Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title: APPARATUS AND METHOD FOR MAGNETICALLY CONTROLLING
A HEARING AID
Background of the invention
[0001] The present invention relates to hearing aids. More particularly,
the invention relates to remote controlled hearing aids.
[0002] Hearing aids often offer adjustable operational parameters to
facilitate maximum hearing capability and comfort to the users. Some
parameters, such as volume or tone, may be conveniently user adjustable.
Other parameters, such as filtering parameters, and automatic gain control
(AGC) parameters are typically adjusted by the acoustician.
[0003] With regard to user adjustable parameters, it is awkward or
difficult to remove the hearing aid for adjustment especially for individuals
with
impaired manual dexterity. Remotely controlled units may be utilized to adjust
such desired functions inconspicuously and without removal of the hearing
aid.
[0004] Various means have been utilized for the remote control of
hearing aids. A remote actuator of some type is necessarily required for all
remote controlled systems. Control signals from the remote actuator have
been by way of several different types of media such as infrared radiation,
ultrasonic signals, radio frequency signals, and acoustical signals.
[0005] Often times different listening situations will warrant different
settings of various adjustable parameters for optimal hearing and comfort.
This need may be addressed by preprogramming various groups of settings
(programs) of the parameters into the memories of the hearing aids. When
entering a different environment the user can select the most suitable group
of
settings of the adjustable parameters. The remote control selection of such
programs has heretofore required transmission of coded or modulated signals
to activate selection of the desired programs. Thus necessitating an
electrically complex remote actuator and receiver circuitry in the hearing
aid.
Obviously, where a remote actuator is inoperable or unavailable, selection of
different programs would be impossible.
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[0006] Remote actuators used to control parameters and select
programs can have complicated controls which can make them difficult to
understand and use by many hearing aid users. Moreover, users with limited
manual dexterity due to arthritis, injuries, or other debilitating illnesses,
may
find it difficult or impossible to operate remote controls with several push-
button controls. Thus, there is a need for a simple to use remote controlled
hearing aid requiring very limited manual dexterity and in which a number of
hearing aid parameters may be controlled, either individually or by way of
program selections.
[0007] As hearing aids have become more sophisticated they have also
become smaller. "Completely in the canal" (CIC) hearing aids are currently
available which are miniaturized sufficiently to fit far enough into the ear
canal
to be out of view. Such placement makes the hearing aid difficult to access
with tools for adjusting the operational parameters. Moreover, such placement
makes remote control where direct access is needed, such as infrared
radiation, difficult or impossible.
[0008] In such state of the art hearing aids there is minimal faceplate
space for sensors or controls such as potentiometers. Thus there is a need for
a means of controlling adjustable operational parameters in state of the art
miniaturized hearing aids without controls or sensors that take up faceplate
space.
Summary of the invention
[0009] An apparatus and method for controlling one or a plurality of
adjustable operational parameters of a hearing aid by the movement of an
external magnetic actuator into and out of proximity with the hearing aid. The
external actuator is hand held and comprises a magnetic source such as a
permanent magnet. The hearing aid has a microphone for generating signals,
hearing aid circuitry for processing the signals, an output transducer for
transforming the processed signals to a user compatible form, and a magnetic
switch, such as a reed switch, connected to the hearing aid circuitry. In one
embodiment, hearing aid circuitry has a plurality of adjustable operational
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parameters and includes control processing circuitry for switching between
and controlling the adjustable operational parameters. The magnetic source is
moved into and out of proximity with the hearing aid a selected number of
times activating or switching "on" the magnetic switch each time. The control
processing circuitry is configured to switch between the adjustable
operational
parameters on sequential activations of the magnetic switch for selection of
an operational parameter to adjust. The control processing circuitry is
further
configured to adjust the selected adjustable operational parameter after the
activation of the magnetic switch is maintained a predetermined amount of
time and to stop the adjustment when the magnetic switch is deactivated.
[0010] In one embodiment, various sets of specific settings of the
adjustable parameters may be programmed into a memory contained in the
hearing aid circuitry in the form of a plurality of programs. The various
programs may be selected by rotating through the programs by sequentially
activating the magnetic switch by moving the actuator into and out of
proximity
with the hearing aid.
[0011] In a second embodiment, the device operates by moving a
magnetic source into proximity with the hearing aid which closes the magnetic
switch and activates the control processing circuitry to start adjusting the
operational parameter. The control processing circuitry is configured to cycle
the operational parameter at a predetermined rate through the range of
available settings while the magnetic source is maintained in said proximity.
When the adjustable parameter is at the desired adjustment position, the
magnetic source is moved out of proximity which stops the adjustment of the
operational parameter. The control circuitry may include a memory circuit to
allow a desired setting of the adjustable operational parameter to be saved
when the hearing aid is turned off. Moreover, a trimmer may be provided to
adjust the adjustable operational parameter to a desired setting upon turning
the device on.
[0012] A feature of the invention is that the adjustment of the
operational parameter may be simply and inconspicuously accomplished by
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minimal movement and motion. The magnetic actuator is simply moved into
proximity with the hearing aid for an amount of time as necessary to adjust
the
parameter, such as volume, to the desired setting and is then moved away.
The user may cycle through the entire range of parameter settings without
moving the actuator away from the hearing aid.
[0013] A feature of the invention is that the circuitry required in the
hearing aid is quite limited in comparison to alternative remote control
devices. The invention utilizes a single logic level input, that is, a single
on/off
switch as compared to modulated infrared radiation and RF signals that
require detection, amplification, and decoding. Moreover, the device utilizes
a
single magnetic switch as opposed to multiple magnetic switches.
[0014] A feature of the invention is that the magnetic actuator utilizes
no electrical circuitry, no electrical components, no batteries, and no moving
parts. As a result, the magnetic actuator offers a very high level of
reliability, is
very durable, has a very long service life, and is essentially maintenance
free.
[0015] A further object and advantage of the invention is that the
remote actuator is small and inconspicuous, and may be easily carried in a
pocket.
[0016] A further object and advantage of the invention is that if the
remote actuator is unavailable, substitute magnets may be utilized for
adjusting the device.
[0017] A further object and advantage of the invention is that the
system is essentially immune from sources of interference which can create
difficulties for systems utilizing RF, infrared, or ultrasonic remote control.
[0018] An additional object and advantage of the invention is that the
device needs a minimal amount of manual dexterity to adjust the operational
parameters. The actuator only needs to be moved into proximity with the reed
switch and maintained within said proximity to adjust the operational
parameters.
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[0019] An additional object and advantage of the invention is that the
device need not be removed from the ear for the adjustment of the adjustable
operational parameters. Moreover, no adjustment tools need be inserted into
the ear for the said adjustment. Nor does the device need to be visually or
physically accessible to adjust the parameters.
[0020] An additional object and advantage of the invention is that
control of operational parameters in the hearing aid is accomplished without
the use of conventional potentiometers and switches.
[0021] An additional object and advantage of the invention is that a
wide variety of operational parameters may be controlled by the external
magnetic actuator.
Brief description of the drawings
[0022] FIG. 1 is a partial sectional view showing a completely in the
canal (CIC) hearing aid system in place which incorporates the invention.
[0023] FIG. 2 is a partial sectional view showing one embodiment of a
CIC hearing aid incorporating the invention.
[0024] FIG. 3 shows a block diagram of one embodiment of the
invention.
[0025] FIG. 4 shows a block diagram of a modern hearing aid with
available adjustable operational parameters.
[0026] FIG. 5 shows a schematic diagram of the embodiment of the
invention shown in FIG. 3.
[0027] FIG. 6 shows a block diagram of an additional embodiment of
the invention.
[0028] FIG. 7 is a schematic of an example of control processing
circuitry that provides for continued cycling between maximum and minimum
settings of an adjustable operational parameter.
[0029] FIG. 8 is a schematic of an example of control processing
circuitry for adjustment of an initial setting when the hearing aid is turned
on.
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[0030] FIG. 9 is a schematic of an example of control processing
circuitry in which the last setting of the adjustable parameter is saved when
the hearing aid is turned off.
Detailed description of the preferred embodiments
[0031] Referring to FIG. 1, a preferred embodiment of the invention is
depicted. The invention is a hearing aid system which principally comprises a
hearing aid 22 which is shown in place in an ear canal 24 and a magnetic
actuator 26 shown in an actuating position at the ear pinna 28. As described
below the hearing aid 22 has a plurality of adjustable operating parameters.
The magnetic actuator 26 includes a magnet portion 30. The hearing aid as
depicted is configured as a "completely in the canal" (CIC) type. The
invention
may also be embodied in the other convention configurations of hearing aids
such as "in the ear", "in the canal", "behind the ear", the eyeglass type,
body
worn aids, and surgically implanted hearing aids. Due to the extreme
miniaturization of CIC hearing aids, the features of the invention are
particularly advantageous in this type of aid.
[0032] FIG. 2 shows a cross sectional view of the CIC hearing aid 22.
The hearing aid 22 includes a housing 32, a magnetic switch shown as a reed
switch 34, a microphone 36, hearing aid circuitry 38, a battery 39 and a
receiver 40.
[0033] FIG. 3 shows a block diagram of one embodiment of the
invention. In this embodiment the remote actuator controls volume increase
and volume decrease. The hearing aid circuitry 38 comprises signal
processing circuitry 44 and control processing circuitry 46. The signal
processing circuitry 44 receives electrical signals generated by the
microphone 36 and processes the signals as desired. Such processing would
typically include amplification, filtering, and limiting. The processed
signals are
transmitted to the receiver 40. The signal processing includes a plurality of
adjustable parameters 50, 52 identified in this embodiment as volume
increase and volume decrease. The control processing circuitry 46 is
connected to the magnetic switch 34 and translates actuations of the
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magnetic switch into control signals to adjust the adjustable operational
parameters volume increase 50 and volume decrease 52. The control
processing circuitry 46 is configured to switch between and adjust the
operational parameters 50, 52 based upon the actuation of the magnetic
switch and the maintenance of the actuation. This is accomplished by
movement of the magnetic actuator into proximity of the hearing aid and
holding the actuator in said proximity. A suitable circuit corresponding to
the
block diagram of FIG. 3 is shown in FIG. 5 and discussed below.
[0034] The embodiment of FIG. 3 utilizes volume increase 50 and
volume decrease 52 as the adjustable operational parameters. In other
configurations, volume could be a single operational parameter. Where used
herein, volume and gain are synonymous. Numerous other adjustable
operational parameters are available to control.
[0035] FIG. 4 exemplifies the adjustable operational parameters that
are available in a modern hearing aid. FIG. 4 is a block diagram of the signal
processing circuitry 44 which includes a number of circuit segments providing
operational functions with associated adjustable operational parameters. It is
not anticipated that all of the operational parameters shown in FIG. 4 would
be adjustable in any particular hearing aid. Suitably, a select number of
operational parameters would be selected for adjustment capabilities in a
hearing aid. The signal from the microphone 36 goes to a preamp 56 in which
the gain 58 is available as an adjustable parameter. The signal then goes to
an input automatic gain control (AGC) 60 in which the threshold 62 and the
AGC ratio 64 are available as adjustable parameters. The output from the
AGC is split into two channels, a high channel 66 and a low channel 68. The
high channel 66 has a high-pass filter 70 with available adjustable parameters
of cutoff 74 and slope 76, and an AGC-compression circuit 78 with available
adjustable parameters of threshold 80, ratio 82, attack time 84, and release
time 86. The low channel 68 has analogous functions and available
adjustable operational parameters. The high channel 66 signal and low
channel 68 signal are combined in a summer 90 with available adjustable
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functions of low channel attenuation 92 and high channel attenuation 94. The
signal then goes to the final power amplifier 100 having maximum power
output 98 available as an adjustable parameter. Volume or gain control 102 is
available on the line 104 to the power amplifier 100. The final power
amplifier
100 amplifies the signal for the output transducer 40.
[0036] FIG. 5 shows a schematic diagram of the embodiment of the
hearing aid 22 of FIG. 3. The hearing aid 22 utilizes a conventional hearing
aid microphone 106 which includes a preamp mounted within the microphone
enclosure and a Class D receiver 108 which comprises a Class D amplifier
included with an earphone. Therefore, the hearing aid circuitry 38, identified
by the dashed lines, is shown extending through the microphone 106 and the
receiver 108. Such microphones and receivers are available from Knowles
Electronics, Itasca, Illinois. The control processing circuitry is comprised
of an
integrated circuit chip 112 which controls the volume increase and the volume
decrease. A battery 114 provides power to the microphone 106, the Class D
receiver 108 and the IC chip 112.
[0037] The volume is increased and decreased by varying the
impedance of the IC through the IC input 116 at (pin 3) and the IC output 118
(pin 2). The IC 112 is suitably a GT560 transconductance block manufactured
by the Gennum Corporation. Details regarding the design and operating
specifications are available in the GT560 Data sheet available from Gennum
Corporation, P.O. Box 489, Station A, Burlington, Ontario, Canada L7R 3Y3.
[0038] The IC chip 112 is configured whereby the impedance is
increased or decreased dependent upon the sequencing and duration of the
shorting of the pin 8 to ground which is accomplished through the actuation of
the magnetic switch 34. Upon shorting of the pin 8, the volume decrease (or
increase) does not commence for a predefined period of time determined by
the value of the capacitor 120. An appropriate period of time would be one to
two seconds. The embodiment of FIG. 5 operates as follows:
[0039] The magnetic actuator 26 is moved into proximity of the hearing
aid 22 and thus the magnetic switch 34, actuating the switch 34. When used
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herein "into proximity" refers to the range from the hearing aid in which the
magnetic actuator will actuate the magnetic switch. The magnetic actuator 26
is maintained in proximity to said switch for a period of time after which the
impedance is ramped upwardly at a predetermined rate resulting in a volume
decrease. The increase in impedance (and decrease in volume) continues as
long as the magnetic actuator 26 is maintained in proximity to the magnetic
switch 34 until the maximum impedance of the IC chip 112 is reached. If the
magnetic actuator 26 is moved out of proximity with the magnetic switch 34,
the increase in impedance freezes at whatever point it is currently at. When
the magnetic actuator 26 is returned to proximity with the magnetic switch 34
the impedance commences ramping downwardly, increasing the volume until
the magnetic actuator 26 is moved out of proximity or until the minimum
impedance is reached. Thus, the sequential movement of the magnetic
actuator 26 into and out of proximity with the hearing aid 22 alternates the
control processing circuitry 46 between the two adjustable operational
parameters of volume decrease and volume increase. Holding the magnetic
actuator 26 within the proximity of the hearing aid increases or decreases the
volume dependent upon which operational parameter is selected.
[0040] An additional embodiment is shown by way of a block diagram
in FIG. 6. In this embodiment the user may, through use of the magnetic
actuator, adjust the volume of the aid and select any of five different
programs
for different listening environments. Each of the five programs provide for
separate settings for five adjustable parameters including volume control.
The programs are groups of settings of the adjustable operational parameters
that would typically be preprogrammed into the hearing aid 22 by the
acoustician through an appropriate interface. The adjustable parameters
could be any of the parameters shown in FIG. 4.
[0041] Continuing to refer to FIG. 6, this embodiment has a microphone
36, a receiver 40, a magnetic switch 34, and hearing aid circuitry 38. The
hearing aid circuitry 38 includes signal processing circuitry 44, and control
processing circuitry 46. The signal processing circuitry 44 has an amplifier
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126 and volume control or variable gain 128 as an adjustable operational
parameter along with four other adjustable operational parameters 130, 132,
134, 136 which may be such as those discussed with reference to FIG. 4
above. The control processing circuitry 46 includes five control circuitry
blocks
142, 144, 146, 148, 150 which translate a digital control word from the volume
control (VC) latch 156 or control latch 158 to switch closures or to adjust a
discrete electrical analog quantity required to change the signal processing
action of the respective adjustable operational parameters 128, 130, 132, 134,
136. The control circuitry blocks 142, 144, 146, 148, 150 are of conventional
design utilizing digital control logic to provide the specific control
settings for
each adjustable parameter. Such control logic is familiar to those skilled in
the
art and will therefore not be further detailed.
[0042] In the embodiment of FIG. .6, the volume control is the only
operational parameter that the user can independently adjust. Initial volume
settings are programmed into each setting memory by the acoustician.
Thereafter, toggling the latch enable 162 through the control logic controls
the
volume gain 128.
[0043] Each settings memory 172, 174, 176, 178, 180 contains a digital
word that translates into a group of settings of the adjustable operational
parameters 128, 130, 132, 134, 136. These memories are suitably read and
loaded by an external programmer, not shown, which interfaces with the
control logic 164 by way of a programming interface 186. The programming
interface 186 may be through various known means such as hard wire, RF or
infrared radiation, acoustic or ultrasonic signals. Ideally the settings
memories
172, 174, 176, 178, 180 should be nonvolatile, to maintain their contents in
the absence of battery power.
[0044] The control logic coordinates the system function by interfacing
the external programmer to settings memories; sequencing, selecting and
transferring a settings memory to the control latch 158; sequencing and
transferring control words to the VC latch 156; reading the switch input 188
from the magnetic switch 34; timing human and programmer interface
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operation; and preserving the volume control setting and settings memory
address in use at power down and transferring these control words to the
appropriate latches at power-on.
[0045] The control bus 160 carries the digital word from the selected
settings memory to the VC latch 156 and control latch 158.
[0046] The details of the hearing aid circuitry and the programming of
the control logic would be apparent to those skilled in the art and therefore
need not be explained in greater detail. Although the exact operating
procedure may obviously vary with the programming of the control logic, the
embodiment of FIG. 6 could be configured to operate as follows:
[0047] The user turns on the aid 22. The aid powers up in the state it
was in when it was turned off. At power on the aid 22 comes up in volume
control mode. To adjust the volume, the user brings the magnetic actuator 26
into proximity with the magnetic switch 34. Continuing to hold the magnetic
actuator 26 in proximity (holding the switch closed) for a predefined period
of
time will begin to change the volume. The control circuitry can be configured
such as to ramp the volume up to maximum volume and then to ramp the
volume down. The volume ramping ceases when the user moves the
magnetic actuator 26 out of proximity. Unless the user specifically accesses
the change memory mode, the aid 22 always stays in volume control mode.
To change the program in use, the magnetic actuator 26 is brought into
proximity with the switch 34 and then removed from said proximity before the
lapse of the predefined period of time. The aid 22 will then switch to the
next
program and the corresponding settings of the adjustable operational
parameters. If the magnetic actuator 26 is again moved into proximity and
immediately removed, the hearing aid 22 will rotate or switch to the next
group
of settings in the next setting memory.
[0048] FIGS. 7, 8 and 9 depict examples of control processing circuitry
to provide alternate control characteristics of an adjustable parameter such
as
volume. These examples show discrete components which are not generally
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suitable for in-the-ear hearing aids. Similar analogous circuitry may be
utilized
in a hybrid IC for miniaturization and placement in the ear.
[0049] FIG. 7 discloses an example of control processing circuitry 46
that provides for ramping up and down by steps and continuous cycling
between minimum and maximum settings. This control circuitry is suitable for
adjusting hearing aid volume. The principle components are a counter
designated with the element number 200, a conversion ladder 201, additional
logic circuitry 203 to control the counter direction, and a clock oscillator
204. A
conventional LS191 counter provides an example of a suitable counter
design. The clock input 202 of the counter 200 is connected to a Schmitt AND
gate clock oscillator 204 comprised of a dual input NAND device 206, with
one input 208 grounded through a capacitor (CT) 210 and a resistor R3 212
bridging the first input 208 and the output 214 of the NAND device 206. The
second input 218 to NAND device 206 is switched to the supply voltage V+
through the magnetic switch 34 and is connected to ground 222 through
resistor R1 224.
[0050] A Power On Reset (POR) circuit 230 comprised of a Schmitt
inverter 232 with the input 234 connected to supply voltage through a
capacitor C1 236 and diode Dl 238, and to ground through resistor R2 240.
The Schmitt inverter 232 outputs to a POR line 242 connected to the LOAD
node 244 of the LS191 counter 200 and to an inverter device 248. The
inverter device 248 outputs to a reset input 249 of a first flip flop 250 and
inputs to the clock input 251 of a second flip flop 252 through a dual input
OR
gate U5 254. The flip flops 250, 252 are conventional type 4013 flip flops.
The other input of the OR gate 254 is connected to the output 214 of the
NAND device 206. The output 256 of flip flop 250 is connected to the D input
258 of the flip flop 252. The Q output 259 of flip flop 252 is connected to
the
UP/DOWN input 260 of the counter 200. The Q output 264 of flip flop 250 is
connected to its D input 266.
[0051] The enable input node 268 of the counter 200 is grounded. The
MAX/MIN output node 270 connects to the clock Cl input 271 of the flip flop
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250. The outputs QA, QB, Qc, QD, designated by the numerals 274, 275, 276,
278 respectively, are connected to the bases of four NMOS transistors Q1,
Q2, Q3, Q4, also designated by the numerals 280, 281, 282, 283. The
collectors 286, 287, 288, 289 are connected to appropriately weighted
resistors RA, RB, Rc, RD, also designated by the numerals 292, 293, 294, 295,
and the emitters 298, 299, 300, 301 are all grounded. The initial logic state
inputs 303 to the counter 200.
[0052] The control processing circuitry 46 operates as follows: When
power is switched on, the clock 205 is disabled by the low signal on the 218
input caused by the R1 224 to ground and the open magnetic switch 34.
When power is initially applied to the Power On Reset (POR) circuit 230, a
logic low POR pulse is momentarily applied to the POR line 242. The POR
pulse is directly applied to the POR line 244. The POR pulse is directly
applied to the LOAD node 224 of the counter 200, which causes an arbitrary
initial, logic state present at inputs INA, INB, INC, and IND to be loaded
into
the counter as a starting value. The POR pulse is inverted by inverter 248,
applying a momentary pulse to the reset input 249 of the first flip flop 250.
This causes a logic low to appear at the Q output of the first flip flop 250
and
consequently, at the D input 258 of the second flip flop 252. This logic low
is
transferred to the second flip flop 252 Q output 259 by a clocking of its
clock
(CL) input 255 by the inverted POR pulse via the OR gate 254. The end result
is an initial low level on the -UP/DOWN input 260 of the counter 200,
configuring the counter 200 as a binary up-counter.
[0053] The initial POR state is maintained until clocking commences by
actuation of the magnetic switch 34. When the switch 34 is closed the clock
oscillator 204 starts and runs continuously as long as the magnetic switch
remains closed. The counter 200 is incremented by one upon each low to
high transition of the clock oscillator 204 until the count reaches 15, or
binary
"1111" on the counter outputs 274, 275, 276, 278. At this point the MIN/MAX
output 270 of the counter 200 goes high for one clock cycle. This toggles the
first flip flop 250 to its alternate state. Initially the Q output 256 changes
from
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low to high. The next clock transition changes this logic high to the -
UP/DOWN input 260 of the counter 200 by way of the second flip flop 252.
The counter 200 now becomes a down counter and proceeds to count from
decimal 15 to 0 on each subsequent clock pulse. When the counter 200
reaches 0, the MIN/MAX output 270 generates another pulse which toggles
itself back up to the "UP" counting mode. The 4 bit binary appearing on the
output of the counter 200 is translated to an analog level by way of the
selective activation of the NMOS transistors 280, 281, 282, 283 resulting in a
resistance between the control output 285 and ground that cycles in steps
between substantially 0 ohms and the total value of the four sequentially
weighted resistors, 292, 293, 294, 295. With reference to FIG. 4, such a
circuitry can be used to control the volume or gain of a hearing aid by way of
connection to the preamp 56, the power amp 100 or the line 104 to the power
amp.
[0054] An embodiment of the invention utilizing the control circuitry of
FIG. 7 would operate as follows: The user turns on the aid 22. To adjust the
volume, the user brings the magnetic actuator 26 into proximity with the
magnetic switch 34. Continuing to hold the magnetic actuator 26 in said
proximity (holding the switch 34 closed) will start to ramp the volume up to
maximum volume and then to ramp the volume down to minimum volume and
so on in a continuing cycle until the user moves the magnetic actuator 26 out
of proximity. If the magnetic actuator 26 is again moved into proximity the
hearing aid 22 volume or gain will again commence cycling until the actuator
26 is moved out of proximity. In this embodiment the volume increase and
volume decrease is considered a single adjustable operation parameter. The
circuitry of FIG. 7 may be suitably adapted for controlling any of the
adjustable
operational parameters of FIG. 4.
[0055] Referring to FIG. 8, the control circuitry of FIG. 7 has been
modified to provide an initial adjustable POR condition. The initial setting
is
adjusted by an external trimmer (RT) 310. At power-on, resistor (R5) 312
holds the inverting input of a comparator (U7) 317 near ground potential, a
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point lower than its noninverting input. This causes the output of the
comparator 314 to approach the supply voltage V+. This signal constitutes a
high logic level and is connected to the second input 218 of the NAND gate
206. The high logic level causes the clock oscillator 204 to run, advancing
the
counter 200. The counter will count upward in increments of one binary digit
for each clock pulse until the clock oscillator 204 is halted by a logic low
which
will occur when the capacitor (C2) 316 reaches a particular charge. The time
the clock oscillator 204 continues to count after power-up thus determines the
count of the counter 200 and thus the initial resistance at the control
output.
As described previously, the variable resistance of the control output 285 is
suitably inserted in the hearing aid signal processing circuitry for control
of the
desired adjustable parameter, for example, volume. Thus, the initial volume
level setting whenever the apparatus is turned on may be adjusted.
[0056] Referring to FIG. 9, an additional modification of the control
circuitry of FIG. 7 allows storage of the last user's volume (or other
adjustable
parameter) setting. This circuit has a memory 326 in the form of a
conventional EEPROM device. The memory 326 is nonvolatile with the
outputs 330, 331, 332, 333 of the memory 326 connected to the initial logic
state inputs 303 of the counter 200 and with the inputs 338 connected to the
outputs 274, 275, 276, 278 of the counter 200. The memory is provided with a
high voltage supply 345, consisting of conventional circuits, well known in
the
art. The state of the counter 200, which directly controls the operation of
the
signal processing circuitry, is always mirrored in the state of the EEPROM
memory 326. When power is removed from the circuit, that is the hearing aid
is turned off, the memory 326 retains the last setting. When the hearing aid
is
turned back on the POR signal at the LOAD input 244 of the counter 200
initiates loading of the contents of the EEPROM memory 326 into the inputs
303 of the counter 200 returning the resistance between the control output
285 and ground to the state it was in prior to the hearing aid being turned
off
and thus returning the signal processing circuitry to its state before it was
turned off. Where, for example, volume is the adjustable operational
parameter controlled by the resistance between the control output 285 and
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ground 222, then the volume is returned to its state before the hearing aid
was turned off.
[0057] Although the magnetic switch 34 has been depicted as a reed
switch, other types of magnetic sensors are anticipated and would be suitable
for this invention. Such sensors would include hall effect semiconductors,
magneto-resistive sensors, and saturable core devices. Where used herein,
magnetic switch is defined to include such sensors. Similarly, the magnetic
actuator may be any magnetic source such as a permanent magnet or an
electromagnet.
[0058] Although the control processing circuitry as shown, particularly
in FIGS. 7, 8, and 9 is digital, it is apparent that analog circuitry would
also be
suitable.
[0059] The present invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof, and it is
therefore desired that the present embodiment be considered in all respects
as illustrative and not restrictive, reference being made to the appended
claims rather than to the foregoing description to indicate the scope of the
invention.
