Accelerometer¶

On this page we will learn

how to measure movement and tilt in three directions
how to read all three values at once
how to recognise gestures such as shaking or turning face up

Terminology

accelerometer – a sensor that measures movement and tilt in three directions and can recognise gestures such as shaking.
axis – an imaginary line, called x, y or z, along which movement is measured.
milli-g – the unit for accelerometer readings, where about 1024 milli-g equals the pull of gravity.
gesture – a movement the accelerometer can recognise, such as shaking, tilting or turning face up.
tuple – a collection of values written in round brackets, like a list, but whose values can't be changed after it is created.
unpacking – storing each value from a tuple or list into its own variable in one line, such as x, y, z = accelerometer.get_values().

The accelerometer measures movement and tilt in three directions and recognises gestures such as shaking or turning face up.

Possible uses:

step counters
shake-to-roll dice
tilt-controlled games
motion alarms

Connect it¶

The accelerometer is built into the micro:bit, so we don't need to connect anything.

Each example is a main.py file. See Your First Program for how to create, upload and run it.
Most examples print readings. Watch them in Thonny's Shell.
Movement is measured along three axes (imaginary lines):
- x → tilting left and right
- y → tilting forwards and backwards
- z → moving up and down
Readings are in milli-g. 0 means level on that axis; about 1024 or -1024 is the pull of gravity.
Gestures are strings: "up", "down", "left", "right", "face up", "face down", "freefall", "3g", "6g", "8g" and "shake".

Set it up¶

The accelerometer is part of the microbit library. We import it at the top of every program:

from microbit import *

Methods¶

Method	Parameters	Returns	Description
`accelerometer.get_x()`	none	int (milli-g)	Movement along the x-axis
`accelerometer.get_y()`	none	int (milli-g)	Movement along the y-axis
`accelerometer.get_z()`	none	int (milli-g)	Movement along the z-axis
`accelerometer.get_values()`	none	tuple `(x, y, z)`	All three readings at once
`accelerometer.current_gesture()`	none	string	The gesture happening right now
`accelerometer.is_gesture(name)`	`name`: gesture string	Boolean	`True` if that gesture is happening right now
`accelerometer.was_gesture(name)`	`name`: gesture string	Boolean	`True` if that gesture happened since the last call
`accelerometer.get_gestures()`	none	tuple of strings	All gestures since the last call, oldest first

`get_x()`¶

Reads how much the micro:bit is tilted or moving left and right.

from microbit import *

# Main loop
while True:
    x = accelerometer.get_x()
    print(x)
    sleep(100)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → gets the x-axis reading and stores it in x.
line 6 → prints the reading in the Shell.
line 7 → waits 100 milliseconds before the loop repeats.

`get_y()`¶

Reads how much the micro:bit is tilted or moving forwards and backwards.

from microbit import *

# Main loop
while True:
    y = accelerometer.get_y()
    print(y)
    sleep(100)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → gets the y-axis reading and stores it in y.
line 6 → prints the reading in the Shell.
line 7 → waits 100 milliseconds before the loop repeats.

`get_z()`¶

Reads how much the micro:bit is moving up and down.

from microbit import *

# Main loop
while True:
    z = accelerometer.get_z()
    print(z)
    sleep(100)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → gets the z-axis reading and stores it in z.
line 6 → prints the reading in the Shell.
line 7 → waits 100 milliseconds before the loop repeats.

`get_values()`¶

Gets all three readings at once as a tuple.

from microbit import *

# Main loop
while True:
    x, y, z = accelerometer.get_values()
    print(x, y, z)
    sleep(100)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → gets all three readings and unpacks them: the first value goes into x, the second into y, the third into z.
line 6 → prints the three readings in the Shell.
line 7 → waits 100 milliseconds before the loop repeats.

Tuples

A tuple is like a list, but its values can't be changed after it is created. It is written with round brackets, for example (1, 2, 3).

`current_gesture()`¶

Returns the name of the gesture happening right now, such as "face up" or "shake".

from microbit import *

# Main loop
while True:
    gesture = accelerometer.current_gesture()
    print(gesture)
    sleep(500)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → gets the current gesture as a string and stores it in gesture.
line 6 → prints the gesture in the Shell.
line 7 → waits 500 milliseconds before the loop repeats.

`is_gesture()`¶

Checks whether a particular gesture is happening right now.

from microbit import *

# Main loop
while True:
    if accelerometer.is_gesture("face up"):
        display.show(Image.HAPPY)
    else:
        display.show(Image.ASLEEP)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → checks if the micro:bit is face up right now.
line 6 → if it is, shows a happy face.
line 7 → if it isn't…
line 8 → …shows a sleeping face.

`was_gesture()`¶

Checks whether a particular gesture has happened since the last check, even if it has finished.

from microbit import *

# Main loop
while True:
    sleep(3000)
    if accelerometer.was_gesture("shake"):
        display.show(Image.HAPPY)
    else:
        display.show(Image.SAD)

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → waits 3 seconds. Shake the micro:bit now.
line 6 → checks if a shake happened since the last check.
line 7 → if it did, shows a happy face.
line 8 → if it didn't…
line 9 → …shows a sad face.

`get_gestures()`¶

Returns every gesture that has happened since the last check, oldest first.

from microbit import *

# Main loop
while True:
    sleep(3000)
    print(accelerometer.get_gestures())

PRIMM

Predict what you think will happen. Be specific.
Run the program.
Time to investigate the code. What does each line do?

Code explanation

line 1 → imports all the commands from the microbit library.
line 4 → starts an endless loop.
line 5 → waits 3 seconds. Move the micro:bit around now.
line 6 → gets every gesture since the last check and prints them in the Shell.

Documentation¶

Documentation is the official guide written by the people who made the code library, and we can use it to look up every method and its parameters, including ones that aren't covered on this page.

BBC micro:bit MicroPython — accelerometer

Exercises¶

PRIMM

Time to modify the code and see what happens.

Starter files are in the accelerometer folder of your tutorial files. Solutions are on the Exercise Solutions page.

Exercise 1¶

Starter: accelerometer/ex1_spirit_level

Can you make a spirit level that shows - if the micro:bit is level left to right, L if the left side is too high, or R if the right side is too high?

Exercise 2¶

Starter: accelerometer/ex2_face_up

Can you make the micro:bit show a happy face if it is face up, or an angry face if it isn't?

Exercise 3¶

Starter: accelerometer/ex3_shake_count

Can you count how many times the micro:bit is shaken in 5 seconds, then show the count?

Exercise 4¶

Starter: accelerometer/ex4_3g

Can you make a program that waits until button A is pressed, then shows whether the micro:bit has experienced 3g since the program started?

Accelerometer¶

Connect it¶

Set it up¶

Methods¶

get_x()¶

get_y()¶

get_z()¶

get_values()¶

current_gesture()¶

is_gesture()¶

was_gesture()¶

get_gestures()¶

Documentation¶

Exercises¶

Exercise 1¶

Exercise 2¶

Exercise 3¶

Exercise 4¶

`get_x()`¶

`get_y()`¶

`get_z()`¶

`get_values()`¶

`current_gesture()`¶

`is_gesture()`¶

`was_gesture()`¶

`get_gestures()`¶