BME680 sensor API

Introduction

This package contains the Bosch Sensortec's BME680 gas sensor API

The sensor driver package includes bme680.h, bme680.c and bme680_defs.h files

Version

File	Version	Date
bme680.c	3.5.7	05 Feb 2018
bme680.h	3.5.7	05 Feb 2018
bme680_defs.h	3.5.7	05 Feb 2018

Integration details

Integrate bme680.h, bme680_defs.h and bme680.c file in to your project.
Include the bme680.h file in your code like below.

#include "bme680.h"

File information

bme680_defs.h : This header file has the constants, macros and datatype declarations.
bme680.h : This header file contains the declarations of the sensor driver APIs.
bme680.c : This source file contains the definitions of the sensor driver APIs.

Supported sensor interfaces

SPI 4-wire
I2C

Usage guide

Initializing the sensor

To initialize the sensor, you will first need to create a device structure. You can do this by creating an instance of the structure bme680_dev. Then go on to fill in the various parameters as shown below

Example for SPI 4-Wire

	struct bme680_dev gas_sensor;

	/* You may assign a chip select identifier to be handled later */
	gas_sensor.dev_id = 0;
	gas_sensor.intf = BME680_SPI_INTF;
	gas_sensor.read = user_spi_read;
	gas_sensor.write = user_spi_write;
	gas_sensor.delay_ms = user_delay_ms;

	int8_t rslt = BME680_OK;
	rslt = bme680_init(&gas_sensor);

Example for I2C

	struct bme680_dev gas_sensor;

	gas_sensor.dev_id = BME680_I2C_ADDR_PRIMARY;
	gas_sensor.intf = BME680_I2C_INTF;
	gas_sensor.read = user_i2c_read;
	gas_sensor.write = user_i2c_write;
	gas_sensor.delay_ms = user_delay_ms;

	int8_t rslt = BME680_OK;
	rslt = bme680_init(&gas_sensor);

Regarding compensation functions for temperature, pressure, humidity and gas we have two implementations.

- Integer version
- floating point version

By default, Integer version is used in the API

If the user needs the floating point version, the user has to un-comment BME680_FLOAT_POINT_COMPENSATION macro in bme680_defs.h file or to add it in the compiler flags.

Configuring the sensor

Example for configuring the sensor in forced mode

	uint8_t set_required_settings;

	/* Set the temperature, pressure and humidity settings */
	gas_sensor.tph_sett.os_hum = BME680_OS_2X;
	gas_sensor.tph_sett.os_pres = BME680_OS_4X;
	gas_sensor.tph_sett.os_temp = BME680_OS_8X;
	gas_sensor.tph_sett.filter = BME680_FILTER_SIZE_3;

	/* Set the remaining gas sensor settings and link the heating profile */
	gas_sensor.gas_sett.run_gas = BME680_ENABLE_GAS_MEAS;
	/* Create a ramp heat waveform in 3 steps */
	gas_sensor.gas_sett.heatr_temp = 320; /* degree Celsius */
	gas_sensor.gas_sett.heatr_dur = 150; /* milliseconds */

	/* Select the power mode */
	/* Must be set before writing the sensor configuration */
	gas_sensor.power_mode = BME680_FORCED_MODE; 

	/* Set the required sensor settings needed */
	set_required_settings = BME680_OST_SEL | BME680_OSP_SEL | BME680_OSH_SEL | BME680_FILTER_SEL 
		| BME680_GAS_SENSOR_SEL;
		
	/* Set the desired sensor configuration */
	rslt = bme680_set_sensor_settings(set_required_settings,&gas_sensor);

	/* Set the power mode */
	rslt = bme680_set_sensor_mode(&gas_sensor);

	/* Get the total measurement duration so as to sleep or wait till the
	 * measurement is complete */
	uint16_t meas_period;
	bme680_get_profile_dur(&meas_period, &gas_sensor);
	user_delay_ms(meas_period); /* Delay till the measurement is ready */

Reading sensor data

Example for reading all sensor data

	struct bme680_field_data data;
	
	while(1) 
	{
		rslt = bme680_get_sensor_data(&data, &gas_sensor);

		printf("T: %.2f degC, P: %.2f hPa, H %.2f %%rH ", data.temperature / 100.0f,
			data.pressure / 100.0f, data.humidity / 1000.0f );
		/* Avoid using measurements from an unstable heating setup */
		if(data.status & BME680_GASM_VALID_MSK)
			printf(", G: %d ohms", data.gas_resistance);
		
		printf("\r\n");
	}

Templates for function pointers


void user_delay_ms(uint32_t period)
{
    /*
     * Return control or wait,
     * for a period amount of milliseconds
     */
}

int8_t user_spi_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to select which Chip Select pin has
     * to be set low to activate the relevant device on the SPI bus
     */

    /*
     * Data on the bus should be like
     * |----------------+---------------------+-------------|
     * | MOSI           | MISO                | Chip Select |
     * |----------------+---------------------|-------------|
     * | (don't care)   | (don't care)        | HIGH        |
     * | (reg_addr)     | (don't care)        | LOW         |
     * | (don't care)   | (reg_data[0])       | LOW         |
     * | (....)         | (....)              | LOW         |
     * | (don't care)   | (reg_data[len - 1]) | LOW         |
     * | (don't care)   | (don't care)        | HIGH        |
     * |----------------+---------------------|-------------|
     */

    return rslt;
}

int8_t user_spi_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to select which Chip Select pin has
     * to be set low to activate the relevant device on the SPI bus
     */

    /*
     * Data on the bus should be like
     * |---------------------+--------------+-------------|
     * | MOSI                | MISO         | Chip Select |
     * |---------------------+--------------|-------------|
     * | (don't care)        | (don't care) | HIGH        |
     * | (reg_addr)          | (don't care) | LOW         |
     * | (reg_data[0])       | (don't care) | LOW         |
     * | (....)              | (....)       | LOW         |
     * | (reg_data[len - 1]) | (don't care) | LOW         |
     * | (don't care)        | (don't care) | HIGH        |
     * |---------------------+--------------|-------------|
     */

    return rslt;
}

int8_t user_i2c_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     */

    /*
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Stop       | -                   |
     * | Start      | -                   |
     * | Read       | (reg_data[0])       |
     * | Read       | (....)              |
     * | Read       | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */

    return rslt;
}

int8_t user_i2c_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     */

    /*
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Write      | (reg_data[0])       |
     * | Write      | (....)              |
     * | Write      | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */

    return rslt;
}

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