sgp40 - Driver for SGP40 Indoor Air Quality Sensor for VOC Measurements¶

group sgp40

Library for calculating concentration of volatile organic compounds.

ESP-IDF driver for SGP40 Indoor Air Quality Sensor for VOC Measurements.

BSD Licensed as described in the file LICENSE

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¶

SGP40_ADDR¶: I2C address.

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

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_OK on success

esp_err_t sgp40_free_desc(sgp40_t *dev)¶

Free device descriptor.

Parameters: dev – Device descriptor
Returns: ESP_OK on success

esp_err_t sgp40_init(sgp40_t *dev)¶

Read device information, initialize the VOC algorithm.

Parameters: dev – Device descriptor
Returns: ESP_OK on success

esp_err_t sgp40_soft_reset(sgp40_t *dev)¶

Reset device, than put it to idle mode.

Parameters: dev – Device descriptor
Returns: ESP_OK on success

esp_err_t sgp40_self_test(sgp40_t *dev)¶

Perform a self-test.

Parameters: dev – Device descriptor
Returns: ESP_OK on 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_OK on 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_OK on 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 VocAlgorithmParams¶: #include <sensirion_voc_algorithm.h>
Struct to hold all the states of the VOC algorithm.

struct sgp40_t¶: #include <sgp40.h>
Device descriptor.