Many people, especially the middle and young age, are actively using smartphones, tablets and other gadgets with an intelligent display. However, few of them thought about the principle of operation of the touch screen and their varieties. Let's try to understand this in more detail.
History of invention
The world's first prototype touchscreen device was used by Sam Harst, a teacher from the United States. In 1970, he developed the idea of reading data from a large number of tape recorders. Automation of this process has become a kind of springboard for the creation of touch monitors, known as Elotouch. The development of a group of Hurst colleagues was published in 1971, which included resistive four-wire technology for determining touch points.
The first computer sensor is considered the PLATO IV system. She also came to the United States, as a result of special studies related to the computerization of education. It consisted of a block panel (256 pieces), operated on the principle of using a grid of infrared streams.
Description
The touch display is an electronic element that visualizes digital information through a tangential action to the surface of the monitor. Different types of these structures respond to several points or one specific factor (change in capacitance and resistance, thermal difference, special pointer).
According to the principle of operation, touch screens are divided as follows:
- Resistive versions.
- Matrix models.
- Capacitive options.
- Surface acoustic modifications.
- Optical sensors and their varieties.
Consider the common models of displays of this category, scope, features and benefits.
How Resistive Touch Screens Work
This is the easiest type of monitor. He reacts to the transformation of the resistance force in the area of contact of a certain object and the surface of the display. The most common and elementary technology includes two main elements in its design:
- The backing panel is made of polyester or a similar polymer, the thickness of which does not exceed several tens of molecules. A transparent part is used to conduct current particles.
- Thin-layer light guide membrane.
Both layers are coated with a special resistive coating. Between them are microscopic ball-shaped insulators.
During operation, the membrane bends, in contact with the substrate, as a result of which the circuit closes. A controller with an analog-to-digital converter responds to the operation, calculating the value of the initial and current resistance, as well as the coordinates of the contact point. Such devices quickly showed their negative sides, as a result of which the engineers improved the design by adding a fifth wire.
Using
Thanks to the simplest principle of the resistive configuration touch screen, it is used everywhere. Design Features:
- low cost;
- resistance to environmental influences, with the exception of negative temperatures;
- good response to contact with any non-sharp suitable object.
Such displays are mounted on top-up and money transfer terminals, ATMs and other devices that are isolated from the environment. Weak protection of the monitor from damage is compensated by the presence of a protective film coating.
The principle of operation of capacitive touch screens
This type of display operates taking into account the possibility of objects of increased capacity to transform into alternating current conductors. The device is a glass panel with resistive spraying. The electrodes placed at the corners supply a weak voltage to the conductive layer. During contact, a current leak is observed if the object has a larger electrical capacity than the screen. The current is recorded in the corner parts, and the information from the indicators is processed by the controller, which calculates the contact area.
The first models used direct current. This simplified the design, however, it crashed if the user had no contact with the surface of the earth. In terms of reliability, these devices exceed resistive counterparts by about 60 times (designed for 200 million clicks). The transparency level is 0.9, the minimum working temperature is up to -15 ° C.
Minuses:
- lack of response to a gloved hand and most foreign objects;
- a coating with a conductor is located in the upper layer, which causes exposure to mechanical stress;
- they are suitable for operation in terminals located in enclosed spaces.
Capacitive projection versions
The principle of operation of the touch screen of smartphones of some configurations is based on this type. An electrode grid is deposited on the inner surface of the device, which, in contact with the human body, forms a capacitor capacitance. After touching the display with your finger, the sensors and the microcontroller process the information, the calculations are sent to the main processor.
Features:
- these designs have all the capabilities of capacitive sensors;
- they can be equipped with a film coating up to 18 millimeters thick, which provides additional protection against mechanical stress;
- contaminants on hard-to-reach conductive parts are removed using the software method.
These configurations are mounted on many personal devices and terminals operating outdoors under the cover. It is worth noting that Apple also prefers projection-capacitive monitors.
Matrix Modifications
These are simplified versions of resistive technology. The membrane is equipped with a number of vertical conductors, the substrate with horizontal analogs. The principle of operation of the touch screen: when touched, the point at which the contact of the conductors is contacted is calculated, the received information is sent to the processor. That, in turn, determines the control signal, after which the device reacts in a predetermined manner, for example, performs an action assigned to a specific button.
Features:
- due to the limited number of conductors, a low accuracy indicator is observed;
- price - the lowest among all sensors;
- multitouch function is realized by polling the display point by point.
The specified model is operated exclusively in outdated devices, it is practically not used in modern times due to the appearance of innovative solutions.
Surface acoustic signals
The principle of operation of the touch screen phones of earlier models was equipped with similar technology. The display is a glass panel in which receivers (two pieces) and piezoelectric transformers are installed, located on opposite angular parts.
From the generator, a frequency electrical signal is supplied to the converters, from where a series of pulses propagates using reflectors. The waves are captured by the sensors, returned to the probes, where they again turn into electric current. Further, the information goes to the controller, in which it is analyzed.
When you touch the screen, the wave characteristics undergo changes with the absorption of part of the energy in a particular place. Based on this information, a point and a touch force are calculated. Displays of this category are available with a film with a thickness of 3 or 6 millimeters, which makes it possible to withstand a light hand stroke without consequences.
Disadvantages:
- disruption in vibration and shaking;
- instability to any pollution;
- the presence of interference due to acoustic signals of a certain configuration;
- low accuracy makes them unsuitable for drawing.
Other types
The device and principle of operation of touch screens, which are used most often, are discussed above. The following is a list of unpopular configuration displays:
- Optical monitors - support multi-touch function, including the large size of the served surface.
- Infrared models - covered with pairs of photodiode LEDs, respond to touch through a microcontroller.
- Induction options - equipped with a special coil and a network of sensitive conductors, used on expensive tablets.
As you can see, there are several options for touch displays. The choice always remains with the consumer.