.. _sgp40_sht4x:

SGP40 and SHT4X: High accuracy digital I2C humidity sensor and multipixel gas sensor
####################################################################################

Description
***********

This sample application periodically measures the ambient temperature, humidity
and a raw gas sensor value from an SGP40 and SHT4X device.
The result is written to the console.

You can choose to use the on-chip T/RH compensation of the SGP40
by feeding the values measured by the SHT4X into it.
This is enabled in the Application by default, you can turn it off
by setting ``APP_USE_COMPENSATION=n``.

The SHT4X has the option to use a heater which makes sense for specific
environments/applications (refer to the datasheet for more information).
To make use of the heater have a look at the Kconfig options for this application.


References
**********

 - `SHT4X sensor <https://www.sensirion.com/en/environmental-sensors/humidity-sensors/humidity-sensor-sht4x/>`_
 - `SGP40 sensor <https://www.sensirion.com/en/environmental-sensors/gas-sensors/sgp40/>`_

Wiring
******

This sample uses the SHT4X and SGP40 sensor controlled using the I2C interface.
Connect Supply: **VDD**, **GND** and Interface: **SDA**, **SCL**.
The supply voltage can be in the 1.7V to 3.6V range.
Depending on the baseboard used, the **SDA** and **SCL** lines require Pull-Up
resistors.

Building and Running
********************

This project outputs sensor data to the console. It requires a SHT4X and a SGP40
sensor. It should work with any platform featuring a I2C peripheral
interface. This example has an example device tree overlay
for the :ref:`blackpill_f411ce` board.


.. zephyr-app-commands::
   :zephyr-app: samples/sensor/sgp40_sht4x
   :board: blackpill_f411ce
   :goals: build flash


Sample Output
=============

.. code-block:: console

        *** Booting Zephyr OS build v2.6.0-rc1-315-g50d8d1187138  ***
        SHT4X: 23.64 Temp. [C] ; 30.74 RH [%] -- SGP40: 30531 Gas [a.u.]
        [00:00:00.250,000] <dbg> SGP40.sgp40_init: SGP40: Selftest succeeded!
        SHT4X: 23.66 Temp. [C] ; 32.16 RH [%] -- SGP40: 30541 Gas [a.u.]
        SHT4X: 23.63 Temp. [C] ; 30.83 RH [%] -- SGP40: 30522 Gas [a.u.]

The datasheet states that the raw sensor signal for the SGP40 ist proportional
to the logarithm of the sensors resistance, hence it is labeled as [a.u.]
(arbitrary units) in the example.