| 摘要 |
PURPOSE:To detect the amount of raindrops which further stick superior in sensitivity even if waterdrops stick in quantities by varying the oscillation frequency of an oscillation circuit according to variation in the difference between two detectors which is caused when a water drop stick on one of the two detectors, and detecting the quantity of the variation. CONSTITUTION:When a raindrop sticks on the surface of a detection electrode plate 1d, a detection electrode 2a and a common electrode 2c, or a detection electrode 2b and the common electrode 2c increase in electrostatic capacity. Consequently, the difference in electrostatic capacity between detection capacitors 15a and 15b varies and the oscillation frequency of the oscillation circuit 9 varies. The oscillation output 9a of the circuit 9 is inputted to a controller 16, passed through the LPF consisting of a resistance 18 and a capacitor 19, and made into a pulse with constant time width by a one-shot circuit 20, and the pulse is passed through an f-V converting circuit 23 and compared with a comparison voltage 26a by a comparing circuit 26; when the pulse exceeds the voltage 26a, an L-level signal is outputted and inverted by an inverter circuit 28 to turn on a TR 34 through an FF 30, and a wiper relay is closed to drive a wiper.
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