Using NeoPixel LEDs with micro:bit

by richard | Jan 18, 2018 | 0 comments

In this project we create some colourful patterns using a set of LEDs. These are special LEDs that can display a range of up to 16 million colours.

You’ll need:

A micro:bit
An LED matrix such as the Kitronic ZIP Halo:
https://www.kitronik.co.uk/5625-zip-halo-for-the-bbc-microbit.html
A micro:bit battery pack

Connect your micro:bit

Using the instructions provided by Kitronic, screw the Halo onto your micro:bit.

Connect the battery pack to the Halo’s power socket, not the micro:bit’s.

Once complete, it should look like this:

Plug the USB cable into USB socket on your computer so that you can flash you code onto the micro:bit.

PeoPixel LED Code

Colours

Colours are defined using a system called RGB, which stands for Red, Green, Blue.

A colour is made by setting a value for red, blue and green, where each value is between 0 and 255, where 255 is the brightest. The number of possible combinations is more than 16 million.

For example, to create red, set a value for red but leave blue and green set to 0. So:

red is 255, 0, 0 (bright)
blue is 0,127, 0 (not so bright)
green is 0, 0, 63 (even less bright)

Or combine colours, like these:

Orange = 255, 127, 0
Purple = 127, 0, 255
Brown is 127, 63, 31

To test everything is working, type in this code.

# halo_fun
# Working with LEDs using NeoPixel Strip

# import microbit libraries
from microbit import *

# Import NeoPixel libraries
import neopixel

# Setup the Neopixel strip on pin0 with a length of 24 LEDs
# These will be numbered 0 to 23
np = neopixel.NeoPixel(pin0, 24)

# Start by clearing the display
np.clear()

# Create a colour (red)
colour = (128, 0, 0)

# Set the first LED to the new colour
np[0] = colour

# Show the LEDs with the new settings
np.show()

Using Loops

One of the best ways to use LEDs is in loops. Here we’ve altered the code to set every LED to the same colour:

# halo_fun
# Working with LEDs using NeoPixel Strip

# import microbit libraries
from microbit import *

# Import NeoPixel libraries
import neopixel

# Setup the Neopixel strip on pin0 with a length of 24 LEDs
# These will be numbered 0 to 23
np = neopixel.NeoPixel(pin0, 24)

# Start by clearing the display
np.clear()

# Create a colour (red)
colour = (128, 0, 0)

# Set each LED to the new colour using a variable called led
for led in range(0, 23):
    np[led] = colour

# Show the LEDs with the new settings
np.show()

The range Function

Python’s range() function is a loop that makes a variable count up (or down). There are three ways to use the range() function.

The first just specifies how many times to count, one at a time, like this:

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The second adds a starting number, like this:

# count from 2 to 5
for i in range(2, 6):
    print(i)

Then we can also set the size of the count, like this:

# count from 20 to 40 in steps of 10
for i in range(20, 50, 10):
    print(i)

Random Colours

We can use random numbers to generate different colours instead of just red. To do this we need to load an extra code library so that we can use random numbers. Add this near the top with the other import statements:

# import random number library
from random import randint

Now we can generate a colour by picking a random value for Red, Green and Blue. We’ll use three variables, one for each colour. Replace:

# Create a colour (red)
colour = (128, 0, 0)

With:

# Create a colour (random red, green & blue)
red = randint(0, 127)
green = randint(0, 127)
blue = randint(0, 127)
colour = (red, green, blue)

You should find that you get a different colour each time you reset the micro:bit.

Other Colours

To turn an LED off we set the colour to black. This is where there is no red, no green and no blue, like this:

# turn off LED (set colour to black)
colour = (0, 0, 0)

To get a bright white light we can set all the colours to the maximum value of 255:

# bright white
colour = (255, 255, 255)

Moving Lights

Using the same loop we can make it look like a colour is moving around the LEDs. The trick is turn off the previous LED before turning on the next one.

As we loop through each LED from 0 to 23 we can calculate the number of the previous LED because it will be one less than the current one. If we are about to turn on LED number 7 we know that the previous one was number 6:

for led in range(0, 24):
    # calculate previous LED number
    old_led = led – 1

When we are on the first LED, with number 0, we can use the last LED instead. This will be useful when we repeat the loop. We need to put all this into an if:

for led in range(0, 24):
    # if we are on the first LED (number 0), get the last one
    if led == 0:
        old_led = 23
    else:
        old_led = led – 1

Completed LED Project Code

# halo_spin.py
# Richard
# LED halo random spinning colours 

# import microbit libraries
from microbit import *

# import random number library
from random import randint

# Import NeoPixel libraries
import neopixel

# How many LEDs are there
max_leds = 24

# Setup the Neopixel strip on pin0 with the length of the LED strip
# These are numbered from 0 upwards
np = neopixel.NeoPixel(pin0, max_leds)

# Start by clearing the display
np.clear()

# Create a colour to turn off an LED
off = (0, 0, 0)

# Loop Forever
while True:
    # Choose a random colour
    red = randint(0, 63)
    green = randint(0, 63)
    blue = randint(0, 63)
    colour = (red, green, blue)

    # Loop through each LED
    for led in range(0, max_leds):
        # Set the led to the colour
        np[led] = colour

        # if we are on the first LED (numer 0), get the last one
        if led == 0:
            old_led = max_leds - 1
        else:
            old_led = led - 1

        # set the old LED to off (black)
        np[old_led] = off

        # Show the LEDs with the new settings
        np.show()

        # pause to slow things down
        sleep(25)