# An Arduino Based UnderWater Sensor Platform

by EdMallon |

Early in 2011 I became fascinated by the open source hardware movement, and saw the potential for new micro controller platforms to replace expensive commercial sensor units with cheap & cheerful DIY equivalents. So this blog is a record of my attempt to build an underwater flow sensor using an Arduino based data logger. My goal for this project is to build a submersible data logger for research in flooded cave systems that costs less than $300 each, and runs for a year on regular AA batteries. Site Link: http://edwardmallon.wordpress.com/ The Arduino is an off the shelf Tiny duino, and the code was just cobbled together from the usual sources on the web, so I don't take any credit there. But I am quite happy with the o-ring underwater housing made from PVC plumbing, as it is very robust, even for a beta unit. And I am sure that many other groups who need a quick waterproof housing could put together the rubber end cap design I came up with in just a few minutes, hopefully saving themselves a few dollars in the process. Once the basic data logger passes the current long term deployment testing, I will be adding many more water quality sensors to the units such as temperature, conductivity, and pressure. I will post progress there as I go along, and I look forward to insights from other collaborators, now that the project has been put online. ### 24 Comments cool!!!! Wow, very cool, Ed. Would you be able to cross-post your blog here? How could we make that easier for you? I think a lot of folks here would be interested in following. Also see this newly posted discussion of dragging underwater loggers: http://publiclab.org/notes/maxliboiron/02-11-2014/underwater-plume-sampling-methods You can subscribe to more updates on this topic by subscribing to this tag: http://publiclab.org/subscribe/tag/water-quality Hi Warren. Nice to meet you. Wrt cross posting, I am wondering about the content that would be most helpful to the audience here, as I interwove (with different types of navigation) posts for two very different audiences in the main project blog. And by cross posting, do you mean just posting links to new blog entries as I make them...or do you mean transferring the actual images and content? Perhaps I should keep the "narrative" posts at my site, and just cross post the "how to build" and technical updates to this forum? Those are the ones most likely to help someone else who is trying to make something. I think my pvc underwater housings would be especially useful to some of the water quality projects you have been sending to me. Also, i'm still new to your site, so forgive me if it takes me a little while to figure out where everything is...in fact I don't even know where these comments are going yet. (...found them...ha!) Hi everyone. I just wanted to post an update as I have done some major code development for the Cave Pearl data logger recently, and a weeks worth of power draw tests have given me a real world idea of how much power it takes to buffer your sensor readings to an I2C eeprom. Essentially 192 block writes(&reads) on an AT24C32 eeprom + 1 SD card write, uses twice as much power as 8 SD card writes. I really did not have any sense of what these numbers were going to be be before trying out this little experiment. Anyone interested, and using an arduino based datalogger, might want to look a the scripts for some ideas for their own project. Cheers! Hi everyone, Just a quick note to say the first gen loggers survived their initial 3 month deployment giving us real water flow data, (6m depth,~ 50% marine salinity). I had some significant doubts about the rubber bottom model, and the pipe clamp did rust a significant amount. Still, I suspect that design could do 6 months before standard stainless steel pipe clamps gave out. The next gen builds are now installed: http://edwardmallon.wordpress.com/read-the-blog/ P.S. I am still in the field for a few days, and internet time is patchy at best. So I will have to respond to any comments next week. cheers! Despite my zeal for the project, I have tried not to bomb everyone here with the many incremental updates as I go along. But I think I might have produced something that could really help people doing citizen science. Basically its cheap DIY datalogger that most could assemble out of 3 components, for about$10-15. Add another tenner and you have an waterproof housing for it as well.

http://edwardmallon.wordpress.com/2014/07/01/a-10-diy-data-logger-is-born/

Anyway, I hope that this helps someone out there who's project needs cheap data-loggers that can be assembled from "off-the-shelf" parts. As I mention in the post, these units will probably run for at least 3-four months on 6 AA batteries.

It's been a while so I thought I would post a project update to Public Lab

1) We had another successful fieldwork season, marking the deployment of the third generation of Cave Pearls, including a new "dry" cave model for sensing drip water in caves: http://edwardmallon.wordpress.com/2014/09/18/field-report-2014-08-25-retrieve-deploy-flow-sensors/

All of the beta generation survived five months under water (Woot!, a full data set!), so we reloaded them with fresh batteries and threw them in the ocean! We are making contacts now with other researchers, and are hoping to calibrate to true point velocity calibration by codeployments with commercial sensors (preferably acoustic Doppler) with the next set of installations around the end of the year.

2) I have updated the DIY datalogger by adding one more component: http://edwardmallon.wordpress.com/2014/10/07/the-diy-data-logger-v2-with-low-power-shut-down-capability/

I have the component cost down to about $15 for the core logging platform. This new design gracefully powers down when the batteries go low, protecting the data. Most of my builds sleep around 0.5-0.6 mA (with an ADXL345 sensor attached) so I am pretty confident that the design will run for about a year on 3x AA batteries IF you have a real BrandName SD card (fakes don't go into low current sleep-mode properly - there are posts about that on the blog if you are interested). I have also included links to all the parts, so anyone who wants to can whip one up. Bread-boarding these takes about an hour, and my current build time for a complete drip sensor is about 4 hours (course by now I have had a fair bit of practice, YMMV :-) P.S. The way I have setup the blog, if you click the links that say ---click here to continue reading the story--- it jumps you to the next narrative post, skipping over the technical updates. I had to do this because a fair number of people were complaining that they did not no how to navigate my "website". After trying to explain what a blog was so many times, I just gave up, and that was my solution. If you actually want all the gory technical details, use the blog navigation at the top of each post. There is much more content to read that way. Hi Everyone Just thought I should post a progress update on the Cave Pearl Project. We finished off 2014 with a challenging field trip that had some great success, and some very frustrating sensor failures. You can read through the field reports on that work starting here: http://edwardmallon.wordpress.com/2015/01/05/field-report-2014-12-10-retrieval-of-the-salt-water-pearls/ But the real reason I am posting is that I have finally figured out how to make reasonable underwater housings from Formufit PVC parts, that have very few fabrication steps: http://edwardmallon.wordpress.com/2015/02/04/a-new-diy-underwater-housing-for-2015/ I have also developed a simple DIY underwater connector system that uses pex tubing adapters, and given all the other water related projects at Public lab, I am hoping that this info helps give them a boost. Cheers! Hi again everybody. I finally got around to posting the Cave Pearl Project on Hackaday, and realized that it turned out to be a pretty concise summary of the current state of the entire project. So I thought I would post a link to that here so that people don't have to wade through my entire blog if all they want is the "readers-digest" version: http://hackaday.io/project/6961-the-cave-pearl-project Just back from our recent fieldwork, and we've had great success with the DS18b20 temperature strings that we deployed back in March. http://edwardmallon.wordpress.com/2015/08/26/field-report-2015-08-12-success-with-ds18b20-temperature-strings/ With all those joins, these are easily the most complicated build I have ever put underwater. And with waterproof DS18b20's being so inexpensive, the parts cost runs between$90-100 for these 20 sensor units. So I even managed to undercut low-end Thermochrons there. Woot!

It's been on my to-do list for ages, but I finally got around to posting the build tutorials for the basic 3 component data logger based on Promini sized Arduino's:

Build Instructions - Part 1 - component preparation

Build Instructions - Part 2 - logger platform assembly

Build Instructions - Part 3 - sensors & housing

Build Instructions - Part 4 - power optimization

That last part on power optimization might be a bit tricky for people just starting out with Arduinos, so I would build the basic three component logger first, just to get the hang of it, before moving on to the advanced build. Hope that helps a few of the people who were interested.

One of my high school teacher friends mentioned that he wanted add Arduino based projects to his science classroom, but after I posted those DIY guides he suggested that my logger build plans still had too much detail (and soldering...) for him to tackle with a class full of high school students. So I cobbled together a simpler Uno-based version that can be jumpered together quickly with a breadboard:

An Arduino UNO based Datalogger for the Classroom

The code posted with the logger captures the temp register from the DS3231 RTC, which has low 0.25C resolution but has actually proven to be pretty accurate compared to other dedicated temp sensors. Hopefully that starter script is simple enough that people don't have too much trouble modifying it for the sensors they want to add.

I am really impressed with the new tutorial. Thanks for that great effort. This definitely lowers the barrier for me to try this. I just dove into eBay for a while and have these items in a shopping cart. Does this collection look like it can be assembled into a working logger? The total cost with shipping is $20.00 (without wires or sensors). Arduino Uno clone$3.61 http://www.ebay.com/itm/161863547083

SD card module $4.99 http://www.ebay.com/itm/401035802070 Real time clock module$4.60 http://www.ebay.com/itm/401015650947

LEDs 20 for $1.67 http://www.ebay.com/itm/301726745400 8 GB micro SD card$2.99 http://www.ebay.com/itm/252096582221

Could an Arduino Nano replace the Uno for this build or are some features missing from the Nano? It might be cool to design a shield for a Nano to connect all the other components to. That could make a tidy package.

Below are some more or less random sensors. I am not sure these sensors operate at the correct voltage, so I'm not sure these will work:

AM2301 DHT21 humidity and temperature sensor $3.41 http://www.ebay.com/itm/301410138124 BMP180 Barometric pressure sensor$1.09 http://www.ebay.com/itm/371449104171

Adafruit MCP9808 temperature sensor $6.68 http://www.ebay.com/itm/161886933708 Can you estimate how long a logger like this could operate on four AA or AAA batteries? I really like the tidy way you wired the breadboard. Do you know what gauge wire is best for breadboarding? Thanks again for your "educational" version. I'm thinking of trying this in parallel with a Riffle to learn what the Riffle is actually doing and highlight the clever things built into a Riffle like the fancy power management. Chris Not sure about that Arduino clone, as I don't know about the chips it's using. But for less than 4 bucks just try it and see. Just don't expect them to be as robust as the real Arduinos. The DS3231 RTC boards should not cost you much more than a buck and neither should the SD card holders, so hunt for the cheap ones with free shipping. Those other parts look ok, just don't forget your limit resistor. I usually use 22 or 24 AWG solid core jumper wire which you can find anywhere. WRT the sensors, just read the specs. Adafruit boards are usually designed with level shifters so that they can run with both 5V unos, and the smaller 3.3v arduinos but you have to read the specs for each sensor. If you can't find the voltage tolerance information in the listing don't buy the sensor because it probably won't work. Also, I buy Adafruit sensors directly from Adafruits online store, same with Sparkfun, etc. I noodle around with dodgy sensors from china all the time because they are cheap enough to experiment with, but it really irritates me when those vendors copy 'real' company logos and then try to pass the stuff off on eBay as genuine. As I outlined in the post, you need at least 6-7 AA batteries to power an UNO, and I expect that would only give you between 2-4 days of operation because the UART chip is always going to use power even if the main processor is sleeping (and with a clone you have no idea how much that might be...) The NANO also uses 5v logic, and has the same UART issue, so it will likely have a similar operating life, but you would have to provide your own voltage regulation (ie: you can't run it from the raw batteries) If you want more lifespan, first build the UNO unit for experimenting and working out the code needed to drive your sensors, and then look at the links I posted earlier for the pro-mini based data logger. That unit runs for at least 3 months on 3xAA's, but you need to solder those parts together, so there would be a significant learning curve there. But I suggest you get your first few loggers working properly on the USB tether first, as that is a real achievement, before you jump into stand alone builds. Thanks for the tip about cheaper SD card modules and RTC modules. I see now how you made your pro-mini logger for$13.00.

One of those sensors I listed (BMP180) says it runs only at 3.3v, so I guess that will not work with the UNO. The others say something like 3.3 - 5.2v so they should be good.

I think I am getting the picture that the challenge in building a logger is power management, especially sleeping. So far I have noticed three different projects succeeding in this:

I'm curious about how these approaches differ. I assume the Pro-mini does not have the UART chip that makes it so hard to sleep the UNO. But the Dead_Bugs_Prototypes logger is based on a UNO and claims to last for months on a 9v battery. I guess @donblair avoided the UART chip on the Riffle? Again, I'm just curious about this because it seems to be quite an art to make an Arduino-based logger last more than a couple of weeks.

Here is an updated list of potential components for the educational build of the Cave Pearl logger ($12.00 without wire or sensors): Arduino Uno clone$3.61 http://www.ebay.com/itm/161863547083

SD card module $0.99 http://www.ebay.com/itm/131132034753 Real time clock module$0.99 http://www.ebay.com/itm/251401815796

LEDs 20 for $1.67 http://www.ebay.com/itm/301726745400 2 GB micro SD card$2.79 http://www.ebay.com/itm/381450686867?var=650599379406

10 colors of 24 AWG solid wire $14.97 http://www.ebay.com/itm/271939281212 Also need a resistor or two. These sensors seem to run on either 3.3 or 5 volts: AM2301 DHT21 humidity and temperature sensor$3.41 http://www.ebay.com/itm/301410138124

Adafruit MCP9808 temperature sensor \$6.68 http://www.ebay.com/itm/161886933708 (not from overseas, but much cheaper shipping than from Adafruit)

Very fun,
Chris

Oh gosh -- Chris, thanks for tagging me in this thread -- I had no idea that this existed! Wow, Ed -- what amazing work you've been doing!! It's going to take me a little while to catch up with everything, but just wanted to say quickly: if you've seen the Riffle project, we've been putting together some of the components you've been using on a single circuit board. The current design might not be so useful for your (fantastic!) enclosure design, as we've made it long and thin in order to fit in a water bottle. But it's simple enough to rearrange the parts into e.g. a disk pattern. I don't know that a single circuit board could be made as cheaply as the version you've assembled from separate boards, but I'm guessing it could be comparable, and might save a lot of work / be less finicky. Let me know if it'd be of interest to design such a board together -- I've fumbled my way through Eagle CAD enough times that I think it wouldn't be so hard. It's now pretty easy to get these boards made and assembled via services like macrofab.com.

I also like the idea that Chris has of making a relevant shield for the Nano!

Ed, it'd be great to pick your brain about power issues. @cfastie -- yes, it looks like the Dead Bug shield bypasses the USB-Serial chip in order to conserve power. The Pro Mini has no such chip (though it has an onboard always-on LED -- I haven't looked, but I'm guessing that Ed removes it). The current version of the Riffle has a circuit that only powers the USB-Serial chip when plugged into USB power; when on a battery, the USB-Serial chip isn't powered. I still haven't looked into the power consumption stats of the Riffle in nearly the sort of detail that Ed has for his setup, but that's a necessary next step.

Looking forward to connecting! - Don

@ cfastie: To be honest I probably would have started with Geir Andersen's shield to if I had known about it back at the beginning of my project. And it's also worth digging through to find his stuff at LetsMakeRobots (eg: http://letsmakerobots.com/node/37728 ) as he has been playing the data logger game for quite a while now.

@donblair: So far I have been avoiding the temptation to move to a custom PCB because what I really want is the flexiblity to customize loggers to suit each experiment and sensor configuration. For example I have been playing with Moteinos to road test the 1284p, side by side with a variety of mini-form factor arduinos like the one from Rocket Scream. The translation of my build plan from one board/mcu combination to the next is pretty trivial, provided you are willing to pay for it with 4-5 hours soldering jumpers. Compared to the time I spend calibrating & deploying them, that build time is still acceptable for me. But I realize that is not the case for everyone.

WRT power issues, read through the blog before you start firing off questions. Then you will see that I am just bringing together stuff that's already out there from Nick Gammon, Jeelabs, Rob Tillaart, etc. and they are much better primary sources than I am. My big contribution is simply building alot of loggers and putting them in the real world to see what happens to them. So I guess I am becoming an expert on how things stop working :-)

Believe it or not, the UNO Datalogger tutorial I posted last year has risen to the top of the traffic stats on our blog, and has generated more than a few requests for me to post a complete parts list, which I finally put together:

https://edwardmallon.wordpress.com/2016/08/08/build-your-own-arduino-classroom/

I'm sure there is nothing on that short list that Public Lab members don't already know, but feel free to pass the link on to any teacher friends who want to use Arduinos as part of their STEM curriculum, but are working within a very limited budget.

Cheers.

We just fired up a new collaborative project, and some of the academics from the other university suggested that our blog was something of a spaghetti monster, and that they had a hard time navigating through it all. So I whipped up a short summary page which summarizes all the latest build instructions:

☀ How to Build an Arduino Data Logger ☀

I've also posted a short video clip from one of our recent deployments on the
Year in review post which might be of interest to others here working on underwater projects. It's worth noting that since the beginning of the project, we've accumulated more than 700 months of operational time with these little guys, and about half of that is in underwater. We have only had one housing failure, and that was from using bad epoxy.

Cheers!

After much experimentation, I finally came up with a simple dithering method that allows you to easily use oversampling to add 4-5 extra bits of resolution to the humble 10-bit ADC on the 328p (aka Arduino) processors:

Enhancing ADC resolution with Dithering & Oversampling

My primary use for this will be reading thermistors at resolutions better than 0.01°C. The technique would work with any resistive sensor, though you might need to tweak the pin currents a bit from one board to the next.

Cheers!

Wow, Ed, this is really cool, and obviously applicable to many sensor projects using Arduinos. Just curious if you'd be interested in posting a more step-by-step how-to post, perhaps linking to your in-depth blog post?

Thanks!

I'm currently working out how to calibrate these oversampled thermistors to a reasonable level without breaking the bank for a high quality reference. But life is fairly intense right now, so I probably won't get that out the door for another month or so. I will try to put more photos, etc in that.

With regards to the how to, all you have to do is connect an 85k ohm resistor from pin D5 to ground, an run the code example I included in the post. That's all there is to it if you use the pin noise technique. When you call the asyncOversample function, change the readPin to whichever ADC input line you have the Thermistor divider on, and set extraBits to a value of 4, 5, or 6. I did not bother configuring the code for more bits than that, because I really did not see much benefit in the data past 6 bits, and it takes a really long time to capture all those samples. In fact most of the time 256 samples (4bits) looked really good.

If you are using an UNO, I would use the triangular dither method which Qwerty outlines in great detail at the freetronics forum, so I was not going to rehash all that material.

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