Understanding GSR Sensors: Principles and Applications

This article explains the basics of GSR (Galvanic Skin Response) sensors, including their features, specifications, and how they function.

Introduction to EDA

EDA, or Electro Dermal Activity, refers to the electrical characteristics of the skin. This encompasses:

• Skin Conductance
• GSR (Galvanic Skin Reaction)
• EDR (Electro Dermal Response)
• PGR (Psych Galvanic Reflex)
• SCR (Skin Conductance Response)
• SSR (Sympathetic Skin Reaction)
• SCL (Skin Conductance Level)

The fundamental principle behind EDA is that skin resistance changes based on the activity of sweat glands.

What is a GSR Sensor?

Definition: A GSR (Galvanic Skin Reaction) sensor measures the electrical conductance of our skin. This electrical conductance varies in proportion to the moisture level of the skin.

The GSR value fluctuates depending on mental or physiological arousal, which affects the amount of sweating produced by the skin.

GSR readings are typically taken by placing electrodes on the fingertips, usually the index and middle fingers. These fingers are preferred because they have less skin thickness and hair, leading to more accurate results.

Features of Grove GSR Sensors

Grove GSR sensors V1.0 and V1.2, manufactured by Seeed Studio and available from Tomson Electronics, have the following features:

• Used to measure emotional arousal and monitor sleep quality.
• Measures the electrical properties of the skin.
• Based on electrical conductance, which is the inverse of resistance (1/resistance).
• Requires two electrodes placed on two fingers of one hand.

Technical Specifications of Grove GSR Sensors

• Operating Voltage: 3.3V / 5V
• Sensitivity: Adjustable via a potentiometer
• Input Signal: Resistance (not conductivity)
• Output Signal: Voltage (analog reading)
• Finger Contact Material: Nickel

GSR Sensor Working Principle

The skin’s conductive voltage reflects a person’s emotional state, such as being stressed or relaxed. This conductive voltage is influenced by sweat production from sweat glands, which are controlled by the nervous system. Changes in skin conductivity, due to sweat secretion, affect the voltage, which is then measured to determine the emotional state.

Here’s a breakdown of how it works:

• Relaxed Condition: When a person is relaxed, sweat secretion is minimal, resulting in high skin resistance and lower conductive voltage.
• Physical Arousal Condition: When a person experiences physical arousal, sweat secretion increases, leading to lower skin resistance and higher conductive voltage.

GSR Sensor Interfacing with Arduino

The following diagram illustrates how to interface a GSR sensor with an Arduino board:

The connections between the GSR sensor and Arduino board are as follows:

• Vcc (GSR sensor side) - 5V (Arduino side)
• GND - GND
• SIG - A0