learning the ropes

If you’re working with an Arduino NG and an SPI controlled device you’re working with is not functioning properly (an AD5206, an accelerometer, etc), you’ll need to perform surgery on your ‘NG to remove the SMD LED from digital pin 13. Idiscovered this while helping YouJeong troubleshoot her AD5206. We looked at everything from the wiring to the AD5206 chips to source code to finally the Arduino itself. The only reason I was able to figure this out is that I saw that YouJeong’s Arduino NG had an LED on pin 13 (which is one of the pins Arduino uses for its SPI interface). I noticed when trying the most basic “blink the LED” program that an LED inserted between digital pin 13 and ground was very dim. When I jumped it in parallel with the SMD LED on the Arduino circuit board it was brighter. Using a multimeter we found that the pin 13 was only giving us 1.92V when pin 13 was set HIGH.

I suggested we search for “Arduino NG SPI” and we found a thread in the Arduino forums about this issue. To rectify the problem, I removed the pin 13 LED from both of her Arduino NG boards and SPI started working properly.

One of the challenges of woodworking in an apartment is finding a place to store pieces of leftover plywood. After I built the IKEA knock-off bookshelf last summer, I stashed the leftovers behind our bed. Kelly and I agreed that these pieces would eventually turn into a cubby system for my studio. As it turned out, the pieces weren’t quite large enough for the desktop hutch I designed, so I created even more scrap lumber. I stacked some of the pieces underneath the couch in the living room, but we were running out of room. The only thing left to do to reduce the stockpile aside from freecycling it or throwing it away was to build again.

Sewing Cubby
One leftover piece of plywood was used to make Kelly’s sewing organizer. She also wanted a cubby system to store some of her batting and yarn.

We started off with some sketches — first exploring possible features of the unit

and then deciding how big we could make it given the available materials.

I fleshed out the design in Google Sketchup so Kelly could get a sense of the proportions and then built it. All joints are butt joints attached with 2″ coarse-thread wood screws.

Speaker Stands
Since days after we moved into our current apartment, our speakers have been perched atop cubes of taped-together CD jewel cases. This helped to eliminate some of the unpleasant boominess, but I’ve never been satisfied with the sound in the room. Months ago, I tried some experiments and found I liked the sound better when the speakers were elevated to ear height while I was seated on the couch. I didn’t think it would be too difficult to make speaker stands; I just didn’t get around to doing it until now.

Height and stability were the most important considerations in my design, so I tried to work with those parameters before considering whether I had enough leftover plywood to actually build the design.

After completing the design, I took stock of my remaining plywood and found I was very short of the material my design required. I considered making the stands shorter, but wasn’t really satisfied with the idea, so I let the design sit for a few days and then realized that by making the uprights thinner, I could still keep the height I wanted.

I revised the design and then began building.

I uploaded the model to the Sketchup 3D Warehouse, so you can download it if you like.

Kelly has been looking for a better way to organize her spools. She’s been keeping the spools in the bottom of her sewing basket. There was plywood left over from the computer desk hutch, so she asked me to build a plywood organizer with pegs on it

I may post this to Instructables one of these days. I already added captions to all of the pictures before uploading them to my Picasa web album. Unfortunately, I couldn’t find an easy way to get the captions show up on this page without hand-editing the HTML.

It’s been awhile since I’ve posted here. Things have been busy at work — and school is out for the summer. I’ve been working to rearrange my home studio/office. Things were getting a bit cramped and I haven’t much felt like creating in the room, so I designed and built a simple hutch for my computer desk.

One of my goals for the summer was to learn how to user Sketchup. Here’s a first sketch of the old room layout.

Once I got the hang of using Sketchup’s “inference engine,” things started getting easier. Here’s the design of my hutch as well as a side table I made out of a recycled desk.

Here are a few phots of the process.

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.

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.

I’m working on a personal art project for my final in Designing for Constraints. The following is my first prototype. I feel pulled in many directions simultaneously — with ITP pulling the hardest. The inner sphere represents me. The springs tug at me in all directions.

I developed this prototype from a simple sketch:

I built the prototype out of materials I already had in my studio:

CD jewel case covers	Old guitar strings and 24 gauge wire spun into springs
	26 gauge wire wrapped around a still central armature

Class feedback:
- Walls of the piece could deform under pressure.
- Piece seems performative — it may require my performance of the object to get its point across. A video might help with this.
- Stretch the box to its limits and videotape it as it breaks

Last night, in preparation for building a perf board, I drew a first draft of the schematic for the Secret Tree.

There are several things to do yet to properly document the project’s electronics:

• Add the clock crystal and other required components for the ATMEGA-8
• Draw a system block diagram
• Draw the finite state machines (although this may be overly complicated

Anyone have suggestions on how to simplify this schematic?

Ai-Chen and I did a bit of rewiring on the Secret Tree circuit board. One of the problems we had last week was that all of the ground wires for the LEDs on the trees were connected to two PCB terminals. I didn’t purchase enough terminal at RadioShack so that every pair could have a ground of its own. This not only made things messy, but it also made the connections suspect.

The other major discovery I made which explained much of the circuit’s random (unintended) behavior was that the two AD5206 chips interfered with one another. I plugged a single LED into each of the twelve outputs (across the two chips) and found that a simple test program didn’t operate properly when both chips were running. As soon as I disconnected the three data lines (CLK, SDI, and CS) from the second chip, the first chip would work properly. I wondered if there might be some sort of “floating” condition when the two chips were used together. Since CLK and SDI were shared, I hypothesized that CS was likely the culprate. To test this, I added 10K pull-down resistors on the chip selects of both chips. It worked! The test program dimmed the lights in the proper sequence rather than skipping around randomly on the third and fourth outputs.

- Continued construction using the perfboard/shrink tubing sensor package and finished two shoe prototypes
- User Test – Patricia (using foamboard prototype + Korg synth module)
- Felt that more sensitivity was needed. She found it difficult to trigger the samples without stomping really hard
- Didn’t like bass drum on the heel; felt it would be more natural on the front
- Cannot tell where the sensor is — perception is that it is close to the center of the shoe
- Feels the system is more responsive with the 10k resistor than with the 2k
- Could play either sitting or standing
- Would like to play along with some other music