Something has gone very wrong with the database encoding on this blog after a recent update, so all my lovely UTF-8 characters have gone mojibake.

Trying to find ways to fix it. It may have to be manual. Remember, kids: have backups before letting WordPress upgrade!

Here’s the Python equivalent of what I think the database has done:

bytes("I ???? UTF-8", encoding='utf-8').decode(encoding='cp1252')
'I 💔 UTF-8'

Quite why my hosting thought a character encoding from last century was appropriate, I’ll never know.

MicroPython MIDI mayhem (kinda)

It pleased me to learn about umidiparser – MIDI file parser for Micropython. Could I use my previous adventures in beepy nonsense to turn a simple MIDI file into a terrible squeaky rendition of same? You betcha!

MIDI seems to be absurdly complex. In all the files I looked at, there didn’t seem to be much of a standard in encoding whether the note duration was in the NOTE_ON event or the NOTE_OFF event. Eventually, I managed to fudge a tiny single channel file that had acceptable note durations in the NOTE_OFF events. Here is the file:

I used the same setup as before:

Raspberry Pi Pico with small piezo speaker connected to pins 23 and 26
piezo between pins 26 and 23

With this code:

# extremely crude MicroPython MIDI demo
# MicroPython / Raspberry Pi Pico - scruss, 2022-08
# see https://github.com/bixb922/umidiparser

import umidiparser
from time import sleep_us
from machine import Pin, PWM

# pin 26 - GP20; just the right distance from GND at pin 23
#  to use one of those PC beepers with the 4-pin headers
pwm = PWM(Pin(20))
led = Pin('LED', Pin.OUT)

def play_tone(freq, usec):
    # play RTTL/midi notes, also flash onboard LED
    # original idea thanks to
    #   https://github.com/dhylands/upy-rtttl
    print('freq = {:6.1f} usec = {:6.1f}'.format(freq, usec))
    if freq > 0:
        pwm.freq(int(freq))       # Set frequency
        pwm.duty_u16(32767)       # 50% duty cycle
    sleep_us(int(0.9 * usec))     # Play for a number of usec
    pwm.duty_u16(0)               # Stop playing for gap between notes
    sleep_us(int(0.1 * usec))     # Pause for a number of usec

# map MIDI notes (0-127) to frequencies. Note 69 is 440 Hz ('A4')
freqs = [440 * 2**((float(x) - 69) / 12) for x in range(128)]

for event in umidiparser.MidiFile("lg2.mid", reuse_event_object=True):
    if event.status == umidiparser.NOTE_OFF and event.channel == 0:
        play_tone(freqs[event.note], event.delta_us)

This isn’t be any means a general MIDI parser, but is rather specialized to play monophonic tunes on channel 0. The result is gloriously awful:

apologies to LG

INA219 Current Sensor and MicroPython

More Micropython programmers — and especially beginners — should know about Awesome MicroPython. It’s a community-curated list of remarkably decent MicroPython libraries, frameworks, software and resources. If you need to interface to a sensor, look there first.

For example, take the INA219 High Side DC Current Sensor. It’s an I²C sensor able to measure up to 26 V, ±3.2 A. It does this by measuring the voltage across a 0.1 ohm precision shunt resistor with its built-in 12-bit ADC. I got a customer return from the store that was cosmetically damaged but still usable, so I thought I’d try it with the simplest module I could find in Awesome MicroPython and see how well it worked.

I guess I needed a test circuit too. Using all of what was immediately handy — a resistor I found on the bench and measured at 150.2 ohm — I came up with this barely useful circuit:

simple circle with 3.3 V DC supply ad two resistors of 150.2 ohms and 0.1 ohms in series
Should indicate a current of 3.3 / (150.2 + 0.1) = 21.96 mA

The INA219 would be happier with a much higher current to measure, but I didn’t have anything handy that could do that.

Looking in Awesome MicroPython’s Current section, I found robert-hh/INA219: INA219 Micropython driver. It doesn’t have much (okay, any) documentation, but it’s a very small module and the code is easy enough to follow. I put the ina219.py module file into the /lib folder of a WeAct Studio RP2040 board, and wrote the following code:

# INA219 demo - uses https://github.com/robert-hh/INA219

from machine import Pin, I2C
import ina219

i = I2C(0, scl=Pin(5), sda=Pin(4))
print("I2C Bus Scan: ", i.scan(), "\n")

sensor = ina219.INA219(i)

# my test circuit is 3V3 supply through 150.2 ohm resistor
r_1 = 150.2
r_s = 0.1  # shunt resistor on INA219 board

# current is returned in milliamps
print("Current       / mA: %8.3f" % (sensor.current))
# shunt_voltage is returned in volts
print("Shunt voltage / mV: %8.3f" % (sensor.shunt_voltage * 1000))
# estimate supply voltage from known resistance * sensed current
print("3V3 (sensed)  / mV: %8.3f" % ((r_1 + r_s) * sensor.current))

with everything wired up like this (Blue = SDA, Yellow = SCL):

breadboard with RP2040 pico board and INA219 sensor board benath it, and the 150 ohm wired as a circuit on the side
all of the wires

Running it produced this:

I2C Bus Scan:  [64] 

Current       / mA:   22.100
Shunt voltage / mV:    2.210
3V3 (sensed)  / mV: 3321.630

So it’s showing just over 22 mA: pretty close to what I calculated!

Kennedy Station roads are open to bikes again!

OpenStreetMap image of a route from north to south through Kennedy Station on roads that have been dug up for the last few years
rather dodgy GPS trail of me riding a bike from Gatineau Trail through Kennedy Station

It feels like forever, but it was probably 2018 that the roads through Kennedy Station were closed to dig the huge hole for the Eglinton Crosstown. So for all that time, I’ve been braving the deadly intersection at Kennedy and Eglinton to get back home from my daily bike ride.

But as of late last week, the roads reopened and I’ve been enjoying the wheee! instead of constant fear of dying. There’s still some work needed, so it’s not all sunbeams and cucumbers:

  • there’s still a misplaced Buses Only sign eastbound on North Service Road. Since this is countermanded by bike and taxi signs on South Service Road continuing the same way, it’s clearly a mistake
  • Transway Crescent is in a horrible state, with nearly six years of heavy construction traffic turning the surface into a knobbly mess. This can, and must, be fixed
  • Perhaps most worrying is permanent signs that suggest the sidewalks will be designated shared-use. They’re far too narrow for that, and have none of the necessary safe entry/exit points. As I’m a road user, the road I will use
  • You still (as before) have to mix it with buses. Bus drivers are professionals, though, and part of the solution.

It works! It works!

on a messy desk, a small USB midi keyboard is connected to a Korg NTS-1 mini synthesizer via a small micro-controller board that acts as a USB host for the Akai keyboard, converting USB MIDI to traditional MIDI for the Korg
Akai LPK25 keyboard has USB MIDI out, but the Korg NTS-1 only has regular MIDI in. The little board in the middle acts as a USB host for the Akai and MIDI source for the Korg

This is great: gdsports/midiuartusbh: MIDI DIN to MIDI USB Host Converter allows your USB MIDI instruments to act as traditional MIDI controllers. It uses a Adafruit Trinket M0 to act as the USB host and MIDI output.

I modified gdsports’ design very slightly:

  1. Instead of using a 74AHCT125 Logic level converter and driver, I used a FET-based SparkFun Logic Level Converter
  2. Instead of a 5-pin DIN socket, I used a 3.5 mm stereo socket.

And it works!

breadboard showing Trinket M0 microcontroller board, logic level shifter, audio socket breakout and two resistors
Breadboard layout for MIDI-standard 3.5 mm output (Korg). The resistors are both 220 ohm, and the boards need 5 V power

Mystery lockdown phone message

“Just a test call. Time to stay home. Stay safe and stay home.”

This message from an unknown caller has sat on our landline answering machine since 2020 or 2021. No idea who or what sent it. All I know is it came in just before noon on a Tuesday morning. The entirely synthesized voice makes me think it’s a junk call, but there’s no scam attached. Just this message, slightly eerie, quite inexplicable.

The Quite Rubbish Clock, mk.2

this is bad and I should feel bad

In early 2013, I must’ve been left unsupervised for too long since I made The Quite Rubbish Clock:

It still isn’t human readable …

Written in (Owen Wilson voice) kind of an obsolete vernacular and running on hardware that’s now best described as “quaint”, it was still absurdly popular at the time. Raspberry Pis were still pretty new, and people were looking for different things to do with them.

I happened across the JASchilz/uQR: QR Code Generator for MicroPython the other day, and remembered I had some tiny OLED screens that were about the same resolution as the old Nokia I’d used in 2013. I wondered: could I …?

small microcontroller board with USB C cable attached and an OLED screen on top. The OLED is displaying a QR code which reads '172731'
OLED Shield on a LOLIN S2 Mini: very smol indeed

The board is a LOLIN S2 Mini with a OLED 0.66 Inch Shield on top, all running MicroPython. One limitation I found in the MicroPython QR library was that it was very picky about input formats, so it only displays the time as HHMMSS with no separators.

Source, of course:

# -*- coding: utf-8 -*-
# yes, the Quite Rubbish Clock rides again ...
# scruss, 2022-06-30
# MicroPython on Lolin S2 Mini with 64 x 48 OLED display
# uses uQR from https://github.com/JASchilz/uQR
# - which has problems detecting times with colons

from machine import Pin, I2C, RTC
import s2mini  # on Lolin ESP32-S2 Mini
import ssd1306
from uQR import QRCode

WIDTH = 64  # screen size
SIZE = 8  # text size
r = RTC()

# set up and clear screen
i2c = I2C(0, scl=Pin(s2mini.I2C_SCL), sda=Pin(s2mini.I2C_SDA))
oled = ssd1306.SSD1306_I2C(WIDTH, HEIGHT, i2c)

def snazz():
    marquee = [
        "   **",
        "   **",
        "   **",
        "   **",
        "   **",
        " ******",
        "  ****",
        "   **",
        " quite",
        " clock",
        "  mk.2",
        " >2022<"
    for s in marquee:
        oled.scroll(0, -SIZE)  # scroll up one text line
        oled.fill_rect(0, HEIGHT-SIZE, WIDTH,
                       SIZE, 0)  # blank last line
        oled.text("%-8s" % s, 0, HEIGHT-SIZE)  # write text

snazz()  # tedious crowd-pleasing intro

qr = QRCode()
while True:
    qr.add_data("%02d%02d%02d" % r.datetime()[4:7])
    qr.border = 1  # default border too big to fit small screen
    m = qr.get_matrix()
    for y in range(len(m)):
        for x in range(len(m[0])):
            # plot a double-sized QR code, centred, inverted
            oled.fill_rect(9 + 2*x, 1 + 2*y, 2, 2, not m[y][x])

If your output is glitchy, you might need to put the following in boot.py:

import machine

This increases the ESP32-S2’s frequency from 160 to 240 MHz.

Canada’s longest running radio program is wrong!

Rob Cruickshank noted the other day:

Naturally, I had to verify this. So I tuned to the WWV 10 MHz time signal on my amateur rig, tuned a portable radio to CBC Radio 1 FM, which broadcasts on 99.1 MHz in Toronto and recorded them together:

Noisy recording of two radios. The WWV 13:00:00 EDT tone is at roughly 9 seconds, and the NRC tone broadcast by CBC is at 19 seconds

Yup: Rob’s right – CBC is broadcasting the NRC 13:00:00 signal at 13:00:10, which for time nerds might as well be the change from Julian to the Gregorian calendar.

Waveform from Audacity showing a low tone at 9s recorded from WWV, and CBC's long beep coming at 19 seconds
Annotated waveform: the CBC long beep is ten seconds after the WWV tone

This recording was made directly from the airwaves. There should be effectively no difference between the signal broadcast times, but here we are with the “National Research Council official time signal” going out at a very wrong time indeed.

Adding RGB LEDs to an illuminated arcade button

Somewhat painterly view of the button doing its thing. The weird clunking sound is my camera’s continuous focus. For a clearer but more flickery view, see here

Following on from a customer query at Elmwood Electronics, I can confirm that one can install install addressable RGB LEDs/NeoPixels inside one of these large buttons. It’s not the easiest build, so whether one should attempt this is another matter entirely.

You’ll need:

  • Large Arcade Button with LED – 60 mm White (tall version) – this is larger and more domed than the flat-top one that Adafruit sells
  • RGB LEDs – I used a generic 8 LED ring, but anything not too tall and under 45 mm in diameter should fit. Either a 7 X WS2812 5050 RGB LED Ring or Adafruit’s NeoPixel Ring – 12 x WS2812 5050 RGB LED with Integrated Drivers could also work
  • Thin (and I mean thin: I used 28 AWG) Silicone Cover Stranded-Core Wire in several colours. You’ll want to cut this quite long at first, as you have to ease it through some tiny holes in the button assembly. If you solder connectors on the end, you won’t be able to disassemble or install the button without cutting them off. Do I speak from experience here? You betcha!
  • The usual soldering/hot gluing/bending/prying/grabbing/cutting tools you already know and love. In addition, you might consider a non-marring spudger and a pair of small(ish) arterial forceps (aka hemostats, aka Kelly forceps, aka fishing hook removal pliers)

I’m not going to cover soldering the wires to the LED PCB in any depth here. You’ll need three wires: 5 V power, Ground and Data. Even though the LEDs I used need 5 V power, they are quite happy with 3.3 V logic on the data line. They need more than 3.3 V power to light, though.

a large arcade machine style button on the left: it has a clear domed top and a threaded base. On the right is the combined microswitch and LED holder that fits into the button base
The button in two pieces, as you might expect to receive it
the top of the button disassembled into its main parts: bezel ring at top left, threaded lock ring at bottom, and main button mechanism. The mechanism is upside down, so the return spring and button actuators can be seen inside the threaded shaft
Main parts of the button top, once you’ve removed the lock ring
Close up of inside the shaft: return spring and its retainer tabs, and button actuators can be seen
First step is to ease the spring out without bending it too much or breaking the retainer tabs
Close up of inside the shaft: the tips of a pair of forceps have eased the top of the spring past its retainers
I used small forceps to ease the spring out. Once you get it started, it unscrews easily from behind the retainers
Close up of inside the shaft: the button actuators have been pushed down the shaft, allowing the top of the button to be pulled out
Now the spring is out the way, you can squeeze in the actuator tabs and push them down the shaft to liberate the button top
button top components arranged: black threaded button base on left, return spring in the middle, and domed clear top with white underside and white actuators sticking down
The button top disassembled
clear button top attached to its white underside. A blunt metal tool (spudger) is pointed at the push-fit join between the two parts
Carefully lever off the clear top with a blunt tool like a spudger. Now would have been a great time to clean dust and other wee bits off your workspace, as they’ll surely end up inside the button, looking nasty
clear button top separated from its white base. A translucent white diffuser is inside the clear top. The white base has a hollow centre and a circular cavity
The button top opened up. The cavity is about 45 mm in diameter and only a few millimetres deep
The microswitch with the LED holder attached on top. The blade of a blunt metal spudger is inserted under a plastic tab that holds the LED holder onto the switch
Removing the LED holder from the microswitch is done by levering open (gently) the plastic tab that clamps the holder onto the switch.
the LED holder at left, and the bare microswitch. The LED holder has an LED in a white plastic retainer, and below it two spade contacts. The switch has three spade connectors: Com(mon) on the base, and "NO 3" (Normally Open) and "NC 2" on the right side. Normal operation connects COM and NO
LED holder and microswitch separated. For normal button operation, the contacts NO and COM become connected when the button is pressed. The spade contacts on the LED holder look like they should come out, and they will (soon)
LED holder disassembled into two parts. The black LED holder base is on the left, with the two conenctor clips slightly blurry at top. On the right is the LED in its white support, pulled out of the holder base
Pull the LED out from the holder, and you’ll see the metal clips that held it in place. These clips have to come out: I found the pushing them in slightly while pulling down on the spade connector eased them out eventually
White button top underside with an 8 RGB LED ring hot glued into it. Three thin insulated wires (from top: yellow (data), red (5 V) and black (GND)) are previously soldered behind the LED board, and are secured against strain with a large deposit of hot glue
LED ring hot glued into place. Make sure that the wires are properly secured, as you don’t want to take this apart again
threaded button base with clear top fitted, seen from underneath. The white button actuators have been pushed back into place, and the three coloured wires are feeding through the hole in the shaft. The return spring is outside the wires, and is being fitted around the retainers inside the shaft
Fit the clear button top back inside the base, feeding the wires through the shaft. Fitting the return spring back in is a bit more chaotic than getting it out. I ended up jamming it in with forceps, and it seemed to sort out okay despite that
underside of the button shaft, with microswitch attached to LED holder. The wires coming from the LED ring inside the button top have been fed through the small cavities where the original LED holder clips/contacts have been removed. The red/black power wires are on the side towards us, while the yellow data wire is behind the microswitch
The really fiddly bit: feeding the wires through the tiny gaps where the LED holder clips/contacts used to be. Even using thin (28 AWG) silicone covered wire, all three wires couldn’t fit down one side. Make sure the wires are pulled gently through, and aren’t snagged anywhere
Fully reassembled button, with microswitch installed into its bayonet connector in the threaded shaft, and the button actuator lined up with the microswitch lever on the left. The yellow data wire is in front of the microswitch at bottom
Finished! Make sure that the switch actuates properly by lining up the LED holder in the bayonets inside the shaft. Of course, you’ll have wanted to install the button in your project before doing this assembly, as you’ll have to feed those pesky wires back through again if you haven’t …

More Magic Designer Nonsense

This is what I simulated earlier – except drawn on a real Magic Designer. Something’s off with what I modelled …
All of these are drawn with the Magic Designer angle set to 57, which puts the crank discs exactly in phase. The blue circle in the middle is an exactly image of a crank disc, if perhaps a very dull plot.

Slightly imperfect Hoot-Nanny/Magic Designer simulation

round figure with three interlaced 6-fold curves picked out in red, green and blue
I even emulated the locating notches at the edge of the paper …

Simulated (and not quite right yet) output from a “HOOT-NANNY” or Magic Designer, a proto-Spirograph toy that drew six-sided curves on round paper sheets. It was made by Howard B. Jones and Co. of Chicago, IL and first sold in 1929. The company’s better known for producing Jones Plugs and Sockets, sometimes known as Cinch-Jones connectors. The “HOOT-NANNY” name was dropped when production moved to the Northern Signal Company of Saukville, WI.

My eBay-acquired Magic Designer is quite beaten up, and doesn’t always produce accurate results. Here’s how one should look, from the instruction pamphlet:

diagram of the Magic Designer toy: central turntable holding paper is rotated by crank at bottom right. On the left are two crank discs (upper and lower) each with a crank pin that can fit into holes along two arms. These arms are joined at a pivot, and in the centre of this pivot is a pencil.

The upper crank disc can be moved in an arc relative to the lower disc. This is controlled by a locking shift lever on the right
I can’t shake the feeling this was originally something like an artillery ranging tool or suchlike

As far as I’ve been able to work out, the parameters of the machine are:

  • central turntable is 6″ in diameter, with 192 gear teeth around the edge;
  • each crank disc is 1″ diameter (32 teeth), with the crank pin at 3/8″ radius;
  • the shift lever has a 10-70 degree scale, which corresponds to moving the upper crank disc between 30-90 degrees of arc from the lower (fixed) crank disc;
  • the pencil arms have 18 holes labelled A to R, at 1/4″ spacing from 5.75 to 1.5″. The perpendicular distance from the pivot holes to the pencil is 5/16″. This small offset makes very little difference to the overall arm length.

If we model the toy with a fixed turntable:

  • the crank pins describe epitrochoids around the edge of the paper;
  • the pencil point traces the intersection of two circles of radius the lengths of the pencil arms, each centred on a crank pin.

A new old calendar

simulated dot-matrix printer on ruled paper layout of an ASCII-art Snoopy in WW1 Air Ace regalia yelling "Curse you Red Baron!" at his imaginary nemesis, and a 2022 calendar laid out on the facing page
not seen the likes of this since ’78, I’ll be bound

It’s unlikely anyone wanted a faux-lineprinter ASCII art calendar for 2022, but you’re getting one anyway. You can print this yourself:

If you want to make your own, here’s a script: snoopycal.sh


  • Original “WW1 Fighter Pilot” Snoopy ASCII art from “SNOOPY.BA” for the DEC PDP-8, written by Mr Kay R. Fisher of DEC some time before July 1973. It’s referred to in the first printing of the “101 Basic Computer Games” book, which was published in 1973.
  • ncal, banner: their respective authors
  • pstext an ascii to PS filter by Dan Judd, usenet comp.lang.postscript, December 1989. I had to really mess around with the output of this program to use a custom font and add the music ruling, but it produces cleaner PostScript than the giant messes that enscript and a2ps have become
  • Font: mnicmp, by me. Based on the DecWriter II font.
  • iffy scripting, scribbly lines: also me.

Autumn in Canada: PicoMite version

more leaves

So I ported autumn in canada from OpenProcessing to PicoMite BASIC on the Raspberry Pi Pico:

a small black screen images with text in the centre: autumn in canada scruss, 2021-11 just watch ...
no leaves
a small black screen images with text in the centre: autumn in canada scruss, 2021-11 just watch ... with one red and one orange maple leaf sitting on top of it
a couple of leaves
a small black screen images with text in the centre: autumn in canada scruss, 2021-11 just watch ... with four red/yellow/orange maple leaves sitting on top of it
more leaves
a small black screen images with text in the centre: autumn in canada scruss, 2021-11 just watch ... with sixteen simulated fallen maple leaves mostly covering it
plenty of leaves
a small black screen image completely covered with many simulated fallen maple leaves
far too many leaves

The biggest thing that tripped me up was that PicoMite BASIC starts arrays at 0. OPTION BASE 1 fixes that oversight. It would have been nice to have OpenProcessing’s HSV colour space, and an editor that could handle lines longer than 80 characters that didn’t threaten to bomb out if you hit the End key, but it’ll serve.

Source below:

' autumn in canada
' scruss, 2021-11
' a take on my https://openprocessing.org/sketch/995420 for picomite

OPTION base 1
' *** initialize polar coords of leaf polygon and colour array
DIM leaf_rad(24), leaf_ang(24), px%(24), py%(24)
FOR i=1 TO 24
    READ leaf_rad(i)
FOR i=1 TO 24
    READ x

DIM integer c%(8)
FOR i=1 TO 8
    READ r%, g%, b%

' *** set up some limits
min_scale%=INT(MIN(MM.HRES, MM.VRES)/8)
max_scale%=INT(MIN(MM.HRES, MM.VRES)/6)
max_x%=MM.HRES - min_x%
max_y%=MM.VRES - min_y%

TEXT MM.HRES/2, INT(MM.VRES/3), "autumn in canada", "CM"
TEXT MM.HRES/2, INT(MM.VRES/2), "scruss, 2021-11", "CM"
TEXT MM.HRES/2, INT(2*MM.VRES/3), "just watch ...", "CM"

    cx% = min_x% + INT(RND * (max_x% - min_x%))
    cy% = min_y% + INT(RND * (max_y% - min_y%))
    angle = min_angle + RND * (max_angle - min_angle)
    sc% = min_scale% + INT(RND * (max_scale% - min_scale%))
    col% = 1 + INT(RND * 7)
    leaf cx%, cy%, sc%, angle, c%(7), c%(col%)
    kt% = kt% + 1
LOOP UNTIL kt% >= 1024


SUB leaf x%, y%, scale%, angle, outline%, fill%
    FOR i=1 TO 24
        px%(i) = INT(x% + scale% * leaf_rad(i) * COS(RAD(angle)+leaf_ang(i)))
        py%(i) = INT(y% - scale% * leaf_rad(i) * SIN(RAD(angle)+leaf_ang(i)))
    NEXT i
    POLYGON 24, px%(), py%(), outline%, fill%

' radii
DATA 0.536, 0.744, 0.608, 0.850, 0.719
DATA 0.836, 0.565, 0.589, 0.211, 0.660, 0.515
DATA 0.801, 0.515, 0.660, 0.211, 0.589, 0.565
DATA 0.836, 0.719, 0.850, 0.608, 0.744, 0.536, 1.000
' angles
DATA 270.000, 307.249, 312.110, 353.267, 356.540
DATA 16.530, 18.774, 33.215, 3.497, 60.659, 72.514
DATA 90.000, 107.486, 119.341, 176.503, 146.785, 161.226
DATA 163.470, 183.460, 186.733, 227.890, 232.751, 270.000, 270.000
' leaf colours
DATA 255,0,0, 255,36,0, 255,72,0, 255,109,0
DATA 255,145,0, 255,182,0, 255,218,0, 255,255,0

You could probably use AUTOSAVE and paste the text into the PicoMite REPL. I used an ILI9341 SPI TFT LCD Touch Panel with my Raspberry Pi Pico along with some rather messy breadboard wiring.

Fun fact: the maple leaf polygon points are derived from the official definition of the flag of Canada.