learning the ropes

We want to be able to sense how far people are pushing the poles in our installation. I thought we could do this by measuring how much force the PVC poles are exerting on the ring they’re sitting in.

Since force sensing resistors from Interlink Electronics are expensive ($5-6/each) and also because I couldn’t see how the fragile FSRs would fit into the holes we planned to use, I wanted to find a better solution.

I discovered it was possible to create FSRs out of wire and plastic wrap. Others have used conductive foam and wire mesh. Reading about linear position sensors also gave some insights.

I took 22 gauge wire from the physcomp lab, stripped it, and bent it back and forth to mimic the “fingers” on the FSRs I purchased from Interlink. After making two wire finger pieces, I wrapped one in seven layers of plastic wrap. I place the second set of wire fingers on the outside of the package and wrapped it into the existing package. My first few tests seemed very promising. When no pressure was applied to the package, the resistance was infinite. When I squashed the package, the resistance dropped down to about 10K.

The next trick was to try to duplicate this behavior on the end of a PVC pipe. We first tried applying the plastic wrap/wire packages around the end of the PVC pipe. The results were less encouraging than my initial experiments.

The homemade sensors were unreliable: either the sensor package was too tightly squashed between the PVC and the surrounding hole (and gave no resistance) or it was too loose and no amoung of bending the pole caused a reading.

On Saturday, Shlomit and I built another prototype of our audio art installation.

We went to Home Depot in search of bamboo and springs, but came back with 1/2″ (ID) PVC and cast iron flanges.

The bamboo remains a cost-effective option ($1.79 for a package of 4-5 x 5′ stalks).

We attached 3/4″ x 1/2″ reducing adapters onto one end of ~5′ x 1/2″ (i.d.) PVC pipes and screwed them into a 3/4″ flanges mounted on a sheet of plywood. We painted the PVC poles hunter green to loosely reference a field of tall grass.

We created the prototype with two poles on it to see how the poles would flex as people move through them.

It was a great day to work outside and we were pleased with the progress we made.

Construction Lessons
- When cutting plywood, cut through the side you wish to display so the ragged edges are hidden
- Plan the flange installation better so the holes will line up on the top and bottom playwood pieces
- We will need to custom cut a 4′x8′ plywood sheet to get the 6′x3′ installation we want

Sound
We made further progress as we began to discuss the sound of the field. Both of us were drawn to the opening bars of Stravinsky’s Rite of Spring. The was some initial confusion about whether we were listening to the “Rite of Spring” or the “Firebird Suite”, but I resolved that as of this writing. The solo oboe (or perhaps clarinet?) provides a mysterious sonic backdrop for exploring a new space. We plan to edit a small sample from the first track and control its playback using the sensors we are planning to attach to the PVC poles. As users enter the installation, they will have the opportunity to push their way through our sound field. Each subsequent PVC pole they push will play the next piece of the sample we’ve chosen. If they walk push through the field at the right speed (according to the mood of the selected piece), they will hear the melody as they move.

Today we experimented with different strategies for sensing the motion of springs. The first was inspired by electric guitar pickups. I thought we might be able to create an electromagnetic pickup to sense the vibrations in the springs. We tried to create a simple electromagnet out of a nail and some transformer wire…. oh, yes… and a power drill.

We scrapped the pickup idea after measuring the resistance of the coil to be 0 Ohms. I was concerned it might short something out. Shlomit also thought we would have more creative possibilities if we used sensors rather than capturing the sound of the springs directly.

Returning to a previous sensing idea, we experimented with a flex sensors.

Flex sensors are not ideal for our application; they only sense motion in one direction and require a fair amount of deflection in order to produce a useful reading. (note for the future… measurement ranges would be useful for documentation purposes)

We also considered mounting the springs on top of a pair of joystick potentiometers to sense X-Y movement. The miniature potentiometer we tried to use for our prototype was too stiff to yield useful results. We wrapped a copper wire around the dial of the potentiometer, hoping that motion of the springs on our installation mockup would move the potetiometer and generate a varying resistance. No luck.

Shlomit and I made some progress on our audio art final. We decided to build a sonic field of springs.

Strategies for sensing movement:

• Flex sensor
• Magnetic pickup (like electric guitar)
• 2-axis potentiometer (joystick)

After brainstorming more about producing sound and sensing movement, we built a tiny prototype, using the technique I discovered while building a prototype for Designing for Constraints.

Shlomit and I are proposing a final project around visualizing the propagation of sound and exploring the physicality of sound.

One of our ideas is an installation which captures the evolution of sound in a space. Colored lights suspended from the ceiling of the space react to sounds created in the space. We draw our inspiration from the ephemeral quality of warm breath in cold winter air. As you exhale, a gentle fog issues from your lips into the surrounding air.

Other ideas surrounding this first proposal are issues of memory and the incarnational power of words. The words we speak and the words we hear are not mere acoustical vibrations. They carry meaning. What if we could see these vibrations as they occured? What if we could see lingering traces of these vibrations?

Our second idea is an installation where the viewer walks through a field of flexible reeds. As the reeds are pushed aside, pleasant sounds are created in the space.