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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 electronic system.
Typically the system will display several icons 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 icon was selected and takes appropriate action. The
phrases Touch Screen and Touch Panel mean the same thing and are
interchangeable.
There are several physical phenomena which can be used to detect a touch including
capacitive, infrared, resistive and surface acoustic wave (SAW). Resistive touchscreens
are the most common because they are simple, low cost and can be activated by finger
tip or any type of stylus. Capacitive technology offers higher transparency at a higher
cost. Surface acoustic wave technology requires more border, more power and a touch by
finger, but gives more durability for public access applications. Among resistive touch
screens, the 4 wire method is most common, and the 5 wire less so. 8 wire resistive is
a variation on 4 wire and 6 wire and 7 wire are variants of the 5 wire method. The
Hampshire Company has posted an excellent application note
How an Analog Resistive Touch Screen Works
comparing these resistive touchscreen technologies. Electronic Products has
a thorough article
Choosing a resistive touch panel for HMI apps.
Kyocera Touch Panels
To give customers the confidence and convenience of a single-vendor solution, Kyocera
offers most LCD models with 4-wire analog resistive touch
panels already mounted by Kyocera.
These touch screens are rated for 1 million touches at a single point, by a 0.8mm
polyacetal stylus. They 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.
Check the 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. There is a tiny vent which must
be kept clear to prevent the touch panel from inflating or auto-touching when the
atmospheric pressure changes.
Touch Panel Connectors for Kyocera LCDs
Kyocera touch panels have an FPC finger to
insert into the customer's board,
usually with 4 contact pads on the upper surface at 1.25 mm pitch.
Below are some connector families which support this style
of connection.
| Manufacturer |
4 Wire 1.25 mm Pitch Connector |
| JST |
FFS series
FE series |
surface mount, non-ZIF
thru-hole, non-ZIF |
| AVX/Elco |
6216 series |
thru hole, side entry, non-ZIF |
| FCi |
HLEM4R-1
HLEM4S-1 |
thru-hole, side entry, non-ZIF
thru-hole, top entry, non-ZIF |
| Oupiin |
2533 series
2532 series |
thru-hole, ZIF
thru-hole, non-ZIF |
Check the LCD drawing in the specification to confirm the details of the FPC finger.
The TCG104VG touch panel is an exception to the above and there may be other
exceptions in the future.
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 must be immediately applied to the other
surface 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
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
an internal parallel bus. Be sure to look for drivers to communicate the touch position
to your operating system.
Writing drivers for common touch-screen interface hardware-- by Kenneth G. Maxwell
is a very 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.
Touch Panel Vendors
Any Kyocera LCD can be fitted with touch panels of several different types of
technologies from many different vendors. Read
Elizabeth Morse's article in Control Engineering
for a brief description of the different touchscreen technologies. Resistive technology
touchscreens are available for most Kyocera LCD sizes. Other technology touchscreens
tend are mostly used for larger display sizes. Power consumption will be a major
consideration, including power for the extra LCD brightness to make up for the light
that is lost in the touch panel. Read
John Stetson's article in Information Display for a discussion of sunlight readability
and touch panels. Read
Integrating your Touch Screen
for a nice discussion of mechanical aspects of touch panel installation.
Major Touchscreen Manufacturers
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