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Joule Thieves

2016-03-25 18:26 electronics

To make something useful out of 'dead' batteries I've been building Joule thief circuits. These circuits are very easy, cheap and fun to build plus it gives me a little bit less bad conscious when going to the recycling bin with the batteries. Watch this BigClive video to learn more.

Below are pictures of one variant. It has a small 3mm green led (salvaged from a broken printer), a hand-wound coil, a resistor and a transistor.

The batteries here came with my first ever (analogue) multimeter. They are 32 years old!. See the date code: 84-04. They still can drive the little led. Amazing. I think running this little green led is a good way to use the last energy stored in these beautiful and truly long-life batteries.


2015-12-29 00:30 supercollider, visuals

Just some hypnotic graphics...

The JavaScript code above is this...

<div style="background-color:black;">
<canvas id="canvas" width="800" height="600"></canvas>
(function () {
  const UPDATERATE = 1000.0 / 60.0 // 60fps
  let frameCount = 0
  let lastTime = -1
  const can = document.getElementById('canvas') // EDIT name of canvas to draw to
  function draw () {
    const currTime = Date.now()
    if (currTime >= (lastTime + UPDATERATE)) {
      lastTime = currTime
      const bottom = can.getBoundingClientRect().bottom
      if (bottom >= 0 && bottom <= (innerHeight + can.height)) { // only draw when visible in browser
        const ctx = can.getContext('2d')
        ctx.fillStyle = '#000'
        ctx.fillRect(0, 0, can.width, can.height)
        ctx.translate(can.width * 0.5, can.height * 0.5)
        ctx.fillStyle = '#FFF'
        const theta = Math.sin(frameCount * 0.001) * Math.PI * 2 * 4
        for (let y = 0; y < can.height; y++) {
          for (let i = 0; i < 10; i++) {
            ctx.rotate(theta * 0.001)
            ctx.fillRect((Math.sin(y * 0.1 + theta + (i * 2)) * 100), y, 2, 2)
        frameCount += 1

Originally this was a quick sketch made in Processing...

//spiral.pde - processing
void setup() {
  size(800, 600);
void draw() {
  translate(width*0.5, height*0.5);
  float theta= sin(frameCount*0.001)*TWO_PI*4;
  for(int y= 0; y<height; y++) {
    for(int i= 0; i<10; i++) {
      rect((sin(y*0.1+theta+(i*2))*100), y, 2, 2);

And then ported to SuperCollider...

//spiral.scd - supercollider
var width= 800, height= 600;
var win= Window("spiral", Rect(100, 100, width, height), false);
var usr= UserView(win, Rect(0, 0, width, height));
var frameCount= 0;
usr.background= Color.black;
usr.drawFunc= {
  var theta= sin(frameCount*0.001)*2pi*4;
  Pen.fillColor= Color.white;
  Pen.translate(width*0.5, height*0.5);
      Pen.fillRect(Rect(sin(y*0.1+theta+(i*2))*100, y, 2, 2));
  frameCount= frameCount+1;
  var nextTime;
  while({win.isClosed.not}, {
    nextTime= Main.elapsedTime+(1/60);


ESP8266 OpenSound Control

2015-07-05 22:29 electronics, supercollider

Here some example Arduino code for sending and receiving OSC via the cheap ESP8266 serial WiFi module.

Note that the Open Sound Control messages here are very basic - only 4 bytes packed into a single 32bit integer.

Optional: connect a separate USB-Serial (FTDI) chip to Arduino pins 2 and 3 to use software serial debugging. Start debugging in a terminal with something like screen /dev/tty.usbserial-A4015TKA 115200

The Arduino code sits and waits for an incoming OSC message (/tap). It then replies by sending out a counter-message (/sti).

//f0 150705
//sending and receiving UDP OSC with an ESP8266
//for an Arduino + ESP8266 with firmware

#include <SoftwareSerial.h>

#define WLAN_SSID  "SSID"
#define WLAN_PASS  "PASS"
#define WLAN_ADDR  "" //laptop running sc
#define PORT  1112 //incoming OSC port
String tag = "/tap"; //incoming OSC addy

SoftwareSerial mySerial(2, 3);

uint8_t buf[16];
byte cnt;
byte id, on, hi, lo;
boolean resp;

void setup() {

  //--OSC message
  buf[0] = 47;   // /
  buf[1] = 115;  // s
  buf[2] = 116;  // t
  buf[3] = 105;  // i
  buf[4] = 0;
  buf[5] = 0;
  buf[6] = 0;
  buf[7] = 0;
  buf[8] = 44;   // ,
  buf[9] = 105;  // i
  buf[10] = 0;
  buf[11] = 0;
  buf[12] = 4;   // a high   (id)
  buf[13] = 3;   // a low    (on)
  buf[14] = 2;   // b high   (hi)
  buf[15] = 0;   // b low    (lo)


  mySerial.print("hard reset...");
  digitalWrite(4, 0);
  pinMode(4, OUTPUT);
  pinMode(4, INPUT);
  resp = Serial.find("ready\r\n");

  resp = Serial.find("OK\r\n");

  do {
    resp = Serial.find("OK\r\n");
  } while (!resp);

  resp = Serial.find("OK\r\n");

  resp = Serial.find("OK\r\n");

void loop() {
  while (Serial.available()) {
    String abc = Serial.readStringUntil('\n');
    if (abc.startsWith("+IPD,4,16:" + tag)) {
      id = abc[22];
      on = abc[23];
      hi = abc[24];
      lo = abc[25];

      buf[15] = cnt++;
      Serial.write(buf, sizeof(buf));
      resp = Serial.find("OK\r\n");

SuperCollider test code:

var last= Main.elapsedTime;
OSCFunc({|msg, time, addr|
  [\id, msg[1]>>24, \on, (msg[1]>>16)&255, \hi, (msg[1]>>8)&255, \lo, msg[1]&255, time-last, addr].postln;
  last= time;
}, \sti);
n= NetAddr("", 1112);  //ESP8266 ip address
f= {|id, on, hi, lo| (id&255<<24)|(on&255<<16)|(hi&255<<8)|(lo&255)};
r= Routine.run({
    n.sendMsg(\tap, f.value(4, 1, i.asInteger>>8&255, i.asInteger%256));

Note: my new and better way to do this is described in this post: /f0blog/f0led/


2015-05-26 00:15 electronics

For a project in collaboration with Stine Janvin Motland I built this 4-channel transducer bass shaker system.

The system has four transducers (Visaton bs 130, 4Ω), two class D stereo amplifiers (2x50W, TDA7492 chip) and a powerful ATX switching power supply (Codecom pm-350c).

I modified the power supply to only give out 12V (yellow&black cables) and also made it start up automatically by shorting the green cable (PS-ON) to ground (black).

There's no volume control so better take care - the system is very hot.


Pd on Raspberry Pi

2014-11-30 17:15 other

Here is a quick tutorial on how to install and run Pure Data headless on a Raspberry Pi. The instructions assume you want to start with a new clean Raspbian system image and do it all from scratch.

The instructions also assume you have a Raspberry model B, a USB soundcard like Terratec's Aureon Dual USB and an ethernet cable with internet access (just connect the ethernet cable between your RPi and your home router).

What you get after following the below tutorial is an SD card with a Pd patch that automatically starts when the RPi is booted.


ssh pi@raspberrypi.local #password is 'raspberry'

See notes below if fail.


When successfully logged in run this on the RPi...

sudo raspi-config

and do the following system configurations...

Log in again from laptop with your new password...

ssh pi@raspberrypi.local
sudo apt-get update #check for new updates
sudo apt-get upgrade #update any old packages
sudo apt-get dist-upgrade #update the distribution

Test sound

lsusb #should list the USB soundcard
aplay -l #should also list the soundcard
sudo speaker-test -t sine -c 2 -Ddefault:CARD=Device #should sound if headphones connected. Stop with ctrl+c

Note: this assumes that your USB soundcard name is Device - check what the aplay command posts and edit the CARD= in the line above if needed.

Install Pd

Download and install Pure Data + required packages with...

sudo apt-get install puredata

Test Pd patches

Copy the following two example Pd patches (or download the attachments below) and save them on your laptop (here assume on the desktop). To copy Pd patches just paste the cryptic text into a plain text editor and save with .pd file extension.


#N canvas 1068 88 450 300 10;
#X obj 238 159 dac~;
#X obj 235 73 osc~ 400;
#X obj 289 73 osc~ 404;
#X msg 126 154 \; pd dsp 1;
#X obj 126 83 loadbang;
#X obj 126 123 del 100;
#X text 42 122 important ->;
#X obj 238 111 *~ 0.2;
#X obj 280 111 *~ 0.2;
#X connect 1 0 7 0;
#X connect 2 0 8 0;
#X connect 4 0 5 0;
#X connect 5 0 3 0;
#X connect 7 0 0 0;
#X connect 8 0 0 1;


#N canvas 1068 88 450 300 10;
#X obj 238 230 dac~;
#X msg 126 154 \; pd dsp 1;
#X obj 126 83 loadbang;
#X obj 126 123 del 100;
#X text 42 122 important ->;
#X obj 238 24 adc~;
#X obj 238 53 delwrite~ del1 500;
#X obj 238 123 delread~ del1 500;
#X obj 259 80 delwrite~ del2 750;
#X obj 280 144 delread~ del2 750;
#X obj 238 182 *~ 0.2;
#X obj 280 182 *~ 0.2;
#X connect 2 0 3 0;
#X connect 3 0 1 0;
#X connect 5 0 6 0;
#X connect 5 1 8 0;
#X connect 7 0 10 0;
#X connect 9 0 11 0;
#X connect 10 0 0 0;
#X connect 11 0 0 1;

Copy Pd files to RPi like this (run this in the terminal on the laptop)...

scp ~/Desktop/testsines.pd pi@raspberrypi.local:/home/pi/
scp ~/Desktop/testmic.pd pi@raspberrypi.local:/home/pi/

This is also how you can transfer more Pd patches later on.

Run Pure Data

ssh pi@raspberrypi.local #log in from laptop again
pd -stderr -nogui -verbose -audiodev 4 testsines.pd #stop with ctrl+c
pd -stderr -nogui -verbose -audiodev 4 testmic.pd #stop with ctrl+c

Note: if no sound test with different audiodev - 4 is usually the USB soundcard. You will also need to connect headphones or speakers for the first example to work. And some kind of audio input (e.g. electret mic or line-in from an MP3 player) for the second example (testmic) patch to work.


Here is how to start Pd and run a patch at boot...

nano autostart.sh #creates a new file. Copy the two lines below into this new file. (save and exit with ctrl+o, return, ctrl+x)

  pd -nogui -audiodev 4 /home/pi/testsines.pd

chmod +x autostart.sh #make the autostart.sh file executable
crontab -e #and add at the end... (again save and exit with ctrl+o, return, ctrl+x)

  @reboot /bin/bash /home/pi/autostart.sh

After rebooting (with the sudo reboot command) the sine tones patch should have started automatically.


ssh pi@raspberrypi.local #log in from laptop once more
sudo pkill pd #stop Pd
sudo halt -p #turn off the RPi safely




SuperCollider Firmata

2014-10-21 13:28 supercollider

clean-up: #57

Just cleaned up an example for SuperCollider and Arduino that I found on my computer. It is demonstrating the SCFirmata class by Eirik Arthur Blekesaune.

//how to read pin A0 with SCFirmata...

//for Arduino1.0.6 and SC3.6.6
//first in Arduino IDE:
//  * select File / Examples / Firmata / StandardFirmata
//  * upload this example to an Arduino
//then in SC install the SCFirmata classes
//  * download zip file https://github.com/blacksound/SCFirmata
//  * extract files and put them in your SC application support directory
//  * recompile SC

d= SerialPort.devices[0]; // or d= "/dev/tty.usbserial-A1001NeZ" - edit number (or string) to match your Arduino
f= FirmataDevice(d);//if it works it should post 'Protocol version: 2.3' after a few seconds

Ndef(\snd, {|freq= 400, amp= 0.5| SinOsc.ar([freq, freq+4].lag(0.08), 0, amp.lag(0.08)).tanh}).play;
f.reportAnalogPin(0, true)  //start reading A0
f.analogPinAction= ({|num, val| [num, val].postln; Ndef(\snd).set(\freq, val.linexp(0, 1023, 400, 800))})//control freq
f.analogPinAction= ({|num, val| [num, val].postln; Ndef(\snd).set(\amp, val.linexp(0, 1023, 0.001, 1))})//control amp instead

f.reportAnalogPin(0, false)  //stop reading A0


2014-10-20 23:31 electronics, supercollider

clean-up: #56

Compared to generating a serial bitstream in audio, analysing and extract serial data from audio is much harder. The SuperCollider code below does it, but the program has limitations and is quite sensitive for noise.

The code takes a string, chops it up into groups of six 8bit bytes and generates a serial audio bitstream from that. Another part listens to this sound and tries to decode it. If it finds six full bytes it sends the result back to sclang via OSC where it is printed.

To test the example connect an audio cable directly from your computer's output to its input (preferably via a small mixer), or change the audioSerial SynthDef to use an internal audio bus. I can also imagine it could function with a mic next to the speakers - but I didn't test this.

If it only prints gibberish try with a different threshold setting, different volume on your computer or use a lower baud rate.

  var baudrate= 9600;
  SynthDef(\serialAudio, {|out= 0, amp= -0.5|  //for sending out serial via audio
    var data= Control.names([\data]).kr(Array.fill(60, 0));  //max 6 bytes
    var src= Duty.ar(1/baudrate, 0, Dseq(data), 2);
    OffsetOut.ar(out, src*amp);
  SynthDef(\audioSerial, {|in= 0, thresh= 0.05|  //for receiving serial via audio
    var raw= 0-SoundIn.ar(in);  //here change to In.ar if trying internal audio bus
    var src= raw>thresh;
    var reading= DelayC.ar(Trig1.ar(src, 1/baudrate*9), 1/baudrate/2, 1/baudrate/2);
    var osc= Phasor.ar(reading, baudrate/SampleRate.ir);
    var clock= (osc-Delay1.ar(osc))<0+Impulse.ar(0);
    var index= PulseCount.ar(clock, reading);
    var stopTrig= index>7;
    var data= Latch.ar(src, index>=#[7, 6, 5, 4, 3, 2, 1]);
    var byte= (1-data).sum{|x, i| 2**(6-i)*x};
    SendReply.ar(stopTrig, '/data', byte);
  OSCFunc({|msg| msg[3].asInteger.asAscii.post}, '/data');

var str= "hello supercollider!";
var baudrate= 9600;
    var data= bytes.collect{|x| [1]++(1-x.asBinaryDigits.reverse)++[0]}.flat;
      Synth(\serialAudio, [\data, data]);

One can use this technique to communicate with another computer via audio. To communicate with a microcontroller (e.g. an Arduino), one needs additional electronics (amplification, rectification). Here's schematic for a bi-directional circuit for talking to a 5V Arduino.

This audio-to-serial technique was used to get input from RFID, touch and bend sensors in our Reflect installation i.e. SuperCollider is running on an iPod Touch and receives all sensor data via audio from an ATmega168 microcontroller.


2014-10-19 23:31 electronics, supercollider

clean-up: #55

Another way (compared to FSK in my previous blog entry) of sending data via audio is to directly generate the serial bit stream using SuperCollider.

To test and learn about these things I first wrote and uploaded a very simple program to an Arduino board. The program just transmitted the bytes 128, 10, 20, 30, 40 and 50.

//Arduino testcode
void setup() {
void loop() {

Then I connected the Arduino serial TX pin (pin1) to the audio line-in of my laptop (via a 1K + 10K voltage divider) and recorded the sound of the serial transmission.

I then analysed the sound by hand and wrote a little program in SuperCollider that could generate similar waveforms.

o= {|chr| [1]++(1-chr.asBinaryDigits.reverse)++[0]};
SynthDef(\serialAudio, {|amp= -0.5|  //for sending out serial via audio
  var data= Control.names([\data]).kr(Array.fill(60, 0));  //max 6 bytes
  var src= Duty.ar(1/9600, 0, Dseq(data), 2);  //baudrate
  OffsetOut.ar(1, src*amp);
Synth(\serialAudio, [\data, [128, 10, 20, 30, 40, 50].collect{|c| o.value(c)}.flat, \amp, -0.5]);

This screenshot show the signal recorded from the Arduino in the first channel, and the SuperCollider generated one in the second.

After all this, I could reverse the process, generate any serial data and send it back to the Arduino RX pin (pin0). A small amplifier circuit in between helped to get a more stable communication going.

This serial-to-audio technique was used to control the 24 LEDs (6 PWM channels) in our Reflect installation i.e. SuperCollider is running on an iPod Touch and sends out serial audio to an ATmega168 microcontroller.

Here is another example that can fade a single led by sending serial commands over audio. Includes schematics for an amplifier circuit plus SuperCollider and Pure Data example code.

And for a more advanced (actually using a much better technique) example see /f0blog/arduino-programming-via-soundcard/.

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