A project to make low-cost benthic weather stations to monitor seabed dynamics with Raspberry Pi cameras and sensors. If this works well in dark, turbid, cloudy waters, it'll work great in clear waters! Plus, it has a computer.
Currently, base cost to build a unit is about $100 USD.
Did you know fish can suffocate underwater? When dissolved oxygen in the water drops below a certain level (a condition called hypoxia), they become stressed and in extreme cases - die. While a number of studies have looked at coastal water quality changes (e.g., hypoxia), we still don't really know how the drivers of hypoxia and benthic processes are linked. So the LoBSTAS's goal is to learn about hypoxia in relation to pictures and videos of the benthic environment.
How is the seafloor changing? What are the currents like? Any 'storms'? How are the plants and animals doing down there? Are they thriving or surviving? Is human activity and waste damaging the coastal environment?
"But don't we already have professional equipment that do these stuff?" Well yes, but they're very expensive. That's why a key goal is to make this project as CHEAP and EASY to build as possible, so that people with limited finances or tech experience can study the seafloor too.
*If you're curious, LoBSTAS stands for Low-cost Benthic Sensing Trap-Attached System. It's a mouthful, I know!
Raspberry Pi Zero W ($10)
Switched to this from the Pi3 because of its smaller size and lower power consumption.
Camera Module with Fisheye lens ($15-20)
I recommend the Sainsmart NoIR Wide Angle FOV160° Camera Module where you can easily adjust the lens focus and swap out different lens. I got mine from Sainsmart.com.
Anker USB Phone Charger 5200 mAh ($20)
Or you can also use a power bank with larger capacity llike 15600 mAh
Schedule 40 Standard PVC Pipe 2"
If you want a bigger unit, use 3" pipes instead of 2".
Female PVC Connector 2"
Protects the window and acts as second waterproof layer.
Note: The project actually started two months ago, so I'm trying to organize and compress logs from my Evernote journal to Hackaday!
There are tons of underwater housing made with PVC everywhere, so my challenge was: can the design be easier or cheaper? Can the parts be easily obtained and cut with tools that most small workshops would have?
In the end, after brainstorming with the team a bit I decided to choose the simplest design on the far left with 4 parts: a end cap/plug, main body, window, and window frame. I didn't have the tools to easily cut circular grooves on the PVC for the O-ring to sit in for the middle design, and the latches on the right design seemed like extra work and parts (I really the easiness of opening and closing it tho).
To ensure a good bond with PVC glue, I picked clear PVC as the window material. It isn't as clear as acrylic, but we'll see how it goes! I couldn't decide whether it'd be better to put the window BEFORE or AFTER the window frame's ledge. Hmmm. So I made two versions!
*EDIT: I later realized acrylic can also be bonded with PVC cement if it has important compounds (MEK and acetone), although not as good as Weld On adhesives that is recommended for acrylic.
After cutting the parts I inspected the PVC coupling in more detail and realized that the coupling I had, had a ledge which was flat at one side, and slanted at the other. To try and fit the slanted edge, I tried used a sander to put some kind of slant on the window. It was crude and didn't fit perfectly, but at least the window fit better than before!
Used PVC primer on contact surfaces, and glued the parts with PVC cement. Those things sure get real sticky fast! It was harder to glue Mario because I had to do it in two stages: one for the coupling 'frame' and then the window. I also used A TON of glue because there was this gap between the window and the body due to the ledge and I wanted to fill that out.
Luigi was much easier to glue! After smearing all the stuff on I placed the window on the body (vertically) then pressed the coupling down on top of them really REALLY hard until all the surfaces was flush. I really like that the window is glued to the body - it is the main, most important contact to prevent leaks. Then the coupling 'frame provides a secondary guard against leaks.
After a day of drying, we brought Mario and Luigi out to the water for first leak tests! I didn't have weights, so I just found some rocks and taped/zip-tied them to the housings. Each housing also had its own Ziptie loop which held pretty well.
They went down to about 16-18ft (about 5m) for a quick check for major leaks, then sat in the water overnight just in case there were minor leaks that needed more time to show. Here's a raw deployment video from a GoPro that I tied to the string:
(Warning: Spinning video may cause dizziness)
From this video, I realized that the field of view decreases A LOT in water, due to a higher refractive index. On land, the whole unit fits into the view of the GoPro's fisheye lens, but in water it barely does! Hmmmm. Looks like super wide angle lens will be the way to go underwater.
I also realized that Luigi was loosely anchored to a rock and this is not ideal for taking images - i'd need a stable anchor/weight like Mario's where the housing is secured to the weight! Unless I really want pictures that 'float' around since the housing is floating and moving with the seafloor currents.
Took them out the next day and there were no leaks. This housing is operational up to 18ft (about 5m) woohoo!
Housing Next Steps:
How far can they go before a leak breaks in?
Can I drill an extra hole somewhere for the sensor?
When you've decided if you want a standard sized 3" or the Mini 2", you'll need to cut three things: the PVC body, the window frame, and the round window.
Tools I used: Chop saw, jigsaw, random orbit sander Materials needed: PVC Cement (and primer), plus all the PVC components
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1.1 BODY Choose a length that your power bank/battery pack and sensor can fit in. I recommend choosing 6-9". I used a chop saw with a circular blade, but you can use any saw/cutter you have to cut the PVC.
Important: make sure one end is as flat as possible for best contact with window! Use a sander/sandpaper for this.
Image: Cutting extras of the coupling after the body is done.
1.2 WINDOW FRAME COUPLING Check the coupling, there should be a ledge in the middle on the inside. If one side is flat and the other is not, the flat side will be facing the window. The other side will be facing the open sea, so cut off the extra length until 0.5" (1.3cm) from the center ledge is left.
The extra 'frame' outside the window may come into the picture of your camera, especially if it has a wide viewing angle.
1.3 THE ROUND WINDOW This is the hardest, as you need to cut round lines with a jigsaw (unless you have a special saw). Place the body on the Acrylic/PVC sheet and trace a circle. Cut the circle with the jigsaw and use the sander to make it round.
Important: As you sand off extra bits, keep checking how well the window matches the body and how well it fits the coupling frame. Test it by putting the body, window, and coupling together.
1.3 GLUE TIME Put PVC primer on ALL contact surfaces, then smear the PVC cement glue generously as well. Make sure there is lots of glue on the contact between the body and the window!
Important: Work fast, PVC cement dries fast. You might have to press the parts together REALLY HARD to get the window and body all the way into the coupling.
1.3 HOLE FOR SENSOR (optional) If you have a sensor that needs to be in the water, drill a hole on the square part of the expansion plug. Sensor should fit nice and smug through the hole. Use epoxy, silicone or some other potting compound to completely fill up the expansion plug from the inside! Put some stuff on the outside near the sensor too.
Important: I recommend you do this last after you've tested the housing underwater, so you can pinpoint if your window is leaking or not.