Patent Publication Number: US-11029768-B2

Title: Position pointer with connector that electrically connects first circuitry and second circuitry while first housing and second housing are mated to each other

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. 119(a) to Japanese Patent Application No. 2012-212777, filed Sep. 26, 2012, which is incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a position pointer in a shape of a pen for use with a position detection apparatus, and particularly to an electronic ink cartridge accommodated in a housing of the position pointer. 
     Description of the Related Art 
     In recent years, a position inputting apparatus is used as an inputting device for a portable apparatus, a tablet type PC (personal computer) and so forth. The position inputting apparatus is configured of a position pointer, in the shape of a pen for example, and a position detection apparatus having an inputting face on which a pointing operation or inputting of symbols, figures and so forth using the position pointer is performed. As the position inputting apparatus of the type described, apparatus of various detection types such as an electromagnetic induction type and a capacitive coupling type have been known. 
     A recent position inputting apparatus includes a pressure sensor provided in a pen-shaped position pointer for sensing pressure applied to a core member serving as a pen tip so that the position pointer has a wring pressure detection function. Based on the writing pressure detection function, it can be detected whether or not a user places the position pointer into contact with the inputting face of the position detection apparatus (“pen down” operation) or with what writing pressure the user operates the position pointer on the inputting face after the pen down operation. 
     As the pressure sensor provided on the position pointer, pressure sensors of various sensing types are available including those of a type wherein pressure applied to the core member is sensed as a variation of the inductance, and those of another type wherein pressure applied to the core member is sensed as a variation of the capacitance. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2002-244806) discloses a position pointer which includes a pressure sensor which varies the inductance of a coil forming a resonance circuit. Pressure applied to a core member is transmitted as a variation of a resonance frequency (or a phase) of a resonance circuit to a position detection apparatus so that the wring pressure can be detected by the position detection apparatus. 
       FIG. 22  is a sectional view of a conventional position pointer  100  which detects the writing pressure from a variation of the inductance. As depicted in  FIG. 22 , the position pointer  100  is configured such that a ferrite core  104  on which a coil  105  is wound and a ferrite chip  102  are opposed to each other with an O-snap ring  103  interposed therebetween such that the ferrite chip  102  moves toward the ferrite core  104  when pressing pressure (writing pressure) is applied to a core member  101 . The O-snap ring  103  used here is a ring-shaped elastic member made of an elastic material such as synthetic resin or synthetic rubber and having a cross section of a shape of the alphabetical letter “O.” 
     In a case  111  of the position pointer  100 , a printed board  114 , a board holder  113 , connecting wires  116  and a buffer member  117  are accommodated in addition to the parts described above. The printed board  114  has a plurality of resonant capacitors  115   a  to  115   h  disposed thereon for setting a resonance frequency of a resonance circuit when no pressure is applied to the core member to a desire value. The board holder  113  holds the printed board  114 . The connecting wires  116  connect the coil  105  to the resonant capacitors  115   a  to  115   h  of the printed board  114  to configure a resonance circuit. The members accommodated in the case  111  are fixed at respective positions by a cap  112 . 
     If the ferrite chip  102 , against which the core member  101  abuts, moves toward the ferrite core  104  in response to pressing force applied to the core member  101 , then the inductance of the coil  105  wound on the ferrite core  104  varies in response to the movement of the ferrite core  104 . Thereupon, the phase (resonance frequency) of an electromagnetic induction signal transmitted from the coil  105  of the resonance circuit varies. The position detection apparatus receives the variation of the phase (resonance frequency) of the electromagnetic induction signal from the position pointer by a loop coil, to thereby detect the writing pressure applied to the core member of the position pointer. 
     Another type of position pointer is known which includes a pressure sensor, wherein the capacitance of a capacitor forming a resonance circuit is varied. In the position pointer, pressure applied to a core member is transmitted as a variation of the resonance frequency (or the phase) of the resonance circuit to a position detection apparatus. 
     For example, Patent Document 2 (Japanese Patent Laid-Open No. Hei 4-96212) discloses a position pointer which uses, as a capacitor which configures a resonance circuit, a variable capacitor the capacitance of which varies in response to pressure applied to a core member. In the position pointer, a variation of the capacitance of the variable capacitor is transmitted as a variation of the resonance frequency (or the phase) of the resonance circuit to a position detection apparatus so that the writing pressure can be detected by the position detection apparatus. 
     The variable capacitor described in Patent Document 2 includes two mechanical structural parts accommodated in an elongated tubular housing—a first conductive member attached to a first end face of cylindrical dielectric member, and a second conductive member disposed on a second end face side of the dielectric member opposite from the first end face and having flexibility such that the second conductive member can be displaced elastically. An opposing face of the second conductive member to the dielectric member is shaped so as to swell (bulge) toward the dielectric member side, for example, in a dome shape. 
     Further, the variable capacitor disclosed in Patent Document 2 includes spacer means for spacing the second conductive member and the second end face of the dielectric member from each other by a small distance except a portion thereof, and a part for applying relative pressure (or displacement) between the second conductive member and the dielectric member. The part which applies the relative pressure or displacement is coupled to the core member of the position pointer of a pen shape. If writing pressure is applied to the position pointer from the first end portion of the housing, then the flexible second conductive member is displaced toward the dielectric member side by force applied in an axial direction to the core member. Consequently, the second conductive member is biased so as to contact the second end face of the dielectric member. Then, the dome-shaped swelling end face of the flexible second conductive member contacts the second end face of the dielectric member over a contacting area corresponding to the pressing force. Therefore, the capacitance formed between the second conductive member and the first conductive member, with the dielectric member interposed therebetween, varies. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1 
     Japanese Patent Laid-Open No. 2002-244806 
     Patent Document 2 
     Japanese Patent Laid-Open No. Hei 4-96212 
     BRIEF SUMMARY 
     Problems to be Solved by the Invention 
     As described above, in the position pointer disclosed in Patent Document 1, such component parts as the core member  101 , ferrite chip  102 , O-snap ring  103 , ferrite core  104  on which the coil  105  is wound, printed board  114 , and board holder  113  which holds the printed board  114  are successively accommodated directly into the space on the inner side of the tubular housing  111  and assembled. Similarly, also in the position pointer disclosed in Patent Document 2, such component parts as a variable capacitor are successively accommodated directly into a space on the inner side of a tubular housing and assembled in addition to such component parts as a core member, a ferrite core on which a coil is wound, a printed board and a board holder which holds the printed board. 
     In this manner, in order to construct a position pointer, conventionally the parts described above must be successively assembled in a housing in the direction of a center axis, and there is a problem that the position pointers are not suitable for mass production. 
     Further, whichever one of a pressure sensor of the type wherein pressure applied to the core member is sensed as a variation of the inductance and another pressure sensor of the type wherein pressure applied to the core member is sensed as a variation of the capacitance is used, it is necessary to adjust the variation characteristic of the inductance or the capacitance with respect to applied pressure so that a detection characteristic or a writing pressure characteristic of a desired “pen down” can be obtained. However, it is conventionally necessary to adjust such characteristics after component parts are assembled in the housing of the position pointer, which is very cumbersome. 
     Besides, if the component parts accommodated in the housing are subject to positional displacement in the housing, then this gives rise to a variation of a circuit constant, resulting in the problem that there is the possibility that normal use of the position pointer may be disabled. For example, in the case of Patent Document 1, if the center axes of the ferrite chip  102  and the ferrite core  104  are displaced from each other or the like, then a circuit constant varies. Consequently, there is the possibility that the variation of the inductance by approaching movement of the ferrite chip  102  may be displaced (shifted) from a desired variation. Similarly, in the case of Patent Document 2, if the center axes of the flexible second conductive member and the dielectric member are displaced from each other or the like, then a circuit constant varies. Consequently, there is the possibility that the variation of the capacitance with respect to the pressure applied to the core member may be displaced from a desired variation. 
     Therefore, a possible solution may include a method of assembling a group of parts at a portion which is elastically biased, such as an O-snap ring and a conductive member, as a module in advance. However, in recent years, it is demanded for a position pointer of a shape of a pen to have a narrower (thinner) shape in view of miniaturization of a portable electronic apparatus such as a PDA or a highly-functional portable telephone terminal (smartphone). Thus, if the part group at the portion which is elastically biased is assembled in advance as a modularized part, then it becomes difficult to miniaturize the modularized part. Therefore, there is a problem that this provides a difficulty in thinning the position pointer of a shape of a pen. 
     Further, when a predetermined part group is assembled to produce a modularized part, time is required for the assembly. Accordingly, the worker must first take time to assemble the modularized part, then to combine the assembled modularized part with other parts into the case  111 . Therefore, another problem is that the productivity is low. 
     Taking the foregoing into consideration, an aspect of the present invention solves the problems described above with a position pointer which includes a pressure sensor that senses pressure applied to a core member. 
     Means for Solving the Problems 
     In order to solve the subject described above, the present invention provides an electronic ink cartridge including: 
     a tubular member including a hollow portion; 
     a core member disposed so as to extend outwardly from a distal end portion of the tubular member in a direction of a center axis of the tubular member; 
     a pressure sensor, which is accommodated in the hollow portion of the tubular member and which senses pressure applied to the core member; 
     a connection member, which is disposed to interpose the pressure sensor between the connection member and the core member along the direction of the center axis of the tubular member and which locks the pressure sensor to the tubular member in the direction of the central axis, wherein the pressure sensor is coupled to the connection member in the direction of the center axis of the tubular member to sense the pressure applied to the core member; and 
     a connection terminal, which is formed on a proximal end face of the connection member and from which an electric characteristic corresponding to the pressure sensed by the pressure sensor is extracted. 
     In the present specification, the term “electronic ink cartridge” is used to refer to a structure that accommodates at least the core member and the pressure sensor, from among the component parts of the position pointer, in the hollow portion of its tubular member, and that is to be accommodated in a housing of the position pointer. The electronic ink cartridge, wherein all of principal components of the position pointer are accommodated in the hollow portion of the tubular member, allows for assembly of the position pointer only by accommodating the electronic ink cartridge into the housing of the position pointer similarly to an ink cartridge of a writing-tool ballpoint pen. Therefore, in the present specification, the tubular member that accommodates therein parts or principal component parts of the position pointer of the electromagnetic induction type is referred to as electronic ink cartridge. 
     In the electronic ink cartridge according to the present invention which has such a configuration as described above, the pressure sensor is accommodated in the hollow portion of the tubular member, and the connection member is fixed to the tubular member on the second end side of the tubular member in the direction of the center axis. Accordingly, the pressure sensor disposed closer to the core member side than the connection member in the direction of the center axis of the tubular member is directly or indirectly coupled to the connection member in the direction of the center axis of the tubular member. Further, the pressure sensor is locked in the tubular member in the direction of the center axis of the tubular member so that it is acted upon by pressure applied to the core member from the first end portion side of the tubular member. Consequently, the pressure sensor accommodated in the tubular member senses the pressure applied to the core member, which is provided so as to extend outwardly from the first end portion side of the tubular member. 
     Accordingly, with the electronic ink cartridge according to the present invention, the pressure sensor is positioned by being accommodated in the tubular member, and when the electronic ink cartridge is accommodated in the housing of the position pointer, a stable and highly reliable electric characteristic can be maintained. 
     Further, in the electronic ink cartridge according to the present invention, a connection terminal, from which an electric characteristic corresponding to pressure applied to the core member and sensed by the pressure sensor can be extracted, is formed on the end face of the connection member on the opening side of the tubular member. This electric characteristic may be not only an electric characteristic of the pressure sensor itself, such as a pressure versus inductance characteristic where the pressure sensor is of the type which senses pressure applied to the core member as a variation of the inductance, or a pressure versus capacitance characteristic where the pressure sensor is of the type which senses pressure applied to the core member as a variation of the capacitance, but also may be other electric characteristics. For example, where the pressure sensor is configured to sense inductance or capacitance which forms a resonance circuit, a resonance frequency versus pressure characteristic of the resonance circuit can be extracted to the connection terminal of the connection member. 
     Further, other electronic circuit connected to the pressure sensor, such as an IC or other components of a resonance circuit that includes the pressure sensor as a component thereof, can be connected readily to the connection terminal provided on the end face of the connection member. In this instance, since it is also easy to connect the components of the IC or the resonance circuit in a juxtaposed relationship in the direction of the center axis of the tubular member, this further contributes to narrowing (thinning) of the position pointer. 
     Further, by incorporating only the electronic ink cartridge according to the present invention or the electronic ink cartridge and peripheral parts necessary for the electronic ink cartridge into the housing of a shape of a pen, the position pointer according to the present invention can be configured. Accordingly, mass production of the position pointer is facilitated. 
     Effect of the Invention 
     By using the electronic ink cartridge according to the present invention, since fabrication of the position pointer is facilitated, the mass productivity can be improved and the reliability of a characteristic of the pressure sensor can be assured. Further, by using the electronic ink cartridge according to the present invention, it is also possible to achieve thinning of the position pointer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are views depicting an electronic ink cartridge according to a first embodiment of the present invention. 
         FIGS. 2A to 2C  are views depicting a configuration of a position pointer according to an embodiment in which the electronic ink cartridge according to the embodiment is incorporated. 
         FIGS. 3A to 3C  are views depicting an example of components of the electronic ink cartridge according to the first embodiment. 
         FIG. 4  is a view depicting an example of components of the electronic ink cartridge according to the first embodiment. 
         FIGS. 5A to 5C  are views depicting an example of components of the electronic ink cartridge according to the first embodiment. 
         FIG. 6  is a circuit diagram depicting an example of an equivalent circuit of the electronic ink cartridge according to the first embodiment. 
         FIG. 7  is a view depicting an equivalent circuit of the position pointer which includes the electronic ink cartridge according to the first embodiment together with a position detection apparatus. 
         FIG. 8  is a view depicting a modification to the electronic ink cartridge of the first embodiment. 
         FIGS. 9A and 9B  are views depicting an electronic ink cartridge according to a second embodiment of the present invention. 
         FIGS. 10A to 10D  are views depicting an example of components of the electronic ink cartridge according to the second embodiment. 
         FIGS. 11A to 11C  are views depicting an example of components of the electronic ink cartridge according to the second embodiment. 
         FIG. 12  is a view depicting an equivalent circuit of a position pointer which includes the electronic ink cartridge according to the second embodiment together with a position detection apparatus. 
         FIG. 13  is a view depicting a flow chart illustrating processing operation of part of the position pointer of the second embodiment according to the present invention. 
         FIG. 14  is a view depicting a flow chart illustrating processing operation of part of the position detection apparatus which is used together with the position pointer of the second embodiment according to the present invention. 
         FIGS. 15A and 15B  are views depicting an electronic ink cartridge according to a third embodiment of the present invention. 
         FIGS. 16A and 16B  are views depicting an example of components of the electronic ink cartridge according to the third embodiment. 
         FIGS. 17A to 17C  are views depicting an example of components of the electronic ink cartridge according to the third embodiment. 
         FIGS. 18A to 18C  are views depicting an example of components of the electronic ink cartridge according to the third embodiment. 
         FIG. 19  is a circuit diagram depicting an example of an equivalent circuit of the electronic ink cartridge according to the third embodiment. 
         FIG. 20  is a view depicting a modification to the electronic ink cartridge of the third embodiment. 
         FIG. 21  is a view depicting an electronic ink cartridge according to a fourth embodiment. 
         FIG. 22  is a view depicting an example of a configuration of a conventional position pointer of the electromagnetic induction type. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A first embodiment is directed to a position pointer of the electromagnetic induction type, to which an electronic ink cartridge according to the present invention is applied. As an example of a pressure sensor, the inductance which configures a resonance circuit provided in a position pointer of the electromagnetic induction type is of the type which varies in response to pressure applied to a core member. In the present first embodiment, the pressure sensor which varies the inductance which configures a resonance circuit has a configuration similar to that of the conventional example described hereinabove with reference to  FIG. 22 . 
       FIGS. 1A to 8  are views depicting an electronic ink cartridge according to a first embodiment of the present invention and an example of a configuration of a position pointer in which the electronic ink cartridge of the first embodiment is used. 
     The position pointer of the first embodiment includes a push switch which is operable in a state in which a user grasps a housing of the position pointer and has a configuration which can change the resonance frequency of a resonance circuit by on/off operation of the push switch. It is to be noted that this push switch is provided at a position proximate to a core member on a peripheral portion of the housing and is also called a side switch. It is to be noted that an on/off operation of the push switch is detected in such a manner as hereinafter described by a position detection apparatus. However, the push switch is allocated to various functions such as, for example, a determination operation input on an electronic apparatus such as a personal computer, in which the position detection apparatus is built, or to which the position detection apparatus is externally connected. 
       FIG. 2A  shows an outline of a general configuration of a position pointer  1  of the present first embodiment. The position pointer  1  has a shape of a pen and includes a cylindrical housing  2 , and component parts of the position pointer  1  are accommodated in an internal space of the housing  2 . In  FIG. 2A , only the housing  2  of the position pointer  1  is depicted in cross-section in order to facilitate understandings of an internal configuration of the housing  2 . 
     The housing  2  of the position pointer  1  of the present first embodiment is made of non magnetic material, for example, resin and configured from a cylindrical lower half  3  having an opening  3   a  on the pen tip side of the housing  2 , and a cylindrical upper half  4  fitted with and coupled to the lower half  3  concentrically. 
     In the inside of the lower half  3 , a hollow portion  3   b  having, for example, a circular sectional shape is provided, and an electronic ink cartridge  10  wherein basic component parts of the position pointer of the electromagnetic induction type are accommodated in a tubular member  5  as depicted in  FIG. 1A  is disposed in the hollow portion  3   b . Further, a through-hole  3   d  is perforated at a portion of a peripheral side face of the lower half  3 , and a pressing element  8  is provided in the through-hole  3   d . Consequently, a push switch  7  provided below the pressing element  8  can be depressed by the pressing element  8 . Details of an internal configuration of the position pointer  1  are hereinafter described. 
     Example of the Configuration of the Electronic Ink Cartridge  10   
     An example of a configuration of the electronic ink cartridge  10  of the present first embodiment is described with reference to  FIGS. 1A and 1B , and  FIGS. 3A to 6 .  FIG. 1A  is a sectional view depicting an internal configuration of the electronic ink cartridge  10 . The electronic ink cartridge  10  of the present example is configured such that basic component parts of the position pointer of the electromagnetic induction type are accommodated in the hollow portion of the tubular member  5 . In particular, a core member  11 , a coil  16  having variable inductance, and a capacitor circuit  18  including a capacitor which cooperates with the coil  16  to configure a resonance circuit are accommodated in the hollow portion of the tubular member  5 . The diameter (inner diameter) of the hollow portion of the tubular member  5  is fixed. Further, in the present example, also the outer diameter of the tubular member  5  is fixed. The tubular member  5  is configured from a nonmagnetic material such as nonmagnetic metal, resin material, glass or ceramics, in the present example, from SUS305 or SUS310S. Further, as shown in  FIGS. 2A to 2C , the tubular member  5  is accommodated in a state in which the direction of the center axis thereof coincides with the direction of the center axis of the housing  2  of the position pointer  1 . 
     It is to be noted that, for the convenience of description, some of the internal component parts of the tubular member  5  of the electronic ink cartridge  10  (a connection member  17  and the capacitor circuit  18  hereinafter described) are not depicted in cross-section in  FIG. 1A , but a cross-sectional view of them is prepared separately as hereinafter described. Meanwhile,  FIG. 1B  is an exploded perspective view depicting a general configuration of the electronic ink cartridge  10 . 
     The tubular member  5  in the present first embodiment is configured from a first tubular member  5 A and a second tubular member  5 B as two separate members separate from each other in the direction of the center axis. In the present example, the first tubular member  5 A and the second tubular member  5 B have a narrow shape such that the outer diameter thereof is, for example, 2.5 mm and the inner diameter thereof is 1.5 mm to 2 mm. 
     An opening  5 Aa that allows a distal end of the core member  11  to extend outwardly therethrough is provided on a first end side of the first tubular member  5 A in the direction of the center axis (axial direction). The diameter of the opening  5 Aa is smaller than the inner diameter of the first tubular member  5 A, and therefore, a stepped portion  5 As is formed on the first end side of the first tubular member  5 A in the direction of the center axis. On the other hand, a second end side of the first tubular member  5 A in the direction of the center axis is formed to have the entire inner diameter thereof as an opening  5 Ab. Meanwhile, the second tubular member  5 B has an opening corresponding to the entire inner diameter thereof at each of the opposite end sides thereof in the direction of the center axis. 
     Further, as depicted in  FIG. 1A , on the outer circumference side face of the opening  5 Ab of the first tubular member  5 A, a threaded portion  5 Ac is formed which engages with a threaded portion  5 Ba formed on an inner wall face of the opening of the second tubular member  5 B on the first end side. Further, on an inner wall face of the second tubular member  5 B in the proximity of the opening on the second end side, a ring-shaped protrusion  5 Bb which fits with a ring-shaped grooved portion  19   a  formed on an outer periphery of a cap  19  made of nonmagnetic material, for example, resin, is formed, for example, by constricting the second tubular member  5 B at the position. 
     Further, as shown in  FIG. 1B , at a predetermined position of the second tubular member  5 B in a circumferential direction of the opening end on the second end side, a cut-out  5 Bc for positioning is formed along the direction of the center axis. Further, a protrusion  19   c  which engages with the cut-out  5 Bc of the second tubular member  5 B is formed on the cap  19 . The cap  19  is locked in the second tubular member  5 B by forcing the protrusion  19   c  into the second tubular member  5 B to be inserted into the cut-out  5 Bc so that the ring-shaped grooved portion  19   a  and the ring-shaped protrusion  5 Bb are fitted with each other. 
     Further, as depicted in  FIGS. 1A and 1B , a coil spring  12 , the core member  11 , a ferrite chip  13  as an example of a second magnetic member, an O-snap ring  14 , a ferrite core  15  as an example of a first magnetic member on which the coil  16  is wound, and the connection member  17  are accommodated in a juxtaposed relationship in this order as viewed from the opening  5 Aa in the first tubular member  5 A such that the center axis of the parts may coincide with each other. 
     The core member  11  in the present embodiment is configured, for example, from resin and has a distal end portion of a diameter extending from the opening  5 Aa of the first tubular member  5 A and a flange portion  11   a . The core member  11  further has a protrusion  11   b  provided substantially at the center of an upper face of the flange portion  11   a . The flange portion  11   a  has a diameter a little smaller than the inner diameter of the first tubular member  5 A so that it can move in the direction of the center axis in the first tubular member  5 A. 
     The ferrite chip  13  has a cylindrical shape of a diameter a little smaller than the inner diameter of the first tubular member  5 A so that it can move in the direction of the center axis in the first tubular member  5 A. Further, the ferrite chip  13  has, on an end face thereof on the core member  11  side in the direction of the center axis, a recessed portion  13   a  into which the protrusion  11   b  formed on the upper face of the flange portion  11   a  of the core member  11  is fitted. The core member  11  is adhered to the ferrite chip  13  by bonding agent or the like in a state in which the protrusion  11   b  and the recessed portion  13   a  fit with each other. Further, a protrusion  13   b  is formed at the center of an end face of the ferrite chip  13  on the ferrite core  15  side in the direction of the center axis. 
     The O-snap ring  14  is configured from an elastic member, for example, an elastic rubber which has an outer diameter smaller than the inner diameter of the first tubular member  5 A and has an inner diameter greater than the diameter of the protrusion  13   b . In this instance, the O-snap ring  14  has a circular cross section having a diameter selected so as to be greater than the height of the protrusion  13   b  of the ferrite chip  13 . 
     The ferrite core  15  has a cylindrical shape, and the diameter thereof including the wound coil  16  is a little smaller than the inner diameter of the first tubular member  5 A. A recessed portion  15   a , into which a positioning protrusion  17   c  at a position of the center axis formed on the connection member  17  is to be fitted, is formed on an end face of the ferrite core  15  on the connection member  17  side in the direction of the center axis. 
     The connection member  17  mechanically connects the ferrite core  15  and the capacitor circuit  18  to each other and establishes electric connection between the coil  16  wound on the ferrite core  15  and the capacitors of the capacitor circuit  18 . 
       FIGS. 3A to 3C  are views depicting an example of a configuration of the connection member  17 .  FIG. 3A  is a view of the connection member  17  as viewed from the side on which the connection member  17  is connected to the ferrite core  15 , and  FIG. 3B  is a sectional view taken along line B-B of  FIG. 3A . Further,  FIG. 3C  is a view of the connection member  17  as viewed from the side on which the connection member  17  is connected to the capacitor circuit  18 . 
     As depicted in  FIGS. 3A and 3B , the connection member  17  is formed by insert molding terminal members  172  and  173  formed from conductive material having elasticity for establishing electric connection between a first end  16   a  and a second end  16   b  of the coil  16  and the first end and the second end of the capacitor circuit  18  in a main body portion  171 . The main body portion is formed from a nonmagnetic member, in the present example, from resin, having a cylindrical shape having an outer diameter substantially equal to the inner diameter of the first tubular member  5 A. 
     Ring-shaped recessed grooves  17   a  and  17   b  are formed at predetermined positions of an outer peripheral face of the main body portion  171  of the connection member  17 . Meanwhile, as shown in  FIG. 1A , ring-shaped protrusions  5 Ad and  5 Ae are formed by constricting the first tubular member  5 A at positions thereof relative to which the ring-shaped recessed grooves  17   a  and  17   b  are positioned when the connection member  17  is accommodated therein, such that they project to the inner wall face side of the first tubular member  5 A. If the connection member  17  is inserted into the first tubular member  5 A in the direction of the center axis, then the connection member  17  is fixed to the first tubular member  5 A by fitting engagement between the ring-shaped recessed grooves  17   a  and  17   b  on the outer peripheral face of the connection member  17  and the ring-shaped protrusions  5 Ad and  5 Ae on the inner wall face of the first tubular member  5 A. 
     Further, the positioning protrusion  17   c  described hereinabove is formed at the center of an end face of the main body portion  171  of the connection member  17  on the ferrite core  15  side. In the present example, the protrusion  17   c  has a shape of a quadrangular prism. The ferrite core  15  and the connection member  17  are coupled to each other by fitting the protrusion  17   c  of the connection member  17  into the recessed portion  15   a  formed on the end face of the ferrite core  15  and adhering the end face of the ferrite core  15  and the flat face of the main body portion  171  of the connection member  17  to each other, for example, by bonding agent. 
     Further, as depicted in  FIG. 3A , recessed grooves  174  and  175  are formed at positions of a peripheral side face of the main body portion  171  of the connection member  17  spaced by an angular distance of 180 degrees from each other such that they extend in the direction of the center axis of the cylinder. First end portions  172   a  and  173   a  of the terminal members  172  and  173  are erected uprightly in the recessed grooves  174  and  175  in a direction perpendicular to the peripheral direction, respectively. Further, at the first end portions  172   a  and  173   a  of the terminal members  172  and  173  erected uprightly in this manner, V-shaped notches  172   b  and  173   b  are formed as depicted in  FIG. 3A . 
     Thus, the first end  16   a  of the coil  16  is force fitted into the V-shaped notch  172   b  of the first end portion  172   a  of the terminal member  172  so as to establish electric connection therebetween as depicted in  FIG. 3B . Further, the second end  16   b  of the coil  16  is force fitted into the V-shaped notch  173   b  at the first end portion  173   a  of the terminal member  173  to establish electric connection therebetween. The ferrite core  15  having the coil  16  wound thereon and the connection member  17  connected to each other in this manner can be handled as one ferrite core module. It is to be noted that the first end  16   a  and the second end  16   b  of the coil  16  are connected to the first end portions  172   a  and  173   a  of the terminal members  172  and  173  erected uprightly in the recessed grooves  174  and  175  of the connection member  17  without extending outwardly from the outer peripheral face of the connection member  17 . Accordingly, the first end  16   a  and the second end  16   b  of the coil  16  are not brought into contact with the inner wall face of the first tubular member  5 A. 
     The second end portion of the terminal member  172  of the connection member  17  is formed as a ring-shaped electrode conductor  172   c  at an end face thereof opposing the end face of the capacitor circuit  18  as depicted in  FIGS. 3B and 3C . Further, at the center of the end face of the connection member  17  opposing the end face of the capacitor circuit  18 , a recessed hole  17   d  is formed at a position spaced apart from the ring-shaped electrode conductor  172   c , as depicted in  FIGS. 3B and 3C . 
     A second end portion  173   c  of the terminal member  173  of the connection member  17  is positioned in the recessed hole  17   d . At the portion of the second end portion  173   c  of the terminal member  173  which is positioned in the recessed hole  17   d , which portion corresponding to a bent portion of the terminal member  173  having elasticity, an insertion hole  173   d  is formed. The ring-shaped electrode conductor  172   c  at the second end portion of the terminal member  172  and the second end portion  173   c  of the terminal member  173  configured in such a manner as described above are provided for connection between first and second terminals of the capacitor circuit  18  as hereinafter described. 
     Accommodation of the Component Parts into the First Tubular Member  5 A of the Electronic Ink Cartridge  10   
     The component parts are assembled and accommodated into the first tubular member  5 A of the electronic ink cartridge  10  in the following manner. 
     Referring to  FIG. 1B , the connection member  17  and the ferrite core  15  on which the coil  16  is wound are connected to each other first. In particular, the protrusion  17   c  at the position of the center axis formed on the connection member  17  and the recessed portion  15   a  formed on the ferrite core  15  are fitted with each other. Further, the first end  16   a  and the second end  16   b  of the coil  16  wound on the ferrite core  15  are connected to the first end portions  172   a  and  173   a  of the terminal members  172  and  173  provided on the connection member  17 , respectively. 
     Then, the recessed portion  13   a  formed on the ferrite chip  13  and the protrusion  11   b  formed on the upper face of the flange portion  11   a  of the core member  11  are fitted with each other, and the coil spring  12  is mounted on the tip end side of the core member  11 . Further, the O-snap ring  14  is disposed around the protrusion  13   b  of the ferrite chip  13 , and the core member  11  and the ferrite chip  13  are inserted into the hollow portion of the first tubular member  5 A in the direction of the center axis from the opening  5 Ab side toward the distal end on the opening  5 Aa side. The core member  11  extends on the distal end side thereof outwardly from the opening  5 Aa of the first tubular member  5 A in a state in which it is normally biased toward the opposite side from the distal end side. 
     Then, the connection member  17  and the ferrite core  15  having the coil  16  wound thereon, which are connected to each other, are inserted in the direction of the center axis into the first tubular member  5 A in such a manner that the ferrite core  15  is opposed to the ferrite chip  13  with the O-snap ring  14  interposed therebetween. At this time, the ring-shaped recessed grooves  17   a  and  17   b  on the outer peripheral face of the connection member  17  are fitted with the ring-shaped protrusions  5 Ad and  5 Ae provided on the inner wall face of the first tubular member  5 A to fix the connection member  17  to the first tubular member  5 A. In the present embodiment, the coil spring  12  is disposed on the distal end side of the core member  11  in the hollow portion of the first tubular member  5 A in such a state that it engages at the first end thereof with the stepped portion  5 As on the distal end side of the core member  11  in the hollow portion of the first tubular member  5 A. Therefore, the flange portion  11   a  of the core member  11 , ferrite chip  13  and O-snap ring  14  on the second end side of the coil spring  12  are normally biased toward the connection member  17  side fixed to the first tubular member  5 A by the elastic biasing force of the coil spring  12 . Consequently, rattling of the members is prevented. 
     In this state, the end face of the connection member  17  on the opposite side from the joining portion to the ferrite core  15  is exposed through the opening  5 Ab of the first tubular member  5 A. Accordingly, the ring-shaped electrode conductor  172   c  of the terminal member  172  formed on the end face of the connection member  17  and the second end portion  173   c  of the terminal member  173  are exposed through the opening  5 Ab and can be contacted from the outside (refer to  FIGS. 1A and 1B , and  FIG. 3C ). 
     It is to be noted that the ring-shaped protrusions  5 Ad and  5 Ae on the inner wall face of the first tubular member  5 A are formed at such positions that the end face of the connection member  17  on the side it is coupled to the capacitor circuit  18  lies flush with the end face of the opening  5 Ab of the first tubular member  5 A. 
     In the present embodiment, a pressure sensor which senses pressure applied to the core member  11  is configured from the ferrite chip  13 , O-snap ring  14 , and ferrite core  15  on which the coil  16  is wound. The ring-shaped electrode conductor  172   c  of the terminal member  172  and the second end portion  173   c  of the terminal member  173  both formed on the end face of the connection member  17  exposed at the opening  5 Ab are connected to the first end  16   a  and the second end  16   b  of the coil  16  wound on the ferrite core  15  as described hereinabove, respectively. The ring-shaped electrode conductor  172   c  and the second end portion  173   c  are connection terminals for establishing electric connection between the first end  16   a  and the second end  16   b  of the coil  16  and the first end and the second end of the capacitor circuit  18 , respectively. 
     Accordingly, the ring-shaped electrode conductor  172   c  of the terminal member  172  and the second end portion  173   c  of the terminal member  173  as the connection terminals formed on the end face of the connection member  17  exposed at the opening  5 Ab exhibit an inductance value, which varies in response to pressure applied to the core member  11 , as an electric characteristic of the pressure sensor. 
     Therefore, the inductance value of the coil  16  can be measured by electrically contacting probe terminals connected to an inductance measuring instrument with the ring-shaped electrode conductor  172   c  of the terminal member  172  and the second end portion  173   c  of the terminal member  173  provided on the end face of the connection member  17 . It is to be noted that the inductance of the coil  16  measured by the inductance measuring instrument in this instance is that in a state in which no pressing force is applied to the core member  11 . 
     Then, by determining the value of the capacitance of the capacitor circuit  18  in response to the measured inductance value of the coil  16 , the resonance frequency of the resonance circuit configured from the coil  16  and the capacitor circuit  18  can be set to a desired value. In particular, even if the inductance value of the coil  16  has some dispersion, the resonance frequency of the resonance circuit configured from the coil  16  and the capacitor circuit  18  can be set to a desired frequency by determining (setting) the capacitance of the capacitor circuit  18  in accordance with the inductance values of such coils  16 . 
     The dispersion of the inductance value of the coil  16  is compensated for by the value of the capacitance set to the capacitor circuit  18  in such a manner as described above. The capacitor circuit  18  having the capacitance value set so that a desired resonance frequency is obtained is connected to the connection member  17  in the direction of the center axis as shown in  FIGS. 1A and 1B . Then, in a state in which the capacitor circuit  18  is accommodated, the second tubular member  5 B is screwed with the first tubular member  5 A at the threaded portions  5 Ac and  5 Ba. Then, the cap  19  is inserted into the second tubular member  5 B and then the opening of the second tubular member  5 B is closed up, whereby the assembly of the tubular member  5  is completed. 
     Now, a configuration of the capacitor circuit  18  is described.  FIG. 4  is a view depicting an example of a configuration of the capacitor circuit  18  in the present embodiment. 
     In the present first embodiment, the capacitor circuit  18  includes a configuration wherein a first capacitor circuit  181  and a second capacitor circuit  182  are coupled to each other in the direction of the center axis as depicted in  FIGS. 1A and 1B , and  FIG. 4 . The first capacitor circuit  181  is connected, when the push switch is in one state, for example, in an off state, in parallel to the coil  16  to configure a resonance circuit. Meanwhile, the second capacitor circuit  182  is connected, when the push switch is in an on state, in parallel to the coil  16  and the first capacitor circuit  181  to configure a resonance circuit. The values of the capacitance of the first capacitor circuit  181  and the second capacitor circuit  182  are set in order to set the resonance frequencies of the resonance circuits configured by them to desired frequencies. 
     The first capacitor circuit  181  and the second capacitor circuit  182  are connected in parallel to each other such that a plurality of chip capacitors  183  are stacked and accommodated in the inside of tubular holders  1810  and  1820  made of, for example, resin as depicted in  FIG. 4 . 
     In the case of the present example, for each of the chip capacitors  183 , a multilayer ceramic capacitor disclosed, for example, in Japanese Patent Laid-Open No. 2009-124155 is used. Each of the chip capacitors  183  of the present example is formed in a shape of a parallelepiped, and a first electrode  184  and a second electrode  185  of each chip capacitor  183  are formed on its end faces opposing each other and extending perpendicularly to the stacking direction of the capacitors in an exposed state across the entire length in the stacking direction, as indicated in solid black in  FIG. 4 . 
     Accordingly, by stacking the chip capacitors  183 , the first electrodes  184  and the second electrodes  185  of all of the stacked number of chip capacitors are connected to each other, and the chip capacitors  183  are connected in parallel to each other. The values of capacitance of the first capacitor circuit  181  and the capacitance of the second capacitor circuit  182  are each set by the value of the capacitance of each of the chip capacitors  183  accommodated in the holders  1810  and  1820 , respectively, and the number of the chip capacitors  183  accommodated therein. 
     It is to be noted that the depth of the hollow portions  1811  and  1821  of the holders  1810  and  1820 , namely, the number of stacked chip capacitors  183 , is set in view of the degree in dispersion of the inductance value of the coil  16  described hereinabove. Then, when the number of chip capacitors  183  accommodated in the hollow portions  1811  and  1821  does not satisfy a predetermined number as a result of optimization of the value of the capacitance by stacking the chip capacitors  183 , in the present example, a dummy chip capacitor or capacitors having substantially no capacitance are accommodated so that the number of chip capacitors  183  in the hollow portions  1811  and  1821  is always equal to the predetermined number. 
     In the case of the present example, on the opening side of the hollow portions  1811  and  1821  of the holders  1810  and  1820 , elastically deformable pawl portions  1812 ,  1813  and  1822 ,  1823  are formed such that they project from wall faces of the holders  1810  and  1820  opposing each other toward the hollow portions  1811  and  1821  side, respectively. The chip capacitors  183  elastically deforms the pawl portions  1812 ,  1813  and  1822 ,  1823  to ride over them until they are accommodated into the hollow portions  1811  and  1821 , respectively. Then, the pawl portions  1812 ,  1813  and  1822 ,  1823  engage with an upper face of the uppermost ones of the chip capacitors  183  accommodated in the hollow portions  1811  and  1821  to lock the chip capacitors  183  entirely in the hollow portions  1811  and  1821 , respectively. 
     On the holder  1810  of the first capacitor circuit  181 , paired terminal members  1814  and  1815  are provided in such a manner as to extend through the holder  1810  between the opposite end faces in the direction of the center axis as indicated by broken lines in  FIG. 4 . The terminal member  1814  is provided in such a manner as to connect to the first electrode  184  of all of the chip capacitors  183  accommodated in the hollow portion  1811 . Meanwhile, the terminal member  1815  is provided in such a manner as to connect to the second electrode  185  of all of the chip capacitors  183  accommodated in the hollow portion  1811 . 
     A first end  1814   a  of the terminal member  1814  is led out to the end face side opposing the connection member  17  and is abutted against and electrically connected to the ring-shaped electrode conductor  172   c  at the second end of the terminal member  172  of the connection member  17  as indicated by a broken line in  FIG. 4 . Meanwhile, a second end  1814   b  of the terminal member  1814  is provided such that it is bent to the outer side with respect to the hollow portion  1811  on the end face side opposing the second capacitor circuit  182  as depicted in  FIG. 4 . 
     Then, a first end  1815   a  of the terminal member  1815  is led out as a rod-like member projecting from a central portion of the end face opposing the connection member  17 , and is inserted into the insertion hole  173   d  formed in the connection member  17  to be electrically connected to the end portion  173   c  of the terminal member  173  as depicted in  FIG. 4 . Meanwhile, a second end  1815   b  of the terminal member  1815  is provided such that it is bent to the outer side with respect to the opening of the hollow portion  1811  on the end face side opposing the second capacitor circuit  182  as depicted in  FIG. 4 . 
     On the holder  1820  of the second capacitor circuit  182 , terminal members  1824  and  1825  are provided such that they extend through the holder  1820  between the opposite end faces in the direction of the center axis as indicated by broken lines in  FIG. 4 . A further (third) terminal member  1826  is provided on the holder  1820 . 
     The terminal member  1824  is provided such that it is connected to the first electrode  184  of all of the chip capacitors  183  accommodated in the hollow portion  1821 . The terminal member  1825  is provided such that it extends through the holder  1820  between the opposite end faces in the direction of the center axis without being connected to the chip capacitors  183  in the hollow portion  1821 . Further, the terminal member  1826  is provided such that it is connected to the second electrode  185  of all of the chip capacitors  183  accommodated in the hollow portion  1821 . However, first end of the terminal member  1826  exists in the holder  1820  and is not exposed to the outside while only the second end of the terminal member  1826  is exposed to the outside. 
     A first end  1824   a  of the terminal member  1824  is led out to the end face side opposing the first capacitor circuit  181  as indicated by a broken line in  FIG. 4  and is abutted against and electrically connected to the second end  1814   b  of the terminal member  1814  of the first capacitor circuit  181 . Meanwhile, a second end  1824   b  of the terminal member  1824  is provided such that it is bent to the outer side with respect to the opening of the hollow portion  1821  on the end face side opposing the end face of the cap  19  as depicted in  FIG. 4 . 
     A first end  1825   a  of the terminal member  1825  is led out to the end face side opposing the first capacitor circuit  181  as indicated by a broken line in  FIG. 4  and is abutted against and electrically connected to the second end  1815   b  of the terminal member  1815  of the first capacitor circuit  181 . Meanwhile, a second end  1825   b  of the terminal member  1825  is provided such that it is led out and exposed to a side portion of the opening of the hollow portion  1821  on the end face side opposing the cap  19  as depicted in  FIG. 4 . 
     A second end  1826   b  of the terminal member  1826  connected to the second electrode  185  of all of the chip capacitors  183  accommodated in the hollow portion  1821  is provided such that it is bent to the outer side with respect to the opening of the hollow portion  1821  on the end face side opposing the end face of the cap  19  as depicted in  FIG. 4 . 
     Further, a protrusion  182   a  is formed at a predetermined position of an outer peripheral portion of the holder  1820  of the second capacitor circuit  182  such that it extends along the direction of the center axis. The protrusion  182   a  is provided for positioning the second capacitor circuit  182  in a peripheral direction in the second tubular member  5 B. The cut-out  5 Bc is formed in the second tubular member  5 B in the direction of the center axis from the opening end on the second end side of the second tubular member  5 B as described hereinabove. The protrusion  182   a  of the second capacitor circuit  182  is inserted in the cut-out  5 Bc to position the second capacitor circuit  182  in the peripheral direction. 
     Further, on the end face of the holder  1810  of the first capacitor circuit  181  opposing the holder  1820  of the second capacitor circuit  182 , fitting recessed holes  1816  and  1817  are formed as depicted in  FIG. 4 . On the end face of the holder  1820  of the second capacitor circuit  182  opposing the holder  1810  of the first capacitor circuit  181 , though not shown, protrusions are formed for fitting with the fitting recessed holes  1816  and  1817  of the holder  1810 . 
     In this instance, though not shown, the fitting recessed holes  1816  and  1817  of the holder  1810  are bent in an L shape, and the protrusions of the holder  1820  are bent at an end thereof in an L shape. Consequently, if the protrusions of the holder  1820  are fitted into the fitting recessed holes  1816  and  1817  of the holder  1810 , then the protrusions of the holder  1820  are elastically biased and inserted into the fitting recessed holes  1816  and  1817 . As a result, the first capacitor circuit  181  and the second capacitor circuit  182  are connected to each other by the bent portions of the protrusions of the holder  1820  and the fitting recessed portions  1816  and  1817  so that the coupling therebetween may not be undone easily. 
     After a value of the inductance of the coil  16  accommodated in the first tubular member  5 A is measured in such a manner as described above, a value of the capacitance, which forms a parallel resonance circuit with the coil  16  having the inductance to provide a desired resonance frequency, is calculated. Then, the plurality of chip capacitors  183  are accommodated into the holder  1810  of the first capacitor circuit  181  so that the calculated capacitance value may be obtained. 
     After the value of the capacitance of the first capacitor circuit  181  is set based on the measured value of the inductance so that a desired resonance frequency may be obtained, the value of the capacitance of the second capacitor circuit  182  is set. The value of the capacitance of the first capacitor circuit  181  can be set from the measured value of the inductance of a desired resonance frequency when the push switch (side switch)  7  is not operated (in one of a switch off state and a switch on state). 
     On the other hand, the value of the capacitance of the second capacitor circuit  182  is set in order that a desired resonance frequency is obtained when the push switch (side switch)  7  is operated (in the other of the switch off state and the switch on state). The value depends on the measured value of the inductance and the value of the capacitance of the first capacitor circuit  181 . 
     In particular, the inductance of the coil accommodated in the first tubular member  5 A is measured in the same state as an actual use state. Since the resonance frequency of the resonance circuit configured from the coil  16  and the first capacitor circuit  181  is known, the value of the capacitance of the first capacitor circuit  181  can be calculated. Accordingly, as the capacitance value of the first capacitor circuit  181 , a value equal to or proximate to the calculated value of the capacitance is set. 
     Further, since the resonance frequency after transition by operating the push switch (side switch)  7  is known, also the value of the capacitance which the second capacitor circuit  182  to be connected in parallel to the first capacitor circuit  181  should have can be calculated depending upon the measured value of the inductance and the value of the capacitance of the first capacitor circuit  181 . 
     This is described more particularly. The inductance of the coil accommodated in the first tubular member  5 A in the same state as an actual use state is represented by L 1 ; the resonance frequency when the push switch  7  is not operated is represented by f 1 ; and the capacitance of the first capacitor circuit  181  is represented by C 1 . In this instance,
 
since  f 1=1/{2·π·( L 1· C 1) 1/2 },
 
the capacitance C 1  is calculated as
 
 C 1=1/{4·π 2   ·f 1 2   ·L 1)}
 
     In particular, since the resonance frequency is f 1  and the inductance of the coil accommodated in the first tubular member  5 A in a state same as an actual use state is measured as L 1 , the capacitance C 1  of the first capacitor circuit  181  can be calculated. Further, if the value actually set as the capacitance of the first capacitor circuit  181  is C 11  proximate to C 1  by measurement of the capacitance, then where the resonance frequency when the push switch  7  is operated is represented by f 2  and the capacitance of the second capacitor circuit  182  by C 2 , then the resonance frequency f 2  is given as
 
 f 2=1/{2·π·( L 1·( C 11+ C 2)) 1/2 },
 
and the value C 2  to be set as the capacitance of the second capacitor circuit  182  is calculated as
 
 C 2=1/{4·π 2   ·f 2 2   ·L 1}− C 11
 
       FIGS. 5A to 5C  show an example of a configuration of the cap  19 .  FIG. 5A  is a view of the cap  19  as viewed from the face side opposing the capacitor circuit  18 , and  FIG. 5B  is a sectional view taken along line C-C of  FIG. 5A . Further,  FIG. 5C  is a view of the cap  19  as viewed from the side opposite from said face side opposing the capacitor circuit  18 . 
     The cap  19  is provided such that terminal members  192  and  193  made of dielectric material are insert-molded on a main body  191  made of nonmagnetic material, in the present example, made of resin. The cap  19  includes a connector  194  with which a distal end of a flexible lead portion  9  led out from a push switch  7  hereinafter described is fitted. 
     As depicted in  FIGS. 1A and 1B , and  FIG. 5C , the main body  191  of the cap  19  generally has a cylindrical shape. The face side of the main body  191  opposing the capacitor circuit  18  is formed as a reduced diameter portion  195  having a diameter such that the reduced diameter portion  195  is inserted into the second tubular member  5 B of the electronic ink cartridge  10 . While, the other portion of the main body  191  is formed as an increased diameter portion  196  having a diameter greater than the outer diameter of the tubular member  5 . A portion of the increased diameter portion  196  of the cap  19  on the opposite side from the side opposing the capacitor circuit  18  has such a shape that a cylindrical shape portion is partly cut away in the direction of the center axis. In the example of the figures, the increased diameter portion  196  is cut away at one half of the cylindrical shape portion thereof such that a flat face  197  parallel to the direction of the center axis is formed. 
     As described hereinabove, the ring-shaped grooved portion  19   a  which fits with the ring-shaped protrusion  5 Bb provided on the inner wall of the opening of the second tubular member  5 B is formed on the reduced diameter portion  195  of the cap  19 . Further, the protrusion  19   c  is formed in the direction of the center axis of the cap  19  on the reduced diameter portion  195  of the cap  19  for engaging with the positioning cut-out  5 Bc formed on the opening end side of the second tubular member  5 B. Furthermore, a threaded portion  19   b  is formed on the increased diameter portion  196  of the cap  19  for threadedly engaging with a threaded portion formed on the inner wall face of the housing of the position pointer  1  as hereinafter described. 
     The terminal members  192  and  193  are provided to establish electric connection between the capacitor circuit  18  and the connector  194  provided on the flat face  197  formed on the increased diameter portion  196 . In particular, a first end  192   a  of the terminal member  192  is led out such that it elastically abuts against the second end  1826   b  of the terminal member  1826  on the end face of the second capacitor circuit  182  on the face of the reduced diameter portion  195  of the cap  19  opposing the capacitor circuit  18 . A second end  192   b  of the terminal member  192  is connected to the first end of the connector  194 . Meanwhile, a first end  193   a  of the terminal member  193  is led out such that it elastically abuts against the second end  1825   b  of the terminal member  1825  on the end face of the second capacitor circuit  182  on the face of the reduced diameter portion  195  of the cap  19  opposing the capacitor circuit  18 . A second end  193   b  of the terminal member  193  is connected to the second end of the connector  194 . It is to be noted that the first end of the connector  194  is connected to a first end of the push switch  7  hereinafter described while the second end of the connector  194  is connected to a second end of the push switch  7 . 
     Assembly of Parts of the Second Tubular Member  5 B of the Electronic Ink Cartridge  10   
     In the present first embodiment, the first capacitor circuit  181  having capacitance whose value has been set in such a manner as described hereinabove is connected to the connection member  17  first. In particular, the first end  1815   a  of the terminal member  1815  of the first capacitor circuit  181  formed in a shape of a rod is inserted into the insertion hole  173   d  of the connection member  17  and connected to the second end portion  173   c  of the terminal member  173  provided on the connection member  17 . Further, the first end  1814   a  of the terminal member  1814  is connected so as to abut against the ring-shaped electrode conductor  172   c  of the connection member  17 . 
     Then, the first capacitor circuit  181  connected to the connection member  17  is accommodated into the hollow portion of the second tubular member  5 B. Then, the threaded portion  5 Ba formed on the inner wall face of the opening of the second tubular member  5 B on the first end side and the threaded portion  5 Ac formed on the outer peripheral side face of the opening  5 Ab of the first tubular member  5 A are screwed with each other to form a unitary tubular body. At this time, the first capacitor circuit  181  is rotated to set a position thereof in a peripheral direction in advance so that the fitting recessed holes  1816  and  1817  on the end face of the first capacitor circuit  181  opposing the second capacitor circuit  182  are engaged with the fitting protrusions of the second capacitor circuit  182 . 
     Thereafter, while the second capacitor circuit  182  having capacitance whose value has been set in such a manner as described hereinabove is mechanically and electrically connected to the first capacitor circuit  181  as described hereinabove with reference to  FIG. 4  while the protrusion  182   a  is engaged with the positioning cut-out  5 Bc of the second tubular member  5 B. 
     Then, the reduced diameter portion  195  of the cap  19  is inserted into the second tubular member  5 B in such a manner that the protrusion  19   c  is engaged with the positioning cut-out  5 Bc. Consequently, the ring-shaped grooved portion  19   a  of the cap  19  and the ring-shaped protrusion  5 Bb of the second tubular member  5 B are fitted with each other to lock the cap  19  in the second tubular member  5 B. At this time, the first end  1825   b  of the terminal member  1825  and the second end  1826   b  of the terminal member  1826  are connected to the first end  193   a  of the terminal member  193  and the first end  192   a  of the terminal member  192  of the cap  19 , respectively. 
     The electronic ink cartridge  10  is assembled in such a manner as described above. In the electronic ink cartridge  10 , the resonance frequency of the parallel resonance circuit configured from the coil  16  and the capacitor circuit  18  built therein is adjusted already in both of the states in which the push switch  7  is off and on. Accordingly, in the present embodiment, when the electronic ink cartridge  10  is accommodated into the housing  2  of the position pointer  1 , adjustment of the resonance frequency is no longer required. 
     Equivalent Circuit to the Electronic Ink Cartridge  10   
     An equivalent circuit to the electronic circuit part including the coil  16 , capacitor circuit  18  and push switch  7  of the electronic ink cartridge  10  described hereinabove is depicted in  FIG. 6 . In this instance, the first end  16   a  and the second end  16   b  of the coil  16  are connected to the first end portion  172   a  of the terminal member  172  and the first end portion  173   a  of the terminal member  173  of the connection member  17 , respectively. 
     In a state in which the first capacitor circuit  181  of the capacitor circuit  18  is coupled to the connection member  17  as described hereinabove, the first end portion  172   a  of the terminal member  172  of the connection member  17  is connected to the first end  1814   a  of the terminal member  1814  of the first capacitor circuit  181  of the capacitor circuit  18  through the ring-shaped electrode conductor  172   c  of the terminal member  172  of the connection member  17 . Further, the first end portion  173   a  of the terminal member  173  of the connection member  17  is connected to the first end  1815   a  of the terminal member  1815  of the first capacitor circuit  181  through the second end portion  173   c  of the terminal member  173  of the connection member  17 . 
     Accordingly, as depicted in  FIG. 6 , the chip capacitors  183  accommodated in the first capacitor circuit  181  are connected in parallel to each other to the coil  16 .  FIG. 6  illustrates a state in which capacitances Ca to Ce of the five chip capacitors  183  are connected in parallel to the inductance of the coil  16 . It is to be noted that the capacitances Ca to Ce of the chip capacitors  183  may be equal to each other or may be different from each other. Since the capacitances Ca to Ce are connected in parallel to each other, the capacitance of the entire first capacitor circuit  181  is equal to the simple sum of the capacitances of the chip capacitors  183  accommodated in the first capacitor circuit  181 . 
     On the other hand, in a state in which the second capacitor circuit  182  is coupled to the first capacitor circuit  181 , the second end  1814   b  of the terminal member  1814  of the first capacitor circuit  181  and the first end  1824   a  of the terminal member  1824  of the second capacitor circuit  182  are electrically connected to each other. Further, the second end  1815   b  of the terminal member  1815  of the first capacitor circuit  181  and the first end  1825   a  of the terminal member  1825  of the second capacitor circuit  182  are electrically connected to each other. Further, as depicted in  FIG. 6 , the push switch  7  is connected between the second end  1826   b  of the terminal member  1826  and the second end  1825   b  of the terminal member  1825  of the second capacitor circuit  182  through the connector  194  of the cap  19 . 
     Accordingly, when the second end  1826   b  of the terminal member  1826  and the second end  1825   b  of the terminal member  1825  are short-circuited, an equivalent state in which the push switch  7  is on is entered. In this state, the chip capacitors  183  accommodated in the second capacitor circuit  182  are connected in parallel to each other to the coil  16  in addition to the chip capacitors  183  of the first capacitor circuit  181 . It is to be noted that  FIG. 6  illustrates a state in which capacitances Cf to Ci of the four chip capacitors  183  are accommodated in the second capacitor circuit  182  and connected in parallel to the inductance of the coil  16 . Also in this state, the capacitances Cf to Ci of the chip capacitors  183  may be equal to each other or may be different from each other. 
     In the present first embodiment, the core member  11 , the coil  16  configuring a pressure sensor and having variable inductance (including the ferrite chip  13 , O-snap ring  14  and ferrite core  15 ) and the connection member  17  are accommodated in a juxtaposed state in this order in the direction of the center axis in the hollow portion of the first tubular member  5 A in such a manner as described above. Further, on the end face of the connection member  17 , the ring-shaped electrode conductor  172   c  and the second end portion  173   c  connected to the first end  16   a  and the second end  16   b  of the coil  16  are formed in a state in which they can be contacted as connection terminals from the outside. Accordingly, when pressure is applied to the core member  11 , inductance of the coil  16  corresponding to the applied pressure appears at the connection terminals. Therefore, if an electric characteristic (inductance) obtained at the connection terminals is measured, then a variation characteristic of the inductance with respect to the pressure applied to the core member  11  can be known. Further, it can be confirmed whether or not the electronic ink cartridge  10  has a desired writing pressure detection characteristic. 
     Further, in the present embodiment, the connection terminals connected to the first end  16   a  and the second end  16   b  of the coil  16  and provided on the connection member  17  are exposed from the first tubular member  5 A. Therefore, the position pointer  1  can be configured only by coupling the first capacitor circuit  181  to the connection member  17  such that the first and second electrodes of the first capacitor circuit  181 , which forms the capacitor circuit  18  having a desired capacitance value, are connected to the connection terminals. Therefore, the configuration is simplified significantly. 
     Furthermore, in the present embodiment, all of the core member  11 , coil  16  having variable inductance, connection member  17  and capacitor circuit  18  are inserted in the electronic ink cartridge  10 , and the electronic ink cartridge  10  is assembled in a state in which adjustment of the resonance frequency has been done already. Accordingly, the position pointer  1  can be configured only by accommodating the electronic ink cartridge  10  into the housing of the position pointer  1 . Therefore, the position pointer  1  in which the electronic ink cartridge  10  can be handled like a replacement core of a boll-point pen can be implemented. 
     Further, as described hereinabove, in the present embodiment, all component parts are disposed in a juxtaposed state in order in the direction of the center axis in the tubular member  5  of the electronic ink cartridge  10  so as to establish not only electric connection but also mechanical coupling thereof. Therefore, there is an effect also that a narrow electronic ink cartridge of such a diameter as, for example, 2.5 mm as in the case of the example described hereinabove can be implemented readily. It is to be noted that the second capacitor circuit  182  is necessitated where the push switch  7  is disposed in the position pointer  1 . However, where the push switch  7  is not disposed in the position pointer  1 , the position pointer  1  can be used by connecting the second capacitor circuit  182  to the first capacitor circuit  181  and short-circuiting the second end  1826   b  of the terminal member  1826  and the second end  1825   b  of the terminal member  1825 . Alternatively, it is also possible to configure the capacitor circuit  18  solely from the first capacitor circuit  181  without connecting the second capacitor circuit  182 . 
     Accommodation of the Electronic Ink Cartridge into the Housing of the Position Pointer 
     The electronic ink cartridge  10  of the present embodiment is mounted on the lower half  3  of the housing  2  of the position pointer  1  and accommodated into the housing  2  as depicted in  FIG. 2A . On the lower half  3  of the housing  2 , the push switch  7  is provided in such a manner as described below before the electronic ink cartridge  10  is inserted. 
     In particular, the through-hole  3   d , for example, of a circular shape or an elliptical shape is provided at part of the peripheral side face of the lower half  3 , and the pressing element  8  for depressing the push switch  7  is disposed in the through-hole  3   d . The pressing element  8  is made of an elastic material such as, for example, elastic rubber. 
     The push switch  7  is disposed in a portion  6   a  formed by cutting away part of a ring-shaped member  6 , whose outer diameter is substantially equal to the inner diameter of the lower half  3 , in a circumferential direction as depicted in  FIG. 2B . This ring-shaped member  6  has a through-hole  6   b  of a diameter greater than the outer diameter of the tubular member  5  of the electronic ink cartridge  10 . 
     In the present embodiment, a stepped portion  3   e  is formed by making the diameter of the hollow portion  3   b  of the lower half  3  on the opening  3   a  side a little smaller than the diameter of the other portion. The ring-shaped member  6  is engaged with the stepped portion  3   e  such that the position thereof in the direction of the center axis is restricted, and is fixed to the lower half  3 , for example, by bonding agent. Consequently, the ring-shaped member is positioned such that a depressed face  7   a  (refer to  FIG. 2B ) of the push switch  7  comes to the position corresponding to the pressing element  8  in the direction of the center axis. 
     In the case of the present example, a lead portion (hereinafter referred to as flexible lead portion)  9  formed of a flexible wiring board for electric connection is led out from the push switch  7  as depicted in  FIG. 2B . Further, a portion of an annular part of the lower half  3 , which is screwed with the cap  19  portion of the electronic ink cartridge  10 , includes a guide groove  3   f  such that it cooperates with the cap  19  to provide an air gap therebetween as depicted in  FIG. 2C , which is a sectional view taken along line A-A of  FIG. 2A . The flexible lead portion  9  led out from the push switch  7  can be led out to the outside of the lower half  3  through the guide groove  3   f  as depicted in  FIGS. 2A and 2C . 
     In this manner, in the present first embodiment, the electronic ink cartridge  10  is inserted in the direction of the center axis of the lower half  3  of the housing  2 , in the inside of which the push switch  7  is attached, from the side opposite to the core member  11  side. In this instance, the electronic ink cartridge  10  is inserted in the direction of the center axis of the lower half  3  through the through-hole  6   b  of the ring-shaped member  6  such that the core member  11  extending outwardly from the tubular member  5  extends to the outside from the opening  3   a  of the lower half  3  of the housing  2  as depicted in  FIG. 2A . 
     The opening  3   a  of the lower half  3  has a diameter greater than the diameter of the core member  11  but smaller than the diameter of the tubular member  5  of the electronic ink cartridge  10 . Accordingly, the electronic ink cartridge  10  engages, on the core member  11  side of the tubular member  5  thereof, with the end portion of the inner wall of the lower half  3  on the opening  3   a  side to restrict the position thereof in the direction of the center axis. 
     Before the electronic ink cartridge  10  is inserted into the lower half  3 , the flexible lead portion  9  led out from the push switch  7  is led out to the cap  19  side of the electronic ink cartridge  10  through the guide groove  3   f . Then, the threaded portion  19   b  of the cap  19  of the electronic ink cartridge  10  is screwed into a threaded portion  3   c  of the lower half  3  thereby to fix the electronic ink cartridge  10  to the lower half  3 . 
     Thereafter, a distal end of the flexible lead portion  9  led out from the push switch  7  is fitted with the connector  194  formed on the cap  19  of the electronic ink cartridge  10  to establish electric connection. Thereafter, the upper half  4  is force fitted with the lower half  3  to complete the position pointer  1  of the present embodiment. In the position pointer  1  of the present embodiment, the electronic ink cartridge  10  can be removably attached to the lower half  3  and can be exchanged readily as described above. Further, the push switch  7  can be connected after the electronic ink cartridge  10  is attached to the lower half  3 , and there is an additional advantage that this connection can be carried out readily. 
     Circuit Configuration for Pointed Position Detection and Writing Pressure Detection 
     In the position pointer  1  of the present embodiment, if pressing force (writing pressure) is applied to the core member  11 , then the ferrite chip  13  is displaced toward the ferrite core  15  side through the O-snap ring  14 , whereupon the inductance of the coil  16  varies and the resonance frequency varies in response to the variation of the inductance. In other words, the resonance frequency (phase) of an electromagnetic induction signal to be transmitted from the coil  16  of the resonance circuit varies. Accordingly, if the position pointer  1  of the present example is used, then the position detection apparatus which has such a circuit configuration depicted in  FIG. 7  as described below can detect a pointed position by the position pointer  1  and the writing pressure by the position pointer  1 . 
     An example of a circuit configuration of the position detection apparatus  200  which carries out detection of a pointed position and detection of writing pressure using the position pointer  1  described above is described with reference to  FIG. 7 .  FIG. 7  is a block diagram depicting an example of a circuit configuration of the position pointer  1  and the position detection apparatus  200 . 
     In the position pointer  1 , as described hereinabove, the capacitance value of the capacitor circuit  18  connected in parallel to the coil  16  is varied in response to on-off operations of the push switch  7  to vary the resonance frequency of the resonance circuit. In the position detection apparatus  200 , a frequency displacement (phase) of the resonance frequency of the resonance circuit of the position pointer  1  is detected to carry out detection of writing pressure or detection of an operation situation of the push switch  7  as hereinafter described. 
     In the position detection apparatus  200 , an X-axis direction loop coil group  211 X and a Y-axis direction loop coil group  212 Y are stacked to form a position detection coil. The loop coil groups  211 X and  212 Y are configured, for example, from n and m rectangular loop coils, respectively. The loop coils which configure the loop coil groups  211 X and  212 Y are disposed in a juxtaposed relationship at equal distances from each other and in a successively overlapping relationship with each other. 
     The position detection apparatus  200  further includes a selection circuit  213  to which the X-axis direction loop coil group  211 X and the Y-axis direction loop coil group  212 Y are connected. The selection circuit  213  successively selects one of the loop coils of the two loop coil groups  211 X and  212 Y. 
     The position detection apparatus  200  further includes an oscillator  221 , a current driver  222 , a switch circuit  223 , a reception amplifier  224 , a detector  225 , a low-pass filter  226 , a sample hold circuit  227 , and an A/D conversion circuit  228 . The position detection apparatus  200  further includes a synchronous detector  229 , another low-pass filter  230 , another sample hold circuit  231 , another A/D conversion circuit  232 , and a processing controlling section  233 . The processing controlling section  233  is configured, for example, of a microcomputer. 
     The oscillator  221  generates an AC signal of a frequency f 0 . The AC signal generated by the oscillator  221  is supplied to the current driver  222  and the synchronous detector  229 . The current driver  222  converts the AC signal supplied thereto from the oscillator  221  into current and outputs the current to the switch circuit  223 . Then switch circuit  223  changes a connection destination (a transmission side terminal T or a reception side terminal R) to which a loop coil selected by the selection circuit  213  is to be connected under the control of the processing controlling section  233 . Of such connection destinations, to the transmission side terminal T and the reception side terminal R, the current driver  222  and the reception amplifier  224  are connected, respectively. 
     An induction voltage generated in the loop coil selected by the selection circuit  213  is sent to the reception amplifier  224  through the selection circuit  213  and the switch circuit  223 . The reception amplifier  224  amplifies the induction voltage supplied thereto from the loop coil and outputs the amplified induction voltage to the detector  225  and the synchronous detector  229 . 
     The detector  225  detects an induction voltage generated in a loop coil, namely, a reception signal, and outputs the detected reception signal to the low-pass filter  226 . The low-pass filter  226  has a cutoff frequency sufficiently lower than the frequency f 0  described above, and converts the output signal of the detector  225  into a DC signal and outputs the DC signal to the sample hold circuit  227 . The sample hold circuit  227  holds a voltage value of the output signal of the low-pass filter  226  at a predetermined timing, particularly, at a predetermined timing within a reception period and outputs the held voltage value to the A/D (Analog to Digital) conversion circuit  228 . The A/D conversion circuit  228  converts an analog output of the sample hold circuit  227  into a digital signal and outputs the digital signal to the processing controlling section  233 . 
     On the other hand, the synchronous detector  229  synchronously detects an output signal of the reception amplifier  224  with an AC signal from the oscillator  221  and outputs a signal of a level having a phase difference between the signals to the low-pass filter  230 . The low-pass filter  230  has a cutoff frequency sufficiently lower than the frequency f 0 , and converts the output signal of the synchronous detector  229  into a DC signal and outputs the DC signal to the sample hold circuit  231 . The sample hold circuit  231  holds a voltage value of the output signal of the low-pass filter  230  at a predetermined timing and outputs the held voltage value to the A/D (Analog to Digital) conversion circuit  232 . The A/D conversion circuit  232  converts an analog output of the sample hold circuit  231  into a digital signal and outputs the digital signal to the processing controlling section  233 . 
     The processing controlling section  233  controls the components of the position detection apparatus  200 . In particular, the processing controlling section  233  controls selection of a loop coil by the selection circuit  213 , changeover of the switch circuit  223 , and timings of the sample hold circuits  227  and  231 . The processing controlling section  233  controls transmission of electromagnetic induction signals with a fixed transmission duration from the X-axis direction loop coil group  211 X and the Y-axis direction loop coil group  212 Y based on input signals from the A/D conversion circuits  228  and  232 . 
     In each loop coil of the X-axis direction loop coil group  211 X and the Y-axis direction loop coil group  212 Y, an induction voltage is generated by an electromagnetic induction signal transmitted from the position pointer  1 . The processing controlling section  233  calculates coordinate values of a pointed position in the X axis direction and the Y axis direction of the position pointer  1  based on the level of the voltage values of the induction voltages generated in the loop coils. Further, the processing controlling section  233  detects based on the level of a signal corresponding to a phase difference between the transmitted electromagnetic induction signal and the received electromagnetic induction signal whether or not the push switch  7  is depressed. 
     In this manner, in the position detection apparatus  200 , the position of the position pointer  1  positioned closely thereto can be detected by the processing controlling section  233 . Besides, the processing controlling section  233  of the position detection apparatus  200  can detect the writing pressure applied to the core member of the position pointer  1  and detect whether or not the push switch  7  on the position pointer  1  is switched on by detecting the phase (frequency displacement) of the received signal. 
     Modifications to the First Embodiment 
     It is to be noted that, while the electronic ink cartridge  10  of the first embodiment described hereinabove is structured such that the tubular member  5  is configured from the first tubular member  5 A and the second tubular member  5 B connected to each other, the tubular member  5  may otherwise be structured in the following manner. In particular, the tubular member  5  is configured only from the first tubular member  5 A, and the core member  11 , the pressure sensor (coil spring  12 , ferrite chip  13 , O-snap ring  14  and ferrite core  15  on which the coil  16  is wound) and the connection member  17  are accommodated in the tubular member  5 . 
       FIG. 8  is a view depicting an example of a configuration of the electronic ink cartridge  10 A of a modification to the first embodiment, and like elements to those of the electronic ink cartridge  10  of the first embodiment described above are denoted by like reference symbols. As shown in  FIG. 8 , in the electronic ink cartridge  10 A of the present example, the tubular member  5 A′ is different from the first tubular member  5 A in the first embodiment described above in the configuration in the proximity of the opening  5 Ab′ to which the connection member  17  is fixed. 
     In particular, in the present example, a threaded portion for threaded engagement with the second tubular member  5 B is not formed in the proximity of the opening  5 Ab′ of the tubular member  5 A′. Instead, the tubular member  5 A′ is formed a little longer in the direction of the center axis than the first tubular member  5 A. Further, a recessed portion  5 AH is configured between an end face of the connection member  17  on which connection terminals to the capacitor circuit  18 ′ are formed and an end face of the opening  5 Ab′ of the tubular member  5 A′. Further, a ring-shaped protrusion  5 Af is formed on an inner wall face of the recessed portion  5 AH. 
     Meanwhile, on a peripheral side face of the first capacitor circuit  181 ′ of the capacitor circuit  18 ′, a ring-shaped recessed groove  181   a  for fitting with the ring-shaped protrusion  5 Af of the recessed portion  5 AH is formed in the proximity of the end face on the connection side to the connection member  17 . 
     Further, in the present modification, the core member  11 , coil spring  12 , ferrite chip  13 , O-snap ring  14 , ferrite core  15  on which the coil  16  is wound and connection member  17  are inserted into the tubular member  5 A′ and ring-shaped recessed grooves  17   a  and  17   b  of the connection member  17  are fitted with the ring-shaped protrusions  5 Ad and  5 Ae to fix the connection member  17  to the tubular member  5 A′. 
     Thereafter, the first capacitor circuit  181 ′ of the capacitor circuit  18 ′ is inserted into the recessed portion  5 AH to insert and fit the rod-shaped first end  1815   a  of the terminal member  1815  into the insertion hole  173   d  of the terminal member  173  in the recessed hole  17   d  of the connection member  17  so as to be connected to the end portion  173   c . Further, the first end  1814   a  of the terminal member  1814  is fitted with and connected to the ring-shaped electrode conductor  172   c  of the connection member  17  to establish connection therebetween. Then, the ring-shaped recessed groove  181   a  is fitted with and locked by the ring-shaped protrusion  5 Af. 
     Then, in the present example, the resulting block in this state is accommodated into the lower half  3  of the housing  2  of the position pointer  1 , and then by screwing the cap  19  with the threaded portion  3   c  of the lower half  3 , the electronic ink cartridge  10 A can be accommodated into and fixed to the position pointer  1  similarly as in the case depicted in  FIG. 2A . It is to be noted that, in this instance, a recessed portion into which part of the second capacitor circuit  182  of the capacitor circuit  18  in the direction of the center axis is to be fitted may be formed on the end face side of the cap  19  opposing the capacitor circuit  18  such that the first ends  192   a  and  193   a  of the terminal members  192  and  193  of the cap  19  in the first embodiment described hereinabove are formed on the bottom of the recessed portion. 
     It is to be noted that, while the modification described above is directed to the case in which the position pointer  1  includes the push switch (side switch)  7 , if the position pointer  1  does not include the push switch  7 , then the connector on the cap  19  for connecting to the push switch  7  is not required. In this instance, the cap  19  may include connection terminals for connecting the first capacitor circuit  181  and the second capacitor circuit  182  in parallel to each other. In particular, where the second capacitor circuit  182  is used as the capacitor circuit  18  together with the first capacitor circuit  181 , connection terminals for allowing conduction of the first end  1825   a  of the second capacitor circuit  182  and the second end  1826   b  of the terminal member  1826  shown in  FIG. 6  are provided on the cap  19 . 
     It is to be noted that, in the case of the configuration of the position pointer which does not include the push switch  7 , the capacitor circuit  18  may be configured solely from the first capacitor circuit  181 , or from the first capacitor circuit  181  and the second capacitor circuit  182  which is connected in parallel to the first capacitor circuit  181 . In this instance, without providing the cap  19 , an end portion of the capacitor circuit  18  may be abutted against a wall portion formed inside the housing  2  of the position pointer  1  so that the electronic ink cartridge may not move in the axial direction in the position pointer  1 . It is to be noted that, in this instance, naturally a protective cap may be placed at the end portion of the capacitor circuit  18  in the direction of the center axis such that the protective cap is abutted against the wall portion formed inside the housing  2  of the position pointer  1 . 
     Second Embodiment 
     The pressure sensor provided in the electronic ink cartridge of the first embodiment described above is configured such that the position of the ferrite core as the first magnetic member is fixed while the ferrite chip as the second magnetic member is biased in the direction of the center axis in response to pressing force applied to the core member to vary the distance between the ferrite core and the ferrite chip, to thereby vary the inductance of the coil wound on the ferrite core in response to the pressing force. 
     In a pressure sensor provided in an electronic ink cartridge of a second embodiment described below, a ferrite core as the first magnetic member is biased in the direction of the center axis in response to pressing force applied to a core member to vary the distance between the ferrite core and a ferrite chip, to thereby vary the inductance of a coil wound on the ferrite core in response to the pressing force. 
     Further, in the present second embodiment, an information transmission circuit is provided in a position pointer such that, as information relating to an electronic ink cartridge or the position pointer, for example, identification information (ID) of the electronic ink cartridge or the position pointer is transmitted to a position detection apparatus. The identification information (ID) is an example of information relating to an electronic ink cartridge. As the identification information, information which specifies a manufacturer, a product number, a production date, a production lot number, a position detection method such as an electromagnetic induction method or a capacitive method, a writing pressure detection method based on an inductive variation or a capacitive variation and so forth of an electronic ink cartridge or a position pointer may be registered into a semiconductor device such as a memory or a register. 
     The position pointer according to the second embodiment to be described below transmits identification information of an electronic ink cartridge to a position detection apparatus. To this end, in the present second embodiment, the position pointer includes an ID transmission circuit  300  as an information transmission circuit. Further, in the present second embodiment, the ID transmission circuit  300  is accommodated in an ID package  320  of a cylindrical shape, which is in turn accommodated in a tubular member. 
       FIGS. 9A and 9B  are views depicting an example of a configuration of an electronic ink cartridge  20 , which is a principal component of the position pointer according to the second embodiment.  FIG. 9A  is a sectional view depicting an internal configuration of the electronic ink cartridge  20 . Also in the present example, for the convenience of description, some of the internal component parts of a tubular member  50  of the electronic ink cartridge  20  are not depicted in cross-section in  FIG. 9A , but a cross-sectional view of them is prepared separately as hereinafter described. Meanwhile,  FIG. 9B  is an exploded perspective view depicting a general configuration of the electronic ink cartridge  20 . In the present second embodiment, like elements to those in the first embodiment are denoted by like reference symbols. 
     It is to be noted that the configuration of the housing of the position pointer of the present second embodiment and the attachment structure of the push switch  7  to the housing are similar to those in the first embodiment, and therefore, illustration and description of them are omitted. 
     As depicted in  FIGS. 9A and 9B , also in the electronic ink cartridge  20 , component parts of the position pointer of the electromagnetic induction type are accommodated in the tubular member  50 . However, in the present second embodiment, the tubular member  50  is not configured from separate members but is formed as a single part member. Also the tubular member  50  in the present second embodiment has a narrow shape having an outer diameter of, for example, 2.5 mm and an inner diameter of, for example, 1.5 mm to 2 mm. Further, the tubular member  50  is configured from a material of a nonmagnetic substance such as a nonmagnetic metal material, a resin material, glass or a ceramic material, for example, from SUS305 or SUS310S. 
     On the first end side of the tubular member  50  in the direction of the center axis, an opening  50   a  for allowing a distal end of a core member  21  to extend outwardly therethrough is provided. The opening  50   a  has a diameter smaller than the inner diameter of the tubular member  50 . Meanwhile, the second end side of the tubular member  50  in the direction of the center axis is formed to have the entire inner diameter thereof as an opening  50   b . On the opening  50   b  side, a cut-out  50   f  is formed for positioning in a peripheral direction such that it extends along the direction of the center axis similarly as in the case of the second tubular member  5 B in the first embodiment described hereinabove. 
     As depicted in  FIGS. 9A and 9B , a coil spring  22 , the core member  21 , a ferrite core  23  as an example of a first magnetic member on which a coil  24  is wound, an O-snap ring  25 , a ferrite chip  26  as an example of a second magnetic member, a connection member  27 , a capacitor circuit  28  and an ID package  320  are accommodated in a juxtaposed relationship in this order as viewed from the opening  50   a  side in the tubular member  50 . The parts mentioned are accommodated in such a state that the directions of the center axes thereof extend along the direction of the center axis of the tubular member  50 . The cap  19  is inserted in the opening  50   b  of the tubular member  50  to close up the opening  50   b  of the tubular member  50 . 
     It is to be noted that, in the present second embodiment, different from the case of the first embodiment, at a point of time at which the connection member  27  is accommodated to a predetermined position of the tubular member  50  in the direction of the center axis, side peripheral face positions  50   c  and  50   d  of the tubular member  50  corresponding to a side peripheral face of the connection member  27  are constricted to form protrusions on the inner peripheral face of the tubular member  50 . Thus, the connection member  27  is pressed against and held and fixed by the tubular member  50  to restrict the position of the connection member  27  so as not to move in the direction of the center axis. 
     On the inner wall face of the tubular member  50  in the proximity of the opening  50   b  on the second end side, a ring-shaped protrusion  50   e  for fitting with a ring-shaped grooved portion  19   a  formed on an outer periphery of the reduced diameter portion  195  of the cap  19  made of a nonmagnetic material such as, for example, resin is formed, for example, by constricting the tubular member  50  at the position. Accordingly, when the cap  19  is inserted into the tubular member  50 , the ring-shaped grooved portion  19   a  formed on the outer periphery of the reduced diameter portion  195  of the cap  19  and the ring-shaped protrusion  50   e  formed on the inner wall face of the tubular member  50  are fitted with each other to pressure-retain the cap  19  thereby to prevent the cap  19  from being separated from the opening  50   b.    
     The configuration of the components accommodated in the inside of the tubular member  50  and assembly of the electronic ink cartridge  20  as well as adjustment of the resonance frequency are described further. 
     The core member  21  in the present second embodiment is configured, for example, from resin. As depicted in  FIG. 9B , the core member  21  has a shape of a rod extending outwardly from the opening  50   a  of the tubular member  50 . Further, in the present second embodiment, a recessed portion  23   a  with which the core member  21  is to be fitted is formed substantially at the center of an end face of the ferrite core  23 , on which the coil  24  is wound, on the core member  21  side in the direction of the center axis. The core member  21  is force fitted, on the opposite side  21   a  thereof to the side extending from the opening  50   a , in the recessed portion  23   a  of the ferrite core  23  and coupled to the ferrite core  23 . In the present embodiment, the core member  21  is removably fitted in the ferrite core  23  and accordingly can be inserted into and removed from the electronic ink cartridge  20 . 
     A recessed portion  23   b  for positioning is formed substantially at the center of an end face of the ferrite core  23  on the opposite side from the core member  21  side in the direction of the center axis. A protrusion  27   a  formed on the end face of the connection member  27  is inserted into the recessed portion  23   b  of the ferrite core  23 , through an O-snap ring  25  made of elastic material such as, for example, rubber, and through the ferrite chip  26  as depicted in  FIG. 9A . In the present example, a through-hole  26   a  into which the protrusion  27   a  of the connection member  27  is inserted is formed in the ferrite chip  26 . The length of the protrusion  27   a  of the connection member  27  in the direction of the center axis is set to a length over which the protrusion  27   a  is inserted in the recessed portion  23   b  of the ferrite core  23 , with the O-snap ring  25  and the ferrite chip  26  interposed therebetween, and the ferrite core  23  can be displaced toward the connection member  27  in the direction of the center axis in response to pressing force applied to the core member  21 . 
       FIGS. 10A to 10D  are views depicting an example of a configuration of the connection member  27 .  FIG. 10A  is a view of the connection member  27  as viewed from the side opposing the end face of the ferrite core  23 , and  FIG. 10B  is a sectional view taken along line D-D of  FIG. 10A .  FIG. 10C  is a view of the connection member  27  as viewed from the side on which the connection member  27  is connected to the capacitor circuit  28 . 
     Similarly to the connection member  17  in the first embodiment, the connection member  27  is formed by insert-molding terminal members  272  and  273  having elasticity for establishing electric connection to a first end  24   a  and a second end  24   b  of the coil  24  and the first end and the second end of the capacitor circuit  28 , respectively, in a main body portion  271  formed from a cylindrical resin member as depicted in  FIGS. 10A and 10B . The protrusion  27   a  for positioning is formed at the center of the end face of the main body portion  271  on the ferrite core  23  side. In the present example, the protrusion  27   a  has a shape of a rod having a circular cross section. 
     Further, as depicted in  FIGS. 10A and 10B , recessed grooves  274  and  275  are formed at positions spaced, in the present example, by an angular distance of 180 degrees from each other on a peripheral side face of the main body portion  271  of the connection member  27  such that they extend along the direction of the center axis of the cylindrical shape. First end portions  272   a  and  273   a  of the terminal members  272  and  273  are erected in a direction perpendicular to the peripheral direction in the recessed grooves  274  and  275 , respectively. The first end portions  272   a  and  273   a  of the terminal members  272  and  273  in the erected state has V-shaped notches  272   b  and  273   b  formed thereon as depicted in  FIG. 10A . As depicted in  FIG. 10B , the first end  24   a  of the coil  24  is force fitted into the V-shaped notch  272   b  of the first end portion  272   a  of the terminal member  272  to establish electric connection therebetween and the second end  24   b  of the coil  24  is force fitted into the V-shaped notch  273   b  of the first end portion  273   a  of the terminal member  273  to establish electric connection therebetween. 
     The second end portion of the terminal member  272  of the connection member  27  is formed as a ring-shaped electrode conductor  272   c  on an end face thereof opposing the end face of the capacitor circuit  28  as depicted in  FIGS. 10B and 10C . 
     Meanwhile, the second end portion of the terminal member  273  of the connection member  27  is formed as a circular conductor  273   c  on the inner side of the ring-shaped electrode conductor  272   c  in a non-contacting relationship with the ring-shaped electrode conductor  272   c  at the second end portion of the terminal member  272 . The ring-shaped electrode conductor  272   c  at the second end portion of the terminal member  272  and the circular conductor  273   c  at the second end portion of the terminal member  273  configured in such a manner as described above are connected to first and second terminals of the capacitor circuit  28  as hereinafter described. 
     In this instance, the connection of the first end  24   a  and the second end  24   b  of the coil  24  to the V-shaped notch  272   b  of the first end portion  272   a  of the terminal member  272  and the V-shaped notch  273   b  of the first end portion  273   a  of the terminal member  273  of the connection member  27  is carried out in a state in which the protrusion  27   a  of the connection member  27  is inserted in the recessed portion  23   b  of the ferrite core  23  through the through-hole  26   a  of the ferrite chip  26  and the through-hole of the O-snap ring  25 . Accordingly, the ferrite core  23  having the coil  24  wound thereon and the connection member  27  which are connected to each other with the O-snap ring  25  and the ferrite chip  26  interposed therebetween can be handled as a single unitized component part. 
     It is to be noted that the first end  24   a  and the second end  24   b  of the coil  24  are connected to the first end portions  272   a  and  273   a  of the terminal members  272  and  273  in the recessed grooves  274  and  275  of the connection member  27 , respectively, and the first end  24   a  and the second end  24   b  of the coil  24  do not contact with the inner wall face of the tubular member  50 . 
     In the present second embodiment, a unitized part group is formed such that the connection member  27  is opposed to the second end face of the ferrite core  23 , on which the coil  24  is wound, with the O-snap ring  25  and the ferrite chip  26  interposed therebetween, and the protrusion  27   a  formed on the end face of the connection member  27  is inserted in the recessed portion  23   b  of the ferrite core  23 . The unitized part group is inserted into the hollow portion, in which the coil spring  22  is inserted in advance, of the tubular member  50  from the opening  50   b  side toward the opening  50   a  side. The core member  21  is force fitted in the ferrite core  23  in a state in which the distal end side of the core member  21  extends outwardly from the opening  50   a  of the tubular member  50 . The core member  21  may be accommodated into the tubular member  50  after it is force fitted into the ferrite core  23  in advance or may be penetrated into the opening  50   a  of the tubular member  50  and force fitted into the ferrite core  23  after the ferrite core  23  and so forth are accommodated into the tubular member  50 . 
     In the present second embodiment, after the connection member  27  is inserted to a predetermined position in the direction of the center axis in the tubular member  50 , at which it is pressed a little into the hollow portion of the tubular member  50  against the biasing force of the coil spring  22 , the tubular member  50  is caulked (constricted) at the positions  50   c  and  50   d  described hereinabove of the tubular member  50  by a predetermined jig. Consequently, the connection member  27  is fixed to the tubular member  50  so that it does not move in the direction of the center axis in the tubular member  50 . 
     In this state, the ferrite core  23 , to which the core member  21  is coupled, O-snap ring  25  and ferrite chip  26  are normally biased toward the connection member  27  side by the coil spring  22  disposed on the core member  21  side in the hollow portion of the tubular member  50 . Consequently, rattling of the members which configure the position pointer is prevented. 
     At this time, the ring-shaped electrode conductor  272   c  and the circular conductor  273   c  which serve as connection terminals are exposed in the tubular member  50  on the end face of the connection member  27  in the tubular member  50  on the capacitor circuit  28  side. 
     Therefore, in the present second embodiment, in order to measure the inductance of the coil  24  in this state, a measuring jig including electrode terminals for electrically connecting to the ring-shaped electrode conductor  272   c  and the circular conductor  273   c  of the connection member  27  is inserted into the tubular member  50 . This measuring jig is connected to the inductance measuring instrument so that the inductance of the coil  24  in a state in which no pressing force is applied to the core member  21  is measured. 
     After the inductance of the coil  24  is measured, capacitance, which cooperates with the coil  24  having the inductance to form a parallel resonance circuit to provide a desired resonance frequency, is calculated in a similar manner as in the first embodiment described hereinabove. Then, the capacitor circuit  28  whose capacitance is set equal to the calculated capacitance value is accommodated into the tubular member  50 . 
     While the capacitor circuit  28  is configured from a first capacitor circuit  281  and a second capacitor circuit  282 , it has a configuration substantially similar to that of the capacitor circuit  18  which is configured from the first capacitor circuit  181  and the second capacitor circuit  182  in the first embodiment. However, since the ring-shaped electrode conductor  272   c  and the circular conductor  273   c  are formed on the end face of the connection member  27  as shown in  FIG. 10C , the first capacitor circuit  281  which configures the capacitor circuit  28  is different in that it includes terminal members of a shape different from that of the terminal members formed on the end face of the connection member  17  of the first capacitor circuit  181  shown in  FIGS. 3A to 3C . 
     In particular, as shown in  FIG. 10D , the first end  1814   a  of the terminal member  1814  of the first capacitor circuit  281  provided on an end face of the holder  1810  of the first capacitor circuit  281  opposing the connection member  27  has a shape corresponding to the width of the ring-shaped electrode conductor  272   c  of the connection member  27 . However, a first end  1815   a ′ of the terminal member  1815  has a circular shape and elastically abuts against the circular conductor  273   c  of the connection member  27 . The configuration of the other part of the first capacitor circuit  281  is similar to that of the first capacitor circuit  181 . 
     On an end face of the second capacitor circuit  282  opposing the ID package  320 , in the present example, fitting recessed holes  2821  and  2822  for fitting with fitting protrusions  3251  and  3252  formed on an end face of the ID package  320  hereinafter described are formed (refer to  FIG. 9B ). The configuration of the other part of the second capacitor circuit  282  is similar to that of the capacitor circuit  182  in the first embodiment. 
       FIGS. 11A to 11C  depict an example of a configuration of the ID package  320 , and  FIG. 11A  is a view depicting an end face of the ID package  320  on the second capacitor circuit  282  side.  FIG. 11B  is a sectional view taken along line E-E of  FIG. 11A . Meanwhile,  FIG. 11C  is a view depicting an end face of the ID package  320  on the cap  19  side. 
     The ID package  320  accommodates the ID transmission circuit  300  in a package  321  formed from resin of a cylindrical shape and has three terminal members  322 ,  323  and  324  as shown in  FIG. 11B . A first end of the ID transmission circuit  300  is electrically connected to the terminal member  322 , and a second end of the ID transmission circuit  300  is electrically connected to the terminal member  324 . 
     As shown in  FIG. 11A , a first end  322   a  of the terminal member  322  is exposed on an end face of the ID package  320  on the second capacitor circuit  282  side such that it abuts against the second end  1824   b  of the terminal member  1824  formed on an end face of the second capacitor circuit  282  on the ID package  320  side. Further, a first end  323   a  of the terminal member  323  is exposed on the end face of the ID package  320  on the second capacitor circuit  282  side such that it abuts against the second end  1826   b  of the terminal member  1826  formed on the end face of the second capacitor circuit  282  on the ID package  320  side. Furthermore, a first end  324   a  of the terminal member  324  is exposed on the end face of the ID package  320  on the second capacitor circuit  282  side such that it abuts against the second end  1825   b  of the terminal member  1825  formed on the end face of the second capacitor circuit  282  on the ID package  320  side. 
     Further, as shown in  FIG. 11C , a second end  323   b  of the terminal member  323  and a second end  324   b  of the terminal member  324  are exposed to the end face of the ID package  320  on the cap  19  side. Only if the terminal member  322  is connected to the first end of the ID transmission circuit  300  in the ID package  320 , then the second end thereof is included in the ID package  320  without being led out to the end face of the ID package  320  on the cap  19  side. 
     On a peripheral portion of the ID package  320 , a protrusion  320   a  extending along the direction of the center axis for engaging with the groove  50   f  formed on the tubular member  50  on the opening  50   b  side and extending in the axial direction is formed. Further, in the present example, the fitting recessed holes  2821  and  2822  similar to the fitting recessed holes  1816  and  1817  (refer to  FIG. 4 ) formed on the end face of the first capacitor circuit  181  described hereinabove are formed on the end face of the second capacitor circuit  282  on the ID package  320  side. 
     Further, as shown in  FIGS. 11A and 11B , the fitting protrusions  3251  and  3252  for fitting with the fitting recessed holes  2821  and  2822  formed on the end face of the second capacitor circuit  282  on the ID package  320  side are formed on the end face of the ID package  320  on the second capacitor circuit  282  side. The fitting protrusions  3251  and  3252  and the fitting recessed holes  2821  and  2822  have configurations similar to those of the fitting protrusions and the fitting recessed holes for coupling of the first and second capacitor circuits  181  and  182  described hereinabove. The ID package  320  is coupled to the second capacitor circuit  282  by fitting the fitting protrusions  3251  and  3252  thereof into the fitting recessed holes  2821  and  2822  of the second capacitor circuit  282 . 
     In this instance, the protrusion  182   a  of the second capacitor circuit  282  and the protrusion  320   a  of the ID package  320  are engaged with the groove  50   f  of the tubular member  50  to carry out positioning of the second capacitor circuit  282  and the ID package  320  in a peripheral direction. Consequently, the second end  1824   b  of the terminal member  1824 , second end  1826   b  of the terminal member  1826  and second end  1825   b  of the terminal member  1825  on the end face of the second capacitor circuit  282  are abutted against and electrically connected to the first end  322   a  of the terminal member  322 , first end  323   a  of the terminal member  323  and first end  324   a  of the terminal member  324  of the ID package  320 , respectively. 
     Thereafter, the reduced diameter portion  195  of the cap  19  is inserted into the tubular member  50  to fit the ring-shaped protrusion  50   e  of the tubular member  50  into the ring-shaped grooved portion  19   a  of the reduced diameter portion  195  to fix the cap  19  to the tubular member  50 . Consequently, the second end  324   b  of the terminal member  324  and the second end  323   b  of the terminal member  323  on the end face of the ID package  320  on the cap  19  side are connected to the first end  192   a  of the terminal member  192  and the first end  193   a  of the terminal member  193  of the cap  19 , respectively. In this instance, the length of the reduced diameter portion  195  of the cap  19  in the direction of the center axis is adjusted in response to the thickness of the ID package  320  in the direction of the center axis. 
     The electronic ink cartridge  20  is assembled in such a manner as described above. In the present electronic ink cartridge  20 , when pressing force in the direction of the center axis is applied to the core member  21 , the ferrite core  23  is displaced to the ferrite chip  26  side through the O-snap ring  25  to vary the distance between the ferrite core  23  and the ferrite chip  26  thereby to vary the inductance of the coil  24 . Then, similarly as in the first embodiment, the resonance frequency (phase) of an electromagnetic induction signal transmitted from the coil  24  of the resonance circuit of the position pointer varies in response to the variation of the inductance of the coil  24 . Consequently, a pointed position and writing pressure by the position pointer can be detected. 
     Then, the electronic ink cartridge  20  is accommodated into the housing  2  similarly to the electronic ink cartridge  10  in the first embodiment. 
     The position pointer of the present second embodiment can achieve working-effects quite similar to those achieved by the first embodiment described hereinabove although it is different in configuration for varying the inductance of the coil for writing pressure detection from the first embodiment. 
     Further, in the electronic ink cartridge  20  of the present second embodiment, when the ID package  320  is accommodated into the tubular member  50  in such a manner as described above, the ID transmission circuit  300  is placed into a state in which it is connected in parallel between the opposite ends of the coil  16 . It is to be noted that it is also possible to connect the ID package  320  in such a manner as to be exposed from the tubular member  50 . 
     Information Transmission Using the ID Transmission Circuit  300   
       FIG. 12  is a view depicting a circuit configuration of the position pointer  1 B and a position detection apparatus  200 B where the configuration is adopted to allow identification information (ID) of the position pointer or an electronic ink cartridge to be transmitted to the position detection apparatus. In  FIG. 12 , the electronic ink cartridge  20  is depicted as a parallel resonance circuit  20 R wherein the first capacitor circuit  281  is connected in parallel to the coil  24  whose inductance varies in response to the writing pressure and to which a series circuit of the second capacitor circuit  282  and the push switch  7  is connected in parallel. The push switch  7  is connected to the connector  194  of the cap  19  of the electronic ink cartridge  10  as depicted in  FIG. 2 . 
     The ID transmission circuit  300  of the position pointer  1 B includes an IC (Integrated Circuit)  301  as an ID generation controlling circuit as depicted in  FIG. 12 . This IC  301  is configured such that it operates by a power supply voltage Vcc obtained by rectifying an AC signal received by the parallel resonance circuit  20 R through an electromagnetic coupling from the position detection apparatus  200 B via a rectification circuit (power supply circuit)  304  configured from a diode  302  and a capacitor  303 . In the ID transmission circuit  300  of the present example, a switch circuit  305  which normally exhibits an open state (is normally open) is provided between the connection end ( 1824   b ) of the parallel resonance circuit  20 R and the power supply circuit  304 . The switch circuit  305  is configured, for example, from a semiconductor switch circuit and exhibits, in its open state, a high impedance state. 
     The switch circuit  305  is controlled so that it is switched on by a switch controlling signal from a switch controlling circuit  306 . The switch controlling circuit  306  generates a switch controlling signal from an AC signal received by the parallel resonance circuit  20 R through electromagnetic coupling from the position detection apparatus  200 B. 
     Further, in the ID transmission circuit  300 , a switch circuit  307  is connected in parallel to the parallel resonance circuit  20 R configured from the coil  24  and the capacitor circuit  28  ( 281  and  282 ). The switch circuit  307  is configured so as to be controlled between on and off by the IC  301 . 
     The IC  301  in the present example stores a manufacturer&#39;s number and a product number of the electronic ink cartridge  20  or the position pointer  1 B and controls the switch circuit  307  between on and off to transmit an ID signal including the manufacturer&#39;s number and the product number, for example, as a digital signal of 8 bits to the position detection apparatus  200 B. 
     On the other hand, the position detection apparatus  200 B of the example of  FIG. 12  is configured such that it includes a current driver  222 B, whose gain can be variably adjusted by a gain controlling signal from the outside, in place of the current driver  222  whose gain is fixed in the configuration of the position detection apparatus  200  depicted in  FIG. 7 . The position detection apparatus  200 B is further configured such that it includes a processing controlling section  233 B in place of the processing controlling section  233  in the configuration of the position detection apparatus  200 . The other components of the position detection apparatus  200 B are quite similar to those of the position detection apparatus  200  described hereinabove with reference to  FIG. 7 . 
     The current driver  222 B is configured such that it receives a gain controlling signal from the processing controlling section  233 B to vary the signal level of the transmission signal. 
     Further, the processing controlling section  233 B is configured, for example, of a microcomputer. The processing controlling section  233 B transfers an electromagnetic induction signal to and from the position pointer  1 B to carry out detection of a position pointed to by the position pointer  1 B and detection of writing pressure applied to the position pointer  1 B similarly to the processing controlling section  233  described hereinabove. In addition, the processing controlling section  233 B supplies a signal for transmission signal level control to the current driver  222 B and supplies an on/off controlling signal for controlling the transmission signal between on and off to the switch circuit  307 . Further, the processing controlling section  233 B carries out a reception process of an ID signal from the position pointer  1 B. The processing controlling section  233 B detects the on/off signal from the position pointer  1 B as a digital signal of several bits, for example, 8 bits, to detect an ID signal as hereinafter described. 
     In the following, transfer of an ID signal between the position pointer  1 B and the position detection apparatus  200 B and a position detection operation and a writing pressure detection operation are described.  FIG. 13  is a flow chart illustrating processing operation of the IC  301  of the position pointer  1 B. As hereinafter described, the process is started when the switch circuit  305  is switched on and the power supply voltage Vcc is supplied from the power supply circuit  304  to the IC  301 . 
     In a state in which the switch circuit  305  is off and the power supply voltage Vcc is not supplied from the power supply circuit  304  to the IC  301 , operation of the IC  301  is stopped. At this time, as viewed from the connection end to the parallel resonance circuit  20 R, in the present example, as viewed from the second terminal  1824   b  of the terminal member  1824  and the second end  1825   b  of the terminal member  1825  of the second capacitor circuit  182  of the capacitor circuit  18 , the ID transmission circuit  300  exhibits a high impedance state. This is equivalent to a state in which substantially nothing is connected to the connection end to the parallel resonance circuit  20 R. Accordingly, at this time, a capacitance component is not connected in parallel to the parallel resonance circuit  20 R, and the resonance frequency of the parallel resonance circuit  20 R is not influenced by the ID transmission circuit  300 . It is to be noted that an electromagnetic induction signal transmitted from the position detection apparatus  200 B is supplied as a synchronizing signal for transfer of an electromagnetic induction signal to and from the position detection apparatus  200 B to the IC  301  through a capacitor  308 . 
       FIG. 14  is a flow chart illustrating processing operation of the processing controlling section  233 B of the position detection apparatus  200 B. When power is supplied to the position detection apparatus  200 B, the processing of  FIG. 14  is executed repetitively. 
     In particular, the processing controlling section  233 B first supplies a gain controlling signal for increasing the signal level of a transmission signal to the current driver  222 B. Consequently, the AC signal of the frequency f 0  from the oscillator  221  is set to a high level by the current driver  222 B and supplied to the loop coil groups  211 X and  212 Y through the selection circuit  213  (step S 21  of  FIG. 14 ). 
     In the position pointer  1 B, the electromagnetic induction signal in the form of the AC signal of the high level from the position detection apparatus  200 B is received by the parallel resonance circuit  20 R. At this time, in response to the high signal level of the AC signal from the position detection apparatus  200 B, the switch controlling circuit  306  generates a switch controlling signal for switching “on” the switch circuit  305  based on the AC signal received by the parallel resonance circuit  20 R. If the switch circuit  305  is switched “on” in accordance with the switch controlling signal, then the power supply voltage Vcc generated by rectifying the AC signal received by the parallel resonance circuit  20 R is supplied from the power supply circuit  304  to the IC  301 . 
     When the power supply voltage Vcc is supplied to the IC  301 , the IC  301  starts operation. The IC  301  generates an ID signal including a manufacturer&#39;s number and a product number of the electronic ink cartridge  20  as a digital signal. The electromagnetic induction signal when the switch circuit  307  is controlled between on and off by the digital signal is transmitted from the position pointer  1 B to the position detection apparatus  200 B (step S 11  of  FIG. 13 ). 
     In particular, when the switch circuit  307  is off, the parallel resonance circuit  20 R can carry out a resonance operation by the AC signal transmitted thereto from the position detection apparatus  200 B and send back the electromagnetic induction signal to the position detection apparatus  200 B. The loop coil of the position detection apparatus  200 B receives the electromagnetic induction signal from the parallel resonance circuit  20 R of the position pointer  1 B. On the other hand, when the switch circuit  307  is on, the parallel resonance circuit  20 R is placed into a state in which the resonance operation with the AC signal from the position pointer  1 B is inhibited. Therefore, the electromagnetic induction signal is not sent back from the parallel resonance circuit  20 R to the position detection apparatus  200 B, and the loop coil of the position detection apparatus  200 B does not receive any signal from the position pointer  1 B. 
     In the present example, the processing controlling section  233 B of the position detection apparatus  200 B carries out detection of presence or absence of a reception signal from the position pointer  1 B repetitively eight times to receive a digital signal of 8 bits. In particular, at step S 21 , the processing controlling section  233 B controls the gain of the current driver  222 B to establish a state in which the transmission signal is signaled with the signal level thereof set high and successively carries out transmission and reception eight times at timings similar to that used for coordinate detection in order to detect the ID signal of 8 bits from the position pointer  1 B. 
     On the other hand, the IC  301  of the position pointer  1 B generates a digital signal of 8 bits corresponding to an ID signal to be transmitted and controls the switch circuit  307  between on and off in synchronism with transmission and reception of the electromagnetic induction signal to and from the position detection apparatus  200 B in response to a digital signal of 8 bits. For example, when a bit of the ID signal is “1,” the switch circuit  307  is switched on. Consequently, as described hereinabove, the electromagnetic induction signal is not sent back from the position pointer  1 B to the position detection apparatus  200 B as described hereinabove. On the other hand, if the bit of the ID signal is “0,” then the switch circuit  307  is switched off. Consequently, the electromagnetic induction signal is sent back from the position pointer  1 B to the position detection apparatus  200 B as described hereinabove. 
     Accordingly, the processing controlling section  233 B of the position detection apparatus  200 B can carry out detection of presence or absence of a reception signal from the position pointer  1 B successively by eight times to receive an ID signal in the form of a digital signal of 8 bits. 
     The processing controlling section  233 B of the position detection apparatus  200 B carries out such processing as described above to determine whether or not an ID signal from the position pointer  1 B is received (step S 22 ). If the processing controlling section  233 B determines that an ID signal has not been able to be received in a predetermined period of time, then the processing returns to step S 21  to carry out transmission of a transmission signal of a high level repetitively by a predetermined number of times. It is to be noted that, when an ID signal has not been able to be received even if the processing controlling section  233 B carries out the reception process of an ID signal repetitively by the predetermined number of times, the processing controlling section  233 B determines that the position pointer  1 B does not have a function of signaling an ID signal. Thus, the processing controlling section  233 B skips the reception process of an ID signal. 
     Then, if it is determined at step S 22  that an ID signal is received, then the processing controlling section  233 B lowers the gain of the current driver  222 B to lower the signal level of the transmission signal to a predetermined level (normal use level) lower than the high level at step S 21 , then transmit the transmission signal (step S 23 ). The predetermined level at this time is a level, at which detection of a pointed position and detection of writing pressure by the position pointer  1 B can be carried out through cooperation with the parallel resonance circuit  20 R of the position pointer  1 B but at which the switch controlling circuit  306  of the position pointer  1 B cannot switch “on” the switch circuit  305 . 
     If the signal level of the electromagnetic induction signal transmitted from the position detection apparatus  200 B is set to the predetermined level (normal use level) in this manner, then the switch controlling circuit  306  of the position pointer  1 B does not output a switch controlling signal for switching on the switch circuit  305 . Therefore, supply of the power supply voltage Vcc from the power supply circuit  304  to the IC  301  stops, and the IC  301  is disabled. Consequently, the processing of the flow chart of  FIG. 13  is ended and the position pointer  1 B stops the transmission of the ID signal. 
     However, the state in which the signal level of the electromagnetic induction signal transmitted from the position detection apparatus  200 B is set to the predetermined level (normal use state) is a state quite similar to that in the case of  FIG. 7 . Therefore, the processing controlling section  233 B of the position detection apparatus  200 B carries out a process of transferring the electromagnetic induction signal to and from the parallel resonance circuit  20 R of the position pointer  1 B to detect a pointed position and writing pressure by the position pointer  1 B in such a manner as described hereinabove in connection with the first embodiment (step S 24 ). 
     Then, the processing controlling section  233 B monitors sending back of the electromagnetic induction signal from the parallel resonance circuit  20 R of the position pointer  1 B and determines whether or not a state in which the position pointer  1 B cannot be detected is established based on that sending back of the electromagnetic induction signal disappears (step S 25 ). If it is determined at step S 25  that the position pointer  1 B has been able to be detected, then the processing controlling section  233 B returns the processing to step S 24 . On the other hand, if it is determined at step S 25  that it has become impossible to detect the position pointer  1 B, then the processing controlling section  233 B returns the processing to step S 21 . At step S 21 , a gain controlling signal for setting the signal level of the transmission signal to the high level is supplied to the current driver  222 B so that the signal level of the transmission signal to be supplied to the loop coil groups  211 X and  212 Y is set to the high level. Then, the processing controlling section  233 B repeats the processes of the steps beginning with step S 21 . 
     With the second embodiment described hereinabove with reference to  FIGS. 11A to 14 , an ID signal for identifying the electronic ink cartridge  20  or the position pointer  1 B can be transmitted from the position pointer  1 B to the position detection apparatus  200 B. Accordingly, in an electronic apparatus which includes the position detection apparatus  200 B, by detecting the ID signal of the electronic ink cartridge  20  or the position pointer  1 B, a predetermined process corresponding to the particular electronic ink cartridge or the position pointer can be allocated. This is very convenient. Further, there is a merit that, by detecting the ID signal of the electronic ink cartridge  20  or the position pointer  1 B, management of a failure or the like of the electronic ink cartridge  20  or the position pointer  1 B is facilitated. 
     Besides, if the position detection apparatus  200 B starts its operation, then it urges the position pointer  1 B to transmit an ID signal provided by the position pointer  1 B. If an ID signal is received once, then operation control is carried out such that the ID transmission circuit  300  is electrically disconnected from the resonance circuit of the position pointer  1 B and detection of a pointed position and detection of writing pressure by the position pointer  1 B are carried out in a normal use state. Further, also when it is determined that an ID signal cannot be received even if the position pointer  1 B is urged by a predetermined number of times to transmit an ID signal provided therefor, operation control is carried out such that detection of a pointed position and detection of writing pressure by the position pointer  1 B can be carried out in a normal use state. Accordingly, also where a position pointer  1 B which does not have a transmission function of an ID signal is used, a special processing operation is unnecessary, and an operation can be carried out free from a sense of discomfort. 
     It is to be noted that, in the example described above, when an electromagnetic induction signal of the high level from the position detection apparatus  200 B is received by the parallel resonance circuit  20 R, the switch controlling circuit  306  of the position pointer  1 B generates a switch controlling signal for switching “on” the switch circuit  305  based on the received electromagnetic induction signal of the high level. Then, the power supply voltage Vcc is supplied to the IC  301  in response to the switch controlling signal. 
     However, the method by which the switch controlling circuit  306  of the position pointer  1 B switches on the switch circuit  305  to supply the power supply voltage Vcc to the IC  301  is not limited to such a method as described above. 
     For example, as another example, it is also possible to adopt such a configuration that a predetermined digital signal is sent from the position detection apparatus  200 B to the position pointer  1 B so that the switch controlling circuit  306  receiving this digital signal generates a switch controlling signal for switching on the switch circuit  305 . 
     In particular, for example, when the position detection apparatus  200 B fails to detect the presence of the position pointer  1 B because it cannot detect a pointed position by the position pointer  1 B, the position detection apparatus  200 B signals the predetermined digital signal as an electromagnetic induction signal through the loop coil groups  211 X and  212 Y. The parallel resonance circuit  20 R of the position pointer  1 B receives the electromagnetic induction signal which has a signal-envelope corresponding to the digital signal and supplies the received electromagnetic induction signal to the switch controlling circuit  306 . 
     The switch controlling circuit  306 , for example, waveform-shapes this signal to envelope-detect the signal to extract the digital signal. Then, the switch controlling circuit  306  generates a switch controlling signal for switching on the switch circuit  305  when the digital signal coincides with a digital signal set in advance. The power supply voltage Vcc is supplied to the IC  301  in accordance with the switch controlling signal. 
     The IC  301  starts operation in response to turning on of the power supply voltage Vcc and sends an ID signal of the position pointer  1 B to the position detection apparatus  200 B through the parallel resonance circuit  20 R. When the ID signal is received, the position detection apparatus  200 B stops the signaling of the predetermined digital signal and changes the operation mode from the ID signal detection mode to the normal use mode, in which a pointed position by the position pointer  1 B is detected so that a detection operation of the pointed position by the position pointer  1 B is carried out. If it has become impossible to receive the predetermined digital signal, then the switch controlling circuit  306  of the position pointer  1 B switches off the switch circuit  305  to stop the supply of the power supply voltage Vcc to the IC  301 . Consequently, the signaling of the ID signal is stopped, and the ID transmission circuit  300  is placed into a high impedance state, in which the ID transmission circuit  300  is electrically disconnected from the connection end to the parallel resonance circuit  20 R. 
     It is to be noted that, when the position pointer  1 B cannot be detected any more, the position detection apparatus  200 B resumes outputting the predetermined digital signal. 
     It is to be noted that, since it is only necessary for the ID transmission circuit  300  to be connected in parallel to the coil  24 , the ID package  320  need not be provided between the capacitor circuit  28  and the cap  19 . For example, the ID transmission circuit  300  may be provided between the connection member  27  and the capacitor circuit  28 . 
     Further, a different connector connected to the second end  1824   b  of the terminal member  1824  and the second end  1825   b  of the terminal member  1825  of the second capacitor circuit  282  may be provided on the cap  19  in addition to the connector  194 . Meanwhile, a circuit section similar to the ID package which includes the ID transmission circuit  300  is provided in the different connector outside the tubular member  50 . 
     Third Embodiment 
     In the first and second embodiments described above, the pressure sensor is configured such that the inductance, which forms a resonance circuit, varies in response to pressure applied to the core member. In contrast, in a third embodiment to be described below, the pressure sensor is configured such that the capacitance of the capacitor, which forms a resonance circuit, varies in response to pressure applied to the core member. Further, in the position pointer of the present third embodiment, the pressure sensor wherein the capacitance varies in response to pressing force applied to the core member is configured from a pressure sensing semiconductor device of the capacitive type which is manufactured in accordance with a MEMS (Micro Electronic Mechanical System) technology. 
       FIGS. 15A and 15B  are views depicting an example of a configuration of an electronic ink cartridge  30  of a position pointer of the present third embodiment.  FIG. 15A  is a sectional view depicting an internal configuration of the electronic ink cartridge  30 . Meanwhile,  FIG. 15B  is an exploded perspective view depicting a general configuration of the electronic ink cartridge  30 . It is to be noted that, also in the present example, for the convenience of description, some of the internal component parts of a tubular member  5 ′ of the electronic ink cartridge  30  are not depicted in cross-section in  FIG. 15A . 
     Further, the configuration of the housing of the position pointer of the present third embodiment and the attachment structure of the push switch  7  to the housing are similar to those in the first embodiment, and therefore, illustration and description of them are omitted. Further, also in the description of the present third embodiment, like components to those in the first embodiment are denoted by like reference symbols, and description of them is omitted. 
     The tubular member  5 ′ is configured from a first tubular member  5 C and a second tubular member  5 D as two separate members separate from each other in the direction of the center axis similarly as in the first embodiment. The first tubular member  5 C and the second tubular member  5 D have a narrow shape having an outer diameter of, for example, 2.5 mm and an inner diameter of, for example, 1.5 mm to 2 mm. Further, the tubular member  5 ′ is configured from a material of a nonmagnetic substance such as a nonmagnetic metal, a resin material, glass or ceramics, in the present example, from a material having conductivity such as, for example, SUS305 or SUS310S. 
     The first tubular member  5 C has a configuration similar to that of the first tubular member  5 A of the first embodiment described hereinabove. In particular, on a first end side of the first tubular member  5 C in the direction of the center axis, an opening  5 Ca for allowing a distal end of a core member  31  to extend outwardly therethrough is provided. Further, in an opening  5 Cb on the second end side of the first tubular member  5 C, a threaded portion  5 Cc for being screwed with the second tubular member  5 D is formed. Also the second tubular member  5 D has a configuration similar to that of the second tubular member  5 B in the first embodiment described hereinabove. In particular, at an opening portion on the first end side of the second tubular member  5 D, a threaded portion  5 Da for being screwed with the first tubular member  5 C is formed. Further, on the second end side of the second tubular member  5 D, a cut-out  5 Db is formed in the direction of the center axis and a ring-shaped protrusion  5 Dc for being screwed with a ring-shaped grooved portion  19   a  formed on a reduced diameter portion  195  of a cap  19 C is formed. 
     As depicted in  FIGS. 15A and 15B , also in the electronic ink cartridge  30  of the present third embodiment, principal parts which form the position pointer of the electromagnetic induction type are all accommodated in the tubular member  5 ′. However, as shown in  FIGS. 15A and 15B , a coil spring  32 , the core member  31 , a pressure sensing semiconductor device  35 , a ferrite core  34  as an example of a magnetic member on which a coil  33  is wound and a connection member  36  are juxtaposed in order as viewed from the opening  5 Ca side and accommodated in the first tubular member  5 C, and a capacitor circuit  18 C is accommodated in the second tubular member  5 D in such a state that the directions of the center axes of the parts coincide with the direction of the center axis of the first tubular member  5 C and the second tubular member  5 D. Further, the cap  19 C is inserted in the opening on the second end side of the second tubular member  5 D to close up the opening of the tubular member  5 ′. The capacitor circuit  18 C is configured from a first capacitor circuit  181 C and a second capacitor circuit  182 C and is configured quite similarly to the capacitor circuit  18  in the first embodiment except that it has s smaller diameter than that of the capacitor circuit  18  in the first embodiment. 
     It is to be noted that, in the present third embodiment, at a point of time at which the coil spring  32 , core member  31 , pressure sensing semiconductor device  35 , ferrite core  34  on which the coil  33  is wound and connection member  36  are accommodated into the first tubular member  5 C, a side peripheral face position of the first tubular member  5 C corresponding to a side peripheral face of the connection member  36  is constricted (caulked) in the direction of the center axis to form protrusions  5 Cd and  5 Ce on an inner peripheral face of the first tubular member  5 C, so that the connection member  36  is pressure contacted with and bound by the first tubular member  5 C to restrict the position of the connection member  36  so as not to move in the direction of the center axis. Then, the pressure sensing semiconductor device  35  and the ferrite core  34  on which the coil  33  is wound are prevented from rattling in the direction of the center axis by biasing force of the coil spring  32  disposed between the opening  5 Ca side of the first tubular member  5 C and the pressure sensing semiconductor device  35 . 
     Thereafter, similarly as in the first embodiment described hereinabove, the capacitor circuit  18 C is coupled to the connection member  36  and the second tubular member  5 D is screwed with and coupled to the first tubular member  5 C, and then the opening at the second end of the second tubular member  5 D is closed up with the cap  19 C. 
     Configuration of the components accommodated in the inside of the tubular member  5 ′ and assembly of the electronic ink cartridge  30  as well as adjustment of the resonance frequency are described furthermore. 
     The core member  31  in the present third embodiment is configured of a rod-like member made of, for example, resin as depicted in  FIGS. 15A and 15B . Further, in the present third embodiment, the core member  31  is inserted as a pressing member into the pressure sensing semiconductor device  35 . 
     The ferrite core  34  has a cylindrical shape having, in the present third embodiment, a fixed diameter, and the coil  33  is wound on the ferrite core  34 . A recessed portion  352  is provided on a bottom face  351   b  side of a package member  351  of the pressure sensing semiconductor device  35  on the opposite side from an upper face  351   a  into which the core member  31  is inserted, and a first end side of the ferrite core  34  in the direction of the center axis is fitted into the recessed portion  352 . 
     Further, a second end side of the ferrite core  34  in the direction of the center axis is fitted with and coupled to the connection member  36  made of, for example, resin. A recessed hole  34   a  into which a protrusion  361  of the connection member  36  is to be fitted is formed at the center of an end face of the ferrite core  34  on the connection member  36  side. 
     Example of the Configuration of the Pressure Sensing Semiconductor Device  35   
     The position pointer of the present third embodiment detects writing pressure as a variation of the capacitance of a capacitor, which forms a resonance circuit together with a coil as described hereinabove. The position pointer of the present third embodiment uses a semiconductor device (pressure sensing chip) fabricated in accordance with a MEMS technology and proposed formerly in Japanese Patent Application No. 2012-015254 co-assigned to the applicant of the present invention as a pressure sensor whose capacitance varies in response to writing pressure. 
     The pressure sensing semiconductor device  35  is configured such that a pressure sensing chip  400  is accommodated in the package member  351  made of, for example, resin in such a state that the pressure sensing chip  400  can be pressed by a pressing member from the outside. The pressing member is called, in the present example, core member  31 . The pressure sensing semiconductor device  35  of the present example has an integrated structure wherein the pressure sensing semiconductor device  35  removably holds the core member  31 , and the ferrite core  34  on which the coil  33  is wound is held by the package member  351 . 
       FIGS. 16A and 16B  are views depicting a configuration of the pressure sensing semiconductor device  35  of the present example.  FIG. 16A  is a vertical sectional view of the pressure sensing semiconductor device  35 . Meanwhile,  FIG. 16B  is a view depicting the pressure sensing chip  400  accommodated in the pressure sensing semiconductor device  35 . 
     The pressure sensing semiconductor device  35  is made of a resin material which has elasticity and is an electric insulating material, for example, silicon rubber. The pressure sensing semiconductor device  35  is configured such that the pressure sensing chip  400  is sealed in the package member  351 , for example, of a cylindrical shape. 
     The pressure sensing chip  400  of the present example is formed from a first electrode  401 , a second electrode  402 , and an insulating layer (dielectric layer)  403  between the first electrode  401  and the second electrode  402  as depicted in  FIG. 16B . The first electrode  401  and the second electrode  402  are configured from a conductor made of single crystal silicon (Si). The insulating layer  403  is configured from an insulating film formed from, in the present example, an oxide film (SiO 2 ). 
     A recessed portion  404  of, for example, a circular shape is formed on the insulating layer  403 , and a space  405  is formed between the insulating layer  403  and the first electrode  401 . A bottom face of the recessed portion  404  is formed as a flat face and has a diameter R of, for example, R=1 mm. The depth of the recessed portion  404  is, in the present example, approximately several tens of microns to several hundreds of microns. If the first electrode  401  is pressed from a face  401   a  side, then it can be displaced so as to be deflected toward the space  405 . 
     The pressure sensing chip  400  having such a configuration as described above is a capacitor by which a capacitance Cv is formed between the first electrode  401  and the second electrode  402 . If pressure P is applied to the first electrode  401  from the face  401   a  side of the first electrode  401  as depicted in  FIG. 16B , then the first electrode  401  is deflected as indicated by a broken line in  FIG. 16B . Thereupon, the distance between the first electrode  401  and the second electrode  402  decreases to increase the capacitance Cv. The deflection amount of the first electrode  401  varies in response to the magnitude of the pressure P applied. Accordingly, the capacitance Cv varies in response to the magnitude of the pressure P applied to the pressure sensing chip  400 . The pressure can be detected based on the variation of the capacitance Cv. 
     In the pressure sensing semiconductor device  35  in the present embodiment, the pressure sensing chip  400  having such a configuration as described above is accommodated in the package member  351  in a state in which the face  401   a  of the first electrode  401  upon which the pressure acts is opposed to the upper face  351   a  of the package member  351  in  FIG. 16A . 
     A communication hole  353  having, for example, a circular cross section is formed in the package member  351  such that it extends from the upper face  351   a  to a location in the proximity of the face  401   a  of the first electrode  401 . Into the communication hole  353 , the core member  31  is inserted as a pressing member for pressing the pressure sensing chip  400  as depicted in  FIG. 15A  and  FIG. 16A . A tapered portion  351   c  is formed on an opening portion side (upper face  351   a  side) of the communication hole  353  of the package member  351 , and an opening of the communication hole  353  has a trumpet shape so that the core member  31  as a pressing member can be easily inserted into the communication hole  353 . 
     Further, as shown in  FIG. 16A , protrusions  354   a  and  354   b  of a shape of an O-snap ring for holding the core member  31  of a shape of a round rod are provided on an inner wall face of the communication hole  353 . In this instance, the inner diameter of the communication hole  353  is equal to or a little larger than the diameter of a contacting portion of the core member  31 . Meanwhile, the inner diameter of the protrusions  354   a  and  354   b  in the shape of an O-snap ring is selected smaller than the diameter of the contacting portion of the core member  31 . 
     Accordingly, when the core member  31  is inserted into the communication hole  353  under the guidance of the tapered portion  351   c  provided on the opening side (upper face  351   a  side) of the package member  351 , it is retained by the protrusions  354   a  and  354   b  of a shape of an O-snap ring. However, the core member  31  can be pulled out from the communication hole  353  by predetermined force. Accordingly, the core member  31  can be readily exchanged. 
     The first electrode  401  of the pressure sensing chip  400  is connected to a first lead terminal  356  formed of a conductor by a gold wire  355 , and the second electrode  402  contacts with and is connected to a second lead terminal  357  formed of a conductor. In the present third embodiment, distal end portions of the first and second lead terminals  356  and  357  are led out such that they extend perpendicularly to the bottom face  351   b  of the package member  351  as depicted in  FIGS. 16A and 16B . 
     On the bottom face  351   b  of the package member  351 , the circular recessed portion  352  having a diameter substantially equal to the diameter of the ferrite core  34  is formed. The depth of the recessed portion  352  is set such that a first end portion of the ferrite core  34 , on which the coil  33  is wound, in the direction of the center axis is fitted in the recessed portion  352 . The ferrite core  34  is inserted into the recessed portion  352  and coupled to the package member  351 , for example, by bonding agent. The first and second lead terminals  356  and  357  are led out from a periphery of the recessed portion  352  through the bottom face  351   b.    
     The first lead terminal  356  and the second lead terminal  357  are electrically connected to terminal members  362  and  363  of the connection member  36  by gold wires, lead wires or the like as hereinafter described. Also, a first end  33   a  and a second end  33   b  of the coil  33  wound on the ferrite core  34  are electrically connected to the terminal members  362  and  363  of the connection member  36 , respectively. 
     An example of a configuration of the connection member  36  is depicted in  FIGS. 17A to 17C .  FIG. 17A  is a view of the connection member  36  as viewed from the side on which the connection member  36  is coupled to the ferrite core  34  in the direction of the center axis of the connection member  36 .  FIG. 17B  is a sectional view taken along line F-F of  FIG. 17A , and  FIG. 17C  is a view depicting an end face of the connection member  36  as viewed from the capacitor circuit  18 C side in the direction of the center axis of the connection member  36 . 
     As described hereinabove, the connection member  36  includes a main body portion  360  made of an electric insulating material such as, for example, resin and having a cylindrical shape of an outer diameter equal to the inner diameter of the first tubular member  5 C. As depicted in  FIGS. 17A and 17B , a recessed hole  364 , into which part of the cylindrical portion of the ferrite core  34  is to be fitted, is provided on an end face of the main body portion  360  of the connection member  36  on the side on which the main body portion  360  is coupled to the ferrite core  34 . Further, the protrusion  361 , which fits with the recessed hole  34   a  formed on an end face of the ferrite core  34 , is formed at the center of the bottom face of the recessed hole  364 . 
     Further, as shown in  FIGS. 17A and 17B , recessed grooves  365  and  366  extending in the direction of the center axis of the cylinder are formed at positions of a peripheral side face of the main body portion  360  of the connection member  36  spaced by an angular distance of 180 degrees from each other. In the recessed grooves  365  and  366 , first end portions  362   a  and  363   a  of the terminal members  362  and  363  are erected in a direction perpendicular to the peripheral direction, respectively. At the first end portions  362   a  and  363   a  of the terminal members  362  and  363  in the erected state, V-shaped notches  362   c ,  362   d  and  363   c ,  363   d  are formed as depicted in  FIG. 17A , respectively. 
     The V-shaped notches  362   c  and  362   d  of the terminal member  362  are provided for connection of the first electrode  401  of the pressure sensing chip  400  of the pressure sensing semiconductor device  35  and the first end  33   a  of the coil  33 . Meanwhile, the V-shaped notches  363   c  and  363   d  of the terminal member  363  are provided for connection of the second electrode  402  of the pressure sensing chip  400  of the pressure sensing semiconductor device  35  and the second end  33   b  of the coil  33 . 
     On an end face of the main body portion  360  of the connection member  36  on the connection side to the capacitor circuit  18 C, a recessed portion  368  into which part of the capacitor circuit  18 C is to be fitted is provided as shown in  FIG. 17B . On a side peripheral face of the recessed portion  368 , a ring-shaped recessed groove  368   a , into which a ring-shaped protrusion  181 Ca (refer to  FIG. 15B ) formed on a peripheral portion of the first capacitor circuit  181 C of the capacitor circuit  18 C is to be fitted, is formed. 
     Further, on a bottom face of the recessed portion  368 , a ring-shaped electrode conductor  362   b  is formed as shown in  FIGS. 17B and 17C  as a second end portion of the terminal member  362  of the connection member  36 . This ring-shaped electrode conductor  362   b  meshes with a first end  1814   a  of a terminal member  1814  of the first capacitor circuit  181 C of the capacitor circuit  18  (refer to  FIG. 4 ). 
     Further, a recessed hole  367  is formed at the center of the bottom face of the recessed portion  368  of the connection member  36  in a state displaced from the ring-shaped electrode conductor  362   b . A second end portion  363   b  of the terminal member  363  of the connection member  36  is formed such that it is positioned in the recessed hole  367 , and a bent portion of the second end portion  363   b  of the terminal member  363  having elasticity positioned in the recessed hole  367  defines an insertion hole  363   e . A first end  1815   a  of a rod-shaped terminal member  1815  of the first capacitor circuit  181 C of the capacitor circuit  18 C is inserted in the insertion hole  363   e  and connected to the second end portion  363   b  of the terminal member  363 . 
     The connection member  36  is coupled by adhesion to the ferrite core  34 , for example, by bonding agent in a state in which the protrusion  361  is fitted in the recessed hole  34   a  on the end face of the ferrite core  34 . Further, lead wires connected to the first and second lead terminals  356  and  357  connected to the first electrode  401  and the second electrode  402  of the pressure sensing chip  400  of the pressure sensing semiconductor device  35  are inserted and connected to the V-shaped notch  362   c  or  362   d  of the first end portion  362   a  of the terminal member  362 , and the V-shaped notch  363   c  or  363   d  of the first end portion  363   a  of the terminal member  363  of the connection member  36 , respectively. Further, the first end  33   a  and the second end  33   b  of the coil  33  are inserted and connected to the V-shaped notch  362   c  or  362   d  of the first end portion  362   a  of the terminal member  362 , and the V-shaped notch  363   c  or  363   d  of the first end portion  363   a  of the terminal member  363  of the connection member  36 , respectively. 
     In this manner, in the present third embodiment, the pressure sensing semiconductor device  35 , ferrite core  34  on which the coil  33  is wound and connection member  36  are coupled to each other so that they can be handled as a single unitized component part. 
     Further, in the present third embodiment, the coil spring  32  is inserted into the hollow portion of the first tubular member  5 C from the opening  5 Cb side, which is opposite from the opening  5 Ca side, toward the opening  5 Ca side. Then, an integrated component part, in which the pressure sensing semiconductor device  35 , ferrite core  34  on which the coil spring  33  is wound and connection member  36  are connected into a single unit, is inserted such that the first end side of the coil spring  32  is abutted against the upper face  351   a  of the pressure sensing semiconductor device  35 . The core member  31  may be inserted and fitted into the pressure sensing semiconductor device  35  in advance and then accommodated into the first tubular member  5 C or may be inserted and fitted into the pressure sensing semiconductor device  35  from the opening  5 Ca side later. 
     It is to be noted that the first electrode  401  and the second electrode  402  of the pressure sensing chip  400  of the pressure sensing semiconductor device  35  and the first end  33   a  and the second end  33   b  of the coil  33  are connected, for example, to the first end portions  362   a  and  363   a  of the terminal members  362  and  363  in the recessed grooves  365  and  366  of the connection member  36 , respectively. Therefore, lead portions of the first electrode  401  and the second electrode  402  of the pressure sensing chip  400  and the first end  33   a  and the second end  33   b  of the coil  33  do not contact with the inner wall face of the first tubular member  5 C. 
     To the connection member  36  accommodated in the first tubular member  5 C in such a manner as described above, the coil  33  and the capacitor circuit  18 C, which configures a parallel resonance circuit together with a capacitor formed of the pressure sensing chip  400 , are connected as hereinafter described. The capacitance of the capacitor circuit  18 C is set to a predetermined value as hereinafter described. 
     In this instance, part of the first capacitor circuit  181 C of the capacitor circuit  18 C is accommodated into the recessed portion  368  of the connection member  36  and the ring-shaped protrusion  181 Ca of the first capacitor circuit  181 C is fitted into the ring-shaped recessed groove  368   a  of the recessed portion  368  to couple the capacitor circuit  18 C to the connection member  36 . In this coupled state, the first end  1814   a  of the terminal member  1814  of the first capacitor circuit  181 C is abutted against and electrically connected to the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  of the connection member  36 . Further, the rod-like first end  1815   a  of the terminal member  1815  of the first capacitor circuit  181 C is inserted into the insertion hole  363   e  of the terminal member  363  of the connection member  36  and electrically connected to the second end portion  363   b.    
     Then, the capacitor circuit  18 C is accommodated into the inside of the second tubular member  5 D. Further, the threaded portion  5 Da formed on the inner wall face of the opening on the first end side of the second tubular member  5 D and the threaded portion  5 Cc formed on an outer peripheral side face of the opening  5 Cb of the first tubular member  5 C are screwed with each other to form an integrated tubular member  5 ′. 
     Then, the reduced diameter portion  195  of the cap  19 C is fitted into the second tubular member  5 D to engage the protrusion  19   c  with the positioning groove  5 Db. At this time, in the present third embodiment, part of the second capacitor circuit  182 C of the capacitor circuit  18 C is inserted into a recessed portion  198  provided on the reduced diameter portion  195  of the cap  19 C to establish electric connection between them. 
     An example of the configuration of the cap  19 C in the present third embodiment is depicted in  FIGS. 18A to 18C .  FIG. 18A  is a view of the cap  19 C as viewed from the face side opposing the capacitor circuit  18 C, and  FIG. 18B  is a view of the cap  19 C as viewed from the side opposite from the face side opposing the capacitor circuit  18 C.  FIG. 18C  is a sectional view taken along line G-G of  FIG. 18A . 
     The cap  19 C has a configuration similar to that of the cap  19  in the first embodiment. However, the cap  19 C is different in configuration of the connection portion to the capacitor circuit  18 C having a diameter smaller than that of the capacitor circuit  18  in the first embodiment. In  FIGS. 18A to 18C , like components to those of the cap  19  in the first embodiment are denoted by like reference symbols. 
     In particular, on an end face of the reduced diameter portion  195  of the cap  19 C in the present third embodiment opposing the second capacitor circuit  182 C, the recessed portion  198 , into which part of the second capacitor circuit  182 C of the capacitor circuit  18 C is to be fitted, is formed as depicted in  FIGS. 18A and 18C . The recessed portion  198  is a circular recessed hole of a diameter substantially equal to the diameter of the second capacitor circuit  182 C. On a side wall of the recessed portion  198 , a ring-shaped recessed groove  198   a , into which a ring-shaped protrusion  182   b  of the second capacitor circuit  182 C is to be fitted, is formed and a center axis direction recessed groove  198   b , into which a center axis direction protrusion  182   a  formed on the second capacitor circuit  182 C is to be fitted, is formed. 
     Further, on a bottom face of the recessed portion  198  of the cap  19 C, the first end portions  192   a  and  193   a  of the terminal members  192  and  193  are provided in an exposed relationship such that they are elastically abutted against the second end  1825   b  of the terminal member  1825  and the second end  1826   b  of the terminal member  1826  on the end face of the second capacitor circuit  182 C. The second end  192   b  of the terminal member  192  is connected to the first end of the connector  194  similarly as in the first embodiment, and the second end  193   b  of the terminal member  193  is connected to the second end of the connector  194 . 
     The reduced diameter portion  195  of the cap  19 C configured in such a manner as described above is inserted into the second tubular member  5 D such that the protrusion  19   c  is engaged with the positioning groove  5 Db and the protrusion  182   a  of the second capacitor circuit  182 C is engaged with the groove  198   b  of the recessed portion  198  of the cap  19 C. Consequently, the ring-shaped grooved portion  19   a  of the cap  19 C and the ring-shaped protrusion  5 Dc of the second tubular member  5 D are fitted with each other to lock the cap  19 C in the second tubular member  5 D. At this time, an end portion of the second capacitor circuit  182 C is inserted into the recessed portion  198  of the cap  19 C, and the ring-shaped protrusion  182   b  is fitted into the ring-shaped recessed groove  198   a  of the recessed portion  198  to couple the capacitor circuit  18 C to the cap  19 C. Then, in this coupled state, the second end  1825   b  of the terminal member  1825  and the second end  1826   b  of the terminal member  1826  of the second capacitor circuit  182 C are connected to the first end  193   a  of the terminal member  193  and the first end  192   a  of the terminal member  192  on the bottom face of the recessed portion  198  of the cap  19 C, respectively. The electronic ink cartridge  30  is assembled in such a manner as described above. 
     Setting of the Capacitance Value of the Capacitor Circuit  18 C 
     As described hereinabove, on the opening  5 Cb side of the first tubular member  5 C in which the connection member  36  is accommodated, the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  and the second end portion  363   b  of the terminal member  363  of the connection member  36  are exposed for contact from the outside. Further, the ring-shaped electrode conductor  362   b  and the second end portion  363   b  are connected to the first end and the second end of the parallel resonance circuit configured from the coil  33  and a capacitor configured from the pressure sensing chip  400 , respectively. Accordingly, an electric characteristic of the parallel resonance circuit configured from the coil  33  and the capacitor configured from the pressure sensing chip  400  can be extracted from the ring-shaped electrode conductor  362   b  of the terminal member  362  and the second end portion  363   b  of the terminal member  363 . 
     In the present embodiment, the ring-shaped electrode conductor  362   b  of the terminal member  362  and the second end portion  363   b  of the terminal member  363  which can be contacted from the outside in this manner are used to set the capacitance of the first capacitor circuit  181 C and the capacitance of the second capacitor circuit  182 C which configure the capacitor circuit  18 C in the following manner. 
     Setting of a capacitance value of the capacitor circuit  18 C is described with reference to an equivalent circuit of  FIG. 19 . As described hereinabove, the parallel circuit of the coil  33  wound on the ferrite core  34  and a variable capacitor  400 C, which forms the pressure sensing chip  400  accommodated in the pressure sensing semiconductor device  35 , is connected between the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  and the second end portion  363   b  of the terminal member  363  of the connection member  36 . At this time, no writing pressure is applied to the core member  31 , and it is assumed that the inductance Lc of the coil  33  at this time and the capacitance CVo of the capacitor  400 C configured from the pressure sensing chip  400  have values each including a dispersion arising from manufacturing process. 
     Therefore, the resonance frequency f 1  of the resonance circuit configured from the inductance Lc of the coil  33  and the capacitance CVo of the capacitor  400 C configured from the pressure sensing chip  400  is measured first using the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  and the second end portion  363   b  of the terminal member  363 . Then, a capacitor having a known capacitance value Co is connected to the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  and the second end portion  363   b  of the terminal member  363  to measure a resonance frequency f 2  similarly. It is to be noted that a resonance frequency f 0  to be set is known, and the capacitance value to be set to the first capacitor circuit  181 C of the capacitor circuit  18 C is represented by Cx.
 
 f   1   2 =1/{4·π 2   ·Lc·CVo} 
 
 f   2   2 =1/{4·π 2   ·Lc ·( CVo+Co )}
 
 f   0   2 =1/{4·π 2   ·Lc ·( CVo+Cx )}
 
     From these equations,
 
 Cx=Co ·( f   2   /f   0 ) 2 ·( f   1   2   −f   0   2 )/( f   1   2   −f   2   2 )
 
is obtained.
 
     As described above, even if the inductance Lc of the coil  33  and the capacitance of the capacitor  400 C configured from the pressure sensing chip  400  are unknown or are values which include some dispersion, the value Cx of the capacitance connected further in parallel to the parallel circuit of the coil  33  and the capacitor  400 C in accordance with the resonance frequency fo to be set can be calculated. In other words, the capacitance, with which the resonance frequency of the resonance circuit of the position pointer when the push switch  7  is off is made equal to the target frequency f 0  (capacitance of the first capacitor circuit  181 C of the capacitor circuit  18 C), can be calculated. Thus, a number of chip capacitors  183  with which the calculated capacitance is obtained are accommodated into the first capacitor circuit  181 C of the capacitor circuit  18 C to set the capacitance of the first capacitor circuit  181 C. 
     Similarly, the capacitance for making the resonance frequency of the resonance circuit, which is configured from the coil  33 , pressure sensing chip  400  and first capacitor circuit  181 C, of the position pointer when the push switch  7  is on, equal to a target frequency f 4  (the capacitance value to be set to the second capacitor circuit  182 C of the capacitor circuit  18 C is represented by Cx 2 ) is calculated in the following manner. 
     Where the capacitance value set for the first capacitor circuit  181 C is represented by Cx 1  (this value is equal to or approximate to Cx), the first capacitor circuit  181 C whose capacitance value is set to Cx 1  is connected to the ring-shaped electrode conductor  362   b  at the second end portion of the terminal member  362  and the second end portion  363   b  of the terminal member  363 , in place of the capacitor whose capacitance value Co is known, so as to similarly measure a resonance frequency f 3 .
 
 f   1   2 =1/{4·π 2   ·Lc·CVo} 
 
 f   3   2 =1/{4·π 2   ·Lc ·( CVo+Cx 1)}
 
 f   4   2 =1/{4·π 2   ·Lc ·( CVo+Cx 1+ Cx 2)}
 
     From these equations,
 
 Cx 2= Cx 1·( f   1   /f   4 ) 2 ·( f   3   2   −f   4   2 )/( f   1   2   −f   3   2 )
 
is obtained.
 
     Then, the capacitance Cx 2  of the second capacitor circuit  182 C of the capacitor circuit  18 C is set so as to become equal to the calculated capacitance Cx 2 . 
     By measuring the resonance frequency in the same state as an actual use state in such a manner as described above, the value of the capacitance of the first capacitor circuit  181 C of the capacitor circuit  18 C can be calculated. Then, a value equal to or proximate to the calculated value of the capacitance is set. 
     Further, since the value to which the resonance frequency value is to be changed by operating the push switch  7  (side switch) is known, also the value of the capacitance of the second capacitor circuit  182 C which depends upon the value of the capacitance of the first capacitor circuit  181 C of the capacitor circuit  18 C can be calculated. 
     In the electronic ink cartridge  30  of the present third embodiment, the resonance frequency of the parallel resonance circuit configured from the coil  33  accommodated in the tubular member  5 ′, capacitor  400 C of the pressure sensing chip  400  and capacitance (Cx 1 , Cx 2 ) set to the capacitor circuit  18 C is in an adjusted state, regardless of whether the push switch  7  is in the off state or the “on” state. Accordingly, in the case of the present third embodiment also, when the electronic ink cartridge  30  is accommodated into the housing  2  of the position pointer, adjustment of the resonance frequency is no longer required. 
     Further, in the present third embodiment, the core member  31 , ferrite core  34  on which the coil  33  is wound and pressure sensing semiconductor device  35  are coupled into an integrated structure and accommodated in the hollow portion of the first tubular member  5 C. Further, the terminals for connection to the capacitor circuit  18 C, to which the first end and the second end of the coil  33  and the first end and the second end of the variable capacitor  400 C configured from the pressure sensing chip  400  are connected, are provided on the end face of the connection member  36  so as to be exposed such that they can be contacted from the outside. 
     Therefore, the resonance frequency of the resonance circuit configured from the coil  33  in a state in which it is accommodated in the first tubular member  5 C and the capacitance of the pressure sensing chip  400  accommodated in the pressure sensing semiconductor device  35  can be measured using the connection terminals provided on the end face of the connection member  36 . Consequently, the capacitance value of the capacitor circuit  18 C, which is connected in parallel to the parallel resonance circuit of the coil  33  and the pressure sensing chip  400  to thereby form another parallel resonance circuit, can be calculated in such a manner as described above. 
     Further, in the embodiment described above, only by coupling the capacitor circuit  18 C to the connection member  36  such that the first electrode and the second electrode of the capacitor circuit  18 C having capacitance set to the desired value are connected to the connection terminals of the connection member  36 , the electronic ink cartridge  30  can be formed in a significantly simplified configuration. 
     Furthermore, in the present third embodiment, the core member  31 , ferrite core  34  on which the coil  33  is wound, pressure sensing semiconductor device  35  as a pressure sensor and capacitor circuit  18 C are inserted in the electronic ink cartridge  30 , and the electronic ink cartridge  30  is in an assemble state in which adjustment of the resonance frequency has been carried out already. Accordingly, the position pointer can be configured only by accommodating the electronic ink cartridge  30  into the housing of the position pointer. Consequently, the position pointer can be achieved, in which the electronic ink cartridge  30  can be handled like a so-called replacement core of a ballpoint pen or the like. 
     Further, similarly as in the embodiments described hereinabove, the component parts are disposed in order in the direction of the center axis in the tubular member  5 ′ of the electronic ink cartridge  30  and electrically connected to each other while being mechanically coupled with each other. Therefore, advantageously, a configuration of an electronic ink cartridge having a narrow (thin) profile as having a diameter of, for example, 2.5 mm can be readily implemented. 
     Modifications to the Third Embodiment 
     Also in the third embodiment described above, by accommodating an ID package which accommodates the ID transmission circuit  300  similar to that of the second embodiment into the tubular member  5 ′, it becomes possible to transmit information such as identification information of the electronic ink cartridge  30  to a position detection apparatus similarly as in the second embodiment. In this instance, since it is only necessary to connect the ID package, in which the ID transmission circuit  300  is accommodated, in parallel to the coil  33 , the ID package may be disposed at a position between the connection member  36  and the capacitor circuit  18 C or another position between the capacitor circuit  18 C and the cap  19 C in the tubular member  5 ′ as can be recognized from the equivalent circuit of  FIG. 19 . 
     Further, in the third embodiment described above, while the pressure sensing chip  400  of the pressure sensing semiconductor device  35  is pressed by the core member  31 , the configuration for transmitting pressure applied to the core member  31  to the pressure sensing chip  400  of the pressure sensing semiconductor device  35  is not limited to this configuration. For example, though not depicted, the following configuration may be adopted. In particular, the core member is provided in a coupled state to the ferrite core as in the second embodiment, and the pressure sensing semiconductor device is disposed on the opposite side from the coupling side of the ferrite core to the core member. Further, the pressing member of the pressure sensing chip is provided on the opposite side from the coupling side of the ferrite core to the core member such that the pressure sensing chip of the pressure sensing semiconductor device is pressed by the pressing member. 
     Further, while, in the third embodiment described above, the pressure sensing semiconductor device  35  and the ferrite core  34  on which the coil  33  is wound are coupled integrally, the pressure sensing semiconductor device  35  and the ferrite core  34  on which the coil  33  is wound may be connected to each other through a different connection member. 
       FIG. 20  is a view depicting an example of a configuration of part of an electronic ink cartridge  30 A in the case just described. 
     In particular, in the example of  FIG. 20 , a different connection member  38  is provided between the pressure sensing semiconductor device  35  and the ferrite core  34 , on which the coil  33  is wound, in addition to the connection member  36 . The connection member  38  includes a protrusion  381  accommodated in the recessed portion  352  of the pressure sensing semiconductor device  35  and includes a tubular portion  382  defining a hollow portion, in which the ferrite core  34  on which the coil  33  is wound is accommodated. The tubular portion  382  has a length such that an end face at its opening side abuts against the connection member  36  connected to the capacitor circuit  18 C. 
     Further, the connection member  38  includes fitting portions  383  and  384  provided on an end face of the tubular portion  382  opposing the pressure sensing semiconductor device  35 , such that the fitting portions  383  and  384  are fitted with the first and second lead terminals  356  and  357  of the pressure sensing semiconductor device  35 . 
     On an end face of the tubular portion  382  formed on the connection member  38  which abuts against the connection member  36 , connection terminals  385  and  386  are provided, which are electrically connected, for example by gold wires, to the fitting portions  383  and  384  fitted with the first and second lead terminals  356  and  357  of the pressure sensing semiconductor device  35 , respectively. For example, gold wires are connected to the connection terminals  385  and  386  such that they are electrically connected to the V-shaped notches  362   c  and  363   c  of the terminal members  362  and  363  of the connection member  36 . 
     Further, the connection member  38  includes ring-shaped recessed grooves  38   a  and  38   b , which are fitted with ring-shaped protrusions  5 Cf and  5 Cg formed on the first tubular member  5 C to fix the connection member  38  to the first tubular member  5 C so that the connection member  38  does not move in the direction of the center axis. Accordingly, in the example of  FIG. 20 , the pressure sensing chip  400  of the pressure sensing semiconductor device  35  can detect the pressure applied to the core member  31  because, since the connection member  38  is fixed to the first tubular member  5 C, the pressure sensing semiconductor device  35  does not move against the pressure applied to the core member  31  in the direction of the center axis. Besides, the ferrite core  34 , on which the coil  33  that forms a resonance circuit together with the pressure sensing semiconductor device  35  is wound, is accommodated in the tubular portion  382  formed on the connection member  38  and is electrically connected in parallel to the pressure sensing semiconductor device  35  and is further connected to the terminal members  362  and  363  provided on the connection member  36 . 
     It is to be noted that, while, in the third embodiment described above, the pressure sensing semiconductor device is used as a pressure sensor whose capacitance varies in response to pressure (writing pressure) applied to the core member, the pressure sensor is not limited to this type. For example, it is also possible to use, as the pressure sensor, a variable capacitor whose capacitance changes in response to pressure (writing pressure) applied to a core member, as disclosed in Japanese Patent Application No. 2012-151357 co-assigned to the applicant of the present invention. 
     In the variable capacitor disclosed in Japanese Patent Application No. 2012-151357, a film electrode of a predetermined shape is formed by disposition on an inner wall face of a hollow portion of an outer side member formed from a cylinder having the hollow space. Meanwhile, also on an outer peripheral face of an inner side member of a post shape, a film electrode of a predetermined shape is formed. The inner side member is accommodated in the hollow space of the outer side member such that it is movable in a direction of the center axis. In this instance, the electrode on the inner wall face of the outer side member and the electrode on the outer peripheral face of the inner side member are opposed to each other with a dielectric interposed therebetween so that a capacitor is formed, which exhibits capacitance corresponding to the area over which the electrodes are opposed to each other. 
     According to this configuration, when pressure is applied in the direction of the center axis to the inner side member from the outside, the inner side member moves relative to the outer side member in the direction of the center axis. Thereupon, the area over which the electrode on the inner wall face of the outer side member and the electrode on the outer peripheral face of the inner side member oppose each other with the dielectric interposed therebetween varies. Accordingly, the capacitance of the capacitor formed between the electrode on the outer side member and the electrode on the inner side member exhibits a capacitance conforming to the applied pressure in response to the variation of the opposing area of the electrodes. 
     A variable capacitor having such a configuration as described above can be formed in the form of a narrow rod, and an electronic ink cartridge in which the variable capacitor is used as a pressure sensor in place of the pressure sensing semiconductor device  35  described above can be configured. 
     Fourth Embodiment 
     In the embodiments described above, a pressure sensor for detecting writing pressure is configured such that it is implemented using an inductance circuit or a capacitor circuit, which configures a resonance circuit provided in a position pointer. On a position detection apparatus side, a frequency displacement (phase displacement) of an electromagnetic induction signal from the position pointer is detected to detect the writing pressure applied to the position pointer. 
     However, by using an IC circuit of the information transmission circuit in the embodiments described above, it is also possible to transmit information of writing pressure as a digital signal from a position pointer to a position detection apparatus, like identification information (ID) of an electronic ink cartridge or a position pointer in the examples described above. A position pointer of the present fourth embodiment is an example which uses such a configuration. 
     A circuit depicted on the upper side in  FIG. 21  is an equivalent circuit of the position pointer  1 D of the present fourth embodiment. A position detection apparatus which carries out position detection and writing pressure detection through electromagnetic coupling to the position pointer  1 D is the position detection apparatus  200  depicted in  FIG. 7  in the case of the first embodiment described hereinabove. 
     A mechanical arrangement configuration of principal components of an electronic ink cartridge  30 D, which configures the position pointer  1 D of the present fourth embodiment, is similar to that of the electronic ink cartridge  30  in the third embodiment described hereinabove with reference to  FIGS. 15A and 15B  or the electronic ink cartridge  30 A of the modification to the third embodiment depicted in  FIG. 20 . However, the electronic ink cartridge  30 D in the present fourth embodiment is different from the electronic ink cartridges  30  and  30 A of the third embodiment and the modification to the third embodiment in the following points. In particular, the first difference is that the ID package  320  in the example of  FIGS. 9A and 9B  described as a modification to the first embodiment is provided between the capacitor circuit  18 C and the cap  19 C. Further, the second difference is that a control circuit  500 , which controls so as to send writing pressure information detected by the pressure sensing chip  400  to the position detection apparatus  200  through electromagnetic coupling, is accommodated in the package member  351  of the pressure sensing semiconductor device  35  together with the pressure sensing chip  400 . 
     In the electronic ink cartridge  30 D of the present fourth embodiment, a parallel resonance circuit  20 R′ is configured from the coil  33  in the tubular member  5 ′ of the electronic ink cartridge  30 D and the first capacitor circuit  181 C and the second capacitor circuit  182 C of the capacitor circuit  18 C as depicted in  FIG. 21 . A first end and a second end of the parallel resonance circuit  20 R′ are connected to a first end and a second end of the ID package  320 , respectively. 
     In the electronic ink cartridge  30 D of the present fourth embodiment, the control circuit  500  is provided between the first end and the second end of the coil  33  as depicted in  FIG. 21 . The control circuit  500  includes a controlling IC  501 . To the IC  501 , a capacitor (capacitance Cv) configured from the pressure sensing chip  400  is connected. Consequently, the IC  501  can detect the capacitance Cv corresponding to the writing pressure. The IC  501  detects writing pressure applied to the position pointer  1 D from the value of the capacitance Cv. 
     The IC  501  is configured such that it operates by a power supply voltage Vcc obtained by rectification of an AC signal received through electromagnetic coupling from the position detection apparatus  200  by the parallel resonance circuit  20 R′ by a driving signal generation circuit  504 . The driving signal generation circuit  504  includes a rectification circuit configured from a diode  502  and a capacitor  503 . Further, in the control circuit  500 , a switch circuit  505  is connected in parallel to the parallel resonance circuit  20 R′. The switch circuit  505  is configured so as to be controlled between on and off by the IC  501 . It is to be noted that, to the IC  501 , an electromagnetic induction signal transmitted from the position detection apparatus  200  is supplied as a synchronizing signal for transfer of an electromagnetic induction signal to and from the position detection apparatus  200  through a capacitor  506 . 
     Further, the IC  501  of the control circuit  500  in the present fourth embodiment detects a value of the capacitance Cv of the variable capacitor configured from the pressure sensing chip  400  as information of writing pressure to the position pointer  1 D. The IC  501  converts the detected writing pressure into a digital signal of, for example, 8 bits and controls the switch circuit  505  using the digital signal corresponding to the writing pressure. 
     Position detection operation and writing pressure detection operation of the position pointer  1 D and the position detection apparatus  200  configured in such a manner as described above are described. 
     The processing controlling section  233  first carries out driving of the drive circuit  222 , selection of the selection circuit  213  and changeover control of the switch circuit  223  in a similar manner as in the embodiments described hereinabove to carry out transfer of an electromagnetic induction signal to and from the position pointer  1 D to determine an X coordinate value and a Y coordinate value of a position pointed to by the position pointer  1 D. 
     After the pointed position of the position pointer  1 D is detected in such a manner as described above, in order to detect writing pressure information of 8 bits from the position pointer  1 D, the processing controlling section  233  carries out transmission of a signal for synchronization of the loop coil in the proximity of the location of the position pointer  1 D for a predetermined period of time. Then, the processing controlling section  233  carries out transmission and reception successively by eight times at timings similar to those used for coordinate detection. In particular, the processing controlling section  233  controls the selection circuit  213  to select a loop coil nearest to the position pointer  1 D (which may be either one of an X axis direction loop coil and a Y axis direction loop coil) in accordance with the detected coordinate values of the position pointer  1 D and then transmits and receives a signal to and from the selected loop coil. 
     Meanwhile, the IC  501  of the control circuit  500  of the position pointer  1 D converts writing pressure obtained corresponding to the capacitance Cv of the pressure sensing chip  400  into a digital signal of 8 bits. Further, the IC  501  controls the switch circuit  505  on and off in synchronism with transmission and reception of a signal from the position detection apparatus  200  based on the digital signal of 8 bits. When the switch circuit  505  is off, the parallel resonance circuit  20 R′ can transmit a signal transmitted thereto from the position detection apparatus  200  back to the position detection apparatus  200 . Therefore, the loop coil of the position detection apparatus  200  receives this signal. On the other hand, when the switch circuit  505  is on, the parallel resonance circuit  20 R′ is in a state in which operation thereof is inhibited. Therefore, the parallel resonance circuit  20 R′ does not transmit a signal back to the position detection apparatus  200 . Consequently, the loop coil of the position detection apparatus  200  does not receive a signal. 
     The processing controlling section  233  of the position detection apparatus  200  carries out detection of presence or absence of a reception signal by eight times to receive the digital signal of 8 bits corresponding to the writing pressure, and consequently can detect writing pressure information from the position pointer  1 D. 
     Other Embodiments and Modifications 
     In the first to third embodiments described hereinabove, the capacitor circuits  18  and  18 C are configured such that chip capacitors are stacked and configured such that capacitance is set by the number of capacitors to be stacked. However, the configuration of the capacitor circuit is not limited to this type. For example, a capacitor as disclosed in Japanese Patent Application No. 2012-128834, co-assigned to the applicant of the present application and configured such that a dielectric sheet on which electrodes of a predetermined pattern shape are formed is wrapped into a rod can be used. In the capacitor disclosed in Japanese Patent Application No. 2012-128834, a capacitor of a shape of a rod is configured such that some of electrode patterns can be cut (severed) or coupled (connected) later to allow later setting of the capacitance. 
     Further, in the embodiments described hereinabove, two connection terminals for establishing electric connection between the first end and the second end of the coil  16 ,  24  or  33  and the first end and the second end of the capacitor circuit  18 ,  28  or  18 C to each other, respectively, are provided on an end face of the connection member  17 ,  27  or  36 , which is disposed between the coil  16 ,  24  or  33  and the capacitor circuit  18 ,  28  or  18 C, on the capacitor circuit  18 ,  28  or  18 C side. However, where the tubular member  5 ,  50  or  5 ′ is made of a material of a nonmagnetic substance having conductivity such as SUS310 in the example described hereinabove, at least one of the two connection terminals described above needs to be disposed on an end face of the connection member  17 ,  27  or  36  while the conductive tubular member  5 ,  50  or  5 ′ is used as the other connection terminal. 
     For example, in the first embodiment described hereinabove, only the second end portion  173   c  of the terminal member  173  is provided on the end face of the connection member  17  opposing the capacitor circuit  18  such that the insertion hole  173   d  is exposed. Further, the ring-shaped electrode conductor  172   c  of the terminal member  172  is exposed not to the end face described above but to a peripheral portion of the main body portion  171  of the connection member  17  so as to be electrically coupled to the first tubular member  5 A. 
     On the other hand, in the first capacitor circuit  181  of the capacitor circuit  18 , the first end  1815   a  of the rod-like member of the terminal member  1815  is formed similarly as in the embodiments described hereinabove. However, the first end  1814   a  of the terminal member  1814  is exposed to a peripheral portion of the holder  1810  so as to be electrically coupled to the second tubular member  5 B. 
     Where such a configuration as described above is applied, the capacitor circuit  18  and the connection member are connected to each other and the first tubular member  5 A and the second tubular member  5 B are screwed with and connected to each other to establish electric connection therebetween. In this instance, the tubular member  5  may be used, for example, as a ground electrode. 
     Also in the second embodiment, for example, the second end portion of the terminal member  273  is formed as the circular conductor  273   c  as in the embodiments described hereinabove on the end face of the connection member  27  on the capacitor circuit  28  side. Meanwhile, the second end portion  272   c  of the terminal member  272  is exposed not to the end face but on a peripheral portion of the main body portion  271  so as to be electrically coupled to the tubular member  50  similarly. 
     Further, the first end  1815   a ′ of the terminal member  1815  of the first capacitor circuit  281  of the capacitor circuit  28  is formed as an electrode of a circular shape which abuts against the circular conductor  273   c  on the end face of the connection member  27  as in the example described hereinabove. However, the first end  1814   a  of the terminal member  1814  is exposed to a peripheral portion of the holder  1810  so as to be electrically coupled to the tubular member  50 . 
     In the case of the present second embodiment, the capacitor circuit  28  is inserted into the tubular member  50  to electrically connect the first end  1814   a  of the terminal member  1814  exposed to the peripheral portion of the holder  1810  to the tubular member  50 . 
     Further, in the third embodiment, the connection member  36  and the capacitor circuit  18 C are configured such that they are modified similarly to the connection member  17  and the capacitor circuit  18  in the first embodiment, respectively. By this configuration, the tubular member  5 ′ can be used as one of the connection electrodes. 
     Further, as described hereinabove, in the electronic ink cartridge of the present invention, a ferrite core on which a coil is wound and a pressure sensor are disposed between an end portion of a tubular member on the side on which a core member is positioned and a connection member. Further, as described hereinabove in connection with the first embodiment or the second embodiment, as an order in which the ferrite core on which the coil is wound and the pressure sensor are arrayed in the direction of the center axis of the tubular member, whichever one of the ferrite core and the pressure sensor may be positioned on the connection member side. Further, the three members including the connection member, ferrite core on which the coil is wound, and pressure sensor may be formed as independent members of each other and connected to each other or may be combined into a unitary member or else two of the three members may be combined into a unitary member. 
     In particular, the electronic ink cartridge can be configured in any of eight combinations of: 
     (1) the sequential connection of the ferrite core on which the coil is wound, pressure sensor, and connection member formed as independent members of each other; 
     (2) the sequential connection of the pressure sensor, ferrite core on which the coil is wound, and connection member formed as independent members of each other; 
     (3) the sequential connection of the ferrite core on which the coil is wound, pressure sensor, and connection member formed in an integrated structure; 
     (4) the sequential connection of the pressure sensor, ferrite core on which the coil is wound, and connection member formed in an integrated structure; 
     (5) connecting the connection member, as an independent member, to the sequential connection of the ferrite core on which the coil is wound and the pressure sensor formed in an integrated structure; 
     (6) connecting the connection member, as an independent member, to the sequential connection of the pressure sensor and the ferrite core, on which the coil is wound, formed in an integrated structure; 
     (7) connecting the connection member provided integrally on the pressure sensor as a unitary member, to the ferrite core on which the coil is wound and which is disposed toward the core member side; and 
     (8) connecting the connection member provided integrally on the ferrite core, on which the coil is wound, as a unitary member, to the pressure sensor which is disposed toward the core member side. 
     It is to be noted that, as described hereinabove, the electronic ink cartridge of the present invention can be handled similarly to an ink cartridge (refill lead) accommodated in a housing, like a ballpoint pen of any writing equipment. As a ballpoint pen, a ballpoint pen of the knock type or the rotary type is known wherein the ink cartridge can be in a state in which the pen tip is accommodated (received) in the housing and another state in which the pen tip projects outwardly of the housing. Also, another type of ballpoint pen is known which permits switching between a plurality of ink cartridges, for example, for different colors, wherein the pen tip thereof is projected from the housing. 
     Thus, the position pointer of the present invention also can be configured in a structure of the knock type or the rotary type for switching an electronic ink cartridge between a state in which the core member is accommodated in the housing and another state in which the core member projects outwardly of the housing. Further, it is also possible for the position pointer of the present invention to adopt a configuration wherein switching between a plurality of electronic ink cartridges, which are different in thickness of their core member, can be carried out or wherein switching between an ink cartridge of a ballpoint pen and an electronic ink cartridge can be carried out. 
     The various embodiments described above can be combined to provide further embodiments. All of the patents, patent application publications, and patent applications referred to in this specification are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, publications and applications to provide yet further embodiments. 
     DESCRIPTION OF REFERENCE SYMBOLS 
       1  . . . Position pointer,  2  . . . Housing,  5 ,  5 ′,  50  . . . Tubular member,  7  . . . Push switch (side switch),  10 ,  20 ,  30  . . . Electronic ink cartridge,  11 ,  21 ,  31  . . . Core member,  13 ,  26  . . . Ferrite chip,  14 ,  25  . . . O-snap ring,  15 ,  23 ,  34  . . . Ferrite core,  16 ,  24 ,  33  . . . Coil,  17 ,  27 ,  36 ,  38  . . . Connection member,  18 ,  18 C . . . Capacitor circuit,  19 ,  19 C . . . Cap,  35  . . . Pressure sensing semiconductor device.