| 摘要 |
A photo-detecting method of the present invention includes the steps of projecting from a light emitting element a pulse-modulated light as pulse-modulated at a light-emitting element drive circuit toward an object; and counting a light-receiving signal, which is converted by the light-emitting element based on either reflected light reflected from the object or transmitted light transmitted through the object, plurality of times in synchronism with a modulation frequency of the pulse-modulated light projected toward the object, so as to detect the object, wherein the modulation frequency of the pulse-modulated light projected toward the object is changed while carrying out the step of counting the light-receiving signal plurality of times. With this method, it is possible to prevent faulty operation when disturbance light or noise enters the light-receiving element without the light-receiving signal.
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