HMC5883L.py

#!/usr/bin/python

import sys
import smbus
import time
import math
import datetime

bus = smbus.SMBus(1)
address = 0x1e

def read_byte(adr):
    return bus.read_byte_data(address, adr)

def read_word(adr):
    high = bus.read_byte_data(address, adr)
    low = bus.read_byte_data(address, adr+1)
    val = (high << 8) + low
    return val

def read_word_2c(adr):
    val = read_word(adr)
    if (val >= 0x8000):
        return -((65535 - val) + 1)
    else:
        return val

def write_byte(adr, value):
    bus.write_byte_data(address, adr, value)

write_byte(0, 0b01110000) # Set to 8 samples @ 15Hz
write_byte(1, 0b00100000) # 1.3 gain LSb / Gauss 1090 (default)
write_byte(2, 0b00000000) # Continuous sampling

scale = 0.92

start = datetime.datetime.now()
end = start+datetime.timedelta(seconds=60)
print start

while True:

	x_out = read_word_2c(3) * scale
	y_out = read_word_2c(7) * scale
	z_out = read_word_2c(5) * scale
	
	bearing  = math.atan2(y_out, x_out) 
	if (bearing < 0):
	    bearing += 2 * math.pi
	
	print "%s,%f"%(datetime.datetime.now()-start,math.degrees(bearing))
	if end-datetime.datetime.now()<datetime.timedelta(seconds=0):
		sys.exit(0)