Datasheet

 2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 7
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
2.0 BASICS OF RESISTIVE
SENSORS
2.1 Terminology
ITO (Indium Tin Oxide) is the resistive coating that
makes up the active area of the touch sensor. ITO is a
transparent semiconductor that is sputtered onto the
touch sensor layers.
Flex or Film or Topsheet
is the top sensor layer that a
user touches. Flex refers to the fact that the top layer
physically flexes from the pressure of a touch.
Stable or Glass
is the bottom sensor layer that
interfaces against the display.
Spacer Adhesive
is a frame of adhesive that connects
the flex and stable layers together around the perimeter
of the sensor.
Spacer Dots
maintain physical and electrical
separation between the flex and stable layers. The dots
are typically printed onto the stable layer.
Bus Bars or Silver Frit electrically connect the ITO on
the flex and stable layers to the sensor’s interface tail.
Bus bars are typically screen printed silver ink. They
are typically much lower in resistivity than the ITO.
X-Axis
is the left and right direction on the touch sensor.
Y-Axi s
is the top and bottom direction on the touch
sensor.
Drive Lines
supply a voltage gradient across the
sensor.
2.2 General
Resistive 4, 5, and 8-wire touch sensors consist of two
facing conductive layers, held in physical separation
from each other. The force of a touch causes the top
layer to deflect and make electrical contact with the
bottom layer.
Touch position measurements are made by applying a
voltage gradient across a layer or axis of the touch
sensor. The touch position voltage for the axis can be
measured using the opposing layer.
A comparison of typical sensor constructions is shown
below in Tabl e 2-1.
The AR1000 Series Resistive Touch Screen
Controllers will work with any manufacturers of analog
resistive 4, 5 and 8-wire touch screens. The
communications and decoding are included, allowing
the user the quickest simplest method of interfacing
analog resistive touch screens into their applications.
The AR1000 Series was designed with an
understanding of the materials and processes that
make up resistive touch screens. The AR1000 Series
Touch Controller is not only reliable, but can enhance
the reliability and longevity of the resistive touch
screen, due to its advanced filtering algorithms and
wide range of operation.
TABLE 2-1: SENSOR COMPARISON
Sensor Comments
4-Wire Less expensive than 5-wire or 8-wire
Lower power than 5-wire
More linear (without correction) than 5-wire
Touch inaccuracies occur from flex layer damage or resistance changes
5-Wire Maintains touch accuracy with flex layer damage
Inherent nonlinearity often requires touch data correction
Touch inaccuracies occur from resistance changes
8-Wire More expensive than 4-wire
Lower power than 5-wire
More linear (without correction) than 5-wire
Touch inaccuracies occur from flex layer damaged
Maintains touch accuracy with resistance changes