This project is an underwater logger that can be build at a very low cost (<20€ per unit) with widely available materials and resources. In many of our projects with schools we focus on the marine environment. We believe that to monitor certain parameters of surface waters can be very beneficial to learn and understand about this captivating setting.

Logger in action

In the following – an educational project is introduced which is fully scalable and interdisciplinary. It can be as complex or as simple as you want it to be, for your educational need. The following can be found bellow:

  • PCB files (gerber files) to get your pcb made (on github)
  • Complete source code for the underwater logger (on github).
  • Instructions/hints on how to build the housing.
  • How to proceed for post-processing (aka how to convert raw data in a pretty graphic).

If anything remains unclear – feel free to contact us. Furthermore we are happy to hear about any builds, suggestions, possible improvements etc.

Actual logger (without batteries)

Technical information and features:

  • the logger is based on the Atmega8 microcontroller
  • powered with 4 AAA batteries
  • the here presented design accommodates for temperature and light-intensity measurements
  • in total two i2c sensors can be connected and three analog sensors
  • two buttons can be used to interface with the logger
  • the data is saved on a microSD card for easy access
  • the housing was successfully tested in up to 30m of water depth (but deeper deployments most certainly will work) and will be tested in the future
To be soldered PCBs

Housing

In the following the simple but functional design of the housing is explained. A PVC tube (containing the logger) is closed of with two methacrylate disks. The sealing is performed with rubber o-rings found in the plumbing section of your home improvement retailer. The disks are tightened with four threaded, inox rods. Choosing transparent methacrylate is important to permit the light-intensity sensor to work.

Materials needed:

  • PVC tube 50mm outer diameter
  • 4x threaded inox rods M6, each about 160mm long
  • 8x M6 nuts
  • two rubber seals 35mm/70mm (inner/outer) diameter
  • two methacrylate disks fabricated according to plan shown bellow
Readily assembled housing for logger

Dimensions for cover disks from methacrylate

Instructions Housing

There a few things to have in mind when making the housing.

  • make sure the seat of the PVC pipe is thoroughly treated with fine sand paper. This will later determine how well the seal works.
  • when tightening: go around in a circle. And don’t exaggerate force to avoid damaging the methacrylate cover

Post Processing with “R”

Once you retrieved the logger you still have to convert the collected data points to something useful. To facilitate this process a simple “R” script is provided in the resources. All you have to do is get the LOG.TXT file from the sd card, point the R script to it and run the script with the start date/time and end date/time (like shown bellow).

Screenshot from R-studio. Enter dates and times in order to align the gathered data points
Example resulting plot from the R script

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