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

SGP40 sensor

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 WeAct Studio Black Pill V2.0 board.

# From the root of the zephyr repository
west build -b blackpill_f411ce samples/sensor/sgp40_sht4x
west flash

Sample Output

*** 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 succeded!
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.