New-Tech Europe Magazine | Sep 2019 | Digital Edition

IMUs: Let Your Host Sleep with On-Board Machine Learning

Rich Miron, Applications Engineer at Digi-Key Electronics processing from the host application processor and how these features can be used in real applications. A quick IMU review

Inertial measurement units (IMUs) are widely used to provide a steady stream of multi-axis position information from accelerometers, gyroscopes, and other sensors. With the many degrees of freedom (DOF) all generating data, the merged data streams from these devices can keep system processors in constant wake mode and tax them as they sift through the raw IMU data to extract useful gesture and system location information. What designers need is a way to offload this sifting function from the main processor. Machine learning may be the answer. After a brief overview of IMU use, this article introduces the 6DOF LSM6DSO from STMicroelectronics. It then uses this device to show how the addition and integration of machine learning and decision tree processing into IMUs can offload real-time position and movement

bias or integration result in a position error called “drift,” which can be compensated for with software. Accelerometers measure linear acceleration, including acceleration components caused by device motion and acceleration due to gravity. The acceleration unit of measurement is g, where 1 g = the earth’s gravitational force = 9.8 meters/second2. Accelerometers are available with one, two, or three axes, which define an X, Y, Z coordinate system. Magnetic sensors measure magnetic field strength, typically in units of microTeslas (µT) or Gauss (100 µT = 1 Gauss). The most common magnetic sensor used for mobile electronics is a three-axis Hall effect magnetometer. By computing the angle of the detected earth’s magnetic field, and comparing that measured angle to gravity as measured by an accelerometer, it

IMUs integrate a number of motion sensors into one device and can provide high accuracy positioning information. They can be used for a variety of applications including consumer (mobile phones), medical (imaging), industrial (robotics), and military (head tracking). They react to the motion of the sensor and incorporate one or more of the following motion sensor types: Gyroscope sensors measure angular position changes, usually expressed in degrees per second. Integrating angular rate over time results in a measured angle of travel that can be used to track changes in orientation. Gyroscopes track relative movement independently from gravity, so errors from sensor

16 l New-Tech Magazine Europe