To test this feature, visit your live site.

Lots of 0 bytes files...

in Device Support

By some reason, I've got lots of 0 bytes files and some correct wav files:

Unit is 24410E085728D5E5 v. 1.0.0 with firmware 1.8.0

SD card (SanDisk Extreme 64Gb U3 A2 XC V30) is far from beeing full. This is the configuration:

Device ID : 24410E085728D5E5

Firmware : AudioMoth-Firmware-Basic (1.8.0)

Time zone : UTC

Sample rate (Hz) : 96000

Gain : Medium

Sleep duration (s) : 1500

Recording duration (s) : 300

Active recording periods : 1

Recording period 1 : 04:00 - 20:00 (UTC)

Earliest recording time : ---------- --:--:--

Latest recording time : ---------- --:--:--

Filter : -

Trigger type : -

Threshold setting : -

Minimum trigger duration (s) : -

Enable LED : Yes

Enable low-voltage cut-off : Yes

Enable battery level indication : Yes

Always require acoustic chime : No

Use daily folder for WAV files : No

Disable 48Hz DC blocking filter : No

Enable energy saver mode : No

Enable low gain range : No

Enable magnetic switch : No

Enable GPS time setting : No

Any idea on why could this be happening? Are 64Gb SDs not reliable?

9 comments

9 Comments

Agustin Lobo

Sep 28, 2022

OK, then I take as lesson learned that we have to check batteries with a tester prior configuration and not rely on the "BAT 4.6V" reported by the config app, in particular for lithium batteries. Thanks a lot.

Alex Rogers

Sep 28, 2022

Replying to

It depends on the tester and whether you can configure the tester to recognise different battery chemistries. The AudioMoth measurement of 4.6V is accurate. The problem is that measuring the voltage of an Energiser Lithium Ultimate battery doesn't give a very good indication of the state of charge since the discharge curve is quite flat. This is the plot from the data sheet of the Energiser Lithium Ultimate battery. It has a strange wobble in the 1mA line which doesn't help either.

With an alkaline battery the discharge curve is much steeper so the cell voltage gives a much clearer indication of the state of charge.

With alkaline batteries, a voltage of 4.6V is fully charged, and the voltage drops steadily with use. For Energiser Lithium Ultimate batteries you probably need to keep track of their days of use (using the value in the Configuration App) in order to estimate how much capacity they have left.

Agustin Lobo

Sep 28, 2022

Thanks for your many advises and expert opinion. I think I could have mistaken the batteries (or some of them) and put used ones instead of new ones. But my concern is: considering the configuration app was reporting "BAT 4.6V" (which I understand is acceptable), how could I have detected that the batteries were actually not good before the deployment?

Alex Rogers

Sep 28, 2022

Replying to

When the USB is connected the batteries are not under any load so it is difficult to get an accurate estimate of their capacity from the voltage. This is particularly so with Energizer Ultimate Lithium batteries which have a very flat discharge curve - the voltage close the start of their life is similar to that at the end of their life. Alkaline batteries have a clearer voltage profile, but you will definitely get a longer deployment period with the Energizer batteries.

Alex Rogers

Sep 26, 2022

The 64GB SD cards are reliable. We've made many months of continuous recording on them. Files that have 0kB length are generally caused by an SD card write error preventing the file from being closed. This occurs rarely with a genuine SD card error, more often with a full SD card, and sometimes when the battery is low. Always reformat the SD cards, rather than deleting files, as sometimes deleting files doesn't free up the space. The operating system just hides the files, rather than removing them from the file allocation table. In this case, I'd suspect that the battery was running down. If you check the header information of the file which was closed correctly, but is a bit shorter than expected, it will likely say that the file was cut short due to a low battery voltage. The same for the other short files that were written. You can see the header comment in on a Mac through the finder. Otherwise, open them with an audio application such as Audacity will allow you to see the information.

Alex Rogers

Sep 27, 2022

Replying to

You won’t be able to read the 0kB file. They have no content and only exist in the file allocation table.

Check the header comment of the files named 20220828_143000.WAV, 20220829_040000.WAV and 20220809_173000.WAV. These are correctly closed files but are shorter than expected. The AudioMoth will probably report that the battery voltage is low.

What type of batteries are you using? If these are alkaline batteries then 3.8 / 3 =. 1.26V per cell is quite low. Under additional load when writing to the SD card and at lower temperatures, the internal voltage drop will likely push it below the threshold.

Agustin Lobo

Sep 27, 2022

Replying to

Right:

20220828_143000.WAV

3 minutes 32 seconds

Recorded at 14:30:00 28/08/2022 (UTC) by AudioMoth 24410E085728D5E5 at medium gain while battery was 4.2V and temperature was 22.6C. Recording stopped due to low voltage.

20220829_040000.WAV

2 minutes 14 seconds

Recorded at 04:00:00 29/08/2022 (UTC) by AudioMoth 24410E085728D5E5 at medium gain while battery was 4.3V and temperature was 11.7C. Recording stopped due to low voltage.

20220829_173000.WAV

28 seconds

Recorded at 17:30:00 29/08/2022 (UTC) by AudioMoth 24410E085728D5E5 at medium gain while battery was 3.8V and temperature was 18.0C. Recording stopped due to low voltage.

While a correct one:

20220828_100000.WAV

5 minutes 0 seconds

Recorded at 10:00:00 28/08/2022 (UTC) by AudioMoth 24410E085728D5E5 at medium gain while battery was 4.6V and temperature was 27.1C.

I'm using https://www.energizer.com/batteries/energizer-ultimate-lithium-batteries.

According to the config app, consumption was estimated at 44 mAh/d and indicated "BAT 4.6V"

I assumed:

* BAT Energizer Ultimate Lithium 3000 mAh, thus 3000/46 = 65d

IS this wrong?

Where you say:

If these are alkaline batteries then 3.8 / 3 =. 1.26V per cell is quite low. Under additional load when writing to the SD card and at lower temperatures, the internal voltage drop will likely push it below the threshold.

How much should it be? I often see BAT > 4.9V

Is 4.9 the threshold you refer to?

Alex Rogers

Sep 27, 2022

Replying to

Yes, that consumption is correct for those settings. It will record for about 2 1/2 hours per day in total and typical consumption at 96kHz is around 15mA. Were the batteries new before the deployment? You should get about 60 days use from the Energizer Ultimate Lithium. However, they do have a very flat discharge curve so it is hard to estimate how much capacity they have left from their voltage, and the voltage is very dependent on the current toward the end of their life. The battery voltage reported in the header is before the recording starts, so the message is indicated that during writing to the SD card the voltage is dropping, and it stops the recording to avoid going too low. What you are seeing is consistent with a set of batteries (or possibly just one battery) that is close to being completely discharged.