Capacitive stylus pen

1. A capacitive stylus pen, comprising:

a power supply;

a coil configured to charge the power supply in a contactless manner during a charge operation, the coil being positioned at a position indicating part of the capacitive stylus pen and magnetically coupled to an external charge device;

an electrode extending through the coil and having an end that protrudes to form a tip of the capacitive stylus pen; and

an alternating-current signal generating circuit configured to supply an alternating-current signal to the electrode, the signal being output from the electrode,

wherein, when the charge operation is not being performed, the coil is set at a fixed potential and shields the electrode, and

wherein, when the capacitive stylus pen is held by a user's hand, the signal output from the electrode is independent of a potential of the user's hand.

2. The capacitive stylus pen of claim 1 , further comprising:

a writing pressure detecting sensor; and

a core body configured to transmit pressure applied at a tip portion of the core body to the writing pressure detecting sensor, the core body including the electrode or a line connecting to the electrode.

3. The capacitive stylus pen of claim 2 , wherein a portion where the writing pressure detecting sensor engages with the core body serves as a contact point for the supply of the alternating-current signal to the electrode.

4. The capacitive stylus pen of claim 1 , wherein the coil is wound around a hollow magnetic core.

5. The capacitive stylus pen of claim 1 , wherein the fixed potential is a ground potential.

6. A capacitive position indicator, comprising:

an electrode core having a first end and a second end;

a charge coil, the electrode core extending through the charge coil, the first end of the electrode core being exposed;

a signal generator configured to generate a signal and supply the signal to the electrode core, which emits a position indicating signal from the first end; and

a power supply configured to be charged in a contactless manner via the charge coil during a charge operation when the charge coil is magnetically coupled to an external charge device, the power supply providing power to the signal generator,

wherein, when the charge operation is not being performed, the charge coil is set at a fixed potential and shields the electrode core, and

wherein, when the capacitive position indicator is held by a user's hand, the signal emitted from the electrode core is independent of a potential of the user's hand.

7. The capacitive position indicator of claim 6 , further comprising:

a detection sensor configured to detect pressure, the detection sensor being physically coupled to the second end of the electrode core, a detected pressure being encoded in the signal generated by the signal generator.

8. The capacitive position indicator of claim 7 , wherein the detection sensor includes a variable capacitor.

9. The capacitive position indicator of claim 7 , wherein the detection sensor detects pressure based on a physical pressure applied to the first end of the electrode core.

10. The capacitive position indicator of claim 7 , wherein a frequency of the signal generated by the signal generator is set based on the detected pressure.

11. The capacitive position indicator of claim 6 , further comprising a detection sensor configured to detect a tilt of the capacitive position indicator relative to a sensor surface, a detected tilt being encoded in the signal generated by the signal generator.

12. The capacitive position indicator of claim 6 , wherein the power supply is an electric double layer capacitor.

13. The capacitive position indicator of claim 6 , wherein the fixed potential is a ground potential.

14. The capacitive position indicator of claim 6 , wherein the charge coil is electrode core is wound around a hollow ferrite core.

15. The capacitive position indicator of claim 6 , wherein the first end of the electrode core has a cone shape.

16. The capacitive position indicator of claim 6 , wherein the first end of the electrode core has a spherical shape.

17. A method, comprising:

contactlessly charging a power supply of a capacitive position indicator during a charge operation by magnetically coupling a charge coil, which is coupled to the power supply, with an external charge device;

powering, by the power supply, a signal generator of the capacitive position indicator;

supplying a signal generated by the signal generator to an electrode core extending through the charge coil;

emitting a position indicating signal from an end of the electrode core protruding from the charge coil; and

shielding the electrode core by setting the charge coil at a fixed potential, when the charge operation is not being performed,

wherein, when the capacitive position indicator is held by a user's hand, the position indicating signal emitted from the electrode core is independent of a potential of the user's hand.

18. The method of claim 17 , further comprising:

detecting a pressure applied to the capacitive position indicator; and

encoding a detected pressure in the signal generated by the signal generator.

19. The method of claim 18 , wherein the encoding of a detected pressure in the signal generated by the signal generator includes setting a frequency of the signal generated by the signal generator based on the detected pressure.

20. The method of claim 17 , further comprising:

detecting a tilt of the capacitive position indicator relative to a sensor surface; and

encoding a detected tilt in the signal generated by the signal generator.