HTU21D Digital Temperature and Humidity Sensor Module, I2C

The HTU21D offers a genuinely clean I2C interface for temperature and humidity sensing, a real convenience over single-wire sensors like the DHT-series since I2C allows multiple sensors to share the same two signal wires alongside any other I2C peripherals already on a project's bus, rather than needing a dedicated pin per sensor.

Humidity measurement covers the full 0 to 100% relative humidity range, with precision rated at 2% RH across the 10 to 95% RH band where most real-world readings fall (the HTU21DA variant specifically). Measurement itself is fast at just 50ms, with a 5-second response time to a changing environment, making it noticeably quicker to react to real humidity changes than slower-sampling alternatives. Long-term drift is rated at a modest -0.5% RH per year, meaning calibration accuracy holds up well over extended deployment rather than degrading quickly.

The board includes built-in 4.7k pull-up resistors on the I2C lines, removing a small but easy-to-forget wiring step that some bare I2C sensor breakouts leave up to the builder. Supply voltage runs from a low 1.5 to 3.6V, making it a genuinely good fit for battery-powered, low-voltage sensor nodes rather than needing a full 5V rail. Physical size is compact at just 16 x 16 x 2.5mm, easy to tuck into tight enclosures.

A printed caution on the product page is worth repeating: full water droplets can damage the sensor, so it's suited to ambient humidity sensing rather than direct wet-environment or submersion use. Builders working on an I2C-based environmental sensor node, a battery-powered weather logger, or any project wanting fast, accurate humidity readings over a clean two-wire bus will find the HTU21D a strong, low-power alternative to single-wire temperature/humidity sensors.