The Digital "Bat Scanner" Detector
|This project has come
to an end. Several key components were either
discontinued, or about to be discontinued. So, after a
run of about 6 years, we decided to close this project,
and concentrate our efforts on some of the newer projects
we have going.
In order to provide continuing support for those who have built the Bat Scanner, we are keeping this archived information available here.
I am still happy to answer questions and offer assistance to anyone who has built this kit. I can even supply some replacement parts ... but not circuit boards. Just email me.
The key idea behind the scanning heterodyne bat detector was to use a 16F628A PIC microprocessor to generate the mixing frequency for an otherwise standard heterodyne detecting circuit. The program that was developed allowed the PIC to enable the heterodyne detector to scan frequencies between any two predefined decades, from 10kHz to 80kHz, in 2 kHz steps. It was also possible to turn off the scanning and manually set the frequency if desired. The PIC also provides the detector with a digital LED display of the frequency that the detector is tuned to.
But there was still one more feature to be added ... a special detection circuit to let the PIC determine when there was a sound. This made it possible to automatically stop or pause the scanning when a sound was detected ... pretty cool :-)
Here is a simplified block diagram of the scanning heterodyne detector:
An electret microphone signal is fed to a two transistor preamplifier which selectively amplifies the frequencies in the ultrasound range. The preamplified ultrasound is fed to an NE612 mixer IC that converts the ultrasound to audible sound, using the reference frequency from the PIC processor. The audible sound is fed to an LM-386 amplifier IC and speaker, as well as back to the PIC so that it can detect when sound is present to pause or stop scanning. Three buttons on the PIC processor allow selection of the tuned frequency, as well as enabling the scanning mode and allowing the setting of various operating parameters.
|Frank worked on the code for the PIC
and made up the first prototypes ... and with a little
tweaking they worked well.
My job was to design the circuit board, and put some final tweaks to the circuitry. We ended up with a 4 layer circuit board. The board has heavy traces, a split power plane, ground plane, solder masking on both sides, and a very readable silk-screened parts layout.
We, and others, have successfully constructed many Bat Scanner detectors over the length of the project.
The idea of a scanning heterodyne wasn't really
new. There have been a couple of expensive commercial detectors
that have had scanning features. But this detector was relatively
low in cost, less than $100 to build, and has a very efficient
Here is a sample bat call with feeding buzz recorded from a BatScanner
Notes on Maintenance ...
Circuit board repairs require a decent temperature controlled soldering iron with a small chisel or conical tip. Good lighting, and a magnifying glass are essential for working with some of the small parts. You also need to be mindful of ESD precautions when handling the semi-conductors - especially the PIC microprocessor chip.
All of the original construction manuals for the Bat Scanner are still online. The firmware HEX file for the PIC processor is also here. If you need a new 16F628A PIC for your Bat Scanner, and don't have a PIC programmer, email me about getting a replacement.
Tony Messina - Las Vegas, Nevada - email: T-Rex@ix.netcom.com