計算機相關專業(yè)畢業(yè)設計電阻式觸摸屏--文獻翻譯

電阻式觸摸屏 簡介 電阻式觸摸屏是一種傳感器，它將矩形區(qū)域中觸摸點 (X,Y)的物理位置轉換為代表 X坐標和 Y坐標的電壓。很多 LCD模塊都采用了電阻式觸摸屏，這種屏幕可以用四線、五線、七線或八線來產(chǎn)生屏幕偏置電壓，同時讀回觸摸點的電壓。 工作原理 電阻觸摸屏的工作原理主要是通過壓力感應原理來實現(xiàn)對屏幕內(nèi)容的操作和控制的，這種觸摸 屏屏體部分是一塊與顯示器表面非常配合的多層復合薄膜，其中第一層為玻璃或有機玻璃底層，第二層為隔層，第三層為多元樹脂表層，表面還涂有一層透明的導電層，上面再蓋有一層外表面經(jīng)硬化處理、光滑 防刮的塑料層。在多元脂表層表面的傳導層及玻璃層感應器是被許多微小的隔層所分隔電流通過表層，輕觸表層壓下時，接觸到底層，控制器同時從四個角讀出相稱的電流及計算手指位置的距離。這種觸摸屏利用兩層高透明的導電層組成觸摸屏，兩層之間距離僅為2.5 微米。當手指觸摸屏幕時，平常相互絕緣的兩層導電層就在觸摸點位置有了一個接觸，因其中一面導電層接通 Y軸方向的 5V均勻電壓場，使得偵測層的電壓由零變?yōu)榉橇?，控制器偵測到這個接通后，進行 A/D 轉換，并將得到的電壓值與 5V 相比，即可得觸摸點的 Y 軸坐標，同理得出 X 軸的坐標，這就是所有電阻技術觸摸屏共同的最基本原理。 觸摸屏包含上下疊合的兩個透明層，四線和八線觸摸屏由兩層具有相同表面電阻的透明阻性材料組成，五線和七線觸摸屏由一個阻性層和一個導電層組成，通常還要用一種彈性材料來將兩層隔開。當觸摸屏表面受到的壓力（如通過筆尖或手指進行按壓）足夠大時，頂層與底層之間會產(chǎn)生接觸。所有的電阻式觸摸屏都采用分壓器原理來產(chǎn)生代表 X 坐標和 Y 坐標的電壓。如圖 3，分壓器是通過將兩個電阻進行串聯(lián)來實現(xiàn)的。上面的電阻（ R1）連接正參考電壓（ VREF），下面的電阻（ R2）接地。兩個電阻連接點處的電壓測量值與下面那 個電阻的阻值成正比。 為了在電阻式觸摸屏上的特定方向測量一個坐標，需要對一個阻性層進行偏置：將它的一邊接 VREF，另一邊接地。同時，將未偏置的那一層連接到一個ADC 的高阻抗輸入端。當觸摸屏上的壓力足夠大，使兩層之間發(fā)生接觸時，電阻性表面被分隔為兩個電阻。它們的阻值與觸摸點到偏置邊緣的距離成正比。觸摸點與接地邊之間的電阻相當于分壓器中下面的那個電阻。因此，在未偏置層上測得的電壓與觸摸點到接地邊之間的距離成正比。 元件分類 四線觸摸屏 四線觸摸屏包含兩個阻性層。其中一層在屏幕的左右邊緣各有一條垂直總線，另 一 層在屏幕的底部和頂部各有一條水平總線，見圖 1。為了在 X軸方向進行測量，將左側總線偏置為 0V，右側總線偏置為 VREF。將頂部或底部總線連接到 ADC，當頂層和底層相接觸時即可作一次測量。 為了在 Y軸方向進行測量，將頂部總線偏置為 VREF，底部總線偏置為 0V。將 ADC輸 入端接左側總線或右側總線，當頂層與底層相接觸時即可對電壓進行測量。圖 2顯示了四線觸摸屏在兩層相接觸時的簡化模型。對于四線觸摸屏，最理想的連接方法是將偏置為 VREF 的總線接 ADC 的正參考輸入端，并將設置為 0V 的總線接 ADC的負參考輸入端。 五線觸 摸屏 五線觸摸屏使用了一個阻性層和一個導電層。導電層有一個觸點，通常在其一側的邊緣。阻性層的四個角上各有一個觸點。為了在 X 軸方向進行測量，將左上角和左下角偏置到 VREF，右上角和右下角接地。由于左、右角為同一電壓，其效果與連接左右側的總線差不多，類似于四線觸摸屏中采用的方法。為了沿 Y軸方向進行測量，將左上角和右上角偏置為 VREF，左下角和右下角偏置為 0V。由于上、下角分別為同一電壓，其效果與連接頂部和底部邊緣的總線大致相同，類似于在四線觸摸屏中采用的方法。這種測量算法的優(yōu)點在于它使左上角和右下角的電壓保持不 變；但如果采用柵格坐標， X 軸和 Y 軸需要反向。對于五線觸摸屏，最佳的連接方法是將左上角（偏置為 VREF）接 ADC 的正參考輸入端，將左下角（偏置為 0V）接 ADC的負參考輸入端。 七線觸摸屏 七線觸摸屏的實現(xiàn)方法除了在左上角和右下角各增加一根線之外，與五線觸摸屏相同。執(zhí)行屏幕測量時，將左上角的一根線連到 VREF，另一根線接 SAR ADC的正參考端。同時，右下角的一根線接 0V，另一根線連接 SAR ADC 的負參考端。導電層仍用來測量分壓器的電壓。 八線觸摸屏 除了在每條總線上各增加一根線之外，八線觸摸屏的實現(xiàn)方法與四 線觸摸屏相同。對于 VREF總線，將一根線用來連接 VREF，另一根線作為 SAR ADC的數(shù)模轉換器的正參考輸入。對于 0V 總線，將一根線用來連接 0V，另一根線作為 SAR ADC的數(shù)模轉換器的負參考輸入。未偏置層上的四根線中，任何一根都可用來測量分壓器的電壓。 元件結構 SAR的實現(xiàn)方法很多，但它的基本結構很簡單，參見圖 3。該結構將模擬輸入電壓（ N）保存在一個跟蹤 /保持器中， N位寄存器被設置為中間值（即 100.0，其中最高位被設置為 1），以執(zhí)行二進 制查找算法。因此，數(shù)模轉換器（ DAC）的輸出（ VDAC）為 VREF的二分之一，這里 VREF為 ADC的參考電壓。之后，再執(zhí)行一個比較操作，以決定 N小于還是大于 VDAC： 如果 N小于 VDAC，比較器輸出邏輯低， N位寄存器的最高位清 0。 如果 N大于 VDAC，比較器輸出邏輯高（或 1）， N位寄存器的最高位保持為 1。 其后， SAR 的控制邏輯移動到下一位，將該位強制置為高，再執(zhí)行下一次比 較。 SAR控制邏輯將重復上述順序操作，直到最后一位。當轉換完成時，寄存器中就得到了一個 N位數(shù)據(jù)字。 圖 4顯示了一個 4位轉換過程的例子，圖中 Y軸和粗線表示 DAC的輸出電壓。在該例中 ： 第一次比較顯示 N小于 VDAC，因此位 3被置 0。隨后 DAC被設置為0b0100并執(zhí)行第二次比較。 在第二次比較中， N大于 VDAC，因此位 2保持為 1。隨后， DAC被設置為 0b0110并執(zhí)行第三次比較。 在第三次比較中，位 1被置 0。 DAC隨后被設置為 0b0101，并執(zhí)行最后一次比較。 在最后一次比較中，由于 N大于 VDAC，位 0保持為 1。 接觸檢驗 所有的觸摸屏都能檢測到是否有觸摸發(fā)生，其方法是用一個弱上拉電阻將其中一層上拉，而用一個強下拉電阻來將另一層下拉。如果 上拉層 的測量電壓大于某個邏輯閾值，就表明沒有觸摸，反之則有觸摸。這種方法存在的問題在于觸摸屏是一個巨大的電容器，此外還可能需要增加觸摸屏引線的電容，以便濾除 LCD 引入的噪聲。弱上拉電阻與大電容器相連會使上升時間變長，可能導致檢測到虛假的觸摸。 四線和八線觸摸屏可以測量出接觸電阻，即圖 5 中的 RTOUCH。 RTOUCH與觸摸壓力近似成正比。要測量觸摸壓力，需要知道觸摸屏中一層或兩層的電阻。圖 6 中的公式給出了計算方法。需要注意的是，如果 Z1 的測量值接近或等于 0（在測量過程中當觸摸點靠近接地的 X總線時），計算將出現(xiàn)一些問 題，通過采用弱上拉方法可以有效改善這個問題。 元件優(yōu)缺點 電阻式觸摸屏的優(yōu)點是它的屏和控制系統(tǒng)都比較便宜，反應靈敏度很好，而且不管是四線電阻觸摸屏還是五線電阻觸摸屏，它們都是一種對外界完全隔離的工作環(huán)境，不怕灰塵和水汽，能適應各種惡劣的環(huán)境。它可以用任何物體來觸摸，穩(wěn)定性能較好。缺點是電阻觸摸屏的外層薄膜容易被劃傷導致觸摸屏不可用，多層結構會導致很大的光損失，對于手持設備通常需要加大背光源來彌補透光性不好的問題，但這樣也會增加電池的消耗。 電阻式觸摸屏的優(yōu)缺點可以歸類為： 1.電阻式觸控屏的精確度高，可到像 素點的級別，適用的最大分辨率可達4096x4096。 2. 屏幕不受灰塵、水汽和油污的影響，可以在較低或較高溫度的環(huán)境下使用。 3. 電阻式觸控屏使用的是壓力感應，可以用任何物體來觸摸，即便是帶著手套也可以操作，并可以用來進行手寫識別。 4. 電阻式觸控屏由于成熟的技術和較低的門檻，成本較為廉價。 5. 電阻式觸控屏能夠設計成多點觸控，但當兩點同時受壓時，屏幕的壓力變得不平衡，導致觸控出現(xiàn)誤差，因而多點觸控的實現(xiàn)程度較難。 6. 電阻式觸控屏較易因為劃傷等導致屏幕觸控部分受損。 Introduction to the resistive touch screen Resistive 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 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 touch Screen screen body part is a piece of and 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 layer 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 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 touching 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 compared 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 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 (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 through 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 the 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, the 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. Therefore, without bias level measured voltage and the distance between the touch point to ground is proportional to the. Element classification 4 line touch screen 4 line touch screen contains two impedance layer. One layer in the left and right edges of the screen there is a vertical bus, the other A layer 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 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 lose The termination on the left side of the bus or on the right side of the bus, when contact with the top and bottom phase 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 up negative reference input of the ADC. Five line of touch screen Touch 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, the 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 measure 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 method 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 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 screen Seven 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 measuring, 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 screen In addition to the 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 converter negative reference input. Not bias level four lines, any one can be used to measure the voltage divider. Element structure SAR 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 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 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 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 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 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 inspection All the touch screen can be detected if there is a touching, its method is to use a weak pull-up resistor pull on one layer, but with a strong pulldown resistor to another layer drop-down. if Pull 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, moreover 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 contact 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 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 disadvantages Resistive touch screen is the advantage of its screen and control systems are cheaper and response sensitivity is good, and whether 4-wire resistive touch scre