JPH0421143Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial field of application) The present invention describes a system for identifying the state of a position indicator, or a system for detecting the designated position of a position indicator and identifying the state of the position indicator. It concerns a tuned circuit.

(Prior art) Prior to filing this application, the applicant filed a patent application in
No. 215696 (filed on September 16, 1988) (hereinafter referred to as Prior Application 1), the state of the position indicator, such as the coordinates to be input, is determined by exchanging radio waves between the tablet and the position indicator. The state of the position indicator that specifies (hereinafter referred to as the pen down state)
We propose a method for identifying (detecting)
Patent Application No. 1983-213970 (filed on September 12, 1986)
(hereinafter referred to as Prior Application 2) proposed a coordinate input device that detects the designated position of a position indicator and identifies its state by exchanging radio waves between a tablet and a position indicator.

To briefly explain the content of Prior Application 1, a signal of a predetermined frequency is applied to an antenna coil provided around the coordinate input range of a tablet to emit radio waves, and the radio waves are received by a tuned circuit provided in a position indicator. let me,
At this time, by causing the antenna coil, which has stopped supplying the signal, to receive radio waves emitted from the coil of the tuned circuit that resonates (tuned), an induced voltage is generated in the antenna coil, and the tuned circuit generates an induced voltage in the antenna coil. The tuning frequency of the circuit is slightly changed in accordance with the change in the state of the position indicator, and the change in the tuning frequency of the tuning circuit is detected as a change in the phase of the induced voltage, whereby the position indicator It is designed to identify the state of

In addition, to briefly explain the content of Prior Application 2, a signal of a predetermined frequency is applied to one of the tablets in which a large number of loop coils are arranged in parallel in the position detection direction. A radio wave is transmitted, the radio wave is received by a tuned circuit provided in the position indicator, and at this time, the radio wave transmitted from the resonant (tuned) coil of the tuned circuit is transmitted to the first one that stopped supplying the signal. By causing the loop coil to receive the signal, an induced voltage is generated in the one loop coil, and this is repeated for all of the multiple loop coils, and the voltage value is determined from the multiple induced voltages generated in each loop coil. is detected, that is, the specified position of the position indicator, and the tuning frequency of the tuning circuit is slightly changed in accordance with the change in the state of the position indicator, so that the tuning frequency of the tuning circuit is detected. The change is detected as a change in the phase of the induced voltage, and the state of the position indicator is thereby identified.

When changing the tuning frequency of the tuning circuit,
There are cases where the frequency is raised and cases where the frequency is lowered, and in either case, the change in frequency is a change in the phase of the induced voltage, that is, an increase in frequency is considered a phase advance, and a decrease in frequency is considered a change in the phase of the induced voltage. It was possible to detect this as a phase lag and identify the state of the position indicator.

Figure 2 shows an example of a conventional tuning circuit.
At one end of the coil L, there are selector switches SW1, SW2,
Connect common contact C of SW3 and SW4, and connect capacitors C1, C2, C3 and C4 to the other end of coil L.
Connect one end of the capacitors C1, C2,
Connect the other ends of C3 and C4 to the normally closed contact NC of changeover switch SW1, the normally open contact NO of changeover switch SW2, the normally open contact NO of changeover switch SW3, and the changeover switch SW.
These are connected to the four normally closed contacts NC.

Assuming that the inductance of the coil L is L, and the capacitance values of the capacitors C1, C2, C3, and C4 are C1, C2, C3, and C4, respectively, the resonance (tuning) frequency is 0 when none of the switches SW1 to SW4 are operated. 0=1/2π{L・(C1+C4)} ^1/2 .

Further, the tuning frequency 1 when the changeover switch SW1 is operated is as follows: 1=1/2π(L·C4)1/2. Further, the tuning frequency 2 when the changeover switch SW2 is operated is 2=1/2π{L・(C1+C2+C4)} ^1/2 . Further, the tuning frequency 3 when the changeover switch SW3 is operated is as follows: 3=1/2π{L・(C1+C3+C4)} ^1/2 . Further, the tuning frequency 4 when the changeover switch SW4 is operated is 4=1/2π(L・C1) ^1/2 .

Here, if C1<C2<C3<C4, then 3<2<
If 0<1<4 and frequency 0 is the same as the frequency of the radio waves emitted from the antenna coil or loop coil, then when switch SW1 is operated, the first phase advance, for example 30°, will be detected. ,
Furthermore, when the changeover switch SW2 is operated, a first phase delay, for example, -30° is detected, and when the changeover switch SW3 is operated, a second phase delay, for example, -60°, is detected, and furthermore, When the changeover switch SW4 is operated, a second phase advance, for example 60°, is detected, and from this, the pen-down state and other states of the position indicator are detected.

Note that the variable capacitor VC connected in parallel to both ends of the coil L is used to match the frequency 0 with the frequency of the radio waves transmitted from the antenna coil or loop coil, but for the sake of simplicity, it will not be described here. In this case, we decided to ignore the capacitance value.

(Problem to be solved by the invention) However, in the above-mentioned tuned circuit, when two switches, for example SW1 and SW2, are operated simultaneously, the frequency x at that time becomes x=1/2π{L・(C2+C4)} ^{1/ 2} , and none of the frequencies 0 to 4 are selected. Also, if switch SW1 and SW4 are operated at the same time, only the coil will be used and no tuning circuit will be configured. Therefore, if two or more switch switches are operated at the same time There was a problem that when the device was operated, the state could no longer be detected.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems and to provide a tuning circuit for a position pointer that does not produce a frequency other than a preset frequency even when two or more switches are operated simultaneously.

(Means for Solving the Problems) In order to solve the above problems, the present invention receives radio waves transmitted from the tablet side, and at this time generates radio waves based on signals generated within the circuit.
In the tuning circuit of the position indicator that is sent back to the tablet side, there are a coil, n (n is an integer of 2 or more) changeover switches each having a normally closed contact, a normally open contact, and a common contact, each having a different capacitance (n+1). ) capacitors, each selector switch is connected in series through a normally closed contact and a common contact, the unconnected common contact is connected to one end of the coil, and the other end of the coil is connected to one end of each capacitor. Then, the other end of each capacitor was connected to a normally open contact and an unconnected normally closed contact of each changeover switch.

(Function) According to the present invention, when none of the plurality of changeover switches is operated, the capacitor whose other end is connected to the normally closed contact of the changeover switch is connected to the coil, and when any of the changeover switches is operated, the capacitor is connected to the coil. , the capacitor connected to the normally open contact of the changeover switch is connected to the coil, and when two or more changeover switches are operated simultaneously, the capacitor connected to the normally open contact of the changeover switch closest to the coil is connected to the coil. Only the capacitors connected to the coil are connected to the coil.

(Embodiment) FIG. 1 shows an embodiment of a tuning circuit for a position pointing device according to the present invention. In the figure, the same components as those of the conventional example shown in FIG. 2 are denoted by the same reference numerals. That is,
L is a coil, SW1 to SW4 are selector switches, C
01, C02, C03, C04 and C05 are capacitors, and VC is a variable capacitor.

Each of the changeover switches SW1 to SW4 is connected in series through its normally closed contact NC and common contact C, that is, the normally closed contact NC of changeover switch SW1 is connected to the common contact C of changeover switch SW2, and the changeover switch SW2 The normally closed contact NC of is connected to the common contact C of the changeover switch SW3, and also the changeover switch
The normally closed contact NC of SW3 is connected to the common contact C of the changeover switch SW4. Further, the unconnected common contact, that is, the common contact C of the changeover switch SW1, is connected to one end of the coil L, and the other end of the coil L is connected to one end of the capacitors C01 to C05. In addition, capacitor C01,
The other ends of C02, C03, C04 and C05 are respectively connected to the normally open contacts NO of the changeover switches SW1, SW2, SW3 and SW4 and the normally closed contacts which are not connected, ie the normally closed contact NC of the changeover switch SW4. Note that although the variable capacitor VC is connected in parallel to both ends of the coil L, its capacitance value is not considered as in the conventional example.

Let the inductor tank of coil L be L, and the capacitance values of capacitors C01, C02, C03, C04, and C05 are C01, C02, C03, C0, respectively.
4 and C05, selector switch SW1-4
When neither is operated, its resonance (synchronization)
The frequency 00 is 00=1/2π(L・C05) ^1/2 .

Further, the tuning frequency 01 when the changeover switch SW1 is operated is 01=1/2π(L・C01) ^1/2 . Further, the tuning frequency 02 when the changeover switch SW2 is operated is 02=1/2π(L・C02) ^1/2 . Further, the tuning frequency 03 when the changeover switch SW3 is operated is 03=1/2π(L・C03) ^1/2 . Further, the tuning frequency 04 when the changeover switch SW4 is operated is 04=1/2π(L・C04) ^1/2 .

Here, C01=C4, C02=C1+C2+C4, C03=
If C1+C3+C4, C04=C1 and C05=C1+C4, 00=0, 01=1, 02=2, 03=3 and
04=4, and according to the operation of the changeover switches SW1 to SW4, a change in the tuning frequency similar to that of the conventional tuning circuit shown in FIG. 2 can be obtained.

On the other hand, in the tuning circuit, there are two changeover switches,
For example, if SW1 and SW2 are operated at the same time,
Changeover switch SW2 by changeover switch SW1
Since the subsequent circuits are disconnected, the only capacitor connected to the coil L is C01. Similarly, when the changeover switches SW2 and SW3 are operated simultaneously, only the capacitor C02 is connected to the coil. In this way, even if two or more switches are operated at the same time, only the capacitor connected to the switch closest to coil L is always connected to coil L, and the tuning frequency is determined based on this. , there is no possibility that the frequency will be other than the preset frequency.

Therefore, according to the embodiment, it is possible to provide the same function as the conventional tuning circuit by simply using the changeover switch in the conventional tuning circuit and changing the wiring and the capacitance value of the capacitor.

As the changeover switches SW1 to SW4, for example, FJ switches (light-load self-supporting P/C plate terminal type, AH148061) manufactured by Matsushita Electric Works, Ltd. can be used.

FIG. 3 shows an example of a position pointing device provided with the above-mentioned tuning circuit, and here a case where the position pointing device is applied to the cursor 10 is shown. The cursor 10 has a transparent indicator 12 made of plastic or the like with a "+" indicator provided on the bottom surface attached to one end of a casing 11 made of a non-metallic material such as synthetic resin, and the switch SW1 on the top surface. ~ SW4 is provided, and the coil L is provided around the indicator 12 so as to surround it, and furthermore, the capacitors C01 to C05 and the variable capacitor VC (Fig. (not shown) is built-in. Although the coil L is shown as a two-turn coil in the drawing, it actually consists of several ten turns.

FIG. 4 shows an embodiment of a coordinate input device using the cursor 10, in which 20 is a tablet, 30 is a control circuit, 31 is a signal generation circuit, and 3
2 and 33 are X-direction and Y-direction selection circuits, 3
4 and 35 are transmission/reception switching circuits, 36 is an XY switching circuit,
37 is a reception timing switching circuit, 38 is a bandpass filter (BPF), 39 is a detector, 40 is a low pass filter (LPF), 41 and 42 are phase detectors (PSD),
43, 44 are low pass filters (LPF), 45, 46
1 is a drive circuit, 47 and 48 are amplifiers, 49 is a host computer, 50 is a display device, and 51 is an output device.

Note that the reference numeral 13 in the cursor 10 represents the entire tuning circuit shown in FIG.

FIG. 5 shows a loop coil group 21 in the X direction and a loop coil group 2 in the Y direction, which constitute the tablet 20.
This figure shows the details of 2. The loop coil group 21 in the X direction consists of a large number, for example, 48 loop coils 21-1, 21-2, . The loop coil group 22 includes a large number of loop coils 22-, which are arranged parallel to each other and overlapping each other along the Y direction, ie, 48 loop coils 22-.
1, 22-2, ...22-48, and the loop coil group 21 in the X direction and the loop coil group 22 in the Y direction are closely overlapped with each other (however,
In the drawing, the two are drawn apart for ease of understanding. ), and is further housed in a case (not shown) made of a non-metallic material. Although each loop coil is configured with one turn here, it may be configured with multiple turns as necessary.

Next, the operation of the device will be explained along with its configuration. First, the manner in which radio waves are transmitted and received between the tablet 20 and the cursor 10, and the signals obtained at this time will be explained with reference to FIG.

The control circuit 30 is composed of a well-known microprocessor, etc., and controls the signal generation circuit 31, and also switches each loop coil of the tablet 20 via the selection circuits 32 and 33 according to the flowchart shown in FIG. It also controls the switching of the coordinate detection direction for the XY switching circuit 36 and the reception timing switching circuit 37, and further converts the output values from the low-pass filters 40, 43, and 44 into analog/digital (A/ D) Convert and execute arithmetic processing to be described later to obtain the input coordinates of the cursor 10, further detect the phase of the received signal, and determine the operating state of the changeover switches SW1 to SW4, that is, the cursor 10.
and send these to the host computer 4.
Send on 9th.

The selection circuit 32 selects the loop coil group 2 in the X direction.
The selection circuit 33 sequentially selects one loop coil from the loop coil group 22 in the Y direction, and each selects one loop coil from the Y-direction loop coil group 22 according to information from the control circuit 30. It works.

The transmission/reception switching circuit 34 connects the selected loop coil in the X direction to a drive circuit 45 and an amplifier 47.
The transmitting/receiving switching circuit 35 alternately connects the selected loop coil in the Y direction to a driving circuit 46 and an amplifier 48, which are connected to a transmitting/receiving switching signal to be described later. operate according to

The signal generating circuit 31 generates the frequency 0, for example
A 500kHz rectangular wave signal A, a signal B whose phase is delayed by 90 degrees of the rectangular wave signal A, a predetermined frequency k, e.g.
Generates a 15.625kHz transmission/reception switching signal C and reception timing signal D. The rectangular wave signal A is sent as is to the phase detector 41, and is converted into a sine wave signal E by a low-pass filter (not shown).
Furthermore, the rectangular wave signal B is sent to either the drive circuit 45 or 46 via the XY switching circuit 36, the rectangular wave signal B is sent to the phase detector 42, and the transmission/reception switching signal C is sent to the transmission/reception switching circuits 34 and 35. Furthermore, the reception timing signal D is sent to the reception timing switching circuit 37.

Now, information for selecting the X direction is received from the control circuit 30.
XY switching circuit 36 and reception timing switching circuit 3
7, the sine wave signal E
is sent to the drive circuit 45 and converted into a balanced signal,
Furthermore, the signal is sent to the transmission/reception switching circuit 34, but since the transmission/reception switching circuit 34 switches and connects either the drive circuit 45 or the amplifier 47 based on the transmission/reception switching signal C, the transmission/reception switching circuit 34 outputs the signal to the selection circuit 32. The signal to be generated is time T (=1/2k), here
The signal F is a 500kHz signal that is output and not output every 32μsec.

The signal F is passed through the selection circuit 32 to one loop coil 21-i (i=
1, 2, . . . 48), and the loop coil 21-i generates radio waves based on the signal F.

At this time, when the cursor 10 is placed on the tablet 20, the radio wave excites the coil L of the cursor 10, causing the tuned circuit 13 to generate an induced voltage G synchronized with the signal F.

Thereafter, when the loop coil 21-i is switched to the amplifier 47 side as the signal F enters a no-signal period, that is, the reception period, the radio wave from the loop coil 21-i immediately disappears, but the induced voltage G It gradually attenuates depending on the loss within the tuning circuit 13.

On the other hand, based on the induced voltage G, the tuning circuit 13
The current flowing through causes the coil L to emit radio waves.
The radio waves are transmitted to the loop coil 2 connected to the amplifier 47.
1-i, the loop coil 21
-i generates an induced voltage due to radio waves from the coil L. The induced voltage is sent from the transmission/reception switching circuit 34 to the amplifier 47 only during the reception period, is amplified, becomes a reception signal H, and is further sent to the reception timing switching circuit 37.

The reception timing switching circuit 37 has an X direction or a Y direction.
One of the direction selection information, here the X direction selection information, and the reception timing signal D, which is essentially an inverted signal of the transmission/reception switching signal C, are input, and the period when the signal D is at a high H level is input. is the received signal H
Since nothing is output during the low L level period, the output is signal I (substantially the received signal H).
) is obtained.

The signal I is sent to a band filter 38, which is a ceramic filter whose natural frequency is f0, and a signal J having an amplitude corresponding to the energy of the frequency f0 component in the signal I. (Strictly speaking, in a state where several signals I are input to the band filter 38 and converged)
is sent to the wave detector 39 and phase detectors 41 and 42.

The signal J input to the detector 39 is detected and rectified to become a signal K, and then passed through a low-pass filter 40 with a sufficiently low cutoff frequency to a voltage value corresponding to approximately 1/2 of the amplitude, for example, Vx. The DC signal M is converted into a DC signal M and sent to the control circuit 30.

The voltage value Vx of the signal M is a value that depends on the distance between the cursor 10 and the loop coil 21-i, here a value that is approximately inversely proportional to the fourth power of the distance, and changes when the loop coil 21-i is switched. In order to do this, the control circuit 30 converts the voltage value Vx obtained for each loop coil into digital values, and performs the arithmetic processing described below on these values.
The input coordinates in the X direction by the cursor 10 are determined. Note that the input coordinates in the Y direction by the cursor 10 are also obtained in the same manner.

On the other hand, the rectangular wave signals A and B are input to the phase detectors 41 and 42 as detection signals,
At this time, assuming that the phase of the signal J almost matches the phase of the rectangular wave signal A, the phase detector 41 outputs a signal N1 (substantially the same as the signal K) which is the positive inversion of the signal J. output, and also phase detector 42
outputs a signal N2 having a waveform that is symmetrical on the positive and negative sides.

The signal N1 is converted by the same low-pass filter 43 to a DC signal O1 (substantially the same as the signal M) having a voltage value corresponding to approximately 1/2 of the amplitude of the signal J, that is, Vx, and then sent to the control circuit 30. Furthermore, the signal N2 is converted into a DC signal O2 by a similar low-pass filter 44 and sent to the control circuit 30, but here, the positive and negative components of the signal N2 from the phase detector 42 are Since they are the same, the voltage value of the output of the low-pass filter 44 is 0 [V].

The control circuit 30 converts the output values of the low-pass filters 43 and 44, here the signals O1 and O2, into digital values, and further uses these digital values to perform the arithmetic processing of the following equation (1). 42, here J and square wave signal A
Find the phase difference θ with

θ=-tan ^-1 (VQ/VP) ...(1) However, VP is the digital value corresponding to the output of the low-pass filter 43, and VQ is the digital value corresponding to the output of the low-pass filter 44.
shows the digital value corresponding to the output of for example,
In the case of the signal J mentioned above, the voltage value of the signal O1 is Vx
However, the voltage value of the signal O2 is 0 [V], that is,
Since VQ=0, the phase difference θ=0°.

Incidentally, the phase of the signal J changes in accordance with the tuning frequency in the tuning circuit 13 of the cursor 10. That is, when the tuning frequency in the tuning circuit 13 is frequency f0, an induced voltage with a frequency of 0 is generated in the tuning circuit 13 during both the signal transmission period and the reception period, and an induced current synchronized with this flows, so that the above-mentioned The frequency and phase of the received signal H (or I) match those of the rectangular wave signal A, and the phase of the signal J also matches those of the rectangular wave signal A.

On the other hand, the tuning frequency in the tuning circuit 28 is a frequency slightly higher than frequency 0, for example, the frequency
1, during the signal transmission period, the tuned circuit 1
3, an induced voltage with a frequency of 0 is generated, but at that time, an induced current with a phase lead flows through the tuned circuit 13, and during the signal reception period, an induced voltage with a frequency of approximately 1 and an induced voltage synchronized with this occur. Since a current flows, the frequency of the received signal H (or I) is slightly higher than the frequency of the rectangular wave signal A, and its phase is also slightly advanced. As mentioned above, since the band filter 38 has only frequency 0 as its frequency, a shift in the frequency of the input signal toward the higher side is outputted as a phase advance, and therefore, the frequency of the signal J is output as a phase advance. The phase is the received signal H
(or I).

Conversely, if the tuning frequency of the tuning circuit 13 is slightly lower than frequency 0, for example the frequency 2, an induced voltage of frequency 0 is generated in the tuning circuit 13 during the signal transmission period; An induced current with a phase lag flows through the tuning circuit 13, and an induced voltage of approximately frequency 2 and an induced current synchronized with this flow during the signal reception period, so the frequency of the received signal H (or I) is The frequency is slightly lower than that of the rectangular wave signal A, and its phase is also slightly delayed. In the bandpass filter 38, the frequency shift toward the lower side of the input signal is outputted as a phase lag, contrary to the case described above, and therefore, the signal J
The phase of the received signal H (or I) is further delayed.

As mentioned above, since the tuning frequency of the tuning circuit 13 changes according to the operation of the changeover switches SW1 to SW4 of the cursor 10, the phase difference θ obtained by the above equation (1) also changes corresponding to the operation.
The phase difference θ is converted into information (hereinafter referred to as state identification information) representing the operating state of the changeover switches SW1 to SW4, that is, the state of the cursor 10, and then sent to the host along with coordinate values in the X and Y directions. The data is sent to the computer 49.

Next, the coordinate detection operation and state identification operation will be explained in detail with reference to FIGS. 7 to 10.

First, when the entire device is powered on and enters the measurement start state, the control circuit 30 sends information for selecting the X direction to the XY switching circuit 36 and the reception timing switching circuit 37, and also
Information for selecting the first loop coil 21-1 among the loop coils 21-1 to 21-48 in the direction is sent to the selection circuit 32, and the selection circuit 32 selects the first loop coil 21-1.
is connected to the transmission/reception switching circuit 34.

The transmission/reception switching circuit 34 switches the loop coil 21-1 to the driving circuit 45 based on the transmission/reception switching signal C described above.
and the amplifier 47, but in this case,
During the 32 μsec transmission period, the drive circuit 45
16 sine wave signals of 500 kHz as shown in Figure a are sent to the loop coil 21-1 (only 5 of them are shown in Figure 6 for convenience of drawing).

The switching between transmission and reception is repeated seven times for one loop coil, here 21-1, as shown in FIG. 8b. The period of repeating these seven transmissions and receptions corresponds to the selection period (448 μsec) of one loop coil.

At this time, an induced voltage is obtained at the output of the amplifier 47 for one loop coil every seven reception periods, but this induced voltage is passed through the reception timing switching circuit 37 to the band filter 38 as described above. It is sent out, averaged, and passed through a detector 39 and a phase detector 4.
1 and 42 and low-pass filters 40, 43, and 44, and then sent to the control circuit 30.

The control circuit 30 inputs the output value of the low-pass filter 40 after A/D conversion, and temporarily stores it as a detected voltage depending on the distance between the cursor 10 and the loop coil 21-1, for example, Vx1.

Next, the control circuit 30 sends information for selecting the loop coil 21-2 to the selection circuit 32, connects the loop coil 21-2 to the transmission/reception switching circuit 34, and adjusts the distance between the cursor 10 and the loop coil 21-2. Obtain the proportional detection voltage Vx2 and memorize it, and from now on,
Similarly, the loop coils 21-3 to 21-48 are sequentially connected to the transmission/reception switching circuit 34, and the detected voltages Vx1 to 21-48 are proportional to the distance in the X direction from the cursor 10 for each loop coil as shown in FIG. 8c. Vx48 (however, only a part of it is shown in an analog representation in FIG. 8c) is stored.

The actual detected voltage is obtained only from several loop coils before and after the position xp where the cursor 10 is placed as the center, as shown in FIG.

The control circuit 30 checks whether the voltage value of the stored detection voltage is above a certain detection level, and if it is below the certain detection level, selects each loop coil in the X direction and performs voltage detection again. Repeatedly, if the detection level is above a certain level, proceed to the next process.

Next, the control circuit 30 sends selection information in the Y direction to the XY switching circuit 36 and the reception timing switching circuit 37, and switches the selection circuit 33 and the transmission/reception switching circuit 35 in the same manner as described above, thereby controlling the low frequency range when transmitting and receiving radio waves. A cursor 10 obtained by A/D converting the output value of the filter 40 and each loop coil 22-1 in the Y direction
The detected voltage depending on the distance to 22-48 is temporarily stored. After this, perform a level check in the same way as above, and if it is below a certain detection level, check again.
Return to the selection of each loop coil in the X direction and voltage detection, and if it is above a certain detection level, calculate the coordinate values of the cursor 10 in the X and Y directions from the stored voltage value as described later. do.

Next, the control circuit 30 selects a loop coil (peak sending information for selecting the coil) to the selection circuit 32 or 33;
The transmission and reception of the radio waves is repeated a plurality of times, for example seven times, and the output values obtained from the low-pass filters 43 and 44 are A/D converted, and the phase difference θ is calculated as described above.

The phase difference θ is converted into state identification information according to the angle, and is sent to the host computer 49 along with the X-direction and Y-direction coordinate values of the cursor 10.
will be forwarded to.

When the first coordinate detection operation and state identification operation are completed in this way, the control circuit 30
As shown in the figure, as the second and subsequent coordinate detection operations, the loop coils 21-1 to 21- in the X direction are
Among the 48 loop coils, a certain number of loop coils, for example 10, are placed around the loop coil where the maximum detected voltage was obtained.
Information for selecting only the main loop coil is sent to the selection circuit 32, and the loop coil 22 in the Y direction is also sent to the selection circuit 32.
Among -1 to 22-48, information for selecting only 10 loop coils, which are a certain number before and after the loop coil for which the maximum detected voltage was obtained, is sent to the selection circuit 33, and the same as above. The output value is obtained, coordinate detection operations in the X direction and Y direction, and state identification operation are performed for the cursor 10, and the obtained coordinate values and state identification information are transferred to the host computer 49, and these steps are repeated thereafter.

In addition, to explain the level check mentioned above in detail, it is checked whether the maximum value of the detected voltage has reached the detection level and which loop coil has the maximum detected voltage,
If the detection level has not been reached, subsequent coordinate calculations, etc. are stopped, and the center of the loop coil to be selected in the next coordinate detection operation and state identification operation is set.

Coordinate values in the X direction or Y direction, for example, the above coordinate values
One method of calculating xp is to approximate the waveform near the maximum value of the detected voltages Vx1 to Vx48 by an appropriate function, and find the coordinates of the maximum value of the function.

For example, in Figure 8c, the maximum detected voltage
By approximating Vx3 and the detection voltages Vx2 and Vx4 on both sides thereof by a quadratic function, it can be calculated as follows (however, each loop coil 21-1 to
Let the coordinate values of the center position of 21-48 be x1 to x48, and the interval therebetween be Δx. ). First, from each voltage and coordinate value, Vx2 = a (x2 - xp) ² + b ... (2) Vx3 = a (x3 - xp) ² + b ... (3) Vx4 = a (x4 - xp) ² + b ... …(4) becomes. Here, a and b are constants (a<0).

Also, x3−x2=Δx ……(5) x4−x2=2Δx ……(6). Substituting equations (5) and (6) into equations (3) and (4) and rearranging, xp=x2+Δx/2{(3Vx2−4Vx3+Vx4)/
(Vx2−2Vx3+Vx4)} ...(7).

Therefore, from each of the detection voltages Vx1 to Vx48, the maximum detection voltage obtained during the level check and the detection voltages before and after it are extracted, and these and the detection voltages of the loop coil from which the maximum detection voltage was obtained are extracted. The coordinate value xp of the cursor 10 can be calculated by performing an operation corresponding to the above-mentioned equation (7) from the coordinate value (known) of the previous loop coil.

On the other hand, the host computer 49
The data sent from the controller is temporarily stored in a buffer memory or the like, and predetermined data processing is executed according to the contents of the status identification information, and the results are displayed on the display device 50 and output as necessary. A hard copy is output from the device 51.

(Effect of the invention) As explained above, according to the invention, since the common contact of the changeover switches is connected to the normally closed contact of the first changeover switch, priority is given to each changeover switch, and two Or, even if more switches are operated at the same time, only the switch closest to the coil will be effective, and the frequency determined by the capacitor and coil, that is, the preset tuning frequency, will be obtained. It has the advantage that it can be realized simply by changing the wiring and capacitance values of capacitors in conventional tuning circuits.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a tuning circuit for a position pointing device according to the present invention, FIG. 2 is a diagram showing an example of a tuning circuit for a conventional position pointing device, and FIG. 3 is a diagram showing an example of a tuning circuit for a conventional position pointing device. 4 is a configuration diagram showing an embodiment of the coordinate input device using the cursor shown in FIG. 3; FIG. 5 is a detailed configuration diagram of the loop coil groups in the X and Y directions of the tablet. , FIG. 6 is a signal waveform diagram of each part in FIG. 4, FIG. 7 is a flowchart of processing in the control circuit, and FIG. 8 a, b, and c are timing diagrams showing basic coordinate detection operations in the control circuit.
FIG. 9 is a diagram showing detection voltages obtained from each loop coil during the first coordinate detection operation, and FIG. 10 is a timing diagram showing the coordinate detection operation and state identification operation from the second time onwards. L...Coil, SW1-SW4...Selector switch, C01, C02, C03, C04, C05...
...Capacitor, NC...Normally closed contact,
NO...Normally open contact, C...Common contact.

Claims (1)

[Scope of claim for utility model registration] A coil in a tuned circuit of a position indicator that receives radio waves transmitted from the tablet side, generates radio waves based on signals generated in the circuit, and sends them back to the tablet side. , n (n is an integer of 2 or more) changeover switches each having a normally closed contact, a normally open contact, and a common contact, and (n+1) capacitors each having a different capacitance value, and each changeover switch is normally closed. Connect in series through contacts and common contacts, connect the unconnected common contact to one end of the coil, connect the other end of the coil to one end of each capacitor, and connect the other end of each capacitor to the normal Connected to open contacts and normally closed contacts that are not connected. A tuning circuit for a position indicator, characterized in that: