I thought I would include my AudioMoth enclosure to the growing list of enclosure solutions out there. Thanks to everyone who have shared their enclosure designs. It made figuring out what I wanted to do much easier.
I purchased everything from AliExpress:
Vent Plugs: https://www.aliexpress.com/item/IP68-Stggo-Gore-Vent-PMF100320-Equivalent-Screw-In-M12-Waterproof-Proteictive-Breather-Vent-Plug-for-Marine/32954329806.html?spm=a2g0s.9042318.104.22.168934c4dLSB8nc
The cases are pretty good quality, but there were occasionally some minor surface imperfections that I had to clean up by scraping with a flat razor so that the AudioMoth would sit flush against the lid. The cases are convenient for mounting, as zip-ties can be fed through the holes to attach to a post, or they can be attached to a surface with screws. Before doing anything else, I tested the cases to see how waterproof they were by keeping them submerged underwater overnight. There was some surface rust starting on the screws but the boxes were completely dry inside. I'm not worried about the screws, but I might replace them with stainless steel ones if rusting becomes an issue. Fortunately, the AudioMoth fits inside the lid of these cases perfectly, so I was able to semi-permanently glue them in place with a hot glue gun. If I need to flash them in the future, the glue should be easy to remove to pull them out. I can still remove the memory card with needle nose pliers and plug a micro-usb cable in with the AudioMoth glued in place. In the future, I might solder some wires to the programming contacts so that I can put the AudioMoth into programming mode without having to remove it from the lid of my case.
I used calipers to measure the distance of the microphone to the edges of the AudioMoth (approx. 4.6 mm) and measured and marked the distance on the lid to drill the hole. The acoustic membranes have a diameter of about 6.75 mm plus an extra 1-2 mm with the adhesive, so I used a 7/32" drill bit (approx 5.5 mm) to drill the hole. After the hole was drilled, I lined up the AudioMoth so that the mic was positioned in the middle of the hole. Next, I marked a line along the edge of the AudioMoth with a permanent marker so that it would be easy to line up the mic after the acoustic membrane was in place. The next time I do this, I will make a jig for drilling the holes in a drill press so that I don't have to measure and mark the hole location each time. Marking the hole location is time consuming, and it is much more prone to error ( I have a few where the mic is off centre).
I wanted to use an additional vent even though the acoustic membrane should act as a vent. The enclosure should be better protected from water infiltration if it can breath good, so I figured it wouldn't hurt to have some extra venting. I used a 15/32" drill bit to drill a hole in the side of the box for the vent plug. It doesn't really matter where this goes as long as it is out of the way of the AudioMoth.
I glued some bubble wrap that came with the AudioMoths into the case to add some support to the device even though the AudioMoth is held in place with some hot glue. I may replace it with something more elegant in the future, but this will work for now. For the six AudioMoths that we currently have and the extra six we have on order, the cost worked out to about $40 per enclosure, but that includes the excess materials (I had to purchase 300 adhesive vents and 100 vent plugs). As we acquire more AudioMoths, the per unit cost of the enclosures will continue to decrease. I think it would be around $10 CAD per enclosure if I had the option of only buying the amount that I needed.