Posted on Feb 7, 2014

The goal was to make a compass sensor compatible with the RCX and have it only take one sensor input port to take a compass reading. We decided to use a Dinsmore analog compass part that has two outputs that need to be combined to determine the direction the compass is pointing. With our design, it takes two readings by the RCX to get one complete

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reading from the compass sensor. Software then must combine those readings together to determine the angle the compass is pointing. We had to do it this way because of power demands by the Dinsmore part and power limitations of the RCX. We wanted to add hardware around the Dinsmore sensor to combine the two outputs into one RCX input. We first tried to put all the "inside/outside crossings" logic into hardware, but we found out the hard way that the RCX can only provide about 10mA of current. It turns out we can only power 1/2 the Dinsmore compass sensor at a time. Rick Sammartino (RickSam from the Mindstorms website) who has been helping me all along, had and idea of reading one curve then the other. This fit well with powering one compass sensor then the other. The Dinsmore compass sensor has two outputs that need to be combined to know the direction you are pointing. Figure 1 shows the compass outputs as they look across a 360 degree turn. It took me a while to make sense of the compass sensor outputs. To determine the outputs` values when pointed a particular direction, draw a verticle line at the angle you want the compass to point. The vertical line intersects with the two output curves only once per vertical line. These intersections are the two output values you can expect when the compass is pointing in that direction. As you rotate the compass, you are basically sliding your vertical line left or right on the...

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