Developing and Testing a Waterproof Enclosure for the AudioMoth Acoustic Logger - Part 1
Thanks and acknowledgments...
We would like to extend our thanks to Mr Andy Avery of Somerset Bat Group, who originally posted the group’s experience with this type of enclosure on the AudioMoth support forum. Andy’s post on the forum can be viewed by clicking on the following link.
Background to the AudioMoth full spectrum acoustic logger...
AudioMoth is a low-cost, full spectrum acoustic logger, which can record uncompressed audio at a range of frequencies, from audible through to ultrasonic, at rates up to 384,000 samples per second. It is for this reason that it has become a popular low-cost option for recording bat echolocation and social calls in the UK. In comparison to other available full spectrum bat detectors, the AudioMoth is tiny, measuring just 6cm x 5cm x 2cm. The detector’s build is relatively simple - it features a circuit board mounted and secured on to a 3-cell AA battery enclosure. However, there is a trade-off in exchange for its low price, size and simple construction - it is not waterproof, and therefore in the absence of any type of additional enclosure would quickly yield to inclement weather.
It is due to it’s inability to repel water that numerous professional and amateur researchers alike have sought to find a low-cost solution to safely deploying the device in the field for periods of time without worrying about poor weather conditions. Solutions have ranged from simple plastic zippered bags, as supplied with the device, through to the modification and use of pre-made electronic enclosures. Having successfully used the supplied plastic zipper bag since we bought our devices last year, albeit in mostly dry conditions, we wanted to explore a more permanent and reliable solution to deploying our devices for longer periods of time within a range of Scottish weather conditions.
Modifying a waterproof electronic enclosure...
On the basis of Andy’s blog from September, we ordered two waterproof plastic electronic instrument enclosure cases from Ebay, which took just over a week to arrive from China - a link to the Ebay listing in provided above in Andy’s blog. The boxes come pre-sealed, so you will need a screwdriver to open them. Once open, you will find the remaining two screws to secure the lid and a silicon seal, which you will need to use to create the seal between the housing of the enclosure and the lid - this actually fits into the under-edge of the lid, just remember not to over-stretch it when you run it along the groove in the underside of the lid.
It wasn't until we got to the next stage that we hit a slight snag… Because we have the first generation AudioMoths, which house the switch and microUSB card proud of the circuit board, the detector wouldn’t sit within the lid as per Andy’s blog. However, all was not in vein, having measured the width of the box, we realised we could house the detector lower in the enclosure provided we removed six small sprews, which was achieved using a drill and a 6mm metal drill-bit, followed by a spot of chiselling and some light sanding to removed any roughness. Once we were finished, we secured the detector using two small wedges of foam to ensure there was sufficient space around the edge of the box to close the lid around the detector. We also enlarged the two ‘lugs’ on the sides of the case so they could accommodate one of our small 5mm python-locks - an essential bit of security for longer deployments in the field.
