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Speaker Pot

2022-07-16 11:25 electronics

As part of the outdoor installation Pop-Up-Sound-Garden, I wanted to put a speaker inside a massiv concrete drain pipe.

speaker in a concrete pipe

I found an unused flower pot that happened to fit the speaker element I had at hand perfectly, and inside the pot there was enough room to add electronics. So this flower pot now runs on 12V and contains a Raspberry Pi Zero W with a USB sound card, a DC-DC converter, and a 3W amplifier. On the Rpi I installed piCore Linux and SuperCollider.

speaker in a pot

The music that SuperCollider is generating is based on tweet0406 with some added bass notes. It all sounds pretty good and loud for such a small mono speaker setup.

Finally, I attached a distance sensor so that the synthetic sounds only start playing when someone passes by or stands in front of the speaker.

f0dist - Wireless Distance sensor OSC

2022-07-04 21:26 electronics

Yet another simple wireless sensor circuit that sends Open Sound Control messages. Here the sensor is the VL53L1X time-of-flight laser module and the microcontroller an ESP8266-01 - all powered by two AA batteries.

There are settings for smoothing, update rate and thresholds which can be controlled by sending OSC messages to the ESP module. See the examples.

Under optimal conditions the sensor can measure accurately up to 4 meters, but in practice I found the maximal range to be more around 3 meters. Speed and precision is fantastic though. It reacts very fast and with millimeter resolution.

Attached below are examples for SuperCollider and MaxMSPJitter, schematics and the firmware (PlatformIO).

distance sensor

distance sensor out in the wild


iMac G3 restoration - Tripple Boot

2021-12-20 14:01 other

This old Blueberry iMac G3 350 MHz was given to me for free many years ago and last winter I finally got around to fixing it up.

iMac G3 blueberry.jpg

Trippel booting

I set up the machine with three different operating systems...

and this computer I use for running various software from back in the days - mostly audio applications like SuperCollider 2.2.16, MaxMSP 4.0.9 with nato.0+55+3d, Mosaic 1.58 and Digital Performer 2.7.
The machine runs well and feels snappy despite it being so old. I optimised Mac OS X Tiger a bit by turning off Spotlight and Dock animations and I also installed ShadowKiller. In Mac OS 9 I removed some unnecessary extensions. OpenBSD is using the lightweight window manager dwm and in order to get the ATI Rage 128 graphics card working I configured Xorg as described in this forum post.


The internal 1/2 AA PRAM battery was dead and I replaced it with a CR2032 coin cell. The holder for the coin cell I soldered right on top of and across the old holder. It should be easy to remove and restore the original battery if ever needed.

iMac G3 battery holder


Some of the electrolytic capacitors inside looked suspicious and bulged so I replaced the seven SMD variants I found on the motherboard. The big through hole capacitors in the power supply section I left untouched. They seemed okay.


The old spinning hard disk was replaced with an SSD. To connect the SSD I bought an IDE to SATA adapter and used the existing 40-pin and power cables. I used velcro to fixate the SSD in place.

iMac G3 motherboard

Unfortunately, this type of IDE adaptor is a bottleneck and will make the SSD underperform. Xbench report that the SSD perform only marginally faster than the original HDD for sequential reading and writing. Random access read/write on the other hand perform 4.5x faster. Taken together, the SSD is not more than around twice as fast as the HDD. Still, it was worth the cost and hassle to swap out the old spinning hard drive. A big plus is that the machine now runs completely silent.

TYPE                SSD       HDD
sequential         44.86  /  39.71
random r/w        136.77  /  30.36
overall disk test  67.56  /  34.41

Freeze issue

I had a strange problem with the OS X system freezing at random times. I suspected the SSD adaptor and the power supply. By coincidence, I later noticed it would take longer until it froze if I only worked in the terminal. As soon as I touched the mouse, the system would lock up. So I tried replacing the optical tracking mouse (manufactured by sempre - model MOU-1T) with the original puck mouse, and then the system ran flawlessly. So the LED mouse caused the system to freeze!
This modern optical tracking mouse must be generating current spikes that the USB port can not handle.

Other things fixed

  • cleaned the inside of the machine and the outside cover
  • applied new thermal paste
  • updated Open Firmware from 4.1.7f4 to 4.1.9f1
  • bought and installed an additional RAM module on eBay

Things still broken

  • CD player is partly broken - it works but won't properly eject - tried to repair it but failed
  • both internal speakers are distorting at louder levels and lower frequencies
  • plastic casing scratched and stained by paint that I couldn't get off
  • no matching Apple keyboard (although I do have a puck mouse)


Even though this is such an old and slow machine (22 years, 350 MHz), it is a lot of fun to use and play around with. It can also be of use as it runs some software that no longer exists and the CRT display gives out a warm nostalgic feeling.
A drawback is that it draws a lot of power. 75-85 Watts in use (mainly depending on screen brightness), 64 Watts in standby (sleep mode with CRT off) and 5.5 Watts when powered off! The change to SSD helped reduce power consumption a little bit (around 8 Watts), but overall it is still high compared to, for example, a Raspberry Pi.

  • SMD electrolytic capacitors €3
  • 120 GB 2,5" Intenso SSD €17
  • IDE 3.5" to SATA (PATA) adapter €9
  • 256 MB PC133 168-pin SDRAM €3

Total cost of restoration: €32


MacBook Pro restoration - Kitchen Radio

2021-12-13 14:24 other

My 14-years old MacBook Pro Core 2 Duo/Late 2006 is since a year acting as a kitchen radio.

The laptop is set up to dual-boot Mac OS X 10.6.8 Snow Leopard and FreeBSD (13.0 at the moment) via the rEFInd boot manager. Though I end up using OS X most of the time just because it boots a lot faster. The battery pack is dead so I need to power it on and off each time I use it.

SpiderWeb is my browser of choice, but I also have ArticFox and InterWeb installed. Performance is alright and I can stream radio and play YouTube videos in 480p - my preferred quality setting. In FreeBSD, I run a recent version of Firefox.

The computer is connected to a set of external computer speakers - a 2.1 subwoofer system - that I got for free and had laying around.

Internet access is handled via WiFi (AirPort Extreme) and the DVD burner (SuperDrive), Bluetooth, microphone, speakers, trackpad, sensors and the camera (iSight) all work.

But this laptop has had a hard life and was with me on many adventures. Quite a few things were broken and I had to repair the keyboard, battery, power supply and fans.

Keyboard repair

The machine suffered a beer accident in Japan in 2008 and after that about a third of the keys on the keyboard wouldn't work. I kept using it for several years with the help of an external USB keyboard.

Last winter I spent a lot of time trying to finally repair this broken keyboard using a multimeter, tape and thin conductive wire...

failed keyboard repair1failed keyboard repair2failed keyboard repair3failed keyboard repair4failed keyboard repair5failed keyboard repair6

Many tracks were broken and corroded but amazingly I got it to work! At one moment, all keys functioned except the led in the caps-lock that wouldn't light up. Also, during the repair, I broke off one of the springy supports for the space bar, so it tilted and didn't react on the left-hand side. Very irritating and impossible to fix (at least by me).

And my repair attempt didn't last. After about a month, a few keys started acting funny, intermittent and finally wouldn't work at all. When even more keys broke, I gave up and ordered a replacement keyboard for this model (A1211) on AliExpress.

Fans repair

The right-hand side fan needed repair. It was stuck as the casing somehow got dented. I cleaned both fans thoroughly and added new silicone grease.

Memory upgrade

I maxed out the RAM by buying two 2 GB memory modules on eBay. There is an issue with this machine though as it can not address more than 3 GB. So even if I now have 4 GB installed, only 3 can be used.

Other things

  • added new thermal paste
  • removed dead battery pack
  • replaced PRAM coin cell
  • replaced the spinning hard disk with an SSD
  • the MagSafe cable was broken. I bought a new one, cracked open the power supply and soldered the new one in place


The machine uses between 20 and 35 Watts in standard operation, and the cost of fixing it up was around €40 in total. It gets a lot of use and will probably last many years to come.

  • 2 x 2 GB DDR2 SDRAM €7
  • 120 GB 2,5" Intenso SSD €17
  • Keyboard €11
  • MagSafe cable €5

TiBook restoration - Offline Laptop

2021-12-10 21:04 other

Last autumn I spent time restoring my old computers. I wanted to start using them for various things again. One, a 20-years old Titanium PowerBook G4 667 MHz, was in good shape and didn't need much work. My idea was to have it as an offline laptop - a distraction-free machine for reading e-books and playing around with a BSD operating system.

offline laptop

I thoroughly cleaned the keyboard and removed dust from inside the fan and air vents. I also replaced the old thermal paste with new. That required some work because to get access to the CPU and heatsink on these models one need to unscrew and disconnect nearly everything inside. But it was interesting and worth the effort. This computer now runs cool and the fan hardly ever turns on. The good guide on iFixit was helpful.

In the process, I also replaced the hard disk with a 16 GB Asiproper mSATA SSD and an mSATA to 2,5" 44pin IDE adapter. That made the laptop faster overall and also made it run much quieter. The old spinning hard disk was quite noisy. There is now only a tiny vining sound during operation (from a coil I believe), but that does not bother me much.

The laptop battery was dead so I removed it and recycled the cells. It is a slight annoyance to have the laptop plugged in with the power adapter cable at all times. I might try to reconstruct the battery pack with new LiPo 18650 cells.
Another drawback with an old PPC machine like this is that its current consumption is fairly high - at least compared to how slow it computes. In use, this laptop draw 21-35 Watts depending on the screen brightness and what I do with the computer, and when completely powered off 3.8 Watts! So I make sure to always unplug it when I'm done using it.

The built-in speakers and the matte display are okay, the DVD player is working and the trackpad and keyboard are very nice to use. It is a joy to type on this laptop and without the battery, the machine doesn't weigh much.

The display hinges feel good but I take extra care not to twist or put stress on the lid as I know these can break on these PowerBook models.

There is 512 MB of RAM installed (2 x 256 modules). I thought of buying more and upgrading to the maximum of 1 GB, but these types of SO-DIMM memory modules are both hard to find and I feel I can't justify the cost as the operating system I'm running (see below) uses less than 70 MB.

Whenever I need to transfer files or get network access I connect an ethernet cable. There is no WiFi or Bluetooth. It should be inconvenient to get online - it's a feature.


For the operating system, I picked OpenBSD. Mainly because I wanted to study and learn more about it, but also because it is still updated and supported for PPC 32-bit machines.
In the process, I also tried FreeBSD, MintPPC, VoidLinuxPPC, Debian and Adelie Linux but encountered various problems. Nothing worked as good and was as easy to install as OpenBSD. Mac OS9 or OSX (10.4 perhaps) would have been other options, but I already have several machines that run these systems.

The following instructions show how to set up OpenBSD version 7.0 on a macppc laptop using another laptop plus a USB stick to prepare the installer.

Note: The internal hard disk will be erased and overwritten.


On another machine (here macOS):

  • download install70.iso for macppc
  • check that the iso file checksum compares with this SHA256 string
    sha256sum ~/Downloads/install70.iso
  • insert an empty USB stick and format it as FAT MBR (I used Disk Utility)
  • write the iso file to the USB stick
    WARNING: This is dangerous! Double-check that you are targeting the USB stick (here disk2) and not some other drive
    diskutil list #and take note of the disk number of the USB stick (here disk2)
    sudo diskutil umount /dev/disk2s1 #make sure disk2s1 the USB stick
    sudo dd if=~/Downloads/install70.iso of=/dev/rdisk2 bs=1m #make sure rdisk2 is the USB stick

Now move the USB stick over to the PowerBook for installation and...

  • power on while holding down the keys O+F+CMD+ALT. This should take you into Open Firmware
  • boot from the USB stick iso with the following command...
    boot usb0/disk:,ofwboot 7.0/macppc/bsd.rd

If that does not work try changing from usb0 to usb1 in the line above. Also, note the space after ofwboot and perhaps edit 7.0 to match the version you downloaded.

The laptop should now have booted and started the OpenBSD installer.


This is easy. Just answer some questions accepting the default answer for the most part. For this PowerBook, there were only two things I choose to do differently: said yes to start X window system by xenodm and said yes to continue without verification.

i #for Install
HOSTNAME #system hostname?
[gem0] #network interface
[autoconf] #IPv4 address
[none] #IPv6 address
PASSWORD #for root account
[yes] #start sshd by default?
yes #X window system started by xenodm?
[no] #change default console?
USERNAME #for user account
[no] #allow root ssh login?
[wd0] #wd0 is internal SSD disk, sd0 is USB
[whole] #use whole disk
[a] #auto layout
disk #location of sets?
no #already mounted
[sd0] #which disk contains the install media?
[7.0/macppc] #pathname to the sets?
yes #continue without verification?
Europe/Berlin #enter a valid timezone
[reboot] #press and hold down O+F+CMD+ALT

Back in Open Firmware set up a few environment variables (it also seem to work without these but for safety)...

setenv auto-boot? true
setenv skip-netboot? true #optional - speeds up booting a little bit
setenv boot-device hd:,ofwboot
shut-down #remove the USB stick, start again and log in as USER


Now OpenBSD should be up and running. Here are a few things I did to set up and customise my system...

Allow doas, do not ask for password for reboot and shutdown:

Replace USER with your username from above...

echo 'permit persist keepenv USER' >> /etc/doas.conf
echo 'permit nopass USER as root cmd reboot' >> /etc/doas.conf
echo 'permit nopass USER as root cmd shutdown' >> /etc/doas.conf

Save the SSD a bit by enabling TRIM:

doas cp /etc/fstab /etc/fstab.bak
doas sed -i 's/rw/rw,softdeb,noatime/g' /etc/fstab

Update the system:

This requires internet access.

doas fw_update -a #optional: install non-free firmware (I didn't)
doas syspatch #patch the system
doas pkg_add -Uuv #update apps and more
doas reboot

Install suckless window manager, terminal, status and launch menus:

It is also possible to skip this section and instead install a more traditional desktop environment like Xfce.

doas pkg_add git nano

git clone https://git.suckless.org/dwm
git clone https://git.suckless.org/dmenu
git clone https://git.suckless.org/st
git clone https://git.suckless.org/slstatus

cd ~/dwm
nano config.mk #uncomment FREETYPEINC = $(X11INC)/freetype2
ftp https://dwm.suckless.org/patches/functionalgaps/dwm-functionalgaps-6.2.diff
git apply dwm-functionalgaps-6.2.diff #optional: patch dwm to use gaps
cp config.def.h config.h
nano config.h #edit the resizemouse line to use SHIFT+ALT+MOUSE for resizing windows
  { ClkClientWin, MODKEY|ShiftMask, Button1, resizemouse, {0} },
doas make install

cd ~/dmenu
nano config.mk #uncomment FREETYPEINC = $(X11INC)/freetype2
cp config.def.h config.h
nano config.h #optional: edit number of lines in launcher...
  static unsigned int lines = 12
doas make install

cd ~/st
nano config.mk #uncomment CPPFLAGS etc. (4 lines)
ftp https://st.suckless.org/patches/alpha/st-alpha-0.8.2.diff
git apply st-alpha-0.8.2.diff #optinal: patch terminal for transparency
doas make install

cd ~/slstatus
nano config.mk #and add -lsndio where it says OpenBSD
cp config.def.h config.h
nano config.h #optional: edit status bar...
  { cpu_perc, " cpu: %s%% |", NULL },
  { ram_used, " mem: %s |", NULL },
  { datetime, "%s", "%F %T" },
doas make install

Unfortunately, slstatus does not work well on this old PowerBook. E.g. cpu_perc returns a constant of 100% and the sensor for temperature is not found.

Turn off additional console window at login:

doas sed -i 's/xconsole/#xconsole/' /etc/X11/xenodm/Xsetup_0

Switch to ZSH shell:

doas pkg_add zsh
chsh -s zsh

Set up the .xsession file:

Adapt en and US below to match your keyboard layout and preferred language.

nano ~/.xsession #and add the following

  export ENV=$HOME/.zshrc
  export LC_CTYPE=en_US.UTF-8
  setxkbmap us
  xidle -program "/usr/X11R6/bin/xlock -mode blank -lockdelay 10 -timeelapsed" -timeout 480 &
  xsetroot -solid black
  slstatus &
  exec dwm

Log out and in again to make the changes work.

Set a wallpaper:

Optional: with feh it is easy to set a desktop background. compton together with the alpha-patched st from above results in a semi-transparent terminal.

doas pkg_add compton feh
nano ~/.xsession #edit and replace xsetroot with the following two lines

  compton &
  ~/.fehbg &

mkdir -p ~/.config
ftp https://wallpapercave.com/wp/QjyrBg9.png #or some other png or jpg
mv QjyrBg9.png ~/.config/wallpaper.png
feh --bg-fill ~/.config/wallpaper.png

Install pdf and epub readers:

doas pkg_add zathura-pdf-poppler epr-reader

Reduce the boot time:

A bit of an annoyance is that OpenBSD takes a long time to boot. 1 minute 45 seconds in my case. This is mainly due to security features that for example shuffle around the address space layout at each boot (ASLR).
To save 25 seconds in boot time I turned off ASLR with the command...

doas rcctl disable library_aslr

This is of course not recommended, but for a machine like this that is mainly offline and for what I'm using it for, I believe it is alright.


All in all, I am very happy with this laptop and that it continues to function and be of use after 20 years.
The cost of fixing this up - the new mSATA SSD plus IDE adapter - was around €20.

Building SuperCollider for piCore Linux 2

2021-07-27 14:32 supercollider

This is an updated version of /f0blog/building-supercollider-for-picore-linux/ which demonstrates how to build, package and install SuperCollider and sc3-plugins for piCore - the Raspberry Pi port of TinyCoreLinux.

The instructions here below are for piCore12.0 (32-bit) while the old post was for piCore-9.0.3. The main difference between the two is that we no longer need to build jack2 ourselves. jack and jack-dev are now included in the piCore repository. This version also compiles SuperCollider with avahi support.


piCore has many advantages over the common Raspbian system. It will boot a lot faster, is extremely light-weight and is easy to customise. And because the whole system always resides in RAM, SD card wear is minimal.

Its immutable-by-default design means one can unplug the power to the Raspberry Pi without performing and waiting for a proper shutdown nor risking corrupting the SD card. It also allows one to experiment without being afraid of messing up. A simple reboot will take the system back to a known state. For changes to be persistent, one must deliberately write them to the SD card (using the command filetool.sh -b).

Some drawbacks are that piCore is more advanced to install and configure and that much common Linux software is missing from the built-in package manager (one will have to compile it oneself - hence this guide).


  • an SD card - 2 GB is plenty
  • a Raspberry pi - here a RPi 3B v1.2
  • an ethernet cable
  • a router with an internet connection
  • a laptop - here running macOS


  • download piCore-12.0.zip
  • burn the zip file to the SD card using for example balenaEtcher
  • put the SD card in the RPi and connect ethernet and 5V power

On the laptop, open a terminal and run the following commands:

ping  #first broadcast ping (stop with ctrl+c)
arp -a  #figure out which IP address the RPi has (here
ssh tc@  #default password: piCore

sudo fdisk -u /dev/mmcblk0  #then press the following keys in order to delete and recreate partition2
 p  #note start of partition2 - StartLBA - usually 139264
 139264  #enter start of partition2 from above
 <RET>  #type return to accept suggestion
 w  #write

filetool.sh -b
sudo reboot

ssh tc@  #pass: piCore

sudo resize2fs /dev/mmcblk0p2  #resize partition2

install dependencies

Assuming piCore is now installed and partition2 resized like above...

#download and install build dependencies
cd /tmp
tce-load -wil cmake compiletc squashfs-tools libudev-dev libsndfile-dev readline-dev libsamplerate-dev avahi-dev jack-dev git
wget http://tinycorelinux.net/9.x/armv6/tcz/fftw-dev.tcz  #from old repository
tce-load -il fftw-dev
sudo /usr/sbin/cache-clear

building SuperCollider

Assuming all dependencies above are installed...

#download and compile SuperCollider
cd /tmp
git clone --branch main --single-branch --recurse-submodules https://github.com/supercollider/supercollider.git
cd supercollider
mkdir build && cd build
sudo make install
cat install_manifest.txt | grep -v "/usr/local/include/\|/usr/local/share/pixmaps/\|/usr/local/share/mime/" > /tmp/sc.list
make clean

#create the SuperCollider tcz extension package
cd /tmp
tar -T /tmp/sc.list -czvf /tmp/sc.tar.gz
mkdir /tmp/pkg && cd /tmp/pkg
tar -xf /tmp/sc.tar.gz
cd ..
mksquashfs pkg/ supercollider.tcz
sudo mv supercollider.tcz ~
rm -rf /tmp/pkg
tce-load -i ~/supercollider.tcz
sclang -h  #just to check that it is working

On the laptop, open another terminal window and download the resulting compressed SuperCollider package:

scp tc@ ~/Downloads  #pass: piCore

building sc3-plugins

Assuming SuperCollider is installed like above...

#download and compile sc3-plugins
cd /tmp
git clone --branch main --single-branch --recursive https://github.com/supercollider/sc3-plugins.git
cd sc3-plugins
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE="Release" -DSUPERNOVA=OFF -DNATIVE=ON -DSC_PATH=../../supercollider/ ..
sudo /usr/sbin/cache-clear
sudo make install
cat install_manifest.txt | grep -v "/HelpSource\|.html\|/Help" > /tmp/scplugs.list
make clean

#create the sc3-plugins tcz extension package
cd /tmp
tar -T /tmp/scplugs.list -czvf /tmp/scplugs.tar.gz --exclude=*/HelpSource --exclude=*.html --exclude=*/Help
mkdir /tmp/pkg && cd /tmp/pkg
tar -xf /tmp/scplugs.tar.gz
cd ..
mksquashfs pkg/ sc3-plugins.tcz
sudo mv sc3-plugins.tcz ~
rm -rf /tmp/pkg

On the laptop, open another terminal window and download the resulting compressed sc3-plugins package:

scp tc@ ~/Downloads  #pass: piCore

Now that the two tcz packages are created and saved to the laptop, we can erase the SD card and start afresh. (It is possible to continue working with the same piCore install, but unused build dependencies would waste some space).


(for future installs you can skip all of the above and start here assuming you have kept the .tcz packages)

  • trash the old system and burn piCore-12.0.zip to the SD card again
  • put the SD card in the RPi and connect ethernet and 5V power

On the laptop, open a terminal and run the following commands:

ping  #first broadcast ping (stop with ctrl+c)
arp -a  #figure out which IP address the RPi has (here
ssh-keygen -R  #resets the ssh keys to be able to log in again
ssh tc@  #default password: piCore

sudo fdisk -u /dev/mmcblk0  #then press the following keys in order to delete and recreate partition2
 p  #note start of partition2 - StartLBA - usually 139264
 139264  #enter start of partition2 from above
 <RET>  #type return to accept suggestion
 w  #write

filetool.sh -b
sudo reboot

ssh tc@  #pass: piCore

sudo resize2fs /dev/mmcblk0p2  #resize partition2

#install dependencies
tce-load -wi alsa alsa-utils jack libsamplerate libavahi libudev readline git nano

On the laptop, open another terminal window and upload the compressed packages:

cd ~/Downloads
scp supercollider.tcz sc3-plugins.tcz tc@

Back on the Raspberry Pi...

cd ~
mv supercollider.tcz sc3-plugins.tcz /mnt/mmcblk0p2/tce/optional/
echo -e "supercollider.tcz\nsc3-plugins.tcz" >> /mnt/mmcblk0p2/tce/onboot.lst
echo -e "\nsudo /usr/local/sbin/alsactl -f /home/tc/mysound.state restore" >> /opt/bootlocal.sh

#autostart - optional
nano autostart.sh  #add the following lines
  jackd -P75 -p16 -dalsa -dhw:0 -r44100 -p1024 -n3 &
  sclang /home/tc/mycode.scd
chmod +x autostart.sh
echo -e "/home/tc/autostart.sh &" >> /opt/bootlocal.sh

nano mycode.scd  #add the following lines
    {SinOsc.ar([400, 404], 0, 0.5)}.play;

nano /opt/bootlocal.sh  #change from ondemand to performance in line 10
  echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

#IMPORTANT - make the changes permanent
filetool.sh -b

sudo reboot

The piCore system should now have SuperCollider installed and (optionally) start at boot.


To adjust the volume log in and run the following commands...

alsamixer  #set volume with arrow keys, ESC to exit
alsactl -f /home/tc/mysound.state store  #save in custom alsa settings file
filetool.sh -b  #make permanent


  • running the make command with flag -j3 will usually just result in a out-of-memory freeze.
  • jackd and SuperCollider will be running as root when autostarting.
  • the start-up time from applying power to SuperCollider is making sound is ~20 seconds.
  • after the first backup (filetool.sh -b) the ssh-keygen -R <IP> will not be needed any longer.
  • remember to change the passwords with passwd.
  • CPU benchmarks are more or less the same as for running SC under Raspbian
  • -dhw:0 is usually the RPi built-in sound card. To use an USB soundcard start jackd with -dhw:1. List available cards with aplay -l

Impulse Train in SuperCollider

2021-07-24 11:44 supercollider

In SuperCollider there are no readily available UGens for creating a fixed number of single sample impulses. One could cobble something together using Demand rate UGens...

c = {|dur = 1, num = 8|
  Duty.ar(Dseq([SampleDur.ir, dur / num - SampleDur.ir], inf), 0, Dseq([1, 0], num));
}.play(fadeTime: 0);

or another variant could be to use a combination of Sweep and Changed...

c= {|dur = 1, num = 8|
  Changed.ar(Sweep.ar(0, num / dur).ceil.min(num));

but there is a more flexible technique using an envelope. The big win doing it like this is that we can play with the envelope's curvature and get different shapes.

//impulse train with curvature
c = {|
  t_go, // trigger
  dur = 1, // total duration in seconds (also frequency)
  cur = 0, // curvature or 'shape'. 0 = pulses at regular intervals
  num = 8, // number of impulses per duration
  amp = 1|
  var env = EnvGen.ar(Env(#[0, 0, 1], [0, dur], cur), t_go);
  var train = Changed.ar(ceil(env * num)) * amp;
  // train = train * (1 - env); // optional decreasing amplitude
  // train = train * env; // optional - increasing amplitude
c.set(\t_go, 1);
c.set(\t_go, 1, \cur, 3, \num, 18); // start slow and go faster
c.set(\t_go, 1, \cur, -2, \num, 18); // slower and slower
c.set(\amp, 0.2);
c.set(\t_go, 1, \cur, 0, \dur, 0.5, \num, 200); // 200 for half a second = 400 Hz

The trick to converting an envelope into discrete impulses is to make the linear 0-1 ramp into whole number steps (scale up with * num and run it through ceil) and then trigger an impulse each time the step changes (using the Changed UGen). Then multiplying the train of impulses with the original envelope is optional. The extra multiplication will fade in or fade out the amplitude over the given duration.

The plot below shows two short bursts. There are 10 impulses spread over 200 samples at a sample rate of 44.1KHz. The top one has its curvature set to 4 and thereby the impulse train gets exponentially faster. In the bottom plot, the curvature is the inverse -4 and thereby the train starts fast and then slows down.

plot of two different impulse trains

And here is the same (top) impulse train again but showing the process from the curved envelope, via the discrete steps and to the resulting impulses.

impulses from an envelope

solar cell with loudspeaker

2020-11-24 16:52 other

Here is a very simple and useful tool that can be built out of a small solar cell and an active speaker (headphones also work). This tool translates light into audio and will allow you to hear how much certain LED or fluorescent lamps flicker. It can be used to test and figure out the quality of LED lamps, learn about PWM dimming and also be a fun way of generating sounds.

I forgot where I learned this trick - it might have been on electronupdate's YouTube channel.

My solar cell came from a broken calculator and the loudspeaker (roxcore) I had since before. The speaker is active i.e. it includes an amplifier and a battery. I simply glued a 3.5mm audio connector to the back of the solar cell and soldered some wires so that the + and - from the cell directly connect to the TIP and GND of the 3.5mm audio jack. One could also add a capacitor in series to remove the DC offset, but I trust that the speaker has one built-in.

Note: check that your solar panel is not generating too high voltage. Mine outputs ~3V maximum and that is okay. Bigger panels usually output 6V or 12V and that might damage your speaker.

The resulting sound is most often a 50Hz hum, but it can also be much more complex and interesting with harmonics, noises, chirps and clicks. The worse LED or fluorescent light fixture the better the sound. Old tungsten and halogen lamps produce a constant voltage (DC) so the result is only silence.

solar cell and loudspeaker 1solar cell and loudspeaker 2

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