JPH0823797B2 - Tablet coordinate input device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tablet coordinate input device, and more particularly to a tablet coordinate input device suitable for image editing and the like.

[Prior art]

Conventionally, a coordinate input device is used to identify a coordinate position within a set coordinate area in a tablet for a personal computer, an image pointing device for a CRT image, a handwriting input device for a word processor, an electronic blackboard, an operation panel, etc. ing.

In this type of device, for example, a tablet as shown in FIG. 6 is used. Base 1 by film sheet
Resistive layers 2a and 2b are applied to one surface of a and 1b to form resistive sheets 8 and 9, and the resistive layer 2 sides are opposed to each other, and a constant interval is provided via an elastic and insulating spacer 3 between the layers. A tablet is formed by arranging the tablet in the table.

In contrast to such a tablet, conventionally, as shown in FIG. 7, the voltages of the power supplies 4 and 5 are individually applied to each of the resistance layers 2a and 2b through the switches 6a, 6b and 7a, 7b. First,
When the switches 6a and 6b are turned on and the switches 7a and 7b are turned off, the voltage E of the power source 4 is applied between the terminals X ₀ and X _{1 of} the resistance layer 2a. If the point P of the resistance layer 2a is pressed in this state, this P
The resistance layers 2a and 2b contact each other at a point. As a result, the voltage V _{X obtained} by dividing the voltage E at the point P appears at the terminal Y ₁ of the resistance layer 2b.
Since this voltage V _X is proportional to the distance in the X direction, the X coordinate of point P can be known from V _X.

Similarly, turn on the switches 7a and 7b and turn on the switches 6a and 6b.
When set to F, a voltage V _Y is generated at the terminal X ₁ of the resistance layer 2a, and the Y coordinate of the point P can be known from this voltage.

However, the conventional coordinate input device requires a switching circuit for the applied voltage to the two resistance sheets and a timing control means for switching the voltage, which makes the program complicated. is there.

〔Purpose〕

The present invention has been made in view of the above, and an object thereof is to provide a tablet coordinate input device capable of reading the coordinate position with a simple configuration.

〔Constitution〕

 Embodiments of the present invention will be described below with reference to the drawings.

 FIG. 1 is a circuit diagram of an embodiment of the present invention.

In FIG. 1, resistors R ₁ and R ₂ are resistance layers 2a shown in FIG.
Is a voltage dividing resistor at the pressing point P of the resistor R ₃ and R ₄ are resistor layers 2b.
Is the voltage dividing resistance at the pressing point P of. _A resistor 11 (R _A ) is connected between the electrode X ₁ and the power supply V _DD . Electrode X ₀ has buffer 12
Are connected, and the A / D converter 13 is connected to the electrode X ₁ . The A / D converters 13 and 14 are connected to the microcomputer 15 via a bus.

In the above structure, when the point P of the tablet 10 is pressed by the input pen or the like, the voltage dividing resistance R is applied to each of the resistance layers 2a and 2b.
_{1 to} R ₄ are formed. At this time, electrodes X ₀ and X ₁ have V ₁ and V
₂ occurs, and the coordinates of the pressing point P can be obtained from these voltages and the values of the resistors R _{1 to} R ₄ .

R ₁ ＞ 0, R ₂ ＞ 0, R ₃ 0, R ₄ 0, …… (3) V _DD ＞ 0 …… (4) R ₁ ＋ R ₂ ＝ R _E …… (5) R ₃ ＋ R ₄ ＝ R _F (6) Based on the above equation, the resistances R _{1 to} R ₄ are calculated as follows.

R ₃ = R _F −R ₄ (8) R ₂ = R _E −R ₁ (10) By calculating R _{1 to} R ₄ , the coordinates of the pressing point on the resistance sheet can be calculated. The voltages V ₁ and V ₂ are A / D converted by the A / D converters 14 and 13 and then read into the microcomputer 15. The microcomputer 15 executes the calculation of the equations (1) to (10) and
Calculate R _{1 to} R ₄ . The coordinates of the pressing point P can be determined by the resistance division ratios of the resistors R ₁ and R ₂ and R ₃ and R ₄ .

In the configuration shown in FIG. 1, the external resistor (R _A ) is provided between the power source V _DD and the electrode X ₁ , but as shown in FIG.
It may be provided between the electrode X ₁ and the ground (resistance R _B ).

Further, in the formula (3), R ₁ > 0 and R ₂ > 0 are set, but this is the case where the pressing point range does not reach the electrode portion of the resistance sheet 12. Therefore, when R ₁ = 0 or R ₂ = 0,
Resistance R ₄ cannot be determined. For such a case, a resistor R _C is inserted between the electrode Y ₁ of the resistance layer 2b and the power source as shown in FIGS. 3 and 4, or the electrode Y ₀ is provided as shown in FIG. By inserting a resistor R _D between this and ground, R ₁ + R _C > 0 or R ₂ + R _D > 0. Therefore, R ₁
R _{1 to} R ₄ can be obtained by setting + R _C → R ₁ and R ₂ + R _D → R ₂ .

By the way, in the configuration of Fig. 1, analog ground (AGND) and analog reference voltage input (V _AREF ) of the A / D converter.
If is fixed, in the circuit of FIGS. 1 and 3,
When the value of the resistor R ₁ becomes small, when the resistors R ₃ and R ₄ are changed, the change of the voltage V ₂ becomes small with respect to the potential difference between the analog ground of the A / D converter and the analog reference voltage. The measurement resolution of ₂ decreases.

Similarly, in the circuits of FIGS. 2 and 4, when the resistance R ₂ becomes smaller, the measurement resolution of the voltage V ₂ becomes lower. In order to prevent this decrease in measurement resolution, in the present invention, as shown in FIG. 1, the output (V ′ ₁ ) of the buffer 12 is connected to the analog ground (AGND) terminal of the A / D converter 13 on the V ₂ measurement side. Connected. With this configuration, if the resistance value of the resistor R ₁ becomes small and the potential difference of V _DD −V ₁ (= V _S ) becomes small, the potential difference between the AGND of the A / D converter 13 and the analog reference voltage becomes small. Getting smaller,
It is possible to prevent a decrease in the measurement resolution of the voltage V ₂ .

Further, as shown in FIG. 5, connects the output voltage V _'1 of buffer were 14 V _AREF terminal of the A / D converter 13 may be configured to ground the AGND. With this configuration, the resistance
As R ₂ changes, the potential difference between AGND and V _AREF (analog reference voltage) of the A / D converter 13 changes. Therefore, the measurement resolution of V ₂ is not reduced.

〔effect〕

As described above, according to the present invention, the switching operation of the applied voltage to the resistance sheet becomes unnecessary and the switching timing operation for the switching becomes unnecessary. Therefore, the configuration and the program can be simplified. You can

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2, 3, and 4 are circuit diagrams showing modified examples of a resistance sheet circuit, and FIG. 5 is another connection of an A / D converter. FIG. 6 is a sectional view showing an example of a tablet, and FIG. 7 is a connection diagram showing a conventional coordinate input device. 1a, 1b …… base, 2a, 2b …… resistive layer, 3 …… spacer,
10 …… tablet, 11, R ₁ ~ R ₄ ,, _RA ~ R _D ...... resistor, 12 ……
Buffer were, 13, 14 ...... A / D converter, 15 ...... _{microcomputer, X 0, X 1, Y} 0, Y 1 ...... electrode.

Claims (3)

[Claims] 1. A tablet in which two resistance sheets provided with electrodes on two sides facing each other are arranged to face each other so as to be contactable by a pressing input through an insulating spacer, and an electrode on one side of one of the resistance sheets. When a voltage is applied between the resistance of which one end is connected and the other end is connected to either the power supply or the ground and the electrode of the other resistance sheet, the voltage is output to each electrode of the one resistance sheet. A tablet coordinate input device comprising: a calculation unit that reads the coordinates of the pressing input point of the tablet based on a voltage. 2. The tablet coordinate input device according to claim 1, further comprising a resistor connected between a power source side electrode of the other resistance sheet and a power source. 3. The tablet coordinate input device according to claim 1, wherein a resistor is connected between the ground-side electrode of the other resistance sheet and the ground.