Pro Mini Datalogger - Basic Starter Sketch

A simple data logger script for our 2019 & 2020 'Classroom Logger' tutorials. This code is hopefully simple enough that anyone can read through it and understand what is happening from the comments. The idea is to provide low power sleep & RTC alarm wakeup functionality as a starting point for student projects.

With minor tweaks this script should run on all of the Pro-Mini based "Modules & Jumper Wires" loggers described in the Sensors paper: http://www.mdpi.com/1424-8220/18/2/530, though the current iteration reads the rail with an internal bandgap trick to support the 'unregulated' 2020 classroom logger update @
https://thecavepearlproject.org/2020/10/22/pro-mini-classroom-datalogger-2020-update/

In general you only have to do four things to add a new sensor to this logger base code:

Download and #include the library that drives your sensor. This is usually provided by the sensor vendor (Adafruit, Sparkfun, etc) but there a plenty of other sources if you google it. Note that there are often many other sensor library options here on GitHub if you search for them.
Connect your sensor as appropriate. I2C sensors are the easiest ones to work with, and should be connected in parallel with the RTC module (which is also an I2C device) The easiest way to do this is via the four-pin cascade port on the RTC and that module also provides 4K7 pullups for the bus.
Add commands to take a reading from that sensor and store it into a variable at the beginning of the main loop. This is usually means adding something like: int YourSensorVariable = libObject.readSensorCommand(); to call the sensor support functions provided by the library.
In the middle of the code where the data is written to the SD card add two more lines:

file.print(YourSensorVariable); // add this to the series of print statements between file.open & file.close();

file.print(","); //add a comma to separate data varaibles (the last entry should use .println instead of .print)

The code saves ascii characters to the SD card as CSV text. This script automatically creates a new sequentially numbered data file on the SD card at startup. To retrive your data, unplug the battery, and then exchange the SD card with a new one. Import the CSV files into any spreadsheet like Excel, Google sheets, or Open Office.

You will find an introduction to the different types of sensors that you can use with the logger at:

Arduino Tutorial: Adding Sensors to Your Data Logger (though it's worth noting that guide referneces an older code base) https://thecavepearlproject.org/2017/12/17/adding-sensors-to-an-arduino-data-logger/

Also note: that I have a directory of little utility scripts that come in very handy when testing your Arduino based data loggers at: https://github.com/EKMallon/Utilities

For a sense of what you can do with the classroom logger, heres a post about creating a custom ‘Leaf Transmittance Index’ based on readings from an IR LED and the red channel of the RGB indicator already on the logger: https://thecavepearlproject.org/2019/08/30/creating-a-normalized-vegetation-index-sensor-with-two-leds/ Although using generic LED’s introduces non-optimal aspects wrt frequency & bandwidth, the trial successfully distinguished ‘healthy’ vs ‘unhealthy’ plant leaves where a simple visual inspection could not. Creating a pseudo NDVI with transmittance rather than reflectance bends the rules a bit: but keep in mind this was meant from the start to be a conceptual proof of concept, rather than a rigorous analytical tool. From a teaching point of view, students would have to create "custom calibrations" for their one-of-a-kind LED combination & for each plant species they work on - but that's actually a useful exercise in and of itself. This fun little hack has legs in that educational context, and it wouldn't take much to tune the idea to a more specific application with better LED selection.

EKMallon/3-Part-ProMiniLogger-StarterSketch_2020

Pro Mini Datalogger - Basic Starter Sketch