Evaluation of a 3D Motion Sensor including Accelerometer and Geomagnetic sensor

This paper presents a development of a 3D motion sensor which detects inertial movements and earth's magnetic fields for a compass heading. It consists of a 3-axis accelerometer, a 2-axis geomagnetic sensor, and a microcontroller. An automatic calibration and measurement system is developed to reduce test lead time. For the geomagnetic sensor part, an accuracy of ±5 degrees, a resolution of ±1 degrees, and a linearity of ±1% in full scale range have been achieved. The accelerometer has a full measurement range of ±2 . Both sensitivity of 819 count/ with a 12-bit analog-to-digital converter and a linearity of ±0.5% in full scale have been achieved. While driving voltage can operate between 2.7 and 3.3 V, current consumption is 3.2 mA at 2.8 V. Thorough reliability test is performed and the σ level of geomagnetic sensor heading accuracy is 5.6σ, and that of accelerometer sensitivities are 4.6σ, 5.6σ, and 4.5σ for x , y , and z axis respectively. Pedometer software is tested and showed 85% of step count accuracy. The dimension of a packaged chip is 8.3 mm × 5.3 mm × 1.5 mm.