JPH0798628A - Wireless coordinate reader - Google Patents

Abstract

PURPOSE:To maintain read precision even if external noise is large by stopping the output of a sense line group when a loop-formed noise detection line arranged on a tablet detects the noise of more than a prescribed value. CONSTITUTION:The noise detection line 20 is arranged on the tablet 21 so that it surrounds an exciting line group 2 and the sense line group 3, and it is connected to a noise detection circuit 22. When an electromagnetic signal is generated by a CRT display device for horizontal scanning, an AC signal SN is generated in the noise detection line 20. The noise detection circuit 22 amplifies the inputted AC signal and selects the AC signal of 300-600kHz. When the output voltage is larger than reference voltage, a switch 26 stops the output of a detection signal IS from a sense line 3, and sets a phase detection circuit 7 and an amplification detection circuit 8 to a temporary stop state. When output voltage from the noise detection circuit 22 becomes smaller than reference voltage, the switch 26 outputs the detection signal IS so as to resume an operation.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a wireless coordinate reader.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 4-44116 discloses a technology of a wireless coordinate reading device capable of discriminating a switch operated by a coordinate indicator. Hereinafter, description will be given with reference to the drawings. ◆ Fig. 3 is a block diagram of the coordinate reading device.
FIG. 4 is a circuit configuration diagram of the coordinate indicator. In the figure, 1 is a tablet in which two excitation lines and three sense lines are laid. Reference numeral 4 denotes an excitation scanning circuit, which is composed of a plurality of electronic switch elements such as analog switches. The excitation signal is supplied with an AC signal DS supplied from the excitation circuit 5 in accordance with an excitation selection signal DA from a control circuit 9 described later. Apply to line 2. The AC signal DS is obtained by converting the digital signal DC of the reference frequency supplied from the control circuit 9 into a predetermined AC signal by the exciting circuit 5. Reference numeral 6 denotes a sense scanning circuit, which is composed of an electronic switch element, selects the sense line 3 designated by the sense selection signal SA from the control circuit 9, and is a signal induced on the sense line 3 (hereinafter, detection signal). IS) is output to the phase detection circuit 7 and the amplification detection circuit 8. The phase detection circuit 7 detects the detection signal I
The phase of S and the digital signal DC are compared and the phase difference signal PS is output to the control circuit 9. The amplification detection circuit 8 detects the detection signal IS
Is amplified and detected, and the amplitude signal AS of the detection signal is output to the control circuit 9. The control circuit 9 is composed of a microprocessor and outputs the signals such as DA, DC, and SA described above. The control circuit 9 also controls the amplitude signal AS and the phase difference signal PS.
The coordinate value is calculated from the above, and which switch of the coordinate indicator 10 has been operated is determined by the method described later. That is, the circuit of the coordinate indicator 10 is an LC resonance circuit in which a switch and a resistor (S ₁₁ , R _11, etc.) connected in series, a coil L ₁₁ and capacitors C ₁₁ , C ₁₂ are connected. Now, the resonance frequency when all the switches are off is f _A (where f _A = 1 / {2π√ (L ₁₁ ·
C ₁₁ )}), the resonance frequency becomes f _B (where f _B = 1 /) by turning on at least one switch.
[2π√ {(L ₁₁ · (C ₁₁ + C ₁₂ )}]).
Also, depending on the value of the resistor connected in series with the switch, L
The loss of the C resonance circuit (that is, the phase of the detection signal) also changes. Therefore, the change in the phase of the detection signal IS is detected to determine which switch is on. By the way, since the coordinate reading device is often used in the vicinity of a cathode ray tube display device (CRT display device) that emits large electromagnetic induction noise to the surroundings, a noise removing means such as a bandpass filter is used in the amplification detection circuit 8. Is provided to prevent the accuracy of reading the coordinates from being deteriorated by the electromagnetic induction noise.

[0003]

However, while the frequency of the AC signal DS is a sine wave of 300 to 600 kHz, the horizontal scanning frequency of the CRT display device is the AC signal D.
Since it is a signal containing a harmonic component close to the frequency of S, it was not possible to sufficiently remove noise. An object of the present invention is to solve the above-mentioned problems and to provide a wireless coordinate reading device with good reading accuracy even when external noise is large.

[0004]

Means for Solving the Problems The above-mentioned problems consist of a tablet having an exciting line group and a sense line group, and a coordinate indicator having a coil, which supplies and supplies an alternating current to the exciting line group. In a wireless coordinate reading device that generates an alternating current in a coil by a rotating magnetic field formed by an alternating current and obtains a coordinate position from an alternating current generated in a sense line group by an alternating magnetic field formed by the alternating current generated in the coil, A noise detection line, a noise detection circuit that outputs a signal when noise of a predetermined value or more is detected, and a switch are provided, and the noise detection line is looped so as to surround the excitation line group and the sense line group. Place it on the tablet, connect the noise detection line and the noise detection circuit, connect the switch and the sense line group and the noise detection circuit, and Operates the switch by the output signal from the circuit, it is solved by configuring so as to stop the output of the sense line groups.

[0005]

The data for reading the coordinates can be reduced in noise.

[0006]

1 is a block diagram of a coordinate reading device showing an embodiment of the present invention, and FIG. 2 is a block diagram of a noise detection circuit. The same parts as those in FIGS. 3 and 4 are designated by the same reference numerals. A noise detection line 20 is laid on the tablet 21 so as to surround the excitation line 2 group and the sense line 3 group,
It is connected to the noise detection circuit 22. The noise detection circuit 22 includes a differential amplifier 23, a bandpass filter 24, and a comparator 25. The reference voltage VS set in advance is connected to the-terminal of the comparator 25. A switch 26 is connected in series to the output terminal of the sense scanning circuit 6. The operation will be described below. The source of noise is assumed to be an electromagnetic signal due to horizontal scanning generated by the CRT display device. Further, the detection of the coordinates and the switch information of the coordinate indicator is the same as that of the above-mentioned conventional technique, and therefore the description thereof will be omitted. When the CRT display device generates an electromagnetic signal for horizontal scanning, an AC signal SN having the same frequency as the horizontal scanning frequency or an integral multiple of the horizontal scanning frequency is generated on the noise detection line 20. The noise detection circuit 22 receives the input AC signal SN as a differential amplifier 23.
Amplified by 300 to 600 kHz, which is close to the frequency of the signal DS
Only the AC signal of z is selected by the bandpass filter 24 and the corresponding voltage is output. The comparator 25 uses the voltage output from the bandpass filter 24 and the reference voltage VS.
When the voltage output from the bandpass filter 24 is higher than the reference voltage VS, the switch 26 is operated to stop the output of the detection signal IS. Then,
The phase detection circuit 7 and the amplification detection circuit 8 are in a suspended state because the input of the detection signal IS is stopped. And
The comparator 25 switches the switch 2 when the voltage output from the bandpass filter 24 becomes lower than the reference voltage VS.
6 is operated to output the detection signal IS again. As a result, the phase detection circuit 7 and the amplification detection circuit 8 restart the operation from the stopped state.

[0007]

As described above, according to the present invention, the data when the noise more than the predetermined value is generated outside is not used. As a result, the reading accuracy can be maintained even when the external noise is large.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a coordinate reading device according to the present invention.

FIG. 2 is a configuration diagram of a noise detection circuit.

FIG. 3 is a configuration diagram of a conventional coordinate reading device.

FIG. 4 is a circuit configuration diagram of a coordinate indicator.

[Explanation of symbols]

1, 21 tablet 2 excitation line 3 sense line 6 sense scan circuit 10 coordinate indicator 20 noise detection line 22 noise detection circuit 23 differential amplifier 24 bandpass filter 25 comparator 26 switch L ₁₁ coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Sakata 2100 Kamiimaizumi, Ebina, Kanagawa Prefecture Hitachi Seiko Co., Ltd.

Claims (1)

[Claims] 1. A rotating magnetic field comprising a tablet having an excitation line group and a sense line group, and a coordinate indicator having a coil, which supplies an alternating current to the excitation line group and is formed by the supplied alternating current. In the wireless coordinate reading device that generates an alternating current in the coil by using the alternating current magnetic field generated by the alternating current generated in the coil to determine the coordinate position from the alternating current generated in the sense line group, a noise detection line and a predetermined value A noise detection circuit that outputs a signal when the above noise is detected, and a switch are provided, and the noise detection line is arranged in a loop so as to surround the excitation line group and the sense line group on the tablet. Connect the noise detection circuit, connect the switch, the sense line group, and the noise detection circuit, and use the output signal from the noise detection circuit to switch. Operating the wireless coordinate reading apparatus characterized by being configured so as to stop the output of the sense line groups.