U.S. patent application number 10/231987 was filed with the patent office on 2004-03-04 for non-contact capacitive sensing system for use in toys.
This patent application is currently assigned to BILL GOODMAN CONSULTING, LLC. Invention is credited to Suzuki, Kent.
Application Number | 20040043696 10/231987 |
Document ID | / |
Family ID | 31976879 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040043696 |
Kind Code |
A1 |
Suzuki, Kent |
March 4, 2004 |
Non-contact capacitive sensing system for use in toys
Abstract
For toys that respond to touch to trigger a particular response,
an activation system utilizes a non-contact capacitive proximity
sensing system that permits activation when a finger, lips or other
body part is close to a sensing area in the form of a hidden flat
conductor under the surface of a toy so that actual touching of the
sensor is not required to activate any of the functions of the toy.
Low capacitance coaxial cable buried in the toy is used to connect
the sensing area to the capacitance detection circuit so that only
the capacitance of the sensing area is measured. Proximity sensing
activation occurs when there is an increase in capacitance at the
sensing area due to the proximity of a body part, with the change
in capacitance being detected through the use of an RC circuit in
the feedback loop of an oscillator whose frequency decreases when
sensed capacitance increases. Self-calibrating techniques involving
adaptive threshold adjustment provide for fail safe sensing in all
environments and across unit-to-unit component variations, with the
thresholds being set each time the toy is turned on, then adjusted
over time as necessary. In one embodiment, multiple sensing areas
are sequentially addressed through a multiplexing circuit and all
audio circuitry is turned off during sensing to prevent capacitance
sensing errors.
Inventors: |
Suzuki, Kent; (Oakland,
CA) |
Correspondence
Address: |
Robert K. Tendler
65 Atlantic Avenue
Boston
MA
02110
US
|
Assignee: |
BILL GOODMAN CONSULTING,
LLC
|
Family ID: |
31976879 |
Appl. No.: |
10/231987 |
Filed: |
August 30, 2002 |
Current U.S.
Class: |
446/268 |
Current CPC
Class: |
A63H 3/28 20130101; H03K
2217/960715 20130101; A63H 2200/00 20130101; A63H 3/001
20130101 |
Class at
Publication: |
446/268 |
International
Class: |
A63H 003/00 |
Claims
What is claimed is:
1. In a battery-operated toy, a system for sensing the proximity of
a human body part to a sensing area at said toy for the activation
of a selected toy response, comprising: A non-contact capacitance
sensing unit within said toy including an electrically conductive
sensing pad, a proximity sensing circuit for the activation of said
toy response and a means for connecting said pad to said proximity
sensing circuit, whereby said pad may be buried beneath the outer
covering of said toy to avoid unsightly visible activation
apparatus.
2. The system of claim 1, wherein said means for connecting said
pad to said proximity sensing circuit includes a shielded
conductor, whereby capacitance sensing is localized to changes in
capacitance at said pad.
3. The system of claim 1, wherein said toy includes multiple pads
distributed about said toy and wherein said proximity sensing
circuit includes a multiplexer for sequentially accessing said
pads.
4. The system of claim 1, and further including an automatic
calibrating unit for sensing capacitances absent the proximity of a
body part and for setting a corresponding capacitance threshold
level, the calibrating unit being self-adaptive.
5. The system of claim 4, wherein said proximity sensing circuit
includes an RC-controlled oscillator and a counter coupled thereto,
the frequency of said oscillator being inversely proportional to
the capacitance associated with said pad, and wherein said
automatic calibrating unit has said corresponding capacitance
threshold level established by the count in said counter.
6. The system of claim 1, wherein said selected toy response is a
predetermined sound, and wherein said toy has a sound generator for
generating said predetermined sound when activated by said toy, and
further including means for inhibiting said proximity sensing
circuit when said sound generator is activated, thereby to
eliminate any false readings of capacitance due to the electrical
noise of said sound generator during capacitance sensing.
7. The system of claim 4, wherein said calibrating unit is
activated when said toy is turned on to establish said capacitance
threshold level.
8. The system of claim 5, wherein said calibrating unit includes
means for adaptively setting said capacitance threshold level.
9. The system of claim 8, wherein said means for adaptively setting
said capacitance threshold level includes a unit for setting said
capacitance threshold level to a maximum value, means for taking a
current capacitance reading, means for ascertaining if the current
capacitance reading is less than said threshold and means
responsive thereto for saving the current capacitance as the new
threshold level.
10. The system of claim 9 and further including means for
establishing if the current capacitance reading is larger than said
threshold by a predetermined margin and for activating said toy
response responsive thereto.
11. A non-contact capacitance sensing system, comprising: an
electrically conductive patch; a length of coaxial cable having a
center conductor coupled to said conductive patch; an RC-controlled
oscillator coupled to said coaxial cable and having an output
frequency inversely proportional to the capacitance associated with
said patch; a counter coupled to the output of said oscillator; and
a threshold circuit coupled to the output of said counter for
indicating the presence of a body part adjacent to said patch when
the count from said counter varies from said threshold, whereby the
adjacency of said body part to said patch is sensed.
12. Apparatus for triggering a predetermined response in a toy,
comprising: a non-contact capacitive proximity system having a
conductive pad for sensing the proximity of a body part adjacent
said pad; and, a threshold circuit for generating a trigger when
the proximity of a body part is sensed.
13. The apparatus of claim 12, wherein the threshold set by said
thresholding circuit is adaptively set.
14. The apparatus of claim 13, wherein said adaptively set
threshold is set when said toy is turned on.
15. The apparatus of claim 14, wherein said adaptively set
threshold is further adjusted after the original setting when said
toy is turned on.
16. The apparatus of claim 15, wherein capacitances associated with
said pad are periodically monitored, with said threshold being
adaptively set when sensed capacitance associated with said pad is
sufficiently different from a previously established threshold.
17. The apparatus of claim 16, wherein said threshold is reset if
the current sensed capacitance is lower than that associated with
said threshold, whereby a capacitance threshold that is set during
the proximity of a body part is adjusted upon removal from
proximity of said body part from said pad.
Description
FIELD OF INVENTION
[0001] This invention relates to non-contact capacitative sensing
and more particularly to its use in toys.
BACKGROUND OF THE INVENTION
[0002] In most toys, a child's interface with an electronic toy is
through the pressing of switches. This results in a rather
unnatural interaction with said toy in order to elicit the desired
electronic response, such as having to squeeze a doll's hand
instead of holding it, or having to press down on a stuffed animal
instead of stroking its fur.
[0003] One way to overcome this drawback is through the use of
capacitive sensing to sense human touch. Capacitive sensing has
been used in many toys in the past to sense touch using conductive
areas on the surface of the toy. The basic premise of this
technology is that when the conductive area is touched, the
capacitance from the person increases the capacitance of the
conductive area, which can be sensed in many different ways. The
problem with this technology is that a conductive area on a toy is
not desirable visually or tactilely. For example, it is difficult
to put external conductive sensing areas on a stuffed animal with
soft fur, or on the face of a doll, without it being visually and
tactilely unappealing. Another disadvantage with this type of touch
sensing is that having the conductive areas external to the toy
makes it much harder to pass CE ESD immunity standards. Because the
user has direct access to the internal circuitry through these
conductive areas, it is quite easy to disrupt and/or damage the
circuit with static discharge. Another disadvantage with having
conductive sensors on surfaces of dolls is that when children dress
the doll in clothes, it hides the conductive areas, rendering them
useless.
[0004] Another method of proximity sensing which has been used in
toys is the sensing of a special stylus which is wired to the toy
itself. One drawback to this method is that if the wire to the
stylus ever breaks or becomes intermittent through metal fatigue,
the toy is rendered useless. Also, for younger children who haven't
learned to write with a pencil, the use of a stylus as a pointing
instrument is awkward.
[0005] Another method used by toys to sense the user's "touch"
without the use of switches is through the use of light-sensing
elements embedded within the doll. When the person's hand covers
the light-sensing element, the decrease in light level is
interpreted as a "touch". The disadvantage of this technology is
that any object that happens to block light to the area is falsely
interpreted as a "touch".
SUMMARY OF THE INVENTION
[0006] This invention also uses capacitive sensing, but differs
from the prior art in the fact that the conductive surface is
buried inside a toy, and the surface is standard molded plastic,
rubber, simulated fur, cloth, or paper, commonly used in toys. The
sense areas are undetectable from the outside of the toy, so the
visual aesthetics of the toy and tactile textures are preserved.
Note that the human body has thin skin and large amounts of fluid
inside. Thus, a human body part such as a finger is a relatively
good conductor inside the skin, which acts like a bag of water with
a thin dielectric covering. The body part thus makes a relatively
good capacitor to earth ground. Even though the sensing area is
referenced to its own ground, which is the negative terminal of one
of the batteries, it has some coupling with earth ground as well.
So when a human body part that acts like a capacitor to ground
comes close to the sensing area, which is one plate of a capacitor,
it changes the frequency of the an RC-controlled oscillator inside
the toy enough to be able to detect it.
[0007] Thus, the capacitive sensing used is proximity sensing of
human skin rather than touch sensing. This proximity sensing must
sense much smaller changes in capacitance than standard touch
sensing because of the finite distance between the conductive
sensing area and the human skin. Also, this method must be very
cost-effective in order to be practical for low-cost toys. This
type of sensing allows very natural, intuitive interaction with a
toy to reliably trigger an electronic response. For example, a
child kissing a doll's cheek or a young toddler pointing at a
letter can be detected by the electronic toy and can elicit the
desired response.
[0008] In one embodiment, in a self-calibrating sequence when the
toy is turned on, the entire capacitive threshold for each sensing
area is first set to zero. A capacitive reading is then taken for
each sensing area. This reading is the capacitance in terms of the
number of oscillator pulses in a predetermined time period.
[0009] If there is no change in sensed capacitance over the
appropriate number of tries, a threshold corresponding to the
number of oscillator counts is stored. It is against this stored
value that subsequent samples of the sensing area are tested. A
body part near the sensing area will cause the capacitance to rise,
and the oscillator frequency to fall, which results in a decreased
number of oscillator pulses and thus a decreased count. When this
count is beneath the previously set threshold by a predetermined
amount or delta, then a `touched` condition is triggered, and the
toy responds appropriately.
[0010] For self-calibration, the capacitance threshold is adaptive
in the sense that if the count representing the capacitance sensed
is above the previously established threshold for a long enough
period, then the threshold is reset to this value.
[0011] Thus for instance, if the sensing area is in the hand of a
doll and the child is grasping the hand of the doll when the system
is turned on, then the initial threshold will reflect a capacitance
of the sensing area plus body part. Later, when the sensing area is
sampled and the child is no longer clutching the hand of the toy,
the capacitance will go down and the count of oscillator pulses
will go up. If this occurs for a number of cycles, then the
threshold is incremented to this new higher number.
[0012] Note that a finger, lips or other body part can be sensed
when the body part is non-contacting, for instance, 1/4-inch away
from the sensing area. This means that the sensing area can be
buried beneath the skin of the toy and even underneath synthetic
fur in the case of a teddy bear, with the toy's actions being
triggered by proximity of the body part. Thus, unsightly sensing
areas are eliminated, making the toy much more appealing.
[0013] In summary, for toys that are to respond to touch to trigger
a particular response, an activation system utilizes a non-contact
capacitive proximity sensing system that permits activation when a
finger, lips or other body part is close to a sensing area in the
form of a hidden flat conductor so that actual touching of the toy
is not required to activate any of the functions of the toy. Low
capacitance coaxial cable buried in the toy is used to connect the
sensing area to the capacitance detection circuit so that the
system is shielded from capacitance other than at the sensing area.
Proximity sensing activation occurs when there is an increase in
capacitance at the sensing area due to the proximity of a body
part, with the change in capacitance being detected through the use
of an RC circuit in the feedback loop of an oscillator whose
frequency goes down when sensed capacitance goes up.
Self-calibrating techniques involving adaptive threshold adjustment
provide for fail safe sensing in all environments and across
unit-to-unit component variations, with the thresholds being set
each time the toy is turned on, then adjusted over time as
necessary. In one embodiment, multiple sensing areas are
sequentially addressed through a multiplexing circuit and all audio
circuitry is turned off during sensing to prevent capacitance
sensing errors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] These and other features of the subject invention will be
better understood in connection with the Detailed Description in
conjunction with the Drawings of which:
[0015] FIG. 1 is a diagrammatic illustration of one embodiment of
the subject invention in which a child is kissing the cheek of a
doll having a sensing area located beneath the skin of the check,
also showing buried coaxial cable coupling a sensing area to
detection circuitry within the doll;
[0016] FIG. 2 is a top view of a sensing area which is a small
piece of copper tape in this embodiment, to which the center
conductor of a coaxial cable is soldered;
[0017] FIG. 3 is a block diagram of the subject system indicating
low capacitance coaxial cable connecting sensing areas through a
multiplexing circuit to an oscillator, the output of which is
coupled to an external event counter within a micro-controller that
counts the number of positive-going pulses from the oscillator
within a certain predetermined period of time, which is stored as
the sensed capacitance;
[0018] FIG. 4 is a simplified schematic representation of the
Schmitt-trigger RC oscillator and a single sensing area when it is
selected by the multiplexer of FIG. 3, the sensing area acting as a
variable capacitance to ground in parallel with the fixed
capacitance of the coaxial cable, PCB, and semiconductor
components, there being a fixed resistor which forms an RC circuit
in the feedback path of the Schmitt-trigger inverter which causes
the circuit to oscillate at a frequency inversely proportional to
the total capacitance; and,
[0019] FIG. 5 is a simplified flow chart showing the programming of
the microprocessor of FIG. 3.
DETAILED DESCRIPTION
[0020] This proximity-sensing scheme involves both the capacitance
sensing areas themselves, the circuitry used to detect a small
change in capacitance, as well as the wiring used to connect the
two.
[0021] Referring now to FIG. 1, what is depicted is a child's toy
in the form of a doll, here illustrated at 10, in which the doll
has a number of sensing areas 12 underneath the skin of the doll.
In this embodiment, the sensing areas are in the feet, hands,
stomach, eyes, mouth, and cheeks of the doll. Each of these sensing
areas is fitted with buried coaxial cables shown in dotted outline
at 14 to connect the sensing areas to the control circuitry of the
doll.
[0022] Also shown is a child generally indicated at 16 using her
lips 18, to activate the doll to perform one of a number of
functions by kissing the doll on the cheek. Other types of
functions may be activated when the child's body part is adjacent
to the other sensing areas so that the doll can be made to respond
in different manners to increased capacitance sensed at different
sensing areas.
[0023] It will be noted that the sensing areas are buried within
the skin of the doll, as are the lengths of coaxial cable to couple
the various sensing areas to control circuitry carried within the
doll.
[0024] Referring to FIG. 2, one such sensing area is illustrated as
including a strip of copper tape 20 to which the center conductor
22 of a coaxial cable 24 is soldered as illustrated at 26. This
inexpensive and simple sensing area comprises a sensor which can be
used in the proximity sensing described above.
[0025] Referring to FIG. 3, a number of sensing areas 30, 32, 34
and 36 are coupled via low capacitance coaxial cable 40 to a
multiplexing circuit 42 shown symbolically as having a number of
taps 44 contacted through a wiper arm 46 to a common tap 48. Each
of these contact points is connected to the center conductor of the
associated coaxial cable, with a resistor R connected between the
center conductor of this coaxial cable and the output of an
oscillator 50. In one embodiment, this oscillator is a
Schmitt-trigger inverter acting as an RC-controlled oscillator. It
will be appreciated that the frequency of the output pulses
generated by this Schmitt-trigger inverter are inversely
proportional to the capacitance at point 44 of the selected tap,
with the output of the oscillator coupled to an external event
counter 56 within a micro-controller 58, with the micro-controller
controlling the addressing of the sensing areas as illustrated by
signals 60. In this embodiment, the micro-controller has an
associated 6-megahertz crystal 68 and a speaker 70 for an audio
output, should such be desired.
[0026] The microprocessor continually scans each of the sensor
areas using the multiplexer to select each one sequentially. When a
body part comes into proximity of a sensing area, micro-controller
58 can sense the increase in capacitance of the particular sensing
area and cause the toy to respond in a preprogrammed way, depending
on the sensing area activated. For instance, if the user touches
the doll's lips, the doll may be made to make a kissing sound,
emanating from speaker 70. Additionally there are many types of
movements or sounds that the doll can make, depending on what is
preprogrammed into micro-controller 58.
[0027] Referring to FIG. 4, oscillator 50 has as its output a
frequency which is inversely proportional to the total capacitance.
The total capacitance is the sum of the variable capacitance
C.sub.v, and the fixed capacitance C.sub.f. Fixed capacitance
C.sub.f is due to the capacitance of the low capacitance coaxial
cable, circuit board, and other electrical components in the
circuit, whereas C.sub.v is variable and depends upon the proximity
of a body part near a sensing area. The RC circuit is formed by a
fixed resistor R in the feedback path of the Schmitt-trigger
inverter oscillator such that the frequency of the output of the
oscillator is changed by variable capacitor C.sub.v due to the
proximity of a human body part to the sensing area.
[0028] In operation, the capacitance sensing areas are small
conductive surface areas made of conductive tape, copper-clad-PCB,
flat copper braid, or any of the many available low-cost conductive
materials used in electronics manufacturing. The material can be
chosen based on cost, manufacturability, and the tactile quality
desired. If the sensing area is to be used in a plush stuffed
animal, for example, the sensing area should be soft and malleable,
such as copper tape or flat copper braid, as to be undetectable
from the outside when the stuffed animal is squeezed. The surface
area used in the preferred embodiment is approximately one square
inch.
[0029] Another feature of the subject invention is the method by
which the above sensing areas are wired to the detection circuitry,
which in one embodiment is on a central circuit board in the toy.
The sensing areas are likely to be spread out all over the toy, and
may be over twelve inches from the circuit board. Low-capacitance
coaxial cable, such as low-cost standard 75-ohm video coax cable,
can be used. The center conductor of the coax cable is used to
connect the capacitive sensing area to the detection circuitry. The
outside shield of the coax cable is connected to ground, and this
prevents the detection circuitry from detecting false capacitance
changes due to human skin near the cabling itself. This method
keeps the capacitance sensing localized to the sensing area
only.
[0030] The detection circuitry must be able to reliably sense very
small changes in capacitance at the remote sensing area, usually a
few picofarads. This small increase in capacitance is a small
percentage of the total capacitance of the coax cable, input
capacitance of the detection circuitry, and stray capacitances on
the circuit board. It would be possible for a very fast
micro-controller to time how long it takes to charge this
capacitance through a resistor with fine enough resolution to
detect this small change in capacitance.
[0031] However, the preferred embodiment of the invention uses an
RC oscillator scheme to allow a low-speed, low-power
micro-controller to detect this small change. In the illustrated
embodiment, micro-controller 58 allows oscillator 50 to run for a
pre-determined amount of time, and counts how many low-to-high
transitions occurred. This allows the minute difference in
oscillator frequency to add up over many cycles, making it easy for
a slower micro-controller to accurately detect the percentage of
change in the capacitance.
[0032] The detection circuitry consists of a single Schmitt-trigger
inverter acting as the RC oscillator 50, which oscillates at a
frequency inversely proportional to the capacitance that it is
connected to. There is an analog multiplexer 42 which selects which
sensing area is connected to the oscillator. A transistor circuit
in an emitter-follower configuration on each sense area may be used
which acts as an analog buffer in order to greatly reduce the
impedance so that the large capacitance of the analog multiplexer
does not affect the oscillation frequency. The output of oscillator
50 is connected to the external event counter 56 input on the
micro-controller. Note that a low-dropout regulator may be used
which regulates the voltage to the analog oscillator/multiplexer
circuit and the micro-controller. This helps to keep the oscillator
frequency from drifting over time, and reacting to noise on the
battery supply. All of the components used in the circuit are
commonly available, mature, low-cost components.
[0033] The software algorithm used in the micro-controller in the
preferred embodiment is described in the flowchart of FIG. 5.
[0034] Referring now to FIG. 5, this flow chart represents the
algorithmic operation of the subject system. In the flowchart and
elsewhere, the term `PAD` is used to refer to a sensing area, and
the two terms are interchangeable. Also, the term `touched` is used
to indicate when a person's skin is near enough to the sensing area
to trigger the capacitive sensing mechanism. The person doesn't
necessarily have to be `touching` the sensing area for this to
occur, since it is proximity sensing. However, the word `touched`
is used throughout this patent in order to make it easier to
understand.
[0035] The capacitance reading that will be referred to in FIG. 5
reflects the actual capacitance at the sensing area, and is
therefore inversely proportional to the actual number of
oscillations counted by the microprocessor. The microprocessor sets
the multiplexer to select the sensing area in question, then counts
the number of oscillations based on its capacitance in a
predetermined period of time, then takes the inverse of that count
to arrive at the capacitance reading. For example, assume that the
counter is an 8-bit counter, the predetermined period is 1 ms (one
millisecond), and that a particular PAD has a quiescent `untouched`
capacitance such that it oscillates at 200 kHz when the PAD is
connected to the RC oscillator. When the microprocessor selects
this PAD using the multiplexer, it will read a count of 200 when it
counts for 1 ms. In one embodiment, the microprocessor could
subtract this count from the 8-bit maximum, 255, in order to arrive
at a `capacitance` reading, in this case a value of 55. When this
PAD is touched, the capacitance will rise, and cause the oscillator
frequency to fall, let's say to 180 kHz. Now, when the
microprocessor takes a reading of this PAD, it will get a count of
180 in 1 ms. Subtracting this from 255, it would arrive at a
`capacitance` reading of 75. As shown in this example, the
capacitance reading as referred to in FIG. 5 reflects the actual
capacitance of the sensing area, not the RC oscillation frequency
or the raw oscillation count.
[0036] More particularly, the micro-controller starts up in a
power-up block 80, then advances to a threshold initialization
block 82, where thresholds of all of the sensing areas are
initialized to the maximum value. Next, the microprocessor advances
to a multiplexer initialization block 84, where it selects the
first of the sensing areas. In this case, the first pad is
selected. As can be seen by block 86, the capacitive sensing
algorithm is inhibited if audio is currently being played through a
speaker. If audio is not currently playing, the counter is allowed
to count the external pulses from the oscillator during a given
time interval, as illustrated at 90. The algorithm prevents
readings from being taken while a sound is being played through the
speaker so that any electrical noise created on the board due to
high current spikes from the audio playback do not give false
readings.
[0037] As illustrated in block 90, the current reading is saved,
and at a decision block 94, it is ascertained if the capacitance
reading for the current pad is less than the pad's calibrated
threshold. It should be noted that the thresholds for all sensing
areas are initially set to the maximum value, so that block 94 is
always true when the toy has just been turned on.
[0038] If, as illustrated at block 94, the current capacitance
reading for the given pad is smaller than its threshold, this
indicates that the threshold may need to be reset. It is first
determined if there were enough readings below the threshold to
warrant a new threshold value, as seen in block 122. This debounce
feature of requiring X number of consecutive readings below the
threshold is utilized to prevent a single noisy reading from
erroneously adjusting the threshold. If there hasn't been X number
of consecutive readings below the threshold, then this pad is
marked as `untouched`, and the threshold value is unchanged, as
illustrated in block 112. If there has been X number of consecutive
readings below the threshold, then this pad is marked as
`untouched`, and the current capacitance reading is established as
the new threshold as seen in block 124, and the process iterates
back.
[0039] In order to ascertain if the current pad is being `touched`,
a determination is made at block 98 whether the current reading is
above this pad's threshold by a given amount. If so, the pad is
marked as being touched.
[0040] As illustrated in block 98, what constitutes a sensing area
being touched is that the current reading minus the current
threshold is larger than a predetermined delta value. If so, then
the PAD is considered `touched`, as illustrated at 100. The delta
value being set to a large enough constant so that the system is
not triggered by noise, which causes minor changes in the sensed
capacitance readings. It should be noted that this delta value may
be set to a different value for each sensing areas. This is useful
for deliberately setting the touch sensitivity differently on the
various sensing areas. In block 98, if the current reading is not
larger than the threshold, or the difference is less than the
predetermined delta, then the pad is marked as `untouched` as
indicated at 112 and at the micro-controller proceeds to block
102.
[0041] Below is an example of how the threshold initially adjusts
to the quiescent capacitance of each sensing area, and why the
continual adaptive threshold algorithm is important. When the unit
is first turned on, all thresholds are set to maximum value. At
this time, each PAD is always going to have a reading that is less
than the threshold in block 94. This is how the system
automatically stores the initial quiescent settings for each pad.
For instance, let's assume that the current capacitance reading is
100 on the left hand of the doll, the threshold starts at 255. The
microprocessor will continually read 100 for the left hand sensing
area until block 122 is true, and 100 is now set as the new
threshold value to which all subsequent readings of the left hand
sensing area is compared.
[0042] The adaptive threshold algorithms is also important in the
case when, for instance, the left hand of the doll is touched when
the unit is first turned on. The quiescent `untouched` reading
should be 100, but the sensing area repeatedly returns a reading of
120 because the left hand is being held by the child, so the
threshold gets set to 120. When the child lets go of the hand, the
reading will jump down to 100 and stay there. When that happens,
the algorithm notices that the reading is less than the stored
threshold, and the `untouched` reading of 100 will now correctly be
stored as the new threshold.
[0043] In one embodiment, even if a PAD is determined to be
`touched`, it is not acted upon immediately. All of the PADS are
read in a single scanning cycle before the appropriate response is
determined. This scheme allows for multiple-PAD detection. For
example, if only one hand is touched, the doll may say "I love to
hold hands with Mommy", but if both hands are held, the doll may
react differently, for example, by singing "Ring around the Rosie".
Block 102 checks to see if all of the PADS have been read, and if
not, the next PAD is selected in block 108 and the reading process
is repeated. If at block 102, it is determined that all PADS have
been read, then block 104 resets the multiplexer to the first PAD.
Block 106 takes into consideration which PAD or combination of PADS
were marked as `touched`, and triggers the appropriate
response.
[0044] In summary, the subject invention has sensing areas that can
detect when human skin is in close proximity. All sensing areas are
inside of a toy, where it is visually and tactilely undetectable by
the user. Moreover, the software algorithm self-calibrates all of
the sensing areas each time it is turned on, so the absolute
capacitance of a given sensing area, its cabling, and detection
circuitry are irrelevant. Moreover, The sensitivity of each area
can be set separately.
[0045] While the subject system has been described in connection
with its use within a doll, it will be appreciated that the subject
system is useful anywhere that proximity sensing is required. It
will be noted that the system may be activated by a person's finger
or other body part which is spaced from the actual sensor itself.
This makes burying of the sensors for whatever reason practical so
that a covering or other layer of material may be interposed
between the sensor and the body part doing the activation of the
system.
[0046] Having now described a few embodiments of the invention, and
some modifications and variations thereto, it should be apparent to
those skilled in the art that the foregoing is merely illustrative
and not limiting, having been presented by the way of example only.
Numerous modifications and other embodiments are within the scope
of one of ordinary skill in the art and are contemplated as falling
within the scope of the invention as limited only by the appended
claims and equivalents thereto.
* * * * *