05_accelerometer.md

Micro:bit Accelerometer

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The BBC micro:bit comes with an accelerometer. An accelerometer can detect and measure how fast something is moving or how it's being tilted. It can sense motion in different directions like up, down, left, and right.

:class: important
Full details can be found at the **[BBC micro:bit MicroPython accelerometer documentation](https://microbit-micropython.readthedocs.io/en/latest/accelerometer.html#module-microbit.accelerometer)**.

Movement

The micro:bit accelerometer measures movement along three axes:

• X - tilting from left to right.
• Y - tilting forwards and backwards.
• Z - moving up and down.

Get x

There is a method for each axis that returns a positive or negative number indicating a measurement in milli-g’s. When the reading is 0 you are “level” along that particular axis.

Below is an example for the x-axis:

:linenos:

:class: notice
- **line 5** → creates an infinite loop, since the condition (`True`) will never be `False`.
- **line 6** → gets the x-axis reading from the accelerometer and stores it in the x_reading variable.
- **line 7** → displays the x_reading on matrix

Get values

You can also get a tuple containing the x, y and z values the micro:bit is experiencing:

Below is an example:

:linenos:

:class: notice
- **line 5** → creates an infinite loop, since the condition (`True`) will never be `False`.
- **line 6** → gets the tuple of the accelerometer reading and stores it in the values variable.
- **line 7** → displays accelerometer readings to the matrix
- **line 8** → waits 1 second

:class: note
Tuples in Python are like lists, but you can't change their values once they're created. They are useful for storing a collection of items that should not be modified. You create a tuple by placing the items inside parentheses, separated by commas, like this: my_tuple = (1, 2, 3).

Movement exercises

1. Change the x-axis example above to show the value for the y-axis
2. Change the x-axis example above to show the value for the z-axis
3. Make a levelling device that shows a - if the x-axis is level, L if the left side is too high or R if the right side is too high.

Gestures

The really interesting side-effect of having an accelerometer is gesture detection. If you move your BBC micro:bit in a certain way (as a gesture) then MicroPython is able to detect this.

MicroPython is able to recognise the following gestures: up, down, left, right, face up, face down, freefall, 3g, 6g, 8g, shake. Gestures are always represented as strings. While most of the names should be obvious, the 3g, 6g and 8g gestures apply when the device encounters these levels of g-force (like when an astronaut is launched into space).

Current gestures

You can get the current gesture by using the current_gesture method which return a string.

Below is an example for displaying the current gesture:

:linenos:

:class: notice
- **line 5** → creates an infinite loop, since the condition (`True`) will never be `False`.
- **line 6** → stores the current gesture in the variable called gesture
- **line 7** → scrolls the gesture across the display
- **line 8** → waits 1 second

Get gestures

The micro:bit can also provide you with a list of historical gestures. It returns a tuple with the latest gesture first.

Below is an example of get_gestures:

:linenos:

:class: notice
- **line 5** → waits 5 seconds
- **line 7** → gets a list of all the guestures that have occured since the micro:bit was turned on and stores it in the variable called gestures
- **line 9** → iterates over the list of gestures
- **line 10** → scroll the current guesture across the display

Was gesture

The was_gesture method check to see if the micro:bit recorded a gesture since the last call.

Below is an example to see if the micro:bit was shaken during the 5 second sleep.

:linenos:

:class: notice
- **line 5** → waits 5 seconds
- **line 7** → checks if micro:bit was shaken since it started
- **line 8** → displays the **YES** image (a tick)
- **line 10** → displays the **NO** image (a cross)

Gesture exercises

1. Make the micro:bit display a happy face if it is face up, or display an angry face if it is not.
2. Make a program that counts the number of times it has been shaken over a five second period
3. Make a program that waits button A is pressed, and then reports if it has experienced 3gs