Skin Response (GSR)

We have being developing a set of GSR (galvanic skin response) devices using cheap external microcontrollers (Arduino).

InterfaceBoxes

Interface boxes showing USB port (left) and GSR and Heart rate ear clip probes

The interface box can either record data internally (time stamped with a real time clock) for later download and analysis, or be connected directly to a controlling computer which will read and record data over the USB interface and may also be presenting stimuli or reading other participant responses in the normal way.

When connected by USB the interface box will appear as a serial device. This requires a ‘driver’ to be installed on the control computer, bu

t does allow complete control over the interface – starting and stoping reading, adjusting parameters and so on.

ArduinoWithPsyGSRboard

Interface box open to show Arduino and custom SoP GSR interface board

Alternatively if the interface box is being used on a strcitly managed computer which doesn’t allow the installation of a driver (for example in schools), the interface box can be confirgured to appear as a Joystick with the GSR reading represented by the x-axis. The USB joystick driver is a standard part of windows so the control program can read the data without having to install a driver.

It is also possible to connect the interface box wirelessly for complete freedom of movement of the participant. This uses an 802.15 Private Area Network which will allow several devices to be connected simultaneously to a single controlling computer.

Skin response changes fairly slowly so generally a reading is taken every 200 milliseconds. The values returned can be calibrated in milli Siemens (the standard unit of conductance) although the absolute value has no intrinsic meaning as it will vary from person to person and from day to day. It is the change in value in response to a stimulus or condition that is the significant measurement.

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