The Cave Pearl Project was founded by two people who are passionate about understanding caves and protecting karst aquifers. They are Edward Mallon and Patricia Beddows. The two have developed a data logging platform from inexpensive pre-made breakout boards, and are using this at the heart of new environmental sensors that anyone can build.
Currently more than 100 of these Arduino based loggers are installed at several well-instrumented field sites, in 4 countries. This monitoring network includes everything from surface weather stations to underground drip monitors & micro-climate recorders. Water level and flow sensors are installed in caves, at coastal outflows, and at locations on the reef. Bore-hole pressure loggers and multi-probe temperature profilers have recently been added to the equipment lineup, and new sensor combinations are in development.
In early 2011, it became clear that open-source micro controllers had the potential to replace expensive commercial sensor units with cheap & cheerful DIY equivalents -provided someone was willing to dedicate the time. The module-based DIY assembly provides learning opportunities for beginner students that are hard to replicate with commercial products: they learn far more by “making it work” despite the obvious limitations of the cheap hardware.
In January 2014, they started a small blog recording the development of a simple water flow sensor using the Arduino platform. The project has grown since then, and those crude early attempts have been refined into a generic data logging platform which can be configured for many different environmental monitoring applications.
Check out their 2 articles regarding Diodes. These are academic projects. Several of the techniques they have developed are expressly designed to give the students solid calibration exercises, rather than using the more typical methods / interchangeable parts one would choose in production environments.
Single Diode Temperature Sensor with Arduino ICU (& reverse-bias leakage)
Creating a Normalized Vegetation Index Sensor with two LEDs