learning the ropes

I found out last week that the Secret Tree was accepted as part of the Maker Faire in San Matteo, CA. Unfortunately, the notice was a bit too short for us to be able to make the trip.

Special thanks to Caleb Clark, Anh Nyugen, and Rucyl Mills for their awesome work in filming the Secret Tree.

They have more episodes at http://techtrek.tv

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?

This afternoon I attempted to connect the Secret Tree circuit board to the LEDs on the tree. Since my test program (adapted from an Arduino tutorial) appeared to be working well I was ready. The first six LED clusters I connected to the terminal blocks worked fine, but the seventh and eighth clusters didn’t operate properly. I tried resetting the Arduino board as well as the MAX patch, but things wouldn’t work consistently. I even saw that a single LED connected to the seventh output didn’t light up consistently. Once I disconnected all of the clusters and returned to single LEDs, the system seemed to function properly. Maybe the LED clusters are drawing too much current and are causing the digital potentiometers to behave erratically.

Back at home, I found a small breadboard wiring problem: I didn’t have a proper connection to ground for the pins 15, 18, 19, and 22 on the second AD5206. Even so, the LEDs connected to the potentiometer outputs related to those pins still lit up. My correction only served to properly extinguish the LEDs when I set the potentiometers on that side of the chip to the maximum 10K resistance.

The light blue wire connected to ground above the AD5206 is the recent addition.

So far, I have tried the following in order to get the software/hardware system working:

• Corresponded with Scott Fitzgerald regarding the MAX patch. He removed the multiple “metro” objects from it and recommended running the system at 9600 baud so as not to overwhelm the PC’s serial buffer.
• Spoke with Leif Krinkle about the MAX patch. He questioned my use of the SimpleMessageSystem for MAX and thought I would be better served by a basic home-brew protocol. I started rewriting the Arduino code and the MAX patch to use a simple protocol based on sending Arduino six bytes of information from MAX using the “pack” object”. I originally asked him how to debug the MAX patch since Arduino and MAX were communicating over the Arduino’s only serial port. It turns out that there is a software serial library that could be used to do this type of debugging.
• Discovered in the course of rewriting the serial protocol that the switch needs debouncing. This is the source of the strange values I saw in MAX/MSP with my new serial code.

Tomorrow I will try using a power supply with more amperage to see if that improves things. Any other suggestions?

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.

We presented the Secret Tree in class on Thursday. Although the MAX patch didn’t work, the piece was well-received. We are in the process of finishing the piece for our midterm presentation.

Work continues on the Secret Tree project. Today we finished cutting out the branches, building a support framework, and unfolded it for the first time. It was almost magical.

I’m working with Ji-Sun Lee and Ai-Chen Lin on a “secret tree” for Living Art. Our assignment is to “Make a Random.”

You can approach the tree and tell it a secret; in fact, it may be that the tree needs to be told secrets in order to stay alive.

Ji-Sun has already constructed a prototype tree.

Ai-Chen and I have been working on MAX/MSP and Arduino code prototypes to record the secrets and transform them into lights on the tree.