AdrianFreed's blog

Jimi Hendrix plays Public Saxophone in Berkeley in 1970

Jim Hendrix introduces his band at the 1970 Berkeley Community Theater concert. It is interesting and revelatory of his guitar style that he introduces himself as playing the "public saxophone".

Jimi Hendrix Night Train 1965

If Hendrix words aren't evidence enough this video of his early days in rock and roll bands surrounded by saxophone players might convince you of my claim that his guitar style involves emulation of horn playing.

Experimental, Portable eTextile Electronics Lab 2010

Now that I have assembled one of the largest collection of e-textile materials and associated tools I am trying to figure out the smallest winning subset that can form a portable lab.

Audio Sine and Square Wave Signal Generator using a Wavetable

Not my first publication, but my first one with some challenging engineering. I did this in my late teens and it was published in a hobby electronics magazine, "Electronics Australia".

I discovered by accident that some folk from Greece published the same ideas in a professional technical journal in 1989 (attached). If you are a scholar of such things it is interesting to compare and contrast the modes of articulation in my vernacular engineering approach with those of the academic paper.

As I review this design from the 1970's I am struck by the exotic mixture of TTL/CMOS logic/CMOS switches, transistors and opamps that were required to pull it off. Although it might seem that such techniques are obsolete, I have seen plenty of recent Arduino designs using resistor networks that have faced the same challenge of creating a function with positive and negative values from binary sources.

Q: How would I do it differently today? A: I would replace the 555 timer and TTL parts for an Arduino and use a rail to rail inverting opamp.

Interestingly the parts required are all still available and the Arduino solution would cost about the same. The main cost difference would probably be from the the two-pole multiway switches which are expensive these days.

eTextile Pressure Sensing Touch Pad

These are built by sandwiching a piece of porous, spacing fabric (e.g. tulle) between two sheets of piezoresistive fabrics (from Eeonyx). For the square pad depicted below rectangular sheets are placed at right angles and wrap around the frame. On the inside they are stapled to a conductive strip on each edge. The four edges are wired to the analog inputs of a suitable microcontroller, e.g.

Two Way Fabric Leaf Switch

This is assembled using hot melt adhesive backed conductive copper fabric.

Pressure Sensing Ball using eeontex Resistive spandex

A hard ball is surrounded by crumpled resistive fabric (nylon and spande)x and trapped by a round ball of silicone with holes in it. Sensing in various orientations is achieved by wrapping conductors between the holes of the silicon ball.

Fabric Slide Potentiometer

A loop of conductive thread is sewn on either side of the base fabric under the flaps. An inverted toggle from a clasp for jeans is used to short each conductor lowering the resistance of the loop.

etextile Leaf Switch with Iron-on hot melt adhesive

Iron on a small strip of the copper fabric to a non-conductive base. Cut the fabric, and fold over a small section and iron it to itself creating a small flap. Attach another piece of fabric, and iron it close enough to come in contact with the small flap.

Soft Circuit LED paper lamp

This simple-to-build lamp uses a flexible LED strip with both back and front firing surface mount LED's to create rich interactions with both paper and the surface the lamp is placed on. The back firing yellow LED's are diffused by the paper. Light from the rear firing red LED's is scattered and illuminates the water mark thru the paper. Direct and scattered light interacts at the edges of the cylinder. A gap in the plastic tape holding the tube together create a slit of light projected behind the lamp.
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