POSITION INPUT DEVICE AND KEYBOARD APPARATUS

Abstract: A position input device which does not need to connect a position indicator to a position detector. The input device can easily obtain expandability of condition setting such as mounting of a large number of switches to the position indicator, and moreover can simplify the circuit. When a resonant circuit (4) provided on the position indicator (5) approaches first and second coupling means (1, 2), electromagnetic couplings (M1 and M2) occur, and a positive feedback loop is formed through a series of route ranging from the output of an amplification circuit (3), first coupling means, electromagnetic coupling (M1), resonant circuit (4) second coupling means (M2) and the input of amplification circuit (3). Accordingly, oscillation occurs at the resonance frequency of the resonant circuit (4) and an oscillation signal (101) can be obtained. The amplitude of the oscillation signal (101) changes in accordance with the position of the position indicator (5), and a position detection circuit (6) obtains position data of the position indicator (5) from the amplitude of the oscillation signal (101). A condition detection circuit (8) can detect switch data of switches (SW1, SW2) set by a condition setting circuit (7) from the frequency of oscillation signal (101).

Description: TECHNICAL FIELD The present invention relates to a position reading apparatus for inputting position information into an external device such as computers, and specifically relates to a wireless position reading apparatus in which a body of a detecting device and a position pointer do not need connecting with a signal wire. Further, the present invention relates to a key board apparatus which outputs switch information to a host system such as a computer, and specifically relates to a key board apparatus applying an oscillation phenomenon. From EP-A-556852, which forms prior art in the sense of Art. 54(3) EPC for the contracting states of Germany, France and Great Britain there is already known a position reading apparatus comprising: an amplifier; a first coupling means connected to the output of the amplifier; a second coupling means connected to the input of the amplifier; a position detecting means connected to the input of the amplifier; and a position pointer device; wherein said position pointer device has a resonant circuit, wherein when the resonant circuit is electromagnetically coupled to both the first coupling means and the second coupling means, the resonant circuit along with the amplifier, the first coupling means and the second coupling means forms a positive feedback loop and composes a frequency oscillator which oscillates at a resonance frequency of the resonant circuit; and wherein the position detecting means obtains position information on the position pointer from amplitude information of an oscillation signal generated by the frequency oscillator. BACKGROUND ART Fig. 35 is a block diagram of a conventional position reading apparatus. A conventional position reading apparatus is disclosed, e.g., by JP-A-47721. First of all, referring to this drawing there will be described operation for detecting a position in the conventional position reading apparatus. The apparatus has a structure that exciting lines 903 and sense lines 902 are laid orthogonally, and each exciting line 903 is sequentially selected by being coupled to a first scanning circuit 908 in turn and each sense line 902 is sequentially selected by being coupled to a second scanning circuit 909 in turn. As the first scanning circuit 908 is supplied with an exciting signal s906 from an exciting circuit 915, the exciting line selected by this circuit generates an a.c. electromagnetic field. A position pointer 906 includes a resonant circuit (hidden from the figure) which resonants with a frequency of the exciting signal s906. Therefore, when the position pointer is put on the sense lines, induction signals s901 generate on the sense lines 902 because of the coupling among the exciting lines 903, the position pointer 906 and the sense lines 902. The second scanning circuit 909 selects each of the sense lines sequentially and thereby the induction signal s901 is guided to a signal processing circuit 904 and is converted into an amplitude signal s905. Further, the amplitude signal is inputted into a position detecting circuit 905 and then the position is calculated from a distribution state as to the induction signal s901 at an intersection point of each exciting line and each sense line. It is necessary to select a plurality of the sense lines in order to obtain the distribution state as to the induction signal s901. In such a conventional position reading apparatus as explained above, calculating the position of one point requires performing selecting operations in matrix in a way that a plurality of the sense lines are selected while each of the exciting lines is selected. For instance, if the five exciting lines and the five sense lines are to be selected respectively, the position of a point is calculated by performing twenty five times of selecting operations in total because the five sense lines are selected whenever one of the exciting lines is selected. Next, referring to Figs. 36(a) and (b), there will be described an operation for detecting a state of switches and so on provided for the position pointer in the conventional position reading apparatus. As shown in Fig 36(a), the position pointer 906 has a construction that the position pointer 906 includes a resonant circuit 907 and the resonant circuit 907 is connected in parallel to a switching circuit 913 in which the switch and a second capacitor are connected in series. Then, when the switch is pushed, a resonance frequency slightly changes. Therefore, as shown in Fig. 36(b), a phase of the induction signal s901 is slightly different between when the switch is on and when the switch is off. A state of the switching circuit 913 can be detected by detecting this phase change ø. Further when a number of switches are provided on the position pointer and many status are required or when the condition settings are required to extend in such the conventional position reading apparatus, for example, by providing a pressure detecting function with the position pointer, such requirements are realized in a manner mentioned below. Detection accuracy is ensured by providing the main body with a detecting circuit capable of detecting a slight change in phase accurately and also stably. At the same time, in the process of manufacturing the position pointer, the resonance frequency of the resonant circuit is accurately adjusted and parts of high stability are used so that even after the adjustment the detection accuracy is highly stable against environmental changes such as temperature change and time passage. In the conventional position reading apparatus, it is necessary that an a.c. electromagnetic field of a predetermined frequency is always generated from the exciting lines. Generation of the a.c. electromagnetic field is required all the time for detecting that the position pointer is placed, even if the position pointer does not exist in the vicinity of the sense liens, that is, even when position detection is not necessary. Therefore, an exclusive exciting circuit is necessary for generating the a.c. electromagnetic field. Further, there is a problem that a position can not be calculated at high speed because the lines required to be selected in matrix as explained above in order to calculate the position of a point. Moreover, as shown in Fig. 37, in the sense lines laid near a periphery of a body of a detecting device, a direct coupling between the exciting line and the sense line is generated in portions A and B. As a result, the induction signal is generated even if the position pointer does not exist. This fact means that induction signal components which are not dependent on the position pointed by the position pointer are added to the sense lines near the periphery of the body of the detecting device, which cause a problem that accuracy of position detection deteriorates around the periphery. Detecting a state of the position pointer, for example, a state of switches, uses a phase difference resulting from a slight difference between the frequency of the exciting signal and the resonance frequency of the resonant circuit, therefore the switching circuit in the position pointer and a phase detecting circuit in the body of the detecting device require very precise frequency setting. Further, the phase difference is required to be generated in each switching circuit in order to detect states of a plurality of the switches, but a range in which phase difference are generated is limited. Therefore, the conventional position reading apparatus can not be constructed so as to be capable of detecting the states of so many switches. Though sixteen or more switches are demanded in the market, it can not be realized in the conventional apparatus. A first object of the present invention is to realize a wireless position reading apparatus which does not require the body of the detecting device and the position pointer to be connected with a signal wire and in which a circuit can be more simplified by eliminating the exciting circuit compared with the conventional apparatus. A second object of the present invention is to realize the position reading apparatus capable of calculating a position with high speed in addition to the above first object. A third object of the present invention is to realize the position reading apparatus in which a peripheral accuracy does not deteriorate in addition to the above first and the second objects. Further, a fourth object of the present invention is to realize the position reading apparatus which can detect a status of a position pointer with a circuit that does not particularly require a precise setting and which can easily detect a plurality of statuses in addition to the above the first to the third objects. Furthermore, a fifth object of the present invention is to provide, by applying the invention to a key board apparatus, a key board apparatus in which a key board operates without power supply and transfers the switch information without contact and further which does not require a space for the large connector in the host system. DISCLOSURE OF INVENTION The above-mentioned objectives are achieved by a position reading apparatus according to independent claim 1 and a key board apparatus according to independent claim 11. The dependent claims 2 - 10 relate to advantageous embodiments of an inventive position reading apparatus according to independent claim 1. The features and advantages of the present invention will be more readily apparent from the following description in conjunction with the drawings, in which: Fig. 1 shows a basic principle of the position reading apparatus described in the present application. Fig. 2 is a block diagram showing a use of the position reading apparatus of fig. 1. Fig. 3 is a block diagram showing the position detecting means 6a of fig. 2. Fig. 4 shows an example of changes in amplitude of the oscillating signal 101 shown in Fig. 3. Fig. 5 shows the second structural example of the first sense line la and the second sense line 2a shown in Fig. 2. Fig. 6 shows the third structural example of the first sense line la and the second sense line 2a shown in Fig. 2. Fig. 7 is a block diagram showing another example of a position reading apparatus. Fig. 8 is a block diagram of the first coupling means 1d of the apparatus of fig. 7. Fig. 9 is a block diagram of the position detecting means 6b of the apparatus of fig. 7. Fig. 10 is a wave form chart of the oscillation signal of the apparatus of fig. 7. Fig. 11 is an explanatory diagram for coordinate calculation of the apparatus of fig. 7. Fig. 12 is a block diagram showing another example of a position reading apparatus. Fig. 13 is a block diagram of the status detecting means 8 of the apparatus of fig. 12. Fig. 14 is a block diagram showing another example of a position reading apparatus. Fig. 15 is a block diagram of the AGC circuit 9 disclosed in the fourth embodiment of the present invention. Fig. 16 is a block diagram of the case where position information is obtained from the input signal 102. Fig. 17 is a principle block diagram of a position reading apparatus. Fig. 18 is an explanatory diagram showing another constructional example of the sense lines in the principle construction of Fig. 17 Figs. 19(a) and (b) are block diagrams of the position detecting circuit in the principle construction of Fig. 17. Figs. 20(a) and (b) are correspondence explanatory diagrams showing a relation between the pointed position and the amplitude of the oscillating signal in the principle construction of Fig. 17. Figs. 21(a) and (b) are correspondence explanatory diagrams showing relation between the pointed height and the amplitude of the oscillating signal in the principle construction of Fig. 17. Fig. 22 is a block diagram showing another example of a position reading apparatus. Fig. 23 is a block diagram showing the position detecting circuit of the apparatus of fig. 22. Fig. 24 is an explanatory diagram showing the oscillating signal of the apparatus of fig. 22. Fig. 25 is an explanatory diagram showing the amplitude of the oscillating signal of the apparatus of fig. 22. Figs. 26(a) and (b) are correspondence explanatory diagrams showing the relation between the pointed position and the amplitude distribution of the oscillating signal of the apparatus of fig. 22. Figs. 27(a) and (b) are correspondence explanatory diagrams showing the relation between the pointed position and the amplitude distribution of the oscillating signal of the apparatus of fig. 22. Figs. 28(a) and (b) are correspondence explanatory diagrams showing the relation between the pointed position and the amplitude distribution of the oscillating signal of the apparatus of fig. 22. Figs. 29(a) and (b) are correspondence explanatory diagrams showing the relation between the pointed position and the value Q of the apparatus of fig. 22. Fig. 30 is a block diagram showing another example of a position reading apparatus. Fig. 31 is a block diagram showing another example of a position reading apparatus. Fig. 32 is a block diagram showing the status detecting circuit of the apparatus of fig. 31. Fig. 33 is a block diagram showing the another example of a position reading apparatus. Fig. 34 is a block diagram showing the AGC circuit of the apparatus of fig. 33. Fig. 35 is a block diagram showing a conventional position reading apparatus. Figs. 36(a) and (b) are explanatory diagrams showing the status detection by the conventional position reading apparatus. Fig. 37 is an explanatory diagrams indicating the problem of the conventional position reading apparatus. Fig. 38 is a block diagram of a key board apparatus. Fig. 39 is a block diagram of a second key board apparatus. Fig. 40 is a perspective view showing the condition of the connection between the key board apparatus and the host system. Fig. 41 is an explanatory diagram showing the connection between the key board apparatus and the host system. DETAILED DESCRIPTION Fig. 1 shows a basic principle of a position reading apparatus. In the Fig. 1, 3 is an amplifier; 1 is a first coupling means connected to an output of the amplifier 3; 2 is a second coupling means connected to an input of the amplifier 3; 4 is a resonant circuit which is electromagnetically coupled to both the first coupling means 1 and the second coupling means 2; 5 is a position pointer having the resonant circuit 4; 101 is an oscillating signal outputted from the amplifier 3; 102 is an input signal inputted into the amplifier 3; 6 is a position detecting means for detecting a position information on the position pointer 5 from an amplitude of the oscillating signal 101; M1 is electromagnetic coupling between the first coupling means 1 and the resonant circuit 4; and M2 is electromagnetic coupling between the second coupling means 2 and the resonant circuit 4. In Fig. 1, when the position pointer 5 is away from the first and the second coupling means 1 and 2 and no electromagnetic coupling exists between the resonant circuit 4 and the first and the second coupling means 1 and 2, a feedback is not formed and oscillation does not occur. However, when the position pointer 5 is in the vicinity of the first and the second coupling means 1 and 2 and thereby the electromagnetic coupling M1 and electromagnetic coupling M2 occur between the resonant circuit 4 and the first and the second coupling means 1 and 2, there is formed a positive feedback loop which includes, as components of a route, the output of the amplifier 3, the first coupling means 1, the electromagnetic coupling M1, the resonant circuit 4, the electromagnetic coupling M2, the second coupling means 2, and the input of the amplifier 3; and thereby there occurs the oscillation at a resonance frequency of the resonant circuit 4. The oscillation is excited by noise made by amplifier 3, natural noise and so on, and is a well-known phenomenon in this kind of oscillation action. If a distance between the resonant circuit 4 and the first and the second coupling means 1 and 2 becomes much smaller, the oscillating frequency does not change; however a feedback amount changes depending on the distance. In other words, the smaller the distance becomes, the further the feedback amount increases and thereby the larger oscillating amplitude can be obtained; on the other hand, the larger the distance becomes, the further the feedback amount decreases and thereby the smaller the oscillating amplitude becomes. In such a way, at the output of the amplifier 3 is obtained the oscillating signal 101 appropriate for the position of the position pointer 5, and the position detecting means can obtain the position information from the amplitude of the oscillating signal 101. Any type of coupling means can be applied as the first and the second coupling means as far as the feedback loop is not directly formed through the first and the second coupling means when they are not electromagnetically coupled to the resonant circuit. Moreover, the position information can be also obtained from the input signal 102 of the amplifier 3 though an absolute value of the amplitude is small. Fig. 2 is a block diagram. In this figure, la is a first sense line, 2a is a second sense line, 3 is the amplifier, 4 is the resonant circuit, 5 is the position pointer, 6a is the position detecting means, 101 is the oscillating signal, 102 is the input signal, and A, B and C are positions pointed by the position pointer 5 respectively. Fig. 3 is a block diagram showing the position detecting means 6a. In the position detecting means, 51 is a rectifier circuit, 52 is a smoothing circuit, 53 is an A - D conversion circuit, 54a is a control circuit composed of a general CPU, 101 is the oscillating signal, and 151 is the oscillating signal before A - D conversion. Fig. 4 is a graph showing an example of amplitude changes of the oscillating signal 151 shown in Fig. 3. A vertical axis represents the amplitude of the oscillating signal 151, and an axis of abscissas represents the position of the position pointer 5 shown in Fig. 2. A, B and C correspond to A, B and C shown in Fig. 2 respectively. Fig. 5 is a second structural example of the first sense line la and the second sense line 2a shown in Fig. 2. 1b is the first sense line, 2b is the second sense line, 5 is the position pointer and 4 is the resonant circuit. Fig. 6 is a third structural example of the first and the second sense line 1a and 2a shown in Fig. 2. 1c is the first sense line, 2c is the second sense line, 5 is the position pointer and 4 is the resonant circuit. An operation of this apparatus will be described below. In Fig. 2, the first and the second sense line 1a and 2a correspond to the first and the second coupling means 1 and 2 shown in Fig. 1, the basic principle diagram respectively. The first sense line 1a and the second sense line 2a are arranged orthogonally on the level; the first sense line 1a is coupled to the output of the amplifier 3 and the second sense line 2a is coupled to the input of the amplifier 3. When the first sense line 1a and the second sense line 2a are orthogonal to each other, if the position pointer 5 does not exist in the vicinity of them, each of them is not electromagnetically coupled to the resonant circuit, so that the feedback is not formed, neither does the oscillation occur. However, if the position pointer 5 is brought close to a cross-point of the first sense line 1a and the second sense line 2a, the resonant circuit 4 is electromagnetically coupled to both the first sense line 1a and the second sense line 2a, and thereby the positive feedback loop is formed. This causes the oscillation to occur and the oscillating signal 101 can be obtained. In the position detecting means 6a, that is, Fig. 3, the oscillating signal 101 is rectified by the rectifier circuit 51, smoothed by the smoothing circuit 52, digitized by the A - D conversion circuit 53, and processed by the control circuit 54a. Fig. 4 shows an example of amplitude changes of the oscillating signal 151 shown in Fig. 3, that is, the oscillating signal before the A - D conversion which are observed when the position pointer 5 is moved, for instance, from the position A to the position C on condition that a height from each of the sense lines to the position pointer 5 is constant in Fig. 2. In Fig. 4, the amplitude shown a symmetrical change. In other words, the amplitude increases when the position pointer is moved from the position A to the position B, decreases from the position B to the position C, and becomes maximum at the position B which is a center of the cross-point of each sense line. Therefore, in Fig. 3 the control circuit 54a can obtain the distance from the position B to the position pointer 5 from the amplitude of the oscillating signal and a table provided beforehand in the control circuit 54a for showing the relation between the amplitude and the distance. The amplifier 3 can be realized with a well-known operational amplifier and so on, and either of an inverted type and a non-inverted type amplifier can be applicable as far as it can form the positive feedback loop by making use of a direction at which the sense line winds up and respective connection of two ends of the sense line. The coupling means must meet the conditions that they are not coupled to the resonant circuit when the resonant circuit does not exist in the vicinity of them and that each of them is coupled to the resonant circuit when the resonant circuit is in the vicinity of them. Such coupling means can have not only the structure composed of the first sense line 1a and the second sense line 2a shown in Fig. 2 but also such a structure as shown in Fig. 5 that one of the sense lines are inverted midway or such a structure as shown in Fig. 6 that both sense lines are crossed three-dimensionally. Next, referring to Figs. 7 to 11, there will be described an apparatus in which each of a first and a second coupling means is composed of a plurality of sense lines and a scanning circuit. Fig. 7 is a block diagram. In this figure, 5 is a position pointer; 1d is a first coupling means, 2d is the second coupling means; 3 is an amplifier, 6b is a position detecting means; S1 is a first sense line group including sense lines y1 to yn; 61 is a first scanning circuit coupling to an output of the amplifier 3 for selecting each line of the first sense line group S1 sequentially; S2 is a second sense line group including sense lines x1 to xm; 62 is a second scanning circuit coupled to an input of the amplifier 3 for selecting each line of the second sense line group S2; 101 is an oscillating signal; 102 is an input signal; 103 is a selection signal for selecting the first sense line group S1; and 104 is a selection signal for selecting the second sense line group S2. The position pointer 5 has a resonant circuit as well as that shown in Fig. 2 though the resonant circuit does not appear in the Fig. 7. Fig. 8 is a structural example of the first coupling means 1d. S1 is the first sense line group; 61 is the first scanning circuit; 201 is a decoder; 211 to 21n are analog switches; 101 is the oscillating signal generated from the output of the amplifier 3; 103 is the selection signal outputted from the position detecting means 6b. Though a detailed drawing of the second coupling means 2d is not shown, the second coupling means 2d has the same structure as that of the first coupling means 1d, and is different from the first coupling means 1d in that it is coupled to the input of the amplifier 3 while the first coupling means 1d is coupled to the output of the amplifier 3. Fig. 9 is a structural example of the position detecting means 6b. 51 is a rectifier circuit; 52 is a smoothing circuit; 53 is an A - D conversion circuit; and 54b is a control circuit composed of a general CPU. Fig. 10 is a waveform diagram showing the oscillating signal and Fig. 11 is an explanatory diagram for calculating a coordinate. The operation of this apparatus will be explained. The following is explanation of the case the position pointer 5 is located where the sense line x4 and the sense line y4 (a portion A in Fig. 7). The first scanning circuit 61, first of all, selects the sense line y1 of the first sense line group S1 with the selection signal 103 outputted from the position detecting means 6b. That is, in Fig. 8 the decoder 201 turns on the analog switch 211 with the selection signal 103 and connects the output of the amplifier to the first sense line y1. On the other hand, during the above operation the second scanning circuit 62 selects each sense line of the second sense line group S2 in such sequence as x1, x2, ... and xm with the selection signal 104 outputted from the position detecting means 6b. After all of the second sense line group is scanned, the first scanning circuit 61 selects the sense line y2 of the first sense line group S1 with the selection signal 103 outputted from the position detecting means 6b and concurrently the second scanning circuit 62 selects each sense line of the second sense line group S2 in such sequence as x1, x2, ... and xm with the selection signal 104 outputted from the position detecting means 6b. From now on such scanning is repeated. Finally, the first scanning circuit 61 selects the sense line yn of the first sense line group S1 and concurrently the second scanning circuit 62 selects each sense line of the second sense line group S2 in such sequence as x1, x2, ... xm. The position detecting means 6b shapes waveforms of the oscillating signals 101 obtained by selecting each of the second sense line group S2 sequentially at the rectifier circuit 51 and the smoothing circuit 52 shown in Fig. 9, and digitizes amplitudes of the waveforms sequentially at the A - D conversion circuit 53, and further processes the digitized signals sequentially at the control circuit 54b. Referring to Fig. 10, the amplitude of the oscillating signal 101 is described in detail. Fig. 10 is a diagram showing the waveform which is obtained when the position pointer 5 is located over the portion A in Fig. 7, and shows the selection signals 103 and 104 inputted into the first scanning circuit 61 and the second scanning circuit 62 respectively and an oscillating signal before being A - D converted at the position detecting means 6b (the signal 151 in Fig. 9). A signal "a" is the oscillating signal which is obtained when the scanning circuit selects the portion A, that is, the first sense line y4 and the second sense line x4, and is the largest signal among the signals which are generated while all the sense lines are scanned. The reason for the above is that a degree of coupling between the resonant circuit of the position pointer 5 and the sense line y4 becomes maximal when the first scanning circuit selects the sense line y4 which is the closest to the position pointer 5 among the first sense line group S1, that a degree of coupling between the resonant circuit of the position pointer 5 and the sense line x4 becomes maximal when the second scanning circuit selects the sense line x4 which is the closest to the position pointer 5 among the second sense line group S2, and that a maximum amount of feedback can be obtained when both of the couplings become maximal. Signals "b" and "c" are the oscillating signals which are obtained when a portion on either side of the portion A respectively, that is, when the first sense line y4 and the second sense line x3 are selected and when the first sense line y4 and the second sense line x5 are selected respectively. In these cases, the degree of coupling between the resonant circuit of the position pointer 5 and the first sense line y4 is as large as that in the case of selecting the portion A. However, the oscillating signals "b" and "c" are smaller in amplitude than the oscillating signal "a" as the distance between the position pointer 5 and the selected second sense line is larger than that in the case of selecting the portion A. Further, signals "d" and "e" are the oscillating signals which are obtained when portions below and above the portion A respectively, that is, when the first sense line y3 and the second sense line x4 are selected and the first sense line y5 and the second sense line x4 are selected respectively. In these cases, the degree of coupling between the resonant circuit of the position pointer 5 and the second sense line x4 is as large as that in the case of selecting the portion A. However, the oscillating signals "d" and "e" are smaller than in amplitude than the oscillating signal "a" as the distance between the position pointer 5 and the selected first sense line is larger that in the case of selecting the portion A. The oscillating signals "a" to "e" have been explained above. The amplitude of other oscillating signals also depends on a relation between the positions of the sense lines which are selected from the first sense line group S1 and the second sense line group S2 respectively and the position of the position pointer 5. Further, as mentioned above, because the first sense line group S1 and the second sense line group S2 are perpendicular to each other, fundamentally the two groups S1 and S2 are not electromagnetically coupled and the oscillation does not occur when the position pointer 5 does not exist near the first and second coupling means. Therefore, as explained above, the amplitude of the oscillating signal can be determined by the relation between the positions of the sense lines which are selected from the first sense line group S1 and the second sense line group S2 respectively and the position of the position pointer 5. The following is explanation of methods for calculating a coordinate by paying attention to some of the five oscillating signals "a" to "e" mentioned above. As a first case, referring to Figs. 11(1) to 11(4) there will be described a method for calculating an x-coordinate by paying attention to the oscillating signals "a", "b" and "c". Fig. 11(1) is an enlarged view of an area around the portion A shown in Fig. 7. Suppose the position pointer 5 travels along a center of a width of the sense line y4 from the center of the width of the sense line x4, L0 to a middle position between the sense lines x4 and x5, L1. Figs. 11(2) and (3) show the oscillating signals "a", "b" and "c" which are generated when the position pointer 5 is located on L0 and L1 respectively. First of all, explanation will be given for a case that the position pointer 5 is located on L0 shown in Fig. 11(2). As mentioned above, the oscillating signals "a", "b" and "c" are signals which are generated when the sense line x4, x3 and x5 are selected respectively while the sense line y4 is selected. In this case, the oscillating signal "a" has the largest amplitude, and the oscillating signals "b" and "c" are equivalent in amplitude because the sense lines x3 and x5 are equally separate from the position pointer 5. Secondly, explanation will be given for the case that the position pointer 5 is located on L1 shown in Fig. 11(3). In this case, the oscillating signals "a" and "c" are equivalent in amplitude because the sense lines x4 and x5 are equally separate from the position pointer 5. Then, the coordinate can be calculated by applying the method proposed by the present applicant (the Japanese Patent Provisional Publication No. 96411/80). Namely, calculation defined by the below expression is done based on the oscillating signal. Q = (V P - V P+1 ) / (V P - V P-1 ) where V P+1 > V P-1 Fig. 11(4) shows a change in value of Q expressed by the (expression-1) which results from moving the position pointer 5 from L0 to L1 by substituting the oscillating signal "a" for V P , the oscillating signal "b" for V P-1 , and the oscillating signal "c" for V P+1 respectively. It is obvious from the above explanation that Q=1 when the position pointer 5 is located on L0 and that Q=0 when the position pointer 5 is located on L1. Further, when the position pointer 5 is located between L0 and L1, Q takes the value 0<Q<1; and there is one-to-one correspondence between each of values representing the positions between L0 and L1 mentioned above and the Q. Therefore, by finding experimentally the characteristics of Q beforehand, it is possible to calculate Q from the oscillating signals "a", "b" and "c" and find from the Q the detailed position of the position pointer 5 between L0 and L1 on the sense line. Further, the x-coordinate can be found from the Q and the position of the sense line A which detects the oscillating signal "a". The details of the method for calculating the coordinate is omitted in the present specification as it is disclosed in the Japanese Patent Provisional Publication No. 96411/80. Next, as a second case, referring to Figs. 11(1) and (4) to (7) there will be described a method for calculating a y-coordinate by paying attention to the oscillating signals "a", "d" and "e". The y-coordinate can be explained in a similar way as well as the above x-coordinate. Suppose in Fig. 11(1) the position pointer 5 travels along a center of a width of the sense line x4 from the center of the width of the sense line y4, L0 to a middle position between the sense lines y4 and y5, L2. Figs. 11(5) and (6) show the oscillating signals "a", "d" and "e" which are generated when the position pointer 5 is located on L0 and L2 respectively. First of all, explanation will be given for a case that the position pointer 5 is located on L0 shown in Fig. 11(5). As mentioned above, the oscillating signals "a", "d" and "e" are signals which are generated when the sense line x4 is selected while the sense lines y4, y3 and y5 are selected respectively. In this case, the oscillating signal "a" has the largest amplitude, and the oscillating signals "d" and "e" are equivalent in amplitude because the sense lines y3 and y5 are equally separate from the position pointer 5. Secondly, there will be explained a case that the position pointer 5 is located in L2 shown in Fig. 11(6). In this case, the oscillating signals "a" and "e" are equivalent in amplitude because the sense lines y4 and y5 are equally separate from the position pointer 5. Therefore, like the above-mentioned case of the x-coordinate, Fig. 11(7) shows the characteristics of Q in the case of moving the position pointer 5 from L0 to L2, which are found by the (expression-1) when the oscillating signals "a", "d" and "e" are substituted for V P , V P-1 and V P+1 respectively. Then, there is obtained the almost same characteristics as those in the case of the x-coordinate shown in Fig. 11(4), and the y-coordinate can be obtained by use of the characteristics of Q as well as the x-coordinate. The above processings are done in the control circuit 54b (shown in Fig. 9) composed of a general CPU. Next, referring to Figs. 12 and 13 there will be described an apparatus which is provided with a status setting means and a status detecting means. Fig. 12 is a block diagram. In Fig. 12, 3 is an amplifier, 1 is a first coupling means, 2 is a second coupling means, 4 is a resonant circuit, 5 is a position pointer, 6 is a position detecting means, 101 is an oscillating signal, 102 is an input signal, M1 and M2 are electromagnetic coupling between the first and second coupling means and the resonant circuit 4, 7 is the status setting means for changing a resonance frequency of the resonant circuit 4, SW1 is a first switch, SW2 is a second switch, and 8 is status detecting means for detecting a condition set by the status setting means 7 from the oscillating signal 101. Fig. 13 is a block diagram showing the status detecting means 8. In this figure, 55 is waveform shaping circuit, 56 is a frequency counter circuit, and 54c is a frequency discriminating circuit composed of a general CPU. There will be described operation of this apparatus. In Fig. 12, the resonant circuit 4 is set with three different resonance frequencies: 300 kHz in the case where the first and the second switch SW1 and SW2 are off, 280 kHz in the case where the first switch SW1 is on, and 260 kHz in the case where the second switch SW2 is on. Therefore, according to the above-mentioned fundamental principle, an output of the amplifier 3 obtains the oscillating signal 101 of 300 kHz when the first and the second switch SW1 and SW2 are off, that of 280 kHz when the first switch SW1 is on, and that of 260 kHz when the second switch is on respectively. Then, the oscillating signal 101 is outputted to the status detecting means 8. In Fig. 13, the waveform shaping circuit 55 waveform-shapes the oscillating signal 101, frequency counter circuit 56 counts the frequency of the oscillating signal, and the frequency discriminating circuit 54c determines whether the obtained frequency is 300 kHz, 280 kHz, or 260 kHz; and thereby setting conditions of the first switch SW1 and the second switch SW2 can be detected. Further, on discriminating the frequency, it is possible to absorb fluctuation in a resonance frequency caused by change in temperature and irregularity of specific value of parts if respective ranges for discrimination are determined. For instance, if the frequency is between 270 kHz and 290 kHz, the first switch SW1 is on. Though this apparatus gives an instance that two switches are mounted on the position pointer 5, the oscillating frequency, that is, the resonance frequency can be set at an arbitrary value within a range in which phase characteristics and gain of the amplifier 3 are guaranteed, for example, between 100 kHz and 1 MHz. Thereby, it is also possible to mount switches more than two on the position pointer 5 and discriminate the frequency with them. For instance, a frequency range between 300 kHz and 500 kHz is equally divided into ten ranges and a switch is allocated to each of the divided ranges every 20 kHz, and thereby ten switches can be allocated in total. Such an allocation of the frequency can be set by taking into consideration range of fluctuation in the resonant frequency caused by change in temperature and irregularity of specific value of parts. Further, if a plurality of position pointers are provided and predetermined frequency ranges are allocated to the respective position pointers, it is also possible to distinguish one position pointer from the others and distinguish the set condition at the same time. This apparatus has a structure that capacitor are connected in parallel in the resonant circuit as the status setting means for changing the frequency of the resonant circuit, and the resonant frequency lowers when the switch is pressed. However, there are many means for changing the resonance frequency as the status setting means other than the switch, for instance, a means for changing the frequency continuously with a pressure sensor and so on and detecting pressure with the status detecting means. It is needless to say that other circuits also can realize the set of the resonance frequency. Additionally, the position detecting means have any structure as far as it can detect the change in frequency. Further, as the first and second coupling means, any of what are explained above can be applied. Next, referring to Figs. 14 to 16 there will be described an apparatus which is provided with an AGC circuit for controlling a gain of an amplifier. Fig. 14 is a block diagram of this apparatus. In this figure, 3a is the amplifier capable of controlling the gain, 1 is a first coupling means, 2 is a second coupling means, 4 is a resonant circuit, 5 is a position pointer, 6 is a position detecting means, 101 is an oscillating signal, 102 is an input signal, M1 and M2 are electromagnetic coupling between the first and the second coupling means and the resonant circuit 4 respectively, 9 is the AGC circuit for controlling the gain of the amplifier 3a, and 105 is a control signal outputted from the AGC circuit. Fig. 15 is a block diagram of the AGC circuit 9. In this figure, 57 is a rectifier circuit, 58 is an integrating circuit, 59 is a comparator, 60 is an amplitude setting means, 101 is the oscillating signal, and 105 is the control signal. Fig. 16 is a structure example in the case of obtaining position information from the input signal 102. Operation of this apparatus will be explained below. In Fig. 14, while the resonant circuit 4 is not coupled to either the first or the second coupling means 1 and 2, the gain of the amplifier 3a is sufficiently increased beforehand. Then, if the resonant circuit 4 approaches the first and the second coupling means 1 and 2 and thereby an oscillation starts, the AGC circuit 9 controls the gain of the amplifier 3a and limits an amplitude of the oscillating signal 101. In other words, in Fig. 15 the AGC circuit 9 rectifies the oscillating signal 101 at the rectifier circuit 57, integrates the rectified signal at the integrating circuit 58, and compares the amplitude of the oscillating signal 101 with the amplitude value set by the amplitude setting means 60 at the comparator 59. Thereby the control signal 105 is outputted to the amplifier 3a so that the amplitude of the oscillating signal 101 remains the amplitude which is set at the amplitude value set by the amplitude setting means 60. If a distance between the resonant circuit 4 and the first and the second coupling means 1 and 2 becomes smaller, the control signal 105 outputted from the AGC circuit 9 changes in accordance with the distance, and the position detecting means 6 can obtain position information on the position pointer 5 from amplitude information on the oscillation which can be obtained from the control signal 105 outputted by the AGC circuit 9. By means of controlling with the AGC circuit 9 in the above manner, the oscillation becomes stable, the amplitude of the oscillating signal 101 becomes constant even if a position of the resonant circuit 4 changes, and the position information can be obtained from the control signal 105 generated by the AGC circuit 9. Further, the position information can be also obtained from the input signal 102 of the amplifier 3a in a similar way though an absolute value in small as indicated in Fig. 16. Moreover, in an combination of the status setting means and the status detecting means described above, it is possible to use the oscillating signal 101 the amlitude of which becomes constant and detect position more stably. The amplifier 3a can be realized also with a well-known amplifier such as a VCA the gain of which can be varied outside of the VCA, for instance, TL026 of T.I. As mentioned above, it is possible to extend further an extent of distance in which detection of the position pointer is available and to obtain more stable oscillation by means of providing the AGC circuit for controlling the gain of the amplifier and utilizing a dynamic range of the amplifier effectively. Further, as the first and the second coupling means, any of those which are explained above can be employed. Next, a principle construction of an improved invention will be explained referring to Figs. 17 to 21. Fig. 17 is a principle block diagram for explaining the principle of position detection of the present invention. A position pointer 5 is used for pointing a position to be inputted and is provided with a resonant circuit 4. A resonance frequency of the resonant circuit 4 is elected by taking into account functions of an amplifier and intensity of electromagnetic coupling which are mentioned below and is set at a few hundreds kHz. A body of a detecting device 301 is provided with a first sense line 1e, a second sense line 2e, an amplifier 3, and a position detecting circuit 305. The first and the second sense line 1e and 2e are, for example, wires laid in a shape of a loop on a printed board, and are laid with a part of the loops overlapped. A laying interval p between the two sense lines is selected so that an effect of direct electromagnetic coupling between the two sense lines is canceled. For instance, the first and the second sense line are laid at such laying intervals p as cause following two induced currents to be induced to the second sense line 2e when an alternating current (left side current i1 = right side current i2) flows through the first sense line 1e. Between the two induced currents, one is induced by the left side current i1 and the other induced current is induced by the right side current i2. The two induced currents are reverse in polarity and equivalent in intensity. The first and the second sense line are laid at the laying intervals p which enable the above conditions to be realized. The first and the second sense line 1e and 2e constructed in the above manner are connected to an output and an input of the amplifier 3 respectively. However, in the above description, the two kinds of the sense lines are referred to as the first and the second line only in order to distinguish the two sense lines for explanation. Because the two sense lines are named the first sense line and the second sense line for explanation in the above and both sense lines are same in construction, functions of the apparatus is completely equivalent to that with the above connection even if the first sense line 1e is connected to the input of the amplifier 3 and the second sense line 2e is connected to the output of the amplifier 3. The electromagnetic coupling among the first and the second sense line 1e and 2e, and the resonant circuit 4, and polarity and gain of the input and the output of the amplifier 3 include conditions for the construction of the inventive apparatus. Therefore, these values are properly selected to design the apparatus. First of all, when the resonant circuit 4 is close to the first and the second sense line 1e and 2e, it is necessary to set phase relation of each coupling among respective elements so that a closed loop circuit composed of the first sense line 1e, the resonant circuit 4, the second sense line 2e and the amplifier 3 becomes a positive feedback loop. Further, the gain of the amplifier 3 must be selected so that oscillation starts, when the gain of the closed loop circuit becomes at least one while the resonant circuit 4 is close to the first and the second sense line. A frequency oscillator formed by the positive feedback loop is a well-known circuit, and it is a commonly well-known technology that oscillation starts, if a positive feedback loop is formed when the loop gain is at least one. In the inventive apparatus, it is necessary that the loop gain changes depending on a distance from the sense lines to the resonant circuit 4, and that when the distance becomes smaller than a predetermined value and electromagnetic coupling becomes stronger, the loop gain becomes to least one and thereby the oscillation starts. The position detecting circuit 305 outputs a position detecting signal s2 by using amplitude information on an oscillating signal s1 which arises from the positive feedback loop. In this constructional example, the position detecting circuit 305 is connected to the output of the amplifier 3. Figs. 19(a) and (b) show examples of the position detecting circuit 305. The circuit shown in Fig. 19(a) is composed of a rectifier circuit 51 and a smoothing circuit 52, and outputs an envelope signal of the oscillating signal s1 as the position detecting signal s2a. As a state of the position detecting signal s2 is converted so that it is easy to utilize the system using position information, the position detecting circuit 305 is added with such an output circuit as a desired output can be obtained. For instance, when it is desired to obtain the position detecting signal s2 in digital value, and A - D conversion circuit 53 is provided on a stage subsequent to the smoothing circuit 52 as shown in Fig. 19(b). Next, an operation of this apparatus will be explained. First, when the position pointer 5 does not exist in vicinity of the sense lines, the closed loop circuit is not constituted and therefore the oscillation does not arise because the first sense line 1e and the second sense line 2e are laid so that a direct electromagnetic coupling is zero. A next step is to suppose a case that the position pointer 5 is put in the vicinity of the sense lines a shown in Fig. 20(a), and moves at a constant height above a surface of the body of the detecting device and in a direction in which the sense lines adjoin, that is, in an x-direction in the figure. In this case, the electromagnetic coupling arises among the first sense line 1e, the second sense line 2e and the resonant circuit 4 and the position feedback loop is constituted including the amplifier 3. Then, the oscillation starts and the oscillating signal s1 is generated. The oscillating signal s1 is input in the position detecting circuit 305 and is rectified and smoothed therein, and then the position detecting circuit 305 outputs the amplitude information as the position detecting signal s2. When the position pointer moves in the X-direction in the Fig. 20, coupling intensity among the sense lines and the resonant circuit 4 changes depending on a position of the position pointer, the gain of the closed loop circuit changes, and an amplitude of the oscillating signal s1 changes. As Fig. 20(a) shows, the amplitude becomes maximal when a center of a coil composing the resonant circuit 4 is at X2, a middle of a region where the first sense line 1e and the second sense line 2e cross, and becomes smaller gradually as the center of the coil moves toward portions around X2. A distribution of the amplitude in the x-direction shows a tendency as shown in Fig. 20(b). However, in this case, for the purpose of explaining the principle there are positions at which the amplitudes becomes equal in the right and the left of X2, that is, the regions X1 and X3 in the figure, and a pointed position can not be specified to be one. However, this will lead to understanding that the amplitude of the oscillating signal s1 has the position information. As explained above, under conditions of a constant height, a constant relation is maintained between the position of the position pointer 5 and the amplitude of the oscillating signal s1, therefore the pointed position is identified from the amplitude information on the oscillating signal s1. The above explanation referring to Fig. 20 is on the case that the position pointer 5 moves in a laying direction of the sense lines while the height of the position pointer 6 is maintained constant. However, it will be easily understood that the height can be detected also when the position pointer moves in the direction of the height. Figs. 21(a) and (b) are diagrams showing a change in amplitude of the oscillating signal s1 which is observed when the position pointer 5 moves from a sense line laying surface h0 in a direction of the height h while the resonant circuit 4 is made not to move in the laying direction of the sense lines. As the amplitude changes uniformly depending on changes in the height h, a pointed height can be identified from the amplitude information on the oscillating signal s1 as well as a detection of the position in the laying direction. There will be explained some constructional variations of the principle construction explained above. First of all, though the explanation of Fig. 17 states that the first sense line 1e and the second sense line 2e are single loop lines, it is also possible to use multiple loop lines in order to intensify the electromagnetic coupling. As it will be explained below, using multiple loop lines is more practical for an actual construction as the position reading apparatus. Fig. 18 is a diagram showing the case fourfold loop lines are laid as the first sense line 1f and the second sense line 2f respectively, and in this case the first and the second sense line are also laid so that the electromagnetic coupling between the two sense lines is canceled. Further, though in Fig. 17 the position detecting circuit 305 is connected to the output of the amplifier 3, it can be connected to other circuits as the need arises because what is required is to input the amplitude information of the oscillating signal s1 into the position detecting circuit 305. For instance, it can be connected to the input of the amplifier 3 also. However, in this case it is necessary to provide an amplifier before the rectifier circuit 51 shown in Fig. 19(a) because the amplitude of the oscillating signal s1 is small. Next, referring to Figs. 22 to 29(a) and (b) there will be described a position reading apparatus applying the principle construction. Fig. 22 is a block diagram showing this position reading apparatus. In Fig. 22, 21, 22, 23 and 24 compose a first sense line group; and 31, 32, 33 and 34 composes a second sense line group. These sense line groups are laid in sense line pitches p in a position detecting direction. To brief an explanation, the explanation will be given on condition that the position is detected only in one direction (a horizontal direction in the figure.) The first sense line group and the second sense line group are laid with a part of loops overlapped as well as in the construction for explaining the principle. For instance, when a sense line 21 is selected as a first sense line and a sense line 31 is selected as a second sense line, electromagnetic coupling between the two sense lines is canceled. All of one ends of the respective sense lines in both sense line groups are grounded. The other ends of the sense lines in the first sense line group are connected to a first scanning circuit 308, and the other ends of the sense liens in the second sense line group are connected to a second scanning circuit 309. The first scanning circuit 308 and the second scanning circuit 309 are composed of a plurality of electronic switch devices such as analogue switches respectively, and one ends of the respective switch devices are connected to each other and form common terminal respectively. Actually, an analogue switch IC, CD4051 and so on can be used for this circuit. Each one of the switch devices is closed by selection signals s3 and s4 which are supplied from a control circuit 311 to be mentioned below, and then each one end of the switch devices is connected to the common terminal respectively. The respective sense lines of the sense line groups are connected to the respective terminals of the first and the second scanning circuit 308 and 309. The common terminals are connected to an excitation/sense switching circuit 310. For explanation to be given later, functions of these circuits are indicated in Tables 1 and 2 and explained concretely. However, these tables (as well as other tables used hereinafter) show only an example for the explanation, and the functions are not limited to those indicated in these tables. In the tables, only a sign is indicated as a name of each signal. Function Table of the First Scanning Circuit 308 s 3 Selected Sense Lines 0 21 1 22 2 23 3 24 Function Table of the Second Scanning Circuit 309 s 4 Selected Sense Lines 0 31 1 32 2 33 3 34 The first sense line selection signal s3 and the second sense line selection signal s4 can be expressed, for example, with binary numerical values which appear on a plurality of signal wires. Therefore, by applying the binary numerical values to these signal wires, the sense line corresponding to the binary numerical value can be selected. For instance, if in Table 1, "2" is applied to the signal wires as the first sense line selection signal s3, the sense line 23 is selected. The excitation/sense switching circuit 310 is basically a switch having two inputs and two outputs. It switches connection between the inputs and the outputs alternately so that the following two states alternate: 1) the first scanning circuit 308 is coupled to an input of an amplifier 3 while the second scanning circuit 309 is coupled to an output of the amplifier 3; and 2) the first scanning circuit 308 is coupled to the output of the amplifier 3 while the second scanning circuit 309 is coupled to the input of the amplifier 3. The circuit shown in Fig. 22 uses an analogue switch IC, CD4052. This IC is composed of two switching circuits having four inputs and one output respectively, and controls the two circuits with the selection signal of one line. In this example, each circuit uses two contacts and the contacts are connected cross, and thereby the above function is realized. Different circuits are used depending on the switching elements used, and this circuit is not a limited one. Table 3 shows the function of this circuit. Function Table of the Excitation/Sense Switch Circuit 310 s 5 Input I1 is coupled to: Input I2 is coupled to: 0 O1 O2 1 O2 O1 In Fig. 22, marks I1 and I2 represent input terminals and marks O1 and O2 represent output terminals. As shown in Table 3, when the excitation/sense switching signal s5 is logic 0, I1 is coupled to O1 and I2 is coupled to O2; further when s5 is logic 1, I1 is coupled to O2 and I2 is coupled to O1. One of the outputs of the excitation/sense switching circuit 310, O1, is connected to the input of the amplifier 3, and the other output O2 is connected to the output of the amplifier 3. A position detecting circuit 305c is constructed as shown in Fig. 23 and has a construction that a position calculating circuit 354 is added to a stage subsequent to the structure for explaining the principle shown in Fig. 19(b). The position calculating circuit 354 is inputted with amplitude information on an oscillating signal which is converted into an digital value at an A - D conversion circuit 53 and the selection signals s3 to s5 which are applied to the first and the second scanning circuit 308 and 309 and the excitation/sense switching circuit 310, and calculates a position pointed by a position pointer 5 from the above input. The control circuit 311 is connected to the first scanning circuit 308, the second scanning circuit 309 and the excitation/sense switching circuit 310 respectively so that the selection signals s3 to s5 are applied to the above three circuits respectively. The control circuit 311 outputs the first and the second sense line selection signal s3 and s4 so that the two adjacent lines are selected simultaneously. Further, every time the control circuit outputs the signals for selecting the sense lines, the excitation/sense switching signal s5 is inverted and each of the first and the second scanning circuit is coupled to each of the input and the output of the amplifier 3 alternately. Next, operation will be explained. The control circuit 311 applies the first sense line selection signal s3 to the first scanning circuit 308, the second sense line selection signal s4 to the second scanning circuit 309, and thereby selects the two adjacent sense lines among the sense line groups. At the same time, the excitation/sense switching signal s5 is applied to the excitation/sense switching circuit 310, and thereby the selected sense lines are coupled to the input and the output of the amplifier 3 respectively. Referring to Fig. 22, there will be described a concrete example of a selection operation. For instance, the first sense line selection signal s3 and the second sense line selection signal s4 are defined as "logic 1" and at the same time, an excitation/sense switching signal s5 is defined as "logic 1." In this case, the sense lines 22 and 32 are selected according to Tables 1 and 2, and the input and the output of the excitation/sense switching circuit 310 are coupled in a manner of I1 - O2 and I2 - O1 according to the Table 3. Therefore, the sense line 22 is coupled to the input of the amplifier 3 and the sense line 32 is coupled to the output of the amplifier 3. For explanation to be given below, hereinafter the sense line coupled to the output of the amplifier 3 is referred to as an exciting sense line and the sense line coupled to the input of the amplifier 3 is referred to as an detecting sense line. In this case, 32 is the exciting sense line and 22 is the detecting sense line. As the explanation of the principle, when the position pointer 5 approaches the selected sense line, a closed loop circuit is constructed with the sense lines, a resonant circuit 4 and the amplifier 3 and thereby oscillation rises. Fig. 20 shows a relationship between a position of the position pointer 5 and an amplitude of the oscillating signal s1 at that time. The amplitude of the oscillating signal s1 includes position information on the position indicated by the position pointer 5. Determining the position by use of this information is a position calculating principle of the inventive position detecting device. The control circuit 311 selects the sense line as described above. This selecting operation is performed to each of the sense lines which totals a number necessary for calculating the position. Generally, the sense line are selected one by one in order of a position detecting direction or the opposite direction. This selecting operation is called "scanning." The order of scanning is not an essential problem. It is not necessary to scan in order and it is also effective to scan at random. There will be explained a case of scanning in the order of the position detecting direction. The number of sense lines necessary for position calculation is, for instance, five in this apparatus. A value of the number is determined by considering the sense line pitch p, a diameter of a coil of a resonant circuit 4 and other parameters, and the above "five" does not have an essential meaning. As it will be described later, any number of sense lines is available as far as the number is enough for the position calculation. Scanning operation will be explained by giving a concrete example. Table 4 is a scanning timing table showing the sense lines selected by scanning and the circuits to which the sense lines are coupled when the five sense lines are sequentially scanned with the sense line 31 as a scanning start sense line. Scanning Timing Table Scanning Number s3 s4 s5 Input of the Amplifier 3 is coupled to: Output of the Amplifier 3 is coupled to: 1 0 0 0 31 21 2 0 1 1 21 32 3 1 1 0 32 22 4 1 2 1 22 33 5 2 2 0 33 23 As shown in Table 4, the adjacent two sense lines are selected at each scanning, and one of the two sense lines is coupled to the input of the amplifier 3 and the other sense line is coupled to the output of the amplifier 3. This scanning process is performed five times sequentially. One of the exciting sense lines and one of the detecting sense line are selected by once of selecting operation. As explained above, the oscillating signal s1 the amplitude of which changes in size depending on a relationship of positions between the sense lines and the resonant circuit 4 is generated on the closed loop circuit composed of these sense lines, the amplifier 3 and the resonant circuit 4. Therefore, the oscillating signals s1 are inputted into the position detecting circuit 305c sequentially by selecting the sense line sequentially. Fig. 24 shows a waveform of the oscillating signals s1 which are inputted into the position detecting circuit 305c. In the example illustrated, the oscillating signal of the maximum amplitude during the scanning process is generated when the sense line 32 turns into the detecting sense line. This indicates that the resonant circuit 4 exists around the sense line 32. The oscillating signals s1 shown in Fig. 24 are rectified and smoothed in the position detecting circuit 305c and are converted into envelope signals shown in Fig. 25. Calculating the position from an envelope of an induced signal can be realized with a method disclosed by the conventional position reading apparatus. A method of calculating a position will be briefly explained according to the construction hereinafter. The position detecting circuit 305c inputs the oscillating signal s1 in itself every time the sense line groups is selected. The oscillating signal s1 is converted into an envelope signal and the envelope signal is converted into a digital value by the A - D conversion circuit 53, and then the digital value is inputted into the position calculating circuit 354. The position calculating circuit 354 is also inputted with the selection signals s3, s4 and s5 which are outputted from the control circuit 311. The position calculating circuit 354 detects the maximum signal and the two respective signals of the two sense lines on both sides of and adjacent to the sense line from which the maximum signal is generated among the envelope signals inputted sequentially. Each signal is given the following marks: Vp the maximum signal called a peak signal Vph the signal of the sense line being laid next to, in the position detecting direction, the sense line from which the maximum signal is outputted Vpℓ the signal of the sense line being laid next to, in a direction opposite to the position detecting direction, the sense line from which the maximum signal is outputted As to the detecting sense line from which the maximum sense signal is outputted, a sense line number of it is converted into the sense line number based on the scanning start sense line, and is memorized. This sense line number is called a peak address, which is represented as Padrs. The peak address indicates an approximate position where the position pointer is placed. Thereby, the position can be detected by a unit of the sense line pitch. The further detailed position is obtained by calculating the peak signal and the signals on both sides of the peak signal. In order to calculate these signals, first a value of Q in Expression-1 is found as follows: Q = (Vp - Vph) / (Vp - Vpl) where Vph > Vpℓ The value of Q has a characteristic mentioned below. A first step is to consider a case that, as shown in Fig. 26, the coil of the resonant circuit 4 is placed at a center of a crossing position of the sense lines 21 and 32, a point "a". When the sense lines 32 and 21 are selected as the exciting sense line and the detecting sense line respectively, the maximum oscillation signal among the scanning process is generated on the closed loop circuit as shown in Fig. 20(b), and the peak signal Vp is inputted into the position calculating circuit 354. The position calculating circuit 354 has been already inputted with the first and the second sense line selection signals s3, s4 and the excitation/sense switching signal s5, so that the sense line 21 is identified as the detecting sense line from these signals. Then, the sense line 21 is converted into a number which is based on a reference sense line number 0 for the sense line 31, and the number is memorized as the peak address Padrs. The peak address in this case is Padrs = 1. 21 is the exciting sense line and 31 is the detecting sense line at the selecting operation one time before the selecting operation at which the maximum oscillating signal is generated. In this case, the oscillating signal smaller than Vp is generated in the closed loop circuit, and Vpℓ is inputted into the position calculating circuit 354. On the other hand, at the selecting operation one time after the selecting operation at which the maximum oscillating signal is generated, similarly 22 is the exciting sense line and 32 is the detecting sense line and Vph is generated on the closed loop circuit. When the coil of the resonant circuit 4 is placed on the point "a", effects of electromagnetic coupling are equal between at the selecting operation one time before and at that one time after, and a ratio of the two signals becomes Vph = Vpℓ. Therefore, Q = 1 according to Expression-2. Next, when the coil of the resonant circuit 4 moves in the position detecting direction as shown in Fig. 27, among couplings between the sense lines, the coupling between the sense lines 31 and 21 and the coupling between the sense lines 21 and 32 becomes smaller than the above, and contrarily the coupling between the sense lines 32 and 22 becomes larger. As a result, Vp and Vpℓ become smaller and Vph becomes larger, and Q in Expression-2 takes a value smaller than 1. When the coil moves further to a position in Fig. 28, namely, moves a half of the sense line pitch from the position in Fig. 26, the value of Q becomes minimal. In this case, the effects of the coupling 21 - 32 and the coupling 32 - 22 becomes equal, Vp = Vph, and Q = 0. When the coil moves left from the position in Fig. 26, Q is obtained by Expression-2 in which Vph and Vpℓ are exchanged. In this case, increases and decreases in Q show the same tendency as the above. Q is a value which takes a value between 1 and 0 every half sense line pitch as shown in Fig. 29 and becomes a value corresponding, one by one, to each of the detailed positions between the sense lines. If characteristics of this Q is found by an experiment in advance, the detailed position between the sense lines can be obtained by finding Q from the amplitude of the oscillating signal. The position pointed by the position pointer 5 can be obtained by performing addition and substraction as the above-mentioned approximate position according to the peak address and the detailed position obtained here. Expressions-3 and 4 are position calculating expressions: Pointed Position = Padrs x p + f(Q) where Vph > Vpℓ otherwise, Pointed Position = Padrs x p - f(Q) where Vph < Vpℓ. Explanation as to the marks will be given below again. Pards : Peak address p : sense line pitch f(Q) : detailed position between the sense lines corresponding to Q In such a manner mentioned above, the position pointed by the position pointer is obtained. There will be added an explanation of some constructional variation. First of all, the structure shown in Fig. 22 is provided with the four first sense lines and the four second sense lines respectively, but the number of the sense lines can be varied arbitrarily depending on a position detecting range when designing the system. The range available for detection is not limited, and this principle can be realized in a vast range of the position reading apparatus from the small apparatus called a tablet to the large apparatus called a digitizer. Further, though the position detecting direction is only one, a horizontal direction in Fig. 22, which is for simplifying the explanation, practically the system is constructed as a two-dimensional position reading apparatus by arranging sense line groups orthogonally both in X and Y directions. It is easily understood to develop the structure explained here in the two-dimensional position reading apparatus. In this case, some constructional variations can be supposed, for instance, the two amplifiers are provided separately in X and Y directions, or one amplifier is provided to be used in common. However, these variations are not essential subjects of the present apparatus but are only design items, so that these variations can be selected arbitrarily for design depending when necessary. The effect of the present apparatus becomes remarkable when the present apparatus is constructed as the two-dimensional position reading apparatus. In the position reading apparatus, the sense lines are scanned individually in each position detecting direction. In order to detect the position of the X-Y two-dimensions, it is necessary to scan only ten times in total, five times in the X-direction and five times in the Y-direction. In the conventional position reading apparatus, it is necessary to scan as many as twenty-five times in total, that is, five time five (5 x 5) in matrix. The present invention enables decreasing a number of times to scan substantially and accelerating the position calculation. Further, a relation between the two sense lines selected at one time of scanning is equivalent at any point in a detecting area, and the electromagnetic coupling between the two sense lines is canceled. In the conventional position reading apparatus, the electromagnetic coupling arises directly between the two sense lines selected near a periphery of a detecting device. However, in the present apparatus, as such direct coupling does not arise, there is no defect that accuracy of position detecting deteriorates. Fig. 30 is a block diagram showing another position reading apparatus. This apparatus is different from the previous one in a first scanning circuit 308d, a second scanning circuit 309d, and coupling between a sense line group and these circuits. The sense line group is not divided into two groups as it is in the previous apparatus. The excitation/sense switching circuit 310 disclosed in the previous apparatus is not provided. A position detecting circuit 305d and a control circuit 311d are also partially different from those in the fifth embodiment. Other parts of this apparatus is the same as those of the previous apparatus. The first scanning circuit 308d and the second scanning circuit 309d are electronic switching devices similar to those of the previous apparatus and include more circuits. Respective sense lines are connected both to the first and the second scanning circuit 308d, 309d in parallel. The control circuit 311d is connected to the first and the second scanning circuits 308d, 309d so as to apply a first sense line selection signal s3d to the first scanning circuit 308d and apply a second sense line selection signal s4d to the second scanning circuit 309d. The position detecting circuits 305d is connected so as to be inputted with an oscillating signal s1 and also the first and the second sense line selection signal s3d, s4d. Next, there will be described operation of this apparatus. The control circuit 311d applies the first and the second sense line selection signal s3d, s4d to the first and the second scanning circuit 308d, 309d respectively, and scans the sense lines. The scanning is performed as well as in the previous apparatus by selecting the two sense lines adjacent and coupling one sense line to an input of an amplifier 3 and the other sense line to an output of the amplifier 3. Table 5 is a timing table showing a timing of scanning in this apparatus. Like Table 4 in the previous apparatus, this table also shows the timing of scanning the five sense lines sequentially with the sense line 31 as a scanning start sense line. Scanning Timing Table Scanning Number s3d s4d Input of the Amplifier 3 is coupled to: Output of the Amplifier 3 is coupled to: 1 1 0 31 21 2 2 1 21 32 3 3 2 32 22 4 4 3 22 33 5 5 4 33 23 When the position pointer 5 is placed near the sense line group and the sense lines are scanned in accordance with Table 5, the oscillating signal s1 according to a position pointed by the position pointer 5 is generated as well as in the previous apparatus. Hereafter, the position pointed by the position pointer can be calculated from the amplitude information on the oscillating signal s1 as well as in the previous apparatus. Though this apparatus also has constructional variations like the previous apparatus, explanation of it is omitted as it is redundant. Next, referring to Figs. 31 and 32 there will be described another apparatus. This apparatus is related to an apparatus that a status setting means is provided in a position pointer and a state of the position pointer is detected by a body of a detecting device. The status setting means is, for example, a push-button switch. By pushing the switch, instructions for position input are given and command information is outputted to an external device. Figs. 31 and 32 are block diagrams showing another position reading apparatus. This apparatus is similar to one for explaining the principle of the improved construction. As shown in Fig. 31, a resonant circuit 4 is connected to a switching circuit 313 in parallel in a position pointer 5e. The switching circuit 313 is a series circuit composed of a switch and a capacitor, and a resonant frequency of the resonant circuit 4 changes by closing the switch. Though this apparatus is provided with only one switching circuit 313, it is also possible that a plurality of switching circuits are provided and a different resonance frequency is determined by closing each of the switching circuits. A feature of the present apparatus is a capability of providing a number of the switching circuits, but it will be described later. On the other hand, a body of a detecting device le is newly provided with a status detecting circuit 312, which is connected to an output of an amplifier 3. The status detecting circuit 312 is constructed as shown in Fig. 32, and is composed of a waveform shaping circuit 321, a frequency counter 322 and a frequency discriminating circuit 323. The waveform shaping circuit 321 converts oscillating signals sl which are sinwave signals into a rectangular wave so that the frequency counter can count them. The frequency counter counts the oscillating signals which are converted into the rectangular wave. The frequency discriminating circuit 323 is a circuit for comparing a count value with a reference value memorized and discriminating a status of the switch circuit. Next, operation of this apparatus will be explained. The position pointer 5e resonates at a frequency fl when the switching circuit 313 is open, and at a frequency f2 when the switching circuit 313 is closed. If the position pointer 5e approaches to a sense line while the switch is open, a closed loop circuit is constructed and starts to oscillate at the frequency f1. The oscillating signals s1 are inputted into the status detecting circuit 312, and at first are converted into the rectangular wave by the waveform shaping circuit 321 and then counted by the frequency counter 322. As the frequency discriminating circuit 323 memorizes a reference value used for discriminating between the frequencies f1 and f2, the circuit compares the reference value and the frequency count value to be inputted, and thereby recognizes whether the switch is open or closed. In this case, the switch is recognized to be open. When the switch is closed, the signal is processed in a similar manner. Processing performed in this apparatus is only to detect the frequency of the oscillating signal which changes according to a status of the switch in the position pointer and to discriminate the frequency by comparing it with the reference value. Therefore, even if the position pointer 5e is provided with a number of the switching circuits, the status detecting circuit 312 can easily discriminate the status of the switching circuits if each of the switching circuits has a different resonance frequency. The conventional position reading appratus requires a highly accurate discriminating circuit, because a frequency of a resonant circuit is slightly shifted by operating a switch and the slight shift is discriminated. On the other hand, the discriminating circuit does not require such high accuracy, because this apparatus can be constructed so that the frequency changes comparably by a large extent. The construction with the frequency counter is given as an example of the construction of the status detecting circuit 312. However, various circuits other than the above circuit can be thought out if it is understandable to use frequency information on the oscillating signal. For instance, to measure a period of the oscillating signal, or to discriminate the frequency after converting the frequency information into voltage information by a f/V converter. The status setting means is explained by taking the circuit with the switch for instance, but there can be other various constructions. For instance, a construction that a pressure detecting device is used instead of the switch and a frequency is continuously changed by pressing pressure. Further, not only a construction with a mechanical switch but also various status setting means can be thought out, for example, a construction with a electronic switch which is controlled by touching the position pointer, and a construction that a frequency is continuously changed according to a position to be touched. Moreover, this embodiment is constructed by applying the status setting means and the status detecting circuit to an explanatory diagram of the principle construction. However, it is also obvious that these means can be applied also to the apparatuses of fig. 22 to 30. In this case, the frequency of the oscillating signal is detecting while scanning, and because the frequency does not change depending on scanning condition, the frequency can be detected by determining a proper timing. Actually, it is advantageous in an aspect of S/N to detect the frequency of a peak signal. Next, there will be described another apparatus referring to Figs. 33 and 34. First, a construction will be explained. As shown in Fig. 33, an amplifier 3a is newly provided with an AGC circuit 9. The AGC circuit 9 is inputted with an oscillating signal s1 and controls a gain of the amplifier 3a according to the signal. The amplifier 3a is designed so as to output a gain control signal s7 to the amplifier 3a and to control an amplitude of the oscillating signal s1 so that it is constant at an output of the amplifier 3 all the time. The amplifier 3a used in this apparatus is an amplifier with a variable gain and is designed so that the gain changes depending on the gain control signal s7. Various designs can be drafted for these circuits depending on what circuit is applied as the amplifier 3a and what signal is outputted as the gain control signal s7. In this embodiment, a voltage-controlled amplifier (VCA) is adopted as the amplifier 3a, and the gain is controlled with the gain control signal s7 which is d.c. voltage. Further, characteristics of the control is predetermined so that the gain becomes high when the gain control signal s7 is small and the gain becomes low when the gain control signal s7 large. For that purpose, the AGC circuit 9, which is constructed as shown in Fig. 34, rectifies and smooths the oscillating signal s1 at the rectifier circuit 341 and the smoothing circuit 342, and thereby outputs d.c. voltage according to the amplitude of the oscillating signal. Next, there will be explained operation of the apparatus. As shown in Fig. 20 used for explaining the principle, the amplitude of the oscillating signal s1 has a feature that it changes depending on a positional relationship between sense lines 1e, 2e and a resonant circuit 4. When the resonant circuit 4 is placed in a center of a cross portion of the sense lines 1e and 2e, the amplitude of the oscillating signal s1 becomes maximal; and as the resonant circuit 4 moves toward a periphery of the cross portion, the amplitude becomes smaller. The amplitude of the oscillating signal s1 changes in a way mentioned above in an absense of the AGC circuit 9. The AGC circuit 9 and the amplifier 3a function in order that fluctuation of the amplitude is made smaller at the output of the amplifier 3a. When the resonant circuit 4 is placed on the center of the cross porition of the sense lines 1e and 2e and thereby electromagnetic coupling is intensified, a feedback amount from the output to an input of the amplifier 3a increases and the amplitude of the oscillating signal s1 also tends to increase. However, the AGC circuit 9 applies the gain control signal s7 to the amplifier 3a so as to cancel the increase in the amplitude. On the other hand, when the resonant circuit 4 moves to the periphery of the cross portion of the sense lines 1e and 2e and thereby the electromagnetic coupling is weakened, the feedback amount from the output to the input of the amplifier 3a discreases and the amplitude of the oscillating signal s1 also tends to decrease. However, the AGC circuit 9 applies the gain control signal s7 to the amplifier 3a so as to cancel the decrease in the amplitude. Because a magnitude of the gain control signal s7 changes depending on a position of the resonant circuit 4, a position detecting circuit 305f can detect a pointed position from the gain control signal s7. The gain control signal s7 is a signal which has been already converted into d.c. voltage, the position detecting circuit 305f does not require a rectifier and a smoothing circuit. Therefore, it is possible to output the gain control signal s7 as it is as a position detecting signal s2f for the most simple construction of the position detecting circuit 305f. As to this apparatus also, some constructional variations are developed. First, the construction for controlling the gain is not limited the above construction. One of circuits having the same function as that of the voltage-controlled amplifier is a current-controlled amplifier. It is evident that this circuit can also realize the gain control. Further, a requirement for an AGC characteristic is only that the gain of a closed loop circuit should be controlled as well. Therefore, it is possible to design an input-output characteristic of the AGC circuit and a control signal-gain characteristic of the amplifier depending on purposes without restrictions. There can be more variations for other details. It is evident that the AGC circuit explained can be realized in the systems according to to apparatuses of fig. 22 to 32. Next, there will be described a key board apparatus applying the above basic construction referring to Fig. 38. Fig. 38 is a block diagram showing a key board apparatus. In Fig. 38, 401 is a key board detecting device, and is provided with an amplifier 3, a first coil 1g, a second coil 2g and a frequency discriminating circuit 413. 402 is a key board, and is provided with series circuits, T1 to Tn, which are composed of switches S1 to Sn and capacitors C1 to Cn respectively, and a third coil 420. Each of the series circuits T1 to Tn and the third coil 420 are coupled in parallel, and form the parallel resonant circuit of LC by closing any of the switches S1 to Sn respectively. The first coil 1g and the second coil 2g have intensive electromagnetic coupling only when any of the switches S1 to Sn is closed and the parallel resonant circuit is constructed; when the switches S1 to Sn are not closed, they are not electromagnetically coupled or the coupling is extremely weak even if they are coupled. The first coil 1g and the second coil 2g shown in Fig. 38 are circular coils. And the second coil 2g is twisted at its diameter and the two coils are piled. In this case, even if some current flows through the first coil 1g and therefrom a magnetic field arises, two opposite magnetic fluxes are generated, which cross the second coil 2g at both sides of the diameter (right and left hands in the Fig. 38) and cancel each other because the second coil 2g is twisted at the diameter; therefore the first coil 1g and the second coil 2g are not directly coupled. Next, operation of this apparatus will be explained. When the switches S1 to Sn of the key board 402 are not closed, the first coil 1g and the second coil 2g are not magnetically coupled to each other as mentioned above, and between the input and the output of the amplifier 3 a feedback is not formed and an oscillation does not arise, either. However, when any of the switches S1 to Sn is closed and the parallel resonant circuit is constructed, the first coil 1g and the second coil 2g, and a resonant circuit including the third coil 420 are electromagnetically coupled to each other respectively. Then, a positive feedback loop is constructed, which includes, as elements of a route, an output of the amplifier 3, the first coil 1g, the parallel resonant circuit including the third coil 420, the second coil 2g, and an input of the amplifier 3, and thereby the oscillation at a resonant frequency of the parallel resonant circuit is generated. As a condition of the oscillation, a sufficient gain of the amplifier 3 and a suitable phase condition are necessary. The first coil 1g and the second coil 2g are provided so that in-phase signals are generated at the input and the output of the amplifier 3 when the third coil 420 is placed above and on the right of the second coil 2g, as shown in Fig. 38. Further, the oscillation is excited by noise made by the amplifier 3 or nature noise, which is a well known phenomenon in this type of oscillation action. When the resonance frequency of the resonant circuit is changed by one of the switches S1 to Sn, an oscillating frequency also changes according to the change similarly. Thereby, the frequency discriminating circuit 413 can detect frequency information on the oscillation frequency from an output signal of the amplifier 3 and detect the pushed switch, and then outputs switch information which is added with proper processings. Though the frequency discriminating circuit 413 detects the frequency information from the output signal of the amplifier 3 in the above embodiment, it is also possible to detect it from an input signal of the amplifier 3. In this case, as the input signal of the amplifier 3 is a minute signal, it is necessary that the frequency discriminating circuit 413 has a function of amplifying a voltage to a predetermined voltage available for frequency detection as a preliminary processing. Next, there will be described another key board apparatus referring to Fig. 39. In Fig. 39, elements with the same marks as those in Fig. 38 show the same elements with the corresponding marks in Fig. 38. 9 is an AGC circuit, which generates a control signal 105 from an output signal of the amplifier 3a, controls a gain of the amplifier 3a and obtains a constant output signal from the amplifier 3a. This type of AGC circuit is a well-known technology. Other construction are the same as those of the above apparatus shown in Fig. 38, and operations are also the same as the above apparatus. Because this apparatus is provided with the AGC circuit 9, a stable oscillating operation is available in a wider range of frequency compared with the above apparatus. Therefore, more switches can be detected. The number of switches which can be detected depends on a range of the oscillating frequency and a resolution of the frequency discriminating circuit 413. For instance, if the amplifier 3a is constructed by using TL026 of Texas Instruments as an amplifier, it is possible to obtain the oscillating frequency range from 100 kHz to 1 MHz by changing the resonance frequency of the resonant circuit in the key board 402. For instance, in order to detect twenty kinds of switches, a frequency range from 200 kHz to 500 kHz is divided into twenty portions, the divided frequency ranges are allocated respectively to the resonance frequencies of the resonant circuit in the key board 402 which are obtained when the respective switches are closed, and the frequency discriminating circuit 413 detects the frequency. Next, there will be described a key board apparatus connected to a host system referring to Figs. 40 to 41. Fig. 40 is a perspective view showing a condition of the connection between the key board apparatus and the host system. In this figure, 403 is the host system which includes a key board detecting device though it is not shown in the figure. 440 is a key board of the key board apparatus, and a third coil is provided in a connection device 441. An example of the host system 403 is a system in which a CPU board and a display are integrated, called as a note computer, a book computer and so on. This apparatus is constructed so that a first coil and a second coil in the key board detecting device provided in the host system and a resonant circuit including a third coil of the key board are electromagnetically couple when the connection device 441 is plugged into the host system 403. Fig. 41 is an explanatory diagram showing the connection device connecting the key board apparatus and the host system, which explains the Fig. 40 in more detail. 420a is the third coil provided in the connection device 441 of the key board, and is connected in parallel to series circuits composed of a plurality of switches and capacitors as disclosed in the above apparatus. 431 is a substrate included in the host system. The first coil 1h and the second coil 2h placed inside the first coil are provided on the substrate 431 in patterns. These coils are connected to an input and an output of the amplifier respectively though they are not shown in the figure. The second coil 2h is composed of a coil portion 2i with one turn and a coil portion 2j with two turns. The two coil portions 2i and 2j are coiled in opposite directions and are laid so that the coil portion 2i is approximately twice as large in area as the coil portion 2j. Therefore, the first coil 1h and the second coil 2h are not directly coupled. Coiling directions are predetermined so that an oscillation starts when the coil portion 2i of the second coil 2h is coupled to the third coil 420a. The oscillation is generated at a predetermined frequency, when the connection device 441 is plugged into the host system 403 and the third coil 420a is over the coil portion 2i of the second coil 2h, and thereby the switch of the key board is closed. Therefore, the connection device 441 can be made to be thinner and it is also possible to connect the key board and the key board detecting device with a small space on the key board detecting device. In the above apparatuses, a small opening is provided in the host system and the connection device is plugged into the opening. However, it is obvious from a principle of electromagnetic induction coupling disclosed by the present invention that it is possible to guide the connection device, for instance, to a bottom surface or a side of the host system and thereby couple the connection device to the coil of the key board detecting device without providing an opening. Further, a shape of the first, the second and the third coil is not limited to a circle and a rectangle mentioned above but other shapes are also available. Especially, as to the first and the second coil, there can be various deformed shapes which do not lead to coupling between the two coils, and it is needless to say that the coils in these shapes can be applied to the present apparatus. INDUSTRIAL APPLICABILITY The position reading apparatus applying the present invention is useful in inputting position coordinates on a drawing or a specified item of a menu sheet put on a tablet to an external equipment such as a computer. Especially the present invention is suitable for improving a wireless position reading apparatus which does not require a body of the detecting device and a position pointer to be connected with a signal wire. Further,the key board apparatus applying the present invention is usefull in transferring switch information to a host system such as a computer. Especially the present invention is suitable for transferring the switch information without contact of the host system and the key board apparatus.

Claims: A position reading apparatus comprising: an amplifier (3); a first coupling means (1) connected to the output of the amplifier (3); a second coupling means (2) connected to the input of the amplifier (3); a gain control means (9) for controlling a gain of the amplifier (3); said gain control means (9) being connected between the output of the amplifier (3) and a control input of the amplifier (3) and said gain control means (9) comparing the amplitude of an oscillating signal (101) output by the amplifier (3) with a preset amplitude value and outputting a control signal (105) to the amplifier (3), so that the amplitude of the oscillating signal (101) remains at the preset amplitude value; a position detecting means (6) connected to the input of the amplifier (3) or the output of the gain control means (9); a position pointer (5) having a resonant circuit (4); wherein when the resonant circuit (4) is electromagnetically coupled to both the first coupling means (1) and the second coupling means (2), the resonant circuit (4) along with the amplifier (3), the first coupling means (1) and the second coupling means (2) forms a positive feedback loop and composes a frequency oscillator which oscillates at a resonance frequency of the resonant circuit (4); and the position detecting means (6) obtains position information of the position of the position pointer (5) relative to a reference coordinate system from amplitude information of an oscillation signal generated by the frequency oscillator, wherein the first coupling means (1) comprises a first sense line group including a plurality of first sense lines (1a) which are parallel to one of an x and a y coordinate rectangular axis and which are also arranged at equivalent intervals, and a first scanning circuit which is a circuit for selecting each of the first sense lines (1a) sequentially and which is connected to the output of the amplifier (3); the second coupling means (2) comprises a second sense line group including a plurality of second sense lines (2a) which are parallel to another of the x and the y coordinate rectangular axis and which are also arranged at equivalent intervals, and a second scanning circuit which is a circuit for selecting each of the second sense lines (2a) sequentially and which is connected to the input of the amplifier (3) ; and the position detecting means (6) obtains the position information on the position pointer from the amplitude information included in an oscillating signal generated by the oscillator which is obtained by scanning the first and the second scanning circuit. The position reading apparatus according to claim 1, further comprising: a status setting means (7) for changing the resonance frequency of the resonant circuit (4); and a status detecting means (8) for detecting a status set by the status setting means (7) from frequency information on the oscillation signal. A position reading apparatus according claim 1, wherein the first coupling means (1) comprises a first sense line (le) being in a shape of the loop and connected to the output of the amplifier (3); the second coupling means (2) comprises a second sense (2e) line being in the shape of the loop and connected to the input of the amplifier (3), the first and the second sense line (1e, 2e) being laid with a part of the loops overlapped so that electromagnetic coupling between the sense lines is cancelled. The position reading apparatus according to claim 3, wherein the position pointer (5) further comprises a status setting means (7) for changing the resonance frequency of the resonant circuit; and wherein a status detecting means (8) is provided for detecting a status set by the status setting means (7) from frequency information on the oscillation signal. A position reading apparatus according to claim 1, wherein the first coupling means (1) comprises a first sense line group composed of a plurality of first sense lines (21, 22, 23, 24) which are in a shape of the loop and which are laid along a position detecting direction at predetermined laying intervals, and a first scanning circuit (308) connected to the first sense line group (21, 22, 23, 24) for selecting each sense line of the first sense line group (21, 22, 23, 24); the second coupling means (2) comprises a second sense line group composed of a plurality of second sense lines (31, 32, 33, 34) which are in the shape of the loop and are laid along the position detecting direction at the predetermined laying intervals, the second sense lines (31, 32, 33, 34) being laid off the sense lines composing the first sense line group (21, 22, 23, 24) by half of the laying intervals respectively, and the first sense line adjacent to the second sense line being laid with a part of the loops overlapped so that electromagnetical coupling between the sense lines is cancelled, and a second scanning circuit (309) connected to the second sense line group (31, 32, 33, 34) for selecting each sense line of the second sense line group (31, 32, 33, 34); the position detecting means (6) comprises an excitation/sense switching circuit (310) connected to the first and the second scanning circuit (308, 309) for coupling each of the first and the second scanning circuit (308, 309) to each of the input and the output of the amplifier (3) alternately, and a control circuit (311) for selecting and controlling each sense line of the sense line groups (21, 22, 23, 24, 31, 32, 33, 34) sequentially by selecting a sense line from both of the first and the second sense line group (21, 22, 23, 24, 31, 32, 33, 34) respectively so that the selected two sense lines are adjacent and then coupling one of the selected sense lines to the input of the amplifier (3) and coupling the other selected sense line to the output of the amplifier (3). The position reading apparatus according to claim 5, wherein the position pointer (5) further comprises a status setting means (7) for changing the resonance frequency of the resonant circuit; and wherein a status detecting means (8) is provided for detecting a status set by the status setting means (7) from frequency information on the oscillation signal. A position reading apparatus according to claim 1, wherein the first coupling means (1) comprises a sense line group composed of a plurality of sense lines (21, 22, 23, 24, 31, 32, 33, 34) which are in a shape of a loop and are laid along a position detecting direction, all of the two adjacent sense lines among the sense line group (21, 22,2 3, 24, 31, 32, 33, 34) being laid with a part of the loops overlapped so that electromagnetic coupling between the two adjacent sense lines is cancelled, and a first scanning circuit (308d) connected to the sense line group (21, 22, 23, 24, 31, 32, 33, 34) for selecting a sense line of the sense line group (21, 22, 23, 24, 31, 32, 33, 34) and coupling the selected sense line to the output of the amplifier (3); the second coupling means (2) comprises said sense line group (21, 22, 23, 24, 31, 32, 33, 34) and a second scanning circuit (309d) connected to the sense line group (21, 22, 23, 24, 31, 32, 33, 34) for selecting a sense line of the sense line group (21, 22, 23, 24, 31, 32, 33, 34) and coupling the sense line to the input of the amplifier (3); the position detecting means (6) comprises a control circuit (311d) for selecting and controlling the sense line group (21, 22, 23, 24, 31, 32, 33, 34) sequentially so as to select all of the two adjacent sense lines from the sense line group (21, 22, 23, 24, 31, 32, 33, 34) by turns with the first and second scanning circuit (308d, 309d) and to couple the selected two adjacent lines to the input and the output of the amplifier (3) by turns. The position reading apparatus according to claim 7, wherein the position pointer further comprises a status setting means (7) for changing the resonance frequency of the resonant circuit; and wherein a status detecting means (8) is provided for detecting a status set by the status setting means (7) from frequency information on the oscillation signal. The position reading apparatus according to any of claims 2, 4, 6 or 8, wherein the status setting means (7) has a plurality of switches so that at least three resonant frequencies can be made thereby. The position reading apparatus according to any of claims 2, 4, 6 or 8, wherein the position reading apparatus has a plurality of the position pointers and resonant frequencies which are determined by the status setting means (7) of each position pointer which are different from each other. A key board apparatus having a plurality of switches (S1, S2, S3, .. ,Sn) and transferring predetermined data with the switch being pushed comprising: a key board detecting device (401a) including an amplifier (3a), a first coil (1g) coupled to the output of the amplifier (3a), a second coil (2g) coupled to the input of the amplifier (3a), a frequency discriminating circuit (413), a gain control means (9) for controlling a gain of the amplifier (3a), said gain control means (9) being connected between the output of the amplifier (3) and a control input of the amplifier (3) and said gain control means (9) comparing the amplitude of an oscillating signal (101) output by the amplifier (3) with a preset amplitude value and outputting a control signal (105) to the amplifier (3), so that the amplitude of the oscillating signal (101) remains at the preset amplitude value; and a key board (402) having a parallel resonant circuit, including a plurality of series circuits (T1, T2, T3, ..., Tn) each of which is composed of the switch (S1, S2, S3, ...., Sn) and a capacitor (C1, C2, C3, ..., Cn) connected in series, and a third coil (420); wherein by being electromagnetically coupled to both the first coil (1g) and the second coil (2g), the parallel resonant circuit forms a positive feedback loop together with the amplifier (3a), the first coil (1g) and the second coil (2g), and thereby forms an oscillating circuit, and the frequency discriminating circuit (413) obtains switch information from frequency information on an oscillation signal generated by the oscillating circuit.

Inventors: MORITA YOSHIYUKI, SAEKI SHINJI, WATANABE TOSHIAKI, SAEKI, SHINJI, WATANABE, TOSHIAKI, MORITA YOSHIYUKI, SEIKO INSTRUMENTS INC., SAEKI, SHINJI, SEIKO INSTRUMENTS INC., WATANABE, TOSHIAKI, SEIKO INSTRUMENTS INC.
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1993
Main classification: G06F3
IPC codes: G06F3