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Compass

On this page we will learn

  • how to calibrate the compass
  • how to find which direction the micro:bit is pointing
  • how to measure magnetic field strength

Terminology

  • magnetometer – a sensor that measures magnetic fields, used by the micro:bit as a compass.
  • magnetic field – the invisible area of magnetic force around a magnet or the Earth.
  • calibration – adjusting a sensor so its readings are accurate, such as tilting the micro:bit until every LED is lit.
  • heading – the direction the top of the micro:bit is pointing, measured in degrees from 0 to 359.
  • nanotesla – a very small unit for measuring the strength of a magnetic field.

The compass (a magnetometer) measures magnetic fields, so it can find which direction the micro:bit is pointing and detect nearby magnets.

Possible uses:

  • navigation tools
  • treasure hunts
  • magnet-triggered switches

Connect it

The compass 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.
  • The compass must be calibrated before it gives headings. Calibration starts automatically the first time a heading is needed: tilt the micro:bit in every direction until all the LEDs are lit.
  • Headings are measured from the top of the micro:bit (the USB socket end), from 0 to 359 degrees. For example, pointing South-East gives 135.

compass headings

Set it up

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

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from microbit import *

Methods

Method Parameters Returns Description
compass.calibrate() none none Starts the calibration game
compass.is_calibrated() none Boolean True if the compass has been calibrated
compass.heading() none int (0–359) The direction the micro:bit is pointing, in degrees
compass.get_field_strength() none int (nanotesla) The strength of the magnetic field around the micro:bit

compass.calibrate()

Starts the calibration game: tilt the micro:bit until every LED is lit.

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from microbit import *

# Setup
compass.calibrate()

# Main loop
while True:
    display.show(Image.YES)

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. 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 calibration. Tilt the micro:bit until every LED is lit.
  • line 7 → starts an endless loop.
  • line 8 → shows a tick once calibration is finished.

compass.is_calibrated()

Checks whether the compass has been calibrated.

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from microbit import *

# Main loop
while True:
    print(compass.is_calibrated())
    sleep(1000)

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. 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 → prints True in the Shell if the compass has been calibrated, or False if it hasn't.
  • line 6 → waits 1 second before the loop repeats.

compass.heading()

Returns the direction the top of the micro:bit is pointing, from 0 to 359 degrees.

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from microbit import *

# Main loop
while True:
    display.scroll(compass.heading())

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. 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 compass heading and scrolls it across the display.

compass.get_field_strength()

Returns the strength of the magnetic field around the micro:bit. It goes up when a magnet is nearby.

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from microbit import *

# Main loop
while True:
    display.scroll(compass.get_field_strength())

PRIMM

  1. Predict what you think will happen. Be specific.
  2. Run the program.
  3. 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 magnetic field strength and scrolls it across the display.

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.

Exercises

PRIMM

Time to modify the code and see what happens.

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

Exercise 1

Starter: compass/ex1_north

Can you make the micro:bit show N when it is pointing North?

Exercise 2

Starter: compass/ex2_eight_points

Can you make the micro:bit show which of the 8 compass directions in the image above it is pointing (N, NE, E, SE, S, SW, W, NW) when button A is pressed?

Exercise 3

Starter: compass/ex3_microtesla

Can you change the get_field_strength() example to show the reading in microtesla with no decimal places? (1 microtesla = 1000 nanotesla)

Exercise 4

Starter: compass/ex4_magnet

Can you make the micro:bit show a happy face when a magnet is touching its right side, and an angry face otherwise?