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

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)

• 2 x Netduino Plus 2 USD60,NZD108 or Netduino 2 USD33,NZD60
• 1 x Grove Base Shield V2 USD8.90
• 1 x Grove LED bar USD3.90
• 1 x Grove GSR Sensor USD9.90