How Do Touch Screens Work?
From mall kiosks to mobile devices, touch screens are everywhere. But how do they work? Today’s Wonder of the Day was inspired by Cohen.
Four-wire resistive touchscreens use the upper and lower layers of the screen “sandwich” to determine X- and Y-axis coordinates. These are based on voltages that are measured by the conductive layer of the polyester coversheet.
Dispersive signal technology
Unlike other touch technologies that distribute an optical field, infrared beams or acoustic waves across the surface and wait for a finger to interrupt their signal, dispersive signal technology detects touch locations passively. This approach makes the system much more resistant to contaminants and static objects. Furthermore, it is unaffected by scratches and other damage to the screen.
The underlying principle of this technology is the piezoelectric effect, a voltage generated when mechanical force is applied to a material. The touchscreen consists of two transparent electrically resistive layers with a gap between them. When a finger touches the screen, the gap closes and the current passes through the screen’s electrode. The system records this change in the screen’s current and converts it into a command.
This system is based on the same principles as other projected capacitance methods, but with some differences. The main difference is the number of rows and columns of sensing electrodes. The system requires a minimum of 16 x 14 x/y capacitance measurements to determine the location of a single finger. This is because the sensor uses both layers to generate the voltage slopes and sense the voltage as shown in Figure 2a. The system also requires four or five-wire structures to apply and sense the voltages. Four-wire structures use the same layer to apply and sense the voltage, while five-wire ones use one layer to apply the voltage and the other to sense it.
Infrared technology
Infrared technology uses an invisible grid of light beams to determine the location of a touch. When a finger or stylus touches the screen, it interrupts the light beams, which are sensed by photo sensors. These sensors are then able to recognize the touch and send the appropriate signal. Infrared touchscreens do not require a special electrode film and can be used with any kind of transparent object, including bare fingers and thin medical gloves. In addition, they can support multiple-touch inputs.
Projected capacitance touchscreens use electrode plates with a conductive and resistant layer that detects the pressure of a finger or stylus. The sensor generates a combined signal based on the position of the touch and the relative velocity. This signal is then digitized and compared to a list of signals corresponding to different locations on the display. Touch screen If the digitized signal matches a specific position on the screen, then the touch is detected.
This technology is commonly used in touchscreens for ATM, factory automation, and plant control systems. It is also widely used in kiosks, ticketing machines, and other large-size applications. This technology is more durable and withstands a wide range of environmental conditions, such as high temperatures and humidity. However, it can be susceptible to dust and water. This may cause erroneous commands to be triggered.
Acoustic pulse recognition
Acoustic pulse recognition is a touch technology that uses acoustic signals to recognize touch locations. It is used on touchscreens for fingers, styluses, and gloves and is resistant to water and contaminants on the screen. It also supports dragging and palm rejection during signature capture. It also has the lowest cost among all touch technologies and is scalable from PDA to 42-inch displays.
The system consists of a screen with a capacitive sensor and a host processor. The sensor detects the position of a finger or stylus by detecting changes in the output voltages of charge amplifiers in the SE lines. These changes are caused by the reduction on the mutual capacitance caused by the presence of a finger. The changes are then transmitted to the host processor via a multiplexer, which then converts them into digital data.
The resistance scheme has been in use for many years and is the most common method for detecting touchscreen locations. It uses four conductive layers separated and crossed in the shape of a matrix. The corners of each layer are connected to perfectly synchronized alternative current (AC) voltage sources, and the touch location is extracted by sampling the difference in the AC signals from these voltage sources at the touched area. Its drawback is that it cannot detect ghost touches and requires an external sensor for calibration. Another option is the projected capacitance scheme, which uses two patterned conductive layers. These layers overlap in horizontal and vertical patterns to detect the touch position. The overlapping areas of these patterns are then converted into x- and y-axis coordinates.
AccuTouch
Designed for high-use environments, AccuTouch touchscreen technology uses clear glass, a stable bottom layer and a flexible cover sheet that makes it more durable than conventional resistive touchscreens. It is scratch resistant and impervious to liquid spills and splashes, humidity and washdown, making it an excellent choice for Touch screen point-of-sale, industrial and medical applications. AccuTouch touchscreens also feature a robust optical surface and a ruggedized design, making them suitable for harsh use in public environments such as lobbies, way-finding or kiosks.
The screen’s conductive coating makes electrical contact when touched by fingernails, gloves, styluses or credit cards. Touches are detected by the conductive layer’s ability to absorb electromagnetic signals, which generates voltages at the edges of the touchscreen. An electronic controller converts these voltages into digital X and Y coordinates that are transmitted to the host computer.
Four-wire resistive screens are the simplest to understand and manufacture. These screens consist of a touchscreen “sandwich” with a stable bottom substrate and a polyester cover sheet that features tiny insulating dots between the layers. The upper and lower layers are coated with uniform indium tin oxide (ITO) with silver bus bars along the edges. The combination of these layers sets up lines of equal potential in both the X and Y axes.
Elo’s state-of-the-art factory produces its own touchscreens, ASICs and touchscreen controllers. Its patented zero-bezel design eliminates the front-bezel, achieving a smooth flat integration for an attractive, modern appearance.
