Touchpad

The touchpad, like other pointing devices ( pointing device ), is usually used to control the menu “ cursor ” (portable electronics), mouse “ pointer ” (computers) or to replace some keyboard keys . Finger movements on the device surface are converted into “cursor” / “pointer” movements on the screen. Touching the surface simulates mouse clicks or keyboard keys .

Touchpads can be placed next to the keyboards of various devices: computers , laptops , electronic keyboard musical instruments , mobile devices.

Touchpads can be placed on the dashboards of consumer and industrial equipment, can be remote (made as separate devices connected to a computer via PS / 2 , USB , proprietary RMI or other), can be made transparent and placed on top of the display (see touch screen ).

Sensitive touchpad surfaces are most often made in the form of a rectangle with rounded corners, but there are also models with surfaces of other shapes (for example, in the form of a circle ). Usually, the touchpad surface does not exceed 50 cm ² .

For a long time, manufacturers could not choose a common name for touchpads of various designs. The terms “glidepoint”, “touch sensitive input device”, “touchpad”, “trackpad” and “pointing device” ^{[2] [3] [4] were used} .

In 1982, the company Apollo Computer equipped its computers for workstations with keyboards, on the right side of which a touchpad was placed ^[5] . A year later, Gavilan SC put the touchpad on top of its keyboards.

In 1988, George Gerfayde ( born George E. Gerpheide ) invented a type of touchpad ^[6] .

In 1989, a touchpad version was developed for the Psion MC 200/400/600 / WORD series of computers ^[7] .

In 1994, the company Cirque Corporation ( English ) released the first touchpad, which became widespread and known under the name "GlidePoint" ^[8] .

In May 1994, Apple Inc. used the GlidePoint touchpad in the PowerBook series ^[9] laptops (see photo ), replacing the trackball with them. After some time, the touchpad series developed by Apple itself and called “trackpads” began to be used in the “ PowerBook ” and “ MacBook ” notebook series.

GlidePoint also used Sharp ^[8] in its products.

Soon, Synaptics brought touchpads, known as the TouchPad, to the market.

Touchpad «TouchPad» in their products used the company Epson ^[8] .

Since the 1990s, touchpads have been used in laptops .

Alternatives to the touchpad on laptops are:

• strain gauge joystick ( pointing stick );
• “ Trackball ” ( eng. Trackball ).

Devices that contain both a touchpad and a “ trackball ” are rarely found ^[10] .

Since its inception, the touchpad has become the most common mouse pointer control device for laptops.

The work of the touchpad is based on measuring the electrical capacity between the finger and the sensor, or between two sensors. Capacitive sensors are located along the vertical and horizontal axes of the touchpad, which allows to determine the position of the finger with the desired accuracy. The sensitive surface of the device is a grid of two layers of metal conductors separated by a layer of thin insulating gasket. The gasket is a polyester film. The conductors in one layer are parallel to each other; layers of conductors are arranged so that conductors from one layer are perpendicular to conductors from another. Two layers of conductors play the role of plates, and the strip plays the role of a dielectric; capacitors are formed at the intersection of perpendicular conductors.

After switching on the device between the capacitor plates an electric field is formed. Preparation of the device for operation begins. The microcontroller supplies voltage to two conductors located in different layers, measures the resistance between them, memorizes the measured value in memory, then stops supplying the voltage and supplies voltage to the other two conductors located in different layers. This is repeated until the microcontroller measures and maintains resistance between each pair of conductors located in different layers.

Next, the device goes into normal operation. The microcontroller continues to measure the resistance between pairs of conductors, but now compares the measured values ​​with those stored in memory. The time it takes for the microcontroller to “take readings from all sensors” ( period T or frequency ν = 1 / T ) is one of the characteristics of the touchpad.

The human body is a good conductor. When a finger approaches the sensitive surface, the finger acts as a capacitor plate; for capacitors located near the finger, there is a change in the electric field, and, accordingly, in capacity. The microcontroller measures the resistance between pairs of conductors and compares the measured values ​​with those stored in memory. Analyzing the deviations of the measured values ​​from the saved microcontroller can determine the coordinates (X, Y) of the touch point and the pressure (Z) exerted on the surface. This is possible due to the fact that the greater the pressure applied to the surface or the greater the number of fingers near the surface, the greater the total capacitance of the capacitor formed by the surface of the device and the finger.

The capacity of the grid capacitors is influenced not only by the finger, but also by external electric fields, and other physical effects. As a result, the capacity is constantly changing ( shaking , eng. Jitter ). To eliminate the jitter of measured values, “filtering” algorithms are used. Algorithms replace sudden changes in measured values ​​with smooth (smooth). Most often, a simple algorithm, called the “averaging window” algorithm, is used. According to this algorithm, the value of the current coordinates is determined by averaging the last two not smoothed values ^[11] :

X _current = (U _new + U _previous ) / 2 ,

Where:

• X _current - smoothed value;
• U _new , U _previous - measured and not smoothed values.

To increase the degree of smoothing of jitter, averaging of three or more new (just measured and not smoothed) values ​​is used or weighted algorithms are used, for example, such:

X _current = 1/2 U _new + 3/4 U _previous .

By measuring the total capacity, you can determine the degree of depression, that is, the third Z coordinate. If there is no finger on the sensitive surface, the Z coordinate is zero. To determine the movement of a finger, the device controls the increase in the Z coordinate over a certain threshold, then calculates the change in the X and Y coordinates until the moment Z equals zero, which corresponds to the end of the movement and the distance of the finger from the sensitive surface of the device. The resulting values ​​of ΔX and ΔY are used further to move the pointer displayed on the screen.

Using the driver software , the touchpad capabilities can be greatly enhanced, but these functions must be supported by the hardware by the touchpad itself. For example, it becomes possible to imitate mouse clicks , imitate mouse wheel rotation, use gestures and multitouch .

List of some features:

• drag and drop (incomplete double tap with one finger sliding);
• pressing the right mouse button (short pressing with two fingers);
• pressing the middle mouse button (short pressing with three fingers);
• mouse wheel rotation (vertical scrolling) (sliding with two fingers);
• vertical scrolling (sliding one finger along a section located on the edge of the sensitive surface on the right or left);
• horizontal scrolling (sliding with one finger along a section located at the edge of the sensitive surface from above or below);
• increase or decrease (sliding of two fingers along a straight line towards each other or each other);
• coup (touch with one finger, sliding with the second finger around the first one in a circle);
• turning over (light touch with three fingers when moving from left to right or right to left);
• emulation of key presses of additional keyboard keys (for example, “Play”, “Pause”, “Search”, “Email”).

Moving your finger along the touchpad to the edge of the sensitive surface and holding it near it can be perceived as a gesture to automatically move the “pointer” in a given direction at a constant speed.

You can disable the laptop's touchpad by pressing the Fn + Fxx key combination, where:

• the Fn key is located next to the Ctrl key;
• Fxx is one of the keys from F1 to F12 .

On some laptops, the touchpad is disabled by a separate button.

Touchpads are fairly low- resolution devices. Allowing touchpads is enough to play logic games, for everyday work with office applications and web browsers , but not enough to work with graphic programs , and makes it almost impossible to play 3D shooters .

• Alps Electric (eng.) . Trade names of touch panels: StickPointer ™, GlidePoint ™, GlidePad ™.
• Cirque Corporation (Eng.) - A subsidiary of Alps Electric .
• Synaptics (English) . TouchPad ™, ClickPad ™, ForcePad ™, SecurePad ™ ^[1] family of devices.
• ElanTech .

• Graphics tablet
• Magic trackpad
• Multitouch
• Touch screen