CA1287114C - Remote monitoring and alarm system employing multiple digitally encoded words - Google Patents

Abstract

REMOTE MONITORING AND ALARM SYSTEM

ABSTRACT
A remote monitoring and alarm system has an FM radio link between a transmitter carried by a person or object being monitored and a receiver to which alarm signals are transmitted from the remote transmitter. Digitally-encoded FM signals are produced at the transmitter at pre-set transmission intervals in the form of multiple digital words detected by the receiver. The receiver is a constant listening device which produces an alarm immediately if at least one of the coded words is not received during any transmission interval. The multiple words serve as redundant words during each transmission interval to minimize false alarms at the receiver due to interference. The multiple coded words are transmitted at minimum time intervals pre-set to maximize the number of coded pulses during each transmission interval while spacing the coded words to permit maximum allowable power transmission. The receiver can monitor two transmitters simultaneously operating at the same carrier frequency by adjusting the coded words so they occur at different periods within the same trans-mission interval to prevent the possibility of total overlap. Emergency conditions monitored include out-of-range, anti-tampering, panic alert, immersion and breathing rate, as well as other selected emergency or status conditions.

Description

128711q [C248:17248:~GM] -1-REMOTE MONITORING AND ALA~ SYSTE~I
FIELD OF THE INVENTION
This invention relates to monitoring systems, and more particularly to a remote monitoring system using a radio frequency link between a transmitter, which is carried by a person or object being monitored, and a portable monitoring receiver. The receiver detects signals from the transmitter and produces alarms or displays information for various emer~ency or status conditions associated with the person or object being monitored.

BACKGROUND OF THE INVENTION
Many children are reported missing each year, either from child abduction or simply from straying away fromparents or guardians who are unaware of their being lost or in danger. A child also may wander away and be lost for several hours before being found by terrified parents, or parents may lose track of a child in crowded surroundings unfamiliar to the small child.
At the same time, caregivers for Alzheimers patients, and others suffering from dementia resulting in the wandering syndrome, experience difficulty in keeping track of those requiring special care. Families and institutions alike have expressed genuine concern for the well-being of the ~371~

1 handicapped, elderly and special patients requiring close observation. Further, the bedridden have been reported to often suffer from sensitive incontinence problems which can aggravate existing symptoms and minimize overall comfort.
5- Swimming pool owners and those involved in recreational activities near the water are well aware of the need for water safety precautions. For instance, small children may wander into the water without appreciating the dangers.
It is not always feasible nor is it reasonable to e~pect that personal supervision of small children by a guardian can always prevent water-related accidents from happening.
There is a need for a safety device that helps a parent or guardian keep track of a person by constan.ly monitoring his or her whereabouts and triggering an alarm to alert the responsible parent or guardian whenever the subject has encountered an emergency, strayed too far, or is otherwise in danger. It has been proposed that such a safety device include a transmitter worn by the subject and a receiver carried by the parent, guardian or caregiver.
In a child monitoring situation, the receiver can be set to monitor the child's whereabouts within a desired radius, and if the child moves beyond the pre-set range, a beeper and warning light on the receive~ alert the parent or guardian. The beeper also can alert the guardian if the transmitter is momentarily removed from the child, submerged in water, or turned off. A call button on the transmitter can be pressed if the child becomes lost or perceives d~nger, such as if a stranger approaches- In a hospital or rest home setting, a call button can be used to transmit an alarm if a patient becomes ill or disorientation occurs.
The patient's whereabouts also can be constantly monitored.
- There is a need to monitor for awidevariety ofemergency situations. For example, emergencies monitored can be out-of-range, immersion, tampering with the transmitter, breathing rate, as examples. Call signaling can be provided, ~2~71~

1 although this may not be considered to have the same priority as other emergencies.
There is also a need to ensure that such a monitoring device has an exceedingly high degree of rellability. For instance, an alarm must be activated at the receiver with essentially 100% accuracy whenever a monitored emergency condition arises, regardless of interfering sources or other similar~mQnit~rin~ systems in c}ose pro~imity. The alarm also should be produced immediately when an emergency is detected, since time is of the essence in most emergency situations.
In addition, it is necessary to reduce the probability of false alarms at the receiver. False alarms have been a major annoyance with monitoring devices previously used in experimental testing. These experimental units have covered a wide geographical range to determine how and whether local conditions will affect radio frequency transmission. It has been learned that false alarms can be produced from interference from ~I sources or electrical noise or from other nearby electronic devices operating at the same radio frequency- Even though interference may be present from overlapping signals from other sources, false alarms even in these situations should be minimized. False alarms are not only annoying, but they are also a source of possible misinformation- An emergency could be detected at the receiver, only to have a later transmitted signal changed by an interfering signal that indicatesthe emergency has been corrected when, in fact, it has not. Alarm failures also should be prevented- Alarm failure can be caused by a second similar transmitter set at the same frequency transmitting an identical address code signal which becomessubstituted forthesignal from the firsttransmitter This may cause the receiver for the first transmitter to operate without producing an alarm when an alarm may be necessary for an emergency situation.

7~14 l It is also desirable to monitor signaIs from more than one transmitter with a single receiver so that one person can monitor the whereabouts of more than one subject ~ithout requiring multiple receivers. Transmitters worn by t~o different subjects, for e~ample, should operate indepen-dently on the same carrier frequency, but without producing false alarms from interfering signals.
Remote monitoring devices also have a number of design requirements which are difficult to achieve concurrently in one small package. For example, in a radio frequency monitorin~ system, it is desirable to obtain maximum po~er transmission, within FCC limits, in order to ma~imize the range over uhich the device is sensitive. There is also a need for a high-sensitivity receiver ~hich can be produced at a lotJ cost and operate with lo-.~ po-~er consu~ption an~
at low voltagesO In addition, there is a need for a safety device combining the ability to operate ~lith lo~J-voltage - digital electronics in the same small package and in close proximity to high-po~er radio frequency energy. Both mus~
work together reliably, without interference or false alarms, and still be made available in a small pac~age at a low cost so the system can be affordable to everyone.
This invention provides an e~tremely reliable radio frequency monitoring system which greatly reduces the probability of false alarms or alarm failure, while ensuring that necessary emergency alarms are immediately and reliably transmitted to the receiver. The system constantly monitors a variety of emergency and status condition including out-of~range, anti-tampering, panic-alert~
immersion and wetness sensing, breathing rate, lo~-battery condition, and the like- The system can independently monitor these functions from more than one transmitter with a single receiver operating on the same carrier frequency substantially without interference, false alarms or alarm failure. The invention also makes it possible to `' . , ', ' ,': . ' , ' ' ' ' ' . .
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~87~1A

1 combine maximum power radio frequency transmission in the same small package and in close proximity to low-voltage digital electronics at a reasonable cost. Range is increased and receiver sensitivity to signals from the transmitter also is increased when compared with radio frequency monitoring systems operating under similar regulations.
In addition, the invention includes a custom digital integrated circuit having utility;for a variety of situations where remote monitoring is desirable. The system can be used in monitoring children, the elderly in rest homes, or those confined to prisons or detention facilities. It can also be used as a water safety device, or for trac~ing the whereabouts of a variety of moving objects.

SU~RY OF THE INVENTION
Briefly, the invention provides a monitoring and alarm system with a radio frequency link bet~;~een a receiver and a remote transmitter carried by a person or object being monitored~a-One embodiment of the inventicn includes 'an-FM tran-smitter that,produ'ces a transmit~ed signal at an F~I~,carrier frequency. The FM signal g-eatly reduces interference from ~I sources or electrical noise. The transmitted signal is a digitally-~ded signal produced at pre-set transmission intervals in the form of multiple digitally coded words detected by the receiver. The receiver is a constant listening device which produces an alarm immediately if none of the coded ~ords is received during any transmission interval. The multiple-coded words sent during each transmission interval minimize false alarms at the receiver due to interference, since the ; ~eceiver needS-toA~aIidly~receive only one of the multiple-coded words during a-given transmission interval in order to not produce an alarm. If none of the coded words,is received in a transmission interval, the receiver will ; 35 produce an emergency alarm.

, 1~?~3~

1 In one embodiment, a factory adjustable encoder shifts the FM carrier frequency, during transmission of the multiple encoded words, for each transmission interval. This greatly reduces the probability of alarm failu~e occurring from the overlap in the frequency of transmit~ed signals from other similar transmitters.
In another embodiment, the multiple-coded words are transmitted at minimum time intervals, which serves to maximize the number of coded words during each transmission interval, while spacing the coded words to permit maximum allowable power transmission.
In one embodiment of the invention, out-of-range information is transmitted to the receiver by adjustments at the receiver that constantly detect a pre-set signal strength value of the signal from the transmit.er. If the magnitude of the signal from the transmitter falls Delow a pre-set sensitivity of the receiver, no signal is received and the receiver immediately produces an alarm.
A signal priority system also is used to transmi~ the signals uhich operate alarms at the receiver. Emergency conditions such as out-of-range, immersion, and tampering with the transmitter, for example, are given highest priority. If an alarm is genera~ed because of any of these occurrences, other signal transmission from the transmitter to the receiver is overridden- This can avoid the possibility of alarm failure. Medium priority can be given to signals such as call-alarm. Lowest priority can be given to status signals such as wetness detection, low battery condition, and the like.
In a further embodiment, the receiver can monitor two transmitters simultaneously operating at the same carrier frequency. The outputs from the two transmitters are adjusted so that their coded words occur at different time periods within the same transmission interval to avoid the probability of overlap. If any coded words from the two l~a7~l4 transmitters should overlap, other valid words produced by the transmitters during the same transmission interval will be transmitted to the receiver, avoiding interference and false alarms. The duration of each of the coded words from both transmitters also can be controlled to maintain signal integrity while permitting near maximum power transmission.

Other embodiments of the invention make it possible to operate at low voltages with low power consumption in combination with the high-power radio frequency link.
Both are made available in the same small package that can be produced at a reasonably low cost.

These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.

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, DRZ~WINGS
FIG. 1 is a perspective view showing the exterior configuration of a housing for a radio frequency receiver portion of the monitoring and alarm system according to principles of this invention.
FIG. 2 is a front elevation view illustrating the exterior of a housing for a radio frequency transmitter of the monitoring and alarm system.
FIG. 3 is a side elevation view taken on line 3-3 of FIG. 2 for better illustrating a mounting clip on the transmitter housing.
FIG. 4 is a rear elevation view ta~en on line 4-4 of FIG. 3.
FIG. 5 is a functional bloc~ diagram illus'rating the circuitry for the radio frequency transmit'er po~tion of the monitoring and alarm system.
FIG. 6 is a functional bloc~ diagram illust~ating the circuitry for the radio frequency receiver portion of the monitoring and alarm system.
FIG. 7 is a fragmentary perspective view sho.Jing a safety clip attached to the transmitter.

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i 2~7114 DETAILED DESCRIPTION
The present invention is described with reference to a remote child monitoring and alarm system. In this system, a radio frequency transmitter worn by the child sends digitally-coded signals to a portable receiver carried by a guardian. ~hen the child strays beyond a desired range, or when other monitored emergency conditions are~ detected,~ the radio-~frequency signal activates an alarm at the receiver. The invention is not intended to belimitedtosuchchildmonitoringandalarmsystems,however, because the invention is useful for a variety of other remote monitoring applications.
Referring to FIG. 1, a portable monitoring receiver 10 contains internal circuitry for receiving digitally-coded FM signals from an F~I transmitter. The receiverhousing has an external mounting clip 12 so the receiver can be worn by a parent or guardian. The exterior of the receiver housing includes a flexible antenna 1~ directly affixed to a printed circuit board contained in the housing.
Zo The exterior of the--receiver housing also includes a number of alarm or status displays and controls. Some of these are located in a recessed region on the front face of the housing. They include an ~_D bar signal strength indicator 16 for displaying a relative approximation of-the distance from the receiver to the transmitter. Thedesired maximum range can be set by a slidable position switch 18. If the range of the person being monitored exceeds the desired range set by the switch 18, an alarm is sounded in the receiver. If the switch is set at the low distance setting, for example, then the receiver will alarm when the person carrying the transmitter exceeds that relatively low distance from the receiver. The high switch setting allows the person to travel longer distances from the receiver before the out-of-range alarm is activated.
The receiver housing also has a battery charging port 20, 1 a slidable on/off switch 22, and an indicator lamp 24 for indicating when battery charging occurs. The on/off switch 22 also can include a check position for checking for valid signal transmission and for determining whether a constant audible update beep tone is received. The receiver housing also can include other alarms and indicator lamps. These can include LED indicator lamps 26 and 28, respectively, for visually indicating detected emergency conditions (described below) in conjunction with sounding corresponding audible alarms. The receiver alarm circuitry is set to produce the same visual alarms via flashing the LED displays 26 or 28 independently of the particular alarm being ~etected. Alternatively, separate LED displays can be activated to indicate the particular emergency being detected. The audible signals produced by the receiver are detected through sound holes 29. The various arrangements of the emergency and status condition warning lamps and displays and the control switches sho-~m in FIG.
1 are illustrated as an example only, since other variations of this arrangement can be used without departing from the scope of the invention.
FIGS. 2 through ~ illustrate a portzble transmitter housing 30 containing circuitry fo~ a digitally-coded FM
transmitter. The transmit'er can be worn by a child whose whereabouts are being monitored- The front face of the housing includes a push button 32 for serving as a manual panic switch or call button to send an alarm to the receiver to alert the guardian when the child believes his or her safety is in danger. The receiver carried by the guardian sounds an alarm when the panic button 32 is activated.
The front face of the transmitter also can include an indicator lamp 34 which blinks at a 4 hz rate to indicate transmission, alarm and status signaling.
As shown best in FIG. 3, the transmitter housing has a rear mounting clip 36 for use in attaching the transmitter ~ za711.4 1 to the child's clothing. The clip 36 can serve as a safety clip to activate a power switch conr.ected to the transmitter circuitry for activating the trans~itter and for sending a signal to the receiver to indicate when the transmitter has been tampered with or is re~oved from the child's clothing. The safety clip is mounted to the housing by a spring-biased roll pin 35. When the safety ~cl-ip--nor~ally a't~ac~hès`thè''hous~ng t`o the child's clothing, the power switch remains closed. The power switch opens when the safety clip is momentarily opened or removed from the clothing, thereby activating an anti-tamper alarm, described in more detail below.
The bottom face of the transmitter housing can include a pair of phone jacks 38 electrically connected to circuitry within the transmitter housing for producing signals sent to the receiver to monitor various conditions such as immersion and wetness, and breathing. If the transmitter senses wetness, or is immersed in water, jr the subject stops breathing, or if any-of the external sensors-or`'probes is unplugged~during'ùse,'àn alarm sounds at the receiver.
The transmit'er and receiver functions are understood best by referring to the functional block diagrams of ~/ FIGS. 5 and 6~ Briefly, the tr~nsmitter serves as a remote transducer worn by the child being monitored. An-emergency warble alarm sounds at the portable monitoringreceiver if the child exceeds a pre-set distance range, falls into water, if transmitter removal is attempted, if the breathing sensor indicates that breathing has stopped, or if the transmitter's call button is pushed. A telephone ringing sound can b`e prbduced at `the'transmitter'if the call button is actuated. Other status alarms are activated if the~wetness sensor probe or pad become wet, or if either the transmitter or receiver battery power becomes low. A sound similar to dripping water can be produced if the wetness sensor is activated. The receiver is constantly ~37~4 1 listening for multiple digitally-coded F;l sig~als from the transmitter at pre-set transmission intervals of about 10 seconds. If a required signal is not received within any transmission interval, such as if a pre-set range is exceeded, an alarm at the receiver is i~ediately activated.
TheFMcarrierandmultiple-codedbursts~itheachtr2nsmission interval reduce the probability of false alarms. The transmitter has a removable battery in a separate adapter (not sho~m) for permitting continuous operation of the transmitter. The transmitter and receiver cireuits are also designed to permit rechargeable operation of both the transmitter and receiver. In addition, the receiver is capable of simultaneously monitoring two tr~nsmitters transmitting at the same carrier frequency.
FIG. 5 schematically illustrates a digitally-coded Frl transmitter 40 which includes an F~I hybrid trans~itter ~2, a2700 logicgatecustomc~losdigitalintegratedcircuit(I.c.) 44, and associated analog components and a rechargeable battery. The transmitter is desigr.ed fo- a ~axi~lu~ battery life. A small 2.~ volt, 60 mah nicad button batter~ ~6 directly powers the custom digital I.C., a 9 vol~ converter 48, and all analog loads. The 9 vol~ converter supplies the hybrid transmitter ~2 and a loi-vol~age battery reference divider 50 with a regulated 9 volts- The transmitter is activated by clipping it to clothing which closes a safety clip switch 52 in response to contact by the external mounting clip 36 on a transmitter s~itch plunger 37, shown in FIG. 7. The plunger 37 can slide into a passage in the transmitter housing for contact with a switch that closes when the clip is in place- The plunger also can be seated in a recess in the clip. ~hen the clip 36 is used to clip the transmitter onto the clothing of the person wearing the transmitter, the clothes create an interference which prevents the plunger from entering fully into the recess in the clip. This forces the plunger into the transmitter ~2~37~4 1 housing where it closes the suitch to indicate that the transmitter has been pro~erly clipped onto the clothing of the person wearing it. The safety clip switch powers all analog loads, activates the digital I.C. via a power-down section 54, and functions as the anti-tamper sensor. ~.hen the transmitter,is not in use, a few microamps of cur-ent continue to flow to the power-down section 5~ of the digital I.C. to maintain function of the pot~er-down section.
About 60 to 120 microamps of current continue to the 9 volt converter from the battery 46. The g volt converter is directly connected to the battery to enhance efficiency due to the relatively large switching currents develoDed during operation.
The radio frequency signal is produced by the FlI
hybrid,transmitter 42. The FM frequency is generated by a surface acoustic wave (SA~) oscillator 56 for f~equency stability. The output of the oscillator 56 is a~plified by an amplifier 58 to produce an output of abou~ 50 to 80 mw ;into,a t4n,ed ,r~esonant printed circuit, a,n~enna 60. ~ The ^20 supply voltage from the, converter 48 is applied to the ~/ oscillator and ,amplifie~ at all times, but neither the oscillator nor the amplifier is turned on until 0.1 ms before a coded signal is to be transmitted.~ At that time, a pre-enable buffer switch 62 produces an output pulse for turning on the oscillator and amplifier before a coded signal is transmitted. The pre-enable function permits the oscillator to stabilize before transmitting. The hybrid transmitter also includes a varactor modulator 66 which receives output signals from a modulator buffer switch 68. A pulse code modulated~PCM) signal is sent to the modulator bu,ffer,switch f,rom a Manchester encoder 70.
When the PCM signal is-sent to the modulator buffer switch, it causes the varactor modulator to shift the 318.0 mhz carrier frequency by 70-100 khz with each "logic 1" trans-mitted. That is, the carrier frequency is shifted when 1 each "logic l" is sent out sothat the receivercan distinguishbet~Jeen a one and a zero.
The digital I.C. 44 provides all timing and logic functions for the transmitter. A 32.768 ~hz watch c-ystal oscillator 72 provides the time base for the digital I.C.
A burst timer 74 causes transmission of four ~Ianchester encoded digital words in rapid succession during each transmission interval of 10.7 seconds. Each coded word output from the Manchester encoder 70 contains an ll-bit factory set address code 75 from aprinted circuitprogramming pad and a 6-bit alarm status data code 77 frcm a data register 78. The output of the burst timer 7~. is applied to a pulse timer 80 that produces four enabling ?ulses at 103 ms intervals during each transmission interval. fiy changing one data bit, ~he transmit'er can ch~nge from operating as the primary or standard transmitter to operating as a second similar but optional FII transmi~'er producing four enabling pulses at 110 ms intervals. T~e kurst timer 7~ instructs the four-pulse timer when to send the pulses during each transmission interval. The burs_ timer sets the transmission intervals at 10.7 secor.ds. The enabling pulses from the four-pulse timer 80 are ap~lied to a 0.1 ms delay timer 82. The delay time~ then sends the time-delayed pulses from the four-pulse timer to the ~Ianchester encoder, delayed by 0.1 ms. At the same ti~e, the four output pulses from the four-pulse timer 80 are applied directly to the pre-enable buffer switch 62 for turning on the oscillator 56 and amplifier 58 in the FiI transmitter 0.1 ms before the digitally-coded signals are received by the oscillator.
The four coded words sent from the ~Ianchester encoder with each burst received from the burst timer minimize false alarms at the receiver due to interference, because the receiver needs to receive only one of the four coded words correctly during each transmission interval. Once a 1 valid word is received, the receiver is reset for the next transmission interval. The coded words are also spaced apart in time to permit maximum power transmission under current FCC regulations. According to Part 15.122 of the FCC Rules, transmitted power is averaged over a 100 ms time interval. The coded words,are transmitted at minimum intervals of 103 ms. Also, the beginning to end of each burst must not exceed 357 ms, under present regulations.
This limits the number,of~words to four fo~ e,ach,transmission interval. The eleventh-bit-of the factory set-code is set to a "logic 1" on a secondary optional transmitter for sending digitally-coded signals at the same FM carrier frequency to the same receiver. This produces llo ms word intervals between the coded words sent by the ~lanchester encoder in the secondary transmitter, and thereby permits the two transmitters to operate independently on the same carrier frequency without mutual interference. ~ith this arrangement, if the burst timing of the standard and secondary,tran,smitters should- coincide or overlap, only one of the four coded words would simultaneo~sly overl~p, leaving three valid transmitted words per transmission interval; or if any of the coded words happens to overlap with one sent from the secondary t~ans~it'er, or from any other independent transmitter, other valid words can be received during the set transmission interval. As a result, false alarms are essentially avoided because the system generates the re,d,undant coded worc,s for each trans-mission interval, and only one valid word needs to be transmitted to the receiver to reset the receiver for the next transmission interval. By sending four coded words over a relatively lon~-:time interval with interdigitation due to their difference in time period, the probability is that at least one coded word will be passed to the receiver from each transmitter without interference. If at least one of the coded words is not received by the receiver during 1 any transmission interval, then an emergency condition is immediately detected~at the receiver, and an alarm at the receiver is activated. The duration of each coded word is limited to about 2 ms to maintain signal integrity while permitting boosting signal power due to FCC averaging over a 100-ms word interval.
As mentioned previously, the transmit~er generates both emergency alarms and status information. ~11 emer~ency alarms (except out-of-range) immediately trig~er the burst timer 74 out of sequence to send a coded burst to the transmitter circuitry, followed by no kurs's for 22.5 seconds, or until the alarm condition is cor-ec_ed.
22.5 second delay timer 8~ controls the ti.me delay ollo:ling a triggered emergency alarm. The burst ti.~- r.o~~ally sends its timing pulses to the l~ancheste- enc^~er each 10.7 seconds, but when the burst timer is trigge~ed by an alarm signal, it immediately sends a timing pulse to the Manchester encoder to send the emergency alar~ to the receiver. After the burst timer is triggered by the emergency condition, the burst timer is disz~led fo- the next 22.5 second time interval to prevent ot;-e~ pulses from being sent by the burst timer during ~he emergency alarm phase. The purpose is to set--a signalir.g priority.
If emergencies such as immersion, tampering sensed hy the anti-tamper switch 36, or breathing failure are detected~
an emergency alarm is immediately generated; andtransmission of other secondary information, such as call-buttonsignaling or wetness detection are overridden. Triggering inputS to the burst timer are controlled through an OR gate 96. The disable inputs to the burst timer are controlled through an OR gate 97. During the "no burst" period, an LED 86 flashes at a 4 hz rate controlled by a 4 hz oscillator 88 coupled to the LED display through an OR gate 90 and buffer switch 92. The burst timer is disabled at the OR
35 gate 97 to prevent any other coded signals from being sent ~-1 out once an emergency alarm has been tri~gered. The purpose is to prevent sending ot~.er digitally codel bursts which could be interfered with e~ternally and which might erroneously inform the receiver that the emergency was later corrected and that the transmitted al2~m signal had simply been a false alar~. That is, by stopping transmission fo these further signals, interference from such signals is prevented, where such signals possibly could reset the alarm and make the alarm cease, while ma~ing the user think that the alarm that sounded ~as a false alarm, ~hen it was not. - -The anti-tamper alarm system sends an alarm signal to the receiver when tampering with the transmitter is detected.
The output from the safety clip switch 52 is coupled to an input of an AND gate 94. The output of the safety clip switch also is coupled to the burst timer 74 through the OR
gate96 whichcontrolsthetriggering inputtothebu~sttimer.
When the safety clip s~7itch:is closed, the po~er-down section 54 is disabled and the digital IC is-powered up, ;zo with all registers and timers being initialized by the system reset 98, which is coupled to the output of the safety clip switch. ~7ithin a few milliseconds, a coded signal is transmitted for indicatiRg that the transmitter has been properly clipped to the person wearing it. An 8-sec./4-sec. delay timer 100 has an output coupled to the input of the AND gate 94. The output from the AND gate 94 is coupled to the 22.S second delay ti~er 84- The AND gate 94 produces a "logic 1" when the inputs from the safety clip switch and the 8-sec./4-sec- delay timer are in a "logic 1" state. The 8-sec. output from the delay timer 100 serves as a disable signal applied as an input to the AND
gate 94. When the 8-sec./4-sec. delay timer starts, it disables the 22.5-sec. delay timer 84- The output from the 22.5-sec. delay timer is coupled to the data register 78. The delay timer output also is connected to the OR

~37114 1 gate 96 that triggers an in~ut to the burst timer and to the disable input of the burst timer through the OR gate 97.
Once the 22.5 second delay timer has been disabled the safety switch clip can be clipped and unclipped at ~
for the first 8 seconds without activating the 22.5 second anti-tamper alarm. The 4 second time delay output from the delay timer 100 is coupled to an input of the OR gate 90 and then to the LED display 86. During the first 4 seconds of the 8 second period after the safety chip is closed the LED86stays ontoindicate reclipping isstill permissible without activating the 22.5 second anti-tamper alarm. If the safety clip s~itch is opened after the 8 second delay period the delay timer 100 times out and enables the AND
gate 94 and the burst timer 7~ is triggered to transmit an immediate anti-tamper alarm signal to the receiver. The anti-tamper alarm can be activated even if the anti-tamper clip switch is opened for a fe~ milliseconds. The anti-tamper alarm signal is followed by no signal transmission to the receiver for the 22.5 second delay time interval even if the transmitter is immediately recli~ed. If the transmitter is immediately reclipped no--al transmissiOn will resume within 22.5 seconds. If the tr2nsmitter is not reclipped, then all transmis-sions cease and the pouer-down section 54 is triggered to power down the I.C. u~l.
The breathing alarm system produces an alarm signal if sensed breathing rate is too fast or too slow. The breathing alarm is controlled by a capacitive sensor (not shown) coupled to a breathing monitor jack 102. The sensor detects abdominal motion and thereby provides breathing information to the breathing alarm system. The breathing sensor can be formed by two small plates about one inch square attached to a semi-rigid plastic substrate and coated with a thin layer of plastic- The plates are held in contact with the abdominal area by a strap around 35 the body. The dielectri~ constant of water is about 80 times ~<

371~4 1 that of air, and since the plates make imperfec~ contact with the body, inhaling increases capacitance, and exhaling causes a reduction in capacitance. No movement causes no change in capacitance. ~hen the breathing monitor plug is inserted into the input jack 102, the breathing monitor is enabled. The 32.768 khz time base serves as the carrier for detecting capacitance changes. The time base signal is connected to one of the capacitor plates, and the other capacitor plate functions as~an output plate.~ During use, the magnitude of the 32.768 khz signal at the output plate varies directly with breathing. The output from the breathing monitor jack 102 is coupled to a lo~t-pass filter 104 which strips the 32.768 khz car-ier fro~ the signal, leaving a low-level, time-varying signal. This signal is amplified by a virtual ground input amplifier 106 with level changes detected by a virtual ground input comparator 108.
The output from the comparator 108 is cou~led to the L~D
display 86 through the OR gate 90 and buffer switch 92.
Bec~use of a small: amount of hysteresls built into the comparator,~ the transmitter LED flic~:ers with a rate and duration proportional to the rate and durationofeach inhaled breath. This confirms that breath`ng is occurring and that the monitor is properly attac~ed to the person being monitored. ~`~
The breathing monitor alarm is produced by coupling the output from the comparator to a 5 to 20 second time interval timer 110. The output of the timer is coupled to the trigger and disable inputs of the burst timer 74 through the OR gates 96 and 97, respectively- If, during any 20 second period, there are either no pulses or more than 40 pulses n$rom the ~cQmparat-or 10~ the timer~ll0 is not reset. This produces a breathing monitoralarmby immediately allowing the burst timer to-send a-breathing monitor fault code to the receiver, followed by no transmissions to the receiver and a continued alarm at the receiver until . , , - . .
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lZ~ 4 1 either breathing resumes or the breathing monitor senso-is unplugged from the jac~ 102. The L~D ~6 flashes at a 4 hz rate during the alarm condition.
The immersion alarm is activated when the transmi~.er is immersed in water. Immersion of the trans~it~er is sensed by the exposed cylindrical conductors of two adjacen.
subminiature phone jacks 102 and 112 at the bottom of the transmitter housing. ~ne of the conduc'ors is at ground potential. The other conductor is pulled to a high potential by a large value resistance and is common to the input of an immersion comparator 114. When water bridges the conductors, the immersion comparator input drops below a comparator reference voltage for activating ~he immersion alarm. The output from the immersion comparator is coupled to the data register 78 and to the triggering and disabling inputs of the burst timer through the OR gates 96 and 97.
The burst timer is i~mediately triggered when the output from the comparator is produced to send an immersion fault code to the receiver. The LED 8~ also flashes at a 4 hz rate. All further transmissions thereby cease until the transmitter is properly dried and resto~ed ~o operation.
The call alarm or panic alert operates as follows.
The call button 32 on the transmit'er is coupled to the data register 78 and to the burst timer 74 through a 22.5 second latch timer 116. When the transmitter call button is momentarily actuated, the 22.5 second timer is latched, which triggers the burst timer to send an immediate call alarm fault code to the receiver, followed by no further signal transmissions for 22.5 seconds. During the 22.5 second time interval, the LED 86 flashes at the 4-hz rate.
At the end of the that period, the call condition resets, and normal transmitter function resumes.
The monitoring system detects diaper wetness and bed wetness. Diaper wetness is sensed by an external two-conductor probe (not shown), and bed wetness is sensed by ~ ~7~4 1 an external two-conductor screen (not shown). The output detected by either wetness sensor is sho~n cou~led to t~e jack 112 on the transmitter housing, although these detectors also could be coupled to other separate input jac~s on the transmitter housing. The sensed wetness information is coupled to a wetness comparator 118. Conductive fluid or water at the sensor pulls the wetness comparator input below a comparator reference input to activate the wetness alarm.~The output from the wetness comparator is -coupled to the data register 78, but not to the burst timer because the wetness alarm is not an emergency condition. The wetness fault code is instead transmitted to the receiver with each burst until the wetness condition is corrected or the sensor is removed from the jack. Other sensors may also plug into the wetness jack, permitting sensing of light, heat, pressure, force, etc.
The voltage output from the 2.5 volt nicad battery is constantly monitored by a low-battery voltage co~parator 120. The-battery voltage is compared with a-factory-set reference resistor divider voltage having a regulated 9 volts from the 9 volt converter 48 as its source. ~ihen the battery voltage falls below the reference divider factory-set voltage, the low-battery comparator causes a lo-~t-battery voltage fault code to be transmitted with each burst until the battery is changed or recharged.
The FM receiver is understood best by referring to the functional block diagram of FIG. 6. The receiver includes a power supply 122, a radio frequency section 124, an intermediate frequency (I.F.) digital integrated circuit (I.C.) 126, a 2700 gate CMOS custom digita I.C.
128, a signal strength meter 129,.-a-power switch~.l30,- and miscellaneous ana~og components- The receiver also has a range switch 131, the signal strength bar indicator 16 (see FIG. 1), red and green transmitter monitor LEDs 132 ~2~7114 -~2-1 and 134 (shown at 26 and 28 in FIG. 1), a c~.arge status LED 136 (shown at 2~ in FIG. 1), and an audible alar~ 13~.
Thepowersupplyprovides2.5voltstoo~eratethe digi~al I.C. and analog loads. It also provides 8.0 vol.s for operating the radio frequency section, the I.F. digital I.C., and a low-battery reference divider 1~0. The main co-~po~ent of the power supply is a pair of series cylindrical nicad cells 142 providing 2.5 volts at 500 mah. A 6 vac household current battery charger 144 permits simultaneous charging of the battery while operating the receiver. An optional DC adapter can permit charging or operating the receiver from 12 vdc automotive current. An optional sol~r panel can permit charging or operating the receiver directly from sunlight. A single adaoter can allo.r an~ of the chargers to charge up to two transmitter batteries while charging the receiver battery. A resistor bet~een the battery charger and the receiver bat'ery pac~ 1~2 drops excess voltage and limits the charge current to t~.e bat'ery pack. The charge status LED 136 is illuminated while the battery pack is being charged. The trans~it_er battery charger adapter is designed the sa~.e way. ~7hen not in use, and with the power switch in the of r position, no current flows from the battery pack to the loads. When the power control switch is moved to the check or on positions, power is provided to all loads. ~lhen in the check position, an audible beep is emitted each time a signal is received (approximately every ten seconds), as well as emitting a flash from the appropriate transmitter monitor LED. ~hen in the on position, only the LED flashes.
The receiver system is a superheterodyne receiver in which the frequency of incoming radio signals is converted to an intermediate frequency by mixing with a locally generated signal. The radio frequency section 124 of the receiver provides a down conversion function by converting 35 the 318.0 mhz FM carrier signal to a 10.7 mhz intermediate 128~14 frequency (I.F.) signal. The 318 mhz signal is received through a 5-inch long antenna 146, which is impedance-matched to 50 ohms with a loading coil in an antenna matching circuit 148. The signal is then coupled to a pre-amplifier 150. The essential signal-to-noise ratio is determined by the gain and noise contribution of the RF
pre-amplifier~ The selected pre-amplifier transistor is based on the RF performance requirements and a demanding current consumption constraint necessary in order to have a product with substantial operational battery life. The output from the pre-amplifier is coupled to a -7 ds mixer, which is a balanced Schottky barrier diode ring type mixer. This mixer is used because of the good performance with variable mismatches experienced in production and because of high immunity to interference. The mixer improves the product operating reliability. The Schottky diode is characterized by nanosecond switching speed, but relatively low voltage. A local oscillator 154 produces a 307.3 mhz signal of sufficient power level to bias the mixer. Oscillation frequency is determined by a surface acoustic wave ~SAW) device designed into a transistor circuit where the DC to RF efficiency is of prime importance to conserve battery life. The output from the mixer 152 is a 10.7 mhæ intermediate frequencyl which is then filtered by a 400 khæ ceramic filter 156 to preserve the difference signal (318.0 mhz - 307.3 mhz = 10.7 mhz).
The output from the filter is then amplified by a high-gain, super low current-consuming transistor stage of a 22 dB intermediate frequency pre-amplifier 158. The entire radio frequency section 124 is designed to operate on very low current ~about 5 ma).

The I.F. digital I.C. stage 126 further processes the 10.7 mhz output from the radio frequency section 124. The I.F. stage 126 amplifies, filters, and detects the FM
;~ signal, 35 as well as providing a signal strength output for operating ~ ~37~4 -2~-1 a signal strength display. The I.F. digital I.C. is soeci-fically selected for its lo~ current consumption of about 2.0 ma to conserve battery life as well as its wide-band capability. Thesignal intotheI.F. digitalI.C. isamplified by a 40 ds amplifier 160. The output impedance of tne amplifier 160 forms a resistive divider with single range switch resistors to ground for limiting range on lo~l and medium range switch settings of the range switch 131.
Range can be set in tens of feet on low range and hundreds of feet on high range, which has no resistor to ground. A
second 10.7 mhz, 400 khz band width ceramic filter 162 is coupled between the 40 dB amplifier 160 and a 50 dB limiter amplifier 164 for further improving the signal-to-noise ratio. The 50 dB limiter amplifier further boosts signal level up to 50 dB as required. The signal fro~ the limiter amplifier 164 is detected by a quad-ature detector 166 to remove the modulation from the 10.7 mhz F-l intermediate frequency carrier signal. Thellanchester data code detected by the receiver is originally in the form of square waves on a DC level. A virtual ground bufCer amplifier 168 amplifies the square wave component to provide a lo-~impedance source to drive the digital I.C. This output from the amplifier 168 represents the digitally coded receiver input signal with all emergency alarm status condition data from the transmitter. This signal is decoded and further processed by the receiver I.C.' ~
Signals from both the 40 dB amplifier and the 50 dB
limiter amplifier are independently rectified by a full-wave rectifier 170 and summed in a voltage-to-current converter 172 to produce an output current logarithmically proportional to signal strength- This output is used to operate the relative signal strength meter 129.
A high-impedance, current-to-voltage converter 174 changes the relative siynal strength current of the I.F.
digital I.C. to a voltage output amplified and changed to ~Z~7~1at -2~
1 a low-impedance source by a buffer am~lifier 176. The output from the buffer amplifier is filtered by a low-pass filter 178 and then fed to a s-e1ement bar L~D driver for a 5-LED signal strength indicator 182. The output of the amplifier is low-pass filtered so that each of the four 2 MS digital words will cause much of the meter's bar to remain illuminated until the next 2 ~IS word arrives. The result is a bar which remains illuminated at a length proportional to relative signal strength with the most significant LED flickering. The 5-element bar LED driver converts the signal level into five discrete steps and drivestheS-LEDbarsignal strength indicator. ~pproximately every ten seconds, the signal streng_h indicator flashes on with the received signal giving a relative approximation of distance to the transmitter.
The digital I.C. performs all timing, logic, alarm generation, and signal decoding for the receiver. It uses a 32.768 khz watch crystal 18~ as its time base. The output signal from the intermediate frequency I.C. (i.e.
;20 from thè amplifier 160)- provides the in~ut signal 186 to the digital I.C. 128. This input signal is processed by a ~Sanc~ester decoder l88 by comparing a 10-bit, factory set address code 190 with the incoming ll-bit address code.
If the first ten bits of the address code cor~elate with the receiver code, a valid output signal 189 is generated by the ~Ianchester decoder. Valid output signals mean that coded information in the decoder matches coded information sent from the transmitter. :For instance, as long as any of the four coded words produced during each transmission interval is received, a valid output is generated. The ~eleventh bit determines--~Lhether the ~alid signal is from the standard transmitter or a secondary transmitter. The remainder of the signal includes alarm fault data, which is latched into a data register 192 for the standard transmitter or an optional data register 194 for the optional or secondary transmitter. The valid out-ut signal from the ~Ianchester dec~er is coupled to a flrst AND gate 196 corresponding to the standard transmitter and to a second AND gate 198 corresponding to the optional 5 transmitter. The standard output signal from the i!anchester decoder is sent to an 8 second timer 200 and to a standard transmitter ENABLE latch 202, the output of which is applied to an 11.1 second standard transmitter timer 204.
This output produces an enabling signal to the 11.1 second 10 timer 204. The output from the first AND gate 196 is coupled as a RESET signal to the 11.1 second timer. The optional transmitter output from the Manchester decoder is similarly coupled to an 8 second timer 206 and an optional tr~nsmitter ENABLE latch 208 to provide an enabling in~ut to an 11.1 15 second optional transmitter timer 210. The valid out~ut signal from the Manchester decoder is cou~led with the optional transmitter output through the second A~iD gate 198 to the optional transmitter timer 210.
I~hen a transmitter is first activated, it immediately 20 sends a burst. If the burst is from the standard transmitter, it starts the 8 second timer and causes the red LED 132 to glow during the 8 second period to indicate that the transmitter clip may still be repositioned without activating the anti-tamper alarm. The 8-second timer is connected to 25 the LED 132 through an OR gate 211. At the end of the 8 second ~eriod, the standard transmitter ENABLE latch is triggered, which causes the standard transmitter timer to start. If no valid signal is received before 11.1 seconds elapses (e.g., the transmitter moves beyond the preset 30 range), a warble oscillator 212 begins and continues until a valid reset signal is received. The optional transmitter signal is detected and monitored in the same manner as the standard transmitter. The 8-second timer is connected to the optional LED 134 through an OR gate 213. The LED
35 signals indicate the time period during which reclipping ~2~7~4 1 is permissible without causing transmission of an alarm signal. The outputs from thestandard and optional ll.lsecond timers are coupled to the warble oscillator 212 t~._ough an OR gate 214. The output from the optional transmit.er also passes through the OR gate 215. The out?ut fro~ the OR gate 214 is coupled to the red L~3 132 ar.d the green LED 134 through a 4 hz oscillator 216. If one of t-.~o previously-functioning transmitters is switched off ~hile the receiver is still operating, the warble alar~ 212 will sound until the receiver power switch is momentarily switched off. This causes the power-up system reset 218 to unlatch both ENABLE latches and ter~inate the alar~.
If neither of the two transmitters is functioning when the receiver power switch is turned on, the receiver will remain silent until a valid signal is first received.
Each time a valid signal is received and indicated by signal 189, a beep timer 191 generates a 25 ms beeping tone at the audible alarm 138.
The data registers 192 and 19~ store alarm fault data received from the transmitter. For exa~ple, ~-hen a valid address signal from a standard transmitter is decoded, the first AND gate 196 strobes high to store the data bits of the Manchester decoder 188 in the -standard data register 192. Each of the six data bits conveys alarm status information. In addition, loss of signal or out-of-range alarm is given at the output of the transmitter timer.
Receiverlowbattery is determinedby the receiver low-battery comparator 280 external to the digital I.C. The alarms are separated into three categories listed in descending order of priority as follows: emergency, call, and status alarms. Emergency alarms include out-of-ran~e, immersionl anti-tampering, and breathing monitor- There is only one call alarm. Status alarms include transmitter low battery, receiver low battery, and wetness detection.

~2~37~14 ~28-1 All emergency alarms are combined at the O~ gate 214 which activates the warble oscillator 212 and disables the call and status alarms at ~ND gates 220, 222, and 224, respectively. The warble oscillator signal corbines with a 3 khz oscillator signal from an oscillator 226 at an ~ND
gate 228 to operate the audible alarm at a low level, through a low-level buffer 229. Simultaneously, the output from an OR gate 230 triggers a ~ second timer 232, which permits four seconds to elapse before switching to an AND gate Z34 to pass the warble oscillator signal through an OR gate 236 to combine at an AND gate 238 to operate the audible alarm at high volume. The audible alarm on high volume is controlled through a high-volume buffer 239. During the audible alar~, the LED 132 is lS flashed by the 4 hz oscillator 216, which is activated by the OR gate 240. The output of the oscillator passes through an OR gate 242 and is passed through either or both of the AND gates 244 and 246, depending upon which of the standard and/or optional transmitters is at fault as sensed at the OR gates 248 and 2So, respectively. If, for example, the standard transmitter is in fault, either (SA) at the output of the OR gate 252 or (S~') at the output of the standard transmitter timer 204-is high. This causes only the red LED 132 to flash at the 4 hz rate. The green LED 134 is activated in a similar manner to produce an emergency alarm for an optional transmitter.
The receiver constantly monitors range information from the multiple coded bursts sent by the transmitter during each 10.7 second transmission interval. Range is determined as a function of the signal strength of the signal received by the receiver. out-of-range is measured by controlling the sensitivity of the receiver. The range s~itch 131 is used to adjust the sensitivity of the receiver.
If a low range is desired, the range switch on the low setting reduces the receiver sensitivity, i.e., its ability ~ ~37~4 1 to receive signals from the trans~itter. Therefo-e, t~.e person wearing the transmitter can e~ceed a sho-ter ou'-of-range distance before the reduced sensitivity will cause the signal to drop out and produce an out-of-ranse alarm. The out-of-range condition produces a loss of signal at the output from the 50 dB amp~ifier 16~
also causes the output from the current-to-vol~age converter ~to drop out so that the -signal strength meter will indicate an out-of-range condition. Loss of signal is detec~ed at the output 186 from the amplifier 168. None of the signals from the transmitter will be received during the 10.7 second transmission interval when loss of sig~al occurs.
In this event, AND gate 196 does not reset the 11.1 second timer 204 and the timer times out and O~ gate 2~0 then activates the warble oscillator 212 to indicate the out--of-range condition. The magnitude of the signals sent to the receiver is used to detect out-of-range. Although the signals sent to the receiver are digitally ccded, the digital codes (for transmission of address and data infor-mation) are not used for transmitting range information.Out-of-range information is transmitted only through the signal strength of the digitally ccded signals, and the range switch adjusts receiver sensitivity to the incoming signals in order to control the level at which the out-of-range alarm is activated.
This technique for detecting out-of-range condition through the use of receiver sensitivity adjustments is important in reducing the overall cost of the receiver.
Signal sensitivity is controlled by the voltage divider which divides the incoming signal so that the output level of the signal can be lower than its input level to use the lower signal level to reduce receiver sensitivity. This technique requires only a few resistors and -a standard switch to accomplish its purpose at a modest cost.

~LZ~71~

1 A call oscillator is generated from 20 pps of 2~ ms, each being switched on and off at a 1 h~ rate. The call alar~
sound resembles a telephone ring. ~ call ti~er 2,3 is activated by call fault data, eit~.er fro~ the star.~rd data register 192, or fro~ the optional data register 19~.
Either signal passes through an OR gate 25~ havi~ an outputwhichdisablesthebeep,wetness,andlow-batteryala~s via an invertor 256 at the AND gates 222 and 22~. The OR
gate 254 also enables the 4 hz oscillator via the OR gate 240, which flashes the LED's 132 or 134 via the OR gate 242, depending upon whether the optional or stand~rd transmitter, or both, are registering a call fault. Ic the standard transmitter is at fault, the out~ut (SC) combines at the AND gate 2~4, via the OR gate 2~8, ~lit~ the output from the OR gate 242 to flash the red LED. ~ call from the optional transmitter flashes the green LED 13~ in a similar fashion. The c211 timer generates the call alarm, which passes through the AND gate 220 and the OR
gate 230 to combine with the 3 khz signal at the ~iD gate 228 to operate the alarm at the low level. Si~ultaneously, the signal output at the OR gate 230 triggers the 4 second timer 232, ~hich activates the high-volume alarm via the AND gate 234, the OR gate 236, and-the AND gate 238 after the 4 second delay has elapsed.
The wetness alarm is a 25 ms pulse at two second intervals generated by a wetness timer 260. This timer is activated by wetness data fault codes, either from the standard or optional transmitters via the OR gate 262.
The output from the wetness timer operates the high-volume 30 alarm via an OR gate 264, the AND gate 224, the OR gate 236, and the AND gate 238. The red LED 132 is flashed with each pulse when an OR gate 266 is activated, which drives the OR gate 248 via an AND 268 simultaneously with the OR gate 264 driving the AND gate 224 and the OR gate 35 242. AND gates 222 and 224 disable the wetness flashing "': . , :
' ' -~, ' ~ .

1 when a call or emergency alarm occurs. The green LED 134 is flashed in a similar way by an OR gate 270 via an AND
gate 272 and the OR gate 250 in conjunction ~ith the OR
gate 264, the AND gate 22~, and the OR gate 2~2.
The transmitter low-battery alar~ comprises a 25 ms pulse followed by a second 25 ms pulse within a 0.5 second interval. The pulses are generated at a transmitter low-battery timer 273 with each ten second transmission trigger received from the OR gate 274 when enabled by an QR gate 276. The LEDs are discriminately driven, and high-volume alarm is functioned using the same gates and in the same manner as in the wetness alarm.
The receiver low-battery alarm is generated within a receiver low-battery timer 278 with each ten second trigger lS from the OR gate 274 when enabled by a receiver low-battery comparator 280. The alarm is t~o 25 ms pulses separated by 62 ms. No LEDs are flashed, but the audible alarm is activated in the same way and with the same gates as the wetness.and 1QW transmitter battery alarm. It--is possible for all three--status al-arms to occur si~ultaneously.
-The following summarizes certain characteristics of the receiver circuitry, the implementation of which will - be apparent to one skilled in the art.
The 10 dB gain RF amplifier consumes less than one milliamp of current and has a 4 dB noise level, with the following selected transistor device electrical character-istics:
collector-emitter breakdown voltage S volts DC (Min.) collector-base breakdown voltage 10 volts DC (Min.) emitter-base breakdown voltage 2 volts DC (Min.) 30 collector cutoff current (Max.-) - 50 nanoamps DC
current gain-bandwidth product 3 GHZ typical collector-base capacitance (Max.) 0.5 picofarads noise figure ~ ~ -4 dB typical The I.F. preamplifier consumes less thah` onë miiliamp of current and has a 22 dB gain, with the following selected S transistor device characteristl~s:

.' , - , .
~ .

12~7114 l collector-emitter brea~dotm voltage 5 volts DC (;lin.) collector-base brea~down voltage lO volts DC (rIin.) emitter-base breakdo~m voltage 2 vol's DC (rlln. ) collector cutoff current (2Iax.) 50 nanoa~.. ps DC
current gain-bandwidth product 3 G-.-Z ty~ical collector-base capacitance (IIax.) 0.5 picorarads 5 noise figure ~ d3 t~pical The intermediate frequency I.C. consu~es less than 2.5 milliamps of current and has a 90 dB gain, with the following selected transistor device characteristics:
power supply voltage 4.5 volts DC (rlIN. ) lO field strength range 90 dB typical field strength accuracy +/- l.5 dB typical I.F. input impedance lSoO OHrlS (r~Ii~.) quadrature output impedance 50,000 oHr~s (rIIN.) ~<

Claims (9)

1. A remote transmitter and alarm system in which a digitally encoded composite output signal from an RF
transmitter carries emergency data, including data representing one or more emergency conditions, and the digitally encoded composite output signal is received by an RF receiver having a processing system which includes, in combination, a receiver sensitivity adjustment means to change the level of signal strength of the received composite signal in proportion to range, and received signal has a digital data component carrying one or more emergency data signals, in which the signal level component of the received composite signal represents range information and a digital carrier component of the received signal represents the emergency information; and the received composite signal is thereafter processed by the processing system to activate an alarm if the signal strength of the signal level component representing range information drops off to a predetermined level, or an alarm is sounded if the processed digital data component of the composite signal provides fault data to activate the alarm to indicate the emergency condition.

2. Apparatus according to claim 1 in which the emergency conditions comprise at least anti-tampering information and breathing rate information.

3. Apparatus according to claim 1 in which the composite signal received by the receiver further includes status information, and including means for inhibiting reception of the status information when an emergency alarm condition is sensed.

4. Apparatus according to claim 1 in which the remote receiver includes an analog data display of continuous range information measured by the received signal level component.

5. Apparatus according to claim 1 in which the digitally encoded output signal sent from the RF transmitter carries emergency data representing a plurality of emergency conditions, and in which the digitally encoded output signal is received by the RF receiver and processed, with different multiple audio alarms being produced in response to each unique emergency condition signal sent from the transmitter to the receiver.

6. A remote transmitter and alarm system in which a digitally encoded output signal received from an RF
transmitter has emergency alarm data representing an emergency condition, and the received output signal is sent to an RF receiver having a low current operating RF section which converts an FM carrier signal component of the output signal to an intermediate frequency FM signal which is passed through a processor that adjusts receiver sensitivity and then boosts the signal to produce a range level signal having modulation removed from the intermediate frequency FM carrier after which a digital component of the received output signal is amplified, to produce a receiver output signal with digitally coded emergency alarm data in which the receiver output signal also has its signal level representative of range to the transmitter as adjusted by the receiver sensitivity adjustment.

7. A remote transmitter and alarm system as claimed in claim 1 which includes an anti-tamper clip in the RF
transmitter, and in which the transmitter produces a digitally encoded output signal when the clip is closed, and the RF receiver receives output signals during each of a series of transmission intervals so that if the clip is tampered with, a switch opens and sends an anti-tamper signal to the receiver to sound an alarm, followed by no signal for a delay period; and if the anti-tamper clip is reattached during the delay period, no alarm is sounded, but if the clip is not attached during the delay period, the alarm signal continues.

8. Apparatus according to claim 7 including providing a short time interval to attach the clip without the alarm starting the delay period.

9. Apparatus according to claim 7, in which the clip is responsive to clothing interference to maintain the switch in its closed position.