Embedded Ultrasonics: A Microcontroller-Based Multichannel Ultrasound Recorder for Behavioural Field Studies

Behavioural studies investigating acoustic communication in animals—particularly echolocating bats—require transducers and recording systems that are lightweight, power-efficient, and easy to deploy. However, capturing high-frequency calls typically demands specialised, high-cost equipment and laptops, which limit portability and scalability in field settings. Advances in embedded microcontrollers and high-fidelity MEMS microphones offer an underexplored opportunity for building compact, affordable, and open-source recorders. These platforms provide design flexibility and a growing support community, but are seldom adapted for multi-channel ultrasonic recording in behavioural research.

To address this gap, I developed Batsy4-Pro , a 4-channel ultrasonic recorder based on the Teensy 4.1 microcontroller. The system uses WM8782 ADCs to acquire synchronised 192 kHz audio streams and records them to a microSD card. The firmware is written in C++ on Arduino IDE and allows flexible configuration of recording parameters, buffering schemes, and triggering logic. The system weighs under 150 g and runs on a 5 V DC power supply, enabling untethered field deployment.

The system also integrates real-time heterodyne monitoring using a PCM5102A DAC, allowing users to audibly monitor bat activity during field experiments, reducing the need for additional equipment and helping field researchers decide when to initiate recordings.

Using a custom-built microphone array, I validated its recording fidelity using both synthetic bat call playbacks under controlled conditions and free-flying bat vocalisations in a natural foraging corridor. Recordings consistently showed high signal-to-noise ratios (>40 dB), suitable for accurate call detection and spatial localisation.

Batsy4-Pro offers an accessible and extensible tool for ultrasonic recording in behavioural, ecological, and neuroethological research, supporting studies where portability, ease of use, and field-readiness are essential. The open-source code and modular design facilitate community-driven development and promote the system’s adoption, enabling the evolution of experimental protocols and recording paradigms, as well as the exploration of novel approaches to behavioural experiments in natural settings.