micro:bit v2 Bubble Leveler

Description

This is a simple implementation of a bubble leveler on the micro:bit v2. It uses the on-board IMU to read acceleration from gravitational orientation and renders a corresponding "bubble" on the micro:bit's LED display. The program rules are as follows:

• The program runs at 5 frames per second (reading the IMU every 200 milliseconds)
• The program starts in "coarse" mode, determining the bubble position by splitting the acceleration range from -500 mG to 500 mG into five intervals of 200 mG each.
• There is an additional "fine" mode, which determines bubble position using a range of -50 mG to 50 mG.
• When the board is upside-down (i.e. the z-acceleration is positive), no bubble is present.
• Pressing the B button on the board will set the bubbler to "fine" mode; pressing the A button will set the bubbler to "coarse" mode.

Build and run

• To build the application without flashing: cargo build --release from repo root
• To build the application and flash to the micro::bit: cargo embed --release from repo root

Implementation details

The IMU is read through the micro:bit's I2C bus, which is instantiated by using the twim module in the microbit's HAL and the dedicated driver crate for the LSM303AGR accelerometer. The actual implementation is quite simple--the render_bubble function takes in an x and y acceleration value and determines the bubble position linearly. render_bubble also takes in a value for the range limit of mG values, allowing for easy extension and switching between coarse/fine modes.

At the start of each frame, the buttons are checked and the range size parameter is updated (if relevant), the bubble position is calculated via render_bubble, and then the display is updated for 200 ms.