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Colour Sensor

On this page we will learn

  • how to connect the Colour Sensor
  • how to read red, green and blue values
  • how to read hue, saturation and value
  • how to identify a colour

Terminology

  • RGB – a way of describing a colour by how much red, green and blue light it contains.
  • HSV – a way of describing a colour by its hue, saturation and value.
  • hue – which colour something is, given as an angle on the colour wheel, such as red 0, green 120 and blue 240.
  • saturation – how intense a colour is, from bright and strong to greyish.
  • value (colour) – how light or dark a colour is.
  • colour wheel – a circle of colours that lets us describe each colour by its position or angle around it.
  • dictionary – a collection that stores values with names, called keys, so we can look each value up by its name.
  • key – the name used to store and look up a value in a dictionary, such as "red" in data["red"].
  • ambient light – the general light in the surroundings.
  • colour temperature – a measure, in kelvin, of how warm (yellowish) or cool (bluish) white light looks.

The PiicoDev Colour Sensor (VEML6040) measures the red, green, blue and white light reflected from an object, and can identify its colour.

Possible uses:

  • sorting objects by colour
  • line-following robots
  • colour-matching games
  • ambient light measurement

Connect it

  1. Connect the sensor to the PiicoDev adapter with a PiicoDev cable. See Using PiicoDev.
  2. Upload these files to the micro:bit with main.py:
    • PiicoDev_Unified.py
    • PiicoDev_VEML6040.py

Two ways to describe colour

RGB describes a colour by how much red, green and blue light it contains. Screens mix these three colours to make every other colour.

HSV describes a colour by:

  • hue → which colour it is, as an angle on the colour wheel: red 0, green 120, blue 240
  • saturation → how intense it is: bright red is high, reddish grey is low
  • value → how light or dark it is

Hue is the easiest way to identify a colour, because one number tells you which colour it is.

colour wheel with hue values

Set it up

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from microbit import *
from PiicoDev_VEML6040 import PiicoDev_VEML6040

sensor = PiicoDev_VEML6040()

Methods

Method Parameters Returns Description
sensor.readRGB() none dictionary: red, green, blue, white (lux), cct (K) Red, green and blue light levels, plus ambient light and colour temperature
sensor.readHSV() none dictionary: hue (0–360), sat, val Hue, saturation and value
sensor.classifyHue(hues, min_brightness=0) hues: dictionary of colour names and hue angles (optional) string The name of the closest colour

readRGB()

Returns the amount of red, green and blue light the sensor sees, plus the ambient light and colour temperature.

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from microbit import *
from PiicoDev_VEML6040 import PiicoDev_VEML6040

# Setup
sensor = PiicoDev_VEML6040()

# Main loop
while True:
    data = sensor.readRGB()
    print(data["red"], data["green"], data["blue"])
    sleep(500)

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 2 → imports the Colour Sensor driver.
  • line 5 → creates the sensor and calls it sensor.
  • line 8 → starts an endless loop.
  • line 9 → reads the RGB values. They are returned as a dictionary and stored in data.
  • line 10 → prints the red, green and blue values from the dictionary.
  • line 11 → waits 500 milliseconds before the loop repeats.

Dictionaries

A dictionary stores values with names (called keys). data["red"] gets the value stored under the key "red".

readHSV()

Returns the colour the sensor sees as hue, saturation and value.

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from microbit import *
from PiicoDev_VEML6040 import PiicoDev_VEML6040

# Setup
sensor = PiicoDev_VEML6040()

# Main loop
while True:
    data = sensor.readHSV()
    print(data["hue"], data["sat"], data["val"])
    sleep(500)

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 2 → imports the Colour Sensor driver.
  • line 5 → creates the sensor and calls it sensor.
  • line 8 → starts an endless loop.
  • line 9 → reads the HSV values as a dictionary and stores them in data.
  • line 10 → prints the hue, sat and val values.
  • line 11 → waits 500 milliseconds before the loop repeats.

classifyHue()

Returns the name of the colour the sensor sees.

By default, classifyHue() chooses from red, yellow, green, cyan, blue and magenta. Pass your own dictionary of names and hue angles to change the choices.

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from microbit import *
from PiicoDev_VEML6040 import PiicoDev_VEML6040

# Setup
sensor = PiicoDev_VEML6040()

# Main loop
while True:
    colour = sensor.classifyHue()
    print(colour)
    sleep(500)

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 2 → imports the Colour Sensor driver.
  • line 5 → creates the sensor and calls it sensor.
  • line 8 → starts an endless loop.
  • line 9 → finds the closest colour name and stores it in colour.
  • line 10 → prints the colour name.
  • line 11 → waits 500 milliseconds before the loop repeats.

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 colour folder of your tutorial files. Solutions are on the Exercise Solutions page.

Exercise 1

Starter: colour/ex1_rgb_dictionary

Can you print the whole dictionary returned by readRGB() every second? What do white and cct show?

Exercise 2

Starter: colour/ex2_show_colour

Can you show the first letter of the colour the sensor is looking at on the micro:bit display? For example, R for red.