JP2001100900A - Coordinate reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coordinate reader, capable of reading coordinates at high speed by shortening timing to read amplitude information out of respective loop coils. SOLUTION: An electronic blackboard is composed of a pen for generating an alternating field and a writing panel. An induced voltage is generated in a loop coil 23 by the pen and amplified by an amplifier 50c, while successively connecting the respective coils 23 by an X coil switching circuit 50a and a Y-coil switching circuit 50b, noises at the time of switching are muted by a mute circuit 46 and filtered by a band pass filter 50b, and the amplitude of partial signals is detected by an amplitude detecting circuit 51 provided with a rectifying circuit and a smoothing circuit. When a voltage from one coil is finished by an A/D converting circuit 52, the smoothing circuit is grounded by a switching circuit 41, and the next coil can be sampled promptly. Thus, coordinates can be read at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate reading apparatus which speeds up processing which can be used for an electronic blackboard or the like.

[0002]

2. Description of the Related Art As a coordinate reading device, for example, when a character or figure is drawn on a white board or the like with a marker pen using ink, the coordinates of the character or figure drawn on the board are read and captured as digital data. A so-called electronic blackboard has been proposed. In this electronic blackboard, a position indicator for giving a change in magnetic field and a plurality of loop coils laid in the X and Y directions are magnetically coupled, and the change in the magnetic field causes the coordinate position of a marker pen which is a position indicator on the board to change. Is to read. In order to read the change in the magnetic field, the signals from each loop coil are sequentially switched, amplitude detection is performed, amplitude information of the input signal of each loop coil is obtained, and position information is calculated based on the amplitude information. In this case, in order to obtain amplitude information, it is necessary to perform amplitude detection on the input signal. To perform the amplitude detection, a smoothing circuit that performs rectification of the input signal and performs smoothing using, for example, an RC parallel circuit is used. Some have been provided. This smoothing circuit makes it possible to smooth the detection signal and prevent carrier leakage to obtain amplitude information. Therefore, it is desirable that the rectified signal be sufficiently smoothed.

[0003]

However, for example, when an RC circuit is used as the smoothing circuit, the rise and fall times of the detection signal due to the smoothing of the amplitude depend on the combination of the values of the resistance R and the capacitance C. It is determined by a fixed time constant. If the capacitance C
If the current flowing into the detector is small, it takes a long time for the detection signal to reach a stable voltage required for measuring the voltage, and it takes time to measure the voltage. on the other hand,
In order to increase the rise of the detection signal, it is necessary to increase the resistance R and increase the current flowing into the capacitance C. In this case, the rise of the voltage rises faster, but once the capacitance C is increased. When charged, the time required until the capacitance C is discharged becomes longer even if the input signal from the loop coil is cut off. That is, immediately after obtaining the amplitude information from one loop coil, even if the loop coil is switched to the next loop coil to obtain the amplitude information, the charge remains in the capacitance C irrespective of the absence of the input. However, since accurate amplitude information cannot be obtained, it is necessary to wait for the discharge of the capacitance C to be completed. as a result,
It takes a certain amount of time to obtain amplitude information from all loop coils, and there is a problem that data cannot be read at high speed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a coordinate reading apparatus capable of performing high-speed coordinate reading by shortening a switching timing for reading amplitude information from each loop coil. And

[0005]

In order to achieve this object, a coordinate reading apparatus according to the first aspect of the present invention comprises a position indicating section for changing a magnetic field and a receiving section having a plurality of loop coils. A coordinate reading device that is provided so as to be magnetically coupled to the position indicating unit, and reads the position of the position indicating unit in the receiving unit based on a change in the magnetic field, wherein the receiving unit sequentially selects and switches the loop coil. And a rectifier circuit, a smoothing circuit, and an amplitude detection circuit for detecting the amplitude of the input signal, reading the amplitude-detected signal at predetermined time intervals, Sampling means for performing a sampling process by comparing the voltage value and storing the voltage value; a switching circuit provided in parallel with the smoothing circuit, one end of which is grounded; It actuates the switching circuit after the end of treatment, characterized in that a discharge control means operable to ground potential with respect to the smoothing circuit.

In the coordinate reading apparatus according to this configuration, the loop coil is sequentially selected and switched by the loop coil selecting means, and the loop coil is input, and the signal inputted by the amplitude detection circuit having the rectifying circuit and the smoothing circuit is subjected to the amplitude detection. After reading the signal amplitude-detected by the sampling means at predetermined time intervals, comparing the amplitudes, performing a sampling process by storing the voltage value, and detecting the peak voltage, the discharge control means By operating a switching circuit provided in parallel with the smoothing circuit and having one end grounded to the ground potential with respect to the smoothing circuit, it is possible to promptly input a voltage to be sampled next to the amplitude detection circuit. Can be. Therefore, when sequentially scanning a large number of coils, the readout timing of the amplitude information from the loop coil can be shortened, and high-speed coordinate reading can be performed.

In the coordinate reading device according to the second aspect of the present invention,
In addition to the configuration of the coordinate reading device according to the first aspect, the loop coil selecting means switches to a next loop coil after a predetermined time has elapsed after the operation of the switching circuit.

In the coordinate reading device according to this configuration, the loop coil selecting means switches to the next loop coil after a predetermined time has elapsed after the operation of the switching circuit.
After the processing of one loop coil is completed, the time until the processing of the next loop coil to be processed can be shortened.
Therefore, when sequentially scanning a large number of coils, the timing for reading out the amplitude information from the loop coil can be further shortened, and high-speed coordinate reading can be performed.

In the coordinate reading device according to the third aspect of the present invention,
In addition to the configuration of the coordinate reading device according to the first aspect, the loop coil selecting means switches the loop coils at predetermined intervals.

In the coordinate reading apparatus according to this configuration, the loop coil is switched at predetermined intervals by the loop coil selecting means, so that simple control can be achieved. The timing for reading the amplitude information from the loop coil can be further shortened, and high-speed coordinate reading can be performed.

[0011] In the coordinate reading apparatus of the invention according to claim 4,
In addition to the configuration of the coordinate reading device according to any one of claims 1 to 3, the position indicating section includes an oscillation circuit that generates an alternating magnetic field having a predetermined frequency.

In the coordinate reading device according to this configuration, since the position indicating section includes the oscillation circuit for generating the alternating magnetic field of the predetermined frequency, a relatively strong signal can be obtained from the position indicating section. By processing a strong signal at a high speed by a receiving unit provided with a switching circuit or the like, coordinates can be read at a high speed against noise.

[0013] In the coordinate reading apparatus according to the fifth aspect of the present invention,
In addition to the configuration of the coordinate reading device according to any one of claims 1 to 4, an input from the loop coil that is activated when the loop coil input by the loop coil selecting means is switched is inhibited or attenuated. A mute circuit is provided.

In the coordinate reading device according to this configuration, when the loop coil input by the loop coil selecting means is switched, the mute circuit for inhibiting or attenuating the input from the loop coil is operated, whereby the loop coil selecting means operates. The effect of switching noise generated when the loop coil is switched can be reduced, and the coordinate reading accuracy can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A coordinate reading apparatus according to the present invention will be described below with reference to the accompanying drawings using an electronic blackboard 1 as a preferred embodiment. Here, an electronic blackboard is used to draw handwritten characters and figures on the board with a pen,
A pen that is a transmitting unit that generates an alternating magnetic field is magnetically coupled to and read by a receiving unit having a plurality of loop coils laid in the back of the pen.

FIG. 1 is an external perspective view showing the main structure of the electronic blackboard 1. As shown in FIG. 1, the electronic whiteboard 1 includes a pen 60 as a position indicating unit and a writing panel 10 as a receiving unit.
First, a pen 60 as a position indicating unit is used.
Will be described with reference to FIG. 3 and FIG.
FIG. 3 is an explanatory diagram showing the internal structure of the pen 60, and FIG.
FIG. 4 is an explanatory diagram illustrating an electrical configuration of the pen 60 illustrated in FIG. 3.

As shown in FIG. 3, the pen 60 is provided with a cylindrical body 61a and a lid 61c detachably attached to the rear end of the body 61a. Inside the body portion 61a, a coil L1 serving as an oscillation coil, an ink cartridge 63 that can be taken out in a direction indicated by an arrow F2, a pen point 62 inserted into the ink cartridge 63, and an alternating magnetic field are generated from the coil L1. A circuit board 69 on which an oscillating circuit and the like for mounting are mounted, and a battery 70 as a power supply for supplying electricity to the circuit board 69 are provided. The coil L1 is formed into an annular shape by being wound 200 times to an inner diameter of about 15 mm and a length of about 15 mm. In addition, the pen tip 62 is arranged at a distance of about 20 mm from the tip of the pen tip 62 that contacts the writing surface 21a (see FIG. 1).

Between the ink cartridge 63 and the circuit board 69, there is provided a push button type switch 67 for supplying and shutting off electricity to the circuit board 69 and the like. The switch 67 connects the pen tip 62 to the writing surface 21.
a (see FIG. 1), the ink cartridge 63 is turned on when the ink cartridge 63 moves in the direction indicated by the arrow F1, and when writing is stopped, the ink cartridge 63 returns to the direction indicated by the arrow F2 by a spring in the switch 67 and turns off. That is, the writing surface 2 is
An alternating magnetic field is generated from the coil L1 only when writing on 1a.

As shown in FIG. 8, the circuit mounted on the circuit board 69 (see FIG. 3) has attributes of the pen 60 (see FIG. 3) such as ink color and pen tip thickness (hereinafter referred to as pen attributes). ), A CR oscillation circuit 69e in which a different modulation frequency is set for each, an LC oscillation circuit 69c that oscillates a carrier that carries a signal oscillated from the CR oscillation circuit 69e, and an oscillation frequency of the LC oscillation circuit 69c Oscillation circuit 69
fSK (Frequency)
Shift Keying) FSK circuit 69d that modulates
It is composed of The oscillation frequency of the carrier wave is determined by the coil L1 which is an inductance and the capacitors C1, C2 and C3 which are capacitances of the LC oscillation circuit 69c, and the modulation frequency fm is determined by the CR oscillation circuit 69c.
e, a capacitor C5 and a resistor R2, and a variable resistor R
3 determined. The frequency deviation of the carrier oscillation frequency is determined by the capacitance of the capacitor C4 of the FSK circuit 69d.

The relationship between the pen attribute and the modulation frequency fm is set as shown in FIG. 10 for explaining the relationship.
In FIG. 10, “thin” indicates that the pen tip 62 (see FIG. 3) is thin, and “thick” indicates that the pen tip 62 is thick. For example, “black thick” indicates the pen 60 whose pen tip 62 is thick and uses black ink. In addition, eraser 4
0 also has a built-in coil, and calculates the erasure range of the eraser 40 based on the signal generated in the loop coil 23 by the alternating magnetic field generated from the coil. Identify.

In FIG. 8, when the switch 67 is turned on, electricity of the battery 70 is supplied to each circuit, and the output of the integrated circuit IC3 of the CR oscillation circuit 69e is output to the MSK of the FSK circuit 69d.
Switching the gate of the OSFET, the capacitor C3
And the capacitor C4 are connected in parallel to change the capacitance, whereby the carrier oscillated from the LC oscillation circuit 69c is frequency-modulated by the signal oscillated from the CR oscillation circuit 69e. In the present embodiment, the center frequency of the carrier is 410 kHz, and the frequency deviation is ± 20 kHz.
It is. In the present embodiment, the integrated circuit IC1 is a TC7SLU04F made by Toshiba, and the integrated circuits IC2 and IC3 are both U04 made by Toshiba. Also, MOS F
ET is 2SK2158. The resistors R1 and R2 are both 1 MΩ, and the variable range of the variable resistor R3 is 0Ω to 1MΩ.
It is. Capacitors C1, C4 and C5 are respectively set to 0.
1 μF, 0.0015 μF, and 100 pF, and the capacitors C2 and C3 are both 0.0033 μF. Further, the battery 70 is an LR44 and its voltage is about 1.5
V.

Next, the configuration of a writing panel 10 as a receiving unit of the electronic whiteboard 1 according to the present embodiment will be described with reference to FIGS. Here, FIG. 2 is an explanatory diagram showing a state in which a personal computer (hereinafter abbreviated as PC) 100 and a printer 200 are connected to the electronic blackboard 1 shown in FIG.

As shown in FIG. 1, the electronic blackboard 1 has a writing panel 10 and a pen 60 for writing on the writing surface 21a.
And an eraser 40 for erasing a written trajectory and data indicating the trajectory. The writing panel 10 includes a frame 11 having a frame shape, and the writing panel main body 20 is incorporated in the frame 11. A plate-like base 12 is attached to the lower end of the front surface of the frame 11 along the lower end so as to project to the front surface. On the upper surface of the table 12, a plurality of stand-shaped recesses 12a for accommodating the pen 60 are formed. On the right side of the concave portion 12a, a flat portion 12b for placing the eraser 40 and the like is formed.

On the front right side of the frame 11, an operation unit 30
Is provided. The operation unit 30 includes a speaker (SP) 31 for reproducing sounds such as operation sounds and warning sounds, and a writing surface 21a.
And a page number display LED 32 for displaying the number of pages storing data (hereinafter, abbreviated as handwritten data) indicating the content written by a 7-segment LED.
A page return button 33 for returning by page, a page forward button 34 for sending one page each time the button is pressed, an erase button 35 for erasing one page each time the stored writing data is pressed, and a printer for storing the stored writing data. 200
(See FIG. 2) and a printer output button 36 to be pressed to output to the PC 100 (FIG. 2).
The electronic blackboard 1 is provided with a PC output button 37 that is pressed to output to the electronic blackboard 1, and a power button 38 that is pressed to activate the electronic whiteboard 1.

A battery case 14 for accommodating four C-size batteries 14a serving as a power source of the electronic blackboard 1 is provided at a lower portion of the front surface of the frame 11, and a lid 14b is opened and closed on the front surface of the battery case 14. Mounted as possible. On the right side of the battery case 14, a volume control knob 13c of the speaker 31 is provided.
On the right side, connectors 13b and 13a are provided. As shown in FIG. 2, the connector 13b has a plug 202 of a connection cable 204 connected to the printer 200.
Is connected, and the plug 102 of the connection cable 104 connected to the PC 100 is connected to the connector 13a.
That is, writing data indicating the content written on the writing surface 21a of the electronic whiteboard 1 is output to the PC 100, and the content written on the electronic whiteboard 1 can be viewed on the monitor 103 provided in the PC 100. Further, it is also possible to output handwriting data to the printer 200 and print the contents handwritten on the electronic blackboard 1 on the printing paper 203.

As shown in FIG. 1, metal fittings 15 for hanging the electronic blackboard 1 on a wall are attached to both ends of the upper end of the back surface of the frame 11. In the present embodiment, the height H1 of the writing surface 21a is 900 mm, and the width W1 is 600 mm. Also, the frame 11 and the table 1
2 is made of a synthetic resin such as PP (polypropylene) so as to be lightweight, and the total weight of the electronic blackboard 1 is 10 kg or less.

Next, the structure of the writing panel main body 20 will be described with reference to FIG. FIG. 4 shows the writing panel body 20.
It is explanatory drawing which shows each component. Writing panel body 20
Has a structure in which a writing sheet 21 having a writing surface 21a, a plate-shaped panel 22, a frame-shaped mounting panel 24 on which a loop coil 23 is laid, and a plate-shaped back panel 25 are sequentially stacked. In this embodiment, the writing sheet 21
Is formed by a PET (polyethylene terephthalate) film bonded to a thickness of 0.1 mm,
The panel 22 is formed of acrylic resin, ABS (acrylonitrile-butadiene-styrene copolymer), PC (polycarbonate) or the like to a thickness of 3.0 mm.
The mounting panel 24 is formed of a foamed resin material such as styrene foam to a thickness of 40 mm, and the back panel 25 is formed of a conductive material such as aluminum to a thickness of 1.0 mm. Furthermore, the entire thickness of the frame 11 that holds each end of the writing panel body 20 is 5
0 mm.

Next, the configuration of the loop coil 23 will be described with reference to FIG. FIG. 5A is an explanatory view showing a part of the configuration of the loop coil 23 shown in FIG. 4, and FIG. 5B is a diagram showing the loop coil 23 shown in FIG.
It is explanatory drawing which shows the width | variety and overlap pitch. In the following description, of the loop coils 23, a loop coil arranged in the X-axis direction is called an X coil, and a loop coil arranged in the Y-axis direction is called a Y coil. Further, each coil constituting the loop coil 23 is simply referred to as a coil.
As shown in FIG. 5A, in the X-axis direction, m X coils X1 to Xm for detecting the X coordinate of the (X, Y) coordinates of the pen 60 and the eraser 40 are arranged. In the Y-axis direction, n coils Y1 to Yn for detecting the Y coordinate are arranged orthogonally to the X coil. The X coil and the Y coil are each formed in a substantially rectangular shape,
The lengths of the long sides of the rectangular portion are P2X and P2Y, respectively.

As shown in FIG. 5B, in the X coil, the length of the short side of the rectangular portion is formed to have a width P1, and the adjacent X coils have a pitch of half the width P1. Each is overlaid. Each of the Y coils is also formed to have a width P1, and adjacent Y coils are each overlapped at a pitch of half the width P1. Each terminal 23a of the loop coil and the X coil is connected to the X coil switching circuit 50a, and each terminal 23b of the Y coil is connected to the Y coil switching circuit 50b (see FIG. 9). Note that the X and Y coil switching circuits 50 are collectively referred to below. As an example, in this embodiment, P1 = 50 mm
P2X = 680 mm, P2Y = 980 m
m. Also, m = 22 and n = 34. Further, both the X coil and the Y coil are formed of a copper wire having a diameter of 0.345 mm and having an insulating film layer (for example, an enamel layer) on the surface.

Next, a position coordinate table for detecting the position coordinates of the pen 60 on the writing surface 21a will be described with reference to FIGS. FIG. 6A shows the X coil X1.
FIG. 6B is an explanatory diagram showing a part of X3.
FIG. 6C is a graph showing the relationship between the voltage generated in the X coils X1 to X3 shown in FIG. 6A and the distance in the width direction, and FIG. 6C is adjacent to the X coils X1 to X3 shown in FIG. 5 is a graph showing a voltage difference between loop coils. FIG. 7 (A)
Is an explanatory diagram showing the position coordinate table as a graph,
FIG. 7B is an explanatory diagram of the position coordinate table.
(C) is an explanatory view showing a storage state of a detection value detected from each X coil.

In FIG. 6, the center lines of the X coils X1, X2, and X3 are C1, C2, and C3, respectively.
1, X2, and X3 are represented by ex1, ex, respectively.
2, ex3. As shown in FIG.
1 to ex3 are the center C1 to C3 of the loop coil, respectively.
, And has a monomodal property that becomes smaller as the end in the longitudinal direction approaches. Each coil is overlapped with a width of 1/2 of P so that its own null point, that is, the point where the voltage ex1 becomes 0 is outside the center of the adjacent coil. In FIGS. 5A, 5B, and 6A, the width is slightly reduced to make it easy to see how the loop coils 23 overlap. As shown in FIG. 6C, the voltage difference between the mutually adjacent loop coils of the X coils X1 to X3 has the maximum value on the centers C1 to C3 of the loop coils, respectively. The graph becomes zero at the midpoint of the long side portion of the graph, that is, at the midpoint of the portion where the adjacent loop coils overlap.

For example, in FIG. 6C, (ex1-e
x2) represents the distance from the center C1 of the X coil X1 to the middle point Q2 of the portion where the X coil X2 is superimposed (1/2 of the superimposed pitch, that is, 4 of P).
1) and (ex1-ex2). Now
If the pen 60 exists at the point Q1, (ex1-ex
If 2) is detected, the distance ΔX1 from the center C1 to the point Q2
Can be detected, so that the X coordinate of the point Q2 can be obtained. In this embodiment, since the coil width P1 is 50 mm, P1 / 4 = 12.5 mm. For example, FIG.
In FIG. 7 (C), when a portion (portion drawn by a solid line) showing the characteristic of (ex1-ex2) is converted into 8-bit digital data, a graph shown in FIG. 7 (A) is obtained. When this graph is converted into a table format, a position coordinate table 58a shown in FIG. 7B is obtained. This position coordinate table 58a
Are stored in the ROM 58 (see FIG. 9) or the like, and are used to calculate the position coordinates of the pen 60.

Next, the main electrical configuration of the electronic blackboard 1 will be described with reference to FIG. FIG. 9 is an explanatory diagram showing the electrical configuration of the electronic whiteboard 1 by blocks. FIG. 19 is a diagram showing a configuration around a conventional amplitude detection circuit, and FIG.
The configuration around the amplitude detection circuit 51 of the present embodiment including the switching circuit 41 and the mute circuit 46 is shown. FIG. 21 shows a modification of the configuration around the amplitude detection circuit 51 of the present embodiment including only a switching circuit.

As shown in FIG. 9, an X coil switching circuit 50a and a Y coil switching circuit 50b for selectively connecting individual coils constituting the loop coil 23 are connected to the loop coil 23. The coil switching circuit 50 includes an input / output circuit (I / O) 53 from the CPU 56.
, An input start signal SS (see FIG. 26) is sent out,
A predetermined coil is connected according to this signal. An amplifier 50c is connected to the X and Y coil switching circuit 50, and a current induced from the selectively connected coil flows and is amplified by the amplifier 50c. A mute circuit 46 is connected to the amplifier 50c.
A control signal is transmitted from U56 via an input / output circuit (I / O) 53, and the mute circuit 46 attenuates the signal output from the amplifier 50c according to this signal. Further, the mute circuit 46 includes a bandpass filter (BPF) 5
0d is connected, the noise in the unnecessary band of the current amplified by the amplifier 50c and appropriately attenuated by the mute circuit 46 is removed. The BPF 50d is composed of, for example, an LC filter or a ceramic filter. The signal from which the unnecessary band signal has been removed by the BPF 50d is sent to the amplitude detection circuit 5
1 and the limiter circuit 54 respectively.

The amplitude detection circuit 51 performs amplitude detection on the input signal, and outputs the signal from the A / D conversion circuit 5.
2, the voltage is digitized and transmitted to the CPU 56 via the input / output circuit (I / O) 53. On the other hand, the limiter 54 converts the sine wave into a square wave, and
The signal is input to the demodulation circuit 55. In the FSK circuit, the input signal is FSK-demodulated and sent to the CPU 56 via the input / output circuit (I / O) 53 for processing.

The control section 2 will be described. A ROM 58 and a RAM 59 are connected to the CPU 56 via a bus to form a well-known computer, and the input / output circuit 53 and the I / O
The control unit 2 is configured together with the F circuit 57. Control unit 2
Performs various controls and calculations. In addition, the control unit 2
Coil switching circuit 50a, Y coil switching circuit 50
b, Send a control signal to the A / D conversion circuit 52, the mute circuit 47, and the FSK demodulation circuit 55. Further, the control unit 2
Is used for input / output to / from the operation unit 30 and the audio circuit 3
A control signal is sent to 1a, and sound is output from the speaker 31.

Next, the configurations of the amplifier 50c, the band-pass filter 50d, the amplitude detection circuit 51 and the like will be described in detail with reference to FIGS. In this description, the same or equivalent parts are denoted by the same reference numerals and description thereof will be omitted.

The configuration of the amplifier 50c, the band-pass filter 50d, the amplitude detection circuit 51, and the like according to the present embodiment will be described with reference to FIGS. In the electronic whiteboard 1 of the present embodiment, the amplifier 50c, the bandpass filter 50d,
The amplitude detection circuit 51 is arranged in this order, a mute circuit 46 is connected between the amplifier 50c and the band-pass filter 50d, and the switching circuit 41 is connected to the amplitude detection circuit 51.
Is connected.

The amplifier 50c has an input resistor R4
And an operational amplifier IC4 and a feedback resistor R5.
Consists of The input is adjusted by the resistor R4, the amplification factor is adjusted by the resistor R5, and the input signal is amplified by the IC4 at a predetermined amplification factor.

The mute circuit 46 is provided with the FET 2 and its source is composed of the IC 4 and the band-pass filter 50 d.
, The drain is grounded, and the gate is connected to the control unit 2. When switching to each coil is performed by the X, Y coil switching circuit 50, a square wave which is a control signal is transmitted from the control unit 2 at a predetermined timing, a voltage is applied to the gate, and the circuit on the source side is
Grounded on the drain side. Therefore, the amplified signal output from the amplifier 50c is bypassed from the band-pass filter 50d side to the mute circuit 46 side. As a result, the gain of the amplifier 50c is reduced, and the signal flowing into the amplitude detection circuit 51 is muted. You. as a result,
The switching noise generated in the X, Y coil switching circuit 50 is attenuated, so that the reading accuracy at the time of reading coordinates is not reduced.

The amplitude detection circuit 51 includes a rectifier circuit 51a and a smoothing circuit 51b. The rectifier circuit 51a includes a capacitor C6 and a diode D1 arranged in series, and a diode D2 having one end grounded, and detects an input signal. The smoothing circuit 51b forms a CR circuit in which the capacitor C7 and the resistor R6 are grounded in parallel, and smoothes the signal detected by the rectifier circuit 51a.

In the switching circuit 41, the FET 3 is arranged, and its source is connected immediately after the smoothing circuit 51b.
The drain is grounded, and the gate is connected to the control unit 2. At the time of A / D conversion, a square wave as a control signal is transmitted from the control unit 2 at a predetermined timing, a voltage is applied to the gate, and the circuit on the source side is grounded on the drain side. Therefore, the smoothing circuit 51b becomes the ground potential, and the electricity charged in the capacitor C7 is discharged. That is, when the signal input to the smoothing circuit 51b is stopped in a state where the capacitor C7 is charged, the switching circuit 41 is operated to bring the smoothing circuit 51b to the ground potential, and the signal output from the smoothing circuit 51b. Can be reduced to zero in a very short time.

Here, FIG.
FIG. 20 is a diagram schematically showing an example of a screen on an oscilloscope of a signal output from the conventional amplitude detection circuit 51 shown in FIG. As shown in FIG. 23, in the signal input to the amplitude detection circuit 51, the rising voltage SVa quickly rises from the start voltage SVo, and immediately reaches the peak voltage SVp. Even if the input signal stops after that,
From this screen, it was confirmed that the falling voltage SVb slowly took a certain amount of time to drop to the discharge voltage SVe.

FIG. 22 is a diagram schematically showing an example of a screen on an oscilloscope of a signal output from the amplitude detection circuit 51 having the switching circuit 41.
As shown in FIG. 22, the signal input to the amplitude detection circuit 51 is such that the rising voltage SVa slowly rises from the start voltage SVo to reach the peak voltage SVp, but the signal input after the peak voltage SVp is detected. Is stopped,
When the switching circuit 41 operates, the falling voltage SVb rapidly drops from the voltage value SV, and it takes only an extremely short time to drop to the discharging voltage SVe.
I was able to confirm from this screen. Here, comparing FIG. 22 and FIG. 23, although the input waveforms are slightly different, in the amplitude detection circuit 51 of the present embodiment including the switching circuit 41 shown in FIG.
It can be seen that the voltage can be reduced in a very short time as compared with the conventional one.

Here, a conventional circuit will be described with reference to FIGS. As shown in FIG. 19, the conventional circuit is
The only difference is that the mute circuit 46 and the switching circuit 41 are not provided. First, the case of the electronic whiteboard 1 not provided with the mute circuit 46 will be described. In the case of the electronic whiteboard not provided with the mute circuit 46, the X and Y coil switching circuit 50 switches the coils when inputting a signal. However, in this case, the switch is opened and closed, and switching noise occurs. This switching noise hinders correct recognition of the amplitude information and frequency information of the input signal, and lowers the coordinate reading and the pen attribute recognition rate.

Next, the operation of the electronic whiteboard 1 without the switching circuit 41 will be described. here,
FIG. 28 is a timing chart illustrating a conventional A / D conversion. As shown in FIG. 28, since the voltage SV of the signal output from the amplitude detection circuit 51 is used for charging the capacitor C7 of the smoothing circuit 51b, a part of the input signal is used as the start voltage SVo at the start of input. Becomes
An output corresponding to the input voltage cannot be immediately output to the A / D conversion circuit 52. The voltage output thereafter depends on the charging rate of the capacitor C7 and the rising voltage S
It shows a gradually increasing voltage change as shown by Va. When the charging of the capacitor C7 is completed, the voltage value becomes the peak voltage SVp and is stabilized. This input start voltage SV
The time from o to the peak voltage SVp is defined as a rise time Tt.

Next, even if the input of the input signal from the coil is stopped by the X and Y coil switching circuit 50, the voltage of the output signal is indicated by the falling voltage SVb because the capacitor C7 is charged. As described above, the voltage is output to the A / D conversion circuit 51 while gradually falling according to the discharge of the capacitor C7, and becomes the discharge voltage SVe. This peak voltage SVp
From discharge voltage SVe to discharge time Dt.

Next, a control method for reading out such output signals, comparing amplitudes, and storing voltage values will be described with reference to FIGS. First, a signal subjected to amplitude detection by the rectifier circuit 51a and smoothed by the smoothing circuit 51b is X, X by an input start signal SS from the control unit 2.
At the same time as input from the Y coil switching circuit 50, A
The voltage of the signal output from the amplitude detection circuit 51 is read out by the / D conversion circuit, and the voltage value SV is digitized and stored in the RAM 59, so-called sampling is performed. Then, the next sampling is performed at a predetermined sampling interval dt, and compared with the previously sampled voltage value SV, if the voltage difference dv is larger than the predetermined value, it is determined that the voltage is rising and the next sampling is performed after the sampling interval dt. And compares it with the voltage value sampled immediately before. Such processing is repeated to perform so-called sample and hold. In this manner, the sample-and-hold operation is repeated, and when the voltage difference dv from the immediately preceding sampling value becomes equal to or smaller than the predetermined value ε as shown in FIG. 28, the control unit determines the peak voltage SVp or the discharge voltage SVe, 2 outputs an input stop signal ES to output X, Y
The connection to the coil is cut off by the coil switching circuit 50, and the input signal is stopped.

Then, as shown in the lower part of FIG. 28, sample-and-hold is repeated at further sampling intervals dt, and the detection of the discharge voltage SVp at which the voltage difference dv from the immediately preceding voltage value has become equal to or less than the predetermined value ε is performed. At this point, it is determined that the discharging of the capacitor C7 has been completed, and the processing of the coil is terminated. Then, after waiting for the end of the processing of the preceding coil, the control unit 2 sends the input start signal SS to the X / Y coil switching circuit 50 to start the processing of the next coil. That is, the processing of the next coil cannot be performed until it is determined that the discharge of the capacitor C7 has been completed.

Here, the rise time Tt from the start voltage SVo to the rise voltage SVa shown in FIG. 28 is increased by increasing the resistance value of the resistor R6 to increase the current input to the capacitor C7. C7
The rise time Tt can be shortened by shortening the time during which is charged. However, the process for the next coil cannot be performed until the time Dt required for discharging the capacitor C7 has elapsed, so that the scanning time cannot be shortened by the time Dt.

Next, the case of the electronic whiteboard 1 of the present embodiment having the switching circuit 41 will be described with reference to FIGS. Here, FIG. 26 shows A of the present embodiment.
4 is a timing chart illustrating the / D conversion.
Since the sample-and-hold processing is the same as the conventional one, the description thereof will be omitted, and the points different from the conventional control method will be described.

As shown in FIG. 26, the X, Y coil switching circuit 50 is connected to a predetermined coil by the sample start signal SS transmitted from the control unit 2 at intervals of the coil switching cycle Ct, and a signal is input. Thereafter, the mute circuit 46 stops operating, and the A / D conversion circuit 52 starts sampling. Then, the rising voltage SV
a, the input stop signal ES is output from the control unit 2 and the mute circuit 46 is detected after the peak voltage SVp is detected.
Is operated, the connection to the coil is cut off by the X, Y coil switching circuit 50, and the input signal is stopped. Thereafter, the switching signal DS is sent from the control unit 2 to the switching circuit 41, and the switching circuit 41 operates.
By the operation of the switching circuit 41, the smoothing circuit 51b becomes the ground voltage after the discharge time Dt, and the output to the A / D conversion circuit 52 becomes zero.

The discharge time Dt in this embodiment is different from the discharge time Dt in the smoothing circuit 51b without the conventional switching circuit 41 as shown in FIG. Dt becomes extremely short, and the input from the next coil becomes possible in an extremely short time after the switching circuit 41 operates. Since the discharge time Dt differs depending on the voltage value, the coil switching cycle Ct is set by setting the total time of the rise time Tt in the case of the voltage value SV at the maximum amplitude Vmax and the discharge time Dt. Even when the processing of the next coil is started, the signal output from the amplitude detection circuit 51 to the A / D conversion circuit 52 can be accurately detected without being affected by the previous coil. .

FIG. 27 shows the A / D of this embodiment.
6 shows a timing chart illustrating a modification example of conversion. In the present embodiment, the input start signal SS output from the control unit 2 is output at intervals of the coil switching cycle Ct set to a predetermined length. However, when the amplitude of the input signal is small, that is, when the voltage is low, the rise time Tt from the start of input from the coil to the detection of the rise voltage SVp is short, and the discharge time Dt is short but short. Therefore, at least the total time of the rise time Tt and the discharge time Dt is a time necessary for detecting the voltage value of one coil, and the next time immediately after the total time of the rise time Tt and the discharge time Dt elapses, It is also conceivable to shift to coil processing.

However, it is difficult to detect the end of the discharge time Dt by sample-and-hold due to a large voltage change dv per unit time dt, and that the discharge time Dt itself is extremely short. Considering that after the rise time Tt of the coil elapses,
Even if the total time of the discharge time Dt at the voltage at the maximum amplitude Vmax is small, the difference is very small. That is, after the elapse of the rise time Tt of the coil, the maximum amplitude Vma
If control is performed so as to shift to the processing of the next coil after the lapse of the total time of the discharge time Dt at the voltage at x, the time required for scanning can be further reduced, and there is no need for complicated control. In the present modified example, the control is performed for such a reason.

A modification of this control will be described with reference to the time chart of FIG. 27. As shown in FIG. 27, the input start signal SS is output from the control unit 2 and the X, Y coil switching circuit 50 outputs the signal. The input stop signal ES is transmitted immediately after the input is started and the peak voltage SVp is detected in the sample-and-hold process, as in the embodiment. Thereafter, after the transmission of the input stop signal ES, the control unit 2 transmits the input start signal SS of the next coil from the control unit 2 when a predetermined time interval It has elapsed based on the input stop signal ES. This interval interval I
Since t is a time corresponding to the discharge time Dt in the voltage SV at the time of the maximum amplitude Vmax, the next input start signal SS
By this time, the detection of the voltage SV of the previous coil has already been completed, and this does not hinder the detection of the voltage SV of the next coil. Therefore, the scan time can be reduced, and the speed of coordinate reading can be increased.
Compared with the scanning method according to the embodiment, the processing speed in the coil where the pen 60 does not exist, that is, the coil in which the induced voltage is not detected is significantly increased.

Next, the electronic blackboard 1 configured as described above
Will be described with reference to FIG. 9 along with FIG. FIG. 11 is a flowchart showing main control contents executed by CPU 56 shown in FIG.

When the process is started (start), the CPU 56 provided in the control device 50 shown in FIG. 9 determines whether or not the power button 38 (see FIG. 1) is pressed to turn on the power (step ( Hereafter, it is abbreviated as S.) 100) When it is determined that the power is ON (S100: Yes), the ROM 58
Control program and position coordinate table 5 stored in
Initial setting, such as loading 8a (see FIG. 7B) into the work area of the RAM 59 (S200), executes coordinate reading / pen information detection processing (S300).

Here, the coordinate reading / pen information detection processing (S
The coordinate reading process in step 300) will be described with reference to the flowchart of FIG. CPU
56 outputs an input start signal SS and an input stop signal ES (see FIG. 26) for sequentially selecting and inputting the X coils X1 to Xm to the X coil switching circuit 50a via the input / output circuit (I / O) 53. Thus, scanning of the X coils X1 to Xm is performed (S302). A signal generated by magnetic coupling between the alternating magnetic field generated from the coil L1 of the pen 60 and one of the X coils is supplied to the amplifier 50c (see FIG. 9).
The amplified signal is filtered by a band-pass filter (BPF) 50 d in an unnecessary band, and amplitude-detected by an amplitude detection circuit 51. Subsequently, the amplitude-detected signal is converted by an A / D conversion circuit 52 into a digital signal corresponding to the amplitude, that is, a voltage value.
The sample-and-hold process is performed, and is input to the CPU 56 via the input / output circuit 53.

FIG. 24 is a flowchart for explaining in detail the control of the X coil scan (S302) in the flowchart of FIG. The control of the X coil scan (S302) in the flowchart of FIG. 12 will be described with reference to this flowchart.

First, an X coil scan (FIG. 12: S30)
When the process 2) is started (FIG. 24: start), initial settings for designating the sampling interval dt, the coil switching cycle Ct, and clearing the storage area (S302).
Perform 2). This designation may be based on a default value. Further, the storage areas V1 and V2, the output storage area, and the like are also initialized. Further, a mute signal is transmitted, the mute circuit 46 (see FIG. 20) is activated, and waits for connection to the coil. Next, the input start signal SS is sent from the control unit 2 to the X coil switching circuit 50a, connected to a predetermined coil, here, the X coil X1 (see FIG. 5), and input is started (S3024). Then, the output of the mute signal is stopped to stop the operation of the mute circuit 46 (S3026), and the amplitude detection circuit 51 starts inputting a signal from the coil.

The control section 2 performs an initial sampling process on the A / D conversion circuit 52 (S3028). First, initial sampling is performed, and the voltage value Sv read at this time is
It is stored in a predetermined storage area V1, and Sv is cleared. Then, it waits until the sampling interval dt elapses (S
3030: No, S3030), when the elapsed time t after sampling becomes t> dt and the sampling interval dt has elapsed (S3030: Yes), the next sampling process is performed to read out the voltage Sv and store it in the predetermined storage area V2 (S3030: No). S3032). Next, the voltage difference between the storage area V1 and the storage area V2 is determined and compared with a predetermined value ε (S303).
4).

If dv = V2−V1 <ε is not satisfied (S
3034: No), the voltage value of the storage area V2 is moved to the storage area V1 as V1 ← V2 (S3036), and the next sampling is performed (S3030, S3032). Then, the voltage difference between the storage area V1 and the storage area V2 is obtained again and compared with the predetermined value ε (S3034).

Here, if dv = V2−V1 <ε (S3034: Yes), the sampling value stored in the storage area V2 is used as the voltage value of the coil, and FIG.
The information is stored in a predetermined output storage area for storage in a predetermined coil area of the voltage value storage area 59a shown in (C) (S3038). Then, the control unit 2 outputs the mute signal MS and activates the mute circuit 46 to prevent the occurrence of switching noise (S3040),
The input stop signal ES is output to the X coil switching means 50a to disconnect the connection with the coil and stop the input from the coil (S3042).

Here, if there is still a coil to be processed next, the process is not terminated (S3044: No), and the control unit 2 waits until the coil switching cycle Ct elapses from the previous coil switching (S3046: No). → S304
6) When the coil switching cycle Ct has elapsed (S3
046: Yes), that is, after outputting the input start signal SS to the X coil switching circuit 50a at regular intervals and connecting to the next coil to be processed (S3024), the output of the mute signal MS is stopped (S3026). ), The operation of the mute circuit 46 is stopped, and a signal from the next coil is input to the amplitude detection circuit 51 (S3026). On the other hand, S3
If it is determined in step 044 that there is no coil to be processed next, it is determined to end (S3044: Ye).
s), the control of the X coil scan (S302) is ended (end), and the pen detection (S30) in the flowchart of FIG.
Move on to the determination of 4).

Next, the control of the X coil scan (S302) in the flowchart of FIG. 12 in a modification of the control method of the present embodiment will be described. FIG. 25 is a flowchart illustrating the control of the X coil scan (S302) in the flowchart of FIG. 12 in a modified example of the above-described control method.

First, an X coil scan (FIG. 12: S30
When the process of 2) is started (FIG. 25: start), initialization (S3122) for designating the sampling interval dt, the interval interval It, and clearing the storage area is performed. This designation may be based on a default value. Further, the storage areas V1 and V2, the output storage area, and the like are also initialized. Also, a mute signal is sent out,
The mute circuit 46 operates and waits for connection to the coil. Next, the input start signal SS is sent from the control unit 2 to the X coil switching circuit 50a, connected to a predetermined coil, here, the X coil X1, and input is started (S3124). Then, the output of the mute signal is stopped and the mute circuit 46 is stopped.
Is stopped (S3126), and the amplitude detection circuit 51
Start inputting the signal from the coil.

The control section 2 causes the A / D conversion circuit 52 to start sampling processing. First, initial sampling is performed, and the voltage value read at this time is stored in a predetermined storage area V1 (S3128), and Sv is cleared. Then, the process waits until the sampling interval dt elapses (S3130: No, S3130). When the elapsed time t from the previous sampling becomes t> dt and the sampling interval dt elapses (S3130: Yes), the next sampling process is performed. The voltage Sv is read out and stored in a predetermined storage area V2 (S3132). Next, the storage area V1
The difference between the voltage of the storage area V2 and the voltage of the storage area V2 is obtained and compared with a predetermined value ε (S3134).

If dv = V2−V1 <ε is not satisfied (S
3134: No), the voltage value of the storage area V2 is moved to the storage area V1 as V1 ← V2 (S3136), and the next sampling is performed (S3130, S3132). Then, the voltage difference between the storage area V1 and the storage area V2 is obtained again and compared with the predetermined value ε.

If dv = V2−V1 <ε, (S
3134: Yes), a predetermined output storage area for storing the sampling value stored in the storage area V2 as a voltage value of the coil in a predetermined coil area of the voltage value storage area 59a shown in FIG. 7C. (S
3138). Then, the control unit 2 outputs the mute signal MS, activates the mute circuit 46 to prevent the occurrence of switching noise (S3140), and then outputs the input stop signal ES to the X coil switching means 50a to output the coil stop signal. Is disconnected, and the input from the coil is stopped (S3142).

Here, if there is still a coil to be processed next, the processing is not terminated (S3144: No), and the control unit 2 waits until the predetermined interval interval It has elapsed after outputting the input stop signal ES. (S3146: No → S3)
146) When the interval It has elapsed (S31)
46: Yes), that is, after a certain interval,
After outputting the input start signal SS to the X coil switching circuit 50a and connecting it to the next coil to be processed (S312
4), the output of the mute signal MS is stopped (S312)
6), the operation of the mute circuit 46 is stopped, and a signal from the next coil is input to the amplitude detection circuit 51 (S312).
6). On the other hand, if it is determined in S3044 that there is no coil to be processed next, it is determined to end (S3144: Yes), and the X coil scan (S3044) is performed.
The control of 2) is completed (end), and the process proceeds to the determination of pen detection (S304) in the flowchart of FIG.

The above is the processing procedure of the modified example of the control method of the electronic whiteboard 1 of the present embodiment. The difference is that, in the control method of the present embodiment, the control unit 2 controls the X coil switching circuit 50a. The next input start signal SS is output at intervals of the coil switching cycle Ct based on the input start signal SS to be output.
Is the interval interval It based on the input stop signal ES.
This is different by outputting the next input start signal SS at intervals of.

In this embodiment, since the input start signal SS only needs to be output at regular intervals, the control is simple. However, as described above, the coil switching cycle Ct of the present embodiment is a time based on the voltage rising time Tt at the time of the maximum amplitude Vmax as shown in FIG. 26, and the interval It is shown in FIG. Thus, the time is based on the discharge time Dt. for that reason,
When the input voltage is small, the processing time becomes shorter in accordance with the voltage in the control method of the modified example, but does not change in the control method of the present embodiment. Therefore, the modified example is more preferable.

Continuing the description with reference to the flowchart of FIG. 12, the CPU 56 determines whether or not the pen 60 has been detected (S304). When it is determined that the pen 60 has been detected (S304: Yes), X coil X1
The voltage values e1 to em indicated by the digital signal input by scanning Xm are read out from the temporarily stored output storage area, and as shown in FIG.
It is sequentially stored in the voltage value storage area 59a of the RAM 59 in association with the coil number of the X coil (S306). Subsequently, the CPU 56 determines the X of the pen 60 according to the following procedure based on each voltage value stored in the voltage value storage area 59a.
The coordinates are calculated (S308). First, the maximum voltage value emax is selected from the voltage values e1 to em stored in the voltage value storage area 59a, and the coil number of the X coil that generated the voltage value emax (hereinafter, referred to as max).
Is stored in the RAM 59. For example, as shown in FIG.
The pen 60 is located at the position Q3, and as shown in FIG. 6B, the voltage value e from each of the X coils X1, X2, X3.
1, e2 and e3 occur, the maximum voltage value e2
And the coil number 2 of the X coil that generated the voltage value e2 is stored in the RAM 59 as max. Then, the CPU 56 determines the voltage value emax ± on both sides of emax.
1 is determined, and the coil number (hereinafter, referred to as max2) of the X coil that has generated the determined voltage value is stored in the RAM 59.

In the example shown in FIG. 6, the voltage value e on both sides of e2
3, e1 is determined to be the larger e3, and its voltage value e
The coil number 3 of the X coil generating 3 is stored in the RAM 59 as max2. Subsequently, the CPU 56
By comparing the coil numbers max and max2 stored in 59, it is determined whether the coil number max2 exists in the + direction or the − direction of the X axis from the coil number max.
If max2 ≧ max, the variable SIDE
Is set to 1 and if max2 <max, the variable S
Set IDE to -1. In the example shown in FIG.
Is in Q3, since max = 2 and max2 = 3, max2> max, and the variable SIDE is set to 1. Subsequently, the CPU 56

DIFF = e (max) −e (max2) (1)

Is calculated, and the position coordinates closest to the calculated DIFF are read out from the position coordinate table 58a stored in the ROM 58 and set as OFFSET. Subsequently, the CPU

X1 = (P1 / 2) × max + OFFSET × SIDE

Is calculated to obtain an X coordinate X1. here,
(P1 / 2) × max is the X of the center of the coil number max.
Indicates coordinates. In the example shown in FIG. 6, the expression (2) is expressed as X = (P
１ ／) × 2 + (e2−e3) × 1, and the X coordinate of the position Q3 is separated from the center line C2 of the X coil X2 by a distance corresponding to (e2−e3) in the + direction of the X axis, for example, ΔX2. Coordinates. Then, the CPU 56 scans each Y coil (S310), and stores the voltage value detected from each Y coil in the voltage value recording area for the Y coil of the RAM 59 (S312). Subsequently, the CPU 56 proceeds to step S3.
08, using the same method as that for calculating the X coordinate.
Is calculated (S314).

Next, the electrical configuration and control for the CPU 56 to determine the pen attribute will be described with reference to FIGS. FIG. 13 is an explanatory diagram showing an electrical configuration of the FSK demodulation circuit 55 (see FIG. 9), and FIG. 14 is an explanatory diagram showing signal waveforms appearing at various parts of the FSK demodulation circuit 55 shown in FIG.

FIG. 15A shows an output signal (hereinafter, referred to as a CR signal) of the CR oscillation circuit 69e (see FIG. 8).
The output signal of the LC oscillation circuit 69c (refer to FIG. 8) (hereinafter referred to as a carrier signal) and the output signal of the limiter circuit 54 (refer to FIG. 9) (hereinafter referred to as a limiter output signal).
FIG. 14 is an explanatory diagram showing a relationship between the count value and a count value obtained by a count circuit 55a (see FIG. 13). FIG. 15B is an explanatory diagram showing how the count value stored in the shift register 55b (see FIG. 13) shifts.

FIG. 16A shows an absolute value comparator 55.
f (see FIG. 13) and the CPU 5
FIG. 16 is an explanatory diagram showing the relationship with the determination cycle of FIG.
(B) is an explanatory diagram showing how the count value K by the counter 55g moves. FIG. 17 shows F in step S318.
18 is a flowchart showing the flow of processing (pen attribute detection processing 1) from the count circuit 55a constituting the SK demodulation circuit 55 to the absolute value comparator 55f, and FIG.
FIG. 14 is a flowchart showing the flow of processing of the counter 55g in S318. Also, FIG.
14 is a flowchart showing the flow of processing of an adder 55i (see FIG. 13) in No. 18. Note that the carrier signal shown in FIG. 15A has, for example, a center frequency of 410 kHz and a frequency deviation of ± 20 kHz as described above. However, for the sake of easy understanding, FIG.
Exaggerate the frequency excursion.

First, FSK for detecting pen attributes
The features of the demodulation circuit 55 will be described with reference to FIG. In the example shown in FIG. 15A, the carrier signal has a high frequency (for example, 430 kHz) during the low level of the CR signal.
z), and is modulated to a low frequency (for example, 390 kHz) during the high level. For this reason,
Assuming that the period of the limiter output signal during the low level of the CR signal is TB, the period of the limiter output signal during the high level of the CR signal is TC longer than TB. Therefore, the count value K for one cycle of the limiter output signal by the count circuit 55a increases when the CR signal changes from a low level to a high level, and decreases when the CR signal changes from a high level to a low level.

That is, by detecting the timing at which the count value K by the count circuit 55a changes, C
The rising or falling timing of the R signal can be detected. Since the time from the change of the count value K to the next change corresponds to a half cycle of the CR signal, if one cycle of the change time of the count value K is measured, Since the period can be obtained, the pen attribute can be detected. Where FSK
An outline of the operation of each component of the demodulation circuit 55 will be described.
The count circuit 55a measures the count value K, and outputs a shift register 55b, a first weighted average circuit 55c, a second weighted average circuit 55d, a subtractor 55e, and an absolute value comparator 5
5f detects the change timing of the count value K, and the counter 55g, the register 55h, and the adder 55i measure the cycle in which the count value K changes. And the CPU 56
Determines the pen attribute based on the added value output from the adder 55i (S318).

Next, the operation of the FSK demodulation circuit 55 will be described in detail. The signal output from the bandpass filter 50d is converted by the limiter circuit 54 into a square wave limiter output signal shown in FIG.
5 is output. Then, when the FSK demodulation circuit 55 detects the rise of the limiter output signal (FIG. 17: S1
0: Yes), and starts counting the cycle of the limiter output signal using the system clock (CLK) (S12).
When the next rise of the limiter output signal is detected (S1
4: Yes), the count value K is output to the shift register 55b (S16), and the count value K is reset (S1).
8). That is, the count circuit 55a measures the length TB or TC of one cycle of the limiter output signal.

In this embodiment, the shift register 55
15B, as shown in FIG. 15B, the count value K for one cycle of the limiter output signal is stored for eight cycles of K1 to K8, and every time the newest count value K is taken in, the oldest count value K is stored. Discarding and shifting each counter value K one by one. The first weighted averaging circuit 55c calculates a value of 3 from the latest count value stored in the shift register 55b.
A weighted average value up to a new count value is calculated first, and the weighted average value (hereinafter, referred to as a first weighted average value) is output to the subtractor 55e. The second weighted average circuit 55d
Calculates a weighted average value from the oldest count value to the third oldest count value stored in the shift register 55b, and calculates the weighted average value (hereinafter, referred to as a second weighted average value) of the subtractor 55e. Output to

The subtractor 55e calculates a difference Δm between the first weighted average value and the second weighted average value, and outputs the difference Δm to the absolute value comparator 55f (FIG. 17: S20). For example, in FIG. 15A, when the first weighted average circuit 55c calculates the weighted average value of the count values K1 to K3, and the second weighted average circuit 55d calculates the weighted average value of the count values K6 to K8, Since the count values K7 and K8 of the count values K6 to K8 are obtained by counting the period TC longer than the period TB of the limiter output signal, the second weighted average value is larger than the first weighted average value. Therefore, by detecting that the second weighted average value has become larger than the first weighted average value, it is possible to detect a change point of the period of the CR signal. That is, if the period of the changing point of the period of the CR signal is detected, the period of the CR signal can be detected.
Attribute information can be recognized.

As described above, since the count values counted in time apart are weighted and averaged by the weighted averaging circuit, even if a certain count value is affected by noise, the influence is reduced.

Next, the processing from the absolute value comparator 55f to the adder 55i will be described with reference to FIG. In FIG. 16, 〜 indicates the count value of the counter 55g. The absolute value comparator 55f calculates the difference Δm
Is compared with a preset threshold value m1, and the difference Δ
It is determined whether or not m is equal to or greater than a threshold value m1 (FIG. 17:
If it is determined that the difference Δm is equal to or larger than the threshold value m1 (S22: Yes), the threshold determination output is changed from a low level to a high level (S24). That is, it is determined that the cycle of the limiter output signal has changed (the rising edge of the CR signal has been detected). For example, FIG.
Assuming that the count value of the shorter cycle TB of the limiter output signal shown in (1) by the count circuit 55a is 10, the count value of the cycle TC is 16, and the threshold value m1 is 2, the count value K
Since 1 to K6 are all 10, the first weighted average value =
(K1 + K2 + K3) / 3 = 10. Further, since the count values K7 and K8 are both 16, the second weighted average value = (K6 + K7 + K8) / 3 = 42/3 = 14, and the difference Δm = 10−14 = −4.

The first weighted averaging circuit 55c and the second weighted averaging circuit 55d are determined based on the ratio between the carrier frequency (the oscillation frequency of the LC oscillation circuit 69c) and the modulation frequency fm, and the circuit complexity. The count value K held by the shift register 55b, that is, the number of periods of the limiter output signal is determined by the ratio of the system clock frequency to the carrier wave frequency.
The frequency is set to be large enough to discriminate the change.

Accordingly, since (absolute value of difference Δm = 4)> (threshold value m1 = 2), the threshold value judgment output changes from low level to high level (FIG. 17: S24). This high level state indicates that the absolute value of the difference Δm is equal to the threshold value m1
The above is maintained until the absolute value comparator 55f determines. When the calculation range of the first weighted averaging circuit 55c and the second weighted averaging circuit 55d reaches a portion passing through the edge of the CR signal, the period of the limiter output signal becomes constant. Calculate the weighted average value of the count value K in the same cycle, the subtraction value by the subtractor 55e becomes 0, and the threshold value determination output remains in the high level state.

On the other hand, when the counter 55g detects that the threshold value judgment output has changed from the low level to the high level (FIG. 18A: S30: Yes), the time during which the judgment output is at the high level, that is, The half cycle of the judgment output is counted using the system clock (S32). The count value is used (FIG. 16B: (B1)). When the absolute value comparator 55f determines that the difference Δm is equal to or larger than the threshold value m1 (FIG. 17: S22:
Yes), the threshold determination output is changed from the high level to the low level (S24). That is, it is determined that the cycle of the limiter output signal has changed (the falling edge of the CR signal has been detected). Accordingly, the counter 55g detects that the threshold value determination output has changed from the high level to the low level (S34 in FIG. 18A: Yes), and FIG.
As shown in (B2) of (B), the count value is output to the register 55h (S36). Then 55g counter
Resets the count value (S38) and counts the time during which the threshold value judgment output is at the low level, that is, the half cycle of the threshold value judgment output (circled B, S3).
2). The count value is used.

Subsequently, the adder 55i determines that the timing at which the count value is held in both the counter 55g and the register 55h, that is, the addition timing (FIG. 1).
8 (B) S50: Yes), the count value held by the counter 55g and the count value held by the register 55h are added (S52), and the added value
6 (S56). At this time, the counter 55g
Outputs the count value to the register 55h as shown in (B3) of FIG. 16B (FIG. 18A: S3
6). Then, the CPU 56 reads the value of the FSK demodulation circuit 55 via the input / output circuit 53, that is, the added value (FIG. 12: S316, FIG. 13), and determines the pen attribute based on the read added value (S318). . For example, when the added value is 245, it is determined that the pen attribute is black and thick as shown in FIG. Also, CPU
56 is a RAM 59 that associates pen attributes with XY coordinates.
To memorize. Writing data stored in such a form
For example, the image is output to the printer 200 (see FIG. 2) and printed in black. The data is output to the PC 100 (see FIG. 2) and displayed on the monitor 103 (see FIG. 2) in black. That is, the writing data can be reproduced according to the attribute of the pen 60.

Subsequently, the adder 55i adds the count value of the register 55h and the count value of the counter 55g and outputs the result to the CPU 56 (FIG. 16 (B): (B)
3)). Thereafter, every time the threshold value determination output changes, the count value of the counter 55g is output to the register 55h, and the adder 55i adds the count value of the counter 55g and the count value held in the register 55h, and performs addition. The cycle of outputting the value to the CPU 56 is repeated. That is, as shown in FIG.
5i adds the latest count value counted by the counter 55g and the immediately preceding count value held in the register 55h and outputs the result to the CPU 56. Therefore, as shown in FIG. The CPU 56 determines the pen attribute based on the latest count value and the added value of the previous count value every half cycle of the threshold value determination output.
Therefore, during the threshold value judgment output, for example, as shown in FIG.
Even if the scan of the loop coil 23 is performed between the times t0 and t1, the next 1
Even if the added value of the cycle (t2 to t4) is not taken, the added value of one cycle of the time t2 to t4 half a cycle after the time t1 may be taken, so that the pen attribute can be determined at high speed.

Here, returning to the description of FIG.
U56 is a page return button 33, a page forward button 3
When the 4 and erase buttons 35 are pressed, page processing such as returning, sending, or erasing the stored writing data in page units is performed (S400). That is, CPU
A 56 receives a switching signal generated by operating various buttons (see FIG. 1) provided on the operation unit 30 via an I / F circuit 57 (see FIG. 9), and stores position coordinate data stored in a RAM 59. A page process such as returning or sending a page to be stored in page units or deleting position coordinate data in page units is performed. Further, the CPU 56 executes a data output process of converting the position coordinate data of the target page from the position data stored in the RAM 59 into an appropriate format and outputting the converted data to the PC 100 or the printer 200 (see FIG. 2) ( S50
0).

Further, the CPU 56 (see FIG. 9) operates the audio circuit 31a (see FIG. 9) based on a switching signal generated when various buttons are pressed, and the speaker (SP) 31 (see FIG. 9). Performs voice output processing for generating operation sounds such as "P" and "B" from FIG.
600). Further, the CPU 56 calculates the wiping locus of the eraser 40 based on the voltage generated in the X coil and the Y coil by the alternating magnetic field generated from the coil built in the eraser 40, and calculates the position coordinate data in the calculated wiping locus. An eraser process for erasing data from the RAM 59 (see FIG. 9) is executed (S700).
(Return) The procedure of S100 to S700 is repeated.

The electronic blackboard 1 according to the embodiment of the present invention comprises:
The following effects are obtained by providing the above configuration and operation. That is, the X, Y coil switching circuit 50 which is the loop coil selecting means shown in FIG.
3 is sequentially selected, switched and input, and the rectifier circuit 51a
A signal input by an amplitude detection circuit 51 (see 21) provided with a signal and a smoothing circuit 51b is amplitude-detected. After reading at time intervals, comparing the amplitudes, storing the voltage value SV, and performing a sampling process to detect the peak voltage SVp,
The control unit 2 serving as the discharge control means operates the switching circuit 41 provided in parallel with the smoothing circuit 51b shown in FIG. 21 and having one end grounded to bring the ground potential to the smoothing circuit 51b, thereby quickly setting the amplitude. There is an effect that the voltage SV to be sampled next can be input to the detection circuit 51. Therefore, when sequentially scanning a large number of loop coils 23, the timing of reading the amplitude information from the loop coils 23 is shortened,
This has the effect of enabling high-speed coordinate reading.

Further, in the electronic blackboard 1 of the present embodiment,
While the control unit 2 and the X and Y coil switching circuit 50 output the input start signal SS from the control unit 2 at regular intervals and switch the loop coil 23 at predetermined intervals, simple control can be performed. In the case where the loop coil 23 is sequentially scanned, the timing of reading the amplitude information from the loop coil 23 is further shortened, so that high-speed coordinate reading can be performed.

In particular, if the control method shown in the modified example,
After the switching circuit 41 is operated and the interval loop It is switched to the next loop coil 23 by the X and Y coil switching circuit 50, the loop coil 2 to be processed next after the processing of one loop coil 23 is completed.
There is an effect that the time until the start of the process 3 can be reduced. Therefore, when scanning a large number of loop coils 23 sequentially, the timing of reading the amplitude information from the loop coils is further shortened, so that high-speed coordinate reading can be performed.

According to the electronic blackboard 1 of the present embodiment, the pen 60, which is the position indicating unit, is provided with the LC oscillation circuit 69c for generating an alternating magnetic field of a predetermined frequency. A signal can be obtained, and by processing this relatively strong signal at a high speed by the writing panel 10 as a receiving unit including the switching circuit 41 and the like, it is possible to read the coordinates at a high speed against noise. There is.

When the loop coil 23 input by the X / Y coil switching circuit 50 is switched, the mute circuit 46 for attenuating the input from the loop coil 23 is activated, whereby the X / Y coil switching circuit 50 operates. There is an effect that the influence of switching noise generated when the loop coil 23 is switched can be reduced, and the coordinate reading accuracy can be improved.

Although the present invention has been described based on one embodiment, the present invention is not limited to the above-described embodiment, and various modifications and changes can be made without departing from the spirit of the present invention. Can be easily inferred.

For example, a position indicator that gives a change in a magnetic field is not limited to the one provided with the coil for generating an alternating magnetic field described in the present embodiment. The indicator may change the magnetic field generated by the receiving unit by the coil, and the receiver may read the change in the magnetic field and read the coordinates. Then, the position indicator does not need to include a complicated oscillation circuit and need not include a battery as a power supply. It is needless to say that even if the circuit does not include the mute circuit 46 as shown in FIG.

[0104]

As is apparent from the above description, according to the coordinate reading apparatus of the first aspect of the present invention, the loop coils are sequentially selected by the loop coil selecting means, switched and input, and the rectifier circuit and the smoothing circuit are connected. The amplitude of the signal input by the amplitude detection circuit provided with the circuit is amplitude-detected, the signal amplitude-detected by the sampling means is read at predetermined time intervals, the amplitude is compared, and the sampling process is performed by storing the voltage value. After detecting the peak voltage, the discharge control means activates the switching circuit provided in parallel with the smoothing circuit and having one end grounded to bring the ground potential to the smoothing circuit, so that the amplitude detection circuit can be quickly operated. There is an effect that a voltage to be sampled next can be input. Therefore, when a large number of coils are sequentially scanned, there is an effect that the timing of reading amplitude information from the loop coil is shortened to enable high-speed coordinate reading.

According to the coordinate reading apparatus of the second aspect of the present invention, in addition to the effect of the coordinate reading apparatus of the first aspect of the present invention, the loop coil selecting means allows the next time after a predetermined time has elapsed after the operation of the switching circuit. By switching to the loop coil, there is an effect that the time from the end of the processing of one loop coil to the start of the processing of the next loop coil to be processed can be shortened. Therefore, when a large number of coils are sequentially scanned, the timing for reading out the amplitude information from the loop coil can be further shortened, so that high-speed coordinate reading can be performed.

According to the coordinate reading device of the third aspect, in addition to the effects of the coordinate reading device of the first aspect,
By performing loop coil switching at predetermined intervals by the loop coil selecting means, simple control can be performed,
When a large number of coils are sequentially scanned, there is an effect that the timing for reading out the amplitude information from the loop coil is further shortened, and high-speed coordinate reading becomes possible.

According to a fourth aspect of the present invention, in addition to the effects of the first to third aspects, the position indicating section generates an alternating magnetic field of a predetermined frequency. With the provision of the oscillation circuit, a relatively strong signal can be obtained from the position indicating unit, and the relatively strong signal is processed at a high speed by the receiving unit including the switching circuit and the like, so that it is strong against noise and There is an effect that coordinates can be read at high speed.

In the coordinate reading apparatus according to the fifth aspect of the present invention,
In addition to the effects of the coordinate reading device according to any one of claims 1 to 4, a mute circuit for inhibiting or attenuating the input from the loop coil when the loop coil input by the loop coil selecting means is switched is operated. By doing so, there is an effect that the influence of switching noise generated when the loop coil is switched by the loop coil selecting means can be reduced, and the coordinate reading accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing a main configuration of an electronic blackboard.

FIG. 2 is an explanatory diagram showing a state in which a personal computer 100 and a printer 200 are connected to the electronic blackboard shown in FIG.

FIG. 3 is an explanatory diagram showing an internal structure of a pen 60.

FIG. 4 is an explanatory diagram showing each component of the writing panel 20.

FIG. 5A is an explanatory view showing a configuration of the loop coil 23 shown in FIG. 4 with a part thereof omitted; (B) It is explanatory drawing which shows the width | variety and overlap pitch of the loop coil 23 shown to FIG. (A).

FIG. 6A is a design diagram showing a part of X coils X1 to X3. FIG. 7B is a graph showing the relationship between the voltage generated in the X coils X1 to X3 shown in FIG. 6A and the distance in the width direction. 7C is a graph showing a voltage difference between mutually adjacent loop coils of the X coils X1 to X3 shown in FIG.

FIG. 7A is an explanatory diagram showing a position coordinate table as a graph. (B) It is explanatory drawing of a position coordinate table. (C) It is explanatory drawing which shows the storage state of the detection value detected from each X coil.

FIG. 8 is an explanatory diagram showing an electrical configuration of the pen 60 shown in FIG.

FIG. 9 is an explanatory diagram showing the electrical configuration of the electronic blackboard 1 by blocks.

FIG. 10 is a diagram illustrating a relationship between a pen attribute and a modulation frequency fm.

11 is a flowchart showing main control contents executed by a CPU 56 shown in FIG.

FIG. 12 is a flowchart illustrating a flow of a coordinate reading process.

13 is an explanatory diagram illustrating an electrical configuration of an FSK demodulation circuit 55. FIG.

14 is an explanatory diagram showing signal waveforms appearing at various parts of the FSK demodulation circuit 55 shown in FIG.

FIG. 15A shows an output signal of a CR oscillation circuit 69e;
FIG. 9 is an explanatory diagram showing a relationship between an output signal of an LC oscillation circuit 69c, an output signal of a limiter circuit 54, and a count value of a count circuit 55a. (B) is an explanatory view showing how the count value stored in the shift register 55b shifts.

16A is an explanatory diagram showing a relationship between a threshold determination output by an absolute value comparator 55f and a determination cycle of a CPU 56. FIG. (B) It is explanatory drawing which shows a mode that the count value by the counter 55g moves.

FIG. 17 is a flowchart showing the flow of processing (pen attribute detection processing 1) from the count circuit 55a to the absolute value comparator 55f that constitutes the FSK demodulation circuit 55.

FIG. 18 is a flowchart showing the flow of processing (pen attribute detection processing 2) of the counter 55g and the adder 55i.

FIG. 19 is a diagram showing a configuration around a conventional amplitude detection circuit.

FIG. 20 shows a switching circuit 41 and a mute circuit 46.
2 shows a configuration around the amplitude detection circuit 51 of the present embodiment provided with the above.

FIG. 21 shows a modification of the configuration around the amplitude detection circuit 51 of the present embodiment provided with only a switching circuit.

FIG. 22 is a diagram schematically showing an example of a screen on an oscilloscope of a signal output from an amplitude detection circuit 51 including a switching circuit 41.

FIG. 23 is a diagram schematically illustrating an example of a screen on an oscilloscope of a signal output from the amplitude detection circuit 51 when the switching circuit 41 is not provided.

FIG. 24 is a flowchart illustrating control of an X coil scan (S302) in the flowchart of FIG. 12;

FIG. 25 is an X coil scan (S302) in the flowchart of FIG. 12 in a modified example of the control method of the present embodiment.
5 is a flowchart for explaining the control of FIG.

FIG. 26 is a timing chart illustrating A / D conversion of this embodiment.

FIG. 27 is a timing chart illustrating a modification of the A / D conversion of the present embodiment.

FIG. 28 is a timing chart illustrating a conventional A / D conversion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electronic blackboard 2 Control part (loop coil selection means, switching means, discharge control means) 10 Writing panel (reception part) 23 Loop coil 41 Switching circuit 46 Mute circuit 50 X and Y coil switching circuit (loop coil selection means) 51 Amplitude Detection circuit 51a Rectification circuit 51b Smoothing circuit 52 A / D conversion circuit (sampling means) 56 CPU 60 Pen (position indicating unit)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C071 CA02 CA05 CD01 DA05 DB04 DC04 EB04 5B068 AA02 AA15 BB14 BC03 BD02 BD07 BE01 BE08 BE12 BE15 5B087 AA01 AE02 BC03 BC34 CC26 CC32 DG02 DJ01

Claims (5)

[Claims] 1. A position indicating section for giving a change in a magnetic field, and a receiving section having a plurality of loop coils are provided so as to be capable of being magnetically coupled to the position indicating section. In a coordinate reading device that reads a position of a position indicating unit, the receiving unit includes a loop coil selecting unit that sequentially selects and switches the loop coil and inputs the loop coil, a rectifier circuit, and a smoothing circuit. An amplitude detection circuit that performs amplitude detection; a sampling unit that performs sampling processing by reading out the amplitude-detected signal at predetermined time intervals, comparing amplitudes, and storing voltage values; and a sampling unit that is provided in parallel with the smoothing circuit. A switching circuit whose one end is grounded, and a ground potential with respect to the smoothing circuit which is operated after the end of the sampling process. And a discharge control means for operating the coordinate reading apparatus. 2. The coordinate reading means according to claim 1, wherein said loop coil selecting means switches to a next loop coil after a lapse of a predetermined time after said switching circuit operates. 3. The coordinate reading apparatus according to claim 1, wherein said loop coil selecting means switches the loop coils at predetermined intervals. 4. The coordinate reading device according to claim 1, wherein the position indicating unit includes an oscillation circuit that generates an alternating magnetic field having a predetermined frequency. 5. The apparatus according to claim 1, further comprising a mute circuit for inhibiting or attenuating an input from the loop coil which is activated when the loop coil input by the loop coil selecting means is switched. 5. The coordinate reading device according to any one of 4.