Cave water level logger

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The aim of this project is to help scientists to understand the nature of chaotic water level changes in Ozerna cave (Ternopilska oblast, Ukraine). Traditionally scientists were using stationary rullers in different parts of the cave to collect data about water level dynamics, but the readings in some parts of the cave can be made only a couple of times a year due to significant difficulties of getting there. So I decided to make an electronic data-logger.



Main requirements:

  • Water level range 0-10m
  • Accuracy - 1 cm
  • Autonomous work time - 180 days (at least)
  • Ability to retrieve data from logger within the cave
  • There are virtually only two types of sensor that can be used (excluding expensive TOF optical sensors) - ultrasound and barometric

Ultrasound sensors were tested, but accuracy was poor, and the large water surface was needed for stable work.

The main problem with barometric sensors is that one sensor is not enough to measure water level. Second sensor is needed to compensate atmospheric pressure fluctuations

There is a similar to my project - The Cave Pearl Project. I've asked them a couple of questions, and Edward Mallon kindly gave me some advices about using barometric pressure sensors under water. I've decided, that MS5803-05BA sensor fits my requirements the most.

The device consists of main and underwater units connected with 20m cable. The main unit is built around STM32L152RD microcontroller. It has microSD card slot and batteries inside. Underwater unit consists of sensor, STM8S003 MCU and differential pair driver. It is hermetically encapsulated with thermal glue.

Current state of the project

  • Logger was installed in cave. Now we have to wait next expedition (in March 2016) to check results.
  • Data was fetched from device in sep. 2015 - measured water level corresponds to ruller data very well! Planning new experiments.