HydroMoth Affordably Records Underwater Acoustic Data
Capture aquatic data up to 60 meters.
Recording audio underwater can be challenging, given the fundamental incompatibility of water and electronics. However, Open Acoustic Devices developed a version of their audio recording prototype platform called HydroMoth, which fits inside a custom underwater case. With this affordable combination, recording sound down to 60 meters underwater is now easy.
HydroMoth is an iteration of an existing Open Acoustic Devices product, the AudioMoth. That board, like HyrdroMoth, has a Silicon Labs EFM32 Gecko processor. A MEMS microphone and analog pre-amplifier with adjustable gain records sound to a microSD card. Sample rates up to 384k samples per second are possible. Power comes from three AA batteries.
While similar enough to use the existing AudioMoth firmware, HydroMoth adds capabilities in several areas. First, a 32.768 kHz MEMS oscillator for the onboard real-time clock improves long-term time stamping accuracy.
Second, Open Acoustic Devices designed the board to fit in an underwater case, which they tested at 30 meters for two months.
Last, there are usability improvements as well. For example, magnetic reed switches start/stop measurements without opening the case, and the status LEDs are now in more visible positions.
Looking at the time-domain waveform and frequency domain spectrogram, one potential application for HydroMoth could be underwater machine learning. Open Acoustic Devices suggests it could monitor boat noise, perform freshwater sound surveys, or assist in cetacean aquatic acoustic studies, as just a few examples.
Two resources are available with more information on how HydroMoth performs in real-world conditions. One is a whitepaper titled "HydroMoth: Testing a prototype low-cost acoustic recorder for aquatic environments." And another is an application note from Open Acoustic Devices.
To get started with underwater acoustic captures, visit the HydroMoth GroupGets campaign. The electronics and underwater case are 135 USD, plus shipping. Optionally you can add a magnetic key fob for actuating the reed relay/switches.