sgp40: Driver for SGP40 Indoor Air Quality Sensor for VOC Measurements
Defines
- F16(x)
- VocAlgorithm_SAMPLING_INTERVAL
- VocAlgorithm_INITIAL_BLACKOUT
- VocAlgorithm_VOC_INDEX_GAIN
- VocAlgorithm_SRAW_STD_INITIAL
- VocAlgorithm_SRAW_STD_BONUS
- VocAlgorithm_TAU_MEAN_VARIANCE_HOURS
- VocAlgorithm_TAU_INITIAL_MEAN
- VocAlgorithm_INIT_DURATION_MEAN
- VocAlgorithm_INIT_TRANSITION_MEAN
- VocAlgorithm_TAU_INITIAL_VARIANCE
- VocAlgorithm_INIT_DURATION_VARIANCE
- VocAlgorithm_INIT_TRANSITION_VARIANCE
- VocAlgorithm_GATING_THRESHOLD
- VocAlgorithm_GATING_THRESHOLD_INITIAL
- VocAlgorithm_GATING_THRESHOLD_TRANSITION
- VocAlgorithm_GATING_MAX_DURATION_MINUTES
- VocAlgorithm_GATING_MAX_RATIO
- VocAlgorithm_SIGMOID_L
- VocAlgorithm_SIGMOID_K
- VocAlgorithm_SIGMOID_X0
- VocAlgorithm_VOC_INDEX_OFFSET_DEFAULT
- VocAlgorithm_LP_TAU_FAST
- VocAlgorithm_LP_TAU_SLOW
- VocAlgorithm_LP_ALPHA
- VocAlgorithm_PERSISTENCE_UPTIME_GAMMA
- VocAlgorithm_MEAN_VARIANCE_ESTIMATOR__GAMMA_SCALING
- VocAlgorithm_MEAN_VARIANCE_ESTIMATOR__FIX16_MAX
Typedefs
- typedef int32_t fix16_t
Functions
- void VocAlgorithm_init(VocAlgorithmParams *params)
Initialize the VOC algorithm parameters.
Call this once at the beginning or whenever the sensor stopped measurements.
- Parameters:
params – Pointer to the VocAlgorithmParams struct
- void VocAlgorithm_get_states(VocAlgorithmParams *params, int32_t *state0, int32_t *state1)
Get current algorithm states.
Retrieved values can be used in VocAlgorithm_set_states() to resume operation after a short interruption, skipping initial learning phase. This feature can only be used after at least 3 hours of continuous operation.
- Parameters:
params – Pointer to the VocAlgorithmParams struct
state0 – State0 to be stored
state1 – State1 to be stored
- void VocAlgorithm_set_states(VocAlgorithmParams *params, int32_t state0, int32_t state1)
Set previously retrieved algorithm states to resume operation after a short interruption, skipping initial learning phase.
This feature should not be used after inerruptions of more than 10 minutes. Call this once after VocAlgorithm_init() and the optional VocAlgorithm_set_tuning_parameters(), if desired. Otherwise, the algorithm will start with initial learning phase.
- Parameters:
params – Pointer to the VocAlgorithmParams struct
state0 – State0 to be restored
state1 – State1 to be restored
- void VocAlgorithm_set_tuning_parameters(VocAlgorithmParams *params, int32_t voc_index_offset, int32_t learning_time_hours, int32_t gating_max_duration_minutes, int32_t std_initial)
Set parameters to customize the VOC algorithm.
Call this once after VocAlgorithm_init(), if desired. Otherwise, the default values will be used.
- Parameters:
params – Pointer to the VocAlgorithmParams struct
voc_index_offset – VOC index representing typical (average) conditions. Range 1..250, default 100
learning_time_hours – Time constant of long-term estimator. Past events will be forgotten after about twice the learning time. Range 1..72 [hours], default 12 [hours]
gating_max_duration_minutes – Maximum duration of gating (freeze of estimator during high VOC index signal). 0 (no gating) or range 1..720 [minutes], default 180 [minutes]
std_initial – Initial estimate for standard deviation. Lower value boosts events during initial learning period, but may result in larger device-to-device variations. Range 10..500, default 50
- void VocAlgorithm_process(VocAlgorithmParams *params, int32_t sraw, int32_t *voc_index)
Calculate the VOC index value from the raw sensor value.
- Parameters:
params – Pointer to the VocAlgorithmParams struct
sraw – Raw value from the SGP40 sensor
voc_index – Calculated VOC index value from the raw sensor value. Zero during initial blackout period and 1..500 afterwards
- struct VocAlgorithmParams
Struct to hold all the states of the VOC algorithm.
Defines
- SGP40_ADDR
I2C address.
Functions
- esp_err_t sgp40_init_desc(sgp40_t *dev, i2c_port_t port, gpio_num_t sda_gpio, gpio_num_t scl_gpio)
Initialize device descriptor.
- Parameters:
dev – Device descriptor
port – I2C port
sda_gpio – SDA GPIO
scl_gpio – SCL GPIO
- Returns:
ESP_OKon success
- esp_err_t sgp40_free_desc(sgp40_t *dev)
Free device descriptor.
- Parameters:
dev – Device descriptor
- Returns:
ESP_OKon success
- esp_err_t sgp40_init(sgp40_t *dev)
Read device information, initialize the VOC algorithm.
- Parameters:
dev – Device descriptor
- Returns:
ESP_OKon success
- esp_err_t sgp40_soft_reset(sgp40_t *dev)
Reset device, than put it to idle mode.
- Parameters:
dev – Device descriptor
- Returns:
ESP_OKon success
- esp_err_t sgp40_self_test(sgp40_t *dev)
Perform a self-test.
- Parameters:
dev – Device descriptor
- Returns:
ESP_OKon success
- esp_err_t sgp40_heater_off(sgp40_t *dev)
Turn hotplate off, stop measurement and put device to idle mode.
- Parameters:
dev – Device descriptor
- Returns:
ESP_OKon success
- esp_err_t sgp40_measure_raw(sgp40_t *dev, float humidity, float temperature, uint16_t *raw)
Perform a measurement.
- Parameters:
dev – Device descriptor
humidity – Relative humidity, percents. Use NaN if you want uncompensated measurement
temperature – Temperature, degrees Celsius. Use NaN if you want uncompensated measurement
raw – [out] Raw value, proportional to the logarithm of the resistance of the sensing element
- Returns:
ESP_OKon success
- esp_err_t sgp40_measure_voc(sgp40_t *dev, float humidity, float temperature, int32_t *voc_index)
Perform a measurement and update VOC index.
- Parameters:
dev – Device descriptor
humidity – Relative humidity, percents. Use NaN if you want uncompensated measurement
temperature – Temperature, degrees Celsius. Use NaN if you want uncompensated measurement
voc_index – [out] Calculated VOC index
- Returns:
- struct sgp40_t
Device descriptor.