Pi skin conductivity

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Pi skin conductivity

Aims:

  • 3 pairs of GPIO pins are used as to capture skin conductivity
  • python reads GIOP (should run as a deamon)
  • OSC sends messages from py to pd


Pis have no ADC, therefore the simple way to read a Pot's value is via a step response technique as explained in http://razzpisampler.oreilly.com/ch08.html


hardware

notes on RPi GPIO

In model 1 there were only 26 in the following configuration

a-and-b-gpio-numbers.png

Model 2 B and 3 B keep the same configuration for the first 26 pins, but expand it to 40 pins, in the following configuration

gpio-numbers-pi2.png

https://cdn-learn.adafruit.com/assets/assets/000/017/944/original/raspberry_pi_40pingpio.png?1405284874

links:

Software

libaries

install pip

apt-get install python-pip

Pi python lib RPi.GPIO https://pypi.python.org/pypi/RPi.GPIO

apt-get install python-rpi.gpio

pyOSC (is not on minibian repos )

pip install pyOSC

scripts

https://git.xpub.nl/repos/pushingscore-gpio.git/

Circuit

rpck_1202.png

I am using 500K variable resistor(pot) instead.

touch pressure

GPIO-touch.jpg

In order to use touch pressure: I kept the circuit only replacing the variable resistor with 2 metal pins.

The result is very interesting.

  • because the circuit is interrupted while no one is touching, the stream or reading is interrupted
  • values can go from:
    • Max: 3 (very strong,wet contact) (0 if there is a metal connection )
    • Min: 273337

Py-osc-pd.png

components

  • Pi cobler
  • Electronics:

Weidmuller PM 5.08 Series 5.08mm Pitch Straight PCB Terminal Block with Leaf Spring, Screw Termination, Through Hole RS-stocknummer: 425-8720 Aantal: 30

Murata Single Layer Ceramic Capacitor (SLCC) 220nF 50 V dc ±10% X7R Dielectric RPER7 Series Through Hole RS-stocknummer: 721-5262 Aantal: 30

RE520-HP, Single-Sided Stripboard FR-2 100 x 160 x 1.5mm FR1 RS-stocknummer: 206-5841 Aantal: 3

circuit on Vero board

Skin conductivity veroboard.png

Skin conductivity circuit.png