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1、电阻式触摸屏简介电阻式触摸屏是一种传感器，它将矩形区域中触摸点(X,Y)的物理位置转换为代表X坐标和Y坐标的电压。很多LCD模块都采用了电阻式触摸屏，这种屏幕可以用四线、五线、七线或八线来产生屏幕偏置电压，同时读回触摸点的电压。工作原理电阻触摸屏的工作原理主要是通过压力感应原理来实现对屏幕内容的操作和控制的，这种触摸 屏屏体部分是一块与显示器表面非常配合的多层复合薄膜，其中第一层为玻璃或有机玻璃底层，第二层为隔层，第三层为多元树脂表层，表面还涂有一层透明的导电层，上面再盖有一层外表面经硬化处理、光滑防刮的塑料层。在多元脂表层表面的传导层及玻璃层感应器是被许多微小的隔层所分隔电流通过表层，轻触表
2、层压下时，接触到底层，控制器同时从四个角读出相称的电流及计算手指位置的距离。这种触摸屏利用两层高透明的导电层组成触摸屏，两层之间距离仅为2.5微米。当手指触摸屏幕时，平常相互绝缘的两层导电层就在触摸点位置有了一个接触，因其中一面导电层接通Y轴方向的5V均匀电压场，使得侦测层的电压由零变为非零，控制器侦测到这个接通后，进行A/D转换，并将得到的电压值与5V相比，即可得触摸点的Y轴坐标，同理得出X轴的坐标，这就是所有电阻技术触摸屏共同的最基本原理。触摸屏包含上下叠合的两个透明层，四线和八线触摸屏由两层具有相同表面电阻的透明阻性材料组成，五线和七线触摸屏由一个阻性层和一个导电层组成，通常还要用一种弹
3、性材料来将两层隔开。当触摸屏表面受到的压力（如通过笔尖或手指进行按压）足够大时，顶层与底层之间会产生接触。所有的电阻式触摸屏都采用分压器原理来产生代表X坐标和Y坐标的电压。如图3，分压器是通过将两个电阻进行串联来实现的。上面的电阻（R1）连接正参考电压（VREF），下面的电阻（R2）接地。两个电阻连接点处的电压测量值与下面那个电阻的阻值成正比。为了在电阻式触摸屏上的特定方向测量一个坐标，需要对一个阻性层进行偏置：将它的一边接VREF，另一边接地。同时，将未偏置的那一层连接到一个ADC的高阻抗输入端。当触摸屏上的压力足够大，使两层之间发生接触时，电阻性表面被分隔为两个电阻。它们的阻值与触摸点到偏
4、置边缘的距离成正比。触摸点与接地边之间的电阻相当于分压器中下面的那个电阻。因此，在未偏置层上测得的电压与触摸点到接地边之间的距离成正比。元件分类四线触摸屏四线触摸屏包含两个阻性层。其中一层在屏幕的左右边缘各有一条垂直总线，另 一层在屏幕的底部和顶部各有一条水平总线，见图1。为了在X轴方向进行测量，将左侧总线偏置为0V，右侧总线偏置为VREF。将顶部或底部总线连接到ADC，当顶层和底层相接触时即可作一次测量。为了在Y轴方向进行测量，将顶部总线偏置为VREF，底部总线偏置为0V。将ADC输 入端接左侧总线或右侧总线，当顶层与底层相接触时即可对电压进行测量。图2显示了四线触摸屏在两层相接触时的简化模
5、型。对于四线触摸屏，最理想的连接方法是将偏置为VREF的总线接ADC的正参考输入端，并将设置为0V的总线接ADC的负参考输入端。五线触摸屏五线触摸屏使用了一个阻性层和一个导电层。导电层有一个触点，通常在其一侧的边缘。阻性层的四个角上各有一个触点。为了在X轴方向进行测量，将左上角和左下角偏置到VREF，右上角和右下角接地。由于左、右角为同一电压，其效果与连接左右侧的总线差不多，类似于四线触摸屏中采用的方法。为了沿Y轴方向进行测量，将左上角和右上角偏置为VREF，左下角和右下角偏置为0V。由于上、下角分别为同一电压，其效果与连接顶部和底部边缘的总线大致相同，类似于在四线触摸屏中采用的方法。这种测量
6、算法的优点在于它使左上角和右下角的电压保持不变；但如果采用栅格坐标，X轴和Y轴需要反向。对于五线触摸屏，最佳的连接方法是将左上角（偏置为VREF）接ADC的正参考输入端，将左下角（偏置为0V）接ADC的负参考输入端。七线触摸屏七线触摸屏的实现方法除了在左上角和右下角各增加一根线之外，与五线触摸屏相同。执行屏幕测量时，将左上角的一根线连到VREF，另一根线接SAR ADC的正参考端。同时，右下角的一根线接0V，另一根线连接SAR ADC的负参考端。导电层仍用来测量分压器的电压。八线触摸屏除了在每条总线上各增加一根线之外，八线触摸屏的实现方法与四线触摸屏相同。对于VREF总线，将一根线用来连接VR
7、EF，另一根线作为SAR ADC的数模转换器的正参考输入。对于0V总线，将一根线用来连接0V，另一根线作为SAR ADC的数模转换器的负参考输入。未偏置层上的四根线中，任何一根都可用来测量分压器的电压。元件结构SAR的实现方法很多，但它的基本结构很简单，参见图3。该结构将模拟输入电压（N）保存在一个跟踪/保持器中，N位寄存器被设置为中间值（即100.0，其中最高位被设置为1），以执行二进 制查找算法。因此，数模转换器（DAC）的输出（VDAC）为VREF的二分之一，这里VREF为ADC的参考电压。之后，再执行一个比较操作，以决定N小于还是大于VDAC： 如果N小于VDAC，比较器输出逻辑低，N
8、位寄存器的最高位清0。 如果N大于VDAC，比较器输出逻辑高（或1），N位寄存器的最高位保持为1。其后，SAR的控制逻辑移动到下一位，将该位强制置为高，再执行下一次比 较。SAR控制逻辑将重复上述顺序操作，直到最后一位。当转换完成时，寄存器中就得到了一个N位数据字。图4显示了一个4位转换过程的例子，图中Y轴和粗线表示DAC的输出电压。在该例中： 第一次比较显示N小于VDAC，因此位3被置0。随后DAC被设置为0b0100并执行第二次比较。 在第二次比较中，N大于VDAC，因此位2保持为1。随后，DAC被设置为0b0110并执行第三次比较。 在第三次比较中，位1被置0。DAC随后被设置为0b01
9、01，并执行最后一次比较。 在最后一次比较中，由于N大于VDAC，位0保持为1。接触检验所有的触摸屏都能检测到是否有触摸发生，其方法是用一个弱上拉电阻将其中一层上拉，而用一个强下拉电阻来将另一层下拉。如果 上拉层的测量电压大于某个逻辑阈值，就表明没有触摸，反之则有触摸。这种方法存在的问题在于触摸屏是一个巨大的电容器，此外还可能需要增加触摸屏引线的电容，以便滤除LCD引入的噪声。弱上拉电阻与大电容器相连会使上升时间变长，可能导致检测到虚假的触摸。四线和八线触摸屏可以测量出接触电阻，即图5中的RTOUCH。RTOUCH与触摸压力近似成正比。要测量触摸压力，需要知道触摸屏中一层或两层的电阻。图6中的
10、公式给出了计算方法。需要注意的是，如果Z1的测量值接近或等于0（在测量过程中当触摸点靠近接地的X总线时），计算将出现一些问题，通过采用弱上拉方法可以有效改善这个问题。元件优缺点电阻式触摸屏的优点是它的屏和控制系统都比较便宜，反应灵敏度很好，而且不管是四线电阻触摸屏还是五线电阻触摸屏，它们都是一种对外界完全隔离的工作环境，不怕灰尘和水汽，能适应各种恶劣的环境。它可以用任何物体来触摸，稳定性能较好。缺点是电阻触摸屏的外层薄膜容易被划伤导致触摸屏不可用，多层结构会导致很大的光损失，对于手持设备通常需要加大背光源来弥补透光性不好的问题，但这样也会增加电池的消耗。电阻式触摸屏的优缺点可以归类为：1.电阻
11、式触控屏的精确度高，可到像素点的级别，适用的最大分辨率可达4096x4096。2. 屏幕不受灰尘、水汽和油污的影响，可以在较低或较高温度的环境下使用。3. 电阻式触控屏使用的是压力感应，可以用任何物体来触摸，即便是带着手套也可以操作，并可以用来进行手写识别。4. 电阻式触控屏由于成熟的技术和较低的门槛，成本较为廉价。5. 电阻式触控屏能够设计成多点触控，但当两点同时受压时，屏幕的压力变得不平衡，导致触控出现误差，因而多点触控的实现程度较难。6. 电阻式触控屏较易因为划伤等导致屏幕触控部分受损。Introduction to the resistive touch screenResistive
12、 touch screen is a kind of sensor, it will be a rectangular area in the touch point (X, Y) the physical location of converted to represent X coordinate and Y coordinate of the voltage. Many LCD module are used the resistive touch screen, the screen can use lines to four, five, seven or eight line to
13、 produce the screen bias voltage, read back the touch points of voltage at the same time.Working principle Resistive touch screen works mainly through pressure induction principle to implement the operation and control of the screen contents, this kind of touchScreen screen body part is a piece of a
14、nd monitor very cooperate with the surface of the multilayer composite film, the first layer of glass or organic glass bottom, the second layer of isolation layer, the third layer for multivariate resin surface, the surface is coated with a layer of transparent conductive layer, the above with a lay
15、er of surface hardening treatment, then smooth scratch-resistant plastic layer. In conducting layer on the surface of the fat layer and the sensor glass layer is separated by many tiny compartment of electric current through the surface, light touch when the surface pressure, come into contact with
16、the ground floor, the controller from the four angles at the same time read to match current and calculate the distance of finger position. This touch screen using two layers of transparent conductive layer of touch screen, the distance between two layers of only 2.5 microns. When the finger touchin
17、g the screen, common mutual insulation two conductive layer on the touch point has A contact, because with A conductive layer on the Y axis direction of the 5 v voltage field, makes the detection layer voltage from zero to A nonzero, controller to detect the connected, A/D conversion, and will be co
18、mpared with 5 v voltage value, can touch points Y coordinate, similarly concluded that the X coordinates, this is all the most basic principle of resistance touch screen technology together.Touch screen contains a composite of two transparent layer from top to bottom, line 4 and line 8 touch screen
19、consists of two layers of transparent with the same surface resistance with resistance material composition, line 5 and line seven touch screen consists of a resistance layer and a conductive layer formed, often with an elastic material to separate two layers. When the touch screen surface pressure
20、(e.g., by pen or finger to press) is large enough, will have contact between top and bottom. All the resistive touch screen adopts the principle of voltage divider to generate the representative coordinates X and Y coordinates of voltage. As shown in figure 3, the voltage divider is implemented thro
21、ugh the two resistors in series. Resistor (R1) of the above connections are reference voltage, VREF), the grounding resistance (R2) below. Two resistor voltage measurement value of the join point and below that is directly proportional to the resistance of the resistor.To resistive touch screen in t
22、he direction of a specific measurement coordinates, a need for a resistance to offset the layer: its side to VREF, on the other side of earth. At the same time, will not offset the layer of the high impedance input terminal connected to an ADC. When the pressure of the touch screen is big enough, th
23、e contact between the two layers, the resistive surface is divided into two resistors. Their resistance and touch points to offset is directly proportional to the distance of the edge. Touch point and below the ground side of the resistor is equal to the voltage divider between the resistance. There
24、fore, without bias level measured voltage and the distance between the touch point to ground is proportional to the.Element classification4 line touch screen4 line touch screen contains two impedance layer. One layer in the left and right edges of the screen there is a vertical bus, the otherA layer
25、 at the bottom of the screen and top each bus has a level, as shown in figure 1. In order to measure in the X direction, will be on the left side of the bus is offset to 0 v, on the right side of the bus bias to VREF. Connected to the ADC will be at the top or the bottom of the bus and when the top
26、and bottom contact can make a measurement.In order to measure in the Y direction, will be at the top of the bus is offset to VREF, bus at the bottom of the bias of 0 v. The ADC to loseThe termination on the left side of the bus or on the right side of the bus, when contact with the top and bottom ph
27、ase can be carried out on the voltage measurement. Figure 2 shows a 4 line touch screen in the simplified model of two layer in contact with. For 4-wire touch screen, the most ideal connection method is to offset for the VREF of ADC bus to pick up the reference input, and will be set to 0 v bus pick
28、 up negative reference input of the ADC.Five line of touch screenTouch screen using a five line impedance layer and a conductive layer. Conductive layer has a contact, often in the side of the edge. Impedance layer on the four corners of each have a contact. In order to measure in the X direction, t
29、he upper left and lower left corner offset to VREF, grounding the upper right corner and the lower right corner. Due to the left and right corner for the same voltage, the effect and connected to the bus is the same as the left and right side, using methods similar to the 4 line touch screen. To mea
30、sure along the Y direction, the upper left corner and upper right corner offset to VREF, lower left and lower right bias of 0 v. Due to the Angle of upper and lower, respectively, for the same voltage, the effect and the link at the top and bottom edges of the bus is roughly same, similar to the met
31、hod used in 4 line touch screen. The advantages of this measuring algorithm is that it makes in the upper left and lower right voltage remains unchanged; But if the raster coordinates, X axis and Y axis to reverse. Touch screen for five line, the best way to connect is the top left corner (offset to
32、 VREF) pick up the ADC is the reference input, the lower left corner (bias of 0 v) negative reference input of the ADC.Seven line of touch screenSeven line method to realize the touch screen but add a line in the upper left and lower right, the same as the five line of touch screen. On screen measur
33、ing, a line of upper left corner to VREF, another thread after SAR ADC is reference. At the same time, the lower right corner of a thread to 0 v, another thread connection SAR ADC negative reference. Conductive layer is used to measure the voltage divider.Eight line of touch screenIn addition to the
34、 increase a thread on each bus, eight line method to realize the touch screen is the same as the 4 line touch screen. To VREF bus, connect a line to VREF, another thread as d/a converter of SAR ADC are reference input. For bus 0 v, connect a line to 0 v, another thread as SAR ADC digital to analog c
35、onverter negative reference input. Not bias level four lines, any one can be used to measure the voltage divider.Element structureSAR implementation method are many, but its basic structure is very simple, see figure 3. This structure to the analog input voltage ( N) stored in a tracking/retainer, N
36、 bit register is set to the median (namely 100. 0, the highest bit is set to 1), to perform a binary search algorithm. As a result, the output of the digital to analog converter (DAC) (VDAC) as the VREF, half here VREF reference voltage to ADC. , and then perform a comparison operation, in order to
37、determine N is less than or greater than the VDAC:if N is less than the VDAC, comparator output logic low, N bit registers the highest level of 0.This if N is greater than the VDAC, comparator output logic (or 1), N - bit register highest level is 1.Since then, the control logic of SAR moving to the
38、 next one, will the compulsory set to high, to execute than the next time. SAR control logic will repeat the order operation, until the last. When the conversion is complete, register had a N bit data word.Figure 4 shows an example of four conversion process, Y axis and thick line in figure said the
39、 DAC output voltage. In this case: the first comparison shows N is less than the VDAC, so bit is 0 3. Then DAC b0100 and execute the second comparison is set to 0.2. The second comparison, N is greater than the VDAC, so keep to 1 bit 2. Subsequently, DAC is set to 0 b0110 and perform the comparison
40、for the third time.3. In comparison, for the third time is 0 bit 1. DAC is then set to 0 b0101, the last time and perform the comparison.4. In comparison, last time because N is greater than the VDAC, keep 1 a 0.Contact inspectionAll the touch screen can be detected if there is a touching, its metho
41、d is to use a weak pull-up resistor pull on one layer, but with a strong pulldown resistor to another layer drop-down. ifPull on the measure the voltage is greater than a certain threshold, the logic layer that no touch, touch. Conversely Problems this way is the touch screen is a large capacitor, m
42、oreover also may need to increase the capacitance touch screen lead, in order to filter out noise introduced in the LCD. Weak pull-up resistors are connected to the large capacitor will make the rise time is long, can lead to false touch is detected.Line 4 and line 8 touch-screen can measure the con
43、tact resistance, namely RTOUCH in figure 5. RTOUCH is proportional to the touch pressure approximation. To measure the touch pressure, need to know a layer or two layers of resistance touch screen. Formula calculation method is given in figure 6. It is important to note, if Z1 measured values close
44、to or equal to zero (in the process of measurement when touch point close to the ground X bus), computing will appear some problems, through the adoption of weak pull-up method can effectively improve the problem.Components advantages and disadvantagesResistive touch screen is the advantage of its s
45、creen and control systems are cheaper and response sensitivity is good, and whether 4-wire resistive touch screen or five wire resistive touch screen, they are a completely isolated to the outside of the work environment, does not fear the dust and water vapor, can adapt to the harsh environment. It
46、 can use any object to touch, stable performance is good. Drawback is resistive touch screen outer membrane is easy to be scratched in touch screen is not available, multilayer structure can lead to great loss of light, and for handheld devices usually increase the back light is required to make up
47、for the transmission of light not good problem, but this will increase the consumption of the battery.The advantages and disadvantages of resistive touch screen can be classified as:1. The accuracy of the resistive touch screen is high, but to the pixel level, the maximum resolution of 4096 x4096 sh
48、all apply.2. The screen is not affected by dust, moisture and oil, can be in low or high temperature environment.3. Resistive touch screen using the pressure sensor, you can use any object to touch, even with gloves, you can operate, and can be used for handwriting recognition.4. The resistive touch
49、 screen because of the mature technology and low threshold, the cost is relatively cheap.5. Resistive touch screen to design into a multi-touch, but when two compression at the same time, the screen of the pressure has become unbalanced, lead to errors, touch and multi-touch realization degree is more difficult.6. Resistive touch screen is more easily lead to damaged touch scre