PRINCIPLE OF TOUCHSCREEN

Arsh Hashmi

Anuj Sharma

Gaurav Bhandari

Deepak Thakur

INTRODUCTION

A touch screen is a two dimensional sensing device display that can detect the presence and location of a touch within the display area.

The term generally refers to touching the display of a device with a finger or hand .

Touchscreen can also scan other passive object such as stylus.

Touchscreen are common in devices such as game consoles, all-in-one computers, tablets computers and smart phones.

The objective of our report titled ‘Principle

of Touchscreen’ is to explain the principles

involved in the working of this technology.

Among the various types of touchscreen

technologies, our main focus will be on the

Resistive And Capacitive touchscreen

HOW DOES A TOUCHSCREEN WORK?

A basic touchscreen has three main components:

TOUCH SENSOR: It is a clear glass panel with a touch responsive surface. The touch sensor/panel is placed over a display screen so that the responsive area of the panel cover the viewable area of the screen. There are several different touch sensor technologies in the market today, each using different method to detect touch input. The sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. This change is used to determine the location of the touch to the screen.

CONTROLLER: The controller is a small

PC card that 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 is usually installed inside the

monitor for integrated monitors or it is

housed in a plastic for external touch add-

ons / overlays.

SOFTWARE DRIVER-The driver is a

software update for the system that allows

the touch screen and system to work

together. It tells the operating system how

to interpret the touch event information

that is sent from the controller.

TYPES OF TOUCH SCREEN TECHNOLOGY

Resistive touchscreen

Capacitive touchscreen

Infrared touchscreen

Surface Acoustic Wave (SAW) touchscreen

Strain gauge touchscreen

Optical imaging touchscreen

Dispersive signal technology touchscreen

RESISTIVE TOUCHSCREEN

Resistive touchscreen systems are the most

common type of touchscreen technology in

today’s market. These devices are used in

many applications, such as cell phones,

handheld games, GPS navigation devices, and

even some digital camera.

TYPES OF RESISTIVE TOUCHSCREEN

4-wire resistive touchscreen

5-wire resistive touchscreen

6-wire resistive touchscreen

7-wire resistive touchscreen

8-wire resistive touchscreen

4-WIRE RESISTIVE TOUCHSCREEN

THE STRUCTURE OF TOUCHSCREEN

The 4 wire resistive touchscreen uses a glass panel with a uniform conductive ITO(indium tin oxide) coating on the one-side surface.

A PET film is tightly suspended over the ITO coating surface of a glass panel.

The glass substrate and the PET film are separated by tiny, transparent insulating dot spacers.

The PET films has a hard coating on the outer side and a conductive ITO coating on the inner side. The structure is film-glass process.

WORKING PRINCIPLE

1. When the screen is touched, it pushes the

conductive ITO coating on the glass. That

results the electrical contact, producing the

voltages. It presents the position touched.

2. The pins (X left) and (X right ) are on the

glass panel, and the pins (Y up) and (Y

down) are the PET film.

3. The microprocessor applies +5V to pin (X left)

on the glass panel, and the voltage is uniformly

decreasing to pin (X right) for 0V because of the

resistive ITO coating on the glass substrate, and

the PET film is grounded. When the touchscreen

is not touched, the controller detects the voltage

on the PET film is 0.The next electric cycle, the

microprocessor applies +5V to pin(Y up) on the

PET film, and the voltage is uniformly

decreasing to pin (Y down) for )V. When the

touchscreen is not touched, the controller

detects the voltage on the glass panel is 0

4. When the touchscreen is touched, a

voltage on the glass substrate proportional

to the X (horizontal) position of the touch

appears on the PET film. This voltage is

digitized by the A/D converter and

subjected to an averaging algorithm. Then

it is stored and transferred to the host.

Hence, the X position is produced.

The next electric cycle, a voltage on the

PET film proportional to the Y(vertical)

position of the touch appears on the glass

substrate. This voltage is digitized by the

A/D converter and subjected to an

averaging algorithm. Then it is stored and

transferred to the host. Hence, the Y

position is produced.

ADVANTAGES:

1.Cost effective and durable.

2.Can work in all climatic condition.

3.Less sensitive to scratches as compared

to capacitive screens.

DISADVANTAGES:

1.Normally does not support multi touch.

2.While using finger, slightly more pressure

needs to be applied.

3.Clarity is lower than capacitive screen.

CAPACITIVE TOUCHSCREENS

They represent the second most widely used

sensing method after resistive film touch

panels.

There are two types of capacitive touch

screen:

1.Surface Capacitive Touch screen

2.Projected Capacitive Touch screen

SURFACE CAPACITIVE TOUCH SCREENN

STRUCTURE-Capacitive touch screen 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 0.0015mm 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.

WORKING PRINCIPLE

Small amount of voltage is applied to the electrodes on the four corners.A human body is an electric conductor, so when you touch the screen with your finger, a slight amount of charge 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.

PROJECTED CAPACITIVE TOUCH SCREEN

STRUCTURE-They are made up of three major components; the sensor glass, the cover glass , and a flexible printed(FPC) with controller. The sensor glass is made of a series of electrodes that are configured into rows and columns. These electrodes are made up of a transparent conductive coating called indium tin oxide. Each electrode is routed with a metal to a connection point where the FPC can be bonded. The FPC generally contains the controller for the touch sensor.

The cover glass is optically bonded on top of

the sensor glass, burying the electrodes

within the stack of the lamination. The cover

glass serves as a dielectric between your

touch and the electrodes of the sensor

glass. It also doubles as a barrier layer

protecting the sensitive electrodes from the

environment and any potential damage.

WORKING PRINCIPLE

Projected capacitive touch screes are made up of a matrix of rows and columns of conductive material, layered on sheets of glass. This can be done by either etching a single conductive layer to form a grid pattern of electrodes, or by etching two separates, perpendicular layers of conductive material with parallel lines or tracks to form a grid. Voltage applied to this grid creates a uniform electrostatic field, which can be measured When a conductive object, such as finger comes into contact with PCT panel, it distorts the local electrostatic field at that point . This is measurable as change in capacitance. Hence the X and Y coordinates can be determined.

ADVANTAGES:

1.Hgh clarity display (up to 90% optical

transparency)

2.Supports multi-touch

3.High touch resolution

4.High sensitivity

DISADVANTAGES:

1.Needs a human finger to register input. It

is not possible to use this screen wearing

gloves

2.Cannot be used in all weather scenarios.