Netduino Galvanic Skin Response(GSR)

One of CodeClub’s sponsors is Orion Health so I have been evaluating sensors suitable for health focused projects. We already use the SeeedStudio Grove Heart rate sensor and Grove EMG Detector, so I purchased a Grove GSR sensor for testing. Galvanic Skin Response(GSR) is a method of measuring the electrical conductivity of the skin, which depends on the amount of sweat on the skin.

Netduino with Grove GSR sensor

Netduino with Grove GSR sensor

The GSR detector outputs a single analog signal which I connected to A0. For the evaluation I averaged the first 3000 samples to determine the initial offset, then sampled roughly every 100mSec.

I’m a bit worried about the robustness of the wires connecting the two probes to the black cable so it will be interesting to see how long they last at Code Club.

I also updated the Minimum and Maximum values with each sample as this appeared to make the display more reliable.

I found the display responded well to me holding my breath for as long as I could.

Pulse rate + EMG + GSR = Polygraph or DIY lie detector maybe a project for next term.

for (int sampleCounter = 0; sampleCounter < calibrationSampleCount; sampleCounter++)
{
   double value = gsr.Read();
   sampleSum += value;
}
offset = sampleSum / calibrationSampleCount ;

I then displayed the magnitude of the adjusted signal on a Seeedstudio LED bar using code written by Famoury Toure

while(true)
{
   double value = emg.Read() - offset;

   if (value < valueMinimum)
   {
      valueMinimum = value;
   }

   if (value > valueMaximum)
   {
      valueMaximum = value;
   }
   range = valueMaximum - valueMinimum;
   if (value < 0)
   {
      value = value / valueMaximum * 10.0;
   }
   else
   {
      value = value / valueMinimum * 10.0;
   }
   Debug.Print("Val " + value.ToString("F3") + " Max " + valueMaximum.ToString("F3") + " Min " +valueMinimum.ToString("F3"));

   int bar = 1;
   value = 10.0 - value;
   bar = bar << (int)value ;
   ledBar.setLED((uint)bar);
   Thread.Sleep(100);
}

Bill of Materials (Prices as at October 2014)

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