ccs811.h File Reference

Driver for the CCS811 gas sensor . More...

#include <stdbool.h>
#include <stdint.h>

Go to the source code of this file.

Classes
struct	ccs811_config_t
	Config object, to be instantiated and values assigned to members before passing the object address into the function init_ccs811(). More...

Enumerations
enum	ccs811_drive_mode_t { drive_mode_idle = 0U , drive_mode_1sec = 1U , drive_mode_10sec = 2U , drive_mode_60sec = 3U }
	Drive modes 0 to 3. More...

Functions
uint8_t	init_ccs811 (ccs811_config_t *p_config)
	Initialisation routine (run once at startup). More...
uint16_t	ccs811_get_eco2_level (void)
	Read eCO2 (equivalent carbon dioxide) level from sensor. More...
uint16_t	ccs811_get_etvoc_level (void)
	Read eTVOC (equivalent total volatile organic compounds) level from sensor. More...
void	ccs811_get_alg_result_data (void)
	Perform a read operation on all 8 bytes of ALG_RESULT_REGISTER. More...
bool	ccs811_data_ready_check (void)
	Read the status register and check if the data ready flag is set. More...
void	ccs811_update_env_data (uint8_t humidity, uint8_t temp)
	(Optional) Write environmental data from another sensor to the CCS811. More...
char *	ccs811_error_to_string (void)
	For error handling/logging. More...

Detailed Description

Driver for the CCS811 gas sensor .

Copyright

Copyright © 2022 by Jason Duffy.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Author

Jason Duffy

Date

4th March 2022

This file provides the basic low-level functionality for the CCS81 gas sensor / air quality sensor. It was tested with the CJMCU-811 module which provides pin breakout to THT for breadboard prototyping, and some peripheral circuitry. The CCS811 eatures an on-board MCU to interface with, greatly reducing the load on the host MCU.

When the sensor is new, a burn-in period of 48hr is necessary for the resistive elements to level out and make readings more accurate. The CCS81 controls the burn-in period, allowing eCO2 and eTVOC readings to be used from first power-on after 60 minutes of operation in modes 1-3.

After early-life (Burn-In) use the conditioning period is the time required to achieve good sensor stability before measuring VOCs after a long idle period. After starting the application and calling init_ccs811(), run the sensor for 20 minutes before accurate readings are generated. The conditioning period must also be observed before writing to the BASELINE register.

This driver was written using the datasheet for the ams CCS81 gas sensor, which can be found at the link below.

See also

https://pdf1.alldatasheet.com/datasheet-pdf/view/1047395/AMSCO/CCS811.html

Definition in file ccs811.h.

Enumeration Type Documentation

ccs811_drive_mode_t

enum ccs811_drive_mode_t

Drive modes 0 to 3.

Mode 4 has been omitted as it does not appear to be particularly useful (only RAW_DATA may be used in mode 4).

Definition at line 66 of file ccs811.h.

{
    drive_mode_idle = 0U,
    drive_mode_1sec = 1U,
    drive_mode_10sec = 2U,
    drive_mode_60sec = 3U,
}ccs811_drive_mode_t;

Function Documentation

init_ccs811()

uint8_t init_ccs811

(

ccs811_config_t *

p_config

)

Initialisation routine (run once at startup).

This function is to be called before any other functions in this file can be called. Instantiate the ccs811_config_t object first, then pass it's address into init_ccs811() to make config data available at file scope.

Parameters

p_config

is a pointer to the ccs811_config_t object.

Returns

An error code is returned as an unsigned 8 bit integer.

Definition at line 133 of file ccs811.c.

{
    p_config_global = p_config; // Make a copy of pointer with file scope. 
    uint8_t ret = 0; // For return value
    init_i2c(BUS_SPEED_100KHZ);
    if (ccs811_read_byte(HW_ID_REG) == CCS811_ID)
    {
        uint8_t status = ccs811_get_status();
        if (bit_is_set(status, APP_VALID_BIT))
        {
            i2c_start();
            i2c_send(CCS811_ADDRESS_W);
            i2c_send(APP_START);
            i2c_stop();
            _delay_ms(100);
 
            uint8_t byte = 0;
            byte |= (p_config_global->drive_mode << DRIVE_MODE_BITS);
            byte |= (p_config_global->interrupt_dataready << INT_DATARDY_BIT);
            byte |= (p_config_global->interrupt_threshold <<INT_THRESH_BIT);
 
            for (uint8_t count = 0; count < ATTEMPTS_MAX; ++count)
            {
                ccs811_write_byte(MEAS_MODE_REG, byte);
                _delay_ms(500);
                uint8_t mode = ccs811_read_byte(MEAS_MODE_REG);
                if (mode == byte)
                {
                    break; // Success
                }
                if (count == (ATTEMPTS_MAX - 1))
                {
                    ret = 3; // Max attempts reached
                }
            }
        }
        else
        {
            ret = 2; // Error - app invalid
        }
    }
    else
    {
        ret = 1; // ccs81 ID failed
    }
    return ret;
}

ccs811_get_eco2_level()

uint16_t ccs811_get_eco2_level

(

void

)

Read eCO2 (equivalent carbon dioxide) level from sensor.

Once the data_ready flag is set, this function can be called.

Returns

eCO2 level in ppm is returned, ranging from (400 - 32768ppm).

Definition at line 182 of file ccs811.c.

{
    uint16_t data = ccs811_read_word(ALG_RESULT_DATA_REG);
    return data;
}

ccs811_get_etvoc_level()

uint16_t ccs811_get_etvoc_level

(

void

)

Read eTVOC (equivalent total volatile organic compounds) level from sensor.

Once the data_ready flag is set, this function can be called.

Returns

eTVOC level in ppb is returned, ranging from (0 - 32768ppb).

Definition at line 189 of file ccs811.c.

{
    uint8_t data = 0;
    ccs811_burst_read(ALG_RESULT_DATA_REG, ETVOC_SIZE);
    uint8_t msb = read_buffer[ETVOC_SIZE - 2];
    data = read_buffer[ETVOC_SIZE - 1];
    data |= (msb << 8);
    return data;
}

ccs811_get_alg_result_data()

void ccs811_get_alg_result_data

(

void

)

Perform a read operation on all 8 bytes of ALG_RESULT_REGISTER.

The data is stored in the read_buffer[] array, and can be extracted using the register size definitions in the source file.

Definition at line 211 of file ccs811.c.

{
    ccs811_burst_read(ALG_RESULT_DATA_REG, ALG_RESULT_DATA_SIZE);
}

ccs811_data_ready_check()

bool ccs811_data_ready_check

(

void

)

Read the status register and check if the data ready flag is set.

Use this function to poll the data ready flag and call the getter functions above only when a new value is ready.

Returns

A boolean value of true is returned if flag is set, otherwise false is returned.

Definition at line 200 of file ccs811.c.

{
    bool ret = false;
    uint8_t status = ccs811_get_status();
    if (bit_is_set(status, DATA_READY_BIT))
    {
        ret =  true;
    }
    return ret;
}

ccs811_update_env_data()

void ccs811_update_env_data	(	uint8_t	humidity,
		uint8_t	temp
	)

(Optional) Write environmental data from another sensor to the CCS811.

The sensor has the capability to use humidity and temperature data in a compensation formula to imporve the accuracy of it's readings.

Parameters

uint8_t	humidity is the Relative Humidity % passed in as an integer.
uint8_t	temp is the temperature in degrees Celcius.

Definition at line 216 of file ccs811.c.

{
    uint8_t lsb = 0;
 
    i2c_start();
    i2c_send(CCS811_ADDRESS_W);
    i2c_send(ENV_DATA_REG);
    i2c_send(humidity << 1);
    i2c_send(lsb);
    i2c_send(((temp + 25) << 1));
    i2c_send(lsb);
    i2c_stop();
}

ccs811_error_to_string()

char * ccs811_error_to_string

(

void

)

For error handling/logging.

If the error flag is set on the status register, call this function to turn the error code into a string message.

Parameters

char*

pointer to the first element of the string is returned.

Definition at line 231 of file ccs811.c.

{
    char *msg;
    uint8_t error = ccs811_read_byte(ERROR_ID_REG);
    if (bit_is_set(error, HEATER_SUPPLY))
    {
        msg = "Heater Supply";
    }
    else if (bit_is_set(error, HEATER_FAULT))
    {
        msg = "Heater Fault";
    }
    else if (bit_is_set(error, MAX_RESISTANCE))
    {
        msg = "Max Resistance";
    }
    else if (bit_is_set(error, MEASMODE_INVALID))
    {
        msg = "Invalid Meas Mode";
    }
    else if (bit_is_set(error, READ_REG_INVALID))
    {
        msg = "Read Reg Invalid";
    }
    else if (bit_is_set(error, WRITE_REG_INVALID))
    {
        msg = "Write Reg Invalid";
    }
    else
    {
        msg = "Unknown Error";
    }
    return msg;
}