ProtoCentral tinyGSR v3 — Absolute Skin Conductance (GSR/EDA) Sensor, Qwiic / STEMMA QT

New in v3: this board is a ground-up redesign of the original tinyGSR. It now reports absolute skin conductance in microsiemens from a zero-drift 0.5 V constant-voltage front end — the earlier board gave a relative, trimpot-set reading with no way to convert it to real units. It adds an on-board 100 kΩ 0.1 % calibration resistor for a one-jumper self-check, a standalone Arduino library that needs no other libraries installed, and a snap electrode lead plus Ag/AgCl electrodes in the box.

The ProtoCentral tinyGSR v3 is an electrodermal activity (EDA / galvanic skin response) sensor that reports absolute skin conductance in microsiemens over I²C — not an arbitrary index that has to be re-trimmed for every board, every subject, and every session. Skin conductance rises and falls with sweat-gland activity driven by the sympathetic nervous system, which makes EDA one of the most direct physiological measures of arousal, stress, and cognitive load available to a maker or a research lab.

How it works: one electrode sits at ground and the other is pinned at 0.5 V by a zero-drift TI OPA2333 in a transimpedance loop. The current the skin draws is converted by a precision 39.2 kΩ 0.1 % feedback resistor and digitised differentially by a TI TLA2022 12-bit ADC, so the 0.5 V pedestal is cancelled in hardware and only the conductance term is measured. Because the excitation voltage and the feedback resistor are both known precision quantities, ADC counts map deterministically to microsiemens — readings are comparable between two boards, and between today and next month.

Self-check in one jumper: an on-board 100 kΩ 0.1 % calibration resistor (exactly 10.00 µS) sits behind the SHORT FOR CAL jumper. Close it, run the calibration example, and the library folds the tolerances of the resistor, the reference and the ADC gain into a single stored scale factor. Open it again and measure a subject. No instrument, no reference sample, no guesswork.

Getting started: install the ProtoCentral tinyGSR Arduino library — search for “ProtoCentral tinyGSR” in the Arduino IDE Library Manager — and run 01-Basic-Conductance-Read. The library is standalone: it drives the on-board ADC directly, so there is nothing else to install. A relaxed tonic level typically reads 1–20 µS, and a deep breath or a sudden sound produces a phasic response (SCR) that rises within one to three seconds. Plug into any Qwiic / STEMMA QT host with no soldering, or wire the 0.1″ VCC / GND / SDA / SCL header to a breadboard.

Everything you need is in the box: the board ships with a 3.5 mm snap electrode lead and a set of disposable Ag/AgCl electrodes, so there is nothing to source before the first measurement. Non-polarizable Ag/AgCl electrodes are what make a stable DC baseline possible — dry metal contacts drift.

Open hardware: the complete KiCad design — schematic, PCB layout, and the exported schematic PDF — lives in the tinyGSR hardware repository under the CERN-OHL-P v2 licence, and the Arduino library is MIT.

Features

• Absolute skin conductance in microsiemens — no per-unit trimming, no arbitrary units
• 0.5 V constant-voltage transimpedance front-end (TI OPA2333 zero-drift op-amp)
• TI TLA2022 12-bit Δ-Σ ADC, differential AIN0–AIN1 measurement over I²C
• On-board 100 kΩ 0.1 % calibration resistor (10.00 µS) behind a solder jumper for one-point self-check
• LM4040-2.0 precision reference with 0.1 % divider setting the excitation voltage
• Two Qwiic / STEMMA QT connectors for solder-free daisy-chaining, plus a 0.1″ header
• 3.3 V – 5 V supply and I/O — level translation on board, so 5 V Arduinos work directly
• Selectable I²C address: 0x48 (default) or 0x49 via the ADDR jumper
• Contact-detect and over-range flags reported by the library
• 3.5 mm jack for the included snap electrode lead, plus E1 / E2 pads
• Four M2.5 mounting holes on a 35 × 25 mm 2-layer board
• Open-source hardware (CERN-OHL-P v2) with an MIT-licensed Arduino library

Applications

• Stress, arousal, and cognitive-load research
• Affective computing and human–computer interaction studies
• Biofeedback and relaxation training
• Psychophysiology teaching labs, where comparable readings between benches matter
• Wearable and multi-sensor physiology prototypes alongside ECG, PPG, and temperature boards

Specifications

• Measurement: absolute skin conductance (µS) and resistance (kΩ)
• Front end: TI OPA2333 zero-drift transimpedance, V_exc ≈ 0.5 V, R_f = 39.2 kΩ 0.1 %
• ADC: TI TLA2022, 12-bit, differential, I²C
• Effective resolution: ~0.006 µS per LSB (oversampled)
• Calibration: on-board R_cal = 100 kΩ 0.1 % = 10.00 µS
• I²C address: 0x48 default, 0x49 selectable
• Supply: 3.3 V – 5 V (VCC and IO)
• Front-end bandwidth: DC – ~18 Hz (EDA phasic activity is ~0.05 – 1 Hz)
• Current into skin: ≤ 50 µA at 0.5 V
• Connectors: 2 × Qwiic / STEMMA QT, 0.1″ 4-pin header, 3.5 mm electrode jack
• Board: 35 × 25 mm, 2-layer

Important notice

This device is not a medical diagnostic instrument. It is intended for evaluation, education, and research use only, and is not FDA, CE, or FCC approved for consumer or clinical use.