Kernel driver sht3x

Supported chips:

Author:

Description

This driver implements support for the Sensirion SHT3x-DIS and STS3x-DIS series of humidity and temperature sensors. Temperature is measured in degrees celsius, relative humidity is expressed as a percentage. In the sysfs interface, all values are scaled by 1000, i.e. the value for 31.5 degrees celsius is 31500.

The device communicates with the I2C protocol. Sensors can have the I2C addresses 0x44 or 0x45 (0x4a or 0x4b for sts3x), depending on the wiring. See How to instantiate I2C devices for methods to instantiate the device.

Even if sht3x sensor supports clock-stretch (blocking mode) and non-stretch (non-blocking mode) in single-shot mode, this driver only supports the latter.

The sht3x sensor supports a single shot mode as well as 5 periodic measure modes, which can be controlled with the update_interval sysfs interface. The allowed update_interval in milliseconds are as follows:

0

single shot mode

2000

0.5 Hz

periodic measurement

1000

1 Hz

periodic measurement

500

2 Hz

periodic measurement

250

4 Hz

periodic measurement

100

10 Hz

periodic measurement

In the periodic measure mode, the sensor automatically triggers a measurement with the configured update interval on the chip. When a temperature or humidity reading exceeds the configured limits, the alert attribute is set to 1 and the alert pin on the sensor is set to high. When the temperature and humidity readings move back between the hysteresis values, the alert bit is set to 0 and the alert pin on the sensor is set to low.

The serial number exposed to debugfs allows for unique identification of the sensors. For sts32, sts33 and sht33, the manufacturer provides calibration certificates through an API.

sysfs-Interface

temp1_input:

temperature input

humidity1_input:

humidity input

temp1_max:

temperature max value

temp1_max_hyst:

temperature hysteresis value for max limit

humidity1_max:

humidity max value

humidity1_max_hyst:

humidity hysteresis value for max limit

temp1_min:

temperature min value

temp1_min_hyst:

temperature hysteresis value for min limit

humidity1_min:

humidity min value

humidity1_min_hyst:

humidity hysteresis value for min limit

temp1_alarm:

alarm flag is set to 1 if the temperature is outside the configured limits. Alarm only works in periodic measure mode

humidity1_alarm:

alarm flag is set to 1 if the humidity is outside the configured limits. Alarm only works in periodic measure mode

heater_enable:

heater enable, heating element removes excess humidity from sensor:

  • 0: turned off

  • 1: turned on

update_interval:

update interval, 0 for single shot, interval in msec for periodic measurement. If the interval is not supported by the sensor, the next faster interval is chosen

repeatability:

write or read repeatability, higher repeatability means longer measurement duration, lower noise level and larger energy consumption:

  • 0: low repeatability

  • 1: medium repeatability

  • 2: high repeatability

debugfs-Interface

serial_number:

unique serial number of the sensor in decimal