Bat Recorder/Detector

(Site content last updated 17th April 2019 – new sound card added)

I started working on this project in summer 2014 to see if it was possible to record bat calls in my garden using a Raspberry Pi, having been inspired by the electronic devices on Tony Messina’s website and also those on Frank Pliquett’s website. Following the success of my early attempts, I have been continuously updating and modifying the design to incorporate new features.  Keep checking back to this site for further updates –  I am working on other features such as sound activated recording and automatic uploading to the cloud (e.g. Dropbox), and will add more details when available.

So far, I have successfully recorded around six or seven different species.  The recorded calls can be analysed and a spectrogram created, which can aid in the identification of the bat.  There are some good books about species identification from bat calls – these are provided in the links page.

The project started with a simple way of recording bat calls using a Raspberry Pi and Audio Card with a single push-button to start and stop recordings. Details of this design can be found here.  I still use this version for unattended recording.

The spring 2016 has the features shown below, each of which can be selected from a colour touch screen.  An overview on how to make this version is here.

An updated version (autumn 2016) with a 5″ colour HDMI touchscreen can be seen below.

NEW: Since the previously used Cirrus Logic Audio Card is no longer in production, I have added details on how to use a newly available sound card (spring 2019) from Audio Injector called the Ultra 2. Further details ore on the Audio Injector Ultra 2 page of this site.

These types of recorder/detector are not meant to replace professional models which are available, but is a good starting point for those interested in bats and cannot justify spending £1500 on a bat recorder/detector with similar features!  It is possible to make a very capable device for around one-tenth of the cost, or less.

Possibilities:

  • Real-time full spectrum recording (192kHz sample rate)
  • Real-time peak frequency display
  • Real-time spectrogram display (4 second update)
  • Continuous time-expansion playback
  • Time-expansion recording
3D Printed Case version

3D Printed Case version with 2.8″ screen

ModMyPi_Case_version

ModMyPi Case version with 2.8″ screen

Capture8

Bat recorder/detector with 5″ HDMI Touchscreen

main_screen_new

Touchscreen display

Real Time full Spectrum Recording

This feature allows for bat calls to be recorded in .wav format and later analysed, which can help with species identification.  Frequencies up to 96kHz can be analysed.

   

20140713092417_13s.wav

Python script used to analyse audio

Spectrograms from recordings made with a Raspberry Pi bat recorder can be found here.

Real Time Peak Frequency Display

The peak frequency display will not only show you the presence of bats, but can also aid in species identification.
Real Time Frequency Display

Real Time Frequency Display

Real Time Spectrogram Display

The real-time spectrogram display updates every four seconds.  The spectrogram shows bat calls in the frequency domain – turning the sound of bat calls into pictures.
This image shows echolocation calls of a Soprano Pipistrelle (around 55kHz) and also social calls (around 20kHz), probably from the same species.
Spectrogram created using SoX

Spectrogram created using SoX

Continuous Time-Expansion Playback

Time-expansion is used to slow down bat calls.  This lowers the frequency into the human hearing range.  Bats flying past will sound like birds.

Time Expansion Recording

This feature allows time-expanded calls to be recorded in .wav format for later analysis or playback.

Real-time Spectrogram Window

It may be possible to have a continually scrolling spectrogram window, showing bat calls in real time, using the Raspberry Pi.  A video of what is possible is shown below, recorded from my Pi3.  I’ll post more information when I have trialled this with real bats.