Arduino synth instructable

My friend and co-geek Mads Høbye has been improving on an old synth project that I started some years back. He has now made an instructable to to share it with the internets.
We are planning to make further improvements and make it into a proper Arduino library.

Some sound demos here: test1 test2 sequencer1 sequencer2 sequencer3 demo1 demo2

Generating high frequencies with AVR ATMEGA (Arduino)

While playing with the touch interface i generated high frequencies with the Arduino. I think this could be useful for other applications so here is the Arduino code for generating high frequencies. Here is a list of possible frequencies.

Bear in mind that the frequency resolution is very low at high frequencies and the duty cycle is not allays 50 %.

Arduino do the Touché dance

The Touché hardware uses a really fancy Direct Digital Synthesizer IC from Analog Devices. It generates a really pure sine wave signal with frequencies between 1kHz and 3.5MHz with crazy high resolution.

While the Arduino is capable of generating frequencies in this range the signal is a square wave with lots of harmonic frequency components and really low frequency resolution.

Simply using this signal with the circuit described in the Touché paper result in a really messy frequency graph due to the harmonics from the square wave.

The solution is to use the filtering properties of the LC circuit to our advantage. By measuring the signal after the inductor (coil) rather than before we only see a nice sine wave shaped signal free of all the unwanted frequency components.

As a result we now see a peak in signal at resonance rather than a notch but the signal contains the same information.

The Arduino is only able to generate about 200 frequencies within the usable frequency range but the signal measured at these frequencies is very clean and stable allowing for interpolation to get better resolution.

We are currently working on algorithms to determine touch gestures from this signal.

Here are some external links about the touch interface:

Original DisneyResearch paper

Instructable by Mads Høbye about how to make it

Online article (w. video) at MEDEA Malmö University

 More may be added.

Replicating Disney research Touché sensing method

A little while ago The people at Disney research released a video showing a new capacitive sensing techneque. We were all amazed over the result and expected some real electronic wizardry to be behind. After reading their paper about the subject it turned out that they used an effect we Tesla coilers often experience.
A tesla coil secondary is a big coil of wire with a doughnut shaped electrode connected to one and the ground to the other. This form what is called a LC resonator. The inductance of the wirer and the capacitance of the doughnut interact to give the whole assembly a specific resonance frequency. Changing either the capacitance or the inductance alters the frequency.
Another property of the assembly is that the ground wire seem to suck in signal at the resonance frequency. If the ground wirer is connected to the output of a signal generator it will draw current from the generator only at the resonance frequency.  Touching the top electrode or even approaching it alters the capacitance.
Assuming the inductance is constant the resonance frequency gives a measure for the capacitance in the system and thus the interaction.
Substituting the Tesla primary winding with a 10mH potted inductor and the top electrode with a roll of solder I replicated the sensing method used by Disney Recearch.

(Less crappy video)

Runner w. spool

Braider with spool-runners and spools

All the bits before attaching motor. 6 out of eventually 18 runners are tested.

Test video with motor

How the braider works

The braider uses 6 gears connected in a circle. Each gear drives a plate with 4 notches. The notches drives pegs mounted on spool runners (red and green dot). The runners are guided by a track following the movement of the grooves except where each of the gears meet. Here a switch track let the runners pass from one plate to another.

Maypole brading machine

While doing some 1910 era props i needed tubular braid around some wirers. I got interested in how these were made and thought I would to make a machine that does tubular braiding.

This is my first prototype:

The idea is that 18 spools are racing around each other in a Møbius knot like pattern. The result is the same as Maypole weaveing.
Here is a short video of the first results:

The method seems to work but I still need to design the actual spools and a sustem for advancing the finished braid.