Hi, I posted a few weeks ago regarding a Vector 2XG electronic compass which
is now working fine, thanks all. I'm now working on parsing some NMEA
sentences from a GPS receiver and comparing the results with the heading
from the compass. I want the PIC to decide if it has to turn left or right
to match the GPS's waypoint data and the compass data. I came up with the
following logical tests to determine the shortest path to the desired
heading :

A = current angle (compass heading)
B = desired angle (GPS waypoint heading)

if A < B then
    if ABS(A-B) > 180 then TURN COUNTER CLOCK-WISE else TURN CLOCK-WISE
else
if A > B then
    if ABS(A-B) < 180 then TURN COUNTER CLOCK-WISE else TURN CLOCK-WISE
else
    NO CORRECTION;

This works fine in a little Windows App I made and I think I could port it
to PIC assembly fairly easily or program it directly in C. However, I feel
it will take a lot of program memory to directly translate every conditional
and math operator (the values are 16 bits wide since there are 360 degrees)
to the PIC. Any suggestions on how to simplify this procedure in PIC
assembly? There must be a simple combination of binary operations that will
give the same result ?!?!?


Thanks,


---------------------------------------------------------------
Tobie Horswill
 Ex Machina
103, rue Dalhousie
Quibec (Quibec) CAN
G1K 4B9
thorswil@exmachina.qc.ca

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