home-assistant.io/source/_components/sensor.htu21d.markdown

layout	title	description	date	sidebar	comments	sharing	footer	logo	ha_category	ha_release	ha_iot_class
page	HTU21D Temperature and humidity sensor	Instructions on how to integrate a HTU21D Temperature and humidity sensor into Home Assistant.	2017-06-10 00:00	true	false	true	true	raspberry-pi.png	Sensor	0.48	Local Push

The htu21d sensor platform allows you to read the temperature and humidity from a HTU21D sensor connected via I2c bus (SDA, SCL pins).

Tested devices:

• Raspberry Pi

To use your HTU21D sensor in your installation, add the following to your configuration.yaml file:

# Example configuration.yaml entry
sensor:
  - platform: htu21d

Configuration variables:

• name (Optional): The name of the sensor
• i2c_bus (Optional): I2c bus where the sensor is. Defaults to 1, for Raspberry Pi 2 and 3.

{% linkable_title Customizing the sensor data %}

Give the values friendly names and icons, add the following to your customize: section.

# Example configuration.yaml entry
customize:
  sensor.htu21d_sensor_temperature:
    icon: mdi:thermometer
    friendly_name: "Temperature"
  sensor.htu21d_sensor_humidity:
    icon: mdi:weather-rainy
    friendly_name: "Humidity"

To create a group, add the following to your groups section.

# Example configuration.yaml entry
group:
  ambient_sensor:
    name: HTU21D Environment sensor
    entities:
      - sensor.htu21d_sensor_temperature
      - sensor.htu21d_sensor_humidity

{% linkable_title Directions for installing smbus support on Raspberry Pi %}

Enable I2c interface with the Raspberry Pi configuration utility:

# pi user environment: Enable i2c interface
$ sudo raspi-config

Select Interfacing options->I2C choose <Yes> and hit Enter, then go to Finish and you'll be prompted to reboot.

Install dependencies for use the smbus-cffi module and enable your homeassistant user to join the i2c group:

# pi user environment: Install i2c dependencies and utilities
$ sudo apt-get install build-essential libi2c-dev i2c-tools python-dev libffi-dev

# pi user environment: Add homeassistant user to the i2c group
$ sudo addgroup homeassistant i2c

# pi user environment: Reboot Raspberry Pi to apply changes
$ sudo reboot

{% linkable_title Check the i2c address of the sensor %}

After installing i2c-tools, a new utility is available to scan the addresses of the connected sensors:

$ /usr/sbin/i2cdetect -y 1

It will output a table like this:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- 23 -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: 40 -- -- -- -- -- UU -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77

So you can see the sensor is present at the 0x40 address (there are more i2c sensors in that Raspberry Pi).