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Challenge:
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.
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