Xylophage

Welcome!

This project was a part of Xylophage, an art installation made for Burning Man 2013.

One of the giant mushrooms can detect approaching humans, which makes it breathing faster (yes, a mushroom can breath too), like if our presence was (surprisingly?) a stressful event.A sincere hug might calm it down and it expresses it with a whining sound...

The repository contains the code to control generated sounds, here is the architecture of the system:

• sensors (touch/distance)

• teensy (micro controller)

• raspberry pi (tiny computer)

• sound !

Electronic trick for the touch sensor interface

This sensor, also called felt sensor, is a home made FSR (Force Sensing Resistor) built with resistive fabric. It acts like a variable resistor but it has a very tiny value (it can have Rmax = 10ohms ). If we want to avoid killing our poor solar charged batteries, it can be tricky to measure its value. A few different techniques exist, we could for example charge a tiny capacitor and measure the charging time but we used a dirty hack that makes it simpler:

We know that digital GPIO current is limited to I = 40mA so if we try to give 5V across our tiny resistor the following rule tells us what the voltage will really be: R x I = V with:

R: tiny resistance
I: limited current
V: real voltage 

So if I = 10ohms, we get: V = 10ohms x 40mA = 400mV (and if we press the sensor R = 0 then V = 0).

The electronic connections look like this:

     __________
    |          |
    |  GPIO -> | --\
    |          |    === FSR --> GND
    |   ADC <- | --/
    |          |
    |          |
    | (teensy) |
    |__________| 

The measurement procedure is the following:

• set the GPIO output to 5V

• we measure the input voltage (ADC)

• set the GPIO output to 0V to save power

Made in SF - 2013

Photos