JP2009282586A - System and method for detecting touching point on touch screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for detecting multiple touching points on a touch screen. <P>SOLUTION: A mechanism is provided to collect voltages read on four terminals of two conductive layers. By changing a reference voltage or an application to a terminal of the four terminals, at least four voltages can be read from the four terminals. These voltages are converted to digital voltages to be processed in a microprocessor in accordance with a set of equations so as to determine the number of the touching points on the touch screen and coordinates thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for a touch screen, and more particularly to a technique for detecting a contact point on a touch screen.

  Touch screens are becoming the primary means of entering information into electronic systems. The technique of detecting multiple contact points is attractive in the field of touch screens. However, techniques for detecting multiple contact points are implemented primarily on optical touch screens and are very expensive for most consumers.

  FIG. 1A is a schematic diagram illustrating a conventional 4-wire resistive touch screen. The 4-wire resistive touch screen has an x conductive layer along the x-axis direction and a y conductive layer along the y-axis direction that is perpendicular to the x-axis direction. The x conductive layer has a positive terminal XP and a negative terminal XN at the end of the x conductive layer in the x-axis direction. The y conductive layer has a positive terminal YP and a negative terminal YN at the end of the y conductive layer in the y-axis direction. The x conductive layer is physically separated from the y conductive layer by a spacer. If a contact point P1 with sufficient pressure appears on the resistive touch screen, the x conductive layer may contact the y conductive layer at the contact point P1. FIG. 1B is a circuit diagram illustrating an equivalent electrical circuit of a resistive touch screen when a single contact point is present on the resistive touch screen.

  Rxplate is provided to represent the total resistance value of the x conductive layer from the negative terminal XN to the positive terminal XP. Since each conductive layer has a uniform linear resistance along each direction, the contact point P1 divides the total resistance value Rxplate into resistors R1 and R3 in proportion to the distance of P1 from XP and XN, respectively. Ryplate is provided to represent the total resistance value of the y conductive layer from the negative terminal YN to the positive terminal YP. The contact point P1 divides the total resistance value Ryplate into resistors R4 and R6 in proportion to the distance of P1 from YP and YN, respectively. Rz is provided to represent the contact resistance value between the x conductive layer and the y conductive layer at the contact point P1. The resistance value Rz is related to the pressure at the contact point P1. Therefore, when the resistance values R3 and R6 are obtained, the x and y coordinates of the contact point P1 are obtained.

In general, two measurements are required to obtain the resistance values R3 and R6. In the first measurement, the terminal XP is connected to the positive reference voltage Vref +, the terminal XN is connected to the negative reference voltage Vref−, for example, ground, and the voltage value V3 at the terminal YP is measured. Next, the following equation is obtained from the equivalent circuit shown in FIG. 1B.
V3 / R3 ＝ V _REF / Rxplate
The above equation is transformed to obtain the following equation.
R3 = Rxplate * V3 / V _REF (Formula 1)
Here, V _REF represents a potential difference between the positive reference voltage Vref + and the negative reference voltage Vref−.

In the second measurement, the terminal YP is connected to the reference voltage Vref +, the terminal YN is grounded, and the voltage value V1 at the terminal XP is measured. Next, the following equation is obtained from the equivalent circuit shown in FIG. 1B.
V1 / R6 ＝ V _REF / Ryplate
The above equation is transformed to obtain the following equation.
R6 = Ryplate * V1 / V _REF (Formula 2)
Here, V _REF represents a potential difference between the positive reference voltage Vref + and the negative reference voltage Vref−.
After the resistance values R3 and R6 are obtained, the x and y coordinates of the contact point P1 are subsequently obtained. However, conventional 4-wire resistive touch screens detect only a single touch point on the touch screen.

  Multiple contact points may be detected. Therefore, there is a need for an improved technique for detecting multiple contact points on a resistive touch screen.

  In order to summarize some aspects of the present invention, some preferred embodiments are briefly introduced below. The titles of this section and the summary or detailed description are simplified or omitted to avoid obscuring the purpose of this section, the summary, and the title. Such simplifications or omissions do not limit the scope of the invention.

  In general, the present invention relates to techniques for detecting a plurality of contact points on a touch screen. According to one aspect of the present invention, a mechanism is provided for collecting voltages read at four terminals of two conductive layers. By changing the reference voltage or the application of any one of the four terminals to the terminal, at least four voltages can be read from the four terminals. These voltages are processed by a microprocessor according to a series of equations and converted to digital voltages to determine the number and coordinates of touch points on the touch screen.

  The present invention may be implemented as a method, system, or part of a system. According to one embodiment, the present invention provides a first or second resistive touch screen on a resistive touch screen having a first conductive layer and a second conductive layer, each having a positive terminal and a negative terminal, and a total of four terminals. This is a method for detecting a plurality of contact points. The method includes setting the positive terminal of the second conductive layer to a positive reference voltage, setting the negative terminal of the second conductive layer to a negative reference voltage, and the first conductive layer. Measuring the voltage value V1 of the positive terminal and the voltage value V2 of the negative terminal of the first conductive layer, setting the positive terminal of the first conductive layer to a positive reference voltage, Setting the negative terminal of the first conductive layer to a negative reference voltage, the voltage value V3 of the positive terminal of the second conductive layer and the voltage value V4 of the negative terminal of the second conductive layer; Measuring, and detecting a contact point on the resistive touch screen according to the voltage values V1 to V4.

  According to another embodiment, the present invention provides at least a resistive touch screen having a first conductive layer and a second conductive layer, each having a positive terminal and a negative terminal, and a total of four terminals. This is a system for detecting one contact point. The system measures at least six voltages of the four terminals by applying either a reference voltage or ground to one or more of the four terminals in at least six ways. A selector for selecting a measurement mode of the resistive touch screen, an analog voltage value obtained in each of the at least six measurement modes is converted into a corresponding digital voltage value, and at least six An analog-to-digital converter that obtains a digital voltage value of the at least one contact point, and receives the six digital voltage values, processes the six digital voltage values according to a series of equations, and the resistive touch of the at least one contact point A microprocessor for deriving coordinates on the screen;

  One of the features, advantages, and benefits of the present invention is to provide a technique for detecting more than one touch point on a touch screen.

  Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the invention when read in conjunction with the accompanying drawings.

  The foregoing and other features, aspects, and advantages of the present invention will be better understood with reference to the following description, appended claims, and accompanying drawings.

  The detailed description of the invention is presented primarily in terms of procedures, steps, logic blocks, processes, or other symbolic representations that directly or indirectly symbolize the operation of an apparatus or system as intended by the invention. These descriptions and representations are those standardly used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art.

  In the specification, the word “one embodiment” or “an embodiment” means that a particular function, structure, or feature described in connection with the embodiment is included in at least one embodiment of the invention. Means. The phrases “in one embodiment” appearing throughout this application are not necessarily all referring to the same embodiment, or separate or replace embodiments that are mutually exclusive with other embodiments. . Further, the order of blocks in the process flow charts or figures, or sequential numbers representing one or more embodiments of the invention do not essentially indicate any particular order, or imply any limitation of the invention. Not a thing.

  Embodiments of the present invention are discussed herein with reference to FIGS. However, one of ordinary skill in the art will readily appreciate that the detailed description given herein with reference to the drawings is for illustrative purposes only and that the invention is not limited to these limiting examples. .

  According to one embodiment of the present invention, a system for detecting a plurality of contact points on a resistive touch screen is provided. FIG. 2 requires an improved technique for detecting multiple contact points on a resistive touch screen. The system 200 may accommodate detection of multiple contact points as well as a single contact point. As shown in FIG. 2, the system 200 includes a resistive touch screen 220, a selector 240, an analog-to-digital converter (ADC) 260, and a microprocessor 280.

  The resistive touch screen 220 has an x conductive layer along the x-axis direction and a y conductive layer along the y-axis direction that is perpendicular to the x-axis direction. The x conductive layer has a positive terminal XP and a negative terminal XN at the end of the x conductive layer in the x-axis direction. The y conductive layer has a positive terminal YP and a negative terminal YN at the end of the y conductive layer in the y-axis direction. Each conductive layer has a uniform linear resistance along the respective direction. In one embodiment, Rxplate is provided to represent the total resistance of the x conductive layer from the negative terminal XN to the positive terminal XP, which is typically about 300Ω. Ryplate is provided to represent the total resistance value, typically about 700Ω, of the y conductive layer from the negative terminal YN to the positive terminal YP. The x conductive layer is physically separated from the y conductive layer by a gap or a spacer. When one contact point with sufficient pressure appears on the resistive touch screen 220, the x conductive layer contacts the y conductive layer at the contact point.

  FIG. 3A schematically illustrates the resistive touch screen 220 when there are two contact points on the resistive touch screen when x2> x1 and y2> y1. Here, x2 and y2 represent the x and y coordinates of the second contact point P2, and x1 and y1 represent the x and y coordinates of the second contact point P1. FIG. 3B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 3A.

  FIG. 4A schematically shows a resistive touch screen 220 when there are two contact points P1, P2 on the resistive touch screen when x2> x1 and y1> y2. FIG. 4B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 4A. FIG. 5A schematically illustrates a resistive touch screen 220 when there are two contact points on the resistive touch screen when x2> x1 and y1 = y2. FIG. 5B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 5A. FIG. 6A schematically illustrates a resistive touch screen 220 when there are two contact points on the resistive touch screen when x2 = x1 and y1 <y2. FIG. 6B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 6A.

  According to one embodiment, the selector 240 selects the measurement mode of the resistive touch screen 220. The selector 240 has six available measurement modes. In the first measurement mode, a positive reference voltage Vref + is supplied to the terminal YP, a negative reference voltage Vref− is supplied to the terminal YN, and the terminal XP is selected as a measurement terminal for measuring the voltage V1. In one embodiment, ground is used as the negative reference voltage Vref−. In the second measurement mode, a positive reference voltage Vref + is supplied to the terminal YP, the terminal YN is grounded, and the terminal XN is selected as a measurement terminal for measuring the voltage V2. In the third measurement mode, a positive reference voltage Vref + is supplied to the terminal XP, the terminal XN is grounded, and the terminal YP is selected as a measurement terminal for measuring the voltage V3. In the fourth measurement mode, a positive reference voltage Vref + is supplied to the terminal XP, the terminal XN is grounded, and the terminal YN is selected as a measurement terminal for measuring the voltage V4. In the fifth measurement mode, a positive reference voltage Vref + is supplied to the terminal YP, the terminal XN is grounded, and the terminal XP is selected as a measurement terminal for measuring the voltage V5. In the sixth measurement mode, a positive reference voltage Vref + is supplied to the terminal YP, the terminal XN is grounded, and the terminal YN is selected as a measurement terminal for measuring the voltage V6. The measurement terminal operates as an output terminal of the selector 240 connected to the ADC 260.

  FIG. 7 is a block diagram illustrating an example of the structure of a selector 240 according to an embodiment of the present invention. The selector 240 includes a positive reference voltage (Vref +) selector 242, a negative reference voltage (Vref−) selector 244, a measurement terminal selector 246, and a mode control unit 248. The mode control unit 248 is provided to control the Vref + selector 242, the Vref− selector 244, and the measurement terminal selector 246 in each measurement mode. The Vref + selector 242 is provided to select one to be connected to the positive reference voltage Vref + from the terminal YP and the terminal XP. The Vref-selector 244 is provided to select one to be connected to the negative reference voltage Vref- from the terminal YN and the terminal XN. The measurement terminal selector 246 is provided to select one of the terminals YP, YN, XP, and XN as a measurement terminal.

Referring again to the figure, the ADC 260 converts the analog measurement voltage V1-V6 to the digital measurement voltage V1-V6. The accuracy of the ADC 260 may be 10 bits or 12 bits. When the accuracy of the ADC 260 is 12 bits, each conductive layer may be divided along each direction with a resolution of 2 ¹² = 4096 divisions. Accordingly, the potential difference V _ref between the positive reference voltage and the negative reference voltage may be set to 4096 for ease of calculation in the following embodiments.

  The microprocessor 280 receives the digital measurement voltage V1-V6 and makes a determination according to the digital measurement voltage V1-V6.

  Refer to FIG. 1B. FIG. 1B shows the case where there is a single contact point on the resistive touch screen. Here it can be seen that V1 must be equal to V2 and V3 must be equal to V4. Refer to FIG. 5B. FIG. 5B shows the case where there are two contact points on the resistive touch screen when x2> x1 and y1 = y2. Here it can be seen that V1 must be equal to V2 and V3 must be equal to V4. Reference is made to FIG. 6B. FIG. 6B shows the case where there are two contact points on the resistive touch screen when x2 = x1 and y1 <y2. Here it can be seen that V1 must be equal to V2 and V3 must be equal to V4. Refer to FIG. 3B. FIG. 3B shows the case where there are two contact points on the resistive touch screen when x2> x1 and y2> y1. Here, it can be seen that V1 must be greater than V2 and V3 must be greater than V4. Refer to FIG. 4B. FIG. 4B shows the case where there are two contact points on the resistive touch screen when x2> x1 and y2 <y1. Here, it can be seen that V1 must be smaller than V2 and V3 must be smaller than V4.

  The microprocessor 280 may derive information about the contact points on the resistive touch screen according to the measured voltages V1-V4. In operation, when V1 = V2 and V3 = V4, the microprocessor 280 may determine that there is a single contact point or two contact points having the same x and y coordinates on the resistive touch screen. When V1> V2 and V3> V4, the microprocessor 280 may determine that there are two contact points on the resistive touch screen when x2> x1 and y2> y1. When V1 <V2 and V3 <V4, the microprocessor 280 may determine that there are two contact points on the resistive touch screen when x2> x1 and y2 <y1.

  In a preferred embodiment, a discrimination threshold THD1, THD2 pair is set when comparing V1 with V2 and V3 with V4. The first discrimination threshold THD1 is less than or equal to zero. Also, the second discrimination threshold THD2 is greater than or equal to zero. The discrimination thresholds THD1 and THD2 are very important for preventing a plurality of contact points from being simultaneously present in a narrow area. In addition, these discrimination thresholds are useful for simply considering a set of strictly grouped contact points as a single point. Changes in the response of resistive touch screen 220 based on electrical noise and temperature can appear confusing as multiple contact points when THD1 and THD2 are set equal to or near zero. Thus, when THD1 ≦ V1−V2 ≦ THD2 and THD1 ≦ V3−V4 ≦ THD2, the microprocessor 280 has a single contact point or two contact points with the same x and y coordinates on the resistive touch screen. You may judge that there is. When V1-V2> THD2 and V3-V4> THD2, the microprocessor 280 may determine that there are two contact points on the resistive touch screen when x2> x1 and y2> y1. When V1-V2 <THD1 and V3-V4 <THD1, the microprocessor 280 may determine that there are two contact points on the resistive touch screen when x2> x1 and y2 <y1.

  For further understanding of the present invention, FIGS. 8A and 8B together illustrate a process or flowchart for detecting single or multiple touch points on a resistive touch screen, according to an embodiment of the present invention.

  In operation 802, the positive terminal YP is connected to the reference voltage Vref +, the negative terminal YN is grounded, and the voltage value V1 of the positive terminal XP and the voltage value V2 of the negative terminal XN are measured.

  In operation 804, the positive terminal XP is connected to the reference voltage Vref +, the negative terminal XN is grounded, and the voltage value V3 of the positive terminal XP and the voltage value V4 of the negative terminal XN are measured.

  In operation 806, a first difference V1-V2 between the voltage values V1 and V2 and a second difference V3-V4 between the voltage values V3 and V4 are determined.

  In act 808, the first difference V1-V2 is compared with the first discrimination threshold THD1 and the second discrimination threshold THD2, and the second difference V3-V4 is compared with the first discrimination threshold THD1 and the second discrimination threshold THD2. Compared with

  When THD1 ≦ V1−V2 ≦ THD2 and THD1 ≦ V3−V4 ≦ THD2, the process is 810 and there is a single contact point or two contact points with the same x and y coordinates on the resistive touch screen. Show. When V1-V2> THD2 and V3-V4> THD2, the process flow is 812, indicating that there are two contact points on the resistive touch screen when x2> x1 and y2> y1. When V1-V2 <THD1 and V3-V4 <THD1, the process flow is 814, indicating that there are two contact points on the resistive touch screen when x2> x1 and y2 <y1.

  Refer to FIG. 8B. After operation 810, processing continues to 816 where the positive terminal YP is connected to the reference voltage Vref +, the negative terminal XN is grounded, and the voltage value V5 at the positive terminal XP and the voltage value V6 at the negative terminal YN are measured.

  In step 818, assume that there is only a single contact point on the resistive touch screen. Next, the first value of the contact resistance Rz at the hypothetical contact point is calculated according to the following equation 3, and the second value of the contact resistance Rz at the hypothetical contact point is calculated according to the following equation 4.

Referring to FIG. 1B, terminal YP is connected to Vref +, terminal XN is grounded, and current passes from terminal YP through terminals R4, Rz, and R3 to terminal XN. It can be seen that the currents are equal to each other everywhere, and therefore:
V5 / R3 = V6 / (R3 + Rz)
The above equation is transformed to obtain the following equation.
Rz = R3 * (V6 / V5-1)
Substituting Equation 1 above into the above equation yields:
Rz ₁ = (V6 / V5-1) * Rxplate * V3 / V _REF (Formula 3)
Referring to FIG. 1B, another equation is obtained.
V5 / R3 = V _REF / (R3 + Rz + R4)
The above equation is transformed to obtain the following equation.
Rz = R3 * (V _REF / V5-1)-R4
Expressions 1 and 2 and Ryplate = R4 + R6 are substituted into the above expression to obtain Expression 4.
_{Rz 2 = (V REF / V5-1} ) * Rxplate * V3 / V REF -Ryplate * (1-V1 / V REF) ( Equation 4)
Therefore, when the measured voltage value V3, V6, and V5 is substituted into Equation 3, V _REF, since the known RXPLATE, first value Rz ₁ of the contact resistance Rz is obtained. Therefore, when the measured voltage value V1, V3, and V5 is substituted into Equation 4, V _REF, RXPLATE, and since Ryplate has been found, the second value Rz ₂ of the contact resistance Rz is obtained.

A difference value Rz ₁ -Rz ₂ between the _first value Rz ₁ and the second value Rz ₂ is obtained according to the following equation.
Delta = Rz ₁ −Rz ₂ = Ryplate * (1-V1 / V _REF ) − (Rxplate * V3 / V _REF ) * (V _REF −V6) / V5
If there is a single contact point on the touch screen, the difference value must be equal to zero. The equivalent electrical circuit of a resistive touch screen when there are two contact points with the same y coordinate on the touch screen as shown in FIG. 5A is shown in FIG. 5B. Due to the equivalent relationship between the y-type circuit and the Δ-type circuit, the circuit shown in FIG. 5B is equivalently shown as the circuit shown in FIG. 5C. here,
_{R1 = R2 * Rz 1 / (} R2 + Rz 1 + Rz 2)
_{R2 = R2 * Rz 2 / (} R2 + Rz 1 + Rz 2)
R3 = Rz ₁ * Rz ₂ / (R2 + Rz ₁ + Rz ₂ )
Furthermore, the voltage values of corresponding terminals shown in FIGS. 5B and 5C are equal to each other. That is, V1 = V1 ′, V2 = V2 ′, V3 = V3 ′, V4 = V4 ′, and V6 = V6 ′.

Therefore, the following equation is obtained.
Delta '= Ryplate * (1- V1 / V REF) - (Rxplate * V3 / V REF) * (V REF -V6) / V5 = 0
Rxplate '= R1 + R3 + R1 + R2 = R1 + R3 + R2 * Rz 1 / (R2 + Rz 1 + Rz 2) + R2 * Rz 2 / (R2 + Rz 1 + Rz 2)
_{= R1 + R2 // (Rz 1} + Rz 2) + R3 <Rxplate
Therefore, if there are two contact points with the same y coordinate on the touch screen as shown in FIG. 5A, Delta <Delta ′ = 0.

Similarly, if there are two contact points with the same x coordinate on the touch screen as shown in FIG. 6A, Delta> Delta ′ = 0. As a result, by analyzing the difference value Rz ₁ -Rz ₂ between the first value Rz ₁ and the second value Rz _2, to obtain the following law. If there is a single contact point on the touch screen, the difference value is close to or equal to zero, and if there are two contact points with the same y coordinate, the difference value is less than zero and the same x If there are two touch points with coordinates, the difference value is greater than zero.

Referring to Figure 8B again, the process proceeds to step 820, the difference value Rz ₁ -Rz ₂ first value Rz ₁ and the second value Rz ₂ is obtained. Then, the difference value Rz ₁ -Rz ₂ is compared with the third discrimination threshold THD3 and fourth discrimination thresholds THD4. The third discrimination threshold THD3 is less than or equal to zero. The fourth discrimination threshold THD4 is greater than or equal to zero. The discrimination thresholds THD3 and THD4 are important for avoiding misjudgment due to fluctuations based on various electrical noises and temperatures.

Operation 822 indicates that there is a single contact point on the resistive touch screen if THD3 ≦ Rz ₁ −Rz ₂ ≦ THD4. Step 824 indicates that there are two contact points with the same y coordinate on the resistive touch screen if Rz ₁ −Rz ₂ ≦ THD3. Step 826 indicates that there are two contact points with the same x coordinate on the resistive touch screen if Rz ₁ −Rz ₂ > THD4.

  The above description has focused primarily on detecting and reporting whether there are one or two contact points on a resistive touch screen. In the following description, an operation when a plurality of contact points is detected will be described.

If two contact points are detected, the coordinates of each contact point are calculated. Therefore, in order to obtain the coordinates of each contact point, R2, R3, R5, R6 , Rz 1, and it is necessary to obtain the value of Rz _2. Therefore, R2, R3, R5, R6 , Rz 1, and requires at least six equations for Rz _2. Thus, R2, R3, R5, R6, if Rz _1, and the at least six equations for Rz ₂ is described in accordance with the measured voltage V1-V6, 2 one known formula, i.e. Rxplate = R1 + R2 + R3 and Ryplate Using R = R4 + R5 + R6, the values of R2, R3, R5, R6, Rz ₁ and Rz ₂ can be determined.

  Since the equivalent electrical circuit shown in FIG. 4B is different from that shown in FIG. 3B, the six equations described according to FIG. 4B may be different from those described according to FIG. 3B. Each is described below. The equivalent electrical circuit shown in FIGS. 5B and 6B is considered a special case of the equivalent electrical circuit shown in FIG. 4B or FIG. 3B and will be described separately.

  Refer to FIG. 3B. Six corresponding equations can be described when there are two contact points P1, P2 on the resistive touch screen when x2> x1 and y2> y1.

When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
Ra = R2 // (Rz ₁ + Rz ₂ + R5)
R = Rz ₁ + Rz ₂ + R2 + R5
Ix = V _REF / (R1 + R3 + Ra)
Here, Ix represents a current flowing through the x conductive layer, Rz ₁ represents the contact resistance of the first contact point P1, Rz ₂ represents the contact resistance of the second contact point P2.

  Referring to FIG. 3B, the following two equations are obtained.

端子YPを基準電圧Vref+に設定し、端子YNを接地すると、次式が得られる。
Rb=R5//(Rz₁+Rz₂+R2)
R=Rz₁+Rz₂+R2+R5
Iy=V_REF/(R4+R6+Rb)
ここでIyはy導電層を流れる電流を表す。

When the terminal YP is set to the reference voltage Vref + and the terminal YN is grounded, the following equation is obtained.
Rb = R5 // (Rz ₁ + Rz ₂ + R2)
R = Rz ₁ + Rz ₂ + R2 + R5
Iy = V _REF / (R4 + R6 + Rb)
Here, Iy represents the current flowing through the y conductive layer.

  Referring to FIG. 3B, the following two equations are obtained.

端子YPを基準電圧Vref+に設定し、端子XNを接地すると、次式が得られる。
Rc=(Rz₁+R2)//(Rz₂+R5)
Ip=V_REF/(Rc+R4+R3)
R=Rz₁+Rz₂+R2+R5
ここでIpはy導電層からx導電層へ流れる電流を表す。

When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
Rc = (Rz ₁ + R2) // (Rz ₂ + R5)
Ip = V _REF / (Rc + R4 + R3)
R = Rz ₁ + Rz ₂ + R2 + R5
Here, Ip represents a current flowing from the y conductive layer to the x conductive layer.

  Referring to FIG. 3B, the following two equations are obtained.

結果として、６個の対応する式(式５乃至１０)は、x2＞x1且つy2＞y1のときに抵抗性タッチスクリーン上に２つの接触点P1、P2がある場合に記載される。次に、式５乃至１０を測定電圧V1−V6に従い解くことにより、２つの既知の式、つまりRxplate=R1+R2+R3及びRyplate=R4+R5+R6を用いて、R2、R3、R5、R6、Rz₁、及びRz₂の値が求められる。最終的に、接触点P1及びP2の座標が求められる。

As a result, six corresponding equations (Equations 5-10) are described when there are two contact points P1, P2 on the resistive touch screen when x2> x1 and y2> y1. Next, by solving equations 5 to 10 according to the measured voltages V1−V6, using two known equations, namely Rxplate = R1 + R2 + R3 and Ryplate = R4 + R5 + R6, R2, R3, R5, Values for R6, Rz ₁ and Rz ₂ are determined. Finally, the coordinates of the contact points P1 and P2 are obtained.

  Refer to FIG. 4B. Six corresponding equations can be described when there are two contact points P1, P2 on the resistive touch screen when x2> x1 and y2 <y1.

When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
Ra = R2 // (Rz ₁ + Rz ₂ + R5)
R = Rz ₁ + Rz ₂ + R2 + R5
Ix = V _REF / (R1 + R3 + Ra)
Here, Ix represents a current flowing through the x conductive layer.

  Referring to FIG. 4B, the following two equations are obtained.

端子YPを基準電圧Vref+に設定し、端子YNを接地すると、次式が得られる。
Rb=R5//(Rz₁+Rz₂+R2)
R=Rz₁+Rz₂+R2+R5
Iy=V_REF/(R4+R6+Rb)
ここでIyはy導電層を流れる電流を表す。

When the terminal YP is set to the reference voltage Vref + and the terminal YN is grounded, the following equation is obtained.
Rb = R5 // (Rz ₁ + Rz ₂ + R2)
R = Rz ₁ + Rz ₂ + R2 + R5
Iy = V _REF / (R4 + R6 + Rb)
Here, Iy represents the current flowing through the y conductive layer.

  Referring to FIG. 4B, the following two equations are obtained.

端子YPを基準電圧Vref+に設定し、端子XNを接地すると、次式が得られる。
Rc=(Rz₁+R2)//(Rz₂+R5)
Ip=V_REF/(Rc+R4+R3)
R=Rz₁+Rz₂+R2+R5
ここでIpはy導電層からx導電層へ流れる電流を表す。

When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
Rc = (Rz ₁ + R2) // (Rz ₂ + R5)
Ip = V _REF / (Rc + R4 + R3)
R = Rz ₁ + Rz ₂ + R2 + R5
Here, Ip represents a current flowing from the y conductive layer to the x conductive layer.

  Referring to FIG. 4B, the following two equations are obtained.

結果として、６個の対応する式(式5’乃至１０’)は、x2＞x1且つy2＜y1のときに抵抗性タッチスクリーン上に２つの接触点P1、P2がある場合に記載される。次に、式５’乃至１０’を測定電圧V1−V6に従い解くことにより、２つの既知の式、つまりRxplate=R1+R2+R3及びRyplate=R4+R5+R6を用いて、R2、R3、R5、R6、Rz₁、及びRz₂の値が求められる。最終的に、接触点P1及びP2の座標が求められる。

As a result, six corresponding equations (Equations 5 ′ to 10 ′) are described when there are two contact points P1, P2 on the resistive touch screen when x2> x1 and y2 <y1. Next, by solving equations 5 ′ to 10 ′ according to the measured voltages V1−V6, using two known equations, namely Rxplate = R1 + R2 + R3 and Ryplate = R4 + R5 + R6, R2, R3, The values of R5, R6, Rz ₁ and Rz ₂ are determined. Finally, the coordinates of the contact points P1 and P2 are obtained.

  When two contact points are detected, the trend of the two contact points is determined. The trend of the two contact points may be forward movement, backward movement, or stationary. The forward movement of the two contact points means that the distance between the two contact points becomes gradually closer. The backward movement of the two contact points means that the distance between the two contact points is gradually increased. The two contact points being stationary means that the distance between the two contact points does not change. Since the two contact points have different distributions, the method for determining the trend of the two contact points may be different.

  Three examples are provided for determining the behavior of two contact points when there are two contact points having the same x-coordinate or the same y-coordinate on the resistive touch screen.

As described above, the difference value Rz ₁ -Rz ₂ in the operation 820 has the following law. If there are two contact points with the same y coordinate, the difference value is less than zero. If there are two contact points with the same x coordinate, the difference value is greater than zero. Further, the difference value Rz ₁ −Rz ₂ further has the following law. The absolute value of the difference value Rz ₁ -Rz ₂ increases as the distance between two contact points having the same y coordinate increases. Similarly, the absolute value of the difference value Rz ₁ −Rz ₂ increases as the distance between two contact points having the same x coordinate increases. Thus, the trend of the two contact points may be determined according to further statistical laws.

  FIG. 9 is a flowchart for determining the trend of two contact points having the same x or y coordinates on a resistive touch screen according to a first embodiment. Operations 902, 904, and 914 are substantially similar to operations 820, 824, and 826, respectively, in FIG. 8B. Accordingly, descriptions regarding operations 902, 904, and 914 are omitted here.

After operation 904, processing proceeds to operation 906, the difference D _CUR -D _PRE between the current difference D _CUR and previous difference D _PRE is calculated. The current difference D _CUR is stored as the next previous difference D _PRE . It should be noted that operation 906 may be performed repeatedly. If D _CUR −D _PRE > Delta_limit, operation 908 indicates that two contact points having the same y coordinate move forward relative to each other. If D _CUR −D _PRE <−Delta_limit, operation 910 indicates that two contact points having the same y coordinate move backward relative to each other. In other cases, two contact points having the same y coordinate are shown to be stationary. Delta_limit functions as a threshold to avoid confusion.

After operation 914, processing proceeds to operation 916, the difference D _CUR -D _PRE between the current difference D _CUR and previous difference D _PRE is calculated. The current difference D _CUR is stored as the next previous difference D _PRE . It should be noted that operation 916 may be performed repeatedly. If D _CUR −D _PRE > Delta_limit, operation 918 indicates that two contact points having the same x coordinate move backward relative to each other. If D _CUR −D _PRE <−Delta_limit, operation 920 indicates that two contact points having the same x coordinate move forward relative to each other. In other cases, two contact points with the same x-coordinate are shown to be stationary.

In a second embodiment, another method is provided for determining the trend of two touch points having the same x or y coordinate on a resistive touch screen. In order to simplify the calculation, it is assumed that the contact pressure at the first contact point P1 is equal to the contact pressure at the second contact point P2. That is, Rz = Rz ₁ = Rz ₂ . Furthermore, it is assumed that two contact points having the same y coordinate move only along the x-axis direction, and two contact points having the same x coordinate move only along the y-axis direction. Therefore, R4 or R6 shown in FIG. 5B does not change when the two contact points move. Also, R1 or R3 shown in FIG. 6B does not change when the two contact points move.

  As shown in FIG. 6A, when two contact points on the resistive touch screen have the same x coordinate, when the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.

ここでIはy導電層からx導電層へ流れる電流を表す。

Here, I represents a current flowing from the y conductive layer to the x conductive layer.

Solving the above two equations yields:
R5 = V5 * (Rz * Rz) / (V6−V5) / R3−2 * Rz (Formula 11)
Equation 11 is a monotonically increasing function when the values of Rz and R3 do not change. That is, as the value of V5 / (V6−V5) increases, the value of R5 also increases. Furthermore, the trend of the two contact points may be determined according to the value of R5. Increasing the value of R5 may indicate that the two contact points are moving backwards relative to each other. Also, a decrease in the value of R5 may indicate that the two contact points move forward relative to each other. Thus, the value of V5 / (V6-V5) can be used to determine the behavior of two contact points that have the same x coordinate.

  As shown in FIG. 5A, when the two contact points have the same y coordinate, when the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.

ここでIはy導電層からx導電層へ流れる電流を表す。

Here, I represents a current flowing from the y conductive layer to the x conductive layer.

Solving the above two equations yields:
R2 = (V _REF −V6) * Rz * Rz / R4 / (V6−V5) −2 * Rz (Equation 12)
Equation 12 is a monotonically increasing function when the values of Rz and R4 do not change. That is, as the value of (V _REF −V6 / (V6−V5) increases, the value of R2 also increases. Furthermore, the trend of the two contact points may be determined according to the value of R2.The value of R2 increases. This may indicate that the two contact points move backward with respect to each other, and a decrease in the value of R2 may indicate that the two contact points move forward with respect to each other, so (V _REF − The value of (V6) / (V6−V5) can be used to determine the behavior of two contact points with the same y coordinate.

  In a third embodiment, another method is provided for determining the trend of two contact points having the same x or y coordinate on a resistive touch screen. In this embodiment, the only premise is that the two contact points coincide with each other. That is, R1 = R3 or R4 = R6.

If there are two touch points on the touch screen with the same y coordinate, the equivalent electrical circuit of the touch screen is shown in FIGS. 5B and 5C. Refer to FIG. 5B. When the terminal YP is set to the reference voltage Vref + and the terminal YN is grounded, the following equation is obtained.
R4 = Ryplate * (V _REF −V1) / V _REF
Refer to FIG. 5B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
R3 = (V6−V5) * R4 / (V _REF −V6)
R3 + R2 = V5 * R4 / (V _REF −V6) (1)
Refer to FIG. 5B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
R1 + R1 = R3 + R1 = (V _REF −V3) * (R3 + R2) / V3 (2)
Refer to FIG. 5C. According to the conventional relationship between y and Δ-type electrical circuit, the following equation is obtained.
R2 = Rxplate−2 * R3 = R1 + R2 + R1 * R2 / R3 (3)
Solve equations (1), (2), and (3),

と仮定すると、以下を得る。
R1=(d+f−e)/2
R2=d−(f−e)
R2=Rxplate−2*(f−R1)
R2の値は、同一のy座標を有する２つの接触点の間の距離を反映する。従って、同一のy座標を有する２つの接触点の動向が決定され得る。

Assuming that we get
R1 = (d + f−e) / 2
R2 = d− (f−e)
R2 = Rxplate−2 * (f−R1)
The value of R2 reflects the distance between two contact points having the same y coordinate. Thus, the trend of two contact points having the same y coordinate can be determined.

  If there are two contact points with the same y coordinate on the touch screen, the equivalent electrical circuit of the touch screen is shown in FIGS. 6B and 6C.

Reference is made to FIG. 6B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
R3 = Rxplate * V3 / V _REF
Reference is made to FIG. 6B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
R3 = (V6−V5) * R3 / V5
R4 + R2 = (V _REF −V6) * R3 / V5
Reference is made to FIG. 6B. When the terminal YP is set to the reference voltage Vref + and the terminal YN is grounded, the following equation is obtained.
R4 + R1 = (R4 + R2 ) * V1 / (V REF -V1) = (V REF -V6) * V1 * R3 / (V5 * (V REF -V1))
Refer to FIG. 6C. According to the conventional relationship between y and Δ-type electrical circuit, the following equation is obtained.
R1 + R2 + R1 * R2 / R3 = Ryplate−R4−R6 = Ryplate−2 * R4
Solve these equations,

と設定すると、以下を得る。
R2=(d+e)/2
R1=(d−e)/2
R5=d+f/R3
R5の値は、同一のx座標を有する２つの接触点の間の距離を反映する。従って、同一のx座標を有する２つの接触点の動向が決定され得る。

To get the following:
R2 = (d + e) / 2
R1 = (d−e) / 2
R5 = d + f / R3
The value of R5 reflects the distance between two contact points having the same x coordinate. Thus, the trend of two contact points having the same x coordinate can be determined.

  If there are two contact points on the resistive touch screen when x2> x1 and y2> y1, two examples of determining the behavior of the two contact points are provided.

In the first embodiment, in order to simplify the calculation, the contact pressure at the first contact point P1 is equal to the contact pressure at the second contact point P2, and the first contact point P1 is the second contact point P2. And symmetric with respect to the center of the resistive touch screen, and x1 = y1 and x2 = y2. This assumption means Rz ₁ = Rz ₂ , R1 = R3, and R4 = R6 shown in FIG. 3B. FIG. 10 schematically illustrates a resistive touch screen 220 when there are two contact points that are centrosymmetric with respect to the center of the resistive touch screen when x2> x1 and y2> y1.

Refer to FIG. 3B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
I _R1 = V _REF / (2 * R1 + (2Rz + R5) // R2)
I _R5 = R2 / (2Rz + R2 + R5) * I _R1
Here, I _R1 represents the current flowing through the resistor R1, I _R5 represents the current flowing through the resistor R5, and it is assumed that V _REF = 4096.

Therefore, the following equation is obtained.
V3−V4 = I _R5 * R5
= R2 / (2Rz + R2 + R5) * I _R1 * R5
= R2 / (2Rz + R2 + R5) * 4096 / (2 * R1 + (2r + R5) // R2) * R5
Assuming P1 and P2 represent the linear resistances of the x and y conductive layers, respectively, each conductive layer can be divided up to 2 ¹² = 4096 divisions along each direction. Therefore, p1 = Rxplate / 4096 and P2 = Ryplate / 4096. The letter x represents the distance between the two contact points and x∈ [0, 4095].

Setting v = V3−V4, substituting R1 = (Rxplate−p1 * x) / 2, R2 = p1 * x, and R5 = P2 * x into the above equation, the following equation is obtained.
v = 4096 * p1 * P2 * x * x / ((4096 * p1−p1 * x) * (p1 * x + P2 * x + 2 * Rz) + p1 * x * (P2 * x + 2 * Rz) (Formula 13)
Refer to FIG. 13B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
I = V _REF / (R3 + R4 + (R2 + Rz) // (R5 + Rz))
V5 = I * R3 + I * (R5 + Rz) / (R2 + R5 + 2Rz) * R2
V6 = I * R3 + I * (R2 + Rz) / (R2 + R5 + 2Rz) * Rz
Here, I represents the current flowing through R3 and R4.

If u = V5−V6, then u = I * ((R5 + Rz) * R2− (R2 + Rz) * Rz) / (R2 + R5 + 2Rz) and R1 = (Rxplate−p1 * x) Substituting / 2, R4 = (Ryplate−P2 * x) / 2, R2 = p1 * x, and R5 = P2 * x into the equation of u, the following equation is obtained.
u = 4096 * 2 * ((P2 * x + Rz) * p1 * x− (p1 * x + Rz) * Rz) / ((4096 * p1−p1 * x + 4096 * P2−P2 * x) * ( 2 * Rz + p1 * x + P2 * x) + 2 * (p1 * x + Rz) * (P2 * x + Rz)) (Equation 14)
Solving equations 13 and 14 yields:
x = 1/2 / (4096 + u) * (33554432 * v * p1 + 8192 * u * p1 * v + 33554432 * v * P2 + 8192 * u * P2 * v + 8192 * (67108864 * p1 * P2 * v ^ 2 + 8192 * u * p1 * P2 * v ^ 2-2−2 * u ^ 2 * p1 * v ^ 2 * P2 + 8192 * u * P2 ^ 2 * v ^ 2 + 2 * u ^ 2 * P2 ^ 2 * v ^ 2−33554432 * u * P2 ^ 2 * v−33554432 * u * p1 * v * P2−8192 * u ^ 2 * P2 ^ 2 * v−8192 * u ^ 2 * p1 * v * P2) ^ (1/2)) / (4096 * P2 + v * p1) (Formula 15)
Therefore, the distance x between the two contact points is obtained according to Equation 15. Therefore, the trend of the two contact points shown in FIG. 10 can be determined.

  In the second embodiment, another method for determining the trend of two contact points when x2> x1 and y2> y1 is described below. In this embodiment, the only premise is that the two contact points are centrosymmetric with respect to each other. That is, R1 = R3 and R4 = R6.

When R2 = x and V _REF = 4096 are set as follows.
R1 = R3 = (XPlate−x) / 2, R4 = R6 = (YPlate−k * x) / 2, R5 = k * x
Here, k is a constant related to the slope of the straight line of the shortest distance formed by two contact points, XPlate is the above-mentioned Rxplate, and YPlate is the above-mentioned Ryplate.

Refer to FIG. 3B. When the terminal YP is set to the reference voltage Vref + and the terminal YN is grounded, the following equation is obtained.
4096 * ((YPlate−k * x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + k * x * (Rz ₂ + x)) − V1 * (k * x * (Rz ₁ + Rz ₂ + x) + (YPlate−k * x) * (x + Rz ₁ + Rz ₂ + k * x)) = 0 (1) 4096 * ((YPlate−k * x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + k * x * (Rz ₂ )) − V2 * (k * x * (Rz ₁ + Rz ₂ + x) + (YPlate−k * x) * (x + Rz ₁ + Rz ₂ + k * x)) = 0 (2)
Refer to FIG. 3B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
4096 * ((XPlate−x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + (k * x + Rz ₂ ) * x) −V5 * (((XPlate−x) / 2 + ( YPlate−k * x) / 2) * (x + k * x + Rz ₁ + Rz ₂ ) + (x + Rz ₁ ) * (k * x + Rz ₂ )) = 0 (3)
4096 * ((XPlate−x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + (x + Rz ₁ ) * Rz ₂ ) −V6 * (((XPlate−x) / 2 + (YPlate −k * x) / 2) * (x + k * x + Rz ₁ + Rz ₂ ) + (x + Rz ₁ ) * (k * x + Rz ₂ )) = 0 (4)
Refer to FIG. 3B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
4096 * ((XPlate−x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + x * (Rz ₂ + k * x)) − Vx * (x * (Rz ₁ + Rz ₂ + k * x) + (XPlate−x) * (x + Rz ₁ + Rz ₂ + k * x)) = 0 (5)
4096 * ((XPlate−x) * (x + k * x + Rz ₁ + Rz ₂ ) / 2 + x * (Rz ₂ )) − VXN * (x * (Rz ₁ + Rz ₂ + k * x) + (XPlate−x) * (x + Rz ₁ + Rz ₂ + k * x)) = 0 (6)
Solving four of equations (1) through (6) with the help of the Matlab tool gives k and x.
k = −1 / 4 * (− 4096 * V5 * YPlate−V5 * Vx * XPlate + 8192 * Vx * XPlate + VXN * XPlate * V5−2 * V6 * XPlate * Vx− (VXN ^ 2 * XPlate ^ 2 * V5 ^ 2 + 16384 * V5 * Vx * XPlate * YPlate * V6−8192 * Vx * V5 ^ 2 * YPlate * XPlate + 16777216 * YPlate ^ 2 * V5 ^ 2 + 8192 * VXN * V5 ^ 2 * XPlate * YPlate− 67108864 * V5 * YPlate * Vx * XPlate-4 * VXN * XPlate ^ 2 * V5 * V6 * Vx−32768 * Vx ^ 2 * XPlate ^ 2 * V6 + 4 * V6 ^ 2 * XPlate ^ 2 * Vx ^ 2− 16384 * V5 * XPlate ^ 2 * Vx ^ 2-2 * V5 ^ 2 * XPlate ^ 2 * Vx * VXN + 16384 * Vx * XPlate ^ 2 * V5 * VXN + 4 * V5 * XPlate ^ 2 * Vx ^ 2 * V6 + V5 ^ 2 * XPlate ^ 2 * Vx ^ 2 + 67108864 * Vx ^ 2 * XPlate ^ 2−8 * V5 ^ 2 * YPlate * VXN * XPlate * Vx + 8 * Vx ^ 2 * V5 ^ 2 * YPlate * XPlate) ^ (1/2)) / V5 / XPlate / (Vx−2048)
x = (− 2048 * V5 * XPlate * k ^ 2 + V5 * k ^ 2 * Vx * XPlate−2048 * V5 * YPlate * k−2048 * V5 * k * XPlate + V5 * k * XPlate * Vx−V6 * XPlate * k * Vx + 4096 * Vx * XPlate * k−2048 * V5 * YPlate−V6 * XPlate * Vx + 4096 * Vx * XPlate + (4096 * V5 ^ 2 * YPlate ^ 2 * k * Vx−2 * Vx ^ 2 * V6 ^ 2 * YPlate * XPlate-8192 * V5 * k * XPlate ^ 2 * Vx ^ 2-2-2 * V5 ^ 2 * YPlate * k ^ 2 * Vx ^ 2 * XPlate-24576 * V6 * XPlate ^ 2 * Vx ^ 2 * k + 67108864 * k * Vx ^ 2 * XPlate ^ 2 + 8192 * XPlate * V6 * YPlate * Vx ^ 2−8192 * XPlate * k * V5 * YPlate * Vx ^ 2 + 4194304 * k ^ 2 * V5 ^ 2 * YPlate ^ 2 + 2 * V6 * XPlate ^ 2 * k * V5 * Vx ^ 2−8192 * XPlate * V5 * YPlate * Vx ^ 2 + 8388608 * V5 ^ 2 * k * YPlate * XPlate + 4194304 * V5 ^ 2 * k ^ 2 * XPlate ^ 2 + 16777216 * k ^ 2 * XPlate * V5 ^ 2 * YPlate + 8388608 * V5 ^ 2 * k ^ 3 * XPlate ^ 2 + 8388608 * YPlate * V5 ^ 2 * XPlate * k ^ 3 + 2 * Vx ^ 2 * V6 ^ 2 * XPlate ^ 2 * k-8192 * V5 ^ 2 * k ^ 3 * XPlate ^ 2 * Vx + 2 * V5 ^ 2 * k ^ 3 * XPlate ^ 2 * Vx ^ 2 + 2 * V6 * XPlate * Vx ^ 2 * V5 * YPlate + 8388608 * k * V5 ^ 2 * YPlate ^ 2-4096 * V6 * YPlate ^ 2 * V5 * Vx-2 * Vx ^ 2 * XPlate ^ 2 * k ^ 3 * V6 * V5−V5 ^ 2 * k ^ 2 * Vx ^ 2 * XPlate ^ 2−16777216 * Vx * XPlate * k ^ 2 * V5 * YPlate−4096 * k ^ 3 * V5 ^ 2 * YPlate * Vx * XPlate + 4096 * Vx * XPlate * k ^ 2 * V6 * YPlate * V5 + V5 ^ 2 * YPlate ^ 2 * Vx ^ 2 + 8192 * V6 * XPlate ^ 2 * k ^ 2 * Vx * V5 + 4096 * V6 * XPlate * k * Vx * V5 * YPlate −4 * V6 * XPlate ^ 2 * k ^ 2 * Vx ^ 2 * V5 + 4 * V6 * XPlate * k * Vx ^ 2 * V5 * YPlate-8192 * Vx ^ 2 * XPlate ^ 2 * k ^ 2 * V6 −4096 * V5 ^ 2 * XPlate ^ 2 * k ^ 4 * Vx−16777216 * V5 * XPlate ^ 2 * k ^ 3 * Vx + 4096 * V5 * XPlate ^ 2 * k ^ 3 * V6 * Vx + 4194304 * V5 ^ 2 * YPlate ^ 2 + 24576 * V5 * k ^ 2 * Vx ^ 2 * XPlate ^ 2−50331648 * V5 * k ^ 2 * Vx * XPlate ^ 2−50331648 * XPlate * V5 * YPlate * k * Vx−4096 * V5 ^ 2 * YPlate * k ^ 2 * Vx * XPlate + 4194304 * V5 ^ 2 * XPlate ^ 2 * k ^ 4 + 16777216 * Vx ^ 2 * XPlate ^ 2 * k ^ 2 + Vx ^ 2 * XPlate ^ 2 * k ^ 2 * V6 ^ 2 + Vx ^ 2 * XPlate ^ 2 * k ^ 4 * V5 ^ 2 + 8192 * Vx ^ 2 * XPlate ^ 2 * k ^ 3 * V5) ^ (1/2)) / Vx / (V5 * k−V6 + 4096)
Here, Vx = V3, VXN = V4, Vy = V1, and VYN = V2.

  Therefore, a distance x between two contact points where x2> x1 and y2> y1 is obtained. Thus, the trend of the two contact points where x2> x1 and y2> y1 can be determined.

  If there are two contact points on the resistive touch screen when x2> x1 and y2 <y1, two examples are provided for determining the behavior of the two contact points.

In the first embodiment, in order to simplify the calculation, the contact pressure at the first contact point P1 is equal to the contact pressure at the second contact point P2, and the first contact point P1 is the second contact point P2. Are symmetric with respect to the center of the resistive touch screen, and x1 = y1 and x2 = y2. This assumption implies Rz ₁ = Rz ₂ , R1 = R3, and R4 = R6 shown in FIG. 4B. FIG. 11 schematically illustrates a resistive touch screen 220 when there are two contact points that are centrosymmetric with respect to the center of the resistive touch screen when x2> x1 and y2 <y1.

Refer to FIG. 4B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
v = V4−V3
= 4096 * p1 * P2 * x * x / ((4096 * p1−p1 * x) * (p1 * x + P2 * x + 2 * Rz) + p1 * x * (P2 * x + 2 * Rz)) (Formula 16)
Refer to FIG. 4B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
I = V _ref / (R3 + R4 + (R2 + R5 + Rz) // Rz)
V5 = I * R3 + I * Rz / (R2 + R5 + 2Rz) * R2
V6 = I * R3 + I * Rz / (R2 + R5 + 2Rz) * (R2 + Rz)
Here, I represents the current flowing through R3 and R4. In this embodiment, it is assumed that Vref + = 4096.
When u = V6−V5, u = I * Rz * Rz / (R2 + R5 + 2Rz).

Substituting R3 = (Rxplate−p1 * x) / 2, R4 = (Ryplate−P2 * x) / 2, R2 = p1 * x, R5 = P2 * x into the equation of u, the following equation is obtained.
u = 4096 * 2 * Rz * Rz / ((4096 * p1 + 4096 * P2−p1 * XP2 * x) * (2 * Rz + p1 * x + P2 * x) + 2 * Rz * (Rz + p1 * x + P2 * x)) (Equation 17)
Solving equations 13 and 14 yields:
x = 1/2 / (− 4096 + u) * (− 33554432 * v * p1 + 8192 * u * p1 * v−33554432 * v * P2 + 8192 * u * P2 * v−8192 * (− 8192 * u * p1 * P2 * v ^ 2 + 2 * u ^ 2 * p1 * v ^ 2 * P2−8192 * u * P2 ^ 2 * v ^ 2 + 2 * u ^ 2 * P2 ^ 2 * v ^ 2 + 33554432 * u * p1 * v * P2 + 33554432 * u * P2 ^ 2 * v-8192 * u ^ 2 * p1 * v * P2-8192 * u ^ 2 * P2 ^ 2 * v) ^ (1/2)) / (4096 * P2 + v * p1) (Formula 18)
Therefore, the distance x between the two contact points is obtained according to Equation 17. Therefore, the trend of the two contact points shown in FIG. 11 can be determined.

  In the second embodiment, another method for determining the trend of two contact points when x2> x1 and y2 <y1 is described below. In this embodiment, the only premise is that the two contact points are centrosymmetric with respect to each other. That is, R1 = R3 and R4 = R6.

When R2 = x and Vref = 4096 are set as follows.
R1 = R3 = (XPlate−x) / 2, R4 = R6 = (YPlate−k * x) / 2, R5 = k * x
Here, k is a constant related to the slope of the straight line of the shortest distance formed by two contact points, XPlate is the above-mentioned Rxplate, and YPlate is the above-mentioned Ryplate.

Refer to FIG. 4B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
4096 * ((YPlate−k * x) * (x + k * x + z1 + z2) / 2 + k * x * (z1 + x)) − VYN * (k * x * (z1 + z2 + x) + (YPlate−k * x) * (x + z1 + z2 + k * x)) = 0 (1 ')
4096 * ((YPlate−k * x) * (x + k * x + z1 + z2) / 2 + k * x * (z1)) − Vy * (k * x * (z1 + z2 + x) + ( YPlate−k * x) * (x + z1 + z2 + k * x)) = 0 (2 ')
Refer to FIG. 4B. When the terminal YP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
((XPlate−x) * (x + k * x + z1 + z2) / 2 + z2 * x) * V6−V5 * ((XPlate−x) * (x + k * x + z1 + z2) / 2 + z2 * (x + z1)) = 0 (3 ')
4096 * z1 * z2− (V6−V5) * ((XPlate−x + YPlate−k * x) * (x + k * x + z1 + z2) / 2 + (x + k * x + z1) * z2 ) = 0 (4 ')
Refer to FIG. 4B. When the terminal XP is set to the reference voltage Vref + and the terminal XN is grounded, the following equation is obtained.
4096 * ((XPlate−x) * (x + k * x + z1 + z2) / 2 + x * (z2 + k * x)) − VXN * (x * (z1 + z2 + k * x) + ( XPlate−x) * (x + z1 + z2 + k * x)) = 0 (5 ')
4096 * ((XPlate−x) * (x + k * x + z1 + z2) / 2 + x * (z2)) − Vx * (x * (z1 + z2 + k * x) + (XPlate−x) * (x + z1 + z2 + k * x)) = 0 (6 ')
Solving four of equations (1 ′) through (6 ′) with the help of the Matlab tool gives k and x.
k = 1/4 * (XPlate * V5 * VXN + 8192 * Vx * XPlate-2 * V6 * Vx * XPlate−4096 * V5 * YPlate−V5 * XPlate * Vx − (− 32768 * V6 * Vx ^ 2 * XPlate ^ 2-2 * XPlate ^ 2 * V5 ^ 2 * VXN * Vx + 4 * XPlate ^ 2 * V5 * V6 * Vx ^ 2 + 16384 * Vx * V6 * V5 * YPlate * XPlate−67108864 * XPlate * V5 * YPlate * Vx + 67108864 * Vx ^ 2 * XPlate ^ 2 + 8192 * XPlate * V5 ^ 2 * YPlate * VXN-8192 * XPlate * V5 ^ 2 * YPlate * Vx-16384 * V5 * XPlate ^ 2 * Vx ^ 2 + 16384 * V5 * XPlate ^ 2 * VXN * Vx + XPlate ^ 2 * V5 ^ 2 * Vx ^ 2 + XPlate ^ 2 * V5 ^ 2 * VXN ^ 2 + 16777216 * V5 ^ 2 * YPlate ^ 2−4 * XPlate ^ 2 * V5 * VXN * V6 * Vx + 4 * V6 ^ 2 * Vx ^ 2 * XPlate ^ 2-8 * XPlate * V5 ^ 2 * YPlate * VXN * Vx + 8 * XPlate * V5 ^ 2 * YPlate * Vx ^ 2 ) ^ (1/2)) / XPlate / V5 / (− 2048 + Vx) x = (XPlate * V5 * k * VXN−XPlate * V5 * k * Vx + XPlate * V5 * VXN−V5 * XPlate * Vx + ( XPlate ^ 2 * V5 ^ 2 * VXN ^ 2 * k ^ 2-2 * k ^ 2 * V5 ^ 2 * XPlate ^ 2 * Vx * VXN + 2 * XPlate ^ 2 * V5 ^ 2 * k * VXN ^ 2− 8 * XPlate ^ 2 * V5 ^ 2 * k * VXN * Vx + 5 * V5 ^ 2 * XPlate ^ 2 * Vx ^ 2 * k ^ 2 + 6 * XPlate ^ 2 * V5 ^ 2 * k * Vx ^ 2 + 4 * XPlate * V5 ^ 2 * YPlate * VXN * Vx−8192 * XPlate * YPlate * V5 ^ 2 * k * VXN−16384 * XPlate ^ 2 * Vx * V5 ^ 2 * k ^ 2 + 8192 * XPlate * YPlate * V5 ^ 2 * k * Vx + 16384 * XPlate ^ 2 * V5 * VXN * Vx * k-16384 * XPlate ^ 2 * V5 * k * Vx ^ 2-2 * XPlate * YPlate * V5 ^ 2 * Vx ^ 2 + 16777216 * XPlate ^ 2 * V5 ^ 2 * k ^ 2-2 * XPlat e * YPlate * V5 ^ 2 * VXN ^ 2) ^ (1/2)) / V5 / (− Vx + VXN + 4096 * k)
Here, Vx = V3, VXN = V4, Vy = V1, and VYN = V2.

  Accordingly, a distance x between two contact points where x2> x1 and y2 <y1 is obtained. Therefore, the trend of the two contact points where x2> x1 and y2 <y1 can be determined.

  The present invention has been described in sufficient detail with a certain degree of particularity. It should be understood by those skilled in the art that the embodiments have been disclosed herein by way of example only, and that numerous modifications may be made to combinations of components and parts without departing from the spirit and scope of the claimed invention. It can be done. Accordingly, the scope of the invention is defined by the appended claims rather than the foregoing embodiments.

1 is a schematic diagram illustrating a conventional 4-wire resistive touch screen. FIG. 5 is a circuit diagram illustrating an equivalent electrical circuit of a resistive touch screen when a single contact point is present on the resistive touch screen. There is a need for an improved technique for detecting multiple contact points on a resistive touch screen. x2> x1 and y2> y1, x2 and y2 represent the x and y coordinates of the second contact point P2, and x1 and y1 represent the x and y coordinates of the second contact point P1, and A resistive touch screen 220 with two contact points is schematically shown. 3C shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 3A. FIG. 6 schematically illustrates a resistive touch screen when there are two contact points on the resistive touch screen when x2> x1 and y1> y2. 4B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 4A. The resistive touch screen 220 is schematically shown when there are two contact points on the resistive touch screen when x2> x1 and y1 = y2. 5B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 5A. The resistive touch screen 220 is schematically shown when there are two contact points on the resistive touch screen when x2 = x1 and y1 <y2. FIG. 6B shows an equivalent circuit of the resistive touch screen 220 shown in FIG. 6A. FIG. 6 is a block diagram illustrating an example of the structure of a selector 240 according to an embodiment of the present invention. FIG. 6 illustrates a process or flowchart for detecting single or multiple touch points on a resistive touch screen according to an embodiment of the present invention. FIG. 6 illustrates a process or flowchart for detecting single or multiple touch points on a resistive touch screen according to an embodiment of the present invention. 3 is a flowchart for determining the trend of two contact points having the same x or y coordinate on a resistive touch screen according to a first embodiment. The resistive touch screen 220 is schematically illustrated when there are two contact points that are centrosymmetric with respect to the center of the resistive touch screen when x2> x1 and y2> y1. The resistive touch screen 220 is schematically shown when there are two contact points that are centrosymmetric with respect to the center of the resistive touch screen when x2> x1 and y2 <y1.

Explanation of symbols

200 System 220 Resistive Touch Screen 240 Selector 242 Vref + Selector 244 Measurement Terminal Selector 246 Vref-Selector 248 Mode Control Unit 260 Analog-to-Digital Converter (ADC)
280 microprocessor P1, the potential difference between the P2 contact point R1~R6 resistance V1~V6 voltage value V _REF Vref + and Vref- as Vref + positive reference voltage Vref- negative reference voltage XN, YN negative terminal XP, YP positive terminal x1 , X2 x coordinate y1, y2 y coordinate

Claims (22)

A method for detecting one or more contact points on a resistive touch screen having a first conductive layer and a second conductive layer, each having a positive terminal and a negative terminal, comprising:
Setting the positive terminal of the second conductive layer to a positive reference voltage;
Setting the negative terminal of the second conductive layer to a negative reference voltage;
Measuring a voltage value V1 of the positive terminal of the first conductive layer and a voltage value V2 of the negative terminal of the first conductive layer;
Setting the positive terminal of the first conductive layer to a positive reference voltage;
Setting the negative terminal of the first conductive layer to a negative reference voltage;
Measuring a voltage value V3 of the positive terminal of the second conductive layer and a voltage value V4 of the negative terminal of the second conductive layer; and on the resistive touch screen according to the voltage values V1 to V4 Detecting the contact point. The first conductive layer extends along the x axis and is referred to as an x conductive layer, the second conductive layer extends along the y axis and is referred to as a y conductive layer,
Detecting a contact point on the resistive touch screen according to the voltage values V1 to V4,
Obtaining a first difference V1-V2 between the voltage values V1 and V2, and a second difference V3-V4 between the voltage values V3 and V4;
Comparing the first difference V1-V2 with a first threshold THD1 and a second threshold THD2, and comparing the second difference V3-V4 with the first threshold THD1 and the second threshold THD2. ,
If THD1 ≦ V1-V2 ≦ THD2 and THD1 ≦ V3-V4 ≦ THD2, indicating that there is a single contact point or two contact points having the same x or y coordinate on the resistive touch screen;
Otherwise, indicating that there are two contact points with different x and y coordinates on the resistive touch screen;
The method of claim 1, wherein the first threshold THD1 is less than or equal to zero and the second threshold THD2 is greater than or equal to zero. Indicating that there are two contact points with different x and y coordinates on the resistive touch screen,
When x2> x1 and y2> y1, x1 and y1 represent the x and y coordinates of the first contact point, and x2 and y2 represent the x and y coordinates of the second contact point, V1−V2> THD2 and V3 If -V4> THD2, indicating that there are two contact points on the resistive touch screen; and
The method of claim 2, further comprising the step of indicating that there are two contact points on the resistive touch screen when V1−V2 <THD1 and V3−V4 <THD1 when x2> x1 and y2 <y1. . After indicating that there is a single contact point or two contact points having the same x or y coordinate on the resistive touch screen;
Setting the positive terminal of the y conductive layer to the positive reference voltage, setting the negative terminal of the x conductive layer to the negative reference voltage, and a voltage value V5 of the negative terminal of the x conductive layer; Measuring a voltage value V6 of the negative terminal of the y conductive layer;
Obtaining a _first value Rz ₁ and a second value Rz ₂ of the contact resistance of the assumed contact point according to the voltage value V5 and the voltage value V6 by two different methods;
Comparison said first value Rz ₁ and calculates the difference value Rz ₁ -Rz ₂ between the second value Rz _2, the difference value Rz ₁ -Rz ₂ and the third threshold THD3 and fourth threshold THD4 Stage to do,
If THD3 ≦ Rz ₁ −Rz ₂ ≦ THD4, indicating that there is a single contact point on the resistive touch screen;
If Rz ₁ −Rz ₂ > THD4, indicating that there are two contact points with the same x coordinate; and
If Rz ₁ −Rz ₂ <THD3, there are two contact points with the same y coordinate,
The method of claim 2, wherein the third threshold THD3 is less than or equal to zero, and the fourth threshold THD4 is greater than or equal to zero. The method of claim 4, further comprising: determining a trend of two contact points having the same x coordinate according to a difference D _CUR -D _PRE between a current difference value D _CUR and a previous difference value D _PRE . Method. According to the difference D _CUR −D _PRE between the current difference value D _CUR and the previous difference value D _PRE , the step of determining the trend of two contact points having the same x coordinate is either Delta_limit is greater than zero or If it is equal to zero,
If D _CUR −D _PRE > Delta_limit, indicating that two touch points with the same x coordinate move back away from each other; and
6. The method of claim 5, comprising: if D _CUR −D _PRE <−Delta_limit, indicating that two touch points with the same x coordinate move forward with respect to each other. The method according to claim 4, further comprising: determining a trend of two contact points having the same y-coordinate according to a difference D _CUR -D _PRE between a current difference value D _CUR and a previous difference value D _PRE . Method. According to the difference D _CUR −D _PRE between the current difference value D _CUR and the previous difference value D _PRE , the step of determining the trend of two contact points having the same y coordinate is either delta_limit is greater than zero or If it is equal to zero,
If D _CUR −D _PRE > Delta_limit, indicating that two contact points with the same y coordinate move forward with respect to each other; and
The method of claim 7, further comprising: if D _CUR −D _PRE <−Delta_limit, indicating that two contact points with the same y coordinate move backward with respect to each other. Obtaining a resistance value R5 between the two contact points along the y-axis direction according to the voltage values V5 and V6;
The method according to claim 4, further comprising: determining a trend of two contact points having the same x coordinate according to the resistance value R5. Obtaining a resistance value R2 between the two contact points along the x-axis direction according to the voltage values V5 and V6;
5. The method of claim 4, further comprising determining a trend of two contact points having the same y coordinate according to the resistance value R2. After the step indicating that there are two contact points on the resistive touch screen, when x2> x1 and y2> y1,
Setting the positive terminal of the y conductive layer to the positive reference voltage, setting the negative terminal of the x conductive layer to the negative reference voltage, and a voltage value V5 of the positive terminal of the x conductive layer; The method according to claim 3, further comprising: measuring a voltage value V6 of the negative terminal of the y conductive layer; and determining coordinates of the two contact points according to the voltage values V1 to V6. After the step indicating that there are two contact points on the resistive touch screen, when x2> x1 and y2> y1,
Setting the positive terminal of the y conductive layer to the positive reference voltage, setting the negative terminal of the x conductive layer to the negative reference voltage, and a voltage value V5 of the positive terminal of the x conductive layer; The method according to claim 3, further comprising: measuring a voltage value V6 of the negative terminal of the y conductive layer; and determining coordinates of the two contact points according to the voltage values V1 to V6. After the step indicating that there are two contact points on the resistive touch screen, when x2> x1 and y2> y1,
Setting the positive terminal of the y conductive layer to the positive reference voltage, setting the negative terminal of the x conductive layer to the negative reference voltage, and a voltage value V5 of the positive terminal of the x conductive layer; Measuring a voltage value V6 of the negative terminal of the y conductive layer;
The contact resistance of the first contact point is equal to the contact resistance of the second contact point, and the first contact point is centrosymmetric with respect to the center of the second contact point and the resistive touch screen. Assuming stage,
The method according to claim 3, further comprising: determining a distance between the two contact points according to the voltage values V3 to V6; and determining a trend of the two contact points according to the distance. After the step indicating that there are two contact points on the resistive touch screen, when x2> x1 and y2 <y1,
Setting the positive terminal of the y conductive layer to the positive reference voltage, setting the negative terminal of the x conductive layer to the negative reference voltage, and a voltage value V5 of the positive terminal of the x conductive layer; Measuring a voltage value V6 of the negative terminal of the y conductive layer;
The contact resistance of the first contact point is equal to the contact resistance of the second contact point, and the first contact point is centrosymmetric with respect to the center of the second contact point and the resistive touch screen. Assuming stage,
The method according to claim 3, further comprising: determining a distance between the two contact points according to the voltage values V3 to V6; and determining a trend of the two contact points according to the distance.   The method of claim 1, wherein the negative reference voltage is ground. A system for detecting at least one contact point on a resistive touch screen having a first conductive layer and a second conductive layer each having a positive terminal and a negative terminal and having a total of four terminals. ,
At least six measurement modes for measuring at least six voltages at the four terminals by applying either a reference voltage or ground to one or more of the four terminals in at least six ways. A selector for selecting a measurement mode of the resistive touch screen,
An analog-to-digital converter that converts analog voltage values obtained in each of the at least six measurement modes into corresponding digital voltage values to obtain at least six digital voltage values; and the six digital voltage values A microprocessor that receives, processes the six digital voltage values according to a series of equations, and derives coordinates on the resistive touch screen of the at least one contact point; The at least six measurement modes are:
A positive reference voltage is applied to the positive terminal of the second conductive layer, a negative reference voltage is applied to the negative terminal of the second conductive layer, and the positive terminal of the first conductive layer is a voltage A first measurement mode, in which V1 is selected as the measurement terminal to be measured;
The positive reference voltage is applied to the positive terminal of the second conductive layer, the negative reference voltage is applied to the negative terminal of the second conductive layer, and the negative terminal of the first conductive layer is A second measurement mode, selected as the measurement terminal at which the voltage V2 is measured,
The positive reference voltage is applied to the positive terminal of the first conductive layer, the negative reference voltage is applied to the negative terminal of the first conductive layer, and the positive terminal of the second conductive layer is A third measurement mode, selected as the measurement terminal at which the voltage V3 is measured,
The positive reference voltage is applied to the positive terminal of the first conductive layer, the negative reference voltage is applied to the negative terminal of the first conductive layer, and the negative terminal of the second conductive layer is A fourth measurement mode, selected as the measurement terminal at which the voltage V4 is measured,
The positive reference voltage is applied to the positive terminal of the second conductive layer, the negative reference voltage is applied to the negative terminal of the first conductive layer, and the positive terminal of the first conductive layer is A fifth measurement mode selected as a measurement terminal at which the voltage V5 is measured; and applying the positive reference voltage to the positive terminal of the second conductive layer and applying a negative reference voltage to the first conductivity 17. The system of claim 16, having a sixth measurement mode applied to the negative terminal of a layer, wherein the negative terminal of the second conductive layer is selected as a measurement terminal at which the voltage V6 is measured. The selector includes a positive reference voltage selector, a negative reference voltage selector, a measurement terminal selector, and a mode control unit.
The mode control unit controls selection of the positive reference voltage selector, the negative reference voltage selector, and the measurement terminal selector in each measurement mode,
The positive reference voltage selector selects one to be connected to the positive reference voltage from the positive terminal of the first conductive layer and the positive terminal of the second conductive layer;
The negative reference voltage selector selects one to be connected to the negative reference voltage from the negative terminal of the first conductive layer and the negative terminal of the second conductive layer;
The system of claim 17, wherein the measurement terminal selector selects one of the four terminals of the two conductive layers as the measurement terminal. x1 and y1 represent the x and y coordinates of the first contact point, and x2 and y2 represent the x and y coordinates of the second contact point,
If V1 = V2 and V3 = 4, the microprocessor determines that there is a single contact point or two contact points with the same x or y coordinate on the resistive touch screen;
When x2> x1 and y2> y1, and when V1> V2 and V3> 4, the microprocessor determines that there are two contact points on the resistive touch screen;
19. The system of claim 18, wherein when x2> x1 and y2 <y1, if V1 <V2 and V3 <4, the microprocessor determines that there are two contact points on the resistive touch screen. At least one on a resistive touch screen having a first conductive layer and a second conductive layer each having a positive terminal and a negative terminal, a total of four terminals, and a total of four terminals A method for detecting a contact point,
The positive terminal of the second conductive layer is set to a positive reference voltage, the negative terminal of the second conductive layer is set to a negative reference voltage, and the voltage of the positive terminal of the first conductive layer Measuring a value V1 and a voltage value V2 of the negative terminal of the first conductive layer;
The positive terminal of the first conductive layer is set to a positive reference voltage, the negative terminal of the first conductive layer is set to a negative reference voltage, and the voltage of the positive terminal of the second conductive layer is set Measuring the value V3 and the voltage value V4 of the negative terminal of the second conductive layer; and setting the positive terminal of the second conductive layer to a positive reference voltage; Setting the negative terminal to a negative reference voltage and measuring the voltage value V5 of the positive terminal of the first conductive layer and the voltage value V6 of the negative terminal of the second conductive layer. .   21. The method according to claim 20, further comprising determining a distribution of two contact points according to the voltage values V1 to V4. The first conductive layer extends along the x axis and is referred to as an x conductive layer, the second conductive layer extends along the y axis and is referred to as a y conductive layer,
Detecting a distribution of contact points on the resistive touch screen according to the voltage values V1 to V4,
Obtaining a first difference V1-V2 between the voltage values V1 and V2, and a second difference V3-V4 between the voltage values V3 and V4;
Comparing the first difference V1-V2 with a first threshold THD1 and a second threshold THD2, and comparing the second difference V3-V4 with the first threshold THD1 and the second threshold THD2. ,as well as
When x2> x1 and y2> y1, x1 and y1 represent the x and y coordinates of the first contact point, and x2 and y2 represent the x and y coordinates of the second contact point, V1−V2> THD2 And if V3-V4> THD2, indicating that there are two contact points on the resistive touch screen;
When x2> x1 and y2 <y1, the first threshold THD1 is less than or equal to zero, and the second threshold THD2 is greater than or equal to zero, V1−V2 <THD1 and V3 24. The method of claim 21, comprising the step of indicating that there are two contact points on the resistive touch screen if -V4 <THD1.

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