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Wireless, Solar-Powered, Acoustic Wave Soil Moisture Detection
System
The advantage of using acoustic waves to measure the moisture
content of soil is that acoustic waves measure the moisture
content in a volume of soil that radiates outward from the
acoustic source to the detector rather than measure the moisture
content at only one point. Each detector is solar-powered
and uses wireless transceivers to send the measured data to
a server. The heart of each source and detector unit (SDU)
is the 68HC908QT4. The SDU’s acoustic source consists of a
piezoelectric speaker excited by a 5-kHz square wave generated
by the 68HC908QT4. The SDU’s detector unit consists of an
electret microphone whose output is AC coupled to a high-gain,
band-pass filter. The result is then peak detected before
being sampled by the microcontroller’s ADC. The ’908QT4 is
connected to a Manchester CODEC and RF transceiver for communications
with a desktop computer.
Cheng-Yang Tan
U.S.
cytan299@netzero.net
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