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.

Clap Sensor part for Fritzing

I have no idea if this wiring would work, but it’s pretty …

For work, I blogged about Verbal MachinesHand Clap Sensor VM-CLAP1 (“Clap on 👏👏, Clap off 👏👏 – Elmwood Electronics”). I’ve made a preliminary part for Fritzing for the board: VM-CLAP1 Clap Sensor for Fritzing.zip

It should work in Breadboard and Schematic mode, but absolutely doesn’t work in PCB mode. This shouldn’t be a problem, as it’s only available as a standalone board. Fritzing doesn’t have any way to create new parts from scratch any more, so I had to base it on a somewhat similar-looking board, the SparkFun Electret Microphone Breakout.

I’m looking forward to see what I can do with gpiozero and the clap sensor.

Blinking on and off with the 74LS42

I want to make an edge-lit numeric display. These were a common technology before numeric LEDs were available. They use 10 illuminated slides to display individual numbers. Here’s my first try at the display:

Homebrew edge lit numeralsThe 74LS42 logic chip (4-Line BCD to 10-Line Decimal Decoder) seems a likely candidate to drive such a display. You feed it a 4-bit binary-coded decimal input, and the chip activates one of ten outputs. It’s a low-voltage version of the old 7441 chip used for driving Nixie tubes. Here’s what I got working as a demo of the 7442, driven by an Arduino:

(Video link for the iframe-averse: https://www.youtube.com/watch?v=cETGB2M8iUw)

From the video you can see that:

  1. The 7442 only passes inputs from 0 (0000b) to 9 (1001b). All other inputs result in no output.
  2. The outputs are really more like 1–10 than 0–9, as a zero input activates the first output.

Making a clean breadboard layout for this circuit was a little more work than I’d anticipated. It just fits on a half-sized breadboard:

Simple 7442 demo circuit, showing BCD inputs (green) and decimal outputs (orange)
Simple 7442 demo circuit, showing BCD inputs (green) and decimal outputs (orange)

Because the 7442 will only activate one output at a time, it’s okay to use a single current-limiting resistor for all ten output LEDs. The chip also uses active low outputs: the outputs go from high to low when activated. The negative side of each LED goes to an output pin, and the chip sinks current when an output is selected, lighting the LED.

The components get in the way of seeing the wiring, so here’s another picture from Fritzing with just the wires and the breadboard:

7442-no_componentsApart from the 74LS42 chip itself, the components I used were 10× 3mm orange LEDs on the outputs and 4× 3mm green LEDs on the inputs. I don’t have a spec for them (they were from a bargain selection box from PCBoard.ca) so my use of ridiculously precise 332 Ω 1% resistors to limit current is a little unnecessary. (I have a bunch of these precision resistors from a project that didn’t go ahead, so using them is cheaper for me than digging about for a 5% one.)

Finally, here’s the Arduino sketch I wrote to drive the chip for the demo video. All it does is cycle through digital outputs 4–7, incrementing a bit every half second.

   SeventyfourFortytwo - Arduino demo of a
   74LS42 - 4-line BCD to 10-line decimal decoder
   Steps through 0-15, two steps per second
   Shows the 74LS42's blocking of values 10-15 as invalid

   Arduino  74LS42
   ======== =======
    4      - 15  Input A (bit 0)
    5      - 14  Input B (bit 1)
    6      - 13  Input C (bit 2)
    7      - 12  Input D (bit 3)

   scruss - 2016-09-23

int n = 0;

void setup() {
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  digitalWrite(4, LOW);
  digitalWrite(5, LOW);
  digitalWrite(6, LOW);
  digitalWrite(7, LOW);

void loop() {
  digitalWrite(4, n & 1);
  digitalWrite(5, n & 2);
  digitalWrite(6, n & 4);
  digitalWrite(7, n & 8);
  if (n > 15) n = 0;

If you felt really fancy, you could drive the LED inputs through PWM, and come up with just the right of flicker to make this look like a Nixie tube. You should also be able to chain the inputs through some shift registers, too.

[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.)

Too much packaging, Newark

Newark really need to get a handle on their packaging.

I’d ordered a bluetooth adapter for my multimeter. It needs a little doohickey to attach to my meter, which Newark sent out by separate cover. This is how it turned up:

newark boxesSee the little orange thing on top? That’s the part. It’s 70×40×15 mm, and made in Malaysia. It was packed bubble wrap in a sturdy little cardboard box (163×73×43 mm, or 12× the volume of the part). That box was then packed in a very solid box (originally shipped from Penang to Gaffney, SC) measuring  200×200×170 mm; that’s 162x the part’s volume. Finally, that box was inside a third box of 330×245×220 mm, or 424× little doohickeys.

Thing is, the little doohickey is a tough injection moulded polymer part. It could probably be dropped in a padded envelope and survive any mail journey.

We’re going to die out for sure.


Built a simple Function Generator with Frequency Counter over the last couple of nights. It’s pretty basic — 0-~500kHz, 0-12V, Sine or Triangular waves — but good enough for my test needs. The frequency counter is basically an Arduino repackaged to feed the attached LCD. The counter isn’t super accurate, but is within 1% of what my multimeter says.

The kit has a fairly high voltage requirement for DC (>= 15V), but this was solved by a quick trip to Active Surplus. $11 bought me a 15V power supply (which delivers around 19V open circuit) and the right kind of barrel jack.

(Talking of neater meters, I didn’t know mine could support the Bluetooth Adaptor reviewed here. Dad’s old Avo couldn’t do that!)

fun trick noisemaker

I just built my first Atari Punk Console, a simple LM556-based noisemaker beloved of the circuit-bending crowd (and pretty much avoided by everyone else). Jimmie P Rodgers sells a nice board (or kit), and I bought a few boards a while back, and only just built one up now.

The board’s a nicely finished little thing:

… and yes, it really only needs three resistors, three capacitors, and the 556, plus the control pots, power, speaker and all-important on/off button. The APC sounds a little like a drunken, flatulent bee banging around in a lager can, so you really want to be able to turn this thing off.

Jimmie designed this to fit in an Altoids tin, but Catherine had discarded a LUSH Massage Bar Tin which looked just about the right size. The tin is made of butter-soft aluminium, so it’s easy to start holes in it with the awl on my Dutch Army knife. It’s bigger than an Altoids tin, so you don’t have to fight to get things in. Lastly, the LUSH tin is nicely curved, and fits in your hands well.

Wit the lid closed, it looks like this:

And the sound? Well …

not your dad’s multimeter

I’d been surviving on a series of sub-$50 multimeters for years. They’d give an approximation of a reading,then fail miserably in a variety of stupid ways. The last one, a rip-off of an Extech, decided to show me how its wires were connected to the probes. “Barely” is a fair description.

So I thought I’d buy a decent meter. One that had heft and gravitas, like the Avo 8 that my dad used to bring home from work. The Avo — seemingly constructed from bakelite, glass and lead — didn’t just take readings, it told you The Truth on its mirrored scale.

So I bought an Agilent. Reliable company, all the right features, beeps politely only when required; a very, very sensible meter. Then I found these in the package:

Dude, what?! Skins on a meter? Meters aren’t toys. Meters are sensible things used by sensible people. We don’t want our work distracted by thoughts of Space!, America!, Sports!, or Some Kind of Bug Thing Eww Squish It Squish It! If you were able to get “skins” for the Avo 8, they would be about Wisden, sheds, and the TSR2.

Despite the sticky nonsense, it’s a good meter. I also managed to catch a Handheld Digital Multimeter Cash Back Offer, so it’s cheaper than competing Flukes and Extechs.

HSV colour cycling LED on Arduino

Pretty much everyone tries the RGB colour cycler when they get their first Arduino. This variant cycles through the HSV colour wheel, though at fixed saturations and values.


// HSV fade/bounce for Arduino - scruss.com - 2010/09/12
// Note that there's some legacy code left in here which seems to do nothing
// but should do no harm ...

// don't futz with these, illicit sums later
#define RED       9 // pin for red LED
#define GREEN    10 // pin for green - never explicitly referenced
#define BLUE     11 // pin for blue - never explicitly referenced
#define SIZE    255
#define DELAY    10
#define HUE_MAX  6.0
#define HUE_DELTA 0.01

long deltas[3] = {
  5, 6, 7 };
long rgb[3];
long rgbval;
// for reasons unknown, if value !=0, the LED doesn't light. Hmm ...
// and saturation seems to be inverted
float hue=0.0, saturation=1.0, value=1.0;

chosen LED SparkFun sku: COM-09264
 has Max Luminosity (RGB): (2800, 6500, 1200)mcd
 so we normalize them all to 1200 mcd -
 R  1200/2800  =  0.428571428571429   =   109/256
 G  1200/6500  =  0.184615384615385   =    47/256
 B  1200/1200  =  1.0                 =   256/256
long bright[3] = {
  109, 47, 256};

long k, temp_value;

void setup () {
  for (k=0; k<3; k++) {
    pinMode(RED + k, OUTPUT);
    analogWrite(RED + k, rgb[k] * bright[k]/256);
    if (random(100) > 50) {
      deltas[k] = -1 * deltas[k]; // randomize direction

void loop() {
  hue += HUE_DELTA;
  if (hue > HUE_MAX) {
  rgbval=HSV_to_RGB(hue, saturation, value);
  rgb[0] = (rgbval & 0x00FF0000) >> 16; // there must be better ways
  rgb[1] = (rgbval & 0x0000FF00) >> 8;
  rgb[2] = rgbval & 0x000000FF;
  for (k=0; k<3; k++) { // for all three colours
    analogWrite(RED + k, rgb[k] * bright[k]/256);

long HSV_to_RGB( float h, float s, float v ) {
  /* modified from Alvy Ray Smith's site: http://www.alvyray.com/Papers/hsv2rgb.htm */
  // H is given on [0, 6]. S and V are given on [0, 1].
  // RGB is returned as a 24-bit long #rrggbb
  int i;
  float m, n, f;

  // not very elegant way of dealing with out of range: return black
  if ((s<0.0) || (s>1.0) || (v<0.0) || (v>1.0)) {
    return 0L;

  if ((h < 0.0) || (h > 6.0)) {
    return long( v * 255 ) + long( v * 255 ) * 256 + long( v * 255 ) * 65536;
  i = floor(h);
  f = h - i;
  if ( !(i&1) ) {
    f = 1 - f; // if i is even
  m = v * (1 - s);
  n = v * (1 - s * f);
  switch (i) {
  case 6:
  case 0:
    return long(v * 255 ) * 65536 + long( n * 255 ) * 256 + long( m * 255);
  case 1:
    return long(n * 255 ) * 65536 + long( v * 255 ) * 256 + long( m * 255);
  case 2:
    return long(m * 255 ) * 65536 + long( v * 255 ) * 256 + long( n * 255);
  case 3:
    return long(m * 255 ) * 65536 + long( n * 255 ) * 256 + long( v * 255);
  case 4:
    return long(n * 255 ) * 65536 + long( m * 255 ) * 256 + long( v * 255);
  case 5:
    return long(v * 255 ) * 65536 + long( m * 255 ) * 256 + long( n * 255);

The circuit is very simple:

  • Digital pin 9 → 165Ω resistor → LED Red pin
  • Digital pin 10 → 100Ω resistor → LED Green pin
  • Digital pin 11 → 100Ω resistor → LED Blue pin
  • GND → LED common cathode.

The different resistor values are to provide a limited current to the Triple Output LED RGB – Diffused, as each channel has different requirements. The 165Ω resistor is actually two 330Ω in parallel; I didn’t have the right value, and this was the closest I could make with what I had.