Driver for the CCS811 gas sensor. More...

#include <util/delay.h>
#include "ccs811.h"
#include "i2c.h"

Macros
#define	CCS811_ADDRESS_W 0xB4

#define	CCS811_ADDRESS_R 0xB5

#define	STATUS_REG 0x00

#define	MEAS_MODE_REG 0x01

#define	ALG_RESULT_DATA_REG 0x02

#define	RAW_DATA_REG 0x03

#define	ENV_DATA_REG 0x05

#define	THRESHOLDS_REG 0x10

#define	BASELINE_REG 0x11

#define	HW_ID_REG 0x20

#define	HW_VERSION_REG 0x21

#define	FW_BOOT_VERSION_REG 0x23

#define	FW_APP_VERSION_REG 0x24

#define	INTERNAL_STATE_REG 0xA0

#define	ERROR_ID_REG 0xE0

#define	SW_RESET_REG 0xFF

#define	ALG_RESULT_DATA_SIZE 8

#define	ETVOC_SIZE 4

#define	RAW_DATA_SIZE 2

#define	ENV_DATA_SIZE 4

#define	THRESHOLDS_SIZE 5

#define	BASELINE_SIZE 2

#define	FW_BOOT_VERSION_SIZE 2

#define	FW_APP_VERSION_SIZE 2

#define	SW_RESET_SIZE 4

#define	APP_START 0xF4

#define	GPIO_WAKE 0x5

#define	HEATER_SUPPLY 5

#define	HEATER_FAULT 4

#define	MAX_RESISTANCE 3

#define	MEASMODE_INVALID 2

#define	READ_REG_INVALID 1

#define	WRITE_REG_INVALID 0

#define	DRIVE_MODE_BITS 4

#define	INT_DATARDY_BIT 3

#define	INT_THRESH_BIT 2

#define	FW_MODE_BIT 7

#define	APP_ERASE_BIT 6

#define	APP_VERIFY_BIT 5

#define	APP_VALID_BIT 4

#define	DATA_READY_BIT 3

#define	ERROR_BIT 0

#define	BUS_SPEED_100KHZ 100000U

#define	ATTEMPTS_MAX 10

#define	CCS811_ID 0x81

Functions
uint8_t	ccs811_read_byte (uint8_t reg)

void	ccs811_burst_read (uint8_t reg, uint8_t length)

uint16_t	ccs811_read_word (uint8_t reg)

void	ccs811_write_byte (uint8_t reg, uint8_t byte)

uint8_t	ccs811_get_status (void)

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...

bool	ccs811_data_ready_check (void)
	Read the status register and check if the data ready flag is set. More...

void	ccs811_get_alg_result_data (void)
	Perform a read operation on all 8 bytes of ALG_RESULT_REGISTER. 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.c.

Macro Definition Documentation

◆ CCS811_ADDRESS_W

#define CCS811_ADDRESS_W 0xB4

Definition at line 61 of file ccs811.c.

◆ CCS811_ADDRESS_R

#define CCS811_ADDRESS_R 0xB5

Definition at line 62 of file ccs811.c.

◆ STATUS_REG

#define STATUS_REG 0x00

Definition at line 65 of file ccs811.c.

◆ MEAS_MODE_REG

#define MEAS_MODE_REG 0x01

Definition at line 66 of file ccs811.c.

◆ ALG_RESULT_DATA_REG

#define ALG_RESULT_DATA_REG 0x02

Definition at line 67 of file ccs811.c.

◆ RAW_DATA_REG

#define RAW_DATA_REG 0x03

Definition at line 68 of file ccs811.c.

◆ ENV_DATA_REG

#define ENV_DATA_REG 0x05

Definition at line 69 of file ccs811.c.

◆ THRESHOLDS_REG

#define THRESHOLDS_REG 0x10

Definition at line 70 of file ccs811.c.

◆ BASELINE_REG

#define BASELINE_REG 0x11

Definition at line 71 of file ccs811.c.

◆ HW_ID_REG

#define HW_ID_REG 0x20

Definition at line 72 of file ccs811.c.

◆ HW_VERSION_REG

#define HW_VERSION_REG 0x21

Definition at line 73 of file ccs811.c.

◆ FW_BOOT_VERSION_REG

#define FW_BOOT_VERSION_REG 0x23

Definition at line 74 of file ccs811.c.

◆ FW_APP_VERSION_REG

#define FW_APP_VERSION_REG 0x24

Definition at line 75 of file ccs811.c.

◆ INTERNAL_STATE_REG

#define INTERNAL_STATE_REG 0xA0

Definition at line 76 of file ccs811.c.

◆ ERROR_ID_REG

#define ERROR_ID_REG 0xE0

Definition at line 77 of file ccs811.c.

◆ SW_RESET_REG

#define SW_RESET_REG 0xFF

Definition at line 78 of file ccs811.c.

◆ ALG_RESULT_DATA_SIZE

#define ALG_RESULT_DATA_SIZE 8

Definition at line 81 of file ccs811.c.

◆ ETVOC_SIZE

#define ETVOC_SIZE 4

Definition at line 82 of file ccs811.c.

◆ RAW_DATA_SIZE

#define RAW_DATA_SIZE 2

Definition at line 83 of file ccs811.c.

◆ ENV_DATA_SIZE

#define ENV_DATA_SIZE 4

Definition at line 84 of file ccs811.c.

◆ THRESHOLDS_SIZE

#define THRESHOLDS_SIZE 5

Definition at line 85 of file ccs811.c.

◆ BASELINE_SIZE

#define BASELINE_SIZE 2

Definition at line 86 of file ccs811.c.

◆ FW_BOOT_VERSION_SIZE

#define FW_BOOT_VERSION_SIZE 2

Definition at line 87 of file ccs811.c.

◆ FW_APP_VERSION_SIZE

#define FW_APP_VERSION_SIZE 2

Definition at line 88 of file ccs811.c.

◆ SW_RESET_SIZE

#define SW_RESET_SIZE 4

Definition at line 89 of file ccs811.c.

◆ APP_START

#define APP_START 0xF4

Definition at line 92 of file ccs811.c.

◆ GPIO_WAKE

#define GPIO_WAKE 0x5

Definition at line 93 of file ccs811.c.

◆ HEATER_SUPPLY

#define HEATER_SUPPLY 5

Definition at line 96 of file ccs811.c.

◆ HEATER_FAULT

#define HEATER_FAULT 4

Definition at line 97 of file ccs811.c.

◆ MAX_RESISTANCE

#define MAX_RESISTANCE 3

Definition at line 98 of file ccs811.c.

◆ MEASMODE_INVALID

#define MEASMODE_INVALID 2

Definition at line 99 of file ccs811.c.

◆ READ_REG_INVALID

#define READ_REG_INVALID 1

Definition at line 100 of file ccs811.c.

◆ WRITE_REG_INVALID

#define WRITE_REG_INVALID 0

Definition at line 101 of file ccs811.c.

◆ DRIVE_MODE_BITS

#define DRIVE_MODE_BITS 4

Definition at line 104 of file ccs811.c.

◆ INT_DATARDY_BIT

#define INT_DATARDY_BIT 3

Definition at line 105 of file ccs811.c.

◆ INT_THRESH_BIT

#define INT_THRESH_BIT 2

Definition at line 106 of file ccs811.c.

◆ FW_MODE_BIT

#define FW_MODE_BIT 7

Definition at line 109 of file ccs811.c.

◆ APP_ERASE_BIT

#define APP_ERASE_BIT 6

Definition at line 110 of file ccs811.c.

◆ APP_VERIFY_BIT

#define APP_VERIFY_BIT 5

Definition at line 111 of file ccs811.c.

◆ APP_VALID_BIT

#define APP_VALID_BIT 4

Definition at line 112 of file ccs811.c.

◆ DATA_READY_BIT

#define DATA_READY_BIT 3

Definition at line 113 of file ccs811.c.

◆ ERROR_BIT

#define ERROR_BIT 0

Definition at line 114 of file ccs811.c.

◆ BUS_SPEED_100KHZ

#define BUS_SPEED_100KHZ 100000U

Definition at line 116 of file ccs811.c.

◆ ATTEMPTS_MAX

#define ATTEMPTS_MAX 10

Definition at line 117 of file ccs811.c.

◆ CCS811_ID

#define CCS811_ID 0x81

Definition at line 118 of file ccs811.c.

Function Documentation

◆ ccs811_read_byte()

uint8_t ccs811_read_byte ( uint8_t reg )

Definition at line 286 of file ccs811.c.

{
    uint8_t byte;
 
    i2c_start();
    i2c_send(CCS811_ADDRESS_W);
    i2c_send(reg);
    i2c_start();
    i2c_send(CCS811_ADDRESS_R);
    byte = i2c_read_no_ack();
    i2c_stop();
    return byte;
}

◆ ccs811_burst_read()

void ccs811_burst_read	(	uint8_t	reg,
		uint8_t	length
	)

Definition at line 300 of file ccs811.c.

{
    i2c_start();
    i2c_send(CCS811_ADDRESS_W);
    i2c_send(reg);
    i2c_start();
    i2c_send(CCS811_ADDRESS_R);
 
    for (uint8_t i = 0; i < length; ++i)
    {
        read_buffer[i] = i2c_read_ack();
    }
    i2c_stop();
}

◆ ccs811_read_word()

uint16_t ccs811_read_word ( uint8_t reg )

Definition at line 315 of file ccs811.c.

{
    uint16_t msb;
    uint16_t byte;
 
    i2c_start();
    i2c_send(CCS811_ADDRESS_W);
    i2c_send(reg);
    i2c_start();
    i2c_send(CCS811_ADDRESS_R);
 
    msb = i2c_read_ack();
    byte = i2c_read_no_ack();
    byte |= (msb << 8);
 
    return byte;
}

◆ ccs811_write_byte()

void ccs811_write_byte	(	uint8_t	reg,
		uint8_t	byte
	)

Definition at line 277 of file ccs811.c.

{
    i2c_start();
    i2c_send(CCS811_ADDRESS_W);
    i2c_send(reg);
    i2c_send(byte);
    i2c_stop();
}

◆ ccs811_get_status()

uint8_t ccs811_get_status ( void )

Definition at line 271 of file ccs811.c.

{
    uint8_t status = ccs811_read_byte(STATUS_REG);
    return status;
}

◆ 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_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_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_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;
}

Macros

Functions

Detailed Description

Macro Definition Documentation

◆ CCS811_ADDRESS_W

◆ CCS811_ADDRESS_R

◆ STATUS_REG

◆ MEAS_MODE_REG

◆ ALG_RESULT_DATA_REG

◆ RAW_DATA_REG

◆ ENV_DATA_REG

◆ THRESHOLDS_REG

◆ BASELINE_REG

◆ HW_ID_REG

◆ HW_VERSION_REG

◆ FW_BOOT_VERSION_REG

◆ FW_APP_VERSION_REG

◆ INTERNAL_STATE_REG

◆ ERROR_ID_REG

◆ SW_RESET_REG

◆ ALG_RESULT_DATA_SIZE

◆ ETVOC_SIZE

◆ RAW_DATA_SIZE

◆ ENV_DATA_SIZE

◆ THRESHOLDS_SIZE

◆ BASELINE_SIZE

◆ FW_BOOT_VERSION_SIZE

◆ FW_APP_VERSION_SIZE

◆ SW_RESET_SIZE

◆ APP_START

◆ GPIO_WAKE

◆ HEATER_SUPPLY

◆ HEATER_FAULT

◆ MAX_RESISTANCE

◆ MEASMODE_INVALID

◆ READ_REG_INVALID

◆ WRITE_REG_INVALID

◆ DRIVE_MODE_BITS

◆ INT_DATARDY_BIT

◆ INT_THRESH_BIT

◆ FW_MODE_BIT

◆ APP_ERASE_BIT

◆ APP_VERIFY_BIT

◆ APP_VALID_BIT

◆ DATA_READY_BIT

◆ ERROR_BIT

◆ BUS_SPEED_100KHZ

◆ ATTEMPTS_MAX

◆ CCS811_ID

Function Documentation

◆ ccs811_read_byte()

◆ ccs811_burst_read()

◆ ccs811_read_word()

◆ ccs811_write_byte()

◆ ccs811_get_status()

◆ init_ccs811()

◆ ccs811_get_eco2_level()

◆ ccs811_get_etvoc_level()

◆ ccs811_data_ready_check()

◆ ccs811_get_alg_result_data()

◆ ccs811_update_env_data()

◆ ccs811_error_to_string()