Other solutions:

My questions about digital compass:

1) Is it possible to use a second gps by bluetooth? The n900 could calculate the direction by difference. (I know that gps is not very exact. But perhaps both bluetooth receivers do the same mistake. So the direction could be correct.)

2) Perhaps the same thing is possible with the gps of the n900 only: you fix a location with gps first (by pressing some button) then you move the the n900 to another place and the n900 calculates the direction by difference.

3) Wintec wsg 1000 http://www.wintec-gps.de/wintec_wsg-1000.php
This external bluetooth gps-receiver has also a compass and other features.
There are even linux development tools for cp2101
http://forum.pocketnavigation.de/for...000-usb-linux/

http://forum.pocketnavigation.de/for...x/#post2209994