About the TeensyBat detector.

The TeensyBat is a d.i.y. bat detector based on a Teensy development board by "PJRC". (Check out pjrc.com for more information about the Teensy development boards)


Cor Berrevoets was inspired by a design made by a German HAM radio amateur, Frank DD4WH.  The first versions were a bunch of loose printed circuitboards connected together by a bunch of wires.

In 2018 I (Edwin Houwertjes) discovered Cor's work and started developing a printed circuitboard, designing a new microphone pre-amplifier and removed a lot of digital noise.

The synergy resulted in a lot more features and and better audio.

Recently Thierry and Adrian joned the crew with good ideas and time to test the software 

This image shows the latest PCB version. We now use more SMD parts, quieter switches and Teeny4.1 board.


Main features:

  • 2.8inch color display that shows a live spectrogram and low,peak and high frequencies.
  • Time-expansion, Heterodyne, Auto-Heterodyne and Frequency division listening modes. (on headphones)
  • Recording up to 384kHz sample rate to micro SD card. (maximum supported size 32Gb, Class10 or better required)
  • Playback on slow speed (1/5 to 1/20 ratio) or full speed (full speed only works up to 281kHz sample rate)
  • Rechargeable lithium battery that easily last a whole summer night. (standard USB (C) charger is needed)
  • External powersupply by standard phone powerbank or charger.
  • Ultrasound  tiggered autorecording 
  • Small size 116x68x36mm (4.7x2.7x1.5in)

"Live" Time Expansion

What is this live time expansion....  Well it is not exactly live ofcourse, it is stored sound played slowed down at a set rate.

Usually bat detectors with time expansion store like 10 seconds of sound, to play that over a 100 second time period. The frequency is a factor 1 lower and the whole recording, incuding all the silence is played.

A bat usually makes call with pauses between them, in the live time expansion mode the TeensyBat uses the call is played back in the pauses between the calls. This works like this, the millisecond a first part of the sound is detected Teensybat simultanoutsly sarts playing the sound. This will result in a delat of a of only few milliseconds. The sound is 10 times longer and lower in frequency and sounds much more musical.


This images shows how the call fits in between the pauses.

Image to explain live time expasnsion showing a bat recording

You can see that the bat sound that was picked up starts playing almost immediately. If you are used to Heterodyne this might sound strange and ofcourse you cen still set TeensyBat to play heterodyne sounds. The big benefit in time expansion is that you hear just about every ultrasonic sound where Heterodyne only "shifts" a small part of the spectrum to the audible range. If you tune it to 40kHz you only hear like 40.1kHz to about 50Khz as 100Hz to 10kHz. A social call or other bat on 20kHz can be missed. In time expansion you will heat both bats or navigation and social call with a clear difference in frequency.



If you like the bootimage you can watch it here.... so you don't have to keep switching off and on your detector .


The photo is taken by Paul van Hoof who makes the most amazing photo's of bats and other wildlife.

Have a look at his website and be amazed.