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Design a system that would alert a snowplow driver when the snow depth has exceeded four inches.
Solution:
I chose an optical approach. A visible red LED packaged in a 10mm package is pulsed at a rate of about 50Hz with 10uS pulses. Twenty four inches away a phototransistor detects the light from the LED. The LED
and the phototransistor are housed in a section of ½ inch PVC pipe, forming a waterproof seal. A piece of PVC plastic covers both the LED and the phototransistor, so snow does not fall directly onto the parts. At a depth of 4 inches, the snow accumulates to a point, where the light path between the
light source and emitter are blocked. The blocked light path will activate an alarm, placed inside the house. A rest button on the electronics box can turn off the alarm. Snow is then cleared off the depth sensor, making it ready for another monitoring cycle.
