Basic Guide to Movement Sensing in Embedded Systems

By John Legg · 18 September 2021 · 2 min read

6DOF IMU 9 Click board for movement sensing

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 orientation 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 heading in relation to magnetic north. This is useful when there is a loss of a SATNAV signal, as it allows navigation to continue.

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 of three axes (x, y, z). These are also known as degrees of freedom (DOF). In addition, devices incorporating two or more such sensors are also available:

Accelerometer, gyroscope and magnetometer axes showing what 6DOF and 9DOF mean — Three sensors, three axes each: 6DOF uses two of them, 9DOF all three.

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 that also have 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. Each device is implemented using MEMS (Micro-Electro-Mechanical Systems) technology, which combines mechanical and electronic components 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 Boards 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.