Touch Screen Technology

1. RESISTIVE AND CAPACITIVE
TOUCH SCREEN
By
Abdul Muqeed
11011A0449

2. Overview
• Introduction
• Working
• Types of technologies
• Resistive touch
• Capacitive touch
• Advantages and advancements
• Conclusion

3. Introduction
• A touch screen 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 touch screen to react to what is displayed
and to control how it is displayed (for example by zooming the
text size).
• The touch screen enables the user to interact directly with what
is displayed, rather than using a mouse, touchpad, or any other
intermediate device.

4. Working
• A touch screen has three main components:
 Touch sensor
 Touch Controller
 Software driver
• The touch screen itself is an input device, so it needs to be
combined with a monitor and a PC to make a complete touch
input system.

5. Touch Sensor
• Each touchscreen uses a different
method to sense touch input. Often
these are a plastic or glass panel placed
under the bezel of the LCD screen.
• A touch screen sensor is a clear glass
panel with a touch responsive surface.
It is placed over a display screen so
that the responsive area of the panel
covers the viewable area of the video
screen.
• The sensor generally has an electrical
current or signal going through it and
touching the screen can cause a signal
change. This change is used to
determine the location of the touch.

6. Touch Controller
• The controller connects between the touch sensor and the PC.
It takes information from the touch sensor and translates it into
information that PC can understand.
• The controller determines what type of interface/connection
will be needed on the PC. Controllers are available that can
connect to a Serial/COM port (PC) or to a USB port.
• MCF227x,PIC 18F452.
Software driver
• The driver allows the touch screen and computer to work
together. It tells the computer's operating system how to
interpret the touch event information that is sent from the
controller.

7. Types of technologies
There are a variety of touch screen technologies that have
different methods of sensing touch
• Resistive touchscreen
• Capacitive touchscreen
• Infrared touchscreen
• Surface acoustic wave (SAW) touchscreen

8. • The resistive touchscreen consists of a flexible top layer made of
Polyethylene (PET) and a rigid bottom layer made of glass.
• Both the layers are coated with a conducting compound called Indium
Tin Oxide (ITO) and then spaced with spacers.
• While the monitor is operational, 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.
Resistive Touchscreen Technology

9. • When the touch screen is
pressed, contact is made
between the grid on the
glass and the grid on the
film.
• The voltage of the circuit is
measured, and the X and Y
coordinates of the touch
position is calculated based
on the amount of
resistance at the point of
contact.
• This analog voltage is
processed by ADC to create
a digital signal that the
device's controller can use
as an input signal from the
user.

10. • One of the big advantages of resistive touch panels is that
they are relatively inexpensive to make. Another is that you
can use almost anything to create an input signal: finger tip,
fingernail, stylus -- just about anything with a smooth tip.
 Resistive touchscreens are of 4 modes
• 4-wire
• 8-wire
• 5 and 7 wire

11. 4-wire
• A 4-wire touch screen is made from two layers, each with a resistive
coating. The bottom layer is rigid, but the top one is flexible. Both layers
are provided with voltage
• The basic idea is to create a voltage divider. Detecting the voltage at the
division point (the touch point) allows for calculating the relative
position of the touch point with respect to the two rails.
• To get the coordinates for a single point, First a voltage is applied across
the x-axis plane, and the contacts for the y-axis plane are allowed to
float.
• The resistive coating on the touch screen creates a voltage gradient
across the plane. If the top layer is pressed, it flexes and makes contact
with the bottom layer.
• The y-axis plane now has a voltage equal to the voltage on the x-axis
plane at the point of contact. The voltage on the y-axis plane can be
measured and used to obtain the x-coordinate.
• The process is repeated again to get the y-coordinate.

13. 8-wire
• An 8-wire touch screen is based on the same basic technology as
a 4-wire touch screen. Again, four wires are used to provide
power at the edges of the touch screen.
• The extra four wires are used to sense the actual voltage applied
at the edges of the touch screen. These sense wires are added to
compensate for offset errors.
• An 8-wire system is more commonly used for larger touch
screens (about twenty centimeters, or eight inches, and up).
• The accuracy of touch point placement degrades as the screen
becomes larger, because the resolution is spread across a bigger
distance.
• Therefore, loss of accuracy due to offset error is a bigger
concern. Hence 8-wire is used for greater accuracy.

14. 5-wire and 7-wire
• 5-wire touch screens make some improvements on the older 4-wire
technology. The construction of the panels are similar, but for a 5-wire
touch screen all four bus bars are connected to the lower, non-flexible
layer of the screen.
• The voltage gradients are always applied to the rigid bottom layer.
Because the voltage gradient layer does not come into direct contact
with the user and does not bend. Hence better durability.
• 7-wire touch screens add two additional sense lines to the 5-wire
interface.
• One sense line is used to detect offset on one of the x-axis bus bars,
and the second is used to detect offset on one of the y-axis bus bars.
Again, this helps to increase the accuracy of touch measurements and
reduce the need for calibration.

15. • 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 electrostatic field, measured as a change in capacitance.
• Capacitive touch gets its name from the electrical distortion that
results in the screen's capacitive field when impressed upon by
body capacitance, or conductor of electric charges.
• This enables capacitive touchscreens to not require any actual
force to be applied to the screen’s surface; at the same time,
capacitive screens typically don't respond to styluses or gloved
hands due to the lack of electrical impulses generated.
Capacitive Touchscreen Technology

16. • Capacitive touchscreen is a
four multi-layer glass. The
two sides of the glass
substrate are coated with
uniform conductive ITO
(indium tin oxide) coating.
• The thickness of 0.0015
millimeter silicon dioxide hard
coating are coated on the
front side of ITO coating layer.
There are electrodes on the
four corners for launching
electric current.

17. • Small amount of voltage is applied
to the electrodes on the four
corners . A human body is an
electric conductor, so when the
screen is touched with a finger, a
slight amount of current is drawn,
creating a voltage drop.
• The current respectively drifts to
the electrodes on the four corners.
Theoretically, the amount of current
that drifts through the four
electrodes should be proportional
to the distance from the touch point
to the four corners.
• The controller precisely calculates
the proportion of the current
passed through the four electrodes
and figures out the X/Y coordinate
of a touch point.

19. Advantages
• Touchscreens improves the human-computer interface and helps
improving the user’s experience.
• Touchscreens provide an easy to understand, intuitive interface
for the human brain.
• Fumbling with a mouse and keyboard isn’t always the easiest
thing to do and touchscreen technology can help as they have
easier hand eye coordination than mice or keyboards
• Touch screens are the fastest pointing devices. No extra work
space is required as with other pointing devices.

20. Multi-touch screens
• multi-touch refers to the ability of a surface to
recognize the presence of more than one or more
than two points of contact with the surface.
• Capacitive display continue to develop thinner and
more accurate touchscreens, with touchscreens
for mobile devices now being produced with 'in-
cell' technology that eliminates a layer, such as
Samsung's Super AMOLED screens, by building the
capacitors inside the display itself.
Advancements
•This type of touchscreen reduces the visible distance (within
millimetres) between the user's finger and what the user is touching on the
screen, creating a more direct contact with the content displayed and
enabling taps and gestures to be more responsive.

21. Conclusion
• As it is very friendly, fast, accurate, easy for the
novices and fun to operate. It has been widely
accepted.
• Today, This Technology is been adopted by computer,
mobile users of all abilities because it is innovative,
simple.
• Designers are trying to use touchscreen to simplify
input commands for largely unsophisticated computer
users.
• In future there may be no usage of mouse and
keyboards as they will be replaced by touchscreens.

22. THANK YOU