground while the collector is connected
to the negative side of horn 126 or alarm means 126. When there is a
non-alarm;condition, all of the eight inputs of OR gate 120 are low. The
output of OR gate 120 will also be low, and transistor 122 is off, keeping
horn 126 off. During a security breach, the input of latch 100 will go to
a voltage greater then 2/3 of the V1 supply voltage. This will set the
latch 100 and the output 102 of the latch 100 will go high. This high
voltage will cause the true output 109 of the true complement buffer 106
to go high which will forward bias the red LED 110. The complement output
113 of the buffer will go low which in turn reverse biases the green LED
111. The result will be that the green LED 111 will go off and red LED 110
will go on. The high output of the latch 100 will cause the output of the
OR gate 120 to go high which turns on transistor 122 causing the horn 126
to sound.
The power for this circuit is provided by a nine volt AC adapter 14. The
power supply circuit 41 consists of zener diode 123 as shown in FIG. 12,
which is used to clamp voltage transients and thereby protect the rest of
the circuit components. Capacitor 124 is used to filter the supply
voltage.
In addition, green LED 42 on the strip lights when the AC adapter is
providing power to the circuit. Resistor 132, in series with the LED 42,
limits the current through LED 42. The voltage across LED 42 will be
approximately two volts with respect to the negative side of the AC
adapter. The voltage between the anode of the green LED 42 and the circuit
ground will be approximately 1.4 volts. The anode of the LED is connected
to the input of a Schmitt trigger inverter 134 which drives a second
Schmitt trigger 136. The output of Schmitt trigger 136 provides a "loss of
AC power" signal to the rest of the circuit via control line 139.
The power supply back-up or energy conservation means including inverters
134 and 136 feeding line 139 as shown below is incorporated into the
circuit by including a 9 volt battery 226 as shown in FIG. 11. In the
event that either the AC adapter was pulled out of its outlet or the AC
power main is turned off, the battery 226 provides the necessary power to
keep the security system in its armed state. A simple recharging circuit
may be incorporated into the back-up supply, however the preferred
embodiment does not utilize a rechargeable battery and circuit.
The battery 226 is isolated from the AC adapter by diodes 128 and 130 which
functions as a deactivating circuit means as described. When the AC main
power is lost, the voltage at the anode of the AC indicator LED 42 becomes
equal to the nine volt supply line which is provided by battery 226 via
line 198. The green LED 42 will go off and the voltage at its anode will
go high. This causes the output of the inverter 134 to go low; this, in
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