Touch Screen Information
The easiest and most flexible user interface for a Liquid Crystal Display is a touch screen overlaying a
Graphic LCD Module. This allows the designer to customize their interface
specifically to their application, to allow dynamic adjustments to the user
interface as the product ages, and to allow for alterations required for
geographically different regions. Pacific
Display Devices typically uses Analog-Resistive Touch Screens, and this
approach gives use the following features:
- Proven Resistive Technology
- Simplicity of Interface Electronics
- Durable Plastic Construction
- Less Susceptible to Accidental Touch
- Ability to use Finger or Stylus to Activate Touch
Screen
- High Linear Analog Output
Pacific Display Devices has integrated analog-resistive Touch Screen
technology into our displays as an standalone feature, where the customer
will integrate their own decoder, or as a fully integrated assembly, where
we have integrated the full decoding electronics. The next sections on
this page will cover touch screen construction, operation, and application
notes specifically set up for configurations used by Pacific Display
Devices.
LCD Touch Screen Construction and Operation
The Analog-Resistive touch screens
typically used by Pacific Display Devices are constructed of two layers of
electrically conductive transparent films facing one another and separated
by a gasket. Each layer has a set of parallel busbars positioned along the
opposite edges and orthogonal to the busbars on the other layer. Busbars
consist of screen-printed conductive ink terminated at the tail. The entire
switch assembly is then mounted on a rigid Glass, Acrylic of Polycarbonate
backer before it is attached to the front of our LCD Modules. Two
opposing layers of Touch Screen are held apart by small separator dots until
they come into contact by a light finger pressure. The voltage signal is
then decoded by the controller to provide the application software with X
and Y coordinates of the touch point.
Decoder Electronics: Data Sheets and Application Notes
Decoding the analog output of the
Touch Screen is relatively easy, there are many one chip solutions made by
several vendors that will remove the elaborate design work. Our
primary selection for a Touch Screen controller is the
ADS7843.
Here is the data sheet and application notes for this choice:
Manufactured by Burr Brown
ADS7846 Chip Data Sheet
