Public Lab Research note

This is an attempt to replicate an activity.

Mini Pearl Logger Replication

by zengirl2 | September 01, 2017 22:25 01 Sep 22:25 | #14818 | #14818

The manual by @cfastie does a good job at explaining the basics of the datalogger. I used the simpler setup since mine was done on a breadboard at the Barn Raising event. Because there are many wires, I actually think this project is best if you just go straight to soldering, especially since two pins in the Arduino are near the center of the board and make them less trustworthy for breadboarding unless you add header pins to them as well. The system works great and I was able to get a read on the built-in temperature sensor both on the serial monitor as well as the SD card. I also fanned the unit to show a change in temperature. Here are my only additions for info:

  • Be sure to select the "ATmega 328(3.3v,8MHz)" from Tools menu
  • double check the Adafruit library for by compiling your code first before uploading. It wouldn't compile for me, but when I used the original RTClib listed for the Cave Pearl logger it worked fine. @cfastie believes he is using Adafruit's version and they both have the same exact name. So, please do post the library you end up using.

This was a fun build and it's great to see how small the SD card module is.


Wow, super!!!

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Leslie, it's really good you got this working. Thanks for troubleshooting the RTC library. It looks like the library I have been using is the MrAlvin version -- the same one that worked for you. I might have followed the same route to that library as you did, although I don't recall doing it (any memories of it are lost in the swirl of troubleshooting everything else last spring). I did not reconfirm that the Adafruit RTC library does not work, but at least we know one that does work. I changed the sketch to point to the MrAlvin library.

That's a good tip to check the settings under tools. This is what it should look like most of the time when using the Mini Pearl Logger (the COM port might differ on your computer):


The sketch that I load onto the Pro Mini for each kit should produce output to the serial monitor like this (your baud rate might differ):


And a file should be created (or appended to) on the microSD card that looks like this:


From your photo it appears that you have the new tiny microSD board that works only at 3.3v (the previous board also worked at 5v so it had voltage regulator/shifter that used a lot of power). This board is standard in the Mini Pearl Logger Kit now.

It also appears that I removed some resistors from the microSD board to reduce power consumption. That was not done to the Pro Mini (or the red LED would not be lit). I don't know if it was done to the RTC. So there are some modifications to do if your goal was to increase longevity on battery power.

Another thing to do to increase longevity is to switch to a smaller microSD card. The kit now includes a 128MB card instead of a 4GB card. The smaller cards sleep better (and/or faster) and noticeably lower the sleep current. It doesn't seem like a very good deal to get an SD card that is so much smaller, but by my calculations, a 128MB card will hold the data from 3.5 million data-logging events. That means you could log data every 10 seconds for a year.

It's good to see an official "Replication." Because that tag is included on your research note, I think your note should be listed on the note you replicated. Your note is not listed, although the list suggests that there is one replication, somewhere. Maybe @warren knows why that is.



Thanks again for getting the logger working.


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@cfastie thanks for pointing out that I used the new small SD card module. Your comments about energy savings are also very helpful. Fascinating that the card size affects power usage as well. There is always so much to learn from you!

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@cfastie here's the link to the known bug currently affecting the display of replications on the original activity:

Thanks for pointing out that this is still an issue!

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