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RGB-led-microbit.md

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title Using RGB LEDs with the microbit
layout text-width-sidebar
meta-description Drive an RGB LED with the microbit
share true
author jez
about Connect a RGB LED to make any colour you wish!
cats external
simple-description RGB LEDs
acknowledgements RGB LED teaser image by Oomlout (CC-BY-2.0). RGB spectrum image public domain.
date 2016-12-23 10:20:00 UTC
date-updated 2016-12-23 10:20:00 UTC

An RGB LED is essentially a red, green and blue LED combined into one package.

RGB LED{:.ui .image}

An RGB LED has four legs: an anode to drive each of the three component colours and a common cathode. The longest pin is the common cathode (-) and is used by all other LEDs in the package.

Each of the colours---red, green and blue---can be made my supplying current to the shorter pins. Usually the order of the pins is the same as the diagram above; but occassionally they can change, and sometimes it's even a common anode.

RGB LED{:.ui .centered .image}

Any coloured light can be made by varying how bright the red, blue and green LEDs are lit. This can be done with pin0.write_analog(n) where n is a value between 0 (off) and 1023 (on full).

{:.ui .dividing .header}

Electronics

220Ω resistors are placed before the each of the anode pins. 220Ω is a safe choice and will cover all RGB LEDs. You can consult the datasheet of the LED if you have it; you may not even need a resistor but it's better safe than sorry!

RGB LED{:.ui .image}

{% include box.html content="which-resistor" %}

{:.ui .dividing .header}

Code

Python

Code to show a yellow light for two seconds then show a red light slowly turning magenta

{% highlight python %} from microbit import *

assign colour names to each of the pins

red = pin0 blue = pin1 green = pin2

while True:

# Make Yellow
red.write_digital(1)
green.write_digital(1)
sleep(2000)			 # Show yellow for 2 seconds

# Turn off Yellow
red.write_digital(0)
green.write_digital(0)

# turn on red
# slowly increment the intensity of blue to make magenta
red.write_digital(1)
for i in range(0,1023):
    blue.write_analog(i)
    sleep(10)

# turn off pins before repeating
red.write_digital(0)
blue.write_digital(0)

{% endhighlight %}

{:.ui .dividing .header}

Notes

  • pin0.analog_write(512) is half as bright as pin0.analog_write(1023).

{% include box.html content="digital-vs-analog" %}

Experiment

  • Use random.randrange(start, stop, step) to generate a random colour every few seconds
  • Use three potentiometers to mix the colours