| 摘要 |
There are provided an infrared light emitting diode 42 operable to emit light in a predetermined cycle; a phototransistor 44 operable to receive light which is emitted by the infrared light emitting diode 42 and reflected from a retroreflective sheet 40 of the operation article 3, and output a light reception signal “Sp”; and a highpass filter unit 116 operable to pass a high frequency component of the light reception signal “Sp”, output the high frequency component as a light reception signal “Ss” and operable to generate a reference voltage. The highpass filter unit 116 supplies the reference voltage to a node to which the light reception signal “Ss” is output, and the processor 110 counts the number of pulses included in the light reception signal “Ss”, and calculates the speed of the operation article 3.
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