The Cave Pearl Project

With their efficient construction, we have more or less standardized on the new 2" housings for the in-cave flow sensors, and we are working with other research groups to redeploy the older 3" models as they get rotated out of the long term sites:

Field Report 2015-12-11: Flow Sensors go Farther & Deeper

Many of these new sites are in the open ocean, and are much higher risk for loss than we could have tolerated when we only had a few loggers to play with. But as a builder, I'm loving the challenges presented by the harsh environment. Forces me to up my game...

Now that the loggers have reached the point where they deliver reliable underwater operation, I am realizing that was only half the battle:

Field Report 2015-12-10: Precision vs Accuracy vs Drift

So I was wondering if anyone here has already tried oversampling IC temperature sensors? Can you really trade power (by taking more samples and averaging them) for more decimal places? And, yes, I realize that has nothing to do with accuracy...

Happy to report that the funnel & cowling turned my cave drip sensors into fairly robust logging rain gauges:

Field Report 2015-12-08: Rain Gauge Success at Rio Secreto

There are still a few design issues to work out regarding things like wind induced false positives, and spiders attempting to block the spouts, but overall the units have delivered great data that agrees with other local records.

These inexpensive units will become a vital part of the monitoring network as it grows.

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 reasonably accurate when compared to 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.

This time round we had a good chunk of data to present at the Geological Society of America conference, and I think that moved the project into something that generated real interest in the academic community. We still had allot of the old guard commenting that grant writing would always be a better use of their time than hardware development (and for them that's probably true...) But there was allot of interest from younger researchers, and I think that's really where creative new approaches to environmental monitoring will be developed with open source hardware.

It's been on my todo list for ages, but I finally got around to posting the 'How to build it' tutorial for the basic 3 component logger:

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)

Hope that helps a few of the people who were interested.

We added large surface area flags to enhance the response of the flow sensing units in caves were the water was flowing slower than 1 cm/s. But like most of my rough & ready DIY solutions, turning the boosted sensors output into something quantitative is a challenge.

In the process of figuring that out I bumped into an equation solver called Eureqa which offers a way to characterize empirical relationships like this in mathematical terms. It's also kind of fun to use (even for a non-mathematical person like me) as you can tweak it in so many ways. Although my application was fairly trivial, I suspect that the program could be very useful to other projects listed here.

One element of diving safety is having a day at the surface before you actually fly back home. So we saved the re-deployment of the Akumal Bay sensors to the end of our trip. Though it's probably not very exciting, finding a good way to clean loggers that have been in the ocean for long periods actually turns out to be important. If I could figure out how to keep the transmission windows clear of bio-growth (for months at a time), I would already have light level loggers on that reef.

A fresh batch of loggers was installed at Rio Secreto, including two of the new Masons hygrometers. Three of the new drip sensor builds are using Moteino Megas rather than my usual 328p based boards, and I am quite keen to see how they perform in the real world. Though none of my loggers use wireless communication yet, I have a few ideas where that might be useful.

We've had great success with the DS18b20 Temperature Strings that we deployed back in March. With all those joins, these are easily the most complicated build I've ever put under water. And with the parts cost running to about $100 for these 20 sensor units, they are more affordable than a set of low-end Thermochrons. Woot!