Tuesday, January 5, 2010
The touchscreen panel is capacative, which means that it requires electro-connectivity in our fingers in order to work. A capacitive touchscreen panel consists of an insulator, e.g. glass, coated with a transparent conductor such as indium tin oxide (ITO). Indium tin oxide is a solid solution and is transparent and colourless in thin layers. As the human body is also a conductor, touching the surface of the screen results in a distortion of the local electrostatic field, measurable as a change in capacitance. Different technologies are used to determine the location of the touch. The location can be passed to a computer running a software which will calculate how the user's touch relates to the computer software.
There are 2 types of capacitance, surface capacitance and projected capacitance. In surface capacitance, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a human finger touches the uncoated surface, a capacitor is dynamically formed. A capacitor is a passive electronic component consisting of a pair of conductors separated by a insulator. The sensor's controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel. As it has no moving parts, it is moderately durable but has limited resolution, which means that it is prone to false signals from parasitic capacitive coupling, and needs calibration during manufacture.
*Parasitic Capacitive Coupling: One signal can capacitively couple with another and cause noise. To reduce coupling, wires are separated as much as possible. Ground planes can also be run between signals that might affect each other.
Surface Capacitance:
Projected Capacitive Touch (PCT) technology is a capacitive technology which permits more accurate and flexible operation, by etching the conductive layer. Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. An XY array is formed either by etching a single layer to form a grid pattern of electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form the grid. Applying voltage to the array creates a grid of capacitors. Bringing a finger near to the surface of the sensor changes the local electrostatic field. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location. The use of a grid permits a higher resolution than resistive technology and also allows multi-touch operation. The greater resolution of PCT allows operation without direct contact, such that the conducting layers can be coated with further protective insulating layers, and operate even under screen protectors, or behind weather and vandal-proof glass. A gloved hand can also register a touch on the sensor surface through a glass window.
Projected Capacitance:
Solving the problem:
Sew some conductive thread in small patches on the fingers of the glove (circle of about 6mm in diameter) and larger patches on the inside area of the fingertip.
+ [ written by SEOWHWEE ] + 3:45 AM