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Touch Panels
A touch panel or touchscreen is a touch-sensitive transparent screen mounted in front
of an LCD. It provides a way for a person to interact with an
computer system.
Typically the system will display buttons on the LCD and expect the user to
select one by touching it. The touch causes some measurable phenomena which is
converted by a controller IC into screen coordinates which are sent into the system.
The system then determines which button was pressed and takes appropriate action. The
phrases Touchscreen, Touch Panel and Touch
Screen mean the same thing and are
interchangeable.
Kyocera Touch Panels
To give customers the confidence and convenience of a
single-vendor solution, Kyocera has long offered most LCD models with
optional 4-wire analog resistive touch screens already
mounted by Kyocera. Starting in 2008, Kyocera began
manufacturing Glass on Glass (G/G) touch panels.
Kyocera now produces LCD modules with the original Film on Glass
(F/G) touch panels, with the new G/G touchscreens or with none.
The thin flexible glass, labeled "upper substrate", is more transparent
than the traditional PET film. When examined side-by-side, the difference
is stunning. G/G touchscreens are as clear as window glass while
F/G panels are hazy.
Advantages of Kyocera Glass on Glass Touch Panels
More transparent because very little haze is applied to the top layer. In F/G touch
screens the upper substrate is wavy, producing Newton rings.
Therefore the top layer must be made hazy so the Newton rings
don't show. On Kyocera's G/G touch panel the upper glass
substrate is straight; almost no Newton rings are produced,
so the haze can be greatly reduced.
Reduced Dead Space because Kyocera's thin film metal conductor patterns strongly
adhere to their substrates, allowing the sealant to be placed over the conductors.
On conventional touchscreens, the thick film silver-paste conductors cannot share space with
the sealant.
More durable because the upper substrate is hard glass rather that soft PET film.
Also the glass flexes with less lateral deformation and greater radius of curvature,
meaning less flexing of the ITO layer on the underside of the glass.
Invisible spacer dots because they are invisibly bonded to the glass top layer.
On conventional touch panels they must be bonded to the bottom glass layer, making their
tops visible under ambient sidelight.
Hermetically sealed on all four sides. Conventional F/G touch screens require
an air gap to equalize the air pressure. This gap can allow moisture to enter the
interior. Kyocera's G/G touch screens do not require pressure equalization because of
the strength of the top glass. So no air gap is required
and unsightly condensate cannot enter.
Better temperature stability because glass is more stable than PET film and
because both layers have the same coefficient of expansion. Actually the LCD limits
the temperature ranges more than the glass-on-glass touch panel.
| Structure (Top/Bottom) |
Film/Glass |
Glass/Glass |
Operating
temperature |
Touch panel only |
-20°C to +70°C |
-30°C to +85°C |
LCD
assembly |
TFT & LED BL |
--- |
-20°C to +70°C |
| STN & LED BL |
0°C to +60°C |
Storage
temperature |
Touch panel only |
-40°C to +80°C |
-40°C to +95°C |
LCD
assembly |
TFT & LED BL |
--- |
-30°C to +80°C |
| STN & LED BL |
-20°C to +60°C |
| Touch actuation force |
0.05 to 0.8N |
0.5 to 2.0N |
Number of actuations, single point,
0.8 mm polyacetal stylus |
1 million |
1 million |
Transmittance |
≥80% |
≥85% |
Hardness |
≥2H |
≥2H |
Linearity |
≤±1.5% |
≤±2.5% |
Chattering |
≤10 msec |
≤10 msec |
Both kinds are also rated for writing 100,00 characters in a 20 x 20mm
area, for handwriting applications. They are stain resistant to Toluene,
Trichloroethylene, Acetone, Alcohol, Gasoline, Machine oil, Ammonia water, Glass
cleaner, Mayonnaise, Catsup, Wine, Salad oil, Vinegar, Lipstick, etc. When
cleaning the touch panel surface, we highly recommend using a soft lint free cloth
with isopropyl alcohol and wiping slowly without excessive pressure.
Kyocera is also offering G/G touch panels for sale as component products. Standard G/G
models are listed near the bottom of the Full Specifications page.
Queries for other sizes and custom pinouts are welcome.
Contact a
KYOCERA Industrial Ceramics Corp. LCD Sales Engineer for details.
Pinout of the Most Common Kyocera Touch Panels
All Kyocera touch panels have a Flex Printed Circuit (FPC) finger to connect to
the customer's 4-wire resistive touch panel controller. The location of the FPC
finger (top or left or bottom) varies with the size of the touch panel.
On the most common Kyocera F/G and G/G touch panels, the 4 contacts are on the upper
surface of the FPC finger at 1.25mm pitch. When looking at the tip of the FPC finger
from the viewpoint of the customer's connector, the contacts are numbered from left
to right.
| # |
Name |
Description |
| 1. |
yU |
Top (upper) edge |
| 2. |
xL |
Left side edge |
| 3. |
yL |
Bottom (lower) edge |
| 4. |
xR |
Right side edge |
There are many exceptions to this arrangement. Some Kyocera touch panels
have their electrical contacts on the bottom surface of the FPC finger. Some
Kyocera touchscreens have different pinout sequences. Some Kyocera touch
screens
have a 1.00 mm contact pitch. Carefully check the outline drawing in the
specification of your LCD for these important details of your touch panel.
The list of available G/G component touch panels at the bottom of the
Full Specifications page gives some indication
of this diversity.
Also check the LCD specifications for restrictions on where and how the customer's bezel
may contact the edge of the touch sensitive surface. Problems can arise if the
gasket around the panel causes a permanent touch.
Connectors for the Most Common Kyocera Touch Panels
Touch Panel Controllers for Kyocera LCDs
To operate a 4 wire resistive touch panel, the system must keep a voltage gradient on
the panel while waiting for a sense voltage to indicate a touch. The sense voltage
gives one coordinate and then the voltages are immediately applied to the other
direction and sensed again to obtain the other coordinate. The need to be on all the
time while awaiting a touch essentially requires that a controller IC be used.
Controller ICs for 4 wire Resistive Touchscreens
There are also other controller manufacturers, especially IC manufacturers specializing in analog
to digital converters. Many vendors have families of ICs, varying by the methods used to communicate
with the microprocessor. Some ICs integrate RS-232 or USB capability. Others are designed for board
level chip-to-chip protocols.
Some vendors also offer Touch Screen Controller boards with USB or RS232 ports, which
can function as mouse replacement devices. When selecting one, make sure it has a connector compatible
with the Kyocera touchscreen FPC finger and that it has a driver compatible with your operating system.
Writing drivers for common touch-screen interface hardware
by Kenneth G. Maxwell is a thorough article on this subject.
Touch Panel Calibration
It is generally agreed that systems featuring 4-wire resistive touch panels should include a calibration routine. Read
How to Calibrate Touch Screens
by Carlos E. Vidales for more information.
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