EarthLCD ezLCD-405, Руководство пользователя

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© 2016 Earth Computers Tech. Inc.
1.5 Touch Screen
1.5.1 Introduction
The ezLCD-­‐405 has a 4-­‐wire resistive analog touch screen. This touch screen consists of two
layers of transparent resistive material with silver ink for electrodes. These two layers are
stacked on an insulating layer of glass, separated by tiny spacer dots. They are interfaced
electrically to the dedicated ezLCD-­‐405 A/D converter. During measurement of a given
coordinate, one of the resistive planes is powered along its axis and the other plane is used to
sense the location of the coordinate on the powered plane.
For example, in case of the X coordinate measurement, the X plane is powered, as shown on
the drawing below. The Y plane is used to sense where the pen is located on the powered plane
as follows: At the location where the pen depresses the touch screen, the planes are shorted.
The voltage measured on the sensed plane is proportional to the location of the touch on the
powered plane. This voltage is then converted by the dedicated ezLCD-­‐405 ADC as shown on
the drawing below.
Note:
The ezLCD-­‐405 touch screen is of the industrial type. It requires bigger activation pressure than
the ones used on PDAs, Cell Phones, etc. Since the distance between X and Y planes is bigger,
this touch screen is more sensitive to an uneven pressure, particularly close to the edges.