This guide covers how to use an Inertial Measurement Unit (IMU) with a Raspberry Pi . This is an updated guide and improves on the old one found here.
I will explain how to get readings from the IMU and convert these raw readings into usable angles. I will also show how to read some of the information in the datasheets for these devices.
This guide focuses on the BerryIMU. However, the theory and principals below can be applied to any digital IMU, just some minor modifications need to be made.
Git repository here
The code can be pulled down to your Raspberry Pi with;
The code for this guide can be found under the gyro_accelerometer_tutorial01_angles directory.
A note about Gyros and Accelerometers
When using the IMU to calculate angles, readings from both the gyro and accelerometer are needed which are then combined. This is because using either on their own will result in inaccurate readings. And a special note about yaw.
Gyros – A gyro measures the rate of rotation, which has to be tracked over time to calculate the current angle. This tracking causes the gyro to drift. However, gyros are good at measuring quick sharp movements.
Accelerometers – Accelerometers are used to sense both static (e.g. gravity) and dynamic (e.g. sudden starts/stops) acceleration. They don’t need to be tracked like a gyro and can measure the current angle at any given time. Accelerometers however are very noisy and are only useful for tracking angles over a long period of time.
Accelerometers cannot measure yaw. To explain it simply, yaw is when the accelerometer is on a flat level surface and it is rotated clockwise or anticlockwise. As the Z-Axis readings will not change, we cannot measure yaw. A gyro and a magnetometer can help you measure yaw. This will be covered in a future guide.
Here is an excellent tutorial about accelerometers and gyros.
Setting up the IMU and I2C
The IMU used for this guide is a BerryIMUv3 which uses a LSM6DSL,
that consists of a 3-axis gyroscope plus a 3-axis accelerometer and a LIS3MDL which is a 3-axis magnetometer.
- LSM6DSL – Accelerometer and gyroscope datasheet can be found here.
- LIS3MDL – Magnetometer datasheet can be found here
This IMU communicates via the I2C interface.
The image below shows how to connect the BerryIMU to a Raspberry Pi
The BerryIMUv3 can also be connected using the Raspberry Pi QWIIC connector and cable;
Continue reading Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi