U.S. patent number 3,772,685 [Application Number 05/239,117] was granted by the patent office on 1973-11-13 for touch responsive electric switch and device for the use thereof.
This patent grant is currently assigned to Bunker Ramo Corporation. Invention is credited to James Vincent Masi.
United States Patent |
3,772,685 |
Masi |
November 13, 1973 |
TOUCH RESPONSIVE ELECTRIC SWITCH AND DEVICE FOR THE USE THEREOF
Abstract
A high impedance, low voltage, electro-optic light valve, such
as, for example, a liquid crystal cell, has one terminal connected
to a source of varying potential and the other terminal connected
to an element adapted to be touched by a person or otherwise
contacted by an impedance path to a potential which is highe or
lower than the varying potential by an amount at least equal to the
excitation potential of the valve. When the element is contacted, a
circuit is completed through the valve, causing its optical
characteristics to change. A touch (contact) responsive switch is
provided by detecting the change in the optical characteristics of
the valve and by generating some sort of output in response
thereto. The switch may be utilized in devices such as a keyboard,
a cable conductor identifier, or a touch response matrix board
where an indication is required as to which of a plurality of
elements has been touched or otherwise contacted. For such
applications, the elements to be touched are connected through a
suitable coding means to a bank of valves. The outputs from the
valve detectors indicate, in a suitable code, the element touched.
This invention relates to a low current electric switch which may
be actuated in response to a person touching an element and to
various devices, including an electronic keyboard, a cable
conductor identifier, and a touch responsive matrix board,
utilizing the switch. BACKGROUND It has been known for many years
that when a person touches a wire or similar electrically
conductive element, the person may serve as a high impedance path
to ground. However, the high impedance of the person results in
extremely small currents flowing through circuits of which he is a
part. Since suitable switching devices for detecting and utilizing
such small currents are not readily available, there has heretofore
been little exploitation of the human conduction phenomenon. In
recent years, however, high impedance, low voltage, electro-optic
light valves, such as nematic liquid crystal cells, have become
available. While these cells have heretofore been utilized
primarily for display purposes, it will be apparent in the
discussion to follow that valves or cells of this type may also be
utilized in high impedance switches, permitting more extensive use
of the human conductivity phenomenon. Switches of this type, being
high impedance devices, require a minimum of power to operate and
have inherently high noise resistance. Further, they may be
fabricated completely from solid state devices, without moving
parts to wear out, and are thus easy to package, of small size with
a thin profile, adaptable for a wide variety of configurations,
rugged, relatively maintenance free, and of extremely long life.
They are thus inexpensive both to manufacture and maintain. For the
reasons indicated above, the switch of this invention may be
advantageously utilized for applications in which a mechanical
switch is now employed. In applications such as, for example, an
elevator switch, the switch of this invention would have a
potentially longer life but would not have the disadvantage of
being spuriously excited by dust or other particles as is the case
with existing electronic photo-detector switches. In the discussion
to follow, an electronic keyboard utilizing the switches of this
invention will also be presented. In addition, the switch of this
invention may be utilized as part of devices for performing
functions not heretofore available. With large cables, some of
which may have several thousand conductors, a problem exists when
connecting the cable in identifying the conductor at one end which
corresponds to a conductor at the other end. Heretofore, a tedious,
time consuming, and extremely expensive ringing operation, normally
requiring two men, has been required to match the conductors. Color
coding of the wire reduces the problem, but by no means eliminates
it. Recently, a device has come on the market which permits one end
of the cable to be attached to terminals and a numeric indication
to be generated of the terminal to which the one end of the
conductor is connected when the other end of the conductor is
touched with a suitable tool. This device, while a vast improvement
over the prior art, still requires that the operator use two hands
in the operation, and is relatively complicated and expensive. The
switch of this invention permits the function to be performed with
only one hand, the finger of the hand touching the conductor
directly, and by use of relatively simple and inexpensive hardware.
A problem also exists in providing a user with the capability of
marking on a cathode ray tube (CRT) or similar display a point
which is to be identified, or at which a function is to be
performed. Heretofore, light pens have been utilized to perform
this function. However, to use a light pen, a special, relatively
expensive CRT is required in addition to the requirement for the
light pen itself. Further, the light pen usually covers a
relatively large area and is thus not adapted for providing
extremely high resolution. Finally, this form of input is sometimes
utilized by children in teaching machine applications. The
relatively hard surface of the light pen could scratch or crack the
face of the CRT if it is improperly operated by a young person. It
would therefore be preferable if the operator could merely touch
the desired spot on the screen with a soft finger or, in
applications where high resolution is required, with the sharp tip
of a conducting stylus. In the discussion to follow, a device will
be described which can either be fitted to the face of a standard
CRT to permit the above functions to be performed or can be used
like a keyboard in conjunction with a cursor on the face of the
screen to indicate a desired point. In the latter mode of
operation, the device functions in place of a pressure responsive
tactile board and may be employed in most applications where such
boards are presently utilized. It should, however, be smaller,
lighter, less subject to noise, longer lasting, require less
maintenance, and require less power than a tactile board. Further,
it can provide direct X-Y output readings without requiring the
scanning of output lines. SUMMARY OF THE INVENTION Briefly, this
invention provides an electronic switch consisting of a high
impedance, low voltage, electro-optic light valve having terminals
on opposite sides. A means is provided for applying a potential to
one terminal of the valve, preferably an AC potential, while the
other terminal is physically and electrically connected by a
suitable means to an element adapted to be touched either directly
or indirectly by a person. The switch could also be operated if the
element is contacted by some other member which is connected
through a high impedance to a potential higher or lower than that
of the AC supply by an amount at least equal to the excitation
potential of the valve. When the element is touched or contacted, a
circuit is completed through the valve, causing the optical
characteristics of the valve to be changed. The final element of
the switch is a means for detecting the change in the optical
characteristics of the valve and of generating some sort of an
output in response thereto. For preferred embodiments of the
invention, the light valve is a liquid crystal cell. A number of
these cells may be utilized as part of a device for detecting the
touching of one of a plurality of elements and for indicating the
element touched. For these devices, a means is provided for
selectively connecting each of the elements to one side of at least
one of the light valves with the AC potential being applied to the
other side of each of the valves. A detecting means is provided for
each of the valves and a means is provided which is responsive to
the detecting means for generating an indication of the element
touched. The element touched may be the key of a keyboard, the end
of a cable conductor where the other end of the conductor is
connected through suitable means to the device, a conductor in a
matrix of conductors attached to the face of a CRT, a touch
responsive matrix board, or the like. The foregoing and other
objects, features and advantages of the invention will be apparent
from the following more particular description of preferred
embodiments of the invention as illustrated in the accompanying
drawings.
Inventors: |
Masi; James Vincent (Monroe,
CT) |
Assignee: |
Bunker Ramo Corporation (Oak
Brook, IL)
|
Family
ID: |
22900686 |
Appl.
No.: |
05/239,117 |
Filed: |
March 29, 1972 |
Current U.S.
Class: |
341/31;
250/214LS; 324/66; 349/12 |
Current CPC
Class: |
H03K
17/962 (20130101); B66B 1/463 (20130101); G06F
3/042 (20130101); G02F 1/13338 (20130101); H01R
43/28 (20130101); G06F 3/0202 (20130101) |
Current International
Class: |
B66B
1/46 (20060101); G06F 3/02 (20060101); G02F
1/13 (20060101); H03K 17/94 (20060101); G02F
1/133 (20060101); H01R 43/28 (20060101); H03K
17/96 (20060101); G06F 3/033 (20060101); G06f
003/02 () |
Field of
Search: |
;350/16R,16P,267
;340/324R,365 ;250/213A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Curtis; Marshall M.
Claims
What is claimed is:
1. An electric switch comprising:
a high impedance, low voltage electro-optic light valve having
terminals on opposite sides thereof, said valve being adapted to
have its optical characteristics changed when a potential exceeding
a predetermined threshold potential is applied across the
valve;
means for applying a potential to one terminal of said valve;
an electrically conductive member which is normally open
circuited;
means for electrically connecting the other terminal of said valve
to said member;
said member being adapted to be touched in a manner to provide a
high impedance path to a potential source which is higher or lower
than the potential applied to said one terminal by an amount at
least equal to the excitation potential of said valve, a circuit
being completed through said valve when said member is touched
causing the optical characteristics of said valve to change;
and
means for detecting the change in the optical charcteristics of
said valve, and for generating an electrical output in response
thereto.
2. A switch of the type described in claim 1 wherein said light
valve is a liquid crystal cell.
3. A switch of the type described in claim 2 wherein said cell
includes a layer of liquid crystal material sandwiched between
layers of conductive material; and
wherein said member is electrically connected to one of said layers
of conductive material.
4. A switch of described type dexcribed in claim 1 wherein
potential applied to said one terminal is varied in accordance with
some pattern.
5. A switch of the type described in claim 4 wherein the potential
applied to said one terminal is an AC potential.
6. A switch of the type described in claim 1 wherein said member is
adapted to be touched by a person, said person serving as a high
impedance path to ground.
7. A switch of the type described in claim 6 wherein said member is
a metal cap connected through suitable means to said one terminal
of the valve.
8. A switch of the type described in claim 7 wherein there are more
than one of said valves; and
wherein said suitable means includes coding means selectively
connecting said first element to one or more of said valves.
9. A switch of the type described in claim 1 wherein said detecting
means includes a light source and a photo-detector device, said
light source and photo-detector device being positioned relative to
each other so that said photo-detector device is energized by said
light source when the optical characteristics of said valve are in
one but not the other of the conditions they may be in.
10. A switch of the type described in claim 9 wherein said light
source is a light emitting diode.
11. A device for detecting a person touching an element and for
generating an electrical output in response thereto comprising:
a high impedance, low voltage, electro-optic light valve having
terminals on opposite sides thereof, said valve being adapted to
have its optical characteristics changed when a potential exceeding
a predetermined threshold potential is applied across the
valve;
means for applying a varying potential to one terminal of said
valve;
means for physically and electrically connecting the other terminal
of the valve to said element, a circuit being completed through
said valve when said element is touched, causing the optical
characteristics of said valve to change; and
means for detecting the change in the optical characteristics of
said valve and for generating said electrical output in response
thereto.
12. A device for detecting the touching of one of a plurality of
elements and for indicating the element touched comprising;
a plurality of high impedance, low voltage, electro-optic light
valves, each of said valves being adapted to have its optical
characteristics changed when a potential exceeding a predetermined
threshold potential is applied across the valve;
means for selectively connecting each of said elements to one side
of at least one of said light valves, a varying potential being
applied to the other side of each of said valves, and a circuit
being completed through each valve to which a touched element is
connected causing a change to occur in the optical characteristics
of each such valve;
means for detecting the change in the optical characteristics of
the valves; and
means responsive to said detecting means for generating an
indication of the element touched.
13. A device of the type described in claim 12 wherein the means
for selectively connecting includes coding means for converting a
single input from the element touched into a plurality of outputs
to said valves.
14. A device of the type described in claim 13 wherein said device
is an electronic keyboard;
wherein said elements are the keys of said keyboard, said keys
being caps of conductive material embedded in an insulating
plate;
and wherein said coding means includes means for connecting each of
said caps to a plurality of outputs to said valves, said outputs
representing, in a selected code, the character designated by the
key touched.
15. A device of the type described in claim 13 wherein said element
is a conductor of a cable, the end of the conductor opposite the
end being touched being connected to a terminal which may be
characterized by certain identifying characters;
and wherein the outputs from said coding means represent in a
selected code the identifying characters of said terminal.
16. A device of the type described in claim 15 wherein said
identifying characters are numbers and said selected code is a
binary code.
17. A device of the type described in claim 15 wherein said
indication generating means includes means for converting the
response to said detecting means into a display code of said
terminal identifying characters, and means responsive to said
converting means for displaying said identifying characters.
18. A device of the type described in claim 13 wherein said element
is the tip of a conductor which is either flush with or projecting
slightly from the face of a plate of insulating material.
19. A device of the type described in claim 18 wherein there are a
plurality of said conductor tips positioned in a predetermined
pattern on the face of said plate;
and wherein said coding means includes means for generating an
indication of the coordinates of each of said conductors.
20. A device of the type described in claim 19 wherein said plate
is of a transparent material and is adapted to be positioned in
front of the face of a cathode ray tube.
21. A device of the type described in claim 12 wherein said light
valves are liquid crystal cells.
22. A device of the type described in claim 12 wherein said
detecting means includes a light source and a photo-detector
device, said light source and photo-detector device being
positioned relative to each other so that said photo-detector
device is energized by said light source when the optical
characteristics of said valve are in one but not the other of the
conditions they may be in.
23. A device of the type described in claim 22 wherein there is a
light source and a photo-detector device for each of said
valves.
24. An electronic keyboard comprising:
a plurality of character designating keys, each formed of a
conductive material;
a plurality of high impedance, low voltage, electro-optic light
valves, each of said valves being adapted to have its optical
characteristics changed when a potential exceeding a predetermined
threshold potential is applied across the valve;
means for connecting each of said keys to one side of a selected
one or more of said light valves, the light valves to which each of
said keys is connected representing, in a selected code, the
character designated by the key;
means for applying a varying potential to the other side of each of
said light valves;
whereby when a key is touched, a high impedance path to ground is
provided, completing a circuit through each valve to which the
touched key is connected, causing the optical characteristics of
each said valve to change;
means for detecting the change in optical characteristics of each
of said valves; and
means responsive to said detecting means for generating coded
outputs representing the designated character for each touched
key.
25. A device operative when a conductor of a cable is contacted at
one end, for indicating which one of a plurality of terminals the
other end of the cable conductor is connected to comprising:
a plurality of high impedance, low voltage, electro-optic light
valves, each of said valves being adapted to have its optical
characteristics changed when a potential exceeding a predetermined
threshold potential is applied across the valve;
means for electrically connecting each of said terminals to one
side of at least one of said light valves, an AC potential being
applied to the other side of each said valves, and a circuit being
completed through each valve to which a terminal is connected when
the conductor connected to the terminal is contacted at said one
end, causing the optical characteristics of each such valve to
change;
means for detecting the change in optical characteristics of the
valves; and
means responsive to said detecting means for indicating the
terminal connected to the conductor which is contacted at said one
end.
26. A device for generating an indication of the coordinates of a
point which is contacted in a selected manner comprising:
a plate of insulating material having a plurality of conductors
positioned therein with their tips either flush with or projecting
slightly from the upper surface of said plate, said conductor tips
being arranged in a predetermined pattern;
a plurality of high impedance, low voltage, electro-optic light
valves, each of said valves being adapted to have its optical
characteristics changed when a potential exceeding a predetermined
threshold potential is applied across the valve;
means for connecting each of said conductors to one side of
selected ones of at least one group of said light valves, the light
valves to which each of said conductors is connected representing
in a selected code the coordinates of the position of said
conductor in the plate;
means for applying a varying potential to the other side of each of
said light valves;
whereby when a conductor is contacted, a circuit is completed
through each valve to which the contacted conductor is connected,
causing the optical characters of each said valve to change;
means for detecting the change in optical characters of each of
said valves; and
means responsive to said detecting means for generating outputs in
a selected code representing the coordinates of the contacted
conductor.
27. A device of the type described in claim 26 wherein said point
is contacted by being touched by a person.
28. A device of the type described in claim 26 wherein said
predetermined pattern is a matrix grid.
29. A device of the type described in claim 27 wherein said
insulating plate is of a transparent material and is adapted to be
positioned in front of a cathode ray tube (CRT) to permit points on
the CRT screen to be identified and an indication of the
coordinates of the identified points to be generated.
30. An electric switch comprising:
A high impedance, low voltage, electro-optic light valve having
terminals on opposite sides thereof, said valve being adapted to
have its optical characteristics changed when a potential exceeding
a predetermined threshold potential is applied across the
valve;
an electrically conductive member adapted to be touched in a
predetermined manner;
means for series connecting said member and valve;
means, including said series connecting means, normally operative
for open circuiting said valve, said means being operative when
said member is touched for completing a circuit through said valve
with the potential thereacross exceeding said excitation potential,
whereby the optical characteristics of said valve are changed;
and
means for detecting the change in the optical characteristics of
said valve, and for generating an electrical output in response
thereto.
Description
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a partially cut away perspective view of a switch
incorporating the teachings of this invention.
FIG. 2 is a semi-schematic diagram of a keyboard utilizing switches
of this invention.
FIG. 3 is a semi-schematic diagram of a cable conductor identifying
device utilizing switches of this invention.
FIG. 4 is a semi-schematic diagram of a matrix plate or board
utilizing the teachings of this invention shown for use in
identifying points on a cathode ray tube.
DETAILED DESCRIPTION OF SWITCH
From FIG. 1, it is seen that the switch for the preferred
embodiment of the invention includes a nematic liquid crystal cell
10. Cells of this type are well known in the art and are normally
employed for display purposes. Cell 10 consists of a pair of plates
12 and 14 which are of glass or some other transparent insulating
material. Plates 12 and 14 each has a layer of transparent
conductive material, 16 and 18 respectively, deposited thereon. A
layer of nematic liquid crystal material 20 is sandwiched between
the plates and the entire unit is sealed by an epoxy or glass
fillet 22. The plates may either be spaced by the fillet or by
means of a polymeric or glass spacer from 6-25 microns thick.
Transparent conductor 18 is electrically connected through a line
23 to a source of AC potential 24. Conductor layer 16 is
electrically connected to a wire 26. Depending on the application,
wire 26 may be connected to additional electrical elements or may
be terminated in a metal cap 28.
In operation, when a person's finger 30 touches cap 28, the cap is
capacitively coupled through the person to ground. The potential of
conductive layer 16 is thus reduced to ground. Assuming that the
potential of AC source 24 is greater than the excitation potential
of cell 10, the liquid crystal material becomes turbulent with its
molecules having dipole moments at various angles. This results in
a dynamic scattering of light applied to the crystal giving the
normally transparent material an opaque appearance. The change in
the optical characteristics of the liquid crystal cell is detected
by use of light source 32 and photo detector 34. As illustrated,
photo cell 34 normally generates an output and has the output
interrupted when the switch is operated. If an output is desired
when the switch is operated, light source 32A (shown dotted) may be
substituted for light source 32. The light from source 32A would
normally pass through cell 10. However, when the cell is excited,
the light is reflected by the opaque liquid crystal layer and is
picked up by photo detector 34 generating the desired output. Light
source 32 may be a light emitting diode to provide an all solid
state switch unit.
A simple and inexpensive switch has thus been provided which may be
operated in a response to human touch. The liquid crystal cell is
itself such a high impedance element (in order of 10 meg ohms) that
the impedance of the person, and any variations or changes therein,
do not affect the operation of the switch. Experiments have
indicated that the switch still functions satisfactorily even when
the person is separated from the floor by a chair and several
layers of rubber mats. However, in spite of its sensitivity, the
switch cannot be spuriously excited by dust, dirt or any other
particle passing in front of it or by contact with any ungrounded
object. Further, the device, utilizing only small solid state
components, may be constructed in a small rugged package and may be
operated maintenance free for extremely long periods of time.
DESCRIPTION OF APPLICATIONS
As indicated previously, the small size, low cost, high
reliability, long life and lack of required maintenance for the
switch of this invention would make it useful in many applications,
such as elevator switches, where mechanical switches are now
employed. Another advantage of these switches is that, because of
the previously indicated high impedance of cell 10, additional
elements may be inserted between the contact point (for example cap
28) and a cell 10 without adversely affecting the performance of
the device. Thus, referring to FIG. 2 in which an electronic
keyboard utilizing the switches of this invention is shown, it is
seen that the keys 28 are metal caps or metal clad caps secured in
a suitable plate 38 of insulating material. Each cap 28 is
connected through a wire 40 to a diode or other equivalent encoding
matrix 42. The number of output lines 26 from matrix 42 would
depend on the output code being utilized. For example, if the
American Standard Code for Information Interchange (ASCII) code is
being utilized, seven output lines 26 would be utilized. Each line
26 is connected to one side of a liquid crystal cell 10 with the
other side of the cell being connected through a common line 23 to
AC source 24. A light emitting diode 32 and photo cell 34 are
provided for each cell 10. Output lines 44 from photo cells 34 are
connected through a suitable logic and control circuit 46 to an
output device.
In operation, each time a key 28 is touched, a circuit is completed
through the appropriate line 40 and the diode matrix to a selected
combination of the lines 26. This causes corresponding ones of the
cells 10 to be operated resulting in outputs on the corresponding
lines 44.
While the lack of "feel" with the keyboard of FIG. 2 and a possible
speed problem resulting from the recovery time of the cells 10 may
limit the usefullness of this device in applications such as
typewriters, the small size and lack of maintenance of the switches
might make them ideal for applications such as in small calculating
machines.
FIG. 3 illustrates another novel application for the switch of this
invention. In this FIG. a cable 50 which may for example have over
5,000 wires in it, and may be of any desired length, has each of
its conductors connected at one end to the terminals of one or more
connector elements 52. Connector elements 52 are mated to
corresponding connector elements 54, the terminals of which are
connected through wires 56 to the inputs of an encoding matrix
circuit 58. Circuit 58 converts the terminal number for each
terminal of elements 52 and 54 into a coded representation (for
example a binary code) of the terminal on encoder circuit output
lines 26. Thus, a cable having 1,000 conductors would require 10
output lines 26 (assuming the use of binary code), while for a
cable having 4,000 conductors, 12 lines 26 would be required. As
with other applications, each line 26 is connected to one side of a
liquid crystal cell 10 with the other side of the cells being
connected through common line 23 to a source of AC potential 24.
Any change in the optical characteristics of the cells 10 is
detected by photo detector circuits 34 and transmitted through
lines 44 to a display encoding circuit 60. Encoder 60 converts the
binary code for the indicated terminal number of other terminal
identifying characters into the code required to operate display
device 62. Display device 62 may, for example, utilize Nixie tubes,
light emitting diodes arrange in suitable matrices, or liquid
crystal cells.
In operation, each conductor of cable 50 would initially be
connected at one end to a terminal of connector element 52. The
elements 52 and 54 would then be mated. The operator then touches
any conductor of the cable 50 at the free end. The touching of this
conductor causes a circuit to be completed through encoder 58 and
the cells 10 corresponding to the binary code for the terminal
number of element 52 connected to the other end of the touched
conductor. The optical state of cells 10 is picked up by detectors
34 and the resulting binary coded number is converted to, for
example, a decimal display code in circuit 60. Display 62 then
generates a decimal indication of the terminal number. The operator
then tags the touched conductor with the determined terminal number
in any one of a variety of known ways. It is apparent that,
utilizing the device of FIG. 3, the identifying of cable conductors
can be easily and quickly accomplished by one relatively unskilled
operator.
FIG. 4 illustrates still another possible application for the
switches of this invention. In this FIG. a plate 66 of a
transparent insulating material is shown mounted to the face of a
standard cathode ray tube (CRT) 68. Embedded in plate 66 and either
flush with the surface thereof or projecting slightly therefrom is
a matrix of wires 70. The wires 70 would each be relatively thin so
as not to interfere with the visability of the display on the CRT.
The density of wires 70 would depend on the resolution required
from the device. Wires 70 are bundled into a cable leading from
plate 66 into an X-Y encoder circuit 72. Encoder 72 generates an
output on lines 74 representing, in a suitable code, the X
coordinate of a wire 70 which is touched and an output on lines 76
representing, in encoded form, the Y coordinate of the touched
wire. Lines 74 and 76 are connected to a bank of X liquid crystal
switches 78 and a bank of Y liquid crystal switches 80
respectively. Each bank of liquid crystal switches generates
outputs on lines 44 which may be utilized for any desired purpose.
For example, in a teaching machine application, the lines 44 could
indicate the coordinates of a multiple choice answer selected by
the student, causing this answer to be recorded in the system and
possibly causing a mark to appear on CRT 68 at the indicated spot
to provide the student with feedback as to the answer he selected.
In applications where resolution finer than that obtainable with a
finger is required, the operator may touch the desired point on
plate 66 with the tip of a sharply pointed conducting stylus.
A potential problem with the device shown in FIG. 4 is that more
than one of the wires 70 may be touched. If the resolution of the
wires 70 is fine enough that this appears to be a potential
problem, additional circuitry may be included in encoder 72 to
average the inputs when two or more simultaneous inputs are
received.
While in FIG. 4 plate 66 is shown mounted directly on CRT 68, plate
66 and its associated circuitry may be housed as a stand-alone
unit. With this arrangement, a visual indication would be provided
on the CRT screen of the position of the finger or stylus on the
plate 66. When the indicator shows that the finger or stylus was
positioned at the desired point, a key (for example of the type
shown in FIG. 2) is operated to cause the coordinates of the point
to be stored in a suitable memory. The stand-alone unit of the type
just described could also be used in numerous other applications
where pressure sensitive boards are presently employed. In such
applications, the device described herein would be potentially less
expensive, smaller in size, less subject to spurious excitation,
and have a potentially longer life. It is apparent that, while in
FIG. 4 wires 70 have been arranged in plate 66 in a matrix grid,
the wires could be arranged in other patterns if desired.
A touch response switch and numerous applications thereof have thus
been provided. While in the discussion so far, a wire 26 is either
directly or indirectly touched by a person in order to operate the
switch, it is apparent that the switch may be operated in response
to the wires 26 being directly or indirectly contacted by an
element providing a conductive path to ground or to a potential
higher or lower than that of AC source 24 by an amount at least
equal to the excitation potential of a liquid crystal cell 10. The
switch might thus, for example, find application as part of a
brushless commutator or in similar applications where detection of
a high impedance connection between two conducting elements is
required. Further, while an AC source 24 has been indicated above
for the preferred embodiments of the invention, a varying DC
potential might also be utilized in some applications. A fixed DC
potential may be used where the switch is not applied as a touch
responsive element and there is pure resistive coupling between the
contacted element and ground. Thus, while the invention has been
particularly shown and described above with reference to preferred
embodiments thereof, it will be apparent to those skilled in the
art that the foregoing and other changes in form and detail may be
made therein without departing from the spirit and scope of the
invention.
* * * * *