Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~7~51~
The presen-t application discloses a cornrnunication
system employing modifications of the multiple (at least two)
Erequency propagation of ultrasonic energy to assure
reliabili-ty in the presence of multipath cancellation which
produces a tempoxary null at a particular time and location for
one of the propagated frequenciesO
In the disclosed embodiments two ultrasonic frequencies
are transmitted omnidirectionally through the atmospheric
medium within a closed space, such as a building, such that
multipath reception is inevitable. The ultrasonic frequencies
are separated in frequency enough to assure ~with subs-tantial
certainty) that nulls at both frequencies do not occur at the
same -time in the same location.
The coding is selected on the basis of frequency or
timed bursts (e.g., binary coded on-off transmission~ or
combinations of both to code the data -to be transmitted at the
two transmitted frequencies in a format that can recover the
data at the receiver whenever one or more of the ultrasonic
energy waves arrives with sufficient magnitude to be detected.
Simplification of equipment and enhanced reliability
are obtained in the preferred embodiments by using sequential
transmission of data bits as the upper and lower sidebands of
a suppressed carrier~ Thus demodulation using the carrier
frequency as a reference produces a single frequency equal to
the sideband off-set upon reception of either or both sidebands.
csm/ ~
.~
`
S~4
SUPERVISED WIRE~ESS SEC~RITY SYSTEM
.
BACXGROUND OF THE INVENTION
A traditional security system consists of a plur-
ality of intrusion sensors loeated at each seeured
opening, sueh as doors and windows. As a rule, the
sensors are magnetieally operated switches. ~hen the
door or window is closed, these switches are held
closed. In a supervised system all the switehes are
eonneeted in series, then conneeted to a eontrol unit.
If one or more switches open or the intereonneeting
wire is cut, the break in the eircuit is detected by
the loeal unit and an alarm condition is reported.
A non-supervised system, which is seldom used,
uses switches which are open when the seeu~ed door
or window is elosed. The switehes close when the
opening is breached. This completes a circui-t whieh
is deteeted by the control unit and an alarm oecurs.
If the wire to the switches is cut before an intrusion
occurs, it is not detected since the eircuit simply
remains open.
Other types of intrusion sensors sueh as
infrared, microwave, and ultrasonic motion deteetors,
or photobeams (eleetric eye), can also be used. Eaeh
sensor contains a relay which is energized when no
intrusion is oecurring. If an intrusion is detected
or the internal-power supply fails, the relay becomes
deenergized and its contacts open breaking the eireuit
(in a supervised system) to signal an alarm.
One of the problems with prior art systems is the
provision o~ supervision where the area to be protee-
ted covers multiple rooms. Wiring the central and
, .
.
:L~t7~5~.~
remote units of- a complete system in such spaces ln-
volves substantial expense at installation time and
except in comm~rcial warehouse space or the like the
wiring must be concealed for aesthetic purposes.
The cost of such installations is prohibitive for the
- individual home or small business and greatly in-
creases the expense for large commercial installations.
The attempt to couple -the elements of a system by
radio link would avoid the problem of wiring but
introduces the problem of interference between
systems and units of a system since the radio waves
transmit throu~h the walls of a building and cause
interference within the system ox with other radio
e~uipment. Th~ Federal Communications Commission (FCC)
in the United States and similar agencies in other
countries do not ordinarily permit periodic communica
tion between automa-tic system elements and thus radio
linked systems are incapable of being supervised, i.e.,
capable of testing their own condition ~or ready
operability in the event of any alarm condition. Ultra-
sonic systems, on the other hand, have their energy
confined by the walls of a room and thus do not present
a problem of interference between units which are
located in adjoining rooms. This property prevents
communication between units of a system which have to
cover more than one room. In addition the problem of
null conditions for ultrasonic energy i5 severe
because the transmission paths change with environmental
parameters such as temperature and humidity such that
communication between ultrasonic units cannot be
assured at any given time even though no null was
experienced when -the unit was installed~
~'7~51~
-3-
SUMMARY OF T~E INVENTION
. ~ . . . _
The present invention provides a supervised
multi-function security system based on ultrasonic
energy transmission which is adapted to overcome the
limitations of previous ultrasonic systems in that
multi-communication between multiroom enclosures is
achieved and the communication signal is frequency
and time redundant in a manner which avoids the loss
of signal due to nulls. The major units of the
10 system are primarily interconnected by ultrasonic ..
sound waves and thus require no installation wires.
Where convenient~ auxiliary units may be connected
into the system by wire or coupling through -the AC
wiring in the building without adding any significant
installation expense or inconvenience.
The system utilizes a plurality of transponders
which can be interrogated from a central data unit
for reporting back operative or inoperative condition
and alarm conditions in the vicinity of local txans-
ponders. Transmission between adjacent rooms is accom-
plished by acoustic repeaters which are adapted to
provide two-way communication between the central
data unit and remote transponders. Multiple functions
are provided by the system by initial programming and
by key control operation of the system once it is
installed.
Accordingly, it is a principal object of the pre-
sent invention to provide a supervised multiroom
capability in a supervised security system which eli-
minates the requirement for wire connection betweenunits and does not present any problems of radio inter-
ference or other regulated energy emission limitation.
.Y~ f~
A further objec-t of the invention is to provide an
economical security sys-tem which makes supervised security
available on an installed basis at a cost less than provided by
present systems and in which the system can be recovered
without expense or defacing of the building in the even-t that it
is desired to remove the system.
Still another object is to provide a supervised
security system which is reliable in terms o-f the communication
of the data required among the multiple units of the system
without the use of wire connections between the primary units
of the system and at the same time permits polling of the units
of the system for periodically checking overall operativeness
thereby to assure that the system is always operative and
capable of detecting and reporting an alarm as intended thereby
complying with requirements for insurance, Underwriter's
Laboratory approval and other advantages such as insurance
discounts.
Therefore, in accordance with the present invention
there is provided a wireless data communication system
operable to transmit information as ultrasonic frequency
signals which are subject to loss caused by nulls due to
multipath signal cancellation at a receiving station
comprising: a plurality of spaced stations capable of
transmission and reception at a plurality of different
ultrasonic frequencies sufficiently separated in frequency to
spatially separate the respective loca-tions of nulls of the
different frequencies due to multipath propagation between
communica-ting stations; means for transmitting the information
by modulating each of -the ultrasonic frequencies wi-th the
cr/~
~ ~7,~5~ ~
same data bits and transmitting each the data bit at the
different ultrasonic frequencies; and ultrasonic receiving
means at each receiving s-tation for recovering the data bits
by detection of any one or all of the ultrasonic frequencies~
These and other objects will become apparent from
the following detailed description taken in conjunction
with the appended drawings.
BRIEF DESCRIPTION OF T~IE DR WINGS
Fig. 1 is a floor plan view of a home illustrating
a typical residential installation of the system of the
invention;
Fig. 2 is a phasor diagram useful in describing the
occurrence of nulls in multipa-th transmission of energy.
Fig. 3 is a plot of signal strength over a period of
hours for an ultrasonic signal at a particular loca~ion and
at a single frequency.
- ~a -
,,~ cr/~
Fig. 4 is a block diagram of the synchronous
detector signal recovery system for a four-frequency
transmission as used in accordance with the disclosed
embodiment.
Fig. 5 shows a basic timing diagram for the
system.
Fig. 6 is a block diagram of a transponder contem-
plated to be embodied as an integrated circuit for use
in various units of the system.
Fig. 7A, B, C is a waveform diagram showing
signal timing in the operation of the transponder of
Fig. 6.
Fig. 8 is a block diagram of the central data
unit of the system.
Fig. 9 is a block diagram of an acoustical
repeater as used in the system.
Fig. 10 is a block diagram of a remote keypad
used in the system.
Fig. 11 is a block diagram of an emergency report-
20 ing unit used in the system.
Fig. 12 is a block diagram showing an alternate
system of the invention using frequency coded informa-
tion.
Fig. 13 is a waveform diagram useful for describ-
25 ing the system of Fig. 12.
Fig. 14 is a block diagram of a further modifica-
tion of the invention having simplified circuit
requirements and low s~andby power consumption.
Fig. 15 is a block diagram of a simplified
30 security system employing the communication system of
Fig. 14.
--6--
DESCRIPTION OF T~E FIRST P~FERRED EMBODI~'r
General Description
The general location and function of the components
of the system will first be described with reference to
Fig. l.
Central Data Unit (CDU)
A Central Data Unit (CDU) (shown and describ-
ed with reference to Fig. 8) is located near an entrance
or other convenient location such as concealed in a
closet. The CDU is powered from the AC mains and has
a constantly charging standby battery for use in the
event of a power failure. It has a single ultrasonic
transducer used for transmitting and receiving which is
located to radiate and receive ultrasonic energy in the
principal space to be protected.
The CDU has a telephone-type keypad which is
used for arming and disarming the system by using
special code numbers. The ~eypad is also used for
programming the system when installed, such as:
-entry/exit codes.
-number of transponders used in -the system.
-which transponders monitor the entrance/
exit.
-entry and exit delay times.
-which transducers are used to repor-t burg-
lary, fire, etc.
-which transducers are to be active 2~ hours
per day.
The CDU has a numerical display used to indicate
information such as:
-which openings are not secure (e.g. open
window~.
-
~7~4
,
7 -
-which openings caused an alarm,
-number of seconds remaining on the entry/
exit timer.
The CDU is normally in the listen mode. It
periodically transmits an interrogation code to all
transponders, each remOtQ unit responds if all is well.
If a unit does not respond,~an alarm is initiated.
The CDU can receiye at any time an unsolicited
response from a transponder which either indicates
intrusion or other alarm or a low battery. If it is
an intrusion, or other alarm event, an alarm is
iniated, or, optionally, the intrusion can be veri
fied by interrogating the transponders, in which event
the unit detecting the intrusion will not respond.
The low battery signal is stored and displayed
at the CDU along with the identity number of the unit
sending the signal so the user can be reminded to
change that transponder's battery.
Transponders
Typically a transponder T is installed next
to each secured opening and connects to the sensing
switch. They can also be connected to other intrusion
sensors such as infrared, microwave, and ultrasonic
motion detectors or photobeams. Each transponder is
individually battery powered and is intended to operate
for one year without servicing. A single ultrasonic
transducer is used for both transmitting and receiving.
A built-in coding switch is used to program each
transponder with its unique identification number when
it is installed.
Normally, the transponder is in the listen
mode. If it receives an interrogation from the CDU,
it responds by transmitting its identity code, provid-
ing that its sensor is in the non-alarm state. If in
the alarm state, it does not respond. When its sensor
~7~ JL 4
- 8 -
transfers to the alarm state, it immediately transmits
its identification code to the CDU. This unsolicited
response is interpreted by the CDU as an alarm. Ii the
battery is low, it will randomly transmit a low
battery code followed by its identity code,
Repeaters
Three types of repeaters are used: - acous-ti-
cal repeaters AR, repeaters AC which signal over the
buildings' AC wiring, and direct wire repeaters where
direct connection to a point in a remote area is easily
accessible. There are also extension wire connected
transducers ET.
The acoustical repeater AR fastens to -the door
seperating a protected area from the CDU. Like a
transponder it is battery powered. Two parallel
connected transducers are used, one on each side of the
door. It is initially in the listen mode. When a
burst of ultrasound is detected from either side o
the door, the repeater responds by transmitting an
ultrasonic burst through both transducers. It receives
from either side of -the door and transmlts from both
sides. There is a delay from reception to retrans
mission due to the time required to process the received
signal.
In passing through a repeater an unsolicited
response from a transponder is delayed once. The
response due, to an interrogation is delayed twice,
once in each direction. This predictable delay is taken
into account by the CDU. To prevPnt delays from com-
pounding only one level of acoustic repea-ting is
allowed. These delays are in addition to transmit
time delays due to the speed of sound.
The AC line and direct connected repea-ters act as
boostér amplifiers. When they are no-t transmitting,
they are relaying back to the C~U a linearly amplified
y~s~
-- 9 --
version of the ultrasound picked up in that area. The
resulting delay is negligible. If the CDU is concealed,
an extension transducer ET can be mounted just outside
enclosure via a short length of wire.
Remote Keypad
The remote keypad unit RKP is an optional
device which is battery powel~ed. It can be used to
communicate with the CDU via u~trasound. If the CDU is
not easily accessible, one or more of these devices can
be mounted near the entrances. It has a telephone type
keypad and a low power liquid crystal display (~CD).
The arm/disarm codes are entered then transmitted to
the CDU. The CDU transmits back a signal acknowledg-
ing successful arming or disarming which is then dis-
played at the remote keypad.
A single transducer is used for transmitting
and receiving.
Only arm/disarm codes can be entered at the
remote keypad since all programming must be done at
the CDU.
"Low battery" is not transmi-tted to the
CDU by this unit. It is displayed on the remote key-
pad itself since it is frequently viewed by the user.
Emergency Transmitters
Emergency transmissions can be made with
battery powered hand-held devices PB which can trans-
mit whenever they are manually activated. When
activated, they transmit continously, overriding all
other communications with the CDU. There are two
emergency codes so both holdup and medical crisis
channels can be used in a single installation. These
devices have an ID code so they can be polled to
insure that they are functioning.
TYPICAL INSTALLATION
The components which have just been briefly'
,. .
~ ~ 7 ~ L~
-- 10 -- ,
described can be arranyed to protect a multiroom en-
closure such as a dwelling as shown in Fig. l.
Switches are placed on all openings to tlle outside,
door, windows, etc. The switches at each location are
connected to a transponder T. A grouping of windows
and their corresponding switches can connect to a
single transponder. The C3U,may conveniently be
mounted inside a storage room with an extension trans-
ducer ET mounted just outside the storeroom door. The
CDU communicates directly with all the transponders T
which are not separated by a physical barrier. Since
there are no doors which close off the kitchen, living
room or dining area, direct communication is possible
to transponders in those areas.
The transponders in the master bedroom, bedrooms
l and 2, and bath l use acoustical repeaters AR to
transfer the signal from one side of their doors to the
other. Because of the delay produced by acoustic
repeaters only one level can be used. For this reason
an AC line repeater is used in bath 2. If an acoustic
repeater were used between bath 2 and the master bed-
room a second level of acoustic repeating would be
present which in the presently disclosed system is not
allowed without modification of the timing.
Bacause a wire run is easily made through the store room
floor, an extension transducer can be installed in
the basement to cover transponders located there. I~
the wire run is more than a few feet, a direct wired
repeater would be used.
A-t the time an installation is made such as the
arrangement shown in Fig. l, the transponders T are
coded with DIP switches to have an identifying preamble
and identification number and the central data unit CDU
is programmed to con-trol the system, store data and
process various type signals such as intrusion, low
battery, entry/exit, identlfication of entry/exit zones
~7~
and the provision of e~it time delay, all as more
completely described hereinafter.
PRINCIPLE OF OPERATION
M_ltipath Interference
The transducers in all units have fixed orienta-
tions for ease of installation and their output pattern
is omnidirectional. The ultrasound thus is scattered
in all directions and can be received from all direct-
ions. The ultrasound travels within a room or other
enclosure from one point to the other via many paths
due to reflections off walls, ceiling, floor, etc. It
can go around corners in hallways, into alcoves, and
other areas not separatad by wall or window type
barriers. It is therefore, inevitable that a trans-
mission arriving at a recieving transducer over differ-
ent paths will arrive with differen-t phase.
If a single ultrasonic frequency is used in an
ultrasonic communication system, fading can occur. This
phenomenon is analogous to HF radio transmission over
long distances where some of the signal reflects off
the ionosphere. Fading is due to the phase difference
between the same signal arriving at the receiving point
via paths of different lengths. At some points in space
thevector sum of these signals is zero. A pickup
device at those points will not receive -the signal. At
other points in space the vector sum is not zero so the
signal can be received there. This is known as destruc-
tive and constructive_interference.
The phasor diagram in Fig. 2 is drawn to illustrate
the same signal arriving via two separate paths.
Actually many paths exist bu-t Fig. 2 illustrates the
phenomenon. Each diagram of Fig. 2 ta), (b), (c), (d),
(e~ and () represents the signal at different points
in space. The amplitude and phase of the two path
~. ~'7~S~
- 12 -
signals differ from diagram to diagram. In Fig. 2(d)
a deep null occurs when the two signals have opposita
phase and the resultant is zero. The amplitudes of the
two signals are equal, but their phase differs by 180.
The probability for a null deep enough to lose the
signal completely is slight, but it is finite and is
dealt with in the present invention to provide a
reliable system.
It is impractical to avoid deep nulls during
installation. If a receiving transducer were placed
at a high energy point during installation, a deep null
could shift to that position later as the temperature
and other climatic parameters vary the speed of sound.
A typical recording of ultrasonic energy vs. time is
shown in Fig. 3 for a single frequency at a single
point in space. There are many minor nulls which do
not affect reception over moderate distances. The
occasional deep null would block the signal completely.
The location of the nulls in space shifts as the
fre~uency is varied. If more than one frequency is
used for signalling, it is extremely improbable for
both frequencies to produce a deep null at the same
points in space at the same time. Accordingly, the
present invention uses multiple frequencies in a manner
which avoids the null problem.
Signalling a_d Coding Format
Four different frequencies are used sequentially
in the presently disclosed preferred enbodiment of the
invention. A crystal oscillator in each unit generates
a precise reference frequency, fR, typically between
25 and ~5 kHz. Using digital techniques, this fra-
quency is shifted up or down by a frequency, fl,
similar to single sideband modulation. Either an upper
or lower sideband of fl can be generated, fR~fl or
fR-fl respectively. Using the same process, another
, .
.
-13-
two frequencies are generated by shifting fR up or down
by a frequency f2 producing fR+f2 or fR-f2. The
frequencies fl and f2 are typically in the range of
100 to 300 Hz and are separated in frequency enough
5 to be separately detected in a frequency discriminator,
for example 65 Hz.
Fig. 4 sh~ws a block diagram of a typical receiver
for recovering fl or f2 signal transmissions throughout
the system. An ultrasonic transducer 41 applies a signal
10 fR~fl, or fR+f2 to synchronous detector 42 which has
reference frequ~ncy fR applied as the switching
frequency to detect the sideband that is present. The
output of detector 42 is applied to a bandpass filter
43 which passes frequencies fl and f2 and rejects fre-
15 quencies outside the band. The detected and selectedsideband, fl or f2, is amplified in amplifier 44 and
applied to frequency discriminator 45. Since the high
frequency components are filtered out only the difference
frequency is amplified. If fR-fl or fR~fl is received,
20 fl emerges fxom the bandpass filter 43. Likewise,
if fR-f2 or fR+f2 is received, f2 results. The
frequency discriminator 45 after the amplifier 44
measures the frequency and produces a logic level at
either its fl output 46 or at its f2 output 47. It is
25 not important whether the upper or lower sideband is
received: onlv that fl or f2 can be recovered and
can be distinguished from one another to produce either
an fl or f2 output at terminals 46 or 47 respectively.
Referring to Fi~r 5, the formatting for data
30 transmissions will be described. Each unit can act as
the transmitter for a given condition. During normal
supervised mode the CDU periodically initiates a scan
of N time slots which interrogates all other units to
establish, by their recognized responses, that the
35 entire system is operative and secure. Transponders
can initiate a transmission to the CDU (an unsolicited
response) to report alarm or low battery condition.
- 14
The remote keypad and the emergency unit can also
initiate transmissions. In each instance when
transmission is in progress the system locks out
initiation of other transmission until the end of
the scan in progress to assure processing the data
from various sources wlthout interference.
The transmission scan is represented in Fig. S and
ls shown having N time slots. An offset of fl is
assigned to the odd numbered time slots, and an offset
of f2 to the even numbered time slots. A data bit
consists of an odd followed by an even time slot. If
a binary one is sent, a burst o~ ultrasound is sent
in both time slots for that data bit - first an
offset by fl then an offset by f2. The recovery of
either or both fl and f2 defines a binary one. One or
the other of the transmissions fl and f2 may be lost
due to a deep null. If fR~fl is transmitted in the first
half, odd time slot, fR-f2 will be sent in the second
half, even time slot. This ensures a greater Erequency
separation reducing the probability of both transmission
frequencies being lost in the same null.
The first four data bit positions, eight time
slots, are assigned to the preamble, Data Bits A,B,C,D.
This preamble defines the ultrasonic transmission as to
type of interrogation, response, data transmission, or
emergency.
The following preambles are transmitted and
recognized as binary words:
Preamble Bits
ABCD
CDU
- Interrogate with Reset 1110
- Interrogate without Reset 1110
_ansponder
- Unsolicited Response - Alarm 1000
- Unsolicited Response - Low Battery 1001
~L~7~5~
- 15 -
Preamble Bil R
ABCD
Remote Key Pad
.
- Data Transmission 1101
Emergenc~ Unit
- ~old Up 1010
- Medical Emergency 1111
- Low Battery (same as transponder) 1001
The first bit A in the preamble is always a
binary one. When the first fl is detected, time slot
1 is established in all units by a timer in each unit
which starts and establishes the frame of reference
for the time slots. If f2 is detected first, it means
that fl was lost in a deep null. To compensate for
this delayed start the timer is advanced by one time
slot.
When the CD~ interrogates the transponders, it
sends out the appropriate preamble. Each transponder
receives -this preamble and responds in one of the time
slo-ts. Only one time slot per transponder, as preset
by a DIP switch which establishes its identity number
as a time slot code position, is used per response to
reduce the scan time. Transponder 1 responds during
time slot 9, i.e., ater the eight time slots for the
preamble. It responds at that time by sending a burst
of ultrasound which is offset in frequency by fl from
fR since slot 9 is an odd time slot. Transponder 2
responds during time slot 10 offset in frequency by
f2 from fR since it is an even time slot.
Each transponder responds with the appropriate
offset frequency fl or f2 and either above or below fR.
The next time each unit responds, it does so with the
same frequency offset fl or f2 but on the opposite
side of fR. If a response is not detected from a unit
during one interrogation due to a deep null, interroga-
tion is repeated. On this second interrogation each
~17~
- 16 -
transducer, including the one which was not detected
on the previous interrogation, responds with its
frequency offset on the opposite side of fR and will
be received. Since deep nulls are rare, double inte-
rrogations are infrequent and the probability thattwo successive responses offset on opposite sides of
fR will be in a deep null is negligible.
When a transponder send~ an unsolicited response
due to an intrusion or low battery, it does so using
two time slots per data bit to be sure this attention
demanding signal is received by the CDU. A trans-
ponder originating a transmission is the only unit
transmitting at that time so there is no crowding of
data. For such conditions the first bit in the pre-
amble locks out all other units for the duration ofthe scan. The CDU recognizes the preamble as an in-
trusion or low battery condition then awaits a response
in a numbered time slot which defines the identity
number of the transponder by its arrival time within
the scan.
The data transmission of a transponder after
sending its preamble occurs during its assigned time
slot and at its assigned frequency offset. It trans-
mits again in the next time slot still at its assigned
frequency but offset on the opposite side of fR. For
example: - If transponder ~5 detects an intrusion it
responds with fR~fl in bit position 13. Then it
transmits fR-fl in bit position 14. If fR~fl is lost
in a deep null, only fR-fl will be detected in time
slot 14. The CDU knows from the preamble that an
unsolicited response is being received. It also
knows that fl, which is detected as a first signal in
time slot 14, is not assigned to that slot, -therefore,
it must be the second transmission from transponder
~5 and is processed as an event identified by the
preamble and localiæed by the time slot 14 arrival
5~4~
- 17 -
time which is the "next time slot" allocated to
transponder #5.
Another reason for assigning different frequencie.s
in alternate time slots is reverberation. Ona
frequency is allowed the duration of two time slots
fot its reverberation to die down. At the alternate
time slot, the frequency assigned to that slot will be
stronger than the reverberation from the previous
frequency. Since the assigned frequency is stronger,
it will predominate and be detected by the frequency
discriminator. The frequency discriminator can only
select one frequency and it selects the strongest if
- both are present.
DETAILED DESCRIPTION OF THE SYSTEM
TRANSPONDER
Referring now to Fig. 6 which is a block diagram
and Fig. 7 which is a waveform and timing diagram,
the transponder will be described in detail. The
transponder is disclosed as a custom made CMOS inte-
~0 grated circuit (IC) for small size and low powerconsumption and includes terminals for connectlon with
particular external circuits and components. This IC
provides economy of manufacture in this form and also
is designed to be used in all the units of the system
which require its various functions. Thus, the IC can
be connected to different external circui-ts and comp-
onents to provide the desired functions of each unit.
A crys-tal oscillator 31 operates continously and
generates fR, the reference frequency, which drives
frequency divider 32. The frequency fR is divided
down to produce the offset frequencies fl and f2 and
drives a timer 33 via AND gate 3 at a frequency, for
example of 200 Hz. When the timer reaches its
maximum count, its output, A, is high and inverter 1
produces a low level. In the transponder the
- 18 -
"continuous operation" terminal of the IC is held low
hence the output of OR 2 is also low. As long as the
output of OR 2 is low AND 3 blocks the signal from the
fre~uency divider 32 to the timer 33; therefore, the
timer 33 stops when it reaches its maximum count. An
intrusion event presets the timer 33 to start a scan
by initiating a count as will be hereinafter described.
It can be seen that by raising the "continous
operation" input to the IC, OR 2 supplies a high state
to AND 3 continuously thus causing the timer to
operate continuously and not stop at its maximum count.
This feature i5 used by the emergency reporting unit
which will be described later with reference to Fig. ll.
Intrusion
For an intrusion event the security system pro-
vides for actuation of a switch 34 or its e~uivalent
as the sensor responsive to the intrusion. The sensor
provides a high level to the sensor input when the
switch 34 opens, waveform E, Fig. 7. If a "lockout"
latch 35 is not set, its output, H, i5 low. The H
output is converted to a high state by inverter 4 the
output of which is applied to AND 5 then OR 6 to pass-the
intrusion signal. If the timer 33 is at its maximum
count its output, A, is high; therefore, AND 7 passes
the intrusion signal and sets the intrusion latch 38.
The intrusion signal from AND 7 also presets the timer
33 to the l count via OR 8 and AND 9. The timer 33
then counts until its maximum count is reached. In
the timing diagram, Fig. 7, the maximum count is shown
at 16 for simplicity. Normally, a larger number would
be used, such as 32 or 64. When the timer 33 is
operating, a data clock is generated, waveform B, de-
fining the time slots.
When the timer 33 is preset, waveform A drops and
.
- 19 -
a prea~ble encoder 36 is activated generating the
ALARM code. The preamble ALARM code is wire-programmed
via the external terminals 37 of the IC. The high
state from an "intrusion" latch 38 reaches AND 10 via
OR 11. This state gates the preamble, which arrives
via OR 17 through AND 10, to OR 12 then to AND 27,
waveform T. Waveform T arrives at AND 27 via an
external connection 39 from an "internal data output"
terminal 61 which jumper 39 connects to a "data input"
terminal 62. The "data input'l terminal 62 is used
without connection 39 by other system components such
as the CDU and remote key pad to inject data directly
to ~ND 27.
The data clock, waveform B, has the correct duty
cycle for transmission. The data clock gates the data
arriving from terminal 62 through AND 27; the resulting
signal is then used to modulate the ultrasonic signal
for transmission. As shown in waveform T, U, and V in
Fig. 7 under the heading UNSOLICITED RESPONSE (ALARM)
the ALARM preamble 1000 and the transponder identity
number are transmitted in the manner now to be des-
cibed.
The instantaneous ultrasonic frequency for trans-
mission is generated by a frequency synthesizer 63.
Waveform D from the timer 33 toggles at half the data
c].ock rate. Waveform C is fundamentally the same as
waveform D except its polarity can be controlled by
exclusive OR 18. As C toggles, it alternately gates
fl and f2 into the frequency offset input 64 of the
synthesizer 63. When the output of Exclusive OR 18
is high, AND 13 conducts and AND 12 does not. When
the output of Exclusive OR 18 is low, AND 12 conducts
and AND 13 does not.
Waveform D reaches an upper/lower sideband control
input 65 of the synthesizer 63 via Exclusive OR 15.
- 20 ~
As waveform D toggles, it alternately selects the upper
and lower sideband. Each time the system operates to
initiate a scan, a sideband reversing flip-flop 66 tog-
gles, to produce waveform F. This toggle reverses the
polarity of waveform D in Exclusive OR 15 so on alter-
nate scans the opposite sidebands of each offsetfrequency are used.
The data pulses, U, from AND 27 ~ey the synthesiz-
ed ultrasonic frequency fO to the signalling output of
AND 16 which in turn drives a transducer 67 with wave-
form V. Waveform U also disables the frequencydiscriminator 45 during transmission so the transmitted
signal will not be detected. In this example, the
transponder has its indentity number encoder 71 pro-
grammecl with number "~". Programming is done with
a DIP switch 72 connected as an external circuit. When
the code "4" time slot is reached, i.e., time slot 12,
"This Time Slot" output 73, produces a pluse waveform
R. Pulse R passes through OR 17, is then gated through
AND 10, and passes through OR 12 and ~ND 27, eventually
reaching AND 16 which gates an ultrasonic frequency
for transimission which is offset by f2 during time
slot 12. A pulse, waveform S, then emerges from a
"Next Time Slot" output 74 of the identity encoder 71
in time slot 13. This pulse, waveform S, reverses the
waveform C output from Exclusive OR 18. Normally,
an fl offset would be sent in position 13. This
r~versal in waveform C generates an offset of f2 in-
stead. The offset of f2 is the opposite sideband rom
time slot 12 because waveform D continues to alternate
normally. Thus the two data pulse transmissions at
the same frequency offset representing an alarm are
separated in carrier frequency to avoid nulls as
previously described.
As the scan ends the maximum coun-t in timer 33 is
reached and timing stops. Waveform A goes high and
.
~7~S~4
the "intrusion" latch 38 resets. The falling side of
waveform G sets the "lockout" latch 35. Waveform H
goes high causing inverter 4 to supply AND 5 with a
low state. No further alarms can be reported since
AND 5 then blocks the sensor input.
Interrogation Without Reset-Alarm Ver_fication
When an alarm transmission is received by the
CDU it may optionally be programmed to send an
interrogation ^or alarm verification. For this option
the CDU sends out the "Interrogate Without Reset"
preamble 1100. The signalling for this condition i9
indicated in Fig. 7 under the heading: INTERROGATION
WITHOUT RESET (ALARM VERIFICATION-OPTIONAL). The first
data bit of this preamble is a binary 1. An offset of
fl is sent followed by an offset of f2. The received
signal at the transponder (Fig. 6) is synchronously
detected using fR as a reference as previously described
(Fig. 4).
The first signal, fl, is recovered by the band-
pass filter 43, amplifier 44, then fre~uency discrimin-
ator 45. The Fl terminal of discriminator 45 goes
high which reaches AND 9 via OR 8. The timer 33 is
stalled at its maximum count, output A is HIGH, so
AND 9 passes the Fl logic level presetting the timer
33 to a number 1 which starts the scan interval as has
been described. If fl were lost due to a deep null,
only f2 would be detected in the second half of the
first data bit. In this case, AND 19 would conduct
passing the F2 outpu~ of the discriminator 45 thus
presetting the timer to a number 2 to compensate for
the late start.
A preamble decoder 67 receives its data, the Fl
or F2 detected outputs, from OR 25. At the end of
the eighth time slot the preamble is decoded by
decoder 67. In this example upon decoding the pre-
amble 1100, an output emerges from the "Interrogate ~-
~iithout Reset" terminal of decoder 67 as waveform K
s~
22 ~
which passes through OR 20 to set a "Respond to
Interrogation" latch 68.
When latch 68 is set, waveform M goes high. The
output from inverter 4 is low due to the "lockout"
latch 35 being set. When it is time to respond (time
slot 12), waveform R goes high; but it is blocked by
AND 21 so no response is transmitted. A response is
never sent during the next time slot, (13 in this
example) during an interrogation since AND 10 is block-
ing as the "intrusion" latch 38 (waveform G) is not
set. This lack of response in time slot 12 i5 inter-
preted by the CDU as an alarm condition.
Interrogation With or Without Reset
The CDU can interrogate with or without reset
at any time according to its program or keyboard
command. As previously described, "Interrogation
Without Rese~" is used to confirm an intrusion
condition. In addition, it may be desirable to delete
areas or protection while maintaining surveillance Of
other areas. By interrogating such areas without reset
the first response after an intrusion sensing event
(e.g., a door opening) sets the intrusion latch 3~ and
lockout latch 35 is set until such time as a preamble
code for interrogation with reset is transmitted.
During the armed condition when the premises are
protected by the system the CDU transmits supervisory
interrogations periodically, e.g., once every l 1~2
minutes, and these scans occur with reset to assure
repeated responses indicating that all is well. When
the premises are occupied the system can be disarmed
or selective areas can be set to respond while others
ignore the interrogation from the CDU as will be
described. The last two scans shown in Fig. 7 show.
routine interrogations with the offset reversing of
sidebands on alternate scans due to waveform F.
- 23 - :
Interrogation With Reset
.
During normal conditions the sensor input is low
(window closed, etc.). As previously described for
-the "Interrogation Without Reset", the timer is stark-
ed upon receipt o~ an Fl or ~2 output from the dis-
ciminator 45 and the preamble decoder 67 supplies an
output, this time via the n Interrogate With Reset"
terminal, waveform L. This pulse L immediately resets
the "lockout" latch 35 such that its output H drops
and the output of inverter 4 rises. This state allows
"This Time Slot" pulse, R, to pass through AND 21 so
an offset of f2 can be transmitted during time slot
12; the CDU thus receives a normal response.
If the "lockout" latch 35 is not set and an
intrusion occurs while a scan is in process, a "wait"
latch 74 is set. Since the timer 33 is operating, its
output, waveform A, is low. AND 7 will not pass the
intrusion signal; hence, the "intrusion" latch 38 will
no-t be set. Inverter 22 supplies a high sta-te to one
input of AND 23 which causes the intrusion signal to
set the "wait" latch 74. At the end of the scan the
"wait" latch 74 is reset as waveform A goes high. The
falling edge from the output of the "wait" latch
activates a delay circuit 75. At the end of the delay,
the delay circuit 75 sets the "intrusion" latch via
OR 6 and AND 7. A normal unsolicited response
indicating intrusion is then initiated.
Low Battery Indicatio
The battery voltage is monitored by a "low
battery" detector 76. Near the end of battery life,
but before it becomes useless, the "low battery"
detector 76 starts generating widely spaced random
pulses. If a scan is not in process, AND 24 passes
the low battery signal setting a "low battery" latch
77. At the same time the timer 33 is preset to a
- 2~ -
number 1 via OR 8 and AND 9 starting a scan. The "low
battery" latch 77 changes the preamble in preamble
encoder 36 so the CDU will know a "low battery" is
being reported and not an alarm. This change in pre-
amble 1001 is indicated in Fig. 7, waveforms P, T, andV by the dotted lines additons thereto. The low
battery preamble, and wavef~rms R and S pass through
OR 17 and AND 10 to be transmitted just like the
intrusion signal previously described.
If a scan is in process, the message is not
transmitted but eventually one will be sent. It takes
days before the battery becomes useless after the "low
battery" de-tector starts generating pulses so there is
no urgency regarding this transmission.
Other Functions
~ any circuits or sources of signals may be
connected to the external terminals of the IC to
adapt it for use by the other system components as will
be described. A "Signal Received in Last Data Bit
Position" output 78 is not used by the transponder.
This signal is only used by the remote key pad unit
and is generated in the following manner. If a data
bit is received at the last bit position of a scan time,
a pulse from the timer 33 occuring at that time is
gated to the output terminal 78 via AND 26.
CENTRAL DATA UNIT (CDU)
Referring to Fig. 8 the arrangement for using the
IC of Fig. 6 as the Central Data Unit will be describ-
ed. A standard microcomputer, ~C, such as the Intel
8048 is programmed to control the system, store data
such as intrusions, low battery, entry/exit zones and
time delays. As shown in Fig. 8, the ~C and the same
IC developed for the transponder are connected to
peripherals to complete the CDU.
- 25 -
The CD~ does not have an identity number so that
input to the IC is not used. When interrogating, the
uC injects the "with" or "without reset" preamble into
the IC. The reference frequency, f~, is derived from
the ~C clock which is crystal controlled. Thus~ a
separate crystal is not used wi-th the IC but fR from
the ~C is injected directly. into crystal input 1.
Several outputs from the IC are provided for the
uC. The timer output indicates to the ~C that a scan
is in process. The data clock is used to manage the
time slots. ~eceived data is obtained by the ~C from
the "fl received" and "f2 received" terminals. The
JC inputs data directly into the "Data In" terminal 62
of the IC and tlses tne "Internal Data Output" terminal
61 primarily to route the preamble back to the "data
in" terminal 6~ at the appropriate time.
The transducer drive and detection circuitry are
the same as that in the transponder. In addition,
there are interface circuits 81 and 82 to permit the
use of direct wire and AC power line repeaters, see
Fig. 1.
The ~C is programmed to the requirements of the
individual installation via its key pad 83. A 2-
digit 7-segment display 84 indicates which transponder
needs attention: -door or window open, low battery,
etc. An "armed/disarmed" display 85 is provided. A
"low battery" indica-tion 86 along with the identity
number of the transponder shown on the 7-segment dis-
play 84 points out which transponder needs a battery.
~he key pad a3 is also used or arming and disarming
the system using special code numbers. When an
intrusion or other alarm event has been detected, an
alarm relay 87 communicates this information in known
manner. Additional outputs are available so a
suitable equipped communicator can furnish additional
information if the alarm is due to holdup, medical
LS~
- 26 -
.
emergency, or fire.
The CDU is powered from the AC line through
power supply 88 and the unit is rendered immune to AC
power failure by means of a stand-by battery 89.
Acoustical Repeater
A feature of the present invention is the
acoustical repeater as shown in Fig. 9 which enables
the system to operate through closed doors and walls
using ultrasonic energy for transmission.
The repeater has no identity number, so those
terminals on the IC are not used. Its preamble i5 '
wire-programmed for the transponder code indicating
low battery and is only used during "low battery"
transmission originating from the repeater.
When any preamble is received, the scan interval
time starts. As code bursts are received, "fl or
f2 received" terminals trigger the pulse generator
91 via OR 1. Assuming the "low battery" latch 77
(Fig. 6) is low, inverter 2 supplies AND 3 with a high
state. This state allows the pulse from the pulse
generator 91 to reach the "data input" terminal via
OR 4. If fl is received, the synthesizer inside the
IC is still generating fl so the pulse causes fl to be
retransmitted immediately.
The repeater is powered by a local battery which
is also connected to a "low battery" detector 92.
If a low ba-ttery condition is detected, the "low
battery" latch 77 inside the IC is set. The output of
inverter 2 causes AND 3 to stop conducting and AND S
routes the internal data back to the "data input"
terminal. This circuit allows an unsolicited response
to be sent with the transponder "low battery" preamble.
No identity number is sent. At the end of this scan,
a "verification" latch 93 is set. Inverter 6 drops
the signal input to AND 3, and for the duration of the
- 27 -
next scan the repeater cannot transmit. Because it
does not retransmit the responses its transponders
cannot respond to the CD~. The transponder identity
number thus indicates to the CDU which repeater has
a low battery. At the end of this scan, the verifica-
tion latch 93 is reset so subsequent signals will be
repeated.
The transducer driving and signal detection
cixcuitry is identical to that in the transponder
except two transducers are connected in parallel, one
for each side of the door, as shown. The repeater can
also be used for signal boost on long distance links
such as in a long hallway where the distance is such
that the attenuatior. makes reception unreliable.
lS The repeater is normally in a listen mode with
its receiver circuits and crystal oscillator 31
operating from its local battery.
Remote Rey Pad
-
The remote key pad shown in Fig. lO has no
identity numher so that input to ths IC is not used.
The Remote Key Pad unit is used to arm and disarm the
system from a location remote from the CDU. Thus,
where the entrance/exit door is too far from the CDU
to permit convenient use, a Remote Key Pad unit can be
kept near the door used to enter and leave the premises.
Data is manually entered into the key pad key-
board lOl which enters it serially into a shift
register 102. The number of digits entered are counted
in counter 103 and the entry of data from keyboard lOl
also starts a timer 105 which sets a short interval
during which code can be entered. When the correct
number of digits for a code is received, the output
of digit counter 103 goes high. This output causes
"code entered" to be displayed on display lO~ and
applied to Sensor Input on the IC via AND 2. If an
incomplete code is entered, no further restarts are
~:~7~l5~4
2~
accepted by the timer 105. At the end of the timing
interval, the timer 105 clears the shift register 102
via OR 1. The shift register 102 can also be manually
cleared by reset button 106. The timer 105 is disabled
when the correct number of digits have been entered
thereby preserving data entered in the shift register
102 for processing.
If a scan is in process in -the CDU or a tran-
sponder the output of timer 33 in the IC is low and AND
gates 2,4, and 6 are disabled. If no scan is in
process, the IC timer 33 output is high. The maximum
count signal from the digit counter 103 passes through
AND 2 to the "sensor" input of the IC which starts a
scan. A "data send" latch 107 is also set. The
"lockout'l latch 35 in the IC is disabled by grounding
that terminal on the IC. The data clock waveform B
is then gated into the shift register 102, sequencing
the data from the shift register 102 into the "data in"
terminal of the IC for transmission. At the end of
the scan interval, the "data send" latch 107 and digit
counter 103 are reset by timer 33 output going high.
If the arming code is sent, the CDU initiates
an "Interrogate With Reset". If all transponders
respond, the system is armed (i.e., all lockou-t la-tches
35 reset) and the CDU sends a binary 1 in the last
data position. The IC supplies a pulse from the
"Signal Received in Last Data Position" terminal.
This pulse arrives just as the IC timer 33 is making
its transition at the end of the scan. This sets an
"Armed/Disarmed" display latch 108 via AND 4. "Armed"
is displayed on display 109. The signal is always re-
ceived in the last data position whenever -the CDU is
armed. If the CDU did not arm due to an open window,
no pulse is received in the last data position and tha
output of inverter 5 is high when the IC timer 33 makes
35 its transition at the end of the scan. This condition ..
5~
- 29 -
resets the "Armed/Disarmed" latch 108 via AND 6 thus
displaying "disarmed" on display 109.
Since this device is viewed frequently by the
user, it displays "low battery" directly on a "low
battery" display 110 when the battery is low rather
than transmitting it to the CDU.
Emergency Reporting Unit - "Panic Button"
The Emergency Reporting Unit (sometimes referred
to as a "panic button") is shown in ~ig. 11. This
unit responds to interrogations from the CDU just like
a transponder. It has an identity number programmed by
a DIP switch so it can be monitored by responding to
interrogation. The preamble is wire-programmed with
the transponder code 1001 so it can report "low
battery" as described for the transponder.
The unit has a switch 111 which is used to se-
lect one of two modes: "Medical Emergency" or Hold-Up"
~i.e., robbery in progress). When a start button 112
is pressed, an !emergency" latch 113 is set. Its out-
put goes high enabling AND 1. If switch 111 is in the
"Medical Emergency" mode, a continous high state from
the battery passes through AND 1 to the "da-ta inl'
terminal via OR 4. Also, the "continous operation" in-
put is high pre~enting the in-terval timer 33 in the
local IC from stopping at the end of the scan interval.
Inverter 2 disables AND 3, so in-ternal data will not
reach the data input.
The high state at the "data inl' terminal causes
a llll...from the data clock, waveform B, to be sent
continously via AND 27. It does so until a "stop"
button 114 is pressed which resets the emergency latch
113. AND 1 then stops supplying a high state to the
"data in". AND 3 now conducts the "internal data out-
put" to the "data in" permitting a normal response to
l5~
- 30 -
interrogation. Also, the "low battery" signal can be
sent.
If the emergency unit is in the "Hold-up" mode
~switch 111 connected to "l~old-Up") when the emergency
latch 113 is set, a 101010...code is sent continously.
Since two time positions are used for a single data
bit, and alternate data bits are ones and zeros, the
data clock is divided by 4 in dividers 115 to send this
code. This divider 115 supplies AND 1 with a high
state for two time slots, then a low state for the next
two time slots, etc. The "~old Up" mode is stopped as
before by pressing the stop button 114.
The CDU is programmed to recognize the different
preambles. The first 4 Bits of the continously trans-
mitted Medical Emergency code (1111) is recognized by
the CDU as a Medical Emexgency preamble and generates
an alarm and indicates to the communicator via a sepa-
rate output, Fig. 8, that it is a Medical Emergency.
By transmitting this continuously, it will eventually
be detected by the CDU even though other communication
may be occuring when the Medical Emergency code is
initiated. As soon as the CDU can receive again, the
first 4 code Bits received will be recognized immedia-
tely. Likewise, if a Hold-Up code is generated and
transmitted (101010...), the first ~ Bits received by
the CDU (1010) will re recognized by the CDU as the
~old-Up preamble and will initiate an appropriate
alarm.
OPERATION
The operation of the system as just described,
will be clear from the foregoing detailed description.
Several additional features of the invention will be
breifly rev.iewed.
.
5:l~
Arming and Disarming the System tat the CDU)
The "arm" code is entered into the keypad. If a
window is ajar, the CDU rejects the arming request
and displays the identity number of that window. The
window is then secured and the "arm" code is entere~
again. If successful this time, "ARMED" is displayed;
the exit timer starts. The user has this length o
time to exit without causing an alarm. Only the door
which has been designated as the entrance/exit can be
used or an immediate alarm results.
When the user returns, he enters via -the same
opening. When that door is opened, the entrance timer
starts which gives him time to reach the CDU and key-
in the "disarm" code. Entry via any other opening
results in an immediate alarm. If too much time is
lS taken without disarming the system, it will ao into ala~m
- at the end of the entry delay. More than one opening
can be designated as an entrance/exit.
Arming and Disarming the System at the Remote
Keypad
This procedure is the same as for using the CDU.
However, if an arming request is rejected, the user
must go to the CDU to see which door or window is
not secured.
Deleting Zones
__ .
Using the keypad on the CDU it can be programmed
to disregard any area during the hours of protection.
The owner of a small business can occupy his office
while the rest of his facility is secure. The trans-
ponders in his area are ignored by the CDU. The
activation of any other transponder results in an
immediate alarm.
~7~S~4
- 3~ -
Control of Battery Drain
During the day some doors are used constantly.
If a transmission occured each time the door were
opened, the battery life would be greatly reduced.
This can be prevented as part of the alarm verifica-
tion sequence. When a door is opened, the trans-
ponder transmits its unsolicited response and sets an
internal latch. When interrogated to verify the alarm,
that transponder does not respond because its latch
is set. Also, if the door is opened again, it will
not transmit its unsolicited alarm code because of
the set latch. .
Since there are two interrogation codes, one,
"interrogate without reset", which is used to verify
an alarm and the other "interrogate with reset" which
resets the latch restoring the transponder to normal
- operation,each can be used selectively to control
particular transponders. During the day the trans-
ponders which are monitoring openings 2~ hours per
day are monitored using the "interrogate without reset"
code. The first time a frequently used door is open-
ed it sends its code and sets its latch. If the
system is disarmed, the CDU ignores this transmission
and the first alarm during occupancy hours can be dis-
carded. Further transmissions are not possible be-
cause of the set latch; thus, the battery is conserved,
When the system is armed, an "interroyate with reset"
code is sent to all transponders. This resets all
latches if all openings are secure and full security
for all sensors is then operative.
While the invention is not limited to any
particular values for the parameters assigned, the
values for a typical small te.g., dwelling house)
system will be given.
If the basic ultrasonic carrier frequency
fR=25kHz, the offset values can be obtaining by digital
1~7~S~L~
.
- 33 -
division to obtain non-harmonically related sideband
frequencies of approximately fl=130.21 Hz and f2=195.31
31 Hz. The frequency synthesizer 63 generates fO as
in a single sideband transmission with only one of the
four frequencies fR*fl, fR-fl~ fR+f2~ or fR-f2, trans-
mltted at any given time slot as controlled by inputs64 and 65.
The interrogation scan may be progra~ned to
occur once every 90 seconds with a duration of 15
seconds per scan. If thereare 32 slots this gives
approximately 0.~7 second per slot. The data cloc~
genera-tes one pulse per slot. The transmission burst
within a slot is 60ms thus permitting adequate transit
time for propagation delay to near and far transponders
and still receive the response within the slot.
The filter for selecting fl and f2 from the
output of the synchronous detector is preferable
passive to conserve ba-ttery power in the self contained
units. For this purpose, a gradual band pass roll off
is used to avoid ringing initially about 6 db/octave
with fl and f2 at approximately the 3 db down fre-
quencies and with 12 db/octave roll off on -the skirts
of the curve.
Obviously, other values for the above specified
parameters can be used to meet the requirements of
compatibility with other equipment ~e,~,, ultrasonic
intrusion detectors~ or to expand the system for large
commercial installations.
The system just described provides reliable
ultrasonic communication of time en~oded data.
Similar reliabilities can be obtained with two
frequency transmissions of frequency coded data. In
such systems, considerable simplification is possible
~ecause of the use of different frequencies to obtain
reliable reception and convey information. Further-
more, frequency coding can be combined with time
;
~7~5~1~
- 34 -
coding in various ways to greatly expand the capabili-
ties of -the system with minimum additiollal equipment
requirements.
Figs.12, 13, 14 and 15 disclose basic requency
coded ultrasonic transmission systems employing the
5 principles of the invention. Such systems can be used ?
independently or combined f~or use in the time encoded
data transmission system previously described.
In this version of the invention, the system also
transmits at multiple frequencies to avoid deep nulls.
In -the systems disclosed in Figs. 12, 13, 14 and 15, a
single quantum of information is transmitted as a burst
of ultrasound consisting of a sequence of two or more
frequencies. The probability of a single ultrasonic
frequency being lost in a deep null is slight but
finite. The chances of two frequencies being lost is
highly improbable. The reliability improves as more
frequencies are used in a burst of ultrasound. From
a practical point of view, two frequencies are adequate
for most uses. This invention is described as
signalling by using two frequencies per burst.
~ s a basic example of multifrequency signalling
in accordance with the invention in which informatio~
encoding is by frequency, Fig. 12 shows three codes
used for signalling by using different frequency groups.
Code 1 consists of frequencies fa and Eb, Only one
of these frequencies needs to survive the transmission
path for a code 1 to be detected at the receiver.
Likewise, code 2 is represented by the pair of
frequencies fc, fd and code 3 by the pair fe, ff,
- More codes could be used by using more pairs of
signalling frequencies,
The system of Fig. 12 has a plurality of code
frequency oscillators 130 a, b; 130 c,d; 130 e, f,
each producing one of the distinct ultrasonic fre-
quencies fa, fb; fc, fd; fe, ff respectively. Each
- 35 -
code pair is applied to a sequence switch 131 from
which a particular code pair can be selected (to send
that code) by a code select switch 132. The selec~ed
code pair frequencies are applied in sequence to a
driver 133 which when enabled applies transmitting
power level signals to the transducer 134. Trans-
missions are initiated by an initiate pulse signal
(Erom any source, such as a sensor or control device)
on terminal 135 which triggers a first interval timer
136 and moves sequencing switches 131 to the upper
terminal. The end of the first timer interval starts
a second interval timer 137. At this instant, -the
sequencing switch 131 transfers to the lower contacts.
The outputs of both timers 135 and 137 pass through
OR 138 the output of which is applied to enable
driver 133 for the duration of both timing intervals.
The receiver in Fig. I2 includes a receiving
transducer 141 the output of which is applied to a
wideband amplifier 142. The output of amplifier 142
is applied to the inputs of bandpass filters 143 each
designed to select only one of the transmitted
ultrasonic frequencies. Any such frequency which i5
present passes through its respective filter 143 and
is detected as a dc voltage by rectifiers 144 indivi-
dual to each filter 143. The rectifiers associated
with each code pair of frequencies apply their detected
outputsto voltage adders 145 respectively. The
outputsof the voltage adders 145 are applied to-
respective threshold circuits 146 which produce code
detected output signals at terminals 147 when the
detection level of signal exceeds -the threshold.
To operate the system of Fig. 12, the code select
switch 132 is rotated to one oE its three positions.
Code 1 is shown being selected in Fig. 12. An initi-
ate pulse on terminal 135 triggers the timer 136 Eor
the first interval. The sequencing switches 131 can
~17~
-36- -
be solid state; mechanical switches are shown to
schematically present the switching function. During
the first timing interval fa is selected (fc and fe
are tentatively selected also but not used because code
1 is selected by switch 132. The end of the first
timing interval triggers the timer 137 for the second
interval. Since the timer 136 for the first interval
is no longer active, the sequencing switches 131
transfer so fb is selected for the second interval.
The OR gate 138 output is high for both intervals
which enables the transmitter driver. Driver power
level signals of fa and then fb reach the transducer
134 and are broadcast sequentially into the room.
These signals are received by receiving transducer
141 and processed as has been described,
Referring now to Fig. 13, the operation for
different transmission medium conditions will be
described for reliable transmission. Again, selection
of code 1 for transmission is assumed, In the first
example in Fig. 12, fa and fb both survive transmission;
neither is in a deep null. Filter 143a produces an
output followed by an output from filter 143b. Each
filter output is rectified to produce a DC voltage
proportional to the signal strength. The outputs
from each pair of rectifiers 144a and 144b are fed to
the adder 1~5(1~. If the voltage from an adder
exceeds the threshold level in 146(1), the output
voltage rises at terminal 147(1) indicating that a
code has been received. In this example both fa and
fb produce a strong DC voltage and the output of the
adder 145(1) remains above the threshold for both
in-tervals.
In the second eY~ample shown in Fig. 13 ~of adder
145(1)], fa is in a deep null while fb is strong. The
output voltage of adder 145(1) is below -the threshold
during the first interval while fa is being transmitted but
~'7~ 4
- 37 -
not received due to the null condition, but it is above
the threshold during the second interval while the
stronger fb signal is being received. The fact that fb
is received, even though fa is not, indicates a code 1
is received.
The bank of oscillators in the transmitting unit
can be replaced by a frequency synthesizer. It can be
con~anded to transmit the frequencies just described
by manual command or automatically in response to a
sensor (temperature, burglar alarm, etc.). Li~ewise,
the bank of filters in the receiving unit can be
replaced by a frequency discriminator designed to be
sensitive to the pairs of frequencies.
In a preferred embodiment, Fig. 14 modifications
which simplify equipment requirements and improve
operational characteristics are shown. A frequency
synthesi~er 151 is used in conjunction with a reference
oscillator 152, typically quartz crystal controlled,
operated at a frequency fR, In the example shown in
Fig. 14, three codes 1,2 and 3 are again assumed and
these are characterized for transmission as frequency
components fl, f2 and f3 respectively. The synthesizer
lSl is shown having fl,f2 and f3 inputs, but it will
be understood that these need not be signals at these
frequencies since they are generated internally. The
synthesizer 151 also has a shift up~down input 153
which controls the actual offset frequency generated
relative to the frequency fR Of oscillator 152.
When the fl input to the synthesizer 151 is
raised while the shift up/down input is high (shift up),
a frequency equal to fR ~ fl is produced. If the shift
up/down input is low (shift down), a frequency equal to
fR ~ fl is produced. This is analogous to independent-
ly producing the upper and lower sideban~sof fl about
fR-
5~
- 38 -
A quantum of information consists of detection
of one of the selected code frequencies, fl, f2 or f3.
The code frequency is transmitted as a hurst of
ultrasonic energy; first half of the burst is the upper
sideband (fR ~ fl) the second half is the lower side-
band (fR - fl). This is similar to the sequential
transmission of fa then fb in Fig. 12. In the follow-
ing description, similar elements will be given the
same reference number, primed, as in Fig. 12.
In Fig. 14 fl is selected by raising the fl
input of synthesizer 151; a transmission is initiated
by momentarily raising the initiate input 135'. The
timer 136' for the first interval is triggered; its
output goes high commanding the synthesizer 151 to
generate the upper side~and (fR + fl). The driver 133'
is enabled via the OR gate 138'. At the end of the
first interval, the falling edge of the fixst timer
136' triggers the second timer 137' for the second
interval causing its output to go high. The driver
20 133' continues to be enabled by the second timer 137'
via the OR gate 138'. ~uring the second interval the
output of the first timer 136' is low so the synthesizer
151 generates the lower sideband of fl, (fR - fl).
The overall transmitting unit of Fig. 14 enclosed
within the dashed line is designated 154.
The receiving unit of Fig. 14 is greatly
simplified over that of Fig. 12. Only a single
frequency determination need be made for each burst of
information. The re~ceiving unit also has a reference
oscillatox 161 producing fR. The received signaL for
code fl consists of the upper sideband (fR ~ fl)
followed by the lower sideband (fR - 1). when the
received signal is combined in a mixer 162 with the
reference frequency fR, then filtered by a low pass
filter 163, only the difference frequency fl remains.
It does not matter if fR + fl or fR - fl were received,
.
s~
~39-
only fl results. Therefore, the sequence of the upper
followed by the lower sideband produces a single fre-
quency which is amplified in amplifier 164 and then fed
to a frequency discriminator 165. Note that the low
pass filter 163, amplifier 164 and discriminator 165 all
need to operate only over a relatively small frequency
range thereby simplifying design and improving relia-
bility.
If one of the sidebands is lost due to fading,
the other very likely will survive, Whether both side~
bands are received, or only one, the appropriate fre~
quency is detected, ~fl in -this example), whlch causes
the appropriate output to rise (1 in this example).
This type of equipment is often battexy powered
particularly in applications where installation effort
and expense are to be minimized. The t.ransmitter only
operates when commanded so power consumption for that
short duration is not critical. The amplifier in the
receiving unit, however, must operate continuously
awaiting a received signal; therefore it must contin-
ually consume battery power. The ultrasonic frequencies
are in the 20 to 40 KHz range, In order to ~btain
significant amplifier gain at these frequencies, an
excessive amount of power supply current is required
to produce the necessary gain bandwidth product to
power the amplifier of Fig. 12, In Fig. 14, however,
the offset frequencies fl, f2, and f3 range from 200
to about 400 Hz above and below fR. Mixing occurs in
the receiver before amplification so the bandwidth
of the signal subsequently amplified is no more than
400 Hz. Sufficient amplifier gain at this frequency
is achievable using an amplifier which draws very
lit-tle power supply current. In the example shown, 3
5~
~40-
channels, or 3 different signalling codes are shown to
illustrate the signalling by use of frequency groups.
This is not a restriction since many more frequency
channels can be used. Furthermore, each of these bursts
of pairs of ultrasonic frequencies can be time sequenced
to convey more information by using a digital code
format. There are many coding foxmats known in the art
which can be used.
A typical frequency for fR is 24 kHz; for fl,
200 Hz; f2, 250 Hz; and f3, 333 Hz, The time for
transmitting each sideband is typically 85 milliseconds
for a total burst duration of 170 milliseconds. A very
basic security system is shown in Fig, 15 which uses
the ultrasonic signalling means of Fig, 14. In Fig. 15
the coding for the fl~ f2 and f3 inputs is derived from
security sensors. A door is monitored by a switch
171 which connects to enable the fl input of trans-
mitter unit 154.A switch 172 in a smoke detector in that
room connects to the f2 input, and a heat detector
switch 173 (for an explisive non-smoldering fire)
connects to the f3 input. When one of these switches
closes, voltage is applied to the appropriate input of
transmitter unit 154. The voltage from the OR gate
rises and is differentiated feeding a positive pulse
via a diode 175 to -the initiate input of transmitter
unit 154. This initiates a transmission, For
example, if the door had opened, fR ~ fl followed by
fR - fl is transmitted in a burst of ultrasound. A
receiving unit 176 corresponding to the receiving unit
of Fig. 14 detects fl and sets the appropriate latch
177 which illuminates the corresponding indicator
light 178 ("penetration"). The guard monitoring the
indicators then takes the necessary action. He can
~7~
reset the latches by means of switch 179 to extinguish
the lights after the emergency is over.
Although the only action shown in Fig. 15 is the
illuminakion of indicator lights, the outputs of the
receiving unit can drive a data gathering computer system
or directly activate an audible alarm.
While only simplified systems incorporating the
invention have been specifically disclosed, the
invention is capable of widely differen-t applications.
Thus by the combination of frequency coding operated
in a time coded overall system greatly expanded data
handling capacity can be achieved. Furthermore, in a
large time sequence coded system the use of a fre-
quency coded signal for special purposes can be bene-
ficial. For example in a large system of the typedisclosed in Fig. 6 where cycle time is long due to the
large number of time slots, frequency coding at
frequency fl can be used for routine operations with
emergency events reported at frequency f2. In such a
system the occurrence of the emergency is thus detected
immediately (as it would be in the Fig. 15 system) but
its identifica-tion as to location would not be deter-
mined until the time slot report on the next scan cycle.
Of course, as previously mentioned, the frequency coding
can be combined to provide a dlgital format to increase
information capacity.
Many modifications of the invention and a multi-
tude of diverse uses and applications of the teachinqs
will now occur to those skilled in the art. The inven-
tion, accordingly, is not to be limited to the systems,disclosed or the uses suggested but encompasses the
broad scope of the appended claims.
