So great to see a device made of hobby electronics and hardware store parts being applied to real world problems and achieving real results. I started development on a data logger device called BoatDetect (https://hackaday.io/project/171951-boatdetect) a few months ago and took inspiration from the Cave Pearl designs. I have learned a lot from all the documentation you have posted on this project. Thank you for sharing.

The thing I like about environmental monitoring is that there are an endless number of challenges to work on so you're never at a loss for something to do next.  Don't be surprised if your boat detector morphs into other useful things over time.  That's been happening constantly on our project.

How did you make the housings? Are those PVC parts with the three screw mounts standard parts? if so, do they have a name?

Those struts are on 2" Formufit table leg caps, availiable at Home Depot, Amazon, etc. All the other parts are just standard off the shelf PVC fittings. There are a few housing variants at:

https://thecavepearlproject.org/2015/02/04/a-new-diy-underwater-housing-for-2015/

Very cool project. PVC is great stuff and easy to work with. Nice job.

@ alex: Like many I have been waiting for the physical print sizes in the low end 3-D printer market to become large enough to be useful for my project, as I would love to use one for internal scaffolding, etc. But with such good results from the current housings, I suspect that I will be sticking with the PVC plumbing for quite a while. The stuff is just so easy to work with, and more importantly, it's available to everyone around the world at low cost.

Great project, these toys look like a ton of fun to build and play with - making stuff with PVC brings me back to potato gun days.

Now that we have reached a decent lifespan with the loggers, I've been considering ways to download the data in-situ with opto-couplers through a transparent window in the housing.  This would be pretty simple to implement, and with the fierce attenuation of RF in sea water, I would have to be almost on top of the units to use wireless anyway. Of course, once you've done the technical dive out to a cave deployment, simply swapping the whole logger with a new unit probably takes less time, and that is a precious commodity when you are down at 20m.

Are you still using the Arduino IDE?

From the outside, it looks like you've gotten comfortable enough with the code to try and graduate to AVR Studio. Manually setting registers is a great way to get dirty with your code and have absolute control over your sleep modes.

Same thing about designing your own circuit boards. Comparing two different Arduino flavours seems strange to me, because you could be looking at _what parts_ of the boards themselves consume power.

Super impressed with how far you've come and how you've stuck with it, though. Read the whole blog, marine environment failure points are really interesting.

Generally I try to keep the code understandable for other beginners, as my current task is bringing a bunch of other researchers who we have partnered with up to speed on their own logger builds.  And for me personally its much more fun to build new different instruments, than to perfect my code past the 'works ok' stage.

WRT different Arduinos, you are absolutely right about the component variations, but I am out to prove that you can make viable loggers with just about anything, including the cheap eBay stuff. 

No doubt there are more marine failures on the way for the amusement of all. The current plan is slowly move the old models "out to pasture" on open ocean deployments - mostly because the cave installations have more complicated logistics, so we would rather have the newer, more reliable builds in the caves.

Something i think this needs.

A way to remotely collect data either nearby real time nearby bluetooth or wifi radio.

idk how these devices preform under water. 

How deep are your sensors?

The underwater units are installed in systems ranging from 5m to about 25m depth. We haven't pushed them much farther than that because finding a good installation site, and hooking everything up, takes some time. Once you get below 20 meters air limitations start to conflict with those other requirements of the dive. I'm just now starting to retire the first gens, and I am tempted to take the electronics out and lower the housings on a line to see how far they could actually go.  My hope is that they will make it past 60 meters, because that kind of range would open up a big chunk of research territory to more projects on a DIY budget.

That is awesome.  I read your blog as well, maybe one of these days I will try it out my self.  You also look like you have your fair share of experience of housing failures, but I would say be careful any way.  I have seen housings blow up because they have a small leak and if left down long enough to equalize then when they are brought up they don't have time to relieve the pressure because the leak is too small.  At the depths you are talking about it shouldn't be too bad, but you wouldn't want a cap to slap you in the face as you are taking it apart.  The worst one that I have seen was an acoustic pinger.  It was sent down to about 8,000ft, and we didn't know there was a problem because we weren't using it.  It came up and set on deck for about 20min and then it sounded like a shotgun went off.  It was a good thing no one was working with it.  

I also wanted to say good job, for using pvc you have a really clean finish for the enclosure.

as a side note, something that we would do with some of our enclosures is fill them with oil (vegetable oil should work)  that way the housing is pressure balanced with the ambient conditions, but the type of sensors that you are using will dictate the viability of this option.  Also, if you can put some type of QD on the housing then you can use one of those garden hand pump sprayers and pump the oil in so that the internal pressure is a little over ambient.

Wow! I have not seen a battery meltdown that dramatic...yet

I've already been thinking about putting oil into the small section connectors for the temperature sensor strings, since they have much smaller o-ring contact surfaces, so are more likely to fail at depth. For the main housing, I would probably go with a wax fill rather than oil simply to make the data retrieval & repair process less messy. But before I try that I still have the option of using schedule 80 pvc, which could extend the depth range by  another 30-50%

25 m is not nearly enough to warrant oil filling - you only see like 35 psi at that depth.  Your PVC can structurally handle ten times that or more I would guess.  But the comment @jlbrian7 made about small leaks is a serious one if you go to deep depths and have an air interior.  I have also seen water leak past a gasket seal or glue seam and compress the air inside the housing, then when you pull your housing up the leaks are very often really slow or sometimes they re-seal as the pressure gradient reverses.  This just makes your device into a bomb.

:) there was no battery.  It was a plastic housing and when it failed - BOOM.  I think that the leak was at the bottom, so all the air inside was compressed.

HI- Did you show these at Pumping Station in January?

I think I had a few drip sensors at that meetup, and one of the old 3" PVC models (?) but I don't think I had anything in the 2" underwater housings ready at that time. I have put together several new sensor combinations with the 2" housing since then, and I've done quite a few experiments to get better performance out of the basic three module logger.  Most of those new builds are out running in a cave/underwater right now, but by early Sept I will have the data from them to show everybody. The real world deployments always teach me something new, so I am careful not to count my chickens just because something seems to work on the bench.

This is a great project.  I am going to make one to monitor my tank for my rainwater catchment system.

You can find a somewhat recent code build at:

https://github.com/EKMallon/The_Cave_Pearl_Project_CODEbuilds/blob/master/_20141002_DripSensors_WithPowerControl/_20141002_DripSensors_WithPowerControl.ino

You will still have to make a number of manual tweaks depending on which sensors you are connecting.  If you look through the setup you should see the "standard pattern" I used to add sensor support. Once you have an "init" function in setup & a "read" function at the start of the main loop all you have to do is change the Pstring print statements that load your sensor data in to EEPROMBuffer. Don't remove the CycleTimeStamp

PString str(EEPROMBuffer, sizeof(EEPROMBuffer)); 
    str = CycleTimeStamp;           //17 / 16 characters without seconds plus comma
    str.print(F(","));
    //str.print(TEMP_Raw);  //4 digits both 12 bit sensors, so 4095 is largest value 
    str.print(IntegerVariable);  //two digits positive
    str.print(F(","));
    str.print(AnotherIntegerVariable); 
    str.print(F(","));  

etc - only up to 28 characters! Pstring simply ignores the extra data if you try to put too much in the buffer.

Then:

    Write_i2c_eeprom_page(EEPROM_ADDRESS, CurrentPageStartAddress, EEPROMBuffer); // whole page is written at once here
    CurrentPageStartAddress += EEPromPageSize;

puts the data into the eeprom till the buffer is full. Moving the data from the buffer to the Sd should card happen automatically but its up to you to make sure you are loading & unloading the same number of eeprom pages per sensor read cycle. A simple 1 or 2 sensor build usually only needs two pages stored per cycle.  You can use real number variables if you want, but the print routine eats more sram on the compile if you do.

I am working on a fairly major re-vamp of the code with faster bus speeds, and a whole bunch of other tweaks, but I don't want to post it till I see the results from the currently deployed loggers and that wont be till the end of August or early September.

I know some of the photos look like they are of different machines but they all share the same 3-component logger at their heart, run essentially the same code, and use off-the-shelf PVC plumbing hardware for the housings.  So the variety is meant to demonstrate the same components in different physical arrangements, because that's kind of the whole point of what I am trying to do.  I2C and one-wire breakout boards make it easy to build interchangeable sensor-caps for the same logger platform if you use standard connectors between the cap and the logger. My current favorites are Deans Micro plugs because they are really solid, but you can use just about anything.