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6V power supply via USB port

Hi,

Is it possible to power Audiomoths with 6V lead batteries via USB port, or would it damage them (almost 7V when fully charged)? I've been looking for a way to power them with a rechargeable high capacity power source. The idea is to avoid soldering cables onto the board/removing the battery-holders, to keep things simple for future users. I've also tested connecting lead batteries via AA battery sized dummies (wood + nails + cables), but this results in noise between 65 and 75 kHz.

All the best

Luisa

9 comments

9 Comments

Luisa

Jul 10

Hi, thank you for the quick reply! So far I only used 2 dummies, that only have a connection to the battery case at one end. Could that have caused the problem?

In the picture the dummies are inserted at the wrong place, this was just to see if they fit at all. The black end would sit where the battery case is connected to where "-" is on the board, and the red end would sit below "+". So both dummies turned around and switched.

Edited

Alex Rogers

Jul 11

Replying to

The noise has a pattern that occurs every 40ms which corresponds to the frequency with which the SD card writes are occurring when recording at 384kHz. This would suggest that the SD card is creating noise on the power line. We normally recommend SanDisk Extreme (red and gold) cards which have low energy consumption and low SD card write currents. Samsung EVO cards are unusual in that they use less energy at high sample rates, but more at low sample rates - https://www.openacousticdevices.info/sd-card-guide. These are big batteries so I would expect them to have very low internal resistance. However, we haven't tried lead-acid batteries before. A poor connection might result in this type of noise.

Luisa

Jul 16

Replying to

Hi, I ran tests with direct connection to the battery, additional plugs in between, 512 GB and 128 GB cards (all Samsung EVO), screw-dummies and nail-dummies and have not been able to reproduce the noise. Maybe it just was due to some non visible damage on the recycled cables.

Some devices picked up on a tiny bit of different noise, that I haven't looked into further yet, but nothing that impacted recording quality or file size dramatically, and also all of them had different setups (cards, plug/no plug, nail/screw). Thank you for the support!

Alex Rogers

Jul 16

Replying to

Great. It's also possible that the noise was external. Laptop power supplies can be very noisy and generate a lot of ultrasonics.

Alex Rogers

Jul 10

Hi Luisa, The 7V input applied to the USB cable would possibly damage the Wonder Gecko microcontroller which includes a regulator to generate the 3.3V USB signals from the expected 5V power supply. You could connect 3 x D-cell batteries through the existing AA battery holder using dummy batteries, use a good quality 5V regulator between the 6V lead battery and the USB cable, or use AudioMoth Dev boards that accept any power supply with a JST connector. It’s not clear why the lead battery applied to the battery terminal would generate additional noise. The input limit is 6V but that is based on the maximum SD card write current load and the thermal limit of the regulator so in reality going to 7V shouldn’t make too much difference. Alex

Alex