What's smaller than an SD card, runs MicroPython from its own tiny flash storage and has a greatbighuge bright Dotstar in the middle? The Adafruit Trinket M0 , of course!
Apart from the hard-wired DotStar colour LED in the middle, it's got a lot going on: capacitive touch sensors, analogue inputs (and one analogue output), USB mouse/keyboard emulation, built-in temperature sensor … I'm sure there's something I've missed.
Programming is easy: plug it into a USB port, and it appears as a flash drive. Open the main.py file, edit it, save it, and your new program's running!
Here's an entirely inessential script to indicate how I feel about anything other than spring and autumn temperatures. I'm at my best when this script's glowing green:
# Trinket M0 - scruss's perpetual Scottish thermometer
# for elmwood electronics - https://elmwood.to/
# CircuitPython 2.0.0
import board
import adafruit_dotstar as dotstar
import microcontroller
import time
# One pixel connected internally
dot = dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1, brightness=0.2)
######################### MAIN LOOP ##############################
message=''
colour=0x000000
while True:
temperature=microcontroller.cpu.temperature
# my own very grumpy temperature scale, in deg C
if (temperature > 23.0):
message='far too hot'
colour=0xff0000 # red
elif (temperature > 5.0):
message='just right'
colour=0x00ff00 # green
else:
message='a tad chilly'
colour=0x0000ff # blue
dot[0]=colour # display colour scale
# send message to serial port with temperature
print("Temperature: %5.1f deg C : %s" % (temperature, message))
time.sleep(0.5)
CircuitPython, Adafruit's fork of MicroPython, is changing pretty quickly, so you'll probably want to look at updating CircuitPython to the latest version. That's easy as double-clicking the Trinket's reset button and dragging the new firmware file onto the board's icon.
For all its awesomeness, CircuitPython isn't exactly quick on the Trinket M0: expect reading sensors a few times a second. But you can also program the M0 in the Arduino IDE, and that's where you'd get real speed out of its ARM core.