8. BitBotXL LEDs

The BitBotXLMotor uses 12x LEDs on pin13.
The neopixel module is used to drive these RGB LEDs.
Each RGB LED can produce a full spectrum of colors 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.

8.1. NeoPixel module

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

8.2. 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 12 LEDs connected to pin13 via: np = neopixel.NeoPixel(pin13, 12).
The variable, np, is the neopixel object that is used to control the LEDs.
from microbit import *
import neopixel


PIN_NUM = pin13
NUM_PIXELS = 12
np = neopixel.NeoPixel(PIN_NUM, NUM_PIXELS)

8.3. Set LED color and brightness

np[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 np[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 color is white.
The code below sets the RGB values to (255, 255, 255) for the LED in position 0.
from microbit import *
import neopixel


np = neopixel.NeoPixel(pin13, 12)
np[0] = (255, 255, 255)
np.show()
The code below sets different colors for the 12 LEDs: np[0] is white (255, 255, 255), np[1] is red (255, 0, 0), np[2] is green (0, 255, 0) and np[3] is blue (0, 0, 255), with all at full brightness.
from microbit import *
import neopixel


np = neopixel.NeoPixel(pin13, 12)
np[0] = (255, 255, 255)
np[1] = (255, 0, 0)
np[2] = (0, 255, 0)
np[3] = (0, 0, 255)
np.show()

Tasks

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

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

  2. Write code to set all the LEDS to yellow for 1 sec, then cyan for 1 sec, then magenta for 1 sec.

8.4. Show LEDs

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

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

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


np = neopixel.NeoPixel(pin13, 12)
np[0] = (255, 255, 255)
np.show()

8.5. Clear LEDs

clear()

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

The code below uses the variable buggy_lights for the neopixel object.
The left lights are at position 0 and 5. They are set to dull blue.
The rear lights are at position 6 and 11. They are set to dull red.
The lights are turned on for 2 seconds then turned off using clear().
from microbit import *
import neopixel


buggyLights = neopixel.NeoPixel(pin13, 12)
dull_blue = [20, 20, 25]
dull_red = [25, 0, 0]
for i in range(6):
    buggyLights[i] = dull_blue
for i in range(6, 12):
    buggyLights[i] = dull_red
buggyLights.show()
sleep(2000)
buggyLights.clear()

Tasks

  1. Modify the code to turn on the left lights for 2 sec then turn on the right lights for 2 sec.

8.6. LED values

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

np[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 color value of the LED at position 0.
from microbit import *
import neopixel


buggy_lights = neopixel.NeoPixel(pin13, 12)
buggy_lights[0] = (255, 0, 0)
for rgb_value in buggy_lights[0]:
    display.scroll(rgb_value)

8.7. color lists

../../_images/rgb_colors.png
A list of colors can be used to create a colorful display.
Two for-loops are used, one nested inside the other.
for color in color_list: loops through the colors.
for led_num in range(12): loops through each LED to set its color.
from microbit import *
import neopixel

buggy_lights = neopixel.NeoPixel(pin13, 12)

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)

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

for color in color_list:
    for led_num in range(12):
        buggy_lights[led_num] = color
    buggy_lights.show()
    sleep(200)

For less bright lights use:

white = (20, 20, 20)
red = (20, 0, 0)
yellow = (20, 20, 0)
green = (0, 128, 0)
cyan = (0, 20, 20)
blue = (0, 0, 20)
magenta = (20, 0, 20)

8.8. Primary and secondary colors

bots/BitBotXL/images/primary_colors.png bots/BitBotXL/images/secondary_colors.png

Tasks

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

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

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