U.S. patent application number 10/124892 was filed with the patent office on 2002-09-12 for input device with capacitive antenna.
This patent application is currently assigned to Logitech Europe S.A.. Invention is credited to Junod, Philippe, Kehlstadt, Florian Max.
Application Number | 20020126094 10/124892 |
Document ID | / |
Family ID | 26948684 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020126094 |
Kind Code |
A1 |
Junod, Philippe ; et
al. |
September 12, 2002 |
Input device with capacitive antenna
Abstract
An input device having a housing and electronic circuitry for
detecting user inputs, and transmitting signals corresponding to
those inputs to an electronic device, such as a computer. An
antenna is provided for transmitting or receiving signals. A hand
detection circuit is provided, which uses said antenna for
detecting the proximity of a user's hand to the housing and
producing a hand detect signal in response. In one embodiment, the
antenna is a capacitive antenna. A capacitor is switched in
parallel with the antenna when it is used in antenna mode, so that
the impact on the antenna signaling of the capacitance of a user's
hand is minimized. In one embodiment, a sleep mode is provided for
the electronic circuitry to conserve power. The hand detect signal
will awaken the input device from its sleep mode.
Inventors: |
Junod, Philippe;
(Romanel-sur-Morges, CH) ; Kehlstadt, Florian Max;
(Aclens, CH) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Logitech Europe S.A.
Romanel-sur-Morges
CH
|
Family ID: |
26948684 |
Appl. No.: |
10/124892 |
Filed: |
April 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10124892 |
Apr 17, 2002 |
|
|
|
09964975 |
Sep 26, 2001 |
|
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|
60261543 |
Jan 12, 2001 |
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Current U.S.
Class: |
345/163 |
Current CPC
Class: |
G06F 3/0383 20130101;
G06F 1/3203 20130101; Y02D 10/00 20180101; H03K 2217/960775
20130101; Y02D 10/155 20180101; G06F 3/03543 20130101; G06F 1/3259
20130101; Y02D 10/173 20180101; G06F 1/3231 20130101 |
Class at
Publication: |
345/163 |
International
Class: |
G09G 005/08 |
Claims
What is claimed is:
1. An input device comprising: a housing; user input electronic
circuitry for detecting user inputs and transmitting signals
corresponding to said inputs to an electronic device; an antenna;
an antenna circuit coupled to said antenna for transmitting or
receiving signals; and a hand detection circuit coupled to said
antenna for detecting the proximity of a user's hand to said
housing using said antenna and producing a hand detect signal.
2. The input device of claim 1 wherein said antenna is an inductive
antenna.
3. The input device of claim 1 wherein said antenna is a capacitive
antenna.
4. The input device of claim 3 further comprising: a capacitor; and
a switch for coupling said capacitor in parallel with said
capacitive antenna when said antenna is used for transmitting or
receiving signals instead of being used for hand detection.
5. The input device of claim 4 wherein said capacitor has a value
more than double the capacitance of a hand.
6. The input device of claim 4 wherein said capacitor has a value
more than ten times the capacitance of a hand.
7. The input device of claim 4 wherein said capacitor has a value
of at least 10 pico farads.
8. The input device of claim 1 further comprising: a sleep-mode
circuit, coupled to said user input electronic circuitry, for
activating a reduced power operation of said user input electronic
circuitry; said sleep mode circuit being responsive to said hand
detect signal to awaken said user input electronic circuitry from
said reduced power operation.
9. The device of claim 1 wherein said input device is a pointing
device and said electronic device is a computer.
10. The device of claim 1 wherein: said antenna comprises first and
second electrodes on said housing for capacitive connection with a
user's hand; and said hand detection circuit comprises a first
circuit, coupled to said first electrode, for determining an amount
of time for charging of a capacitance connected to said first
circuit, and a second circuit, coupled to said second electrode,
for determining an amount of time for discharging of a capacitance
connected to said second circuit.
11. The device of claim 10 wherein said first circuit comprises: a
comparator; a controller coupled to an output of said comparator; a
voltage divider feedback circuit coupled between an output and a
reference voltage input of said comparator; a detection capacitor
coupled between said first electrode and a signal input of said
comparator; and a switching circuit selectively coupling said
signal input of said comparator to high and low voltage
supplies.
12. The device of claim 1 wherein said input device is a mouse, and
said user input electronic circuitry is an optical module for
reflecting light off a surface and detecting movement of said mouse
relative to said surface.
13. An input device comprising: a housing; user input electronic
circuitry for detecting user inputs and transmitting signals
corresponding to said inputs to an electronic device; a capacitive
antenna; an antenna circuit coupled to said antenna for
transmitting or receiving signals; a hand detection circuit coupled
to said antenna for detecting the proximity of a user's hand to
said housing using said antenna and producing a hand detect signal;
a capacitor; and a switch for coupling said capacitor in parallel
with said capacitive antenna when said antenna is used for
transmitting or receiving signals instead of being used for hand
detection.
14. An input device comprising: a housing; user input electronic
circuitry for detecting user inputs and transmitting signals
corresponding to said inputs to an electronic device; a capacitive
antenna; an antenna circuit coupled to said antenna for
transmitting or receiving signals; a hand detection circuit coupled
to said antenna for detecting the proximity of a user's hand to
said housing using said antenna and producing a hand detect signal;
a capacitor, said capacitor having a value of at least 10 pico
farads; a switch for coupling said capacitor in parallel with said
capacitive antenna when said antenna is used for transmitting or
receiving signals instead of being used for hand detection; a
sleep-mode circuit, coupled to said user input electronic
circuitry, for activating a reduced power operation of said user
input electronic circuitry; and said sleep mode circuit being
responsive to said hand detect signal to awaken said user input
electronic circuitry from said reduced power operation.
15. A method for operating an input device comprising: detecting
user inputs and transmitting signals corresponding to said inputs
to an electronic device external to said input device; transmitting
or receiving signals using an antenna; and detecting the proximity
of a user's hand to said input device using said antenna and
producing a hand detect signal.
16. The method of claim 15 wherein said detecting the proximity of
a user's hand detects a change in capacitance due to said proximity
of a user's hand.
17. The method of claim 16 further comprising switching a capacitor
in parallel with said antenna when said antenna is used for
transmitting or receiving signals instead of being used for hand
detection.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-part of U.S.
application Ser. No. 09/964,975, filed Sep. 26, 2001, entitled
"Input Device With Hand Detection" , which is a non-provisional of
U.S. application Ser. No. 60/261,543, filed Jan. 12, 2001, which
disclosures are incorporated herein by reference.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0002] The present invention relates to input devices, in
particular pointing devices such as mice, and more particularly to
antennas for such devices.
[0003] Wireless mice, trackballs and other devices use batteries
and an antenna to transmit to a receiving unit connected to a
computer. Different types of antennas could be used, such as a
capacitive or an inductive antenna. One concern especially with
capacitive antennas is the capacitive interference of the human
hand on the mouse. An additional concern with a battery-operated
unit is limiting power consumption, and providing a sleep mode
capability that does not interfere with the antenna function.
[0004] In many instances, it is desired to bring a pointing device
into a power saving mode. For example, Universal Serial Bus (USB)
specifications require a low power device in suspend mode to
consume less than 500 uA overall. Similarly, a wireless, battery
operated pointing device must limit its power consumption to a
minimum when the user is either not present or not using the
device. Two strategies have been applied to reach this goal, namely
the interrupt approach and the activity monitoring approach.
[0005] The interrupt approach relies on the interrupt input found
in the device microcontroller. This input, when asserted, activates
built-in wake-up circuitry that brings the device back into an
active mode, from an idle state in which power consumption is
minimal. When the device is idle, the wake-up circuitry is active
but requires a very small amount of power. In this configuration,
the interrupt input is connected to a switch that the user must
depress to activate (wake up) the device. In the activity
monitoring approach, some monitoring activity is started in a
periodic manner to verify that a user is not soliciting the device
in any way. In a mouse, activity monitoring requires flashing the
encoder Light Emitting Diodes (LEDs) and reading back the
photodetector signals in order to detect a potential horizontal
movement, a rather power hungry task. If activity is detected, the
device resumes an active state. In this approach, battery saving is
obtained thanks to the long idle time between two activity
monitoring periods. This approach is less effective than the former
since monitoring typically requires more power than that required
in the microcontroller idle state.
[0006] While the two approaches have proven to be very effective,
both suffer from their own limitations. The interrupt approach
limitation is the fact that a pointing device must be "wakened up"
by clicking on a switch when in power saving mode, e.g. there is no
automatic waking up when the user moves the pointing device as is
currently the case in Logitech products. On the other hand, the
monitoring approach doesn't require a clicking wake up action, but
suffers from a rather long latency time when the device is in this
monitoring mode, the shortening the latency time being in
contradiction with the power saving objectives.
[0007] The problem of power consumption is particularly troublesome
in the new mice using an optical module, which detects the
reflection of light off a surface to determine mouse movement. When
such a device is made wireless, requiring a transmitter (e.g.,
radio or infrared) as well, it is difficult to have the batteries
last more than a couple of months. Accordingly, it is desirable to
have an improved, automatic power saving mode.
[0008] As discussed below, the present invention provides such an
improved power saving mode by using hand detection to activate an
input device, such as a mouse. In one embodiment, the hand
detection uses capacitive detection. Hand detection and capacitive
detection have been used in other applications, a few of which are
discussed below. For example, touchpads use capacitive detection to
detect the location of a finger on a touchpad.
[0009] U.S. Pat. No. 5,341,036 is an example of hand detection
being used to activate a system. In that patent, a machine operator
control station is activated when both hands of the operator are
detected on the control inputs.
[0010] U.S. Pat. No. 4,919,429 shows the detection of a hand by an
optical beam being broken. The detection of the hand activates
certain routines of a hand skill amusement game.
[0011] Capacitive switches have also been used in other
applications, such as detecting the touch of a user on a lamp, and
turning on the lamp.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention provides an input device having a
housing and electronic circuitry for detecting user inputs, and
transmitting signals corresponding to those inputs to an electronic
device, such as a computer. An antenna is provided for transmitting
or receiving signals. A hand detection circuit is provided, which
uses said antenna for detecting the proximity of a user's hand to
the housing and producing a hand detect signal in response.
[0013] In one embodiment, the antenna is a capacitive antenna. A
capacitor is switched in parallel with the antenna when it is used
in antenna mode, so that the impact on the antenna signaling of the
capacitance of a user's hand is minimized.
[0014] In one embodiment, a sleep mode is provided for the
electronic circuitry to conserve power. The hand detect signal will
awaken the input device from its sleep mode.
[0015] For a further understanding of the nature and advantages of
the invention, references should be made to the following
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a mouse incorporating the
capacitive hand detection electrodes according to an embodiment of
the invention.
[0017] FIGS. 2A and 2B illustrate the capacitive hand detection
circuit embodiment for direct and indirect coupling of the hand,
respectively.
[0018] FIGS. 3 and 4 are timing diagrams illustrating the charge up
and discharge cycles for the first and second electrodes,
respectively, with no hand and the hand on.
[0019] FIG. 5 is a diagram illustrating the use of both exposed
electrodes on the side of a mouse and electrodes inside the top
cover of a mouse in parallel.
[0020] FIG. 6 is a more detailed circuit diagram of one embodiment
of a capacitive detection circuit for one electrode according to
one embodiment of the invention.
[0021] FIG. 7 is a block diagram illustrating capacitive plates
used for both antenna and hand detection functions.
[0022] FIG. 8 is a block diagram of the antenna RF circuit of FIG.
7.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 illustrates a mouse 10 having a top housing cover 16
beneath which, in phantom, are shown sheet electrodes 14 and 18.
Additionally, an exposed electrode 20 is shown on a side 22 of the
mouse. A similar electrode can be mounted on the other side, not
shown. The electrodes 14, 18, or/and 20, are connected to a
capacitive detection circuit for detecting when a hand is touching
or in close proximity to those electrodes.
[0024] FIG. 2A illustrates, at a high level, the operation of the
capacitive detection circuit. FIG. 2A illustrates a direct
connection from the hand to the detection circuit, such as through
exposed electrode 20 and a corresponding second electrode 20'. When
the hand touches these, the capacitance of the body 24 to an earth
ground 26 is connected in series with the electrodes. As shown,
first electrode 20 is connected through a capacitor 28 and a
resistor 30 to one input of a comparator 32. Similarly, the second
electrode 20'is connected through a capacitor 34 and a resistor 36
to another comparator 38. The inputs to the comparators are
compared to a reference threshold to determine how long it takes
for the capacitance connected to the measurement node to charge or
discharge. As shown, a switch 40 connects the measurement node of
comparator 32 to either ground (Vss) or to the positive voltage
supply (Vcc). Similarly, a switch 42 connects the measurement node
of comparator 38 to the same references.
[0025] However, switches 40 and 42 operate to connect one
comparator to Vcc, while the other comparator is connected to Vss,
and vice versa. Thus, one electrode and its capacitance will be
charging up, while the other one is discharging. This simultaneous
measurement in opposing directions provides that an internal
virtual ground 44 will mimic the earth ground, allowing the
detection of the user's hand, which user is naturally capacitively
coupled to the real earth ground. The capacitance measured when the
user's hand is in proximity to the electrodes is contrasted with
the capacitance when the user's hand is not near. Without the
user's hand, there is no connection to earth ground 26, and the
electrodes are floating. Thus, the only capacitance is parasitic
capacitance to the internal virtual ground 44 of the device.
[0026] FIG. 2B illustrates the same circuit as FIG. 2A, except that
instead of an exposed electrode directly contacted by the hand,
there is a gap between electrodes 14 and 18 to the user's hand.
This gap itself forms the desired measurement capacitance
corresponding to capacitors 28 and 34 in FIG. 2A.
[0027] When the user is not placing his/her hand on the mouse, the
capacitance is determined by the parasitic capacitor (a few pF)
present on the measurement node. When the hand is located on the
device, close to the parasitic capacitor, the overall capacitance
is determined by a combined capacitor consisting of the parasitic
capacitor and the measurement capacitor (28, 34).
[0028] The measurement capacitor models the capacitive coupling
from the measurement node to local ground. It is connected to the
measurement node on one end and to local ground via the user
hand/body on the other end. It includes a coupling capacitor from
inside the device to the hand, and a body-to-local earth capacitor,
all connected in series. In one embodiment, the coupling
capacitance is maximized by covering a large portion of the device
surface, on the internal side, with an internal conductive layer,
such as metal foil. It is the dominant term when compared to the
other one (because it is the lowest value in the chain), on the
order of 5 to 10 pF.
[0029] Since the device can be connected to a portable computer in
one embodiment, and can be floating with respect to local earth, a
virtual earth is generated inside the pointing device. This
detection system relies on a double capacitance measurement, thus
necessitating two charge/discharge-time-measurement circuits, each
with its parasitic capacitor and internal conductive layer. In this
configuration, one system measures its measurement node charging
up, while the other measures its respective node charging down, and
then the other way around in an alternated up/down manner. If the
coupling from the two measurement nodes to local earth is
symmetrical, the system ground is at a virtual earth.
[0030] The two parasitic capacitors are connected to an internal
conductive layer, each covering a distinct portion of the internal
surface, but close enough to produce a somewhat similar coupling to
the hand resting over the device on the external surface. This
enforces a rather symmetrical coupling if the entire hand covers
the pointing device body, and allows virtual earth generation. In
an alternate embodiment, the two internal conductive layers consist
of two sets interleaved strips; each set being connected to its
respective internal parasitic capacitor.
[0031] The hand detection circuit can be used both with the
interrupt method and the monitoring method. In the interrupt
method, the hand detection circuit operates in stand-alone mode by
executing the capacitance measurements on a periodical time basis,
for example every 500 ms. When a hand is detected, a signal at the
output of the circuit and connected to the interrupt input of the
pointing device microcontroller is asserted. Activating the
interrupt input brings the device out of the idle state, which is
then ready to operate.
[0032] In the monitoring method, the pointing device requests, on a
periodical manner, capacitance measurements. If the output hand
detector is asserted, the system resumes full power operation. If
not, the system goes idle for a known duration after which a new
capacitance measurement phase is requested.
[0033] Improved power saving and/or reduced latency time occurs
when the energy to complete a full capacitance measurement is less
than that of activity monitoring.
[0034] Due to the intrinsic lower energy requirement of a hand
detection circuit, both a better trade-off between power saving and
latency time; and an automatic power-on are possible. Examples of
trade-offs include significant power saving with equivalent latency
time, or moderate power saving together with a smaller latency
time, while both options do not require any button clicking.
[0035] FIG. 3 shows a first signal waveform 46 with the charging
and discharging times illustrated as times T0, with no hand
present. The charging cycle charges up to the 2/3 Vcc threshold,
while the discharging cycle discharges from Vcc down to a 1/3 Vcc
threshold. A second waveform 48 illustrates the change in the
charging time due the presence of the hand, indicated by dTf.
Similar waveforms 72 and 74 are illustrated in FIG. 4 for the
second electrode.
[0036] By adding the four measurements (the charge and discharge
times of 48, and the charge and discharge times of 74), there is a
cumulative change in capacitance of 4XdTf. Firmware embedded in the
pointing device will compare that sum (both electrodes together) to
a time reference in order to determine whether the hand is present
or not. The threshold can be automatically readjusted each time
after the hand was detected as touching the pointing device, or
after it is detected as lifting off the pointing device. This will
compensate for the parasitic capacitances (which do not vary
depending on the hand being present or not). Thus, the system needs
no factory adjustments. Preferably, the difference in capacitance
is about between 1 and 4 pF. Less than 1 pF would risk having the
system too sensitive, such that even vibrations of the electrode
interconnections could be detected. 4pF is about what is practical
through the plastic case of a mouse.
[0037] If the input device is not referenced (not connected) to
earth ground, any voltage may be present between the local voltage
reference of the electronics and earth ground. This could lead to
overflow or underflow of the counters in the controller for
counting the charge and discharge times. By driving the two inputs
in phase opposition, and connecting them to the same body
capacitance, one circuit will try to discharge the body
capacitance, while the other is trying to charge it, thus
offsetting the body capacitance. This leaves the measurement
capacitance on the two electrodes to be charged or discharged.
[0038] A push-pull configuration can also be used to measure the
differential capacitance between the two electrodes, which augments
when a common conductive element (the hand) is covering them both,
whatever the potential of those elements may be versus the
reference potential of the sensing circuitry.
[0039] FIG. 5 illustrates an embodiment in which both touch sensors
in direct, galvanic contact with hand or fingers are wired in
parallel with capacitive sensors mounted on the underside of a top
case housing. In the example shown, two discrete electrodes 84 and
86 are exposed outside the case for direct contact with a user's
finger. These may be close together on one side of the housing, or
on opposite sides where they can be contacted by the grasping
fingers of a user. Instead of simply two capacitive sensors on the
inside of the top of a case, the diagram shows four interleaved
sensors, with electrodes 88 and 90 being connected to a first
electrode 84, and electrodes 92 and 94 being connected to a second
electrode connected to electrode 86. External electrodes 84 and 86
require discrete capacitors, shown as capacitors 96 and 98. For the
other electrodes (which are on the internal side of the case, i.e.,
not accessible to the user) the case itself provides the dielectric
for capacitive coupling with the user's finger. This is a good
embodiment for cost reasons, although it only allows a proximity
detector instead of an actual-touch sensor.
[0040] FIG. 6 is a block diagram of the capacitive detection
circuit connected to each electrode. This embodiment shows a
discrete capacitor (50, corresponding to capacitors 28 and 34 of
FIG. 2A) that makes each external electrode an actual-touch sensor.
In the example shown, an electrode 14 is connected to a sensing
capacitor 50 and through a resistor 52 to a pull-up/pull-down
resistor 54. In practice, the capacitor may be simply a gap in the
wiring to the electrode. This gap can be created in a number of
ways. A Mylar (Dupont's trademark for polyester foil) sheet can be
used as a dielectric between the wiring connection and the
electrode. This provides a well-characterized dielectric, with a
well-characterized thickness, wedged between the conductor's
terminal and the electrode, so that the resulting capacitance is
well determined in spite of differences in tolerances during
manufacturing. A flexible PC board could be used, with the flexible
substrate itself causing the gap, i.e. the dielectric, between the
electrode and the wiring. In one embodiment, the gap is about 50
microns, although the gap used can vary widely depending on the
dielectric, etc. In one embodiment a wire is simply not stripped
after it is cut, leaving its insulation intact up to the end. Then
it is inserted through a hole in the electrode that has the same
diameter as the insulation's external diameter. Or the electrode
may be made of two pieces that are assembled around the insulated
wire so that this is surrounded by the electrode. This makes a
cylindrical or tubular capacitor at no material cost, where the
wire jacket is the dielectric.
[0041] When the finger 12 makes contact with electrode 14, the body
capacitance 56 is placed in series with the detection capacitance
50 and resistor 52. When a galvanic contact is made between the
finger and the contact electrode, the amount of the capacitance is
measured at an input to comparator 58 by measuring the amount of
time to either charge up or discharge the capacitance. In the
embodiment shown, a switch 60 is closed to connect a node 62 to
ground, allowing a measurement of the amount of time for the
capacitance to discharge. Subsequently, a switch 64 can close, and
switch 60 open, to measure the amount of time for the capacitance
to charge from the power supply. These charge up and charge down
times are illustrated in FIGS. 3A and 3B, with T0 being the amount
of time in the absence of a finger. The presence of a finger is
indicated by dTf. Additional noise cancels out between the charge
up and charge down cycles.
[0042] The threshold on the other input of comparator 58 is set by
feedback from its output through a resistor 66, in combination with
a voltage divider of resistors 68 and 70. The output of comparator
58 will alternate between a 0 and 1 value, causing the threshold to
alternate between 0.33 and 0.66 of the supply voltage, Vcc. For
more details about the construction and operation of a capacitive
detection circuit, reference should be made to copending patent
application Ser. No. 60/258,133, filed Dec. 22, 2000, entitled
"Pointing Device with Solid State Roller," assigned to the same
Assignee as this application, the disclosure of which is hereby
incorporated by reference.
[0043] The output of comparator 58 is provided to a controller 72.
The controller also controls the opening and closing of clamp
switches 60 and 64. The controller can also analyze the signal from
the electrode, and a separate signal from a similar circuit for a
second electrode, to determine the presence of a finger and the
movement direction of a hand.
[0044] FIG. 7 illustrates a human hand 120, with its associated
capacitance, approaching two capacitive plates or foils 122 and
124. Plates or foils 122 and 124 form two capacitive electrodes
which are connected to a hand detect circuit 126 for detecting the
presence of a hand. In addition, these two electrodes 122 and 124
are connected to an RF circuit 128 for driving and/or receiving
signals using the electrodes 122 and 124 as a capacitive antenna. A
switch 130 switches a capacitor 132 in parallel with the electrodes
during antenna mode. The extra capacitor 132 reduces the
sensitivity of the antenna to the capacitance of hand 120 during
antenna functions. In the embodiment shown, switch 130 is also used
to switch the RF circuit 128 into contact with the two electrodes.
However, an alternate embodiment could have the RF circuit
permanently connected, with only the capacitor switched in and
out.
[0045] When the device enters a sleep mode, such as described
above, the switch disconnects the external capacitor 132 and RF
circuit 128, and connects to a hand detect circuit 126. Again, in
an alternate embodiment, hand detect circuit 126 can be permanently
attached to the electrodes. The removal of capacitor 132 provides
the sensitivity to the hand to enable hand detect circuit 126 to
function. The present invention thus uses the same electrodes for
both the antenna and hand detect function. This provides a low-cost
hand detection with a high efficiency capacitive antenna for a
cordless device.
[0046] Preferably, capacitor 132 is much larger than the
capacitance of a hand. Typically, a hand has approximately one pF.
Accordingly, a capacitance much greater than one pF should be
added, such as a capacitor in the range of 10-20 pF (however, the
actual capacitor size is related to the antenna geometry. For very
small sensors, a capacitor less than 10 pF may be required).
Alternately, instead of simply adding the capacitor, a tuning
circuit could be used.
[0047] The antenna could be mounted in any of a number of places.
For example, the antenna could be printed on a printed circuit
board (PCB), which also contains the other circuitry of the mouse,
trackball, or other device. Alternately, the capacitive electrodes
could be foil attached to the inside of the upper housing of the
input device, or in other locations such as described earlier.
[0048] Preferably, the capacitive electrodes are foil, wire or
plates, and should be metallic. They can be square-shaped as
illustrated in FIG. 7, or could have rounded corners, or could have
a completely different shape.
[0049] In an alternate embodiment, an inductive or coil antenna
could be used, such as by providing loops on the PCB. The inductive
antenna could also be used to detect the hand presence. The hand
presence is used to wake up from the sleep mode. The entering into
the sleep mode is typically done by the detection of the absence of
user activity for a specified period of time.
[0050] FIG. 8 illustrates the circuitry which would comprise RF
block 128 of FIG. 7. An oscillator 134 is provided, with its signal
being provided to a modulator 136. The modulator modulates a data
signal indicating the mouse movements and button presses on a line
138, and provides the modulated signal to an antenna driver 140.
The antenna driver provides its signal through a matching circuit
142 to the capacitive antenna 144. Alternately, the capacitive
antenna could be used for receiving signals, which are then
provided as data to the controller of the mouse on data lines 138
or through an alternate path.
[0051] In one embodiment, during a running mode, the hand detection
circuit 126 is powered down, limiting the amount of power required
by the device. The RF circuitry can also be powered down in between
the transmissions of data. The input switches and the movement
sensor of the mouse will be powered, and upon detecting movement or
activation, will provide signals to the controller, which can then
activate the RF circuit to transmit the signal. Alternately, the RF
circuit could be left on all the time.
[0052] In the absence of any inputs after a certain period of time,
such as one minute, a true sleep mode can be entered. The
controller would be in a stop mode, the RF circuitry would be
turned off, and the hand detect circuit 126 would be turned on. The
controller can reawaken periodically to determine if a hand has
been detected. For example, it could reawaken every 100 mS. If no
hand is detected, it would go back to sleep. If it is detected, it
would awaken the device from the sleep mode.
[0053] As will be understood by those of skill in the art, the
present invention may be embodied in other specific forms without
departing from the essential characteristics thereof. For example,
instead of being a pointing device connected to a computer, the
input device could be a remote control for controlling a TV or a
stereo, or any other electronic equipment. The technique of the
invention can also be applied to a gaming device. In particular,
hand detection is useful for force-feedback joysticks where a
"dead-man switch" has to be implemented in order to prevent the
handle from moving when no hand is grasping it. Alternately, other
capacitive detection circuits could be used, or an inductive
detection circuit and an inductive antenna. Accordingly, the
foregoing description is intended to be illustrative, but not
limiting, of the scope of the invention which is set forth in the
following claims.
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