Implementation of Capacitive

touchscreen in Smart devices

Aseem Avinab

1st Year M.Tech

Power Electronics and Drives

Id- RA1412011010029

1

Contents Introduction 3

History 4

How touch screen work 5

Types of Touch screen 6

Grid pattern design 11

Sub pixel interpolation algorithm 14

Comparison between grid pattern 16

Advantages 18

Disadvantages 19

2

Introduction Touchscreen is an electronic visual display that can detect the

presence and position of touch within the display area.

The touchscreen enables the user to interact directly with

what is displayed

The popularity of smartphones, tablets, and many types of

information appliances is driving the demand and acceptance

of common touchscreens for portable and functional

electronics

Trend toward acceptance of touchscreens as a highly

desirable user interface component and have begun to

integrate touchscreens into the fundamental design of their

product

3

History Historians generally consider the first

finger-driven touchscreen to have been

invented by E.A. Johnson in 1965 at

United Kingdom which was capacitive.

In 1970 first resistive touchscreen was

invented.

First commercial computer was introduced

by HP with SONY CRT surrounded by

infrared transmitter and detector 1983

First cellphone with touch screen

Technology was invented by IBM

in 1993

4

How touch screen works

A basic touch screen has three main components: a touch

sensor, a controller, and a software driver

A touch screen sensor is a clear glass panel

with a touch responsive surface

The controller is a small PC card that

connects between the touch sensor and the PC

The driver is a software update for the PC system that

allows the touch screen and computer to work together

5

Types of Touch screen

Resistive Touch Screen

Infrared Touch Screen

Surface Acoustic Wave Touchscreen

Capacitive Touch Screen

6

Resistive Touch Screen

Two layers of conductive material

Touch creates contact between

resistive layers completing circuit

Disadvantages

Polyester surface can be damaged

Lower endurance (35 million touches)

Multi touch support not available yet

User has to apply pressure for it to work

7

Infrared Touch ScreenUses infrared LEDs and matching

photo detectors

Touching screen interrupts LEDs and

is detected by camera

Controller able to calculate coordinates

from camera data

Disadvantages

Surface obstructions can cause a false touch

It is very sensitive and can be activated by stray touches.

Low resolution

Parallax problems

8

Surface acoustic Touchscreen

The technology is based on two transducers

Touch is detected by the phenomena of

reflection and refraction

Disadvantages

Moving liquids or condensation can cause false touches

Solid contaminants create non-touch areas until removed

Doesn't support drag or draw effectively

9

Capacitive Touch screen

Two types of capacitive sensing technology

Surface capacitive technology

Projected capacitive technology

Two types of Projected capacitive sensing technology

Mutual Capacitance where the object alters the mutual

coupling between row and column electrodes

Self-Capacitance where the object loads the sensor or

increases the parasitic capacitance to ground

10

Grid pattern design

Diamond grid panel (When a basic element is repeated in

both horizontal and vertical direction in two separate layers

and then put on top of each other, a whole diamond shaped

pattern is formed)

11

Interleaved pattern (The main objective of the designer was

to devise a grid pattern which will reduce the number of

basic elements or electrodes in a capacitive system by

interleaving the electrodes which will in turn create a larger

region where the finger when sensed by the two adjacent

electrodes will result in better interpolation result and also

less number of basic elements in the panel)

12

Angled cross grid pattern (grid design of a capacitive

sensing apparatus in which the shape of the basic element

looks like two angled crosses)

13

Sub pixel interpolation

algorithms for single pixel touchAn approximate model of a point can be a 2-D Gaussian point as

its edges are smooth and blurred. Basic equation of such a profile

will be

14

Sub pixel interpolation

algorithms for multi pixel touch

ri = Maximum value of row

reading

r(i-1)= Reading in the row below

the maximum

r(i+1)= Reading in the row above

the maximum

15

Comparison between grid pattern Using diagonal movement

16

Using circular movement 17

Advantages of capacitive touch

Scratch resistant, durable surface

High endurance (225 million touches)

Very accurate

Good optical clarity

Liquids won't affect touch screen performance

Not affected by dirt, grease, moisture

Multi touch support available

User doesn’t need to apply any force

More responsive than resistive touchscreens

18

Disadvantages

Does not work with gloved fingers or stylus

More expensive due to production cost

Gets damaged pretty easily when dropped

Not as accurate as resistive touchscreens

19

References1. ^ Larry K. Baxter (1996). Capacitive Sensors

(http://books.google.com/books?id=Tjd2laRnO4wC&pg=PA138&dq

=capacitive+sensors+mouse&lr=&as_brr=3&as_pt=ALLTYPES&ei

=sMOASe ONJIHmyATKlLWzCw). John Wiley and Sons. p. 138.

ISBN 978-0-7803--5351-0

2. ^ Wilson Tracy." HowStuffWorks"Multi-touchSystems""

(http://electronics .howstuff works.com/iphone2.htm). Retrieved

August 9, 2009.

3. ^ Resistive Touchscreen (http://resistivetouchscreen.org /)

4. ^"Using resistive touch screens for human/machine interface"

(http: //www.ti.com /lit/an/slyt209a/slyt209a.pdf). Texas Instruments.

5. ^ Touch Screen Calibration (http: //globaldisplayengineering.com

/Touch_Screen_ Calibration.php) Global Display Engineering

20

6.^ Larry K. Baxter (1996). Capacitive Sensors(http:// books.google.com/books?id=Tjd2laRnO4wC&pg=PA138&dq=capacitive+sensors+mouse&lr=&as_brr=3&as_pt=ALLTYPES&ei=sMOASe ONJIHmyATKlLWzCw). John Wiley and Sons. p. 138. ISBN 978-0-7803-5351-0.

7. ^ Wilson, Tracy. "HowStuffWorks "Multi-touch Systems"" (http:// electronics. howstuffworks.com/iphone2.htm). Retrieved August 9, 2009

8. ^ US Pat No 5,305,017 5,861,875

9. ^ e.g. U.S. Pat. No. 4,736,191

10. ^ J. A. Harley, “Capacitive touch screen or touchpad for finger or stylus,” U.S. Patent US2010/0026655 A1, Feb. 4, 2010.

11. ^ A. A. Tareev, “Touchpad with interleaved traces,” U.S. Patent 6 147 680, Nov. 14, 2000

21

12. ^ R. L. Mackey, “Sensor Patterns for a Capacitive Sensing

Apparatus,” U.S. Patent 7 129 935, Oct. 31, 2006.

13. ^ R. B. Fisher and D. K. Naidu, “A comparison of algorithms for

subpixel peak detection,” in Image Technology—Advances in Image

Processing, Multimedia and Machine Vision. NewYork,NY,USA:

Springer-Verlag, 1996, pp. 385–404

14. ^ I. Baharav and R. Kakarala, “Capacitive touch sensing: Signal

and image processing algorithms,” in Proc. SPIE Conf. on Comput.

Imag., San Francisco, CA, USA, Jan. 2011.

22