Basic Guide to Movement Sensing in Embedded Systems

The most common embedded system that most of us use is a Smartphone. The Smartphone has a built-in Inertial Measurement Unit (IMU) and can sense its position and movement using the following sensors:

Gyroscope

The Smartphone can determine its orientation by the use of an Electronic Gyroscope. The gyroscope measures angular velocity.

This 3-axis device helps it take action as a result of different movements such as phone rotation. In non-phone applications, you can use it to stabilise a platform or drone.

Accelerometer

The Accelerometer measures linear or straight-line acceleration in each of 3-axes. The Accelerometer is designed for measuring an increase or decrease in velocity (also known as the rate of change of velocity). An Accelerometer is not able to measure rotational acceleration and is helpful for impact detection.

Magnetometer

The Smartphone can detect its position precisely on the earth by using satellite navigation (SATNAV). It can also measure the magnetic field strength making it able to act as an Electronic Compass to determine its position in relation to Magnetic North and South. This is useful when there is a loss of a SATNAV signal as it allows navigation to take place still.

What are 6DOF and 9DOF IMU Devices?

Individual devices capable of measuring acceleration, rotational velocity (gyroscope) and magnetic field are available. Each device can measure in each or three axes (x, y, z). These are also known as Degree of Freedom (DOF). In addition, devices incorporation two or more such devices are also available:

• 6DOF IMU Devices, These devices usually include a 3-axis Accelerometer and a 3-Axis Gyroscope. Both together are known as 6DOF devices.
• 9DOF IMU Devices. Less common are devices, also having a 3-axis Magnetometer. These are known as 9DOF devices.

Using an IMU in Embedded Systems

The three different types of IMU components are available as separate devices and combined. The technology used to implement each device uses MEMS (Micro-ElectroMechanical System). MEMS technology combines mechanical and electronic components are built using integrated circuit techniques.

Getting Started

An ideal learning tool for IMU devices is the MikroE range of Click Boards. Over 1,000 different Click Board are available, each focusing on a single active device such as an accelerometer, gyroscope, magnetic field detector or complete combination (6DOF IMU or 9DOF IMU) device.