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EXCTR-network close up.

EXCTR-network close up.

The Spatial Aural Exciter is a project initiated by Samy Kramer. It is essentially a cheap multichannel system consisting of small synthesizer boards that can be connected together in different configurations. Systems can comprise of hundreds of boards. Especially in large systems allow generating big masses of sound that can be moved in space. Individual boards are based on ATMega328 microcontroller and are compatible with Arduino libraries.

Example of exctr-network configuration.

Example of exctr-network configuration.

Exctr-system consists of several different parts. One part is a software running on computer that is sending parameters for individual synthesizer nodes. The communication between computer and individual nodes is done by using MIDI like protocol. The synthesizer nodes are connected in series. Commands are sent from the computer to the string of nodes. Nodes will forward the data to the next node until correct receiver has been reached. Largest practical length for one string is around 40 nodes. In larger networks, multiplexer nodes can be used to combine parallel strings to one network.

Individual synthesizer nodes are small electronic boards consisting mainly on ATmega328 microcontroller and a piezo speaker. The software turns microcontroller to a simple monophonic synthesizer. As one would expect, one can alter the waveform, frequency and amplitude in real time. Band limited sound synthesis algorithms are currently under development.

Exctr-system has been exhibited in several exhibitions over the Europe. Currently this project is actively developed and so far biggest configuration will be exhibited in Turku July 2014.

The software for the single board can be found at The official website of the project can be found at

Hacking at the summer cottage

A typical mökki (~summer cottage) moment of a hacker.

Act 2: The Spirit of a Real Life Avatar is the second part of a living media project The New Degrees of Freedom by Jenna Sutela with collaborators. The essential part of this performance are ten larynx players that are used in transforming audience members to copies/avatars of the main protagonist (Jenna Sutela). Audience can then witness a dialogue (conceptually more like a monologue) between her and the avatars. The trailer/documentation shot at the art biennial Antagon in August 2013 will hopefully give you some idea.

My task for this project was to design a mobile sound system that would consist of several independent audio players and would allow the dialog to be reproduced in sync with the live speech of protagonist. Basically a bit of hacking, some sound design and a few hours of audio engineering. I’m giving here a brief peek of the final system, but as there is a bit of magic involved I’m not able to reveal all the secrets here. However, below, you will get a glance of the core of the larynx player electronics. Larynx player enclosures are custom 3D prints (semi) accurately modeled after human voice box by Emmy Maruta. We worked closely together to ensure that electronics could be fit and installed to the final print.

Mutilated X-mini MINI II capsule speaker with VS1000 OGG player.

Mutilated X-mini MINI II capsule speaker with VS1000 audio player.

The electronics for this project needed to be cheap, small and mobile. Requirement of mobility means that there has to be battery or accu of some sort involved. When the budget for the electronics is fairly small, usually the best route is to find a product that does something pretty similar you want to be done and hack it. After checking through several products I bumped into product called X-mini MINI II capsule speaker. It is basically a cheap mobile speaker that was able to give just enough volume to match level of loud speech. As it had an inbuilt accu, it had already all the electronics required for loading it. When gutted (and parts of the circuit board amputated in order to minimize the footprint) and equiped with a stamp sized VS1000 Audio module (more info on this at my previous post) it was still possible to fit it into a fairly small enclosure. After the speaker electronics board was reverse-engineered, it was quite straight forward to connect line outs of VS1000 audio player to the inputs of the player and take the 3.8V power — just enough for the player — from the accu. Power switch had to be moved to another location on the board for better accessibility. Of course I needed to make a bunch, which went quite nicely even with minimal amount of tools I had with me at the summer cottage where the final build took place.

Hard work demands sturdy tools.

An old school soldering stand I found under the barn.

synakynä schematics

I gave a workshop as part of Super Public Art School (for a second time) in Titanik Gallery 6 June 2013. The topic was a hand shake between visual and sound arts: a synthesizer pencil. I named it Synakynä (a pencil synth in Finnish). Below you can witness some fooling around with first working (after many failed) prototype.

Synakynä is augmented version of drawdio but it uses ATtiny85 microcontroller instead of a 555 timer. This greatly expands the sonic range of the instrument. At the workshop, preprogrammed ATtinys are provided, but if you wish to modify the code and upload it by yourself, source code for Synakynä is available and written using Arduino IDE. One also needs to install ATtiny definitions. To upload the code you can use either ISP programmer or Arduino board as described in previous link.

To play Synakynä, you need to draw continuous and as thick line as possible on paper while touching one end of the line with your other hand. This will cause a small current to flow through the circuits of the pencil, your drawing and your body (study the diagram above for the details). The microcontroller is measuring amount of current and using this information to alter pitch of the synthesizer and tempo of blips. It is also possible to replace pencil with more or less anything (fruits, food, skin) that has similar resistance. Feel free to experiment.

The current code has multiple different modes written into it. Every time Synakyna is switched on, different mode will be chosen.

Parts list:

  • Pencil (HB,2B, as soft as possible)
  • Piezo
  • ATtiny85 (+ optional 8-dip socket)
  • 300k resistor
  • 680pF capacitor
  • Power switch
  • Battery holder (2032)
  • Battery (2032, 3V)
  • Piece of spot board (22×9 holes)
  • Metal wire, uninsulated
  • Wire
  • Piece of aluminum foil or copper tape

Tools needed:

  • Soldering iron and solder
  • Wire strippers
  • Knife or saw
  • Pencil sharpener

The circuit board is constructed on spot board by using thin metal wire to form the actual circuit. It is a neat little technique that is for some reason surprisingly rare. Compared to etched or strip boards this technique allows improvising the actual layout of the board on the fly without spending huge effort on layout design. Those not keen on improvising can find a fairly compact layout below.


Synakynä layout suggestion.

Stuff drawn with pen are on the copper side of the board while parts drawn with pencil are on top side of the circuit board. Pay attention for the trace going to the left leg of the piezo. It should go past the trace coming from the power switch at the top side of the board. Diagram is from the top side (the side the components are) of the board.

pkas paks

Above you’ll see results of the workshop. Ten synths were built and all of them successfully. Well done!