Gas and Environmental Sensors

Humidity, pressure, gas and air-quality sensors for weather stations and safety devices.

Easy

Humidity + temperature: DHT22 (simple, slow), SHT31/SHT4x (accurate, I2C).
Pressure: BMP280/BME280 — also gives altitude (about 12 Pa per metre near sea level).
Gas: MQ-series (heated metal-oxide; MQ-2 smoke/LPG, MQ-135 air quality) need warm-up and calibration; electrochemical cells for CO; NDIR sensors (SCD40, MH-Z19) for true CO₂.
Particulates: laser PM2.5 sensors (PMS5003, SPS30).

Cheap gas sensors indicate trends, not certified measurements — never rely on them alone for life-safety alarms.

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