How touchscreen works?
- Author:Think
- Source:FlintStone
- Release on :2015-05-15
Next, the above-mentioned various types of touchscreen brief overview:
1, resistive touch screen (resistive touch screen works)
1.1 Four-wire resistive screen
1.2 five-wire resistive screen
2, capacitive touch screen, infrared touch screen (infrared touch screen works)
Surface acoustic wave touch screen (Surface acoustic wave touch screen works)
Surface acoustic wave touch screen features of a high-resolution, light transmission rate. Highly durable, good scratch resistance (relative to the resistors, capacitors and other surface of the film). Responsive. Environmental factors independent of temperature, humidity and other factors, high resolution, long life (maintenance under good circumstances 50 million); high transmittance (92%), to maintain a clear and bright image quality; not drift, just installed a correction; a third axis (ie pressure-axis) response, currently used more in public places. Surface acoustic screen requires frequent maintenance because the dust, oil or liquid beverage contamination in surface of the panel, will block the touch screen surface waveguide groove, so waves can not transmit properly, or the waveform changes the controller can not properly identify, thus affecting the normal use of the touch screen, the user should pay strict attention to sanitation. We must often wipe the screen surface to keep clean the screen surface, and regularly conduct a thorough erased.
Here isResistive touch screenDetails,
Now that all four lines are used to navigate modified resistive touch screen)
Resistive touch screen is a sensor that will touch point in the rectangular area (X, Y) is converted to the representative of the physical location of X and Y coordinates of the voltage. Many LCD module uses a resistive touch screen, the screen can be four or five lines, seven lines or eight lines to generate screen bias voltage, while reading back resistive touch screen is basically a film plus glass structure, film and the adjacent side of the glass are coated with ITO (Indium Tin Oxides, Nano indium tin oxide) coatings, ITO has good conductivity and transparency. When the touch operation, the film will be exposed to the lower ITO glass upper ITO, outgoing corresponding electrical signal via the sensor, to the processor through the switching circuit, through the operation on the screen is converted to X, Y values, and the completion point choose action, and presented on the screen.
Touch screenPrinciple
Touch screen contains two vertically stacked transparent layers, four-wire and eight-wire touch screen consists of two layers with the same surface resistance of transparent resistive material, five lines and seven wire resistive touch screen consists of a layer and a conductive layer, usually use of an elastic material to the two layers are separated. When the pressure on the touch screen surface (such as pressed by the pen or finger) is large enough, it will produce contact between the top and bottom. All resistive touch screen are used to generate a voltage divider principle on behalf of X and Y coordinates of the voltage. For a specific direction on the resistive touch screen coordinate measurement, the need for a resistive layer bias: its one side connected to VREF, ground on the other side. At the same time, it will not offset the layer is connected to a high-impedance input of the ADC. When the pressure on the touch screen large enough so that when contact occurs between the two layers, resistive surface is divided into two resistors. From the edge of their bias resistance is proportional to the touch point. Resistive touch point between the edge and the ground below the equivalent of the divider resistors. Therefore, on a non-bias layer measured voltage proportional to the distance and the touch point between the ground side
Four-wire touch screen
Four-wire resistive touch screen consists of two layers. One layer around the edge of the screen have a vertical bus, another bus have a horizontal bottom and top of the screen,
. In order to measure the X-axis direction, the left bus bias is 0V, the right side of the bus biased to VREF. The top or bottom of the bus is connected to ADC, when in contact with the top and bottom to make a measurement. 1 in order to measure the Y-axis direction, the top bus biased to VREF, the bottom bus biased to 0V. The ADC input termination on the left or right side of the bus the bus, when the top and bottom contact voltage can be measured. Figure 2 shows a simplified model of four-wire touch screen when in contact with two layers. For four-wire touch screen, the best connection method is biased to the VREF bus interface ADC positive reference input, and set to 0V the bus interface ADC negative reference input.
Five-wire touch screen
Five-wire touch screen uses a resistive layer and a conductive layer. A contact conductive layer, usually at its side edges. On each of the four corners of the resistive layer is a contact. In order to measure the X-axis direction, the upper left and lower left corner biased to VREF, upper right and lower right corner of the ground. Because the left and right corner of the same voltage, the effect of connecting the left and right side of the bus is similar to the method used in four-wire touch screen is similar.
In order to measure the Y-axis direction, the top left and right biased to VREF, lower left and lower right corner of the bias is 0V. Since the upper and lower angles are the same voltage, the effect of connecting the top and bottom edges of the bus substantially the same method used in four-wire touch screen is similar. The advantage of this measuring method is that it allows the upper left and lower right corner of the voltage remain unchanged; but if the grid coordinates, X-axis and Y-axis needs reverse. For the five-wire touch screen, the best approach is to connect the upper left corner (biased to VREF) being connected to the ADC reference input, the lower left corner (biased to 0V) to the negative reference input of the ADC.
Seven wire touch screen
Implementation seven lines in addition to a touch screen in the upper left and lower right corner of each increase a line outside, with the same five-wire touch screen. When performing measurement screen, upper-left corner of a wire connected to VREF, the other line connected SAR ADC positive reference terminal. Meanwhile, the lower-right corner of a line connected 0V, another wire connect the negative reference terminal of SAR ADC. The conductive layer is still used to measure the voltage divider. :
Eight-wire touch screen
In addition to the bus each increased by one on each line outside the eight-wire touch screen implementation with the same four-wire touch screen. For VREF bus, a wire used to connect the VREF, the other line as a SAR ADC DAC positive reference input. For 0V bus, a wire used to connect the 0V, the other line as a negative reference input SAR ADC's DAC. Four lines unbiased layer, any one can be used to measure the voltage divider. Detecting the presence of contacts, all of the touch screen can detect whether a touch occurs, the method is to use a weak pull-up resistor, the pull on the floor, but with a strong pull-down resistor will drop down another. If the measured voltage is greater than a pull-layer logic threshold, it means that there is no touch, otherwise touch. This method has a problem in that the touch screen is a large capacitor, you may also need to increase the capacitance of the touch screen lead to filter out noise introduced LCD. Large pull-up resistor and capacitor connected to the weak will rise time becomes longer, could lead to a false touch detection.
Southern Stars Enterprises Co., Ltd. has focused on the initial R and D design and manufacture of more than 60 different models of digital signage devices and systems, including flash players LCD display, touch screen, Touch screen advertising, Such as LCD digital signage, LCD advertising display (screen), POP advertising player, POS digital signage players, networked digital signage systems.