Hi everybody!
Our organization recently deployed 21 AudioMoths for recording birds, bats and grasshoppers. They were set to record 3 times 2 hours per day during one week, and encased in the waterproof case. Batteries are no older than one year and were fully charged a couple of days before deployment. The AMs sat in the fields for maybe 3-4 days before recording periods started.
After getting the AMs back from the field, I noticed that about only a third of the devices recorded correctly. 14 AMs either recorded no files at all (3 devices), stopped recording after a few days (2) or recorded increasingly short periods during the week (6).
I updated the AMs to the newest firmware before deployment (version 1.7.1). We recorded using the same settings last year and got much longer recorded periods.
Is it possible the batteries are two weak? I inspected the .wav metadata of the files recorded on one device using exiftool, and battery voltage seemed to have been fine.
Temperatures got to around 0°C and at the beginning of the week there was some strong rain. I don't think this should pose a problem?
However, the decreasing file size over time suggests some kind of voltage problem.
What else can I do to find the cause of these problems and prevent them from happening in the future?
Thank you kindly for your suggestions! 😊
PS: I attached the config file as .txt.
If the files are shorter than expected, but are readable, then the WAV file comments will always report the reason for stopping early. Normally this is a report that the voltage was too low. What batteries and what SD cards were you using. However, in this case, the config file attached here also shows that you were using an amplitude threshold recording. This will only make recordings when the amplitude of the signal is above the set threshold, and the resulting recordings will be shorter than the total recording time. Was this intentional? You can use the expansion tools in the configuration app to expand the T.WAV files to their original length, with the 'unrecorded' sections replaced with silent periods.
Thanks for the response!
We chose the amplitude threshold consciously and it worked fine during the recording periods last year (only recording acoustic events over the threshold), but the very small files at the end of the recording periods (only a couple of kB in some cases) is a new phenomenon for me.
We are using Ansmann 2850mAh NiMH batteries and Transcend S300 SD cards with 256GB.
I had a look at the WAV comments: The reason for stopping recording early really was the low voltage.
I also tested the batteries, which were weaker or even completely dead in the cases where the recordings were shorter than expected (or there were no recordings at all).
A colleague doing a similar recording task noted drained batteries after 2-3 days of recording for only one hour.
At the moment, I suspect that we are using the wrong type of battery. On the AM battery case it says 1.5V and we are using 1.2V batteries.
Interestingly, in some cases, the comments said "low voltage" when the voltage was at maybe 3.8V while other devices continued working at that voltage.
The rated capacity of 2850mAh is multiples of what the AMs would need in our setup, so that shouldn't be the problem?
Maybe the voltage was enough last year, but now that the batteries are already a bit older, the voltage output starts to drop?
Thanks again and best regards!