| 摘要 |
This invention provides a position detection device that makes it possible to tell, in the form of multiple discrete levels, how much stored power is left in a position indicator. Said position indicator is provided with the following: an electricity-storing element comprising a battery or an electric double-layer capacitor; an AC-signal generation circuit that generates an AC signal for transmission towards a tablet; a modulation circuit that modulates said AC signal in accordance with position-indicator information represented by a binary code; and a state-of-charge detection circuit that detects the state of charge of the electricity-storing element. The frequency with which a specific bit of the position-indicator information is set to either 0 or 1 is varied in accordance with the detected state of charge. The tablet is provided with an information-receiving means for receiving the position-indicator information from the position indicator, and the state of charge of the electricity-storing element is detected from the frequency with which the aforementioned specific bit of the received position-indicator information is either 0 or 1. |
