Bat Detectors
Listen to the Bats!

Simple Bat Detector designed
by Tony Messina
(frequency division type)

Here is a schematic drawing of a Frequency Division
Bat Detector. The drawing by L. Jones is similar to
the circuit used in the detector above.

Click image for a larger view

Bat Detector by Larry (heterodyne type)

Heterodyne Detector:
      The Heterodyne detector works similar to a radio receiving a signal from a radio station. The signal is received by the receive transducer and amplified. It is then mixed with a local frequency that is generated in the detector circuit. The signal is again amplified to drive the speaker or headphones. The audible bat sound we hear is the difference between the original bat frequency and the frequency generated in the detector circuit. These detectors are also quite small. They make some background noise but are more sensitive. The frequency is tunable so we can adjust for the sounds of different species of bats. The detector shown to the left is a Heterodyne type.

Schematic of a heterodyne bat detector.

Click image for a larger JPEG view.
(from Popular Electronics 1994)

      The circuit shown here is for a heterodyne bat detector. This was first presented by Popular Electronics magazine as an Ultrasound Detector, in 1994. Construction is straight forward and can be laid out very much as the schematic shows. I built mine on a 2-3/4"X1-3/4" IC project board. I found that using shielded cable for connection to the level and frequency controls helped reduce any feedback. I think in the next one I build I'll use LM386 amplifier ICs in place of the input transistors so that I can get a little more gain.
      My detector works very well. The range is about 60' for good bat chirps. There is very little background noise and no interfering noise from hands on the case. I was able to increase the range to about 75' using my 12" parabolic dish with a 40KHz transducer mounted at the focal point. See: notes and picture of my "Parabolic Dish Transducer."

      This Heterodyne Bat Detector was built with a circuit similar to the one above except, I experimented using ICs for the first amplifier stages instead of transistors. The first stage is a LM358 op-amp with an adjustable gain trimmer and the second stage is a LM386 set up for 20 gain. Also, the output stage is a LM386 set up for adjustable gain of up to 200 with a 10uf capacitor and a 10k trimmer pot. Included are a speaker and a headphone jack. The eyes of the bat flash when a bat sound is detected.

Click for larger image

Click for a schematic in JPG format

Click for larger image.

Click for larger image.

      My new Frequency Division bat detector is built from the original Tony Messina design with some changes in parts value and a few additional parts. After some experimenting, I got it to work as well as the original Enhanced Simple Bat Detector. The small case goes neatly into a shirt pocket. Already, I have listened to bats in our garden at about 75 ft. distance. The schematic for this detector is similar to the first one on this page, the Simple Bat Detector.

      Click  here   for the schematic in pdf format.

Waveform of a bat flying near our horse paddock.
Recorded from the heterodyne detector above.

      This picture (a waveform) of bat sounds, was recorded using a heterodyne bat detector and a hand held tape recorder. The sound from the recorder is converted, using computer software, to a picture. Here we can see the bat is making 10 - 12 chirps per second. Near the center there is a section of concentrated sound where the bat buzzed after an insect. The buzz consists of many more chirps per second as the bat speeds up its echolocation signal so as not to miss its prey. This waveform duration is about 8 seconds as the bat circled near my head. The dark horizontal line along the center is background noise from the recorder.

      Listen to this bat chirp sequence and you will hear the same feeding buzz that you can see in the above waveform graphic. Click image

      Here is a bat chirp recorded from a Frequency Division Bat Detector.

Click image

Waveform of a bat-synthesized sound.

      Here the waveform is a synthesized bat sound made with my bat simulator "Bat Amigo". The signal is emitted from the transducer in spurts at about 40KHz. The chirps sound like a bat, heard through a bat detector but the pattern is unlike that of a bat. This little device is handy for testing the operation of my bat detectors and for checking, comparatively, the range.

Bat Buddy

Bat Buddy circuit board

      "Bat Buddy" is my bat simulator, a little-black-box which houses an electronic circuit. It makes ultrasonic sounds in the frequency range of some common bats. The circuit has three oscillators which simply generate three frequencies which are mixed, amplified and applied to the transmit transducer. The LED flashes as the ultrasonic sounds are generated and it has an output jack so I can measure the frequency with my oscilloscope. With Bat Buddy I can adjust the output level to be more comparable with what we are hearing from real bats. Also, the type of output is selectable for bat chirps or a sustained signal for testing bat detectors. The frequency range of Bat Buddy is variable from 25 KHz to 60 KHz.

Bat Simulator Schematic

Click for a larger image and parts list in PDF format.

      The schematic drawing shown here (with my modifications) was found on the NJSAS web site. See links page. The frequency adjustment is made with R5 and the output level with R10. D1 is shown in the parts list as a bridge rectifier but I actually used four 1N914 diodes wired as a bridge. The ICs are: IC1, 74HCT04N, a hex inverter, IC2, 74HCT08N, a quad AND gate (two of the AND gates are used) and LM386, an audio amplifier. C1, C3, C4 and C6 are electrolytic capacitors—note polarity. The ultra-sonic frequency can be read by connecting from J1 to a frequency counter or a multimeter with frequency read out.

Audio/Visual Bat Detector

      Here is another of my experiments in building bat detectors. This one displays a visual of the bat chirps with LEDs as well as providing the sound. The video section is built around a CD4017BE decade counter. At the front end a high gain amplifier is built through three of the op amps in a TL074CN quad op amp IC. The fourth op amp is wired as a oscillator to drive the decade counter.
      The decade counter drives the LEDs sequencing about one for every 10KHz. With a 40KHz transducer the frequency is limited, so the effective range of the LED sequence is from about 20 to 50 KHz.
      The audio section of the "A/V Detector" is a standard frequency division detector using LM386N audio amplifiers and a CD4024BE as a binary divider. There is an internal speaker, a headphone jack, and switches for power and to select audio, visual or both at the same time. The enclosure I used for this detector is an old dial-up modem case that I once used with a one-time Mac Plus computer.