 |
|
.
|
|
Though many who study bats work with ultrasound as a natural extension of their studies, the true nature of ultrasound is many times misunderstood. The concepts of standing waves, echo cancellation and enhancment, acoustic focus, and others, may be understood in terms of the physics, but not readily grasped in terms of practical environmental experiences. Given the opportunity to work with standardized and repeatable ultrasound signals in various situations, researchers can get a more intuitive feel for the strange characteristics ultrasound can exhibit. That is one of the ideas that led me to design the Bat Chirp board. Another design objective was to develop a method for accurately setting the sensitivity of multiple bat detectors so that they are comparable in terms of their detection range. By matching sensitivity thresholds, comparisons of the data collected with these bat detectors can be more meaningful, though environmental variations will still cause differences in their overall detection ranges. The Bat Chirp board satisfies this goal as well. |
|
|
The Bat Chirp uses a PIC
microprocessor to digitally synthesize 3 different
acoustic ultrasound reference signals. The first signal is a basic 40 kHz continuous tone. The 40 tone is useful for demonstrating doppler shift - done by using a heterodyne detector set just off from the 40 kHz signal frequency, and moving the detector towards and away from the Bat Chirp board. The second signal is dual chirp which
alternates between 40kHz and 62kHz. The dual chirp signal
was designed to simplify matching the sensitivity
thresholds on multiple frequency division detectors, such
as the Anabat II. |
| The last signal is a synthetic
bat call sequence, composed of variously timed chirps,
intermixed with feeding-buzz-like sequences. This signal
does a nice job of providing an artificial
bat for demonstrating bat
echolocation calls and their detection, as well as for
testing bat call recording equipment with a repeatable
bat-like call structure. Here is a .WAV file that is what a portion of the artificial bat call sequence would sound like through an Anabat detector, with a division ratio of 16 selected. ChrpSamp.wav - 365k |
|
 |
The Bat Chirp is
straightforward to use. Snap in a 9 volt battery to power
it up, and press the small push-button on the printed
circuit board to step to the signal you want to use. The
red LED on the board indicates which signal is active,
and confirms that the circuit is operating. The 40kHz
output signal amplitude of all Bat Chirp
boards is preset to a standardized level when shipped,
but can be easily readjusted in the field with a small
screwdriver, or similar tool. A calibration mark on the
level control facilitates resetting the output of the Bat Chirp
back to standard. |
I have a small quantity of the Bat Chirp boards left. If you are interested in purchasing one, please send me an email at T-Rex@ix.netcom.com You can also download or view
the Bat
Chirp instruction sheet ( Adobe PDF file )
on line click
here !! ( Note that the Bat Chirp
on the PDF sheet, shows an older version of the circuit
board ) |
|
