A Node-RED node to query and receive data from Measurement Specialities HTU21D humidity and temperature sensors. These pre-calibrated sensors are interfaced using the I2C bus. The node also calculates the dewpoint temperature from the measured humidity and temperature.

Use npm to install this package locally in the Node-RED data directory (by default, $HOME/.node-red):

cd $HOME/.node-red
npm install node-red-contrib-htu21d

Alternatively, it can be installed globally:

npm install -g node-red-contrib-htu21d

The nodes will be added to the palette the next time node-RED is started.

This node uses the htu21d npm package to access the device over an I2C bus. This is generally supported only on Linux. The bus device name (e.g. /dev/i2c-1) is configurable: only one actual sensor is allowed on each bus, but the bus can be shared with any other I2C device not using the (7-bit) address 0x40.

The output message payload holds the following properties:

humidity - relative humidity in %

temperature - temperature in ˚C or ˚F as configured

dewpoint - calculated dewpoint in ˚C or ˚F as configured

Measurements are repeated at a configurable interval: each measurement takes just over 0.1 second.