Touchpad - AbsoluteAstronomy.com

Pointing device

A pointing device is an input interface that allows a user to input spatial data to a computer...

Tactile sensor

The term tactile sensor usually refers to a transducer that is sensitive to touch, force, or pressure. Tactile sensors are employed wherever interactions between a contact surface and the environment are to be measured and registered...

, a specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. Touch pads are a common feature of laptop computers, and they are also used as a substitute for a mouse

Mouse (computing)

In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons...

where desk space is scarce. Because they vary in size, they can also be found on personal digital assistant

Personal digital assistant

A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...

s (PDAs) and some portable media player

Portable media player

A portable media player or digital audio player, is a consumer electronics device that is capable of storing and playing digital media such as audio, images, video, documents, etc. the data is typically stored on a hard drive, microdrive, or flash memory. In contrast, analog portable audio...

s. Stand-alone Trackpads

Magic Trackpad

The Magic Trackpad is a multi-touch trackpad produced by Apple Inc. Announced on July 27, 2010, it is similar to the trackpad found on the current MacBook family of laptops, albeit 80% larger...

are also manufactured for wireless function.

Operation and Function

Touchpads operate in one of several ways, including capacitive sensing

Capacitive sensing

In electrical engineering, capacitive sensing is a technology based on capacitive coupling that is used in many different types of sensors, including those to detect and measure: proximity, position or displacement, humidity, fluid level, and acceleration...

and conductance sensing. The most common technology used entails sensing the capacitive virtual ground

Virtual ground

Virtual ground is a node of the circuit that is maintained at a steady reference potential, without being connected directly to the reference potential...

effect of a finger, or the capacitance between sensor

Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

s. Capacitance-based touchpads will not sense the tip of a pencil or other similar implement. Gloved fingers may also be problematic.

If the computer is powered by an external power supply unit (PSU), the detailed construction of the PSU will influence the virtual ground effect; a touchpad may work properly with one PSU but be jerky or malfunction with another. This has been known to cause touchpad problems when a manufacturer's PSU, which will have been designed to work with the touchpad, is replaced by a different type. This effect can be checked by touching a metallic part of the computer with the other hand and seeing if operation is restored. In some cases touching the (insulated) power supply with some part of the body, or using the computer on the lap instead of on a desk, can restore correct operation.

While touchpads, like touchscreens, by their design are able to sense absolute position, resolution 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

Mouse (computing)

that is lifted and put back on a surface. Hardware buttons equivalent to a standard mouse's left and right buttons are positioned below, above, or beside the touchpad. Netbooks sometimes employ the last in an attempt to save space.

Some touchpads and associated device driver

Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....

software may interpret tapping the pad as a click, and a tap followed by a continuous pointing motion (a "click-and-a-half") can indicate dragging. Tactile touchpads allow for clicking and dragging by incorporating button functionality into the surface of the touchpad itself. To select, one presses down on the touchpad instead of a physical button. To drag, instead performing the "click-and-a-half" technique, one presses down while on the object, drags without releasing pressure and lets go when done. 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 have "hotspots", locations on the touchpad used for functionality beyond a mouse. For example, on certain touchpads, moving the finger along an edge of the touch pad will act as a scroll wheel

Scroll wheel

A scroll wheel is a hard plastic or rubbery disc on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons.- Functionality :...

, controlling the scrollbar

Scrollbar

A scrollbar is an object in a graphical user interface with which continuous text, pictures or anything else can be scrolled including time in video applications, i.e., viewed even if it does not fit into the space in a computer display, window, or viewport...

and scrolling the window

Window (computing)

In computing, a window is a visual area containing some kind of user interface. It usually has a rectangular shape that can overlap with the area of other windows...

that has the focus

Focus (computing)

In computing, the focus indicates the component of the graphical user interface which is currently selected to receive input. Text entered at the keyboard or pasted from a clipboard is sent to the component which currently has the focus. Moving the focus away from a specific user interface element...

vertically or horizontally. Apple uses two-finger dragging for scrolling on their trackpads. Also, some touchpad drivers support tap zones, regions where a tap will execute a function, for example, pausing the media player or launching an application

Application software

Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

. All of these functions are implemented in the touchpad device driver

Device driver

In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....

software, and can be disabled.

History

As touchpads began to be introduced in laptops in the early 1990s, there was often confusion as to what the product should be called. No consistent term was used, and references varied, such as: glidepoint, touch sensitive input device, touchpad, trackpad, and pointing device.
Users were often presented the option to purchase a pointer stick, touchpad, or trackball. Combinations of the devices were common, though touchpads and trackballs were usually included at the exclusion of the other.

Cirque

Cirque Corporation

Cirque Corporation is a Salt Lake City, Utah-based company which developed and commercialized the first successful capacitive touchpad, now widely used in notebook computers. Cirque presently develops and sells a variety of touch input products, both in OEM and end-user retail form. Cirque was...

distributed the first widely available touchpad, branded as GlidePoint. The touchpads included in Apple Computers’ PowerBooks were based upon Cirque’s GlidePoint technology; another early adopter of the GlidePoint pointing device was Sharp. Later, Synaptics

Synaptics

Synaptics develops human interface solutions for many major consumer electronics companies, such as Apple Inc., Asus, Acer, Dell, Gateway, HP, HTC, Lenovo, LG, Logitech, Nokia, Samsung, Sony, Sony Ericsson, Toshiba and several others...

introduced their touchpad into the marketplace, branded the TouchPad. Epson was an early adopter of this product.

Use in devices

Early Apollo

Apollo Computer

Apollo Computer, Inc., founded 1980 in Chelmsford, Massachusetts by William Poduska and others, developed and produced Apollo/Domain workstations in the 1980s. Along with Symbolics and Sun Microsystems, Apollo was one of the first vendors of graphical workstations in the 1980s...

desktop computers were equipped with a touchpad on the right side of the keyboard.

Touchpads are primarily used in self-contained portable laptop

Laptop

A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

computers and do not require a flat surface near the machine. The touchpad is close to the keyboard, and only very short finger movements are required to move the cursor across the display screen; while advantageous, this also makes it possible for a user's thumb to move the mouse cursor accidentally while typing. Touchpad functionality is available for desktop computers in keyboards with built-in touchpads.

One-dimensional touchpads are the primary control interface for menu navigation on the currently produced iPod Classic

IPod classic

The iPod Classic is a portable media player marketed by Apple Inc...

portable music player, where they are referred to as "click wheels" since they only sense motion along one axis which is wrapped around like a wheel. Creative Labs also uses a touchpad for their Zen

Creative Zen

The Creative ZEN is a range of digital audio players and portable media players made by Creative Technology. The players evolved from the now-defunct NOMAD brand through the NOMAD Jukebox series...

line of MP3 players, beginning with the Zen Touch. The second-generation Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

Zune

Zune is a digital media brand owned by Microsoft which includes a line of portable media players, a digital media player software for Windows machines, a music subscription service known as a 'Zune Music Pass', music and video streaming for the Xbox 360 via the Zune Software, music, TV and movie...

product line (the Zune 80/120 and Zune 4/8) uses touch for the Zune Pad

Zune Pad

The Zune Pad, which is a squircle, is the primary control mechanism for Zune 4, 8, 16, 80 and 120. The pad lets users scroll through a long list of songs with a few flicks of the finger, then press the button to select tracks or change the volume....

.

Apple's PowerBook 500 series was the first laptop to carry such a device, which Apple refers to as a "trackpad". When introduced in May 1994 it replaced the trackball

Trackball

A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor...

of previous PowerBook

PowerBook

The PowerBook was a line of Macintosh laptop computers that was designed, manufactured and sold by Apple Computer, Inc. from 1991 to 2006. During its lifetime, the PowerBook went through several major revisions and redesigns, often being the first to incorporate features that would later become...

models. Apple's more recent laptops feature trackpads that can sense up to eleven fingers simultaneously, providing more options for input, such as the ability to bring up the context menu

Context menu

A context menu is a menu in a graphical user interface that appears upon user interaction, such as a right mouse click or middle click mouse operation...

by tapping two fingers. In late 2008 Apple's revisions of the MacBook

MacBook

The MacBook was a brand of Macintosh notebook computers built by Apple Inc. First introduced in May 2006, it replaced the iBook and 12-inch PowerBook series of notebooks as a part of the Apple–Intel transition. Positioned as the low end of the MacBook family, the Apple MacBook was aimed at the...

and MacBook Pro

MacBook Pro

The MacBook Pro is a line of Macintosh portable computers introduced in January 2006 by Apple. It replaced the PowerBook G4 and was the second model, after the iMac, to be announced in the Apple–Intel transition...

incorporated a "Tactile Touchpad" design with button functionality incorporated into the tracking surface.

Psion PLC

Psion PLC

Psion is a designer and manufacturer of rugged mobile handheld computers for commercial and industrial applications. The company is headquartered in London, England with major operations in Mississauga, Ontario, Canada and additional company offices in Europe, the United States, Asia, Latin...

's Psion MC 200/400/600/WORD Series, introduced in 1989, came with a new mouse-replacing input device similar to a touchpad, although more closely resembling a graphics tablet

Graphics tablet

A graphics tablet is a computer input device that enables a user to hand-draw images and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures...

, as the cursor was positioned by clicking on a specific point on the pad, instead of moving it in the direction of a stroke.

Theory of operation

There are two principal means by which touchpads work. In the matrix approach, a series of conductors

Electrical conductor

In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

are arranged in an array of parallel lines in two layers, separated by an insulator and crossing each other at right angle

Right angle

In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two halves of a straight line. More precisely, if a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles...

s 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

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

. When a virtual ground

Virtual ground

Virtual ground is a node of the circuit that is maintained at a steady reference potential, without being connected directly to the reference potential...

, such as a finger, is placed over one of the intersections between the conductive layer some of the electrical field is shunted

Shunt (electrical)

In electronics, a shunt is a device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.-Defective...

to this ground point, resulting in a change in the apparent capacitance at that location. This method received awarded to George Gerpheide in April 1994.

The capacitive shunt method, described in an application note by Analog Devices

Analog Devices

Analog Devices, Inc. , known as ADI, is an American multinational semiconductor company specializing in data conversion and signal conditioning technology, headquartered in Norwood, Massachusetts...

, senses the change in capacitance

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.

Operation and Function

History

Use in devices

Theory of operation

See also