CCS811 I2C

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mongoose-os-libs/ccs811-i2c	mgos_ccs811.h

A Mongoose library for AMS CCS811 integrated circuit.

Sensor details

The CCS811 is an ultra-low power digital gas sensor solution which integrates a metal oxide (MOX) gas sensor to detect a wide range of Volatile Organic Compounds (VOCs) for indoor air quality monitoring with a microcontroller unit (MCU), which includes an Analog-to-Digital converter (ADC), and an I2C interface.

CCS811 is based on ams unique micro-hotplate technology which enables a highly reliable solution for gas sensors, very fast cycle times and a significant reduction in average power consumption.

The integrated MCU manages the sensor driver modes and measurements. The I2C digital interface significantly simplifies the hardware and software design, enabling a faster time to market.

CCS811 supports intelligent algorithms to process raw sensor measurements to output a TVOC value or equivalent CO2 (eCO2) levels, where the main cause of VOCs is from humans.

CCS811 supports multiple measurement modes that have been optimized for low-power consumption during an active sensor measurement and idle mode extending battery life in portable applications.

See datasheet for implementation details.

A great place to buy a ready made and tested unit is at Adafruit.

Example application

An example program using a timer to read data from the sensor every 5 seconds:

#include "mgos.h"
#include "mgos_i2c.h"
#include "mgos_ccs811.h"

static struct mgos_ccs811 *s_ccs811;

static void timer_cb(void *user_data) {
  float eco2, tvoc;

  eco2=mgos_ccs811_get_eco2(s_ccs811);
  tvoc=mgos_ccs811_get_tvoc(s_ccs811);

  LOG(LL_INFO, ("ccs811 eCO2=%.0fppm TVOC=%.0fppb", eco2, tvoc));

  (void) user_data;
}

enum mgos_app_init_result mgos_app_init(void) {
  struct mgos_i2c *i2c;

  i2c=mgos_i2c_get_global();
  if (!i2c) {
    LOG(LL_ERROR, ("I2C bus missing, set i2c.enable=true in mos.yml"));
  } else {
    s_ccs811=mgos_ccs811_create(i2c, 0x5a); // Default I2C address
    if (s_ccs811) {
      mgos_set_timer(5000, true, timer_cb, NULL);
    } else {
      LOG(LL_ERROR, ("Could not initialize sensor"));
    }
  }
  return MGOS_APP_INIT_SUCCESS;
}

Disclaimer

This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.

_read

uint32_t read;                 // calls to _read()
  uint32_t read_success;         // successful _read()
  uint32_t read_success_cached;  // calls to _read() which were cached
  // Note: read_errors := read - read_success - read_success_cached
  double   read_success_usecs;   // time spent in successful uncached _read()
};

value of mg_time() upon last call to _read()

mgos_ccs811_create

struct mgos_ccs811 *mgos_ccs811_create(struct mgos_i2c *i2c, uint8_t i2caddr);

Initialize a CCS811 on the I2C bus i2c at address specified in i2caddr parameter (default CCS811 is on address 0x5A). The sensor will be polled for validity, upon success a new struct mgos_ccs811 is allocated and returned. If the device could not be found, NULL is returned.

mgos_ccs811_destroy

void mgos_ccs811_destroy(struct mgos_ccs811 **sensor);

Destroy the data structure associated with a CCS811 device. The reference to the pointer of the struct mgos_ccs811 has to be provided, and upon successful destruction, its associated memory will be freed and the pointer set to NULL.

mgos_ccs811_read

bool mgos_ccs811_read(struct mgos_ccs811 *sensor);

The sensor will be polled for its temperature and humidity data. If the poll has occured in the last MGOS_CCS811_READ_DELAY seconds, the cached data is used (so as not to repeatedly poll the bus upon subsequent calls).

mgos_ccs811_setDriveMode

bool mgos_ccs811_setDriveMode(struct mgos_ccs811 *sensor, enum mgos_ccs811_drive_mode_t mode);

Set the drive mode of the CCS811 sensor based on the mode argument Returns true on success, false otherwise.

mgos_ccs811_getDriveMode

bool mgos_ccs811_getDriveMode(struct mgos_ccs811 *sensor, uint8_t *mode);

Retrieve the current drive mode (which will be one of enum mgos_ccs811_drive_mode_t values into the byte pointed to by mode. Returns true on success, false otherwise.

mgos_ccs811_get_eco2

float mgos_ccs811_get_eco2(struct mgos_ccs811 *sensor);

The sensor will be polled for its effective CO2 data. If the poll has occured in the last MGOS_CCS811_READ_DELAY seconds, the cached data is used (so as not to repeatedly poll the bus upon subsequent calls).

Returns a value in eCO2 parts per million on success, NAN otherwise.

mgos_ccs811_get_tvoc

float mgos_ccs811_get_tvoc(struct mgos_ccs811 *sensor);

The sensor will be polled for its Volatile Organic Compounds (TVOC) data. If the poll has occured in the last MGOS_CCS811_READ_DELAY seconds, the cached data is used (so as not to repeatedly poll the bus upon subsequent calls).

Returns a value in TVOC parts per billion on success, NAN otherwise.

mgos_ccs811_getStats

bool mgos_ccs811_getStats(struct mgos_ccs811 *sensor, struct mgos_ccs811_stats *stats);

Returns the running statistics on the sensor interaction, the user provides a pointer to a struct mgos_ccs811_stats object, which is filled in by this call.

Upon success, true is returned. Otherwise, false is returned, in which case the contents of stats is undetermined.

mgos_ccs811_i2c_init

bool mgos_ccs811_i2c_init(void);

Initialization function for MGOS -- currently a noop.

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