The Magic Wand Example

Introduction

The magic wand example shows how to detect gestures using an accelerometer. Different types of accelerometers are easily available:

• The ADXL345 is a tree axis digital accelerometer by Analog Devices
  I wrote a pure MircoPython driver for the ADXL345 available at https://github.com/uraich/IoT-Course/tree/master/exercises/solutions/exercise_16/adxl345.
  
  
• The MPU6050 is a six axis device (Gyro and Accelerometer) from Ivensense. It is described by its datasheet and the register description document.
  Jeff Rowberg has written a very complete MPU6050 driver for the Arduino in C++, which includes access to its Digital Motion Processor, whose description cannot be found anywhere on the WEB. I ported this driver to MicroPython together with a few example programs drafted after Jeff's C++ examples: https://github.com/uraich/IoT-Course/tree/master/exercises/solutions/exercise_16/mpu6050.
  
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• The LIS2dH MEMS digital output motion sensor from ST Microelectronics is an ultra low power high performance 3 axis accelerometer.

I mounted the accelerometer onto a WeMos D1 prototype board. With the triple base and the CPU this makes up for a stable assembly that can easily be moved without cable contact problems.

Hardware connections

The MPU6050 is connected to the WeMos D1 bus as follows:

The ADXL345 is connected as follows:

Providing a training data set

In order to provide a training data set we must be able to record gestures. We must therefore provide a program that recognizes the start and the end of a gesture (movement and inactivity detection) and which records the accelerometer data of the gesture onto a file. Gesture detection is of course also needed to be able to feed the accelerometer data into the trained model, which will then recognize the gesture.

-- Uli Raich - 2022-02-02

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