XloBorg – compass & accelerometer for the Raspberry Pi

Posted by Mike Redrobe | Posted in Technology | Posted on 20-06-2013

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This week, PiBorg released XLoBorg – a 3 Axis Accelerometer and 3 Axis Magnetometer add-on for the Raspberry Pi

XloBorg Compass and Accelerometer

Since its so new the current software only gives the raw magnetometer x y z values:

mX = +00371, mY = -00053, mZ = +02539

Magnetic flux strength values aren’t much use to us mere humans,
what we really want is a nice easy 0-360 degree heading value.

Maths to the rescue !

We can find the angle from those “lengths” with arc tan Y/X

heading = math.atan2 (mY,mX)
(For simplicity I’m assuming the Pi is level… a more complicated method would include accelerometer data)

Here’s my full python code to read the sensor, and convert to degrees:

#!/usr/bin/env python

# Load the XLoBorg library
import XLoBorg

# Load maths library
import math

# Tell the library to disable diagnostic printouts
XLoBorg.printFunction = XLoBorg.NoPrint

# Start the XLoBorg module (sets up devices)
XLoBorg.Init()

# Read and display the raw magnetometer readings

mx,my,mz = XLoBorg.ReadCompassRaw()

print 'mX = %+06d, mY = %+06d, mZ = %+06d' % XLoBorg.ReadCompassRaw()

# get the heading in radians
heading = math.atan2 (my,mx)

# Correct negative values

if (heading < 0):
heading = heading + (2 * math.pi)

# convert to degrees

heading = heading * 180/math.pi;

print 'Heading: ', heading

Much better:

mX = +00371, mY = -00053, mZ = +02539
Heading: 351 degrees

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