SR Engineering College
• A Touchscreen is an electronic visual display that the user can control
through simple or multi-touch gestures by touching the screen with a
special stylus/pen and-or one or more fingers.
• The user can use the touchscreen to react to what is displayed and to
control how it is displayed (for example by zooming the text size).
• They are common in devices such as game consoles, computers,
tablet PCs, and smartphones.
• Touchscreen technology is the direct manipulation type gesture based
• The first ever touchscreen was developed by E.A Johnson at the Royal Radar
Establishment, Malvern, UK in the late 1960s.
• In 1971, a milestone to touchscreen technology was developed by Doctor Sam Hurst, an instructor at
the University of Kentucky Research Foundation. It was a touch sensor named ‘Elograph’.
• In 1977, Siemens Corporation financed an effort by Elographics to produce the first curved glass touch
sensor interface, which became the first device to have the name "touch screen" attached to it.
• In 1983, the computer manufacturing company, Hewlett-Packard introduced the HP-150, a home
computer with touch screen technology.
• In 1993, Apple released the Newton PDA, equipped with handwriting recognition.
• In 2002, Microsoft introduced the Windows XP Tablet edition and started its entry into touch
• In 2007, Apple introduced the king of smart phones, the iPhone, with nothing but touch screen
A Touchscreen consists of three main components:
Touchscreen Sensor: It is a clear glass panel with touch responsive surface. It
is placed over the display screen so that the responsive area of the panel
covers the viewable area of the video screen.
Controller: It is a small PC card that connects the touch sensor and the
PC, takes information from the touch sensor and translates into information
that the PC can understand.
Software Driver: The Driver is a software update for the PC system that
allows the touchscreen and computer to work together. It tells the Operating
System how to interpret the touch event information that is sent from the
• A resistive touchscreen panel comprises several layers, the most important
of which are two thin, transparent electrically-resistive layers separated by
a thin space.
• It consists of a flexible top layer made of
Polyethylene (PET) and a rigid bottom layer made
• An electric current flows between the two layers.
When a touch is made, the flexible screen presses
down and touches the bottom layer.
• A change in electrical current is hence detected and the coordinates
of the point of touch is calculated by the controller and parsed into
readable signals for the operating system to react accordingly.
• One layer has conductive connections along its sides, the other along
top and bottom. A voltage is applied to one layer, and sensed by the
• Some of the popular devices that use Resistive Touchscreen are
Nintendo DS, Nokia N97, HTC Touch Pro2, HTC Tattoo, Sony Ericsson
Pros and Cons:
• Resistive touch is used in restaurants, factories and hospitals due to
its high resistance to liquids and contaminants.
• low cost
• Additionally, as only sufficient pressure is necessary for the touch to
be sensed, they may be used with gloves on, or by using anything
rigid as a finger/stylus substitute.
• The need to press down, and a risk of damage by sharp objects.
• They suffer from poorer contrast, due to having additional reflections
from the extra layer of material placed over the screen.
• A capacitive touchscreen panel consists of an insulator such as glass,
coated with a transparent conductor such as indium tin oxide (ITO).
• As the human body is also an electrical conductor, touching the
surface of the screen results in a distortion of the screen's
• The location is then sent to the controller for processing.
• A simple parallel plate capacitor has two
conductors separated by a dielectric
• In this basic technology, only one side of
the insulator is coated with a conductive
• A small voltage is applied to the layer,
resulting in a uniform electrostatic field.
• When a conductor, such as a human finger,
touches the uncoated surface, a capacitor is dynamically formed.
• The capacitive systems transmit almost 90% of light from the monitor.
• Some of the devices using capacitive touchscreen are Motorola
Xoom, Samsung Galaxy Tab, Samsung Galaxy SII, Apple’s iPad.
• Two types of Capacitive Touch:
• Surface Capacitive Touch
• Projected Capacitive Touch
Pros and Cons:
• The surface capacitive touchscreen is moderately durable and needs
calibration during manufacture.
• Since a conductive material is required to operate this screen, passive
stylus cannot be used for surface capacitive touchscreen.
Surface Acoustic Wave Touch:
• This technology uses ultrasonic waves that pass over the touchscreen panel.
• This Touchscreen technology contains two
transducers(transmitting and receiving)
placed along the X-axis and Y-axis of the
monitor’s glass plate along with some
• The waves propagate across the glass and
are reflected back to the sensors.
• This change in the ultrasonic waves
registers the position of the touch event
and sends this information to the controller for processing.
Surface Acoustic Wave Touch
• This change in the ultrasonic waves registers the position of the touch
event and sends this information to the controller for processing.
• These reflectors reflect all electrical signals sent from one transducer
• This technology provides excellent throughput and image clarity.
• It is used in gaming, computer based training, public pay
phones, point-of-information kiosks etc.
Surface Acoustic Wave Touch
Pros and Cons:
• Almost 100% clarity is obtained as no metallic layers are present on
• It can be operated using passive devices like stylus, glove or finger
• Scratch resistant, faster response.
• Surface Acoustic Wave touchscreen panels can be damaged by
• Contaminants on the surface can also interfere with the functionality
of the touchscreen.
• An infrared touchscreen uses an array of X-Y infrared LED and photo detector
pairs around the edges of the screen to detect a disruption in the pattern of
• These LED beams cross each other in vertical
and horizontal patterns.
• A translucent acrylic sheet is used as a rear
projection screen to display information. The
edges of the acrylic sheet are illuminated by
infrared LEDs, and infrared cameras are
focused on the back of the sheet.
Pros and Cons:
• Unlike capacitive touchscreens, infrared touchscreens do not require
any patterning on the glass which increases durability and optical
clarity of the overall system.
• It can detect essentially any input including a finger, gloved finger,
stylus or pen.
• It is generally used in outdoor applications and point of sale systems
which cannot rely on a conductor (such as a bare finger) to activate
• These are sensitive to dirt/dust that can interfere with the IR beams,
and suffer from parallax in curved surfaces and accidental press when
the user hovers his/her finger over the screen while searching for the
item to be selected.