Dear AudioMoth community,
I am currently on fieldwork and I am using the AudioMoths for two different setups:
A long-term experiment lasting 3 days, with around 18 hours of recordings per day. This is repeated 3 times (so 9 days in total). All 16 AudioMoths are used. (finished experiment)
Daily experiments with 4hrs of recordings in the evening and 5 hrs in the evening. 14 AudioMoths were placed in cones to record one individual animal. (ongoing experiment)
For both these setups I require synchronised recordings, hence all AudioMoths have been flashed with the GPS Sync firmware. I have attached the SETTINGS.txt files for both setups.
I am currently doing the daily experiments and more and more AudioMoths keep showing up with SD-card failures or other forms of data loss. So far, 9/16 AudioMoths needed a replacement SD card. Of the AudioMoths with this issue, battery levels were generally good (>4.7 V). All AudioMoths are equipped with Energizer Ultimate Lithium batteries and Sandisk Extreme microSD card 64 GB. Temperatures inside the cone can get somewhat hot (< 34 C) as it is summer.
Does anyone have suggestions on what could be the problem? I am happy to replace the SD cards, but I'd like to know the root cause. My ideas of potential causes are:
My recording schedule during the long-term experiment is too extensive. The AudioMoth writes out files every 4-5 hours. Could this cause a strain on the SD-cards?
The AudioMoth get too hot inside the cones, which may harm the SD card or other processes.
Any help is appreciated.
Other users have reported high energy use from SanDisk cards made in Taiwan but this doesn't seem to be the problem here. It may be that the battery voltage is dropping significantly throughout the long recording as the GPS modules take quite a lot of current. Are these GPS hats with AA batteries? Reformatting the cards is always a good move as some operating systems will hide files rather than deleting them and AudioMoth isn't able to delete the hidden files whilst it is writing. This sometimes causes SD cards to become full and give SD card write errors while there is still apparently space left. It would be safer to make a sequence of short recordings. You can use sleep and record cycles within the recording period as long as the sleep period is longer than the recordingFixDuration. The recordingFixDuration is currently 900 seconds - 120 seconds should be sufficient to get a fix in warm start so you could record for 58 minutes and then sleep for 2 minutes. This would mean that the recordings are shorter and there is less likelihood of an SD card write error corrupting the entire period.
Depending on the accuracy you need, you might also be able to switch back to the standard AudioMoth firmware which now has more support for GPS synchronisation before and after each recording, and the ability to generate _SYNC.WAV file from the recorded GPS data. This will lessen the load on the batteries as the GPS module is not run throughout the recording. The recording will typically be synchronised to a few millisecond, rather than better than one microsecond, when using the AudioMoth-GPS-Sync firmware.