TOUCHSCREEN TECHNOLOGY

INTRODUCTION

A Touchscreen Technology is an input device that allows the user to PC software directly by touching the display screen.

It allows the user to directly interact with the PC softwares without using the primary input devices such as the mouse or keyboard.

It enables the peoples to use the computer or its functions without any training.

HOW DOES A TOUCHSCREEN WORKS ?

It basically comprises of the 5 elements:

1. Bezel or Front Panel:- The bezel forms the outermost skin of the touch screen. It is the protective layer of the screen so as to protect it from the scratches and

marks. Also used for sensing the touch made by the user.

2. LCD :- The screen is basically made by the LED and Cathode ray tube. It is based on the principle that a small electrical change takes place in the crystal array of LCD where it gets pressure from the touch.

3. Touch sensor :- It is the clear glass panel sensitive to touch. The touch sensor is made to fit on the screen and it displays the electric current through the screen so when the user touches the screen the change in voltage is detected by the sensor and passes the signal to the controller.

4. Touch controller :- This is a microcontroller based integrated circuit present between the touch sensor and embedded system. It transfers the information from touch sensor to the embedded system.

5. System Software :- The driver allows the touchscreen and computer to work together, it

converts the bus information. It tells the operating system

how to interpret the information sent by the controller. The touchscreen driver works like a mouse of the PC.

There are basically 6 types of touchscreens :

1. Resistive Touchscreen

2. Capacitive Touchscreen

3. SAW (Surface Acoustic Wave) Touchscreen

4. Infrared Touchscreen

5. Optical Imaging Touchscreen

6. Strain Gauge Touchscreen

1. RESISTIVE TOUCHSCREEN

The resistive touchscreen consists of two layers X-layer and Y-layer.

These layers are flexible are made by the ITO (Indium Tin Oxide) which is an excellent conductor.

There is a thin air gap between these two layers. It is just like a sandwiched arrangement.

The X-layer works in X-axis means the left and right side of the screen and Y-layer works in Y- axis i.e the top and bottom of screen.

The touch is sensed as the right part is driven to a known voltage and left to the ground.

In the X-layer wires are connected at right and left side and top to bottom in Y-layer. The electrodes are connected at the four corners for the electrical contact with circuit.

So when the screen is touched the two layers come in contact with each other both layers senses the voltage vertically and horizontally and the information of the touched position is

send to the CPU by the controller.

2. CAPACITIVE TOUCHSCREEN

There are two types of capacitive touchscreens :

1. Projected capacitive touchscreen

2. Surface capacitive touchscreen

PROJECTED CAPACITIVE

The projected capacitive are same as of resisitive type contains two ITO layers, but these glass layers are etched and the perpendicular strips are made at the end of the layer.

These strips forms the grid pattern like pixels projects the electric field.

So when the user touches the screen it changes the measured capacitance values of the electrode which is generally of 15pF.

SURFACE CAPACITIVE

In the surface capacitance the only one ITO glass layer is used.

The computer measure the capacitance from all the four corners.

Then the four separate measurements, the X and Y coordinates of the touch point are calculated, the capacitance is of 15 pF.

SURFACE CAPACITIVE

3. SAW (Surface Acoustic Wave)

In this technology a pure glass panel is used

and the piezoelectric transducers and reflectors are used.

The transducers are placed at the four corner

on the X and Y axis and reflectors are fixed at the four sides.

The controller sends the electric signal to the

transducers and these converts the signal into the waveforms.

So when the user touches the screen it absorbs the portion of the wave travelling.

The received signal is then compared with the stored digital map, the change is recognised and the coordinate calculated.

Surface Acoustic Wave

4. INFRARED TOUCHSCREEN

In this technique the LED and photodetectors are used.

The LED beams cross over the glass panel horizontally and vertically, also the photodetector is used to spread the electrical signal on the glass panel.

The photodetector gets enhance by the visible rays of the LED and produces the electrical signal.

These photodetectors and LED are fixed at the corners of the glass panel.

So when we touch the screen this electrostatic beam disrupted and so the exact location of the touch is being send to the controller.

Infrared Touchscreen

5. OPTICAL IMAGING TOUCHSCREEN

In the optical imaging touch screen the image sensors are placed at the corners of the screen and the infrared backlights are focused from the sides of the screen on the glass panel.

When we touch the screen, the touch shows up the shadow and the image sensors locate the touch and even the size of touch object and send information to controller.

Optical Imaging Touchscreen

6. STRAIN GAUGE TOUCHSCREEN

In the strain gauge technology the screen is mounted on the four springs at the corners.

The strain gauge are used to determine the deflection in the screen when it is touched.

The strain gauges convert the force applied into the electrical signal by the expansion and contraction of the wires cause deflection in the resistance.

STRAIN GAUGE TOUCHSCREEN

ADVANTAGES

Touchscreen gadgets usually have simple user interface and are more intutive.

Replaces keyboards and mouse.

Operated using a stylus or a glove finger.

High clarity, completely sealable.

High resolution and accuracy.

Faster response.

DISADVANTAGES

Big screen leads to low battery.

This devices require massive computing power.

When an application crashes without crashing the operating system you can’t get the main menu as the whole screen becomes unresponsive.

Screen gets very dirty.

They have low precision.

Screen can damage by the sharp objects.

APPLICATIONS

Mobile and PC applications.

Restaurant systems.

Employee time clock.

Industrial process control.

Computer access for physically disabled.

Gaming systems.

Trade show displays.

Point-of-sale terminals.

Informational kiosks.

THANK YOU

SUBMITTED BY : VIDHI GAUTAM