9-Axis IMU LESSON 3: Understanding How Accelerometers Work

In this lesson we describe how the acceleromters on chips like the Adafruit BNO055 work. They work based on microscopic masses suspended on springs on the chip. As the chip moves, the suspended masses respond to the motion, and the gaps between the suspended masses and the substrate changes. The chips detect these changes in position by monitoring the capacitance between the suspended mass and the substrate, or between the suspended masses and carefully designed interdigitated fingers between the mass and the substrate. C=eA/d, e is the dielectric constant of the material, A is the area of the capacitor, and d is the gap between the two capacitor plates. Changes in measured capacitance come from either a change in A or a change in d. Both d and A change in response to motion, so by monitoring the capacitance of the suspended mass, acceleration can be inferred. The video below explains clearly how this works.

Code for Getting Raw Acceleration Data from the BNO055 9-axis Inertial Measurement Sensor.

The code below is for demo purposes only, and should not be used in any real applications. It just demonstrates how to work with this sensor in benchtop presentations.

Inertial Measurement

I have been playing around with some accelerometers, magnetometers, and gyros. You can do some pretty cool stuff if you get these going and then send the data to Vpython over the serial port. I will be giving more details on this project in future posts, but for now, this video shows some of what is possible. I will be posting code when I get things further along and cleaned up.