Touch
Introduction
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Driver
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4-Wire Resistive Touch Panel Four-wire resistive touch panel uses the principal of voltage drop to detect the coordinate on the panel. The structure of 4-wire resistive touch panel consists of electrically conductive film as top layer, electrically conductive glass as bottom layer, and spacer dot between the two layers. During operation, a 5V electrical current is applied to the conductive film and conductive glass. When the user presses the touch panel with finger or stylus, voltage change occurs. This action triggers top conductive film to provide X (or Y) axis and bottom conductive glass to provide Y (or X) axis, thus report back the coordinate of the touch taken place.
5-Wire Resistive Touch Panel Five-wire resistive touch panel constructs of electrically conductive film on top and electrically conductive glass at bottom, separated by spacer dot in between. Compare to 4-wire resistive, the four corners of the bottom conductive glass in a 5-wire resistive also have the function to detect electric current flow. During operation 5V electrical current is applied to the conductive film and conductive glass. When the user presses the touch panel with finger or stylus, top film and bottom glass will conduct to form electrical signal. The bottom conductive glass calculates XY coordinates with the position of the current flow and the distance among the four corners, thus calculates the position of the touch taken place.
8-Wire Resistive Touch Panel The principal of 8-wire resistive touch panel is actually the same as 4-wire. Four-wire resistive touch panel has one lead wire at each of the four sides, with total of four lead wires. However, surrounding environment or electronic devices may affect the interpretation of voltage on 4-wire resistive, which influences the accuracy of the coordinates. To overcome this problem, 8-wire resistive touch panel has two lead wires at the four sides, total of eight lead wires, to strengthen the accuracy of voltage reading, thus enhance the accuracy of the coordinate.
Surface Capacitive Touch Panel Surface capacitive touch panel uses a piece of electrically conductive glass, with four corners of the glass that can detect electric current flow. During operation, small amount of voltage is applied to the conductive glass. When the user uses finger to touch the touch panel, the human body will absorb very light amount of electrical current. At the same time, the conductive glass calculates XY coordinates with the position where electrical current is absorbed and the distance among the four corners, thus calculates the position of the touch taken place.
Projective Capacitive Touch Panel Projective capacitive is also called matrix capacitive or digital capacitive. The well-known APPLE multi-touch uses the application of such technology. Matrix capacitive can be viewed as a panel with hundreds or thousands of independent, transparent sensor switches to detect ON/OFF signal transmission. When the finger touches the touch panel, it turns on some of the switches, and the touch IC will use these switches to determine touch gestures. This technique requires transparent lead wire design, usually processed by lithography, sputtering, etc., results in more sophisticated wiring, which is best-suited for small size application. The key to this technology lies with the touch IC in use; however, each IC supplier has different advantages in multi-touch interpretation, displacement interpretation, handwriting interpretation, etc. Currently there is no mainstream specification.
Surface Acoustic Wave (SAW) Touch Panel Surface acoustic wave (SAW for short), as implied in the name, uses ultrasonic wave as medium to locate position on the touch panel. SAW touch panel consists of ultrasonic transmitting transducer, ultrasonic receiving transducer, reflection stripes, and SAW touch controller. The controller first transmits 5MHz electric signal to transmitting transducer. Then the transducer converts the signal to ultrasonic wave and spreads throughout the touch panel. When the ultrasonic wave hits the reflection stripes, the wave changes the path and ultimately goes to the receiving transducer, and the receiving transducer converts the wave back to electrical signal and stores data into the controller. When finger touches the touch panel, it absorbs portion of the ultrasonic wave, resulting in energy difference between transmitting and receiving transducer. The controller then uses the energy difference to calculate the coordinate.
Infrared (IR) Touch Panel Infrared touch panel uses infrared as medium to locate position on the touch panel, and the touch panel consists of infrared backlight and infrared receptor located at the four edges. During operation the touch panel is covered with light beams in matrix arrangement. When finger or stylus touches the touch panel, it blocks part of the light, and receptor cannot sense the light beam. Touch panel then locate the touch by calculating the position of the light beam blockage.
Digital Type Touch Panel Digital type touch panel applies the simplest touch sensor principal. The structure of digital type touch panel is the same as 4-wire resistive touch panel, with conductive film on top, spacer dot in the middle, and conductive glass at the bottom. Manufacturer first design the active area of the touch panel. The conductive top film and bottom glass are processed by etching X and Y axis wires independently, and then both layers are separated by spacer dot in between to form open circuit. During operation, the user presses onto the active area of the touch panel, forcing the open circuit (off) to short circuit (on), and then sending the signal to the computer to operate. Digital type touch panel is suitable for electronic devices with simple application interface, such as remote control, calculators, etc.
Electromagnetic Digitizer Electromagnetic digitizer operates based on electromagnetic sensing; it involves the use of an electromagnetic pen that functions as a signal transmitter while the electromagnetic board acts as a receiver. When the transmitter is brought close to the panel surface, the change in magnetic flux is registered for the system to compute and define the coordinates of the touch event.
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AiM TOUCH Taiwan All Rights Reserved
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