The basic principle of the touch screen is that the touch screen is installed on the front of the display with finger or other objects. The position of the touch is detected by the touch screen controller and sent to the CPU by the interface (such as RS-232 serial port).
Touch screen system generally consists of two parts, a touch screen controller (card) and a touch detection device. The main role of the touch screen controller (card) is to receive the touch information from the touch point detection device and convert it into contact coordinates, then send it to the CPU, which can receive the command from CPU.
1 resistance touch screen (resistive touch screen working principle diagram)
The resistive touch screen body part is a multilayer composite film matched with the display surface, by a layer of glass or organic glass as a base, the surface is coated with a layer of transparent conductive layer, which is covered with a layer of outer surface hardening treatment, smooth scratch resistant plastic layer, the inner surface is also coated with a layer of transparent conductive layer, there are many small (less than 1/1000 inches) between the two layers of transparent insulation.
When the fingers touch the screen, the two layers of insulation are in contact with the 5V axis direction, which makes the detection layer's voltage from zero to zero, which is connected to the D / A conversion, and the obtained voltage value can be compared with the Y X axis coordinate, which is the most basic principle of all resistance technology touch screen. The key of resistance type touch screen is material science and technology. Resistance screen according to the number of the lead wire, divided into four lines, five lines, six lines and other multi line resistance touch screen. Resistance type touch screen in strengthening glass surfaces were coated with two layers of OTI transparent metal oxide conducting layer and the outermost layer of OTI coating as a conductive body and the second layer OTI is through a sophisticated network attached two directions anyway to + 5V 0V voltage field, OTI between two layers to tiny transparent isolation points separated. When the finger touch the screen, the two layer OTI conductive layer will appear a contact point, the computer at the same time detect the voltage and current, calculate the position of the touch, the reaction rate is 10-20ms.
Five wire resistive touch screen is used in the outer layer of the good ductility of nickel coating material, the outer conductive layer due to the frequent touch, the use of good ductility of nickel gold material purpose is to extend the service life, but the process cost is relatively high. Although it is good to have good ductility, it is not suitable for the working face of the resistance touch screen because it has high electric conductivity, and the metal is not easy to thickness.
Resistive touch screen is a completely isolated environment, not afraid of dust and water vapor, it can use any object to touch, can be used to draw pictures, more suitable for the use of industrial control field and office limited. Resistive touch screen is a common drawback is because the outer layer composite film of plastic materials, do not know too sharp or the use of force touch may scratch the whole touch screen scrapped as a result. However, within the limits, the scratch will only hurt the outer conductive layer, the outer conductive layer of the scratch for the five wire resistive touch screen is not related, and the four wire resistive touch screen is fatal.
2 capacitive touch screen:
Is the use of the human body of current sensing work. Capacitive touch screen is a four layer composite glass screen, the inner surface of the glass screen and interlayer ITO, the outermost layer is a thin layer of silica glass layer, laminated ITO coating as the working surface, the four angle leads to four electrodes, the inner layer ITO to ensure a good working environment. When the fingers touch the metal layer, the electric field due to the human body, the users and the touch screen surface formed by a coupling capacitor, for high-frequency current, capacitance is the conductor directly, so the fingers from the point of contact to absorb a very small current. This current is drawn from the four corners of the touch screen, and the current flowing through the four electrodes is proportional to the distance between the four angles, and the controller is obtained by calculating the ratio of the four currents. Capacitive touch screen features:
- resistance to most environmental pollutants.
- the body becomes a part of the line, so the drift phenomenon is quite serious.
- wear gloves do not work.
- the need for frequent calibration.
- not suitable for metal cabinet.
- when the outside world when the inductance and magnetic induction, the touch screen failure.
3 infrared touch screen (infrared touch screen working principle diagram)
Infrared touch screen is the use of Y, X direction of the infrared matrix to detect and locate the user's touch. Infrared touch screen in front of the monitor installation of the outer frame of a circuit board, circuit board in the sides of the screen layout infrared emitting tube and infrared receiving tube, corresponding horizontal and vertical cross infrared matrix formation. Users in the touch screen, the fingers will be blocked by the position of the horizontal and vertical infrared, which can judge the touch point in the position of the screen. Any touch of the object can change the contact on the infrared touch screen operation. The infrared touch screen is not affected by the current, voltage and electrostatic interference, which is suitable for the harsh environmental conditions, and the infrared technology is the development trend of the touch screen products. Touch screen with acoustic and other materials