U.S. patent number 3,914,753 [Application Number 05/425,195] was granted by the patent office on 1975-10-21 for intruder alarm system.
This patent grant is currently assigned to Franciscan Enterprises, Inc.. Invention is credited to Fan Pong Cho.
United States Patent |
3,914,753 |
Cho |
October 21, 1975 |
Intruder alarm system
Abstract
In an intruder detector a beam of electro-magnetic energy pulses
is directed across a space to be protected and onto a
photodetector, the electrical pulse output of the photodetector
being utilized to discharge a capacitor in one pulse. When the
charge on the capacitor exceeds a threshold amount an alarm is thus
sounded in response to the absence for a time of electromagnetic
energy pulses falling on the detector. The photodetector is
preferably a phototransistor with its base electrode biased so that
the phototransistor doubles as an amplifier. A timing circuit is
provided to continue to sound an alarm for the same preset period
of time after each interruption of the electromagnetic energy beam
pulses. The intruder alarm receiver of the electro-magnetic energy
pulses is either self-contained or operated in conjunction with a
remote master control unit, the two units being connected so that
an alarm will sound at the master control unit if a wire connecting
the two is broken, all without the necessity for extra continuity
checking conductors.
Inventors: |
Cho; Fan Pong (Kowloon,
HK) |
Assignee: |
Franciscan Enterprises, Inc.
(Sunnyvale, CA)
|
Family
ID: |
23685571 |
Appl.
No.: |
05/425,195 |
Filed: |
December 17, 1973 |
Current U.S.
Class: |
340/511; 340/556;
340/512 |
Current CPC
Class: |
G08B
13/183 (20130101) |
Current International
Class: |
G08B
13/183 (20060101); G08B 13/18 (20060101); G08B
013/18 () |
Field of
Search: |
;340/258B,276,409
;307/311 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
General Electric Semiconductor Products Dept., High Voltage
Transistors Planar Passivated, (45.63); Syracuse, N.Y.,
1966..
|
Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: Limbach, Limbach & Sutton
Claims
I claim:
1. An electronic circuit for detecting the existence of an object
in a space through which an electro-magnetic radiation beam passes,
comprising:
a phototransistor having emitter, collector and base
electrodes,
means for directing electro-magnetic radiation onto said
phototransistor, whereby said phototransistor may be exposed to
said electro-magnetic radiation beam,
said collector and emitter electrodes being connected in series
with a load resistor across a two terminal voltage supply,
means connected between said voltage supply and said base electrode
of the phototransistor for providing a bias that increases the zero
radiation signal collector current at least several times a normal
collector current that exists when the base terminal remains
unconnected, said bias further set for said phototransistor to
operate in a non-linear gain region with a collector bias current
below that which causes the phototransistor to operate with linear
gain characteristics,
an object indicating device having two states, one state indicating
an object present and another state indicating an object not to be
present, and
means responsive to the voltage drop across said load resistor for
driving said indicating device so that it is in one of its said
states when said phototransistor is receiving electromagnetic
energy and another state when that electro-magentic energy has been
interrupted for a selected period of time.
2. An electronic circuit according to claim 1 wherein said
indicating device driving means comprises a non-linear
semi-conductor amplifier element that is biased to operate in a
range of its non-linearity with its steady state current at a very
low value, whereby said amplifier draws very little current when no
signal is impressed thereon.
3. The electronic circuit according to claim 1 wherein said
indicating device means comprises:
a direct current voltage supply source,
a storage capacitor connected to said voltage source through a
series connected resistor, whereby said voltage supply source
normally charges said capacitor at a rate determined by the values
of said capacitor and resistor,
means receiving said voltage across said load resistor for
establishing substantially a short circuit across said capacitor
means in response to electro-magnetic energy striking the
phototransistor, whereby said storage capacitor is immediately
discharged by a pulse of electro-magnetic energy of adequate
intensity striking the phototransistor, and
means monitoring the voltage level of said storage capacitor for
initiating a change of state of said intruder indicating device
when said capacitor voltage increases to a predetermined level.
4. The electronic circuit according to claim 3 wherein the object
detecting device state change initiating means includes means for
instantaneously charging a second storage capacitor simultaneously
with a change of state of such indicating device,
means for slowly discharging said second capacitor,
means monitoring the voltage across said second storage capacitor
for reversing the change of state of said indicating device when
the second capacitor discharges down to a predetermined voltage
level.
5. The electronic circuit according to claim 1 which additionally
comprises a pulsed source of electro-magnetic radiation adapted to
form said radiation into a beam that may be directed at said
phototransistor, said pulses all having the same polarity with
substantially no electro-magnetic energy intensity in the period
between pulses.
6. The circuit of claim 1, wherein said bias providing means is a
resistance connected between said base electrode and one of the
terminals of said voltage supply, and further wherein said circuit
additionally comprises a capacitance connected between said base
electrode and the other of said voltage terminals.
7. The circuit of claim 1, wherein said indicating device driving
means includes a capacitive coupling between said indicating device
and a point of connection of said load resistor and an electrode of
said phototransistor.
8. An electronic circuit for detecting the existence of an object
in a space through which a time amplitude varying electro-magentic
energy beam passes, comprising:
a voltage supply source,
a storage capacitor connected to said voltage source through a
series connected resistor, whereby said voltage supply source
normally charges said capacitor at a rate determined by the values
of said capacitor and resistor,
means including a photodetector for producing a time varying
electrical signal that is derived from a time amplitude varying
electro-magnetic energy signal that strikes said photodetector,
means receiving said time varying electrical signal for
establishing substantially a short circuit across said capacitor in
response to an electro-magnetic energy signal striking the
photodetector, whereby said storage capacitor is immediately
discharged upon receipt of an electro-magnetic energy pulse of
adequate intensity that strikes the photodetector, and
means monitoring the voltage level of said storage capacitor for
initiating an alarm when said capacitor voltage increases to a
predetermined level.
9. The electronic circuit according to claim 8 wherein said
capacitor short circuit includes a three terminal semi-conductor
device with two of its terminals being connected directly across
said capacitor without any additional electronic components
connected in series therewith, a third terminal of said
semi-conductor device being a control terminal which switches on
and off an electrical path between its said two terminals in
response to the voltage at said third terminal, said third terminal
being connected to receive said time varying electrical signal from
the photodetector.
10. The electronic circuit according to claim 8 which additionally
comprises means for generating an optical beam adapted to be
directed a distance onto said photodetector, said beam generating
means including means for forming an optical beam of periodic
single polarity pulses with substantially zero intensity between
pulses.
11. The circuit of claim 8 which additionally comprises means
controlling said alarm for maintaining the alarm in an active state
for a predetermined time after initiated by said alarm initiating
means.
12. The circuit of claim 8 wherein said photodetector is a
phototransistor biased in a non-linear gain region with a signal
output many times an output when said phototransistor is operated
as a photodiode.
13. An electronic circuit for detecting the existence of an object
in a space through which a time varying optical signal beam passes,
comprising:
a voltage supply source,
a first storage capacitor connected to said voltage source through
a series connected resistor, whereby said voltage supply source
normally charges said capacitor at a rate determined by the values
of said capacitor and resistor,
means including a photodetector for producing a time varying
electrical signal that is derived from a time varying optical
signal that strikes said photodetector,
means responsive to the light detector time varying output signal
for establishing a discharge path across said first capacitor that
discharges said first capacitor faster than said resistor permits
the first capacitor to charge,
means monitoring the voltage level of said storage capacitor for
instantaneously charging a second storage capacitor when the
voltage across said first storage capacitor reaches a predetermined
threshold level,
means for slowly discharging said second capacitor,
means monitoring the voltage across said second storage capacitor
for emitting a control signal that is initiated when said second
capacitor storage means charges said second capacitor and which is
terminated when the second capacitor discharges to a predetermined
voltage level, and
means receiving said control signal for generating an alarm in
response thereto, whereby the alarm is operative for a length of
time after each charging of the second storage capacitor that is
determined by the discharge time constant of the second storage
capacitor and the predetermined voltage level which causes the
control signal to be terminated.
14. Apparatus for remotely indicating the existence of a desired
condition, comprising:
means forming a unit of apparatus for detecting the existence of
said desired condition,
means forming a second distinct unit of apparatus for indicating
the existence of said desired condition,
means including first, second and third connectors on each of said
detector unit and indicating unit for interconnecting the units by
first, second and third conductors, respectively,
an electronic power supply as part of said indicating unit and
connected to develop a supply voltage between said second and third
connectors of said indicating unit,
said detecting unit including an output semi-conductor device that
is normally held in a conductive state across the first and second
connectors of the detecting unit but is connected to be switched to
a non-conductive state when said desired condition is detected,
a load element within said indicating unit extending between its
said first and third connectors of said indicating unit, and
means as part of the indicating unit for operating an indicating
device when a voltage across said load element increases
significantly, whereby when either said first, second or third
conductors are cut the indicating device will give this warning
without any additional elements necessary between the two
units.
15. The system according to claim 14 wherein said detecting unit
includes a photodetector and means for focusing an optical beam
onto said photodetector, thereby to provide an intruder alarm
system which cannot be disabled by an intruder without setting off
the indicating device.
Description
BACKGROUND OF THE INVENTION
The detection of an intruding person or object in a building or in
an outdoors area along a line of sight path is desired in a great
number of circumstances. An intruder in a line of sight path is
detected, according to one system, by the generation of a beam of
invisible electro-magnetic energy pulses, usually in the infrared
frequency range. A transmitter of such pulses is positioned at one
location and the beam of light is directed along a line of sight to
a receiver at a distant location. The receiver is designed to sound
an alarm or give some other indication of the presence of the
intruder when pulses of a predetermined time interval are not
received at the receiver. One example of this is described in a
magazine EDN/EEE of Mar. 15, 1972, page 62. U.S. Pat. Nos.
3,534,351 -- Harden and 3,605,082 -- Matthews also describe such
systems. However, the systems of prior art suffer from certain
disadvantages of high power requirements, a high probability of
falsely triggering their alarm and an ability of a intruder to
disable the alarm system.
Accordingly, it is an object of the present invention to provide an
intruder alarm system with a reduced power consumption and a
minimum number of circuit components.
It is another object of the present invention to provide an
intruder alarm with a reduced probability of being falsely
triggered.
It is yet another object of the present invention to provide an
intruder alarm system with a separately spaced units that cannnot
be unknowningly disabled by communicating wires therebetween being
cut.
It is still another object of the present invention to provide an
intruder alarm system which is compatible with commercially
available door and window intruder sensors (in addition to optical
path beam receivers) and also with fire sensors in order to provide
complete integrated intruder and fire alarm system.
SUMMARY OF THE INVENTION
An electro-magnetic energy pulse receiver is provided with a
phototransistor with its base biased so that the operation of a
phototransistor is in a region of higher gain than if the base
terminal is left unattached as is the usual case with existing
devices and techniques. That is, light pulses received by the
phototransistor appear as electrical pulses at its collector output
with greater magnitude, possibly by a factor of 10, over the
magnitude of the electrical pulse output for the same light pulse
intensity with the base of the phototransistor unbiased.
A transistor amplifier of the single polarity output pulses of the
phototransistor as its base biased at a very low level so that the
transistor amplifier is operating on a non-linear portion of its
characteristic curve. That is, the bias is set so that the
amplification of the single polarity pulses from the
phototransistor is much greater then it would be for pulses with an
opposite polarity. The result is that the power consumption by this
amplifier stage is reduced since the collector current of this
transistor amplifier is at a very low level in between pulses.
Reduction of power comsumption is extremely important in intruder
alarm systems since it is generally desired to operate then from
batteries so that they are not dependent on the continuity of
commercial power.
In order to detect when an intruder has passed through the
electro-magnetic energy pulse beam, the amplified electrical pulses
from the phototransistor are applied to a switching transistor
which discharges a first storage capacitor for the duration of each
received pulse. This capacitor is normally charged by a low current
through a resistor connected in series with the capacitor and the
direct current voltage source. When a few pulses are blocked by an
intruder passing through the electro-magnetic energy beam, the
voltage across the capacitor rises until it reaches a set threshold
value which is detected to initiate an alarm. The switching
transistor which discharges the storage capacitor during each
received light pulse is connected directly across the capacitor
without any other impedance element in series therewith and is
designed to discharge the capacitor substantially completely upon
the receipt of one pulse. This has the advantage that the voltage
is not permitted to build up across the capacitor when a few random
pulses are not received because of dust, insects flying through the
beam, and similar reasons. Thus, false triggering of the alarm from
such causes is significantly reduced.
Once the voltage in this first storage capacitor exceeds the
detected threshold level, an alarm is initiated by appropriate
triggering circuits. The duration of the alarm, usually of an audio
type, is made to be independent of the length of the time that the
electro-magnetic energy beam is broken so that the alarm may be set
to sound for a sufficient time to alert someone nearby. This is
accomplished by a second capacitor that is immediately charged when
the alarm is initiated while a threshold trigger circuit monitors
the voltage across the capacitor. This voltage is permitted to
decay at a controlled rate to turn off the alarm when the capacitor
voltage reaches a preset minimum. The length of alarm sounding is
controlled by the time constant of the discharge path of the
capacitor and by the lower threshold value which is sensed to turn
off the alarm activating circuits.
For a more complete alarm system and for other reasons, it is often
desirable to locate the alarm a distance from the electro-magnetic
pulse beam receiver. The receiver is connected to a remote master
control unit including the alarm by a number of conductors
necessary to communicate an alarm initiating signal and power. If
any one of the communicating conductors is broken by an intruder,
the alarm system will not be disabled but rather the alarm receives
an initiating signal in the same manner as it is turned on by an
intruder breaking the electro-magnetic energy pulse beam. This is
accomplished in part by sending a DC signal between the receiver
and master control units for activating the alarm having a level
that is the same as will be seen by the master control unit if one
of the signal communicating conductors is cut. In a specific form,
this is accomplished by including as an output element of the
receiver a semi-conductor element which is rendered normally
conductive expect when the alarm is to be sounded. A load element
of this output semi-conductor device is positioned at the input of
the master control unit and supplies from there the power necessary
to operate the receiver output semi-conductor element. No alarm is
sounded when the receiver output semi-conductor element is turned
on and drawing current through its load element. When any of the
output line from this transistor, a common conductor or a power
line are broken by an intruder, the alarm is sounded. No additional
wires or other physical paraphernalia are required to detect the
breaking of the communicating conductor between receiver and master
control units.
Other objects, advantages and features of the various aspects of
the present invention will become apparent from the following
description of a preferred embodiment thereof which should be taken
in conjunction with the accompanying drawings. In the preferred
embodiment of the invention to be described, a infrared beam of
pulses is utilized but it will, of course, be understood that
visible light of other kinds of radiation may be directed across an
area to be protected as well. Also, it will be appreciated from the
following description that many of the circuit concepts and
features have general application in other specific intruder
alarms.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates very generally the major components of an
intruder alarm utilizing the various aspects of the present
invention;
FIG. 2 is a preferred circuit diagram of a receiver unit;
FIG. 3 illustrates generally a typical transistor characteristic
curve;
FIG. 4 shows sample waveforms at various points in the circuit of
FIG. 2;
FIG. 5 is a circuit diagram of one form of a master control unit
which may optionally be utilized in conjunction with the light beam
receiver of FIG. 2; and
FIG. 6 illustrates generally a remote alarm unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIG. 1, a light beam transmitter includes a
power supply 11 which may be any convenient source of energy such
as a battery, house power, etc. A pulse generator 12 receives power
from the supply 11 and drives a light emitting diode 13 with a
train of periodically recurring narrow width pulses. For a usual
application of an intruder alarm, it is desires that the light beam
be invisible. With this requirement, the diode 13 is a standard
gallium arsenide diode which emits infra-red radiation of a
frequency just outside the visible spectrum. The radiation emitted
by the diode 13 is in the form of narrow width pulses wherein the
pulse generator 12 essentially and repetitively turns the diode 13
on and off.
The pulsed light beam generator also includes a lens 14 which
produces a collimated light beam 15 which is directed at a light
gathering lens 16 that is part of a receiver unit 17. The receiver
17 includes an alarm 18 which maybe any indicating device and is
described in the example herein as an audio alarm. The indicating
device 18 is activated by the receiver 17 when pulses within a
predetermined time interval are not consecutively received by the
receiver 17. A series of pulses would be missing from the light
beam when an intruder passes through that beam. It is this
condition of an intruder being present that is desired to be
detected and indicated by the alarm 18.
The receiver 17 is shown to be completely self-contained including
an alarm. It may be desirable, however, in many circumstances to
have a master control unit 19 interconnected by cable 20 to the
receiver 17 and remotely positioned therefrom. In this case, the
alarm 18 will be deactivated with a similar alarm 21 of the master
control unit 19 being activated in its place. The receiver 17 is
described in detail with respect to FIG. 2 and the master control
unit 19 is described in detail with respect to FIG. 5. The master
control unit, as described hereinafter, makes possible the
connection of a number of receivers of the type of receiver 17 and
also permits connection of available fire, door and window opening
sensors. When the master unit 19 is utilized, not only is the alarm
function transferred to the master unit from the receiver 17 but
also the power supply is transferred thereto. By maintaining the
power and alarm in the same physical unit, the chances of disabling
the alarm circuits by cutting the wires interconnecting the units
is rendered virtually impossible, as described hereinafter.
Referring to FIG. 2, the details of the receiver unit 17 in FIG. 1
are described. A phototransistor 113 of a commonly available type
is connected with its emitter connected directly to a common
potential bus 22. The collector of the transistor 113 is connected
through a series resistor 114 to a voltage bus 23. A coupling
capacitor 115 is connected to the collector of the phototransistor
113 and presents at a terminal 25 a time varying electrical signal
in accordance with the time varying optical signal impressed upon
the phototransistor 113 through its lens 16.
Instead of using the phototransistor 113 as a photo-diode as has
previously been done by omitting connection to its base lead, the
circuit of FIG. 2 provides a resistor 112 between the voltage
supply line 23 and the base lead of the phototransistor 113 for
biasing the phototransistor into a region of operation that permits
the phototransistor 113 to double as an amplifier. That is, the
current supplied to the base through the resistor 112 increases the
steady state collector current I.sub.c that would exist in the
phototransistor 113 when the base lead remains unconnected to other
circuit components. Referring briefly to FIG. 3, a typical curve
for a transistor gain versus collector current I.sub.c is shown.
Without the base lead of the phototransistor 113 connected to a
biasing source, the collector current would be a very low value,
such as in the region of 94 as shown in FIG. 3. By biasing the base
of the phototransistor 113 in a manner illustrated in FIG. 2, this
steady state (no signal) current may be increased to a value such
as that indicated at 96 of FIG. 3. As a result, the overall gain of
the phototransistor 113 is increased. A capacitor 111 is connected
between the common point and the base lead of the phototransistor
113 as well in order to reduce static pick-up by the
phototransistor 113.
The electrical pulse signal at the terminal 25 is then applied to a
pulse amplifier whose primary element is a transistor 117. The
emitter of this transistor is connected directly to the voltage
supply line 23 while its collector is connected through a series
resistor 118 to the common line 22. A biasing resistor 116 is
connected between the base lead of the amplifying transistor 117
and the common line 22 in order to increase the steady state (no
signal) collector current in the trannsistor 117 a small amount.
Therefore, a pulse signal applied to the base lead of the
transistor 117 is amplified and coupled through a capacitor 119 to
an output terminal 27. In order to conserve battery power, the
transistor 117 is biased by its base resistor 116 to a non-linear
region of its gain characteristic curve of the type illustrated in
FIG. 3. This is, the collector current I.sub.c for the transistor
117 with no signal applied to its base is set by the value of its
biasing resistor 116 to be on a steeply sloping portion of its gain
curve as illustrated in FIG. 3, such as in the region of 98. It is
usually the practice to bias an amplifying transistor so that its
signal operates in the flat region 99 of its characteristic curve
(FIG. 3) but in this case since we are dealing with single polarity
pulses, the zero or no pulse collector may be placed in the region
such as 98 (FIG. 3). This significantly reduces the current drain
on the power source between the pulses.
The amplified electrical pulses are then applied from the terminal
27 to the base of a transistor 121 which is biased by a base
resistor 120 to be normally non-conductive. As soon as enough
current flows through the base resistor 120 from the signal
impressed at the terminal 27, usually enough to create a voltage
drop of about 0.6 volts which is the forward voltage drop across a
semi-conductor junction of the transistor 121, transistor 121
becomes conductive. Therefore, as a pulse rises from zero past this
lower threshold value at the terminal 27, the transistor 121 is
rendered conductive to draw large current to discharge a first
storage capacitor 123. This first storage capacitor 123 is
connected across the collector and emitter of the transistor 121
directly without any resistance or any impedance elements connected
in series therewith so as to facilitate this discharge. The first
storage capacitor 123 normally is being slowly charged through the
resistor 122 since this series circuit combination is always
connected between the voltage supply line 23 and the common line
22. When the transistor 121 is rendered conductive by an input
pulse, however, the capacitor 123 is practically shorted out and is
thus rapidly discharged. The typical impedance of a transistor 121
in its conductive state is less than 100 ohms, so the capacitor 123
is rapidly discharged. The width of each of the pulses 15 are made
sufficient so that the transistor 121 is on long enough for
particular circuit components chosen to completely or substantially
completely discharge the capacitor 123 for each pulse. A buffer
transistor 124 is provided to prevent current drain on the
capacitor 123. The collector of the transistor 124 is connected
directly to the voltage supply line 23, its base to one side of the
capacitor 123 and its emitter through series resistors 125 and 126
to the common line 22. The junction between the resistors 125 and
126 in the emitter circuit of the transistor 124 provide the output
voltage at a terminal 28 which is subsequently utilized.
Referring to FIG. 4, some voltage waveforms of the circuits
described up until this point with respect to FIG. 2 may be
observed. FIG. 4(a) shows the light pulses being generated by the
transmitter unit and directed across a space to be protected onto
the phototransistor 113. If there is an interruption or a blockage
of this beam temporarily, a few pulses will not reach the
phototransistor 113, as indicated in FIG. 4(b). The pulse train
shown in FIG. 4(b) is that received by the phototransistor 113 when
an intruder passes through the beam 15.
The voltage across the capacitor 123 is illustrated in FIG. 4(c).
The voltage at the terminal 28 has substantially the same waveform
but a different magnitude. From FIG. 4(c) it can be seen how the
voltage builds up across the capacitor 123 during the time that
pulses are not received. As soon as a pulse 29 is received after
the period of interruption, the capacitor 123 is completely
discharged by the transistor 121. It is this rising voltage which
is monitored by subsequent circuits of FIG. 2 to sound the alarm
18.
An amplifying transistor 127 is unbiased and receives a signal at
its base from the terminal 28. The emitter of the transistor 127 is
connected directly to the common line 22 while its collector is
connected through series resistors 128 and 129 to the voltage
supply line 23. The signal at a terminal 30 is derived from the
junction between the series connected resistors 128 and 129. This
signal is applied to a base electrode of a transistor 150 which is
also unbiased and has its emitter connected directly to the voltage
supply line 23 and its collector connected through a switch 153 and
a second storage capacitor 151 to the common line 22. A diode 152
is connected across the transistor 150 and switch 153 between the
capacitor 151 and the voltage supply line 23. A load resistor 154
is connected between the collector of the transistor 150 and the
common line 22.
The transistors 127 and 150 are normally in an "off" condition
until the voltage builds up across the capacitor 123 to a certain
threshold level such as the level 31 indicated in FIG. 4(c). When
this happens, a terminal 32 at the output of the alarm timer
circuit becomes connected directly to the voltage supply line 23
through the transistor 150 which is now in its "on" state. The
exact threshold level 31 is determined by the characteristics of
the unbiased transistors 127 and 150 as well as the relative values
of the voltage dividers 125, 126 and 128, 129. This threshold level
31 is set to require the omission of light beam pulses for a set
period time (such as the time for two pulses) so that the alarm
will be sounded only when the beam is completely broken by an
intruder and will not be accidently sounded by a bug flying through
the beam, dust etc. which may block only one pulse.
FIG. 4(d) shows the voltage at the collector of the transistor 127
with respect to the common line 22. The turning on of transistor
127 at the threshold level 31 drops the voltage of its collector to
substantially zero volts, that potential of the common line 22.
This same signal, but in different magnitudes, is applied to the
base of the transistor 150 and thus the transistor 150 remains
turned on for the same length of time until the capacitor 123
becomes discharged. When the transistor 150 is turned on, the
capacitor 151 is rapidly charged to the full voltage since it is
effectively placed directly between the voltage supply line 23 and
the common line 22. When the transistor 150 is again turned off in
response to the first storage capacitor 123 being discharged by a
received light pulse, the capacitor 151 slowly discharges through
the resistor 154 at a rate determined by the time constant of the
resistor 154 and capacitor 151 combination. A voltage waveform at
the output terminal 32 of the alarm timer is shown in FIG. 4(e)
wherein a full voltage is impressed for a time across the second
storage capacitor 151 while the transistor 150 is on, and then the
voltage across the capacitor 151 begins to decay as it is
discharged through the resistor 154. This signal at the terminal 32
permits the alarm 18 to be sounded for a period of time that is set
independently of the time that the light beam is broken by an
intruder.
A trigger circuit receives this signal of FIG. 4(e) at the terminal
32 and provides at an output terminal 33 a control signal as
illustrated in FIG. 4(f) which is initiated when the capacitor 151
is first charged above a threshold level 34 of FIG. 4(e). The
control signal ends, as shown in FIG. 4(f) when the second storage
capacitor 151 discharges to a second threshold level 35. This
control signal at the terminal 33 as illustrated in FIG. 4(f) can
then be used to operate any kind of alarm system but is shown in
FIG. 2 to turn on a multivibrator circuit which gives an audio
signal at an output terminal 36. The audio signal drives a
loudspeaker or other audio alarm 18 through power amplifier
transistors 173 and 174. The length of time, therefore, that the
alarm 18 is sounded depends upon the value of the second threshold
level 35 that is set by the trigger circuit and also the time
constant of the capacitor 151 and resistor 154. If it is desired
that the alarm 18 only sound during the period of interruption of
the light beam 15, the switch 153 is opened and the capacitor 151
is not operative, thereby not maintaining the sounding of the alarm
18. The switch 153 is convenient in case an occupant of a dwelling
desires to turn off the alarm after the beam has been broken or
wishes to check to see if the beam is still broken at any
particular instant when the alarm is sounding. The diode 152
discharges the capacitor 151 very rapidly if power is lost in the
power line 23, such as by turning off the main supply power.
Transistors 157 and 160, along with resistors 155, 156, 158, 159
and 161 form the threshold circuit between the terminals 32 and 33
which senses the voltage on the collector electrode of the
transistor 150 through the terminal 32. Positive feedback within
the trigger circuit through the resistor 156 causes the threshold
circuit to have an upper threshold 34 and a lower threshold 35
(FIG. 4(e)). When the transistor 150 becomes conductive,
transistors 157 and 160 are switched to their conductive state.
When the voltage at the terminal 32 drops below the second
threshold level 35, the transistors 157 and 160 switch back to
their non-conductive state. This trigger circuit is similar in
philosophy to the well known Schmidt circuit.
An ordinary multivibrator circuit is established between the
terminals 33 and 36 and includes transistors 166 and 170,
capacitors 165 and 169 and resistors 164, 167, 168, 171 and 172.
The control signal at the terminal 33 operates the multivibrator
circuit through bias resistors 167 and 168. Thus, an audio signal
is generated at its output terminal 36 by the multivibrator when
the control signal at the input 33 is up for a period as shown in
FIG. 4(f). A diode 163 and capacitor 162 suppress the signal
generated by the multivibrator and keep it isolated from the rest
of the circuit.
The receiver may be provided with an internal voltage source 176 or
may receive its voltage through a line 37 from the master control
device 19 at a receiver terminal 38. A switch 175 is provided in
the receiver for selecting whether an internal or an external
voltage source is utilized. Since it is desired to have the voltage
source of an intruder alarm system in the same unit as its alarm
unit, a switch 177 is provided to be ganged with the switch 175 so
that the alarm 18 is rendered inoperative when a master unit
voltage source is utilized. The switches 175 and 177 are shown in
FIG. 2 in their positions wherein the receiver is utilized without
a master unit 19. These switches would be thrown to their opposite
positions if a master unit 19 is utilized.
The receiver is also provided with a common terminal 39 for
communicating through a line 40 to the master control unit 19.
Also, a terminal 41 is provided for sending a signal through a line
42 to a master control unit when an intruder has blocked the pulsed
light beam. Only three lines 37, 40 and 42 are therefore required
as the interconnection 20 of FIG. 1 between the receivers 17 and
master control unit 19. An inverting transistor 132 has its
collector connected directly to the output terminal 41 of the
receiver unit and its emitter terminal connected directly to the
common line 22. The base terminal of the transistor 132 is
connected between a voltage dividing circuit of series resistors
130 and 131 which are connected between the collector of the
transistor 127 and the common line 22. It will be noted that there
is no load resistor associated with the inverter transistor 132 in
the receiver unit of FIG. 2 but rather it is included in the master
control unit, as explained hereinafter with respect to FIG. 5. When
the receiver unit is interconnected with the master control unit,
the voltage at the output 41 increases from a substantially zero
level, as the transistor 132 becomes nonconductive during the time
that an intruder is blocking the light beam 15.
Referring to FIG. 5, a master control unit 19 having the alarm 21
is illustrated in detail. Since the alarm timer, trigger circuit,
multivibrator and audio alarm circuits of the master unit
illustrated in FIG. 5 are substantially the same as those described
above with respect to the receiver of FIG. 2, these circuit blocks
will not be described again but rather their components are
identified with the same numbers that were used in FIG. 2 except
that the reference numbers utilized in FIG. 5 include a prime (')
mark following the corresponding number. It will also be noted that
these circuits are operating with different polarities for
convenience but that they are in principal the same as those
described above with respect to the receiver of FIG. 2.
Referring to the input circuits of the master unit of FIG. 5, a
terminal 41' connects the collector of the receiver inverter
transistor 132 through the line 42 to a collector load resistor 200
which is also connected to a voltage supply line 43 of the master
control unit. A terminal 38' is provided for connection with a
voltage supply line 37 which goes to the receiver of FIG. 2.
Similarly, a terminal 39' is provided for connecting with the
common line 40 that extends between the receiver of FIG. 2 and the
master control unit of FIG. 5. The signal at the collector of the
inverter 132 (FIG. 2) is applied to base terminal of a transistor
223 through series connected diode 201 and resistor 221. A
capacitor 222 extending between the base of the transistor 223 and
a common line 44 of the master control unit, in conjunction with
the resistors 220 and 221, dampens the circuit to eliminate any
high frequency noise that may exist as a result of being induced in
the lines connecting the master control unit with the remote
receiver. When an intruder blocks the pulsed light beam 15, the
inverter transistor 132 is turned "off" and this causes the voltage
at the terminal 41' of the master control unit to suddenly go up as
illustrated in FIG. 4(g). While the inverter transistor 132 of the
receiver is turned on when no intruder is in the path of the light
beam 15, the voltage at the terminal 41' is substantially zero
which renders the transistors 223 of FIG. 5 nonconductive. When
either the light beam 15 is broken by an intruder for sufficient
time to turn off the transistor 132 or the line 42 is cut, the
transistor 223 is rendered conductive which results in sounding the
alarm 21.
The collector of the transistor 223 is connected directly with the
voltage supply line 43 while its emitter is connected through
series resistors 224 and 225 to a common line 44. A point between
the resistors 224 and 225 is connected to a base of a transistor
226 which has its emitter connected directly to the common line 44
and its collector connected through series load resistors 227 and
228 to the voltage supply line 43. When the transistor 223 becomes
conductive by either an intruder breaking the light beam 15 or the
line 42 being cut, the transistor 226 also becomes conductive and
applies its collector voltage through a series resistor 232 to a
base connection of the transistor 150' as part of an alarm timer.
The alarm timer shown in FIG. 5 operates in the same way as
described in detail with respect to the receiver circuits of FIG.
2.
It will be noted that if the common conductor 40 interconnecting
the receiver of FIG. 2 in the master control unit of FIG. 5 is
broken, or if the power supply conductor 37 is severed by someone
attempting to disable the alarm, the inverting transistor 132 will
become non-conductive and this will turn on the transistor 223 of
the master control unit with a resulting sounding of the alarm.
This circuitry is an extremely simple way of providing a
"fail-safe" system.
This technique also has the advantage that a plurality of receivers
such as that illustrated in FIG. 2 may be connected with a single
master control unit of FIG. 5. Referring to FIG. 5, a second input
41" may be connected to an output terminal 41 of a second receiver.
The input circuit of FIG. 5 includes a resistor 202 and diode 203
which are counterparts of the first input circuit elements 200 and
201. If a remote receiver unit is not, however, connected to the
terminal 41" then a jumper 46 must connect the terminal 41" to the
common terminal 39' in order to prevent constant sounding of the
alarm 21. For fire protection and for detecting when a door or
window is opened, normally closed detectors may be connected to the
master unit of FIG. 5 to sound an alarm when these sensors detect a
condition for which they are designed. Other inputs may be added to
the master unit of FIG. 5 as desired. A separate terminal or a
plurality of similarly connected terminals 47 are attached to the
junction between the series load resistors 227 and 228 of the
transistor 226. The terminal 47 is provided for connection with
normally open circuit sensors. A closing of the sensor circuit with
respect to the common terminal 39' causes the alarm 21 to sound.
Therefore, the master unit of FIG. 5 is very flexible.
Referring to FIG. 6, a remote alarm 48 is shown very generally
having input terminals 49, 50, 51 and 52. These terminals are
designed for connection by cables to terminals 53, 54, 55 and 56,
respectively, of the master control unit of FIG. 5. The inverting
transistors 132' of FIG. 5 operates in the same manner as described
with respect to the inverter 132 of FIG. 2. There is a fail-safe
interconnection between the master control unit and the remote
alarm unit 48. A battery source 57 may be provided in the remote
alarm unit 48 for driving both the master control unit of FIG. 5
and the remote receiver of FIG. 2, if desired. Alternately, a
voltage source 277 may be applied across the terminals 54 and 56 of
the master control unit if the remote alarm unit of FIG. 6 is not
utilized or if a power source at the master is desired for some
reason. Generally, however, the voltage source should be in the
same unit as the alarm, this being the remote alarm unit 48 when it
is utilized. In either case, a switch 276 of the master unit of
FIG. 5 turns on the power to the master unit (FIG. 5) and its
associated receiver unit.
The terminals 53, 54 and 56 are counterparts, respectively, of
terminals 41, 39 and 38 of the receiver of FIG. 2. The fourth
terminal 55 which is provided in the master of FIG. 5 provides an
additional function of enabling a remote alarm unit 48 of FIG. 6 if
it is used when power is applied to the master unit. If the master
unit of FIG. 5 is turned off a remote alarm in the unit 48 should
be deactivated or it will continuously sound. Therefore, a signal
is developed at the terminal 55 from a collector terminal of a
transistor 264 which tells the remote unit 48 when power is applied
to the master control unit and thus enables operation of the alarm
unit 48. A second transistor 262 has its base connected through a
series resistance 258 to the voltage supply line 43. The transistor
264, with its emitter connected directly to the common line 44, is
biased through a resistor 263 from the voltage input terminal
56.
It will be understood that the various aspects of the present
invention have been described with respect to a specific intruder
alarm system but it will be understood that the invention is
entitled to protection within the full scope of the appended
claims.
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