[191
`limited States Patent
`
`Adams
`
`11 11
`
`[45]
`
`4,295,472
`
`Oct. 20, 1981
`
`[54] HEART RATE MONITOR
`
`[75]
`
`_
`John M. Adams, Mesa, Ariz.
`Inventor:
`.
`_
`.
`.
`,
`[73] A551g11ee: Medtromc, Inc., M1nneapolis, Minn.
`{21] Appl. No.: 80,597
`
`[22] Filed:
`
`Oct. 1, 1979
`
`[63]
`
`.
`.
`Related U-S- Appl1catxon Data
`Continuation of Ser. No. 851,030, Nov. 14, 1977, aban-
`doned, which is a continuation of Ser. No. 714,873,
`Aug. 16. 1976, abandoned-
`[51]
`Int. Cl.3 ............................................... A61N 5/04
`[52] US. Cl. ............................... 128/690; 128/706
`
`[58] Field of Search ............... 128/690, 706, 710, 642,
`123/734, 689
`
`[56]
`
`C' d
`R f
`1te
`e erences
`U.S. PATENT DOCUMENTS
`3 144,018
`8/1964 Head ................................... 128/642
`
`3,870,034
`5/1975 James
`........................... 128/734
`4,009,708
`3/1977 Fay, Jr.
`............................... 128/690
`
`1 28/690,
`................I........
`5/1978 Sasaki‘ et a1.
`4,091,610
`4,120,294 10/1978 Wolfe .................................». 128/710
`,
`
`Primary Examiner—William E. Kamm
`Attorney, Agent, or Firm——Carl A. Forest; Lew _
`Schwartz; Joseph F. Breimayer
`'
`
`,
`ABSTRACT
`[57]
`A wrist watch size heart rate monitor coupled with a ‘
`flexible metal expansion band detects a electrocardiac
`signal on one arm and applies that detected signal to
`electronic circuitry within the monitor. Means are also
`included for receiving a second electrocardiac signal
`from the other arm ‘0 obtain an electrocardiac lead I
`signal- The receiving means may be a contact member
`adapted to being placed in physical Contact with a see-
`0nd flexible metal expansion band around the wrist of
`the other arm and having a like contact member associ-
`ated therewith or the receiving means may be metal
`members adapted to having the thumb and a finger of
`the hand 0f the Other arm Squeezed thereagaimt-
`
`4 Claims, 6 Drawing Figures
`
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`SUPPLY i
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`

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`US Patent
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`Oct. 20, 1981
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`Sheet 1 of 3
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`4,295,472
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`US. Patent
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`‘Oct. 20, 1981
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`Sheet 3 of 3
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`4,295,472
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`l
`
`HEART RATE MONITOR
`
`4,295,472
`
`This is a continuation of application Ser. No. 85l,030
`filed Nov. 14, 1977, now abandoned which was itself a
`continuation of application Ser. No. 714,873 filed Aug.
`16, 1976, abandoned.
`This invention relates to cardiac monitoring and
`more particularly to apparatus for detecting and provid-
`ing cardiac signals to processing circuitry.
`In the prior art, many devices exist which are adapted
`to be used in measuring the heart rate of a subject. The
`devices vary from sophisticated, computer-controlled
`apparatus capable of monitoring a plurality of patients
`simultaneously to small,
`individual patient units de-
`signed to monitor only the heart rate. Of these latter
`type devices, the majority accomplish the task of mea—
`suring the heart rate by measuring the pulse rate and are
`implemented in the form of a wrist band with pressure
`sensitive or sound sensitive transducers affixed to the
`band and positioned on the wrist adjacent to the palm of
`the hands
`In addition to the pulse monitoring devices, some
`small
`individual devices measure the electrocardiac
`signal which may be detected from the skin of the sub-
`ject. This has been done by wires running from the
`device to electrodes affixed by conventional means to
`the chest area of the subject. In this manner, a conven-
`tional electrocardiac signal is detected by the electrodes
`and applied through the wires to the device. The device
`may be adapted for use by the subject at several differ-
`ent places of the body. For instance, the device may
`include a small box-like configuration adapted to be
`worn on the belt of the subject or the device may be in
`the form of a wrist band adapted for being worn around
`the wrist. A problem, however, is that the wires leading
`from the chest area to the device, wherever it may be
`placed, are prone to disconnection and breakage as the
`subject moves, thereby terminating the ability of the
`device to monitor.
`The reason that wires have been utilized in measuring
`the electrocardiac activity in the past is that it has been
`thought that it is necessary to continuously monitor the
`patient. However, in many instances, it is only neces-
`sary to take an instantaneous reading of the heart rate.
`For instance, if a subject has previously suffered a coro-
`nary attack and has recovered sufficiently to lead a
`normal, or near normal, life with the exception that his
`heart rate should be limited to a certain maximum, it
`would only be necessary to take a measurement of the
`heart rate during strenuous activity, such as exercising.
`In this case, a continual monitoring of the cardiac activ-
`ity of that subject’s heart would be wasteful. utilization
`of the power source (battery) powering the device. Of
`course the prior art apparatus could be modified by
`placing a simple switch on the device to render it active
`only when desired by the subject. However, the prob-
`lem of wires running from the patient’s chest area to the
`area where the device is located, still remains.
`In accordance with one preferred embodiment of this
`invention, there is provided a cardiac signal detecter
`including a housing containing circuitry for processing
`a pair of electric signals, each one of which manifests
`the electric signal at a different limb of a person, and
`further including a band member of an electrically con-
`ductive material. selected to be capable of detecting
`electric signals on the skin of such person, said band
`being affixed to said housing and of a size to allow the
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`housing and band combination to firmly contact one of
`the limbs. The band is in electric communication with
`the circuitry to provide the signal at said one limb as
`one of the pair of signals. In addition, there is provided
`receiving means mechanically fixed to the housing and
`band combination and electrically isolated therefrom.
`The receiving means is in electrical communication
`with the circuitry and adapted to receive, by contact, an
`electric signal from the other limb and to provide such
`received signal to the circuitry as the other one of the
`pair of signals.
`A preferred embodiment of this invention is hereafter
`described with specific reference being made to the
`following FIGS., in which:
`FIG. 1 shows a pair of wrist band detectors adapted
`for use with circuitry associated with one of the wrist
`bands;
`FIG. 2 shows the face of the housing containing the
`circuitry for processing the signals detected by the de-
`tectors of FIG. 1;
`FIG. 3 shows an alternate embodiment of the housing
`containing the circuitry shown in FIG. 1; and
`FIG. 4 shows the orientation of FIGS. 40 and 4b
`which in turn show, in block format, a circuit diagram
`for processing the signals detected by the apparatus
`shown in FIG. 1 or FIG. 3.
`Referring now to FIG. 1, a pair of wrist bands 10 and
`12 each adapted to be worn on a different wrist of a
`subject are shown. Wrist band 10 includes the housing
`14, a contact member 16 and a pair of flexible metal
`expansion members 18 and 20, connecting housing 14
`contact 16.
`‘
`Housing 14 contains the electronic circuitry used in
`processing the pair of signals representing a lead I elec-
`trocardiac lead signal. This circuitry will be described
`in detail hereafter with respect to FIGS. 4a and 4b,
`arranged as shown in FIG. 4. As is wellknown in the
`art, a lead I electrocardiac signal is derived from the left
`and right hand wrists of the subject and measures the
`electrical activity of the heart along a plane running
`generally parallel to the ground as a patient is in an
`upright position.
`Contact member 16 includes a conductive portion 22
`and an insulator portion 24 arranged so that conductive
`portion 22 is not in electrical communication with ex-
`pansion members 18 or 20. A wire 26 or other electrical
`conducting member connects conductive portion 22 to
`the circuitry within housing 14.
`Expansion members 18 and 20 may be similar to con—
`ventional metal expansion watch bands. However,
`members 18 and 20 should be of a material capable of
`detecting electrical signals appearing on the skin when
`in firm contact with the skin. In addition, members 18
`and 20 should beconstructed to conduct the detected
`electric signal to the electric circuitry within housing
`14, with which circuitry members 18 and 20 are in elec-
`trical communication. Expansion members 18 and 20
`should also be constructed to be adjustable by either
`deleting or adding links therein so that the entire wrist‘ ,-
`band 10 can be sized to fit firmly around the wrist of the
`subject thereby allowing a firm contact between bands
`18 and 20 and the skin to achieve good electrical detec—
`tion of the skin signals. Further, bands 18 and 20 should
`be of an adequate width to allow sufficient surface area
`for good contact.
`,
`,
`_ .
`,
`Band 12 is similar to band‘lO with the exception that
`no housing for electrical circuitry is included and no
`insulator portion, such as portion 24,
`is , included in
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`contact member 28. More specifically, band 12 consists
`of conductive contact member 28 and a flexible metal
`expansion member 30 of similar design to members 18
`and 20. If desired, member 30 may be divided in halfand
`a conventional wrist watch can be inserted in a manner
`similar to the inclusion of housing 14 in band 10.
`Band 12 is adapted to be worn on the wrist opposite
`of band 10. When it is desired to take the subject’s heart
`rate, contact member 28 is placed in firm contact with
`contact member 16. In this manner, the electrocardiac
`skin signal detected by expansion member 30 from the
`wrist upon which band 12 is worn are applied electri-
`cally through contact member 28 to the conductive
`portion 22 of contact member 16. From portion 22, the
`electrical signal is applied through wire 26 to the elec-
`tronic circuitry in housing 14. At the same time, the
`signal from the other wrist is detected by expansion
`members 18 and 2t] and applied directly to the electric
`circuitry within housing 14.
`At this point it should be noted that the exposed
`surface areas of contact members 16 and 28 are designed
`to provide a good electrical connection when physi-
`cally placed in contact with one another. Such design
`may include similar size and a mirror image non-flat
`surfaces.
`Housing 14 also includes a pair of switches 32 and 34.
`Each of switches 32 and 34 includes a pair of pushbut-
`tons, one of which will always extend out further than
`the other. To cause either one of switches 32 or 34 to
`change states, it is necessary to depress the more ex-
`posed button thereof. Switch 32 is an ON/OFF switch
`which should only be in the On state when measuring
`the heart rate and switch 34 is a 6/60 second selector
`switch, that is, the rate can be selectively measured by
`counting R-waves for six seconds and reporting ten
`times that count as beats per minute or the rate can be
`measured by counting R—waves for sixty seconds and
`reporting that count directly as beats per minute. Both
`switches 32 and 34 affect the electronic circuitry within
`housing 14 in the manner described with respect to
`FIG. 4a.
`.
`it should be
`With respect to ON/OFF switch 32,
`noted that a pressure sensitive switch in contact mem-
`ber 16 of FIG. 1 or contacts 40 and 42 of FIG. 3 could
`serve the same function with the advantage that the
`subject would not forget to turn the unit on or off.
`Referring now to FIG. 2, the face of housing 14 is
`shown and includes a three-digit display 36 with each
`digit consisting of seven illuminable segments. Selected
`ones of each of the segments can be illuminated to cause
`any of the digits 0—9 to be displayed in each digit of
`display 36. Display 36 may be any conventional digital
`display.
`Referring now to FIG. 3, a face plate 38 is shown
`which constitutes an alternate embodiment to the appa—
`ratus shown in FIG. 1. The only difference between
`housing 38 shown in FIG. 3 and housing 14 shown in
`FIGS. 1 and 2 is the addition of contact members 40 and
`42. Members 40 and 42 are positioned on the periphery
`of housing 38 in a position approximately 90 degrees
`from the axis through the flexible members 18 and 20. In
`utilizing housing 38, the second watch band 12 appara-
`tus shown in FIG. 1 is eliminated. Rather, the thumb
`and one of the fingers of the hand remote from the limb
`wearing the monitoring apparatus are placed firmly in
`contact with contact members 40 and 42. In this man—
`ner, the electrocardiac signal present on the skin at the
`fingertips is transmitted through members 40 and 42 to
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`the circuitry within housing 38. A word of caution with
`regard to the utilization the embodiment shown in FIG.
`3 is that some individuals may have calloused fingertips
`that could prevent adequate signal transmission from
`the skin to contacts 40 and 42.
`Referring now to FIGS. 40 and b, arranged as shown
`in FIG. 4, a block diagram of the circuitry 50 contained
`within housing 14 is shown. The two signals from the
`wrists of the subject wearing the apparatus of either
`FIG. 1 or FIG. 3 are applied respectively to terminals
`52 and 54. Terminal 54 is connected to a point of refer-
`ence potential, such as system ground and terminal 52 is
`connected to the amplifying input of amplifier 56. The
`amplified signal from amplifier 56 is passed through a
`low—pass filter, which may filter out all signals having a
`frequency above, for instance, 20 hertz to thereby elimi-
`nate 6|) cycle and muscle noise.
`The output of low—pass filter 58 is connected to the
`input of a voltage threshold sensitive circuit 60, such as
`a Schmitt trigger. Circuit 60 provides a pulse signal
`each time the voltage applied thereto exceeds the set
`threshold voltage there. The threshold voltage of cir-
`cuit 60 is adjusted to be responsive only to the R-wave
`of the electrocardiac signal so as to provide a pulse each
`time an R-wave occurs. It should be noted that the
`R-wave of an electrocardiac signal is a positive excur—
`sion of the signal to a point of maximum amplitude of
`the signal. The R-wave is normally proceeded by a
`smaller magnitude positive excursion known as the
`P-wave and followed by another smaller magnitude
`positive excursion known as the T—wave. Although not
`shown in the Figures herein, a potentiometer adjust-
`ment to Schmitt trigger 60 may be provided on housing
`14 to allow the threshold magnitude to be adjusted so
`that Schmitt trigger 60 is only triggered by the R-wave
`and not the P— or T-waves for the individual patient
`utilizing the rate monitoring apparatus.
`The output pulse from Schmitt trigger 60 is provided
`to a “one-shot”, or monostable multivibrator, 62, which
`provides a controlled pulse signal each time an R-wave
`is detected by Schmitt trigger 60. The output from
`“one—shot” 62 is provided through a refractory circuit
`64 back to an inhibit input of Schmitt trigger 60. Refrac-
`tory circuit 64 may be simply another “one—shot" circuit
`which inhibits Schmitt trigger 60 from providing an-
`other pulse for a certain time (e.g., the width of the
`pulse provided therefrom) after the detection of the
`initial R—wave. Refractory circuit 64 is provided to
`prevent a large magnitude T-wave from being detected
`as a second R-wave or, on the other hand, in the event
`that a P-wave is detected as an R-wave, refractory
`circuit 64 prevents the R-wave shortly following the
`P-wave from being detected as a second R-wavc.
`Again, a potentiometer adjustment (not shown) may be
`incorporated in housing 14 to allow the refractory time
`to be adjusted, depending upon the patient's normal
`heart rate and the maximum rate to which the patient’s
`heart should be allowed to be.
`The signal processing circuitry consisting of amplifier
`56, filter 58, Schmitt trigger 60, one-shot 62 and refrac-
`tory circuit 64 is all under the operability control of
`power supply 66. For clarity, the application of power
`+V to each of these components is not shown. How-
`ever, it should be understood that this is the case as well
`as power being supplied to each of the other compo-
`nents described with respect
`to the block diagram
`shown in FIG. 4. As previously mentioned, the output
`from power supply 66 is under the control of switch 32
`
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`

`4,295,472
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`5
`such that when switch 32 is closed power +V can be
`applied. However, when switch 32 is open, the power
`to each of the components in circuit 50 is cut off and
`thus the components are non-operative.
`The output from one-shot 62 is a pulse substantially
`coincident in time with each R-wave of the electrocar-
`diac signal. This pulse is processed by the remainder of
`the logic circuitry in the manner hereafter described.
`The heart of the logic circuitry is the six second timer
`68 which provides a pulse every six seconds. 6/60
`switch 34 actually is a three-bank switch consisting of
`switches 34a, 34b and 34c with each switch having a
`switching arm and a pair of output poles shown sche-
`matically in the upper or lower positions in which the
`switch arm may be placed in. The switch arms of
`switches 34a and 34b are both connected to the output
`of the six second timer 68. The upper contact of switch
`340 and the lower contact of switch 34b are both dis-
`connected from any other component within the sys-
`tem. The lower contact of switch 34a is connected to a
`conventional divide by 10 circuit which provides an
`output pulse after ten input pulses have been provided
`thereto, or, in the case of circuit 50, every sixty seconds.
`The upper terminal of switch 341) is connected to the
`output of the divide by ten circuit 70. Thus, when
`switch 34 is in the “up” position, divide by ten circuit 70
`is bypassed and, a pulse appears at the output of divide
`by ten circuit 70 every six seconds and when switch 34
`is in the “down” position, a pulse appears at the output
`of divide by ten circuit 70 every sixty seconds.
`The upper terminal of switch 34c is connected to +V
`voltage which herein is equivalent to a logic “1” signal.
`Connected to the lower terminal of switch 34c is refer-
`ence, or ground, voltage which herein is equivalent to a
`logic “0” signal.
`The timing pulse from the output of divide by ten
`circuit 70, when switch 34 is in the “down” position or
`from the upper terminal of switch 34b when switch 34
`is in the “up” position, is provided as the input to one-
`shot circuit 72 to cause a desired width pulse to be
`provided therefrom. The output pulse from one-shot 72
`is provided to the enable input to each of twenty-one
`AND gates 74, which are divided into three groups of
`seven gates each. The output from one-shot 72 is also
`connected to the reset input of each of three decade
`counters 76, 78, and 80, with the counter 76 constituting
`the least significant digit and counter 80 constituting the
`most significant digit. Counters 76, 78 and 80 are de-
`signed to respond to the trailing edge of the pulse from
`one-shot 72 to be'reset to a count of zero upon its occur—
`rance.
`
`6
`display to display the value of the BCD signal. Each of
`the seven outputs from each of the convertor circuits
`88, 90, and 92 are applied through the associated AND
`gate 74 at the time the gate is enabled by the pulse from
`one--shot 72, to a latch circuit, represented1n the block
`diagram as one of the latches1n the seven latch circuits
`96, 98, and 100. In addition, the pulse signal from the
`output of divide by ten circuit 70 or the upper terminal
`of switch 34b is applied to the reset input of each latch
`in latch circuits 96, 98, and 100. The output signals from
`each of the latches 96, 98, and 100 are applied respec-
`tively to seven-segment display devices 102, 104, and
`106.
`
`The operation of circuit 50 will hereinafter be de-
`scribed. First, assuming that switch 34 is in the “up” or
`six second position, as shownin FIG. 4a, a pulse will be
`provided to trigger one-shot 72 every six seconds Coin-
`cident with each latch1n latch circuits 96,98, and 100IS
`reset and after one--shot 721s triggered, decade counters
`76, 78, and 80 are reset at the trailing edge of the one-
`shot 72 pulse. When switch 34 is in the “up” position, a
`+V voltage, or logic “1”, is applied to the enable input
`of AND gate 82 and a negative voltage, or logic “0”, is
`applied through inverter 86 to the enable input of AND
`gate 84. Thus, AND gate 82 is enabled and passes the
`detected R-wave pulses from oneshot 62 to the second
`stage decade counter 78. Each time a pulse is applied to
`decade counter 78 it is incremented by one. After six
`seconds, a pulse is applied to clear the latches in latch
`circuits 96, 98, and 100 and to cause a pulse to be pro-
`vided from one-shot 72. This pulse enables each of the
`AND gates 74 to provide the signals stored by counters
`76, 78, and 80, as converted by converters 88, 90, and
`92, to latches 96, 98, and 100. It should be noted that
`with switch arm 34c in the “up” position, the least sig-
`nificant stage decade counter 76 is bypassed and thus
`maintains a zero count therein. In this situation, the
`seven latches in latches 96 are set to cause display 102 to
`display a numerical zero as the least significant digit of
`the display 36, whereby the rate displayed is ten times
`the number of pulses counted during the six second
`interval. Thus, if six pulses had been provided from
`one-shot 62 during the six second interval, display 104
`would have a six appearing thereon and displays 102
`and 106 would each have a zero displayed thereon or in
`other words, a heart rate of 60 would be displayed. On
`the other hand, if twelve pulses had been counted dur-
`ing the six second interval, decade counter 78 would
`contain a two and decade counter 80 a one count. There
`would be applied through in the manner previously
`described to diSplays 104 and 106 with display 102 being
`zero, whereby a count of 120 would be displayed.
`The trailing edge of the pulse from one-shot 72 would
`then reset each of the counters 76, 78,'and 80 and the
`above process would be repeated again until such time
`as another pulse appeared at the input of one-shot 72
`which pulse would clear the latches in latch circuits 96,
`98, and 100 and cause one-s-hot 72 to provide a pulse to
`enable gate 74.
`When switch 34is placed1n the “down" position, or
`sixty second position, it requires ten pulses from the six
`second timer 68 to be applied through divide by ten
`circuit 70 before a pulse is'applied to one-shot 72'. Be- '
`tween one-shot 72 pulses, pulses provided at the output
`of one-shot 62 are applied through enabled AND gate
`84 to decade counter 76. In this instance, ground volt-
`age from switch 346is inverted by invertor 86 and then
`applied to enable ANDgate 84, whereby least signifi-
`
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`When switch 34c is in the “up” position, +V voltage
`is applied to the enabled input of AND gate 82 so that
`the pulses corresponding to the detected R—waves of the
`electrocardiac signal appearing at the output of one-
`shot 62 are applied through AND gate 82 to the input of
`decade counter 78. When switch 34c is in the “down”
`position, ground voltage is applied through inverter 86,
`and from there as a +V voltage, or logic “1” signal, to
`the enable input of AND gate 84, so that the pulses
`corresponding to the detected R-waves are applied .
`through AND gate 84 to the input of decade counter 76.
`The four outputs from each stage of the decade
`counters 76, 78, and 80 are respectively applied to four-
`bit to seven-segment convertor circuits 88, 90, and 92
`which convert a four line binary coded decimal (BCD)
`signal from counters 76, 78, or 80 to an appropriate
`seven line signal which will cause a seven segment
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`4,295,472
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`8
`said display means displays the number of detected
`and counted heartbeats;
`
`7
`cant counter 76 is not bypassed and the count therein is
`displayed on display 102 in the manner previously de-
`scribed.
`What is claimed is:
`1. A cardiac signal detector comprising:
`a housing containing circuitry for detecting and
`counting individual heartbeats of a person as said
`heartbeats are manifested by a pair of electric sig-
`nals, each one of which signals manifests the elec-
`trocardiac potential at a different limb of said per-
`son, said circuitry including means for selecting the
`time during which said detected beats are counted
`to be six or sixty seconds;
`a band member of an electrically conductive material
`selected to be capable of detecting electric signals 15
`on the skin of such person, said band being affixed
`.
`.
`.
`.
`.
`to said housmg and said housmg and band combi-
`nation being capable of firmly contacting one of
`said limbs, said band and housing combination fur-
`ther being in electric communication with said 20
`circuitry to provide the signal at said one limb as
`one of said pair of signals;
`receiving means electrically isolated from said hous-
`ing and band combination, said receiving means
`being adapted for physical contact with said other 25
`limb and being in electrical communication with
`said circuitry to provide the other one of said pair
`of signals;
`display means for providing a signal representative of
`the heart rate of said person;
`timing means responsive to the state of said means for
`Selecting for providing timing signals to cause said
`detecting beats to be counted for said selected time;
`means responsive to said timing signals and the
`counted beats for providing signals representative 35
`of the heart rate of said person to said display
`means;
`means responsive to said means for selecting whereby
`in the event a sixty second timing signal is selected,
`
`30
`
`and
`decade means responsive to said means for selecting
`whereby in the event a six second timing signal is
`selected, said display means displays ten times the
`number of detected and counted heartbeats.
`2. The invention according to claim 1 wherein said
`decade means comprises means for applying the count
`10 of said detecting and counting means to the “10’s" and
`higher significant digits of said display.
`3_ A cardiac signal detector comprising:
`a housing containing circuitry for sensing a pair of
`electric signals, each one of which manifests the
`electric si
`al at a different limb of a erson-
`.
`p
`’
`gn
`.
`a first band member of an electrically conductive
`.
`.
`.
`material selected to be capable of detecting electric
`51g."als on the 5km, 0f such person, ,Sald fir,“ band
`fbemgbaffiéied tobsa1d h0115';an and saidlhousfmfg 311d
`"St
`an
`com mation . 6mg capab e o
`irm y
`contacting one of said limbs, said first band and
`housing combination firth? being 1" electr1° com—
`munication with said circuitry to prov1de the Signal
`at said one hmb as one Of 531d P?” 0f Signals;
`.
`a $600“?! band member or electrically conductive
`material selected to be capable of detecting electric
`Signals on the skin of said person and adapted to
`firmly COUtaCt the other one Of said pair 0f limbs;
`and
`.
`.
`.
`a contact plate carried by S_ald fir-(ft band and housmg
`combination and electrically isolated therefrom,
`said contact plate further being adapted for physi-
`cal contact with said second band member and in
`electrical communication with said circuitry to
`provide the other one of said pair of signals.
`4. The invention according to claim 3 wherein said
`contact plate is carried by said first band member.
`"‘
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`’1‘
`'1‘
`
`4O
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`
`