| 摘要 |
<p>PURPOSE:To ensure application of a position detector for luminous point even under illumination of a fluorescent lamp by connecting the light emitting part of a light pen to an AC power supply whose frequency can be optionally set and also connecting a position detecting element for luminous point to a wave detecting circuit via a filter circuit that transmits only the lighting frequency of the light pen. CONSTITUTION:A light pen 1 is connected to an AC power supply 3 and the frequency of an alternating current of the power supply 3 optionally set by an oscillator 4. In this case, a frequency is set out of the frequencies of a fluorescent lamp that produces the disturbance light. A filter circuit 5 transmits the photodetecting frequency out of the lighting frequency of the pen 1. The light emitting frequency of the pen 1 is different from that of the fluorescent lamp that produces the disturbance light. As a result, a position detecting element 2 for luminous point is not affected by the light of the fluorescent lamp and receives just the light of a spot shape from the pen 1.</p> |
