demonstration system for providing enlarged projected image of calculator
FIELD OF THE INVENTION
This invention relates in general to a display demonstration system for
providing an enlarged projected image of the display of an electronic data
processing apparatus, and more particularly to such a display
demonstration system for providing an enlarged projected image of a
calculator display for viewing in a classroom environment or the like.
BACKGROUND OF THE INVENTION
In many situations, it is desirable to project the display of a calculator
or computer onto a large screen for group viewing. In particular, it is
often desirable for a teacher to operate a computing device while the
display is projected onto a large screen for viewing by the entire class.
Present day solutions, however, have not been effective in providing a low
cost solution which is easily operated by the speaker/teacher.
One such solution is to use a calculator which has an opening in its case
such that light may be transmitted through the display itself. The
calculator is set upon the base of an overhead projector. Thus, the
display acts as a transparency and its image may be projected to a large
This approach has significant problems. First, due to the size of the
calculator display, the image projected is generally too small to be
comfortably viewed by the audience. Second, the base of the overhead is
capable of generating significant heat, which affects the LCD display,
eventually making the entire display opaque. Third, since the entire
calculator sits on the base of the overhead projector, the speaker must
stare into the light emitted by the base while operating the calculator.
Another approach is typically used with computers. This approach provides
a liquid crystal display (LCD) pallet of about the same size as a
typically transparency used on an overhead projector. The pallet is placed
on the overhead projector and is driven by the computer. Because of the
size of the LCD and because of the additional hardware necessary to cool
the display, this alternative results in a high system cost.
Therefore, a need has arisen for a display which may be used in
conjunction with an overhead projector which provides a large projected
image at low cost and which is less susceptible to heat related
performance degradation than prior art solutions.
SUMMARY OF THE INVENTION
In accordance with the present invention, a display demonstration system
is provided for projecting calculator and computer displays onto a large
screen for group viewing, which substantially eliminates or prevents the
disadvantages associated with prior display devices.
The present invention provides a display which may be coupled to the
computing device to receive display data from the computing device and
through which light may be transmitted. A platform is operable to elevate
the display to a predetermined distance from the base of the overhead
projector. A lens assembly is positioned between the display and the
overhead lens of the overhead projector such that an enlarged image of the
display may be projected.
The present invention provides significant advantages over the prior art.
First, the invention provides a low cost solution which is less
susceptible to heat related performance degradation than the prior art. A
larger projected image is provided by the additional lens coupled to the
platform. The display may be operated from a remote location, enhancing
its use in the classroom. Further, temperature compensation circuitry may
be provided in the display to minimize contrast changes in the projected
image. Also, a separate contrast control may be provided in the display to
optimize the projected image.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the
advantages thereof, reference is now made to the following descriptions
taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates a perspective view of a first embodiment of the present
FIG. 2 illustrates a block diagram of an embodiment of the present
invention using a calculating and a displaying device coupled with an
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the present invention is best understood by
referring to FIGS. 1-2 of the drawings, like numerals being used for like
and corresponding parts of the various drawings.
FIG. 1 illustrates a perspective view of the present invention. A overhead
projector 10 comprises a base unit 12 which projects light upwards through
a lens 14. The light is projected through the overhead lens assembly 16
which includes one or more lenses and a plurality of mirrors to project
the light to a screen (not shown). The lens assembly 16 is slideably
engaged on an arm 18. Overhead projectors of this type are manufactured
and sold by a number of companies.
A computing device 20, shown in FIG. 1 as a calculator having a local
display 21 (preferably a graphics display), is coupled to a remote display
22 by a cable 24. The remote display includes a contrast control knob 25
and is described in greater detail in connection with FIG. 2. The remote
display 22 is held above the base lens 14 on a platform 26 having legs 28.
A lens 30 is positioned between the remote display 22 and the overhead
lens assembly 16. A heat shield 31 is placed on top of the base lens 14.
The heat shield 31 is preferably a white, or light colored, foam board
having a window 32 formed therein such that the display device 22 is
shielded from excess heat from the base unit 12, except for the light
needed to project the display. A light colored heat shield will avoid heat
retention which could damage the base lens 14.
The platform 26, legs 28 and lens 30 may be provided in a single unit. A
suitable unit is commercially available from the Polaroid Corporation;
this unit is intended for projecting Polaroid color-graph type 691
In operation, the remote display 22 generates the same image as is present
on the computing device 20. Because the remote display 22 is elevated from
the base unit 12, it is subjected to much less heat than would a display
which is lying on the base lens 14. The heat shield 31 further reduces the
amount of heat received by the remote display 22. The lens 30 magnifies
the image of the remote display 22.
FIG. 2 illustrates a block diagram of an embodiment of the calculator 20
and display unit 22 coupled by a cable 24. The calculator 20 comprises a
microprocessor 34 coupled to a keyboard 36 and to ROM and RAM memories 38
and 40, respectively. The microprocessor 34 is further coupled to a row
display driver 42, a column display driver 44 and a line driver/buffer 46.
The row and column display drivers 42 and 44 are connected to the LCD (or
other suitable display) 47.
The line driver/buffer drives the cable 24. The cable 24 is also connected
to row and column display drivers 48 and 50 of the remote display 22. The
row and column display drivers 48 and 50 are coupled to a temperature and
contrast control circuit 52. An LCD (or other suitable display) 54 is
connected to the row and column display drivers 48 and to the temperature
and contrast control circuit 52.
In the preferred embodiment, the LCDs 47 and 54 each comprise a LCD
matrix, for example, a 64 row .times. 96 column display. The LCDs are
driven by row display drivers 42 and 48 which may comprises, for example,
Toshiba T7900 LCD drivers. Similarly, the display columns are driven by
column display drivers 44 and 50 which may comprise Toshiba T7778A
integrated circuits. Depending upon the size of the display, more than one
of the LCD driver integrated circuits may be necessary.
The microprocessor circuit 34 is programmed by ROM 38 and performs the
desired features of the calculator 20. The microprocessor may include a
gate array to drive the display drivers.
The line driver/buffer 46 drives the signals from the microprocessor 34
over the cable 24 to the row and column display drivers 48 and 50. A cable
length of ten feet has been found to be adequate for remote use of the
calculator without degradation of the signals, although a longer cable
could be used.
The temperature and contrast control circuitry performs two functions.
First, the voltages to the LCD 54 may be adjusted by the user using a
potentiometer on the remote display 22, thereby allowing the user to
manually adjust the contrast of the LCD 54. The potentiometer affects the
voltages generated by a resistive ladder driving the LCD 54. Further, the
temperature and contrast control circuitry 52 adjusts the voltages to the
LCD 54 automatically as the temperature of the remote display 22 changes.
As the temperature of the display changes, the resistance provided by a
thermistor located proximate the LCD 54 changes accordingly. The
thermistor affects the voltages generated by the resistive ladder driving
the LCD 54, and thus, controls the contrast of the LCD.
In operation, the circuit of FIG. 2 produces the same signals to both sets
of display drivers. Thus, the image displayed by the LCDs 47 and 54 is
always identical. The calculator 20 can be operated normally by the
teacher, who views the LCD 47 on the calculator. The remote display 22
replicates the image on its LCD 54, which may be displayed to the
audience. Therefore, the speaker/teacher need not face the viewgraph or
the enlarged image. Accordingly, the speaker/teacher may address the
audience directly while performing calculations on the calculator 20.
The present invention also solves the problems of heat degradation of the
display through use of the elevated platform, the temperature
compensation, and the heat shield. Thus, the present invention can be used
for extended periods of time without noticeable deterioration to the
enlarged image of the display.
While the present invention has been described in conjunction with a
relatively low resolution calculator display, a high resolution display
could be provided for use with a computer. The smaller screen size as
compared to present day pallets would reduce the cost and enhance its
portability. The aforementioned advantages regarding heat degradation
would further reduce the cost of the display by eliminating the need for
costly cooling devices.
Although the present invention has been described in detail, it should be
understood that various changes, substitutions and alterations can be made
herein without departing from the spirit and scope of the invention as
defined by the appended claims.