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Geophone is an amplifier and a frequency analyzer for geometric sensors
such as the SM-24 geophone element from ION Geophysical Corp.

The amplifier is provided as an Arduino shield and the frequency analyzer is
implemented in software on the Arduino.  Because of the memory usage an
Arduino Mega or an Arduino Due is required.  Other Arduino versions with
at least 4 Kbytes of SRAM will require modifications in the code.

The Arduino code is richly commented and should be easy to understand and/or
modify.

For the Arduino Mega, use a single-supply operational amplifier capable of
working at 5V (such as an OP213) and set a jumper on JP3 to 5V mode.  For
the Arduino Due, use a single-supply operational amplifier working at 3.3V
(such as a TLC272 or an LT1215) to avoid damaging the Arduino's analog input.
JP3 should be placed in 3.3 mode.

Every second the Arduino software reports frequency components from 0 to 256
Hz and their measured amplitudes for amplitudes that exceed a programmed
threshold over the serial port.  The amplitudes are not calibrated; you will
have to perform a calibration yourself to translate the amplitudes into
ground movement in, e.g., meters per second.

The threshold may be changed by transmitting a new value followed by a
newline character.  The threshold is stored in EEPROM.

The frequency analysis lends itself directly to a 3D (or colored) time/
frequency plot that displays the intensities of different frequencies versus
time.  The Scilab script geoplot.sce reads a log file with the output and
generates such an image; geophone.log is a short sample of the output.


Geosampler.ino is a simple piece of software that samples the geophone
output at a rate of 512 samples per second and outputs the values over the
serial port.

read-serial-log.c provides sample C code that reads the serial output from
Geophone.ino and adds a timestamp.  The output may be plotted using the
createheatmap.pl perl script, which generates a JPEG file with the graphical
output.