Principle of touchscreen1.
- 1. PRINCIPLE OF TOUCHSCREEN Arsh Hashmi Anuj Sharma Gaurav Bhandari Deepak Thakur
- 2. 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.
- 3. 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
- 4. 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.
- 6. 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.
- 8. 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.
- 9. 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
- 10. 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.
- 11. TYPES OF RESISTIVE TOUCHSCREEN 4-wire resistive touchscreen 5-wire resistive touchscreen 6-wire resistive touchscreen 7-wire resistive touchscreen 8-wire resistive touchscreen
- 12. 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.
- 14. 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.
- 15. 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
- 16. 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.
- 17. 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.
- 19. 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.
- 20. 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
- 21. 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.
- 23. 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.
- 25. 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.
- 26. 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.
- 28. 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.
- 30. 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.