| 摘要 |
PURPOSE:To improve weatherability and durability and eliminate the influence of external light by installing a raindrop sensor part consisting of a light emitting element and a photodetector on the inner side of front glass of a vehicle or the like. CONSTITUTION:A light emitting element 1 is driven by an oscillating circuit 7 and a light emitting circuit 8, and casts modulated light of a constant frequency into glass 2 of a vehicle at the angle theta of theta1<theta<theta2 where the critical angle of the glass and air is defined as theta1 and the critical angle of the glass and water as theta2. After the modulated light is totally reflected once or more in the glass 2, it is taken out by a mounting element 4 and is detected by a photodetector 5. The output of a photodetecting circuit 9 is converted via a band pass filter 10 and an amplifier circuit 11 to a DC level in a smoothing circuit 12. The DC output of the circuit 12 of the level changing with the presence or the absence of a rain drop 6 is supplied to a wiper motor control circuit 13. Thereby, the wiper is operated surely without receiving the influence of noise of external light or the like at all. |
