5. MOVEMotor LEDs

The MOVEMotor uses 4 ZIP LEDs (WS2812) on pin8.
The neopixel module is used to drive these RGB LEDs.
Each RGB LED can produce a full spectrum of colours independent to all of the other RGB LEDs.
In RGB, R stands for red, G stands for green, and B stands for blue.
Each ZIP LED has a Red, Green and Blue element within the LED, and each of these can have brightness set from 0 to 255.

5.1. NeoPixel module

The neopixel module allows use of multiple RGB LEDs connected to one pin so that each can have their own colour and brightness set.
First, import the neopixel library with import neopixel.
from microbit import *
import neopixel

5.2. Set up LEDs

neopixel.NeoPixel(pin, n)
Initialise a strip of RGB LEDs.
pin is the pin that they are connected by.
n is the number of LEDs.
The code below sets up the 4 LEDs connected to pin8 via: lights = neopixel.NeoPixel(pin8, 4).
The variable, lights, is the neopixel object that is used to control the LEDs.
from microbit import *
import neopixel


lights = neopixel.NeoPixel(pin8, 4)

5.3. Set LED colour and brightness

lights[n] = (red, green, blue)

Set the red, green and blue brightness from 0 to 255 for a RGB LED at position n.

Each LED is set by indexing it (like with a Python list, starting from 0).
e.g. the LED in position 0 is lights[0].
Neopixels are given RGB (red, green, blue) values between 0-255 as a tuple.
A value of 0 is off, while 255 is full brightness.
When red, green and blue are all full brightness, i.e. (255, 255, 255), the colour is white.
The code below sets the RGB values to (255, 255, 255) for the LED in position 0.
from microbit import *
import neopixel


lights = neopixel.NeoPixel(pin8, 4)
lights[0] = (255, 255, 255)
lights.show()
The code below sets different colours for the 4 LEDs: lights[0] is white (255, 255, 255), lights[1] is red (255, 0, 0), lights[2] is green (0, 255, 0) and lights[3] is blue (0, 0, 255), with all at full brightness.
from microbit import *
import neopixel


lights = neopixel.NeoPixel(pin8, 4)
lights[0] = (255, 255, 255)
lights[1] = (255, 0, 0)
lights[2] = (0, 255, 0)
lights[3] = (0, 0, 255)
lights.show()

Tasks

For quick RGB values for common colours, see https://www.rapidtables.com/web/color/RGB_Color.html

  1. Write code to set the last LEDS at position 1, 2 and 3 to yellow, cyan and magenta.

5.4. Show LEDs

Setting the colours for LEDs doesn’t change the displayed colour of the LEDs until show() is used on the neopixel object that was set up. e.g. lights.show()
show()

Show the LEDs using their colour settings. This must be called for any updates to the LEDs to become visible.

The code below displays the set colours for the neopixel LEDS using lights.show()
from microbit import *
import neopixel


lights = neopixel.NeoPixel(pin8, 4)
lights[0] = (255, 255, 255)
lights.show()

5.5. Clear LEDs

clear()

Clear all the LEDs so that they have no colours set and turns off the LEDs.

The code below uses the variable lights for the neopixel object.
The front lights are at position 0 and 1. They are set to dull blue.
The rear lights are at position 2 and 3. They are set to dull red.
The lights are turned on for 2 seconds then turned off using clear().
from microbit import *
import neopixel


lights = NeoPixel(pin8, 4)
dull_blue = [20, 20, 25]
dull_red = [25, 0, 0]
lights[0] = dull_blue
lights[1] = dull_blue
lights[2] = dull_red
lights[3] = dull_red
lights.show()
sleep(2000)
lights.clear()

Tasks

  1. Modify the code to turn on the front lights for 2 sec then turn on the rear lights for 2 sec.

5.6. LED values

To read the colour of a specific RGB LED use its index position.

lights[n]

Return the red, green and blue value for the RGB LED at position n.

The code below sets the LED, at position 0, to red using the tuple (255, 0, 0).
The for loop displays each colour value of the LED at position 0.
from microbit import *
import neopixel


lights = neopixel.NeoPixel(pin8, 4)
lights[0] = (255, 0, 0)
for rgb_value in lights[0]:
    display.scroll(rgb_value)

5.7. Colour lists

A list of colours can be used to create a colourful display.
Two for-loops are used, one nested inside the other.
for colour in colour_list: loops through the colours.
for led_num in range(4): loops through each LED to set its colour.
from microbit import *
import neopixel

lights = neopixel.NeoPixel(pin8, 4)

white = (255, 255, 255)
red = (255, 0, 0)
yellow = (255, 255, 0)
green = (0, 128, 0)
cyan = (0, 255, 255)
blue = (0, 0, 255)
magenta = (255, 0, 255)

colour_list = [white, red, yellow, green, cyan, blue, magenta]

for colour in colour_list:
    for led_num in range(4):
        lights[led_num] = colour
    lights.show()
    sleep(200)

5.8. Primary and secondary colours

../../_images/primary_colours2.png ../../_images/secondary_colours2.png

Tasks

See https://www.indezine.com/products/powerpoint/learn/color/color-rgb.html

  1. Modify the code to use a shorter list of colours, with just the primary colours.

  2. Modify the code to use a shorter list of colours, with just the secondary colours.