Sensors¶
PuffiAir includes a suite of advanced environmental sensors. Each one plays a key role in monitoring indoor air quality in real time. Below is a breakdown of each supported sensor and what it measures:
SCD40 — CO₂ Sensor¶
The SCD40 is a photoacoustic NDIR (Non-Dispersive Infrared) sensor developed by Sensirion, designed for accurate measurement of carbon dioxide (CO₂) concentration in indoor environments.
Sensor Type¶
- Technology: Miniaturized photoacoustic NDIR
- Sensing Principle: CO₂ molecules absorb infrared light and generate a pressure wave (sound) that is measured via a microphone
- Advantage: No optical cavity needed, enabling compact size and robustness
Measurement Details¶
- Output: CO₂ concentration in parts per million (ppm)
- Typical Range: 400 – 5000 ppm
- Resolution: ±(50 ppm + 5% of reading)
SGP41 — VOC Index Sensor¶
The SGP41 is a next-generation gas sensor developed by Sensirion, designed to detect indoor air pollution caused by volatile organic compounds (VOCs) and output a standardized VOC Index for easy interpretation.
Sensor Type¶
- Technology: MOX (Metal-Oxide Semiconductor)
- Output: VOC Index (range: 0–500+)
- Features:
- Outputs a processed VOC Index rather than raw resistance or voltage
- Enhanced humidity compensation
- Ideal for smart home and energy-efficient air quality systems
MICS5524 — Gas Sensor (Analog)¶
The MICS5524 is an analog MOS-type (metal-oxide semiconductor) gas sensor used for detecting a variety of combustible and harmful gases, such as methane (CH₄), carbon monoxide (CO), smoke, and alcohol vapors.
Sensor Type¶
- Technology: MOS (Metal Oxide Semiconductor)
- Output: Analog voltage (0 – 3.3V)
- Detection: Changes in resistance based on gas presence, converted via ADC
Measurement Notes¶
- Data is raw: The sensor outputs a general-purpose analog value, not a specific gas concentration
- No gas classification: It cannot distinguish between gas types (e.g., smoke vs CO)
- Used for threshold detection: Commonly used to detect presence of "something abnormal" in the air
SHT31 — Temperature & Humidity Sensor¶
The SHT31 is a digital temperature and humidity sensor developed by Sensirion, offering high accuracy, fast response time, and excellent long-term stability for environmental monitoring.
Sensor Type¶
- Technology: Digital CMOS-based sensor with calibrated I²C output
- Output:
- Temperature (°C)
- Relative Humidity (%)
- Accuracy:
- ±0.3°C (typ.)
- ±2% RH (typ.)
Offset Calibration
Users can manually apply temperature and humidity offsets via the PuffiAir setup page to adjust for sensor placement or enclosure effects.
Additional Notes
PuffiAir uses this sensor to provide temperature and humidity compensation for the SGP41 VOC sensor, as VOC readings are highly sensitive to ambient conditions.
DPS310 — Barometric Pressure Sensor¶
The DPS310 is a high-precision digital barometric pressure sensor developed by Infineon, designed for both environmental monitoring and altitude estimation. It measures absolute air pressure and can also calculate altitude changes.
Sensor Type¶
- Technology: MEMS-based capacitive pressure sensing
- Output:
- Pressure (in hectopascals, hPa)
- Optional:
- Altitude (via software calculation, not implemented by default)
- Accuracy:
- ±1 hPa
- Resolution: <0.002 hPa
Additional Notes
PuffiAir uses this sensor to optionally compensate the SCD40’s CO₂ readings, as SCD40 supports ambient pressure input
Unlike temperature or humidity, pressure changes are slower but useful for long-term trend analysis
SPS30 — Particulate Matter (PM) Sensor¶
The MCERTS-certified SPS30 particulate matter (PM) sensor marks a new technological breakthrough in optical PM sensors. Its measurement principle is based on laser scattering and makes use of Sensirion's innovative contamination-resistance technology. This technology, together with high-quality and long-lasting components, enables precise measurements from the device's first operation and throughout its lifetime of more than ten years.
Sensor Type¶
- Technology: Laser scattering with optical particle counter (OPC)
- Measured Parameters:
- PM1.0, PM2.5, PM4.0, PM10
- Values are given in µg/m³ (micrograms per cubic meter)
- Typical Accuracy: ±10 µg/m³ or ±10% (whichever is greater)
- Output Update Rate: 1 reading per second
Output Characteristics¶
- Highly sensitive to small particles such as smoke and combustion exhaust
- Not affected by gas/vapor (only solid/liquid particles)
- Factory calibrated, no need for user calibration
- Can operate 24/7 with long-term stability
Additional Notes
- PuffiAir firmware includes automatic fan cleaning logic for the SPS30
- This ensures long-term accuracy by periodically spinning the fan to expel dust buildup (e.g., once every 7 days)