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README.md

Stellar Unicorn (MicroPython)

Stellar Unicorn offers 16x16 bright RGB LEDs driven by Pico W's PIO in addition to a 1W amplifier + speaker, a collection of system and user buttons, and two Qw/ST connectors for adding external sensors and devices. Woha!

You can buy one here: https://shop.pimoroni.com/products/stellar-unicorn

These are not your everyday RGB LEDs!

Internally Stellar Unicorn applies gamma correction to the supplied image data and updates the display with 14-bit precision resulting in extremely linear visual output - including at the low end.

The display is refreshed around 300 times per second (300fps!) allowing for rock solid stability even when being filmed, no smearing or flickering even when in motion.

No strobing or brightness stepping here folks - it's the perfect backdrop for your tricked out streaming setup!

Getting started

The Stellar Unicorn library provides a collection of methods that allow you to easily access all of the features on the board.

Drawing is primarily handled via our PicoGraphics library which provides a comprehensive selection of drawing methods - once your drawing work is complete you pass the PicoGraphics object to Stellar Unicorn to have it displayed on the screen.

Example Program
Interleaved Framebuffer
Function Reference

Example Program

The following example shows how to scroll a simple message across the display.

from stellar import StellarUnicorn
from picographics import PicoGraphics, DISPLAY_STELLAR_UNICORN
import time

# create a PicoGraphics framebuffer to draw into
graphics = PicoGraphics(display=DISPLAY_STELLAR_UNICORN)

# create our StellarUnicorn object
su = StellarUnicorn()

# start position for scrolling (off the side of the display)
scroll = float(-StellarUnicorn.WIDTH)

# message to scroll
MESSAGE = "Pirate. Monkey. Robot. Ninja."

# pen colours to draw with
BLACK = graphics.create_pen(0, 0, 0)
YELLOW = graphics.create_pen(255, 255, 0)

while True:
    # determine the scroll position of the text
    width = graphics.measure_text(MESSAGE, 1)
    scroll += 0.25
    if scroll > width:
      scroll = float(-StellarUnicorn.WIDTH)

    # clear the graphics object
    graphics.set_pen(BLACK)
    graphics.clear()

    # draw the text
    graphics.set_pen(YELLOW)
    graphics.text(MESSAGE, round(0 - scroll), 2, -1, 0.55)

    # update the display
    su.update(graphics)

    time.sleep(0.02)

Interleaved Framebuffer

Stellar Unicorn takes advantage of the RP2040's PIOs to drive screen updates - this is what gives it the performance it needs to render with 14-bit precision at over 300 frames per second.

The PIO is a powerful, but limited, tool. It has no way to access memory at random and minimal support for decision making and branching. All it can really do is process a stream of data/instructions in order.

This means that we need to be clever about the way we pass data into the PIO program, the information needs to be delivered in the exact order that the PIO will need to process it. To achieve this we "interleave" our framebuffer - each frame of BCM data is passed one after another with values for the current row, pixel count, and timing inserted as needed:

row 0 data:
  for each bcd frame:
    bit    : data
          0: 00110110                           // row pixel count (minus one)
    1  - 53: xxxxxbgr, xxxxxbgr, xxxxxbgr, ...  // pixel data
    54 - 55: xxxxxxxx, xxxxxxxx                 // dummy bytes to dword align
         56: xxxxrrrr                           // row select bits
    57 - 59: tttttttt, tttttttt, tttttttt       // bcd tick count (0-65536)

row 1 data:
  ...

If you're working with our library then you don't need to worry about any of these details, they are handled for you.

Function Reference

Imports and Objects

To access these functions, you'll need to first import the relevant libraries and then set up a Stellar Unicorn object:

from stellar import StellarUnicorn

su = StellarUnicorn()

or (with PicoGraphics):

from stellar import StellarUnicorn
from picographics import PicoGraphics, DISPLAY_STELLAR_UNICORN

su = StellarUnicorn()
graphics = PicoGraphics(display=DISPLAY_STELLAR_UNICORN)

System State

`set_brightness(value)`

Set the brightness - value is supplied as a floating point value between 0.0 and 1.0.

`get_brightness()`

Returns the current brightness as a value between 0.0 and 1.0.

`adjust_brightness(delta)`

Adjust the brightness of the display - delta is supplied as a floating point value and will be added to the current brightness (and then clamped to the range 0.0 to 1.0).

For example:

su.set_brightness(0.5)
su.adjust_brightness(0.1)  # brightness is now 0.6
su.adjust_brightness(0.7)  # brightness is now 1.0
su.adjust_brightness(-0.2)  # brightness is now 0.8

`set_volume(value)`

Set the volume - value is supplied as a floating point value between 0.0 and 1.0.

`get_volume()`

Returns the current volume as a value between 0.0 and 1.0.

`adjust_volume(delta)`

Adjust the volume - delta is supplied as a floating point value and will be added to the current volume (and then clamped to the range 0.0 to 1.0).

For example:

su.set_volume(0.5)
su.set_volume(0.1)  # volume is now 0.6
su.adjust_volume(0.7)  # volume is now 1.0
su.adjust_volume(-0.2)  # volume is now 0.8

`light()`

Get the current value seen by the onboard light sensor as a value between 0 and 4095.

`is_pressed(button)`

Returns true if the requested button is currently pressed.

There are a set of constants in the StellarUnicorn class that represent each of the buttons. The brightness, sleep, and volume buttons are not tied to hardware functions (they are implemented entirely in software) so can also be used for user functions if preferred. Here's a list of the constants and their associated pin numbers:

SWITCH_A               =  0
SWITCH_B               =  1
SWITCH_C               =  3
SWITCH_D               =  6
SWITCH_SLEEP           = 27
SWITCH_VOLUME_UP       =  7
SWITCH_VOLUME_DOWN     =  8
SWITCH_BRIGHTNESS_UP   = 21
SWITCH_BRIGHTNESS_DOWN = 26

For example:

while not su.is_pressed(StellarUnicorn.SWITCH_A):
    # wait for switch A to be pressed
    pass

print("We did it! We pressed switch A! Heck yeah!")

Drawing

`update(PicoGraphics)`

The PicoGraphics library provides a collection of powerful drawing methods to make things simple.

The image on the PicoGraphics object provided is copied to the interleaved framebuffer with gamma correction applied.

For example (assuming you've set up your Stellar Unicorn and PicoGraphics objects up as we did above):

su.update(graphics)

⚠️ If you've used PicoGraphics on our other boards note that this update function works a little differently. Here it's a Stellar Unicorn function to which you need to pass a PicoGraphics object to.

`clear()`

Clear the contents of the interleaved framebuffer. This will make your Stellar Unicorn display turn off. To show an image again, call the update() function as described above.

Audio

Audio functionality is supported by our PicoSynth library which allows you to create multiple voice channels with ADSR (attack decay sustain release) envelopes. It provides a similar set of functionality to the classic SID chip in the Commodore 64.

`play_sample(data)`

Play the provided 16-bit audio sample. data must point to a bytearray that contains 16-bit PCM data. The number of samples is retrieved from the array's length.

`synth_channel(channel)`

Gets a Channel object which can then be configured with voice, ADSR envelope, etc.

`play_synth()`

Start the synth playing.

`stop_playing()`

Stops any currently playing audio.

Channel Reference

configure(waveforms=None, frequency=None, volume=None,
          attack=None, decay=None, sustain=None,
          release=None, pulse_width=None)
restore()
waveforms()
waveforms(waveforms)
frequency()
frequency(frequency)
volume()
volume(volume)
attack_duration()
attack_duration(duration)
decay_duration()
decay_duration(duration)
sustain_level()
sustain_level(level)
release_duration()
release_duration(duration)
pulse_width()
pulse_width(width)
trigger_attack() # start the channel playing
trigger_release() # stop the channel playing
play_tone(frequency, volume=None, attack=None, release=None)

Constants

`WIDTH` & `HEIGHT`

The width and height of Stellar Unicorn are available in constants WIDTH and HEIGHT.

For example:

num_pixels = StellarUnicorn.WIDTH * StellarUnicorn.HEIGHT
print(num_pixels)

Using Breakouts

Stellar Unicorn has two Qw/ST (Qwiic/STEMMA QT) connectors. Breakouts with Qw/ST connectors, can be plugged straight in with a JST-SH to JST-SH cable. You can connect I2C Breakout Garden breakouts without Qw/ST connectors using a JST-SH to JST-SH cable and a Qw/ST to Breakout Garden adaptor.

List of breakouts currently supported in our C++/MicroPython build

Stellar Unicorn uses GP4 and GP5 for its I2C interface. You can use the constants in the shared pimoroni module to set up the I2C interface:

from pimoroni_i2c import PimoroniI2C
from pimoroni import BREAKOUT_GARDEN_I2C_PINS

i2c = PimoroniI2C(**BREAKOUT_GARDEN_I2C_PINS)

Alternatively, you can specify the pin numbers directly:

from pimoroni_i2c import PimoroniI2C

i2c = PimoroniI2C(sda=4, scl=5)

README.md

Stellar Unicorn (MicroPython)

These are not your everyday RGB LEDs!

Getting started

Example Program

Interleaved Framebuffer

Function Reference

Imports and Objects

System State

set_brightness(value)

get_brightness()

adjust_brightness(delta)

set_volume(value)

get_volume()

adjust_volume(delta)

light()

is_pressed(button)

Drawing

update(PicoGraphics)

clear()

Audio

play_sample(data)

synth_channel(channel)

play_synth()

stop_playing()

Channel Reference

Constants

WIDTH & HEIGHT

Using Breakouts

`set_brightness(value)`

`get_brightness()`

`adjust_brightness(delta)`

`set_volume(value)`

`get_volume()`

`adjust_volume(delta)`

`light()`

`is_pressed(button)`

`update(PicoGraphics)`

`clear()`

`play_sample(data)`

`synth_channel(channel)`

`play_synth()`

`stop_playing()`

`WIDTH` & `HEIGHT`