This section documents the technical literature underpinning the sensor design and firmware decisions. Each entry includes a key claim extracted for academic use.
Electrochemical Gas Sensors
IEC 60079-29-1:2016
Explosive atmospheres — Part 29-1: Gas detectors — Performance requirements of detectors for flammable gases
Key claim: Two-point calibration (zero air + span gas at certified concentration) is the normative method for electrochemical sensor calibration. Calibration interval must not exceed 6 months in service.
City Technology Ltd — 7H H₂S Sensor Datasheet
Revision: March 2018
Key claim: Sensitivity is −50 ± 20 nA/ppm at 20°C. Response time T₉₀ ≤ 30 seconds (typically 15–25 s). Temperature coefficient: −0.5 to −1.0% signal/°C above 20°C.
Key claim: Cross-sensitivity to SO₂ is +10 to +40%, meaning SO₂ produces a false positive H₂S reading. Humidity changes of ±10%RH produce ≤2% signal change.
Signal Conditioning
Razavi, B. (2001). Design of Analog CMOS Integrated Circuits. McGraw-Hill.
Key claim: The transimpedance amplifier (TIA) converts sensor current to voltage with gain = R_feedback (Ω). Noise contribution from R_feedback is $v_n = \sqrt{4kTR\Delta f}$ V/√Hz (Johnson noise).
Horowitz, P. & Hill, W. (2015). The Art of Electronics (3rd ed.). Cambridge University Press.
Key claim: For a 10 nA/ppm sensor with 100 MΩ TIA feedback resistor, sensitivity is 1 V/ppm. Reducing R_feedback reduces sensitivity but also reduces noise and improves bandwidth.
ADC and Oversampling
STMicroelectronics. RM0440 — STM32G4 Reference Manual. Rev 8, 2023.
Key claim: Hardware oversampling with ratio N and right-shift = log₂(N) gives noise reduction of √N with no CPU overhead. For 8× oversampling, effective noise floor reduces by factor of 2.83 (≈ 1.5 bits effective resolution gain).
Key claim: ADC1 internal reference (VREFINT) is calibrated at production at 30°C with ±3 mV accuracy. Using the VREFINT reading to compute actual VDD compensates for power supply variation, improving absolute accuracy.
Stability and Drift Compensation
Kenny, J.S. et al. (2001). Electrochemical sensors for environmental gas monitoring. Sensors and Actuators B: Chemical, 80(1), 7–12.
Key claim: Electrochemical H₂S sensors exhibit baseline drift of 1–5% per month under normal operating conditions. Drift is primarily caused by electrolyte concentration changes and electrode fouling. Regular zero recalibration (without span recalibration) is effective for compensating baseline drift.
Embedded Systems
Levy, H. The RTIC Book. https://rtic.rs (2024).
Key claim: RTIC’s static priority ceiling protocol guarantees deadlock-free shared resource access without a runtime scheduler. Task latency is bounded by the highest-priority task’s execution time.
Notes for Academic Report
When citing sensor characteristics, prefer the manufacturer datasheet over secondary sources. The IEC 60079-29-1 standard is the primary normative reference for performance requirements and calibration procedures. For ADC oversampling theory, cite the STM32G4 Reference Manual directly.
All experimental data in this system was collected with the firmware at version 0.1.0 (February 2026) on custom PCB with STM32G431KB at 170 MHz.