Apple touchpad
Touchpads operate in one of several ways, including capacitive sensing and conductance sensing. The most common technology used today entails sensing the capacitance of a finger, or the capacitance between sensors. Because of the property being sensed, capacitance-based touchpads will not sense the tip of a pencil or other similar implement. Gloved fingers will generally also be problematic (such as in a cleanroom environment).
While touchpads, like touchscreens, by their design are able to sense absolute positions, precision is limited by their size. For common use as a pointer device, the dragging motion of a finger is translated into a finer, relative motion of the cursor on the screen, analogous to the handling of a mouse that is lifted and put back on a surface. The buttons are below, above or sideways — the latter is often[original research?] used for compact devices, such as Netbooks — for the pad serve as standard mouse buttons. Depending on the model of touchpad and drivers behind it, you may also click by tapping your finger on the touchpad, and drag with a tap followed by a continuous pointing motion (a "click-and-a-half"). Touchpad drivers can also allow the use of multiple fingers to facilitate the other mouse buttons (commonly two-finger tapping for the center button).
Some touchpads also have "hotspots": locations on the touchpad that indicate user intentions other than pointing. For example, on certain touchpads, moving the finger along an edge of the touch pad will act as a scroll wheel, controlling the scrollbar and scrolling the window that has the focus vertically or horizontally depending on which edge is stroked. Apple uses two-finger dragging gesture for scrolling on their trackpads. However, these are driver dependent functions and can be disabled. Also, certain touchpad drivers allow for tap zones, regions whereby a tap will execute a function. For example, pausing the media player or launching an application.
Theory behind operation
There are two principal means by which touchpads work. In the matrix approach, a series of conductors are arranged in an array of parallel lines in two layers, separated by an insulator and crossing each other at right angles to form a grid. A high frequency signal is applied sequentially between pairs in this two-dimensional grid array. The current that passes between the nodes is proportional to the capacitance. When a virtual ground, such as a finger, is placed over one of the intersections between the conductive layer some of the electrical field is shunted to this ground point, resulting in a change in the apparent capacitance at that location. This method received U.S. Patent 5,305,017 awarded to George Gerpheide in April 1994.
The capacitive shunt method, described in an application note by Analog Devices,[6] senses the change in capacitance between a transmitter and receiver that are on opposite sides of the sensor. The transmitter creates an electric field which oscillates at 200-300 kHz. If a ground point, such as the finger, is placed between the transmitter and receiver, some of the field lines are shunted away, decreasing the apparent capacitance.
Multi Touchpad
Scrolling TrackPad is the name for one of Apple Inc.'s patent-pending trackpads, used in their MacBook and MacBook Pro laptop computers. They were previously used in the PowerBook and iBook lines, prior to Apple's switch to Intel processors. It lets users scroll in an arbitrary direction by touching the pad with two fingers instead of one, and then moving their fingers across the pad in the direction they wish to scroll. For comparison, many laptop touchpads instead set aside an area along the right edge and bottom edge of the pad, and moving a single finger in these areas performs a vertical or horizontal scroll operation, respectively. Current MacBooks, MacBook Pros and MacBook Airs have a Multi-Touch pad.
Compaq touch-pad
