The Cave Pearl Project

I finally put together the prequel – months after the I2C registers tutorial was released... but hey if Hollywood can do it....

Adding Sensors to an Arduino Data Logger

This adds to the set for beginners that I’ve been working on for my teacher friends. There are so many different kinds of sensors, that there is necessarily a lot missing from that post (like async serial..). So Adding Sensors (part 2) will follow in the new year when I can grab the time.

I know it's been ages since I posted, but I've been working on a complete overhaul of the code-base for our data loggers. In the process of untangling all that spagetti, I standardized the I2C sensor functions and posted a little tutorial about it on the project blog:

https://edwardmallon.wordpress.com/2017/11/03/configuring-i2c-sensors-with-arduino/

Even when I grab an off-the-shelf library for something, there are usually a few registers that I have to set before a sensor runs in a mode appropriate for environmental monitoring. 

While breadboard loggers are quick, the connections tend to be a bit too fragile for serious testing. So I've come up with a configuration based on a screw-terminal expansion board that breaks out all the pins nicely:

Arduino Data Logger: 2017 Build Update

As a bonus, I've also described modifications that bring this 4-part logger below 0.02 mA sleep current. Current assembly time for the basic unit is under one hour.

I saved SD power control to the end of my quest for low power logging, because I was worried about the potential weirdness that could arise with the Arduino libraries. But after a reasonably thorough round of tests it does seem to be working OK with a BJT switching the ground line.

Switching off SD cards for Low Power Data Logging

This brings these penny-part loggers into multi year territory on 3xAAs.

I'm slowly learning my way through the lmitations of the Arduino platform, and I recently stumbled into the issues with cheap regulators & bandgap references

Calibrating Oversampled Thermistors

I'm sure I will be kicking the "resolution vs accuracy" can around the block a few more time before this project is done.

I could never find many decent explanations of how to do oversampling with an Arduino, and it has been bugging me for a while as the technique seemed like such a good idea.

So I decided to do something about it:

Enhancing Arduino ADC resolution with Dithering & Oversampling

Now before the old hands pat me on the head, saying "That's nice dear..." I just want to mention that it took more test runs than I even want to think about to get this stuff sorted out. So if that information was all lying around somewhere the whole time, and I just missed it... don't tell me about it... I don't think I could handle the news :-)

We just fired up a new collaborative project, and some of the academics from the other university suggested that the 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 brings together all the latest version info:

☀ How to Build an Arduino Data Logger ☀

There's probably nothing new there for this crowd, but 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.

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 doing underwater projects.

Cheers!

I haven't had a whole lot of spare time for updates lately, but I did manage a short year in review post over the holidays:

2016 Cave Pearl Project ‘Year in Review’

I generally avoid waxing philosophical on the project blog, but once in a while it kinda just leaks out...

After watching people build loggers based on the plans I released last year, I realized that simply learning to solder was the biggest challenge they faced. So I reconfigured the basic logger design to use crimped jumpers: 2016 ProMini Build Update

The changes bring the platform in under $10, and reduce the assembly time below 2 hours (for me). The students still need about 6 hours to assemble a platform from scratch, but I figure that is pretty good for folks with no experience.

So it turns out that you can put I2C sensors on the end of some very long cables:

Field Report 2016-07-09

This opens up some interesting environmental monitoring possibilities. Much as I love the long runs I get with DS18B's, there aren't many other sensors in the one-wire world. But if I eventually get I2C out to 50m, then my problems would be solved...