Many people, especially middle-aged and young people, actively use smartphones, tablets and other smart display gadgets. 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.
Invention Story
For the first time in the world, a prototype touch device was used by Sam Hurst, a teacher from the USA. He developed the idea in 1970 of reading data from a large number of strip chart recorders. Automation of this process has become a kind of springboard to the creation of touch monitors, known as Elotouch. The development of a group of Hurst colleagues was published in 1971, which included a resistive four-wire technology for determining touch points.
The PLATO IV system is considered to be the first computer sensor. It was also released in the USA, as a result of special studies related to the computerization of education. It consisted of a block panel (256 pieces), functioned according tothe principle of using a grid of infrared streams.
Description
The touch display is an electronic element that visualizes digital information by touching the surface of the monitor. Different types of these structures react to several moments 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.
Let's consider common display models of this category, scope, features and benefits.
How resistive touch screens work
This is the simplest type of monitor. It reacts to the transformation of the resistance force in the area of touching a certain object and the display surface. The most common and elementary technology includes two main elements in its design:
- Panel-substrate of polyester or similar polymer, the thickness of which does not exceed a few tens of molecules. The transparent part serves to conduct current particles.
- Light-transmitting thin plastic membrane.
Both layers are coated with a special resistive coating. Between them are microscopic ball-shaped insulators.
During operation, the membrane flexes in contact withsubstrate, as a result of which the circuit is closed. The controller with an analog-to-digital converter reacts 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.
Use
Due to the simple principle of operation of the resistive configuration touch screen, it is used everywhere. Design Features:
- low cost;
- resistance to environmental influences, except for negative temperatures;
- good reaction to contact with any non-sharp suitable object.
Such displays are mounted on replenishment and money transfer terminals, ATMs and other devices that are isolated from the environment. The weak protection of the monitor from damage is compensated by the presence of a protective film coating.
How capacitive touch screens work
This type of display functions taking into account the ability of objects of increased capacity to transform into conductors of alternating electric current. The device is a glass panel with resistive coating. Electrodes placed at the corners apply a weak voltage to the conductive layer. During contact, current leakage is observed if the object has a greater electrical capacitance than the screen. The current is fixed in the corner parts, and the information fromindicators goes to the controller for processing, which calculates the touch area.
The first models used direct current. This simplified the design, however, it failed if the user did not have contact with the ground. In terms of reliability, these devices exceed resistive counterparts by about 60 times (designed for 200 million clicks). Transparency level - 0, 9, minimum operating temperature - up to -15 °C.
Cons:
- lack of reaction to gloved hand and most foreign objects;
- coating with conductor is located in the top layer, which causes susceptibility to mechanical stress;
- they are suitable for indoor terminals.
Capacitive projection versions
The operation principle of the touch screen of smartphones of some configurations is based on this type. An electrode grid is applied on the inner surface of the device, which, when 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 impact;
- contaminants on hard-to-reach conductive parts are removed using the software method.
The specified configurations are mounted on many personal devices and terminals operating outdoors under cover. It is worth noting that Apple also favors projected 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 counterparts. The principle of operation of the touch screen: when touched, the point at which the contact of the conductors occurred is calculated, the information received is sent to the processor. That, in turn, determines the control signal, after which the device reacts in a given way, for example, performs an action assigned to a specific button.
Features:
- due to the limited number of conductors, there is a low accuracy rate;
- price is the lowest among all sensors;
- the multi-touch function is implemented by polling the display point by point.
The indicated model is used exclusively in obsolete devices, it is practically not used in modern times due to the emergence of innovative solutions.
Surface acoustic signals
How the touch screen of early phones was equipped with similar technology. The display is a glass panel in which receivers (two pieces) are embedded and piezoelectric transformers are placed on opposite corners.
From the generator, a frequency electrical signal is supplied to the converters, from where a series ofpulses are propagated by means of reflectors. The waves are picked up by sensors, returned to the probe, where they are converted back into electric current. Further, the information goes to the controller, in which it is analyzed.
When you touch the screen, the characteristics of the wave undergo changes with the absorption of part of the energy in a particular place. Based on this information, the point and force of contact are calculated. Displays in this category are available with a film thickness of 3 or 6 millimeters, which allows you to withstand a slight blow from your hand without consequences.
Flaws:
- violation of work in conditions of vibration and shaking;
- instability to any pollution;
- interference due to acoustic signals of a certain configuration;
- low precision makes them unusable for drawing.
Other species
The device and the principle of operation of touch screens, which are used most often, are discussed above. The following is a list of displays of unpopular configurations:
- Optical monitors - support multi-touch, including large footprints.
- Infrared models - covered with pairs of photodiode LEDs, react 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 screens. The choice is always up to the consumer.
