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CAVE INSTRUMENTATION: MAPPING UNIT


Author: Jose Ojeda

Introduction


Traditionally, caves have been mapped by the use of compass, tape and inclinometer.

We want to replace these by:

  • Electronic compass and inclinometer
  • Laser distance meter
  • Storing data by electronic means

The wanted specifications were:

  • 0.1 degree resolution in compass direction.
  • 0.1 degree resolution in tilt plane (inclination).
  • Able to measure up to almost 90 degree inclination.
  • Distance measurement resolution of cm and range up to 100m.
  • Unit should be samll and able to withstand high humidity, best waterproof.
  • Price should be kept low.

We started doing internet search looking for equipment matching these requirements. There were equipment able to do compass direction, inclination and range measurement, but they were usually too bulky and too expensive for us. Price was from US$ 20 000 and upwards. These are often equipment used for construction work, and Leica Geosystem is a major provider.

CaveMapper parts


Due to low price criteria it was obvious that we had to use of-the-shelf components, and our job were to find a low power computer that could control and read data from the different sensors. The data should then be stored on non-volatile memory.

After some investigation we ended up with the following components.

  • We chose a combined electronic compass and inclinometer from True North Technology, the Revolution 2X (see reference). It had a 0.1 degree resolution in compass and inclination. The inclination range was only +/- 40 degrees and did not fullfill our initial specs, but we were not able to find any with such a high range within our budget.
  • For the distance meter we chose a laser product from Dimitix, which actually is a rebuilt Leica Disto, but more ruggeddized and can be operated using serial communications. This unit can measure with mm accuracy up to almost 100m. The range depends on ambient light. In daylight maximal range is lower.
  • A AtomBasic Pro 28-M was used as the computer integrating all the sensors. It is a small and low power microcontroller. It has 2 hardware serial ports (with data buffer), and you can setup up several software serial ports (without data buffer). So decisive moments were many serial ports, some prior experience, and a nice Basic development environment (MBasic).
  • uMMC a MMC memory card unit is used to store the data. The microcontroller communicated with the uMMC via serial communication. The user controls the unit with two push buttons together with the LCD display.

Development


Started with building a board for the Basic Atom Pro 28-M microcontroller. It has an integrated circuit for TTL to RS-232 level conversion and reverse. Power management, shuting down if battery goes under a certain voltage.

The BasicAtom Pro hidden under all the cables to LCD display, mmc card unit and sensors
Figure 2. The BasicAtom Pro hidden under all the cables to the LCD display, mmc card unit, and sensors. Dimitix is the grey unit on the left side, and the Revolution is the black unit to the right of the power supply.

The version 7.2 of the Atom Pro development environment was used. The newer beta version 8.0 had errors and did not compile the code.

Documentation


Reference


Compass, inclinometer

Laser distance meter with data output

Small computer for control and data storage. Using the BasicAtomPro microcontroller for controlling all the sensors and storing the data.

Waterproof case

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Page last modified on September 30, 2011, at 09:43 AM
Electronics workshop
Department of Earth Science - University of Bergen
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