Automatic Actuation of a Windshield Wiper Mechanism
Advisors: Dr. B. D. Huggins and Dr. J. W. Sennott
Present intermittent windshield wipers require manual control of the
time between wiper actuation, thus causing frustration for many drivers.
This motivated the development of the "Smart Wipe" device to adjust wiper
actuation in accordance with the surface density of moisture on the windshield.
Critical design aspects included the sensor, sensor location, low cost,
response time, sensitivity, overall size, and ease of installation for
the secondary market. An investigation of sensor technology to measure
the moisture density on the windshield was carried out. This research led
to several techniques including capacitive, optical, and ultrasonic. A
capacitive sensor based on parallel wires was selected due to low cost,
ease of implementation, and overall ability to generate an accurate signal.
Next came the generation of a sensor model that related physical parameters
and water density to the capacitance of the structure. A major step was
the consideration of a circuit to convert this capacitance into a voltage
or frequency. The NE-555 timer in the astable mode of operation, generating
a square wave with a frequency inversely proportional to input capacitance,
was selected. Windshield wiper control is accomplished by measuring this
frequency in a microprocessor. The microprocessor monitors the changing
frequency to generate an actuation signal.
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