About this Project

The hydrometric pendulum idea works equally well in a "float&anchor" configuration, allowing open water deployments.

The hydrometric pendulum idea also works in a “float & anchor” configuration: allowing us to  deploy them in open water environments.

Early in 2011 I realized that open source microcontroller boards had the potential to replace expensive commercial sensor units with cheap & cheerful DIY equivalents. In January 2014, I started this blog to record my first attempt to build a simple flow sensor using an Arduino. The project has grown quite a bit since then, and my current goal is to create a generic underwater  logging platform which can be adapted for many different environmental  monitoring  applications.

This ‘lowest common denominator’ approach means that any component in the build (including the Arduino) can be changed to suit the available parts without requiring a significant re-write of the operating code.  My performance benchmark is at least one full year of operation on three AA batteries, and with that system as a foundation, I will build instruments that focus on a theme of water because of it’s crucial role sustaining us, and connecting everything we do to the natural world.

The current logger base unit. Many different sensors can be attached.

A three component logger forms the base unit, and the modules can be rearranged to fit into different housing shapes.

Anyone can learn to build something like this from scratch, and I hope that this blog is a useful contribution to the Makers movement; engaging people with environmental  issues and giving them a chance to actively participate as citizen scientists.  So if you want to start a project of your own, you can go straight to the How to build a Datalogger page, or you can browse through my ongoing adventures from the place where it all startedThere have been many successes & many failures along the way, and I still learn something new every day…

– Ed


31 Responses to About this Project

  1. Grace Cagle says:

    Wow, I’m so happy to have come across this page. Thank you for your diligent documentation! I can’t wait to see how I can use this information. I especially enjoyed your writing on the inception of the project.

  2. cpadi says:

    Your blog is an outstanding source of technical information, ideas and links… Thanks for sharing!

  3. Dan Cross says:

    Wow, I can’t tell you how much I’ve been enjoying this blog. As a relatively recent “Maker” (and ham radio nerd) things like this have been extremely inspiring! Thanks for it and keep it up.

  4. Great blog. Motivated me to buy an Arduino and begin prototyping a pressure sensor for monitoring cave stream water depths. Curious: What temperature sensor would you recommend given your experiences? Thanks.

    • edmallon says:

      To date I have been working with I2C breakouts (Sparkfuns tmp102 & Adafruits MCP9808) and one-wire DS18b20’s. All give you 0.0625C resolution but the MCP9808 gives a reasonably decent ±0.25 accuracy. The DS18s take quite a bit of calibration because there is a large amount of quality variation, but they have the strength that you can hook so many of them to very long wires. This multi-drop aspect of the DS18B20’s keeps bringing me back to that sensor over and over again. To be honest, all of them are ‘just OK’ as most of the caves we work in have less than 1 degree Celsius of variation all year. But what I really want for the cave work is an affordable sensor that can give me ±0.1C accuracy and 0.01C resolution. RTDs and Thermistors can deliver that but I have not had a chance to play with them yet.

      [Update] In 2017 I got the thermistors working at high resolution with better than ±0.2C accuracy .

  5. jesadaph says:

    Thank You for Sharing Your Knowledge. Great blog , I’m never seen before.

  6. Christophe C. says:

    Thanks for your blog and sharing information. I’ll come back on it to search for Arduino information, power consumption reduction, sensors selection and epoxy pouring. For now, you just took 2 hours of my work day .. pfff.

  7. Mark Woods says:

    Great work!

  8. Jimmys says:

    Thank you! You are a big source of inspiration even to hardened engineers. The reading of the articles is a joy and also I learned a great deal for sensors calibration and what not. Also the density of information you provide is fantastic I truly consider this blog a Arduino university. If you need to deploy to Crete, I will be GLAD to help. Over a hundred caves in the island are waiting.

  9. koitoliver says:

    Thank you for this inspiring blog. Do you happen to have any experience on coupling the pro mini with ultrasonic sensor to log stage height?

  10. Luis Skinner says:

    Hi Ed ! It is a very nice and impressive work you did ! And the amount and quality of environmental data is amazing.

    I’m Marine Biologist in Brazil and I am trying to develop one similar project to monitor both, intertidal rocky shore temperatures and some water variables like salinity, light, currents and others.

    My first step is to build a cable, using arduino and 12 DS18B20 sensors. I really appreciate if you could support me in this.

    Best regards,

    Luis

  11. Paul Wood says:

    We are looking at doing a data logger project for river monitoring. I just want to say this is an extremely well done blog that, through your generosity, will save us countless hours going down unnecessary rabbit holes in building a submersible pressure gauge. Thanks!

  12. Herve says:

    Hi,
    I just want to say “thanks” for writting this blog. it is really interesting and fun to read.
    I like a lot your style and it very great to see real life arduino projects … and a very usefull project !
    Thanks for sharing.

    About the ATMEGA328p 10 bits ADC limititation … you can perhaps have a look on “MassDuino Nano” based on MD-328D MCU with 16 bit ADC (available with or without onboard usb to serial)

    • edmallon says:

      Always interested in hearing about a new board, but when I checked the MD-328D data sheet, the specs say only a 12-bit ADC. Although there are commands for things like analogRead_16bits() they capture only 125 sps. The slow sampling rate makes me highly suspicious that they are simply doing oversampling in software with the chips internal noise to provide dither. Since it is easy to do that with the 328P based boards to achieve higher ADC resolution, I would have to find another reason to try out the MassDuino.

  13. Hey Ed,
    I’m building an underwater ambient light and temperature monitor for use on coral reefs and heavily relying on some of your housing construction tips. I know you’ve experimented with the DS18B20 waterproof thermometers for your temperature chain, but you replace their original cables. What have you found to be the most cost-efficient, corrosion and water resistant cable for long-term deployments? I’ll have cable lengths from 2 – 5 m, and will need the jackets to hold up in salt water for 6+ months. Any suggestions on a specific jacketed, 3+ core wire for this application?

    • edmallon says:

      I have yet to hunt down a good cable supplier for long rolls. For now I’m using silicone jacket M12C-SIL-4-R-F-15 cable from Omega.com for shallow work, but I have only recently started testing it past 20m, and those units are still out on deployment so I don’t know if they will survive. For deeper sites I would recommend the tougher M12C-PUR-4-R-F-15, but it’s stiff, and coils enough to be annoying compared to the beautifully supple silicone cables under water. Both jacket types easily handle salt water, but at 300′, your biggest problem is compression of the cable jacket causing the cable to tear away from the epoxy that you potted the end connector in. It’s possible that cable glands would handle this better by pre-compressing the jackets, and I would look at the ones used by diving light suppliers or other high-end temp chain vendors.

      • Austin Greene says:

        Gotcha, thanks for the link. As a new PhD student I’m looking to do this on a budget, so the silicone and polyurethane might be a bit out of pocket at the moment. Have you tested or considered a rubber-jacket SOOW or SJOOW service cable? The SOOW seems listed as waterproof, yet for some reason the SJOOW isn’t usually (despite still being labeled as waterproof via the second “O” in the name. An 18/3 cable is only about $0.50/ft so its budget friendly – if perhaps a bit big. Most are EPDM jacketed, same as our O-Rings so I’d think they’d be ok. Thoughts?

      • edmallon says:

        I looked at service cables, but they are just way too thick for our work. Remember that most sensors barely draw 10-20mA. Also the PUR jacketed cable from omega is still cheaper on a per foot basis, and it’s really robust.

      • Austin Greene says:

        Gotcha, I’ll give the PUR cable another look. From what I saw the webpage didn’t offer an option without the connector, making it about $1 / ft at the cheapest for 10m after shipping. It would be great to get it without the connector, I’ll call them.

        I can’t seem to find much on this and am a novice, but is there a reason why having low currents over a big cable (16 awg) would be a problem if its for short distances?

      • edmallon says:

        No problem at all with the current, but as a general principle, I find that moving to smaller, lighter parts makes most aspects of building things easier when they are appropriate. For example, I almost always use tiny 1/8 watt resistors now, because they let me fit things into tight places more easily. But for your first prototypes I wouldn’t worry about it; just getting the darned thing working is an accomplishment!

  14. Greg K. says:

    Edward, great and inspiring work!
    I built data loggers for my PhD based on your work and I was wondering how i may cite you or the Cave Pearl Project? Have you published these designs?
    Regards
    Greg

  15. Greg K. says:

    No rush, I’m probably gonna defend next year so I guess your paper will be out by then. I will check the presentations anyway. Thanks again for the everything!

    G.

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