AUTOMATIC WIPER ACTUATOR FOR A VEHICLE WINDOW

A control system for a motor driven wiper on a vehicle window comprises a voltage generator effective to generate a first rectangular voltage wave having a substantially constant frequency and duty cycle and apparatus effective to derive two additional rectangular voltage waves from the first: a second delayed from the first by a first delay and a third delayed from the first by a second delay dependent upon the capacitance of a capacitor affected by moisture on the vehicle window. One of the second and third rectangular voltage waves may also be inverted. The three rectangular voltage waves are provided to the inputs of an AND gate having an output effective to trigger a retriggerable monostable multivibrator having an energized output period longer in duration than a cycle of the rectangular voltage wave to drive the wiper motor when the level of moisture on the window in the vicinity of the capacitor is sufficiently high. The first delay may be adjustable by the vehicle operator to vary the moisture sensitivity of the system. If the capacitor is placed within the wipe pattern just above the inner wipe postion, a fully automatic control may be provided.