The Idea: Interactive Flyers

For the midterm project, Jamie Allen, Shannon Bain, and I built interactive flyers for the bulletin board in the hallway. Shannon drew a beautiful picture of a chimp holding a beer can with the caption “How ‘Bout Some Free Beer, Chump?”RecyclingBin1. Like most flyers offering goods and services, this one had pull-off tabs of paper. When a user reached to rip off a paper tab, a nearby recycling bin began emmitting a musical interpretation of live samples of the sound in the hallway. Our intention was to draw the casual observer into a relationship with the flyer and the ambient sound of the hallway that would lead them to play it as a theremin-like instrument.

The technology behind The Idea

Technically-speaking, the project consisted of 3 flyers on top of conductive foam. Each conductive foam piece was wired up to a seperate Quantum QT300 capacitive sensor. The three sensors then fed this capacitive information back to a BX-24 microcontroller. The BX-24 converted these signals into three channels of MIDI messages (one for each sensor) which were then sent out through a midi interface to a laptop (suspended from the ceiling) running Max/MSP. Max/MSP used this information as input to a program (called a patch in the Max/MSP lingo) that produced the noises coming out of the speakers in the recycling bin. Click here to download the Max/MSP patch

Originally, we had built Voltage-controlled oscillators using TLC-555 timer and LM386 amplifier chips. On their own, they produced some great (but absolutely unreliable) sounds. However, once we began using the BX-24 to vary the input voltage, we found that the BX-24’s outputs were not suitable for controlling a voltage-controlled oscillator. Neither the pulseOut command nor the putDAC command produced a convincing change of pitch. The pitch from the oscillators would change a bit and then quickly revert back to a “stable” pitch which represented no input.

I suppose the nature of pulse-width modulation is not suitable for audio information since we could clearly hear the rate of pulsing. When using PWM to control lighting, we rarely even notice the pulsing of the lights, we only see a dimming or brightening of the light, but our ears are more discriminating. Another issue may have been the fact that a pulse is a square wave, and we weren’t able to totally round-out the waveform using low-pass filters. Regardless of the cause, we dropped the idea of using own home-made oscillators and settled on using Max/MSP to do the sound processing.

The QT300 capacitive sensors were relatively new and virtually undocumented, and Jamie struggled for days to get them to send back meaningful data. He ended up writing his own serial communication driver for the BX-24 from scratch (check his website for more on this). The rate at which the QT300 collects and transmits data is very slow for translating into music, and these technical difficulties necessitated a creative interpretation of the data for the sound production.

The Sounds of a Recycling Bin

The Max/MSP patch was sporadically recording live sounds in the hallway. By moving hands in front of the three interactive flyers, the casual user was able to change the playback speed of the sample (which also shifts the pitch), the starting point of the sample (effectively making it shorter), and the amplitude. These same controls simultaneously affected the pitch, ring modulation, and amplitude of a simple oscillator. The combination of the two produced a very organic, unpredictable sound. By opening the lid of the recycling bin, we were also able to get feedback between the speakers and the microphone, which is where things got interesting…

Listen to mp3 files of the crazy recycling bin here:

…and if you like that, click here: