U.S. patent application number 09/227140 was filed with the patent office on 2001-08-09 for micropower cap acitance-based proximity sensor.
Invention is credited to HAVEY, GARY D., LEWIS, STEVEN A..
Application Number | 20010011894 09/227140 |
Document ID | / |
Family ID | 22851923 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011894 |
Kind Code |
A1 |
HAVEY, GARY D. ; et
al. |
August 9, 2001 |
MICROPOWER CAP ACITANCE-BASED PROXIMITY SENSOR
Abstract
The present invention is a proximity detector for an electronic
device. The proximity detector utilizes two capacitors which share
a common electrode. The two capacitors are located on the housing
of the electronic device. The capacitors are arranged so that when
the electronic device is used in its normal orientation, a portion
of the operator's body will occlude one of the capacitors, but not
the other. The close proximity of the operator's body will change
the electric field surrounding the capacitor. Thus, the capacitance
of the occluded capacitor will be different than the unencumbered
capacitor. A detection circuit is coupled to the capacitors and to
the power supply of the device. The circuit uses very little power,
and maintains the electronic device in a standby or powered down
mode. Only when the circuit detects a difference in the capacitance
generated by the two capacitors, will it allow full power to be
delivered to the electronic device.
Inventors: |
HAVEY, GARY D.; (MAPLE
GROVE, MN) ; LEWIS, STEVEN A.; (EDINA, MN) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
22851923 |
Appl. No.: |
09/227140 |
Filed: |
January 7, 1999 |
Current U.S.
Class: |
324/662 |
Current CPC
Class: |
G01V 3/088 20130101 |
Class at
Publication: |
324/662 |
International
Class: |
G01R 027/26 |
Claims
What is claimed is:
1. A capacitance based proximity detector for detecting the
presence of an object proximate one of a plurality of capacitors,
comprising: a first capacitor; a second capacitor coupled to the
first capacitor; and a circuit, coupled to the first and second
capacitor to detect a capacitance of the first and second
capacitors, the circuit providing a first output when the
capacitance of the first capacitor is equal to the capacitance of
the second capacitor, and a second output when the capacitance of
the first capacitor is not equal to the capacitance of the second
capacitor.
2. The proximity detector of claim 1, further comprising: an
electronic device; a power supply; a housing, the housing
containing the electronic device, the first capacitor, the second
capacitor, the circuit, and the power supply; wherein the circuit
is coupled between the power supply and the electronic device so
that power is supplied to the electronic device only when the
circuit provides the second output.
3. The proximity detector of claim 2, further comprising: an outer
wall, the outer wall providing one surface of the housing; and the
first capacitor is mounted proximate the second capacitor in the
outer wall.
4. The proximity detector of claim 3, further comprising: an
eyepiece, the eyepiece is coupled to the outer wall and the
electronic device; wherein the first capacitor and the second
capacitor are mounted within the outer wall so that when an
operator views through the eyepiece, either the first capacitor or
the second capacitor, but not both, is occluded by a portion of the
operator's face, causing an electric field surrounding the first
capacitor to be different than an electric field surrounding the
second capacitor.
5. The proximity detector of claim 4, wherein the electronic device
is a digital camera.
6. The proximity detector of claim 4, wherein the electronic device
is a video camera.
7. The proximity detector of claim 4, wherein the electronic device
is a monocular scope.
8. The proximity detector of claim 7, wherein the monocular scope
is a night vision device.
9. The proximity detector of claim 4, wherein the electronic device
is a binocular device.
10. The proximity detector of claim 4, wherein the electronic
device is a portable computer display.
11. The proximity detector of claim 2, wherein the power supply is
a battery.
12. The proximity detector of claim 11, wherein the battery is
rechargeable.
13. A proximity detector for an electronic device, comprising: a
housing, the housing containing the electronic device; a power
supply, the power supply providing power to the electronic device,
and mounted within the housing; a first electrode, a second
electrode and a third electrode mounted in an outer wall of the
housing; a first capacitor, the first capacitor including the first
electrode and the second electrode; a second capacitor, the second
capacitor including the second electrode and the third electrode; a
proximity detection circuit coupled to the electronic device and to
the power supply, the proximity detection circuit including: a
logic gate driven by a clock, the logic gate coupled to the first
capacitor and the second capacitor, and receiving power from the
power supply, the logic gate and clock providing an input signal
into the first capacitor and the second capacitor; a first
amplifier and filter coupled to the first capacitor for receiving a
first signal from the first capacitor, and providing a first
output; a second amplifier and filter coupled to the second
capacitor for receiving a second signal from the second capacitor,
and providing a second output; an inverter coupled to the second
amplifier and filter, for inverting the second output; and a
summing circuit, the summing circuit coupled to the inverter and
the first amplifier and filter, wherein the summing circuit
produces a first control signal when the first output is equal to
the second output, and produces a second control signal when the
first output is not equal to the second output; wherein, the
electronic device only receives full power from the power supply
when the summing circuit generates the second output.
14. The proximity detector of claim 13, further comprising an
eyepiece, the eyepiece coupled to the housing, wherein the first,
second, and third electrodes are mounted in the housing in a
configuration relative to the eyepiece, so that when an operator
views through the eyepiece, two, but only two, of the electrodes
are occluded by a portion of the operator's face.
15. The proximity detector of claim 13, wherein the electronic
device is changed from a no-power status to a full power status by
the summing circuit.
16. The proximity detector of claim 13, wherein the electronic
device is changed from a low power status to a full power status by
the summing circuit.
17. The proximity detector of claim 13, wherein the power supply
includes a battery.
18. The proximity detector of claim 17, wherein the battery is
rechargeable.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] Many modern electronic devices use batteries to provide
power. The use of batteries is advantageous because it allows the
device to be used virtually anywhere. People have become accustomed
to using devices which use rechargeable or easily disposable
batteries. These devices include digital cameras, video recorders,
lap top computers and cellular phones. For many of these devices,
power consumption is generally not a problem. The device is simply
turned on when needed, used, and shut off when finished. Thus, the
battery is only drained when the device is actually being used.
[0003] For some devices, the operator may wish to use the device
for an extended period of time, but only on an intermittent basis.
For instance, when traveling in darkness in an outdoor environment,
a person might use a night vision monocular scope to clearly view
selected objects. During actual movement, however, the person may
find it awkward to constantly look through the device. To use the
device most efficiently, the person may cease movement, raise the
device to their eye, look through it, and subsequently return it to
a carrying position. Then the person would continue moving. While
this may be an efficient way of using the device, it is not an
efficient way of using the power supply because, the device is
constantly using power, even while in the carrying position.
[0004] One simple solution would be to simply turn the device on
and off. However, this can be clumsy and awkward, thus slowing the
person down and detracting them from other tasks. Furthermore, many
battery powered devices have relatively long power up and power
down periods. More sophisticated devices might even have software
applications which must be booted. All this renders it impractical
to consistently be turning such devices manually on and off.
[0005] To solve this problem, some devices have incorporated a
switch near the eye piece. When the operator looks through the
device, their head contacts the eye piece thus causing the switch
to turn the power on. In devices with long power-up times, the eye
piece does not turn the device entirely on and off, but rather
switches it from a low to high power state.
[0006] While providing a relatively simple and economical solution
to the problem, the use of such a switch has many drawbacks. In
order to be comfortably used, the switch must be relatively easy to
engage. As such, many types of unintended contact will turn the
device on and off. For instance, when carrying the monocular night
vision scope in their hand, a person may bump the eye piece against
their leg or other portion of their body thus inadvertently turning
the device on. If such inadvertent contacts are frequent, there
will not be any savings in power consumption from the incorporation
of such a switch. An additional problem exists for users of such
devices who wear eye glasses. The eye piece of the device must be
pressed firmly up against the glasses, thus causing the glasses to
press into the operator's head, which may cause pain or
discomfort.
[0007] Another power reduction device is the use of an infrared
sensor incorporated near the electronic device. The eye detector
may detect heat from a person in close proximity or actually emit
infrared beams and detect their reflection to determine when the
device should be powered up. Simply detecting heat from a person is
not always efficient because heat is generated by every portion of
the body. Once again, causing the device to be powered up when it
is not actually intended to be used, thus wasting power. Emitting
infrared beams to detect the reflection causes two separate
problems. First the emitter-detector uses a relatively high amount
of power itself, thus negating many of the benefits intended to be
derived. Second, such projected infrared beams can be detected by
many extraneous sources, which is of particular concern when these
devices are used in military operations.
[0008] With both the heat sensor and the emitter/detector
combination, a problem exists for people who wear eye glasses as
the lenses of the glasses may deflect infrared radiation thus
preventing the detector from noting their presence and turning the
device on.
[0009] Some electronic devices may use a complicated eye-imaging
detector. Such a detector also suffers in that it uses a relatively
large amount of power. In addition, the optics required to perform
such imaging often increase the size of the device beyond what is
commercially desired. Therefore, there exists a need to provide a
simple and efficient proximity detector which brings the device
from a low power usage state to a high power usage state.
SUMMARY OF THE INVENTION
[0010] The present device uses capacitive plates located near the
eyepiece of an electronic device. The capacitive plates are
connected to relatively simple circuitry which uses a minimal
amount of power. Three capacitive plates forming two capacitors are
placed near the eyepiece. The two capacitors share the middle
plate. The capacitive plates are aligned with respect to the
eyepiece in such a way that when the operator looks at the
eyepiece, their nose and cheek will cover one, but only one, of the
capacitors. When the electronic device is in a stand-by or powered
down mode, with no object in front of either capacitor, the output
of both capacitors will be identical. When raised to eye level and
one of the capacitors is covered by the operator's face, the
electric field surrounding the covered capacitor changes. Thus,
that capacitor will have a different output than the uncovered one.
This differential in capacitance is registered by the circuitry and
the device is powered up. When the device is in stand-by mode and
the operator inadvertently covers both capacitors, for example, by
resting the device against his leg, the device will not
unintentionally be powered up. This is because if both capacitors
are covered by the same object, the capacitance of both capacitors
will be identical and hence there will be no differential.
[0011] It is an object of the present invention to provide a
proximity detector for an electronic device which conserves
power.
[0012] It is another object of the present invention to provide a
proximity detector which, when activated brings an electronic
device from a low- or no-power status to a powered on status.
[0013] It is a further object of the present invention to provide a
proximity detector which reliably powers on the electronic device
only when the device is actually intended to be used.
[0014] It is yet a further object of the present invention to
provide a proximity detector which minimizes the occurrence of a
false detection.
[0015] It is still another object of the present invention to
provide a proximity detector that uses very little power.
[0016] It is still yet another object of the present invention to
provide a proximity detector which is not affected by the use of
eyeglasses.
[0017] It is a further object of the present invention to provide a
proximity detector which occupies a relatively small amount of
space within an electronic device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a front view of an electronic device using the
differential capacitors of the present invention which are shown in
sectional line.
[0019] FIG. 2 is a top view of the electrical device using the
differential capacitor of the present invention.
[0020] FIG. 3 is a block diagram of the circuitry of the
differential capacitive analyzer of the proximity detector.
[0021] FIG. 4 is a circuit diagram of a differential capacitive
analyzer of the proximity detector.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Turning now to FIG. 1, a first embodiment of the present
invention will be described in which like reference numerals will
be used to describe like elements. An electronic device 10 has a
housing 14 and an eyepiece 12 medially disposed thereon. Electronic
device 10 is meant to be representative of a wide variety of
commercially available electronic products. For example, the
monocular arrangement shown could be used with a night vision
scope, a video camera, a digital camera or any other type of
hand-held portable electronic display. Though not shown, housing 14
could be configured to be used with a binocular arrangement, or a
device which does not use an eyepiece at all, such as a cellular
phone. A first electrode 17, a second electrode 18 and a third
electrode 19 are spaced in parallel arrangement within housing 14.
The three electrodes 17, 18, 19 in turn form a first capacitor 20
and a second capacitor 22. These two separate capacitors have one
electrode 18 in common.
[0023] Within FIG. 2 is shown a proximity detection circuit 24 as
it is connected to a power supply or battery 15. Proximity
detection circuit 24 serves to detect a differential in capacitance
between capacitor 20 and capacitor 22. If such a differential is
detected, power is allowed to flow from battery or power source 15
to power up the electronic device 10.
[0024] The general operation of the proximity detection circuit 24
will be explained with reference to the block diagram of FIG. 3.
Clock circuit/logic gate 26 provides a logic signal to first
capacitor 20 and second capacitor 22. The capacitance of first
capacitor 20 and second capacitor 22 are converted into a current
and pass to their respective amplifier/filter circuits 28 and 30.
The signal from first capacitor 20 is then run through an inverter
circuit 22. This inverted signal and the signal from capacitor 22
are directed into a summing circuit 34. In a stand-by mode, the
output from capacitor 20 and capacitor 22 should be the same.
Therefore, when the signal for one is inverted and added to the
other, the net result is zero. When the net result is zero, summing
circuit 34 outputs a predetermined output 36. If the capacitance of
the first capacitor 20 and second capacitor 22 are not identical,
then when one signal is inverted and both are summed together, the
net result will be something other than zero and the output of the
summing circuit 34 will trigger the electronic device 10 to be
powered up.
[0025] The detailed operation of one embodiment of the proximity
detection circuit 24 will be explained with reference to FIG. 4.
With reference to capacitor 20, when the logic signal from clock 26
is high, the upper set of switches 38 are closed, and the lower set
of switches 40 are open. Alternatively, when low, the lower set of
switches 40 are closed and the upper set of switches 38 are open.
The left side of the switches 38, 40 therefore get connected to a
power supply V, while the right side of the switch is at virtual
ground. The current that flows in the course of charging the
capacitor 20, flows toward a first summing junction 42. When the
control signal from clock 26 goes low, the left side of the
capacitor 20 gets connected to ground while the right side remains
at the virtual ground. The current required to reverse the polarity
on capacitor 20 comes from a second summing junction 44. The
voltages at the outputs of the two amplifiers 46, 48 therefore go
in opposite directions in response to the charge that is
transferred from the capacitor 20.
[0026] Capacitor 20 and capacitor 22 share one electrode 18, that
electrode being located medially between the two capacitors. The
explanation as to capacitor 20 also applies to capacitor 22 except
that the polarity of the charge transfer is reversed. While the
first pair of electrodes (capacitor 20) is injecting current into
the upper summing junction, the second pair of electrodes
(capacitor 22) is extracting current from this same junction. This
differential arrangement thus rejects the capacitance that is
common to the capacitors 20 and 22 and shows only the differences.
Of course, the same arrangement could be made using two separate
and distinct capacitors wherein an electrode from each capacitor is
electrically connected, thus arriving at the same shared electrical
configuration.
[0027] To create a single output which represents the capacitance,
the signal from amplifier 46 is inverted (with respect to the
virtual ground) by inverter 32. Then it is added to the signal from
amplifier 48 by summing circuit 34. The clock feed-through and
charge injection errors that the switches introduce are common mode
signals insofar as amplifiers 46, 48 are concerned, so these errors
cancel out after one signal is inverted and added to the other.
[0028] Referring back to FIG. 1, the operation of the electronic
device 10 will be explained. To use the electronic device 10, a
master power switch is turned on, thereby providing power to the
proximity detector circuit 24. In devices which require a
relatively long power up period, this would occur now, then the
system would switch to a power conserving standby mode. When the
operator wishes to use the electronic device 10, it is simply
raised to eye level. As the operator looks through eyepiece 12, his
nose and cheek will occlude one of the capacitors 20,22. As a
result, the electric field surrounding the occluded capacitor will
change, thus generating a differential which is detected by the
circuit 24. This triggers the circuit 24 to allow the electronic
device to obtain full power and perform its predetermined function.
When the task is complete, the operator simply lowers the
electronic device 10. Since both capacitors 20,22 are once again
subject to the same electric field, there is no longer a
differential to be detected by the circuit 24. As such, the circuit
24 triggers the device 10 to return to a low or no-power
status.
[0029] Those skilled in the art will further appreciate that the
present invention may be embodied in other specific forms without
departing from the spirit or central attributes thereof. In that
the foregoing description of the present invention discloses only
exemplary embodiments thereof, it is to be understood that other
variations are contemplated as being within the scope of the
present invention. Accordingly, the present invention is not
limited in the particular embodiments which have been described in
detail therein. Rather, reference should be made to the appended
claims as indicative of the scope and content of the present
invention.
* * * * *