CircuitPython NeoPixel Library Using SPI
Created by Carter Nelson
https://learn.adafruit.com/circuitpython-neopixels-using-spi
Last updated on 2024-06-03 02:56:27 PM EDT
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Overview
NeoPixels are really great in terms of pin use. They only require three pins, and two of
those are power and ground. They only need one pin for data which is used for all the
NeoPixels attached. Amazing.
However, this comes at the cost of requiring the data signal maintain a very specific
timing requirement. See here(https://adafru.it/jFu) for some details from the excellent
NeoPixel Uberguide(https://adafru.it/oe1).
The NeoPixel SPI Hack
This is a pretty cool hack. The key enabling feature is the much faster relative speed
of the SPI bus compared to the NeoPixel data signals. The NeoPixel data signal runs
at 800kHz = 0.8MHz with some older ones running even slower at 400kHz = 0.4MHz.
A SPI bus can be clocked in the 10s of MHz - orders of magnitude faster than
NeoPixel!
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This hack takes advantage of that faster speed to "synthesize" the NeoPixel data
signal on the SPI's MOSI pin. In its most simple form, the hack turns every bit of
NeoPixel data into a specific byte in the SPI data. There only two bytes that matter -
one that represents a NeoPixel 0 bit, and one that represents a NeoPixel 1 bit.
Once the desired NeoPixel data has been translated into SPI data, it is simply clocked
out on the SPI bus. The SPI bus frequency is set such that the data comes out at the
expected NeoPixel timing. Then, by wiring the SPI MOSI pin to the NeoPixel data in
pin, you can drive NeoPixels using the SPI bus. From the NeoPixel's point of view, it
just sees the specific data signal it expects and you get happy blinky NeoPixels.
SPI Support in CircuitPython NeoPixel Library
All this work has been done for you via a new NeoPixel_SPI class that can be found in
the CircuitPython NeoPixel SPI library(https://adafru.it/NHd). When driving NeoPixels
via a SPI port, you simply use this class. After the initial setup, you can then use the
NeoPixels as normal.
Let's see some examples.
FT232H Example
Using the SPI port option of an FT232H, we can drive NeoPixels from any PC with a
USB port. See here for details about getting the FT232H installed and setup for your
specific operating system:
CircuitPython FT232H Guide
https://adafru.it/Gbs
And of course, also install the NeoPixel library:
sudo pip3 install adafruit-circuitpython-neopixel-spi
FT232H Wiring
The wiring is pretty simple.
FT232H 5V to NeoPixel VIN
FT232H GND to NeoPixel GND
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FT232H D1 to NeoPixel DIN
Note how only the MOSI (D1) pin of the SPI port is used. The other SPI pins, including
SCLK, are not used at all.
Once you are wired up, try running the program in the Example Code section.
python3 neo_ring.py
Example Code
Once you've gone through the setup specific to your hardware, you should be able to
run this example code on any of them.
•
Don't forget to set the BLINKA_FT232H environment variable. See guide linked
above for OS specific details.
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This example was written for the 12 pixel RGB NeoPixel ring(http://adafru.it/1643)
shown in the wiring diagrams. To use with other NeoPixel products, change
NUM_PIXELS and PIXEL_ORDER to match your setup. You can also change or add
colors to the COLORS tuple and change the speed via DELAY.
Save this as neo_ring.py:
import time
import board
import neopixel_spi as neopixel
NUM_PIXELS = 12
PIXEL_ORDER = neopixel.GRB
COLORS = (0xFF0000, 0x00FF00, 0x0000FF)
DELAY = 0.1
spi = board.SPI()
pixels = neopixel.NeoPixel_SPI(spi,
NUM_PIXELS,
pixel_order=PIXEL_ORDER,
auto_write=False)
while True:
for color in COLORS:
for i in range(NUM_PIXELS):
pixels[i] = color
pixels.show()
time.sleep(DELAY)
pixels.fill(0)
If you are using the FT232H, don't forget to set the BLINKA_FT232H
environment variable.
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