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sgp40 is a gas sensor used for measuring the air quality. This driver is reading the raw resistance value which can be passed to an userspace algorithm for further calculation. The raw value is also used to calculate an estimated absolute voc index in the range from 0 to 500. For this purpose the raw_mean value of the resistance for which the index value is 250 might be set up as a calibration step. This can be done with in_resistance_calibbias. Compensation of relative humidity and temperature is supported and can be used by writing to output values of out_humidityrelative_raw and out_temp_raw. There is a predecesor sensor type (sgp30) already existing. This driver module was not extended because the new sensor is quite different in its i2c telegrams. Signed-off-by: Andreas Klinger <ak@it-klinger.de> Reported-by: kernel test robot <lkp@intel.com> Link: https://lore.kernel.org/r/20210804154641.GA3237@arbad Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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What: /sys/bus/iio/devices/iio:deviceX/out_temp_raw Date: August 2021 KernelVersion: 5.15 Contact: Andreas Klinger ak@it-klinger.de Description: Set the temperature. This value is sent to the sensor for temperature compensation. Default value: 25000 (25 °C)
What: /sys/bus/iio/devices/iio:deviceX/out_humidityrelative_raw Date: August 2021 KernelVersion: 5.15 Contact: Andreas Klinger ak@it-klinger.de Description: Set the relative humidity. This value is sent to the sensor for humidity compensation. Default value: 50000 (50 % relative humidity)
What: /sys/bus/iio/devices/iio:deviceX/in_resistance_calibbias Date: August 2021 KernelVersion: 5.15 Contact: Andreas Klinger ak@it-klinger.de Description: Set the bias value for the resistance which is used for calculation of in_concentration_input as follows:
x = (in_resistance_raw - in_resistance_calibbias) * 0.65
in_concentration_input = 500 / (1 + e^x)
Default value: 30000