Mounted next to the controller, in line with the centre of the board is an MPU6050 6-axis sensor on a GY-521 breakout board. It is connected to the microcontroller via I2C, powered with 5v and can data connect to board with either 3.3v or 5v

Pro Mini:

• A4 I2C - SDA
• A5 I2C - SCL

D1 Mini:

• D2  4  I2C - SDA
• D1   5  I2C - SCL

Wemos D1 Mini (ESP-8266):

• D1   5  GPIO5  IO  I2C - SCL
• D2  4  GPIO4  IO  I2C - SDA

• MPU6050:             X=Right/Left, Y=Forward/Backward, Z=Up/Down
• orientation (byte):  0=flat, 1=upside-down, 2=up, 3=down, 4=left-side, 5=right-side
• direction (byte):     -1=stationary, 0=forward, 1=back, 2=up, 3=down, 4=left, 5=right

The software has several calibration routines to help work out where it is in space and time. 

• A full calibration is run when the board can be placed on a level, solid surface for quite some time, preferably leaving the room please, haha funny, your jumping is not helping.
• Short calibrations are run at startup when the board is placed on the ground. Current and saved data is compared to make slight adjustments to centre the orientation. 
• Short calibrations can also be run by request, at intervals, or whenever needed by the program to self-correct.

Orientation sensor data is used to switch light modes, change the speed of the animation, activate an emergency beacon, indicate when the board leans round a corner and mix with the wheel sensors to produce LED effects.

TODO: Fix upside-down register. Seems to have a blind spot/gimbal lockout point?

TODO: Proper calibration system with menu.

Software uses a custom library for ease of access. 

https://github.com/mattThurstan/MT_BoardOrientation

• BoardOrientation - attempt to move all board mpu6050 sensor related items to a single library
  • 20 milliseconds read interval
  • 100 milliseconds main orientation read interval