Retain documentation on how the voc index is actually calculated in driver code as it'll be removed in Documentation. This is a follow up on patch "[PATCH] iio: ABI: remove duplicate in_resistance_calibbias" from David. Signed-off-by: Andreas Klinger <ak@xxxxxxxxxxxxx> --- drivers/iio/chemical/sgp40.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/iio/chemical/sgp40.c b/drivers/iio/chemical/sgp40.c index 7f0de14a1956..07d8ab830211 100644 --- a/drivers/iio/chemical/sgp40.c +++ b/drivers/iio/chemical/sgp40.c @@ -14,11 +14,16 @@ * 1) read raw logarithmic resistance value from sensor * --> useful to pass it to the algorithm of the sensor vendor for * measuring deteriorations and improvements of air quality. + * It can be read from the attribute in_resistance_raw. * - * 2) calculate an estimated absolute voc index (0 - 500 index points) for - * measuring the air quality. + * 2) calculate an estimated absolute voc index (in_concentration_input) + * with 0 - 500 index points) for measuring the air quality. * For this purpose the value of the resistance for which the voc index - * will be 250 can be set up using calibbias. + * will be 250 can be set up using in_resistance_calibbias (default 30000). + * + * The voc index is calculated as: + * x = (in_resistance_raw - in_resistance_calibbias) * 0.65 + * in_concentration_input = 500 / (1 + e^x) * * Compensation values of relative humidity and temperature can be set up * by writing to the out values of temp and humidityrelative. -- 2.39.2
Attachment:
signature.asc
Description: PGP signature
