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Touch Screens
How Does A Touch Screen Respond To Touch?
Venkatesh Vaidyanathan
Touch screens are so standard these days that we can hardly remember
the magic and awe they brought when they entered the world stage.
Even today’s toddlers handle touch screen devices with ease when they
want to play their favorite video game or watch their cartoons on YouTube.
Although they are everywhere these days, how do these touch screens
work?
Is there only one type? Let’s take a closer look at the first kind of
touch screen ever introduced.
Resistive Touchscreens
These are
the most basic and familiar types of touchscreens out there.
Resistive
touchscreens are used in ATMs and kiosks in supermarkets.
A
resistive touch screen consists of two thin flexible metallic layers separated
by a small gap.
These two
layers contain an electric current running through them. When someone touches
the top flexible layer of the screen, it pushes down and touches the bottom
layer, thus interrupting the flow of current.
The
device can detect this contact precisely where it occurred, which may
correspond to the desired button a person was attempting to push.
A resistive touch screen is solely responsive to pressure and is
oblivious to what actually touches the screen.
Anything from a finger to a glove or a stylus will all work on such a
resistive touch screen.
Swiping and multi-touch features are not supported by this kind of
screen. This is why resistive touch screens are not used in smartphones.
The actual display is also always behind glass, which makes the
viewing experience of these screens a bit more hazy.
Capacitive Touchscreens
Capacitive
touch screens are the second-most popular choice for manufacturers when it
comes to implementing touchscreens.
A
capacitive touchscreen employs the use of a transparent electrode layer. This
layer is placed on top of a glass panel and then covered by a protective layer.
When a
finger touches the screen, some of the electrical charges transfer from the
screen to the user.
Sensors
present on all four sides of the screen can detect this decrease in electric
current. A controller is present that detects the point on the
screen a person has touched.
The
unique feature of the capacitive touch screen is that it will only operate at
the touch of a human being or a stylus.
The
advantage of a capacitive touch screen is that it has great image clarity in
comparison to resistive touchscreens. It has a durable screen with extreme
resistance to surface contaminants and liquids, such as dust, grease and water.
However,
the downside to these is that they are highly susceptible to electromagnetic
interference and radio frequency interference.
The working of Projected Capacitive Touchscreen is very similar to
regular capacitive touchscreens, but they do possess two significant advantages
over normal capacitive touchscreens: they are responsive to surgical
gloves or thin cotton gloves, and they make multi-touch features possible.
Multi-touch relates to when two fingers simultaneously activate
the touchscreen.
A projected capacitive touchscreen consists of a sheet of glass with
embedded transparent electrode films and an IC chip, which creates a
three-dimensional electrostatic field.
A change in the electrical currents is detected when a finger touches
the screen. A touch point is then detected.
Projected capacitive touchscreens are being used more and more in
different industries, and are generally chosen over regular capacitive
touchscreens because of their durability.
Infrared Touchscreens and SAW Touch
Unlike other technologies, infrared touchscreens do not
overlay the screen with an extra layer. These types of touchscreens are based
on light beam interruption technology.
An infrared touchscreen uses infrared emitters and receivers
to create an invisible grid of infrared light beams across the screen.
Not having an extra film or layer means the best possible
image quality and clarity. A sensor detects a person’s touch when an object
interrupts the light beams.
This enables multi-touch and also does not require the user
to apply pressure to register a touch.
Even if the screen is scratched, it works completely fine,
and other objects aside from one’s fingers can be used to work with this
touchscreen.
The disadvantage to this technology is that sunlight can
sometimes affect its functionality.
A Surface Acoustic Wave (SAW) touchscreen works a
little differently than resistive and capacitive touchscreens.
SAW
touchscreens use transducers mounted on the edge of a glass panel. The
transducers create an invisible grid of ultrasonic waves on the
surface that are received by sensors, hence the name surface acoustic
wave.
When a
user touches the screen, some of this wave is absorbed. The receivers locate
the touch point and send this information to the computer.
SAW
touchscreens can be activated using a finger, a gloved hand or even a stylus.
They are easy to use and offer high visibility, in addition to boasting high
optical clarity and a long touch life.
They do
have a few disadvantages, namely that they cannot be activated with hard
objects, e.g., pens, credit cards or fingernails.
False
touches are also a risk, especially by water droplets, while solid contaminants
on the screen can create non-touch areas until the dust or dirt is removed.
Venkatesh is an Electrical and Electronics Engineer from SRM
Institute of Science and Technology, India. He is deeply fascinated by Robotics
and Artificial Intelligence. He is also a chess aficionado, He likes studying
chess classics from the 1800 and 1900’s. He enjoys writing about science and
technology as he finds the intricacies which come with each topic fascinating.
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