| 摘要 |
PURPOSE:To automatically obtain optimum wiping operation in accordance with the sticking condition of water drops or the like on the surface of a wind shield pane of an automobile or the like, by detecting a variation in the light transmissivity of the windshield glass due to the water drops or the like sticking thereto, and by controlling the drive of a wiper device in accordance with a result of the detection. CONSTITUTION:An on-board engine is driven so as to deliver a turn-on signal to an LED drive circuit 2 for energizing a light emitting diode D. A wiper switch 9 is set to, for example, an automatic mode terminal A1. Then a light beam from the diode D is incident upon a front windshield pane 1, and there after irradiates a photo-transistor Tr. In this phase, if water drops or the like stick to the outer surface of the windshield pane 1, the light transmissivity between both end faces 1a and 1b thereof is lowered. Accordingly, the current running through the phototransistor Tr is also lowered, resulting a drop in the voltage of a connecting point P. As a result, a comparator 7 delivers a wiper start signal when the output voltage Vd of a differential amplifier 4 becomes lower than a reference voltage Verf1.
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