Install Noisy Grains of Sand code

The code for this project is available in the Adafruit Learning System Github here. In the code listing below, you can click code.py and save it to your computer. 

Now that you have CircuitPython installed, you simply need to place the code.py file onto the NeoTrellis M4 by copying it into the mounted USB folder named CIRCUITPY.

Install Sound File

One of the great things that makes the NeoTrellis M4 different from other LED matrices is that it can play sounds! We should take advantage of that for this grains of sand demo.

I recommend this water click sound. This is derived from a Creative Commons licensed sound available on FreeSound, and I have processed it to work well on the NeoTrellisM4 (PS - the author of this sound really likes this demo!).

Copy water-click.wav onto your CIRCUITPY drive in the main directory.

There are many other sound files available which could more humorous or suitable for your application. Please feel free to experiment!

# Digital sand demo uses the accelerometer to move sand particles in a
# realistic way.  Tilt the board to see the sand grains tumble around and light
# up LEDs.  Based on the code created by Phil Burgess and Dave Astels, see:
#   https://learn.adafruit.com/digital-sand-dotstar-circuitpython-edition/code
#   https://learn.adafruit.com/animated-led-sand
# Ported to NeoTrellis M4 by John Thurmond.
#
# The MIT License (MIT)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

import math
import random
import board
import audioio
import busio
import adafruit_trellism4
import adafruit_adxl34x

N_GRAINS = 8  # Number of grains of sand
WIDTH = 8  # Display width in pixels
HEIGHT = 4  # Display height in pixels
NUMBER_PIXELS = WIDTH * HEIGHT
MAX_FPS = 20  # Maximum redraw rate, frames/second
MAX_X = WIDTH * 256 - 1
MAX_Y = HEIGHT * 256 - 1

class Grain:
    """A simple struct to hold position and velocity information
    for a single grain."""

    def __init__(self):
        """Initialize grain position and velocity."""
        self.x = 0
        self.y = 0
        self.vx = 0
        self.vy = 0

grains = [Grain() for _ in range(N_GRAINS)]

color = random.randint(1, 254) # Set a random color to start
current_press = set() # Get ready for button presses

# Set up Trellis and accelerometer
trellis = adafruit_trellism4.TrellisM4Express(rotation=0)
i2c = busio.I2C(board.ACCELEROMETER_SCL, board.ACCELEROMETER_SDA)
sensor = adafruit_adxl34x.ADXL345(i2c)

# Add tap detection - with a pretty hard tap
sensor.enable_tap_detection(threshold=50)

color_mode = 0

oldidx = 0
newidx = 0
delta = 0
newx = 0
newy = 0

occupied_bits = [False for _ in range(WIDTH * HEIGHT)]

# Add Audio file...
f = open("water-click.wav", "rb")
wav = audioio.WaveFile(f)
print("%d channels, %d bits per sample, %d Hz sample rate " %
      (wav.channel_count, wav.bits_per_sample, wav.sample_rate))
audio = audioio.AudioOut(board.A1)
#audio.play(wav)

def index_of_xy(x, y):
    """Convert an x/column and y/row into an index into
    a linear pixel array.

    :param int x: column value
    :param int y: row value
    """
    return (y >> 8) * WIDTH + (x >> 8)

def already_present(limit, x, y):
    """Check if a pixel is already used.

    :param int limit: the index into the grain array of
    the grain being assigned a pixel Only grains already
    allocated need to be checks against.
    :param int x: proposed clumn value for the new grain
    :param int y: proposed row valuse for the new grain
    """
    for j in range(limit):
        if x == grains[j].x or y == grains[j].y:
            return True
    return False

def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return 0, 0, 0
    if pos < 85:
        return int(255 - pos*3), int(pos*3), 0
    if pos < 170:
        pos -= 85
        return 0, int(255 - pos*3), int(pos*3)
    pos -= 170
    return int(pos * 3), 0, int(255 - (pos*3))

for g in grains:
    placed = False
    while not placed:
        g.x = random.randint(0, WIDTH * 256 - 1)
        g.y = random.randint(0, HEIGHT * 256 - 1)
        placed = not occupied_bits[index_of_xy(g.x, g.y)]
    occupied_bits[index_of_xy(g.x, g.y)] = True
    g.vx = 0
    g.vy = 0

while True:
    # Check for tap and adjust color mode
    if sensor.events['tap']:
        color_mode += 1
    if color_mode > 2:
        color_mode = 0

    # Display frame rendered on prior pass.  It's done immediately after the
    # FPS sync (rather than after rendering) for consistent animation timing.

    for i in range(NUMBER_PIXELS):

        # Some color options:

        # Random color every refresh
        if color_mode == 0:
            if occupied_bits[i]:
                trellis.pixels[(i%8, i//8)] = wheel(random.randint(1, 254))
            else:
                trellis.pixels[(i%8, i//8)] = (0, 0, 0)
        # Color by pixel
        if color_mode == 1:
            trellis.pixels[(i%8, i//8)] = wheel(i*2) if occupied_bits[i] else (0, 0, 0)

        # Change color to random on button press, or cycle when you hold one down
        if color_mode == 2:
            trellis.pixels[(i%8, i//8)] = wheel(color) if occupied_bits[i] else (0, 0, 0)

    # Change color to a new random color on button press
    pressed = set(trellis.pressed_keys)
    for press in pressed - current_press:
        if press:
            print("Pressed:", press)
            color = random.randint(1, 254)
            print("Color:", color)

    # Read accelerometer...
    f_x, f_y, f_z = sensor.acceleration

    # I had to manually scale these to get them in the -128 to 128 range-ish - should be done better
    f_x = int(f_x * 9.80665 * 16704/1000)
    f_y = int(f_y * 9.80665 * 16704/1000)
    f_z = int(f_z * 9.80665 * 16704/1000)

    ax = f_x >> 3  # Transform accelerometer axes
    ay = f_y >> 3  # to grain coordinate space
    az = abs(f_z) >> 6  # Random motion factor

    print("%6d %6d %6d"%(ax,ay,az))
    az = 1 if (az >= 3) else (4 - az)  # Clip & invert
    ax -= az  # Subtract motion factor from X, Y
    ay -= az
    az2 = (az << 1) + 1  # Range of random motion to add back in

    # Adjust axes for the NeoTrellis M4 (reuses code above rather than fixing it - inefficient)
    ax2 = ax
    ax = -ay
    ay = ax2

    # ...and apply 2D accel vector to grain velocities...
    v2 = 0  # Velocity squared
    v = 0.0  # Absolute velociy
    for g in grains:

        g.vx += ax + random.randint(0, az2)  # A little randomness makes
        g.vy += ay + random.randint(0, az2)  # tall stacks topple better!

        # Terminal velocity (in any direction) is 256 units -- equal to
        # 1 pixel -- which keeps moving grains from passing through each other
        # and other such mayhem.  Though it takes some extra math, velocity is
        # clipped as a 2D vector (not separately-limited X & Y) so that
        # diagonal movement isn't faster

        v2 = g.vx * g.vx + g.vy * g.vy
        if v2 > 65536:  # If v^2 > 65536, then v > 256
            v = math.floor(math.sqrt(v2))  # Velocity vector magnitude
            g.vx = (g.vx // v) << 8  # Maintain heading
            g.vy = (g.vy // v) << 8  # Limit magnitude

    # ...then update position of each grain, one at a time, checking for
    # collisions and having them react.  This really seems like it shouldn't
    # work, as only one grain is considered at a time while the rest are
    # regarded as stationary.  Yet this naive algorithm, taking many not-
    # technically-quite-correct steps, and repeated quickly enough,
    # visually integrates into something that somewhat resembles physics.
    # (I'd initially tried implementing this as a bunch of concurrent and
    # "realistic" elastic collisions among circular grains, but the
    # calculations and volument of code quickly got out of hand for both
    # the tiny 8-bit AVR microcontroller and my tiny dinosaur brain.)

    for g in grains:
        newx = g.x + g.vx  # New position in grain space
        newy = g.y + g.vy
        if newx > MAX_X:  # If grain would go out of bounds
            newx = MAX_X  # keep it inside, and
            g.vx //= -2  # give a slight bounce off the wall
        elif newx < 0:
            newx = 0
            g.vx //= -2
        if newy > MAX_Y:
            newy = MAX_Y
            g.vy //= -2
        elif newy < 0:
            newy = 0
            g.vy //= -2

        oldidx = index_of_xy(g.x, g.y)  # prior pixel
        newidx = index_of_xy(newx, newy)  # new pixel
        # If grain is moving to a new pixel...
        if oldidx != newidx and occupied_bits[newidx]:
            # but if that pixel is already occupied...
            # What direction when blocked?
            delta = abs(newidx - oldidx)
            if delta == 1:  # 1 pixel left or right
                newx = g.x  # cancel x motion
                # and bounce X velocity (Y is ok)
                g.vx //= -2
                newidx = oldidx  # no pixel change
            elif delta == WIDTH:  # 1 pixel up or down
                newy = g.y  # cancel Y motion
                # and bounce Y velocity (X is ok)
                g.vy //= -2
                newidx = oldidx  # no pixel change
            else:  # Diagonal intersection is more tricky...
                # Try skidding along just one axis of motion if
                # possible (start w/ faster axis). Because we've
                # already established that diagonal (both-axis)
                # motion is occurring, moving on either axis alone
                # WILL change the pixel index, no need to check
                # that again.
                if abs(g.vx) > abs(g.vy):  # x axis is faster
                    newidx = index_of_xy(newx, g.y)
                    # that pixel is free, take it! But...
                    if not occupied_bits[newidx]:
                        newy = g.y  # cancel Y motion
                        g.vy //= -2  # and bounce Y velocity
                    else:  # X pixel is taken, so try Y...
                        newidx = index_of_xy(g.x, newy)
                        # Pixel is free, take it, but first...
                        if not occupied_bits[newidx]:
                            newx = g.x  # Cancel X motion
                            g.vx //= -2  # Bounce X velocity
                        else:  # both spots are occupied
                            newx = g.x  # Cancel X & Y motion
                            newy = g.y
                            g.vx //= -2  # Bounce X & Y velocity
                            g.vy //= -2
                            newidx = oldidx  # Not moving
                else:  # y axis is faster. start there
                    newidx = index_of_xy(g.x, newy)
                    # Pixel's free! Take it! But...
                    if not occupied_bits[newidx]:
                        newx = g.x  # Cancel X motion
                        g.vx //= -2  # Bounce X velocity
                    else:  # Y pixel is taken, so try X...
                        newidx = index_of_xy(newx, g.y)
                        # Pixel is free, take it, but first...
                        if not occupied_bits[newidx]:
                            newy = g.y  # cancel Y motion
                            g.vy //= -2  # and bounce Y velocity
                        else:  # both spots are occupied
                            newx = g.x  # Cancel X & Y motion
                            newy = g.y
                            g.vx //= -2  # Bounce X & Y velocity
                            g.vy //= -2
                            newidx = oldidx  # Not moving
        occupied_bits[oldidx] = False
        occupied_bits[newidx] = True
        if oldidx != newidx:
            audio.play(wav) # If there's an update, play the sound
        g.x = newx
        g.y = newy

Sanity Check

Assuming you've done everything correctly, your mounted USB folder on your NeoTrellis M4 should look something that what's on the left, with the code.py and water-click.wav file in place.

If this is the case, you should be up and running - now go play!

This guide was first published on Feb 13, 2019. It was last updated on Feb 13, 2019. This page (Code) was last updated on Nov 17, 2019.