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  • Writer's picture1/4" Jack Of All Trades

Physical Computing Christmas 3 - Capacitive Unpredictability and Enclosure Construction

Updated: Jan 6, 2021

The enclosure for the decorative synth so far, details at the bottom

Abandoning Capacitive Touch

I have unfortunately been forced to abandon capacitive touch sensors for the purposes of this project, they proved far too unreliable and temperamental for use as audio controls. The difficulty using the MPR121 library with the Mozzi library was the first major issue due to a conflict with <Wire.h> that I could not solve (see first Christmas post), which forced me to try use the Arduino capacitive sensor library, which simply was not as effective or reliable as I had found the MPR121 library to be.

I ran a few tests with simple foil pads as well as painted strips on cut glass with capacitive paint, but the results were so unpredictable that I decided against further development.

Testing capacitive paint on glass with wildly unpredictable results.

As a result I began experimenting with light dependent resistors to try and get some interesting results from audio visual feedback, I tried using an LDR to trigger an envelope but this also proved rather unpredictable and sonically the results were not satisfactory.

My response to this has been to delve deeper into the audio synthesis of Mozzi to try and get more interesting results whilst also trying to develop the audio-visual interaction between Mozzi and the LED strip. I have done this by adding an additional voice to the synth and by adding some feedback delay for more interesting sonic variety. However I am fast approaching the limit of the Arduino (having used approximately 80% of its memory at this point) and occasionally hear small clicks and pops in the sound, so I may in fact have to dial back some amount of audio content to ensure the final sonic result is as interesting as possible.

Enclosure Construction 1: The Plan

I had always imagined the final project looking like a cross between a valve amplifier and the clavecin oculaire from the 18th century. A box enclosure at the bottom with a glass tower on top for the colourful LED strips. With a freshly cut wine bottle, which turned out cleaner than all previous attempts, I set about

Above: A valve amplifier.

Below: Louis-Bertrand Castel's clavecin oculaire.

Enclosure Construction 2: The Early Stages

From the inception of the project I have wanted to use recycled materials wherever possible for the construction of the synth's enclosure. For the enclosure's construction I used The glass bottle serves as a way to make the LEDs visible.

I cut around the bottle with a craft knife for a nice snug fit, although it is a bit small when simply placed in the box. However, the LED strip only has adhesive on the back, so I needed a core of some sort to attach it to. To solve this I used a discarded kitchen roll holder, which also dealt he problem of the the glass sinking into the box too far, as now it rests on top of the cardboard core without movement thanks to the close cut of the cardboard box.

The next (and final) step is finalising the code, cutting holes for the potentiometers and various cables and soldering everything to perf boards!


The final bottle cut (not perfect, but what is?) along with repurposed cardboard box and kitchen roll holder for the enclosure.

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