VM-CLAP1 👏 sensor + gpiozero on Raspberry Pi

Well, that was easy!

Since the Verbal Machines VM-CLAP1 sensor is an open collector type — that is, it sinks current when triggered — it behaves like a simple button to gpiozero, the Raspberry Pi Python GPIO library. If you attach a callback function to the sensor’s when_pressed event, your Python script will call that function every time it registers a clap.

The wiring is as simple as it could be:

 VM-CLAP1: Raspberry Pi:
 ========= =============
      GND → GND
      PWR → 3V3
      OUT → GPIO 4

This example code just prints clap! when the board picks up a 👏:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# Raspberry Pi gpiozero test for
# Verbal Machines VM-CLAP1 clap sensor
#   scruss - 2017-06
# Wiring:
#  VM-CLAP1:    Raspberry Pi:
#  =========    =============
#    GND     →   GND
#    PWR     →   3V3
#    OUT     →   GPIO 4

from gpiozero import Button
from signal import pause

def clapping():

clap = Button(4)
clap.when_pressed = clapping

This is a trivial example, but at least it shows that anything you can do with a button, you can also do with this hand-clap sensor.

more geometry to colour in

Click on image to download as PDF

based on the main repeating pattern from a Pierced Window Screen at The Metropolitan Museum of Art — particularly this image.

mnicmp: the DECwriter lives again!

I just made and uploaded this to FontLibrary: mnicmp.

This is meant more as an exercise in learning FontForge‘s programming back-end, and definitely showed me that FontForge is incredibly powerful. After the learning comes silliness, so I ended up turning the dots into something like:

I learned you really have to consider a dot-matrix font to be an array of points rather than a glyph, because otherwise you get the dots coming out the wrong sort of oval:

Blue font has been italicized as a whole, while the black dots were done properly

You don’t want to know what it did to the stars …

Local archive: mnicmp.zip

Apple II on Raspberry Pi

C’mon let’s all die of dysentery on the Oregon Trail!

Building and installing the linapple-pie Apple IIe emulator is relatively easy on the Raspberry Pi:

sudo apt install libcurl4-openssl-dev libzip-dev zlib1g-dev libsdl1.2-dev libsdl-gfx1.2-dev libsdl-image1.2-dev libsdl-sound1.2-dev build-essential git
git clone https://github.com/dabonetn/linapple-pie.git
cd linapple-pie/src
sudo make install

This also works on an x86_64 Ubuntu machine. It does also install on a PocketCHIP (even if it takes a really long time) but I can’t get the display resolution to fit correctly.

some OpenSCAD 2D SVG things for Josh …

I’ve found that OpenSCAD is really good for producing 2d designs in a very small amount of code. Here are three examples to play with:

Diagonal Section through Menger sponge (SVG) (OpenSCAD source) — this may take a while to render, as it’s making a Menger sponge in 3D and then slicing through it to make the projection.

(If you take out the projection() clause, it looks like this in 3D:


Pattern from Ak Medrese, Nigde, Turkey (SVG) (OpenSCAD source) — design after a construction by Eric Broug.

Basis of a pattern from the Alhambra (SVG) (OpenSCAD source)

Moar UNCLE …

Yep, Marcus Gipps is at it again with a new Kickstarter campaign:

As part of my research into the JP Martin archives, I discovered both a biography of JPM himself, written by his daughter Stella Currey, and around 50 pages of unpublished Uncle stories which either didn’t make it into the finished books, or were heavily reworked. I’m now running a kickstarter to publish these two things in one volume of around 400 pages, which will be available in paperback, ebook or a limited hardback with the same specifications as THE COMPLETE UNCLE. The details are all here:

My latest kickstarter campaign, to publish a biography of JP Martin, creator of UNCLE, is now live!

If you’re able to back this new kickstarter, thank you very much – we’ve already hit our goal, but the more support I get now, the more copies I can print for the bookshops. And apologies if you’ve already backed, or have had this email more than once.

Unpublished UNCLE tales & JP Martin – Father of Uncle

I am, of course, already on it like stink on Beaver Hateman.

the old freezer baggie and Goo Gone trick

acrylic in a freezer baggie with Goo Gone to soak off backing
Getting the backing paper off laser cut acrylic is a pain. Some people recommend d-limonene, a citrus-derived solvent that is the main active ingredient of Goo Gone.

Pour a little Goo Gone into a tough freezer baggie, and place your acrylic part inside. Seal it up, and lay it flat for a few minutes. After that, flip it over and let the other side soak for a few. Open the bag and fish out your work. The backing paper should just slough off. Now rinse off the acrylic with washing-up liquid/dish detergent and warm water, taking care not to scrape the surface. You should now have a perfectly clean and shiny acrylic object. The d-limonene has the pleasant side-effect of de-stinkifying the cut plastic, too.

You should be able to re-use the Goo Gone baggie many times if you’re careful. You might not be able to rinse Goo Gone down the drain where you are; please check local regulations.

(The piece is the non-broken version of this.)

File under “because I can”

Some ideas are truly brilliant:
they resonate immediately with
all of humanity. Some ideas
are merely great: in time,
their value becomes clear
to all. Some ideas, however,
are like this one ...

The “Coo~Coo” Raspberry Pi Zero Case

Coo~Coo Raspberry Pi Zero Case - built
Coo~Coo Raspberry Pi Zero Case

I’d tried making several Raspberry Pi Zero enclosures, but none of them quite worked. My needs are pretty simple, but I do need to be able to fit a full 40 pin strain-relieved (possibly keyed) header into the device while keeping questing fingers and dropped conductors off the circuit board.

Coo~Coo case in fluo acrylic
Coo~Coo case in fluo acrylic

So working from a (scaled) version of the Raspberry Pi Zero Mechanical Drawing, I made a case that meets some very basic requirements:

  1. Conserves material: The Coo~Coo uses just under 80 × 80 mm of 3 mm ply or acrylic, plus four nylon machine screws, nuts and washers.
  2. Takes a full-sized GPIO header with a little headroom.
  3. Provides edge protection for the µSD and connectors.
  4. Has only a single cut layer, with no time-wasting engraved rasters.
  5. Needs only simple tools to make: really only needs diagonal cutters to snip off half of the nylon screw heads. Needle-nose pliers might help too, as there are some fiddly small parts.
  6. Free as in CC0. Yup, since this is derived from the Raspberry Pi Foundation’s copyrighted drawing, my modifications didn’t really add anything of value. Thus I waive all copyright and related or neighbouring rights on my additions:


    To the extent possible under law, Stewart C. Russell has waived all copyright and related or neighbouring rights to the “Coo~Coo” Raspberry Pi Zero Case. This work is published from: Canada.

Why the odd “Coo~Coo” name? Well, look at the pattern of spacer washers and half-spacer washers:

Coo~Coo in the cutter

To save material, I arranged these washers inside the GPIO cutout. I realised that I could spell COO~COO. It’s even clearer on the cutting document:

Coo~Coo — PDF for cutting is linked under the image

Update: here’s a revised path that cut well with acrylic and probably will work slightly better on plywood, too: coo-coo-rpi_zero-acryl.zip
(If you do use acrylic, let me introduce you to one of the marvels of backing-paper removal: d-limonene. This fruity solvent — present in products like Goo Gone — causes backing paper to slough off with only a few minutes’ soaking. It washes off to a clean shine with water and dish soap/washing up liquid. I have just saved you fingernails from certain damage!)

The cutting path in the PDF could use a little clean up if you want to try this design in acrylic. The base of the design has been flipped so that any laser flare will be hidden inside the case.

You’ll need four M2.5 or M3 nylon screws of 20 mm length, plus 8 washers and 4 nuts. M3 screws of this length are easier to get, but the mounting holes in the Raspberry Pi Zero are only 2¾ mm in diameter. You can thin the M3 screws down slightly by lightly twisting them inside a piece of folded fine sandpaper. You’ll still have to push them through the Raspberry Pi Zero circuit board with a little force, though.

Cutting & Assembly Instructions

  1. If you have it, place some fine wire mesh or sacrificial heavy card-stock between the laser cutter honeycomb bed and the plywood. The spacer washers are just the right size to fall through the cutter bed and be lost inside the discard hopper.
  2. Cut the piece as normal.
  3. Remove the work from the laser cutter. Masking tape applied over the washers will stop them falling out.
  4. Take the top piece, and thread the other two screws through the holes by the HDMI and PWR labels.
    (It may be easier to do these one at a time)
  5. Place two of the full spacer washers over each screw.
  6. Push the screws through the Raspberry Pi Zero board. M2.5 screws won’t need any force, but M3 will need some coaxing, possibly even cajoling.
  7. Place a nylon washer on each of the two screws under the Raspberry Pi Zero board.
  8. Take the base and flip it horizontally so the screw holes match the top.
  9. Very loosely attach the nuts to each of the screws.
    (You’ll need the slack to fit the top two screws and their C-shaped spacers)
  10. Feed the top two screws through the half-holes by the GPIO cutout in the case and the Raspberry Pi Zero board. Again, coaxing and/or cajoling may be required if you used M3 ones.
  11. Put nylon washers over the screws between the Raspberry Pi Zero board and the base.
  12. Very loosely attach the nuts to the top two screws.
  13. (This is the fiddly bit) Stack two of the half spacers and put them on each screw. You need to get the screws tight enough to just grip the spacers against the case, but not too much or you won’t be able to align them to let the GPIO connector fit in the gap. Tightening the screws at the HDMI and PWR ports can help with this, too.
  14. Nip off half of the heads from two of the nylon screws. This will allow the GPIO connector to fit easily.
  15. Tighten all the screws (finger tight is fine) and make sure the trimmed heads align with the edge of the GPIO cutout.
Raspberry Pi Zero in Coo~Coo case showing GPIO and spacers
Raspberry Pi Zero in Coo~Coo case showing GPIO and spacers

The new Raspberry Pi Zero with camera connector should also fit, but I don’t have one to test it.

FifteenTwenty UltraLight: single-stroke OTF for CNC/plotting

Screenshot from 2016-05-08 17-18-31Following on from FifteenTwenty, I made a hairline/single stroke version of the font especially for CNC use. This is a slight misuse of the OpenType format, but if you’re plotting/CNCing/laser cutting, the filled paths of standard fonts don’t work so well. Single-line (or stroke) fonts used to be possible in PostScript — the version of Courier shipped with early Apple LaserWriter printers was composed of strokes, rather than filled paths — but have fallen out of favour. If you have a device with a defined tool width, it’s better to let the tool make the width of the mark/cut. Here’s the hairline font plotted with a 0.7 mm pen to illustrate what I mean:

1520hairlineThis font is almost invisible on screen or on a regular printer, so I don’t recommend installing it unless you have specific CNC/plotting needs. Please note that the font will cause your device to follow the tool path of each letter twice.

Download: FifteenTwenty-master.zip FifteenTwenty-UltraLight.zip (or more options …)

[tɒk bɒks] — a tiny hardware speech synthesizer/TTS

[tɒk bɒks]: case
[tɒk bɒks]: case
[tɒk bɒks]: inside
[tɒk bɒks]: inside. The observant amongst you will notice that the speech board is 1/10″ further in than it should be for ideal alignment with the USB serial adapter.
Back in the 1980s, the now-defunct Digital Equipment Corporation (“DEC”) sold a hardware speech synthesizer based on Dennis Klatt’s research at MIT.  These DECTalk boxes were compact and robust, and — despite not having the greatest speech quality — gave valuable speech, telephone and reading accessibility to many people. Stephen Hawking’s distinctive voice is from a pre-DEC version of the MIT hardware.

DEC is long gone, and the licensing of DECTalk has wandered off into mostly software. Much to the annoyance of those in earshot, I’ve always enjoyed dabbling in speech synthesis. DECTalk hardware remains expensive, partly because of demand from electronic music producers (its vocoder-like burr is on countless tracks), but also because there are still many people who rely on it for daily life. I couldn’t justify buying a real DECTalk, but I found this: the Parallax Emic 2 Text-to-Speech Module.  For about $80, this stamp-sized board brings a hardware DECTalk implementation to embedded projects.

The Emic 2 is really marketed to microcontroller hobbyists: Make Your Arduino Speak! sorta thing. But I wanted to make a DECTalk-ish hardware box, with serial input, a speaker, and switchable headphone/line jack.  [tɒk bɒks] (a fair approximation of how I pronounce “Talk Box”) is the result.


  • Parallax Emic 2 Text-to-Speech Module
  • OSEPP FTDI USB-Serial Breakout — there are many USB-Serial boards that would do this, but two points in this one’s favour are: i) it has header pins for breadboard use, and ii) I had a spare one.
  • Small 8Ω speaker element — the one I used is most likely a headphone element, bought from Active Surplus (RIP). This should be as small as you can get away with (and still hear) as the USB-Serial connection isn’t designed to supply audio power.
  • Header pins and sockets
  • Toggle switch
  • Small project box with perfboard
  • Jumper wires and solder


Emic 2             Serial
======             ======
 GND                GND
 5V                 Vcc
 SOUT               RXD
 SIN                TXD

Emic 2             Speaker
======             =======
 SP-                -
 SP+  (via switch)  +

Using it

You’ll need some kind of serial terminal connection. In a pinch, you can use the serial monitor that is in the Arduino development environment. Either way, identify your serial port (/dev/ttyUSBN, COMN:, or /dev/tty-usbserialNNNN) and find a way to send 9600 baud, 8N1 characters to it. Hit Return, and you should be greeted by the Emic 2’s : prompt (or a ?, followed by :). Whether you get the prompt or not depends on whether local echo is set or not. Either way, try sending this line:

SAll watched over by machines of loving grace.

You should hear a voice say the title of Richard Brautigan’s lovely poem All Watched Over by Machines of Loving Grace (caution: video link contains nekkid hippies). You should get the : prompt back once the the speech has stopped. And that’s all there is to it: send an S, followed by up to 1023 bytes of (basically ASCII) text, followed by a newline, and it will be spoken. There’s more detail, of course, in the Emic 2 documentation and the Emic 2 Epson/Fonix DECTalk 501 User’s Guide for changing voices, etc. Yes, you can make it sing. No, you probably shouldn’t, though.


  1. The Emic 2 has no serial flow control, so you have to wait until the module stops speaking (or you send it the stop command) before you can send more. The easiest way is to poll the serial port and see if there’s the : prompt waiting. Until you see the prompt, any text you send it may be lost.
  2. The Emic 2 is an embedded device; Unicode is a bit of a stretch. It’s supposed to accept ISO Latin-1 8-bit characters (handy for Spanish mode), though.
  3. Starting every speech line with S may make this board incompatible with assistive technology software such as the JAWS screen reader. I don’t think that this was the goal for Emic 2’s designers (Grand Idea Studio), however.
  4. The output from the audio jack has a fair bit of noise on it, and you need to set the volume quite low to avoid hiss and hum. Your experience may be different, as I may have accidentally made a ground loop. There is a faintly  audible click at the start and end of the text, too.
  5. The Emic 2 uses DECTalk v5 commands and phonemes. Many DECTalk resources on the web (like these songs) use v4 or older, which are subtly incompatible. I haven’t found a reliable conversion protocol yet.

To end, here’s the Emic 2’s “Dennis” voice reading all of Brautigan’s All Watched Over By Machines of Loving Grace:

(plain link: molg-dennis-140wpm-16khz.mp3)

(even plainer link if you can’t decode MP2 files: molg-dennis-140wpm.mp3)

(recorded and edited for length with Audacity. No hippies — nekkid, or otherwise — were harmed in the making of this recording.)


I think that I shall never see / A directory lovely as a tree
I think that I shall never see / A directory lovely as a tree

This is from Arz Fine Foods. Their logo is a tree. On this receipt, they’ve got a tree alright, but no-one expected an MS-DOS directory tree. I think, as we sort of say in Scotland, that someone made an arz of this …

(I’m not hating on Arz, btw. They have an epic selection of foods, including fresh Sukkari dates.)

Progress on Hershey font outlines

Hershey Simplex says Hello

I still have lots of work to do, but at least now I can make buffered outlines of the 1967-vintage Hershey character glyphs into Fontforge-friendly vectors.

My goal is to release these as OTF fonts, rendered as it they’d been drawn by a constant line width pen plotter or film recorder, as was used in Dr Hershey’s day. Frank at Kiosk Fonts has loftier goals, and may actually release pretty fonts one day …

If death is not the end …

Alan Rickman reads Robyn Hitchcock’s poem “If Death is not the End …¨

Update: Robyn posted a better recording via twitter: audioBoom / Alan Rickman reads If Death Is Not The End