The Cave Pearl Project

I've been noodling around with an ADS1115 differential ADC, piping the output into to the serial plotter tool in the Arduino IDE:

Using the Arduino UNO as a basic Data Acquisition system

I know you can get things like the DI-145 for $30, and that any good scope (actually any bad scope) would put this thing to shame, but the thing is, it was just fun to play with because the auto-scaling y-axis meant that you always saw something on the output.

That's worth a heck of allot if you are trying to motivate people in a classroom environment.

It's been ages since I posted, and I've been taking my first serious look at using analog sensors with an Arduino. I thought thermistors would be easy enough....

Better Thermistor Reading with an Arduino: Series Resistors & Aref

And they are...sort of...until you start trying to power them from a digital pin (which was a mistake) or speeding up the ADC, or simply using cheap eBay crap like I usually do...

Anyway, I'm finally getting the hang of it, and if I can weave enough tests into the schedule to sort out the last few details, I promise the next post will be interesting...

A report card of sorts on the first four temp chains.

Field Report 2016-03-27: Progress on the DS18B20 Temp.Strings

With the pre-epoxy calibration time for each sensor, and each 12 node segment taking about a day to assemble, these represent the largest investment a single instrument for the project. In return for that we get a ton of data.

I have been building them with cheap eBay DS18's (~ $1.75 each) which have about a 30% DOA rate, so I'm surprised that none of the actual sensors failed during those deployments.

I've been working towards bringing our entire network of flow sensors to the 'standard' builds, & sensors but that means that there are always a few 'stragglers' from the the early generations to deal with that use different sensors, or have different internal configurations. Instead of retiring them, we simply move them out to more unusual deployments:

Field Report 2016-03-25: Monitoring in Coastal Mangroves

These units ended up being deployed upside down, as the salt->fresh water transition and the internal battery position changed the buoyancy enough that they did not float properly in their normal orientation. I should be able to sort the signs in post, provided that the units are still there a few months from now. The flat end surface is probably going to give us allot more bluff body vortex shedding in these high velocity flows....

Just back from a fieldwork trip, and another of our temperature sensors has failed to go the distance in the underwater environment:

Field Report 2016-03-17: MCP9808 Fails Under Pressure

I've retired that generation of sensor caps and will likely go back to the waterproof DS18b's, some which have been running under water for more than two years now. (inside a stainless steel sheath)

After working my way through batch normalization, and giving Ice & Steam point calibration a shot, I finally bit the bullet and laid down $200 for a Reference Thermapen ( accuracy ±0.04°C) which paid for itself with a huge reduction in the amount of time it takes to do the job:

DS18B20 Calibration: We finally nailed it!

All-in the current system set me back about $300 including the T-pen, drill bits that cost more than the aluminum, and a clunky old water bath that was only $25 on eBay since its front display is off by about 5 degrees. To be honest you could skip that last bit and just use some warm water in a bucket to generate those cooling curves.

Sensor failures almost always show up as a hit on the battery discharge curve, but there are plenty of other things that show up on the graph for loggers that are still working: Another look at battery discharge curves...

I will add more of these plots to the post as I come across them, since I haven't found many other sources discussing these sorts of 'non lethal' performance issues.

Another great trip, though we both felt pretty ragged by the end:

Field Report 2015-12-20: Winding Down…

My fingers are crossed for the new DS18b20 strings that we deployed and I am just now digging into all that fresh data. Determining if the Masons Hygrometer actually worked will be challenging, because the standard humidiy sensors just went to 100% for the duration, which I know is false from the literature published by groups with vastly more money for professional kit.

We now have four DS18b20 sensor string prototypes in the wild:

Field Report 2015-12-15: New DS18B20 Sensor Chains Installed

We are getting pretty good data from them, but I dearly wish there was one more bit of resolution on those sensors. If anyone knows a trick to accomplish that, I'm all ears...

With the Christmas tourist season bearing down on us, I decided not to do the usual round of RTC resets:

Re-install the Drip Monitoring Network

We have these units scheduled for rotation some time in mid 2016, and that will give me the ability to do a nine month drift check on the cheap eBay DS3231 RTC's we have been using. Dispite dire warnings about them in the forums, we have had far fewer problems with them than I was expecting. Basically if a board has not been ruined by the dodgy soldering that you commonly see, the chip itself seems to operate within spec.