Specifications

4 Chapter 1 - Introduction
The AccuTouch Touchscreen
The AccuTouch Model E274 touchscreen consists of a glass panel formed to
match the shape of the underlying display surface. A hard-coated plastic cover
sheet is suspended over the surface of the glass by tiny separator dots. The cover
sheet may be clear for best image clarity or have an anti-glare finish. See Figure 1-
1 for detail on the construction of the AccuTouch touchscreen.
The glass is covered with a uniform resistive coating, and the plastic cover sheet
has a conductive coating. With a light touch on the cover sheet, the conductive
coating on the plastic contacts the resistive coating on the glass. There is an
electrical drive connection to each of the four corners of the resistive coating, and
a pickup connection to the coating on the cover sheet. When the proper DC
voltages are applied to the drive connections, the voltage at the pickup connection
is proportional to the position of the touch.
Figure 1-1. AccuTouch Touchscreen
The logical sequence of operation for the SmartSet controller, used in combination
with the E274 touchscreen, is as follows:
1. When the controller is waiting for a touch, the resistive layer of the
touchscreen (the coating on the glass) is biased at +5V through all four drive
lines, and the cover sheet is grounded through a high resistance. When the
touchscreen is not being touched, the voltage on the cover sheet remains at
zero. The voltage level of the cover sheet is continuously converted by the
analog to digital converter (ADC) and monitored by the microprocessor on the
controller. When the touchscreen is touched, the microprocessor detects the
rise in the voltage of the cover sheet and begins coordinate conversion.