Implementation of capacitive touch screen in smart devices
- 1. Implementation of Capacitive touchscreen in Smart devices Aseem Avinab 1st Year M.Tech Power Electronics and Drives Id- RA1412011010029 1
- 2. 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
- 3. 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
- 4. 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
- 5. 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
- 6. Types of Touch screen Resistive Touch Screen Infrared Touch Screen Surface Acoustic Wave Touchscreen Capacitive Touch Screen 6
- 7. 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
- 8. Infrared Touch Screen Uses 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
- 9. 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
- 10. 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
- 11. 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
- 12. 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
- 13. 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
- 14. Sub pixel interpolation algorithms for single pixel touch An 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
- 15. 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
- 16. Comparison between grid pattern Using diagonal movement 16
- 17. Using circular movement 17
- 18. 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
- 19. 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
- 20. References 1. ^ 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
- 21. 6.^ Larry K. Baxter (1996). Capacitive Sensors(http:// books.google.com/books?id=Tjd2laRnO4wC&pg=PA138&dq=capac itive+sensors+mouse&lr=&as_brr=3&as_pt=ALLTYPES&ei=sMOA Se 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
- 22. 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