The Compass

by Web FishJan 6, 2013 @ 02:03pm

Provides information about about momentary vessel orientation with respect to the earth's magnetic field (compass), as well as earth's gravitational field (accelerometer). Basic navigation instrument.

  • Current selection: LSM303DLHC 3D Compass and Accelerometer
  • Status: Finalized

  • Criteria: Sensitivity, standard I/O, small physical footprint, cost 
  • Finalists: Sparkfun HMC6352, Sparkfun LSM303 Breakout Board, Pololu LSM303DLHC 3D Compass and Accelerometer
  • Main decision factors: Cost, standard I2C bus interface

 (click image for larger view) 

Spec highlights:

  • Dimensions: 0.5" × 0.8" × 0.1" (13 × 20 × 3 mm)
  • Weight without header pins: 0.6 g (0.02 oz)
  • Operating voltage: 2.5 to 5.5 V
  • Supply current: 10 mA
  • Sensitivity range (configurable):
    • Accelerometer: ±2, ±4, ±8, or ±16 g
    • Magnetometer: ±1.3, ±1.9, ±2.5, ±4.0, ±4.7, ±5.6, or ±8.1 gauss

 

Caveats:

  • Still unclear how well (if at all) the tilt compensation will work in a constant motion (sea waves) environment;
  • Unclear whether we'll be able to use built-in accelerometer to determine vessel orientation up/down (current flip status) - again, due to constant acceleration changes from riding surface waves;