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Touchpad

technology Maturity 11-13 Next article →

A touchpad, also called a trackpad, is a specialized pointing device. It uses a flat surface containing a tactile sensor to detect finger position and motion. This sensor translates physical movements into 2D motion on a computer screen. This motion controls a pointer within a graphical user interface. While desktop computers usually rely on mice, touchpads are the standard for laptop computers. They are useful because they occupy very little space. This small size allowed them to be used in portable media players and personal digital assistants (PDAs).

Macbook touchpad
Macbook touchpad

Most modern touchpads function through capacitive sensing. This technology relies on the electrical properties of the human body. When a finger touches the pad, it causes a change in capacitance, which is the ability to store an electrical charge. Because of this, capacitive touchpads will not detect a pencil or other ungrounded, non-conducting tools. They also struggle to sense fingers covered by insulating gloves. This is why capacitive sensing is rarely used for medical hardware. While touchpads sense an absolute position, their resolution is limited by their physical size. To move a cursor across a large screen, users use a dragging motion. This creates a relative motion, similar to how a user might lift and reposition a computer mouse.

Acer CB5-311 series touchpad
Acer CB5-311 series touchpad

There are different ways to design the physical and logical interface of a touchpad. Some models feature hardware buttons located next to the pad, acting like standard mouse buttons. Other designs are called clickpads. In a clickpad, the entire surface acts as a button. The device driver software then interprets a click as a left or right click based on where the fingers land. Some advanced touchpads are tactile. These incorporate clicking functionality directly into the surface itself. To select an item, a user presses down on the surface. To drag an item, the user presses down, maintains pressure while moving, and then releases.

Surface RT
Surface RT

Modern technology has introduced even more complex ways to interact with these surfaces. Many touchpads now feature multitouch capabilities. This allows the sensor to detect up to five fingers at the same time. Users can use specific gestures, such as two-finger tapping to trigger a right-click or two-finger dragging to scroll. Some devices also include "hotspots." These are specific locations on the pad assigned to special functions. For example, sliding a finger along the edge of a pad can act as a scroll wheel. Drivers can also support "tap zones," where a quick tap executes a specific command like pausing media.

Touchpad at keyboard G80-11900 by Cherry GmbH
Touchpad at keyboard G80-11900 by Cherry GmbH

The history of the touchpad involves many different companies and evolving designs. In 1980, Xerox introduced one of the first touchpads on the Xerox 860 workstation. This circular device was called the "Cat," which stood for capacitance-activated transducer. By 1982, Apollo desktop computers included touchpads on their keyboards. In 1983, the Gavilan SC became the first battery-powered clamshell laptop to feature a touchpad. Interestingly, this model mounted the pad above the keyboard, which is different from the standard placement used today. In 1994, Cirque introduced the GlidePoint, the first widely available touchpad. That same year, Apple released the PowerBook 500 series, which used GlidePoint technology and introduced the term "trackpad."

Curve8520TrackPad
Curve8520TrackPad

Engineers use two principal methods to make these devices work: the matrix approach and the capacitive shunt method. In the matrix approach, conductors are arranged in a grid of parallel lines across two layers. A high-frequency signal is sent through this grid. When a finger acts as a virtual ground, it shunts the electrical field, changing the capacitance at that intersection. This method was awarded to George Gerpheide in April 1994. The capacitive shunt method senses changes in capacitance between a transmitter and a receiver on opposite sides of the sensor. The transmitter creates an electric field that oscillates at 200 to 300 kHz. If a finger is placed in the path, it shunts the field lines and decreases the apparent capacitance.

Touchpads are now found in a wide variety of electronics beyond standard laptops. Some are one-dimensional, meaning they only sense motion along one axis. This is seen in the "click wheels" of iPod Classic players and the Zune Pad on Microsoft Zune products. Even smartphones have utilized this technology, such as the optical trackpads on BlackBerry Curve devices. Recently, on September 9, 2024, Apple introduced a new one-dimensional trackpad on the iPhone 16 series called "Camera Control." This component uses a force sensor to detect pressure and a capacitance sensor to detect sliding motions for adjusting camera settings like zoom or exposure.

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🖼️ Images & Media (5)
File:Acer CB5-311 series touchpad.jpg
Acer CB5-311 series touchpad.jpg
File:Macbook touchpad.jpg
Macbook touchpad.jpg
File:Touchpad at keyboard G80-11900 by Cherry GmbH.jpg
Touchpad at keyboard G80-11900 by Cherry GmbH.jpg
File:Curve8520TrackPad.jpg
Curve8520TrackPad.jpg
File:Surface_RT.jpg
Surface_RT.jpg
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