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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 !
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
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