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Prepared by: Spencer Jackson Dept. of Electrical and Computer Engineering Utah State University

ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Projected Capacitance Touchscreen (PCT) sensor. Prepared by: Spencer Jackson Dept. of Electrical and Computer Engineering Utah State University

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Prepared by: Spencer Jackson Dept. of Electrical and Computer Engineering Utah State University

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  1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Projected Capacitance Touchscreen (PCT) sensor Prepared by: Spencer Jackson Dept. of Electrical and Computer Engineering Utah State University E: ssjackson71@gmail.com; T: (435)797-2757; F: (435)797-3054 (ECE Dept.) 3/11/2010

  2. Outline • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration in application (application notes) • Major specifications • Limitations • And many more relevant issues in applications (such as, how to choose, cost information, where to buy etc.) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Reference list • howstuffworks.com • http://electronics.howstuffworks.com/iphone.htm • Wikipedia • http://en.wikipedia.org/wiki/Touch_screen#Projected_capacitance • http://en.wikipedia.org/wiki/Capacitive_sensing • Freepatentsonline.com • http://www.freepatentsonline.com/20060097991.pdf ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. To explore further (survival pointers of web references etc) • howstuff works.com • http://electronics.howstuffworks.com/iphone.htm • Youtube • http://www.youtube.com/watch?v=6GidQX9VjIQ&feature=fvw • http://www.youtube.com/results?search_query=Iphone+multiple+touch&search_type=&aq=f ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. Major applications • Touch Screens • Consumer Products: • iPhone/iPod Touch • Motorola Droid • Palm Pilot • Microsoft Zune • Google Nexus One • Information Kiosks • Point of Sale Terminal (register) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. Major Applications http://www.apple.com/iphone/buy/ http://www.google.com/phone/static/nexus-one-specs-shot.png http://upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Pixi.png/250px-Pixi.png http://www.visualplanet.biz/graphics/touch/touchfoil38_thumb.jpg http://www.sharpusa.com/ForBusiness/POSSolutions/PointOfSaleSystems/UPX300C.aspx ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Working Principle • Projected Capacitance touchscreens (PCT) sense a change of capacitance on or near their surface • Rows and columns of sensors act like many sensors in a grid • Capacitance increases when the body comes close (due to the high water content of humans) • Continual charge/discharge cycle detects changes • Interpretation of multiple touches on a screen is software intensive ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. Advantages of PCT • Rigid screen is durable • Sleek feel • High accuracy • Multiple touch, and gesture sensing • No stylus to lose ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Capacitive vs. Resistive Touchscreen • Capacitive • Two separate conducting layers have a capacitive charge • Placing a finger on/near the screen changes the capacitive charge held by the layers • Can use rigid surface (glass) • Resistive • Two conductive layers are separated by a small gap • Pressure on the screen surface causes a connection between layers changing resistance • Must have flexible screen surface ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. Capacitive vs. Resistive Touchscreen http://www.eetasia.com/ARTICLES/2007JUL/C/EEOL_2007JUL09_STECH_INTD_NP_fig1.jpg http://static.howstuffworks.com/gif/iphone-11.gif ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. Projected vs Surface Capacitance • Projected (PCT) • Grid on layers creates an xy table of small capacitive screens or sensors • Can detect multiple touches, higher accuracy and even motions made above the sensor • Requires much more advanced signal processing • Standard • Sensor usually only measures changes of capacitance along one axis at corners • Simple but not very accurate • Only single touches allowed ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. 2 Methods of PCT http://static.howstuffworks.com/gif/iphone-8.jpg http://static.howstuffworks.com/gif/iphone-9.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. 2 Methods of PCT • Rows of drivers and columns of sensors • Easier to make many rows and columns • Mutual capacitance means the capacitive interaction between the driver and sensor • Change in capacitance effects the charge stored • Matrix of electrodes • Easier to tell where individual touches are • Self capacitance means each electrode is charged and discharged in a read cycle • Change in capacitance due to touch effects the discharge time ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. Signal Processing http://static.howstuffworks.com/gif/iphone-10.gif ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. Application Notes • Be prepared for signal processing • Noise reduction • Edge detection • Motion detection • Multiple inputs (touches) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Major Specifications • Projection – some require surface contact others project up to 20mm away • Size and resolution (size~inches to feet, resolution~mm) • Clarity – ability to see display underneath (90% light transmission) • Software included – may or may not support multi-touch ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Limitations • Oil from fingers traps dust on screen which interferes with capacitance • Cannot be used with stylus or non-conductive material (most gloves) • Requires powerful signal processor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Availability • Sizes range from a few inches to 18 feet [1] or more • Prices range from dollars in bulk to a few thousand dollars for a large screen (with display) [1] http://multi-touch-screen.com/store_wall.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Availability • Not readily available for hobbyists • Tear up an iphone or other consumer product • In bulk buy from: • http://www.zytronic.co.uk/index.php • http://www.elotouch.com • http://multi-touch-screen.com/store_accessories.html • Apple’s supplier: Balda AG [1] [1] http://texyt.com/iphone+manufacturer+supplier+assembler+not+apple+00113 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  20. Conclusion • Mostly for human interaction • For applications like limit switches a traditional capacitive sensor is more than adequate • Offers many advantages over other touch screen methods ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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