e-Textile Musical Instruments

Circuit Layout Design Patterns for eTextiles Appliqués with Conductive Fabric

In the usual approach to PCB layout traces are laid out to connect signals and power to the pads of packaged parts and I/O connectors. This is a style that evolved for very high speed digital circuits. One usually also employs ground and/or power planes or a ground flood.

This style is not convenient for eTextile Appliqués which are most commonly single-sided and are based on cut traces rather than etched boards.

There is an older style of PCB layout that is more suitable for low-speed e-textiles that I remember seeing with old transistor radios. The style is almost all copper with just a few lines etched away to separate conductors.

This makes designs more robust with multiple parts soldered on and removed and with multiple sewing points at the edges.

It also makes for less weeding and more surface area that will be fused/glued to the base fabric.

It was also common for many of the traces in these radios to be curved.

For the eTextile Spring Break I guided Martin De Bie through some iterations of his original Textilo design that includes this new thinking on layout and a further insight regarding the 8-pin DIP packages commonly used now by eTextile electronics experiments (with the ATTINY and 555 timer being common choices). This insight is to start the design from the DIP package and imagine the negative space of the smallest amount of conductive fabric that needs to be weeded to separate the 8 pins and combine the constraint of roughly equal area given to the conductors attached to each pin. This results in a motif with 8 radial lines and 8 triangles between them.

Here is the original textilo with its elegant pads to sew to:

large_textilo.jpg

Here is the next version with more conductive material to work with alongside the prototype of a radial design. The radial design includes serpentine interdigitation to allow for touch interaction:

sidebyside.jpg

Nicole Yi Messier picked up on this radial design pattern for her wearable 555 timer based FM radio transmitter:

transmitter555.png

FastTouch Open Source Arduino Library for Fast, Portable, Low Fidelity Capacitive Sensing

The fast touch algorithm reimplemented in the library available here was developed for my FingerPhone Instrument. The fast touch library senses touch on any digital I/O pin on many embedded controllers with the Arduino IDE. This includes Atmega 8-bit, SAMD21, and Teensy. This includes most pins on most micro-controllers. A few micro controllers have analog input pins that can't also do digital I/O . The library relies on the ability to enable a built-in pull-up resistor on the pin being sensed. Here is the algorithm:
  • set the pin to output a LOW value for 1uS or so.
  • set the pin to output a high via a built-in pulp resistor.
  • Read the pin regularly and evenly while it reads a low value.
  • The sensed value is reported as a function of the time it takes for the pull-up to bring the pin to a high value. This depends on whether the pin is touched.

    The example code provided with the library uses the Arduino Tone library to sound pitches according to which pins are touched.

    Notice that each call to the fast touch library implements a cycle of a relaxation oscillator.

    I am indebted to Alice Giordani for exemplifying use of the library so well in this dreamcatcher:

  • Augmented Electric Guitar

    Experimental surface sensing for fingerstyle players

    e-textile Interactive Demonstration at Maker Faire 2007

    My table at Maker Faire 2007 including my first e-textile work with peizoresistive fabric, and my duotouch pad and floor sensors.

    In 2016 I made the video below of a tear-down of those e-textiles with Hannah Perner Wilson.

    Our Maker Faire table also include some great interactive demos whipped together by Andy Schmeder.

    Michael Zbyszynski dropped in and talked about his Ikea bowl speakers.

    It was great that Dan Overholt was nearby demonstrating his e-field sensor array.

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