Maker Advent Calendar Day #12: RGB LED Strip!

It’s the final day of your 12 Projects of Codemas Advent Calendar! Today we're playing with an RGB LED Strip, but these aren't regular LEDs, these are addressable LEDs - meaning we can code all sorts of colours, patterns and sequences!

Time for some ultra-festive blinky!

Warning: Some of today's activities contain flashing lights which may not be suitable for those with photosensitive epilepsy.

Box #12 Contents

In this box you will find:

• 1x Custom addressable LED Strip with male jumper wires

Today’s Project

Today's a BIG one! We're going to learn how to light up the LEDs in our strip individually, how to code different colours and colour lists, how to create a light chaser, then a light chaser speed-controller using our potentiometer from day #4, some button colour control then fading effects - PHEW!

Before we start, let's talk about what an addressable LED is...

Addressable RGB LEDs

The LEDs in your strip are WS2812 Addressable LEDs, sometimes called 'NeoPixels' (which is a branded version from our good friends over at Adafruit).

These are are a special kind of LED that actually contain three small LEDs inside each  - one red, one green and one blue, which we mix to create lots of different colours with our code. This is why it's called an RGB strip - Red, Green, Blue! We'll talk more about that in a moment.

Each of these LEDs has a tiny controller chip inside that allows us to address (talk to) them individually in our code, unlike more traditional lighting options which light the entire strip in a single colour. However, because of this, they always need a microcontroller to tell them what to do.

With much longer strips you would usually have to worry about external power, resistors and other technicalities, however the compact custom strip in your box is short enough to allow us to avoid all of these distractions. We will be powering it from a different pin this time though, the VBUS pin (physical pin 40) as this will provide the full 5V the strip needs rather than the 3.3V pin we've used so far.

We’ve also had this LED strip made especially for this calendar with handy jumper wires so you don’t need to mess around with connectors and tools.

Step 1: Construct the Circuit

Disconnect your Pico from the USB port on your PC so that it's safe to amend our circuit. 

We're starting with a mostly bare breadboard so remove any other parts that may still be in place from yesterday, which should look like this:

Next grab your LED strip and fit the three wires as follows:

• Place the red wire into the VBUS pin (physical pin 40) - NOT the 3V3 pin this time!
• Fit the black wire into the GND pin, which is physical pin 38.
• Fit the green wire to GPIO 28 (physical pin 34)

Next we add one of our buttons and the potentiometer. Fit them to the left of the Pico as shown below - remember that your potentiometer will have a gap between each of the legs unlike our diagram:

Let's wire the button next. Our button will need the usual 3.3V, not the 5V on the VBUS pin we're using for the LED strip:

• Connect the left leg of the button to the upper red channel
• Connect the the right leg of the button to GPIO 15 (Physical pin 20)
• Then use another wire to connect the 3.3V pin (physical pin 36) to the upper red channel

Finally we connect the potentiometer with three wires as follows:

• Connect the left leg to the GND pin on physical pin 18
• Connect the middle leg to GPIO 26 (physical pin 31)
• Connect the right leg to the upper red channel (3.3V)

Activity 1: Minimal Starter Program - One LED

Time to twinkle - plug your Pico back in to the USB port on your computer and we'll get this thing all lit up!

Now, whilst we could just straight into something flashy and colourful with all the bells and whistles, we want to guide you through some easy examples first so you can understand how the code works.

This minimal example lights the first LED in red, just to get to grips with how the library works, which is now included within MicroPython so we don't need to install anything. Handy!

These strips can show lots of different colours as they are RGB strips - let's cover that first.

What is RGB?

RGB stands for Red Green Blue - it's a colour system used in computing to display colours on a computer display.

The three colours can be combined to show a huge range of different colours. With RGB each of the three colours can be set to an intensity value between 0 and 255. As each of the three colours has 255 possible different intensity values, technically there are 16777216 possible colour combinations (although your eyes probably wouldn't notice the difference between a lot of these when they're used with LEDs).

RGB with LEDs

How does this relate to our LED strip? Well, as we mentioned earlier, inside each of these clever LEDs are three smaller LEDS - one red, one green and one blue. We send code to the strip to set the RGB intensity value for each LED allowing it to mix and show different colours. Cool huh?!

There are lots of online tools to help you find the RGB values for your desired colour, such as this handy page from RapidTables. For example, basic red is 255,0,0.

The Code

Our example code imports 'neopixel' which is the name of the library now included in MicroPython to drive these kinds of addressable LEDs.

To set the LED strip up, line 7 sets the pin number for the strip (GPIO28) and the number of LEDs on the strip (15). We can now refer to it using 'strip' in our code.

To send data to the LED strip, we first write what we want it to do, then use strip.write() to send it to the strip - a bit like how our OLED display worked yesterday.

In the example below, we use strip[0] = (255,0,0). The [0] is telling our strip to drive the first LED only, because the first LED starts at 0, the second is 1 and so on. The numbers in the brackets are for the RGB value - we're using 255,0,0 which is red at the brightest intensity.

Copy the example below over to Thonny, run the code, then try the following tasks to get the hang of things:

• Try changing the 255 to 10, what happens? It should reduce the intensity.
• Try changing the RGB value to 0,10,0 - what happens? It should change the colour to green.
• Now try changing the [0] to [7] - what happens? It should light the 8th LED (because remember, the LED numbering starts with 0)
• Use an online RGB colour finder tool to identify and display your favourite colour

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)
        
# Select the first pixel (pixel 0)
# Set the RGB colour (red)
strip[0] = (255,0,0)

# Send the data to the strip
strip.write()

Activity 2: Using Multiple LEDS

Our next step is to drive more LEDs in our strip. We'll first show you a basic method of doing this, then a more efficient method, and then a much better method which will keep your code nice and compact.

To light more of our LEDs, we need to tell MicroPython which LEDs we want to send data to. So far we've only told MicroPython to light up LED 0 (the first LED).

A Basic Method

A basic way to do this is to just add more lines, changing the [0] to whatever number LED we want to light up.

The example below does exactly this, which will light up the first five LEDs in red on your strip. Give it a try then keep adding additional lines until you have a line for each of the 15 LEDs in the strip. Then we'll show you a better way...

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)
        
# Select the first pixel (pixel 0)
# Set the RGB colour (red)
strip[0] = (255,0,0)
strip[1] = (255,0,0)
strip[2] = (255,0,0)
strip[3] = (255,0,0)
strip[4] = (255,0,0)

# Send the data to the strip
strip.write()

A Better Method

Let's improve our code to save the number of lines we're using whilst making things a bit clearer.

The only thing our code is changing is the pin number for each of the 15 LEDs, so we can make use of a for loop and the range function that we've used previously.

We use a for loop to iterate over each LED on our strip. We know we have 15 LEDs, so we use for i in range(15): to tell this code block to iterate over a range of 15.

This range (using i) is 'injected' into our LED strip line as we use strip[i] = (255,0,0). It does this for the entire range of 15 LEDs, then once the for loop has completed, the final line writes this data to the strip which makes them all light up.

This still isn't the best way to simply fill the entire strip, but this example will be useful later on when we want to run some effects - so it's a good one to try!

Try the example code below to see for yourself (we went for yellow this time):

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# iterate over 15 leds
for i in range(15):
    
    # Set each LED in the range to yellow
    strip[i] = (255,255,0)

# Send the data to the strip
strip.write()

An Even Better Method!

Want to simply light the entire strip without any flexibility? It's super-simple - just use strip.fill((255,0,0)) and it'll light as many LEDs as you have defined in the setup line (15 for us). Make sure you use two sets of brackets with this one!

Try the simple example below (splash of turquoise anyone?), then have a play around with the RGB colour codes:

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Fill the strip with turquoise
strip.fill((72,209,204))

# Send the data to the strip
strip.write()

Activity 3: Better Colour Management

We now know how to light multiple LEDs, and we know how to create RGB colours. Let's show you a few tricks to help you manage colours a little easier, then we can move on to some really fun stuff!

Your program currently uses the RGB values to set a colour, but when you're looking back and reviewing your code it can be difficult to remember what they are. A better way is to create colour variables with the colour's name.

Colour variables

We've used variables a lot over the last twelve days, so you might already know what to do here but we're going to show you just in case!

We're going to take the example above (activity 2) and add variables for five different colours. We can then use these colours in our LED strip code to easily change the colour by just using the colour's name - such as strip[i] = (red).

Give the code below a try and then try changing the colour name in the brackets to one from our variables:

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Colour variables
red = 255,0,0
green = 0,255,0
blue = 0,0,255
yellow = 255,255,0
pink = 255,20,147

# iterate over 15 leds
for i in range(15):
    
    # Set each LED in the range to pink
    strip[i] = (pink)

# Send the data to the strip
strip.write()

Colour Lists

Now that we have our colour variables set up, we can also create a list of these colours which we can use later in a for loop to iterate over, allowing us to work through a selection of colours in our code. But what are lists in MicroPython?

Lists

Lists are another handy tool for your MicroPython toolbox. They are essentially a variable with multiple items inside. The items inside can be any data type - strings, integers, variables etc...simple!

Let's run a quick example, then we'll use lists in the next activity.

The short example below creates a list called 'mylist' and includes four strings inside square brackets separated by commas. That's it - lists are as simple as that!

In our example we then print this list by using the list name (variable) in the print line. Pop this into Thonny and give it a try:

mylist = ["Dasher","Dancer","Prancer","Vixen"]

print(mylist)

Activity 4: Light Chaser

Let's step it up a gear and create something really cool - a light chaser. How very festive!

In our example below we've created a list of colour variables called colours. We have also placed our LED code in an endless while loop, which contains a for loop with a nested for loop inside it.

Why use a nested for loop?

A nested for loop allows us to iterate over the colours first, then iterate over the LEDs.

The code is saying "For every colour in the colours list, run my code block" - and that code block then includes another for loop that runs this colour through our range of 15 LEDs. Once the range has run out, it jumps back to the initial for loop for the next colour and does it all over again.

We use j for colours and i for the LED range - if you remember from previous boxes, it doesn't matter what we use here. We could use 'colour' instead of 'j' and 'led' instead of 'i'. There are no rules here, just traditions!

When to Write Data

Another key change is when we write the data to the strip.

Earlier the strip.write() was outside of and after the for loop, waiting for the loop to finish setting all of the 15 LEDs before writing data. This time we write the data within the for loop after each iteration (after each single LED is set).

This means the for loop finds the next LED in the range and lights it up before moving on to the next LED, which gives a chasing effect to the LED strip rather than writing all 15 at the same time. 

We also use a simple time delay before writing the data to set the speed for the chaser.

That's a lot to take in, so try the code below and re-read the above whilst watching it dazzle. We'd also encourage you to add more colours and play with the time delay (setting it to 0.01 makes it super blinky!):

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Colour variables
red = 255,0,0
green = 0,255,0
blue= 0,0,255

# Define colour list
colours = [red, green, blue]

while True: # Run forever

    # Iterate over the colours
    for j in colours:
        
        # Then iterate over 15 leds
        for i in range(15):
            
            # Set each LED in the range to red
            strip[i] = (j)
            
            # Delay - the speed of the chaser
            time.sleep(0.1)
            
            # Send the data to the strip
            strip.write()

Activity 5: Speed-Controlled Light Chaser

We're now going to re-introduce our potentiometer to our code to allow us to control the speed of the light chaser. We will use the potentiometer ADC reading and use this to drive a variable for the time delay - just like we did in box #4 to control the speed of the flashing LEDs.

The Code

We don't have to change our original light chaser code much to achieve this, we simply:

• Add ADC to our imports
• Set up the GPIO pin for the potentiometer
• Add a line of code within the nested for loop to read the potentiometer into a variable, then divide that number to make it more useful as a time delay
• Use that reading variable to drive our time delay

Tip: If we didn't divide the sensor reading, we would be sending values from 0 to 65535 to our time delay (as seconds), which would be far too slow for the effect we're looking for. 

Copy this over to Thonny and give it ago. As you turn the potentiometer left, it should reduce the time delay and make the lights chase faster.

You can change the number we divide the reading by to increase/decrease the minimum delay, or perhaps add some more of your favourite colours as variables and include them in the list?

# Imports
import time
from machine import Pin, ADC
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Set up the potentiometer on ADC pin 26
potentiometer = ADC(Pin(26))

# Colour variables
red = 255,0,0
green = 0,255,0
blue= 0,0,255

# Define colour list
colours = [red, green, blue]

while True: # Run forever

    # Iterate over the colours
    for j in colours:
        
        # Then iterate over 15 leds
        for i in range(15):
            
            # Set the next LED in the range to light with a colour
            strip[i] = (j)
            
            # Read the potentiometer
            # Divide the reading to make it more usable as a time delay
            mydelay = potentiometer.read_u16() / 50000
            
            # Delay - the speed of the chaser
            time.sleep(mydelay)
            
            # Send the data to the strip
            strip.write()

Activity 6: Button Colour Control

We're going to hop back to using strip.fill to completely fill our LED strip with a single colour, however this time we're going to use our button to change the colour of the strip. This sounds simple but we need to change our approach to make it work.

Instead of entering the colour directly into the code using something like strip.fill((red)), or using a for loop to automatically iterate through our list of colours in order, we're going to use another method which uses the index of each colour in our colour list...but what is an index?

What is a List Index?

Each item in a list is given an index. This means that each item in a list is given a number, starting from zero.

Let's take our current list which is [red, green, blue]. The index for this list would be 0, 1 and 2. 0 = red, 1 = green and 2 = blue.

We can use this to pick a specific colour from our list by changing how we use the strip.fill line. For example, strip.fill((colours[1])) will use index 1 from the colours list - which is green.

You're probably thinking "but we could just use strip.fill((green))". This is true, however as the index uses a number, it allows us to easily change that number (and therefore the colour) with our button using variables.

Our code also needs to know the length of our index (how many colours we have in our list) so that our code doesn't try to use an index number that is outside of our list's range. For this we use len...

Wait, who is Len?

No not Len - len! We use len to return the number of items in a list. We simply use 'len' followed by the name of the list in brackets.

If our list looks like this:

colours = [red, green, blue]

Then we would use len in the following way to count and print how many items are in our list (which would be 3):

print(len(colours))

Try the following quick example to see this in action:

# Colour variables
red = 255,0,0
green = 0,255,0
blue= 0,0,255

# Define colour list
colours = [red, green, blue]

print(len(colours))

The Code

This is where everything above should come together and make sense (we hope!).

Our code example below has some new variables:

• myindex - we use this as an index number to select a colour from our list. We change this number when the button is pressed to move it to the next number in the index (the next colour)
• indexlength - this counts the number of items in our colour list (3, in our example). However, as we're using this to identify the last number in our index, we have to -1 at the end (because there are 3 items in our list, but as these will be indexed as 0,1 and 2, we want our maximum index value to be 2)

The example code below uses a while loop that does nothing (just a delay) until a button is pressed. Once the button is pressed, it uses an if statement to check what the current myindex variable value is.

If the myindex variable is less than the indexlength variable (if myindex is less than 2), it will add +1 to the myindex variable. We also use an else statement under this (to catch when myindex is 3) which resets myindex back to 0.

Regardless of whether the if statement or else statement has triggered, both will alter the myindex variable then move to the code below them.

These final lines of code update the strip.fill with the index number using the myindex variable, and then writes the data to the LED strip. We only write the data to the LED strip here as this means data is only written when there is a change - if the button isn't pressed, nothing happens.

Have a good look through the code example, then copy it over to Thonny to try it for yourself:

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define our button pin
button = Pin(15, Pin.IN, Pin.PULL_DOWN)

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Colour variables
red = 255,0,0
green = 0,255,0
blue= 0,0,255

# Define colour list
colours = [red, green, blue]

# Create index variable starting at 0
myindex = 0

# Variable with the number of items in our list (3)
# We -1 as the index starts at 0, and we want to use this for the colour list index number (0, 1 or 2)
# This is useful as it means we don't have to count the colours if we add more
indexlength = len(colours) -1

while True: # Run forever
    
    time.sleep(0.4) # Delay
    
    if button() == 1: # If button pressed
        
        # If the index variable is less than or equal to the lengh of the index
        if myindex < indexlength:
            
            # Add +1 to the index variable
            myindex = myindex + 1
        
        # If the index variable is over the index length
        else:
            
            # Set index variable back to 0 (the first item in our list)
            myindex = 0
            
        ## Now this code runs AFTER the if statements...
        
        # Fill the strip with the current list index colour
        strip.fill((colours[myindex]))
            
        # Write the data to the LED strip
        strip.write()

Activity 7: Fading

Now let's try fading our LED strip in and out - it's surprisingly easy with some simple for loop code, and it gives us a chance to show you another way to use the range function.

Our example below uses a while loop with two for loops inside it, both using the range function.

These for loops iterate the red R value (from RGB) used in the strip.fill line below them, so that each iteration is changes the R value. You can see where we use i instead of a value in strip.fill((i,0,0)).

Additional Range Parameters

You'll also notice that the range brackets contain three numbers! Whereas previously we've just specified a single number to iterate over, using the three values (parameters) lets you can specify the:

• Start of the range
• End of the range
• Step for each iteration

Our example below uses for i in range(0,255,1) which is setting the start of the range to 0, the end of the range at 255, and telling the code to increase by 1 step each iteration.

What this does is change our Red value by 1 step every iteration, starting at 1 and ending at 255. This creates a fading effect as the intensity moves from 1 (dim) to 255 (bright) very quickly, using the delay we have set.

The next for loop does the same thing, but in reverse. Yes - you can go backwards with the range function! So we set our range to start at 255 instead of 1, and end at 1 instead of 255. The step is -1 so that we continually take 1 away from that starting 255 value.

Try the code below, then try playing with the colour values - try using i in other places such as strip.fill((i,0,i)) or add fixed values to the other colours such as strip.fill((i,0,50)):

# Imports
import time
from machine import Pin
from neopixel import NeoPixel

# Define the strip pin number (28) and number of LEDs (15)
strip = NeoPixel(Pin(28), 15)

# Variable for the fade speed
delay = 0.005

while True: # Run forever
    
    # Iterate from 1 to 255 in steps of 1
    for i in range(1,255,1):
        
        # Fill the strip using the iterated R value
        strip.fill((i,0,0))
        
        # Write the data to the LED strip
        strip.write()
        
        # Delay
        time.sleep(delay)
        
    # iterate from 255 to 1 in steps of -1
    for i in range(255,1,-1):
        
        # Fill the strip using the iterated R value
        strip.fill((i,0,0))
        
        # Write the data to the LED strip
        strip.write()
        
        # Delay
        time.sleep(delay)

Day #12 Complete!

This was a little longer than some of our other days as these LED strips are such a fun and versatile part to play with (and there's so much more you can do!).

We're pretty sure most of you will be turning your strip into a fancy monitor backlight - perhaps some will combine it with the PIR to turn it on when there's motion in front of their PC, or maybe some cleverly hidden break beam sensors will be used as a hand-activated colour changer? Whatever you make, we'd love to hear about your projects in the comments section!

So what did we cover on day #12? Today you have:

• Learnt what an addressable LED is and why they're sooo fun!
• Built a circuit with addressable LEDs
• Learnt about RGB and how to create colours with RGB values (and where to find them)
• Learnt how to code addressable LEDs with MicroPython
• Learnt different ways to light the entire strip...some more efficient than others!
• Created colour variables
• Leant how to create and use lists in MicroPython, including list indexes
• Used nested for loops
• Leant how to use len in MicroPython
• Faded addressable LEDs using range (both counting up and down)

Over to you...

That's it folks, it's the end of the Maker Advent Calendar :( We know many of you wanted this to last the traditional full 25 days, however the world is in a funny ol' place right now and we wanted this to be as affordable and accessible to as many people as possible.

We really hope you've enjoyed following along each day, and we really hope you'll continue your journey as a maker, using your selection of components to make fun projects, experimenting using different parts together to make awesome projects.

We've only just scratched the surface on what's possible with this fantastic little microcontroller and the components you've discovered over the last 12 days - there's so much more to learn and experience!

If you would like to expand your selection of components for the Pico, the store is full of goodies - be sure to check out our dedicated Raspberry Pi Pico section too!

More Resources

The internet is jam-packed full of projects and examples using the Raspberry Pi Pico and MicroPython, and 99.9% of this information is free - so don't stop now! We've even had some great examples from makers in the comments sections of the calendar along the way.

Search Engines are your best friend when it comes to making and coding. Forums, blogs, tutorials, social network user groups and more are at your fingertips and hold and endless amount of examples, code snippets, previous discussions and useful information.

A good starting place for inspiration and a great community is the Raspberry Pi forum, specifically the Pico section. Just don't forget to always search before asking a question!

That's all Folks!

Have a wonderful festive period and a Happy New Year, from everyone at The Pi Hut!

We used Fritzing to create the breadboard wiring diagram images for this page.