Abstract:
A position detecting device includes: a position indicator including a signal generator configured to generate an alternating-current signal, a plurality of electrodes, a switch circuit configured to supply the alternating-current signal to selected one(s) of the electrodes based on a predetermined electrode-selection pattern, and a pattern information transmitter configured to transmit pattern information indicating a set predetermined pattern. A tablet includes electrodes disposed in a flat surface manner, a signal position detector configured to obtain a coordinate position of the alternating-current signal transmitted from said selected one(s) of the electrodes on a tablet surface based on distribution of a signal level induced in each of the tablet electrodes by the alternating-current signal, a pattern information receiver, and a rotation angle calculator configured to calculate a rotation angle of the position indicator about a perpendicular direction to the tablet surface based on a plurality of coordinate positions obtained according to the received pattern information.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority under 35 U.S.C. 119(a) to Japanese Patent Application No. 2012-176102, filed Aug. 8, 2012, which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to position detecting devices and position indicators thereof, and particularly to a position detecting device capable of detecting a tilt of a position indicator having a pen shape, and/or a rotation angle of the position indicator about an axis defined by the perpendicular direction to a tablet surface, and a position indicator thereof. 
         [0004]    2. Description of the Related Art 
         [0005]    As this type of device, a position detecting device of the electromagnetic induction system is disclosed in Patent Document 1 (Japanese Patent Laid-open No. Hei 8-30374). According to an embodiment example of Patent Document 1, two magnetic cores are juxtaposed at the tip portion of a position indicator having a pen shape, and a control coil wound around only one magnetic core and a transmission coil that is so wound as to bundle two magnetic cores are provided. Both ends of the control coil are controlled to the on- or off-state by an electronic switch. Based on this, the distribution of magnetic flux made by a current flowing in the transmission coil is controlled to calculate a rotation angle of the position indicator about the pen axis (aligned with the perpendicular direction to the tablet surface), which is obtained as two coordinate positions in the position detecting device (hereinafter referred to as a “tablet” in this specification). 
         [0006]    In another embodiment example of Patent Document 1, three magnetic cores are juxtaposed at the tip portion of a position indicator having a pen shape, and three control coils wound around the respective magnetic cores and a transmission coil that is so wound as to bundle three magnetic cores are provided. By controlling the respective control coils similarly, a tilt of the position indicator relative to the tablet is calculated. 
       SUMMARY OF THE INVENTION 
       [0007]    The pen-shaped position indicator of the above-described Patent Document 1 has a problem that the pen is thick because two magnetic cores are juxtaposed at the tip part. Attempting to thin the magnetic cores to solve this problem causes the following problems. 
         [0008]    As a first problem, the distance between the centers of two magnetic cores is shortened and thus the distance between two coordinates detected by the tablet is also shortened. This lowers the resolution and accuracy in calculation of a rotation angle. This is attributed also to the switch to control the control coil. This analog switch is configured by a semiconductor circuit and therefore it is difficult to sufficiently lower the resistance value when it is turned on. Accordingly, it is difficult to sufficiently suppress magnetic flux passing through the magnetic core surrounded by the control coil. Therefore, two coordinates detected by the tablet are obtained as values closer to each other than the actual core positions. 
         [0009]    A second problem in thinning the magnetic cores is that shock due to, e.g., dropping of the pen breaks the core more easily. That the use purpose of this kind of device is shifting to portable tablets in recent years is also one of the reasons why demands for slimmer pens are increasing. 
         [0010]    Another problem (third problem) of the position detecting device described in Patent Document 1 is that integration with (finger) touch detection is difficult. In recent years, multi-touch input of the electrostatic induction system has come to be widely used and demands for a tablet device allowing both multi-touch input (by a finger) and pen input are increasing. However, in contrast to a tablet of the electrostatic induction system, which uses a sensor obtained by arranging electrodes along the X direction and the Y direction, the tablet of the electromagnetic induction system of Patent Document 1 needs to have a sensor obtained by arranging loop coils and therefore it is difficult to provide the tablet sensor as a sensor compatible with both multi-touch input and pen input. 
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       [0011]    According to aspects of the invention, all of the above-described first, second, and third problems are solved. Specifically, according to a first aspect, a thin position indicator is provided whose rotation angle and tilt relative to the tablet surface can be accurately obtained. 
         [0012]    According to a second aspect, a tough (durable) position indicator is provided that is not easily broken due to shock of, e.g., being dropped even when it is made to have a thin profile. 
         [0013]    According to a third aspect, a position detecting device is provided, in which a sensor part of a touch panel based on the electrostatic coupling system can be used also as a tablet part. 
         [0014]    According to an exemplary embodiment, a position detecting device is provided that uses electrostatic coupling between a tablet and a position indicator. In the case of using electromagnetic induction as in the invention described in Patent Document 1 described above, if the coil of the position indicator is thinned, not only the accuracy of detection of coordinates and rotation angle is significantly lowered but also a core material as the core of the coil is easily broken. The present invention makes improvements for the position detecting device of the electrostatic coupling system, in which a coil does not need to be used in the position indicator, and has the following configuration. 
         [0015]    The position indicator includes a signal generator that generates an alternating-current signal, a plurality of electrodes disposed at a position indicating part (e.g., a pen tip part), a switch circuit that supplies the alternating-current signal to selected one(s) of the electrodes based on a predetermined electrode-selection pattern, and a pattern information transmitter that transmits, to the tablet, pattern information indicating a set predetermined pattern when the pattern is switched by the switch circuit. 
         [0016]    The tablet includes a plurality of electrodes disposed in a flat surface manner and a signal position detector that obtains the coordinate position of the alternating-current signal transmitted from said selected one(s) of the electrodes on the tablet surface based on distribution of the level of a signal induced in each of the tablet electrodes disposed in the flat surface manner. The tablet further includes a pattern information receiver that receives the pattern information transmitted from the position indicator, and a rotation angle calculator that calculates a rotation angle of the position indicator about the perpendicular direction to the tablet surface based on a plurality of coordinate positions obtained according to the received pattern information. 
         [0017]    Furthermore, as another mode of the present invention, the present invention has the following configuration in conjunction with the above-described configuration. 
         [0018]    In the position indicator, at least three electrodes are provided at the position indicating part (e.g., the pen tip part) and at least three kinds of predetermined patterns are provided as electrode-selection patterns selectable by the switch circuit. 
         [0019]    The tablet includes the plurality of electrodes disposed in a flat surface manner and the signal position detector that obtains the coordinate position of the alternating-current signal transmitted from said selected one(s) of the electrodes on the tablet surface based on distribution of the level of a signal induced in each of the plurality of electrodes disposed in the flat surface manner by the alternating-current signal transmitted from the position indicator. The tablet further includes the pattern information receiver that receives the pattern information transmitted from the position indicator, and a tilt angle calculator that calculates a tilt angle of the position indicator relative to the tablet surface based on at least three coordinate positions and at least three signal intensities obtained according to the at least three kinds of predetermined patterns indicated by the pattern information received by the pattern information receiver. 
         [0020]    According to embodiments of the present invention, the plural electrodes are provided at the position indicating part (e.g., pen tip part) of the position indicator and the driven electrode(s) is switched time-wise serially. This allows for determining a rotation angle of the position indicator about the perpendicular direction to the tablet surface as well as a tilt of the position indicator relative to the tablet surface. 
         [0021]    According to embodiments of the present invention, electrostatic coupling with the tablet is used. Thus, the position indicator, whose rotation angle and tilt can be obtained, can be realized in a thin profile. 
         [0022]    According to embodiments of the present invention, a magnetic material such as a ferrite core does not need to be used for the position indicator. Therefore, even when the position indicator, whose rotation angle and tilt can be obtained, is formed into a thin shape, the position indicator is not easily broken due to shock from, e.g., being dropped. 
         [0023]    According to embodiments of the present invention, a coordinate position is obtained by electrostatic coupling with the tablet. Therefore, the tablet sensor can be used commonly as the sensor for a touch panel of the electrostatic system, while at the same time achieving a position indicator whose rotation angle and tilt can be obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0024]      FIG. 1  is a structural diagram of a position indicating part in a position indicator of a first embodiment example of the present invention; 
           [0025]      FIG. 2  is a sectional view of a core in the position indicator of the first embodiment example of the present invention; 
           [0026]      FIG. 3  is a circuit configuration diagram of the position indicator of the first embodiment example of the present invention; 
           [0027]      FIG. 4  is a diagram for explaining the operation of the position indicator of the first embodiment example of the present invention; 
           [0028]      FIG. 5  is a configuration diagram of a tablet; 
           [0029]      FIG. 6  is a diagram for explaining X-axis whole surface scan operation in the tablet; 
           [0030]      FIG. 7  is a diagram for explaining transition operation to partial scan in the tablet; 
           [0031]      FIGS. 8A-8B  are diagrams that together constitute a single diagram of  FIG. 8  for explaining partial scan operation in the tablet of the first embodiment example of the present invention; 
           [0032]      FIG. 9  is a diagram for explaining the principle of rotation angle measurement; 
           [0033]      FIG. 10  is a structural diagram of a position indicating part in a position indicator of a second embodiment example of the present invention; 
           [0034]      FIG. 11  is a diagram showing the arrangement of electrodes in the position indicator of the second embodiment example of the present invention; 
           [0035]      FIG. 12  is a circuit configuration diagram of the position indicator of the second embodiment example of the present invention; 
           [0036]      FIG. 13  is a diagram for explaining the operation of the position indicator of the second embodiment example of the present invention; 
           [0037]      FIGS. 14A-14B  are diagrams that together constitute a single diagram of  FIG. 14  for explaining partial scan operation in a tablet of the second embodiment example of the present invention; 
           [0038]      FIG. 15  is a structural diagram of a position indicating part in a position indicator of a third embodiment example of the present invention; 
           [0039]      FIG. 16  is a diagram showing the arrangement of electrodes in the position indicator of the third embodiment example of the present invention; 
           [0040]      FIG. 17  is a circuit configuration diagram of the position indicator of the third embodiment example of the present invention; 
           [0041]      FIG. 18  is a diagram for explaining the operation of the position indicator of the third embodiment example of the present invention; 
           [0042]      FIGS. 19A-19B  are diagrams that together constitute a single diagram of  FIG. 19  for explaining partial scan operation in a tablet of the third embodiment example of the present invention; 
           [0043]      FIG. 20  is a diagram for explaining the principle of measurement of a tilt of the position indicator of the third embodiment example of the present invention; and 
           [0044]      FIG. 21  is a diagram for explaining examples of other shapes of the tip part of the position indicator. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]    Three embodiment examples will be specifically described below as position detecting devices and position indicators thereof according to embodiments of this invention with reference to the drawings. 
       First Embodiment Example 
       [0046]      FIG. 1  is a diagram showing the structure of a position indicating part in a position indicator of a first embodiment example according to the present invention. In  FIG. 1 , numeral  11  denotes a core that transmits pressure applied to the pen tip and it is molded by an insulating material such as plastic. Numeral  12  denotes a variable-capacitance capacitor whose capacitance changes depending on the writing pressure applied via the core  11  and, e.g., such as the one disclosed in Japanese Patent Laid-open No. Hei 4-96212 (Patent Document 2). The variable-capacitance capacitor  12  has a coupling part to the core  11  as disclosed in the above-described Patent Document 2 and this coupling part is so configured as to slightly move together with the core  11  depending on the writing pressure applied to the core  11 . 
         [0047]    Numerals  13  and  14  denote electrodes and they are buried in the core  11 .  FIG. 2  is a sectional view when the core  11 , in which the electrodes  13  and  14  are buried, is cut. Numeral  15  denotes a printed board. A terminal of the variable-capacitance capacitor  12  and the electrodes  13  and  14  are connected to the printed board  15  and circuit components to be described later are mounted on the printed board  15 . In the following description, the electrode  13  will be referred to as the L electrode and the electrode  14  will be referred to as the R electrode. 
         [0048]      FIG. 3  is a circuit configuration diagram of the position indicator of the first embodiment example according to the present invention. In  FIG. 3 , the same component as that in  FIG. 1  is shown by the same numeral. That is, numeral  12  denotes the variable-capacitance capacitor and numerals  13  and  14  denote the L electrode and the R electrode, respectively. Transistors TR 1  to TR 3  configure an oscillation circuit that oscillates with a resonant frequency depending on a coil L 1  and capacitors C 1  and C 2 . A coil L 2  is coupled to the coil L 1  and boosts an AC voltage generated in the coil L 1  to supply a signal of a high voltage to the L electrode  13  and the R electrode  14 . Numeral  16  denotes an analog switch for supplying a signal (d) generated in the coil L 2  to only either one of the L electrode  13  and the R electrode  14 . 
         [0049]    Numeral  17  denotes a microprocessor that operates based on a predetermined program and numeral  18  denotes a battery. An output signal (b) from a terminal P 1  of the microprocessor  17  controls the above-described oscillation circuit to the on- or off-state via a transistor TR 4 . An output signal (a) from a terminal P 2  is supplied to the analog switch  16 . In the present embodiment example, the L electrode  13  is selected when the output signal (a) from the terminal P 2  is at the low level and the R electrode  14  is selected when it is at the high level. 
         [0050]    As described later, the microprocessor  17  sets a terminal P 3  to the high level output state or the input state based on the predetermined program to thereby charge/discharge the variable-capacitance capacitor  12  and obtain the value of the writing pressure applied to the core  11 . 
         [0051]    Numeral  19  denotes a DC/DC converter that boosts the voltage of the battery  18  to generate a power source of a high voltage VP. The voltage VP is used as a power source to make the analog switch  16  operate and needs to be a voltage with amplitude higher than that of the signal d generated in the coil L 2 . A capacitor C 3  is to add an offset voltage so that the signal (d) generated in the coil L 2  may swing in the range of zero to VP. 
         [0052]      FIG. 4  is a diagram showing the operation of the position indicator of the first embodiment example configured in this manner and shows how the signals a, b, c, and d in  FIG. 3  change. The microprocessor  17  carries out control to keep the terminal P 1  (signal b) at the high level for a certain period with the terminal P 2  (signal a) set to the low level. Thereby, the signal (d) is radiated from the L electrode  13  for the certain period continuously (continuous transmission period: L, in  FIG. 4 ). In this continuous transmission period, the microprocessor  17  controls the terminal P 3  to obtain the writing pressure applied to the variable-capacitance capacitor  12 . Specifically, the microprocessor  17  sets the terminal P 3  to the high level output state to charge the variable-capacitance capacitor  12 . 
         [0053]    Next, the terminal P 3  is switched to the input state. At this time, the charge accumulated in the variable-capacitance capacitor  12  is discharged by a resistor connected in parallel to it. Thus, the voltage (c) of the variable-capacitance capacitor  12  gradually decreases. A time Tp from the switch of the terminal P 3  to the input state until the voltage c is dropped to a threshold is obtained. This time Tp is equivalent to the writing pressure to be obtained and the writing pressure is obtained as a 10-bit value in the present embodiment example. 
         [0054]    Upon ending this continuous transmission period (L), the microprocessor  17  controls the terminal P 1  to the high or low level with a predetermined cycle (Td) to thereby perform amplitude-shift keying (ASK) modulation. At this time, the terminal P 1  is invariably set to the high level as the first round of the control (start signal: L, in  FIG. 4 ). This is to allow the tablet side to accurately determine the subsequent data transmission timing. 
         [0055]    In the period of Td following this start signal (L), the terminal P 1  is set to the low level in this operation (sign: L, in  FIG. 4 ). This is for distinction from the case in which the terminal P 2  (signal a) is set to the high level as described later. 
         [0056]    Subsequently to the sign (L), the 10-bit writing pressure data obtained by the above-described operation is sequentially transmitted. Specifically, the terminal P 1  is controlled to the low level when the transmission data is 0 and the terminal P 1  is controlled to the high level when the transmission data is 1 (writing pressure data transmission period: L, in  FIG. 4 ).  FIG. 4  shows the case in which the writing pressure to be transmitted is “0101110101.” 
         [0057]    Upon ending the transmission of the 10-bit writing pressure data, the microprocessor  17  sets the terminal P 2  (signal a) to the high level to switch the analog switch  16  to the R side. This provides the state in which a signal is transmitted from the R electrode  14 . Also at this time, the terminals P 1  and P 3  are controlled exactly as with the above-described case of transmission by the L electrode to sequentially execute processing of continuous transmission (R), start signal (R), sign (R), and writing pressure data transmission (R). At the time of the sign (R), the terminal P 1  is set to the high level. 
         [0058]    In the position indicator of the present embodiment example, transmission is performed with alternate switching between a first pattern in which only the L electrode is selected and a second pattern in which only the R electrode is selected. Furthermore, the “sign” information following the start signal is set to “0” when the selection is made in the first pattern and the “sign” information following the start signal is set to “1” when the selection is made in the second pattern. Such operation is to identify, on the tablet side, whether the immediately previous continuous transmission is from the L electrode or from the R electrode, and is one of features of the present invention. 
         [0059]      FIG. 5  shows a configuration diagram of the tablet in the present embodiment example. The present embodiment example shows, as the tablet, a configuration that obtains indicated position and rotation angle of a position indicator  20  configured as described above and is capable also of detecting a touch position by a finger fg. 
         [0060]    In  FIG. 5 , numeral  20  denotes the position indicator shown in  FIGS. 1 to 3  and the frequency of a signal transmitted from the position indicator  20  is defined as f 1 . Numeral  21  denotes a tablet sensor whose base material is transparent glass. An X electrode group arranged in the X direction is provided on the front surface of the tablet sensor  21  and a Y electrode group arranged in the Y direction is provided on the back surface. These X electrode group and Y electrode group are formed as transparent electrodes by indium tin oxide (ITO). The tablet sensor  21  is disposed on a display device (not shown) and an input can be made directly to its display place by the position indicator  20 , the finger fg of the user, etc. 
         [0061]    Numeral  22  denotes an X selection circuit that selects one electrode from the X electrode group and numeral  23  denotes a Y selection circuit that selects one electrode from the Y electrode group. The present embodiment example will be explained based on the assumption that the number of X electrodes is 40 (X 1  to X 40 ) and the number of Y electrodes is 30 (Y 1  to Y 30 ). 
         [0062]    Numeral  24  denotes an oscillator for supplying a drive signal to the Y electrodes when the present embodiment example is operated for touch detection and the oscillation frequency is defined as f 2 . Numeral  25  denotes a switch circuit that switches the connection target of the Y electrode selected by the Y selection circuit  23  to the oscillator  24  or the side of an amplification circuit to be described later. Numeral  26  denotes a control circuit to control the respective parts in the tablet of the present embodiment example. Specifically, when this device is operated for touch detection, a control signal e from the control circuit  26  to the switch circuit  25  is set to the high level “1” to select the side of the oscillator  24 . When this device detects the position indicator  20 , the control signal e is set to the low level “0” to select the amplification circuit side. 
         [0063]    Numeral  27  denotes a switch circuit. It selects the X electrode selected by the X selection circuit  22  or selects the Y electrode selected by the Y selection circuit  23  via the switch circuit  25  to connect it to an amplification circuit  28 . Specifically, when this device is operated for touch detection, a control signal f from the control circuit  26  to the switch circuit  27  is set to the low level “0” to select the side of the X selection circuit  22 . When this device is operated to detect the position indicator  20  and the X-axis coordinate of the position indicator  20  is to be obtained, the control signal f is set to the low level “0” to select the side of the X selection circuit  22 . When this device is operated to detect the position indicator  20  and the Y-axis coordinate of the position indicator  20  is to be obtained, the control signal f is set to the high level “1” to select the side of the Y selection circuit  23 . 
         [0064]    In  FIG. 5 , numeral  28  denotes the amplification circuit and numeral  29  denotes a gain control circuit. The output of the amplification circuit  28  is connected to the gain control circuit  29  and is so set as to become an output signal at a proper level by a control signal g from the control circuit  26 . 
         [0065]    Numeral  30  denotes a band-pass filter circuit having a predetermined band width centered at the frequency f 1  or the frequency f 2 . This center frequency is switched by a control signal h from the control circuit  26 . The frequency is switched to f 1  when this device carries out operation of detecting the position indicator  20 , and is switched to f 2  when touch detection operation is carried out. 
         [0066]    In  FIG. 5 , numeral  31  denotes a detection circuit and numeral  32  denotes an analog/digital (AD) converter. Numeral  33  denotes a microprocessor. An output signal of the band-pass filter circuit  30  is detected by the detection circuit  31  and is converted to a digital value by the AD conversion circuit  32  based on a control signal j from the control circuit  26 . This digital data k is read and processed by the microprocessor  33 . 
         [0067]    The control circuit  26  supplies a control signal m and a control signal n to the X selection circuit  22  and the Y selection circuit  23 , respectively, to select one electrode from each of the X electrode group and the Y electrode group. 
         [0068]    The microprocessor  33  includes ROM and RAM inside and operates by a program stored in the ROM. The microprocessor  33  outputs a control signal p to control the control circuit  26  so that the control circuit  26  may output the control signals e to j, m, and n at predetermined timing. 
         [0069]    Operation when the tablet of the present embodiment example configured in this manner performs touch detection will be briefly described. As described above, in the touch detection, the switch circuit  25  is connected to the side of the oscillation circuit  24  to supply the drive signal to the Y electrode selected by the Y selection circuit  23 . Furthermore, the X electrode selected by the X selection circuit  22  is connected to the amplification circuit  28  via the switch circuit  27  and the signal level from the amplification circuit  28  is converted to a digital value by the AD conversion circuit  32  via the gain control circuit  29 , the band-pass filter circuit  30 , and the detection circuit  31 . 
         [0070]    At this time, if a finger is made to touch the intersection of the respective electrodes selected by the X selection circuit  22  and the Y selection circuit  23 , the detected signal level is lower than the level when a finger is absent. Therefore, if the signal level when a finger is absent is obtained in advance for all intersections of the X electrodes and the Y electrodes, the touch position can be obtained from the position at which the signal level is lowered. 
         [0071]    Operation when the tablet of the present embodiment example detects indicated position and rotation angle of the position indicator  20  will be described below. The microprocessor  33  outputs the control signal p to the control circuit  26  so that the control signal e may be set to the low level “0” to select the amplification circuit side in the switch circuit  25  and the control signal f may be set to the low level “0” to select the X electrode side in the switch circuit  27 . In this state, only the X electrode selected by the X selection circuit  22  is connected to the amplification circuit  28  and the Y electrode is connected to neither the amplification circuit  28  nor the oscillation circuit  24 . 
         [0072]      FIG. 6  shows X-axis whole surface scan operation for obtaining the rough X-direction position of the position indicator  20  on the tablet sensor  21 . The microprocessor  33  makes the control circuit  26  output the control signal m that causes the X selection circuit  22  to select the electrode X 1 , and reads the signal level (k) at this time. The microprocessor  33  reads the signal level (k) while making the control circuit  26  sequentially switch the electrode selected by the X selection circuit  22  to the electrodes X 2 , X 3 , X 4  . . . . 
         [0073]    At this time, if the detected signal level does not reach a predetermined value with all electrodes X 1  to X 40 , the microprocessor  33  determines that the position indicator  20  is not present on the tablet sensor  21  and repeats the operation of  FIG. 6 . If a signal at a level equal to or higher than the predetermined value is detected from any of the electrodes X 1  to X 40 , the microprocessor  33  stores the number of the X electrode from which the highest signal level is detected (in  FIG. 6 , X 11 ). 
         [0074]    Upon getting to know that the position indicator  20  is present near the electrode X 11 , the microprocessor  33  carries out transition operation to partial scan.  FIG. 7  is a diagram for explaining the transition operation to the partial scan in the tablet. This transition operation to the partial scan is operation for the microprocessor  33  to synchronize the timing with the operation of the position indicator  20  by detecting the start time of the continuous transmission period of the position indicator  20  when the position indicator  20  repeats operation like that shown in  FIG. 4 , and to obtain the rough position about the Y-axis. 
         [0075]    In  FIG. 7 , the microprocessor  33  controls the control circuit  26  so that the X selection circuit  22  may select the electrode X 11  obtained in the above-described X-axis whole surface scan operation. At this time, a signal corresponding to the signal transmitted from the position indicator  20  is induced in the electrode X 11  and a voltage corresponding to its signal level is generated in the detection circuit  31 . The microprocessor  33  makes the AD conversion circuit  32  operate with a constant cycle to read the signal level (k). This cycle of the operation of the AD conversion circuit  32  is set to a time sufficiently shorter than the cycle of transmission by the position indicator  20  in the writing pressure data transmission period. 
         [0076]    When the signal level output by the AD conversion circuit  32  is equal to or higher than a predetermined value for a certain time (Ts) continuously, the microprocessor  33  determines that the continuous transmission period of the position indicator  20  has been started and transitions to Y-axis whole surface scan operation ( FIG. 7 ). This time Ts is set to a time sufficiently longer than the cycle of transmission by the position indicator  20  in the writing pressure data transmission period. 
         [0077]    The microprocessor  33  controls the control circuit  26  so that the control signal f may be set to the high level “1” to select the Y electrode side in the switch circuit  27 . Furthermore, the Y selection circuit  23  sequentially selects the electrodes from Y 1  to Y 30  and the AD conversion circuit  32  is operated to read the signal level (k). At this time, the microprocessor  33  stores the electrode from which the highest signal level is detected. The explanation of the present embodiment example will be made based on the assumption that the highest signal level is detected from the electrode Y 20 . 
         [0078]    After the Y selection circuit  23  selects the last electrode Y 30  and detection of the signal level is ended, the microprocessor  33  carries out operation for waiting for the end of the continuous transmission period of the position indicator  20 . The microprocessor  33  controls the control circuit  26  so that the control signal f may be set to the low level “0” to select the X electrode side in the switch circuit  27 . Furthermore, the microprocessor  33  carries out control to make the X selection circuit  22  select the electrode X 11 . At this time, a signal at a level equal to or higher than the above-described predetermined value is detected if transmission from the position indicator  20  still continues. The time at which the received signal level comes short of the predetermined value is the end time of the continuous transmission from the position indicator  20 . Subsequently, the position indicator  20  enters the writing pressure data transmission period. However, the detailed position of the position indicator  20  has not yet been obtained at this timing. Thus, the microprocessor  33  does not read writing pressure data and transitions to partial scan operation shown in  FIGS. 8A-8B . 
         [0079]      FIGS. 8A-8B  are diagrams that together constitute a single diagram of  FIG. 8  for explaining the partial scan operation in the tablet of the present embodiment example. When the signal level output by the AD conversion circuit  32  is equal to or higher than the predetermined value for the certain time (Ts) continuously while the electrode X 11  is selected, the microprocessor  33  determines that the continuous transmission period of the position indicator  20  has been started and transitions to coordinate detection operation (step  1  in  FIG. 8A ). This time Ts is the same as that explained with  FIG. 7  and is set to a time sufficiently longer than the cycle of transmission by the position indicator  20  in the writing pressure data transmission period. 
         [0080]    In order to obtain the X coordinate of the signal from the position indicator  20 , the microprocessor  33  makes the X selection circuit  22  sequentially select five electrodes centered at X 11  (X 9  to X 13 ) with the control signal f kept at the low level “0,” and makes the AD conversion circuit  32  operate to read the signal level (step  1 ). At this time, the number of the electrode from which the highest signal level is detected (X 11 , in this example) and this signal level (Vpx 0 ) are stored. In addition, the levels detected with both electrodes adjacent to this electrode are stored as Vax 0  and Vbx 0  (step  1 ). 
         [0081]    Next, in order to obtain the Y coordinate of the signal from the position indicator  20 , the microprocessor  33  sets the control signal f to the high level “1.” Furthermore, the microprocessor  33  makes the Y selection circuit  23  sequentially select five electrodes centered at Y 20  (Y 18  to Y 22 ) and reads the signal level (step  1 ). At this time, the number of the electrode from which the highest signal level is detected (Y 20 , in this example) and this signal level (Vpy 0 ) are stored. In addition, the levels detected with both electrodes adjacent to this electrode are stored as Vay 0  and Vby 0  (step  1 ). The obtained signal levels Vpx 0 , Vax 0 , Vbx 0 , Vpy 0 , Vay 0 , and Vby 0  are used for calculation of coordinate values by a calculation equation to be described later. 
         [0082]    Next, the microprocessor  33  carries out operation for waiting for the end of the continuous transmission period of the position indicator  20 . The microprocessor  33  sets the control signal f to the low level “0” and carries out control to make the X selection circuit  22  select the electrode X 11 , from which the peak level is detected in the above-described coordinate detection operation. At this time, the time at which the received signal level comes short of the predetermined value is the end time of the continuous transmission from the position indicator  20  (step  1 ). 
         [0083]    Upon detecting the end of the continuous transmission from the position indicator  20 , the microprocessor  33  enters operation of detecting the timing of the start signal transmitted prior to writing pressure data (step  2 ). The microprocessor  33  carries out control to repeatedly activate the AD conversion circuit  32  with the electrode X 11  selected, and stores the time at which the signal level becomes equal to or higher than the above-described predetermined value as t 1 . The microprocessor  33  starts operation of data reception from the position indicator  20  from the time after waiting for a certain time Tw from the time t 1  (step  2 ). This time Tw is set to the time from the end of transmission of the start signal from the position indicator  20  to the timing at which the signal level received by the tablet becomes almost zero, and this time is obtained in advance. 
         [0084]    The microprocessor  33  activates a timer (not shown) simultaneously with the timing at which the above-described waiting time reaches Tw. This timer repeatedly counts values from zero to the value corresponding with the above-described time Td (cycle of data transmission from the position indicator  20 ) (step  2 ). In the operation period of one cycle of the timer, the microprocessor  33  repeatedly activates the AD conversion circuit  32  and reads the signal level. If the signal level during this period never reaches the above-described predetermined value, the microprocessor  33  determines that transmission from the position indicator  20  is not made and stores the data of this round as “0.” If a signal level equal to or higher than the predetermined value is detected in this period, the microprocessor  33  determines that transmission from the position indicator  20  is made and stores the data of this round as “1” (step  2 ). 
         [0085]    The above-described timer count is performed eleven times and 11-bit data is stored. In this data, the data of the first round is equivalent to the “sign” shown in  FIG. 4 . Because this sign is 0 in step  2  in  FIG. 8A , it turns out that the coordinates calculated from the signal levels Vpx 0 , Vax 0 , Vbx 0 , Vpy 0 , Vay 0 , and Vby 0  obtained in step  1  are the coordinate position corresponding to the L electrode of the position indicator  20 . The remaining 10-bit data represents the writing pressure value measured in the position indicator  20  in the period of step  1 . 
         [0086]    Although the electrode from which the maximum level is detected (X 11 ) is selected from the X-axis electrodes and data is received in step  2 , this step may be carried out by selecting the electrode from which the maximum level is detected (Y 20 ) from the Y-axis electrodes. 
         [0087]    Upon ending the reception of the 11-bit data in step  2 , the microprocessor  33  transitions to operation of detecting the start of the continuous transmission period of the position indicator  20 . The microprocessor  33  repeatedly detects the signal level received with the electrode X 11  selected. When this reception level is equal to or higher than the predetermined value for the certain time (Ts) continuously, the microprocessor  33  determines that the continuous transmission period of the position indicator  20  has been started and transitions to coordinate detection operation (step  3  in  FIG. 8B ). 
         [0088]    In order to obtain the X coordinate of the signal from the position indicator  20 , the microprocessor  33  makes the X selection circuit  22  sequentially select five electrodes centered at X 11  (X 9  to X 13 ) with the control signal f kept at the low level “0,” and makes the AD conversion circuit  32  operate to read the signal level (step  3 ). At this time, the number of the electrode from which the highest signal level is detected (X 11 , in this example) and this signal level (Vpx 1 ) are stored. In addition, the levels detected with both electrodes adjacent to this electrode are stored as Vax 1  and Vbx 1  (step  3 ). 
         [0089]    Next, in order to obtain the Y coordinate of the signal from the position indicator  20 , the microprocessor  33  sets the control signal f to the high level “1.” Furthermore, the microprocessor  33  makes the Y selection circuit  23  sequentially select five electrodes centered at Y 20  (Y 18  to Y 22 ) and reads the signal level (step  3 ). At this time, the number of the electrode from which the highest signal level is detected (Y 20 , in this example) and this signal level (Vpy 1 ) are stored. In addition, the levels detected with both electrodes adjacent to this electrode are stored as Vay 1  and Vby 1  (step  3 ). The obtained signal levels Vpx 1 , Vax 1 , Vbx 1 , Vpy 1 , Vay 1 , and Vby 1  are used for calculation of coordinate values by a calculation equation to be described later. 
         [0090]    Next, the microprocessor  33  carries out operation for waiting for the end of the continuous transmission period of the position indicator  20 . The microprocessor  33  sets the control signal f to the low level “0” and carries out control to make the X selection circuit  22  select the electrode X 11 , from which the peak level is detected in the above-described coordinate detection operation. At this time, the time at which the received signal level comes short of the predetermined value is the end time of the continuous transmission from the position indicator  20  (step  3 ). 
         [0091]    Upon detecting the end of the continuous transmission from the position indicator  20 , the microprocessor  33  enters operation of detecting the timing of the start signal transmitted prior to writing pressure data (step  4 ). The microprocessor  33  carries out control to repeatedly activate the AD conversion circuit  32  with the electrode X 11  selected, and stores the time at which the signal level becomes equal to or higher than the above-described predetermined value as t 2 . The microprocessor  33  starts operation of data reception from the position indicator  20  from the time after waiting for the certain time Tw from the time t 2  (step  4 ). This Tw is set to the same time as that in step  2 . 
         [0092]    The microprocessor  33  activates the timer simultaneously with the timing at which the above-described waiting time reaches Tw and receives 11-bit data from the position indicator  20  exactly as with the above-described step  2  (step  4 ). The data of the first round is equivalent to the “sign” shown in  FIG. 4 . Because this sign is 1 in step  4  in  FIG. 8B , it turns out that the coordinates calculated from the signal levels Vpx 1 , Vax 1 , Vbx 1 , Vpy 1 , Vay 1 , and Vby 1  obtained in step  3  are the coordinate position corresponding to the R electrode of the position indicator  20 . The remaining 10-bit data represents the writing pressure value measured in the position indicator  20  in the period of step  3 . In this manner, identification as to which electrode of the position indicator  20  the transmission is made from is allowed by the specific data value from the position indicator  20 . This is one of features of the present invention. 
         [0093]    Although the electrode from which the maximum level is detected (X 11 ) is selected from the X-axis electrodes and data is received also in step  4 , this step may be carried out by selecting the electrode from which the maximum level is detected (Y 20 ) from the Y-axis electrodes. 
         [0094]    In the present embodiment example, the transmission from the position indicator  20  by the L electrode and the transmission by the R electrode are alternately repeated. Therefore, by repeatedly carrying out step  1  to step  4  in  FIG. 8B  as the operation of the tablet side, the coordinates, rotation angle, and writing pressure of the position indicator  20  can be continuously obtained. 
         [0095]    The method for obtaining the coordinate position and rotation angle of the position indicator  20  from the reception levels obtained in the above-described step  1  and step  3  will be described below. 
         [0096]    Coordinate values (X 0 , Y 0 ) by the L electrode of the position indicator  20  are calculated from the reception levels Vpx 0 , Vax 0 , Vbx 0 , Vpy 0 , Vay 0 , and Vby 0  obtained in step  1  by the following equation (1) and equation (2), respectively. 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     
                       P 
                        
                       
                           
                       
                        
                       x 
                        
                       
                           
                       
                        
                       0 
                     
                     + 
                     
                       
                         Dx 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             px 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0097]    In this equation, Px 0  is the coordinate position of the electrode from which the maximum level is detected regarding the X axis (X 11 , in this example) and Dx is the arrangement pitch between the X-axis electrodes. 
         [0000]    
       
         
           
             
               
                 
                   
                     Y 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     
                       P 
                        
                       
                           
                       
                        
                       y 
                        
                       
                           
                       
                        
                       0 
                     
                     + 
                     
                       
                         y 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             py 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             0 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0098]    In this equation, Py 0  is the coordinate position of the electrode from which the maximum level is detected regarding the Y axis (Y 20 , in this example) and Dy is the arrangement pitch between the Y-axis electrodes. 
         [0099]    Similarly, coordinate values (X 1 , Y 1 ) by the R electrode of the position indicator  20  are calculated from the reception levels Vpx 1 , Vax 1 , Vbx 1 , Vpy 1 , Vay 1 , and Vby 1  obtained in step  3  by the following equation (3) and equation (4), respectively. 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       P 
                        
                       
                           
                       
                        
                       x 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       
                         Dx 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             px 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0100]    In this equation, Px 1  is the coordinate position of the electrode from which the maximum level is detected regarding the X axis (X 11 , in this example) and Dx is the arrangement pitch between the X-axis electrodes. 
         [0000]    
       
         
           
             
               
                 
                   
                     Y 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       Py 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       
                         Dy 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             py 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0101]    In this equation, Py 1  is the coordinate position of the electrode from which the maximum level is detected regarding the Y axis (Y 20 , in this example) and Dy is the arrangement pitch between the Y-axis electrodes. 
         [0102]      FIG. 9  is a principle diagram for calculating a rotation angle 8 of the position indicator  20  about the axis defined as the perpendicular direction to the tablet surface, based on two pairs of coordinate values (X 0 , Y 0 ) and (X 1 , Y 1 ). In this diagram, the orientation of the R electrode corresponding to the coordinate values (X 1 , Y 1 ) is defined by employing the positive direction of the Y axis as the basis (θ=0) and defining the range of θ as −180°&lt;θ≦+180°. In this case, the rotation angle θ of the position indicator  20  is calculated from X 0 , Y 0 , X 1 , and Y 1  as shown by the following equations (5) to (9). 
         [0103]    When Y 1 &gt;Y 0   
         [0000]    
       
         
           
             
               
                 
                   θ 
                   = 
                   
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         
                           
                             X 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             X 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                         
                           
                             Y 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             Y 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0104]    When Y 1 =Y 0  and X 1 &gt;X 0   
         [0000]      θ=90°  (6)
 
         [0105]    When Y 1 =Y 0  and X 1 &lt;X 0   
         [0000]      θ=−90°  (7)
 
         [0106]    When Y 1 &lt;Y 0  and X 1 ≧X 0   
         [0000]    
       
         
           
             
               
                 
                   θ 
                   = 
                   
                     
                       180 
                        
                       ° 
                     
                     + 
                     
                       
                         tan 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               X 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               X 
                                
                               
                                   
                               
                                
                               0 
                             
                           
                           
                             
                               Y 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               Y 
                                
                               
                                   
                               
                                
                               0 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0107]    When Y 1 &lt;Y 0  and X 1 &lt;X 0   
         [0000]    
       
         
           
             
               
                 
                   θ 
                   = 
                   
                     
                       
                         - 
                         180 
                       
                        
                       ° 
                     
                     + 
                     
                       
                         tan 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               X 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               X 
                                
                               
                                   
                               
                                
                               0 
                             
                           
                           
                             
                               Y 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               Y 
                                
                               
                                   
                               
                                
                               0 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
         [0108]    In the present embodiment example, the Y-axis positive direction is defined as the basis of the rotation angle and the orientation of the R electrode (relative to the basis) is obtained as an angle. However, the X axis may be defined as the basis and the orientation of the L electrode may be obtained. 
         [0109]    In the present embodiment example, the same information (writing pressure) is sent both in data transmission by the L electrode and in data transmission by the R electrode of the position indicator  20 . However, another kind of information may be sent in one of them or only sign information may be sent as one of the data to shorten the time. Furthermore, only one of the L electrode and the R electrode may be used for data transmission and the tablet may determine the electrode, with which the immediately previous continuous transmission is performed, based on whether data transmission from the position indicator  20  has been made. Moreover, the frequency of transmission may be changed between transmission from the L electrode and transmission from the R electrode to differentiate them or the length of the continuous transmission may be changed for differentiation. 
         [0110]    In the present embodiment example, the electrodes of the position indicator  20  are exposed to the tip part of the core  11 . However, they may be covered by the material of the core  11 , such as plastic. 
       Second Embodiment Example 
       [0111]      FIG. 10  is a diagram showing the structure of a position indicating part in a position indicator of a second embodiment example according to the present invention. In  FIG. 10 , the same part as that in  FIG. 1  is given the same reference numeral. That is, numeral  12  denotes a variable-capacitance capacitor whose capacitance changes depending on the writing pressure and numeral  15  denotes a printed board. A core  35  is coupled to the variable-capacitance capacitor  12  and the writing pressure applied to the tip of the core  35  is detected. Numeral  36  denotes a chassis and a hole through which the core  35  passes is made at its tip part. 
         [0112]    Two electrodes  37  and  38  are provided at the tip part of the chassis  36  and  FIG. 11  is a diagram showing the arrangement thereof. The following description will be so made that the electrodes  37  and  38  are called the L electrode and the R electrode, respectively. 
         [0113]      FIG. 12  is a circuit configuration diagram of the position indicator of the second embodiment example according to the present invention. In  FIG. 12 , the same part as that in  FIG. 3  or  FIG. 10  is given the same reference numeral. That is, numeral  12  denotes the variable-capacitance capacitor. Numerals  37  and  38  denote the L electrode and the R electrode, respectively. Numerals  17 ,  18 , and  19  denote a microprocessor, a battery, and a DC/DC converter, respectively. 
         [0114]    The difference between the configuration of the position indicator of the second embodiment example shown in  FIG. 12  and the configuration of the position indicator  20  of the first embodiment example shown in  FIG. 3  is as follows. In the first embodiment example, one of two electrodes is connected to the coil L 2  with alternate switching. In contrast, in the present embodiment example, the electrode  37  (L electrode) is always connected to the coil L 2  and an analog switch  39  is provided between the electrode  38  (R electrode) and the coil L 2  and is controlled to the on- or off-state. 
         [0115]    Specifically, when the terminal P 2  (signal a) of the microprocessor  17  is set to the high level, the analog switch  39  becomes the on-state and thus the signal (d) generated in the coil L 2  is applied to both the L electrode and the R electrode. When the terminal P 2  (signal a) of the microprocessor  17  is set to the low level, the analog switch  39  becomes the off-state and thus the signal (d) generated in the coil L 2  is applied to only the L electrode. 
         [0116]    The voltage VP obtained by the DC/DC converter  19  is used as a power supply to operate the analog switch  39  similarly to the first embodiment example. 
         [0117]      FIG. 13  is a diagram showing the operation of the position indicator of the second embodiment example and shows how the signals a, b, c, and d in  FIG. 12  change. The microprocessor  17  carries out control to keep the terminal P 1  (signal b) at the high level for a certain period with the terminal P 2  (signal a) set to the high level. Thereby, the signal (d) is radiated from the L electrode and the R electrode for the certain period continuously (continuous transmission period: L+R, in  FIG. 13 ). In this continuous transmission period, the microprocessor  17  obtains the writing pressure applied to the variable-capacitance capacitor  12  similarly to the first embodiment example. 
         [0118]    Upon ending this continuous transmission period, the microprocessor  17  performs ASK modulation by controlling the terminal P 1  with the cycle Td exactly as with the first embodiment example. A sign (L+R) following the start signal at this time is set to “0” indicating that the immediately previous continuous transmission is made by two electrodes. Subsequently to this sign transmission, 10-bit writing pressure data obtained in the above-described continuous transmission period is transmitted similarly to the first embodiment example. 
         [0119]    Upon ending the transmission of the writing pressure data, the microprocessor  17  sets the terminal P 2  (signal a) to the low level to turn off the analog switch  39 . This provides the state in which a signal is transmitted from only the L electrode  37 . Also at this time, the terminal P 1  is similarly controlled to perform continuous transmission (L) and writing pressure detection is performed. 
         [0120]    Upon ending this continuous transmission period, the microprocessor  17  sets the terminal P 2  (signal a) to the high level so that the subsequent data transmission may be made by two electrodes. The purpose thereof is to allow the tablet to surely detect data of the writing pressure and so forth by transmitting the data by two electrodes. The microprocessor  17  performs ASK modulation by controlling the terminal P 1  with the cycle Td similarly to the above description. A sign (L) following the start signal at this time is set to “1” indicating that the immediately previous continuous transmission is made by only the L electrode. Subsequently to this sign transmission, 10-bit writing pressure data obtained in the above-described continuous transmission period is sequentially transmitted. 
         [0121]    In the position indicator of the present embodiment example, transmission is performed with alternate switching between a first pattern in which both the L electrode and the R electrode are selected and a second pattern in which only the L electrode is selected. Furthermore, the “sign” information following the start signal is set to “0” when the selection is made in the first pattern and the “sign” information following the start signal is set to “1” when the selection is made in the second pattern. Such operation is to identify, on the tablet side, whether the immediately previous continuous transmission is from two electrodes or from only the L electrode, and is one of features of the present invention. 
         [0122]    Also in the present embodiment example, the tablet having the same configuration as that of the first embodiment example ( FIG. 5 ) is used. Operation of detecting indicated position and rotation angle when the position indicator of the present embodiment example is placed on the tablet of  FIG. 5  will be described below. 
         [0123]    Also in the present embodiment example, operation for obtaining the rough position of the position indicator is carried out as shown in  FIGS. 6 and 7  similarly to the first embodiment example. In  FIG. 7 , the Y-axis whole surface scan operation after detection of continuous transmission from the position indicator may be carried out in the continuous transmission period in which transmission from the position indicator is made by two electrodes or may be carried out in the continuous transmission period in which transmission is made by only the L electrode. The explanation of the present embodiment example will also be made based on the assumption that the signal of the maximum level is detected from the electrode X 11  in the X-axis whole surface scan operation in  FIG. 6  and the signal of the maximum level is detected from the electrode Y 20  in the Y-axis whole surface scan operation in  FIG. 7 . 
         [0124]      FIGS. 14A-14B  are diagrams that together constitute a single diagram of  FIG. 14 , which shows partial scan operation of the second embodiment example. The difference of the partial scan operation according to the present embodiment example from the partial scan operation of the first embodiment example ( FIGS. 8A-8B ) is as follows. In the present embodiment example, the coordinates obtained by coordinate detection operation (step  1  in  FIG. 14A ) immediately before the “sign” data from the position indicator is transmitted as “0” indicate the midpoint position between the L electrode and the R electrode (i.e., the position of the core  35 ). Furthermore, the coordinates obtained by coordinate detection operation (step  3  in  FIG. 14B ) immediately before the “sign” data from the position indicator is transmitted as “1” indicate the position corresponding to the L electrode. The other operation is the same as that in the first embodiment example. 
         [0125]    Also in the present embodiment example, coordinate values indicating the midpoint position between the L electrode and the R electrode of the position indicator are calculated as (X 0 , Y 0 ) from the reception levels Vpx 0 , Vax 0 , Vbx 0 , Vpy 0 , Vay 0 , and Vby 0  obtained in step  1  by using the above-described equation (1) and equation (2). 
         [0126]    Furthermore, coordinate values corresponding to the position of the L electrode of the position indicator are calculated as (X 1 , Y 1 ) from the reception levels Vpx 1 , Vax 1 , Vbx 1 , Vpy 1 , Vay 1 , and Vby 1  obtained in step  3  by using the above-described equation (3) and equation (4). 
         [0127]    The principle diagram of  FIG. 9  is applied also to the present embodiment example, so that the orientation of the L electrode corresponding to the coordinate values (X 1 , Y 1 ) is defined by employing the positive direction of the Y axis as the basis (θ=0) and defining the range of θ as −180°&lt;θ≦+180°. In this case, the rotation angle θ of the position indicator is calculated by the above-described equations (5) to (9) with use of X 0 , Y 0 , X 1 , and Y 1  in exactly the same way. 
         [0128]    In the present embodiment example, the same information (writing pressure) is sent both in data transmission by two electrodes of the position indicator and in data transmission by only the L electrode. However, another kind of information may be sent in one of them or only sign information may be sent as one of the data to shorten the time. Furthermore, data transmission may be performed only at the time of the transmission by two electrodes and the tablet may make the determination depending on whether data transmission from the position indicator has been made. Alternatively, the length of the continuous transmission may be changed to differentiate the transmission. 
         [0129]    Although the electrodes of the position indicator are provided at the tip part of the chassis  36  in the present embodiment example, they may be provided on the core  35  similarly to the first embodiment example. 
       Third Embodiment Example 
       [0130]      FIG. 15  is a diagram showing the structure of a position indicating part in a position indicator of a third embodiment example according to the present invention. In the present embodiment example, an example is shown in which three electrodes are disposed in the position indicator and a tilt of the position indicator relative to the tablet is obtained in addition to a rotation angle thereof. 
         [0131]    In  FIG. 15 , the same part as that in  FIG. 10  is given the same reference numeral. That is, numeral  12  denotes a variable-capacitance capacitor whose capacitance changes depending on the writing pressure. Numerals  15 ,  35 , and  36  denote a printed board, a core, and a chassis, respectively. 
         [0132]    Three electrodes  40 ,  41 , and  42  are provided at the tip part of the chassis  36  and  FIG. 16  is a diagram showing the arrangement thereof. These three electrodes are connected to the printed board  15  by a connection line (not shown). 
         [0133]      FIG. 17  is a circuit configuration diagram of the position indicator of the third embodiment example according to the present invention. In  FIG. 17 , the same part as that in  FIG. 15  or  FIG. 3  is given the same reference numeral. That is, numeral  12  denotes the variable-capacitance capacitor. Numerals  40  to  42  denote the electrodes. Numerals  17 ,  18 , and  19  denote a microprocessor, a battery, and a DC/DC converter, respectively. 
         [0134]    The difference of the configuration shown in  FIG. 17  from the first embodiment example ( FIG. 3 ) is as follows. In the first embodiment example, one of two electrodes is connected to the coil L 2  with alternate switching. In contrast, in the present embodiment example, one of three electrodes  40  to  42  is connected to the coil L 2  with sequential switching. An analog multiplexer  43  is provided between the electrodes  40  to  42  and the coil L 2  and one is selected among the electrode  40 , the electrode  41 , and the electrode  42  by setting of two terminals of the microprocessor  17  (P 2  and P 4 ). Signals from two terminals of the microprocessor  17  (P 2  and P 4 ) are referred to collectively as the “signal a” here. 
         [0135]    The voltage VP obtained by the DC/DC converter  19  is used as a power supply to operate the analog multiplexer  43  similarly to the first embodiment example. 
         [0136]      FIG. 18  is a diagram showing the operation of the position indicator of the third embodiment example and shows how the signals a, b, c, and d in  FIG. 17  change. The microprocessor  17  carries out control to keep the terminal P 1  (signal b) at the high level for a certain period with the electrode  40  selected by the setting by the signal a. Thereby, the signal (d) is radiated from the electrode  40  for the certain period continuously (continuous transmission period  1 , in  FIG. 18 ). In this continuous transmission period, the microprocessor  17  obtains the writing pressure applied to the variable-capacitance capacitor  12  similarly to the first embodiment example. 
         [0137]    Upon ending this continuous transmission period, the microprocessor  17  performs ASK modulation by controlling the terminal P 1  with the cycle Td exactly as with the first embodiment example. The “sign” following the “start signal” at this time is set to “0” indicating that the immediately previous continuous transmission is made by the electrode  40 . Subsequently to this sign transmission, 10-bit writing pressure data obtained in the above-described continuous transmission period  1  is transmitted similarly to the first embodiment example. 
         [0138]    Upon ending the transmission of the writing pressure data, the microprocessor  17  switches the setting by the signal a to select the electrode  41 , and similarly controls the terminal P 1  to perform continuous transmission (continuous transmission period  2 , in  FIG. 18 ). At this time, writing pressure detection like that performed in continuous transmission period  1  is not performed in the present embodiment example. 
         [0139]    Upon the end of this continuous transmission period  2 , the microprocessor  17  performs ASK modulation by controlling the terminal P 1  with the cycle Td while keeping of the selection of the electrode  41  by the setting by the signal a. The “sign” following the start signal at this time is transmitted as “1.” 
         [0140]    Upon ending this sign transmission, the microprocessor  17  switches the setting by the signal a to select the electrode  42 , and similarly controls the terminal P 1  to perform continuous transmission (continuous transmission period  3 , in  FIG. 18 ). Also at this time, writing pressure detection like that performed in continuous transmission period  1  is not performed. 
         [0141]    Upon the end of this continuous transmission period, the microprocessor  17  performs ASK modulation by controlling the terminal P 1  with the cycle Td while keeping of the selection of the electrode  42  by the setting by the signal a. Also at this time, the “sign” following the start signal is transmitted as “1.” 
         [0142]    In the position indicator of the present embodiment example, the following patterns are set: a first pattern in which only the electrode  40  is selected, a second pattern in which only the electrode  41  is selected, and a third pattern in which only the electrode  42  is selected. Transmission is performed with sequential repetition of the patterns, i.e., like in the second pattern subsequently to the first pattern, in the third pattern subsequently to the second pattern, and in the first pattern subsequently to the third pattern. Furthermore, the “sign” information following the start signal is set to “0” when the selection is made in the first pattern and the “sign” information following the start signal is set to “1” when the selection is made in the second pattern and the third pattern. Therefore, the tablet side can identify which electrode of the position indicator a signal is transmitted from by considering the above-described transmission order. These operations are one of features of the present invention. 
         [0143]    Also in the present embodiment example, the tablet having the same configuration as that of the first embodiment example ( FIG. 5 ) is used. Operation of detecting indicated position, rotation angle, and tilt relative to the tablet surface when the position indicator of the present embodiment example is placed on the tablet of  FIG. 5  will be described below. 
         [0144]    Also in the present embodiment example, operation for obtaining the rough position of the position indicator is carried out as shown in  FIGS. 6 and 7  similarly to the first embodiment example. In  FIG. 7 , any electrode may be used for transmission from the position indicator in the continuous transmission period in which the Y-axis whole surface scan operation after detection of continuous transmission from the position indicator is carried out. The explanation of the present embodiment example will also be made based on the assumption that the signal of the maximum level is detected from the electrode X 11  in the X-axis whole surface scan operation in  FIG. 6  and the signal of the maximum level is detected from the electrode Y 20  in the Y-axis whole surface scan operation in  FIG. 7 . 
         [0145]      FIGS. 19A-19B  together constitute a single diagram of  FIG. 19 , which shows partial scan operation of the third embodiment example. Also in the present embodiment example, after a signal continuing for the certain time (Ts) or longer from the position indicator is detected, coordinate detection operation of the X axis and the Y axis is carried out. Then, data sent subsequently to continuous transmission from the position indicator is received. This data is transmitted subsequently to the “start signal” also as shown in  FIG. 18 . In the present embodiment example, if “0” is received as the “sign” following immediately after the “start signal,” the data reception operation is continuously carried out to receive 10-bit writing pressure data. If “1” is received as the “sign,” the data reception operation is ended and transition to operation for detecting continuous transmission from the position indicator is made. 
         [0146]    In  FIG. 19A , “0” is received as the sign in step  2 . Thus, in the immediately previous coordinate detection operation (step  1 ), the level and coordinate position based on a signal transmitted from the electrode  40  of the position indicator are obtained. In the subsequent coordinate detection operation (step  3 ), the level and coordinate position based on a signal transmitted from the electrode  41  of the position indicator are obtained. In the further subsequent coordinate detection operation (step  5 ), the level and coordinate position based on a signal transmitted from the electrode  42  of the position indicator are obtained. 
         [0147]    In the present embodiment example, in order to obtain the tilt of the position indicator by using the reception levels obtained in the respective coordinate detection operations of step  1 , step  3 , and step  5 , the gain value set in the gain control circuit  29  of the tablet circuit ( FIG. 5 ) is set identical in these respective coordinate detection operations. 
         [0148]    Coordinate values (X 1 , Y 1 ) by the electrode  40  of the position indicator are calculated from the reception levels Vpx 1 , Vax 1 , Vbx 1 , Vpy 1 , Vay 1 , and Vby 1  obtained in step  1  by the above-described equation (3) and equation (4). 
         [0149]    Furthermore, coordinate values (X 2 , Y 2 ) by the electrode  41  of the position indicator are obtained from reception levels Vpx 2 , Vax 2 , Vbx 2 , Vpy 2 , Vay 2 , and Vby 2  obtained in step  3  by the following equation (10) and equation (11). 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       Px 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       
                         
                           D 
                            
                           
                               
                           
                            
                           x 
                         
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             px 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0150]    In this equation, Px 2  is the coordinate position of the electrode from which the maximum level is detected regarding the X axis (X 11 , in this example) and Dx is the arrangement pitch between the X-axis electrodes. 
         [0000]    
       
         
           
             
               
                 
                   
                     Y 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       Py 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       
                         Dy 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             py 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0151]    In this equation, Py 2  is the coordinate position of the electrode from which the maximum level is detected regarding the Y axis (Y 20 , in this example) and Dy is the arrangement pitch between the Y-axis electrodes. 
         [0152]    Coordinate values (X 3 , Y 3 ) by the electrode  42  of the position indicator are obtained from reception levels Vpx 3 , Vax 3 , Vbx 3 , Vpy 3 , Vay 3 , and Vby 3  obtained in step  5  by the following equation (12) and equation (13). 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                      
                     
                         
                     
                      
                     3 
                   
                   = 
                   
                     
                       Px 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       
                         Dx 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             px 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ax 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             bx 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0153]    In this equation, Px 3  is the coordinate position of the electrode from which the maximum level is detected regarding the X axis (X 11 , in this example) and Dx is the arrangement pitch between the X-axis electrodes. 
         [0000]    
       
         
           
             
               
                 
                   
                     Y 
                      
                     
                         
                     
                      
                     3 
                   
                   = 
                   
                     
                       Py 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       
                         Dy 
                         2 
                       
                       × 
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         
                           
                             2 
                             × 
                             V 
                              
                             
                                 
                             
                              
                             py 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             ay 
                              
                             
                                 
                             
                              
                             3 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             by 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
         [0154]    In this equation, Py 3  is the coordinate position of the electrode from which the maximum level is detected regarding the Y axis (Y 20 , in this example) and Dy is the arrangement pitch between the Y-axis electrodes. 
         [0155]    Coordinate values (X 0 , Y 0 ) corresponding to the core  35  of the position indicator can be obtained as the center point of three obtained coordinate values (X 1 , Y 1 ), (X 2 , Y 2 ), and (X 3 , Y 3 ) by the following equation (14) and equation (15). 
         [0000]    
       
         
           
             
               
                 
                   
                     X 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     
                       
                         X 
                          
                         
                             
                         
                          
                         1 
                       
                       + 
                       
                         X 
                          
                         
                             
                         
                          
                         2 
                       
                       + 
                       
                         X 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     3 
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
             
               
                 
                   
                     Y 
                      
                     
                         
                     
                      
                     0 
                   
                   = 
                   
                     
                       
                         Y 
                          
                         
                             
                         
                          
                         1 
                       
                       + 
                       
                         Y 
                          
                         
                             
                         
                          
                         2 
                       
                       + 
                       
                         Y 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     3 
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
         [0156]    The principle diagram of  FIG. 9  is applied also to the present embodiment example, so that the orientation of the electrode  40  corresponding to the coordinate values (X 1 , Y 1 ) is defined by employing the positive direction of the Y axis as the basis (θ=0) and defining the range of θ as −180°&lt;θ≦+180°. In this case, the rotation angle θ of the position indicator is calculated by the above-described equations (5) to (9) with use of X 0 , Y 0 , X 1 , and Y 1  in exactly the same way. 
         [0157]    In the present embodiment example, a tilt of the position indicator can be obtained from the respective received signal intensities from three electrodes of the position indicator. As the received signal intensity, the level at the time of the X-axis coordinate detection may be used or the level at the time of the Y-axis coordinate detection may be used. Here, the level at the time of the X-axis coordinate detection is used. 
         [0158]    Received signal intensity (V 1 ) by the electrode  40  is obtained by correction calculation by the following equation (16) based on the X electrode positions of the tablet. 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       px 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           ) 
                         
                         2 
                       
                       
                         8 
                         × 
                         
                           ( 
                           
                             
                               
                                 2 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               px 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
         [0159]    Received signal intensity (V 2 ) by the electrode  41  is obtained by the following equation (17). 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       px 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               2 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           ) 
                         
                         2 
                       
                       
                         8 
                         × 
                         
                           ( 
                           
                             
                               
                                 2 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               px 
                                
                               
                                   
                               
                                
                               2 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               2 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
         
       
     
         [0160]    Received signal intensity (V 3 ) by the electrode  42  is obtained by the following equation (18). 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     3 
                   
                   = 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       px 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                           ) 
                         
                         2 
                       
                       
                         8 
                         × 
                         
                           ( 
                           
                             
                               
                                 2 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               px 
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               ax 
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               bx 
                                
                               
                                   
                               
                                
                               3 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
         [0161]      FIG. 20  is a principle diagram for obtaining the tilt of the position indicator by using the received signal intensities V 1 , V 2 , and V 3  from three electrodes. In  FIG. 20 , the height direction from the sensor surface ( 21  in  FIG. 5 ) of the tablet is employed as the z axis and the coordinate axes are so set that the center G of an equilateral triangle configured by A, B, and C corresponding to the tips of the electrodes  40 ,  41 , and  42 , respectively, of the position indicator exists on the yz plane and point A corresponding to the tip of the electrode  40  exists on the z axis. When the coordinates of the respective points at this time are represented as point A (0, 0, z 1 ), point B (x 2 , y 2 , z 2 ), point C (x 3 , y 3 , z 3 ), and point G (0, yg, zg), the tilt (θx, θy) of the position indicator is obtained as shown by the following equation (19) and equation (20). 
         [0000]    
       
         
           
             
               
                 
                   
                     sin 
                      
                     
                         
                     
                      
                     θ 
                      
                     
                         
                     
                      
                     x 
                   
                   = 
                   
                     
                       
                         z 
                          
                         
                             
                         
                          
                         2 
                       
                       - 
                       
                         z 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     r 
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
         [0000]    (r: the length of one side of the equilateral triangle) 
         [0000]    
       
         
           
             
               
                 
                   
                     sin 
                      
                     
                         
                     
                      
                     θ 
                      
                     
                         
                     
                      
                     y 
                   
                   = 
                   
                     
                       
                         
                           2 
                           · 
                           z 
                         
                          
                         
                             
                         
                          
                         1 
                       
                       - 
                       
                         z 
                          
                         
                             
                         
                          
                         2 
                       
                       - 
                       
                           
                       
                        
                       
                         z 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     
                       r 
                        
                       
                         
                             
                         
                       
                        
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   20 
                   ) 
                 
               
             
           
         
       
     
         [0000]    (slope of the segment coupling point A and the midpoint between B and C) 
         [0162]    The distances (z 1 , z 2 , z 3 ) of point A, point B, and point C, which are the tip positions of three electrodes of the position indicator, from the tablet sensor surface are almost inversely proportional to the received signal intensities V 1 , V 2 , and V 3 . Therefore, the relationships are represented as the following equation (21) and equation (22) with use of α as a proportionality coefficient. 
         [0163]    z 1 =α/V 1 , z 2 =α/V 2 , z 3 =α/V 3  therefore, θx and θy are represented as follows 
         [0000]    
       
         
           
             
               
                 
                   
                     θ 
                      
                     
                         
                     
                      
                     x 
                   
                   = 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
                      
                     
                       
                         α 
                          
                         
                           ( 
                           
                             
                               V 
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           ) 
                         
                       
                       
                         
                           r 
                           · 
                           V 
                         
                          
                         
                             
                         
                          
                         
                           2 
                           · 
                           V 
                         
                          
                         
                             
                         
                          
                         3 
                       
                     
                   
                 
               
               
                 
                   ( 
                   21 
                   ) 
                 
               
             
             
               
                 
                   
                     θ 
                      
                     
                         
                     
                      
                     y 
                   
                   = 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
                      
                     
                       
                         α 
                          
                         
                           ( 
                           
                             
                               
                                 2 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               
                                 2 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               
                                 1 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               3 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               
                                 1 
                                 · 
                                 V 
                               
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           ) 
                         
                       
                       
                         
                           r 
                           · 
                           V 
                         
                          
                         
                             
                         
                          
                         
                           1 
                           · 
                           V 
                         
                          
                         
                             
                         
                          
                         
                           2 
                           · 
                           V 
                         
                          
                         
                             
                         
                          
                         
                           3 
                           · 
                           
                             
                                 
                             
                           
                         
                          
                         3 
                       
                     
                   
                 
               
               
                 
                   ( 
                   22 
                   ) 
                 
               
             
           
         
       
     
         [0164]    Because α/r is a constant, obtaining this value in advance can obtain θx and θy from the above relationship equations. 
         [0165]    Although three electrodes of the position indicator are provided at the tip part of the chassis  36  in the present embodiment example, they may be provided on the core like in the first embodiment example. 
         [0166]    In the present embodiment example, rotation angle and tilt of the position indicator can be detected. Therefore, it is possible to shape the tip part in an asymmetric (non-symmetric) shape like those shown in  FIG. 21  for example; then, software may be used to generate (detect user input of) drawings according to the obtained rotation angle and tilt. 
         [0167]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.