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Build a Simple Bat
Detector
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Tony Messina - Las Vegas, NV
Ever since my grade school years I've been fascinated with the
way a bat uses ultrasound to "see" in the dark.
The bat's echolocation skills let it avoid small obstacles, and
even catch insects, while in flight. I learned that bats are,
ultrasonically speaking, very loud --- so loud, that some of them have special ear flaps
that close when they generate an ultrasound pulse so they won't
make themselves deaf. I thought something this loud should be
easy to detect !
On retirement, I decided to undertake the design of an ultra-portable,
personal bat detector. A picture of my original prototype unit is
shown at the left. It is small in size, lightweight, easy to
build, and can cost as little as $25 in parts. It turned out to
be an amazingly simple yet effective circuit so I dubbed it the Simple
Bat Detector.
I originally published the circuit for the Simple Bat
Detector in 1997. Since then, I've received emails from all
over the world, corresponding with many who have built the
detector from the information published on these pages.
In 1998, I designed a circuit board for
an enhanced version of the detector, which is still available. I've
been thrilled by the many comments of folks who have used the Simple
Bat Detector to hear a bats echo call for the very first time....
and have come to admire and respect the bat as I do.
The Simple Bat Detector has found its way to: Australia, Belgium, Canada, the Canary Islands, the Cayman Islands, China, Cyprus, the Czech Republic, Costa Rica, Denmark, England, Finland, France, Germany, Ghana, Greece, India, Ireland, Italy, Japan, Poland, Malaysia, Mexico, the Netherlands, New Zealand, Scotland, Singapore, South Africa, Spain, Sweden, Switzerland, Taiwan, Wales, and all over the United States.
Simple Bat Detector builders in the United Kingdom ... Lee Rogers may still have some circuit boards for purchase in the UK !! email him at: lrogers222@hotmail.com
How the SIMPLE BAT
DETECTOR works...
The Simple Bat Detector is a frequency division
type device. Frequency division type detectors allow you to hear
ultrasonic sound by digitally scaling the frequency down into the
human hearing range. For instance, a western pipistrelle bat
emits ultrasonic sound in the range of
53 to 91 kHz. If you divide that frequency by 16, the new
frequency range is 3.3 to 5.7 kHz, easily within our hearing
range. Because the division is done digitally, all amplitude
information is lost. Ultrasonic sources processed by the detector
convert to sounds like geiger-counter clicks and chirps.
The basic circuit of the Simple Bat Detector is shown in
the schematic diagram to the right. It is essentially composed of
3 integrated circuits, or ICs. The signal from an ultrasonic
transducer is fed to IC-1, an LM386 audio amplifier, which is
configured to provide a signal gain of 200. The signal is coupled
to IC-2, a second LM386, by a .05 uf capacitor. IC-2 is
configured to provide an additional gain of 20, for a total
system gain of 4,000. The output of IC-2 is direct coupled to the
input of IC-3, a 7 stage CMOS digital divider circuit. The input
stage of the divider acts as a zero crossing detector, triggering
on the negative transition of the signal from IC-2. The divide by
16 output is connected to a potentiometer, which serves as an
audio level control. A high impedance ceramic earphone is
connected to the output of the level control. The 10K level
control is a small printed circuit pot that is set and forgotten.
The detector circuit is powered by a nine volt battery. ( The
numbers next to the IC nodes refer to the pin numbers of the IC's.
Note the additional pins listed at the bottom of the schematic
that need to be tied to ground. )
A major advantage of a frequency division detector is that
it is a wide band device ... that means it will let you hear all
detectable bat sounds without the need to tune the
detector to any particular frequency. Heterodyne detectors,
which process ultrasonic sound in the analog domain, only
convert a small range of frequencies at any given time - you must
select which frequencies to listen to. If you tune up around 60
kHz to listen for a pipistrelle, you may not hear the big brown
bats flying nearby. The frequency division detector works
in the digital domain, converting the full spectrum of
sound that the transducer is able to detect. So you get to listen
to all of the ultrasonic sounds around you, without missing
anything due to unfortunate tuning choices. I feel this no-knobs-needed
characteristic of the frequency division detector makes it
a great choice for the casual bat observer, and student.
Building a SIMPLE BAT
DETECTOR...
Although I have designed a circuit board for an enhanced version of the Simple Bat
Detector, it is important to note that the basic circuit
shown above is very effective - and parts are available world-wide.
Many have built the detector in the same manner as I did with my
original prototype - on perf board - as shown to the left. If you
don't want to use the perf-board
technique, the circuit can always be assembled on the enhanced
PCB - as shown to the right. The circuit assembly is then mounted
inside the case with hot-melt glue.
The ultrasonic transducer is mounted to the front panel by
drilling 2 small holes for the transducer pins, and bending the
pins over after inserting them through the panel. If a detuning
coil is used, it is soldered in parallel across the transducer
leads, on the back of the front panel. Keep all wire lengths
short, in particular, the leads from the circuit board to the
transducer. Very high gains are being generated in IC-1 and IC-2,
and long leads can cause unwanted feedback and oscillation!
The picture above, and to the right also shows a method for
installing an external volume control, if you feel one is needed.
The wiring of the earphone jack is
also a little tricky, as it is doubling as the power switch ...
so pay careful attention to the schematic above.
In order to accommodate various transducers, you can easily tailor the gain of the two LM386 IC's. An additional resistor can be added in series with the 10uf capacitor to reduce the gain of IC-1. A resistor / capacitor combination can also be added between pins 1 and 8 of IC-2 to increase it's gain. In this way the total system gain can vary anywhere from 400 to 40,000. Be sure to keep the positive side of the capacitor towards pin #1 on the LM386.
If you're experienced in electronics assembly,
you can usually build a Simple Bat Detector in a single
evening. I've constructed a series of Step
By Step detector assembly pages that detail how the detector
can be assembled from the parts listed on this site. I always try
to have a small supply of circuit
boards on hand for the Simple Bat Detector.
As far as bat detector cases go, you can use the enclosure on the
parts list, or go creative ... This
is an area where you can cut cost with a little imaginative
engineering. Here are a couple of prime examples...
To the left is a picture of a Simple Bat Detector
that was cleverly designed by Hisafumi Tateno, in Japan,
using a plastic jar as the case. A film container was
employed as a battery holder. This design has the added
benefit of letting you see what's inside, as well as
listening to bats ! The picture to the right is a detector I built for Jackie, my spouse. Being married to a batty person like me, she deserved something special. I used an off-white enclosure, and added a cloisonné bat pin that I had found in a gift shop. |
The instructions on this site have been made as complete as
possible to allow anyone to build the detector, with whatever
local resources that can be found. A special resource list has been compiled with part numbers, component
sources, and email contacts in several countries. I try to keep
this list as current as possible based on information I get from Simple
Bat Detector builders via email.
Updates on the Simple Bat Detector ...
A bat call recorded with a Simple Bat Detector ... BatCall1.wav (64KB). |
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Assembling the Simple Bat Detector ... Step-By-Step. |
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Frank has an interesting device that uses a Simple Bat Detector circuit ... |
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The Simple Bat Detector circuit can be used with an Arduino !! |
The Simple Bat Detector project is over 25 years old... it is still possible to find the parts, but I won't be revising these pages any further. I do still have some PCB's and other parts for those who would like to build a Simple Bat Detector, in case you do run into problems finding parts. I'm not ordering any more PCBs, but I do have quite a few still on hand. I can even supply a quantity of them for anyone who is looking for a STEM or Scouting or ??? project !!
Any questions ... just email me !!
Tony Messina - Las Vegas, Nevada - email: T-Rex@ix.netcom.com ... last update July, 2022