Use IMUs for precise location data when GPS won’t suffice
Figure 3: Digilent’s 410-326 9-axis IMU/barometer uses an STMicroelectronics’ LSM9DS1 iNEMU IMU that combines a 3D accelerometer, a 3D gyroscope, and a 3D magnetometer into one package. (Image source: Digilent)
Thales Visionix's NavChip Precision 6-axis MEMS IMU is derived from military technology, performing positional data acquisition and processing at a 1 kHz rate. It then processes and integrates the data down to a 200 Hz (or lower) user selectable rate. It also performs compensation using factory calibration and embedded temperature sensors to correct the other sensors’ biases, scale factors, and misalignments. The specifications for its accelerometer and magnetometer are: ■ Accelerometer: Full-scale angular rate of 2000°/s ■ Magnetometer: Full-scale acceleration of ±16g
The NavChip module has both a TTL UART and an SPI port, and it has a 1 pulse/second input for synchronization with a GPS module. It’s available in the V14447-03-02 RS-422 evaluation kit for easier prototyping. The module has built-in test (BIT) modes for testing on command, along with continuous diagnostic monitoring. It is factory calibrated and temperature compensated over an operating temperature range of -40°C to +85°C. The factory calibration and temperature compensation allows Thales to add a series of stability specifications to the NavChip
module’s data sheet that are not to be found on most other commercial IMU data sheets: ■ Gyro bias in-run stability: 5°/ hour ■ Angular random walk: 0.18°/√hour ■ Velocity random walk: 0.03 meters/second/√hour The software angle With all of the IMUs listed in this article, the software that extracts the raw sensor data is not difficult to write as demonstrated by the Arduino code listing above. However, the integration of these sensor
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