How does touch screen work?
Touch
screen is very amazing invention which reduces the space occupied by the
keypad in the mobile gadgets. As a result the gadgets are being more
compact in size and the display is being bigger. Touch screen has become
so popular that most of the new gadgets being launched is using a touch
sensible display.
After
using a touch sensible display a tech geek would wonder how is this
working? What type of circuitry is used in this display? I would tell
you how touch screen works in this article.
A
touch screen is a two dimensional sensing device which is made of two
sheets of material separated by small spacers. Generally a sheet of
glass is used as a bottom layer and a sheet of Polyethylene(PET) is used
as a top layer. Polyethylene is a flexible material.
These
two sheets are covered with a resistive substance which is usually a
metal compound named Indium Tin Oxide (ITO). Thin layer of ITO is
uniformly spreaded onto each glass and PET layer. Small bumps named
spacer dots are added onto the glass over the resistive coating. This
spacer dots creates space between two layers and prevents accidental or a
false touch.
When
someone touches the display, the PET film is pressed down so the two
resistive surfaces touch each other which completes the circuit. The
position of this touch can be calculated by a touch screen controller
circuit.
The
controller circuit uses two dimensional system to determine the point
of touch. The basic two dimensional system is shown in the figure.
By measuring the value of X and Y you can determine the position of touch.
In
a touch screen display there is two different circuit for measurement
of X and Y position. The circuit for measuring X position is shown in
the below figure.
As
you can see from the figure that there is different value of resistance
for each point on the X line. By measuring the value of this resistance
you can determine the X position.
The circuit for measuring Y position is shown in figure.
The
function of this circuit is also same as the circuit for X position. As
you can see from the figure that there is different value of resistance
for each point on the Y line. By measuring the value of this resistance
you can determine the Y position.
Thus the controller circuit can determine the position of touch in the display.
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