dCompass
The Dexter Industries dCompass is a compass sensor for LEGO MINDSTORMS NXT. This compact sensor detects magnetic fields for navigation. Using a magnetic sensor, the sensor is able to measure the earth's magnetic field and returns a magnetic heading, telling you which way your robot is heading. The device can be used without calibration and can be calibrated with software to account for magnetic fields to deliver a highly accurate compass heading. The sensor is supported in NXT-G, Labview, and RobotC. The sensor communicates with the NXT via I2C and can be placed on any port.