| 摘要 |
<p>PURPOSE:To eliminate a code between an erase and another circuit by providing a switch, for which a tuning circuit is constituted when an erase member is abutted to the writing surface of a blackboard main body. CONSTITUTION:When the erase is operated on the writing surface of the blackboard main body, switches 121 and 122 are operated and the tuning circuit, which is composed of a coil 123 and capacitors 124 and 125, is constituted. In such a case, when an electric wave to have a prescribed frequency is transmitted from an antenna coil in the blackboard main body side, the induction voltage of a prescribed frequency is generated in this tuning circuit. A current flows into the tuning circuit by this induction voltage and the electric wave of the almost same frequency as the prescribed frequency is transmitted from the coil 23. However, since the current is continued to flow without rapidly attenuated even when the electric wave from the antenna coil, the induction voltage to be almost same as the prescribed frequency is generated in the antenna coil. Accordingly, the usage of the eraser is discriminated in the blackboard main body side.</p> |
