Rather than use the Adafruit trade name, these are more properly called WS2812 LEDs. Each one contains a tiny microcontroller and it only takes three connections to drive a long chain of addressable colour LEDs. The downside is that the protocol to drive these is a bit of a bear, and really needs an accurate, fast clock signal to be reliable.
The STM32F411 chip does have just such a clock, and the generic micropython-ws2812 library slightly misuses the SPI bus to handle the signalling. The wiring’s simple:
F411 GND to WS2812 GND;
F411 3V3 to WS2812 5V;
F411 PA7 (SPI1_MOSI) PB15 (SPI2_MOSI) to WS2812 DIn
Next, copy ws2812.py into the WeAct F411’s flash. Now create a script to drive the LEDs. Here’s one to drive 8 LEDs, modified from the library’s advanced example:
# -*- coding: utf-8 -*-
import time
import math
from ws2812 import WS2812
ring = WS2812(spi_bus=2, led_count=8, intensity=0.1)
def data_generator(led_count):
data = [(0, 0, 0) for i in range(led_count)]
step = 0
while True:
red = int((1 + math.sin(step * 0.1324)) * 127)
green = int((1 + math.sin(step * 0.1654)) * 127)
blue = int((1 + math.sin(step * 0.1)) * 127)
data[step % led_count] = (red, green, blue)
yield data
step += 1
for data in data_generator(ring.led_count):
ring.show(data)
time.sleep_ms(100)
Previously I said you’d see your WS2812s flicker and shimmer from the SPI bus noise. I thought it was cool, but I suspect it was also why the external flash on my F411 board just died. By pumping data into PA7, I was also hammering the flash chip’s DI line …
Volker Forster at Universal Solder was kind enough to send me a couple of these boards for free when I asked about availability. By way of thanks, I’m writing this article about what’s neat about these micro-controller boards.
always neat packaging from Universal Solder
Can I just say how nicely packaged Universal Solder’s own or customized products are? They want it to get to you, and they want it to work.
I’d previously played around with Blue Pill and Black Pill boards with limited success. Yes, they’re cheap and powerful, but getting the toolchain to work reliably was so much work. So when I read about the WeAct STM32F411CEU6 board on the MicroPython forum, I knew they’d be a much better bet.
Canaduino Black Pill Carrier Board with STM32F411 (and battery) installed
Let’s start with the STM32 Screw Terminal Adapter:
Canaduino Black Pill Carrier Board (front)
It’s a neat, solid board built on a black 1.6 mm thick PCB. Apart from the obvious screw terminals — essential for long-term industrial installations — it adds three handy features:
a real-time clock battery. If you’re using a micro-controller for data logging, an RTC battery helps you keep timestamps accurate even if the device loses power.
mounting holes! This may seem a small thing, but if you can mount your micro-controller solidly, your project will look much more professional and last longer too.
A 6–30 V DC regulator. Connect this voltage between Vin and GND and the regulator will keep the board happy. From the helpful graph on the back of the board, it doesn’t look as if things start getting efficient until around 12 V, but it’s really nice to have a choice.
Canaduino Black Pill Carrier Board (back)
I made a little slip-case for this board so it wouldn’t short out on the workbench. The project is here: Canaduino STM32 Screw Terminal board tray and you can download a snapshot here:
Gone are the lumpy pin headers of the earlier Blue and Black Pill boards, replaced by tactile switches. The iffy micro USB connectors are replaced by much more solid USB C connectors. According to STM32-base, the STM32F411 has:
100 MHz ARM Cortex-M4 core. This brings fast (single-precision) floating point so you don’t have to fret over integer maths
512 K Flash, 128 K RAM. MicroPython runs in this, but more flash is always helpful
Lots of digital and analogue I/O, including a 12-bit ADC
A user LED and user input switch.
About the only advanced features it’s missing are a true RNG, a DAC for analogue outputs, and WiFi. But on top of all this, Volker added:
the all-important 128 Mbit flash chip (and capacitor) fitted by Universal Solder
128 Mbit of Flash! This gives the board roughly 16 MB of storage that, when used with MicroPython, appears as a small USB drive for your programs and data. I found I was able to read the ADC more than 22,000 times/second under MicroPython, so who needs slow-to-deploy compiled code?
I had to run make a couple of times before it would build, but it built and installed quickly. This board doesn’t take UF2 image files that other boards use, so the installation is a little more complicated than other. But it works!
Once flashed, you should have a USB device with two important MicroPython files on it: boot.py and main.py. boot.py is best left alone, but main.py can be used for your program. I’m going into more details in a later article, but how about replacing the main.py program with the fanciest version if Blink you ever saw:
# main.py -- fancy Blink (scruss, 2020-05)
from pyb import LED
from machine import Timer
tim = Timer(-1)
tim.init(period=1000, mode=Timer.PERIODIC,
callback=lambda t: LED(1).toggle())
None of that blocking delay() nonsense: we’re using a periodic timer to toggle the user LED every second!
debugging the mystery huge potentiometer using two ADC channels
I’m really impressed with the Universal Solder-modified board as an experimentation/discovery platform. MicroPython makes development and testing really quick and easy.
[and about the mystery huge potentiometer: it’s a Computer Instruments Corporation Model 206-IG multi-turn, multi-track potentiometer I picked up from the free table at a nerd event. I think it’s a 1950s (so Servo-control/Cybernetics age) analogue equivalent of a shaft encoder, looking at the patent. Best I can tell is that each pot (there are two, stacked, with precision bearings) appears to have two 120° 10k ohm sweep tracks offset 90° to one another. The four wipers are labelled -COS, -SIN, +COS and +SIN. If anyone knows more about the thing, let me know!]
It’s not really in a useful form factor, but it’s got some sensors and outputs:
an LDR on the ADC channel
RGB LED for PWM on pins 15, 12 & 13
red LEDs pins 16, 14, 5, 4, 0, 2 with inverted logic: set them low to light them.
My board can’t quite be the earliest of the early, as it has 1 MB of flash. This is enough to install MicroPython, so I wrote a tiny test program for the outputs:
run a binary counter every second on the six red LEDs;
cycle through a colour wheel on the RGB LED while this is happening.
Here’s the code:
# esp8266 old explorer board
# see https://www.esp8266.com/wiki/lib/exe/detail.php?id=esp8266-dev-boards&media=esp8266-12_mod.png
from time import sleep
from machine import Pin, PWM
# LEDs are 16, 14, 5, 4, 0, 2 - L to R
# inverted logic: 1 = off
leds = [Pin(2, Pin.OUT, value=1), Pin(0, Pin.OUT, value=1), Pin(4, Pin.OUT, value=1), Pin(
5, Pin.OUT, value=1), Pin(14, Pin.OUT, value=1), Pin(16, Pin.OUT, value=1)]
# RGB for PWM on [15, 12, 13]
rgb = (PWM(Pin(15)), PWM(Pin(12)), PWM(Pin(13)))
# LDR on ADC
def cos_wheel(pos):
# Input a value 0 to 255 to get a colour value.
# scruss (Stewart Russell) - 2019-03 - CC-BY-SA
from math import cos, pi
if pos < 0:
return (0, 0, 0)
pos %= 256
pos /= 255.0
return (int(255 * (1 + cos(pos * 2 * pi)) / 2),
int(255 * (1 + cos((pos - 1 / 3.0) * 2 * pi)) / 2),
int(255 * (1 + cos((pos - 2 / 3.0) * 2 * pi)) / 2))
i = 1
while True:
i = i + 1
i = i % 64
w = cos_wheel(4 * i)
for j in range(3):
rgb[j].duty(4 * w[j])
for k in range(6):
if i & (1 << k):
leds[k].value(0)
else:
leds[k].value(1)
sleep(1)
The PC I put together a few years ago (well, Scott Sullivan told me which bits to get, I bought them and assembled it) is still working really well. It was quite spiffy in its day — i7-4790K, 32 GB DDR3, Asus H97M-E — and is quite fast enough for me.
One thing, though, has never worked. The hardware serial port (the old kind, not the USB kind) refused to do anything. Only in the last day or so did I work out why and managed to fix it.
PC serial ports for roughly the last 25 years connected to the motherboard like this:
The important thing about a switch is that it has two electrically isolated parts that come together to close a circuit. And that’s exactly what the Swingline® 747® stapler doesn’t have: its entire metal body and mechanism is electrically conductive. So we have to rig something up …
Tape, paperclip and alligator clip make up one half of the switch… while a handy ledge at the back of the staple dispenser provides a connection for alligator clip #2
Did I say take the staples out yet? No? Take the staples out of the stapler. Possibly even before doing anything else.
The code we’re going to run on the Circuit Playground Express is very simple:
Set up pin 1 (helpfully named A7 on the board) as an input. Turn off all the LEDs
If pin 1 is shorted to ground, increase a counter and light successive numbers of LEDs round the CPX’s face
If the counter reaches 10, play the sample, reset the counter and turn off all the LEDs
repeat from “If pin 1 is shorted to ground …” until too bored to continue.
Here’s the code:
# SIM-SimStapler / RealStapler - scruss, 2020-04
# circuitpython on CPX - stapler between D1 (A7) and GND
from adafruit_circuitplayground import cp
import board
from digitalio import DigitalInOut, Direction, Pull
import time
# set up stapler on pin D1 (port A7): goes LOW when pressed
stapler = DigitalInOut(board.D1)
stapler.direction = Direction.INPUT
stapler.pull = Pull.UP
# set up pixels - not too bright
cp.pixels.brightness = 0.1
# turn all pixels off
for i in range(10):
cp.pixels[i] = (0, 0, 0)
count = 0
while True:
# stapler pressed, so increase count
if not stapler.value:
count = count + 1
# only count first press, not if held
while not stapler.value:
pass
time.sleep(0.1)
# light up pixels clockwise for each press
for i in range(count):
cp.pixels[9 - i] = (0, 255, 0)
# get a bonus Penelope Keith every ten presses
if count == 10:
cp.play_file("splendid.wav")
# turn all pixels off after bonus
for i in range(count):
cp.pixels[i] = (0, 0, 0)
# and reset counter for next time
count = 0
Here’s the code and sample ready to be copied to your CIRCUITPYTHON drive:
(The sample is a slightly tweaked version of Freeverse’s original Bonus.wav. I ran it through an equalizer to make it sound less awful through the CPX’s tinny little speaker. I was also today years old when I found out that the sample wasn’t Penelope Keith from To the Manor Born, but Jen Krasinski, a staffer at Freeverse.)
The connection (singular) is simple:
Alligator clips to A7 (in reality, D1) and GND
Have an appropriate amount of fun!
I suppose I could also have done this on the BrainPad, but I haven’t set it up with MicroPython yet, and I don’t have time to drag coding blocks around. Also, this is not any project to associate with the word “brain” …
