SGP40MOX(4) FreeBSD Kernel Interfaces Manual SGP40MOX(4)
NAME
sgp40mox - Driver for Sensirion SGP40 MOx gas sensor
SYNOPSIS
sgp40mox* at iic? addr 0x59
DESCRIPTION
The sgp40mox driver provides an air quality measurement from the SGP40
sensor via the envsys(4) framework. The sgp40mox addr argument selects
the address at the iic(4) bus. The crc validity and temperature and %RH
compensation can be changed through sysctl(8) nodes.
In order to calculate the VOC index, the volatile organic compounds
index, which is the measure of air quality the sensor is polled once a
second and the raw sensor value is fed into the Sensirion VOC algorithm.
This VOC algorithm used in this driver is licensed under a 3 clause BSD
license and was pulled from the Sensirion Github repository at
https://github.com/Sensirion/embedded-sgp.
SYSCTL VARIABLES
The following sysctl(3) variables are provided:
hw.sgp40mox0.compensation.temperature
This should be set to the temperature in Celsius of the
environment that the sensor is in. The valid values are from -45
to 130 degrees Celsius.
hw.sgp40mox0.compensation.humidity
This should be set to the %RH of the environment that the sensor
is in. The valid values are from 0 to 100.
For the best performance of the VOC algorithm it is important
that the temperature and %RH compensation values be current and
set using the sysctl(3) variables mentioned above. This data
will need to be pulled from another source, such as a another
sensor in the environment that the SGP40 is in.
hw.sgp40mox0.ignorecrc
If set, the crc calculation will be ignored on the calls to the
chip for the purposes of measurement.
hw.sgp40mox0.debug
If the driver is compiled with SGP40_DEBUG, this node will appear
and can be used to set the debugging level.
hw.sgp40mox0.readattempts
To read the air quality metric from the chip requires that the
command be sent, then a delay must be observed before a read can
be done to get the values back. The delays are documented in the
data sheet for the chip. The driver will attempt to read back
the values readattempts number of times. The default is 10 which
should be more than enough for most purposes.
SEE ALSO
envsys(4), iic(4), envstat(8), sysctl(8)
HISTORY
The sgp40mox driver first appeared in NetBSD 10.0.
AUTHORS
The sgp40mox driver was written by Brad Spencer <
[email protected]>.
BUGS
The driver does not make complete use of the VOC algorithm. In
particular, there is no need to restart the algorithm from scratch if
there is a stoppage of polling for less than 10 minutes. The driver does
not have the ability to determine that, and therefore assumes that the
sensor is completely cold each time the driver attaches to the chip.
The temperature and humidity compensation could be allowed to contain
fractional degrees Celsius and %RH. The driver only supports setting
whole numbers for either of those.
FreeBSD 14.1-RELEASE-p8 October 7, 2021 FreeBSD 14.1-RELEASE-p8