Last time I talked about the firmware and software application we were going to implement for the Rx-LIVE integration. I got some help from Evan to button that up, and the details are covered in the Bristlemouth Dev Kit guide [here]. The end result is the Spotter in the system now sends periodic reports of all tag detections collected in a configurable sampling window!
In this post, I’ll go over the steps I took to mount the RX-live to the Bristlemouth Development Kit so that it can talk through the Smart Mooring system to a Sofar Spotter buoy. At the end, I’ll be ready to deploy the system in the water for some actual field testing.
Bristlemouth Development Kit
Sofar has put together a package of hardware called the Bristlemouth Development Kit which is intended to get developers up and running with a Bristlemouth integration quickly. The idea of the Development Kit is that it allows integration to happen quickly and easily to prove a system out in real field conditions, and later on, once a device has been validated, a developer may choose to make a custom Bristlemouth interface for their device that is more streamlined and optimized for their application. For what we’re doing now, the Development Kit is perfect. The Development Kit includes the Development Board which we’ve already started to use in previous posts for this project as well as the mechanical hardware needed to mount devices to a Smart Mooring system.
The main pieces of hardware in the Development Kit include a waterproof tube with end caps that houses the Dev Board and any other wiring or electronics needed to support a given payload. One of the end caps has ports for attaching Bristlemouth Jumpers to interface with the Smart Mooring cable, and the other end cap is blank so any desired penetrator can be added. The whole assembly is designed to be mounted to a Smart Mooring Casket which is the node that interfaces one Smart Mooring cable end to another. The Dev Kit also includes two Mounting Brackets that are used to mount the enclosure tube and any other cylindrical payload to the Casket. Conveniently, the RX-live fits very nicely onto a Mounting Bracket so the whole assembly should go together intuitively without much (if any) custom mechanical engineering needed!
As an overview, what we’ll want to do is connect the Rx-LIVE to the Dev Board using the 8-pin SubConn cable it is designed for, then convert that signal (both power and data) into Bristlemouth Format in the Dev Board which will be connected to a Spotter buoy through Bristlemouth.
Subconn Passthrough
The first step to plugging everything in will be wiring the Rx-LIVE to the Dev Board. The Rx-LIVE uses an 8-pin SubConn cable, with a nominal diameter of 9.2mm. To pass that cable into the Dev Kit Tube, I’ll use a Blue Robotics 9.5mm WetLink penetrator going into the blank end cap that came in the Dev Kit. Nick Raymond at Sofar recently posted a great write-up on how he drilled holes into his Dev Kit end cap to accept some WetLink penetrators and I’ll plan to follow the same guidelines, but with just one hole instead of three. Looking at the spec sheet for the 9.5mm WetLink penetrator, I can see that it uses M14 threading, so I’ll plan to drill a 14mm (very close fit) hole for that to go through. I didn’t have a 14mm bit lying around, so I ordered one on Amazon which only cost about $10.
For critical drilling operations like this, proper fixturing is really important. I used a drill press vise to hold the endcap level, and clamped the vice to the drill press table. I double-checked that my desired hole location would leave enough room for the WetLink nut to have room to spin and be gripped inside the end cap and carefully aligned that location with the tip of the drill bit placed in the drill press. In retrospect it also would have been a good idea to put tape on top of the end cap where I planned to drill the hole to protect that surface from scratches while drilling. The WetLink uses a face-seal o-ring, so any scratches on the sealing surface surrounding the hole could cause a leak. I also cut slowly and carefully to make sure I didn’t take any big chips out of the beginning of the hole in order to protect the flatness of that sealing surface.
I followed Blue Robotics’ tutorial on how to properly install a cable into their WetLink penetrator. Their guide is better than what I can describe or show, so it’s best to just follow the link to their instructions. The only difference in procedure for me was that I had a really hard time fitting the SubConn cable into the tight hole on the WetLink Bulkhead, so I put a little bit of Nyogel 760G onto the outer jacket of the cable to help lubricate it so it could be pulled through. Since Blue’s instructions caution that lubrication should not be present on the seal, I wiped the residual lubricant off of the jacket using isopropyl alcohol after the cable was inserted. I also placed the face-seal O-ring for the WetLink in its groove with a light amount of 760G lubrication and inspected it carefully to assure there were no hairs or defects that could affect that seal.
Now I was ready to insert the WetLink penetrator into the hole in the end cap. I inspected the sealing surface one last time for scratches or debris and pressed the penetrator into place, then hand tightened the backing nut on the opposite side. I didn’t have the tools Blue recommends for tightening these parts, so I just used two wrenches I had nearby to tighten the bulkhead and nut together firmly.
I soldered the appropriate wires from the Subconn cable to the same connector I had used during testing with the Dev Board, and double checked for the correct continuity with a multimeter. After plugging everything in, this is what the wiring looks like:
Now it was time to put everything together.
I used the included hardware to mount the DevKit to one of the mounting brackets on our Smart Mooring, and zip ties to mount the Rx-LIVE to the other. For long-term deployments, Id use stainless steel hose clamps to hold the Rx-LIVE to the Mounting Bracket, but for short-term testing like what I was planning for, zip ties worked fine.
Before placing the system in the water, I visually checked for the dark ‘engagement line’ between the o-rings on each end cap and the inside of the acrylic tube around their entire circumference. I also placed the system in a tub of fresh water for several minutes and inspected it afterward to make sure there were no leaks before deploying it in sea water. A freshwater leak with the electronics turned off is less likely to cause damage to the internal electronics than one in salt water with electronics on.
Everything looked good. I added a small anchor I had for a quick one-day test deployment in shallow water, and I placed the tag transmitter that Innovasea had also lent us in a mesh bag tied to the Spotter buoy to see if we could detect it through the integrated system.
I paddled out to a shallow cove in San Francisco Bay near where I live and placed the system in the water. Within about 20 minutes, Evan messaged me to say he saw some tag detections come in through the Spotter interface. The system seems to be working!!
Now we’d really love to try this system out in an area where real tagged animals are swimming by. If anyone here on the forums has access to a habitat where these types of tags are being used, we’d love to test the system out in a real-world environment!