Wednesday, April 15, 2009
Cheap GSR and Temperature Biofeedback
Galvanic Skin Resistance and Temperature changes are digitally displayed as a resistance on the $1.99 Cen-Tech Multimeter. The size of stainless steel clamp ($.99/5) can be adjusted for fit and the NTC thermistor (white tubular object on index finger, $.68) is glued to the clamp and held securely in contact with the finger. The switch is sandwiched between two disposable contact lense containers. Safety warnings on the meter say not to let the probes have contact the skin so I made sure the very low voltage would be at the fingers and wouldn't go across the heart.
I have been able to raise my fingertip temperature. The resistance of the thermister actually drops with a temperature increase so the number goes down. The galvanic skin response fluctuates a great deal and there is a need for some contact gel. Plain water with a little salt works well but evaporation influences the reading. There are recipes for gels on the web. Maybe you know something that works as well as the hospital/lab grade stuff. Let me know.
Eventually this probe will hook up to one of my Arduino boards and the data will be collected, saved and displayed along with other biofeedback data. The record keeping is an important aspect and I am keeping some notes to document the components used as well as the personal measurement variations. Much more on this later.