JPH0115085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a coordinate detection device, and particularly includes a substrate provided with a resistive film and an impedance added thereto, and detects coordinates indicated by the impedance. The present invention relates to a coordinate detection device that detects values.

(2) Technology background With the development of office automation, etc.
2. Description of the Related Art It is common practice to input and process figures, characters, etc. into computers. Keyboards are a typical input device for drawings, letters, etc., but there are other ways to input drawings, letters, etc. by specifying a position on a specific board with your finger or pen, and inputting the coordinates. There is a coordinate input device that does this.

(3) Prior art and problems One method of the above coordinate input device is as follows.
There is a method in which a large number of sensors are arranged in a grid on a board, and the coordinates are determined by a signal from the sensor at the position by pointing with a finger or a pen. However, in this type of system, the accuracy of inputting coordinates is determined by the density of the sensors arranged, so there is a problem that it is difficult to input coordinates with high accuracy.

Another method of coordinate input device uses a resistive film as an input board, flows current from both ends of the resistive film to an impedance connection point (point of contact with a finger or pen, etc.), and calculates the coordinates of the connection point from the current ratio. There is a method called. The principle of such a system is shown in FIG. The left terminal 2 of the resistive film 1, which is made of uniform material, has a
Terminal 5 on one side of power supply 8 is connected via current measuring device 9 . A terminal 5 on one side of a power source 8 is also connected to the right terminal 3 of the resistive film 1 via a current measuring device 10 . The other terminal of power supply 8 is grounded to earth 7 . The output of the current measuring device 9 is connected to the AD converter 11, and the output of the current measuring device 10 is connected to the AD converter 12.
connected to. The outputs of AD converters 11 and 12 are connected to control device 13 . Then, an arbitrary position 4 on the resistive film 1 is indicated by an impedance 7 such as a finger or a pointing pen whose one side is grounded to the earth 7 . As a result, the coordinates X (0≦X≦1) of an arbitrary position 4 on the resistive film 1 where the left end coordinate is 0 and the right end coordinate is 1 are specified.

In this state, the resistance value between terminals 2 and 4 is
Let R _x and the resistance value between terminals 3 and 4 be R _1-x . Also, the current flowing from terminals 2 to 4 is I _x , and the current flowing from terminals 3 to 4
Let the current flowing in I _{1-x be I 1-x} . At this time, since the resistance value of a resistive film made of a uniform material is proportional to the length of the resistor, the coordinates X of the indicated point 4 are: X=R _x / (R _x + R _1-x ) ...(1) given by. Further, since the voltage drop due to the resistance value R _x and the voltage drop due to the resistance value R _1-x are equal, the following relationship is established: R _x I _x = R _1-x I _1-x (2). From equations (1) and (2), X=I _1-x / (I _x + I _1-x ) ...(3). That is, the coordinate X of the designated point 4 can be determined if the current I _x flowing between the terminals 2 and 4 and the current I _1-x flowing between the terminals 3 and 4 are known. Therefore, these currents I _x and I _1-x are detected as voltage values by current measuring devices 9 and 10, converted into digital values by AD converters 11 and 12, respectively, and then converted by control device 13. By calculating the above equation (3), the coordinate X can be determined as a digital value.

According to such a conventional method, the coordinate X of any position on the resistive film 1 (the left end coordinate is 0, the right end coordinate is 1, and a value between them) can be determined as a digital value. However, as the current measuring devices 9 and 10 for measuring current, operational amplifiers and the like are required to convert the current into voltage, and
High quantization accuracy is used to obtain the value of
The AD converters 11 and 12 are required, which makes the circuit complicated and increases the cost.

As a technique for solving the above-mentioned problems, there is a "coordinate detection device" for which an application has already been filed. This is the second
As shown in the figure (the detailed principle will be described later), by adding a buffer circuit to both ends of the resistive film, the equivalent impedance seen from one end of the resistive film and the coordinates of the indicated point have a specific functional relationship. By utilizing this fact, the value of the equivalent impedance is detected and the coordinates of the indicated point are detected.
According to this method, highly accurate coordinate detection can be performed with a simple circuit configuration. However, although this method is very effective when the value of impedance for specifying coordinates is constant in advance, coordinates cannot be detected when the impedance is uncertain. For example, when finger touch is used to indicate coordinates and human body capacitance is used as impedance, there is a problem that the above method cannot be used directly because the capacitance varies depending on the person and location (50 pF to 150 pF).

(4) Purpose of the Invention In order to eliminate the above-mentioned problems, the present invention compares the equivalent impedances seen from both ends of the resistive film based on the principle of coordinate detection from the equivalent impedances, and further calculates the equivalent impedances multiple times. By measuring and averaging the impedance values, it is possible to specify coordinates using impedance values that are uncertain. At the same time, by providing individual switch means on each of the four edges of the square resistive film, it is possible to detect two-dimensional coordinates. The purpose of the present invention is to provide a coordinate detection device that achieves the following.

(5) Structure of the Invention According to the present invention, the above object includes a coordinate input panel having a resistive film disposed on a substrate, a coordinate indicating means for indicating one point on the resistive film, and a coordinate input panel connected to both ends of the resistive film. a buffer circuit that maintains the potentials at both ends in a constant relationship; a switching means that alternately switches and connects both ends of the resistive film and both ends of the buffer circuit;
detecting means connected to one end of the buffer circuit and detecting the impedance between the one end and the ground of the coordinate indicating means for each case switched by the switching means; It is an object of the present invention to provide a coordinate detecting device characterized by having a calculating means for calculating a coordinate position on the coordinate input panel indicated by a coordinate indicating means.

(6) Examples of the invention Examples of the invention will be described in detail below.

FIG. 2 is a diagram for explaining the principle of coordinate detection from equivalent impedance, which is the basis when implementing the present invention. The resistive film 1 is the same as the conventional example explained in Fig. 1, and one side is connected to the ground 1.
The point 4 is indicated by an impedance Z ₀ (corresponding to an indicating pen) grounded to the point 7, and its coordinates X are detected. In this case as well, the coordinates of the left terminal 2 of the resistive film 1 are 0, the coordinates of the right terminal 3 are 1, and the coordinate X of the indicated point 4 takes a value of 0≦X≦1.

The difference between this principle and the conventional example shown in FIG. 1 is that both terminals of the resistive film 1 are not connected to a power source as in the conventional example shown in FIG. Instead, terminal 14 is connected to terminal 2 and to terminal 3 via operational amplifier 15. That is, the terminal 14 is connected to the non-inverting input of the operational amplifier 15, and the output of the operational amplifier 15 is connected to the terminal 3. Also, the output of operational amplifier 15 is
Also connected to its own inverting input.

In the circuit configured as described above, the operational amplifier 15 is a buffer circuit that operates as a voltage follower. That is, the feature of the principle is that the terminals 2 and 3 of the resistive film 1 are connected by a buffer circuit. With this configuration, the potentials of terminals 2 and 3 with respect to ground 17 become equal, and the input impedance of operational amplifier 15 can be considered infinite, so that the current at terminal 14 flows from terminal 3 to pointing point 4. The characteristic is that no current is included. In other words, since the current flowing from the terminal 3 to the pointing point 4 is independently supplied from the operational amplifier 15, the current flowing through the terminal 14 is the current flowing from the terminal 2 to the pointing point 4 itself. Now, assume that the potential of the terminals 2 and 3 with respect to the ground 17 is V, and the potential of the indicated point 4 with respect to the ground 17 is Va. Further, the resistance values between terminals 2 and 4 and between terminals 3 and 4 are respectively assumed to be R _x and R _1-x as in the case of FIG. Let Z be the equivalent impedance that combines Z ₀ , R _x and R _1-x between the terminal 14 and the ground 17. This principle utilizes the fact that the coordinate X becomes a function of this impedance Z. Let's calculate this impedance Z below.

First, the current Va/Z ₀ flowing through impedance Z ₀
is the current ( _V-
Va) Current flowing through R _x and R _1-x (V-Va)/R _1-x
is the sum of That is, (V-Va) [(1/R _x )+(1/R _1-x )] = (Va/Z ₀ )...(4). However, in reality, for the reason mentioned above, the current V/Z flowing through the equivalent impedance Z becomes equal to the current (V-Va)/R _x flowing through R _x . That is, V/Z=(V-Va)/R _x (5). When calculating Z by eliminating V and Va from equations (4) and (5), Z = R _x + Z ₀ [(R _x +R _1-x )/R _1-x )] ...(6 ) becomes. Here, make sure that R _x + R _1-x is sufficiently small compared to the size of impedance Z ₀ |Z ₀ |
If R _x , R _1-x and Z ₀ are set, equation (6) approximately becomes Z≒Z ₀ [(R _x + R _1-x )/R _1-x ] ...(7) can do. Here, since the resistive film 1 is the same as the conventional example shown in Fig. 1, the above formula (1) (conventional example) is modified and R _1-x = [(1-X)/X] R _x ...(8) becomes. Substituting equation (8) into equation (7) and connecting with an equal sign to find X, we get X=1−(Z ₀ /Z) ……(9). As can be seen from equation (9), by using the configuration shown in Figure 2, the coordinate X of the pointing point 4 becomes inversely proportional to the equivalent impedance Z between the terminal 14 and the ground 17. There is. Therefore, the value of the coordinate X can be calculated by measuring the values of the equivalent impedance Z and the impedance Z ₀ and calculating the equation (9).

To summarize the principle above, both terminals of the resistive film 1 are connected by a buffer circuit using a voltage follower, and the resistance value of the resistive film 1 is compared to the impedance Z ₀ of the pointing pen for indicating the pointing point. Set it so that it is sufficiently small. Then, the impedance Z ₀ is measured in advance, and the equivalent impedance Z between the terminal 14 and the ground 17 is measured by an appropriate measuring means. By calculating equation (9) using Z and Z ₀ thus determined, the coordinate X of the indicated point 4 can be detected.

As a specific example of the impedance in the configuration shown in FIG. 2, consider a case where the impedance Z ₀ is a capacitance. Now let its capacity be C ₀
Then, Z ₀ =1/jωC ₀ ...(10). Here, j is a symbol representing a complex quantity, and ω is the angular frequency of the signal added to the capacitance. Expression (10)
Substituting into equation (7) and connecting with an equal sign, we get Z=1/jω[C ₀ (R _1-x /(R _x +R _1-x )}]...(11). Therefore, terminal 14 and It can be seen that the equivalent impedance Z between the ground 17 is also an equivalent capacitance with a capacitance value of C=C ₀ {R _1-x /(R _x +R _1-x )} (12).

When determining X using equations (8) and (12), it becomes X=1-(C/C ₀ )...(13). From the above, if capacitance is used for impedance Z ₀ , the equivalent impedance between terminal 14 and ground 17 is also capacitance, and from those values (13)
The coordinate X can be determined from the formula.

According to the above principle, by attaching a variable capacitance digital oscillator and its oscillation period measuring device to the terminal 14, for example, equation (13) can be calculated from the relationship between the oscillation periods. At this time, the capacitance C ₀ can be measured by bringing the indicating point 4 to the left terminal 2 of the resistive film 1.

However, the method described above is very effective when the capacitance C ₀ is constant, such as with an indicator pen, but when the human body capacitance measured by a finger touch is used as the capacitance C ₀ , the measurement becomes difficult. Since the capacitance value changes during the process, the above method cannot be used directly. In addition, if there is stray capacitance between each of the left terminal 2 and right terminal 3 and the ground 17,
Errors in the calculation of the equivalent impedance Z (equivalent capacitance C) due to these factors cannot be ignored.
FIG. 3 shows the principle of the present invention in consideration of such a case.

First, the configuration of FIG. 3a is almost the same as that of FIG. However, a variable capacitance digital oscillator 20 is connected to the terminal 14, and its output pulse is taken out from the terminal 21. Also, instruction point 4
A finger touch 18 having a variable capacitance value C _B is used as the indicating means. Also, terminal 2 and ground 1
There is a stray capacitance with a capacitance value C _sx between
There is also a capacitance value between terminal 3 and ground 17.
Assume that there is a stray capacitance C _s1-x . Equivalent capacitance between terminal 14 and ground 17 in this state
Let's find C _x . In this case terminal 2 and ground 17
The equivalent capacitance value between is given by replacing C ₀ with C _B in equation (12) in FIG. 2 above.
And the stray capacitance value C _s1-x can be ignored because terminal 3 is connected to the operational amplifier 15 with low impedance, and the stray capacitance value C _sx is between the above terminal 2 and ground 17.
It is connected in parallel with the equivalent capacitance value between. Therefore, the equivalent capacitance C _x is calculated using the above equation (12) as follows: C _x1 =C _sx +C _B {R _1-x /(R _x +R _1-x )} (14). The operation of the variable capacitance digital oscillator 20 will be described later. Next, the connection between the operational amplifier 15 and the oscillator 20 in FIG. 3a is completely reversed between terminals 2 and 3 to form the connection as shown in FIG. 3b. Assuming that the connection switching at this time is performed in a very short time (about 5 msec), it can be considered that the stray capacitance values C _sx , C _s1-x and the human body capacitance value C _B do not change. And the equivalent capacitance between terminal 19 and ground 17 in the case of Fig. 3b
Let's calculate C _x2 . In this case, in equation (14) above, C _sx is replaced by C _S1-x , the relationship between R _x and R _1-x is reversed, and C _B is considered to be a constant value within a short time, so C _x2 = C _s1-x + C _B {R _x / (R _x + R _1-x )}...(15).

Here, if it is assumed that the connection of the circuit in FIG. 3a and the connection of the circuit in _FIG . ) and (15), R _1-x = {(C _x1 -C _sx ) _/ (C _x2 -C _sx )}. R _x ...(16) becomes. This relationship and the conventional example shown in FIG.
From equation (1), _the coordinates _X of _{the indicated point 4} are _{: x2} −C _s1-x )} ...(17) This equation (17) is the basic equation of the principle of coordinate detection according to the present invention.

In other words, to summarize the basic principle of coordinate detection according to the present invention, the present invention provides a third
It has a means for quickly switching the connections of the circuits as shown in Figures a and 3b, and has an equivalent capacitance C _x1 (third
Figure a) and the equivalent capacitance between terminal 19 and earth 17
C _x2 (Fig. 3b), and further has means for detecting stray capacitances C _sx and C _s1-x , and their capacitance values C _x1 , C _x2 , C _sx
By calculating the above _equation (17) using

Each of the above capacitances is then detected by the variable capacitance digital oscillator 20 in FIGS. 3a and 3b.
The oscillation period of the output pulse from the terminal 21 of the variable capacitance digital oscillator 20 is now proportional to the equivalent capacitance value between the terminal 14 or 19 and the ground 17. Therefore, if the oscillation period in the case of Fig. 3 a is T _x1 , and the above proportionality constant is k, then T _x1 = k・C _x1 ...(18) Similarly, the oscillation period in the case of Fig. 3 b If T _x2 is T x2, then T _x2 = k・C _x2 (19).

The equivalent capacitances C _x1 and C _x2 are detected as the oscillation periods T _x1 and T _x2 of the output pulse from the terminal 21 as shown in equations (18) and (19) above. Further, the stray capacitance C _s1-x is determined as the equivalent capacitance value in the state where the finger touch 18 is not touched in FIG. 3a. In other words, this can be considered as a case where R _1-x becomes 0 in the above equation (14).
Therefore _, if the oscillation period of the output pulse from the terminal 21 with no finger _touch 18 in _{FIG .} Finger touch 18 in Figure 3 a
It is detected as an oscillation period T _sx with no oscillation period T sx . Similarly, the stray capacitance C _s1-x can be calculated by touching the finger 1 in Figure 3b.
Since it can be found as the equivalent capacitance value without 8 (this is the case where R _x is 0 in the above equation (15)),
The oscillation period of the output pulse from terminal 21 at that time is
Assuming T _s1-x , it is detected as T _s1-x =k·C _s1-x (21).

The above equations (18), (19), (20), and (21) can be converted to the above equation (17).
Substituting _into the formula, _the coordinate x of _the indicated point ₄ is _as follows _: Can calculate. That is, in the present invention, the third
By first finding the oscillation period when there is no finger touch 18 in each state of Figures a and b, and then finding the oscillation cycle in each state of Figure 3 a and b when there is finger touch 18, The coordinates of the point 4 indicated by the finger touch 18 are calculated from equation (22) corresponding to equation (17). An important point of the present invention is that when there is a finger touch 18, the connection of the circuits shown in FIGS. 3a and 3b can be switched in a short time.

The above is the principle of coordinate detection according to the present invention,
Next, FIG. 4 shows the configuration of an embodiment of the present invention which is capable of detecting two-dimensional coordinates using this principle.

In FIG. 4, the touch panel 22 has a structure in which a transparent resistive film is formed on a glass substrate and further covered with a SiO ₂ vapor deposited film. An analog switch array 23 is connected to the left side of the touch panel 22 by m switch lines A _x11 , A _x12 , ..., A _x1n , and the other terminals of these switch lines are connected to the connection line L _{1 .}
are commonly connected. Further, on the right side of the touch panel 22, an analog switch array 24 is connected to the analog switch array 23 by m respective switch lines A _x21 , A _x22 , . . . A _x2n ,
The other terminals of these switch wires are commonly connected to the connection wire _L2 . Furthermore, an analog switch array 25 is connected to the top edge of the touch panel by n switch wires A _Y11 , A _Y12 , A _Y13 , ..., A _Y1o , and the other terminals of these switch wires are connected to the connection wire _L1. Commonly connected. Similarly, an analog switch array 26 is connected to the lower end of the touch panel 22 by n switch lines A _x21 , A _x22 , A _x23 , . . . A _x2o corresponding to the analog switch array 25, and these switches The other terminals of the lines are commonly connected to the connection line _L2 .

The control terminals of the analog switch arrays 23 and 24 are connected to the switch control line C ₁ , and the control terminals of the analog switch arrays 25 and 26 are connected to the switch control line C ₁ via inverters 31 and 32.
The switch control line _C1 is connected to the control device 30.
connected to. The connection line L ₁ is connected to the switch S ₁ of the analog switch 27, and the switch S ₁ is connected to the terminal
Selectively connected to I ₁ or O ₁ . The connection line _L2 is also connected to the switch _S2 of the analog switch 27, and the switch _S2 is selectively connected to the terminal _I2 or _O2 . A control terminal of analog switch 27 is connected to switch control line C ₂ , and switch control line C ₂ is connected to control device 30 . Also operational amplifier 28
The non-inverting input terminal of is the terminal of analog switch 27.
It is connected to I ₁ and I ₂ and also to the capacitance terminal of the variable capacitance digital oscillator 29 . The inverting input terminal of the operational amplifier 28 is connected to the output terminal of the operational amplifier 28, and the output terminal of the operational amplifier 28 is connected to the terminals O ₁ and O ₂ of the analog switch 27.
The output terminal of the variable capacitance digital oscillator 29 is connected to the control device 30, and the output terminal 3 of the control device 30 is connected to the control device 30.
Detected coordinate values are output to 1. The coordinates on the touch panel 22 are specified by touching the finger 32. The changing human body capacity at that time
C _B and its ground is 33.

In the coordinate detection device configured as above, analog switch arrays 23, 24, 25, and 2
6 can be alternately opened and closed in the X direction (the left-right direction of the touch panel 22) or the Y direction (the vertical direction of the touch panel 22) by means of a switch control line _C1 . For example, when analog switch arrays 23 and 24 are turned on, analog switches 25 and 26 are turned off. Further, the operational amplifier 28 is a voltage follower circuit, and its input and output terminals are alternately connected to connection lines L ₁ and L ₂ by a switch control line C ₂ in the analog switch 27. ing. It is also assumed that the human body capacitance C _B caused by the finger touch 32 includes the capacitance of the SiO ₂ vapor deposited film.

Next, in this embodiment, touch 3 on the touch panel 22.
The operation when step 2 is performed will be explained over time.

1 First, a high level signal is output from the control device 30 to the switch control line _C1 , and the analog switch arrays 23 and 24 are turned on and the analog switch arrays 25 and 26 are turned on.
is off. This is inverter 31 and 32
by.

1-1 In this state, a high level signal is output from the control device 30 to the switch control line _C2 , and in the analog switch 27, switch _S1 is connected to terminal _I1 , and switch _S2 is connected to terminal _O2 . . From the above, the equivalent circuit of the operational amplifier 28 and touch panel 22 is shown in Figure 3a.
will be exactly the same. As a result, the variable capacitance digital oscillator outputs an output panel with an oscillation period T _x1 corresponding to the equivalent capacitance value C _x1 between the left end of the touch panel 22 and the ground 33. The oscillation period T _x1 of this output pulse is measured by a timer and a counter within the control device 30 and stored. In this state, touch 3 again.
The oscillation period T _sx when there is no 2 is measured and stored in advance, and corresponds to the stray capacitance C _sx at the left end of the touch panel 22.

1-2 Next, the signal on the switch control line _C2 becomes low level, and in the analog switch 27, the switch _S1 is connected to the terminal _O1 , and the switch _S2 is connected to the terminal _I2 . At this time, the signal on the switch control line _C1 remains at high level. With this operation, the equivalent circuit becomes exactly the same as that shown in FIG. 3b. As a result, the variable capacitance digital oscillator outputs an output pulse with an oscillation period T _x2 corresponding to the equivalent capacitance value C _x2 between the right end of the touch panel 22 and the ground 33.
The oscillation period T _x2 of this output panel is
0 is measured and stored. Also, the oscillation cycle when there is no finger touch 32 in this state
T _s1-x is also measured and stored in advance,
This is the stray capacitance at the right end of touch panel 22.
Compatible with C _s1-x .

1-3 T _x1 found by the above operations,
Using T _x2 , T _sx , and T _s1-x , the equation (22) is calculated by the arithmetic unit in the control device 30, and when the finger touch 32 on the touch panel 22
The horizontal coordinates of , that is, the X coordinates are detected and output to the output terminal 31 . In this case, the X coordinate of the left end of the touch panel 22 is 0,
The X coordinate of the right end is 1, and the detected X coordinate has a value between 0 and 1.

2 Next, the signal on the switch control line _C1 becomes low level, and the analog switch arrays 25 and 26
is turned on, and 23 and 24 are turned off.

In the following operations, the horizontal direction of the touch panel 22 is switched to the vertical direction, and the vertical coordinates of the finger touch 32 on the touch panel 22 are changed in exactly the same way.
That is, the y coordinate is detected and output to the output terminal 31. In this case, the Y coordinate of the top end of the touch panel 22 is 0, and the Y coordinate of the bottom end is 1.

Through the above operations, the two-dimensional coordinates of the finger touch 32 on the touch panel 22 can be determined with high accuracy. Each operation time for the switch control is performed in a time-division manner at short time intervals (about 5 msec).

Next, an embodiment for determining the above-mentioned X and Y coordinates with higher precision will be described. In the above embodiment, it is assumed that the human body capacitance does not change while T _x1 and T _x2 are determined, but in reality, the human body capacitance changes slightly during that time, and there is a limit to the detection accuracy. Therefore, the above operations 1-1 and 1-2 are repeated several times (l times, preferably l = 2 to 4), and the measured values T _x1i and T _x2i of each time are evaluated as follows. The arithmetic device calculates (T _x1i - T _sx ) and (T _x2i - T _s1-x ), and calculates the values n times. That is, calculate _l 〓 ⁱ⁼¹ (T _x1i −T _sx ) _l 〓 ⁱ⁼¹ (T _x2i −T _s1-x ). After _{the above l measurements} and _calculations ^, from ^the _{above results} ^, T _x2i −T _s1-x )} ...(23) The X coordinate is calculated and detected as follows, and is output to the output terminal 31. This value is the detected coordinate value X _i in each measurement cycle, X _i = (T _x2i − T _s1-x )/{(T _x1i − T _sx ) + (T _x2i − T _s
1-x )}...(24), which effectively averages out the variations in detected coordinate values due to changes in human body capacity while determining T _x1i and T _x2i , and provides highly accurate X coordinates. This makes detection possible. The Y coordinate can be considered in exactly the same way.

What is important in the embodiments according to the present invention is to complete the above operations in a time-sharing manner in a short enough time that the human body capacitance due to finger touching can be considered constant, and if this is achieved, even if the human body capacitance value is Even if the coordinates are fixed, it is possible to accurately detect the coordinates.

At this time, the analog switch, the variable capacitance digital oscillator 29, and the counter and arithmetic unit in the control device can be easily realized, and the overall cost can be reduced while maintaining high reliability.

Furthermore, although this embodiment was concerned with the detection of two-dimensional coordinates, it goes without saying that it can be used to detect one-dimensional coordinates based on the principle shown in FIG. Naturally, the present invention can also be applied to coordinate indicating means other than finger touch.

In another embodiment of the present invention, a transparent resistive film can be placed on a part of a CRT display device of a terminal such as a computer and used as a touch panel for inputting information. Furthermore, even when impedance other than capacitance is used as the coordinate indicating means, similar effects can be obtained by formulating equations corresponding to equations (14) to (22) and the like.

(7) Effects of the Invention According to the present invention, it is possible to measure the equivalent impedance seen from both ends of a resistive film in a time-division manner, and furthermore, it is possible to calculate the weighted average of several measurements for these measurement results. This makes it possible to accurately detect coordinates even when the impedance of the coordinate indicating means is uncertain.

Furthermore, by making it possible to time-divisionally measure the coordinates in the left and right and up and down directions, it becomes possible to detect two-dimensional coordinates under the above conditions.

Further, according to the present invention, it is possible to provide a coordinate detection device with low cost and high reliability.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional coordinate detection device, Fig. 2 is an explanatory diagram of the basic principle behind the present invention, Fig. 3 a and b is an explanatory diagram of the principle of the coordinate detection device according to the present invention, and Fig. 4 1 is a configuration diagram of a coordinate detection device according to the present invention. 22...Touch panel, 23, 24, 25, 2
6... Analog switch array, 27... Analog switch, 28... Operational amplifier, 29... Capacity variable digital oscillator, 30... Control device, C ₁ ,
C ₂ ...Switch control line.

Claims (1)

[Scope of Claims] 1. A coordinate input panel having a resistive film disposed on a substrate, a coordinate indicating means for indicating one point on the resistive film, and a coordinate indicating means connected to both ends of the resistive film to set the potentials at both ends in a fixed relationship. a buffer circuit that maintains the buffer circuit, a switching means that alternately switches and connects both ends of the resistive film and both ends of the buffer circuit, and is connected to one end of the buffer circuit and switches an impedance viewed from the one end by the switching means. and a calculation means for calculating the coordinate position on the coordinate input panel indicated by the coordinate indicating means using the output value of the detecting means. coordinate detection device. 2. The coordinate input panel is a secondary coordinate input panel in which a resistive film having four ends is arranged, and any two opposing ends of the four ends of the resistive film are selected, and the two ends and both ends of the buffer circuit are selected. switching means for alternately switching and connecting the buffer circuit; means connected to one end of the buffer circuit for detecting the impedance seen from the one end in each case selectively switched by the switching means; Coordinate detection according to claim 1, further comprising calculation means for calculating a two-dimensional coordinate position on the coordinate input panel indicated by the coordinate instruction means using an output value. Device. 3. The coordinate detecting device according to claim 1 or 2, wherein the coordinate indicating means is a finger touch. 4. The coordinate detection device according to claim 1 or 2, wherein the resistive film on the substrate is covered with an insulating film. 5. The coordinate detection device according to claim 1, 2, or 4, wherein the substrate, the resistive film, and the insulating film are each transparent. 6. Claim 1, wherein the coordinate input panel is installed on a display screen.
The coordinate detection device according to item 1 or 2 or 3. 7. The coordinate detection device according to claim 1, wherein the buffer circuit is a voltage follower circuit. 8. A coordinate input panel having a resistive film arranged on a substrate, a coordinate indicating means for indicating a point on the resistive film, and a buffer circuit connected to both ends of the resistive film to keep the potentials at both ends in a constant relationship; a switching means for alternately switching and connecting both ends of the resistive film and both ends of the buffer circuit; and a plurality of measurements in which the impedance connected to one end of the buffer circuit and viewed from the one end is switched by the switching means. a detection means for checking for cycles and a first for calculating an average value of a plurality of output values from the detection means;
and a second calculating means for calculating the coordinate position on the coordinate input panel specified by the coordinate specifying means based on the output value of the first calculating means. coordinate detection device. 9. The coordinate input panel is a two-dimensional coordinate input panel in which a resistive film having four ends is arranged, and any two opposing ends of the four ends of the resistive film are selected,
switching means for alternately switching and connecting the two ends and both ends of the buffer circuit; and a plurality of switching means connected to one end of the buffer circuit and having the impedance seen from the one end selectively switched by the switching means. means for detecting a measurement cycle; a first calculation means for calculating an average value of a plurality of output values from the detection means; and a coordinate indication means based on the output value of the first calculation means. 9. The coordinate detection device according to claim 8, further comprising second calculation means for calculating a two-dimensional coordinate position on said coordinate input panel. 10. The coordinate detection device according to claim 8 or 9, wherein the coordinate indicating means is a finger touch. 11. Claim 8, wherein the resistive film on the substrate is covered with an insulating film.
9. The coordinate detection device according to item 9. 12. The coordinate detection device according to claim 8, 9, or 11, wherein the substrate, the resistive film, and the insulating film are each transparent. 13. The coordinate detection device according to claim 8, 9, or 11, wherein the coordinate input panel is installed on a display screen. 14. The coordinate detection device according to claim 8, wherein the buffer circuit is a voltage follower circuit.