JPH08137607A - Coordinate input device - Google Patents

Abstract

PURPOSE: To provide the coordinate input device in which a coordinate is inputted with high precision by using fingers of the operator and an input pen. CONSTITUTION: The input device is provided with a tablet 1 arranging plural X and Y electrodes 4, 5 on both upper and lower sides of a glass board 6 as a matrix, an oscillation circuit 11 connecting to each X electrode 4 via an analog switch 10, and an input pen 2 incorporating an oscillation circuit 25, and when a coordinate is inputted by using the input pen 2, a voltage oscillated from the input pen 2 is applied to each of the electrodes 4, 5 through a capacitor and a voltage in response to a distance from each of the electrodes 4, 5 to the input pen 2 is outputted to conduct prescribed arithmetic operation is applied to the output voltage thereby deciding the coordinate of the input pens 2. On the other hand, when a coordinate is inputted by using fingers 3 of the operator, an analog switch 10 is thrown to the position of the oscillation circuit 11, a voltage with a prescribed frequency is sequentially applied to each X electrode 4 from the oscillation circuit 11 and a voltage applied between the X, Y electrodes 4, 5 via a capacitor is changed through the reduction in the capacitance attended with the contact of the fingers 3 to decide the coordinates of the fingers 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type coordinate input device, and more particularly to a coordinate input device for inputting coordinates using both an operator's finger and an input pen.

[0002]

2. Description of the Related Art In recent years, transparent tablets have been used in LCDs and CRs.
It is installed in front of the display screen such as T, and the input pen is moved on the tablet to input handwritten information such as characters and figures on the display screen, or the operator's finger is brought into contact with the tablet to display the display screen. There has been proposed a coordinate input device for performing menu selection and the like.

FIG. 10 is an explanatory view schematically showing a conventional example of this type of coordinate input device. In FIG. 10, a tablet indicated by a symbol T is a transparent resistance film such as ITO on the entire surface of a transparent base material. A constant AC voltage is applied to the electrodes at the four corners of the tablet T. now,
When the operator's finger is brought into contact with an arbitrary position on the surface of the tablet T, a current flows from each electrode to the finger through the resistive film based on the change in impedance by the finger. At this time, the current value detected from each electrode changes depending on the distances from the four corners of the tablet T to the finger. Therefore, assuming that the straight lines connecting the electrode pairs facing each other are the X-axis and the Y-axis, respectively, the fingers touch each other. The coordinates (X, Y) can be obtained as X = i ₁ / (i ₁ + i ₃ ) Y = i ₂ / (i ₂ + i ₄ ). On the other hand, when the operator holds an input pen connected to the main body through a cable and brings a conductive pen tip attached to the tip of the input pen into contact with an arbitrary position on the surface of the tablet T, the resistance film and the input from each electrode. Electric current flows through the pen to the body. At this time, the current value detected from each electrode changes in accordance with the distance from the four corners of the tablet T to the pen tip of the input pen, so that the current value detected from each electrode is the same as in the case of the finger described above. Based on this, the coordinates (X, Y) with which the input pen touches can be obtained.

[0004]

However, in the above-described conventional coordinate input device, when dirt, oil, or other foreign matter adheres to the pen tip of the input pen, the finger, or the surface of the resistance film of the tablet T, the input pen is used. There is a problem that the coordinates of the finger and the finger cannot be detected with high accuracy, and in some cases, the coordinates cannot be detected. Also, since it is necessary to connect the input pen to the main body via a cable, the operability when using the input pen is poor, and S / N due to external noise
There was also the problem of a poor ratio.

The present invention has been made in view of the circumstances of the prior art as described above, and an object thereof is to provide a coordinate input device capable of highly accurately inputting coordinates using both an operator's finger and an input pen. To provide.

[0006]

In order to achieve the above object, the present invention provides a tablet in which a plurality of X electrodes and Y electrodes arranged at equal pitch intervals are laminated in a matrix with an insulating layer interposed therebetween. , First coordinate detecting means for detecting the pointing position of the input pen on the tablet, second coordinate detecting means for detecting the pointing position of the finger on the tablet, and the first and second coordinate detecting means The first coordinate detecting means includes pulse generating means for oscillating a voltage of a predetermined frequency, which is built in the input pen, and is applied to each electrode from the input pen. Voltage detection means for detecting a voltage that is detected, and calculation means for calculating the coordinates of the input pen from the voltage value detected by the voltage detection means.
A pulse generating means for sequentially applying a voltage of a predetermined frequency to one of the X and Y electrodes, and X associated with the contact of the finger.
And voltage detecting means for detecting a voltage change between the Y electrodes,
The most main feature is that it has a calculating means for calculating the coordinates of the finger from the voltage value detected by the voltage detecting means. Further, in the above configuration, the switching means compares the voltage output from each of the electrodes with a reference value, and when the output voltage increases with respect to the reference value, the first coordinate detection means is selected. When the output voltage is selected and the output voltage is reduced with respect to the reference value, the second coordinate detecting means is selected. Further, in the above configuration, the switching means has a switching means that is driven in a time-division manner and switches at predetermined time intervals, and the first coordinate detecting means and the second coordinate detecting means according to the switching of the switching means. I chose to and.

[0007]

When inputting coordinates using the input pen, the first coordinate detecting means is selected by the switching means, and the input pen is pressed against an arbitrary position on the tablet. Then, the voltage oscillated from the input pen is applied to each electrode of the tablet arranged in a matrix through the electrostatic capacitance, and the applied voltage depends on the electrostatic capacitance (distance) between the input pen and each electrode. Because of the change, a voltage corresponding to the distance to the input pen is output from each electrode, and the maximum voltage value is output from the electrode closest to the input pen. By subjecting this output voltage to a desired calculation process, for example, the pitch between the electrodes is P, the voltage value from the electrode with the maximum applied voltage is V ₁ , and the voltage values from both electrodes adjacent to the electrode are respectively. V ₂ , V ₃ (however V ₂
≧ V ₃ ), the deviation amount L in the electrode arrangement direction between the input pen and the electrode closest to the input pen is L = P (V ₁ V ₂ −V ₁ V ₃ ) / 2 (V ₁ V ₃ + V ₁ V ₂ −2V ₂ V ₃ ), and by adding this L value to the coordinates of the electrode closest to the input pen, the coordinates of the input pen can be detected.

On the other hand, in the case of inputting coordinates using the operator's finger, the switching means selects the second coordinate detecting means, and the finger is brought into contact with an arbitrary position on the tablet. Then
A voltage having a predetermined frequency is sequentially applied from the pulse generating means to one of the X and Y electrodes of the tablet, and a voltage is applied between the X and Y electrodes through a capacitance. Since this electrostatic capacitance is reduced by the touch of the finger, the coordinates of the finger can be detected from the minimum voltage value.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram showing a schematic configuration of a coordinate input device according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of a tablet provided in the coordinate input device of FIG. 1, FIG. 3 is a sectional view of the tablet, and FIG. Is a configuration diagram of an input pen used in the coordinate input device of FIG. 1, and FIG. 5 is a circuit diagram of the input pen.

In FIG. 1, reference numeral 1 is a tablet, reference numeral 2 is an input pen, reference numeral 3 is an operator's finger,
The tablet 1 is installed on the front surface of a liquid crystal display (LCD) 30 or a CRT screen (not shown), and coordinates can be input using an input pen 2 and a finger 3. As shown in FIGS. 2 and 3, the tablet 1 includes a plurality of X electrodes 4 (X ₁ , X ₂ , ..., X _n ) and a Y electrode 5 which are orthogonal to each other.
Transparent glass substrate 6 having (Y ₁ , Y ₂ , ..., Y _n ).
And a transparent shield film 8 adhered on the lower surface of the glass substrate 6, and a transparent protective film 7 adhered on the upper surface of the glass substrate 6, and the protective film 7 is formed by the X electrode 4 In addition to the function to protect the
The shield film 8 has a function of blocking noise to the liquid crystal display device 30. The X electrode 4 and the Y electrode 5 are I
It is made of a transparent conductive material such as TO, the X electrodes 4 are arranged on the upper surface of the glass substrate 6 at equal pitch P intervals, and the Y electrodes 5 are also arranged on the lower surface of the glass substrate 6 at equal pitch P intervals. The X electrode 4 and each Y electrode 5 are made of an insulating glass substrate 6
Are arranged in a matrix form.

Returning to FIG. 1, one end of each X electrode 4 has an X
The side multiplexer 9 is connected, and an analog switch 10 is connected to the X side multiplexer 9.
This analog switch 10 has a first and a second contact 10
a and 10b, and the oscillation circuit 11 is provided at the first contact 10a.
Is connected. In addition, the second of the analog switch 10
An A / D converter 14 is connected to the contact 10b of the A / D converter via an amplifier circuit 12 and a filter circuit 13, and
The converter 14 is connected to the CPU 15. This C
The PU 15 is the closest to the input pen 2 based on the data output from the A / D converter 14 and the voltage detection means that determines the electrode closest to the input pen 2 or the finger 3, or an arithmetic expression described later. Built-in computing means for computing the amount of deviation of the input pen 2 between the electrode and the adjacent electrode, and also incorporating switching means for switching the analog switch 10 to one of the first and second contacts 10a, 10b. The coordinates of the input pen 2 or the finger 3 calculated by the CPU 15 are output to the host computer 16. Meanwhile, a Y-side multiplexer 17 is provided at one end of each Y electrode 5.
Is connected to the Y side multiplexer 17, and the A / D converter 14 is connected to the Y side multiplexer 17 via an amplifier circuit 18 and a filter circuit 19. These circuit components are mounted on the peripheral portion of the glass substrate 6 so as not to interfere with the electrodes 4 and 5, and are connected to the host computer 16 via a cable (not shown).

As shown in FIG. 4, the input pen 2 is formed in a cylindrical shape suitable for an operator to hold and operate, and a button battery 20 and a printed circuit board 21 are incorporated therein. The tip of the input pen 2 has a conductive nib 22.
Is held by the spring 23 so that it can come in and out,
The circumference of the pen tip 22 is covered with an insulating cap 24. Circuit components of the oscillation circuit 25 shown in FIG. 5 are mounted on the printed circuit board 21, and the periphery of the printed circuit board 21 is covered with a metallic shield member 26. The oscillation circuit 25 is simply configured by a coil, a low power consumption transistor, etc., and is driven by the button battery 20. A switch 27 is interposed between the oscillator circuit 25 and the button battery 20. Both fixed contacts 27a and 27b of the switch 27 are fixed to the printed circuit board 21, and a movable contact 27c of the switch 27 is fixed.
Is fixed to the pen tip 22. Therefore, when the input pen 2 is not in use, the pen tip 22 is urged by the spring 23, and the movable contact 27c becomes the fixed contact 27.
Since they are separated from a and 27b, the switch 27 is turned off and the oscillation circuit 25 does not operate. On the other hand, input pen 2
In the use state in which the tablet 1 is pressed against the tablet 1, the pen tip 22 retreats slightly inward against the spring force of the pulling 23, and the movable contact 27c moves the fixed contacts 27a, 2a.
Since the switch 27 is turned on, the switch 27 is turned on, the oscillator circuit 25 operates, and a voltage of a predetermined frequency is output from the tip of the pen tip 22.

Next, the operation of the coordinate input device configured as described above will be described. First, the case of inputting coordinates using the input pen 2 will be described. In this case, the operator holds the input pen 2 by hand, and the pen tip 2 of the input pen 2
2 is pressed to an arbitrary position on the tablet 1 directly or via a sheet not shown, and the oscillation circuit 25 built in the input pen 2 is operated to output a voltage of a predetermined frequency from the tip of the pen tip 22. . On the other hand, on the tablet 1 side, the analog switch 10 is switched to the second contact 10b side by a signal from the switching means built in the CPU 15 (this switching operation will be described later). Side multiplexer 9
To sequentially turn on the X-side multiplexer 9 to SW ₁ to SW _n . Then, as shown in FIG. 6, each X electrode 4
A voltage oscillated from the input pen 2 is applied to (X ₁ , X ₂ , ..., X _n ) through a capacitance, and the applied voltage is applied between the pen tip 22 of the input pen 2 and each X electrode 4. Since the capacitance changes according to the capacitance, that is, the distance between the pen tip 22 and each X electrode 4, a voltage corresponding to the distance from each X electrode 4 to the pen tip 22 is output. The voltage output from each X electrode 4 is amplified by the amplifier circuit 12, then the noise component is removed by the filter circuit 13 and converted into DC, and the DC converted signal is digitalized by the A / D converter 14. After being converted, the data is read by the CPU 15.
The voltage detecting means built in the CPU 15 uses the input pen 2 based on the data output from the A / D converter 14.
The X electrode 4 closest to the X electrode is determined, and the voltage values applied to the X electrode 4 and the X electrodes 4 located on both sides of the X electrode 4 are sent to the calculating means, and the calculating means is based on these three voltage values. Then, the deviation amount of the input pen 2 between the X electrode 4 closest to the input pen 2 and the adjacent X electrode 4 is calculated.

That is, for three consecutive X electrodes 4 (hereinafter, these are referred to as A electrode, B electrode, C electrode),
When the pen tip 22 of the input pen 2 has a positional relationship as shown in FIG. 7, as shown in FIG. 8, the magnitude of the voltage value output from each electrode A, B, C is the maximum at the B electrode. At V ₁ , A
It becomes smaller in the order of V _{2 of} the electrode and V ₃ of the C electrode. Here, when the respective theoretical values are obtained based on the theory that the voltage value output from each electrode A, B, C is inversely proportional to the square of the distance to the pen tip 22, the voltage value at the A electrode is = V ₂ = K / r ₁ ² = K / [H ² + (P-L) ² ] ......... Voltage value at B electrode = V ₁ = K / r ₂ ² = K / (H ² + L ² ) …………………… The voltage value at the C electrode = V ₃ = K / r ₃ ² = K / [H ² + (P + L) ² ] ………… (where r ₁ is the A electrode) To the nib 22, r ₂ is the distance from the B electrode to the nib 22, r ₃ is the distance from the C electrode to the nib 22, and H is the length of the perpendicular from the nib 22 to the electrode formation surface. , L is B on the electrode formation surface
The amount of deviation from the electrode to the pen tip 22, P is the pitch between the X electrodes 4, and K is a constant). Then, by solving the simultaneous equations of these equations, L = P (V ₁ V ₂ −V ₁ V ₃ ) / 2 (V ₁ V ₃ + V ₁ V ₂ −2V ₂ V ₃ ) ... Become. As is clear from this formula, since L is unrelated to the size of H, there is a case where the input pen 2 is directly pressed on the protective film 7 of the tablet 1 for handwriting input.
Regardless of the case where the input pen 2 is pressed against a sheet such as a drawing paper placed on the tablet 1 for handwriting input, the voltage value V ₁ output from the known P and the three electrodes A, B, C , V ₂ , V ₃ can be obtained.

Coordinate detection of the input pen 2 in the Y-axis direction is similar to the above, and in this case, the CPU 15 operates the Y-side multiplexer 17 and switches the Y-side multiplexer 17 to SW.
_{1 to} SW _n are sequentially turned on. Then, as shown in FIG. 6, the pen tip 2 is attached to each Y electrode 5 (Y ₁ , Y ₂ , ..., Y _n ).
Voltages corresponding to the distance up to 2 are output. These voltages are amplified by the amplifier circuit 18, then digitized by the A / D converter 14 via the filter circuit 19, and the data is read by the CPU 15. Then, the CPU 15 determines the Y electrode 5 closest to the input pen 2 and performs the same calculation as the above equation to detect the coordinates of the input pen 2 in the Y-axis direction. Further, after determining the coordinates of the input pen 2 in the X and Y axis directions in this way, the CPU 1
5 sends this position information to the host computer 16,
A diagram or the like according to the movement of the input pen 2 is displayed on a CRT screen (not shown).

Next, the case of inputting coordinates with the operator's finger 3 will be described. In this case, the analog switch 10 is switched to the first contact 10a side by a signal from the switching means built in the CPU 15, and X The oscillation circuit 11 is connected to the side multiplexer 9. In this state, the CPU 15 operates the X-side multiplexer 9 and the Y-side multiplexer 17, and the SW of the X-side multiplexer 9
₁ to turn on the SW ₁ of the Y-side multiplexer 17 from ~S
W _n is sequentially turned on, and then S of the X-side multiplexer 9
Similarly, for W _{2 to} SW _n , after turning on each Y
SW ₁ to SW _n of the side multiplexer 17 are sequentially turned on. Then, since the oscillation waveform is input from the oscillation circuit 11 to each X electrode 4 (X ₁ , X ₂ , ..., X _n ), FIG.
, Each X electrode 4 and each Y electrode 5 (Y
_A voltage is applied to ₁ , ₁ , Y ₂ , ..., Y _n ) through the electrostatic capacitance C ₁ .

In this state, as shown in FIG. 9 (b), when the operator presses his / her finger 3 to an arbitrary position on the tablet 1, a part of the lines of electric force is pulled out by the finger 3 and the X electrode. Since the electrostatic capacitance formed between 4 and the Y electrode 5 decreases from C ₁ to C ₂ , each Y electrode 5 outputs a voltage according to the change in the electrostatic capacitance. Then, the voltage output from each Y electrode 5 is input to the A / D converter 14 via the amplifier circuit 18 and the filter circuit 13 as in the case of detecting the coordinates of the input pen 2 in the Y-axis direction, and the A After being digitized by the / D converter 14, the data is read by the CPU 15. The voltage detection means built in the CPU 15 determines the Y electrode 5 having the smallest voltage value and the X electrode 4 corresponding to the Y electrode 5 based on the data output from the A / D converter 14, The coordinates of 3 in the X and Y axis directions are detected. Further, after determining the coordinates of the finger 3 in the X and Y axis directions in this way, the CPU 15 sends this position information to the host computer 16, and the contact position of the finger 3 in the menu displayed on the liquid crystal display screen. Select the menu corresponding to.

The switching means of the analog switch 10 described above is, for example, a time-division drive in which the first contact 10a side and the second contact 10b side are automatically switched every predetermined time, and the CPU 15 periodically inputs the input. The detection means of the pen 2 and the detection means of the finger 3 may be switched. In this case, the switching of the analog switch 10 is performed in several mms,
If the scanning of the multiplexers 9 and 17 on the X and Y sides is performed for several μs, the data is sent to the host computer 16 in units of several mms. The coordinate detection of 3 can be performed accurately.

Alternatively, when a start-up switch (not shown) for turning on the tablet 1 is turned on, the analog switch 10 is automatically switched to the first contact 10a side, and A
Based on the data output from the / D converter 14,
The CPU 15 may detect whether the voltage applied to each Y electrode 5 has increased or decreased with respect to the reference value. That is, when the voltage applied to the Y electrode 5 increases with respect to the reference value, it is determined that the input pen 2 is pressed against the tablet 1, and the coordinate detection of the input pen 2 described above is performed. Then, when there is no change in the voltage after the elapse of the predetermined time, the analog switch 10 is automatically set to the second contact 1
When the voltage applied to the Y electrode 5 decreases with respect to the reference value by switching to the 0b side, it is determined that the finger 3 is in contact with the tablet 1, and the coordinate detection of the finger 3 described above is performed.

The present invention is not limited to the above embodiment,
For example, the coordinates of the input pen 2 may be detected by an arithmetic expression other than the above expression based on the voltage values output from the plurality of X and Y electrodes 4 and 5. Also, tablet 1
The configuration of is not limited to the above embodiment, and for example, each X electrode 4
Instead of forming the film on the upper surface of the glass substrate 6, a protective film 7
May be formed on the lower surface of each of the X, Y electrodes 4,
It is also possible to form all of 5, the protective film 7, and the shield film 8 on the glass substrate 6 by using a film forming technique such as printing or CVD. Furthermore, analog switch 10
It is also possible to manually perform the switching operation of.

[0021]

As described above, according to the present invention,
The position information when the input pen is pressed against the tablet is
A voltage is applied from the oscillating input pen to each electrode of the tablet through capacitance, and detection is performed based on the output voltage that changes according to the distance between the input pen and each electrode, and the operator's finger is placed on the tablet. The position information at the time of contact is obtained by sequentially applying a voltage of a predetermined frequency from the pulse generating means to one of the X and Y electrodes of the tablet.
Since the voltage applied through the electrostatic capacitance between the electrodes changes due to the decrease in the electrostatic capacitance due to the touch of the finger, it is detected, so coordinate input is performed using both the operator's finger and the input pen. In doing so, the detection accuracy can be improved by eliminating the influence of dirt, oil, etc., and the operability can be improved by omitting the cable of the input pen.

In addition, when the voltage output from each electrode is compared with the increase and decrease of the reference value and the switching means is operated based on the result, or the switching means is driven in a time-division manner and selected at predetermined time intervals. In this case, it is possible to automatically determine which one of the input pen and the finger is used as the pointing tool, and to detect the coordinates of the input pen or the finger according to each usage pattern. Operability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a coordinate input device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a tablet included in the coordinate input device of FIG.

FIG. 3 is a sectional view of the tablet.

4 is a configuration diagram of an input pen used in the coordinate input device of FIG. 1. FIG.

FIG. 5 is a circuit diagram of the input pen.

FIG. 6 is an explanatory diagram showing a detection operation of the input pen.

FIG. 7 is an explanatory diagram showing a positional relationship between the input pen and three electrodes.

FIG. 8 is an explanatory diagram showing a positional relationship between an output voltage and three electrodes.

FIG. 9 is an explanatory diagram showing a finger detection operation.

FIG. 10 is an explanatory diagram schematically showing a conventional coordinate input device.

[Explanation of symbols] 1 tablet 2 input pen 3 finger 4 X electrode 5 Y electrode 6 glass substrate 9 X side multiplexer 10 analog switch 10a first contact point 10b second contact point 11 oscillator circuit 15 CPU 17 Y side multiplexer 22 pen tip 24 Cap 25 Oscillator 27 Switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kinya Inoue 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Yoshihisa Endo 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alp Su Electric Co., Ltd. (72) Inventor Tadashi Umame 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd.

Claims (4)

[Claims] 1. A tablet in which a plurality of X electrodes and Y electrodes arranged at equal pitches are stacked in a matrix with an insulating layer interposed therebetween, and a first tablet for detecting a pointing position of an input pen on the tablet. The coordinate detecting means, second coordinate detecting means for detecting a finger pointing position on the tablet, and switching means for selecting one of the first and second coordinate detecting means are provided. The coordinate detecting means is a pulse generating means for oscillating a voltage of a predetermined frequency built in the input pen, a voltage detecting means for detecting a voltage applied from the input pen to each electrode, and a voltage detecting means for detecting the voltage. Calculating means for calculating the coordinates of the input pen from the voltage value of the input pen, and the second coordinate detecting means is a pulse applying means for sequentially applying a voltage of a predetermined frequency to one of the X and Y electrodes. And generating means, voltage detecting means for detecting a voltage change between the X and Y electrodes due to contact of the finger, and calculating means for calculating coordinates of the finger from a voltage value detected by the voltage detecting means. A coordinate input device characterized by the above. 2. The switching means compares the voltage output from each of the electrodes with a reference value, and selects the first coordinate detection means when the output voltage increases with respect to the reference value. The coordinate input device according to claim 1, wherein the second coordinate detecting means is selected when the output voltage decreases with respect to a reference value. 3. The switching means has a switch means which is driven in a time division manner and switches at a predetermined time interval, and the first coordinate detecting means and the second coordinate detecting means are switched in response to the switching of the switch means.
2. The coordinate detecting means according to claim 1 is selected.
The coordinate input device described in. 4. A tablet in which a plurality of X electrodes and Y electrodes arranged at equal pitch intervals are laminated in a matrix with an insulating layer interposed therebetween, and a voltage of a predetermined frequency is applied to one of the X and Y electrodes. Is sequentially applied, voltage detecting means for detecting a voltage change according to a change in capacitance between the X and Y electrodes due to contact of the finger with the tablet, and voltage detecting means for detecting the voltage change. The coordinate input device according to claim 1, further comprising a calculation unit that calculates the coordinates of the finger from a voltage value.